STS-121


STS-121 was a 2006 Space Shuttle mission to the International Space Station flown by on its 32nd flight. The main purposes of the mission were to test new safety and repair techniques introduced following the Columbia disaster of February 2003 as well as to deliver supplies, equipment, and European Space Agency astronaut Thomas Reiter to the ISS.
After two weather-related delays, the shuttle successfully launched on Tuesday, July 4, 2006, at 14:37:55 EDT. It was the first and only shuttle launch on the United States' Independence Day. The mission lasted for 13 days before landing at the Kennedy Space Center on July 17, 2006, at 09:14:43 EDT.
STS-121 was also designated the ISS Assembly Mission ULF 1.1. As the mission followed on from STS-114 in carrying out the recommendations made in response to the Columbia Accident Investigation Board report, it was considered a Return to Flight test mission. Its successful launch and landing led NASA to fully resume regular Space Shuttle launches in the construction of the ISS.

Crew

Crew notes

Thomas Reiter's position was previously planned to be filled by Sergey Volkov before the launch of STS-121 was postponed until July 2006.
British-born astronaut Piers Sellers replaced Carlos Noriega who was originally scheduled to be on the STS-121 mission NASA announced on Thursday, July 15, 2004. This was due to an undisclosed, temporary medical condition.
The transfer of Reiter to the ISS returned the station to a three crew member staffing level. After the loss of Columbia and the grounding of the Shuttle fleet, only two people had been residing on the ISS.

Shuttle hardware

  • External Tank: ET-119
  • Solid Rocket Boosters: BI-126 & RSRM-93
  • SSMEs: s/n 2045, 2051, 2056
  • OMS engines: LP-01/35 RP-03/33

    Crew seat assignments

Mission background

During the STS-121 mission to the International Space Station, the crew of continued to test new equipment and procedures for the inspection and repair of the thermal protection system that is designed to increase the safety of the Space Shuttles. It also delivered more supplies and cargo for future ISS expansion.
After the Columbia accident, NASA decided that two test flights would be required and that activities that were originally assigned to STS-114 would need to be divided into two missions because of the addition of post-Columbia safety tests. Before the accident, Columbia had been assigned to missions STS-118 and STS-121. The STS-118 mission, also an International Space Station flight, was at first reassigned to Discovery, but was later assigned to.
The STS-121 mission was originally to have sent Columbia to service the Hubble Space Telescope. However, that servicing mission was given another designation on the manifest before the disaster and the designation of STS-121 once again became available. Since STS-115 through STS-120 were already delegated to existing missions, NASA selected the lowest available mission designation for the second test flight. Hence, the mission following STS-114 is STS-121.
The STS-121 test flight mission was originally to be flown aboard Atlantis in September 2005, after Discovery flew STS-114, but a problem with the landing gear of Atlantis moved Discovery ahead to fly STS-121. After the return of Discovery to California following the completion of STS-114, scheduling again changed. Atlantis was moved up to fly the STS-115 mission and Discovery was to fly the STS-121 mission as originally planned. The launch of the STS-121 mission was delayed until July 2006 as well, due to an unresolved foam debris and the Engine Cut Off sensor issue from STS-114.
On May 12, 2006, Discovery was moved from the Orbiter Processing Facility to the Vehicle Assembly Building, where it was mated to its External Tank and SRBs. Rollout to Pad 39B occurred on May 19, 2006, ahead of the planned launch, during the July 2006 launch window, which existed for about ten minutes each day between July 1 and 19.

Equipment delivered to the ISS

Key items delivered, as part of over 2 tons of cargo included:
Multi Purpose Logistics Module Leonardo on its 4th flight, 7th MPLM overall, carrying:
  • −80 °C Freezer
  • The European Modular Cultivation System for biological experiments.
  • New oxygen generation system
  • New cycling machine for the ISS crew
  • Replacement common cabin air assembly heat exchanger used to control the internal air temperature of the ISS.
All of the above equipment was installed in the Destiny Laboratory Module.
Also carried in the payload bay was an Integrated Cargo Carrier with the Trailing Umbilical System for the Mobile Transporter
, an EATCS/Pump Module, two Fixed Grapple Bars for PM and TUS relocation during EVA and an LMC carrying the DTO-848 TPS Repair Box.

Timeline

The shuttle was docked to the ISS for the majority of the flight. For much of the time the shuttle was at the ISS the Multi-Purpose Logistics Module Leonardo was mated and accessible to the crew for the transfer of equipment, supplies, returned experiments and trash.
Three spacewalks were carried out on the mission, the third was dependent on sufficient consumables being available and two alternate timelines were planned, with and without the final spacewalk. There were also additional "Get Ahead" tasks planned for the crew to do at the ISS if they found themselves with more time than planned, one such get ahead task was completed on EVA 2. The crew were able to take the majority of one day off, during which they explored the ISS, took photographs, and conducted press interviews.

July 1 (Launch attempt 1)

Events throughout the day went according to plan, one exception being an abnormal temperature reading on thruster L5L. The launch window was from 3:48:41 to 3:53:02 p.m. At 3:42, while in the T−9 built-in hold, mission control decided to postpone launch because anvil clouds and lightning were detected within of the launch area and path. Launch was rescheduled for July 2 at 3:26 p.m.
STS-121 was the first launch during which NASA took special precautions to deter vultures, particularly the local turkey vulture, from flying over the area. Efforts included the swift removal of roadkill and other dead animals from areas around the launch site. This followed a near miss during STS-114.

July 2 (Launch attempt 2)

Again, the countdown continued according to schedule with a launch time of 3:26 p.m. At 9:30am on July 2, the NASA launch blog reported that the "shuttle weather officer forecasts a 70-percent chance of weather prohibiting a launch this afternoon due to thunderstorms and anvil clouds. There is a 60-percent chance of weather prohibiting launch should there be a 24-hour turnaround, and a 40-percent chance with a 48-hour delay. If we scrub today due to weather, mission managers will meet later to decide if they want to make a third consecutive launch attempt or stand down for one day and try again on Tuesday."
At 1:14 p.m., the launch director made a final decision to scrub again due to unfavorable weather conditions. The next launch attempt was scheduled for around 2:38 p.m. on July 4.

July 3 (No launch attempt)

The shuttle's fuel cells were replenished to improve the chances of having enough electrical power on orbit to enable the third planned space walk to take place.
Image:STS-121-foam.jpg|thumb|center|500px|Images, from left to right showing 1. The external fuel tank area showing the location of the liquid oxygen feedline bracket. 2. Detail of the bracket showing cracked and missing foam. 3. Fragment of foam that fell off. Photo credit: NASA
Cracks and a region where a piece of foam had come off were discovered in the insulation on the upper part of the external fuel tanks. The foam came off a bracket which held an oxygen line in place. The fragment that fell off weighed 0.0056 pounds and, according to NASA, would not be big enough to damage the shuttle if it were to come off during flight. The thermal stresses of repeated filling and emptying the fuel tank with the cryogenic fuel are known to cause a degree of damage to the insulation foam.

July 4 (Launch and flight day 1)

At 8:35 a.m. the backup circuit breaker controlling the primary heaters on the segment joints of both solid rocket boosters was noticed to have failed. Consideration was given to a repair on the pad. However, this was not done as the heaters are only used in colder weather, and the primary heater was functional.
For the third launch attempt, there was only a 20% chance of weather preventing launch according to NASA.
At 2:37:55 PM Eastern Daylight Time, Space Shuttle Discovery launched from the Kennedy Space Center at Cape Canaveral, Florida. This was the third attempt at launch. It was also the first US Space Shuttle to launch on the United States' Independence Day.
During and after launch much attention was paid to monitoring the external tank for the loss of insulation foam. The shuttle was equipped with a number of new cameras, and video was also taken from spotter planes. Each solid rocket booster contained three cameras - one to monitor the separation, and two focused on the leading edge. The video from these was not to be broadcast, but recorded for later retrieval from the solid rocket boosters. A further camera was placed on the external tank, as during STS-114, to broadcast live images on NASA TV during launch. The first thing two of the crew from the mid-deck did when the main engines cut out was leave their seats to take photographs and video of the external tank. One of the factors that was potentially affecting the choice of day within the launch window was the lighting conditions for this imagery, as the sun's slightly different angle on the different days affected the location of shadows on the external tank. However, the day to day difference in lighting was determined to be relatively unimportant, particularly as the lighting conditions depended to a great degree on a more unpredictable factor — the degree to which the external tank tumbles on separation.
During the launch, NASA TV broadcast a view from the external tank camera mounted between the Shuttle and the external tank. Unlike the previous two missions, no foam breakage or foam pieces were easily seen falling off the tank. However, upon close inspection of the many cameras covering the launch NASA has revealed several small pieces of debris were seen jetting away from the tank. Generally, though, these were seen after the time NASA was most concerned about.
Image:STS-121 floating ice.jpg|thumb|left|200px|A piece of ice videoed by Michael Fossum from STS-121.
About 23 minutes into the flight, further debris was observed floating beside the orbiter as reported by Mission Specialist Michael Fossum. His transmission was broadcast live on NASA TV. Fossum initially described the debris as a with straps attached, a description which would fit a thermal protection system blanket. Such a blanket was noted to be flapping on the previous mission, STS-114, but was not of concern as it protects a section of the vehicle which does not get particularly hot. Analysis of video images on the ground has indicated that the debris observed was strips of ice formed on the outside of an engine nozzle, which sublimated and disintegrated during observation. Very similar ice formations were seen on earlier missions.
Video analysis also revealed a tile shim which came out during main engine start.
The orbital maneuvering system thruster in which a heater failed prior to launch was warmed by pointing it at the Sun; thus it was possible to be used during ISS rendezvous docking operations.