Suppose
you wish to launch a 50-kg payload into space. To launch those
50 kg you may need 50 kg of fuel. But wait, now you need to
lift 100 kg, so you need to add more fuel to lift the original
fuel. Adding more fuel adds more weight so you'll need to add
more fuel which adds more weight...
As
it turns out, over 90% of the weight of a rocket is fuel. You
have to haul around a huge, empty gas tank once you make it
into outer space. That is why many rockets are multistage.
For another solution to the fuel-weight dilemma, you could
build a...
...laser-propelled
airbreathing engine
The Lightcraft is a vehicle that carries no fuel. Instead, the
craft gets its energy from a ground-based laser. Pulses from
the laser strike a mirror at the rear of the craft and are focused
into a propulsion chamber. The concentrated laser pulses superheat
the air into a 54 000° F plasma which then expands
explosively out the back to produce thrust. Air then reenters
the chamber just in time for another laser pulse. Viola, you
have power without carrying any fuel (at least while you are
in the atmosphere).
Before
the test flights, the scientists spun the craft. Why did they
do this? What problem do you suppose they are trying to solve
by having the craft spin?
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