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Technical Paper

Weathering of Thermal Control Coatings

2007-07-09
2007-01-3020
Spacecraft radiators reject heat to their surroundings. Radiators can be deployable or mounted on the body of the spacecraft. NASA's Crew Exploration Vehicle is to use body mounted radiators. Coatings play an important role in heat rejection. The coatings provide the radiator surface with the desired optical properties of low solar absorptance and high infrared emittance. These specialized surfaces are applied to the radiator panel in a number of ways, including conventional spraying, plasma spraying, or as an appliqué. Not specifically designed for a weathering environment, little is known about the durability of conventional paints, coatings, and appliqués upon exposure to weathering and subsequent exposure to solar wind and ultraviolet radiation exposure. In addition to maintaining their desired optical properties, the coatings must also continue to adhere to the underlying radiator panel.
Technical Paper

Thermal Vacuum Testing of the Capillary Pumped Loop Flight Experiment

1994-06-01
941599
The Capillary Pumped Loop Flight Experiment (CAPL) is a prototype of the Earth Observing System (EOS) instrument thermal control systems, which are based on two-phase heat transfer technology. The CAPL experiment has been functionally tested in a thermal vacuum chamber at NASA's Goddard Space Flight Center (GSFC). The tests performed included start-up tests, simulated EOS instrument power profiles, low and high power profiles, a variety of uneven coldplate heating tests, subcooling requirement tests, an induced deprime test, reprimes, saturation temperature changes, and a hybrid (mechanical pump-assist) test. There were a few unexpected evaporator deprimes, but overall the testing was successful. The results of all of the tests are discussed, with emphasis on the deprimes and suspected causes.
Technical Paper

Thermal Performance of Capillary Pumped Loops Onboard Terra Spacecraft

2004-07-19
2004-01-2504
The Terra spacecraft is the flagship of NASA’s Earth Science Enterprise. It provides global data on the atmosphere, land, and oceans, as well as their interactions with solar radiation and one another. Three Terra instruments utilize Capillary Pumped Heat Transport Systems (CPHTS) for temperature control. Each CPHTS, consisting of two capillary pumped loops (CPLs) and several heat pipes and electrical heaters, is designed for instrument heat loads ranging from 25W to 264W. The working fluid is ammonia. Since the launch of the Terra spacecraft in December 1999, each CPHTS has been providing a stable interface temperature specified by the instrument under all modes of spacecraft and instrument operations. The ability to change the CPHTS operating temperature upon demand while in service has also extended the useful life of one instrument. This paper describes the design and on-orbit performance of the CPHTS thermal systems.
Technical Paper

Thermal Performance and Operational Characteristics of Loop Heat Pipe (NRL LHP)

1998-07-13
981813
In this paper, results of the NRL LHP experimental studies, conducted by Naval Research Laboratory (NRL) and NASA Goddard Space Flight Center, will be presented. Emphasis in this test program is to examine the “turnkey” startup of the NRL LHP and its operational characteristics. Series of tests were performed, including startup tests, power cycling tests, low power tests, and high power tests. The NRL LHP has demonstrated very robust operations throughout the tests. In addition, hysteresis was found at low power operations. Importance of the two-phase dynamics in the evaporator core is realized, which has shown significant effects on loop operations.
Technical Paper

Thermal Design And Performance Of The Space Support Equipment For The Hubble Space Telescope Second Servicing Mission

1997-07-01
972527
New Space Support Equipment (SSE) components developed for the Hubble Space Telescope Second Servicing Mission are described, with particular emphasis on how flight experience from the 1993 First Servicing Mission was utilized in the design and testing process. The new components include the Second Axial Carrier (SAC) Axial Scientific Instrument Protective Enclosure (ASIPE), the magnetic-damped SAC ASIPE Load Isolation System, the Enhanced Power Distribution and Switching Unit (EPDSU), and the Multi-Mission Orbital Replacement Unit Protective Enclosure (MOPE). Analytical modeling predictions are compared with on-orbit data from the Hubble Space Telescope (HST) Second Servicing Mission. Those involved in thermal designs of hardware for use on the Shuttle or Space Station, particularly with astronaut interaction, may find interest in this paper.
Technical Paper

Thermal Assessment of Swift Instrument Module Thermal Control System during First 2.5 Years in Flight

2007-07-09
2007-01-3083
On Day 97, 2005, a temperature excursion of the Burst Alert Telescope (BAT) loop heat pipe (LHP) #1 compensation chamber (CC) caused this LHP shut down. It had no impact on the Gamma Ray Burst (GRB) detection because LHP #0 was nominal. After LHP #1 was started up and its primary heat controller was disabled on Day 98, both LHPs have been nominal. On Day 337, 2004, the X-Ray Telescope (XRT) thermo-electric cooler (TEC) power supply (PS) suffered a single point failure. The charge-coupled device (CCD) has been cooled by the radiator passively to -50°C or colder most of the time. The CCD temperature meets the main objective of pinpointing GRB afterglow positions. With these anomalies overcome, the Instrument Module (IM) thermal control system (TCS) is nominal during the first 2.5 years in flight.
Technical Paper

Thermal Assessment of Swift BAT Instrument Thermal Control System in Flight

2005-07-11
2005-01-3037
The Burst Alert Telescope (BAT) instrument of the Swift mission consists of a telescope assembly, a Power Converter Box (PCB), and a pair of Image Processor Electronics (IPE) boxes (a primary and a redundant). The telescope assembly Detector Array thermal control system includes eight constant conductance heat pipes (CCHPs), two loop heat pipes (LHPs), a radiator that has AZ-Tek's AZW-LA-II low solar absorptance white paint, and precision heater controllers that have adjustable set points in flight. The PCB and IPEs have Z93P white paint radiators. Swift was successfully launched into orbit on November 20, 2004. This paper presents a thermal assessment of the BAT instrument thermal control system during the first six months in flight.
Technical Paper

Thermal Analyses and Design Considerations of NASA’s Passively Cooled 35 K Next Generation Space Telescope (NGST)

1999-07-12
1999-01-2083
The configuration and thermal analyses of NASA’s Next Generation Space Telescope (NGST) Yardstick concept utilizing a novel sunshield approach for passive cooling is described. The NGST mission concept of a large aperture optical telescope passively cooled to less than 40 K and instrument detectors passively cooled to below 30 K is unique from any other mission flown to date. Achieving such a low operational temperature requires reducing by a factor of several thousand the internal heat dissipation and environmental heating of the telescope. The techniques for achieving these requirements, i.e. orbit selection, configuration, etc., along with the supporting thermal analyses are described.
Technical Paper

The Cryogenic Thermal System Design of NASA’s James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM)

2005-07-11
2005-01-3041
The thermal design and modeling of NASA’s James Webb Space Telescope (JWST) Integrated Science Instrument Module (ISIM) is described. The ISIM utilizes a series of large radiators to passively cool its three near-infrared instruments to below 37 Kelvin. A single mid-infrared instrument is further cooled to below 7 Kelvin via stored solid Hydrogen (SH2). These complex cooling requirements, combined with the JWST concept of a large deployed aperture optical telescope, also passively cooled to below 50 Kelvin, makes JWST one of the most unique and thermally challenging space missions flown to date. Currently in the preliminary design stage and scheduled for launch in 2010, NASA’s JWST is expected to replace the Hubble Space Telescope as the premier space based astronomical observatory.
Technical Paper

The CEV Smart Buyer Team Effort: A Summary of the Crew Module & Service Module Thermal Design Architecture

2007-07-09
2007-01-3046
The NASA-wide CEV Smart Buyer Team (SBT) was assembled in January 2006 and was tasked with the development of a NASA in-house design for the CEV Crew Module (CM), Service Module (SM), and Launch Abort System (LAS). This effort drew upon over 250 engineers from all of the 10 NASA Centers. In 6 weeks, this in-house design was developed. The Thermal Systems Team was responsible for the definition of the active and passive design architecture. The SBT effort for Thermal Systems can be best characterized as a design architecting activity. Proof-of-concepts were assessed through system-level trade studies and analyses using simplified modeling. This nimble design approach permitted definition of a point design and assessing its design robustness in a timely fashion. This paper will describe the architecting process and present trade studies and proposed thermal designs
Technical Paper

Testing of a Miniature Loop Heat Pipe Using a Thermal Electrical Cooler for Temperature Control

2004-07-19
2004-01-2505
This paper describes the design and testing of a miniature loop heat pipe (LHP) having a 7 mm outer diameter (O.D.) evaporator with an integral compensation chamber (CC). The vapor line and liquid line are made of 1.59mm O.D. stainless steel tubing. A thermoelectric (TEC) is installed on the CC and the hot side of the TEC is connected to the evaporator through a copper strap. By changing the direction of the electric current provided by a bi-polar power supply, the TEC can heat or cool the CC. Tests performed in the laboratory included start-up, power cycle, sink temperature cycle, and CC temperature control with the test article being placed in horizontal and vertical positions. The LHP demonstrated very robust operation in all tests where the heat load varied between 0.5W and 140W, and the sink temperature varied between 243K and 293K. The heat leak from the evaporator to the CC was extremely small.
Technical Paper

Testing of A Loop Heat Pipe Subjected to Variable Accelerating Forces, Part 2: Temperature Stability

2000-07-10
2000-01-2489
Loop Heat Pipes (LHPs) are being considered for cooling of military combat vehicles and spinning spacecraft. In these applications, it is important to understand the effect of an accelerating force on the performance of LHPs. In order to investigate such an effect, a miniature LHP was installed on a spin table and subjected to variable accelerating forces by spinning the table at different angular speeds. Several patterns of accelerating forces were applied, i.e. continuous spin at different speeds and periodic spin at different speeds and frequencies. The resulting centrifugal accelerations ranged from 1.2 g's to 4.8 g's. This paper presents the second part of the experimental study, i.e. the effect of an accelerating force on the LHP operating temperature. It has been known that the LHP operating temperature under a stationary condition is a function of the evaporator power and the condenser sink temperature when the compensation temperature is not actively controlled.
Technical Paper

Testing of A Loop Heat Pipe Subjected to Variable Accelerating Forces, Part 1: Start-up

2000-07-10
2000-01-2488
Loop Heat Pipes (LHPs) are being considered for cooling of military combat vehicles and spinning spacecraft. In these applications, it is important to understand the effect of an accelerating force on the performance of LHPs. In order to investigate such an effect, a miniature LHP was installed on a spin table and subjected to variable accelerating forces by spinning the table at different angular speeds. Several patterns of accelerating forces were applied, i.e. continuous spin at different speeds and periodic spin at different speeds and frequencies. The resulting centrifugal accelerations ranged from 1.2 g's to 4.8 g's. This paper presents the first part of the experimental study, i.e. the effects of an accelerating force on the LHP start-up. Tests were conducted by varying the heat load to the evaporator, condenser sink temperature, and LHP orientation relative to the direction of the accelerating force.
Technical Paper

Performance of the CAPL 2 Flight Experiment

1996-07-01
961432
This paper describes flight test results of the CAPL 2 Flight Experiment, which is a full scale prototype of a capillary pumped loop (CPL) heat transport system to be used for thermal control of the Earth Observing System (EOS-AM) instruments. One unique feature of CAPL 2 is its capillary starter pump cold plate design, which consists of a single capillary starter pump and two heat pipes. The starter pump enhances start-up success due to its self-priming capability, and provides the necessary capillary pumping force for the entire loop. The heat pipes provide the required isothermalization of the cold plate. Flight tests included those pertinent to specific EOS applications and those intended for verifying generic CPL operating characteristics and performance limits. Experimental results confirmed that the starter pump was indeed self-priming and the loop could be successfully started every time.
Technical Paper

Next Generation Space Telescope (NGST) Pathfinder Experiment Inflatable Sunshield in Space (ISIS)

1999-10-19
1999-01-5517
The Next Generation Space Telescope (NGST) design requires a large sunshield to passively cool the telescope and detectors to temperatures in the 60° to 100° Kelvin range. The government yardstick design for the NGST observatory has baselined an inflatable sunshield. The NGST project plans to fly a one-third-scale sunshield during a Shuttle flight in late 2000. The Inflatable Sunshield in Space (ISIS) experiment will demonstrate stable deployment of a large, multilayer thin film sunshield and ridigization of inflatable struts. A new method of modeling large membrane systems will be developed, and data will be obtained in order to validate the model. The flight experiment will also demonstrate the viability of the thermal approach by verifying separation and flatness of membrane layers.
Journal Article

Lessons Learned from the Wide Field Camera 3 TV1 and TV2 Thermal Vacuum Test Campaigns

2008-06-29
2008-01-2038
The Wide Field Camera 3 (WFC3) instrument has undergone two complete thermal vacuum tests (TV1 and TV2), during which valuable lessons were learned regarding test configuration, test execution, model capabilities, and modeling practices. The very complex thermal design of WFC3 produced a number of challenging aspects to ground testing with numerous ThermoElectric Coolers and heat pipes, not all of which were functional. Lessons learned during TV1 resulted in significant upgrades to the model capabilities and a change in the test environment approach for TV2. These upgrades proved invaluable during TV2 when pre-test modeling assumptions proved to be false. Each of the lessons learned relate to one of two following broad statements: 1. Ensure the design can be tested and that the effect of non-flight like conditions is well understood, particularly with respect to non passive devices (TECs, Heat Pipes, etc) 2.
Technical Paper

Lessons Learned from Hubble Space Telescope ExtraVehicular Activity Servicing Missions

2001-07-09
2001-01-2204
NASA’s Hubble Space Telescope was designed for periodic servicing by Space Shuttle astronauts performing extravehicular activities (EVAs), to service, maintain, repair, and upgrade the telescope. Through three successful servicing missions to date, EVA processes have been developed by applying a series of important lessons learned. These lessons learned are also applicable to many other future human spaceflight and robotic missions, such as International Space Station, satellite retrieval and servicing, and long-duration spaceflight. HST has become NASA’s pathfinder for observatories, EVA development, and EVA mission execution.
Technical Paper

Investigation of Low Power Operation in a Loop Heat Pipe

2001-07-09
2001-01-2192
This paper presents test results of an experimental study of low power operation in a loop heat pipe. The main objective was to demonstrate how changes in the vapor void fraction inside the evaporator core would affect the loop behavior. The fluid inventory and the relative tilt between the evaporator and the compensation chamber were varied so as to create different vapor void fractions in the evaporator core. The effect on the loop start-up, operating temperature, and capillary limit was investigated. Test results indicate that the vapor void fraction inside the evaporator core is the single most important factor in determining the loop operation at low powers.
Technical Paper

In-Flight Thermal Performance of the Geoscience Laser Altimeter System (GLAS) Instrument

2003-07-07
2003-01-2421
The Geoscience Laser Altimeter System (GLAS) instrument is NASA Goddard Space Flight Center's first application of Loop Heat Pipe technology that provides selectable/stable temperature levels for the lasers and other electronics over a widely varying mission environment. GLAS was successfully launched as the sole science instrument aboard the Ice, Clouds, and Land Elevation Satellite (ICESat) from Vandenberg AFB at 4:45pm PST on January 12, 2003. After SC commissioning, the LHPs started easily and have provided selectable and stable temperatures for the lasers and other electronics. This paper discusses the thermal development background and testing, along with details of early flight thermal performance data.
Technical Paper

Hydrodynamic Aspects of Capillary Pumped Loops

1996-07-01
961435
The the past, the design of a Capillary Pumped Loop involved mainly on the thermodynamics and heat transfer aspects of the system. The fluid flow dynamics of the working fluid were deemed benign to the system performance. Recently theoretical and experimental studies have revealed several mechanisms that led to the deprime of the capillary pumps. These mechanisms were all related to the dynamics of the fluid movement inside the loop.
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