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Message no. 1
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Laser rocketry (was Re: Old news)
Date: Mon, 24 Aug 1998 10:48:39 -0700
>Adam Getchell wrote:
>
><snip>
>
> Thanks. Now I have the info I needed to complete the background for
>introducing it in my game :).
>
> BTW, wouldn't a laser rocket be sorta like a reactionless drive?
>Not in concept, but in the fact that it needs no reaction mass?

No. The "reaction mass" is the photons themselves, or if you prefer, the
light pressure. All systems, in general, obey the law of conservation of
linear momentum. Laser rockets of this sort aren't practical.

The modern approach is to use a high powered ground station to vaporize
fuel on the rocket to generate lift. This saves the weight of the engine,
but not the fuel. Out in space, one could use a solar sail to also save the
weight of the fuel, but this would require an array of very powerful lasers
and a lot of patience as it will not generate much thrust.

> Bira

--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 2
From: David Foster <fixer@*******.TLH.FL.US>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Mon, 24 Aug 1998 14:45:15 -0400
On Mon, 24 Aug 1998, Adam Getchell wrote:

->The modern approach is to use a high powered ground station to vaporize
->fuel on the rocket to generate lift. This saves the weight of the engine,
->but not the fuel. Out in space, one could use a solar sail to also save the
->weight of the fuel, but this would require an array of very powerful lasers
->and a lot of patience as it will not generate much thrust.

I still prefer the approach for long distance travel of using old
unexploded nukes (read about it somewhere). Set off the nukes behind you
(everything is shielded) with a large very very tough shield behind you to
catch the blast and push you forward. Very low mass, very high output of
energy. Now, if only it wasn't so radioactive.... ]:-)

Fixer --------------} The easy I do before breakfast,
the difficult I do all day long,
the impossible only during the week,
and miracles performed on an as-needed basis....

Now tell me, what was your problem?
Message no. 3
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Mon, 24 Aug 1998 13:57:32 -0700
> I still prefer the approach for long distance travel of using old
>unexploded nukes (read about it somewhere). Set off the nukes behind you
>(everything is shielded) with a large very very tough shield behind you to
>catch the blast and push you forward. Very low mass, very high output of
>energy. Now, if only it wasn't so radioactive.... ]:-)

That was called the Daedalus project.

You can't use "old unexploded nukes" except to recycle the warheads. For a
tritium triggered warhead (almost the entire U.S. arsenal) you have to
replace those parts as well. The nuclear bombs that are used in this
propulsion system have to be a specific configuration and yield. You
wouldn't want to do this trick with any 10 MT "bunker busters" or
cobalt-salted nukes. ;-)

Daedalus ends up providing a fair amount of thrust. The long term numbers
crunching is that the specific impulse of a fusion rocket would be higher,
but that Daedalus would have an order of magnitude better fuel efficiency.

>Fixer --------------} The easy I do before breakfast,
--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 4
From: Mike Bobroff <Airwasp@***.COM>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Mon, 24 Aug 1998 20:06:23 EDT
In a message dated 8/24/98 12:49:03 PM US Eastern Standard Time,
acgetchell@*******.EDU writes:

> > BTW, wouldn't a laser rocket be sorta like a reactionless drive?
> >Not in concept, but in the fact that it needs no reaction mass?
>
> No. The "reaction mass" is the photons themselves, or if you prefer, the
> light pressure. All systems, in general, obey the law of conservation of
> linear momentum. Laser rockets of this sort aren't practical.
>
> The modern approach is to use a high powered ground station to vaporize
> fuel on the rocket to generate lift. This saves the weight of the engine,
> but not the fuel. Out in space, one could use a solar sail to also save the
> weight of the fuel, but this would require an array of very powerful lasers
> and a lot of patience as it will not generate much thrust.

Hmmm, there was another system that currently under further development, going
from something the size of a frisbee to something a bit larger in diameter.
What they are doing is producing plasma underneath the vehicle, and then a
ground laser ignites the plasma, which in turn generates the lift for the
vehicle to go into the air. Accoring to the researchers, IIRC, they say they
will have a working scale model in about 10 to 15 years from now.

-Herc
------ The Best Mechanic you can ever have.
Message no. 5
From: Geoff Skellams <geoff.skellams@*********.COM.AU>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 10:13:42 +1000
On Shadowrun Discussion, Mike Bobroff[SMTP:Airwasp@***.COM] wrote:
> Hmmm, there was another system that currently under further
development, going
> from something the size of a frisbee to something a bit larger in
diameter.
> What they are doing is producing plasma underneath the vehicle, and
then a
> ground laser ignites the plasma, which in turn generates the lift for
the
> vehicle to go into the air. Accoring to the researchers, IIRC, they
say they
> will have a working scale model in about 10 to 15 years from now.

I saw something like this on a documentary sometime last year. At the
moment, they have a carefully shaped lauch vehicle, which has an
underside like half a torus (a doughnut shape), which is coated with
some sort of special reflective coating. They fire a laser onto the
underside, and the shape of the bottom focuses the light energy onto the
outer rim of the saucer. This then creates plasma out of the air which
goes pop and lauches the vehicle into the air. It's pretty cool to watch
the model, which is about the size of a dinner plate shoot up into the
air of the lab.

cheers
G

--
Geoff Skellams R&D - TOWER Software
Email Address: geoff.skellams@*********.com.au
Homepage: http://www.towersoft.com.au/staff/geoff/
ICQ Number: 2815165

"That rates about a 9.5 on my weird-shit-o-meter"
- Will Smith in "Men in Black"
Message no. 6
From: Robert Watkins <robert.watkins@******.COM>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 10:18:24 +1000
Adam Getchell writes:
> The modern approach is to use a high powered ground station to vaporize
> fuel on the rocket to generate lift. This saves the weight of the engine,
> but not the fuel. Out in space, one could use a solar sail to
> also save the
> weight of the fuel, but this would require an array of very
> powerful lasers
> and a lot of patience as it will not generate much thrust.

It wasn't that long ago that a trip from Tokyo to London took several
months. Patience, I think, is permissible over this scale. :)

I remember seeing the numbers being crunched on interplanetary transport. If
you can accelerate at something like 0.001g the entire trip (except for the
turn-around time, of course), then there isn't anywhere in the solar system
you can't reach in a couple of months. Certainly all the moderately
interesting real-estate is within fairly easy reach. All we have to do is
figure out a way to make a light-sail (we know how to make a closed
environment last a few months).

--
.sig deleted to conserve electrons. robert.watkins@******.com
Message no. 7
From: K is the Symbol <Ereskanti@***.COM>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 03:16:11 EDT
In a message dated 8/24/1998 1:38:03 PM US Eastern Standard Time,
fixer@*******.TLH.FL.US writes:

> I still prefer the approach for long distance travel of using old
> unexploded nukes (read about it somewhere). Set off the nukes behind you
> (everything is shielded) with a large very very tough shield behind you to
> catch the blast and push you forward. Very low mass, very high output of
> energy. Now, if only it wasn't so radioactive.... ]:-)
>
Ah yes, the Sagan approach to Mars Travel. I remember this one very well
actually. I always got a kick out of the "blast shield" that would be built
at the rear of the vessel myself. Sagan was estimating this would only take
the "Martian Voyagers" a few weeks to reach mars, vs. the several month/year
travel with more conventional methods.

-K
Message no. 8
From: Steve Collins <einan@*********.NET>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 16:14:48 -0400
>In a message dated 8/24/1998 1:38:03 PM US Eastern Standard Time,
>fixer@*******.TLH.FL.US writes:
>
>> I still prefer the approach for long distance travel of using old
>> unexploded nukes (read about it somewhere). Set off the nukes behind you
>> (everything is shielded) with a large very very tough shield behind you to
>> catch the blast and push you forward. Very low mass, very high output of
>> energy. Now, if only it wasn't so radioactive.... ]:-)
>>
>Ah yes, the Sagan approach to Mars Travel. I remember this one very well
>actually. I always got a kick out of the "blast shield" that would be built
>at the rear of the vessel myself. Sagan was estimating this would only take
>the "Martian Voyagers" a few weeks to reach mars, vs. the several month/year
>travel with more conventional methods.
>
>-K
>
I don't think Dr Sagan thought this one up it was originaly from a 60's
military project called Orion although I suppose Dr Sagan could have
worked on the project. If you want more info on this propulsion system
read Footfall By Niven and Pournelle.

Steve
Message no. 9
From: David Foster <fixer@*******.TLH.FL.US>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 16:17:17 -0400
On Tue, 25 Aug 1998, Steve Collins wrote:

->>In a message dated 8/24/1998 1:38:03 PM US Eastern Standard Time,
->>fixer@*******.TLH.FL.US writes:
<snip my section about nuke propulsion>
<snip the section about Sagan - Mars Travel>

->I don't think Dr Sagan thought this one up it was originaly from a 60's
->military project called Orion although I suppose Dr Sagan could have
->worked on the project. If you want more info on this propulsion system
->read Footfall By Niven and Pournelle.

That's where I remember it from! We're way off SR now. I
reccomend we stop.

Fixer --------------} The easy I do before breakfast,
the difficult I do all day long,
the impossible only during the week,
and miracles performed on an as-needed basis....

Now tell me, what was your problem?
Message no. 10
From: Adam Getchell <acgetchell@*******.EDU>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 13:58:11 -0700
>I remember seeing the numbers being crunched on interplanetary transport. If
>you can accelerate at something like 0.001g the entire trip (except for the
>turn-around time, of course), then there isn't anywhere in the solar system
>you can't reach in a couple of months. Certainly all the moderately
>interesting real-estate is within fairly easy reach. All we have to do is
>figure out a way to make a light-sail (we know how to make a closed
>environment last a few months).

Well, maybe not to Pluto. Assuming constant thrust and turnaround, you can
approximate time by the formula T = 2 * sqrt (D/A) where D = distance and A
= acceleration (formula in MKS).

Pluto is ~ 30 Astronomical Units out, at ~ 150 million km per AU = 1.5 x
10^11 meters. As a crude approximation, not considering Hohman transfer
orbits or too much orbital mechanics it would be about 40 AU to Pluto.
0.001 g equals about 0.01 m/s^2 of acceleration, so plugging the above
numbers into the equation yields a travel time of roughly 567 days. If you
could boost acceleration to 0.01 gs = 0.1 m/s^2 travel time would drop to
179 days, and of course 1 g of acceleration would get you there 18 days.

>.sig deleted to conserve electrons. robert.watkins@******.com

There are plenty of electrons! ;-)
--Adam

acgetchell@*******.edu
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
Message no. 11
From: Robert Watkins <robert.watkins@******.COM>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Wed, 26 Aug 1998 08:52:53 +1000
> >.sig deleted to conserve electrons. robert.watkins@******.com
>
> There are plenty of electrons! ;-)

Reading that profile of Laudhrer you pointed me to made me think that this
trivial sig of mine has more significance than previously thought. By
conserving electrons, I'm not producing heat. ;-)

--
.sig deleted to conserve electrons. robert.watkins@******.com
Message no. 12
From: Greg Symons <gsymons@******.TEMPLE.EDU>
Subject: Re: Laser rocketry (was Re: Old news)
Date: Tue, 25 Aug 1998 23:25:15 -0400
At 6:52 PM -0400 8/25/98, Robert Watkins wrote:

>> >.sig deleted to conserve electrons. robert.watkins@******.com
>>
>> There are plenty of electrons! ;-)
>
>Reading that profile of Laudhrer you pointed me to made me think that this
>trivial sig of mine has more significance than previously thought. By
>conserving electrons, I'm not producing heat. ;-)

Unless you've actually deleted the sig... then you are:)

>
>--
>.sig deleted to conserve electrons. robert.watkins@******.com


***********************************************************************
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* \\(oo) Seanchai/ and Follower of Bri\de *
* /-----\\\/ *
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