[meteorite-list] Speed-of-light question

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed, 26 Aug 2009 19:16:14 -0500
Message-ID: <gqjb951i66h1pi0kp4raap08qoh5b8o72h_at_4ax.com>

One more post on this-- I remembered that way back at the dawn of time (okay,
the dawn of the 1990s) in my college English 101 class, I did a paper on fast
interstellar travel. I haven't looked at it in years, as I avoid looking at
most of my early writings for the fear of it being cringe-worthy bad. This one
doesn't look TOO bad, though-- don't be too hard on past 18/19 year old me. I
can't find the works cited section, but here's the body of the text, with some
relevance to this topic (if off topic for the list in general).


(quoted fossil document)



     Popular science fiction productions such as Star Wars, Star Trek, and Dr.
Who portray traveling from star to star to be commonplace and even trivial, with
large ships, the equivalent of luxury liners, traveling interstellar distances
in a matter of hours. Traveling to another star seems simpler than crossing an
ocean in the times of Columbus. In reality, the laws of physics show that fast
interstellar travel will be very difficult, if not impossible, to accomplish.
     According to Carl Sagan, an astronomer at Cornell University, "Fast
interstellar space flight with ship velocity approaching the speed of light, is
an objective not for a hundred years but for a thousand or ten thousand" (Sagan
203). Another scientist states "although casual observers of the space travel
scene may view starflight as only a modest step beyond trips to the planets in
our solar system, it will in fact be inordinately more difficult" (Woodcock 39).
He continues by explaining that the farthest man has yet traveled, our moon, is
400,000 Km away. The nearest star, on the other hand, is 40,000,000,000,000 Km
away. In a scale model of the solar system between the Earth and the moon being
1 cm, the distance to the The fastest traveling spacecraft to date, Pioneer 10,
Had a top speed of 51,800 kph and a final cruising speed of 40,000 kph (Darling
99). At this speed, it would take over 100,000 years to travel to the nearest
star. Clearly this is not fast. To get to its destination in a reasonable
amount of time, the ship's speed must be increased drastically.
     This increase in speed runs into both physical and engineering problems.
Unlike classical Newtonian physics, which says that an increase in force applied
to an object will result in an equal increase in speed, Einstein's equations
show that as an object's speed increases, so does its mass, so that even more
force has to be applied to increase its speed by the same amount. and more so
that near the speed of light most energy applied goes to an increase in mass and
almost none to increase in speed (Asimov 207). What this means from a practical
standpoint is
that to travel faster will require much more fuel to be carried.What type of
fuel will be used? According to one scientist "for interstellar travel,
chemical propulsion rockets are woefully inadequate; other technologies must be
brought into play" (Darling 95). Chemical rockets burn a very large amount of
fuel to produce a relatively small amount of energy. Even other technologies,
none of which have been developed, do not look very promising.
     Many different technologies have been proposed, all of which have flaws and
none of which will be easy to develop and maintain. Fission rockets would
circulate a liquid, such as liquid hydrogen, through a fission reactor. The
liquid would be heated into a gas and thrust out the back of the ship. This is
one of the simplest technologies; but will provide too little thrust for fast
interstellar travel. Another idea is the ion rocket, which accelerates the
charged particles produced by a fission reaction through an electric field.
With an exhaust speed of around 50 kph, this is still too slow. Ion rockets
with exhaust speeds of up to 1000 kph might be possible, but to accelerate to 10
percent of the speed of light would take a mass ratio of 10 trillion to 1,
meaning that 10 billion metric tons of fuel would be needed for every kilogram
of payload. Fusion rockets are manageable, with exhaust speeds of up to 10,000
kph. Accelerating to 10 percent of the speed of light would take only 20
kilograms of fuel for each kilogram of payload. This is only to accelerate,
however. The ship must also slow down when it reaches the destination, and the
fuel that is used to slow down must be accelerated along with it. That means to
reach the destination would take 20 squared or 400 kilograms of fuel for each
kilogram of payload. Square this again for the trip back to Earth, and it takes
80 metric tons of propellant for each kilogram of payload that returns
to Earth (Darling 96). Even matter-antimatter, the most efficient fuel
possible, would take 100 kilograms of fuel for every kilogram of payload on a
round trip at 98 percent of the speed of light (Asimov 231-6).
     Even if the problems with sheer mass of fuel to be used are overcome, there
are still problems to be dealt with. According to one scientist, if a
traditional rocket design were to be used, there would have to be several meters
of solid tungsten shielding between the reactors and the cockpit, plus tons of
equipment to cool the metal, which will ass even more mass to be accelerated.
Not only will the voyagers have to worry about radiation from the fuel supply,
but also from space itself. According to Relativity, there is no difference
between a ship moving rapidly through space and the ship standing still and the
universe rushing past the ship. This means that the faster anything travels,
the harder objects in its path hit it. At 10 percent of the speed of light a
collision with an object the size of a pea would release as much energy as a
small atomic bomb (Woodcock 45-6). As the ship approaches the speed of light
very closely, even the surrounding hydrogen atoms would be energetic enough to
be high energy radiation. As they strike the ship in large numbers, they would
heat it up enough to destroy it.
     There are other factors involved besides pure physics. Many medical
problems result from long-duration space trips. Among these problems are
deossification of the bones, partial atrophy of the muscles and depression of
the immune system (Steele 36-50). It would also take a special breed of person
to make these voyages; someone highly skilled in many sciences, able to get
along with the same small group of people for long periods of time, but still
able to cope with isolation from the rest of the Earth's population. Even with
the correct ship design and the correct crew roster, the ship will be difficult
to build, requiring an unprecedented level of co-operation between nations. A
starship, if built, would have to be assembled in orbit, using yet-to-be built
space stations and factories and hundreds if not thousands of construction
workers in space. The ship itself would be on the order of a thousand meters in
length, weigh a million metric tons, and cost a trillion dollars (Woodcock 47).
For these reasons, plus other factors, it is very unlikely man will ever utilize
fast interstellar travel. Much of the glory of science fiction, therefore is
just a pipe-dream.
Received on Wed 26 Aug 2009 08:16:14 PM PDT