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Space Exploration/Rentry to Earth from space

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Question
I just saw the movie "Gravity". One question has always puzzled me. Here's what I think I know: the earth's gravity is pulling objects toward it. In order to maintain an orbit around the earth and object #like a satellite# has to maintain a certain speed. When I watch shows of earlier space missions, the capsules always reenter backwards with a heat shield. My question: why does the shuttle #or earlier capsules# have to reenter the earth's atmosphere at such high speeds and create all that heat? Why can't they slow down and just drop into the atmosphere and deploy a chute? I know I'm probably missing something basic.

Answer
Hi, Kadry, thanks for writing.  For a spacecraft to slow down that much, it would take about as much energy as it did to make it go into orbit, which means the orbiting object would be huge, taking about twice the size and energy to get into space.  The reentry used now uses the atmosphere to slow the spacecraft down (releasing the speed energy as heat energy), using a small amount of fuel to decrease the altitude so the spacecraft drops into the atmosphere.  It's all a matter of fuel conservation.  Also, if the spacecraft slowed down enough to parachute, it would have already dropped into the atmosphere-it takes time to slow from about 5 miles a second to parachuting speed.  It's also a matter of physics and altitude being too low for it to work.  Write anytime.

Space Exploration

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Kenneth Renshaw

Expertise

Answer basic space flight questions, research info on specific space flights. Answer questions on astronomy

Experience

Amateur astronomer and avid astronomy/space flight fan for 31 years.

Organizations
Official NASA/JPL Solar System Ambassador for Arkansas and Missouri (one of about 300 nationwide). (http://www2.jpl.nasa.gov/ambassador/profiles/Kenneth_Renshaw.htm)

Publications
Numerous local and area newspapers.

Education/Credentials
AA/BME/MME

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