( . 

CORONAGRAPH OBSERVATIONS AND ANALYSES 

OF THE ULTRAVIOLET SOLAR CORONA 

NASA Grant No.: NAG 5-613 

Semiannual Status Report Nos. 10, 11, 12, 13 

For the period 1 April 1987 through 31 March 1989 

Principal Investigator 

Dr. John L. Kohl 

Prepared for 

National Aeronautics and Space Administration 

Wallops Island, VA 23337 

Smithsonian Institution 

Astrophysical Observatory 

Cambridge, MA 02138 

The Smithsonian Astrophysical Observatory 

is a member of the 

Harvard-Smithsonian Center for Astrophysics I I 

The NASA Technical Officer for this grant is Mr. Larry J. Early, Code 840.0, 

Goddard Space Flight Center/Wallops Flight Facility, Wallops Island, VA 23337. 

[NASA-CE-1858 30) CCRCFIASRAifI OBSELVATZLNS N 89 -2 84 76 

Seffiiaucual Status iicport, 1 ;lbr. l~r37 - 31 

Mar, 1989 :SfiIltl,:;Otii.iil tistropiiysicdl (JfiCldS 

Obscrvdtory) 26 CSCL 03~ ~3/92 0224568 

AND ANALYSFS OF 132 IJL-’H.iVLOiET SDI.AEc COP\=’?& 
INTRODUCTION 

The major activities on the Spartan Ultraviolet Coronal Spectrometer project 

during the present reporting period include both scientific and experimental/technical 

efforts. 

In the scientific area, a detailed analysis of the previously reported 

Doppler-dimming of HI Ly-a from our July 1982 rocket fight has determined an outflow 

velocity at 2 solar radii from sun-center (R,) to be between 153 and 251 km/s at 67% 

confidence. That measurement can best be characterized as strong evidence of 

eupersonic outflow within 2 R, in a coronal hole. Development of uv spectroscopic 

diagnostic techniques has continued with the publication of two papers on the 

interpretation of HI Ly-a line profiles, a review paper and several talks. 

The technical activities have been very demanding. Following the preliminary 

integration activity at GSFC in 1986, several improvements were made to the instrument 

that will result in enhanced scientific performance or in regaining a capability that had 

deteriorated during the delay time in the launch date. Activities in the former category 

included testing and characterizing the detector for OVI radiation, characterizing a 

serrated occulter at uv and visible wavelengths, fabricating and testing telescope mirrors 

with improved edges, testing and evaluating a new array detector system, modifying the 

slit mask mechanism and installing a mask in the instrument to block the Ly-a 

resonance line when the electron scattered component is being observed. Each of these 

improvements has been implemented in the instrument. It has been necessary to replace 

several devices which degraded during the delay time. The replacement effort has proven 

to be time consuming. All of the telescope mirrors were replaced, recoated, re-installed 

and aligned within the telescope mechanism. The entire instrument was then realigned. 

The vac-ion pump on the OVI detector became erratic due to wear and was replaced. 

The photocathodes could not be exposed to air during the replacement process. Tests 
Page 2 

were required (in vacuum) before and after the replacement to ensure that the detector 

was not damaged. Several electronic components experienced random failures and had to 

be replaced. These potted components are difficult to replace and the diagnostics to 

identify faulty components are more difficult when potting is present. The flight vacuum 

gauges failed and required testing and maintenance. These are just a few examples of 

the efforts required to maintain an instrument of the Spartan class during the extended 

delay. 

Also during the delay, the instrument experienced problems with the high voltage 

These high voltage/high current 

We spent a considerable effort procuring and 

power supplies used to power the vac-ion pumps. 

supplies proved to have a faulty design, 

testing appropriate power supplies for this purpose. 

In order to ensure that the instrument could be maintained over a prolonged 

period, the documentation, especially that describing the electronics, was upgraded to an 

appropriate level. 

The instrument has now been shipped to GSFC for integration with the White 

Light Coronagraph (provided by HAO) and the Spartan Instrument Carrier and Service 

Module. We expect that it will be returned to SA0 in May 1989 when it will go 

through a full characterization, calibration and stray light evaluation. The 

characterization includes laboratory simulations of the new diagnostic technique for 

electron temperature. Final 

observing programs will then be written and the associated master sequencer list will be 

delivered to GSFC. We expect to deliver the instrument for final integration checks at 

GSFC about six to eight months before launch. Following the first flight, we will carry 

out a full radiometric calibration and characterization to establish the instrument 

characteristics during the flight. 

This activity is expected to take eight to ten months. 
Page 3 

The following scientific papers were presented and/or published during the report 

period: 

1. Esser, R. and Withbroe, G. L., “Effect of a Quiet Background on Line 

Observations from Coronal Holes”, presented at meeting on Activity in Cool 

Star Envelopes, Tromso, Norway, (1987). Published in conference 

proceedings. 

2. Withbroe, G. L., “Physics of the Corona and Inner Solar Wind”, colloquium 

presented at NASA Goddard Space Flight Center. 

3. Kohl, J. L., Weiser, H., and Livi, S., “Spectroscopic Measurements of Solar 

Wind Parameters Near the Sun”, presented at Yosemite conference on 

Outstanding Problems in Solar Plasma Physics: Theory and Instrumentation. 

To be published in conference proceedings (in press). 

4. Withbroe, G. L., “The Temperature Structure, Mass and Energy Flow in the 

Corona and Inner Solar Wind”, Astrophys. J. - 325, 442 (1988). 

5. Esser, R. and Withbroe, G. L., “Line-of-Sight Effects on Spectroscopic 

Measurements in the Inner Solar Wind Region”, J. Geophys. Res. (1988), in 

press. 

6. Gardner, L.D., Kohl, J.L., Weiser., H., Strachan, L., Fisher, R., and Sime, D., 

“Observations of the Extended Solar Corona from a Spartan Carrier,”, Bull. 

Am. Astron. SOC. 21, - 840 (1989). 

7. Strachan, L., Kohl, J.L., Munro, R.H., and Withbroe, G.L., “Doppler Dimming 

Measurement of Solar Outflow,” Bull. Am. Astron. SOC. 21, - 840 (1989). 
Page 4 

UVCS results also stimulated several other research papers and lectures including: 

“Models for the Corona and Inner Solar Wind”, by G. L. Withbroe, presented at the 

meeting of the AAS Solar Physics Division in Hawaii (1987); 

“Acceleration of the Solar Wind as Inferred from Observations”, invited paper by G. L. 

Withbroe, presented at Solar Wind 6 and published in the proceedings; 

“The Solar Wind Mass Flux”, by G. L. Withbroe, Astrophys. J. - 337, L49 (1989); 

“The Solar Wind and Its Coronal Origins”, invited paper by G. L. Withbroe, W. C. 

Feldman, H. Ahluwalia presented at conference on The Solar Interior and 

Atmosphere, submitted for publication (1989). 

SCIENTIFIC RESULTS FROM THE PRESENT REPORTING PERIOD 

The major efforts in this area during the reporting period were: 1) a detailed 

study of the UV and white light measurements from the 1982 rocket flight, 2) a review 

paper by Kohl, Weiser, and Livi, 3) two papers on the interpretation of Lyman alpha line 

profiles, and 4) a paper which used rocket Lyman alpha and other data to construct solar 

wind models. 

In the July 20, 1982 rocket flight of the UVCS, Lyman alpha and white light 

measurements were acquired in a large, polar coronal hole. A detailed analysis and 

interpretation of these data has been carried out by L. Strachan for a major section of 

his Ph.D. dissertation. Measurements of the profiles and intensities of the resonantly 

scattered hydrogen Lyman alpha iadiation (from UVCS) have been analyzed in 

conjunction with electron densities derived from the white light measurements (from the 
Page 5 

HA0 WLC). A model of the terrestrial exosphere was calculated in order to correct 

the intensities and line profiles for the effects of absorption and emission of Lyman alpha 

by the geocorona (Withbroe et al. 1985, Astrophys. J., - 297, 324). The geocoronal model 

calculations were checked using the Lyman alpha measurements at 3.5 R,. In the 

coronal hole the measurements at 3.5 R, appear to be dominated by the geocoronal 

emission. The latter can be distinguished from coronal emission by its narrow profile. 

The intensities were calibrated using the preflight radiometric calibration. [A careful 

analysis of the preflight and postflight calibrations and the measurements acquired during 

the flight showed that the instrument calibration most likely changed during reentry due 

to contamination caused by the melting of the insulation of a WLC cable which rested 

on the inside of the rocket skin. The cable was damaged due to excessive heat being 

absorbed. ] 

The Lyman alpha profiles at 2.0 R, are non-symmetrical. Given the large flow 

velocities expected (from the Doppler-dimming measurements discassed below), a likely 

explanation for the profile shape is that the coronal component is Doppler-shifted with 

respect to the geocoronal emission by the line-of-sight component of the coronal outflow 

velocity. 

The detailed analysis of the Lyman alpha intensities suggest that they are strongly 

Doppler-dimmed at 1.5 and 2.0 R,. That is, the intensities predicted for a static model 

are three to five times larger than observed. A careful examination of the various 

sources of error suggests that the Doppler-dimming at 2.0 R, indicates an outflow 

velocity between 153 and 251 km/s with 67% confidence. This takes the uncertainties 

in the model (e.g. uncertainties in the electron density, electron temperature, and 

geocoronal correction) as well as the measurement uncertainties into account. The 

uncertainties in the rocket measuremmts do not support a determination at a 90% 

confidence level (Le., 1.80). [The uncertainty is expected to be much lower with Spartan 

measurements, because of the larger number of parameters measured, including the 
Page 6 

electron temperature, and much better statistical accuracy of the data.) Details of this 

analysis are given in Strachan’s thesis, which is in preparation. J. Kohl, H. Weiser, and 

S. Livi presented a review paper at the Yosemite conference on Outstanding Problems in 

Solar System Plasma Physics: Theory and Instrumentation. The paper, entitled 

“Spectroscopic Measurements of Solar Wind Parameters Near the Sun”, will be published 

in the conference proceedings. “Instrumentation ... and 

plasma diagnostic techniques ... are being developed to obtain a detailed empirical 

description of solar wind acceleration regions at heights between the coronal base and 

about 10 solar radii from sun center (Ra). The goal of this work is to determine a 

sufficient number of observational parameters to constrain, significantly, theories of solar 

wind acceleration, coronal heating and solar wind composition. Although a substantial 

amount of data on the electron density structure of the corona already exists, there are 

only isolated measurements of other critical plasma parameters, except for observations 

of regions near the base of the corona (r < 1.3 Ra).” 

The abstract is as follows: 

Ultraviolet spectroscopy provides a capability to expand greatly the number of 

plasma parameters that can be specified by means of remote sensing techniques. 

Ultraviolet measurements of spectral line profiles determine the random velocity 

distributions and effective temperatures of protons, minor ions and electrons. Ion 

densities, and chemical abundances are derivable from the collisional component of the 

observed resonant line intensities. Outflow velocities can be determined from Doppler 

shifts and Doppler dimming of spectral lines. R. Esser and G. Withbroe have been 

studying the interpretation of coronal line profiles made in coronal holes which are 

surrounded by denser regions. The results have been reported in two papers: (1) 

“Effect of a Quiet Background on Line Observations from Coronal Holes”, presented at a 

meeting on Activity in Cool Star Envelopes, in Tromso, Norway, and published in the 

conference proceedings, and (2) “Line-of-Sight Effects on Spectroscopic Measurements in 

the Inner Solar Wind Region”, to be published in the Journal of Geophysical Research. 
Page 7 

The abstract of the latter paper states: “The effect of the integration along the line of 

sight on the spectral line profiles of the resonantly scattered Lyman alpha radiation 

emitted by low density coronal holes at heights above 1.5 R, is investigated. It is 

shown how the spectral lines from this region are influenced by the Lyman alpha 

emission from surrounding regions with higher densities. The coronal hole and the 

surrounding areas are described by a two-fluid solar wind model. It is shown that the 

line-of -sight effects can be important for the interpretation of the Lyman alpha spectral 

line measurements in the outer corona and solar wind.* The paper also discusses how 

the shapes of spectral line profiles and tomographic techniques can be used to separate 

emission components from the coronal hole and surrounding regions. These techniques 

are applicable to any optically thin coronal line observed at the limb. 

Measurements of coronal Lyman alpha emission played an important role in a 

major study of the inner solar wind by Withbroe. This paper, “The Temperature 

Structure, Mass, and Energy Flow in the Corona and Inner Solar Wind”, was published 

in the Astrophysical Journal. The abstract reads as follows: “Data from remote-sensing 

and ‘in situ’ instruments are used as empirical constraints on a radiative energy balance 

model in order to determine the radial variations of coronal temperatures, densities and 

outflow speeds in several types of coronal holes and in a quiet, unstructured region of the 

corona. The one fluid solar wind model used in the investigation includes the effects of 

radiative and inward conductive losses in the low corona and the chromospheric-coronal 

transition region. It satisfactorily accounts for a variety of measurements of coronal 

and solar wind parameters for an equatorial coronal hole, polar coronal holes at solar 

minimum and solar maximum, and an unstructured quiet region of the corona. The 

results indicate that the total nonradiative energy input in magnetically open coronal 

regions is 5 f 1 x lo5 ergs cm-2 s-’. Most of the energy heating the coronal plasma 

appears to be dissipated within 2 R, of the solar surface with a characteristic 

dissipation length which varies approximately as Po”, where Po is the pressure at the base 
Page 8 

of the corona and -2 < a < -1. The results of the study also provide insights for future 

development of a comprehensive physical model for open magnetic regions which can 

account for the low densities in coronal holes and the generation of low- and high-speed 

solar wind.” 

SUMMARY OF EXPERIMENTAL/TECHNICAL ACTIVITIES 

The major technical activities during the report period consisted of implementing 

the modifications to the instrument resulting from the 1986 preliminary integration and 

test activity at NASA/GSFC, testing and evaluating the new discrete anode array 

detector and integrating it into the UVCS payload, testing the OVI detector and 

integrating it into the payload, testing the serrated edge occulter system, procuring and 

testing replacement high voltage power supplies for the detector vac-ion pumps, running 

limited thermal tests on the complete system, undertaking final preparations of the 

instrument, shipping the UVCS to NASA/GSFC, integrating the UVCS with the WLC 

experiment at NASA/GSFC, co-aligning and co-registering the UVCS with the WLC, 

integrating the experiments with the Spartan 201 spacecraft, running functional tests on 

the Spartan 201, and carrying out environmental testing of the Spartan 201 payload 

including vibration testing, magnetic calibration, EM1 testing, acoustic testing, mass 

property measurements, and thermal-vacuum testing. 

The new discrete anode array detector for HI Ly-a, which replaced the earlier unit 

that had suffered unacceptable gain losses, was delivered to SA0 by the Ball Aerospace 

Systems Division in November 1986. Subsequent to its arrival at SAO, a series of 

subsystem tests were performed on the array. These included measuring the pulse height 

distribution, dark count rate, resolut‘on, cross-talk, count rate linearity, count rate 

statistics, system counting efficiency, and cathode uniformity. The optimum high voltage 

settings for the MCP and field electrodes were determined and set. The noise 
Page 9 

characteristics of representative channels were determined, and the lowest threshold for 

reliable operation was established and set. Subsequent to the above, the detector was 

installed in the spectrometer, optically aligned, and several tests were repeated. In 

evaluating the cross-talk among the 90 anodes in the detector, the cross-talk between 

the fine anodes, between the coarse anodes, and between the fine and coarse anodes was 

examined. These cross-talk tests resulted in several modifications to the instrument to 

enhance performance: the entrance slit for the narrow HI Lyman-ar line was reduced in 

height, a mask, which lowered the cross-talk by almost an order of magnitude, was 

installed immediately in front of the detector to block light falling on the central two 

coarse pixels and the disk mask was modified to open-up the 12 p pinhole to 

approximately 1 mm which will now allow the instrument to make an independent T, 

observation. 

The OVI detector high voltage cable was potted at the detector, and the vac-ion 

pump associated with the detector was replaced with a new flight unit. The cross-talk 

induced by the OVI detector into array detector electronics, a problem which had been 

discovered during the last reporting period, was evaluated, and the preliminary amplifier 

discriminator electronics were modified to eliminate the problem. The optimum 

threshold settings for the OVI detector were determined, and the detector subsystem 

tests and radiometric calibration were repeated to verify performance. Following these 

activities, the detector was installed in the spectrometer and optically aligned. 

The serrated edge occulter system was designed, the serrated units procured, and 

laboratory testing carried out to compare the new serrated system with the straight edge 

system used on the previous rocket flights. Test results indicated approximately an 

order of magnitude improvement in the stray light suppression at visible wavelengths 

(5000-6000 A) and approximately a fac’,or of four improvement at A1235 A. In light of 

these results, the serrated edge system was incorporated into the Spartan instrument. 

The search continued for an alternative high voltage power supply to power our 
Page 10 

Vac-Ion pumps during and immediately preceding flight. A vendor with personnel 

experienced in manufacturing similar power supplies for use in aerospace applications 

was selected, and an order for three units (2 flight plus 1 spare) was placed with them 

in November 1987 for an early 1988 delivery. Unfortunately subsequent to receiving the 

order, this particular company experienced serious financial difficulties and was unable to 

deliver the supplies despite SAO’s efforts to expedite the order. Another search for an 

acceptable supplier was undertaken, and an order was placed for three power supplies in 

early December 1988. These units were delivered to SA0 in late January 1989, tested, 

and integrated with the Spartan payload in February 1989. After a week or so of 

operation in the UVCS, the units began failing. GSFC undertook an analysis of the 

failures and traced the faults to cracks, most likely caused during assembly, in the 

insulation on the supplies’ high voltage output connectors. The problem is being 

corrected. 

During mid-1988, limited thermal testing was undertaken on the complete 

instrument and two potentially serious problems were uncovered. The first involved the 

telescope mirror assembly. It was determined that relatively small excursions in 

temperature caused the two telescope mirrors to tilt with respect to each other in such a 

way that the instantaneous field-of-view of the resonantly scattered Ly-a! profile would no 

longer coincide with the field-of-view the OVI intensities. The cause of the problem 

was located, the mirror assembly was modified, and the solution was verified via 

repeated testing. 

The second temperature related problem was associated with the flight electronics. 

The failure manifested itself in a lack of response to inputs from the flight system GSE, 

and the GSE display would fail to show updated housekeeping data. The interval 

between failures was random, although temperature related. At ambient temperatures 

below 27°C the system appeared reliable while above this temperature the system would 

fail repeatedly. The primary cause of the problem was traced to a defective filter 
Page 11 

capacitor in the 5 volt power supply for the memory board. In the course of tracking 

down the bad capacitor, two minor logic problems on the memory board and controller 

board were found and corrected. 

Several changes were made to the flight software. All inadequacies noted during 

the preliminary integration have now been corrected. Software to read the temperature 

sensors and include them in the PCM stream was developed, tested, and verified. 

Overall software verification continued, and verification aids were improved. Software to 

simulate some abnormal operating conditions was developed in order to test the system’s 

ability to respond to these conditions. A hardware-software watchdog timer was 

implemented which resets the electronics if an abnormal lack of activity is detected. 

Some software simplifications were made. 

In the electronics area, a major effort went into updating the electronics 

documentation. This included generating a complete set of cable drawings, and reviewing 

and updating all electrical schematics. Payload hazard reports for the Phase 2 Flight 

Safety Package were completed and returned to GSFC. The analog housekeeping and 

temperature sub-multiplexer system, which are located on the Analog Housekeeping 

board, were calibrated. Spare disk drives for the GSE system were ordered and checked 

out. A flight spare for the Memory/ACS Interface board was fabricated and tested. 

The UART board, which is used primarily during ground operations, was loaded with 

high-reliability components, tested, and installed in the flight system so as to increase the 

overall system reliability. The calibrated sun sensor (LISS) was received from 

NASA/GSFC, installed on the UVCS, and the associated UVCS pointing alarm circuitry 

was calibrated and tested. The passive PCM simulator GSE interface cabling was 

replaced with the TDP interface system, and the UVCS GSE was modified accordingly. 

The cold cathode vacuum gauge was completely refurbished, tested, calibrated, 

and installed in the instrument to provide vacuum readings when the system is 

evacuated. 
Page 12 

Thermal vacuum tests were run on the disk mask mechanism to verify that this 

unit would operate in vacuum for longer periods than originally planned. There appears 

to be no problem, and this system will be operated for approximately 40 minute 

intervals twice during the mission when making the T, observation. 

The discovery of deterioration of the mirror coatings forced the procurement of 

new telescope mirrors. Prior to initiating fabrication, several methods of minimizing 

light scattering off the critical edge of the mirror were evaluated, and the optimum 

approach was incorporated into the new mirrors. 

At that time, it was determined that it would be valuable to the program to have 

a spare mirror arm assembly complete with a full complement of optics installed but 

uncoated. This would allow us to coat the optics very close to the time of launch with 

less of an adverse impact on the UVCS integration schedule, and thus allow for a quicker 

turn around in the future should the mirror coatings have to be replaced again. The 

spare components were ordered and have been fabricated and fit-checked. The remaining 

task involves potting the uncoated optics into their mirror cells. A new mirror potting 

fixture to minimize contamination of the optics by the potting process was also designed, 

fabricated, and tested. 

Several areas related to the laboratory facilities were also improved during this 

period. A small vacuum chamber (0.75 meter diameter by 1.2 meters long) was 

transferred to the UVCS program and refurbished to provide another vacuum test 

chamber to allow tests on various components to proceed in parallel. The diffusion 

pump originally used with this chamber was replaced with a new 400 liter/sec horizontal 

turbomolecular pump provided at no cost to the program. Other horizontal 

turbomolecular pumps used on the large vacuum calibration system were refurbished. A 

new X-Y-Z-0 vacuum compatible, CompiLter driven, motorized positioning system was 

provided at no cost to the program and has been used extensively in testing and 

calibrating various elements of the system. Several new TC gauges and controllers as 
Page 13 

well as an ionization gauge controller and associated gauges were also provided at no cost 

to the program and have been used effectively on both of the vacuum calibration and 

test facilities. Both vacuum chambers were thoroughly cleaned, and calibrated 

contamination monitor mirrors were procured to allow for controlled contamination 

monitoring of both chambers. A filter system for the purge line was purchased and 

installed on the large vacuum chamber in order to minimize particulate contamination of 

the system during vacuum venting operations. The clean showers associated with the 

large vacuum chamber were refurbished and relocated to maximize cleanliness in the 

vicinity of access openings. The monochrometer associated with the large vacuum 

chamber was also refurbished and fitted with a new VUV hollow cathode light source 

including a differential pumping unit, which was provided at no cost to the program. 

An automated safety vent-up system for the small vacuum chamber was designed, 

fabricated, installed, and tested. A similar system will be provided in the future for 

the large vacuum system. A new remotely driven collimator mirror drive assembly was 

designed and fabricated to replace the existing drive, which has had a history of failures. 

In addition, a light trap, to minimize stray light from the monochrometer, was designed, 

fabricated, and installed behind the new collimator assembly. 

Prior to shipment to NASA/GSFC, all components of the UVCS instrument that 

had been removed since the return of the system to SA0 were replaced and aligned as 

required. This involved a complete realignment of the optical system including all 

mirrors, gratings, internal and external occulters, sunlight traps, LISS assembly, and 

alignment flats. 

The system was prepared for shipment to NASA/GSFC, and arrived at GSFC 

on 31 October 1988. Subsequent to arrival, the system was unpacked and functionally 

tested to assure that no damage occurred in transit. The UVCS was then coaligned 

with the WLC instrument, and a coregistration was performed. The interface between 

the UVCS electronics and the Spartan 201 ACS and PFCS systems was verified, and the 
Page 14 

electronics were installed in the Spartan Service Module (SM). The combined UVCS and 

WLC experiments were mounted into the Spartan Instrument Carrier (IC), and the IC 

was mated with the SM. A vacuum test on the fully integrated IC was performed, and 

SA0 verified detector performance at VUV wavelength using the new calibration 

bulkhead, which was designed and fabricated by SA0 and included a new portable 

deuterium light source provided at no cost to the program. 

Following this successful calibration test, the Spartan was transported to the test 

facilities and exposed to flight level vibration. Subsequent coalignment and 

coregistration checks of the instruments showed that movement had occurred during the 

shake, and modifications were made to the NASA provided alignment fittings on the 

IC-instrument kinematic mount. After a second vibration test, coalignment checks 

showed no external mechanical movement, but coregistration checks again showed that 

movement appeared to have taken place between the two instruments. At this time it is 

thought that this may be due to an internal movement of the WLC CCD detector which 

is coupled to the fin on the IC. 

In early March the full-up Spartan 201 system underwent a magnetic calibration 

and then proceeded to EM1 testing. Acoustic testing and mass properties were carried 

out near the end of March 1989. Mission profile tests at ambient temperature and 

pressure are planned for early April, and thermal-vacuum tests on the full-up system for 

late April. It is expected that the UVCS will be returned to SA0 in early May. 

INTEGRATION AND TEST ACTIVITIES 

Reassembly of the instrument was completed at SAO. Included was installation 

of the OVI detector, the telescope mirrors and drive, the sunlight trap, and the detector 

amplifier box, development and implementation of a scheme for heat sinking the disk 

mask solenoid, the setting of the Ly-cr grating to first order, and the setting of the OVI 
Page 15 

grating to zeroth order. Functional tests of the disk mask and telescope mirror 

mechanisms were carried out. Electrical tests of the detectors and their acquisition 

electronics were done. The detectors were also checked to make sure they could respond 

to ultraviolet light. The Flight System Controller was checked for correct performance. 

The ground support equipment (GSE) was also checked. After verification of correct 

performance, the instrument and supporting equipment were packed for shipment to 

GSFC. 

Upon arrival at GSFC, functional tests were again carried out prior to co-assembly 

of HAWS white light coronagraph (WLC) with our ultraviolet coronal spectrometer 

(UVCS). No malfunctions were found. The two instruments were put into a measured 

alignment condition and then incorporated into the Spartan 201 spacecraft. The 

assembled spacecraft was then sent to Goddard’s vibration facility where it was vibrated 

at protoflight levels. Although all systems internal to the UVCS successfully passed the 

vibration test, the relative alignment of the UVCS and WLC changed by approximately 

one arc-minute, an amount considered unacceptable. Engineering changes in the 

mounting system were incorporated by GSFC. The instruments were then re-mated, 

aligned to an accuracy sufficient for launch, and reassembled into the Spartan Instrument 

Carrier. The Instrument Carrier was returned to the vibration test facility where it 

underwent tests to flight levels. The second test was successful, relative alignments 

having held to within a tolerance of 10 arc-seconds. Again no malfunctions of systems 

internal to the UVCS were noted. There continue to be problems with the 

co-registration of the two instruments at about the one arc minute level. 

Two 4-hour tests of the full Spartan system weie carried out. No failures of the 

UVCS systems were noted during the tasts. 

New high voltage power supplie. for operating the vac-ion pumps on the detector 

systems have been acquired and installed. Although problems have been encountered 

with the new supplies, we believe we understand the difficulties and find the supplies 
Page 16 

to be completely satisfactory, once the difficulties are corrected. 

The Spartan 201 spacecraft was entirely assembled. It underwent magnetic 

calibration tests at GSFC’s magnetic test facility. EM1 testing was also completed, 

Acoustics testing and weight and center of gravity measurements were done during the 

last week of March. Mission profile and thermal-vacuum tests are planned for the 

month of April. 

ELECTRONICS ACTIVITIES 

During the period of time from April 1987 to March 1989, progress on the 

UVCS electronics has been made in several areas: the flight system, the GSE, and in 

documentation. 

Flight System 

Several things were done to the preamplifier-discriminator boards. Ten channels 

of coarse pixels which had previously not been implemented were configured using new 

Amptek A-111)s. Two 

coarse channels which had been disabled, C19 and C22, were re-enabled. It was found 

that the OVI detector was causing some cross-talk with the channels adjacent to it on the 

PAD circuit boards due to the large size of its output signal. It was thus necessary to 

design and install a network to reduce the signal before it entered the board. 

Thresholds of these were set to match the other channels. 

In the analog housekeeping system, some channels were found to be susceptible to 

noise. Thermal housekeeping channels were modified 

to give consistent scale factors. Finally the analog housekeeping board was recalibrated. 

This data 

allowed us to set upper and lower limits for the error signals that we receive from the 

Filtering was added as required. 

Calibration data for the LISS on the UVCS was obtained from GSFC. 
Page 17 

LISS. In the interest of reliability, we decided to replace the limit-setting trimpots 

with fixed resistors. Since we ignore roll errors, we also decided that the ACS roll signal 

alarm circuit should be disconnected 

Two trouble areas consumed a large amount of time. The flight system was 

found to be subject to a sporadic loss of synchronization. This manifested itself so 

infrequently that troubleshooting was difficult. The problem was traced to a power 

supply filter capacitor on the memory board. This capacitor was sent out for analysis 

and was determined to have been of faulty manufacture. Since replacing it we have had 

no more incidents. The other problem area involved the high voltage power supplies that 

power the ion pumps on our detectors. We experienced some difficulty in finding and 

obtaining suitable power supplies. We currently have three units that have gone through 

portions of the integration activity at NASA/GSFC. Unfortunately all three of them 

have experienced failures during integration. The cause is a defect in the high voltage 

connectors on the supplies’ outputs. The supplies otherwise are rugged and completely 

suited to our application. We are at present negotiating with the manufacturer for their 

replacement. 

Most of the work on the GSE was done to prepare for our integration at GSFC. 

Because of the new clean room that was built for our integration, we were forced to 

make new interface cables between our GSE and the flight electronics. The new 

arrangement has the flight system in the clean room and the support electronics in an 

adjacent control room. The cables must now go through the wall via bulkhead 

feedthroughs, and are about fifty feet in total length. To accommodate this increased 

length, the GSE electronics were r&iodified to add line drivers. 

Some redesign was done on the interface between the Goddard TDP system and 
Page 18 

our GSE. This interface lets us read the PCM data stream when the UVCS is integrated 

in the Spartan service module. In the past, hooking up the TDP interface was a 

cumbersome procedure. The modification makes it much simpler and more reliable. 

Documentation 

A significant amount of effort went into improving the documentation for the 

flight electronics system and GSE. All electrical drawings were reviewed and updated. 

Areas that had been changed via handwritten notes were clarified. The form in which 

we keep cable and interconnection information was changed. Originally they were kept 

in wire run lists which were organized in notebooks. The method proved to be difficult 

to use and to maintain. The system was changed so that all wire lists are now entered 

into electrical drawings and are under the same configuration control as all other UVCS 

drawings. The reorganization has been completed for the flight system and is underway 

for the GSE.