Interstellar Propulsion idea using an Asteroid and a few comets!
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## Interstellar Propulsion idea using an Asteroid and a few comets!

#1
August 13th 04, 05:36 PM
 Andrew Nowicki external usenet poster Posts: n/a
Interstellar Propulsion idea using an Asteroid and a few comets!

Comets and asteroids can provide the mass that
is needed to generate thrust. In addition to
the reaction mass you need source of energy -- most
likely nuclear fission energy. The rocket equation
determines final velocity of your spacecraft:

V = (exhaust_gas_velocity) natural_logarithm (total_mass / dry_cargo_mass)

The total_mass includes everything: rocket engine,
structural parts, propellant, and cargo. The
dry_cargo_mass is the mass of the rocket engine,
structural parts and cargo. The ratio of total_mass
to dry_cargo_mass is called mass ratio (MR).

You have not invented anything of substance.
Interstellar travel is unlikely because it is
dangerous, expensive, and takes too much time.

Wild interstellar travel ideas:
http://www.lerc.nasa.gov/WWW/PAO/html/warp/bibliog.htm
#2
August 14th 04, 03:09 PM
 Sander Vesik external usenet poster Posts: n/a

In sci.space.policy Andrew Nowicki wrote:
Comets and asteroids can provide the mass that
is needed to generate thrust. In addition to
the reaction mass you need source of energy -- most
likely nuclear fission energy. The rocket equation
determines final velocity of your spacecraft:

V = (exhaust_gas_velocity) natural_logarithm (total_mass / dry_cargo_mass)

The total_mass includes everything: rocket engine,
structural parts, propellant, and cargo. The
dry_cargo_mass is the mass of the rocket engine,
structural parts and cargo. The ratio of total_mass
to dry_cargo_mass is called mass ratio (MR).

You have not invented anything of substance.
Interstellar travel is unlikely because it is
dangerous, expensive, and takes too much time.

Expensive and timeconsuming, sure, but where is teh extra danger?

Wild interstellar travel ideas:
http://www.lerc.nasa.gov/WWW/PAO/html/warp/bibliog.htm

--
Sander

+++ Out of cheese error +++
#3
August 14th 04, 03:09 PM
 Sander Vesik external usenet poster Posts: n/a

In sci.space.policy Andrew Nowicki wrote:
Comets and asteroids can provide the mass that
is needed to generate thrust. In addition to
the reaction mass you need source of energy -- most
likely nuclear fission energy. The rocket equation
determines final velocity of your spacecraft:

V = (exhaust_gas_velocity) natural_logarithm (total_mass / dry_cargo_mass)

The total_mass includes everything: rocket engine,
structural parts, propellant, and cargo. The
dry_cargo_mass is the mass of the rocket engine,
structural parts and cargo. The ratio of total_mass
to dry_cargo_mass is called mass ratio (MR).

You have not invented anything of substance.
Interstellar travel is unlikely because it is
dangerous, expensive, and takes too much time.

Expensive and timeconsuming, sure, but where is teh extra danger?

Wild interstellar travel ideas:
http://www.lerc.nasa.gov/WWW/PAO/html/warp/bibliog.htm

--
Sander

+++ Out of cheese error +++
#4
August 15th 04, 10:26 PM
 Perplexed in Peoria external usenet poster Posts: n/a

"James Nicoll" wrote in message ...
In article ,
Alan wrote:
Okay, you're zipping merrily along in your asteroid-starship at .1c,
and you detect a small comet 6 light-hours dead ahead. You'll be there
in 2 1/2 days. What do you do?

You can't very well collide with the thing, at .1c. Talk about having
a bad day! Capture it? How? At .1c? Or even .0001c? Send a robotic
mining probe ahead, to mine the comet, then accelerate it's mining
output to match your velocity as you fly by? If your robotic probe
could do that in 2 1/2 days, why have you spent so long sitting in

Well, robots can in theory be made more robust than humans.
The power output implied by braking from 0.1 in 2 1/2 days is pretty
impressive, though.

If I had to use Oort cloud objects in a story I would use one
of the following methods:

1: Islands

No fast transport at all, but if you can use a comet for raw
materials to live off of, you don't need fast transport. As each comet
is settled and filled up, population pressure encourages the slow spread
of humans to other, unoccupied worldlettes. In the pessimistic version,
the inevitable slow leak of volatiles from habitats combined with the
finite size of oort cloud bodies leads to an endless series of Henderson
Islands, stripped of their volatiles, orbited by now lifeless habitats.

2a: Relays

Small robot probes are sent out via snail-drive to set up robust
electromagnetic cannon to fire prepared fuel capsules into the path of
fast, crewed ships.

2b: Relays

The material of the Oort cloud bodies are used to build rectennas
used to relay power from the Sun to the starships.

Or, as long as we are dealing with sci fi, make the "ship" really big -
several AU in diameter, large enough so that its perimeter can contain
dozens of inner Oort cloud objects at once. The ship is more in the nature
of a fleet than a ship, except that its components are held together
by a web of tethers and held apart by momentum exchange transfers of
material. The velocity of this fleet thru space is not large - a few
km/sec. As is moves, it needs to consume some Oort cloud objects to
replenish its volatile stores, hence it also needs to capture and
catapult other Oort cloud objects behind it to compensate for the
momentum lost due to its feeding activities.

I'm thinking that the net velocity of such a fleet, as well as the
internal velocities of its components, must be limited to within an
order of magnitude or so of the characteristic velocity of the tether
materials that hold it together. Overall, it will be something of
a cross between an animated spider web and an amoeba.

However, if we ever develop some kind of "tractor beam" - even if
both attracted parties have to participate in generating it - then
there is no clear limit to how fast such an amoeba can scuttle.

#5
August 16th 04, 07:51 PM
 Perplexed in Peoria external usenet poster Posts: n/a

"Grimble Gromble" wrote in message ...
Because exponential growth will always outstrip polynomial growth at some
stage, humans (who tend to reproduce exponentially) will inevitably exhaust
any supplies they can reach (cubic polynomial even at the speed of light)
and are going to have to control their population sooner or later. Why not
sooner?

While I agree with the basic thrust of your post, there are some quibbles
that are worth mentioning.

1. Humans do not "have to" control their population. All biological
species "tend to" reproduce exponentially. They don't control their
own population. Their population is controlled for them.

2. Population growth need not be the same in all regions of human
habitation. In fact, if migration is a slow process, it probably
won't be. It is quite possible to have a situation in which human
population in the center is stagnant or decreasing, whereas growth on
the frontier remains fully exponential. With the frontier expanding
outward into an infinite universe at constant speed, this quasi-steady-
state of growth can persist indefinitely. In theory, at least. Of
course, this is only exponential economic and population growth at the
frontier. I am assuming implicitly here that technology is stagnant.

3. If technology is not stagnant, and growth continually requires
fewer and fewer physical resources, it is at least conceivable that
your cubic polynomial / speed of light limitation becomes irrelevant.
You forgot to account for the Fitzgerald-Lorentz contraction and time
dilation. If humanity can expand at a constant acceleration (rather
than a constant Newtonian velocity) an infinite universe can provide
exponentially increasing space for packing human bodies within the
expanding frontier.

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