[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: starship-design: Re: Re: regarding fuel expenditures
On Sunday, November 16, 1997 10:40 PM, Isaac Kuo [SMTP:kuo@bit.csc.lsu.edu]
wrote:
> I think you mean 1/30 of a percent of c (100km/s).
What, you think I am trying to go to Mars?
> The disadvantages are the increased structural strength, and increased
> heat rejection capability (to deal with solar heating).
No, it was fairly explicit, a crewed ship would be limited by its
acceleration to a final cruise velocity of 0.003 c (Matloff & Mallove,
JBIS, 1981 & 1983 also Ehricke, JBIS, 1972) and Icarus, with a 1 km sail
would attain 0.012 c without any additional boost from beamed power
(Eshleman, Science, 1979). Forward actually proposed a combination of the
Perihelion maneuver and beamed power to reach the 0.03 c figure. Beamed
power alone pushed Starwisp to 0.20 c in a few days. Starwisp is designed
from the start to withstand hundreds of g's acceleration and these figures
take it into account (Forward, Journal of Spacecraft and Rockets, 1985). As
for thermal shielding see Ehricke, JBIS, 1972.
> Huh? I know of the electronics for Copperhead warheads which sustain
> in excess of 10,000gees, but they are artillery shells. However,
> because of this hardenning Copperhead shells cost 100 times as much
> per round as Hellfire missiles (which have more range and pack
> more punch).
Umm, you'll just have to take my word for this one, the systems are still
classified.
> Starwisp would get ripped apart by tidal forces if you swung it
> around the sun. There is a _big_ difference between a tiny
> little microchip mounted on relatively thick, sturdy, silicon
> substrate, and a kilometer wide wire mesh thinner than aluminum
> foil.
Again, Forward's design allowed for this. Rightly or wrongly, I don't have
the time or the inclination to second guess his engineering.
> It uses a powerful laser to accelerate,
> so it doesn't require any on board fuel.
No, it uses a microwave beam from a power satellite to accelerate, NOT a
laser.
> Actually it isn't. It still requires a huge laser which we can't
> build yet, a kilometer wide sail which we can't design yet,
> miniaturized electronics which we don't have yet, and a super
> huge fresnel lens which we can't even begin to design yet.
Okay, so I was stretching that part a little bit <G> that was why I said
VIRTUALLY though. BTW, Starwisp doesn't use a fresnel lens either. You are
confusing your designs...
> However achieving this data will require probes like NASA's 1000AU
> proposal--relatively heavy probes packed with useful sensors.
Which interestingly enough will probably use fusion thrusters...
> Forward's Starwisp would only transmit low resolution images of
> the target system as it flew by. Given our advances in telescope
> technology, it's not clear Starwisp would ever be worth it.
Conceded, on this point you are completely correct. IF the only thing
Starwisp can do is relay back images, we can probably do better with
telescopes.
Isaac, I am not defending sails, I prefer fusion or antimatter powered
engines actually. But sails do have some usefulness and most of this
argument was settled almost 20 years ago. This is OLD information. If you
don't believe me, go to the Advanced Propulsion Concepts conference at JPL
next March. I believe there are SEVERAL papers being presented on advanced
solar sail concepts.
Lee
(o o)
------------------------------------------------------oOO--(_)--OOo-----
----
Up the airy mountain,
Down the rushy glen,
We daren't go a-hunting
For fear of little men;
William Allingham, Ireland, 1850