Hubble Space Telescope Servicing Mission Research Articles

THE COSMIC ORIGINS SPECTROGRAPH

The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph with unprecedented sensitivity that was installed into the Hubble Space Telescope (HST) in May 2009, during HST Servicing Mission 4 (STS-125). We present the design philosophy and summarize the key characteristics of the instrument that will be of interest to potential observers. For faint targets, with flux F_lambda ~ 1.0E10-14 ergs/s/cm2/Angstrom, COS can achieve comparable signal to noise (when compared to STIS echelle modes) in 1-2% of the observing time. This has led to a significant increase in the total data volume and data quality available to the community. For example, in the first 20 months of science operation (September 2009 - June 2011) the cumulative redshift pathlength of extragalactic sight lines sampled by COS is 9 times that sampled at moderate resolution in 19 previous years of Hubble observations. COS programs have observed 214 distinct lines of sight suitable for study of the intergalactic medium as of June 2011. COS has measured, for the first time with high reliability, broad Lya absorbers and Ne VIII in the intergalactic medium, and observed the HeII reionization epoch along multiple sightlines. COS has detected the first CO emission and absorption in the UV spectra of low-mass circumstellar disks at the epoch of giant planet formation, and detected multiple ionization states of metals in extra-solar planetary atmospheres. In the coming years, COS will continue its census of intergalactic gas, probe galactic and cosmic structure, and explore physics in our solar system and Galaxy.

A GPS Receiver for High-Altitude Satellite Navigation

Although GPS has found wide application for precision spacecraft navigation and formation flying applications in low Earth orbit (LEO), its application to geosynchronous (GEO) and other high-altitude missions has been limited to an experimental role because of the sparsity and weakness of the GPS signals present there. To fill this gap, NASA Goddard Space Flight Center (GSFC) has developed a new space-borne GPS receiver called Navigator that can operate effectively in the full range of Earth orbiting missions from LEO to GEO and beyond. Navigator employs special signal processing algorithms in radiation-hardened hardware that enable very fast signal acquisition capabilities and, more importantly, greatly improved sensitivity (a 10-dB improvement over previous space-based GPS receivers). Because of these unique capabilities, Navigator has generated a large amount of interest in the spacecraft navigation community. The first flight version of the receiver has been integrated into a relative-navigation experiment on the Shuttle-based Hubble Space Telescope Servicing Mission 4, due to launch in 2009. Navigator will be also serving as a critical navigation sensor on NASA's Magnetospheric Multiscale mission, which is one of NASA's first high-altitude formation-flying missions, NASA's Global Precipitation Measurement mission, and the Air Force Research Lab's Plug-and-Play spacecraft. Finally, key aspects of the Navigator design are being integrated into a GPS receiver being developed for NASA's Orion Crew Exploration Vehicle.

The cosmic origins spectrograph: capabilities and prelaunch performance

The Cosmic Origins Spectrograph (COS) is an ultraviolet spectrograph scheduled for installation in the Hubble Space Telescope (HST) during HST Servicing Mission 4, currently planned to occur in August 2008. COS was designed to maximize sensitivity to faint point sources, and will provide limiting sensitivities at moderate spectral resolutions (R∼20,000) that are a factor of 2 to >10 times better than those provided by previous ultraviolet spectrographs on HST. Here, we present an overview of the some of the science areas that will be addressed by COS observations and provide a summary of the capabilities of COS and the expected on-orbit performance.

Infrared detectors for WFC3 on the Hubble Space Telescope

Rockwell Scientific Company is developing a new type of HgCdTe 1K 1K detector, called WFC3-1R, with cutoff wavelength at 1.7 m and 150K operating temperature. The detector will be installed on the Wide Field Camera 3, the fourth generation panchromatic instrument for the Hubble Space Telescope (HST) to be installed during HST Servicing Mission 4, currently scheduled for 2004. The detector uses HgCdTe MBE grown on a CdZnTe substrate and a new type of multiplexer, the Hawaii-1R MUX. Six lots of detectors have been produced so far, and have demonstrated the capability to meet or exceed the project requirements. In particular, detectors show quantum efficiency as high as ~90% at =1.4-1.6 m and greater than 50% at >1.0 m, readout noise of 30 e- rms with double correlated sampling, and dark current <0.2 e/s/pix at 150K. We illustrate the behavior of the reference pixels, showing that they allow the compensation of drifts in the dc output level. A number of detectors show a peculiar instability related to the variations of diode polarization, still under investigation. We also report on the environmental testing needed to qualify the WFC3- 1R detectors as suitable for flight on the HST. We finally provide an update of the project status.

Environmental Exposure Conditions for Teflon® Fluorinated Ethylene Propylene on the Hubble Space Telescope

The outer layer of Teflon® fluorinated ethylene propylene (FEP) multi-layer insulation (MLI) on the Hubble Space Telescope (HST) was observed to be significantly cracked at the time of the Second HST Servicing Mission (SM2), 6.8 years after HST was launched into low Earth orbit (LEO). Comparatively minor embrittlement and cracking were also observed in the FEP materials retrieved from solar-facing surfaces on the HST at the time of the First Servicing Mission (3.6 years exposure). After SM2, a failure review board was convened to address the problem of degradation of MLI on the HST. In order for this board to determine possible degradation mechanisms, it was necessary to consider all environmental constituents to which the FEP MLI surfaces were exposed. Based on measurements and various models, the environmental exposure conditions for the FEP surfaces on the HST were estimated, including: the number and temperature ranges of thermal cycles; equivalent sun hours; fluence and absorbed radiation dose of x-rays, trapped protons and electrons and plasma electrons and protons; and atomic oxygen (AO) fluence. This paper presents the environmental exposure conditions for FEP on the HST, briefly describing the possible roles of the environmental factors in the observed FEP embrittlement and providing references to the published works which describe in detail testing and analysis related to FEP degradation on the HST.