Space Cryogenics: The ECOSTRESS Instrument After Four Years in Space

ECOSTRESS_NASAThe ECOSystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) instrument is a multispectral thermal infrared imaging radiometer, and its primary mission is to investigate and understand how climate change affects water and carbon usage on Earth.[1] The instrument measures the surface temperature of Earth with a resolution that is able to capture individual farm fields.[2] The data collected by ECOSTRESS is processed into a product called the Evaporative Stress Index, which indicates whether plants are stressed and if a drought is likely to occur.[2] 

In early July 2022, ECOSTRESS will have operated for four years in space. Launched on June 29, 2018, and originally scheduled for a one-year science mission, its mission has been extended multiple times, with the current planned end of operations scheduled for September 2023. The instrument was transported to the International Space Station (ISS) as unpressurized cargo aboard a SpaceX Falcon 9 rocket that launched from Cape Canaveral Air Force Station Space Launch Complex 40. On July 2, 2018, the spacecraft successfully arrived and docked at the ISS, and on July 5, ECOSTRESS was extracted from the cargo trunk and installed on the Japanese Experiment Module- External Facility (JEM-EF) by robotic arm. The following day, the instrument was successfully powered on and officially began its science mission.
The ECOSTRESS instrument is housed in a six-sided box roughly two meters by one meter by one meter. The nadir panel of the box has a baffle opening that is roughly one meter by 0.25 meters. A scan mirror continuously rotating at approximately 0.423 Hz in- side the enclosure allows for the focal plane array (FPA) to cyclically see the temperature of two different blackbody targets within the enclosure as well as the earth. The instrument electronics boxes populate one of the two meters by one-meter side panels of the enclosure, and one of the enclosure ends is comprised of the payload interface unit. This interface unit is Government Furnished Equipment that is like an umbilical cord for the instrument and used to make the electrical, thermal and mechanical connections to the JEM-EF module.
The thermal control system of ECOSTRESS consists of a combination of active and passive components to maintain the instrument temperatures within the allowable limits. The FPA detector is maintained at 65 K by two Thales Cryogenics LPT9310-HP cryocoolers[3] and is surrounded by a cold shield that operates at 130 K and is cooled by a single LPT9310-HP cooler. The waste heat generated by the three cryocoolers, electron- ics and one of the blackbody targets is removed by non-planar cold plates and tube-on plate heat exchangers.[4] The heat is then transported by a single-phase circulating fluid loop in the JEM-EF module to radiators external to the space station. In fact, requirements were in place to limit the radiative heat exchange between the instrument and its surroundings. This limitation on radiative heat transfer out of the instrument made compliance with the JEM-EF pumped fluid loop requirements for pressure drop and outlet fluid temperature with a given minimum specified mass flow rate one of the key thermal design drivers of ECOSTRESS.[1] The fluid loop requirements, together with the limited available electrical power for the cryocoolers, led to the development of high-efficiency cryocoolers[3] as well as high-efficiency non-planar heat exchangers.[4]
The Thales Cryogenics commercial off-the-shelf (COTS) LPT9310 flight-qualfied cryocooler is optimized for operation at 80 K, and its power consumption to pro- vide cooling to the ECOSTRESS FPA at 65 K was prohibitively large; so Thales developed a high-performance version of their LPT9310 that was optimized for 60 K and preserved the form, fit and flight qualified elements of the COTS LPT9310.[3] In addition, the surfaces of the LPT9310 coolers from which heat needs to be rejected are curved, making effective and efficient heat removal challenging. Meeting the JEM-EF fluid loop requirements for pressure drop required highly optimized, custom designed non-planar heat exchangers to effectively remove the heat of the cryo- coolers.[4] 

The instrument is approaching four years of operation in space, with its over- all thermal performance as predicted and no changes to cryocooler performance. To date, all three cryocoolers have accumulated over 32,000 operating hours. On the 210th day after the initial power-on, a fault condition was detected, and the instrument put itself into standby mode with the coolers off. [1] On the 258th day, the instrument went through a planned power cycle for firmware updates that left the coolers off for 45 days. [1] The coolers have since undergone eleven additional short duration power cycles to date. The heat rejection system, including the custom cryocooler heat exchangers, has performed as expected by maintaining all components within their allowable flight temperatures while meeting the fluid loop requirements for pressure drop and outlet fluid temperature. 

The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). ©2022. California Institute of Technology. Government sponsor- ship acknowledged. 

[1] Cha, J., et al. (2020). Thermal Design and On- orbit Performance of the ECOSTRESS Instrument. IOP Conference Series: Materials Science and Engineering. Vol. 755. No. 1. IOP Publishing. 
[3] Arts, R., et al. (2016). LPT9310 COTS cooler for ECOSTRESS. International Cryocooler Conference. 
[4] Cha, Jeff, Brian Carroll, and Memo Romero. (2017) Heat Rejection System for Thermal Management in Space Using Non-planar Liquid Cooled Cold Plates. 47th International Conference on Environmental Systems.

Image: ECOSTRESS attaching to the ISS. Credit: NASA

[Originally published in Cold Facts Vol. 38, Num. 3, Space Cryogenics Column]

Share this post:

Comments on "Space Cryogenics: The ECOSTRESS Instrument After Four Years in Space"

Comments 0-5 of 0

Please login to comment