Launch Management

views updated

Launch Management

A sleeping cylindrical giant points upward from a large concrete slab. Next to it stands the launch tower, pumping fuel into the cylinder and ferrying technicians up and down the length of its body. The voice of the launch controller intones: "T minus one second . . . ignition." The giant roars up into the sky, impaled on a pillar of fire and smoke.

Flowery metaphors aside, this is an ordinary, everyday rocket launch. However, the steps leading up to that moment are anything but ordinary. Understanding these steps requires a basic knowledge of how rockets are built.

To escape Earth's gravity, rockets utilize a technique called staging. A staged rocket consists of two or more cylindrical rocket bodies stacked one on top of another. Each stage has its own propellant, tanks, engines, and instrumentation. The first stage does the heavy lifting of getting the vehicle off the ground. When its fuel runs out, the empty stage is jettisoned and falls back to Earth, after which the next stage takes over. Since dead weight is dropped continuously, staging reduces the total amount of propellant needed to put people or satellites into orbit.

Standing Up versus Lying Down

The process of attaching the stages of a rocket to one another is known as integration, and it can be done in one of two ways—vertically and horizontally. Most American launch vehicles, including the space shuttle, are assembled vertically—standing up.

The payload and the upper stage are first put together, or mated, in an integration and test facility. Then the payload is sealed within a protective compartment known as the payload fairing (the nose cone) and transported to the launch pad, where the stages are placed on top of one another by cranes.

The alternative method, favored by Russia and other countries, is horizontal integration. With this approach the rocket is built lying flat and then is transported to the pad and hoisted upright. Horizontally integrated rockets such as the Ukrainian Zenit-2 can be rolled out, erected, and launched in a matter of hours. By contrast, the large, vertically assembled American rocket the Titan IV can tie up a pad for several months, and even the space shuttle can wait on the pad up to four weeks before blastoff.

Counting Down

The countdown begins from a few hours to a few days before launch (T-0). That time is taken up by extensive tests and fueling procedures. Rockets that use solid propellants, such as the space shuttle's solid rocket boosters, arrive with the propellant already stored inside them in a puttylike form. Liquid propellants such as liquid oxygen/liquid hydrogen (LOX/LH₂) must be pumped onboard at the launch site.

An hour or two before launch the guidance software that controls the vehicle's ascent is loaded. This is delayed until the "last minute" so that accurate weather data can be incorporated.

As liftoff approaches, various batteries within the vehicle are switched on. Since most rocket flights last only eight or nine minutes, long-lived batteries are unnecessary. However, if the countdown must be stopped after the batteries have been switched on, they may run out prematurely, requiring the launch to be scrubbed while the batteries are replaced.

If everything goes smoothly, when T-0 arrives, the rocket ignites and the mission begins. This moment, representing the culmination of countless hours of work by the ground crew (in the case of the space shuttle, 11,000 people at Cape Canaveral), is a time for celebration and relief.

Recycled Space

With the exception of the space shuttle, all launch vehicles today are one-use only. This makes getting into space very expensive. The key to reducing these costs is the development of reusable launch vehicles (RLVs), which will operate like aircraft: After each flight they will undergo inspection, refueling, and reloading and then launch again within hours. By comparison, a 747 airplane can spend 21 hours of each day flying, with only minimal maintenance on the ground. When such efficiency is achieved in space launches, the cost of getting into space will drop precipitously.

In March 2001 the National Aeronautics and Space Agency (NASA) canceled the X-33 and X-34 experimental vehicle programs, two of the major pillars in the agency's efforts to develop an RLV to replace the space shuttle. NASA and prime contractor Lockheed Martin spent nearly $1.3 billion on the X-33, which was intended to pioneer single-stage-to-orbit launch technology. Escalating costs and engineering difficulties led to the program's cancellation.

NASA is still striving to develop a successor to the space shuttle through the $4.5 billion Space Launch Initiative. Under this program, NASA is scheduled to begin development of a new RLV in 2006.

see also Launch Industry (volume 1); Launch Sites (volume 3); Launch Vehicles, Reusable (volume 1); Reusable Launch Vehicles (volume 4); Spaceports (volume 1).

Jefferson Morris

Bibliography

Angelo, Joseph. Encyclopedia of Space Exploration. New York: Facts on File, 2000.

Isakowitz, Steven J., Joseph P. Hopkins, Jr., and Joshua B. Hopkins. International Reference Guide to Space Launch Systems. Reston, VA: American Institute of Aeronautics and Astronautics, 1999.

Lee, Wayne. To Rise From Earth: An Easy-to-Understand Guide to Spaceflight. New York: Checkmark Books, 1995.