As we are celebrating 50th anniversary of space technology, which has
revolutionised our lives, I am pasting an article from New Scientist.
Way to go; How hard can it really be to launch yourself into
space, asks Stephen Battersby
Stephen Battersby
HERE's how to make it into outer space. Step 1: fill a big tube
with fuel. Step 2: make a hole in one end. Step 3: light the
fuse... and whoosh, there you are.
Could there be any more to it? There is nothing in the way. You
don't have to reach any magical "escape velocity". And you don't
have to go very far.
Space tour operators are aiming for the Karman line, 100
kilometres up, which is roughly the altitude at which aeroplanes
don't work any more, because they would have to travel so fast to
get useful lift from the tenuous atmosphere that they would
effectively orbit the Earth. Conversely, the Karman line is too
low for satellites: that same atmosphere would quickly drag them
down.
Double the altitude to 200 kilometres, and the atmosphere becomes
thin enough that a spacecraft could orbit a few times before
being dragged back to Earth. You'll need to be travelling
horizontally at orbital velocity - 7.8 kilometres per second -
when you get up there, though, so that Earth's gravity bends your
path into a perfect circle. Then you can spend some time in
orbit, doing somersaults, playing with globules of drink and
pointing to your house from time to time.
How much fuel you need depends crucially on the speed at which the
exhaust exits your rocket, and that depends on how explosive your
fuel mixture is. Gunpowder - the most popular rocket fuel of all
time, if you count fireworks - will give you an exhaust velocity
of up to 1 kilometre per second.
Besides their payloads, rockets must also lift their own fuel, so
trying to go much faster than the exhaust velocity you soon hit
the law of diminishing returns. To accelerate a 1-tonne vehicle
to 7.8 kilometres per second, you'd need to burn an awfully big
pile of powder: 2500 tonnes of it, to be precise. Allowing for
the weight of the tanks to hold it all, the great space firework
becomes all but impossible.Frugal fuel
Using NASA's favourite chemical fuel mix - liquid hydrogen and
liquid oxygen - exhaust velocity can reach about 4 kilometres per
second. In theory, a 1-tonne capsule only needs about 6 tonnes of
such fuel to reach low-orbit speeds. In practice, it amounts to
rather more fuel than that, but the upshot is that you only need
several times the payload in fuel, not thousands of times.
There are other snags for the do-it-yourself rocketeer, though.
Being so explosive, the liquid oxygen-hydrogen combination is
hard to handle safely, so the pumps and engines must be
sophisticated pieces of engineering. Then you have stability and
guidance to sort out. And let's not forget the small matter of
getting back down in one, preferably unroasted, piece. Re-entry
is the most difficult part of all, with the risks of burning up
or bouncing off the atmosphere.
So can we all go? There are probably still enough fossil fuels
left on Earth to send all 6.5 billion of us into orbit by burning
aviation-grade fuels or by generating electricity to electrolyse
water into hydrogen and oxygen. If that happened, though, it
might not be worth coming back down again.
The environmentally aware space tourist could instead use
electricity from renewable sources. Solar cells on your roof
might gather 10 kilowatt-hours per day, enough to electrolyse a
couple of kilograms of water, so you'd only have to wait 15 years
to collect enough for a trip to space. Just enough time to get
into shape for the journey.
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