[meteorite-list] Dawn Journal - November 30, 2010 stupid question

[Göran Axelsson]

The reaction wheels is powered by electricity from the solar panels. The 
reason (as I understands it) to power down the reaction wheels is to 
minimize the wear on bearings and motors.
Using the attitude jets for turning is just another way of aiming the 
craft. What they have done is simply slowed down the speed it turns. A 
small acceleration and a small brake takes less fuel than a larger 
acceleration and a harder brake. It just takes longer time.

For a solar powered spacecraft energy is free, reaction mass is 
expensive. The hydrazine and xenon is basically the same thing, to xenon 
energy is added from solar power while hydrazine contains it in it's 
chemical structure.

/Göran

Steve Dunklee wrote:
> This might be a stupid question but I was wondering if a future craft similar to this could use the ion propulsion unit to power the reaction wheels. And if the rection wheels or gyros are powered up to full speed before the launch if it could reduce the amount of energy neeeded? In addition a high powered maser could be used for attitude adjustment from earth or space withought using the energy aboard the craft. If designed correctly the craft could be repowered for attitude adjustment indefinately from earth instead of having to launch the energy from earth. Cheers Steve
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