Soyuz TMA-21 ("Gagarin") was a Soyuz flight to the International Space Station (ISS). It transported three members of the Expedition 27 crew to the ISS, and docked at the station on April 6, 2011. TMA-21 is the 109th flight of a Soyuz spacecraft, the first of which launched in 1967. The Soyuz remained attached to the space station as a lifeboat, throughout the remainder of Expedition 27 and through the end of Expedition 28, and returned to Earth on September 16, 2011.

The launch of Soyuz TMA-21 was devoted to the 50th anniversary of the first manned space mission, which was conducted by YuriGargarin on April 12, 1961. The COSPAR International ID of Soyuz TMA-21 is 2011-012A

The TMA-21 spacecraft has been affected by a few problems during its processing flow, which is a rarity for the Soyuz spacecraft.

In October 2010, the Descent Module (SA) on the Soyuz TMA-20 spacecraft was damaged during transit by train to the Baikonur Cosmodrome, due to human error in the way the Soyuz was secured to the train carriage. This damage required TMA-20’s SA to be removed and replaced with a new one, while the damaged SA was sent back to the factory for repair, which was safely completed.

That same repaired SA is being used on Soyuz TMA-21, which will pose no extra risk to the mission.

Soyuz TMA-21 was also affected by an issue with a capacitor in the spacecraft’s electrical system, which pushed the launch back from the original date of 30th March to today (4th April) in order to allow repairs to be carried out.
The Soyuz spacecraft is composed of three elements attached end-to-end - the Orbital Module, the Descent Module and the Instrumentation/Propulsion Module. The crew occupied the central element, the Descent Module. The other two modules are jettisoned prior to re-entry. They burn up in the atmosphere, so only the Descent Module returned to Earth.

The deorbit burn lasted 260 seconds. Having shed two-thirds of its mass, the Soyuz reached Entry Interface - a point 400,000 feet (121.9 kilometers) above the Earth, where friction due to the thickening atmosphere began to heat its outer surfaces. With only 23 minutes left before it lands on the grassy plains of central Asia, attention in the module turned to slowing its rate of descent.

Eight minutes later, the spacecraft was streaking through the sky at a rate of 755 feet (230 meters) per second. Before it touched down, its speed slowed to only 5 feet (1.5 meter) per second, and it lands at an even lower speed than that. Several onboard features ensure that the vehicle and crew land safely and in relative comfort.

Four parachutes, deployed 15 minutes before landing, dramatically slowed the vehicle's rate of descent. Two pilot parachutes were the first to be released, and a drogue chute attached to the second one followed immediately after. The drogue, measuring 24 square meters (258 square feet) in area, slowed the rate of descent from 755 feet (230 meters) per second to 262 feet (80 meters) per second.

The main parachute was the last to emerge. It is the largest chute, with a surface area of 10,764 square feet (1,000 square meters). Its harnesses shifted the vehicle's attitude to a 30-degree angle relative to the ground, dissipating heat, and then shifted it again to a straight vertical descent prior to landing.

The main chute slowed the Soyuz to a descent rate of only 24 feet (7.3 meters) per second, which is still too fast for a comfortable landing. One second before touchdown, two sets of three small engines on the bottom of the vehicle fired, slowing the vehicle to soften the landing.

Selected as a NASA Astronaut in 2000, Garan performed three EVAs during STS-124 in June 2008. He was scheduled to perform one EVA during the STS-135 mission in July, thus becoming the last ever person to spacewalk outside the Space Shuttle. Garan is the founder of the Manna Energy Foundation, an organisation which aims to implement a new system of making portable water in the villages of Rwanda in Africa.

The Soyuz TMA-21 spacecraft is of the older TMA variant (200 series), as opposed to the newer TMA-M variant (700 series), which recently conducted its first flight on the Soyuz TMA-01M mission.

At the time of STS-1, the Russian and US space programs were rivals, but 30 years later, both programs co-operate with each other in the ISS Program. During its flight, the Gagarin Soyuz will also mark the 50th anniversary of the first American spaceflight by Alan Shepard.