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A New Spin on the Constellation Program
08.08.07

Joysticks are used to control all sorts of things -- video games, wheelchairs, cranes, elevators and even some lawn mowers.

Instead of using a joystick for games, imagine using one to control the speed of a 20-foot (6.1m) diameter fan capable of accelerating air from a rest position to 66 miles per hour in a matter of seconds.

Then imagine that you're a NASA engineer conducting a wind tunnel test on a new spacecraft model -- a test that could potentially save the lives of astronauts depends upon your skill with the joystick because you're controlling how fast the tunnel's fan spins.

NASA engineer prepares to release a scale model of the Orion crew vehicle into the Vertical Spin Tunnel air stream

Image to right: A NASA engineer prepares to release an Orion crew vehicle scale model into the air stream in the Vertical Spin Tunnel. Click image to see a larger version of the photograph. Credit: NASA/Sean Smith

It's not all fun and games at NASA Langley's 20 foot-Vertical Spin Tunnel, also known as the VST. The facility has been used in testing aircraft and spacecraft since 1941.

Today the spin tunnel is the only operational wind tunnel of its kind in the Western Hemisphere that conducts free-spin research using dynamically-scaled, free-flying models. It investigates spinning, tumbling and free-fall characteristics of aircraft and spacecraft. But it's different from most wind tunnels that you might have seen because the air in the test section flows upward rather than horizontally.

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"The United States Air Force has one at the Air Force Research Lab at Wright Patterson Air Force Base in Dayton, Ohio," said Mike Fremaux, a research engineer at Langley's tunnel. "They do not do free-spin testing [there] any more, not since the 1960s."

Fremaux explained that other research-oriented spin tunnels exist in France, Germany, Russia and coming soon in China. Some spin tunnel facilities, such as a location in England, have been turned into recreational complexes for indoor skydiving.

"Although the VST is in its seventh decade of operation, it still plays a critical role in NASA research, national defense and aviation safety because the problems it was designed to deal with, like spins and other out-of-control phenomena are still beyond reliable prediction by our best computational fluid dynamics codes," said Fremaux.

Currently the spin tunnel is supporting NASA's Constellation program. From the initial take-off of the Ares I launch vehicle to the safe re-entry of the Orion crew vehicle into Earth's atmosphere, the spin tunnel is involved in design testing. It's also testing the dynamic stability of the Orion launch abort vehicle (LAV), the crew module (CM), the Orion alternate launch abort system (ALAS) and the Orion crew module drogue parachutes.

"In the LAV, CM and ALAS tests," said Fremaux. "we have gotten a good understanding of the dynamic stability of the vehicle when it is flying tower-forward, as it will during the initial part of its fight, and heat shield-forward, which it will do just before the tower is jettisoned and the parachutes deploy."

Fremaux explains that dynamic stability tests examine the tendency of a model or vehicle to perform unwanted motions. These tests observe whether wobbling motions decay or stabilize.

In studying the re-entry of the Orion capsule into Earth's atmosphere, the spin tunnel is testing the drogue parachutes. These chutes will deploy from the capsule to lower the speed of its descent and stabilize the vehicle prior to the main parachutes opening. The results from the tests will help guide designs to create a parachute system that will help Orion land safely.

The Vertical Spin Tunnel has been around for a while, but it's still an important resource for testing and evaluating aircraft and spacecraft designs.

Rachel C. Samples
NASA Langley Research Center