Technology Focus

Electronics/Computers

Software

Materials

Mechanics

Machinery/Automation

Manufacturing & Prototyping

Bio-Medical

Physical Sciences

Information Sciences

Books and Reports

02-07 February 2007

NASA Tech Briefs, February 2007 1

INTRODUCTION

Tech Briefs are short announcements of innovations originating from research and development activities of the National Aeronautics and Space Administration. They emphasize

information considered likely to be transferable across industrial, regional, or disciplinary lines

and are issued to encourage commercial application.

Availability of NASA Tech Briefs and TSPs

Requests for individual Tech Briefs or for Technical Support Packages (TSPs) announced herein should

be addressed to

National Technology Transfer Center

Telephone No. (800) 678-6882 or via World Wide Web at www2.nttc.edu/leads/

Please reference the control numbers appearing at the end of each Tech Brief. Information on NASA’s 

Innovative Partnerships Program (IPP), its documents, and services is also available at the same facility or

on the World Wide Web at http://ipp.nasa.gov.

Innovative Partnerships Offices are located at NASA field centers to provide technology-transfer access to

industrial users. Inquiries can be made by contacting NASA field centers listed below.

Ames Research Center

Lisa L. Lockyer

(650) 604-1754

lisa.l.lockyer@nasa.gov

Dryden Flight Research Center

Gregory Poteat

(661) 276-3872

greg.poteat@dfrc.nasa.gov

Goddard Space Flight Center

Nona Cheeks

(301) 286-5810

nona.k.cheeks@nasa.gov

Jet Propulsion Laboratory

Ken Wolfenbarger

(818) 354-3821

james.k.wolfenbarger@jpl.nasa.gov

Johnson Space Center

Michele Brekke

(281) 483-4614

michele.a.brekke@nasa.gov

Kennedy Space Center

David R. Makufka

(321) 867-6227

david.r.makufka@nasa.gov

Langley Research Center

Martin Waszak

(757) 864-4015

martin.r.waszak@nasa.gov

Glenn Research Center

Robert Lawrence

(216) 433-2921

robert.f.lawrence@nasa.gov

Marshall Space Flight Center

Vernotto McMillan

(256) 544-2615

vernotto.mcmillan@msfc.nasa.gov

Stennis Space Center

John Bailey

(228) 688-1660 

john.w.bailey@nasa.gov

Carl Ray, Program Executive

Small Business Innovation 

Research (SBIR) & Small 

Business Technology 

Transfer (STTR) Programs

(202) 358-4652

carl.g.ray@nasa.gov

Merle McKenzie, Director

Innovative Partnerships 

Program Office

(202) 358-2560

merle.mckenzie-1@nasa.gov

NASA Field Centers and Program Offices

5 Technology Focus: 

Test & Measurement

5 Calibration Test Set for a Phase-Comparison

Digital Tracker

5 Wireless Acoustic Measurement System

6 Spiral Orbit Tribometer 

7 Arrays of Miniature Microphones for

Aeroacoustic Testing

8 Predicting Rocket or Jet Noise in Real Time

8 Computational Workbench for Multibody

Dynamics

9 Electronics/Computers

9 High-Power, High-Efficiency Ka-Band Space

Traveling-Wave Tube 

9 Gratings and Random Reflectors for Near-Infrared

PIN Diodes

10 Optically Transparent Split-Ring Antennas for 1 to

10 GHz

11 Ice-Penetrating Robot for Scientific Exploration

12 Power-Amplifier Module for 145 to 165 GHz

12 Aerial Videography From Locally Launched

Rockets

13 SiC Multi-Chip Power Modules as Power-System

Building Blocks 

15 Software

15 Automated Design of Restraint Layer of an

Inflatable Vessel

15 TMS for Instantiating a Knowledge Base With

Incomplete Data

15 Simulating Flights of Future Launch Vehicles and

Spacecraft

15 Control Code for Bearingless SwitchedReluctance Motor

16 Machine Aided Indexing and the NASA Thesaurus

16 Arbitrating Control of Control and Display Units

16 Web-Based Software for Managing Research

16 Driver Code for Adaptive Optics

17 Materials

17 Ceramic Paste for Patching High-Temperature

Insulation

17 Fabrication of Polyimide-Matrix/Carbon and

Boron-Fiber Tape

18 Protective Skins for Aerogel Monoliths

19 Mechanics

19 Code Assesses Risks Posed by Meteoroids and

Orbital Debris

19 Asymmetric Bulkheads for Cylindrical Pressure

Vessels

21 Machinery/Automation

21 Self-Regulating Water-Separator System for Fuel

Cells

23 Manufacturing & Prototyping

23 Self-Advancing Step-Tap Drills

25 Physical Sciences

25 Array of Bolometers for SubmillimeterWavelength Operation

25 Delta-Doped CCDs as Detector Arrays in Mass

Spectrometers

26 Arrays of Bundles of Carbon Nanotubes as Field

Emitters

29 Books & Reports

29 Staggering Inflation To Stabilize Attitude of a

Solar Sail

29 Bare Conductive Tether for Decelerating a

Spacecraft

02-07 February 2007

NASA Tech Briefs, February 2007 3

This document was prepared under the sponsorship of the National Aeronautics and Space Administration. Neither the United States Government nor any person acting on behalf of the United States Government assumes any liability resulting from the use of the information contained

in this document, or warrants that such use will be free from privately owned rights.

NASA Tech Briefs, February 2007 5

Technology Focus: Test & Measurement

An apparatus that generates four signals

at a frequency of 7.1 GHz having precisely

controlled relative phases and equal amplitudes has been designed and built. This

apparatus is intended mainly for use in

computer-controlled automated calibration and testing of a phase-comparison

digital tracker (PCDT) that measures the

relative phases of replicas of the same Xband signal received by four antenna elements in an array. (The relative direction

of incidence of the signal on the array is

then computed from the relative phases.)

The present apparatus can also be used to

generate precisely phased signals for steering a beam transmitted from a phased antenna array.

The apparatus (see figure) includes a

7.1-GHz signal generator, the output of

which is fed to a four-way splitter. Each of

the four splitter outputs is attenuated by

10 dB and fed as input to a vector modulator, wherein DC bias voltages are used

to control the in-phase (I) and quadrature (Q) signal components. The bias

voltages are generated by digital-to-analog-converter circuits on a control board

that receives its digital control input

from a computer running a LabVIEW

program. The outputs of the vector modulators are further attenuated by 10 dB,

then presented at high-grade radio-frequency connectors. The attenuation reduces the effects of changing mismatch

and reflections.

The apparatus was calibrated in a

process in which the bias voltages were

first stepped through all possible IQ settings. Then in a reverse interpolation performed by use of MATLAB software, a

lookup table containing 3,600 IQ settings, representing equal amplitude and

phase increments of 0.1°, was created for

each vector modulator. During operation

of the apparatus, these lookup tables are

used in calibrating the PCDT.

This work was done by Amy Boas, Samuel Li,

and Robert McMaster of Caltech for NASA’s Jet

Propulsion Laboratory. Further information

is contained in a TSP (see page 1).

NPO-42813

Four-Way

Splitter

Vector

Modulator

I Q

Output 1

Vector

Modulator

I Q

Output 2

Vector

Modulator

I Q

Output 3

Vector

Modulator

10-dB Pads

APC-7 (or Equivalent)

High-Grade Connectors

I Q

Output 4

Control

Board Computer

7.1-GHz

Signal

Generator

APC-7 (or Equivalent)

High-Grade Connector

Calibration Test Set for a Phase-Comparison Digital Tracker

Four equal-amplitude signals are generated at selectable phase increments of 0.1°.

NASA’s Jet Propulsion Laboratory, Pasadena, California

The PCDT Calibration Test Set contains four computer-controlled vector modulators that produced selectably phased replicas of a 7.1-GHz input signal.

Wireless Acoustic Measurement System

This system supplants older, less-capable, cable-connected systems.

Stennis Space Center, Mississippi

A prototype wireless acoustic measurement system (WAMS) is one of two

main subsystems of the Acoustic Prediction/ Measurement Tool, which comprises software, acoustic instrumentation, and electronic hardware

combined to afford integrated capabilities for predicting and measuring noise

emitted by rocket and jet engines. The

other main subsystem is described in

the article on page 8.

The WAMS includes analog acoustic

measurement instrumentation and analog and digital electronic circuitry combined with computer wireless local-area

networking to enable (1) measurement

of sound-pressure levels at multiple locations in the sound field of an engine

under test and (2) recording and processing of the measurement data. At

each field location, the measurements

are taken by a portable unit, denoted a

field station. There are ten field stations,

each of which can take two channels of

measurements.

Each field station is equipped with two

instrumentation microphones, a microATX computer, a wireless network

adapter, an environmental enclosure, a

directional radio antenna, and a battery

power supply. The environmental enclosure shields the computer from weather

and from extreme acoustically induced

vibrations. The power supply is based on

a marine-service lead-acid storage battery that has enough capacity to support

operation for as long as 10 hours.

A desktop computer serves as a control server for the WAMS. The server is

connected to a wireless router for communication with the field stations via a

wireless local-area network that complies

with wireless-network standard 802.11b

of the Institute of Electrical and Electronics Engineers. The router and the
6 NASA Tech Briefs, February 2007

Spiral Orbit Tribometer 

Friction and lubricant degradation rate can be quantified rapidly.

John H. Glenn Research Center, Cleveland, Ohio

The spiral orbit tribometer (SOT)

bridges the gap between full-scale life

testing and typically unrealistic accelerated life testing of ball-bearing lubricants in conjunction with bearing ball

and race materials. The SOT operates

under realistic conditions and quickly

produces results, thereby providing information that can guide the selection

of lubricant, ball, and race materials

early in a design process.

The SOT is based upon a simplified,

retainerless thrust bearing comprising

one ball between flat races (see figure).

The SOT measures lubricant consumption and degradation rates and friction

coefficients in boundary lubricated

rolling and pivoting contacts.

The ball is pressed between the lower

and upper races with a controlled force

and the lower plate is rotated. The combination of load and rotation causes the

ball to move in a nearly circular orbit

that is, more precisely, an opening spiral. The spiral’s pitch is directly related

to the friction coefficient. At the end of

the orbit, the ball contacts the guide

plate, restoring the orbit to its original

radius. The orbit is repeatable throughout the entire test. A force transducer,

mounted in-line with the guide plate,

measures the force between the ball

and the guide plate, which directly relates to the friction coefficient. The

SOT, shown in the figure, can operate

in under ultra-high vacuum (10–9 Torr)

or in a variety of gases at atmospheric

pressure. The load force can be adjusted between 45 and 450 N. By varying the load force and ball diameter,

mean Hertzian stresses between 0.5 and

5.0 GPa can be obtained. The ball’s orbital speed range is between 1 and 100

rpm.

For most of the orbit, the ball undergoes pure rolling with pivot; however,

when the ball contacts the guide plate,

sliding also occurs. The period of contact

with the guide plate, termed the “scrub,”

is the most tribologically severe part of the

orbit and is when the majority of the lubricant’s tribo-degradation occurs.

Typically, a small amount of lubricant

(≈50 μg) is applied to the ball at the beginning of a test. Such a minute lubricant amount usually degrades within

one or two days. The test duration can

be varied by adjusting the initial

amount of lubricant and/or the load

force. A test is terminated when the luThe Spiral-Orbit Tribometer is based on a retainerless flat thrust bearing. The ball is squeezed between the

upper and lower flat races while the lower flat race is rotated, causing the ball to orbit in an opening spiral.

Upper 

Flat Race 

Lowe

Flat Race 

Ball Under Tes Guide Plate 

Upper 

Flat Race

Lowe

Flat Race 

Ball Under Tes Guide Plate 

LEW-17912-1 A B P 12-05-05 LE 

wireless network adapters are controlled

by use of Linux-compatible driver software. The server runs custom Linux software for synchronizing the recording of

measurement data in the field stations.

The software includes a module that

provides an intuitive graphical user interface through which an operator at

the control server can control the operations of the field stations for calibration

and for recording of measurement data.

A test engineer positions and activates

the WAMS. The WAMS automatically establishes the wireless network. Next, the

engineer performs pretest calibrations.

Then the engineer executes the test and

measurement procedures. After the test,

the raw measurement files are copied

and transferred, through the wireless

network, to a hard disk in the control

server. Subsequently, the data are

processed into 1

⁄3-octave spectrograms.

This work was done by Paul D. Anderson

and Wade D. Dorland of AI Signal Research,

Inc., and Ronald L. Jolly of Total Solutions,

Inc. for Stennis Space Center.

Inquiries concerning rights for the commercial use of this invention should be addressed

to the Intellectual Property Manager, Stennis

Space Center, (228) 688-1929. Refer to SSC00215-2.
NASA Tech Briefs, February 2007 7

A phased-array system comprised of

custom-made and commercially available microelectromechanical system

(MEMS) silicon microphones and custom ancillary hardware has been developed for use in aeroacoustic testing in

hard-walled and acoustically treated

wind tunnels. Recent advances in the

areas of multi-channel signal processing

and beam forming have driven the construction of phased arrays containing

ever-greater numbers of microphones.

Traditional obstacles to this trend have

been posed by (1) the high costs of conventional condenser microphones, associated cabling, and support electronics

and (2) the difficulty of mounting conventional microphones in the precise locations required for high-density arrays.

The present development overcomes

these obstacles.

One of the hallmarks of the new system is a series of fabricated platforms on

which multiple microphones can be

mounted. These mounting platforms,

consisting of flexible polyimide circuitboard material (see left side of figure),

include all the necessary microphone

power and signal interconnects. A single bus line connects all microphones to

a common power supply, while the signal lines terminate in one or more data

buses on the sides of the circuit board.

To minimize cross talk between array

channels, ground lines are interposed as

shields between all the data bus signal

lines. The MEMS microphones are electrically connected to the boards via solder pads that are built into the printed

wiring. These flexible circuit boards

share many characteristics with their traditional rigid counterparts, but can be

manufactured much thinner, as small as

0.1 millimeter, and much lighter with

boards weighing as much as 75 percent

less than traditional rigid ones.

For a typical hard-walled wind-tunnel

installation, the flexible printed-circuit

board is bonded to the tunnel wall and

covered with a face sheet that contains

precise cutouts for the microphones.

Once the face sheet is mounted, a

smooth surface is established over the

entire array due to the flush mounting

of all microphones (see right side of figure). The face sheet is made from a continuous glass-woven-fabric base impregnated with an epoxy resin binder. This

material offers a combination of high

mechanical strength and low dielectric

loss, making it suitable for withstanding

the harsh test section environment present in many wind tunnels, while at the

same time protecting the underlying

polyimide board.

Customized signal-conditioning hardware consisting of line drivers and antialiasing filters are coupled with the

array. The line drivers are constructed

using low-supply-current, high-gainbandwidth operational amplifiers designed to transmit the microphone signals several dozen feet from the array to

external acquisition hardware. The

anti-alias filters consist of individual

Chebyshev low-pass filters (one for each

microphone channel) housed on small

printed-circuit boards mounted on one

or more motherboards. The

mother/daughter board design results

in a modular system, which is easy to

debug and service and which enables

the filter characteristics to be changed

by swapping daughter boards with ones

containing different filter parameters.

The filter outputs are passed to commercially-available acquisition hardware

to digitize and store the conditioned microphone signals. Wind-tunnel testing

of the new MEMS microphone polyimide mounting system shows that the

array performance is comparable to

that of traditional arrays, but with significantly less cost of construction.

This work was done by Qamar A. Shams,

William M. Humphreys, Bradley S. Sealey, Scott

M. Bartram, Allan J. Zuckerwar, Toby

Comeaux, and James K. Adams of Langley Research Center. Further information is contained in a TSP (see page 1). LAR-17171-1

Arrays of Miniature Microphones for Aeroacoustic Testing

MEMS microphones are mounted on flexible printed-circuit boards.

Langley Research Center, Hampton, Virginia

An Array of MEMS Microphones (left) and a Face Sheet (right) are shown. The array is formed on a

flexible printed-circuit board. The array can readily be affixed to a curved wind-tunnel surface for use

in aeroacoustic testing. The face sheet containing small rectangular cutouts for the microphones is

placed over an array like that on the left to provide a smooth outer surface.

MEMS Microphones 

Flexible 

Printed-Circuit Board 

bricant fails. Failure is defined when the

friction coefficient rises beyond a predefined limit, which is usually two to three

times the starting friction coefficient.

The lifetime of the lubricant is then

quantified as the total number of ball

orbits completed divided by initial

amount of lubricant on the ball. Typically, four tests are done for each condition and their results averaged for statistical significance in the test data. Relative lifetimes for various materials can

be compared and can be directly correlated with relative lifetimes in real applications. 

This work was done by Stephen V. Pepper and

William R. Jones, Jr. of Glenn Research Center, Edward Kingsbury of Interesting Rolling

Contact, and Mark J. Jansen of the University of

Toledo. Further information is contained in a

TSP (see page 1).

Inquiries concerning rights for the commercial

use of this invention should be addressed to

NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8,

21000 Brookpark Road, Cleveland, Ohio

44135. Refer to LEW-17912-1.
8 NASA Tech Briefs, February 2007

Predicting Rocket or Jet Noise in Real Time

Measurement data can be analyzed in real time.

Stennis Space Center, Mississippi

A semi-empirical theoretical model

and a C++ computer program that implements the model have been developed

for use in predicting the noise generated

by a rocket or jet engine. The computer

program, entitled the Realtime Rocket

and Jet Engine Noise Analysis and Prediction Software, is one of two main subsystems of the Acoustic Prediction/Measurement Tool, which comprises

software, acoustic instrumentation, and

electronic hardware combined to afford

integrated capabilities for real-time prediction and measurement of noise emitted by rocket and jet engines. [The other

main subsystem, consisting largely of

acoustic instrumentation and electronic

hardware, is described in “Wireless

Acoustic Measurement System,” which

appears elsewhere in this section.]

The theoretical model was derived

from the fundamental laws of fluid mechanics, as first was done by M. J.

Lighthill in his now famous theory of

aerodynamically generated sound. The

far-field approximation of the Lighthill

theory is incorporated into this model.

Many other contributions from various

researchers have also been introduced

into the model. The model accounts for

two noise components: shear noise and

self noise. The final result of the model

is expressed in terms of a volume integral of the acoustic intensities attributable to these two components, subject to

various directivity coefficients.

The computer program was written to

solve the volume integral. The inputs required by the program are two data files

from a computational fluid dynamics

(CFD) simulation of the flow of interest:

the computational-grid file and the solution file. The CFD solution should be one

that has been obtained for conditions that

closely approximate those of an experimental test that is yet to be performed.

In the current state of development of

the model and software, it is recommended that the observation points lie

along a radius at an angle >60° from the

jet axis. The software provides, and is

driven via, a graphical user interface,

which facilitates its use. Optionally, the

program accepts additional input in the

form of data on the measured sound

pressure level as a function of frequency

at a given far-field location, preferably at

an angle of 90° from the jet axis. The

user is prompted to use default empirical constants or to choose constants

based the measurement data. The user

can view the results and compare them

with other computational or experimental data. Once satisfied with the results,

the user can save a graph of the results

in a file that can be imported into documents.

This program was written by Kader Frendi

of the University of Alabama in Huntsville

for Stennis Space Center.

In accordance with Public Law 96-517,

the contractor has elected to retain title to this

invention. Inquiries concerning rights for its

commercial use should be addressed to:

Dr. Kader Frendi

The University of Alabama

5000 Technology Drive, Room THN264

Huntsville, AL 35899

Phone No.: (256) 824-7206

E-mail: frendi@eng.uah.edu

Refer to SSC-00215-1, volume and number of this NASA Tech Briefs issue, and the

page number.

PyCraft is a computer program that

provides an interactive, workbenchlike

computing environment for developing

and testing algorithms for multibody dynamics. Examples of multibody dynamic

systems amenable to analysis with the

help of PyCraft include land vehicles,

spacecraft, robots, and molecular models. PyCraft is based on the Spatial-Operator-Algebra (SOA) formulation for multibody dynamics. The SOA operators

enable construction of simple and compact representations of complex multibody dynamical equations. Within the PyCraft computational workbench, users

can, essentially, use the high-level SOA

operator notation to represent the variety

of dynamical quantities and algorithms

and to perform computations interactively. PyCraft provides a Python-language

interface to underlying C++ code. Working with SOA concepts, a user can create

and manipulate Python-level operator

classes in order to implement and evaluate new dynamical quantities and algorithms. During use of PyCraft, virtually all

SOA-based algorithms are available for

computational experiments.

This program was written by Abhinandan

Jain of Caltech for NASA’s Jet Propulsion

Laboratory. Further information is contained in a TSP (see page 1).

This software is available for commercial

licensing. Please contact Karina Edmonds of

the California Institute of Technology at

(626) 395-2322. Refer to NPO-42891.

Computational Workbench for Multibody Dynamics

NASA’s Jet Propulsion Laboratory, Pasadena, California
NASA Tech Briefs, February 2007 9

The L-3 Communications Model 999H

traveling-wave tube (TWT) has been

demonstrated to generate an output

power of 144 W at 60-percent overall efficiency in continuous-wave operation over

the frequency band from 31.8 to 32.3

GHz. The best TWT heretofore commercially available for operation in the affected frequency band is characterized by

an output power of only 35 W and an efficiency of 50 percent. Moreover, whereas

prior TWTs are limited to single output

power levels, it has been shown that the

output power of the Model 999H can be

varied from 54 to 144 W.

A TWT is a vacuum electronic device

used to amplify microwave signals. TWTs

are typically used in free-space communication systems because they are capable of operating at power and efficiency

levels significantly higher than those of

solid-state devices. In a TWT, an electron

beam is generated by an electron gun

consisting of a cathode, focusing electrodes, and an anode. The electrons pass

through a hole in the anode and are focused into a cylindrical beam by a stack

of periodic permanent magnets and

travel along the axis of an electrically

conductive helix, along which propagates an electromagnetic wave that has

been launched by an input signal that is

to be amplified.

The beam travels within the helix at a

velocity close to the phase velocity of the

electromagnetic wave. The electromagnetic field decelerates some of the electrons and accelerates others, causing the

beam to become formed into electron

bunches, which further interact with the

electromagnetic wave in such a manner

as to surrender kinetic energy to the

wave, thereby amplifying the wave. The

net result is to amplify the input signal by

a factor of about 100,000. After the electrons have passed along the helix, they

impinge on electrodes in a collector. The

collector decelerates the electrons in

such a manner as to recover most of the

remaining kinetic energy and thereby

significantly increase the power efficiency of the TWT.

The increase in power and efficiency

of L-3 Communications Model 999H

TWT over those of prior TWTs are attributable to several factors: 

• Beam-focusing components feature

new designs for improved thermal capability and increased operating stability. 

• Advanced computational modeling of

the interaction of the microwave signal

with the electron beam made it possible to modify designs of components

to attain high efficiency over a wide

range of power levels. 

• Improved wide-band waveguide-to-circuit coupling and wide-band, highpower radio-frequency windows were

developed. 

• A four-stage depressed collector was optimized by use of MICHELLE, a Naval

Research Laboratory computer code for

modeling guns and collectors in TWTs. 

This work was done by Richard Krawczyk, Jeffrey Wilson, Rainee Simons, Wallace Williams

and Kul Bhasin of Glenn Research Center

and Neal Robbins, Daniel Dibb, William Menninger, Xiaoling Zhai, Robert Benton, and

James Burdette of L-3 Communications Electron

Technologies, Inc. Further information is contained in a TSP (see page 1).

Inquiries concerning rights for the commercial use of this invention should be addressed

to NASA Glenn Research Center, Innovative

Partnerships Office, Attn: Steve Fedor, Mail

Stop 4–8, 21000 Brookpark Road, Cleveland,

Ohio 44135. Refer to LEW-17900-1.

Electronics/Computers

High-Power, High-Efficiency Ka-Band Space Traveling-Wave Tube 

Improved designs of critical components contribute to increased power and efficiency. 

John H. Glenn Research Center, Cleveland, Ohio

Gratings and Random Reflectors for Near-Infrared PIN Diodes

Quantum efficiency would be increased.

NASA’s Jet Propulsion Laboratory, Pasadena, California

Crossed diffraction gratings and random reflectors have been proposed as

means to increase the quantum efficiencies of InGaAs/InP positive/intrinsic/

negative (PIN) diodes designed to operate as near-infrared photodetectors. The

proposal is meant especially to apply to

focal-plane imaging arrays of such photodetectors to be used for near-infrared

imaging. A further increase in quantum

efficiency near the short-wavelength

limit of the near-infrared spectrum of

such a photodetector array could be effected by removing the InP substrate of

the array.

The use of crossed diffraction gratings and random reflectors as optical

devices for increasing the quantum efficiencies of quantum-well infrared photodetectors (QWIPs) was discussed in

several prior NASA Tech Briefs articles.

While the optical effects of crossed gratings and random reflectors as applied

to PIN photodiodes would be similar to

those of crossed gratings and random

reflectors as applied to QWIPs, the

physical mechanisms by which these optical effects would enhance efficiency

differ between the PIN-photodiode and

QWIP cases:

• In a QWIP, the multiple-quantum-well

layers are typically oriented parallel to

the focal plane and therefore perpendicular or nearly perpendicular to the

direction of incidence of infrared

light. By virtue of the applicable quantum selection rules, light polarized

parallel to the focal plane (as normally incident light is) cannot excite

charge carriers and, hence, cannot be

detected. A pair of crossed gratings or

a random reflector scatters normally

or nearly normally incident light so

that a significant portion of it attains a

component of polarization normal to
10 NASA Tech Briefs, February 2007

the focal plane and, hence, can excite

charge carriers.

• A pair of crossed gratings or a random

reflector on a PIN photodiode would

also scatter light into directions away

from the perpendicular to the focal

plane. However, in this case, the reason for redirecting light away from the

perpendicular is to increase the length

of the optical path through the detector to increase the probability of absorption of photons and thereby increase the resulting excitation of

charge carriers.

A pair of crossed gratings or a random reflector according to the proposal would be fabricated as an integral part of photodetector structure

on the face opposite the focal plane

(see figure). In the presence of

crossed gratings, light would make

four passes through the device before

departing. In the presence of a random reflector, a significant portion of

the light would make more than four

passes: After each bounce, light would

be scattered at a different random

angle, and would have a chance to escape only when it was reflected, relative to the normal, at an angle less

than the critical angle for total internal reflection. Given the indices of refraction of the photodiode materials,

this angle would be about 17°. This

amounts to a very narrow cone for escape of trapped light.

This work was done by Sarath Gunapala,

Sumith Bandara, John Liu, and David Ting

of Caltech for NASA’s Jet Propulsion Laboratory. Further information is contained in a

TSP (see page 1).

In accordance with Public Law 96-517,

the contractor has elected to retain title to this

invention. Inquiries concerning rights for its

commercial use should be addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak Grove Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: iaoffice@jpl.nasa.gov

Refer to NPO-30509, volume and number of this

NASA Tech Briefs issue, and the page number.

Crossed Diffraction Gratings or a Random Reflector would be fabricated on the back (here, the top) face of a PIN photodiode in each pixel of an imaging

array of such photodiodes.

ritical Angle for Total

Internal Reflection

Random Reflector on Surface

One Pixel

Crossed Gratings

Cavity Between Pixels for

rapping Light Within the Pixels

Thin GaAs Substrate

scaping Light

ncident Light

Escaping Light

CROSSED GRATINGS RANDOM REFLECTOR

Incident Light

One Pixel

NPO30509

3-18-02 bs

Split-ring antennas made from optically

transparent, electrically conductive films

have been invented for applications in

which there are requirements for compact

antennas capable of operation over much

or all of the frequency band from 1 to 10

GHz. Primary examples of such applications include wireless local-area networks

and industrial, scientific, and medical

(ISM) applications. These antennas can

be conveniently located on such surfaces

as those of automobile windows and display screens of diverse hand-held electronic units. They are fabricated by conventional printed-circuit techniques and

can easily be integrated with solid-state

amplifier circuits to enhance gain.

The structure of an antenna of this

type includes an antenna/feed layer supported on the top or outer face of a dielectric (e.g., glass) and, optionally, a

ground layer on the bottom or inner

face of the substrate. The ring can be in

the form of either a conductive strip or a

slot in the antenna/feed layer. The ring

can be of rectangular, square, circular,

elliptical, or other suitable shape and

can be excited by means of a microstrip,

slot line, or coplanar waveguide. For example, the antenna shown in the figure

features a square conductive-strip split

ring with a microstrip feed.

In general, an antenna fed at its external boundary in the manner of this invention presents very high impedance,

thereby creating an impedance-matching

problem. Splitting the ring — that is, cutting a notch through the ring — offers a

solution to the problem in that the notch

fixes the location of maximum electric

field, which location is directly related to

the impedance. Thus, an excellent impedance match can be achieved through

proper choice of the location of the notch.

In geometric layout, such a ring antenna structure is typically between 1

⁄4 and 1

⁄3 the size of a patch antenna capable of

operating in the same frequency range.

This miniaturization of the antenna is desirable, not only because it contributes to

overall miniaturization of equipment, but

Optically Transparent Split-Ring Antennas for 1 to 10 GHz

Advantages include ultra-wide-band operation, miniaturization, and excellent impedance matching.

John H. Glenn Research Center, Cleveland, Ohio
NASA Tech Briefs, February 2007 11

also because minimization of the extent

of the optically transparent, electrically

conductive film helps to minimize the

electrical loss associated with the surface

resistance (≈5 ohms per square) of the

transparent, electrically conductive film

material.

Incidentally, even at ≈5 ohms per

square, this surface resistance is significantly less than that of indium tin oxide

film (typically > 25 ohms per square),

which, heretofore has been the transparent, electrically conductive film material of

choice. At the time of writing this article,

information on the composition of the

lower-resistance film used in the antennas

of this invention was not available.

This work was done by Richard Q. Lee

and Rainee N. Simons of Glenn Research

Center. Further information is contained in

a TSP (see page 1).

Inquiries concerning rights for the commercial use of this invention should be addressed

to NASA Glenn Research Center, Innovative

Partnerships Office, Attn: Steve Fedor, Mail

Stop 4–8, 21000 Brookpark Road, Cleveland,

Ohio 44135. Refer to LEW-17925-1.

Ice-Penetrating Robot for Scientific Exploration

A compact probe contains advanced power, instrumentation, navigation, control, and

communication systems. 

NASA’s Jet Propulsion Laboratory, Pasadena, California

The cryo-hydro integrated robotic

penetrator system (CHIRPS) is a partially developed instrumentation system

that includes a probe designed to

deeply penetrate the Europan ice sheet

in a search for signs of life. The CHIRPS

could also be used on Earth for similar

exploration of the polar ice caps — especially at Lake Vostok in Antarctica.

The CHIRPS probe advances downward

by a combination of simple melting of

ice (typically for upper, non-compacted

layers of an ice sheet) or by a combination of melting of ice and pumping of

meltwater (typically, for deeper, compacted layers). The heat and electric

power for melting, pumping, and operating all of the onboard instrumentation and electronic circuitry are supplied by radioisotope power sources

(RPSs) and thermoelectric converters

energized by the RPSs. The instrumentation and electronic circuitry includes

miniature guidance and control sensors

and an advanced autonomous control

system that has fault-management capabilities.

The CHIRPS probe is about 1 m long

and 15 cm in diameter. The RPSs generate a total thermal power of 1.8 kW. Initially, as this power melts the surrounding

ice, a meltwater jacket about 1 mm thick

forms around the probe. The center of

gravity of the probe is well forward

(down), so that the probe is vertically stabilized like a pendulum. Heat is circulated to the nose by means of miniature

pumps and heat pipes.

The probe melts ice to advance in a

step-wise manner: Heat is applied to the

nose to open up a melt void, then heat

is applied to the side to allow the probe

to slip down into the melt void. The

melt void behind the probe is allowed

to re-freeze. Four quadrant heaters on

the nose and another four quadrant

heaters on the rear (upper) surface of

the probe are individually controllable

for steering: Turning on two adjacent

nose heaters on the nose and two adjacent heaters on the opposite side at the

rear causes melt voids to form on opposing sides, such that the probe descends at an angle from vertical. This

steering capability can be used to avoid

debris trapped in the ice or to maneuver closer to a trapped object of scientific interest.

The probe contains a system that ingests

meltwater, heats the water, and pumps the

heated water to form a jet out of a central

orifice on the nose. The jet removes debris

and contributes to the melting of ice in

front of the probe. The external pressure

of the ice is utilized to drive some of the

meltwater into a channel on the outside of

the probe shell, across a membrane, into

miniature pumps, which supply water samples to the onboard scientific instruments.

The guidance and control sensors include a three-axis inclinometer, a forwardlooking acoustic imager, and sensors for

measuring temperature, pressure, flow

rate, and pump-motor current. There is

also a tether-payout encoder and a tetheractuator/brake current sensor for use in

the event that the probe is connected to

surface instrumentation via a tether cable

(typically, for a shallow penetration). The

electronic circuitry includes a power conditioner, telemetry driver, master controller,

digital-to-analog and analog-to-digital converters, instrument drivers, and memory

circuits, including data buffers.

At the rear (upper end) of the fully developed probe, for radio communication

with the surface instrumentation in the

event that a tether cable was not used (typically, during a deep penetration), there

would be a primary radio transceiver and

its antenna. Behind this antenna there

would be 13 radio relay units, denoted ice

transceivers, each between 2 and 3 cm

thick and about 10 cm in diameter. The

transceivers would be released, one at a

time, into the rear slush and allowed to become frozen in place for relaying signals

between the probe and the surface. The

release depths would be chosen on the

basis of signal strength and of the temperature and electrical conductivity of the ice.

In the event of an ice sheet over a body

of liquid water (as in Lake Vostok), as the

probe approached the ice/liquid interface, the acoustic imager would sense the

interface. At this point, the front portion

of the probe carrying the heat source and

instruments would separate from the rear

portion of the probe. The ice would refreeze around the aft body, which would

thereafter serve as an anchor and a communication relay. The front portion would

descend through the water on a tether,

sampling the water for signs of life.

This work was done by Wayne Zimmerman,

Frank Carsey, and Lloyd French of Caltech for

NASA’s Jet Propulsion Laboratory. Further information is contained in a TSP (see

page 1).

NPO-40747

This Square Split-Ring Antenna operates with a

voltage standing-wave ratio of 2 or less over the

entire ISM frequency band.

LEW-17925-1 ABPI 06-23-05 LE
12 NASA Tech Briefs, February 2007

Power-Amplifier Module for 145 to 165 GHz

This module represents the highest frequency solid-state power amplifier to date. 

NASA’s Jet Propulsion Laboratory, Pasadena, California

A power-amplifier module that operates in the frequency

range of 145 to 165 GHz has been designed and constructed

as a combination of (1) a previously developed monolithic

microwave integrated circuit (MMIC) power amplifier and

(2) a waveguide module. The amplifier chip was needed for

driving a high-electron-mobility-transistor (HEMT) frequency doubler. While it was feasible to connect the amplifier

and frequency-doubler chips by use of wire bonds, it was

found to be much more convenient to test the amplifier and

doubler chips separately. To facilitate separate testing, it was

decided to package the amplifier and doubler chips in separate waveguide modules. Figure 1 shows the resulting amplifier module.

The amplifier chip was described in “MMIC HEMT Power

Amplifier for 140 to 170 GHz” (NPO-30127), NASA Tech

Briefs, Vol. 27, No. 11, (November 2003), page 49. To recapitulate: This is a three-stage MMIC power amplifier that utilizes

HEMTs as gain elements. The amplifier was originally designed to operate in the frequency range of 140 to 170 GHz.

The waveguide module is based on a previously developed

lower frequency module, redesigned to support operation in

the frequency range of 140 to 220 GHz.

Figure 2 presents results of one of several tests of the amplifier module — measurements of output power and gain as

functions of input power at an output frequency of 150 GHz.

Such an amplifier module has many applications to test equipment for power sources above 100 GHz.

This work was done by Lorene Samoska and Alejandro Peralta of

Caltech for NASA’s Jet Propulsion Laboratory. Further information is contained in a TSP (see page 1).NPO-40260

Figure 1. The Amplifier Is Packaged in a WR5 waveguide module, with electric-field-plane alumina probes to interface the chip to the waveguide, and

bypass capacitors to suppress low-frequency oscillations. The module is compact and can easily be integrated into a test system or with wafer probes. 

Complete Module

(Longest Dimension About 0.75 in.)

Module Partly Disassembled 

to Show Amplifier

NPO-40260 FIG 1 ABPI 05-25-04 LE

Figure 2. Output Power and Gain at 150 GHz were measured as functions

of input power. The output power exhibited saturation at 13 dBm.

NPO-40260 FIG 2 ABPI 06-20-03 LE

Input Power, dBm

Output Power dBm or Gain dB

0

10

0

20 -15 10 -5 0 10 15

Output Power

Gain

Aerial Videography From Locally Launched Rockets

Images of an event or scene are rapidly collected, processed, and displayed.

Stennis Space Center, Mississippi

A method of quickly collecting digital

imagery of ground areas from video cameras carried aboard locally launched rockets has been developed. The method can

be used, for example, to record rare or

episodic events or to gather image data to

guide decisions regarding treatment of

agricultural fields or fighting wildfires.

The method involves acquisition and

digitization of a video frame at a known

time along with information on the position and orientation of the rocket and

camera at that time. The position and orientation data are obtained by use of a

Global Positioning System receiver and a

digital magnetic compass carried aboard

the rocket. These data are radioed to a

ground station, where they are processed,

by a real-time algorithm, into georeferenced position and orientation data. The

algorithm also generates a file of transformation parameters that account for the

variation of image magnification and distortion associated with the position and

orientation of the camera relative to the

ground scene depicted in the image. As

the altitude, horizontal position, and ori-
NASA Tech Briefs, February 2007 13

entation of the rocket change between

image frames, the algorithm calculates the

corresponding new georeferenced position and orientation data and the associated transformation parameters.

The output imagery can be rendered

in any of a variety of formats. The figure

presents an example of one such format.

This work was done by Stacey D. Lyle of

Conrad Blucher Institute for Surveying and

Science at Texas A&M University—Corpus

Christi for Stennis Space Center.

In accordance with Public Law 96-517,

the contractor has elected to retain title to this

invention. Inquiries concerning rights for its

commercial use should be addressed to:

Texas A&M — Corpus Christi

6300 Ocean Dr.

Corpus Christi, Texas 78412

Phone No.: (361) 825-3712

E-mail: slyle@falcon.tamucc.edu

Refer to SSC-00214-1, volume and number of this NASA Tech Briefs issue, and the

page number.

A Digitized, Transformed Image acquired from a video camera aboard a rocket was superimposed on

a scan of an aerial image of a larger area that contains most of the video-image scene.

SSC-00214 ABPI 08-30-06 LE

SiC Multi-Chip Power Modules as Power-System Building Blocks 

Fault-tolerant power-supply systems could be constructed and expanded relatively inexpensively.

John H. Glenn Research Center, Cleveland, Ohio

The term “SiC MCPMs” (wherein

“MCPM” signifies “multi-chip power

module”) denotes electronic power-supply modules containing multiple silicon

carbide power devices and silicon-on-insulator (SOI) control integrated-circuit

chips. SiC MCPMs are being developed

as building blocks of advanced expandable, reconfigurable, fault-tolerant

power-supply systems. Exploiting the

ability of SiC semiconductor devices to

operate at temperatures, breakdown

voltages, and current densities significantly greater than those of conventional Si devices, the designs of SiC

MCPMs and of systems comprising multiple SiC MCPMs are expected to afford

a greater degree of miniaturization

through stacking of modules with reduced requirements for heat sinking.

Moreover, the higher-temperature capabilities of SiC MCPMs could enable operation in environments hotter than Sibased power systems can withstand.

The stacked SiC MCPMs in a given system can be electrically connected in series, parallel, or a series/parallel combination to increase the overall

power-handling capability of the system.

In addition to power connections, the

modules have communication connections. The SOI controllers in the modules

communicate with each other as nodes of

a decentralized control network, in which

no single controller exerts overall command of the system. Control functions effected via the network include synchronization of switching of power devices

and rapid reconfiguration of power connections to enable the power system to

continue to supply power to a load in

the event of failure of one of the modules.

In addition to serving as building

blocks of reliable power-supply systems,

SiC MCPMs could be augmented with external control circuitry to make them perform additional power-handling functions as needed for specific applications:

typical functions could include regulating voltages, storing energy, and driving

motors. Because identical SiC MCPM

building blocks could be utilized in a variety of ways, the cost and difficulty of designing new, highly reliable power systems would be reduced considerably.

Several prototype DC-to-DC powerconverter modules containing SiC powerswitching devices were designed and built

to demonstrate the feasibility of the SiC

MCPM concept. In anticipation of a future need for operation at high temperature, the circuitry in the modules includes high-temperature inductors and

capacitors. These modules were designed

to be stacked to construct a system of four

modules electrically connected in series

and/or parallel.

The packaging of the modules is designed to satisfy requirements for series

and parallel interconnection among

modules, high power density, high thermal efficiency, small size, and light

weight. Each module includes four output power connectors — two for serial

and two for parallel output power connections among the modules. Each

module also includes two signal connectors, electrically isolated from the power

connectors, that afford four zones for

signal interconnections among the SOI

controllers. Finally, each module includes two input power connectors,

through which it receives power from an

in-line power bus. This design feature is

included in anticipation of a custom-designed power bus incorporating sockets

compatible with “snap-on” type connectors to enable rapid replacement of

failed modules.

The distributed control hardware and

software enable power conversion to continue uninterrupted when as many as two
14 NASA Tech Briefs, February 2007

modules fail. Essential to distributed control is an arbitrated, shared communication bus. The arbitration protocol enables asynchronous bidirectional

messaging without concern for data collisions and loss of messages. In tests of the

four-module system in which failures of as

many as two modules were simulated,

measurement results showed that the system reconfigured itself rapidly enough in

response to the failures to continue delivering power to a load without interruption and with minimum output-voltage

sag. The transient time associated with a

failure was found to be <5 ms, of which

<350 μs was consumed by software and

the rest was consumed by operation of bypass relays. 

This work was done by Alexander Lostetter

and Steven Franks of Arkansas Power Electronics International, Inc. for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed

to NASA Glenn Research Center, Innovative

Partnerships Office, Attn: Steve Fedor, Mail

Stop 4–8, 21000 Brookpark Road, Cleveland,

Ohio 44135. Refer to LEW-18008-1.
NASA Tech Briefs, February 2007 15

Software

Automated Design of 

Restraint Layer of an 

Inflatable Vessel

A Mathcad computer program largely

automates the design and analysis of the

restraint layer (the primary load-bearing

layer) of an inflatable vessel that consists

of one or more sections having cylindrical, toroidal, and/or spherical shape(s). A

restraint layer typically comprises webbing

in the form of multiple straps. The design

task includes choosing indexing locations

along the straps, computing the load at

every location in each strap, computing

the resulting stretch at each location, and

computing the amount of undersizing required of each strap so that, once the vessel is inflated and the straps thus

stretched, the vessel can be expected to

assume the desired shape. 

Prior to the development of this program, the design task was performed by

use of a difficult-to-use spreadsheet program that required manual addition of

rows and columns depending on the

numbers of strap rows and columns of a

given design. In contrast, this program

is completely parametric and includes

logic that automatically adds or deletes

rows and columns as needed. With minimal input from the user, this program

automatically computes indexing locations, strap lengths, undersizing requirements, and all design data required to produce detailed drawings

and assembly procedures. It also generates textual comments that help the

user understand the calculations.

This program was written by Gary

Spexarth of Johnson Space Center. Further information is contained in a TSP (see

page 1).

This invention is owned by NASA, and a

patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its

commercial development should be addressed to

the Patent Counsel, Johnson Space Center,

(281) 483-0837. Refer to MSC-23906.

TMS for Instantiating a

Knowledge Base With 

Incomplete Data

A computer program that belongs to

the class known among software experts

as output truth-maintenance-systems

(output TMSs) has been devised as one

of a number of software tools for reducing the size of the knowledge base that

must be searched during execution of artificial-intelligence software of the rulebased inference-engine type in a case in

which data are missing. This program determines whether the consequences of

activation of two or more rules can be

combined without causing a logical inconsistency. For example, in a case involving hypothetical scenarios that could

lead to turning a given device on or off,

the program determines whether a scenario involving a given combination of

rules could lead to turning the device

both on and off at the same time, in

which case that combination of rules

would not be included in the scenario.

This program was written by Mark James of

Caltech for NASA’s Jet Propulsion Laboratory. Further information is contained in a

TSP (see page 1).

This software is available for commercial

licensing. Please contact Karina Edmonds of

the California Institute of Technology at

(626) 395-2322. Refer to NPO-42710.

Simulating Flights of 

Future Launch Vehicles and 

Spacecraft

Marshall Aerospace Vehicle Representation in C (MAVERIC) is a computer

program for generic, low-to-high-fidelity

simulation of the flight(s) of one or

more launch vehicle(s) or spacecraft.

MAVERIC is designed to accommodate

multi-staged vehicles, powered serially or

in parallel, with multiple engines, tanks,

and cargo elements. Engines can be of

jet or conventional rocket types, using either liquid or solid propellants. 

MAVERIC includes generic subsystem

software models for propulsion systems,

mass properties, reaction control systems, aerodynamic properties, guidance

systems, and navigation systems. Simulations can be started at points other than

liftoff. Also included are guidance-system software models that accommodate

the ascent, orbit, coasting, deorbiting,

entry, terminal-area-energy-management, approach, and landing phases of

flight. 

Options to use different wind profiles

and atmospheres are included. A Monte

Carlo capability is provided for modeling dispersions associated with atmospheric effects (including winds), propulsion, navigation, aerodynamics, and

mass properties. Failures of engines and

other subsystems can be modeled. The

program is written in the C programming language, which makes it possible

for the program to have high degrees of

modularity, reusability, and maintainability, thereby also facilitating modification for modeling new vehicles.

This program was written by James W. McCarter of Marshall Space Flight Center.

Further information is contained in a TSP

(see page 1).

This invention is owned by NASA, and a

patent application has been filed. For further

information, contact Sammy Nabors, MSFC

Commercialization Assistance Lead, at

sammy.a.nabors@nasa.gov. Refer to MFS31989-1.

Control Code for Bearing- less Switched-Reluctance

Motor

A computer program has been devised for controlling a machine that is an

integral combination of magnetic bearings and a switched-reluctance motor.

The motor contains an eight-pole stator

and a hybrid rotor, which has both (1) a

circular lamination stack for levitation

and (2) a six-pole lamination stack for

rotation. The program computes drive

and levitation currents for the stator

windings with real-time feedback control. During normal operation, two of

the four pairs of opposing stator poles

(each pair at right angles to the other

pair) levitate the rotor. The remaining

two pairs of stator poles exert torque on

the six-pole rotor lamination stack to

produce rotation. This version is executable in a control-loop time of 40 μs

on a Pentium (or equivalent) processor

that operates at a clock speed of 400

MHz. The program can be expanded, by

addition of logic blocks, to enable control of position along additional axes.

The code enables adjustment of operational parameters (e.g., motor speed

and stiffness, and damping parameters

of magnetic bearings) through computer keyboard key presses. 

This program was written by Carlos R.

Morrison of Glenn Research Center. Further information is contained in a TSP (see

page 1).
16 NASA Tech Briefs, February 2007

Inquiries concerning rights for the commercial use of this invention should be addressed

to NASA Glenn Research Center, Innovative

Partnerships Office, Attn: Steve Fedor, Mail

Stop 4–8, 21000 Brookpark Road, Cleveland,

Ohio 44135. Refer to LEW-17964-1.

Machine Aided Indexing

and the NASA Thesaurus

Machine Aided Indexing (MAI) is a

Web-based application program for aiding the indexing of literature in the

NASA Scientific and Technical Information

(STI) Database. MAI was designed to be

a convenient, fully interactive tool for

determining the subject matter of documents and identifying keywords. The

heart of MAI is a natural-language

processor that accepts, as input, any

user-supplied text, including abstracts,

full documents, and Web pages. Within

seconds, the text is analyzed and a

ranked list of terms is generated. The

17,800 terms of the NASA Thesaurus

serve as the foundation of the knowledge base used by MAI. The NASA Thesaurus defines a standard vocabulary,

the use of which enables MAI to assist in

ensuring that STI documents are uniformly and consistently accessible. Of

particular interest to traditional users of

the NASA Thesaurus, MAI incorporates

a fully searchable thesaurus display

module that affords word-search and hierarchy-navigation capabilities that

make it much easier and less time-consuming to look up terms and browse,

relative to lookup and browsing in older

print and Portable Document Format

(PDF) digital versions of the Thesaurus.

In addition, because MAI is centrally

hosted, the Thesaurus data are always

current.

This program was written by Bill 

von Ofenheim for Langley Research Center. For further information, access

http://mai.larc.nasa.gov.

LAR-17110-1

Arbitrating Control of 

Control and Display Units

The ARINC 739 Switch is a computer

program that arbitrates control of two

multi-function control and display units

(MCDUs) between (1) a commercial

flight-management computer (FMC)

and (2) NASA software used in research

on transport aircraft. (MCDUs are the

primary interfaces between pilots and

FMCs on many commercial aircraft.)

This program was recently redesigned

into a software library that can be embedded in research application programs. As part of the redesign, this software was combined with software for

creating custom pages of information to

be displayed on a CDU. This software

commands independent switching of

the left (pilot’s) and right (copilot’s)

MCDUs. For example, a custom CDU

page can control the left CDU while the

FMC controls the right CDU. The software uses menu keys to switch control of

the CDU between the FMC or a custom

CDU page. The software provides an interface that enables custom CDU pages

to insert keystrokes into the FMC’s CDU

input interface. This feature allows the

custom CDU pages to manipulate the

FMC as if it were a pilot. 

This program was written by Michael M.

Madden of Langley Research Center

and Paul C. Sugden of Unisys Corp. Further information is contained in a TSP

(see page 1).

LAR-17178-1

Web-Based Software for

Managing Research

aeroCOMPASS is a software system,

originally designed to aid in the management of wind tunnels at Langley Research Center, that could be adapted to

provide similar aid to other enterprises

in which research is performed in common laboratory facilities by users who

may be geographically dispersed. Included in aeroCOMPASS is Web-interface software that provides a single,

convenient portal to a set of projectand test-related software tools and

other application programs. The heart

of aeroCOMPASS is a user-oriented

document-management software subsystem that enables geographically dispersed users to easily share and manage

a variety of documents. A principle of

“write once, read many” is implemented throughout aeroCOMPASS to

eliminate the need for multiple entry of

the same information. The Web framework of aeroCOMPASS provides links

to client-side application programs that

are fully integrated with databases and

server-side application programs. Other

subsystems of aeroCOMPASS include

ones for reserving hardware, tracking

of requests and feedback from users,

generating interactive notes, administration of a customer-satisfaction questionnaire, managing execution of tests,

managing archives of metadata about

tests, planning tests, and providing online help and instruction for users.

This program was written by Sherwood T.

Hoadley; Anthony M. Ingraldi; Kerry M.

Gough; Charles Fox, Jr.; Catherine K. Cronin;

Andrew G. Hagemann; Guy T. Kemmerly;

and Wesley L. Goodman of Langley Research

Center. For further information, access

http://aerocompass.larc.nasa.gov.

This invention is owned by NASA, and a

patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its

commercial development should be addressed to

the Patent Counsel, Langley Research Center, at

(757) 864-3521. Refer to LAR-16442.

Driver Code for Adaptive

Optics

A special-purpose computer code for

a deformable-mirror adaptive-optics

control system transmits pixel-registered control from (1) a personal computer running software that generates

the control data to (2) a circuit board

with 128 digital-to-analog converters

(DACs) that generate voltages to drive

the deformable-mirror actuators. This

program reads control-voltage codes

from a text file, then sends them, via

the computer’s parallel port, to a circuit board with four AD5535 (or equivalent) chips. Whereas a similar prior

computer program was capable of

transmitting data to only one chip at a

time, this program can send data to

four chips simultaneously. This program is in the form of C-language code

that can be compiled and linked into

an adaptive-optics software system. The

program as supplied includes source

code for integration into the adaptiveoptics software, documentation, and a

component that provides a demonstration of loading DAC codes from a text

file. On a standard Windows desktop

computer, the software can update 128

channels in 10 ms. On Real-Time Linux

with a digital I/O card, the software can

update 1024 channels (8 boards in parallel) every 8 ms.

This program was written by Shanti Rao of

Caltech for NASA’s Jet Propulsion Laboratory. Further information is contained in

a TSP (see page 1).

The software used in this innovation is

available for commercial licensing. Please

contact Karina Edmonds of the California

Institute of Technology at (626) 395-2322.

Refer to NPO-43107.
NASA Tech Briefs, February 2007 17

A ceramic paste that can be applied relatively easily, either by itself or in combination with one or more layer(s) of hightemperature ceramic fabrics, such as

silicon carbide or zirconia, has been invented as a means of patching cracks or

holes in the reinforced carbon-carbon forward surfaces of a space shuttle in orbit before returning to Earth. The paste or the

paste/fabric combination could also be

used to repair rocket-motor combustion

chambers, and could be used on Earth to

patch similar high-temperature structures.

The specified chemical composition of

the paste admits of a number of variations,

and the exact proportions of its constituents are proprietary. In general, the

paste consists of (1) silicon carbide, possibly with addition of (2) hafnium carbide,

zirconium carbide, zirconium boride, silicon tetraboride, silicon hexaboride, or

other metal carbides or oxides blended

with (3) a silazane-based polymer.

Because the paste is viscous and sticky at

normal terrestrial and outer-space ambient

temperatures, high-temperature ceramic

fabrics such as silicon carbide or zirconia

fabric impregnated with the paste (or the

paste alone) sticks to the damaged surface

to which it is applied. Once the patch has

been applied, it is smoothed to minimize

edge steps as required [forward-facing

edge steps must be ≤0.030 in. (≤0.76 mm)

in the original intended space-shuttle application]. The patch is then heated to a

curing temperature thereby converting it

from a flexible material to a hard, tough

material. The curing temperature is 375 to

450 °F (≈190 to 230 °C).

In torch tests and arc-jet tests, the cured

paste was found to be capable of withstanding a temperature of 3,500 °F

(≈1,900 °C) for 15 minutes. As such, the

material appears to satisfy the requirement, in the original space-shuttle application, to withstand re-entry temperatures of

≈3,000 °F (≈1,600 °C).

This work was done by Steven J. Adam,

James V. Tompkins, Gordon R. Toombs, Pete

Hogensen, and Douglas G. Soden of The Boeing Co. for Johnson Space Center.

Title to this invention has been waived under

the provisions of the National Aeronautics and

Space Act {42 U.S.C. 2457(f)}, to The Boeing

Company. Inquiries concerning licenses for its

commercial development should be addressed to:

The Boeing Company

PO Box 2515

2201 Seal Beach Blvd.

Seal Beach, CA 90740-1515

Refer to MSC-23942, volume and number

of this NASA Tech Briefs issue, and the

page number.

Materials

Ceramic Paste for Patching High-Temperature Insulation

Repairs can be performed by use of simple techniques.

Lyndon B. Johnson Space Center, Houston, Texas

Fabrication of Polyimide-Matrix/Carbon and Boron-Fiber Tape

Production costs can be reduced and compression strengths increased.

Langley Research Center, Hampton, Virginia

The term “HYCARB” denotes a hybrid

composite of polyimide matrices reinforced with carbon and boron fibers. HYCARB and an improved process for fabricating dry HYCARB tapes have been

invented in a continuing effort to develop lightweight, strong composite materials for aerospace vehicles. Like other

composite tapes in this line of development, HYCARB tapes are intended to be

used to build up laminated structures

having possibly complex shapes by

means of automated tow placement

(ATP) — a process in which a computercontrolled multiaxis machine lays down

prepreg tape or tows. The special significance of the present process for making

dry HYCARB for ATP is that it contributes to the reduction of the overall

cost of manufacturing boron-reinforced

composite-material structures while making it possible to realize increased compression strengths.

The present process for making HYCARB tapes incorporates a “wet to dry”

process developed previously at Langley

Research Center. In the “wet to dry”

process, a flattened bundle of carbon fiber

tows, pulled along a continuous production line between pairs of rollers, is impregnated with a solution of a poly(amide acid)

This Photomicrograph shows a cross of a specimen containing one layer of boron fibers.

100 μm

LAR15852

10-8-02 bs
18 NASA Tech Briefs, February 2007

in N-methyl-2-pyrrolidinone (NMP), then

most of the NMP is removed by evaporation in hot air. In the present case, the

polyamide acid is, more specifically, that of

LaRCTM IAX (or equivalent) thermoplastic

polyimide, and the fibers are, more specifically, Manganite IM7 (or equivalent) polyacrylonitrile-based carbon filaments that

have a diameter of 5.2 μm and are supplied in 12,000-filament tows.

The present process stands in contrast

to a prior process in which HYCARB

tape was made by pressing boron fibers

into the face of a wet carbon-fiber/

poly(amide acid) prepreg tape — that is,

a prepreg tape from which the NMP solvent had not been removed. In the present process, one or more layer(s) of sideby-side boron fibers are pressed between

dry prepreg tapes that have been prepared by the aforementioned “wet to

dry” process. The multilayer tape is then

heated to imidize the matrix material

and remove most of the remaining solvent, and is pressed to consolidate the

multiple layers into a dense tape.

For tests, specimens of HYCARB tapes

and laminated composite panels made

from HYCARB tape were prepared as

follows: HYCARB tapes were fabricated

as described above. Each panel was

made by laying down ten layers of tape,

containing, variously, one, two, or three

boron-fiber plies and the remainder carbon-fiber-only plies (see figure). Each

panel was made by laying down ten layers of tape. Each panel was then cured

by heating to a temperature of 225 °C

for 15 minutes, then pressing at 200 psi

(≈1.4 MPa) while heating to 371 °C,

holding at 371 °C for 1 hour, then continuing to hold pressure during cooling.

Control specimens that were otherwise

identical except that they did not contain boron fibers also were prepared. In

room-temperature flexural tests, the HYCARB specimens performed comparably to the control specimens; in roomtemperature, open-hole compression

tests, the HYCARB specimens performed slightly better, by amounts that

increased with boron content.

This work was done by Harry L. Belvin

and Roberto J. Cano of Langley Research

Center and Monte Treasure and Thomas

W. Shahood of Textron Specialty Materials.

Further information is contained in a TSP

(see page 1).

This invention is owned by NASA, and a

patent application has been filed. Inquiries

concerning nonexclusive or exclusive license

for its commercial development should be addressed to the Patent Counsel, Langley Research Center, at (757) 864-3521. Refer to

LAR-15852.

A method of imparting relatively hard

protective outer skins to aerogel monoliths has been developed. Even more

than aerogel beads, aerogel monoliths

are attractive as thermal-insulation materials, but the commercial utilization of

aerogel monoliths in thermal-insulation

panels has been inhibited by their

fragility and the consequent difficulty of

handling them. Therefore, there is a

need to afford sufficient protection to

aerogel monoliths to facilitate handling,

without compromising the attractive

bulk properties (low density, high porosity, low thermal conductivity, high surface area, and low permittivity) of aerogel materials. The present method was

devised to satisfy this need.

The essence of the present method is to

coat an aerogel monolith with an outer

polymeric skin, by painting or spraying.

Apparently, the reason spraying and

painting were not attempted until now is

that it is well known in the aerogel industry that aerogels collapse in contact with

liquids. In the present method, one prevents such collapse through the proper

choice of coating liquid and process conditions: In particular, one uses a viscous

polymer precursor liquid and (a) carefully controls the amount of liquid applied and/or (b) causes the liquid to become cured to the desired hard polymeric

layer rapidly enough that there is not sufficient time for the liquid to percolate

into the aerogel bulk.

The method has been demonstrated by

use of isocyanates, which, upon exposure

to atmospheric moisture, become cured

to polyurethane/polyurea-type coats. The

method has also been demonstrated by

use of commercial epoxy resins. The

method could also be implemented by

use of a variety of other resins, including

polyimide precursors (for forming hightemperature-resistant protective skins) or

perfluorinated monomers (for forming

coats that impart hydrophobicity and

some increase in strength).

This work was done by Nicholas Leventis,

James C. Johnston, Maria A. Kuczmarski,

and Mary Ann B. Meador of Glenn Research Center. Further information is contained in a TSP (see page 1).

Inquiries concerning rights for the commercial use of this invention should be addressed

to NASA Glenn Research Center, Commercial

Technology Office, Attn: Steve Fedor, Mail Stop

4–8, 21000 Brookpark Road, Cleveland, Ohio

44135. Refer to LEW-17605-1.

Protective Skins for Aerogel Monoliths

Viscous polymer precursors are applied, then polymerized before they can percolate in.

John H. Glenn Research Center, Cleveland, Ohio
NASA Tech Briefs, February 2007 19

Asymmetric bulkheads are proposed

for the ends of vertically oriented cylindrical pressure vessels. These bulkheads,

which would feature both convex and

concave contours, would offer advantages

over purely convex, purely concave, and

flat bulkheads (see figure). Intended originally to be applied to large tanks that

hold propellant liquids for launching

spacecraft, the asymmetric-bulkhead concept may also be attractive for terrestrial

pressure vessels for which there are requirements to maximize volumetric and

mass efficiencies.

A description of the relative advantages

and disadvantages of prior symmetric

bulkhead configurations is prerequisite to

understanding the advantages of the proposed asymmetric configuration:

• In order to obtain adequate strength,

flat bulkheads must be made thicker,

relative to concave and convex bulkheads; the difference in thickness is

such that, other things being equal,

pressure vessels with flat bulkheads

must be made heavier than ones with

concave or convex bulkheads.

• Convex bulkhead designs increase

overall tank lengths, thereby necessitating additional supporting structure

for keeping tanks vertical.

• Concave bulkhead configurations increase tank lengths and detract from

Asymmetric Bulkheads for Cylindrical Pressure Vessels

These bulkheads would offer advantages over prior concave, convex, and flat bulkheads.

Marshall Space Flight Center, Alabama

These Pressure-Vessel Configurations have the same radius (R) and volume (4πR3/3). The different shapes are shown here to illustrate the advantages and

disadvantages of each. This is a representative but not exhaustive set of configurations, and is limited to single, non-nested pressure vessels for the sake

of simplicity.

R

R evel of 

Residual Fluid 

ortex 

FLAT 

ULKHEADS 

R

SPHERICAL 

ULKHEADS 

R

CONVEX ELLIPSOIDAL 

ULKHEADS 

R

CONCAVE 

ULKHEADS 

0.86 R

R

ASYMMETRIC 

ULKHEADS 

1.33 R

0.71 R

0.3 R

0.71 R

Mechanics

Code Assesses Risks Posed by Meteoroids and Orbital Debris

Lyndon B. Johnson Space Center, Houston, Texas

BUMPER II version 1.92e is a computer code for assessing the risk of damage from impacts of micrometeoroids

and orbital debris on the International

Space Station (ISS), including those

parts of the ISS covered by shielding that

affords partial protection against such

impacts. (Other versions of BUMPER II

have been written for other spacecraft.)

Bumper II quantifies the probability of

penetration of shielding and the damage to spacecraft equipment as functions

of the size, shape, and orientation of the

spacecraft; the parameters of its orbit;

failure criteria that quantify impact damage at the threshold of failure for each

spacecraft surface; and the impact-damage resistance of each spacecraft surface

as defined by “ballistic limit equations”

that return the size of a failure-causing

particle as a function of target parameters (including materials, configurations, thicknesses, and gap distances)

and impact conditions (impact velocity

and the density and shape of the impactor). BUMPER II version 1.92e contains several dozen ballistic limit equations that are based on results from

thousands of hypervelocity impact tests

conducted by NASA on ISS shielding

and other hardware, and on results from

numerical simulations of impacts.

This program was written by Eric L.

Christiansen and Justin Kerr of Johnson

Space Center; Dana Lear, Jim Hyde, and

Tom Prior of Lockheed Martin Corp.; and

Russell Graves of The Boeing Company,

Inc. For further information, contact the

Johnson Commercial Technology Office at

(281) 483-3809.

MSC-23774
20 NASA Tech Briefs, February 2007

volumetric efficiency, even though

they do not necessitate additional supporting structure.

• The shape of a bulkhead affects the proportion of residual fluid in a tank — that

is, the portion of fluid that unavoidably

remains in the tank during outflow and

hence cannot be used. In this regard, a

flat bulkhead is disadvantageous in two

respects: (1) It lacks a single low point

for optimum placement of an outlet and

(2) a vortex that forms at the outlet during outflow prevents a relatively large

amount of fluid from leaving the tank.

• A concave bulkhead also lacks a single

low point for optimum placement of

an outlet.

Like purely concave and purely convex

bulkhead configurations, the proposed

asymmetric bulkhead configurations

would be more mass-efficient than is the

flat bulkhead configuration. In comparison with both purely convex and purely

concave configurations, the proposed

asymmetric configurations would offer

greater volumetric efficiency. Relative to a

purely convex bulkhead configuration, the

corresponding asymmetric configuration

would result in a shorter tank, thus demanding less supporting structure. An

asymmetric configuration provides a low

point for optimum location of a drain, and

the convex shape at the drain location

minimizes the amount of residual fluid.

This work was done by Donald B. Ford of Marshall Space Flight Center.

This is the invention of a NASA employee,

and a patent application has been filed. Inquiries concerning license for its commercial

development may be addressed to the inventor: 

Donald B. Ford 

Phone No.: (256) 544-2454

E-mail: Donald.B.Ford@nasa.gov

Refer to MFS-31626-1.
NASA Tech Briefs, February 2007 21

A proposed system would perform

multiple coordinated functions in regulating the pressure of the oxidant gas

(usually, pure oxygen) flowing to a fuelcell stack and in removing excess product water that is generated in the normal

fuel-cell operation. The system could

function in the presence or absence of

gravitation, and in any orientation in a

gravitational field.

Unlike some prior systems for removing product water, the proposed

system would not depend on hydrophobicity or hydrophilicity of surfaces that are subject to fouling and,

consequently, to gradual deterioration

in performance. Also unlike some

prior systems, the proposed system

would not include actively controlled

electric motors for pumping; instead,

motive power for separation and

pumping away of product water would

be derived primarily from the oxidant

flow and perhaps secondarily from the

fuel flow. The net effect of these and

other features would be to make the

proposed system more reliable and

safer, relative to the prior systems.

The proposed system (see figure)

would include a pressure regulator and

sensor in the oxidant supply just upstream from an ejector reactant pump.

The pressure of the oxidant supply

would depend on the consumption flow.

In one of two control subsystems, the

pressure of oxidant flowing from the

supply to the ejector would be sensed

and used to control the speed of a set of

a reciprocating constant-displacement

pump so that the volumetric flow of

nominally incompressible water away

from the system would slightly exceed

the rate at which water was produced by

the fuel cell(s).

The two-phase (gas/liquid water) outlet stream from the fuel cell(s) would

enter the water separator, a turbinelike

centrifugal separator machine driven primarily by the oxidant gas stream. A second control subsystem would utilize feedback derived from the compressibility of

the outlet stream: As the separator was

emptied of liquid water, the compressibility of the pumped stream would increase.

The compressibility would be sensed, and

an increase in compressibility beyond a

preset point (signifying a decrease in

water content below an optimum low

level) would cause the outflow from the

reciprocating pump to be diverted back

to the separator to recycle some water.

This work was done by Arturo Vasquez,

Kerri McCurdy, and Karla F. Bradley of

Johnson Space Center.

This invention is owned by NASA, and a

patent application has been filed. Inquiries

concerning nonexclusive or exclusive license

for its commercial development should be addressed to the Patent Counsel, Johnson Space

Center, (281) 483-0837. Refer to MSC23668.

Machinery/Automation

Self-Regulating Water-Separator System for Fuel Cells

This system would not depend on hydrophobic or hydrophilic surfaces.

Lyndon B. Johnson Space Center, Houston, Texas

The Self-Regulating Water-Separator System would derive its pumping and water-separating power

from the flow of oxidant gas to the fuel-cell stack. Optionally, the fuel flow could be utilized as an

auxiliary power source during operation of the fuel cell at low power.

Auxiliary 

Turbine 

Turbinelike 

Centrifugal 

Water Separator 

Water Outlet 

uel-Cell 

tack jector 

Control 

Subsystem 

Two-Phase 

Return 

Constant-Displacement 

Reciprocating Pump Drawing not to scale. 

Two-Phase 

Outlet Stream 

Coupling 

ressure Regulator 

nd Sensor 

uel Supply 

MFS-23668 ABPI 8-1-03 bs

Compressibility 

Sensor 

Oxidant 

Supply 

NASA Tech Briefs, February 2007 23

Self-Advancing Step-Tap Drills

It is not necessary to apply axial drilling forces.

Lyndon B. Johnson Space Center, Houston, Texas

Self-advancing tool bits that are hybrids

of drills and stepped taps make it possible

to form threaded holes wider than about

1/2 in. (about 13 mm) without applying

any more axial force than is necessary for

forming narrower pilot holes. These selfadvancing stepped-tap drills were invented

for use by space-suited astronauts performing repairs on reinforced carbon/carbon

space-shuttle leading edges during space

walks, in which the ability to apply axial

drilling forces is severely limited. Self-advancing stepped-tap drills could also be

used on Earth for making wide holes without applying large axial forces.

A self-advancing stepped-tap drill (see

figure) includes several sections having progressively larger diameters, typically in increments between 0.030 and 0.060 in. (between about 0.8 and about 1.5 mm). The

tip section, which is the narrowest, is a pilot

drill bit that typically has a diameter between 1/8 and 3/16 in. (between about 3.2

and about 4.8 mm). The length of the pilotdrill section is chosen, according to the

thickness of the object to be drilled and

tapped, so that the pilot hole is completed

before engagement of the first tap section.

Provided that the cutting-edge geometry of

the drill bit is optimized for the material to

be drilled, only a relatively small axial force

[typically of the order of a few pounds (of

the order of 10 newtons)] must be applied

during drilling of the pilot hole. Once the

first tap section engages the pilot hole, it is

no longer necessary for the drill operator to

apply axial force: the thread engagement

between the tap and the workpiece provides the axial force to advance the tool bit.

Like the pilot-drill section, each tap section must be long enough to complete its

hole before engagement of the next,

slightly wider tap section. The precise values of the increments in diameter, the

thread pitch, the rake angle of the tap cutting edge, and other geometric parameters

of the tap sections must be chosen, in consideration of the workpiece material and

thickness, to prevent stripping of threads

during the drilling/tapping operation. A

stop-lip or shoulder at the shank end of the

widest tap section prevents further passage

of the tool bit through the hole.

There is a large potential market for selfadvancing stepped-tap drills in settings in

which hand-held drills are used. Applied

axial drilling forces can be quite large: it is

not unusual to exert axial forces as much as

75 lb (≈330 N) when drilling holes up to

about 1 in. (≈25 mm) in diameter. A person

usually bears down on a drill with body

weight to facilitate downward drilling, and

drilling upward is extremely fatiguing.

Repetitive drilling, which is often done in

the construction industry, is fatiguing and

limits worker productivity. Moreover, applying a large axial force with a hand-held drill

can be dangerous: the drill bit can grab the

workpiece, causing the workpiece to spin

or tearing the drill from the worker’s hand. 

By making it unnecessary to apply large

axial drilling forces, self-advancing

stepped-tap drills could reduce fatigue

while contributing to safety and productivity. Self-advancing stepped-tap drills could

be made in a variety of designs optimized

for making holes of specific diameters in

specific workpiece materials having specific thicknesses. For applications in which

the threads were not merely incidental to

making the holes but were also needed to

engage bolts, the tool bits would also be

optimized for specific thread geometries.

This work was done by Donald R. Pettit

and Charles J. Camarda of Johnson Space

Center, Ronald K. Penner of Langley Research Center, and Larry D. Franklin of Action Tool Service, Inc. Further information is

contained in a TSP (see page 1).

This invention is owned by NASA, and a

patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its

commercial development should be addressed to

the Patent Counsel, Johnson Space Center,

These Tool Bits are examples of many variations on the basic theme of a self-advancing stepped-tap drill. (281) 483-0837. Refer to MSC-23954.

Manufacturing & Prototyping

NASA Tech Briefs, February 2007 25

Physical Sciences

Array of Bolometers for Submillimeter-Wavelength Operation

This is a prototype of arrays for astrophysical imaging and photometry.

NASA’s Jet Propulsion Laboratory, Pasadena, California

A feed-horn-coupled monolithic array

of micromesh bolometers is undergoing

development for use in a photometric

camera. The array is designed for conducting astrophysical observations in a

wavelength band centered at 350 μm.

The bolometers are improved versions

of previously developed bolometers

comprising metalized Si3N4 micromesh

radiation absorbers coupled with neutron-transmutation-doped Ge thermistors. Incident radiation heats the absorbers above a base temperature,

changing the electrical resistance of

each thermistor. In the present array of

improved bolometers (see figure), the

thermistors are attached to the micromesh absorbers by indium bump bonds

and are addressed by use of lithographed, vapor-deposited electrical

leads. This architecture reduces the heat

capacity and minimizes the thermal conductivity to 1/20 and 1/300, respectively, of earlier versions of these detectors, with consequent improvement in

sensitivity and speed of response.

The micromesh bolometers, intended to

operate under an optical background set by

thermal emission from an ambient-temperature space-borne telescope, are designed

such that the random arrival of photons

(“photon noise”) dominates the noise

sources arising from the detector and readout electronics. The micromesh is designed

to be a highly thermally and optically efficient absorber with a limiting response

time of about 100 μs. The absorber and

thermistor heat capacity are minimized in

order to give rapid speed of response. Due

to the minimization of the absorber volume, the dominant source of heat capacity

arises from the thermistor.

The array demonstrates a dark noiseequivalent power of 2.9 ⋅ 10-17 W/(Hz)1/2

and a mean heat capacity of 1.3 pJ/K at a

detector temperature of 0.390 K from a

0.300 K cold plate. The optical efficiency of

the bolometer and feedhorn array, measured by comparing the responses to blackbody calibration sources, lies between 0.4

and 0.6. Photon noise dominates over detector noise arising from phonon, Johnson, and amplifier noise, as measured

under the design background conditions.

The ratio of total noise to photon noise is

found to be 1.21 at an absorbed optical

power of 2.4 pW. The array shows high stability with excess noise found to be negligible at frequencies as low as 30 mHz.

This work was done by James Bock and

Anthony Turner of Caltech for NASA’s Jet

Propulsion Laboratory. Further information is contained in a TSP (see page 1).

NPO-30290

This Array of Micromesh Bolometers was designed for photometry at a wavelength of 350 μm. Each

device includes a 725-μm-diameter micromesh absorber with a grid spacing of 72.5 μm and a grid filling factor of 0.077. A thermistor is located on one side of each absorber and is electrically addressed

by two leads deposited on a single 18-μm-wide supporting member. The pixel spacing is 1.75 mm.

NPO30290 ABPI 9-25-04 CC

Delta-Doped CCDs as Detector Arrays in Mass Spectrometers

Improved performance is obtained with reduced size, mass, and power.

NASA’s Jet Propulsion Laboratory, Pasadena, California

In a conventional mass spectrometer,

charged particles (ions) are dispersed

through a magnetic sector onto an MCP

at an output (focal) plane. In the MCP,

the impinging charged particles excite

electron cascades that afford signal gain.

Electrons leaving the MCP can be read

out by any of a variety of means; most

commonly, they are post-accelerated onto

a solid-state detector array, wherein the

electron pulses are converted to photons,

which, in turn, are converted to measurable electric-current pulses by photodetectors. Each step in the conversion from the

impinging charged particles to the output
26 NASA Tech Briefs, February 2007

current pulses reduces spatial resolution

and increases noise, thereby reducing the

overall sensitivity and performance of the

mass spectrometer. Hence, it would be

preferable to make a direct measurement

of the spatial distribution of charged particles impinging on the focal plane.

The utility of delta-doped CCDs as detectors of charged particles was reported

in two articles in NASA Tech Briefs, Vol.

22, No. 7 (July 1998): “Delta-Doped

CCDs as Low-Energy-Particle Detectors”

(NPO-20178) on page 48 and “DeltaDoped CCDs for Measuring Energies of

Positive Ions” (NPO-20253) on page 50.

In the present developmental miniature

mass spectrometers, the above mentioned miniaturization and performance advantages contributed by the use

of delta-doped CCDs are combined with

the advantages afforded by the Mattauch-Herzog design. The MattauchHerzog design is a double-focusing spectrometer design involving an electric

and a magnetic sector, where the ions of

different masses are spatially separated

along the focal plane of magnetic sector.

A delta-doped CCD at the focal plane

measures the signals of all the chargedparticle species simultaneously at high

sensitivity and high resolution, thereby

nearly instantaneously providing a complete, high-quality mass spectrum. The

simultaneous nature of the measurement of ions stands in contrast to that of

a scanning mass spectrometer, in which

abundances of different masses are

measured at successive times.

This work was done by Shouleh Nikzad,

Todd Jones, April Jewell, and Mahadeva Sinha

of Caltech for NASA’s Jet Propulsion Laboratory. Further information is contained in a

TSP (see page 1).

In accordance with Public Law 96-517,

the contractor has elected to retain title to this

invention. Inquiries concerning rights for its

commercial use should be addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak Grove Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: iaoffice@jpl.nasa.gov

Refer to NPO-41378, volume and number

of this NASA Tech Briefs issue, and the

page number.

Arrays of Bundles of Carbon Nanotubes as Field Emitters

Area-averaged current densities exceed those of arrays of single nanotubes.

NASA’s Jet Propulsion Laboratory, Pasadena, California

Experiments have shown that with suitable choices of critical dimensions, planar

arrays of bundles of carbon nanotubes

(see figure) can serve as high-current-density field emitter (cold-cathode) electron

sources. Whereas some hot-cathode electron sources must be operated at supply

potentials of thousands of volts, these

cold-cathode sources generate comparable current densities when operated at

tens of volts. Consequently, arrays of bundles of carbon nanotubes might prove

useful as cold-cathode sources in miniature, lightweight electron-beam devices

(e.g., nanoklystrons) soon to be developed.

Prior to the experiments, all reported

efforts to develop carbon-nanotubebased field-emission sources had yielded

low current densities — from a few hundred microamperes to a few hundred

milliamperes per square centimeter. An

electrostatic screening effect, in which

taller nanotubes screen the shorter ones

from participating in field emission, was

conjectured to be what restricts the

emission of electrons to such low levels.

It was further conjectured that the

screening effect could be reduced and

thus emission levels increased by increasing the spacing between nanotubes

to at least by a factor of one to two times

the height of the nanotubes. While this

change might increase the emission

from individual nanotubes, it would decrease the number of nanotubes per

unit area and thereby reduce the total

possible emission current. Therefore, to

maximize the area-averaged current

density, it would be necessary to find an

optimum combination of nanotube

spacing and nanotube height. 

The present concept of using an array of

bundles of nanotubes arises partly from the

concept of optimizing the spacing and

height of field emitters. It also arises partly

from the idea that single nanotubes may

have short lifetimes as field emitters,

whereas bundles of nanotubes could afford

redundancy so that the loss of a single nanotube would not significantly reduce the

overall field emission. 

In preparation for the experiments,

planar arrays of bundles of carbon nanotubes having various bundle diameters,

bundle heights, and bundle spacings were

fabricated. The fabrication process can be

summarized as follows: Electron-beam lithography was used to form planar arrays

NPO40817 of iron dots having various thicknesses ABPI 9-21-05 CC

μm

10 μm

μm

10μm

This Scanning Electron Micrograph shows bundles of carbon nanotubes, each 70 μm high and 5 μm in

diameter. The gaps between adjacent bundles are about 5 μm wide. The bundles stand up because

their constituent nanotubes support each other. The inset is a magnified image of the top of one bundle, showing individual nanotube tips.
NASA Tech Briefs, February 2007 27

and having diameters and inter-dot spacings corresponding to the desired diameters and spacings of the carbon-nanotube

bundles. The dots served as catalysts for

the growth of carbon nanotubes: Bundles

of multiwalled 20-nm-diameter carbon

nanotubes were grown on the iron dots by

chemical vapor deposition. The average

height of the bundles was 70 ± 2μm. The

heights of the bundles were found to depend on the thicknesses of the iron dots.

The tallest bundles (112 μm high) were

found on iron dots 8 μm thick. 

In the experiments, field emission

from these arrays was measured in a

vacuum chamber by use of a 100-μm-diameter probe anode. The highest nondestructive area-averaged current densities (about 1.5 to 1.8 A/cm2

) were

observed on arrays of bundles of 1- to

2-μm diameter and spacings of 5 μm at

an applied electric field of about 4.5

V/μm.

This work was done by Harish Manohara

and Michael Bronkowski of Caltech for

NASA’s Jet Propulsion Laboratory. For

further information, access the Technical

Support Package (TSP) free on-line at

www.techbriefs.com/tsp under the Physical

Sciences category.

In accordance with Public Law 96-517,

the contractor has elected to retain title to this

invention. Inquiries concerning rights for its

commercial use should be addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak Grove Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: iaoffice@jpl.nasa.gov

Refer to NPO-40817, volume and number

of this NASA Tech Briefs issue, and the

page number.

NASA Tech Briefs, February 2007 29

Books & Reports

Staggering Inflation To Stabilize Attitude of a 

Solar Sail

A document presents computationalsimulation studies of a concept for stabilizing the attitude of a spacecraft during deployment of such structures as a

solar sail or other structures supported

by inflatable booms. Specifically, the

solar sail considered in this paper is a

square sail with inflatable booms and attitude control vanes at the corners. The

sail inflates from its stowed configuration into a square sail with four segments and four vanes at the tips. Basically, the concept is one of controlling

the rates of inflation of the booms to

utilize in mass-distribution properties

to effect changes in the system’s angular momentum. 

More specifically, what was studied

were the effects of staggering inflation of

each boom by holding it at constant

length for specified intervals between intervals of increasing length until full

length is reached. The studies included

sensitivity analyses of effects of variations

in mass properties, boom lengths, rates

of increase in boom length, initial rates

of rotation of the spacecraft, and several

asymmetries that could arise during deployment. 

The studies led to the conclusion that

the final attitude of the spacecraft

could be modified by varying the parameters of staggered inflation. Computational studies also showed that by

feeding back attitude and attitude-rate

measurements so that corrective action

is taken during the deployment, the

final attitude can be maintained very

closely to the initial attitude, thus mitigating the attitude changes incurred

during deployment and caused by modeling errors. Moreover, it was found

that by optimizing the ratio between

the holding and length-increasing intervals in deployment of a boom, one

could cause deployment to track a desired deployment profile to place the

entire spacecraft in a desired attitude at

the end of deployment.

This work was done by Marco Quadrelli

and John West of Caltech for NASA’s Jet

Propulsion Laboratory. Further information is contained in a TSP (see page 1).

NPO-42176

Bare Conductive 

Tether for Decelerating

a Spacecraft

A document describes a prototype of

electrically conductive tethers to be used

primarily to decelerate spacecraft

and/or generate electric power for the

spacecraft. Like prior such tethers, this

tether is designed so that when it is deployed from a spacecraft in orbit, its motion across the terrestrial magnetic field

induces an electric current. The Lorentz

force on the current decelerates the

spacecraft. Optionally, the current can

be exploited to convert some orbital kinetic energy to electric energy for spacecraft systems. Whereas the conductive

portions of prior such tethers are covered with electrical insulation except for

end electrodes that make contact with

the ionosphere, this tether includes a

conductive portion that is insulated

along part of its length but deliberately

left bare along a substantial remaining

portion of its length to make contact

with the ionosphere. The conductive

portions of the tether are made of

coated thin aluminum wires wrapped

around strong, lightweight aromatic

polyamide braids. The main advantages

of the present partly-bare-tether design

over the prior all-insulated-tether design

include greater resistance to degradation by the impact of monatomic oxygen

at orbital altitude and speed and greater

efficiency in collecting electrons from

the ionosphere.

This work was done by Les Johnson, Jason

Vaughn, Ken Welzyn, and Judy Ballance of

Marshall Space Flight Center; Joe Carroll

of Tether Applications; Enrico Lorenzini and

Bob Estes of the Smithsonian Astrophysical

Observatory; Pete Schuler, Hamid “Bob” Mojazza, and John Lennhoff of Triton Systems;

and Kai Shen Hwang of Computer Sciences

Corp. Further information is contained in a

TSP (see page 1).

This invention is owned by NASA, and a

patent application has been filed. For further

information, contact Sammy Nabors, MSFC

Commercialization Assistance Lead, at

sammy.a.nabors@nasa.gov. Refer to MFS31490-1.


National Aeronautics and

Space Administration