Early mission plans

Three different concept mission plans were evaluated: The first would be to use a shuttle-to-shuttle docking, where the rescue shuttle docks with the damaged shuttle, by flying upside down and backwards, relative to the damaged shuttle. It was unclear whether this would be practical, as the forward structure of either orbiter could collide with the payload bay of the other, resulting in damage to both orbiters. The second option that was evaluated, would be for the rescue orbiter to rendezvous with the damaged orbiter, and perform station-keeping while using its Remote Manipulator System (RMS) to transfer crew from the damaged orbiter. This mission plan would result in heavy fuel consumption. The third concept would be for the damaged orbiter to grapple the rescue orbiter using its RMS, eliminating the need for station-keeping. The rescue orbiter would then transfer crew using its RMS, as in the second option, and would be more fuel efficient than the station-keeping option.

The concept that was eventually decided upon was a modified version of the third concept. The rescue orbiter would use its RMS to grapple the end of the damaged orbiter's RMS.

Preparations

After its most recent mission (STS-123

STS-123

-Mission parameters:* Mass:* Orbiter liftoff: * Orbiter landing: * Perigee: 336 kilometers * Apogee: 346 kilometers * Inclination: 51.6 degrees* Period: 91.6min-Mission payloads:...

), Endeavour was taken to the Orbiter Processing Facility

Orbiter Processing Facility

An Orbiter Processing Facility was one of three hangars where U.S. space shuttle orbiters underwent maintenance between flights. All three such facilities, OPF-1, OPF-2 and OPF-3, were located at NASA's Kennedy Space Center in Florida at Launch Complex 39.They were located west of the Vehicle...

 for routine maintenance. Following the maintenance, Endeavour was on stand-by for STS-326 which would have been flown in the case that STS-124

STS-124

STS-124 was a Space Shuttle mission, flown by Space Shuttle Discovery to the International Space Station. Discovery launched on 31 May 2008 at 17:02 EDT, moved from an earlier scheduled launch date of 25 May 2008, and landed safely at the Kennedy Space Center's Shuttle Landing Facility, at 11:15...

 would not have been able to return to Earth safely. Stacking of the solid rocket booster

Solid rocket booster

Solid rocket boosters or Solid Rocket Motors, SRM, are used to provide thrust in spacecraft launches from the launchpad up to burnout of the SRBs. Many launch vehicles include SRBs, including the Ariane 5, Atlas V , and the NASA Space Shuttle...

s (SRB) began on 11 July 2008. One month later, the external tank

Space Shuttle external tank

A Space Shuttle External Tank is the component of the Space Shuttle launch vehicle that contains the liquid hydrogen fuel and liquid oxygen oxidizer. During lift-off and ascent it supplies the fuel and oxidizer under pressure to the three Space Shuttle Main Engines in the orbiter...

 arrived at KSC and was mated with the SRBs on 29 August 2008. Endeavour joined the stack on 12 September 2008 and was rolled out to Pad 39B one week later.

Since STS-126 launched before STS-125, Atlantis was rolled back to the VAB on 20 October, and Endeavour rolled around to Launch Pad 39A on 23 October. When it was time to launch STS-125, Atlantis rolled out to pad 39A.

Mission plan

The Mission would not have included the extended heatshield inspection normally performed on flight day two. Instead, an inspection would have been performed after the crew was rescued. On flight day two, Endeavour would have performed the rendezvous and grapple with Atlantis. On flight day three, the first EVA

Extra-vehicular activity

Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...

 would have been performed. During the first EVA, Megan McArthur, Andrew Feustel and John Grunsfeld would have set up a tether between the airlocks. They would have also transferred a large size Extravehicular Mobility Unit

Extravehicular Mobility Unit

The Space Shuttle/International Space Station Extravehicular Mobility Unit is an independent anthropomorphic system that provides environmental protection, mobility, life support, and communications for a Space Shuttle or International Space Station crew member to perform extra-vehicular activity...

 (EMU) and, after McArthur had repressurized, transferred McArthur's EMU back to Atlantis. Afterwards they would have repressurized on Endeavour, ending flight day two activities.

The final two EVA were planned for flight day three. During the first, Grunsfeld would have depressurized on Endeavour in order to assist Gregory Johnson and Michael Massimino in transferring an EMU to Atlantis. He and Johnson would then repressurize on Endeavour, and Massimino would have gone back to Atlantis. He, along with Scott Altman and Michael Good would have taken the rest of the equipment and themselves to Endeavour during the final EVA. They would have been standing by in case the RMS system should malfunction. The damaged orbiter would have been commanded by the ground to deorbit and go through landing procedures over the Pacific, with the impact area being north of Hawaii. On flight day five, Endeavour would have had a full heat shield inspection, and land on flight day eight.

This mission could have marked the end of the Space Shuttle program, as it is considered unlikely that the program would have been able to continue with just two remaining orbiter

Space Shuttle Orbiter

The Space Shuttle orbiter was the orbital spacecraft of the Space Shuttle program operated by NASA, the space agency of the United States. The orbiter was a reusable winged "space-plane", a mixture of rockets, spacecraft, and aircraft...

s, Discovery

Space Shuttle Discovery

Space Shuttle Discovery is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States, and was operational from its maiden flight, STS-41-D on August 30, 1984, until its final landing during STS-133 on March 9, 2011...

and Endeavour

Space Shuttle Endeavour

Space Shuttle Endeavour is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States. Endeavour was the fifth and final spaceworthy NASA space shuttle to be built, constructed as a replacement for Challenger...

.

On Thursday, 21 May 2009, NASA officially released Endeavour from the rescue mission, freeing the orbiter to begin processing for STS-127

STS-127

STS-127 was a NASA Space Shuttle mission to the International Space Station . It was the twenty-third flight of . The primary purpose of the STS-127 mission was to deliver and install the final two components of the Japanese Experiment Module: the Exposed Facility , and the Exposed Section of the...

. This also allowed NASA to continue processing LC-39B for the upcoming Ares I-X launch, as during the stand-down period, NASA installed a new lightning protection system, similar to those found on the Atlas V

Atlas V

Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...

 and Delta IV pads, to protect the newer, taller Ares I rocket from lightning strikes.

External links

• CBS Space News – Launch Team