-Z- (Z@Gundam.Com)
Wed, 27 Oct 1999 20:20:23 -0700


At 08:30 10/27/1999 -0700, you wrote:
>1) isn't it all as simple as ---> if an object
>possesses enough power to fly/hover in atmosphere, it
>possesses enough strength to get out of orbit and out
>into space (and anywhere in space, given enough fuel)?

If that were so, then we need only put big air tanks on conventional jet
planes, turning them into rockets, and fly up into space.

Gravity is a continuous acceleration of 9.80665 m/sec/sec (32.174
ft/sec/sec), so the only way to get out of the gravity well is to overcome
it by either applying a continuous counter-acceleration of, say, 10
m/sec/sec (32.8084 ft/sec/sec) -- which is apparently what you're
suggesting here -- or applying a tremendous acceleration of, say, 10 gee in
a short burst. We do it by the big boost method because we haven't figured
out a way to do the continuous boost method. Among the more obvious
problems with constant boost is the question of what you're going to use
for propellant and how you're going to lift it all.

We have engines capable of boosting with sufficient force to lift a ship in
a smooth, continuous thrust up to space. What we don't have is away to
supply all the fuel it will take to do that -- like a fruitfly trying to
lift an orange.

>and a gundam can hover right?

I don't think so. A Dom can hover, but I think the Gundam jumps like a
flea, using bursts from its backpack.

>2) you're telling me that virtually any volume of
>space in space is within gravitational pull of one
>planet/asteroid/star or another?

Everything in the universe attracts everything else in the universe. It's
not that gravity is all that strong, it's just that it's omnipresent. You
fall to the ground because your center of mass and the Earth's center of
mass exert a continuous mutual attraction -- and the Earth's mass is 6
quadrillion times as strong as yours.

If the Earth weren't here, you'd still be in orbit around the Sun. This
is, after all, the Solar system -- everything out to the Oort Cloud orbits
the Sun. Get past the Oort Cloud and you'll be free of the Sun's gravity
and not yet within reach of one of the nearer stars, but you'll be in the
gravitational field of the Milky Way galaxy, as is just about everything
you can see with the naked eye -- 100 billion stars. Get out of the
galaxy, and you'll be within the field of the galactic group, in which the
Milky Way, Andromeda and dozens (maybe hundreds) of other galaxies swarm.
And so on.

>3) what the hell is a spacesuit for? aside from
>providing an enclosed oxygenated environment that's
>not freezing... what do spacesuits do to help
>"withstand the rigors of outer space" (as i seem to
>read very often)? what does a spacesuit/flightsuit do
>to help against g forces? (what are they made of, for
>that matter?)

Spacesuits protect against three elements of space: vacuum, radiation, and
temperature differential.

Vacuum has two aspects that will kill you, the first and most obvious being
a lack of life-sustaining air. The other is a lack of external pressure,
which keeps you from boiling away. Y'see, the human body's 90% water and
the boiling point of water drops as the pressure drops. It's 100C/212F
at the Earth's surface, where the ambient air pressure is 1.03323 kgf/cm^2
(14.6959 psi), but it drops to around 80C (175F) at the top of Mount
Everest -- if you try and make soup, your cooking time will increase
dramatically because you have to boil the water twice as long to get the
same effect. When the pressure drops below a certain point, all the water
in your body begins to boil, with icky results. So a spacesuit not only
keeps the air in for you to breath, but the air pressure up to a sufficient
level to keep you from wasting away. If the pressure drops very suddenly,
you'd rupture -- that's called explosive decompression -- but anoxia (lack
of oxygen) and embolism (think vapor lock, only inside your veins) are just
as dangerous and a not nearly so obvious.

Radiation -- think sunburn. The Earth has miles and miles of
radiation-absorbing atmosphere between us and the Sun and we still can get
burned badly enough to require hospitalization, to say nothing of heat
stroke. Add in solar x-rays, cosmic radiation and other stuff that our
atmosphere screens out altogether. I'd expect that all space colonists
would have a deep tan....

Temperature differential has been addressed sufficiently in other message,
I think. Add to this the fact that space is a vacuum and vacuum is an
insulator, so what heat you pick up -- and generate yourself -- can only be
lost through radiation. A spacesuit has a heat-exchange system that
transfers the heat from your body to the surface of the suit and spreads
the heat from the sunward side over to the shaded side.

Current EVA suits are made of two inner layers of Beta cloth (boron fiber,
similar to optical fiber, woven in an airtight mesh), three to four layers
of insulating cloth and mylar, a layer of specialized metalized fabric, and
an outer layer of Beta cloth. This is worn over an undergarment that
provides a cooling flow of oxygen and a water-tubing heat-exchange around
the body and attachments for a communication belt, urine collection
equipment and a biomedical instrumentation belt. The pressure portion of
the suit provides 0.386688 kgf/cm^2 (5.5 psi) pressure to all parts of the
body except the head, where oxygen at 0.263651 kgf/cm^2 (3.75 psi) pressure
is supplied by the helmet.

>4) that reentry stuff...it's atmospheric friction that
>causes the burn, right? what if the angle of entry is
>so shallow (say, 1 degree)...would that eliminate
>reentry problems? (y'know, kinda float around for a
>while, before dropping like a rock?)

Atmospheric friction is a function of the speed or re-entry, which is in
turn a function of the speed of your orbit, which is a function of gravity.

Let's get back to basics. What is an orbit? It's a fall around the Earth.
 Classic Newton scenario: you have a cannon on top of a mountain so high
that it sticks out of the atmosphere, where there's no friction. You fire
the cannon and the ball goes flying out in a straight line, tangent to the
curved surface of the Earth. But gravity pulls the ball toward the center
of the Earth and it falls -- in an arc, whose curvature is a function of
the speed of ball and the gravity of the Earth. Put in a larger charge and
the ball goes faster and thus farther from the muzzle, but it still falls
back to Earth, in a longer arc. Keep increasing the charge and the ball
will eventually fall completely around the Earth, its arc now equal to the
Earth's circumference at that altitude.

That's an orbit -- a circular path around the planet, where the force of
gravity is offset by the forward momentum of the ball.

But each charge has increased the speed of the ball and, by the time it
achieves orbit, it's traveling at least 20 times the speed of sound. If it
re-enters, it hits the atmosphere at a velocity just under that of its
orbital speed, close to Mach 20. The faster you try to slow down while
above the atmosphere, the less time you have to decelerate, because
deceleration causes you to drop from orbit, so you end up at the same speed
no matter what you do.

Enter heat shielding, because you can't change you mass or your velocity
enough to prevent the extreme friction you'll generate going through that
mass of air at that speed.

>what about slingshot maneuvers? they utilize the
>planet/star's gravity, but aren't caught in
>reentry...?

They don't get close enough to hit atmosphere or they swing by objects that
have no atmosphere. A slingshot is a controlled fall, in which you let the
planet or whatever pull you in, like a power dive, but your trajectory is a
close tangent to the surface and, by the time you get there, you're
traveling and at a near-perpendicular angle anf going too fast for that
same gravity to drag on you as you go by. The closest Terrestrial analogy
is a game of crack-the-whip, where everyone in a chain imparts their
angular momentum to the guy on the end.

>-garrick
>damn glad to be on solid ground, where there's less
>physics involved :)

There's even MORE physics involved at ground level, along with a good deal
of chemistry, but you grew up with it and so you don't think of it as such.
 But you dress appropriately for the weather, wear sunscreen, drink plenty
of liquids and don't stand under trees during a lightning storm -- all
sensible safeguards against the physical hazards of Earth's surface.

-Z-

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