PEAR corner: Space Shuttle: The Mission

The process of sending a crew to the outer space starts in the Vehicle Assembly Building (VAB). There, the orbiter, external tank (ET) and solid rocket busters (SRB) are attached. The VAB is located at NASA’s Kennedy Space Center (KSC) and it is the largest one story building in the world. It covers 3.25 hectares (8 acres) and it is 160 meters (525 ft) tall, 218 meters (716 ft) long and 158 meters (518 ft) wide.

From top left to right. Vehicle Assembly Building. Assembly of the solid rocket boosters.

Joining of external tank and solid rocket boosters. Stack of the orbiter

When the space shuttle is ready, the crawler transporters pick it up and transport it to the launch platform (launch pad 39A), this action is also know as “rollout”. During the rollout, the crawler travels 3.5 miles (5.6 kms) through a road called “crawlerway”. The crawler has a mass of 2,721 tones. It has 8 tracks (two on each corner). The vehicle measures 131 ft (40m) by 114 ft (35m). It is 20ft height and each side of the vehicle can be raised and lowered independently. It travels at a speed of 1 mi/hr (1.6Km/hr) loaded and 2 mi/hr (3.2 km/hr) unloaded. After completing the crawlerway, the space shuttle waits until the day of its blast off.

From left to right. The space shuttle leaving the VAB. Space shuttle rolling out to the launch Pad 39A.

Mission STS-133. Discovery last rollout

On the day of the lift off, seven seconds before the launch, the space shuttle main engines (SSME) are fired. When the count down reaches zero the Solid Rocket Busters (SRB) are ignited and the space shuttle blast off. During the lift off, both SMB and SSME provide a 6,600,000 and 1.2 million pounds of thrust respectively. The destination of the crew is the Low Earth Orbit (LEO). The space shuttle must accelerate from zero to 28,968 km/hr (18,000 mi/hr) to reach that orbit.

The ascent is divided in two stages. At the end of the first stage, two minutes after the lift off, the SRB propellant is exhausted and both rockets are jettisoned. Then the SRB fall into the ocean, where they are recovered. In the second stage, the space shuttle is thrusted only by the SSME. Then, 8.5 minutes later, the shuttle reaches the LEO orbit and a few seconds after the external tank is jettisoned and burned in the atmosphere.

On the lift off, the space shuttle weighs 2.04 million kg (4.5 million pounds). One minute after the space shuttle has consumed 1.5 million pounds of fuel and has reached a speed of 1,609 km/hr (1,000 mph).

Count down Summary

T-20 minutes: Pre-launch functions are controlled by ground computer network and launch site
T-31 seconds: Ground computer network enables onboard automatic launch sequence

T-6.6 seconds: Three shuttle main engines ignite in staggered intervals 120 millisecodns apart.

T-3 seconds: Shuttle main engines commanded to lift off position.

T-0 seconds: On board computer ignite solid rocket boosters, three main engines at 100% of thrust level, the space shuttle lift off.

First Stage Summary

T+20 seconds: Shuttle rolls 180 degrees at a 78 degree pitch

T+60 seconds: Space shuttle main engines throttled up to 104% of thrust

T+2:06 minutes: Solid Rocket boosters separate

T+7:40 minutes: Space shuttle main engines throttled down t maintain acceleration bellow 3G’s for structural limits.

T+8:30 minutes: Main engines cut-off sequence begins

T+8:33 minutes: Space shuttle main engines throttled down 65% of thrust

T+8:40 minutes: Space shuttle main engines cut off automatic sequence confirm. Main Engines shut down an begin external tank separation sequence.

T+8:58 minutes: External tank separates from orbiter.

Mission STS-133. Discovery last launch

Mission STS-133. Recovery of the solid rocket boosters

After main engines shut down, the orbiter start spinning around the Earth in an egg shaped orbit. To avoid the orbiter re-enter into atmosphere and fall, 35 minutes after, when the shuttle reaches the highest point of the egg-shape orbit, both SSME are fired around three minutes to position the orbiter in a safe altitude keeping it above the atmosphere.

De-orbit and Landing

An on-orbit checkout is performed a day before de orbit. Before de-orbit, the orbiter rotates 180 degrees and the orbital maneuvering system engines (OMS) are fire to slowly get into the atmosphere. This process is called de-orbit burn. The fire burn lasts about three minutes. The firing takes place usually half a world away from the intended landing site. For example, to land in Kennedy Space center, the fire burn should start when the orbiter is above the Indian Ocean.

Before the orbiter reaches the atmosphere the left over fuel in the OMS is burn for precautions.

The orbiter reaches the atmosphere 25 minutes later approximately. Then, it is oriented around 40 degrees from horizontal to keep black thermal tiles on the underside facing the majority of the heat generated with can be up to 648.9 °C (3,000 °F). During re-entry, flights control computer is in charge. When the orbiter reaches 15,240 m (50,000 ft) high, commander takes over manual control of the approaching landing. So far, the orbiter can reach speeds up to three times sound speed (this is know as March 3). When the orbiter is aligned with the runaway, it is nose is angled down horizontal. It drops toward runaway 20 times faster than a commercial aircraft. Around 610 m (2,000 ft) commander pulls the nose and deploy the landing gears. On the touchdown he deploys the drag chute, which is in a compartment located below the tail, and begins to drop orbiter’s nose gear slowly towards the runaway. Before the wheels stop the drag chute is jettisoned.