Hubble Facts

National Aeronautics and

Space Administration

FS-96(04)-008-GSFC

The Hubble Space Telescope Second Servicing Mission (SM-2)

Solid State Recorder (SSR)

A state-of-the-art, Solid State Recorder (SSR) will be installed on the Hubble Space Telescope (HST) during the Second Servicing Mission (SM-2) scheduled for early 1997. This new type of digital recorder will replace one of the current, reel-to-reel recorders now in orbit. The data management system of the HST includes three tape recorders to store engineering or science data that can not be transmitted to the ground immediately.

The SSR, developed at Goddard Space Flight Center in Greenbelt, Md., is designed so that a space walking astronaut can easily replace any one of the original recorders with an SSR. This new recorder has an expected on-orbit life of at least eight years and will add to the efficiency of operations on the HST.

Why is the Solid State Recorder Better?

Unlike the 1970s-style reel-to-reel recorders, the SSR has no reels, no tape, and no moving parts to wear out and limit lifetime. Data is digitally stored in computer-like memory chips until HST's operators at Goddard Space Flight Center command the SSR to play it back.

Although the SSR is about the same size as a reel-to-reel recorder, it can store over ten times as much data. The Solid State Recorder stores 12 gigabits of data, while the tape recorder it replaces can store only 1.2 gigabits.

The Solid State Recorder provides much more flexibility than a reel-to-reel recorder. A tape recorder must first record data and then be commanded to play back that data. The SSR can simultaneously record and playback different data records. Similar to watching one program on your TV while at the same time, recording another on your VCR. Thus, one Solid State Recorder can perform the functions of two separate mechanical recorders.

Reel-to-reel tape recorders can fall victim to single-point failures, such as a break in the tape. But the Solid State Recorder is designed to grow old gracefully, compensating for situations such as a bad chip or a bad module. If the failure is too difficult to correct, HST operators can tell the Solid State Recorder to stop using that area. The SSR will then skip around the bad memory area and not store data in that location.

What is the SSR memory?

There are two memory units in the SSR. Each unit is a microelectronics device with 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 failure in a chip, a single row of the chips can be skipped over leaving the rest of memory fully functional.

Why does the HST need recorders?

HST communicates with the ground through NASA's Tracking and Data Relay Satellite System (TDRSS). The engineering information from the spacecraft systems and the science data from the astronomical instruments can either be sent directly to the Space Telescope Operations Control Center at the Goddard Space Flight Center or recorded and played back at a later time.

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 HST. 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 SSR with its larger capacity and flexibility exclusively for science data storage. This will accommodate the higher data rates from the new instruments and promote greater efficiency in operations.

SSR CHARACTERISTICS

Size 12x9x7 in (30x23x18 cm)

Weight 25 lb (11.3 kg)

For additional Information contact:

Tammy Jones

Goddard Space Flight Center

Office of Public Affairs

(301) 286-5566

Internet: http://www.gsfc.nasa.gov