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Mission emblem
Mission emblem STS-121
Mission dates
Mission: STS-121
COSPAR-ID : 2006-028A
Crew: 7th
Begin: July 4, 2006, 18:37:55  UTC
Starting place: Kennedy Space Center , LC-39B
Space station: ISS
Coupling: July 6, 2006, 14:52 UTC
Decoupling: July 15, 2006, 10:08 UTC
Duration on the ISS: 8d 19h 16min
Number of EVA : 3
Landing: July 17, 2006, 13:15:49 UTC
Landing place: Kennedy Space Center, Lane 15
Flight duration: 12d 18h ​​37min 54s (until standstill)
Earth orbits: 202
Track height: 340 km
Covered track: 8.5 million km
Payload: MPLM Leonardo
Team photo
v.  l.  No.  Stephanie Wilson, Michael Fossum, Steven Lindsey, Piers Sellers, Mark Kelly, Thomas Reiter, Lisa Nowak
v. l. No. Stephanie Wilson, Michael Fossum, Steven Lindsey, Piers Sellers, Mark Kelly, Thomas Reiter, Lisa Nowak
◄ Before / After ►
STS-114 STS-115

STS-121 ( English S pace T ransportation S ystem ) is the mission name for the flight of the US space shuttle Discovery (OV-103), which started on July 4, 2006 . It was the 115th space shuttle mission, the 32nd flight of the space shuttle Discovery and the 18th flight of a shuttle to the International Space Station (ISS).


Shuttle crew

ISS crew outward flight

ISS expedition 13 / ISS expedition 14


Ground crew

  • Flight supervisor: Steve Stich during take-off and landing; Tony Ceccacci, Paul Dye, and Norm Knight while in orbit; ( ISS flight controllers: Rick LaBrode, Annette Hasbrook and Matt Abbott)
  • Start leader: Michael D. Leinbach
  • Liaison Spokesperson ( CapComs ): Steve Frick during take-off and landing; Rick Mastracchio, Lee Archambault, and Steve Swanson while in orbit; (ISS-CapComs: Julie Payette , Megan McArthur and Thadd Bowers)

Mission overview

After the Columbia accident in February 2003, this was the second test flight after STS-114 to resume shuttle flights, which NASA had put under the motto "Return to Flight". The first step was to prove that the improvements made after STS-107 and STS-114 work. Therefore, special care was taken to ensure that no pieces of the foam insulation of the outer tank flake off. In fact, only a few parts that did not pose a risk came loose during take-off.

As with the last shuttle flight, which occurred a year earlier, a lot of time in orbit was spent examining the space shuttle's heat shield for damage. These inspections were carried out using the 15 meter long scanning arm (OBSS) . Connected to the orbiter's robotic arm (RMS) , the surface - especially the underside of the ferry - can be examined in detail. In addition, it was tested how resilient the mechanical arms are when they are connected to one another. For this purpose, a platform was installed at the end of the OBSS during an EVA , which carried two astronauts. If the system of RMS and OBSS were to be stable enough, it would in future be possible to bring an astronaut close to damaged tiles in order to be able to repair them. The repair of the sensitive heat protection tiles was also the aim of another EVA, in which a newly developed filler was tested under space conditions.

With the flight, the crew of the ISS was increased by one crew member. For the first time since Expedition 6 , three space travelers were working on the station. The German astronaut Thomas Reiter stayed on the ISS for the next six months after the mission. In addition, the transport of goods was one of the tasks of STS-121. A large part of the over 4 tons of freight was brought to the station with the logistics module Leonardo (2.4 tons).

NASA described the flight as a complete success because all tasks were completed.


Original plans

The STS-121 is an inserted flight that NASA added to its program in 2003. It had been found that the tasks to be performed by STS-114 after the forced break caused by the Columbia crash would be too extensive for a mission. For NASA, STS-114 and STS-121 are therefore connected to one another. She sees both missions as test flights documenting the resumption of shuttle flights under the name "Return to Flight".

The first planning was for a start in November 2004, when NASA management assumed in autumn 2003 that STS-114 would be able to carry out in September 2004. With the postponement of STS-114, the start of STS-121 should also be delayed. When the Discovery finally left for the ISS in late July 2005, the space shuttle Atlantis was to follow two months later. During the start of STS-114, however, parts of the foam insulation of the outer tank came off again . Therefore, the US space agency suspended all further flights before the Discovery returned to Earth. First, it should finally be clarified why parts of the insulation repeatedly flake off and a solution should be found.

The outer tank will be transported to Cape Canaveral

A start can be expected in November 2005 at the earliest, explained William Gerstenmaier, the then head of the ISS program and responsible for investigating the loosening insulation, shortly after the landing of STS-114. Just a week later, Gerstenmaier had to admit that a lot more time was needed - at least half a year. All three external tanks already shipped would be sent back to the manufacturer, the Michoud Assembly Facility (MAF) in Louisiana , for revision , he said. In addition, it would have been decided to swap the orbiter. As with STS-114, Discovery will be tasked with carrying out STS-121 in order to be able to use Atlantis for the STS-115 mission . During this mission, heavy components are to be flown to the ISS. This decision was made because the Atlantis is slightly lighter than the Discovery and can therefore carry more payload.

As a result, there were a number of incidents and other problems, both with the orbiter and the outer tank, which further delayed the program.

Problems with the outer tank

Since Hurricane Katrina in late August 2005 badly damaged the MAF, which is located east of New Orleans , NASA was forced to postpone the start to May 2006. The MAF plant was under water, there was no electricity and at times it was used by the US military as a base for relief operations. In addition, the workers had enough problems of their own, as more than half had become homeless. The MAF did not resume work until the beginning of November.

The so-called PAL thresholds (Protuberance Air Load) have been identified as a possible cause of the problems with the foam insulation. These thresholds cover the fuel lines to the orbiter running on the outside of the tank with foam to protect them against air turbulence. However, this insulation is very exposed and easily flakes off. In December 2005 NASA therefore decided to dispense with the PAL thresholds at least for this flight. A correspondingly modified model arrived at the Kennedy Space Center (KSC) in early March 2006 .

The outer tank is mounted on the solid fuel rocket

Another problem was the fuel sensors in the outer tank, which had already delayed the launch of the STS-114. The so-called engine cutoff sensors (ECOs), which measure the fill levels, showed irregularities during tests. You should switch off the main engines in good time if the tank is too low prematurely. This prevents the turbo pumps from idling, cranking and exploding, which would seriously damage the orbiter. In mid-March, Wayne Hale , the manager of the NASA shuttle program, announced that the sensors would be replaced as a precaution. A start date in May could therefore not be kept.

At the beginning of April new problems with the external tank became apparent. In wind tunnel tests with a true-to-original model of the tank, which NASA had carried out by the US Air Force in their huge facility near Tullahoma ( Tennessee ), parts of the insulation had flaked off again. This time in the area of ​​the so-called frost thresholds (seven of these “ice / frost ramps”, each about 30 centimeters long, are located in the hydrogen area and two in the oxygen area). They ensure that no ice forms on the lines on the outside of the tank when the ice-cold fuel is filled. The sleepers had been redesigned to reduce the amount of insulation applied.

The tank was connected to the two already assembled solid fuel rockets in the VAB on the launch platform in mid-April . NASA had previously decided to fly this mission with the old frost bumps after the unsuccessful wind tunnel tests. However, some of the NASA and Lockheed Martin engineers were in favor of waiting until a more secure configuration had been found to launch. Others, including Shuttle Manager Wayne Hale, were against it because they didn't want to make a second major change besides removing the PAL sleepers.

On May 4th, those responsible decided not to carry out a refueling test. Because of the problems with the ECO sensors, there had been considerations to fill the external tank at the beginning of June, in order to test the behavior of the sensors under real conditions. However, it was feared that repeated filling could lead to cracks in the insulation material. These would increase the risk of parts flaking off because air turbulence could form.

In June the tank was finally declared airworthy.

Problems with the orbiter

The Leonardo module is being prepared for launch

During the preparations for launch, an accident occurred in the orbiter processing facility of the orbiter at KSC at the beginning of March . A lamp broke and shards of glass fell into the open payload bay. Technicians removed the broken pieces with telescopic lifting platforms. The insulation of the robotic arm (RMS) was slightly damaged, creating a three centimeter long, invisible crack. The damaged part of the RMS was sent to the manufacturer in Canada for repair and further inspection. The repaired piece arrived at the KSC at the end of March. After the arm was reassembled and its functionality checked, it was installed in the orbiter shortly before Easter.

Discovery on the launch pad

The work on the orbiter was thus completed and it was transferred to the VAB on May 12th. There the Discovery was connected to the external tank and the two solid fuel rockets and placed on the launch platform. Exactly a week later, the ferry was rolled to the launch pad.

On June 17, during the traditional flight readiness review, all Discovery systems were declared ready for take-off and the preliminary take-off date (July 1) was confirmed.

Replacement orbiter

As with the previous flight (STS-114), NASA had a second orbiter ready in case the Discovery was damaged during launch. The Atlantis would have carried out the rescue mission under the designation STS-300 at the end of August at the earliest and brought the STS-121 crew safely to earth. Until then, the astronauts would have had to wait on the ISS. The space station's resources would be enough for nine people - six shuttle and three ISS space travelers - according to NASA for twelve weeks.

This is the first mission where it is possible to land the space shuttle remotely. For this purpose, the Discovery has an 8.5 meter long cable on board, which connects the controls of the flight deck with a control box in the middle deck and allows the ground control to land the shuttle unmanned. This allows the control center in Houston to carry out actions that the pilots would otherwise - for example extend the landing gear or activate the braking parachute.

Mission history

The 115th space shuttle mission (the 90th since the Challenger disaster ) began on July 4 at 18:38 UTC after the first two launch attempts had to be canceled due to adverse weather conditions.

1st attempt to start, July 1, 2006

The countdown began on June 28, 2006 at 21:00 UTC at the T-43 hour mark. The day before the crew, who had previously trained at the Johnson Space Center in Houston , arrived at KSC . At the beginning of the countdown, NASA meteorologists assumed a probability of 40 percent that the start could take place as planned. It was feared that summer thunderstorms could occur. This fear was justified because as early as June 27th, lightning had struck a distribution system near the launch pad.

The crew was woken up shortly after 9:00 UTC, had breakfast and put on their orange ACES take-off and landing suits ( Advanced Crew Escape Suits ). At around 16:00 UTC all astronauts left the crew quarters, drove to the launch pad and boarded the space shuttle.

Despite the afternoon showers, the countdown was not canceled. Only at 19:41 UTC, eight minutes before the planned take-off, was the countdown clock stopped and the start postponed by 24 hours. Thunderclouds had approached the KSC up to 35 kilometers, but the safety regulations require a minimum distance of 55 kilometers. Possible lightning strikes would have prevented a possible emergency landing of the orbiter at the launch site.

2nd attempt to start, July 2, 2006

The second launch attempt was scheduled for July 2nd at 19:26 UTC . Regarding the weather situation, things looked even worse for the second start attempt than the day before: NASA stated the probability of having to postpone the start again due to bad weather at 70 percent. In the afternoon there was actually a thunderstorm over the starting area.

At 17:14 UTC, when the crew had already boarded and buckled up, NASA canceled the start again due to the uncertain weather conditions. It was postponed for two days to July 4th. The 48-hour shift was necessary to refill the liquid oxygen and liquid hydrogen tanks in the shuttle's payload bay. This operates the fuel cells that supply the on-board electrical system. They had been working continuously since July 1st at 4:00 UTC.

3. Attempt and start, July 4, 2006

Launch of the STS-121 mission

The start succeeded with the third attempt on July 4th. The Discovery took off from the launch pad punctually at the set time at 18:37:55 UTC . This time, the meteorologists also had no objections: It was a sunny day with an air temperature of 30 degrees Celsius and light clouds.

The day before, a 13 cm long crack in the foam insulation was discovered on a strut of the oxygen supply line from the external tank . In addition, a piece of foam 8 centimeters tall and half a centimeter thick was found on the launch platform, which had come loose from this point. Due to its weight of 2.5 grams, however, this piece of foam would not have posed any danger to the orbiter if it had fallen off the tank during take-off and hit the orbiter.

Position and close-up of the loosened insulation piece

During the take-off, some small parts fell off the outer tank again. According to NASA, three or four pieces came off just under three minutes after leaving the ramp and another piece came off two minutes later. You couldn't say whether it was ice or parts of the insulation. Astronauts Fossum and Wilson were tasked with filming the separation of the tank. Fossum reported that he could see what looked like a piece of cloth and was floating between the orbiter and the tank. It is about one and a half to maybe two and a half meters tall. He suspected it was a piece of the heat shield. However, image evaluations showed that it was a large sheet of ice.

Shuttle program manager Wayne Hale stated at an initial press conference that the tank had worked “very, very well”. Nothing was discovered to give cause for concern.

1st Mission Day, July 4, 2006

One and a half hours after the space shuttle took off, the loading bay doors were opened and the communication and on-board systems checked.

2nd Mission Day, July 5, 2006

The goal of the first full day in orbit was to check the space shuttle's heat shield for any damage. Spread over the day - for a total of six and a half hours - the heat protection tiles were examined with the new OBSS inspection arm ( Orbital Boom Sensor System ), which was first used on the STS-114 a year ago .

The nose of the orbiter and the right wing were inspected centimeter by centimeter with high-resolution cameras and laser sensors because these areas are no longer accessible with the robotic arm after docking with the station. The astronauts Wilson, Nowak and Fossum took it in turns because it is very tiring to concentrate on watching the filmed areas on the monitor for a long time.

An initial evaluation of the inspection of the heat shield showed that it only suffered minor damage when it took off. Flight Director Tony Ceccacci said it was too early to be final. The final analysis would not be available for about two days. A filler strip was only discovered on the right wing, which protruded between two heat protection tiles. However, this was not at a critical point and did not necessarily have to be removed. In addition, three white spots were also found on the right wing, which, according to Ceccacci, were most likely bird droppings. The engineers would examine the images further to be sure.

While the mission specialists took turns doing the complex inspection on the robot arm, Commander Lindsey and Pilot Kelly brought the space shuttle closer and closer to the ISS by switching on the maneuvering engines several times. The spacesuits were also checked for functionality.

3rd Mission Day, July 6, 2006

Discovery approaches the ISS

The third day of flight was all about the International Space Station (ISS): When the orbiter reached the station, it stopped 180 meters away. As with STS-114, Commander Steven Lindsey slowly rotated the Discovery by 360 ° across its transverse axis exactly one hour before docking so that the ISS crew could take high-resolution photos of the underside of the ferry. 350 images were taken within nine minutes and immediately sent to the control center in Houston . The evaluation showed that the heat shield was completely intact.

Exactly according to the schedule, the Discovery docked with the ISS at 14:52 UTC. After the necessary leak tests, the hatches were opened. Permission to do this came 20 minutes earlier than planned at 16:30 UTC. The seven-person Discovery crew was warmly welcomed by the two ISS hosts. It was the first visit for Vinogradov and Williams since they took over the station in early April.

After a brief safety briefing, the bucket seat brought by the shuttle was installed by Reiter in the Russian Soyuz spacecraft . He officially belonged to the crew of the space station.

4th Mission Day, July 7, 2006

On the fourth day of the flight, the Leonardo logistics module, manufactured in Italy, was lifted out of the Discovery's hold with the robot arm of the space station and connected to the ISS. One and a half hours later than planned in the flight plan, Leonardo was docked at 12:15 UTC on the Unity module . It contained over three tons of goods, pieces of equipment and experiments that were urgently needed by the 13th permanent crew of the ISS. The astronauts later began unloading the container, which took several days.

During the further course of the day, mission specialists Nowak and Wilson, together with Pilot Kelly, devoted another four-hour inspection of the orbiter's heat protection tiles. The program included selected areas that were noticed during the first scan. Including the leading edges of the wing and the protruding filler strips. On the last flight a year earlier, NASA had decided to order an egress (EVA) to remove the plastic strips that had come off.

Flight Director Tony Ceccacci announced that the Mission Committee has approved an additional day of flight. This means that a third EVA will be carried out by the two astronauts Fossum and Sellers . If necessary, the two filler strips would be removed. A third EVA was originally planned, but was canceled long before the start because the workload was too extensive for the team.

5th Mission Day, July 8, 2006

The first of a total of three EVAs was scheduled for July 8th . EVA-1 began at 13:17 UTC when the veteran mission specialist Piers Sellers and newcomer Mike Fossum switched their spacesuits to internal power. Shortly afterwards, they left the space station through the Quest airlock .

Fossum and Sellers on the RMS / OBSS system during EVA

One of the EVA's goals was to replace a damaged cable in the mobile transporter. In addition, the robotic arm (RMS) of the orbiter was connected to the inspection arm ( OBSS) - as was done to check the tile status. NASA wanted to find out whether the 30-meter-long RMS / OBSS system is stable enough to carry astronauts and to serve as a work platform in the event of a tile repair. Steered by Lisa Nowak and Stephanie Wilson from the shuttle cockpit, Sellers first climbed onto the platform at the end of the OBSS. Fossum was added later and had initially observed everything from the payload bay. Contrary to the expectations of the engineers, any vibrations that occurred were dampened very quickly. The connection between RMS and OBSS seemed stable enough for work, which, however, still had to be verified by analyzing the information collected. The first field mission ended at 20:48 UTC after 7 hours and 31 minutes.

John Shannon, chairman of flight control, announced that the analysis of the data on the condition of the heat protection tiles had been completed. Except for one point, the heat shield is in excellent condition. The technicians would only have to analyze the recordings on one of the protruding filler strips on the underside of the Discovery.

6th Mission Day, July 9, 2006

The main focus of activities on the sixth day of flight was the further unloading of Leonardo . According to NASA, only 20 percent of all goods from Discovery and Leonardo had been brought into the ISS at the beginning of this working day .

At around 16:00 UTC , all nine space travelers gave a detailed press conference in the Destiny module . When asked about his flight to the Mir space station a decade ago and a comparison to the current mission, Reiter replied that the ISS already offers more space than the fully developed Russian station. Everything is much more generously dimensioned. At the moment a full workload has to be completed, so that there is little time for other things. When the space shuttle undocked, he would immediately begin his fitness program in order to be able to cope with the physical strains of the upcoming spacecraft at the beginning of August without any problems. He is looking forward to leaving with his US colleague.

Immediately before the day came to an end for the astronauts, the ground control provided them with good news: the NASA engineers had carefully checked all data and recordings of the heat shield and it was "one hundred percent clear for re-entry". The Discovery crew received the news with relief.

7th Mission Day, July 10, 2006

The crew of the Discovery was woken up at 6:08 UTC to the song "Clocks" by the group Coldplay . His family had chosen it for Piers Sellers , who later in the day was carrying out his fifth EVA . The space station crew was woken up to the standard tone half an hour later.

Mike Fossum on the Mobile Transporter

Sellers and Mike Fossum exited the Quest lock at 12:14 UTC as scheduled and began the second EVA of this mission. First, the two of them lifted an ammonia pump (it is needed for the space station's cooling system) out of the space shuttle's hold and stowed it in the ISS's “spare parts store”. It is a reserve device that will only be needed once the ISS has been expanded. This pump was used on August 16, 2010 by Tracy Caldwell-Dyson and Douglas Wheelock to replace the broken original pump in the S1 support structure on an EVA .

However, the main task of the exit was to replace a television and data cable, which is important for the function of the ISS transport trolley - officially known as Mobile Transporter (MT). It is used to bring the station's robotic arm to where it is needed. The car had failed exactly seven months ago when a disconnect device in the MT cut one of the two data cables. Fossum and Sellers were able to complete all the tasks set by the EVA, which ended after 6 hours and 47 minutes.

During the outside work there was some excitement when the small rescue device ( SAFER ) peeled off Sellers' spacesuit. Although he was not in danger because he was still connected to the "rocket backpack" with a safety line, Fossum came to his aid to reattach SAFER.

All shuttle astronauts were involved in the EVA activities, while the three ISS men continued to unload the Leonardo module .

8th Mission Day, July 11, 2006

Flight control was delighted with the outcome of the second spacecraft activity . Initial data showed that the ISS transport vehicle (MT) that had been repaired the day before is fully functional again. It is indispensable for the further expansion of the space station. In the morning e-mail, the control center thanked the “all-workers” for their work.

Phil Engelauf, the chief flight director, said that the flight history of the Discovery is optimistic that the Atlantis can take off as planned at the end of August.

The main task of the eighth day of flight was the further unloading of the Leonardo module . In the end, the astronauts had reloaded around 90 percent of all goods. In addition, Piers Sellers and Mike Fossum were waiting for their spacesuits for their third exit.

After lunch, the astronauts received an "important" call from the Oval Office of the White House: US President George Bush congratulated the ISS residents on their good work around 14:30 UTC.

9th Mission Day, July 12, 2006

For the ninth day, the third exit (EVA) was the focus of activities. At 11:20 UTC , Piers Sellers and Mike Fossum disembarked via the space station's Quest airlock . After installing a foot mount on the ISS robotic arm , Sellers tied to it and was hoisted over the space shuttle's payload bay. With an infrared camera , he made individual images and a 20-second film of the wing leading edges. With the help of these recordings, NASA engineers want to track down damage that cannot be found on the surface.

Mike Fossum in the payload bay

Then the two astronauts tried out repair methods on heat protection tiles . For this purpose, there was a pallet with a dozen prepared tiles in the payload bay. After the Columbia crash in February 2003, NASA worked on repair techniques for the heat shield. A special filler that is supposed to seal small cracks and joints is still in the development stage. Fossum and Sellers experimented with the glue to see how well it could be applied and spread in space conditions. Thereafter, infrared images were also taken of the test tiles. For comparison, photos and a one-minute film were made of both the treated and the untreated tiles. The third and final EVA of this mission ended after 7 hours and 11 minutes.

During the EVA, Piers Sellers lost a spatula he had used to apply the glue. Ground control was able to observe the floating tool with the camera and came to the conclusion that its trajectory posed no danger to the orbiter or the station. It is very rare for tools to be lost during an outboard operation.

The three-person crew of the space station loaded the logistics module Leonardo during the EVA . In total, almost two tons of unneeded equipment had to be brought back to earth for analysis of ready samples and waste.

10th Mission Day, July 13, 2006

After the very busy days, the flight control gave the astronauts a few hours of free time, which, however, was repeatedly interrupted by official interviews and television broadcasts.

Thomas Reiter had to complete the first of these official program points around 8:15 UTC . Bavarian students had a quarter of an hour to ask the German about his first impressions on the space station. They were 7th grade high school students who were invited to the DLR control center in Oberpfaffenhofen . Reiter explained that his work was "extremely interesting" if one was initially busy maintaining the on-board systems before starting the experiments. The weightlessness demonstrated tab by levitating a handbook on camera and did a headstand.

In the meantime, a problem had arisen in one of the space shuttle systems: Two of the three auxiliary power systems (APUs) that operate the hydraulics showed small deviations. One device had a small pressure drop and the other APU had a defect in thermoregulation. The engineers at the control center went to look for the cause in order to be able to eliminate the errors.

11th Mission Day, July 14, 2006

After the last remaining freight was stowed in the logistics module Leonardo , the spacemen locked the container. At 13:32 UTC , mission specialists Stephanie Wilson and Lisa Nowak Leonardo disconnected from the Unity ISS module and anchored the cargo container in the orbiter's hold at 15:00 UTC.

Later in the day, the astronauts examined parts of the space shuttle for micrometeorite impacts . For this purpose - as happened at the beginning of the mission - the robot arm of the shuttle was connected to the inspection arm (OBSS) . The OBSS systems then inspected the left wing.

NASA engineers were still investigating the cause of the hydraulic power unit (APU) problems that had occurred the day before. Wayne Hale , head of the space shuttle program, said he believed the defect would not affect the upcoming landing. The pressure loss in one of the three APUs operated with hydrazine is said to be so low that the risk of fire is also unlikely. They are still investigating whether hydrazine is leaking at all, or nitrogen, which is keeping the tank under pressure. (The shuttle is able to land with just one APU.)

12th Mission Day, July 15, 2006

ISS after placing the Discovery

After 8 days, 19 hours and 16 minutes, the Discovery docked punctually at 10:08 UTC from the space station and left the German Thomas Reiter behind. This is the first time in exactly three years that a three-person permanent crew has been working on board the ISS. Two hours earlier, the crews said their goodbyes and closed the hatches.

After the separation, the team checked the space shuttle one last time for traces of micrometeorite impacts . First the right wing of the orbiter was scanned with the inspection arm and then the heat protection tiles on the nose. Until the Discovery began its return flight, it was around 75 kilometers from the space station. This made it possible to return to the ISS at any time in the event of problems.

Regarding the small leak in one of the turbines (APUs) for the operation of the hydraulic units, NASA decided to wait for the flight control system to be checked the next day. If the leak rate had increased, the defective APU would have run empty.

13th Mission Day, July 16, 2006

The six-person crew of the orbiter made final preparations on board for the return home. At around 8:00 UTC , the pilots began checking the flight control system. During the one-hour procedure, the hydraulics supplied by the auxiliary power units (APUs) were also tested . In the end, the pilots were able to report that there were no problems with the units. All three APUs showed normal values.

NASA engineers completed the review of the final OBSS inspection later in the day . The search for microscopic impacts was negative. At about 14:00 UTC, the control center radioed the Discovery that no damage had been found to the heat shield and that the landing planned for the next day could be carried out.

14th Mission Day and Landing, July 17, 2006

There were two landing options at KSC for a landing on the 14th day of the mission : 13:14 UTC and at 14:50 UTC.

At first there were considerations to include the alternate landing sites at Edwards Air Force Base in California and White Sands Missile Range in New Mexico , as it could have been that only two APUs were working. A landing with only two APUs would have been made under stricter weather regulations. But the responsible flight director Steve Stich announced the day before after checking the defective APU that only the KSC in Florida would be used for the July 17th landing. If the landing had been postponed to the next day or the day after that, Edwards and White Sands could have been activated as additional landing sites.

The only uncertainty factor was the weather: a rainy area was approaching from the north. NASA guidelines stipulate that the landing must be canceled if a rain or thunderstorm front has drawn up within 55 kilometers of KSC.

Landing of the Discovery at KSC

The cargo hold doors were closed at 9:35 UTC. Flight control had waited until the last opportunity before making its decision to approve the re-entry. Finally, the first landing opportunity (13:14 UTC) was used. At 11:56 UTC Houston gave the go-ahead for the three-minute ignition of the brake engines, which began at 12:07 UTC.

The landing took place punctually at 13:14:43 UTC under a cloudy sky on runway 15 of the KSC. Less than a minute later, the space shuttle came to a halt at 13:15:49 UTC.

First, Commander Steven Lindsey was supposed to land the Discovery on runway 33. However, ten minutes after the re-entry began, a rainy area had formed south of the KSC. Therefore, during the approach, the control center ordered the switch to the route several dozen kilometers further north. The Discovery was approaching KSC from the southwest. To destroy the kinetic energy, she made a long left turn about five minutes before touching down. It was raining where the ferry should originally have made this curve. Therefore, NASA decided to approach the runway from the north. The KSC has only one runway. If the runway is approached from the south (330 °) it is runway 33, if the shuttle hovers in from the north (150 °) it is called runway 15.

About an hour and a half after the space shuttle landed, the crew made their mandatory tour of the orbiter after being medically examined and found healthy. Also there were NASA Director Mike Griffin and Bill Gerstenmaier, the person responsible for space operations. Commander Lindsey told the press that this was his fourth flight and that he always walked around the ferry afterwards, but that he had never seen a vehicle that looked so clean. He was alluding to the damage to the heat protection tiles on the space shuttle. After landing, 96 small damages (a dozen of them larger than 2.5 centimeters) were found. According to NASA, these were fewer finds than before, the inspection after the last flight revealed over 150 defective tiles.

Wake-up calls

The STS-121 crew received the following wake-up calls from ground control for the new working day:

See also

Web links

Commons : STS-121  - collection of images, videos and audio files

Individual evidence

  1. New Tools on STS-121 (English)
  2. Spacewalkers Install Spare Ammonia Pump. NASA, August 16, 2010, accessed August 17, 2010 .
This article was added to the list of excellent articles on August 17, 2006 in this version .