Why can't we fly a plane into space
what stops it from just flying higher and
higher until it in space.
well there are several issues but
assuming we are in something like a
normal jet airliner then one of the main
problems is the air or lack of it as we
get closer to space.
a plane flies because it is propelled
forward the wings which shaped to make
the air flow faster of the top of them
rather than the bottom generate lift as
the plane goes faster the wings create
more lists when the lift is greater than
the weight to the plane it will climb into
the air. As our playing climbs higher and
higher into the atmosphere the air
becomes less and less dense the plane to
fly faster to create more iift until
eventually it reaches an altitude where
the engines either cease to function
correctly because of the lack of oxygen
or the air is too thin to create enough lift.
Just as we need air to breathe then the
engine need oxygen to burn to create
thrust to propel the plane forward just
engines however engines can work at higher
altitudes than people. We humans have a
limit about 8,000 meters or 26,000 feet
above which is what climbers
call the "Death Zone", this is where there
is not enough oxygen for humans to
survive for sustained period. The summit
of Mount Everest is 29,000 feet high in
the air density there is about
33% of that at sea level.
This means that with each breath you
take you're only getting
33% of the oxygen. If you want to
stay at this altitude without additional
oxygen you would suffer from a condition
called hypoxia were due to a lack of
oxygen to the body starts to slow shut
down and die.
At 12,000 meters or 40,000 feet which is
the upper limit for most modern
airliners the air density is about
18% of that at sea level. If you
were in a plane that had a rapid
decompression at 40,000 feet you'll have
about five maybe ten seconds to get your
emergency oxygen mask on before you
became unconscious. The highest flying
jet plane in level flight was the
Lockheed SR-71 blackbird with a height
of 85,069 feet 42,929 meters
and where the a density is just 2% of
that sea level. At that height it's
traveling at mach 3.2 or 2190 miles an
hour. The SR-71 pilots had to wear a full
pressure suit with its own oxygen supply
in case of a cockpit decompression or
emergency ejection and this was put to the
test when you 1966 an SR-71 piloted by
Bill Weaver disintegrated that mach 3.1
at an altitude the 78,000 feet as it was
performing a test flight to ironically
optimizing performance. At that altitude
your blood will boil in a similar way to
when you open a bottle of fizzy drink as
the nitrogen in your blood to the gas in
the low-pressure atmosphere. The pressure
suit work and Weaver survived the
descent from 78,000 feet but tragically
the navigator Jim's Zwayer died of a broken
neck resulting from break of the
plane. Now while you would think that the
SR-71 soft to get into space you need to
reach what is called "escape velocity"
this is where you are traveling faster
than gravity is pulling you back to work
and that is 25,020 miles an
hour or 40,270 km/h and
and if that wasn't a problem there's
also to recognized altitude at where
space starts at 328,000 ft
or 100,000 meters
well over three times the
highest flight of the SR-71. Normal jet
engines like those in the SR-71 have a
maximum air speed limits for around
about Mach 3.5 or 2695 miles now beyond
that the air pressure and temperature
becomes too high for compresses and the
engine to effectively. For hypersonic
speeds, experimental unmanned aircraft
like NASA X-43 use what is called a scramjet
engine. The X-43 is currently the fastest
free flying air-breathing aircraft in
the world having flown at mach 9.6 or 7310
miles an hour in November of 2004.
Scramjets do away with the turbine
compressors of the jet engine so they
have no moving parts instead they use
shock waves in the engine to compress
the raise the temperature in the engine to
burn fuel and create trust an in theory
they can fly up to Mach 20 and possibly
beyond. The problem with this is that
they won't work at speeds of less than
around Mach 5 so they have to be
brought up to speed by rocket engine
booster before they can operate, which is
how NASA x43 worked. They also won't
work in space because there is no air
with oxygen in to combust the fuel
So this why space vehicles are
launched by Rockets. Rockets can have
much more power and can operate from a
speed of zero on the launchpad to Mach 33 and
beyond which is the escape velocity of
Earth. One of the earliest experimental
space planes was the North American X-15
which reached a height of 353,000 feet
or 107,000 meters 1963 and was
powered by a liquid rocket danger but it
had to be carried up to 45,000 feet
attached to the underside with B-52
bomber before being released. Then of
course we've had space shuttle the
Soviet version of the Space Shuttle
the "Buran", SpaceShipOne and the Boeing X-37,
all of which were examples of space
planes but we're really just rocket powered gliders.
Rocket differ from Jets
because they bring their own oxygen to
burn the fuel and don't rely on the
atmospheric oxygen.
This means that they can working space
equally as well as in the atmosphere. The
problem with rockets is that because they
need to bring the oxidizer with they makes
them very heavily. Look at the space
Shuttle for example, the external fuel
and the tanks to hold it along with the two
solid rocket boosters weighed 1,940 metric
tonnes at liftoff and that's without the
space shuttle. All of which has to be
carried along with the shuttle to the
edge of space where they are they
jettisoned. The maximum payload the shuttle
could deliver it into a low earth orbit was
27.5 metric tons, which as a payload
fraction is just 1.3% of the total
take off weight.
Rockets however can create huge amount
of power, so they can achieve the
speed that is need to escape the pull
of gravity and go into orbit and Beyond.
But what of the future, will we ever get
planes that can take off from an
aircraft runway, fly into space and then
return back to a runway. There are
still considerable technical issues to
overcome but one design which looks
promising is the Skylon. This is an SSTO
or Single Stage To Orbit design meaning
that unlike a rocket, it stays in one
piece rather than having a separate main
booster stage which detaches and return
to Earth and then a smaller second stage
which one goes on to orbit. The key
technology makes Skylon work is the SABRE or
Synergetic Air Breathing Rocket Engines.
Now these are kind of hybrid jet rocket
engine which can take off like a normal
jet engine, breathe air upto 93,000 feet
and at a speed up to Mach 5.4 when then
switches to rocket mode and can fly
into space for up to 800 kilometers 500
miles above the earth. It would then
return to the Earth's atmosphere and
land as normal air-breathing plane to be
checked, refueled and ready for launch.
Because it uses more efficient engines
and the lift of the wings it would use
only 20% of the fuel compared
to a conventional rocket. It would still
need to bring it oxidizer for the rocket
portion of the journey but a lot less
that will be required for a normal
rocket. This allows for a larger payload
when compared to the total weight around
5.5% compared to the shuttles 1.3%.
Unmanned flight test of the Skylon
could be happening by 2025, if all goes
well but a
potentially large flying in ointment is the
recent advances in reusable rockets like
SpaceX Falcon f9r and the Blue Origin
New Shepherd. These could make the
development costs to the Skylon
expensive for satellite deployment and
supplying the International Space
Station. One thing which could come out
though, is a rocket less version of the
SABRE engine which could make hypersonic
air travel more a viable option than using
a scramjet.
Only time will tell but this is an
exciting time for both the future of air
and space travel, so we may yet see the
plane that can fly to space. So as always
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