Subject:
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Re: Wings [was: Re: Building big]
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Newsgroups:
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lugnet.space, lugnet.loc.au
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Date:
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Tue, 19 Jun 2001 21:38:07 GMT
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Viewed:
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6987 times
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"Jesse Alan Long" <joyous4god2@yahoo.com> writes:
> The Apollo space craft were essentially rockets that allowed for humans to
> live inside of them in a small compartment and your fuel was primarily used
> for sending you into outer space and not necessarily down from space.
It's more complicated than that. The rocket was a several-stage
affair; the first few stages would drop off and burn up as you head up
through the atmosphere; by the time you reach orbit only a small
amount of rocket is left. The Lunar Module (LEM) was very much not
streamlined or rocket-shaped, and was stored inside the rocket. Once
they got into Earth orbit, the LEM was removed from the rocket, which
was then dropped into the atmosphere, leaving only the command module
and LEM. These units then left Earth orbit together for the moon,
propelled by the command module's rocket engine.
When they got to lunar orbit, the LEM was detatched and two of the men
went to the surface while the third orbited in the command module.
The LEM's rocket was used to soften the lunar landing. Since the
moon's gravity is only 1/6 that of Earth's, and there is no atmosphere
on the moon to cause friction, the LEM did not need to be streamlined,
or have wings, or a heat shield. After the mission was complete, the
LEM then divided in half - the part with landing gear and the main
engine was left on the moon, and the part with the astronauts took off
using yet another rocket engine up to meet with the command module.
When the crew returned to earth, the only part of the whole spacecraft
which survived was the crew compartment of the command module.
Instead of using wings to provide lift, the module was equipped with a
heat shield which took the friction from the Earth's atmosphere and
kept the resulting heat away from the astronauts. The friction on the
heat shield slowed the module to a reasonable speed, and finally
parachutes were used to slow it further, until it landed in the ocean.
> The
> fuel that was left from the trip into outer space provided the protection
> from entering into the atmosphere too fast by using retro rockets but even
> with the use of retro rockets, you were accelerating so fast towards the
> earth that you has to land in the ocean or else you would disentigrate
> either from the heat or the impact on the earth and either way, you would
> die from your trip to the moon.
This is not true - retro rockets were used for landing on the moon,
since there is no atmosphere to provide the friction which would slow
the craft down. But when returning to Earth, the atmosphere was used
as a brake, using a heat shield. No rockets were used at all on Earth
re-entry. The friction slowed down the craft enough that they could
then deploy parachutes for a soft landing in the ocean.
Also, the term "accelerate" means to speed up. When re-entering the
atmosphere, you are slowing down, not speeding up. Physicists would
call that reverse acceleration, but in common use you wouldn't use the
term "accelerate".
You are speeding so fast towards the Earth that you have a lot of
friction when you hit the atmosphere, and need to find a way of
dealing with the friction. The Apollo craft (and Mercury and Gemini
before them) used a round, mostly flat heat shield. The Space Shuttle
is covered with special tiles which dissipate the heat - the bottom of
its wings and fuselage act as a heat shield. Once you have slowed
down enough that you don't have so much friction, you can then use
wings, parachutes, retro rockets, or other methods to slow down even
more so that you can make a soft landing. But in the initial phase of
re-entry, the atmospheric friction would burn up the wings (unless
specially built, like the Shuttle's), rockets, or parachutes.
Also, landing in the ocean really isn't that important: the Russians
built similarly designed craft, although they never went to the moon,
but they land on the ground! The Soyuz craft that they used for their
space missions (and still do, to resupply the International Space
Station, and Mir before that) operate on the same principle - a rocket
launches it into orbit, and a heat shield and parachute are used to
slow it down on re-entry - the difference is, they land on the ground
instead of in the water. Landing in the ocean is easier for the USA
as we have a more advanced Navy, and more sea ports. Russia doesn't
really have any good ports, and most of their Navy is in the form of
submarines. So they chose to land on the ground instead.
If you've ever done a bellyflop into a swimming pool, you know that
water doesn't necessarily make a soft landing. If you've ever jumped
off a rock high above the water and landed wrong, it can hurt almost
as much as landing on the ground. People commit suicide by jumping
off bridges, because the impact on the water from 200 feet up will
kill most people. Landing on water doesn't really help very much -
it's the parachutes that kept the astronauts alive, not the ocean.
> The comment on the antennas is still true
> because there are millions of tons of space debris that is flying around
> that could damage such equipment on a ship.
Antennae and other items can be damaged in re-entry. But in orbit,
interplanetary travel, etc., the debris is very uncommon. You are
correct that there are millions of tons of debris. However, space is
just so huge that the odds of finding a piece of debris and being
unable to steer around it is very unlikely. Satellites, space
stations, Apollo ships, NASA's robotic probes to the outer planets,
etc. all have antennas and solar panels and similar things sticking
out in all directions. They are almost never hit by debris.
> There are two other points that
> you fail to consider and the first point is some of these space craft are
> horribly bulky and therefore not very streamlined in their structure. These
> space craft would be considered very easy targets by their enemies.
If you are talking about a scenario where there are enemies, then this
may be a valid concern. Streamlining is not really what would make
you a more difficult target, however - moving very fast and being very
small is more effective. The shape is not so important as the size -
you want to make a small target.
However, there are not necessarily any enemies in space. I design
spaceships in a peaceful universe where Earth has colonized the near
planets and moons, and has some orbiting space stations. Commercial
cargo ships, mining ships, pleasure craft, etc. are the types of ships
I prefer to build. None of my ships are armed for combat. But not
everyone builds for my universe :-)
> The
> second point that you failed to consider is if the concept of gravity did
> not exist in space, then what not only holds the planets into their orbits
> but also holds the stars and galaxies in their orbits and makes comets and
> asteroids hurtle through space? The only way that I know of in my mind that
> gravity can not exist is within a scientific laboratory. Space has less
> gravity than a planet, star, galaxy, asteroid, or comet and space does not
> nave a lack of gravity inside that realm of the universe.
OK, to be more precise: gravity does exist, but you don't feel the
same kind of pull that you feel on Earth. If you are in orbit, you
are actually falling all the way around the body you are orbiting.
An airplane needs to have wings to keep from crashing into Earth. A
helicopter's rotors blow air downwards to push it upwards. But in
space, the gravitational pull does not have the same kind of effect.
If you are orbiting, you do not need to do anything to stay in orbit:
you can turn the engines off, and wings are not required. If you are
flying to the moon, for example, you basically set a course, burn the
rocket to accelerate enough to pull free of Earth's gravity, and then
shut off the engine and drift in the right direction. When you get
closer to the moon its gravity will start to pull you away from a
straight line, and if you've set your course correctly, a slight burst
from the retro-rocket will put you in lunar orbit.
So you are right - there is gravity in space. But it doesn't have the
same sort of effect as on a planet: so wings are not necessary (and
there's no air for them to operate against anyway), and you don't need
to constantly run the engines as you would in an airplane.
--Bill.
--
William R Ward bill@wards.net http://www.wards.net/~bill/
(formerly known as hermit@bayview.com)
-----------------------------------------------------------------------------
Life is too important to take seriously.
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Message is in Reply To:
 | | Re: Wings [was: Re: Building big]
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| (...) The Apollo space craft were essentially rockets that allowed for humans to live inside of them in a small compartment and your fuel was primarily used for sending you into outer space and not necessarily down from space. The fuel that was left (...) (23 years ago, 19-Jun-01, to lugnet.space, lugnet.loc.au)
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