The fourth servicing mission (SM-4) for the Hubble Space Telescope (HST) offered an impressive and unprecedented set of advanced technologies that may yield the most remarkable discoveries and imaging to date of Earth, the solar system, and beyond. The mission was, according to Deputy Associate Director for the HST Development Project Frank Cepollina, “the most complicated mission – from a servicing perspective – that NASA has ever flown.”
The technology list for SM-4 included nearly 50 technologies, more than 20 of which were flown to orbit for the first time. SM-4 goals should result in a complete rejuvenation of the 18-year-old HST, enhancing its capabilities with cutting- edge instruments as well as two intricate repairs. These were achieved by many key NASA Goddard Space Flight Center (GSFC) technologies in the hands of skilled astronauts.
Making Room for Innovation
Achieving a lighter payload in order to accommodate more instruments on SM-4 was the goal behind the shuttle’s new super-lightweight interchangeable carrier (SLIC), composed in part by another new technology – Titanium Metal Matrix (TMC). Offering nearly double the carrying capacity of previous carriers, SLIC’s load included the new Wide Field Camera 3, new batteries, and other hardware and instruments weighing in excess of 3,000 pounds. Two of the six struts on SLIC are composed of TMC, which also was flown in space for the first time on SM-4.
TMC has been used on commercial and military jets and is highly valued for offering greater stiffness, resistance against fracture, and lighter weight compared with alternative materials. In fact, the replacement of regular titanium with TMC resulted in a 20% reduction in weight and a 20% increase in strength for SLIC.
Advanced Power Tool Aids Repair
Repairs of HST’s Space Telescope Imaging Spectrograph (STIS) and Advanced Camera for Surveys (ACS) are highly intricate operations. A new Mini Power Tool (MPT), developed by ATK Space Systems and Jackson & Tull, aided the repairs. The MPT is a small, self-contained, battery-powered, handheld device that can also be used as a nonpowered manual wrench. Astronauts use the MPT to apply torque to various mechanical interfaces and fasteners.
The design is highly ergonomic to maximize in-hand comfort, reduce finger fatigue, and achieve precision positioning. The design helped to ensure that the astronaut’s “down the nose” view was free of obstruction and an LED array delivered illumination, both helping to maximize worksite visibility. The MPT also delivered unprecedented motorized torque capability for its size, thanks to its custom-designed, high-performance brushless DC motor in a 1"- diameter housing. In addition, the MPT’s unique modular design simplified testing and assembly as well as onorbit troubleshooting, since problems could be isolated to individual modules.
IR Detectors for Sensitive Imaging
In addition to HST’s new Cosmic Origins Spectrograph (COS), the new Wide Field Camera 3 (WFC3) will enable a new era of discovery for HST. Compared with the previous imager, WFC3 is significantly more sensitive and boasts a much larger field of view, yielding infrared (IR) survey efficiencies 10 to 30 times greater than previously achieved. These advancements are made possible in part by new, cutting-edge Mercury-Cadmium-Telluride (HgCdTe) IR detectors. The technology is the result of a newly tailored composition of previously existing HgCdTe IR arrays to achieve a 1.7-micron wavelength cutoff.
The new composition eliminates the need for expendable cryogen or a complex mechanical refrigerator, because the detectors are able to run with very low dark current at a temperature of 145K, achievable with a passive radiator and thermoelectric cooling. The detectors are also relatively insensitive to thermal radiation from HST’s warm optics.
Testing of Relative Navigation
A new relative navigation sensor (RNS) system also was tested on SM-4, including three cameras and an avionics package to record images and estimate real-time attitude and positioning of HST relative to the shuttle during capture and deployment of the telescope. RNS’s SpaceCube technology provides an advanced, reconfigurable spaceflight processor that hosts all RNS pose, command, and data handling, as well as camera control software. Also key to RNS is GSFC’s Navigator – an autonomous, real-time, fully spaceflightqualified GPS receiver with exceptional capabilities for fast signal acquisition and weak signal tracking.
The technology gathers and forwards composite raw data, processed data, and telemetry information including inertial position and velocity, channel tracking, and estimated range from HST to the shuttle.
These technologies are just a handful of the many advances flown on SM-4. For more information about the mission technologies, visit: www.nasa.gov/mission_pages/hubble/servicing/SM4/main/index.html.