The cryogenic thermal vacuum/thermal balance test of the James Webb Space Telescope (JWST) combined Optical Telescope Element (OTE)/Integrated Science Instrument Module (ISIM), known as the OTIS, at the Johnson Space Center (JSC) Chamber A in 2017 was likely the most complex test ever performed by NASA for an unmanned mission. The test of the combined flight Optical Telescope and ISIM elements was prefaced by years of modifications to chamber facilities, and included three extensive precursor tests of non-flight and flight hardware to establish safe and optimal test operational procedures. One critical part of the test preparation was planning for off-nominal events that could arise, including appropriate responses. In some cases, assurance of personnel and payload safety required modification of original test hardware and procedures which had to be validated before the final test could begin. This planning proved especially prescient for the OTIS test, as Hurricane Harvey struck the Houston area during the test in August 2017, and consequences for the precious payload could have been severe. This paper describes the extent of the thermal off-nominal planning undertaken for the OTIS test, including including safing for hurricanes, and some real-life effects of Hurricane Harvey on the test conduct. Documentation of the consequences and mitigations for these events are discussed. The importance of off-nominal planning for future thermal vacuum/thermal balance tests is illustrated

Cleveland, Paul E.

Comber, Brian J.

Glazer, Stuart D.

Ousley, Wes

Yang, Kan

NASA Technical Reports Server

1Off-Nominal Planning for the Cryogenic Vacuum Test of 
the JWST Optical Telescope Element/Integrated Science 
Instrument Module at JSC
ICES Paper 2018283
Stuart D. Glazer, NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA, 20771
Kan Yang, NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA, 20771
Brian J. Comber, Genesis Engineering Solutions, Inc., Lanham, Maryland, USA, 20706
Wes Ousley, Genesis Engineering Solutions, Inc., Lanham, Maryland, USA, 20706
Paul E. Cleveland, Energy Solutions International, LLC., Laytonsville, MD 20882
https://ntrs.nasa.gov/search.jsp?R=20180004556 2019-08-31T15:34:15+00:00Z
Agenda
2
• Description of Flight Observatory, ISIM Element, OTE Element
• JWST ISIM, OTE Thermal Test Program
• Principal OTIS Test Thermal Objectives
• Constraints and Limitations
• Pre-test Prediction vs. Actual As Run Profile
• Off-Nominal Planning, Events Considered, Mitigations Developed
• Hurricane Harvey Consequences
• Conclusions, Recommendations for Off-Nominal Testing Planning for 
other Projects
Murphy’s Law
3
"Anything that can go wrong will go wrong.“
-Edward A. Murphy, Aerospace Engineer at Edwards AFB, 1949
Major Components of  JWST Observatory
4
Integrated Science Instrument Module (ISIM), Flight 
Configuration
5
Optical Telescope Element + ISIM Element (OTIS)  Test 
Configuration
6
OTIS Being Readied for Test, Prior to Entry into JSC 
Chamber A
7
Major ISIM Element TV/TB Tests in SES Facility 
at GSFC
8
Major OTE/OTIS TV/TB Tests in Chamber A at JSC
9
Principal OTIS Thermal Test Objectives
10
Primary Objective of OTIS TV/TB test was considered verification of optical requirements, but 
included many other tests.  Only one thermal balance point was planned. The five principal 
thermal objectives defined were:
• OTIS Temperature Limits and Constraints - The OTIS temperature limits and constraints shall 
conform to the requirements found in OTIS Limitations and Constraints Implementation 
Plan.
• Boundary and Influence temperatures - The test shall verify at thermal balance the element-
to-element and key subsystem boundary temperatures and interface temperatures and/or 
rates as specified in OTIS Thermal Operation Document
• Thermal Model Validation - The test shall verify OTIS system thermal workmanship, and 
provide thermal balance test data to validate the OTIS thermal model. 
• Model Validation Tolerances  - The data collected shall be sufficient to validate the models 
consistent with the numerical requirements found in JWST Systems Analysis and Model 
Validation Plan
• OTIS Heat Strap Workmanship Test - The test shall perform a workmanship thermal 
conductance assessment of the flight SI heat straps in the OTIS test configuration at 
operating temperatures.
Thermal-Applicable Limitations and Constraints
11
Source Document: “OTIS JSC Constraints & Limitations Implementation Plan” 
• Constraints are put in place to avoid actions, conditions, or events, which if realized, 
will result in damage to flight hardware.
• Limitations are put in place to avoid actions, conditions, or events, which have the 
potential for temporarily impacting performance or resulting in loss of test time.
• Several Hundred L&C’s divided into two groups
• Thermal Applicable – Monitored and alarmed by OTIS Thermal Team (92 total)
• 84 Constraints
• 8 Limitations
• Non Applicable - Not monitored by OTIS Thermal Team
• Most thermal constraints and limitations were designed to avoid contamination, 
overstressing of structural elements and instruments.  They defined absolute 
temperature limits, rates of change, gradients within structures, instruments, and 
temperature relationships between instruments, optics, thermal boundaries, usage 
of heaters 
Pre-Test OTIS Profile Prediction
12
As-Run OTIS Test Profile
13
Pumpdown / 
Pre-Cryo Warm 
Vac (8 days)
Post-Cryo
Warm 
Vac / 
Repress 
(4 days)
Cooldown (32 
Days)
Cryo-Stable (32 Days) Warmup (19 days)
Hurricane Harvey
OTIS Susceptibility to Off-Nominal Events (1 of 2) 
14
• Large temperature range of components 
• Electrical boxes in IEC: 278K
• Near IR instruments, instrument detectors: 36.5K - 42.8K, Mid Infrared Instr.: 6.2K
• Flight radiators: 30K-40K; 
• Telescope optics generally in the 40K-60K range.  
• GHe shroud, other thermal boundaries: 20K, LN2 shroud: 80K  
• Complexity of GSE 
• 16 individually controlled GHe flow valves: 7 for shroud, 9 for individual DSER’s & 
thermal boundaries plus supplemental heater circuits for precise temp. control
• Nominal cooldown from ambient to steady state cold planned over 3 weeks
• To control stress in mechanical components (rate limitations, gradient restrictions).
• Nominal warmup planned over 3 weeks  
• Nominal warmup carefully choreographed, reliant on precise thermal control of 
shroud, multiple thermal boundaries, instruments. N2 frozen on He shrouds 
released at ~27K - 34K, caused pressure increase which changed heat transfer 
mechanism to FMHT, causing rapid temperature and gradient changes, with 
possible effect on structural component integrity.  Large number of rate, gradient 
C&L’s identified.  
OTIS Susceptibility to Off-Nominal Events (2 of 2)
15
• Contamination from water moisture, particulates, molecular contaminants a major 
concern  
• Sensitive optics in telescope and instruments must be warmer than surroundings 
during warmup, cooldown to avoid water and molecular contaminants collecting 
on critical surfaces.  Key instrument, optical temperatures kept close to each other 
during critical parts of transitions to avoid cross-contamination. 
• Extremely high value flight payload
• Long test duration 93 days, very high test cost
Pre-Test Preparations for Off-Nominal Events (1 of 2)
16
• Extensive preparations made during test planning and development:  
• Critical power supplies, test data, control systems on UPS, diesel generator circuits; 
• spare power supplies/temperature measurement equipment available; 
• redundant flight/test sensors identified, added to control heater circuits; 
• Pre-test checkout of JSC facilities (N2 system, He compressors, control software). 
• Test GSE checked to assure proper operation and safety of payload during off-
nominal conditions. 
• Roof repairs made to Building 32 (Chamber A, cleanroom, control room)
• Alternate control room in Building 30 prepared and checked.   
• Critical test control equipment covered with plastic sheeting to protect from potential 
water damage if it rained heavily. 
• Potential for hurricanes was identified early on
• Volunteer Hurricane Rideout Team and Recovery Team members identified and 
took required FEMA training.  Rideout team members  also took physical exams.
Pre-Test Preparations for Off-Nominal Events (2 of 2)
17
• Thermal staffing shift schedule 
• Established for entire anticipated test period prior to test start.  
• Multiple thermal engineers on shift 24/7 throughout test, with “floaters” 
(experienced senior thermal engineers with background in JWST) always present in 
Houston area, ready to assist and replace scheduled shift support if necessary. 
• Thermal support personnel undertook test support and safety training.
Additional OTIS Off-Nominal Planning
18
• Subsystems directed to perform extensive planning for off-nominal events, to assure safety of 
personnel and flight hardware.  
• Payload thermal developed OTIS Off-Nominal Thermal Consequences and Mitigations 
Workbook. 
• Excel spreadsheet, reviewed/approved by GSE thermal, facilities, Flight systems teams, 
identified the following 10 major events, and developed mitigation actions to be taken 
by Payload thermal, GSE thermal, facilities, test director, depending on test thermal 
state (see next page): 
• Partial Loss of Vacuum pumps; 
• Loss of LN2 System; 
• Loss of He system-Train 1 – CPP; 
• Loss of He system – Train 3-Shroud, DSERs; 
• Loss of SC Simulator; 
• Loss of IRSU; 
• Loss of Eclipse; 
• Loss of the Thermal Test Set (TTS) data system; 
• Loss of the Fusion data system; 
• Loss of Facility Electrical Power (Loss of both Helium refrigerators. partial loss of 
vacuum pumps); 
• An Emergency Safing Procedure, and a Safing procedure if 48 hours available (in preparation 
for hurricane or other natural disaster) were also developed. 
OTIS Off-Nominal Planning – Mitigations during 
Specific Test Periods 
19
Note: These predicted test periods were based on an earlier version of the pre-test thermal model
Major Off-Nominal Events during ISIM, OTE, OTIS Tests
20
Test Date Event Consequences
OSIM Cryo-Cal 1 6/12/2013 Derecho (high wind storm) – extended
power loss in area
Impacts to personnel availability
ISIM CV1 10/1/2013-
10/17/2013
17-day US Government shutdown Test placed on “hold” – no progress
ISIM CV2 7/3/2014 Emergency light in test control room caught
fire
Control room evacuated, test on hold until smoke cleared
ISIM CV2 7/8/2014 Thunderstorm – Power outage at facility Emergency generator did not start automatically. He compressor off for ~
30 minutes. Shroud warmed, test time lost.
ISIM CV2 7/9/2014 Thunderstorm – Lightning strike at GSFC Lost cooling water for He compressor. Facility electrician was not on shift
to restore power to cooling water. Shroud warmed, test time lost.
ISIM CV2 7/10/2014 Continue from above event He compressor turned off without cooling water.
ISIM CV2 10/3/2014 Fire alarm in B10 basement (part of GSFC
thermal test complex)
Thermal engineers, control personnel briefly evacuated (<30 minutes),
test resumed without incident
ISIM CV3 1/22/2016
through
1/25/2016
Extreme blizzard ~2 to 3 feet snow in area Extremely hazardous travel conditions. Test personnel either sheltered at
GSFC or if staying within 1 mile of GSFC, were transported to/from GSFC
by persons with heavy trucks. Test continued without loss of any facilities.
OTE Pathfinder Water pipe break in basement of test
complex at JSC
Primary He compressor Train 3 unavailable during event, had to switch to
alternate Train 3 use.
OTIS 8/26/2017
through
8/30/2017
Hurricane Harvey hits Houston area.
Weather conditions during the hurricane
JSC included thunderstorms, tornado
watches, flood warnings, and periods of
severe rainfall (Houston received ~1270 mm
(50 inches) of rain in 4 days).
Extreme care had to be used in transit between hotels and JSC for test
personnel. Shifts were extended to 12 hours to minimize travel, some
people slept at JSC for a few nights, and active optical testing was curtailed
for a time. JSC center was closed for ~9 days to regular JSC employees
from the start of the hurricane until facilities could be verified as safe for
return. Meanwhile, roof of Building 32 (test building) leaked, resulting in
substantial use of plastic sheeting to keep critical electronic equipment in
the building and the control center dry and safe.
Principal concerns included potential loss of electrical power, and inability
to refill LN2 tanks. Loss of power would have resulted in loss of He Train
3, and would have required warming to LN2 temperature. Loss of LN2
would have eventually resulted in full warmup
We were fortunate that neither occurred during the Hurricane, as they
would have had week(s) of impact to test time. Since we had just entered
Cryo-stable phase of test, most test objectives had not yet been met.
21
• Massive blizzard warnings (for Greenbelt MD) at least 4 days before blizzard arrival 
(January 21, 2016)
• Preparations made for locals to shelter at GSFC for several days, arrangements made 
to ferry non-local test participants to/from local hotels in privately owned trucks
• 21-34 inches snow in Washington DC area (NASA/GSFC received ~21 inches)
• Test progress not impacted!
Dealing with ISIM CV3 Blizzard
OTIS Test: Hurricane Harvey Storm Warnings
22
Monday, August 21 Wednesday, August 23
(Photos Credit: L. Feinberg)
Hurricane forecasts were monitored daily 
throughout OTIS test.  Initial warnings of 
possible Hurricane Harvey impacting Houston 
area ~5 days before landfall
Initial Preparations for Harvey
23
(Photo Credit: L. Feinberg)
• By Friday, August 25, 
Project had purchased 
40 air mattresses, set up 
in conference rooms 
• Project had stockpiled 
food rations for several 
days
• Potential effect on personnel more severe than blizzard during ISIM CV3 test, 
since most test participants were non-resident in Houston area and had to fly in 
from around the US and world to staff test.
• Plans made to extend shifts to 12 hours to minimize travel to/from hotels
• Hurricane Ride-out team members were identified, prepared to stay at JSC
• Hurricane safing procedures reviewed, plans to deal with individual system 
failures printed (on laminated paper)
Dealing with Harvey: Initial impacts - Saturday night into 
Sunday morning, August 26/27
24
JSC Parking Lot B32 (Photo Credit: L. Feinberg)
Weather conditions
• ~20 inches of rain overnight at JSC, 45-50 
inches total in Houston area (over 4 days)
• Flash flooding, storm, and tornado 
warnings all night
Impacts to personnel, JSC
• Extremely hazardous travel, several 
experienced test support personnel called 
in to JSC prior to landfall in case Center 
access became impossible
• Only JSC entrance was closed for several 
hours due to flooding
Impact to Test
• OTIS test continued, but optical testing 
temporarily curtailed
Dealing with Harvey: During, after Landfall 
25
Water Damage in B32 OTIS Control 
Room, despite pre-test roof repairs
Plastic Sheeting installed to Protect control 
computers and data stations
Dealing with Harvey: Several Days after Landfall
26
(Photos Credit: L. Feinberg)
• Hurricane was slow moving, bands of intense 
rainfall, winds persisted for 4 days
• Carpools organized using high ground clearance 
trucks/SUV’s to ferry personnel to/from hotels 
because of local road flooding  
• 12 hour shifts until local flooding eased
• Road flooding in Houston prevented timely LN2 
deliveries for ~ 3 days (only had 5 days reserve 
on-hand before LN2 shroud would warm, 
causing premature test warmup).  Great efforts 
made to bring in LN2 from alternate supplier
• Fortunately, JSC area did not lose commercial 
power, which would have resulted in premature 
test end
• Commercial air travel from local airports was 
impacted for several days after the hurricane.  
NASA GSFC, NGAS, BATC made special 
arrangements to provide replacement test 
support crews 
Payoff of the OTIS Off-Nominal Planning
27
Pre-test planning resulted in a highly successful TV/TB test;
• Extreme flexibility, redundancy built into the facility and GSE thermal controls and 
data systems enabled flexible and rapid reaction to small differences between 
modeled and actual transient performance.  
• No unplanned warmup/cooldown due to off-nominal events
• Extremely detailed and careful pre-test thermal modeling resulted in 1 brief 
constraint violation during cooldown, 4 during warmup, none considered serious 
enough to warrant Problem Failure Report
• Pretest securing of critical electronic GSE with plastic sheeting protected that 
equipment and helped safeguard the payload during the hurricane.  Project dealt 
with severe hurricane conditions without major impact to test schedule
• Plans were ready to conduct unplanned partial/complete payload warmup if 
conditions worsened during the hurricane.
Recommendations for Off-Nominal Planning for TV/TB 
Tests of Flight Payloads (1 of 2)
28
Enhance personnel and flight hardware safety with appropriate planning:
• Low hanging fruit should always be addressed:
• Provide spares for critical GSE power supplies, make sure personnel trained to 
replace them
• Provide/install redundant sensors for controlled heaters, and redundant GSE heater 
circuits
• Provide/install backup power supply for critical thermal boundaries, power supplies, 
test measurement equipment, data systems, control electronics, facilities, to allow 
continued testing or safe test end (UPS, diesel generator)
• Make sure well trained test support personnel available to replace scheduled shift 
personnel in case of illness, accidents
Recommendations for Off-Nominal Planning for TV/TB 
Tests of Flight Payloads (2 of 2)
29
• Prior to major thermal vacuum tests, projects should list potential events and their 
effects, and evaluate risks of failures of GSE, flight hardware, flight software, facilities, 
utilities, personnel evacuations, etc. in terms of impact to flight hardware damage and 
potential programmatic impact for repairs; schedule; cost.  Project must be willing to 
accept remaining risks.
• Make as many facility, utility provisions as robust as possible.  Demonstrate pre-test 
(without risking flight hardware).
• Even if certain potential facility or utility failures cannot be prevented, evaluate potential 
damage, devise test workarounds or emergency procedures
Acknowledgement for All Test Teams
• The authors wish to acknowledge the hard work and dedication of the Project and 
Test Directors, Payload Thermal, GSE Thermal, Contamination, Cryo Support, 
Instrument, Optics, Facilities, and all other support teams for a successful test.
• Payload Thermal support team on shift during Hurricane Harvey shown below


Off-Nominal Planning for the Cryogenic Vacuum Test of the JWST Optical Telescope Element/Integrated Science Instrument Module at JSC

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