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soph

Member

Registered: 2002-11-24

Posts: 1,492

Re: Power Limits of Advanced Propulsion

this seems great for cargo deliveries (hell, it might even make orbital hangars practical), but my interest in SSTO's is as a fast airplane.  the market would be HUGE.  it could be extremely versatile, delivering people and goods to space and earth on the same, short trip.

is there any work being done over there on that type of vehicle?

and i plan on checkin it out, kinda busy atm.

Preston

Banned

Registered: 2002-06-02

Posts: 72

Re: Power Limits of Advanced Propulsion

I'd also tend to favor something like a spaceplane SSTO or hypersonic tether assisted launch than one of those nuclear monsters sending hundreds of people to space at once...

dicktice

Member

From: Nova Scotia, Canada

Registered: 2002-11-01

Posts: 1,764

Re: Power Limits of Advanced Propulsion

I never heard of a 'hypersonic tether assisted launch," although I endorse orbital-transfer tether assists, and orbit-to-escape velocity tethered launch schemes--which take place entirely in space--but "hypersonic" means atmosphere to me. Could you explain please?

GuineaPig

Banned

Registered: 2002-12-14

Posts: 2

Re: Power Limits of Advanced Propulsion

In addition to lightcraft, there are Microwave Electrothermal  Thrusters (MET's).  By heating the exhaust gases away from the thruster walls without the use of electrodes, they can achieve ISPs much greater than NERVA, with thrust densities much higher than ion grid or hall thrusters.  An MET thruster that uses a large external microwave source beamed to the craft /might/ have sufficient thrust-to-weight for ground launch.

Here is a link to a detailed paper describing various types of electric propulsion:
http://www.aip.org/tip/INPHFA/vol-6/iss-5/p16.pdf
The above paper does not describe MET's much however; they are pretty new, technology-wise.

mauk2

Banned

Registered: 2002-12-10

Posts: 29

Re: Power Limits of Advanced Propulsion

soph, preston:

I'd also tend to favor something like a spaceplane SSTO or hypersonic tether assisted launch than one of those nuclear monsters sending hundreds of people to space at once...

I am curious as to what sort of a spaceplane you would want?  What cargo capacity, fuel, etc?

I feel a SSTO space plane is quite doable, IF you are willing to make it nuclear powered/assisted.  If you are not willing to use nuclear power, then it can't be done with any useful mass fraction.

For nuclear powered designs, I have seen types using a NERVA style core to simply power your way to orbit using air as reaction mass, switching over to water/hydrogen as you get above the air.

I have seen pure antimatter powered SSTO planes as well.  (These are FIERCE!)

I have seen a nuclear assisted design, where hydrogen is heated to 2500 C in a NERVA-style core and the exhaust is then combusted with external air at low heights, switching to pure rocket operations at high levels.

The real problem with planes is the runways and landing-gear design.  Plus, wings are mainly dead weight on the trip up to orbit, and lifting bodies tend to have a HIGH landing speed.

This means that spaceplanes don't scale in size very well. 

And size counts. 

soph

Member

Registered: 2002-11-24

Posts: 1,492

Re: Power Limits of Advanced Propulsion

lets say we have a spaceplane with the cargo and passenger capacity of a 747.  This would be great for getting a good amount of people and good around the globe quickly, and could be mass produced for many trips to many locations. 

assume we use the most lightweight heat-resistant material available.  and the wingspan doesnt have to be as great, because with nuclear or similar engines, youre not using the air to carry you quite as much (you could quickly leave the atmosphere, go into orbit, and come down near the destination).  you could also use retractable wings.

mauk2

Banned

Registered: 2002-12-10

Posts: 29

Re: Power Limits of Advanced Propulsion

Oh, you are thinking about a sub-orbital system, like the "Orient Express" ideas that got kicked around in the late 80's.

<shrug>  While that is a worthwhile field of development, it does nothing at all to get us (as a race) access to the vast resources of the Solar System.

I like my standard of living, and I see no reason why a peasant in Bangladesh should not have a decent shot of attaining one just as good.  Scarcity of resources is the true root of many of our problems, getting off Earth is the solution.

It seems simple to me, I just don't understand why it gets so much resistance.

Preston

Banned

Registered: 2002-06-02

Posts: 72

Re: Power Limits of Advanced Propulsion

Woops, I was away for a few days --

Tether assisted hypersonic spaceplanes are a combonation of the suborbital hypersonic spaceplane concept and tethers. It's the same idea behind other tether systems, extended to assisting the launch of suborbital payloads. A nice paper on it is here: http://www.whidbey.com/forward/pdf/tp158.pdf and some more can be found here: http://www.whidbey.com/forward/TechPubs.html (page with all the papers the late Robert L. Forward has ever gotten published)

So a suborbital system can be used as a stepping stone to greater things.

From what I can tell, HASTOL doesn't give you a payload beyond 10 tonnes, but that's for the earliest systems, and it can eventually be made better (bigger solar arrays for raising the orbit of the tether boost facility, and a more massive tether boost facility). In any event, it seems like a good way to get passengers into orbit.

soph

Member

Registered: 2002-11-24

Posts: 1,492

Re: Power Limits of Advanced Propulsion

what i was thinking of a scramjet type plane that could be used for space deliveries as well (ex. ISS).  i believe Zubrin mentioned something about space entry in his pioneer rocketplane proposal.  this is what i had in mind, with all my previous suggestions as well.