[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] 

> 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 

> 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 

> 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 

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.


                                                          (o o)
Up the airy mountain,
Down the rushy glen,
We daren't go a-hunting
For fear of little men;

William Allingham, Ireland, 1850