By John McHale
GREENBELT, Md. - NASA Astronauts improved the Hubble Space Telescope`s electronic data storage capability during their recent maintenance mission by installing a solid state data recorder, which provides more flexibility and stores more memory than the craft`s current recorders.
The solid-state recorder replaces one of Hubble`s three older reel-to-reel data recorders. The new device was developed at the National Aeronautics and Space Administration Goddard Space Flight Center in Greenbelt, Md., with engineers from the Litton Systems Inc. Amecom Division in College Park, Md.
The new recorder is smaller, lighter, and provides greater flexibility and reliability than the magnetic recorder it replaces, and can store 10 times more data. The solid-state recorder stores 12 gigabits of data, while the tape recorder it replaces can store only 1.2 gigabits.
It also contains a MIPS R3000 RISC microprocessor, and uses a MIL-STD 1773 fiber optic serial data bus, says David Scheve, observatory development manager at Goddard. Hubble engineers used a 1 megabit-per-second fiber optic 1773 data bus because it has a stronger immunity to radiation-induced electromagnetic interference than its copper-based MIL-STD 1553 counterpart, he says.
Unlike its predecessors, the new data recorder has no reels, no tape, and no other moving parts to wear out. Data stores digitally in memory chips until Hubble`s operators at Goddard command the recorder to play it back.
There are two memory units in the new recorder. Each unit has 16-megabit chips stacked ten to a stack with two stacks in a package and six packages in an array. There are three arrays in a group. In the event of a chip failure, a single row of the chips can be skipped, leaving the rest of memory functional.
The recorder can simultaneously record and play back different data streams. It is similar to watching one program on TV while at the same time, recording another on a VCR, say NASA officials. Thus, one solid state recorder can perform the functions of two separate reel-to-reel recorders.
Hubble communicates with the ground through NASA`s Tracking and Data Relay Satellite System (TDRSS). The engineering information from spacecraft systems and the science data from the astronomical instruments can either be sent directly to the Space Telescope Operations Control Center at Goddard or recorded and played back later.
Data is recorded if a TDRSS link is not available for scheduling or if one of the TDRSS satellites is not within range of the Hubble. The current operations procedure is to record all science data to ensure continuity and safeguard against any possible loss of unique information.
Post-servicing mission plans are to use the recorder exclusively to store science data, according to a NASA statement. This will accommodate higher data rates from new instruments and promote greater efficiency in operations than the older Hubble recorders.
The new recorder has an expected on-orbit life of at least eight years.
Plans call for one of the other two tape recorders to be replaced, but with a spare reel-to-reel unit. If one of the other tape recorders fail, future servicing missions may replace it with a solid state device. "If it ain`t broke we won`t fix it," Scheve says.
The Hubble Space Telescope, pictured above, has a highly reliable mass-storage system with the recent addition of solid-state memory.
