Nine minutes prior to main engine engine ignition an automatic hold comes into effect for confirmation of launch status. Each mission has a series of launch windows. In the case of space station missions, each window is relatively short to ensure minimum energy is used to place the orbiter on an intercept course. In the case of other missions, the launch window is dependent, among other factors, on the required ground track for earth observation. A launch can be delayed for any number of reasons, including mechanical discrepancies or bad weather at Kennedy Space Center or any of the emergency landing sites in Spain or North Africa.
The main engines ignite 6 seconds prior to launch to balance the weight of the shuttle assembly with their thrust. Firing the solid rocket boosters is what lifts the assembly from the launch pad. As the space shuttle clears the launch tower, control for the remainder of the mission passes from the Firing Room at Kennedy Space Center in Florida to Mission Control at Johnson Space Center in Texas.
The big white cloud at launch is steam. A very powerful acoustic wave is generated at solid rocket booster ignition that can damage the shuttle assembly. Thousands of gallons of water are released into a pit at the moment of ignition thus generating the steam. Such an acoustic wave caused damage to the orbiter's heat shield tiles on the very first launch of "Columbia".
The solid rocket boosters are each attached to the launch pad with four explosive bolts. These bolts detonate simultaneously with booster ignition, allowing the space shuttle assembly to lift off. Each crewmember is presented with bolt fragments sometime after their return from a mission.
During the initial climb, the shuttle assembly must reduce thrust (and thus acceleration) to avoid aerodynamic overstress in the lower atmosphere. The assembly accelerates so quickly that the dynamic pressure (wind in your face) could otherwise cause unintended bits to fall off. If you have watched and heard the launch commentary, you have probably heard "Engines throttle up" which signifies reaching an altitude in which the atmosphere is less dense, thus allowing maximum thrust (104%) to be applied.
Two minutes after launch the solid rocket boosters are jettisoned. This is plainly visible from the ground as the rockets extinguish then fly off at opposite angles from the external tank. These boosters parachute into the ocean and are retrieved for use another day.
Approximately eight minutes afer launch, the main engines shut down and the external tank is jettisoned. A crewmember is responsible for photographing the tank as it departs from the orbiter before it falls into the atmosphere and burns up during re-entry.
The orbiter is now at the apogee of an orbit that if not corrected will result in atmospheric re-entry halfway round the world. The orbital maneuvering system engines ("cannons" as I have heard them described) are then fired to "circularize" (NASA-speak) the trajectory and stabilize the orbit.
The orbiter is maneuvered into whatever position is required for the work at hand, usually tail-first relative to the flightpath with the belly facing away from Earth. The payload bay doors then are opened to dissipate heat generated by the orbiter's systems.
Once in stable orbit the crew packs and unpacks as required and commences work on the mission objectives. These may vary among a wide range of experiments and observations, depending on the mission objectives and science payloads aboard.
For answers to the commonly asked question, "How do astronauts go to the toilet?", please visit the appropriate links below.
The day before landing, the crew packs and unpacks as required for re-entry. The commander and pilot also conduct orbiter systems checks to ensure correct operation.
- The re-entry sequence starts when the payload bay doors are closed and about one-half orbit prior to re-entry the orbital maneuvering engines are fired to reduce velocity from 17,000 mph.
The orbiter is then maneuvered to the nose-first and nose-up attitude required to for thermal protection and produce the desired flightpath in the atmosphere. Depending on the re-entry path and lighting conditions, ground observers can view the orbiter as it flies towards its landing sight. In the summer of 2000, we in Houston watched as "Atlantis" streaked by in the stratosphere on its way to Kennedy Space Center.
As the orbiter descends into denser air its aerodynamic control surfaces become effective and a series of S-turns are flown to dissipate energy, finally passing over the landing strip (usually Kennedy Space Center) at about 50,000 feet, signified to ground observers by sonic booms. The orbiter is flown manually around the heading alignment cone, an imaginary geometric figure off the end of the landing strip which positions the orbiter at the correct altitude, airspeed and glidepath once its wings are leveled.
The approach glidepath varies between 17-19 degrees (six times steeper than that of an airliner) while the orbiter descends the height of Mount Everest in a matter of seconds. At 1,700 feet above the ground, the commander pulls the nose up for a preflare which both reduces airspeed and the glidepath to three degrees. At 300 feet altitude, the pilot lowers the landing gear and a few seconds later the orbiter touches down nose high at about 200 mph, depending on weight. After the nosewheel touches down the pilot deploys the drag chute after which the orbiter rolls to a stop.
The foregoing are the personal observations of Jean-Pierre Harrison and do not constitute an official statement or endorsement by NASA or any NASA employee or contractor.
