Do spaceships reduce speed before re-entry?

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Chris Gerber

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Do spaceships reduce speed before re-entry?
« on: 07/02/2011 07:30:03 »
Chris Gerber asked the Naked Scientists:
   
Hi Chris,
 
I know that 'spaceships' have to maintain a certain speed to stay in orbit.

Why can't they reduce speed in space before re-entry, to minimize the effect of friction and  the resulting heat?
 
Regards,
 
Chris Gerber

What do you think?
« Last Edit: 07/02/2011 07:30:03 by _system »

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Offline graham.d

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Do spaceships reduce speed before re-entry?
« Reply #1 on: 07/02/2011 09:19:01 »
Spacecraft reduce speed to lower their orbit so as effect a re-entry into the atmosphere. They then use the friction of the atmosphere to slow them down. In order to reduce speed to a low value prior to entering the atmosphere (and not use atmospheric braking) they would have to carry a significant amount of fuel to effect this. Also, gravity would be continually trying to accelerate them downwards and, in the very thin upper atmosphere, a high velocity would be reached unless countered by again using large amounts of fuel. With current technology it would not be practical to try to carry sufficient fuel to do this when atmospheric braking is effectively free.