# Presentation: 947546

## GALILEO PROBE THERMAL CONTROLDr. Thomas Rust, III (Tom)Principal Engineer, ThermalBoeing Satellite Development Center (BSDC) El Segundo, CA USAJune 29, 2006

## Boeing Satellite Development Center (BSDC) formerly known as Hughes Space & Communications Company provided the Galileo Probe system & Orbiter mounted relay radio hardware (RRH)
Galileo VEEGA (Venus-Earth-Earth Gravitational Assist) mission began 18 October 1989 launched on Space Shuttle Atlantis (STS-34)
first in-flight Probe check-out 8 days after launch, all systems nominal
second in-flight check-out December 1990, 4 days prior to Earth fly-by
Next major event April 1991 when Orbiter High Gain Antenna (HGA) failed to deploy (HGA was not the responsibility of Boeing)
maneuvers to thermally cycle the HGA mechanism were conducted from late 1991 through early 1993, used CTE mismatch to free mechanical hang-up
BSDC responsibility was to make sure Probe & RRH not damaged by maneuvers
resulted in cycling & elevated temperatures of BSDC hardware as compared to initial design for stable cold soak
Final Probe check-out March 1995 followed by Probe release July 1995
Probe descent & encounter were successfully executed 7 December 1995
BSDC support extended through October 1996 due to loss of HGA
Low Gain Antenna (LGA) 10,000 times slower data rate than HGA
longer playback time, but still 100% successful Probe mission with no HGA

- Galileo VEEGA (Venus-Earth-Earth Gravitational Assist) mission began 18 October 1989 launched on Space Shuttle Atlantis (STS-34)
- first in-flight Probe check-out 8 days after launch, all systems nominal
- second in-flight check-out December 1990, 4 days prior to Earth fly-by
- Next major event April 1991 when Orbiter High Gain Antenna (HGA) failed to deploy (HGA was not the responsibility of Boeing)
- maneuvers to thermally cycle the HGA mechanism were conducted from late 1991 through early 1993, used CTE mismatch to free mechanical hang-up
- BSDC responsibility was to make sure Probe & RRH not damaged by maneuvers
- resulted in cycling & elevated temperatures of BSDC hardware as compared to initial design for stable cold soak
- Final Probe check-out March 1995 followed by Probe release July 1995
- Probe descent & encounter were successfully executed 7 December 1995
- BSDC support extended through October 1996 due to loss of HGA
- Low Gain Antenna (LGA) 10,000 times slower data rate than HGA
- longer playback time, but still 100% successful Probe mission with no HGA

## Three main phases of Galileo Probe mission
Cruise is time from launch until Probe is released from Orbiter
cruise duration was approximately 6 years for Galileo Probe
gravitational assist by going around Venus & back around Earth (VEEGA)
spacecraft gathered data on Gaspra & Ida asteroids & Shoemaker-Levy 9 comet
maneuvers intended for HGA mechanism cycling occurred during Cruise
Coast phase includes time from release from the Orbiter until encountering  Jovian atmosphere
temperatures verified to be within +3oC of predicts just prior to release
Probe timer activated 6 hours prior to entry, almost dead center of window
coast duration approximately 150 days, no telemetry during coast
data 3 hrs. & 20 min. prior to entry show Probe temperatures -3oC to 2oC
this is as close as possible to the -1oC predicted prior to launch
no additional thermal discussion of Galileo Probe coast phase, uneventful
Descent phase is from the time the Probe entered the Jovian atmosphere until it stopped providing data back to the Orbiter (end of its mission)
two notable conditions seen during Descent, one thermally related
Probe mission 100% successful with HGA & two minor Descent anomalies
shows adequate implementation of redundancy & thermal margin

- _Cruise_ is time from launch until Probe is released from Orbiter
- cruise duration was approximately 6 years for Galileo Probe
- gravitational assist by going around Venus & back around Earth (VEEGA)
- spacecraft gathered data on Gaspra & Ida asteroids & Shoemaker-Levy 9 comet
- maneuvers intended for HGA mechanism cycling occurred during Cruise
- _Coast_ phase includes time from release from the Orbiter until encountering  Jovian atmosphere
- temperatures verified to be within _+_3oC of predicts just prior to release
- Probe timer activated 6 hours prior to entry, almost dead center of window
- coast duration approximately 150 days, no telemetry during coast
- data 3 hrs. & 20 min. prior to entry show Probe temperatures -3oC to 2oC
- this is as close as possible to the -1oC predicted prior to launch
- no additional thermal discussion of Galileo Probe coast phase, uneventful
- _Descent_ phase is from the time the Probe entered the Jovian atmosphere until it stopped providing data back to the Orbiter (end of its mission)
- two notable conditions seen during Descent, one thermally related
- Probe mission 100% successful with HGA & two minor Descent anomalies
- shows adequate implementation of redundancy & thermal margin

## Layout of Probe & RRA on Spacecraft during Cruise

- Probe

- RAA

- SUN

## RRH hardware: receiver, oscillator (USO), RR Antenna (RRA)
RRH units in well controlled thermal environment within Orbiter
receiver & USO standard electronic unit allowable temperature ranges
non-operating survival temperature range -20oC to +50oC
operating temperature range -10oC to +50oC
temperature telemetry within allowable range during all mission phases
larger variations than seen on Probe due to changes in Orbiter configuration
all temperatures between -2oC to 23oC, spikes up to 37oC when operated
RRH unit temperatures during Probe descent 35oC – 37oC
did not change at all during 1 hour descent, met stability requirement
no issues with RRH units thermal control during any mission phase
RRA external to orbiter, facing away from sun so extremely cold
samples tested in liquid Helium for exposure to -220oC, well below LN2
special investigation into solar loading being concentrated onto antenna feed cup during HGA maneuvers, not designed for exposure to sun & cycling
photometric mapping allowed ambient P/T verification of focused energy
collimated light source & photometer determine if multiple sun loading occurs
performed test on old Qualification RRA shipped from JPL to BSDC
RR antenna performed as predicted during all mission phases

- RRH units in well controlled thermal environment within Orbiter
- receiver & USO standard electronic unit allowable temperature ranges
- non-operating survival temperature range -20oC to +50oC
- operating temperature range -10oC to +50oC
- temperature telemetry within allowable range during all mission phases
- larger variations than seen on Probe due to changes in Orbiter configuration
- all temperatures between -2oC to 23oC, spikes up to 37oC when operated
- RRH unit temperatures during Probe descent 35oC – 37oC
- did not change at all during 1 hour descent, met stability requirement
- no issues with RRH units thermal control during any mission phase
- RRA external to orbiter, facing away from sun so extremely cold
- samples tested in liquid Helium for exposure to -220oC, well below LN2
- special investigation into solar loading being concentrated onto antenna feed cup during HGA maneuvers, not designed for exposure to sun & cycling
- photometric mapping allowed ambient P/T verification of focused energy
- collimated light source & photometer determine if multiple sun loading occurs
- performed test on old Qualification RRA shipped from JPL to BSDC
- RR antenna performed as predicted during all mission phases

## Cruise Probe thermal performance as predicted prior to launch with additional analysis of HGA maneuvers
Goal to maintain Probe temperatures at 0oC & stable
optimal storage temperature for Li/SO2 main Probe batteries
safe temperature for “off” electronics units & no thermal cycling
Probe thermal control consisted of MLI blankets (>50 layers), low  gold tape external surface, 36 radioisotope heater units (RHUs)
Telemetry showed all temperatures between -3oC & +3oC
some telemetry reached -4oC just prior to release
well within Probe main battery Acceptance range of -15oC to +20oC
other hardware had wider allowable temperature ranges
Only exceptions were during HGA maneuvers
turn HGA away from sun, resulted in Probe & RRA turning into sun
attempt to free mechanism by cooling it, resulted in Probe & RRA warming
approval from battery experts as well as extensive review of other hardware designs to go to 40oC for 13 planned HGA excursions
two flight rules limiting maneuver angles & distance from sun implemented as result of HGA maneuver thermal study
any maneuver over 165o limited to outside 1.45 Au, Probe/Orbiter Separation device < 71oC
any maneuver over 90o limited to outside 1.30 Au, RRA dipole < 100oC
only 7 excursions actually executed, telemetry showed 33oC reached within Probe
did not free stuck HGA, also did not harm Probe/RRH hardware

- Goal to maintain Probe temperatures at 0oC & stable
**optimal storage temperature for Li/SO****2**** main Probe batteries**
**safe temperature for “off” electronics units & no thermal cycling**
**Probe thermal control consisted of MLI blankets (>50 layers), low ******** gold tape external surface, 36 radioisotope heater units (RHUs)**
- Telemetry showed all temperatures between -3oC & +3oC
**some telemetry reached -4****o****C just prior to release**
**well within Probe main battery Acceptance range of -15****o****C to +20****o****C**
- other hardware had wider allowable temperature ranges
- Only exceptions were during HGA maneuvers
**turn HGA away from sun, resulted in Probe & RRA turning into sun**
- attempt to free mechanism by cooling it, resulted in Probe & RRA warming
**approval from battery experts as well as extensive review of other hardware designs to go to 40****o****C for 13 planned HGA excursions**
**two flight rules limiting maneuver angles & distance from sun implemented as result of HGA maneuver thermal study**
- any maneuver over 165o limited to outside 1.45 Au, Probe/Orbiter Separation device _<_ 71oC
- any maneuver over 90o limited to outside 1.30 Au, RRA dipole _<_ 100oC
**only 7 excursions actually executed, telemetry showed 33****o****C reached within Probe**
**did not free stuck HGA, also did not harm Probe/RRH hardware**

## Probe temperature telemetry during cruise

## Probe Descent - two noted conditions
First parachute deployment occurred 53 seconds later than planned
equivalent to 5 minutes of parachute descent (of about 60 minutes total)
cause blamed on crossed harness wires between G-switches & DCP
Probe mission started deeper in atmosphere than expected
higher dynamic load due to denser atmosphere when chute deploys
all dynamic loads determined to be less than qualification levels
no significant impact to data return or mission science
no significant impact to Probe temperatures or thermal control
theory higher dynamic loads cause MLI to separate resulting in poor performance
tested well beyond 228 g entry force, not believed to cause of thermal extremes 
Second noted condition was that Probe temperature extremes were cooler initially & then hotter during later stages of Descent
pre-entry temperature matched thermal predict (end of Coast phase)
verified by telemetry both at 3 hours & at 20 minutes prior to entry
thermal control (gold tape) survived maneuvers & performed as expected
atmospheric composition very close to predicts, not the cause
indicates greater heat transfer to environment than expected during descent

- First parachute deployment occurred 53 seconds later than planned
- equivalent to 5 minutes of parachute descent (of about 60 minutes total)
- cause blamed on crossed harness wires between G-switches & DCP
- Probe mission started deeper in atmosphere than expected
- higher dynamic load due to denser atmosphere when chute deploys
- all dynamic loads determined to be less than qualification levels
- no significant impact to data return or mission science
- no significant impact to Probe temperatures or thermal control
- theory higher dynamic loads cause MLI to separate resulting in poor performance
- tested well beyond 228 g entry force, not believed to cause of thermal extremes
- Second noted condition was that Probe temperature extremes were cooler initially & then hotter during later stages of Descent
- pre-entry temperature matched thermal predict (end of Coast phase)
- verified by telemetry both at 3 hours & at 20 minutes prior to entry
- thermal control (gold tape) survived maneuvers & performed as expected
- atmospheric composition very close to predicts, not the cause
- indicates greater heat transfer to environment than expected during descent

## Layout of Probe equipment

## Flight Atmosphere & Aerofairing Temperatures

## Probe Descent met all requirements, successful mission
Contract requirement for one string function down to 10 bar pressure or to reach 0.1 bar plus 48 minutes (turned out to be 13 bars)
Probe clearly met both contractual requirements, 100% successful mission
all science instruments collected valid data to 10 bars, Entry (E)+35 minutes
most science instruments gathered data well beyond that
all instruments maintained within Acceptance range down to E+48 minutes
Pre-launch time requirement interpreted to be E+51.3 minutes
noted pre-launch goal to be E+60 minutes, not a requirement
post-launch goal was changed to E+75 minutes, not a requirement
Transmitter (TX) reached its 60oC qualification limit at E+38 minutes
kept functioning up to 115oC when both strings shut down at E+59 minutes
All hardware continued to function well beyond its Qual temperature
should have gathered calibration data beyond Qual range
used EM units at JPL to gather calibration data after descent
Final contract close-out conclusion - “All Probe subsystems met or exceeded the mission duration requirements”

- Contract requirement for one string function down to 10 bar pressure or to reach 0.1 bar plus 48 minutes (turned out to be 13 bars)
- Probe clearly met both contractual requirements, 100% successful mission
- all science instruments collected valid data to 10 bars, Entry (E)+35 minutes
- most science instruments gathered data well beyond that
- all instruments maintained within Acceptance range down to E+48 minutes
- Pre-launch time requirement interpreted to be E+51.3 minutes
- noted pre-launch goal to be E+60 minutes, not a requirement
- post-launch goal was changed to E+75 minutes, not a requirement
- Transmitter (TX) reached its 60oC qualification limit at E+38 minutes
- kept functioning up to 115oC when both strings shut down at E+59 minutes
- All hardware continued to function well beyond its Qual temperature
- should have gathered calibration data beyond Qual range
- used EM units at JPL to gather calibration data after descent
- Final contract close-out conclusion - “_**All Probe subsystems met or exceeded the mission duration requirements**_”

## Descent temperature data
Science bay & aft compartment (communication bay) temperatures noticeably more extreme than predicted
slightly colder during initial entry & hotter at end of mission
Helium Abundance Detector (HAD) right on predicts
Be chassis, foam & MLI enclosure, isolated inlet-unit & unit-shelf
Neutral Mass Spectrometer (NMS) also matched predicts
large unit individually isolated from Probe environment
Forward bay temperatures much closer to predicts
main batteries & DCP unit, large massive units
Sample of extreme temperatures
cold generally at E+1.1 minutes, hot always at E+59 minutes
Aerofairing	-116oC to +145oC
Transmitter	-18oC to +115oC
Main shelf	-30oC to +106oC
DCP	-11oC to +57oC
Main batteries	-4oC to +49oC

- Science bay & aft compartment (communication bay) temperatures noticeably more extreme than predicted
- slightly colder during initial entry & hotter at end of mission
- Helium Abundance Detector (HAD) right on predicts
- Be chassis, foam & MLI enclosure, isolated inlet-unit & unit-shelf
- Neutral Mass Spectrometer (NMS) also matched predicts
- large unit individually isolated from Probe environment
- Forward bay temperatures much closer to predicts
- main batteries & DCP unit, large massive units
- Sample of extreme temperatures
- cold generally at E+1.1 minutes, hot always at E+59 minutes
- Aerofairing	-116oC to +145oC
- Transmitter	-18oC to +115oC
- Main shelf	-30oC to +106oC
- DCP	-11oC to +57oC
- Main batteries	-4oC to +49oC

## Descent Pressure/Temperature Test (DPT)
DPT ground test data used in place of analytical models
Pre-launch analytical model not simulating developmental test results
analytical models abandoned, used DPT empirical data only
Final DPT comprised of flight hardware except science instruments Engineering Models & no live pyro/separation devices
goal to simulate thermal conditions down to E+48 minutes
chamber unable to quench, required to cool > 100oC in 64 seconds
initial cool down based on extracting equivalent amount of energy
Significant differences between DPT & flight not accounted for until post-entry correlation
DPT performed in 1-g vs. 2.6g in flight, not feasible to simulate higher g
natural convection proportional to g0.3 & buoyancy proportional to g0.5 
DPT 100% He vs. 10% He + 90% H2 in flight, safety issue in test
different properties of H2 enhances buoyancy & convection, viscosity 2x higher
DPT stagnant vs. full aerodynamically driven motion in flight
dynamic motion in flight greatly enhances convection & mass movement
flight spinning at 10 RPM plus 250 disturbances of +0.6m/s2 every 96 seconds

- DPT ground test data used in place of analytical models
- Pre-launch analytical model not simulating developmental test results
- analytical models abandoned, used DPT empirical data only
- Final DPT comprised of flight hardware except science instruments Engineering Models & no live pyro/separation devices
- goal to simulate thermal conditions down to E+48 minutes
- chamber unable to quench, required to cool > 100oC in 64 seconds
- initial cool down based on extracting equivalent amount of energy
- Significant differences between DPT & flight not accounted for until post-entry correlation
- DPT performed in 1-g vs. 2.6g in flight, not feasible to simulate higher g
- natural convection proportional to g0.3 & buoyancy proportional to g0.5
- DPT 100% He vs. 10% He + 90% H2 in flight, safety issue in test
- different properties of H2 enhances buoyancy & convection, viscosity 2x higher
- DPT stagnant vs. full aerodynamically driven motion in flight
- dynamic motion in flight greatly enhances convection & mass movement
- flight spinning at 10 RPM plus 250 disturbances of _+_0.6m/s2 every 96 seconds

## Transmitter Temperatures, Flight & DPT

## DCP Temperatures, Flight & DPT

## Main Battery Temperatures, Flight & DPT

## Correlation of Flight to DPT data
Created new Probe thermal model with advanced modeling techniques
significant improvements in analysis techniques between 1983 & 1997
1997 model tools included MSC/Patran, TRASYS, & HSCinda
more advanced tools available today (Sinda/Fluint for thermal-fluid coupling)
Model constructed to easily changed 4 critical thermal parameters
convection heat transfer coefficient
mass entry & flow rate
Probe spin rate
gas buoyancy contribution
Initially calculated flight parameters close to matching flight data
increased buoyancy term 10x to better match flight data, no other changes
Applied parameters to DPT after correcting for known differences
decreased convection term by 0.76 & buoyancy term by 0.58 to account for gravity & gas property differences
initially not well matched to DPT data, temperatures too extreme
needed to also drop convection coefficient by 10x to better match DPT data
large mass flow decrease would not match data, concluded no flight MLI failure
Why such a large increase in convection between DPT & flight?
flight spinning at 10 RPM plus 250 disturbances of +0.6m/s2 every 96 seconds
increased buffeting, turbulence, & small increased flow accounts for differences

- Created new Probe thermal model with advanced modeling techniques
- significant improvements in analysis techniques between 1983 & 1997
- 1997 model tools included MSC/Patran, TRASYS, & HSCinda
- more advanced tools available today (Sinda/Fluint for thermal-fluid coupling)
- Model constructed to easily changed 4 critical thermal parameters
- convection heat transfer coefficient
- mass entry & flow rate
- Probe spin rate
- gas buoyancy contribution
- Initially calculated flight parameters close to matching flight data
- increased buoyancy term 10x to better match flight data, no other changes
- Applied parameters to DPT after correcting for known differences
- decreased convection term by 0.76 & buoyancy term by 0.58 to account for gravity & gas property differences
- initially not well matched to DPT data, temperatures too extreme
- needed to also drop convection coefficient by 10x to better match DPT data
- large mass flow decrease would not match data, concluded no flight MLI failure
- Why such a large increase in convection between DPT & flight?
- flight spinning at 10 RPM plus 250 disturbances of _+_0.6m/s2 every 96 seconds
- increased buffeting, turbulence, & small increased flow accounts for differences

## Lessons learned & recommendations for future
Improve analytical modeling capability, don’t just ignore analysis
pre-launch temperatures based strictly on DPT data, no test is ever 100% flight-like
always need combination of both test & analysis
Probe Descent analyses must include coupled thermal & aerodynamic effects
even if sealed, buffeting & movement significantly impacts convection internal to Probe
Diligence required in identifying differences between test & flight
BSDC has better system in place today with extensive ‘test as you fly’ reviews
no emphasis in 1983 to identify & account for differences in DPT vs. flight
post-entry correlation revealed several differences that were not taken into account
Obtain calibration data well beyond the expected temperature extremes
equipment will most likely survive & produce data beyond its Qualification range
knew data would be gathered until it stopped coming, calibrate over widest range possible
system margin did not account for any extremes beyond expected temperatures
during DPT units saw -14oC, only 6oC margin on cold end to calibration limit of -20oC
similarly not much margin on hot end, DPT data at +44oC vs. +60oC calibration limit
Consider individual insulation systems and/or sealed entry vessel
BSDC Pioneer Venus Probe temperatures matched entry predicts with sealed vessel
beware of other complications, sealed vessels have their own peculiar set of problems
use foam plus individual unit blankets along with larger cavity close-out blankets (redundant insulation systems) to limit convective currents & mass flow
Helium Abundance Detector (HAD) implemented this & was most benign thermally of all science instruments

- Improve analytical modeling capability, don’t just ignore analysis
**pre-launch temperatures based strictly on DPT data, no test is ever 100% flight-like**
- always need combination of both test & analysis
**Probe Descent analyses must include coupled thermal & aerodynamic effects**
- even if sealed, buffeting & movement significantly impacts convection internal to Probe
- Diligence required in identifying differences between test & flight
**BSDC has better system in place today with extensive ‘test as you fly’ reviews**
**no emphasis in 1983 to identify & account for differences in DPT vs. flight**
**post-entry correlation revealed several differences that were not taken into account**
- Obtain calibration data well beyond the expected temperature extremes
**equipment will most likely survive & produce data beyond its Qualification range**
- knew data would be gathered until it stopped coming, calibrate over widest range possible
**system margin did not account for any extremes beyond expected temperatures**
- during DPT units saw -14oC, only 6oC margin on cold end to calibration limit of -20oC
- similarly not much margin on hot end, DPT data at +44oC vs. +60oC calibration limit
- Consider individual insulation systems and/or sealed entry vessel
**BSDC Pioneer Venus Probe temperatures matched entry predicts with sealed vessel**
- beware of other complications, sealed vessels have their own peculiar set of problems
**use foam plus individual unit blankets along with larger cavity close-out blankets (redundant insulation systems) to limit convective currents & mass flow**
- Helium Abundance Detector (HAD) implemented this & was most benign thermally of all science instruments

## References
HS-373-3099, “Galileo Probe Coast & Transit Thermal Vacuum Test Report,” Bruce Drolen, 27 June 1983.
HS-373-4657, “Galileo Probe/RRH Off-Sun Maneuvers Thermal Study Results,” Tom Rust, 31 August 1992.
HS-373-6000, “Galileo Probe Mission Operations Final Report,” Bernie Dagarin, September 1996.
1997 AIAA Applied Aerodynamics, Plasmadynamics and Lasers, and Thermophysics Conference 97-2456, “Galileo Probe Descent Post-Flight Thermal Correlation Analysis,” Brian Mischel, Tom Rust, and Fred Linkchorst, 23 June 1997.

- HS-373-3099, “Galileo Probe Coast & Transit Thermal Vacuum Test Report,” Bruce Drolen, 27 June 1983.
- HS-373-4657, “Galileo Probe/RRH Off-Sun Maneuvers Thermal Study Results,” Tom Rust, 31 August 1992.
- HS-373-6000, “Galileo Probe Mission Operations Final Report,” Bernie Dagarin, September 1996.
- 1997 AIAA Applied Aerodynamics, Plasmadynamics and Lasers, and Thermophysics Conference 97-2456, “Galileo Probe Descent Post-Flight Thermal Correlation Analysis,” Brian Mischel, Tom Rust, and Fred Linkchorst, 23 June 1997.