[AR] Re: Way OT question: degerate matter thrusters?
- From: Christopher Buchanan Shay <chrisshay1@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 14 Mar 2015 16:29:06 -0400
Red mercury theatre:
http://www.tor.com/stories/2012/07/a-tall-tail
On Thu, Feb 19, 2015 at 4:27 AM, Monroe L. King Jr. <
monroe@xxxxxxxxxxxxxxxxxx> wrote:
> If compression of that level where possible I can think of a gillion
> better ways than compressing air for propulsion.
>
> Illogical
>
> Monroe
>
> > -------- Original Message --------
> > Subject: [AR] Re: Way OT question: degerate matter thrusters?
> > From: Peter Fairbrother <zenadsl6186@xxxxxxxxx>
> > Date: Thu, February 19, 2015 1:46 am
> > To: arocket@xxxxxxxxxxxxx
> >
> >
> > On 18/02/15 21:22, Lloyd Droppers wrote:
> > > I'm not a physicist so I won't talk much about the properties of
> > > degenerate matter. Rather, I will stay with the cold, hard science of
> > > single stage to orbit cold gas thrusters made of space elevator fiber.
> > >
> > > The basics of this are the rocket equation
> DV=Isp*ln(m_initial/m_final).
> > > You said orbit, so lets say LEO DV=9200 m/s. And if we just use N2
> > > instead of air (it's 75% of air, and you probably don't want Oxygen at
> > > that high of a pressure) and assume a simple rocket at 300K Chamber
> > > temperature (I don't know how to design a degenerate Air to room
> > > temperature heat exchanger, but I'll assume it is possible) and a gamma
> > > of 1.4 gives a 1.7 max CF from RPE so that gives you a 75s Isp. This
> > > means that your initial mass would have to be 270000x larger than your
> > > initial mass so that is a tiny payload, but it is physically possible.
> > >
> > > If you just need to get to space before your other engines can kick in,
> > > that is 1500 m/s DV. This is only a 7.7x initial mass to final mass
> > > ratio - about the same mass ratio as a single stage rocket is today.
> > >
> > > Now, let's run some numbers for real world best case Air rockets.
> First,
> > > what pressure do you want to be at? As it turns out, super high
> > > pressures don't help your density that much and, more importantly, they
> > > are worse for your pressure to density ratio which is maximum at the
> > > supercritical transition. But let's say 5000psi for some reasonable
> > > density. And lets assume an ideal sphere that uses all of the N2 and no
> > > payload or mass other than the tank.
> > >
> > > With Al 6061-T6 you can get 390 m/s, maybe up to 50,000 ft
> > > With Maraging Steel 350 (the best strength to weight metal) you get 770
> > > m/s, probably just over 100 kft 1/3rd the way to space
> > > With a tank of pure spectra 2000 (the best strength to weight thing I
> > > know of) you get 2295 m/s - We made it! Now to make a perfect spherical
> > > structure with no binder.
> > > But with something that could make a space elevator (~ 10x better than
> > > the spectra) you get 4100 m/s - a two stage vehicle and you might make
> orbit
> > >
> > > Now if we used hydrogen at 10000 psi instead of nitrogen, we get a 290s
> > > Isp, but at a much lower density it still improves performance and you
> > > can get to 9500 m/s - Single stage to orbit!
> > >
> > > Sorry, I was nerd sniped and thought I should share. All joking aside,
> > > cold gas thrusters are useful, but I think Niven was probably just
> using
> > > a literary Deus Ex Machina when he talked about degenerate matter.
> >
> > It would take a whole passel of energy to force matter into
> > near-degenerate condition. If you then let it expand then the repulsion
> > between particles would cause them to gain great velocity. We are
> > potentially talking about a good fraction of the speed of light here.
> >
> > So yes, I think it would work, and it would make a good sci-fi drive.
> > But as to how it could be done in practice ...
> >
> >
> > Note that in an ordinary gas the particles do not repel each other, so
> > as the gas expands and the distance between the particles increases they
> > do not gain energy. As the particles are on average moving away from
> > each other, when they bounce off each other their speed drops a little,
> > and this causes cooling.
> >
> > Expanding from the near-degenerate state, where increasing the
> > seperation of the particles releases mind-boggling amounts of energy,
> > the increased energy would completely overwhelm the cooling effect.
> >
> > Suddenly releasing the compression would result in a release of energy
> > which would be more powerful than a similarly-sized atom bomb going off.
> > Depending on exact conditions, it could be considerably more powerful.
> >
> > -- Peter Fairbrother
> > >
> > > Lloyd
> > >
> > > On Wed, Feb 18, 2015 at 11:35 AM, Galejs, Robert - 1007 - MITLL
> > > <galejs@xxxxxxxxxx <mailto:galejs@xxxxxxxxxx>> wrote:
> > >
> > > I know this is way off-topic, but it has always had me wondering
> and
> > > it seems like Arocket has the appropriate knowledge base to address
> > > this (or, at least wildly speculate)...____
> > >
> > > __ __
> > >
> > > In some of Larry Niven's sci-fi stories, he imagines rocket
> > > thrusters (between the ground and orbit) based on super-compressed
> > > air (supposedly "nearly degenerate matter"). Would such thrusters
> > > theoretically work, or are there some thermodynamic (or other
> > > physics) limitations that come into play?____
> > >
> > > __ __
> > >
> > > Thanks,____
> > >
> > > __ __
> > >
> > > Robert____
> > >
> > >
>
>
--
Christopher Shay <https://sites.google.com/site/chrisshay1/>
(407) 566-8256
(321) 443-1451 - Mobile
chrisshay1@xxxxxxxxx
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