Melora Larson

NGST MIRI instrument

The MIRI is the mid-IR (5-28μm) instrument for NGST and provides for imaging, cororographic, high- and low-resolution spectroscopic capabilities. Unlike to the other instruments on NGST, the MIRI must be cooled - to reduce the thermal background from the optics and because the detectors require an operating temperature of about 7k.. In this paper we summarise the science goals, the proposed overall opto-mechanical concept, the thermal design aspects, the detectors and the expected sensitivity of the instrument.

Thermal and contamination control of the mid-infrared instrument for JWST

The Mid-Infrared Instrument (MIRI) is the coldest and longest wavelength (5-28 micron) science instrument on-board the James Webb Space Telescope observatory and provides imaging, coronography and high and low resolution spectroscopy. The MIRI thermal design is driven by a requirement to cool the detectors to a temperature below 7.1 Kelvin. The MIRI Optics Module (OM) is accommodated within the JWST Integrated Science Instrument Module (ISIM) which is passively cooled to between 32 and 40 K. Thermal isolation between the OM and the ISIM is therefore required, with active cooling of the OM provided by a dedicated cryostat, the MIRI Dewar. Heat transfer to the Dewar must be minimised to achieve the five year mission life with an acceptable system mass. Stringent cleanliness levels are necessary in order to maintain the optical throughput and the performance of thermal control surfaces. The ISIM (and MIRI OM) is launched warm, therefore care must be taken during the on-orbit cooldown phase, when outgassing of water and other contaminants is anticipated from composite structures within the ISIM. Given the strong link between surface temperature and contamination levels, it is essential that the MIRI thermal and contamination control philosophies are developed concurrently.

Tλ depression in 4He by a heat current along the λ-line

Abstract We report measurements of the depression of the superfluid transition temperature by a heat current ( 1⩽Q⩽100 μW / cm 2 ) along the λ -line (SVP⩽ P ⩽21.6xa0bar). Experimental data can be represented by Δ T λ / T λ =( Q / Q 0 ) x . The exponent, x , is universal and pressure independent as expected, but its value (about 0.9) is higher than the theoretical prediction (0.745) and the earlier experimental value (0.813) at SVP. The amplitude, Q 0 , shows a pressure dependence that is in qualitative agreement with the theoretical prediction, but its value is lower than the predicted and earlier experimental values at SVP. At P =21.6 bar, measurements were also performed in a reduced effective gravity (0.2 g ), and these results show that the gravity effect in our measurements is small.

Use of Model Payload for Europa Mission development IEEE aerospace conference

During the long early development of the Europa Mission concept, the team used a hypothetical, straw-man payload, called the Model Payload, to assist in the development of a complete mission design. The Model Payload comprised a suite of science instruments, and was structured to meet the science objectives of the mission. The science objectives were defined in terms of a set of specific physical measurements that would need to be made, including quality attributes such as resolution, accuracy, coverage, etc. The Model Payload was designed to acquire these data with the required attributes. A set of notional instruments was chosen to be able to meet the full set of science objectives. Each notional instrument was based on current capabilities and technologies of actual, similar instruments, and modeled with enough detail to be able to estimate aspects of the instrument such as power usage, pointing stability needs, thermal accommodation needs, etc. This paper discusses the basis for the Model Payload and how it was used to develop the mission design, observation and data acquisition strategy, needed spacecraft capabilities, spacecraft-payload interface needs, mission system requirements, and operational scenarios. Then we present a comparison of the Model Payload to the actual payload, recently selected by NASA for the proposed Europa Mission. The focus is on how well this process enveloped and constrained the design space and guided the development and analysis of not only instrument requirements, but also those of the flight system and the mission operations system. Specifically, we discuss those areas in which the Selected Payload drove the mission design and which areas remained unchanged. Lastly, we present lessons learned from the use of a Model Payload.

James Webb Space Telescope Mid-Infrared Instrument cooler systems engineering

On the James Webb Space Telescope (JWST), the Mid-Infrared Instrument (MIRI) is unique among the four science instruments in that it operates around 7K as opposed to 40K like the other three near infrared instruments. Remote cooling of the MIRI is achieved through the use of a Joule-Thomson (J-T) Cooler, which is precooled by a multistage Pulse Tube Cooler. The MIRI Cooler systems engineering is elaborate because the Cooler spans a multitude of regions in the observatory that are thermally and mechanically unique with interfaces that encompass a number of different organizations. This paper will discuss how a significant change to the MIRI Cooling System from a solid hydrogen Dewar to a Cooler was achieved after the instrument Preliminary Design Review (PDR), and it will examine any system compromises or impacts that resulted from this change so late in the instrument design. A general overview of the Dewar and the Cooler systems management, the roles of the systems teams in the different organizations, how the requirements are managed in such an elaborate environment, and the distinct design and Integration and Test (I&T) challenges will also be provided.

The reconfiguration of the low temperature microgravity physics facility

The Jet Propulsion Laboratory (JPL) is building the Low Temperature Microgravity Physics Facility (LTMPF) as a multi-user research facility for the International Space Station.

FUNDAMENTAL PHYSICS ON THE JEM-EF: THE Low TEMPERATURE MICROGRAVITY PHYSICS EXPERIMENTS FACILITY

The Low Temperature Microgravity Physics Experiments Facility (LTMPEF) takes advantage of the long-duration microgravity environment provided by the International Space Station and the payload accommodation of the Japanese Experiment Modules Exposed Facility (JEM-EF) to provide a NASA facility for fundamental physics research. Environmental factors influencing the quality of the experiments such as the vibration created within and by the Space Station, the charged-particle environment in low-Earth orbit, and the EMI environment will be discussed. Descriptions of the approved and candidate experiments will be presented as part of this presentation.

SIRTF telescope test facility: the first year

The SIRTF Telescope Test Facility (STTF) consists of an optical dewar for testing mirrors of up to 1m diameter and f < 6 at temperatures from 300K to 5K and a phase shift interferometer for optical characterization. The STTF was brought on-line in early 1995. The STTF was initially used to cool a 50cm diameter beryllium mirror that had been previously tested at NASA Ames Research Center. The initial tests validated the performance of the STTF by proving that the STTF could cool a mirror to 5K and achieve high quality optical data on the mirror, consistent with the previous results achieved at NASA Ames. The STTF has also been used to provide cryogenic optical testing of the ultra- lightweight 85cm diameter beryllium primary mirror assembly for the Infrared Telescope Technology Testbed (ITTT). Currently the facility is preparing for testing the complete ITTT. Also, the long wavelength photon background in the facility will be measured and characterized in 1996.

SIRTF telescope test facility

In this paper we describe the key features of the SIRTF Telescope Test Facility developed at the Jet Propulsion Laboratory. Information on the cryogenic performance including details of the test cycle time and cryogen hold time are included. Emphasis is on the operation of the facility. Data are presented on the cryogenic optical testing of the ultra-lightweight 85 cm diameter beryllium primary mirror assembly for the infrared telescope technology testbed.