1. Space Based Infrared System
Geosynchronous (GEO-1) Thermal Vacuum Testing
Background
Thermal vacuum testing is the most
comprehensive risk mitigation component
of the integrated spacecraft environmental
test program. The test verifies satellite
performance in a simulated space environ-
ment with temperature extremes beyond
that which the satellite is expected to
experience on orbit.
The fundamental purpose of thermal
vacuum testing is to understand the satel-
lite’s performance through environmental
extremes and thus increase mission assur-
ance through a test-like-you-fly environ-
mental testing program.
This extremely complex test was
performed on the GEO-1 space vehicle
consisting of an integrated spacecraft bus
and payload.
The contractor/government team worked
collectively to make this a highly success-
ful test phase.
What is a thermal vacuum test? What is tested during closed door thermal vacuum testing?
This proto-qualification–level test quali- The under-vacuum portion of the GEO-1 thermal vacuum test was conducted in 66 days and
fied the GEO-1 space vehicle to operate included three complete thermal cycles and five thermal balance runs. The thermal cycles were
in the space environment. It demonstrated conducted at more stressing temperatures (proto-qualification levels) than anticipated during
that the integrated payload and spacecraft operational use.
bus can withstand the anticipated thermal The closed door thermal vacuum testing included:
environment in the vacuum of space. • Guidance, navigation, and control subsystem closed loop testing
The test also demonstrated the space • Thermal control heater performance and temperature monitor response
vehicle’s functional performance in the
• Electrical power subsystem switching and distribution
simulated space environment and obtained
• Communications subsystem operations
payload and spacecraft bus thermal data to
confirm that its thermal design and work- • Payload basic operation and signal processing
manship are sound. Thermal data is also • Deployment of a unique contamination door assembly that protects the sensitive infrared
required for correlation with the spacecraft sensors during assembly, test, launch, and transfer orbit
thermal model, which will be critical if • Other spacecraft and payload mission operations.
unforeseen on-orbit events are encountered.
Approximately 200 test requirements Thermal vacuum factoids
and 25 Space Segment requirements were • More than 150 flight heaters and 300 flight temperature sensors were verified to demon-
verified during the functional performance strate proper functional performance of the thermal control subsystem.
testing of the spacecraft and payload. • The thermal vacuum chamber temperatures ranged from -4°F to +86°F, and the payload
This included primary, redundant, and focal plane temperature reached -243°F. The focal plane must be at this extremely cold
cross-strap modes of the space vehicle and temperature to identify dim targets from 22,000 miles away.
payload. • The thermal vacuum test was conducted in a cylindrical 40- x 80-ft horizontal chamber, a
space larger than a volleyball court but smaller than a basketball court. The chamber is a
What is open door thermal dual door entry thermal vacuum chamber (100K clean room) located in Sunnyvale, Calif.
vacuum testing? • In the thermal vacuum chamber, the satellite weighs approximately 5,000 pounds,
Open door thermal vacuum testing veri- equivalent to a Humvee.
fies that the space vehicle is ready to begin • It takes six hours to pump down to the required vacuum.
thermal vacuum testing. Open door testing • Pressure is maintained at 0.0133 pascals (0.0001 torr) or less. The standard atmospheric
provides an ambient temperature and pres- pressure at sea level is 101 kilo pascals (760 torr). Therefore, the pressure is reduced by
sure baseline for closed door testing. more than 10 million times (7 order of magnitude).

2. Closed door thermal vacuum testing details The way forward
The space vehicle was in flight configuration except for two deployable Over the next four months, the SBIRS team
mechanisms (solar arrays and deployable light shade), both of which are integrated will be removing the satellite from the thermal
after Final Integrated System Test and before delivery to the launch site. The test vacuum chamber and disconnecting the thermal
sequence consisted of a series of sequential verifications to ensure that power test mechanical ground support equipment. Some
could be safely applied to the space vehicle and could be safely controlled and
preplanned rework to remove and replace
distributed.
components will also be conducted.
Functional testing of the space vehicle utilized test scripts previously developed
The satellite will then proceed through the Final
for the Baseline Integrated System Test (BIST) to permit comparing similar test
configurations and the trending of data. Integrated System Test (FIST), which is the last
The space vehicle was tested in both primary and redundant hardware major functional test phase of the program prior
configurations. to launch. FIST is almost identical to BIST
During the thermal vacuum test, the space vehicle executed its launch and (Baseline Integrated System Test) and demon-
transfer orbit scenarios. strates that the space vehicle is ready for launch
The thermal model was verified through space vehicle non-operational cold, following exposure to the environmental test
nominal cold, and nominal hot operating environments. program (acoustics, shock, and thermal vacuum).
Data was collected and analyzed to demonstrate proper functional performance During FIST the space vehicle will be taken
of the thermal control subsystem. through functional testing to obtain a perfor-
mance baseline that can be compared to the BIST
Test phases demonstrated baseline. These baselines are essential once the
Thermal vacuum testing demonstrated five mission operations scenarios:
satellite is on orbit and post-launch performance
• Pre-launch and ascent sequences
is assessed.
• Normal mission operations (primary and redundant sides)
After FIST an end-to-end system test will be
• Safemode with appendages stowed (simulated). The appendages are the solar
conducted using the operational ground system to
arrays, high-gain antennas, and deployable light shade. The stowed mode
command and control the satellite in the factory.
represents the spacecraft configuration during launch and transfer orbit.
Finally, final flight installs will be performed to
• Safemode with appendages deployed (simulated). This represents the space
place the satellite in the final launch configuration
vehicle on-orbit configuration.
and prepare it for transport to the launch base.
The payload was powered on and functionality was demonstrated.
During this phase, final installation of the flight
batteries, solar arrays, and deployable light shade
will occur.
Conclusion
Successful completion of environmental testing
provides the joint government/industry SBIRS
team with high confidence in the functional capa-
bilities of this complex space vehicle for launch
and on-orbit operations with 100% mission
success.
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