12–14 Oct 2021
on-line
Europe/Amsterdam timezone

Design and Development of the SXI Thermal Balance Test

14 Oct 2021, 12:00
30m
on-line

on-line

thermal testing Thermal Testing

Speaker

Mr Nicholas Eaton (Space Acoustics GmbH)

Description

Design and Development of the SXI Thermal Balance Test

Nicholas Eaton *† (Space Acoustics, SXI Thermal Lead
Andrew Cheney †† (Space Research Centre, University of Leicester), SXI Systems Engineer
Steve Sembay †† (Space Research Centre, University of Leicester), SXI Principal Investigator
* Speaker, † Author, †† Co-author

The Soft X-ray Imager, or SXI, is one of four instrument and experiment packages on the SMILE spacecraft. SMILE is a joint ESA/CAS science mission due for launch in 2024. SXI is a wide-field lobster-eye telescope using micropore optics to spectrally map the location, shape, and motion of Earth's magnetospheric boundaries, including the bow shock, magnetopause, and cusps, by observing emission from the solar wind charge exchange process.
The SXI Telescope is equipped with two large X-ray-sensitive CCD detectors – located in the optical bench behind the radiator – covering the 0.2 keV to 2.5 keV energy band, and has an optic field of view spanning 15.5° × 26°. SXI is developed, built, and calibrated at the University of Leicester (UoL), UK, with contributions from institutions throughout Europe. The University of Leicester lead the design and manufacturing of the complete thermal test GSE. Space Acoustics are part of the Swiss consortium which provides the radiator thermal subsystem, MLI design and instrument thermal lead. The UK Space Agency (UKSA) funded the SXI MLI, thermal testing and elaborate thermal test GSE, partly in response to technical/programmatic and travel challenges from the pandemic. ESA TEC-MTV team have been very active in supporting the SXI thermal engineering since 2017 and made significant contributions to the STM test engineering.
SXI detectors operate at around -115°C and are cooled by a large space-facing radiator which is part of the Telescope, the other side of the SXI is sun exposed. A passive thermal control system with heaters keeps the CCDs near the optimum operating temperature to mitigate against the effects of radiation damage and maintains the detectors above their survival temperature limit. SXI operates in a highly elliptical Earth orbit, a heavy shutter covers the detectors to protect from radiation during passage through the Van Allen belts. Stable temperature conditions throughout the long observations phases is required. The thermal design of the SXI is quite challenging, achieving the low and stable detector temperatures within the constraints of the mechanical design, SC installation and mission parameters. The thermal engineering of SXI began in 2017, a key stage is the STM thermal test which began preparation in 2020, the test started in August 2021 in the 2.2 m diameter x 2.2 m length thermal vacuum chamber at Airbus in Stevenage.
The subject of this presentation is the design, development and operation of the thermal test hardware for the SXI STM thermal balance test. The challenges of the test were mainly driven by the requirement to validate the thermal analysis model in a range of mission relevant conditions and to reproduce the thermal boundaries and orbit conditions as accurately as possible. The pandemic restricted on-site access to the test to a few days for set up, the test operation needed to be performed remotely from Leicester. The design and development of this complex real-time remote control and monitoring for both SXI Instrument and Thermal Test GSE thermal control, utilising conventional heaters and sensors was part of the test development work and is explored in the presentation.
The STM thermal balance test is performed in a large chamber with LN2-filled shroud covering most of the internal surface. The UL-manufactured and designed GSE provides the thermal boundaries, comprising a baseplate and detailed representation of the platform module equipment with all surfaces temperature-controlled to reproduce the interface temperatures and radiative conditions of space hot/cold operational, cold survival and transient phases. Sun-side thermal loading is provided by a heater enclosure. The SXI Instrument STM comprises a comprehensive replica of the flight Telescope, mass/thermal dummy electronics units and flight-representative harnesses. The platform module and GSE is well-insulated with MLI to limit the heat leak into the chamber and parasitic heat incident on the radiator surfaces. Detailed analyses of the test setup were used to support the GSE design, and will be described in the presentation.
A criterion was to achieve very similar temperatures for all parts of the SXI in the test to the predicted in-orbit cases, and in-orbit analyses were compared with models of the test setup, which were improved iteratively. The SXI thermal control system, using both nominal and redundant operational and survival heater patches on the large radiator, will be operated during the test and the data used to verify sizing. A high density of temperature sensors is used to support an accurate model correlation, their placement was optimised with the thermal models. Some components were unavailable for the test, in this case accurate dummies were designed and produced, using representative materials, geometries and surface coatings. All harnesses were present and exactly reproduce the current flight hardware designs.
The test set up was developed with the possibility to re-use for the PFM tests, the wide range of thermal cycling and accurate thermal balance conditions achievable with this equipment will be of value in the qualification of the flight unit and the experience gained in operating and evaluating the STM test should provide an improved and low-risk test for the PFM next year. First results from the operation of the STM test and correlation with the GSE thermal design models will be presented and initial lessons-learned discussed.

Primary authors

Mr Nicholas Eaton (Space Acoustics GmbH) Dr Steven Sembay (University of Leicester) Mr Andrew Cheney (University of Leicester)

Presentation materials