High efficiency drives

Mike,

Two comments:
1) Whether solar of nuclear are used, I recommend that you evaluate the use of an energy storage system because the mass driver will constitute a peak load that is likely to be over 10x the nominal power capacity of the power plant. Hence, using the solar or nuclear reactor to charge up the storage medium for peak loading will make better use of the resources. If solar is used, then it makes sense to up-grade the storage system to provide power for the two weeks of darkness. A flywheel generator/motor is one I would recommend.

2) Mass drivers work according to the equation MV, and so the way to maximize the effect is to use the highest possible velocity. Why not look beyond throwing rocks and consider a plasma drive like the VASIMR which was recently described in Scientific American (Nov. 2000)? It too would require solar or nuclear power. Large take-off thrusts would not be practical, however, but perhaps you can think of a way around this?

Cheers,

Tom
From: Mike Combs
To: spacesettlers@egroups.com
Sent: Monday, January 01, 2001 6:57 PM
Subject: [spacesettlers] Re: High efficiency drives

--- In spacesettlers@egroups.com, "Tom Tucker (Olympia)"
wrote:
> Mike,
>
> So, what would you power your mass driver with? Nuclear fission?
Chemical? Solar?

It was proposed that the lunar catapult be solar powered. At an
earlier point of these studies there was a small, buried nuclear
reactor at the moonbase. Later on, the reactor was gone, and there
were only solar panels. I think they had decided that solar was OK
for the mass driver, even if it meant that it could only opperate 2
weeks out of every four (you'd need some downtime for repair and
maintenance anyway). I would assume some storage method was used to
get the moonbase through the 2 week long night. I think there was a
push to eliminate the nuclear reactor due to people's concerns about
launch accidents. Given the difficulties faced by the much more
modest Cassini probe, that's probably just being realistic.

A mass driver being used as an inter-orbital tug would most certainly
be solar powered since it would have continuous solar power available
to it (except for when it was in LEO).

> What diameter projectile?

O'Neill assumed spheres of sintered lunar soil about the diameter of
a softball.

> What velocity do you anticipate
> achieving for the projectile?

The lunar mass driver catapult was launching at about lunar escape
speed, which is 2.4 km/sec. I think the interorbital tug would eject
its reaction mass even faster. Seems like someone said the exhaust
velocity would be in excess of Earth escape, so that reaction mass
would not contribute significantly to orbital debris.

> Keeping alternatives on the table helps with comparative analysis
later when more options are available.

Oh, sure. I've had people advocate slingshots and lunar skyhooks to
me over mass drivers. I still tend to favor mass drivers, but I'm
for whatever turns out to work best in the end.

> Being more pragmatic, I think that we are many decades away from
space colonization and asteroid mining due to critical "missing
technological links" in the chain of tools that are needed. Chiefly,
these are:
>
> 1) Reduction in cost to achieve LEO and beyond,

I'd agree that we wouldn't even want to get started before we had at
least a 10-fold reduction in launch costs. Maybe more.

> 2) Advanced remote technology to mine and to maintain mining
equipment on an asteroid that may be far far away. Neural net
ethnology will be crucial IMO along with VR and machines able to
repair themselves.

Telepresence may help us out in HEO and even as far out as the moon.
But you are correct that we would need actual AI for asteroids due to
their distance. I'm sure robotics will come into play. But what mix
of humans and robots we can expect is open to controversy, and
depends powerfully on how rapidly technology advances, and when we
get started.

The 70's studies assumed we could do it with 70's technology. Of
course they assumed a human to robot ratio which will probably turn
out to be higher than the eventual reality.

> 3) Design and test viable life support systems for space colonies.

Absolutely.

Regards,
Mike Combs

Two comments:
1) Whether solar of nuclear are used, I recommend that you evaluate the use of an energy storage system because the mass driver will constitute a peak load that is likely to be over 10x the nominal power capacity of the power plant. Hence, using the solar or nuclear reactor to charge up the storage medium for peak loading will make better use of the resources. If solar is used, then it makes sense to up-grade the storage system to provide power for the two weeks of darkness. A flywheel generator/motor is one I would recommend.

2) Mass drivers work according to the equation MV, and so the way to maximize the effect is to use the highest possible velocity. Why not look beyond throwing rocks and consider a plasma drive like the VASIMR which was recently described in Scientific American (Nov. 2000)? It too would require solar or nuclear power. Large take-off thrusts would not be practical, however, but perhaps you can think of a way around this?

Cheers,

Tom
From:
Mike Combs
To:
spacesettlers@egroups.com
Sent:
Monday, January 01, 2001 6:57 PM
Subject:
[spacesettlers] Re: High efficiency drives
--- In
spacesettlers@...m
, "Tom Tucker (Olympia)"
<
tntucker@c
...> wrote:
> Mike,
>
> So, what would you power your mass driver with? Nuclear fission?
Chemical? Solar?
It was proposed that the lunar catapult be solar powered. At an
earlier point of these studies there was a small, buried nuclear
reactor at the moonbase. Later on, the reactor was gone, and there
were only solar panels. I think they had decided that solar was OK
for the mass driver, even if it meant that it could only opperate 2
weeks out of every four (you'd need some downtime for repair and
maintenance anyway). I would assume some storage method was used to
get the moonbase through the 2 week long night. I think there was a
push to eliminate the nuclear reactor due to people's concerns about
launch accidents. Given the difficulties faced by the much more
modest Cassini probe, that's probably just being realistic.
A mass driver being used as an inter-orbital tug would most certainly
be solar powered since it would have continuous solar power available
to it (except for when it was in LEO).
> What diameter projectile?
O'Neill assumed spheres of sintered lunar soil about the diameter of
a softball.
> What velocity do you anticipate
> achieving for the projectile?
The lunar mass driver catapult was launching at about lunar escape
speed, which is 2.4 km/sec. I think the interorbital tug would eject
its reaction mass even faster. Seems like someone said the exhaust
velocity would be in excess of Earth escape, so that reaction mass
would not contribute significantly to orbital debris.
> Keeping alternatives on the table helps with comparative analysis
later when more options are available.
Oh, sure. I've had people advocate slingshots and lunar skyhooks to
me over mass drivers. I still tend to favor mass drivers, but I'm
for whatever turns out to work best in the end.
> Being more pragmatic, I think that we are many decades away from
space colonization and asteroid mining due to critical "missing
technological links" in the chain of tools that are needed. Chiefly,
these are:
>
> 1) Reduction in cost to achieve LEO and beyond,
I'd agree that we wouldn't even want to get started before we had at
least a 10-fold reduction in launch costs. Maybe more.
> 2) Advanced remote technology to mine and to maintain mining
equipment on an asteroid that may be far far away. Neural net
ethnology will be crucial IMO along with VR and machines able to
repair themselves.
Telepresence may help us out in HEO and even as far out as the moon.
But you are correct that we would need actual AI for asteroids due to
their distance. I'm sure robotics will come into play. But what mix
of humans and robots we can expect is open to controversy, and
depends powerfully on how rapidly technology advances, and when we
get started.
The 70's studies assumed we could do it with 70's technology. Of
course they assumed a human to robot ratio which will probably turn
out to be higher than the eventual reality.
> 3) Design and test viable life support systems for space colonies.
Absolutely.
Regards,
Mike Combs