UC Student Launches Herself Into History

When NASA launches the Gravity Probe B space mission on April 17, it will change Jeannette Dehmer’s world.  Dehmer, a University of Cincinnati aerospace junior, will know she helped make scientific history in getting the satellite off the ground.

It’s all thanks to a recent, long-term work experience Dehmer designed as part of her

College of Engineering

cooperative-education requirement.  (Co-op, or cooperative education, refers to the practice in which students alternate time spent in the classroom with paid, professional work related to their major.)

From April-December 2003, Dehmer worked with Lockheed Martin Space Systems Company in Sunnyvale, Calif., helping to prepare the NASA/Stanford University satellite for its coming liftoff from Vandenberg Air Force Base in southern California.  It’s a project that’s been long in the making, since the idea for this probe and the scientific experiment it will carry were first proposed in 1960.  Lockheed Martin has been working on the project for just shy of 20 years. 

The satellite, known as Gravity Probe B, will remain in space for about 18 months and will use the world’s most precise gyroscopes to test two important aspects of Albert Einstein’s General Theory of Relativity that deals with the curvature of the time/space continuum and Earth’s effect on the continuum.  Basically, Einstein predicted that space and time are distorted by the presence of massive objects, like planets.  The GP-B mission will shape our understanding of Einstein’s theory and will help solidify our understanding of topics like black holes and the evolution of the universe.  If the results of the relativity probe are not consistent with Einstein’s theory, it would significantly change the scientific perception of the universe’s structure and the motion of matter.  (If you’re really into it, look below for more links.  For the rest of us, it pretty much suffices to know that the project is one of the most sophisticated physical experiments ever attempted, and it’s making scientific history.) 

Recalls Dehmer, “I learned about the probe my first day at work, and by the third day, I was in the hi-bay actually staring at it.  I was hired into a group that worked one test for the spacecraft and was supposed to move on to other things at its completion.  By that time, however, I wasn’t ready to move on, so I asked to join the Gravity Probe B team.  I thought, ‘What’s the worst that can happen?  They say, ‘No.’” 

Obviously, that didn’t happen.  And since, according to Dehmer, “The excitement of it all is incredible.  There have only been about 200 people all told who have worked on this project at Lockheed Martin over the last 20 years.  They’ve been working on this almost as long as I’ve been alive.”

While Stanford and NASA have designed the experiment within the satellite, Lockheed Martin designed and tested the satellite itself.  Making sure the vehicle was ready to launch was where Dehmer fit in.  “All satellites are different,” she explains.  “Each one is built for a different purpose, so each one is a unique challenge.  And, with each one, you’re not going to get another shot at it, so everything has to be rigorously prepared, tested and retested for the big day.”

Dehmer ran a variety of checks, including what’s called the “thermal vacuum test.”  In this procedure, the 21-foot-long satellite is placed within a sealed chamber.  The air is pumped out, thus simulating the vacuum of space.  Lamps above the surface of the satellite mimic the heat and radiation of the sun to assess the craft’s ability to withstand the temperature extremes Gravity Probe B will encounter in orbit.

Dehmer was monitoring the thermal vacuum tests for about a month back in the spring, and she admits to being nervous at being given so much responsibility.  “I was both happy at being treated like a regular employee, but I was also happy that there was another thermal engineer on hand,” she recalls.

Another test that Dehmer helped to run involved the craft’s propellant.  Basically, Gravity Probe B will move in space under power provided by helium.  Liquid helium will be stored on the craft in a container called the “dewar” which Dehmer likens to a thermos.  Some of this liquid helium will be evaporated as a gas that is then vented through the 16 thrusters, which will, in turn, then power the vehicle’s movement.  Says Dehmer, “It’s like how an air-filled balloon is propelled when you let go of the balloon neck, and the release of air sends the balloon airborne.” 

Dehmer performed flow-rate testing of the spacecraft’s 16 thrusters.  “It all takes much longer than it probably sounds,” she adds.  “It takes time to set up the equipment for each thruster, run the test and log the results.  Because of the effects of gravity, we have to test the thrusters while they’re in a horizontal configuration.  Therefore, we had to tilt the vehicle into a vertical position to test the last four.”

In all of the tests, Dehmer reports that nothing went terribly wrong.  “We found that some of the thermostats weren’t hooked up correctly to the heater tape (through which current passes to heat components of  the spacecraft when it’s not exposed to the sun’s heat).  We also found some contamination of one of the thrusters, and that was cleaned up.”

Because the satellite’s launch is approaching, the vehicle was moved in July to California’s Vandenberg Air Force Base.  That’s where it’s slated to launch on April 17 aboard a Boeing Delta II rocket.  Once in space, it will settle into an almost perfect circular polar orbit around the earth. 

Dehmer helped with the loading, transport and unloading of the craft, all of which is a very delicate process:  “You have to be so careful when you’re putting it on the truck.  We’re constantly testing the vibrations and how those are affecting the craft.  It took an entire day just to load the probe on a truck….” 

Links for more info on Gravity Probe B:
http://einstein.stanford.edu
http://www.gravityprobeb.com
http://www.ksc.nasa.gov/elvnew/gpb/index.htm