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ATO #112 - June 24, 2000


PART 1: Upcoming Chats
PART 2: Project News
PART 3: The Arc Jets in Action

 Beat the Heat: Thermal Protection Chats!
 We will be chatting and with researchers from the Space
 Technology Division at NASA Ames Research Center. I think you will find
 this fascinating and a worthwhile topic. This will introduce you to the
 topic of materials for thermal protection and the use of computer models
 for predicting the heat generated by vehicles entering different
 planetary atmospheres. This is a very important topic for those of you
 who plan to travel in space in the near future.
 Tuesday, June 27, 2000 10 AM Pacific
 George Raiche, Research Scientist
 George studies how well spacecraft perform as they enter a planets
 atmosphere. Read his bio at http://quest.nasa.gov/aero/team/raiche.html
 Tuesday, July 11, 2000 10 AM Pacific
 Christine Johnson, Researcher,
 Christine has been doing tests on thermal protection materials that can 
 be made into flexible materials which can be made into thermal blankets,
 not the kind you sleep with but the kind they wrap over the top of
 shuttle. How's that for cool?

 Virtual Skies is an air traffic management project for students and
 teachers in Grades 9-12. It will be a "project based learning
 activity" with hands on multimedia to enhance student decision making   
 and problem solving skills. Materials will be tied to the National
 Standards in Mathematics, Science, Technology, Geography and Language
 Arts. Stay tuned for more news as we crank up over the summer!

 Planetary Flight is an aerospace project for Grades 4-8. (more reason to
 attend summer chats). This will be an inquiry based learning project to
 design an airplane to fly on Mars. The stuff dreams are made of!! We will
 also be keeping you posted on this one this summer.

by George Raiche
June 23, 2000
The Arc Jet Facility at NASA Ames Research Center is used for studying
thermal protection materials. An example of a thermal protection material
is the ceramic tile on the Shuttle Orbiter. It uses heat and supersonic
speeds to simulate the energy experienced by a vehicle reentering the
Earth's atmosphere. Various materials are tested to see if they provide
effective thermal protection.

The arc jet sustains a standing bolt of lightning that heats the air up to
15,000 degrees Celsius. You can think of it as similar to a welding torch.
There is a huge arc of electrical energy that jumps across a gap between
two conductors. Air is blown through the lightning bolt and it gets heated
up. The air is actually stored at high pressure to achieve supersonic
speeds. The air is released once the arc is started. The air, heated by
the arc, expands through a nozzle which connects to a vacuum chamber.
This chamber is pumped by a building-sized vacuum pump, one of the largest
in the world. As the hot air moves through the nozzle, it expands, cools,
and accelerates, just like water through a garden hose. Now the air is
cooler (about 1000 degrees) but moving at supersonic speed.

When this supersonic air strikes a stationary object (the test model), a
shock wave forms over the model. The shock wave forms because the
collision speed is greater than the speed that the air molecules can flow
(the speed of sound), so the air molecules pile up and recompress. This
same compression effect is what happens during reentry, except the   
spacecraft is moving while the atmosphere is stationary.

This compression causes the temperature to rise again, just a few
centimeters away from the model surface. The temperature in the shock wave
is about 5000 degrees, about the same as for reentry. We measure the
temperatures of the shock wave, the model surface, and the interior of the
model, and compare them with computer calculations. There are several
different sets of computer sensors that collect data during a test. One  
type of measurement taken records the caloric heat or the energy of
the gas and the other type of data collection uses laser diagnostics. We
also inspect the size and strength of the model before and after the test,
to study how well it withstands this simulated reentry.

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