Laser Radar for Spacecraft Guidance Applications

Carl Christian Liebe, Alex Abramovici, Randy K. Bartman, Robert L.
Bunker, Jacob Chapsky, Cheng-Chih Chu, Daniel Clouse, James W. Dillon,
Bob Hausmann, Hamid Hemmati, Richard P. Kornfeld, Clint Kwa, Sohrab
Mobasser, Michael Newell, Curtis Padgett, W. Thomas Roberts, Gary
Spiers, Zachary Warfield, Malcolm Wright

Jet Propulsion Laboratory (JPL), California Institute of Technology

4800 Oak Grove Dr., Pasadena CA 91109-8099

818 354 7837

<carl.c.liebe@jpl.nasa.gov>

*Abstract ―* A flight qualified laser radar called LAMP (LAser MaPper)
is under development at JPL. LAMP is a guidance and control sensor that
can form 3 dimensional images of its field of regard. The maps can be
used for spacecraft rendezvous, docking, and hazard avoidance during
landing and for rover traverse planning. LAMP operates by emitting high
power, short duration laser pulses, which are directed by an internal
gimbaled mirror in azimuth and elevation. When the laser pulses impinge
on a surface, a small amount of the light is reflected back to the
sensor and is collected by a telescope. On the way out, a laser actuated
trigger starts a counter that is stopped by the return pulse. The
counter value (time of flight) is proportional to the distance to the
object. This paper describes the detailed design of the LAMP sensor.

**TABLE OF CONTENTS**

[**1. INTRODUCTION** 1](#__RefHeading___Toc27642491)

[**2. LAMP SYSTEMS DESIGN** 2](#__RefHeading___Toc27642492)

[**3. LAMP PACKAGING** 3](#__RefHeading___Toc27642493)

[**4. LASER TRANSMITTER** 4](#__RefHeading___Toc27642494)

[**5. SCANNER** 6](#__RefHeading___Toc27642495)

[**6. LASER RECEIVER** 7](#__RefHeading___Toc27642496)

[**7. DIGITAL ELECTRONICS** 9](#__RefHeading___Toc27642497)

[**8. SOFTWARE SUBSYSTEM** 11](#__RefHeading___Toc27642498)

[**9. POWER SUBSYSTEM** 11](#__RefHeading___Toc27642499)

[**10. ESTIMATED S/N RATIO** 12](#__RefHeading___Toc27642500)

[**11. SUMMARY** 13](#__RefHeading___Toc27642501)

[**REFERENCES** 13](#__RefHeading___Toc27642502)

[]{#__RefHeading___Toc27642491 .anchor}**1. INTRODUCTION**

A flight qualified, low mass, and low power 3 dimensional laser radar
will enable a number of new missions and capabilities \[1\]. Therefore,
the Mars Technology Program at JPL has undertaken the development of a
laser radar for guidance and navigation applications. The development of
the instrument called LAMP (LAser MaPper) was initiated in year 2000 and
will be flight demonstrated in year 2004 \[2\].

[^1][^2]

A laser range finder is a device that measures the distance to a target,
but the beam orientation is fixed. This is different from a laser radar,
where the orientation of the beam can be changed. Laser range finders
have been demonstrated on a number of previous missions as shown in
Table 1. The primary use of laser range finders has been to obtain
scientific data. This is fundamentally different from LAMP that will be
used as a guidance and navigation sensor.

**Table 1**. Missions using laser range finders

  ---------------------- ------------- ------------------- ----------------
  **Mission**            **Year**      **Functionality**   **Status**

  Apollo 15              1971          Ranging             Success

  Mars Orbiter Laser     1992          Ranging             Spacecraft lost
  Altimeter 1                                              

  Clementine             1994          Ranging             Success

  Lidar Inspace          1994          Profiling           Success
  Technology experiment                                    

  Balkan                 1995          Profiling           Success

  NEAR                   1996          Ranging             Success

  Shuttle Laser          1996          Ranging             Success
  Altimeter 1                                              

  Mars Orbiter Laser     1996          Ranging             Success
  Altimeter 2                                              

  Shuttle Laser          1997          Ranging             Success
  Altimeter 2                                              

  MPL/DS2                1999          Profiling           Spacecraft lost

  Icesat/GLAS            2003          Ranging / Profiling 

  Calipso                2004          Profiling           

  Messenger -- Discovery Future        Ranging             
  Program Mercury                                          
  mission                                                  

  DAWN -- Ranging --     Future        Profiling           
  Discovery Program                                        
  asteroid mission                                         
  ---------------------- ------------- ------------------- ----------------

The following guidance and navigation applications for LAMP are
identified and discussed: 1) Capture of a Mars sample in Mars orbit. 2)
Hazard avoidance sensor during smart landing on Mars. 3) Traverse
planning for Mars rovers, 4) Rendezvous or docking with another
spacecraft in earth orbit, 5) Small body landing/exploration/mapping.

[1) Capture of Mars sample in Mars orbit:]{.underline} A future goal of
the Mars program is to return a sample from Mars to Earth for detailed
analysis. This is to be accomplished by sending a spacecraft to the
Martian surface, which will collect a soil sample, package it into a
grapefruit sized container covered with retroreflectors for ease of
location and launch it into Mars orbit. Subsequently, a Mars orbiting
spacecraft will use a LAMP system to locate and home in on the sample
for capture and return to Earth. \[3\]\[4\].

[2) Hazard avoidance sensor during smart landing on Mars:]{.underline}
Previous landings on Mars have utilized either radar-controlled
retrorockets or airbags to land on comparatively flat terrains with
minimal hazards. Future missions will require landings in more
geologically interesting areas of Mars \[5\]. Therefore, a sensor that
is able to guide the spacecraft away from large boulders and hazards on
the martian surface in the final stage of descent is required. The LAMP
sensor can make topographical maps of the surface with sufficient range
and resolution to guide a lander to a safe landing spot.

[3) Traverse planning for Mars rovers:]{.underline} The successful Mars
Sojourner Rover and the twin Mars Exploration Rovers currently being
built are using stereovision cameras to form 3 dimensional images of
their proximity \[6\]. This approach only works in the daylight and has
low accuracy at long distances. LAMP has neither of these limitations,
enabling more capable path planning.

[4) Rendezvous or docking with another spacecraft in Earth
orbit:]{.underline} LAMP can be used as the terminal sensor for
rendezvous with other spacecraft in Earth orbit. LAMP is planned to make
a flight demonstration of this capability in the near term \[2\].

[5) Small body landing/exploration:]{.underline} LAMP can be used as
both a science instrument and a landing sensor on an asteroid or comet
nucleus. LAMP can be used to generate a topographical map of the surface
and determine the rotation of the body, and it can be used as a combined
altimeter and hazard avoidance sensor during an actual landing \[7\].

A microwave radar system could also be used to support some of the same
missions, but would require more resources (i.e. size, mass and power)
and would provide poorer performance. The angular beam width of LAMP is
designed to be only 0.02º, as compared to a typical 10º beamwidth of a
microwave radar with a 10 cm aperture. In a rendezvous scenario, the
larger beam width is not prohibitive, since it is possible to do loping
to increase the angular resolution \[8\]. However, when generating a
topographical map of a surface, the microwave-based radar has much lower
resolution (or larger antennas).

[]{#__RefHeading___Toc27642492 .anchor}**2. LAMP SYSTEMS DESIGN**

LAMP emits short, intense Q-switched pulses of infrared light, directed
into the field by a lightweight rapidly steering 2-axis gimbaled optical
mirror. When the light pulses encounter an object a portion of the
pulses are scattered back, though the gimbaled reflector, into a 5 cm
Cassegrain telescope. The range to the object is determined by measuring
the elapsed time between the emission of the Q-switched pulse and its
detection at the focal plane of the telescope.

A diagram of the LAMP system is shown in Figure 1. By sweeping the
internal gimbaled mirror, it is possible to form a three dimensional
image of objects in front of LAMP, similar to the operation of
conventional pulsed radar \[8\].

The ranging laser on LAMP is a passively Q-switched Nd:YAG microchip
laser. The pulse repetition frequency (PRF) is about 10 KHz and the
pulse energy is about 10 μJ with a wavelength of 1064 nm. An external
2.5W pump diode laser at 808 nm is connected though an optical fiber to
the microchip laser. The diode pump laser is housed in a separate
thermally controlled package because its temperature must be maintained
to within 0.3°C to efficiently pump the microchip laser. Temperature
excursions exceeding this leads to poor absorption of the pump light and
results in reduced microchip laser output. The laser beam emitted by the
microchip is shaped by optics to have a 0.02° divergence.

When a laser pulse is emitted from the Nd:YAG microchip laser, some of
the scattered light is detected by a fast Si-PIN detector, which starts
a timer. A very fast Avalanche Photo Diode (APD) is mounted behind the
classical Cassegrain telescope coupled to a series of high bandwidth
amplifiers. When the light pulse returns, it generates a signal in the
amplifiers that stops the timers when the signal crosses different
thresholds. Since the dynamic range of the returned signal spans orders
of magnitude a second Si-PIN detector is used to stop the timing chip
when the APD approaches saturation. The timing chip has a clock
frequency of 80 MHz, but is able to interpolate to a resolution of 390
ps, equivalent to \~2.5 GHz.

The 2-axis gimbal allows programmable, 2 axis motion of a 5 cm diameter
beryllium mirror. It has an angular motion of 10° on both axes and a
sweep rate of 10°/sec with the slow axis and up to 1000º/sec using the
fast axis. Thus, it can scan a 10ºx10º area in 1 second[^3]. A Vertical
Cavity Surface Emitting Laser (VCSEL) behind the scan mirror is
continually reflected from the back of the mirror onto a position
sensing detector (PSD). At the time that the laser pulse is emitted, the
VCSEL spot on the detector unambiguously indicates the angular position
of the scan mirror and consequently, the position in the field from
which the pulse is returning.

**Figure 1 -** LAMP block diagram

The LAMP processor is a 12.5 MHz, 32-bit MIPS R3000 Synova Processor
with memory and RS422 interface. The processor controls the gimbal,
monitors/controls temperature, reads the laser levels, reads the timing
chip etc. The operating system is based on VxWorks. The processor/memory
can accommodate various user applications. Table 2 summarizes key LAMP
parameters and Figure 1 shows a block diagram of LAMP.

**Table 2.** Key LAMP parameters

  --------------------------------------- -------------------------------
  Beam divergence                         0.02º

  Pulse repetition frequency              10 KHz

  Mass                                    6.4 kg

  Power consumption (without heaters)     33 Watts

  Detection range (7 mm retro reflector)  \>10 km

  Detection range (lambertian surface)    2.5 km

  Range accuracy                          Offset: 10 cm +0.04% of range,
                                          random error 12 cm (3σ)

  Sun exclusion angle                     3º

  Pointing accuracy                       0.06º offset and 0.06º error
                                          (3σ)
  --------------------------------------- -------------------------------

[]{#__RefHeading___Toc27642493 .anchor}**3. LAMP PACKAGING**

The LAMP Sensor consists of three separate units, the Optical Head
Assembly (OHA), the Pump Diode Module (PDM) and the Electronics Assembly
(EA). The function of the OHA is to transmit and receive a pulsed laser
signal that scans over the field of view while the PDM houses a diode
laser that provides continuous laser input to the microchip laser is
located in the OHA. The PDM is isolated from the OHA because of a
narrow-band temperature control requirement on the diode laser. Finally,
the electronics assembly houses the driving electronics and the
processor/communications.

The OHA consists of a chassis (optical bench), access covers and
sub-assemblies responsible for performing the functions of the unit. The
sub-assemblies include: laser launch optics, 2-axis gimbal, a telescope,
detector assemblies, and passive optical elements. A rendering is shown
in Figure 2 and a photograph is shown in Figure 3.

In addition to these major sub-assemblies, the OHA includes several
minor components such as a solar filter, fold mirror, window, and
scanner encoder. The solar filter is a piece of glass, with a diameter
of 52 mm, located between the scanner and the telescope that only
transmits laser light (and Sun light in a narrow band pass around the
laser wavelength). The fold mirror, which is positioned along the
telescope axis, directs the light at a 90° angle from the launch optics
to the gimbal mirror. The window is a piece of sapphire glass that
allows the laser beam to exit and enter the sensor. The window is tilted
at an angle with respect to the nominal optical axis to reduce the
amount of back-scattered light into the telescope.

![](media/image2.png){width="3.1972222222222224in"
height="2.7069444444444444in"}

**Figure 2 -** Optical Head Assembly

![](media/image3.png){width="3.15in" height="2.3631944444444444in"}

**Figure 3 -** Photograph of the LAMP optical head assembly without the
top panel. The laser beam has been added for illustration.

The optical bench is the component to which all the parts and assemblies
in the OHA mount. The optical bench also contains four mounting feet for
mounting the OHA to the spacecraft. The optical bench is a single piece
part machined out of a block of aluminum. The optical bench is designed
to provide alignment stability for the optical elements when subjected
to the thermal and structural environments of space missions. The back
cover is the panel used to mount the electrical interfaces of the OHA.
These electrical interfaces include connectors for the scanner, detector
power and timing signals, and the fiber for the laser.

The second unit comprising the LAMP sensor is the Pump Diode Module
(PDM). The PDM houses the laser diode that supplies the continuous laser
input to the 1064 nm YAG crystal. The PDM is connected to the OHA via a
fiber optic cable. The function of the PDM is to maintain the
temperature of the laser diode within a narrow band about its nominal
(20±0.3°C). The PDM consists of a housing, cover, laser diode, circuit
card assembly, temperature sensor, heating element and connectors. The
housing and cover are machined from aluminum and provide a thermally
conductive path for dissipating the heat from the laser diode and
heating element.

![](media/image4.png){width="2.9791666666666665in"
height="2.1in"}**Figure 4 -** Pump Diode Module

The Electronics Unit consists of seven electronic modules inside a
machined aluminum housing. The modules are: processor board, I/O board,
driver board for the scanner, timing board for measuring time of flight,
power supply, current driver for the pump laser and high voltage supply
for the APD detector. The backplane and module designs are based on the
CompactPCI 3U Packaging Specification \[9\] and the I/O connectors are
mounted on the front panels of the 3U modules. The unit is conduction
cooled and the power dissipation of the unit is about 30 watts. Heat is
transferred by conduction from the electronic modules to the unit
housing via heat sink bars on the printed wiring boards. A rendering of
the EA is shown in Figure 5.

![](media/image5.png){width="3.33125in" height="2.561111111111111in"}

**Figure 5 -**Rendering of the electronics assembly

[]{#__RefHeading___Toc27642494 .anchor}**4. LASER TRANSMITTER**

To meet the stringent power and thermal requirements of the system, the
pump laser is thermally controlled with a large radiator to space and a
heating element. The temperature set point is 17ºC-23ºC with an accuracy
of 0.3ºC. A commercial fiber coupled pump laser with 2.5 W output from a
200-micron core fiber was chosen. The PDM maintains the temperature set
point +/- 0.3ºC to avoid changes in the wavelength. The pump laser is a
standard 808 nm broad area laser diode that emits a multimode beam up to
approximately 3 W continuous wave power. The device has an internal
monitor photodiode for diagnostics as well as a thermistor temperature
sensor for the closed loop temperature control.

The flight laser system will use an up-screened commercial part. The
qualification and screening process has been tailored from Telcordia
certification (GR 468-CORE) commonly used in power laser devices with
some additional requirements due to the space environment. The main
difference is the inclusion of radiation testing. Preliminary testing
has shown that the overall laser system is not very susceptible to the
radiation environment expected with any effects being annealed out at
the higher optical powers. The fiber coupling to the laser head will
also undergo pre-conditioning to ensure no degradation on orbit. A photo
of the pump laser diode is shown in Figure 6.

![](media/image6.jpeg){width="2.1333333333333333in" height="1.6in"}

**Figure 6 -** Photo of the pump laser

LAMP requires a compact, lightweight pulsed laser transmitter with
energy per pulse of 10 μJ at a PRF of \~10 KHz, a pulse-width rise time
of less than 2 nsec, and no nulls in the far-field pattern of the beam.
Stable average power, and low jitter and repeatable PRF are highly
desirable. A passively Q-switched microchip Nd:YAG laser was selected as
the laser transmitter. These lasers are simple, compact, and reliable
sources with 1 to 100 kHz of PRF and nsec level pulses. The absence of
control elements and continuous-wave laser pumping is a clear advantage
of these lasers. The output wavelength depends on the host crystal used.
Nd:YAG, Nd:YVO4 and Nd:LSB crystals were studied in detail along with a
variety of passive Q-switched crystals including Cr:YAG. Based on the
analysis, the requirements and on the commercial availability of the
crystals with the required specifications, the Nd:YAG/Cr:YAG combination
was selected. The pump diode is coupled to the crystal combination via a
0.29 pitch Graded Index (GRIN) lens. A sketch of the laser system is
shown in Figure 7 and Figure 8 shows a photograph of the microchip
laser.

**Figure 7 -** Sketch of the laser transmitter

![](media/image7.jpeg){width="2.5027777777777778in"
height="1.7555555555555555in"}

**Figure 8 -** Photograph of the microchip laser

A diagram of the LAMP optics is shown in Figure 9. The transmit optics
consists of three elements that collect the output from the microchip
laser and expand it up to provide a 0.35 mrad divergence output beam.
This output beam is reflected off an adjustable turning mirror that is
used for transmit/receive alignment. A second fixed turning mirror that
is in the shadow of the secondary mirror reflects the beam onto an axis
that is parallel to the receiver optical axis. The beam reflects off the
scan mirror and is transmitted out to the target through a sapphire
window.

![](media/image8.jpeg){width="3.3493055555555555in"
height="2.279166666666667in"}

**Figure 9 -** Diagram of the LAMP transmit and receive optics

The laser launch optics is housed in a part referred to as the laser
optics block. The laser optics block provides the mounting interface
between the microchip laser, the optical bench and the laser launch
optics. The axial position of the convex lens (shown in Figure 10) is
adjustable thus allowing one to optimize the laser beam. Lastly, the
launch optics includes a tip-tilt adjustable mechanism to control the
orientation of a 90° turning mirror. This adjustment is used to co-align
the output beam from the sensor with the telescope axis. The alignment
of the optics block is not sensitive to translation or to rotation about
the axis of the output beam. However, the alignment is very sensitive to
in-plane rotations of the optics block with respect to the output beam.
The optics block mounts directly to the optical bench to provide a
highly conductive thermal path for heat dissipated in the laser crystal.
This mounting scheme provides adequate constraints on the two in-plane
rotations. The last feature of the launch optics is the start-pulse
detector located on a Circuit Card Assembly (CCA). This circuit will be
described later in this paper. A rendering of the laser optics block is
shown in Figure 10.

![](media/image9.png){width="3.4229166666666666in"
height="1.7166666666666666in"}![](media/image10.png){width="2.123611111111111in"
height="1.6902777777777778in"}

**Figure 10 -** Laser optics block

[]{#__RefHeading___Toc27642495 .anchor}**5. SCANNER**

The purpose of the 2-axis gimbal (scanner) is to point the outgoing
laser beam and collect the incoming reflected signal. The 2-axis gimbal
consists of a mirror mounted to a yoke capable of rotating about two
axes, azimuth and elevation. The mirror is nominally oriented at a 45°
angle with respect to both the telescope axis and sensor output axis.
The maximum angular range of the scan mirror about the azimuth axis,
defined to be collinear with the telescope axis, is ±5°. The maximum
rate of rotation about the azimuth axis is 1 Hz. The maximum angular
range of the scan mirror about the elevation axis, which is normal to
the plane defined by the azimuth axis and sensor output axis, is ±3°
(since the laser beam is reflected off the mirror, this results in a
range of ±6° for the beam). The maximum rate of rotation about the
azimuth axis is 100 Hz. The angular motion of the mirror about both axes
is controlled by a spring-actuator system. The springs are trefoil
flexures integrated into the yoke that have a specified rotational
stiffness (non-linear), while the actuators consist of coils and
magnets. The electromotive force generated when current is applied
through the coils creates a moment about the azimuth and/or elevation
axis. The amount of current (proportional to the voltage across each
coil) is proportional to the moment about each axis. The angular
deflection about each axis is a function of the moment and the
rotational stiffness. Therefore, the angular rotation about each axis is
a function of the voltage across each set of coils. The 2-axis gimbal
utilizes various materials to meet its functional requirements. The
mirror is machined from beryllium to reduce mass and provide high
stiffness. The magnets are neodymium-iron-born to produce a strong
magnetic field for the coils. Finally, the yoke is made from titanium to
optimize the stiffness, strength and fatigue properties of the trefoil
flexures. A rendering of the scanner is shown in Figure 11.

![](media/image11.png){width="1.8701388888888888in"
height="2.56875in"}![](media/image12.png){width="3.229861111111111in"
height="2.3375in"}

**Figure 11 --** Rendering of the 2 axis gimbal

The scanner board in the electronics assembly serves two functions. The
first is to provide efficient drive for the slow and fast axes of the
2-axis gimbal assembly. The second is to monitor the position of the
beam at all times since the 2-axis gimbal is operated in an open loop
fashion.

The drive for the fast axis provides +/- 0.2A peak for the voice coil.
This input in full scan mode is a triangular waveform that normally has
a 20 ms period. A linear drive is utilized because of the relative low
power level (as opposed to utilizing Pulse Width Modulation (PWM) based
circuitry). The electronics protect the scanner from being driven
against the mechanical stops. The slow drive signal is likewise
triangular and has a period of 1 second in full FOV scans. A PWM drive
signal for the slow axis is produced by the IO board. This simplifies
the scanner board drive circuitry. The peak drive required by the slow
scanner axis is +/- 0.7 A. A choice of two gain levels is provided to
allow increased resolution at small angles.

The scanner encoder measures the angular orientation of the scan mirror
by measuring the position of a laser beam reflected from a mirror
mounted on the back of the scan mirror. A VCSEL is used to illuminate
the scanning mirror. This was chosen because of the low optical power
requirement, a reasonable beam quality and the fact that these types of
lasers are very robust with extensive environmental testing being
performed for the telecom market. The laser has a nominal output power
of 1 mW at 850 nm and includes a monitor photodiode in a TO-46 can
\[10\]. The light is reflected off of a small lightweight mirror mounted
on the back of the gimbal mirror. The Position Sensing Detector (PSD)
\[11\] is a 1 cm square, bi-lateral device. This detector senses the
location of the focused VCSEL laser spot. The 4 outputs from the PSD are
processed though 2 standard transimpedance amplifiers and 2 biased ones.
The analog-processed data are sent to the I/O board and from there to
the software that calculates the orientation of the outgoing beam.

[]{#__RefHeading___Toc27642496 .anchor}**6. LASER RECEIVER**

The telescope assembly receives the incoming return beam from the scan
mirror and focuses the beam onto the detector elements. The telescope
assembly consists of five parts; barrel, primary mirror, secondary
mirror support, secondary mirror and baffle. The challenge in designing
this telescope was the requirement that the focal length be as short as
possible to accommodate the tight packaging requirements of the sensor.
The telescope receives a 50 mm diameter beam and focuses it on a spot
approximately 15 mm behind the back surface of the telescope. The
primary and secondary mirrors utilize bipod flexure mounting feet to
create a statically determinant interface between the mirrors and the
support structure. These features are necessary to relieve the mirror of
any pre-loaded stresses during assembly that may deform the mirror
surface. The telescope includes a means of adjusting the axial position
of the secondary mirror with respect to the primary mirror. This
adjustment, which consists of shims, barrel and secondary mirror
support, is used to position the focal point of the telescope at the
desired location. A rendering and a photograph of the telescope are
shown in Figure 12.

![](media/image13.png){width="3.254166666666667in"
height="2.5416666666666665in"}![](media/image14.png){width="2.2194444444444446in"
height="2.504861111111111in"}

**Figure 12 --** Rendering and photograph of the LAMP telescope

As shown in Figure 9, the return signal passes back through the front
window, off the scan mirror and through a 100 nm notch filter that
minimizes the solar background. The signal then enters the 5 cm aperture
F2.5 Casegrain telescope shown in Figure 12 that focuses the signal down
onto the detectors. A beam splitter is used to split the stop pulse
between two detectors.

The detector assembly consists of two CCAs, a beam splitter, and an
adjuster mechanism. The detectors used to measure the incoming beam are
located on each of the CCA's. The CCA's and beam splitter are mounted
together such that the APD detector receives 99% of the light passing
through the beam splitter, while the Si PIN detector receives the
remaining 1% reflected light. Once assembled, the positions of the
detectors and beam splitter are fixed with respect to each other. The
detectors and beam splitter mount to an adjuster assembly that provides
the interface to the optical bench. The adjuster provides translation of
the detectors in all three axes, thus the detectors can be properly
aligned with the focal point of the telescope. This is shown in Figure
13.

![](media/image15.png){width="2.863888888888889in"
height="2.4493055555555556in"}![](media/image16.png){width="2.657638888888889in"
height="1.788888888888889in"}

**Figure 13 -** Detector Assembly

The primary sensor is an Avalanche Photodiode (APD), which utilizes a
strong electric field across the device to obtain an avalanche gain of
approximately 200 to the return signal. This is necessary to amplify the
return pulse sufficiently to meet the range requirements. The APD chosen
for this application is the Perkin Elmer C30954E, chosen for its high
quantum efficiency (\~0.4) at 1064 nm, and its rapid response time of 2
nsec \[12\]. Both the gain and the breakdown voltage of this detector
are strongly affected by temperature, requiring thermal monitoring of
the APD and variable bias application to maintain a constant gain. The
dark current at 20ºC is 300 nA after receiving a total dose of 10
Krad(Si). The detectors were purchased in bulk, and tested and
flight-qualified by JPL for optimal performance in the anticipated
environment. At close range, the return pulse will saturate the APD. To
meet the range resolution under these conditions, a silicon PIN detector
with much lower quantum efficiency (0.05), but an equivalent 2 nsec rise
time is used. The detector is model PSS 0.25-5 from Pacific Silicon
Sensor. The same detector type is also used to sense the timing of the
exiting laser pulse by observing the residual pulse light scattered by
the optical surfaces of the transmitting optics in the laser optics
block.

The APD receiver operates with approximately 300 volts reverse bias to
provide the required amplification of \~200 for the electrons produced
by the APD. Provisions are made so that it is possible to change the
reverse bias to accommodate the temperature variations and to reduce the
APD gain as the target gets closer to the instrument. The APD circuitry
is shown in Figure 14.

**Figure 14** - The APD circuitry

The 47 KOhm resistor shown in Figure 14 is used to limit the APD current
under condition of excessive amounts of light striking the APD. It also
provides some protection to the APD if it inadvertently enters the
Geiger mode. Also, it provides some filtering for the HV signal. The
100-pF capacitor serves to supply just enough energy to the APD to
support "normal" level light pulses. The capacitance shunting the 10K
resistor is due to the APD, the amplifier input, the Schottky diode
limiter and to some parasitics. The total capacitance is estimated to be
4-5 pF resulting in a network bandwidth of 4 MHz (time constant \~40
ns). While the light pulse rise time is 2 ns, the narrow bandwidth of
this network does not impact it, but it dramatically reduces the Johnson
noise contribution of the 10K Ohm load resistor. The laser PRF is
\~10KHz and is not impacted by the 40 ns time constant. The resistor R
has a small value and is used to get a signal with lower amplitude. The
output from the APD is fed to a 200 MHz low noise amplifier with a
voltage gain of \~21. This is sketched in Figure 15.

**Figure 15 -** The OPA687 amplifier circuitry

The OPA687 is configured as a voltage feedback amplifier with a gain
bandwidth of 3.9 GHz, 0.9 nV/√Hz and 2.0 pA/√Hz noise. The thermal noise
of the 10Kohm resistor is 26 μV~RMS~ \[13\]. The input referred noise of
the amplifier is \~ 0.9nV/√Hz·√200MHz = 13 μV~RMS.~ The input referred
current noise of the amplifiers is 2.5nA/√Hz·10KOhm·√4MHz = 50 μV~RMS.~
The S/N ratio will be discussed later in this paper. The output of the
receiver is back terminated with 50 ohms and drives the comparator/latch
though a coaxial cable. In order to protect the receiver amplifier a
Schottky diode is used across the input of the amplifier. Tests have
shown that the diode is capable of protecting the amplifier chip.

When LAMP is ranging a bright close target, the APD will receive \~5 μJ
pulses. This could potentially damage the APD and the receiver
amplifier, but this is mitigated by reducing the high voltage reverse
bias (under software control) to reduce the gain of the APD. This
however, does not reduce the energy absorbed by the APD. Tests run of
the APD with 10 μJ pulses has shown that the APD is immune to these
short duration pulses and since the repetition rate is 10 kHz less than
100 mW is dissipated in the APD.

The Si PIN receiver and the start receiver are similar in design to the
APD circuit. The demands on these circuits are much reduced and the
detectors are operating at a few volts of reverse bias into a similar
amplifier stage.

The timing board receives a "laser start" and five "laser stop" signals
from the receivers in the optical head and produces 5 distances
corresponding to the 5 "stops". The maximum distance measurement
corresponds to \~470km. A block diagram of the timing board and the stop
channels are shown in Figure 16.

The analog pulses coming from the optical head must be processed
suitably before they can be used for the timing chip. The start pulse is
level detected and is applied though a matched delay to the timing chip
start input. The output of the start chip detector gates 4 of the 5 stop
channels though AND gates. The delay can also be extended under the
control of the IO board. The purpose of this delay circuitry is to
prevent the output of the detectors from reaching the timing chip while
the outgoing pulse is still being scattering in the optics. Efforts have
been made to minimize the internal scattering in the optical head.

Stop channel #1 is treated differently than the other stops. Its output
is not inhibited by the start detector output. Therefore the output of
stop #1 is immediately available for the timing chip. This is used for
short distance measurements. It gets around the internal scattering
problem by having its threshold set higher than the largest scattering
signal. The other four stop channels are used to measure ranges distant
enough to allow the scattering to decay sufficiently as to not affect
the system.

A scenario of a pulse coming from a great distance is shown in Figure
17. The Figure shows how the internal scattered light is gated out, and
how the dim pulse returning is only bright enough to be detected by 2 of
the 5 channels. Please note that due to the finite rise time of the
laser, the stop pulse for stop #5 is generated a fraction of a ns before
the stop of stop #4.

In Figure 17, it is observed that the timing of the stop pulses was not
simultaneous, but was different at the ns level. This information can be
used to infer the brightness of the pulse and thereby improve the range
estimate. The two highest gain signals are integrated and processed by 2
A/Ds to provide intensity information about the targets. Emphasis was
placed on delay tracing within the timing board and a temperature
sensor, which allows for calibration of the channels output vs.
temperature.

The functionality of the timing chip resembles 5 stopwatches. The timing
chip could in principle be implemented using a 2.5 GHz accurate and
highly stable oscillator and a binary counter for each channel. However,
such a design is difficult and would have a very high power consumption
of several watts. Also, Meta stable errors would be quite numerous at
such a high frequency. (Meta stable errors stem from the asynchronous
relationship between the local clock and the arrival of the laser
pulses.)

The timing chip was custom made at the Technical University of Oulu
\[14\]. The chip is free of Meta stable errors and has an LSB resolution
of 390 ps at a power consumption of 100 mW. The chip is designed by
creating a 32-bit stage phase locked loop, which is synchronized with
the 80 MHz[^4].

The timing chip is used to estimate the fraction of a clock cycle not
captured by counting the elapsed time between outgoing and return pulses
using an 80MHz clock. When the timing chip estimates the elapsed time
between start and stop, it counts the time using the 80MHz clock.
However, when it encounters the start pulse, it also reads the start
interpolation register that contains information on the position of the
traveling wave. The same thing happens when the stop signal is
encountered. This whole process is illustrated in Figure 18.

[]{#__RefHeading___Toc27642497 .anchor}**7. DIGITAL ELECTRONICS**

The Lamp Processor is a radiation hardened R3000 microprocessor that has
4 Mbytes of EEPROM memory and 64 Mbytes of SDRAM memory. At its maximum
processor speed of 12.5 MHz it has a throughput of 10 MIPS. The software
programmable clock rate feature allows for the system clock to be
divided down to as low as \~100KHz which enables approximately a factor
of 100 in power savings. Along with the processor and memory the board
has an 8 channel DMA FPGA that is utilized to communicate with the I/O
board. The serial interface FPGA can be programmed for synchronous or
asynchronous protocols up to 4 Mbits/second. Software reset capability
and a watchdog timer are implemented. The processor board is a 3U card

**Figure 16 -** Block diagram of the timing board and the stop channels

**Figure 17 -** Signals and timing diagram when receiving a dim pulse

format and has a nominal power draw of 2.9 watts at the maximum system
clock and the serial and backplane DMA features running. A block diagram
of the processor is shown in Figure 19. Board capability is summarized
in Table 3.

![](media/image19.wmf)**Figure 19 -** LAMP Processor Board Block Diagram

The I/O board provides all interface connections from the processor to
the rest of the system. The only communications to the processor is
through direct memory access port with 4 I/O request/grant channels. All
instructions come through this port. The I/O board provides the
horizontal and vertical scanning capability, which is driven through DMA
instructions. The horizontal axis output is through a 12-bit D/A with a
+/- 5V drive. The vertical axis is through a PWM output. All other
output is through the digital control output word. Onboard input and
output FIFO's help reduce the amount of DMA activity.

Inputs are read from the timing board and assembled into the round trip
time information of the laser pulse. Two A/D converters are used to read
the gimbal mirror angles along with other voltage and temperature data.
This data is read when the laser fires and sent back though the DMA port
to the processor along with a time tag. A block diagram of the I/O board
is shown in Figure 20.

The LAMP processing architecture is designed to support the different
applications described in the beginning of this paper. The processor has
sufficient computational power to process 10,000 3D points per second.
This data can be used to determine relative motion between the
spacecraft and a body (Mars landing, small body rendezvous), hazard
evaluation (landing), surface mapping, or to support rendezvous
operations (acquiring and tracking of a spacecraft/object). LAMP is also
capable of transferring all collected data (via a serial port) to the
spacecraft for further analysis or download.

[]{#__RefHeading___Toc27642498 .anchor}**8. SOFTWARE SUBSYSTEM**

The software is functionally divided into two parts. An application
specific process(es) that directs the data collection effort (when and
how to scan), processes the data to retrieve relative motion information
or hazard locations, and sends the information/data to the spacecraft
via the serial port. The application software sits on top of a set of
generic software routines called LAMPOS. LAMPOS provides the device
drivers and auxiliary routines needed for communication and to control
the LAMP hardware (power control, scanner control, IO operations, data
formatting and movement). In addition, LAMPOS has routines that allows
for sharing resources and providing process controls (starting and
ending process, intra-process communication, clean-up, etc.).

![](media/image20.png){width="3.5625in" height="4.054166666666666in"}

**Figure 20 -** Block diagram of the I/O board

[]{#__RefHeading___Toc27642499 .anchor}**9. POWER SUBSYSTEM**

The power subsystem consists of three main components: The digital and
analog power converter, the current source power supply and the high
voltage power supply. The digital and analog power converter consists of
5V, 3.3V and 2.5V,

**Figure 18.** Timing estimation, Elapsed time: 3 \* 12.5 ns + 7 \* 390
ps - 28 \* 390 ps = 29.31 ns

**Table 3** LAMP Processor Board Capabilities Summary

  ----------------- ----------------- ----------------- -----------------
  Processor         12.5MHz           10MIPs            Rad Hard

  SDRAM             64Mbytes          EDACed            20Krad

  EEPROM            4Mbytes           EDACed            40Krad

  RS-232 UARTS      2 Channels        38Kbits/sec       Rad Hard

  RS-422 Sync       1 Channel         1.5Mbits/sec      100Krad
                    downlink                            

  RS-422 Async      1 Channel Uplink  480Kbits/sec      100Krad

  DMA               8 Channel         12Mbytes/sec      Rad Hard

  Watch Dog Timer,                                      
  Software                                              
  programmable                                          
  system clock and                                      
  Reset                                                 
  ----------------- ----------------- ----------------- -----------------

which provide power to the digital circuits, and low noise ±5V and ±15V
provide power to the analog circuits. It receives its input from the
spacecraft 28V bus. In addition to DC/DC power converters, it also
provides control circuitry for synchronization, ON/OFF command for the
analog converters, temperature sensing, under voltage detection and slow
start circuit to reduce input surge current. The current source power
supply provides constant current for the pump laser. The control
circuitry includes 5 digital bits to adjust output current, ON/OFF
command and temperature sensing. The high voltage power supply is an
adjustable voltage supply, which provides voltage to the APD. It can
supply voltages up to 500V and 1 mA of current. The control circuitry
consists of 2 digital bits to adjust the output voltage and temperature
control to compensate the output voltage.

[]{#__RefHeading___Toc27642500 .anchor}**10. ESTIMATED S/N RATIO**

This section will show a calculation of the expected signal to noise
ratio in LAMP. A scenario, when ranging a single 7-mm retroreflector at
a distance of 5 km was chosen. The scenario is relevant for Mars
applications when trying to detect an orbiting sample canister as
discussed in the introduction of this paper. In Table 4 is shown a
"photon budget" and different signal levels in Volts.

**Table 4.** Signal to noise ratio terms for ranging a retroreflector

+---+--------------------------------------------+---------+-----------+
|   | **Signal**                                 | Value   | Unit      |
+---+--------------------------------------------+---------+-----------+
| 1 | No. photons in pulse emitted from LAMP     | 2       | Photons   |
|   |                                            | .41E+13 |           |
+---+--------------------------------------------+---------+-----------+
| 2 | No. photons intercepted by 7mm             | 3       | photons   |
|   | retroreflector                             | .85E+08 |           |
+---+--------------------------------------------+---------+-----------+
| 3 | Backscattered photons on intercepted by    | 1       | photons   |
|   | detector                                   | .01E+05 |           |
+---+--------------------------------------------+---------+-----------+
| 4 | Photoelectrons generated by laser pulse    | 1       | Photo     |
|   |                                            | .42E+06 |           |
|   |                                            |         | electrons |
+---+--------------------------------------------+---------+-----------+
| 5 | Voltage generated by laser pulse           | 5       | Volt      |
|   |                                            | .04E-02 |           |
+---+--------------------------------------------+---------+-----------+
|   | **Noise**                                  |         |           |
+---+--------------------------------------------+---------+-----------+
| 6 | Photon noise                               | 5       | Volt      |
|   |                                            | .99E-04 |           |
+---+--------------------------------------------+---------+-----------+
| 7 | APD gain noise                             | 3       | Volt      |
|   |                                            | .56E-03 |           |
+---+--------------------------------------------+---------+-----------+
| 8 | Dark current                               | 1       | Volt      |
|   |                                            | .96E-05 |           |
+---+--------------------------------------------+---------+-----------+
| 9 | APD noise                                  | 7       | Volt      |
|   |                                            | .00E-04 |           |
+---+--------------------------------------------+---------+-----------+
| 1 | Johnson Noise                              | 2       | Volt      |
| 0 |                                            | .60E-05 |           |
+---+--------------------------------------------+---------+-----------+
| 1 | Input referred amplifier noise             | 1       | Volt      |
| 1 |                                            | .27E-05 |           |
+---+--------------------------------------------+---------+-----------+
| 1 | Input referred current noise               | 5       | Volt      |
| 2 |                                            | .00E-05 |           |
+---+--------------------------------------------+---------+-----------+
| 1 | Sun induced background signal              | 1       | Volt      |
| 3 |                                            | .95E-05 |           |
+---+--------------------------------------------+---------+-----------+
| 1 | RSS of noise voltages                      | 3       | Volt      |
| 4 |                                            | .68E-03 |           |
+---+--------------------------------------------+---------+-----------+
| * | **S/N**                                    | *       |           |
| * |                                            | *13.7** |           |
| 1 |                                            |         |           |
| 5 |                                            |         |           |
| * |                                            |         |           |
| * |                                            |         |           |
+---+--------------------------------------------+---------+-----------+

The following explanation is given for the numbers in Table 4:

1\) The laser pulses are 10 μJ at 1064 nm. It is assumed that 50% of the
photons are lost in the launch optics and 90% are transmitted though the
exit window.

2\) The outgoing beam divergence is 0.35mrads. This result in a beam
area of 2.4 m^2^ at 5 km. Therefore, only 1.6·10^-5^ of the photons will
intercept a 7mm diameter retro reflector.

3\) The photons intercepted by the retroreflector have a very small beam
divergence, but due to diffraction the 7mm retroreflector results in a
0.39 mrad returning beam divergence. Also, it is assumed that only 80%
of the photons are transmitted in the retroreflector. The returning beam
has an area of 3.1 m^2^ at LAMP. The telescope has an aperture of
1.8·10^-3^ m^2^. Also, it is assumed that 10% of the photons are lost in
the front window, 69% is transmitted in the telescope and 90% is
transmitted though the solar filter.

4\) The shape of the laser pulse is that it rises sharply and has a much
slower decay. In order to achieve accurate timing of the pulse, it is
desirable to detect the pulse at the sharply rising part of the pulse.
Therefore, it is required to detect the first 20% of the pulse. Also,
only (conservative) 35% of the photons are converted into photoelectrons
in the APD detector. The detected photoelectrons are on average
multiplied with 200 in the APD diode.

5\) The pulse coming from the APD is stored in a 4.5 pF capacitor (as
shown in Figure 14).

6\) The photoelectron noise is the square root of the detected
photoelectrons multiplied by 200 (gain in the APD) and converted to a
voltage over the 4.5 pF capacitance.

7\) As a first order approximation it is assumed that the gain noise of
the APD is square root of 200 = 14 photoelectrons. This noise is
generated for every single photoelectron and converted into a voltage.

8\) The dark current of the APD at 40ºC and after having received total
radiation dose is less than 3 μA. The bandwidth is 4MHz. Therefore the
dark current noise is sqrt(2·*e*·I~DC~·B) = 2nA or 19.6 mV \[15\].

9\) The APS noise is less than 35 pA/sqrt (Hz). The input bandwidth of
the APD amplifier (shown in Figure 15) is 4 MHz.

10\) Johnson noise over a 10 KOhms resistor with 4 MHz bandwidth \[13\].

11\) Described under APD previous

12\) Described under APD previous.

13\) In this number it was assumed that the sun is shining on the front
glass (but outside the 3º-exclusion angle from the sun). 10% of the sun
is absorbed in the front glass and re-emitted homogeneously in all
directions. Some of this light reaches the detector. The DC value is
converted into a voltage.

14\) The noise sources are RSSed together.

15\) The signal to noise is 13.7, which is sufficient to detect a
signal. It is observed that the dominant noise source is the APD gain,
which is proportional to the signal. This means that LAMP has much
longer detection range. Redoing the entire calculation shows that the
S/N at 10 km is still \>4.

[]{#__RefHeading___Toc27642501 .anchor}**11. SUMMARY**

This paper has described a laser radar that is being developed at JPL.
The laser radar is designed as guidance and navigation sensor for
rendezvous, landing and traverse planning applications. It will form a 3
dimensional image of its field of view. A block diagram of the sensor is
shown and the overall system design is discussed. LAMP consists of 3
individual boxes: 1) an optical head with gimbal, lasers, optics and
detectors. 2) Electronics Assembly consisting of the processor, I/O
boards, power supplies, drivers and timing board. 3) A small module
containing the pump laser that has its temperature controlled very
accurately. The laser transmitter consists of an 808 nm diode pump laser
that pumps a passively Q-switched Nd-YAG laser. When the laser pulses
leave the sensor, they bounce off a beryllium mirror that determines the
orientation of the beam. The outgoing laser pulses will hit a target and
a small fraction of the pulse will be scattered back to the sensor,
where it is collected by a telescope and detected by an APD detector.
The time of flight is proportional to the distance to the target and
registered for all points. The signal to noise ratio achieved in LAMP is
also discussed.

[]{#__RefHeading___Toc27642502 .anchor}**REFERENCES**

\[1\] D.Tratt, R. Menzies, R.Bartman, H. Hemmati: Scanning Laser Radar
Development for Solar System Exploration Applications, 20^th^
International Laser Radar Conference, Vichy, France, July 10-14, 2000.

\[2\] R.P.Kornfeld et al: New Millennium ST6 Autonomous

Rendezvous Experiment (ARX), Paper accepted at the 2003 IEEE Aerospace
Conference, Montana March 2003.

\[3\] Christian Cazaux et al: The NASA/CNES Mars sample return - A
status report, Source\
IAF, International Astronautical Congress, 52nd, Toulouse, France, Oct.
1-5, 2001,

\[4\] D. Clouse et al: Covering a sphere with retroreflectors, 2001 IEEE
Aerospace Conference, Big Sky, MT, Mar. 10-17, 2001, Piscataway, US,
IEEE, 2001, p. 1495-1506.

\[5\] Mars Technology Program, Proceedings of i-SAIRAS 2001, URL:
<http://www.space.gc.ca/csa_sectors/generic_space_tech/spa_craft_eng/rob_aut/isairas/default.asp>,
cited 11/18/02.

\[6\] A.Eisenman et al: Mars exploration rover engineering cameras,
Fifth Conference on Sensors, Systems, and Next-Generation Satellites,
Toulouse, France, Sept. 17-21, 2001, Bellingham, WA, Society of
Photo-Optical Instrumentation Engineers, 2001, p. 288-297.

\[7\] T.D.Cole: NEAR Laser Rangefinder: A tool for the Mapping and
Topologic Study of Asteroid 433 Eros, URL:
<http://pdssbn.astro.umd.edu/NEARdb/documents/nlr/nlr.pdf>, cited
11/18/2002.

\[8\] G.W.Stimson: Introduction to Airborne Radar, SciTech Publishing
Inc., ISBN: 0-7803-3491-4.

\[9\] PICMG 2.0 Revision 3.0 dated October 1, 1999. PCI Industrial
Computer Manufacturers Group (PICMG) PICMG, 401 Edgewater Place, Suite
500, Wakefield, MA 01880 USA, URL: http://www.picmg.org

\[10\] URL: http://content.honeywell.com/vcsel/products/datacom.stm,
<http://www.emcore.com/PDF/TO-46.PDF>, cited 11/18/01

\[11\] Sitek, Sweden: URL: <http://www.sitek.se/pdf/psd/2l10sp.pdf>,
cited 11/18/02

\[12\] Perkin Elmer: URL:
<http://opto.perkinelmer.com/producttemplates/SubCat2.asp?levelId=14494&s=2&ss=1>,
cited 11/18/02

\[13\] E.A Bahaa et al: Fundamentals of Photonics, Wiley-Interscience;
ISBN: 0471839655;

\[14\] University of Oulu, Finland: URL:
<http://www.infotech.oulu.fi/Annual/1999/HSELE.html>, cited 10/2/02

\[15\] P.Horowitz and Winfield Hill: The art of electronics, Cambridge
University Press, 1989, ISBN:0-521-37095-7.

**ACKNOWLEDGEMENT**

The authors of this paper would like to thanks the Mars Technology
Program at the Jet Propulsion Laboratory, California Institute of
Technology for providing the funding for this work.

The research described in this paper was carried out at the Jet
Propulsion Laboratory, California Institute of Technology and was
sponsored by the National Aeronautics and Space Administration.
References herein to any specific commercial product, process or service
by trademark, manufacturer, or otherwise, does not constitute or imply
its endorsement by the United States Government or the Jet Propulsion
Laboratory, California Institute of Technology.

**BIOGRAPHIES**

![](media/image21.jpeg){width="0.85in" height="1.125in"}**Dr.** **Carl
Christian Liebe** received the M.S.E.E. degree in 1991 and the Ph.D.
degree in 1994 from the Department of Electro physics, Technical
University of Denmark. Since 1997, he has been an employee at the Jet
Propulsion Laboratory, California Institute of Technology. Currently, he
is a senior member of the technical staff in the Precision Motion
Control Systems and Celestial Sensors Group. His research interests are
new technologies and applications for avionics sensors. He is the
systems engineer for LAMP. He has authored/co-authored more than 40
papers.

![](media/image22.png){width="0.8333333333333334in"
height="1.09375in"}**Dr. Alex Abramovici** received a Ph.D. in physics
from the Weizmann Institute of Science, Israel in 1985. Has joined JPL
in 1996. He has worked on ground-based interferometric gravitational
wave detectors, and on airborne and space based laser metrology and
interferometry measurements. Alex is responsible for the LAMP signal
electronics.

![](media/image23.png){width="0.8333333333333334in"
height="1.1125in"}**Randy K. Bartman** received a B.S. degree in physics
from California Institute of Technology in 1977. At which point he
became an employee of the Jet Propulsion Laboratory. Randy Bartman is
the deputy section manager for the Interferometry Systems and Technology
Multidivisional Section. His research interests include lasers, and
interferometry. Randy is the chief engineer for LAMP.

![](media/image24.png){width="0.8576388888888888in"
height="1.132638888888889in"}**Robert L. Bunker** is a graduate of the
California Institute of Technology, and has spent the last 33 years at
JPL designing and managing spacecraft avionics systems, including more
than 10 years in line management of flight avionics systems.  His
experience includes spacecraft computer systems, advanced VLSI and
system design for radiation and Single Event Effects environments, and
celestial sensors used for spacecraft attitude control.  He has worked
on Mariner, Viking, Voyager, Galileo, Cassini, Mars Global Surveyor and
Mars Odyssey spacecraft, as well as providing guidance and leadership
for JPL institutional programs in flight VLSI design and model based
spacecraft system/subsystem design methodologies. Mr. Bunker is a
Principal Engineer and has received recognition for his innovative
contributions to the interplanetary program and has authored several
papers on advanced electro-optical sensors and computers for use on
planetary spacecraft. Currently, Mr. Bunker is the Project Manager for
the Autonomous Rendezvous Experiment (ARX) and the Laser Mapper (LAMP)
development, which is the flight sensor used by ARX.

![](media/image25.png){width="0.8340277777777778in"
height="1.1145833333333333in"}**Jacob Chapsky** is a senior electronics
design engineer with 46 years of experience in designing military, space
and industrial subsystems. He has an M.S.E.E. degree from USC. He was a
chief scientist at Hughes Aircraft where he was responsible for many
space-deployed subsystems. As a principal engineer at California
Institute of Technology he played a critical part with his designs in
achieving the 2·10^-9^ m/√Hz noise floor for the Gravitational Wave
detector. He was also a program engineer for 2 Apollo instruments
deployed on the Moon in 1969. Jake is working on the LAMP signal
electronics.

![](media/image26.png){width="0.8645833333333334in"
height="1.1145833333333333in"}**Dr. Cheng-Chih Chu** is the Group
Supervisor of Simulation and Verification Group at JPL, responsible for
the development and implementation of simulation tools and verification
process for the avionic subsystem in support of various JPL missions.
Dr. Chu received his M.S. degree in Electrical Engineering and Ph.D.
degree in Control Science from University of Minnesota in 1985. He has
18 years of extensive experience in program and technical management,
GNC system design and analysis and has authored over 40 publications. He
initiated the LAMP task in 1999 as part of Mars Technology Program and
was the task manager from 1999 to 2000.

![](media/image27.png)**Dr. Daniel Clouse** received the B.A. degree in
Computer Science from the University of California, Berkeley in 1982,
the M.S. degree in Computer Science from the University of California,
San Diego (UCSD) in 1992, and the Ph.D. degree in Cognitive Science and
Computer Science from UCSD in 1998. He is a Member of the Technical
Staff at the Jet Propulsion Laboratory, California Institute of
Technology in the Machine Vision group of the Mobility Section. His
interests include vision processing, neural networks, language
translation, and word sense disambiguation. Dan is responsible for the
LAMP software.

![](media/image28.png){width="0.8194444444444444in"
height="1.00625in"}**James W. Dillon**, Received his BSEE in 1967 from
Indiana Institute of Technology. He came to JPL in 1974 and worked many
projects including VLBI (very long baseline interferometry), The Human
Genome Project, Hypercube, Cassini, and Pathfinder. He is a Senior
Engineer in the Electronics Design group and is currently doing the
Processor I/O board design for LAMP.

![](media/image29.wmf)**Bob Hausmann** has over 40 years experience in
the mechanical design and electronic packaging of defense and aerospace
electronic systems. He has directed packaging engineering activities on
shipboard, aircraft, land based vehicles, and space electronic systems.
He is currently a senior engineer in the Electronics Packaging and
Manufacturing Section at the Jet Propulsion Laboratory and has led
electronic packaging teams on the Cassini, Cloudsat, and LAMP Programs.
Bob has a BSME degree from California State University -- Los Angeles
and an MBA degree from California State University -- Fullerton. He is
an active member of the IMAPS and SMTA engineering technical societies
and a senior member of the IEEE.

![](media/image30.wmf)**Dr. Hamid Hemmati**, Ph.D. Physics 1981, joined
JPL in 1986 and is now supervisor of the Optical Communications Group.
His research field includes: free-space laser-communications,
solid-state lasers and electro-optical instrumentation. He has been
involved in several space laser experiments, including the GOPEX
project, the Japanese laser communications experiment, and LAMP/ST6
project. Hamid is responsible for the microchip laser.

![](media/image31.wmf)**Dr. Richard P. Kornfeld** received a Diploma
(M.Sc.) in Electrical Engineering from the Swiss Federal Institute of
Technology (ETH) in Zurich, in 1994 and a Ph.D. degree in Aeronautics
and Astronautics from MIT in 1999. In 1994-1995 he was with McDonnell
Douglas Aerospace (now Boeing) in St. Louis, Missouri. Since 1999 he has
been at the NASA/Caltech Jet Propulsion Laboratory where he is a Senior
Engineer in the Advanced Concepts and Architecture Group in the Avionic
Systems Engineering Section. He currently serves as the ARX/LAMP Project
Engineer and ARX Lead Systems Engineer.

![](media/image32.png){width="0.8333333333333334in"
height="1.1236111111111111in"}**Clint Kwa** received his B.Sc. and M.Sc.
degrees from University of Southern California in 1975 and 1976
respectively. He has held various engineering positions in commercial
industries. He joined JPL in 1990; his involvement includes Drop Physic
Module, Cassini and TES programs. In 1999, he joined the Power and
Sensor Electronics Section at JPL as a Senior Engineer. Clint is
responsible for the LAMP power supplies.

![](media/image33.jpeg){width="0.8666666666666667in"
height="1.125in"}**Dr.** **Sohrab Mobasser** received his Ph.D. from
Stevens Institute of Technology at New Jersey in experimental
solid-state physics in 1982. He is a Senior Member of the Engineering
Staff at the Jet Propulsion Laboratory, California Institute of
Technology. Sohrab has more than 18 years of aerospace industry
experience, most of it in spacecraft attitude determination. His work
can be found on many planetary missions, from the Galileo mission to
Jupiter to the successful Pathfinder mission to Mars and the Cassini
mission to Saturn. His current interests are new technology and
applications for autonomous attitude determination. Sohrab is
responsible for LAMP I&T.

![](media/image34.jpeg){width="0.8569444444444444in"
height="1.1375in"}**Michael Newell** has seventeen years of experience
designing and analyzing digital and analog systems for space flight. His
flight work includes design of integrated circuits design for the
Cassini Spacecraft, lead designer of the APEX flight experiment,
avionics lead of the Deep Impact project along with design analysis on
the Sojourner Rover. In addition to his work in Flight Avionics, he has
been investigating operation of CMOS devices at cryogenic temperatures
for use in space for the past seven year. He is the task manager of
extreme temperature electronics in the NASA Electronics Parts Program.
He has a patent and a NASA Space Act Award for his work on a space
32-bit risk processor MCM with reconfigurable hardware. He has a BSEE
from the California State Polytechnic University, Pomona. Mike is the
hardware lead engineer on LAMP.

![](media/image35.png){width="0.9090277777777778in"
height="1.16875in"}**Dr. Curtis Padgett** received his Ph.D. from the
Computer Science and Engineering Department at the University of
California at San Diego (UCSD) in 1998. He received his M.S. degree from
the same department in 1992. He has been employed at the Jet Propulsion
Laboratory, California Institute of Technology, Pasadena since 1993. He
is a Senior Member of the Technical Staff in the Machine Vision group of
the Mobility Section where he works on remote sensing applications for
space systems. His research interests include algorithm optimization,
machine vision, and artificial intelligence applied in classification
and pattern recognition tasks. Curtis is the software lead engineer on
LAMP.

![](media/image36.png){width="0.875in" height="1.125in"}**Dr. W. Thomas
Roberts** received a B.Sc. (1981) and a M.Sc. (1985) from The University
of Alabama and then worked at the Nichols Research Corporation. He moved
to the Optical Sciences Center, University of Arizona in 1994 where he
got the M.Sc. in 1996 and the Ph.D. in 2001. Tom has been employed at
the Jet Propulsion Laboratory, California Institute of Technology,
Pasadena since 2001. He is currently a Senior Member of the Technical
Staff in the Optical Communications Group where he works on developing
high-efficiency Q-switched Nd:YVO4 lasers for deep-space optical
communication and is the cognizant engineer for the LAMP detectors. Tom
is the author of papers in magnetospheric physics, Radiometric Analysis,
Satellite Sensor Characteristics, Infrared Detector Development, and
Guide Star Laser Development.

![](media/image37.png){width="0.9243055555555556in"
height="1.25in"}**Gary Spiers** is the Acting Supervisor for the Laser
Remote Sensing Group at JPL. He currently holds a Lidar related visiting
scientist position with UCAR and is a member of a number of Lidar
working groups and committees. Prior to joining JPL he was the Coherent
Lidar Systems Engineer for the EO-2 Space Readiness Coherent Lidar
Experiment (SPARCLE) and participated in other earlier Doppler wind
Lidar efforts at NASA MSFC. He received his BSc degree in physics and
his MSc in Lasers and their applications in 1984 and 1985 respectively
from Essex University, England. Between 1985 and 1990 he carried out
research in TEA carbon dioxide, excimer and free-electron lasers at
Heriot-Watt University in Edinburgh, Scotland and participated in ESA
studies for a space based Doppler Lidar. Gary is responsible for the
LAMP optics.

![](media/image38.png){width="0.9270833333333334in"
height="1.2215277777777778in"}**Zachary Warfield** received a B.S. in
mechanical engineering from University of Notre Dame in 1998 and a M.S.
in Aeronautics & Astronautics from Massachusetts Institute of Technology
in 2001. He currently is employed at the Jet Propulsion Laboratory,
California Institute of Technology, in the Structures and Mechanisms
Group of the Mechanical Engineering Section. He is currently the
mechanical lead for the LAMP sensor development.

![](media/image39.png){width="0.9048611111111111in"
height="1.207638888888889in"}**Dr.** **Malcolm Wright** received the
B.Sc. (hons) degree (1984) and M.Sc. degree (1986) in physics from
Victoria University of Wellington, New Zealand, and Ph.D. degree (1992)
in physics from the University of New Mexico, Albuquerque, NM with
research undertaken for the latter at the Chemical Laser Branch of the
Phillips Laboratory, Kirtland AFB, NM. Following postdoctoral research
at the Center for High Technology Materials, University of New Mexico,
he was with the Semiconductor Laser Branch of the Air Force Research
Lab, Kirtland AFB, NM developing high power semiconductor
lasers. Currently he is with the Optical Communications Group at the Jet
Propulsion Lab., California Institute of Technology, developing laser
based communication systems for future NASA flight projects. His
research interests include dynamics of high speed lasers for free space
optical communications and space qualification of semiconductor and
fiber based lasers for space borne applications. He has authored
numerous technical papers and presentations and is a member of the
American Physical Society. Malcolm is responsible for the Pump and VCSEL
lasers for LAMP

[^1]: 0-7803-7651-X/03/\$17.00 © 2003 IEEE

[^2]: IEEEAC paper #1066, Updated December 11, 2002

[^3]: With the current beam divergence of 0.02 degrees, and a sampling
    rate of approximately 0.1 degrees spacing in both azimuth and
    elevation, a small grid of data points is generated which is
    representative of the surface topography, but could conceivable,
    miss small objects between the sample points. A simple solution to
    this is to expand the beam divergence, but at the expense of the
    maximum operating range.

[^4]: In other words to put 32 digital buffers in series and have a
    clock signal propagate though the buffers as a "wave"