Coming home: steps of a shuttle's re-entry
Amina Ali, CBC Newsonline | Feb. 3, 2003
A shuttle's lift-off and re-entry are considered the most dangerous moments of a space mission. In 1986, the space shuttle Challenger exploded when a flame from a leaky joint on one of the solid rocket boosters ignited the fuel in an external fuel tank.
In 1967 and 1971, four Soviet cosmonauts died during re-entry. But in 42 years of human space flight in the U.S., there were no landing accidents until the space shuttle Columbia disaster on Feb. 1, 2003.
When the shuttle initially comes down, it is travelling at Mach 25 – 25 times the speed of sound, or over 30,000 kilometres per hour. It has to eventually slow down to zero to land.
To slow down, the shuttle turns energy into a lot of friction and heat. As the shuttle drops to about 20,000 km/h, the astronauts on board can see a huge fireball out the window.
"We are being buffeted by this tremendous atmosphere we bump into," said former Canadian astronaut Roberta Bondar.
The extreme heat can reach 1,650 degrees Celsius.
Shuttle Re-entry |
When all goes well, the shuttle goes through a series of steps to slow down enough to land safely:
1) The shuttle's orbiter flips upside down to gain protection from solar heat and radiation.
2) After receiving the command from mission control, the shuttle crew fires its rear thrusters to move into a tail-first position to help slow it down.
3) Crew fires rear thrusters again to orient the orbiter with its bottom facing the atmosphere at about a 40-degree angle. Shuttle returns to nose-first position.
4) Leftover fuel is burned as a safety precaution (the fuel faces the most heat during re-entry).
5) As the atmosphere burns outside, the astronauts lose communication for about 12 minutes. To get rid of more speed, the shuttle goes through a series of wide "S" turns, like a skier going down a hill.
6) When the orbiter reaches 610 metres above the ground, the shuttle falls at a steep angle. Landing gear is deployed 25 seconds before touch down.
Former NASA mission control specialist Jim Oberg notes most disasters aren't caused by one mishap, but by a chain of events that all conspire to go wrong on the same day.
In the case of the space shuttle Columbia, so far investigators are looking into two main things that may have gone wrong. But they caution many other factors could have been at work.
First, during liftoff, a piece of foam appears to have come off the left side of Columbia and hits the underside of its wing. After the launch, engineers thought there hadn't been much damage from the foam.
But no one could see the underside of the shuttle, and the tiles that protect the shuttle from high temperatures may have been knocked off.
Secondly, something may have gone wrong as the shuttle was attempting to re-enter the atmosphere. As the shuttle was making an "S" turn to the left, sensor readings suggested something was wrong with the elevators at the back of the shuttle. The elevators help the shuttle to turn.
If the elevators aren't working, or if there is a hydraulic problem, or if the equipment was knocked off completely, then the shuttle can't steer. It would be like a high-speed car that spins out after losing its steering.
If the shuttle loses its orientation, it will turn sideways or roll over, losing its aerodynamic shape. In a matter of seconds, the high pressure from the air hitting the fast-moving ship would tear it apart.
Sources:
NASA- Deorbit and Landing,
How Stuff Works: Re-entry and Landing ,
Space Science Group/Northwestern State University: Shuttle Re-entry and Landing,
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