March 27, 2008

Space Shuttle Upside Down

Stupid Question ™
March 23, 2000
By John Ruch
© 2000

Q: Why does the space shuttle rotate while taking off instead of just going straight up?
—Kaleb Wilson

A: The space shuttle has an attitude problem. “Attitude,” of course, is the orientation of a spaceship on its vertical, horizontal and longitudinal axes.

Unlike most rockets, the space shuttle is both too heavy and too fragile (what with those little wings) to be hurled straight up into space. Instead, it sneaks its way into space upside-down and on a gently curving path.

At liftoff, the shuttle goes straight up only about 40 feet above the launchpad tower. Then it begins a combined right-and roll and angled ascent. Known variously as the “roll program,” “roll maneuver” or “tilt maneuver,” it results after about 20 seconds in the shuttle traveling upside down at about a 78-degree angle, and in an eastward direction.

Later on, the angle smooths out to a horizontal path, and the orbiter (the actual spacecraft part) actually makes a dive back toward Earth to pick up momentum that gets it going fast enough to launch into orbit. The orbiter remains upside down the whole time, and usually stays upside down in orbit, flipping over only to re-enter Earth’s atmosphere.

The roll program accomplishes several things. Obviously, it’s necessary for putting the shuttle on the right course, and in such a way that the 115-ton orbiter can get enough momentum to escape the atmosphere.

The angled ascent also reduces aerodynamic loads on the shuttle, which among other things keeps the wings from snapping off. The maximum air pressure (or “max Q”) that the shuttle can sustain is 580 pounds per square inch, and it hits that mark during launch.

The main purpose in placing the orbiter upside down is to get the rockets and fuel tank out of the way so the crew can see the ground and horizon. That would simplify any emergency-landing flying they might have to do. The upside-down attitude also improves radio contact, since it means there’s less metal between the ground and the orbiter’s antennas.

The orbiter generally remains “upside down” (a relative term in weightless space) in orbit unless there’s a good reason to flip it over. It saves energy, and ensures the crew (and its scientific cameras) a good view of Earth through the windows.

If you’re worried about the astronauts’ faces going crimson from hanging upside down during the launch, fear not. The downward pull is negligible compared to the force—three times that of gravity—pushing them back into their seats when accelerating up to 17,000 mph.

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