Ascent

As we now have an idea about the construction and working of shuttles. Let us see the various steps involved in launching a shuttle, orbiting it around a planet/moon and then bringing the shuttle safely to earth.

Pre-launch preparation

As the shuttle rests on the pad fully fueled, it weighs about 4.5 million pounds or 2 million kg and it is supported on the solid rocket boosters (explained in construction of shuttle). The pre-launch preparations begin at T minus 31 seconds:

1. T minus 31 s - the on-board computers take over the launch sequence.
2. T minus 6.6 s - the shuttles main engines are ignited one at a time (0.12 s apart). The engines build up to more than 90 percent of their maximum thrust.
3. T minus 3 s - shuttle main engines are in lift-off position.
4. T minus 0.3 s -the SRBs are ignited and the shuttle lifts off the pad.

First stage

The first stage extends from the SRB ignition to its separation.

The space shuttle lifts off the pad at 0.3s after the SRB ignition and rises vertically in altitude till it is approximately at a height of 41 feet. The vehicle maneuvers into position with the orbiter head down, with wings level and aligned with the launch pad. The orbiter flies upside down during the ascent phase. SRB separation occurs six seconds after the SRB separation sequence software detects both SRB chamber pressures below 50 psi (pound per square inch). At SRB separation, the first stage is complete, and the software automatically shifts to second stage.

Second Stage

Second-stage ascent begins at SRB separation and extends uptill main engine cutoff and external tank separation. The main engines are commanded to begin throttling at 10-percent thrust per second to 65-percent thrust. This is held for approximately 6.7 seconds, and the engines are shut down. The vehicle altitude is frozen. During this time a signal is generated which confirms that main engine has been shutdown.

The external tank software sends the commands to close the 17-inch orbiter/external tank line feeding liquid oxygen and hydrogen and disconnects valves. The onboard general-purpose computers perform ET separation automatically.

During second-stage ascent, the flight crew monitors the onboard systems to ensure that the major events occur correctly and on time.

At time t plus 10.5 minutes orbital maneuvering system (OMS) engine fires to place the space shuttle into low earth orbit and at time t plus 45 minutes OMS engine fires again to place the vehicle into higher, circular orbit.

The space shuttle is now in outer space and continues with its mission.