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STS-103

STS-103 (Space)

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STS-103 was a Hubble Space Telescope servicing mission by Space Shuttle (8 pics) Discovery. The mission launched from Kennedy Space Center, Florida, on dec. 19, 1999 (20 years ago).

Mission highlights

The primary objective of STS-103 was the Hubble Servicing Mission 3A. STS-103 had four scheduled Extravehicular Activity (EVA) days where four crew members will work in pairs on alternating days to renew and refurbish the telescope.

NASA officials decided to move up part of the servicing mission that had been scheduled for Jun. 2000 (19 years ago) after three of the telescope's six gyroscopes failed. Three gyroscopes must be working to meet the telescope's very precise pointing requirements, and the telescope's flight rules dictated that NASA consider a "call-up" mission before a fourth gyroscope failed. Four new gyros were installed during the first servicing mission (STS-61) in dec. of 1993 (26 years ago) and all six gyros were working during the second servicing mission (STS-82) in Feb. 1997 (22 years ago). Since then, a gyro failed in 1997 (22 years ago), another in 1998 (21 years ago) and a third in 1999 (20 years ago). The Hubble team believes they understand the cause of the failures, although they cannot be certain until the gyros are returned from space. Having fewer than three working gyroscopes would preclude science observations, although the telescope would remain safely in orbit until a servicing crew arrived.

In addition to replacing all six gyroscopes on the dec. flight, the crew will replace a guidance sensor, the spacecraft's computer and install a voltage/temperature kit for the spacecraft's batteries. A new transmitter, solid state recorder and thermal insulation blankets will also be installed.

Hubble's gyros spin at a constant rate of 19,200 rpm on gas bearings. This wheel is mounted in a sealed cylinder, which floats in a thick fluid. Electricity is carried to the motor by thin wires (approximately the size of a human hair). It is believed that oxygen in the pressurized air used during the assembly process caused the wires to corrode and break. The new gyros were assembled using nitrogen instead of oxygen. Each gyroscope is packaged in a Rate Sensor assembly. The Rate Sensors are packaged in pairs into an assembly called a Rate Sensor Unit (RSU's). It is the RSU's that the STS-103's astronauts will be changing. The RSU's each weigh 24.3 pounds (11.0 kg) and are 12.8 by 10.5 by 8.9 inches (325 by 267 by 226 mm) in size.

In addition to replacing all six gyroscopes on the dec. flight, the crew will replace a Fine Guidance Sensor (FGS) and the spacecraft's computer. The new computer will reduce the burden of flight software maintenance and significantly lower costs. The new computer is 20 times faster and has six times the memory of the current DF-224 computer used on Hubble. It weighs 70.5 pounds (32.0 kg) and is 18.8 by 18 by 13 inches (478 by 457 by 330 mm) in size. The FGS being installed is a refurbished unit that was returned from Servicing Mission 2. It weighs 478 pounds (217 kg) and is 5.5 by 4 by 2 feet (1.68 by 1.22 by 0.61 m) in size.

A voltage/temperature improvement kit (VIK) will be also be installed to protect spacecraft batteries from overcharging and overheating when the spacecraft goes into safe mode. The VIK modifies the charge cutoff voltage to a lower level to prevent battery overcharging and associated overheating. The VIK weighs about 3 pounds (1.4 kg).

The repair mission will also install a new S-Band Single Access Transmitter (SSAT). Hubble has two identical SSATs onboard and can operate with only one. The SSATs send data from Hubble through NASA's Tracking Data Relay Satellite System (TDRSS) to the ground. The new transmitter will replace one that failed in 1998 (21 years ago). The SSAT weighs 8.5 pounds (3.9 kg) and is 14 by 8 by 2¾ inches (356 by 203 by 70 mm).

A spare solid state recorder will also be installed to allow efficient handling of high-volume data. Prior to the second servicing mission, Hubble used three 1970 (49 years ago) style reel-to-reel tape recorders. During the second servicing mission one of these mechanical recorders was replaced with a digital solid state recorder. During this mission a second mechanical recorder will be replaced by a second Solid State Recorder. The new recorder can hold approximately 10 times as much data as the old unit (12 gigabytes instead of 1.2 gigabytes). The recorder weighs 25 pounds (11.3 kg) and is 12 by 9 by 7 inches in size.

Finally, the EVA crew will replace the telescopes outer insulation that has degraded. The insulation is necessary to control the internal temperature on the Hubble. The New Outer Blanket Layer (NOBL) and Shell/Shield Replacement Fabric (SSRF) will help protect Hubble from the harsh environment of space. It protects the telescope from the severe and rapid temperature changes it experiences during each 90 minute orbit as it moves from sunlight to darkness.

STS-103 will also carry hundreds of thousands of student signatures as part of the Student Signatures in Space (S3) program. The unique project provides elementary schools (selected on a rotating basis) with special posters to be autographed by students, then scanned onto disks and carried aboard a NASA Space Shuttle (8 pics) mission.

On STS-103, the shuttle Discovery reached the highest orbit ever flown in the program's history, at the apogee of 609 kilometers (378 miles) above Earth.

Crew

Commander: Curtis L. Brown (Sixth spaceflight)
Pilot: Scott J. Kelly (First spaceflight)
Mission Specialist 1: Steven L. Smith (Third spaceflight)
Mission Specialist 2: Jean-François Clervoy, ESA (Third spaceflight)
Mission Specialist 3: John M. Grunsfeld (Third spaceflight)
Mission Specialist 4: C. Michael Foale (Fifth spaceflight)
Mission Specialist 5: Claude Nicollier, ESA (Fourth spaceflight)


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