Ways to sidestep gravity?

Al Globus wrote:

> A few years ago I saw a talk about a working laser powered vehicle. The
> vehicle was about the size of a cigarette pack and was accelerated
> straight up, very rapidly, to an altitude of perhaps a few hundred
> meters (I don't really remember exactly). The speaker showed a video of
> the real McCoy (not a simulation). Obviously, an orbital vehicle for
> humans is some ways off, but at least the concept has been physically
> demonstrated on a small scale.

Not really the same concept, although related. That concept
uses the laser from underneath, and uses extremely high
temperatures; and was intending to be air breathing; and
specifically required a pulsed laser. There's a website
at http://www-aero.meche.rpi.edu/Curriculum/TAVD/ .

OTOH this concept uses only 1000C and heats from the side of
the vehicle via the heat exchanger; and does not airbreath.

Also, IRC the fuel fraction of the demonstrator design by
Mirabo was about 3%. I can't see how that would make orbit,
even with very high ISP. This one is far more conservative and
practical.

Also, there's an even more subtle problem- the lightcraft
concept uses pulsed lasers. There's currently no pulsed
laser that is powerful enough to launch even 1kg to LEO; and
there is none planned. Such lasers are very expensive-
the one they used was made as part of the SDI, and no more
powerful laser is available or likely to be built.

OTOH the heat exchanger based concept can use continuous
heating and semiconductor lasers, which are far, far more
cost effective, bringing the system cost way down. Additionally
these are getting cheaper all the time as they are used for
other purposes and are being mass produced.

> On Monday, April 29, 2002, at 05:25 PM, Ian Woollard wrote:
>
>>Lucio de Souza Coelho wrote:
>>
>>
>>>I have already converted myself to the Space Elevator Cult. It will
>>>come and
>>>free us all! ;-)
>>>
>>
>>It might. It might not though. Until we have the material AND
>>the manufacturing process AND the money we ain't gonna get
>>there.
>>
>>Still, I went to a talk yesterday about laser powered launch
>>systems. The guy described a system of using a 100 Mw laser
>>(cost: around $1 billion, dropping at 30% per year in price
>>currently) used to point at hydrogen monopropellent vehicle
>>the vehicle uses a heat exchanger to boil the LH upto a
>>relatively low temperature 1000C and then chucks it out through
>>a conventional or aerospike nozzle.
>>
>>The ISP turns out to be 600, c.f. the space shuttle SSME ISP
>>of ~450 (the reason is that the space shuttle uses LOX/LH but
>>this system would use just LH, so the average exhaust velocity
>>goes up- Ox is heavy and reduces the ISP.)
>>
>>This makes the vehicle much simpler, cheaper and more powerful.
>>He was talking a few tens of k per vehicle, either expendable
>>or reusable I guess. Noteably, turbopumps are not required.
>>
>>He was talking of a 500kg vehicle delivering 140kg to LEO,
>>although it wasn't SSTO. He thinks the price ends up south
>>of $100/kg... It's not clear whether 140kg is enough to launch
>>a person, but even if it doesn't the system is very scalable.
>>
>>The system seems about 5 years off right now; including R&D.
>>
>>Oh yeah, this guy Jordin Kare who did the talk isn't an
>>amateur- he's worked on many different projects for the
>>government; including some classified projects.
>>
>>The cost of the laser isn't as big a problem as you might
>>think. If it enabled space tourism (and it easily could in
>>my opinion), the cost would be amortised over upto 35000
>>launches in the first year alone.
>>
>>
>>--
>>- Ian Woollard (ian.woollard@...)
>>
>>"Is a planetary surface the right place for an expanding
>>technological civilization?"
>>- Gerard O'Neill
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
> Space tourism could be our ticket to the stars. Save your pennies,
> suborbital flights for $100,000 may start in 2005! See
> http://www.spaceadventures.com/suborbital/index.html for details.
>
> Al Globus
> CSC at NASA Ames Research Center
> http://www.nas.nasa.gov/~globus/home.html
>

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill