||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (October 2010)|
Astronauts Steven Smith and John Grunsfeld replacing rate sensor units
|Mission type||HST servicing|
|Mission duration||7 days, 23 hours, 11 minutes 34 seconds|
|Distance travelled||5,230,000 kilometres (3,250,000 mi)|
|Spacecraft||Space Shuttle Discovery|
|Launch mass||112,493 kilograms (248,000 lb)|
|Landing mass||95,768 kilograms (211,130 lb)|
|Members||Curtis L. Brown, Jr.
Scott J. Kelly
Steven L. Smith
John M. Grunsfeld
C. Michael Foale
|EVA duration||24 hours, 33 minutes|
|Start of mission|
|Launch date||20 December 1999 00:50:00UTC|
|Launch site||Kennedy LC-39A|
|End of mission|
|Landing date||28 December 1999 00:01:34UTC|
|Landing site||Kennedy SLF Runway 33|
|Perigee||563 kilometres (350 mi)|
|Apogee||609 kilometres (378 mi)|
|Capture of Hubble|
|RMS capture||22 December 1999, 00:34 UTC|
|RMS release||25 December 1999, 11:03 UTC|
Left to right; C. Michael Foale, Claude Nicollier, Scott J. Kelly, Curtis L. Brown, Jr., Jean-Francois Clervoy, John M. Grunsfeld and Steven L. Smith
|Commander||Curtis L. Brown, Jr.
|Pilot||Scott J. Kelly
|Mission Specialist 1||Steven L. Smith
|Mission Specialist 2||Jean-François Clervoy, ESA
|Mission Specialist 3||John M. Grunsfeld
|Mission Specialist 4||C. Michael Foale
|Mission Specialist 5||Claude Nicollier, ESA
Space walks 
- Smith and Grunsfeld – EVA 1
- EVA 1 start: 22 December 1999 – 18:54 UTC
- EVA 1 end: 23 December 1999 – 03:09 UTC
- Duration: 8 hours, 15 minutes
- Foale and Nicollier – EVA 2
- EVA 2 start: 23 December 1999 – 19:06 UTC
- EVA 2 end: 24 December 1999 – 03:16 UTC
- Duration: 8 hours, 10 minutes
- Smith and Grunsfeld – EVA 3
- EVA 3 start: 24 December 1999 – 19:17 UTC
- EVA 3 end: 25 December 1999 – 03:25 UTC
- Duration: 8 hours, 08 minutes
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 worked 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 June 2000 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 December 1993 and all six gyros were working during the second servicing mission (STS-82) in February 1997. Since then, a gyro failed in 1997, another in 1998 and a third in 1999. The Hubble team believed they understood the cause of the failures, although they could not be certain until the gyros were returned from space. Having fewer than three working gyroscopes would have precluded science observations, although the telescope would have remained safely in orbit until a servicing crew arrived.
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). It is the RSUs that the STS-103's astronauts changed. The RSUs each weigh 11.0 kilograms (24 lb) 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 December flight, the crew replaced a Fine Guidance Sensor (FGS) and the spacecraft's computer. The new computer reduced the burden of flight software maintenance and significantly lowered costs. The new computer was 20 times faster and had six times the memory of the DF-224 computer previously used on Hubble. It weighs 32.0 kilograms (71 lb) and is 18.8 by 18 by 13 inches (478 by 457 by 330 mm) in size. The FGS installed was a refurbished unit that was returned from Servicing Mission 2. It weighs 217 kilograms (480 lb) 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) was also 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 1.4 kilograms (3.1 lb).
The repair mission also installed 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 replaced one that failed in 1998. The SSAT weighs 3.9 kilograms (8.6 lb) and is 14 by 8 by 2¾ inches (356 by 203 by 70 mm).
A spare solid state recorder was also installed to allow efficient handling of high-volume data. Prior to the second servicing mission, Hubble used three 1970s-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 was replaced by a second Solid State Recorder. The new recorder could hold approximately 10 times as much data as the old unit (12 gigabytes instead of 1.2 gigabytes). The recorder weighs 11.3 kilograms (25 lb) and is 12 by 9 by 7 inches in size.
Finally, the EVA crew replaced the telescope's outer insulation that had 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) 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 also carried hundreds of thousands of student signatures as part of the Student Signatures in Space (S3) program. The unique project provided 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 mission.
On STS-103, Discovery reached the highest orbit ever flown in the program's history, at the apogee of 609 kilometers (378 mi) above Earth. It was the Discovery's last solo spaceflight. All later missions by Discovery were International Space Station missions.
Astronaut John Grunsfeld, who was one of the mission specialists on this mission, brought a "Planet Mars Flag" aboard Discovery.
|Attempt||Planned||Result||Turnaround||Reason||Decision point||Weather go (%)||Notes|
|1||6 Dec 1999, 2:37:00 am||Scrubbed||---||Technical||Additional wiring inspection|
|2||16 Dec 1999, 9:18:00 pm||Scrubbed||10 days, 18 hours, 41 minutes||Technical||Concern about fuel line welds|
|3||18 Dec 1999, 8:21:00 pm||Scrubbed||1 day, 23 hours, 3 minutes||Weather|
|4||19 Dec 1999, 7:50:00 pm||Success||0 days, 23 hours, 29 minutes||60%|
Wake-up calls 
NASA began a tradition of playing music to astronauts during the Gemini program, which was first used to wake up a flight crew during Apollo 15. Each track is specially chosen, often by their families, and usually has a special meaning to an individual member of the crew, or is applicable to their daily activities.
|Day 2||"Takin' Care of Business"||Bachman–Turner Overdrive||wav[dead link] mp3[dead link]
|Day 3||"Rendezvous"||Bruce Springsteen||wav[dead link] mp3[dead link]
|Day 4||"Hucklebuck"||Beau Jocque and the Zydeco Hi-Rollers||wav[dead link] mp3[dead link]
|Day 6||"Magic Carpet Ride"||Steppenwolf||wav[dead link] mp3[dead link]
|Day 7||"I'll Be Home for Christmas"||Bing Crosby||wav[dead link] mp3[dead link]
|Day 8||"We’re So Good Together"||Reba McEntire||wav[dead link] mp3[dead link]
|Day 9||"The Cup of Life"||Ricky Martin||wav[dead link] mp3[dead link]
See also 
- Space science
- Space shuttle
- List of space shuttle missions
- List of human spaceflights chronologically
- Planet Mars Flag, which was brought along on the mission
- "STS-103 Mission Status Report #05". Encyclopedia Astronautica. 21 December 1999. Retrieved 6 May 2013.
- "STS-103 Mission Status Report #14". Encyclopedia Astronautica. 26 December 1999. Retrieved 6 May 2013.
- "External tank weld issue appears resolved". CBS News. Retrieved 30 August 2009.
- Fries, Colin (25 June 2007). "Chronology of Wakeup Calls" (PDF). NASA. Retrieved 13 August 2007.
- NASA (11 May 2009). "STS-103 Wakeup Calls". NASA. Retrieved 31 July 2009.