This talk summarizes experimental effort to characterize the outgassing rate of rod heaters (Watrods) used for GOES-R thermal vacuum testing. QCM data obtained with unbaked rods indicated that the outgassing exceeded the allowable budget. We then pre-baked the watrods for 16 hours at ambient pressure and determined that pre-baking reduced the amount of outgassed material by a factor of 4

Brieda, L.

Bush, J.

Gordon, T.

Pfeiffer, R.

Studer, R.

Van Loon, S.

NASA Technical Reports Server

Outgassing Characterization of Rod 
Heaters used for GOES-R Thermal 
Vacuum Testing
L. Brieda1, T. Gordon2, R. Studer3, R. Pfeiffer4, J. Bush4, S. Van Loon4
1Particle In Cell Consulting LLC
2SGT, Inc.
3ASRC, Inc.
4Lockheed Martin
Contamination, Coatings, Materials, and Planetary Protection Workshop 
July 29-31, 2015
https://ntrs.nasa.gov/search.jsp?R=20180003108 2019-08-31T16:36:08+00:00Z
Rod Heater Outgassing Characterization
2
• Past experiences of Code 546 Contamination Engineers indicated 
that rod heaters (e.g. calrods or watrods) may be a source of 
molecular contamination
– For instance, SDO chamber required over 100 hours of bakeoff
– However, has been used on other projects (LADEE, etc..) without issues
• GOES-R TVAC configuration uses such heaters (Watlow watrod)
– GOES-R is highly contamination sensitive – needed to verify these heaters 
will not contaminate the flight hardware, chamber, or MGSE
• This presentation summarizes the outgassing characterization 
effort and the subsequent bakeout
Summary
Rod Heater Outgassing Characterization
3
• Cold walls used for the entirety of the test
• Spacecraft enclosed in an MGSE watrod cage
– Some sections use heater plates instead of watrods
GOES-R TVAC Configuration
Watrod cages
Solar pointing platform
GOES-R spacecraft
Rod Heater Outgassing Characterization
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• Objective was to characterize outgassing from a virgin, un-baked watrod
– Two rods placed in a stainless steel cylinder with opening on one end, facing reflector 
– 450oC nominal temperature during TVAC per thermal model, but margin up to 600oC
• Used a 90oC reflector plate to protect TQCM crystal, LN2 chamber shroud
• Testing performed at LM Sunnyvale
Outgassing Characterization
VEGA I  TV Chamber
Base Plate
Calrods (2) 
0.475” dia
Stainless 
Tube 5.87” dia
Chamber Monorail
TQCM
Reflector Plate
w/heater tape 
set to 90°C max
LN2 Shroud
20 Gauge Hi –Temp Tc wire 
wrapped around monorail 
and tube 3 places for support
Shield to protect TQCM from end cap radiation
8
”
8”
Rod Heater Outgassing Characterization
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Experimental Setup
Stainless steel cylinder
Aperture
Reflector plate
QCM
Rod Heater Outgassing Characterization
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Thermocouples
• The two watrods were instrumented with thermocouples
Rod Heater Outgassing Characterization
7
Post-test observations
• Molecular deposition was observed on both endplates
Rod Heater Outgassing Characterization
8
• Figure below shows the TQCM frequency and thermocouple data 
over the test duration
– Temperature rise non-linear due to controller issues (power instead of 
temperature control)
Test Results
Rod Heater Outgassing Characterization
9
• Frequency rate indicates spike around 400oC and a secondary spike 
around 550oC
Frequency Rate
This spike corresponds to the expected temperature during TVAC!
Rod Heater Outgassing Characterization
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• The setup was modeled in Thermal Desktop
– Obtained 3.66 × 10−4 viewfactor between QCM crystal and the aperture
• Rod outgassing rate can be obtained from mass balance
Γ𝑤𝑤𝑟𝑟𝐴𝐴𝑤𝑤𝑟𝑟𝑓𝑓𝑣𝑣 = Γ𝑄𝑄𝑄𝑄𝑄𝑄𝐴𝐴𝑄𝑄𝑄𝑄𝑄𝑄
– Note, this rate only includes the fraction condensable below 90oC
• Using ½” QCM crystal diameter, and 2x 48”x0.475” diameter watrods we obtain 
1 Hz/hr|𝑞𝑞𝑞𝑞𝑞𝑞 = 3.74 Hz/hr|𝑤𝑤𝑟𝑟
– Use 1.96× 10−9 g/cm2/hz QCM sensitivity to convert
• At peak observed deposition rate of 1869 Hz/hr, watrod outgassing was 3.82 ×10−9 g/cm2/sec = 𝟏𝟏.𝟑𝟑𝟑𝟑 × 𝟏𝟏𝟏𝟏−𝟓𝟓 g/cm2/hr
– At the end, watrods outgassing at 18 Hz/hr, corresponds to 1.32 × 10−7 g/cm2/hr
Outgassing Rate
GIRD801 requirement: 
GSE hardware used in vacuum testing shall outgas less than 1x10-8 g/cm2-hr at 
10°C above the maximum survival temperature of the flight hardware that they 
are tested with when measured with a QCM held at -65°C (208 K).
During the test, the QCM was held only at -20°C
Rod Heater Outgassing Characterization
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• The spacecraft thermal vacuum test (SCTV) will utilize approximately 1123 
linear feet of watrods, .475” diameter
• Rods vary in overall length from ~28” to ~153”
• 600C maximum surface temperature
• 4.1x10-5 g/cm2 measured outgassing source fluence
• 449 Angstroms calculated deposition on external spacecraft surfaces if left as-
received
• Not possible to remove majority of deposition by subsequent baking due to 
high source temperature
• Removal from spacecraft surfaces not practical by other means (solvents, 
scrubbing, etc.)
• Conclusion: Some outgas mitigation must be performed on watrods prior to 
use in SCTV
Observations
Rod Heater Outgassing Characterization
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1. Pre-bake watrods in vacuum chamber
– Need a vacuum chamber where high-temp deposition to chamber is acceptable
– Needs to be batched due to power requirements and chamber dissipation
2. Pre-bake watrods in ambient atmosphere
– Test was performed to determine that this outgassing method achieved acceptable 
results
– Results in minimal deposition on GSE during chamber certification
3. Bake virgin watrods during GSE Bakeout / Chamber Certification
– TQCMs must be covered or removed for watrod bake to avoid contamination –
implies 2-phase bakeout and break of chamber in the middle
– High-temp deposition would occur on chamber shrouds and GSE, thickness estimated 
at 100 to ~600 Angstroms
– Mechanical stability of the deposit is unknown, although observations point to it 
being stable; i.e. won’t flake off during SCTV
– Likely not an acceptable solution to facility owners
Mitigation Options
Option 2 most practical – thenew watrods
pre-baked in ambient pressure for 16 hours
Rod Heater Outgassing Characterization
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Un- and pre-baked comparison, frequency
Rod Heater Outgassing Characterization
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Un- and pre-baked comparison, frequency rate
Rod Heater Outgassing Characterization
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• Unbaked watrods: 4560 to 8404 Hz, 3844 Hz mass loss
• Pre-baked watrods: 3942 to 4711 Hz, 769 Hz mass loss
– Pre-baking reduced outgassed mass by a factor of 4 
– This calculation took into account difference of view factors, 0.000292 vs 0.000366
• TGA also indicates that pre-baking reduces high temperature constituent
Un- and Pre-baked comparison
Rod Heater Outgassing Characterization
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• The mass collected on the reemission plate represents the mass 
condensable above 90oC.  
– During the first test the mass collected indicated a source fluence from the 
cal rods of 1.31 × 10−5 g/cm2.  This is 47% of the total mass compared to 
53% that was condensable below 90oC.
– During the second test of the pre-conditioned watrods, the mass collected 
indicated a source fluence from the watrods of 8.1 × 10−7 g/cm2.  This is 9% 
of the total mass compared to 91% that was condensable below 90C.
• The conclusion is that the pre-bakeout reduced the watrod
outgassing (mass condensable above 90oC) by 94%.
Mass on Reemission Plate
Rod Heater Outgassing Characterization
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• GOES-R watrods were subsequently prebaked in an ambient air 
facility at Lockheed Martin
– 16 hours at 600C, baked in batches per power constraints (about 50kW per 
batch)
• Watrods were then activated during MGSE bake out
– Did not observer any significant deposition on the TQCMs
Ambient Bakeout
Thermocouple data from 
ambient bakeout
Rod Heater Outgassing Characterization
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• We designed and executed a test to determine the outgassing rate 
of unbaked watrods
• The test indicated that virgin watrods can be a source of 
contamination
• Pre-baking in air reduces outgassing of mass condensable below 
90oC by a factor of 4
• Performed ambient air bakeout of all watrods used in GOES-R 
TVAC
• MGSE bakeout was successful with acceptable outgassing rates
• Questions?
Conclusion


Outgassing Characterization of Rod Heaters Used for GOES-R Thermal Vacuum Testing

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