Re: "Rockets not carrying fuel" and the space tower.
From: bz (bz+sp_at_ch100-5.chem.lsu.edu)
Date: 03/29/05
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Date: Tue, 29 Mar 2005 10:15:07 +0000 (UTC)
mmeron@cars3.uchicago.edu wrote in
news:4%52e.22$45.3956@news.uchicago.edu:
> In article <Xns9627C8D4E68E7WQAHBGMXSZHVspammote@130.39.198.139>, bz
> <bz+sp@ch100-5.chem.lsu.edu> writes:
>>mmeron@cars3.uchicago.edu wrote in
>>news:NC12e.19$45.3195@news.uchicago.edu:
>>
>>> In article <ky12e.60128$xX3.28598@twister.socal.rr.com>, "Mike Rhino"
>>> <october2003@alexanderpics.com> writes:
>>>>If you wanted to send energy to a rocket, you would be better off with
>>>>a laser. In that case, the rocket would still need fuel, but it
>>>>wouldn't need anything that burns. The fuel tank would contain
>>>>ammonia and nothing else. The back of the rocket would have a concave
>>>>mirror that concentrates the laser light on one spot. Ammonia would
>>>>be sent to that spot, heat up, and be ejected as exhaust.
>>>>
>>> And the advantage over "something that burns" would be? I mean other
>>> than saying "I'm high tech, I'm using a laser":-)
>>>
>>
>>The energy to orbit a vehicle can be generated on earth and beamed to
>>the vehicle, rather than trying to carry all that energy(mass) with you.
>>
> Since the mass you carry carries energy with it, there is no extra
> burden involved.
There is the mass of the fuel and the tanks to carry the fuel, the pumps to
move the fuel and the rocket engines to accelerate the loaded tanks, etc.
At the moment of lift off, ALL of this, plus the payload must be lifted and
accelerated.
Of course, Most of the fuel is used in the first few seconds, and it goes
to lifting the rest of the fuel.
Most of the launch vehicle never even makes it into orbit.
What if you never had to lift any of that off of the launch pad?
> You could only get an advantage here if you could
> deliver *more* energy from the ground than you can get by burning the
> fuel on board. Now, a medium size satellite launching rocket
> generates power at the rate of 10 GW or so.
Compute how much energy you need to lift the rocket PLUS fuel.
Compute how much energy you need to lift the payload ONLY.
We don't need anything near 10 GW.
> Do you've any laser
> that's capable of generating CW power at anything near this rate?
I worked with a CO2 laser that DELIVERED 500 watts, CW, in 1973. It was
much bigger than the 50 watt CW laser we also used.
I have worked with YAG lasers and dye lasers also. I have some idea of how
big they are and how (in)efficient they are.
I am sure that a bank of lasers, with their beams bounced from mirrors,
could deliver enough energy to get a few tons of payload into orbit.
Not that I think a bank of CO2 lasers would necessarily be the best to use.
There might be a better wavelength to use.
> What would you power it with? How would you dissipate the waste heat
> (remember, just few percent of the energy used to power the laser
> emerges as a beam, the rest is waste heat).
There would be much less waste heat than is currently generated.
>
>>You don't even need to carry fuel. Heated Air can act as a pulse jet.
>>
> Calculate the amount of air present and available for heating at any
> given moment. Other than grantmanship, this is laughable.
Some laughed at Orvill and Wilber too.
>>If you want to carry a reaction mass, why not water?
>>
>>http://www.space.com/businesstechnology/technology/laser_propulsion_
>>000705.html
>>
>>Google for
>>"laser powered" spacecraft launch
>>
> As I said, grantmanship. Try to calculate numbers instead of waving
> hands.
You only need to lift the payload, you DON't need the launch vehicle.
That makes a big difference.
-- bz please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set. bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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