Thermal Considerations for Reducing the Cooldown and Warmup Duration of the James Webb Space Telescope OTIS Cryo-Vacuum Test

Date

2017-07-16

Journal Title

Journal ISSN

Volume Title

Publisher

47th International Conference on Environmental Systems

Abstract

The James Webb Space Telescope (JWST), set to launch in 2018, is NASA’s next-generation flagship telescope. The Optical Telescope Element (OTE) and Integrated Science Instrument Module (ISIM) contain all of the optical surfaces and instruments to capture and analyze the telescope’s infrared targets. The integrated OTE and ISIM are denoted as “OTIS”, and will be tested as a single unit in a critical thermal-vacuum test in mid-2017 at NASA Johnson Space Center’s Chamber A facility. The payload will be evaluated for workmanship and functionality in a 20K simulated flight environment during this thermal-vacuum test. However, the sheer thermal mass of the OTIS payload as well as the restrictive gradient and rate constraints placed on test components precludes rapid cooldown or warmup to its steady-state cryo-balance condition. Due to hardware safety considerations, injection of helium gas for free molecular heat transfer was also not an option. Consequently, first-cut estimations through thermal analysis predicted that transient radiative cooldown from ambient temperatures while maintaining limits and constraints would take 35 days; warmup similarly would take 30 days. The current work discusses methods to reduce transition times from the original estimate through modulation of boundary temperatures and environmental conditions. By optimizing helium shroud rates and heater usage, as well as rigorously reexamining previously imposed constraints, savings of up to three days on cooldown and more than a week on warmup can be achieved. The efficiencies gained through these methods allow the JWST thermal test team to create faster cooldown and warmup profiles, thus reducing the overall duration and cost of the test while keeping all of the required test operations.

Description

Kan Yang, NASA Goddard Space Flight Center (GSFC), USA
Stuart Glazer, NASA Goddard Space Flight Center (GSFC), USA
Wes Ousley, Genesis Engineering Solutions, Inc., USA
William Burt, Genesis Engineering Solutions, Inc., USA
ICES108: Thermal Control of Cryogenic Instruments and Optical Systems
The 47th International Conference on Environmental Systems was held in South Carolina, USA on 16 July 2017 through 20 July 2017.

Keywords

james webb space telescope, JWST, cryo-vacuum testing, OTIS, ISIM, thermal testing

Citation