[AR] Re: Way OT question: degerate matter thrusters?
- From: rsteinke@xxxxxxxxxxx
- To: arocket@xxxxxxxxxxxxx
- Date: Wed, 18 Feb 2015 14:41:07 -0700
I'll nit-pick this a little. At higher pressures you can use higher
expansion ratios, which give better Isp. A 100,000 psi air rocket
with a 1000x expansion ratio will get better Isp than a party baloon
at the same temperature, but the effect is smaller than the effect of
temperature.
----- Original Message -----
From: "Ian Woollard"
To:
Cc:
Sent:Wed, 18 Feb 2015 21:02:09 +0000
Subject:[AR] Re: Way OT question: degerate matter thrusters?
It's not the pressure, it's the temperature that matters. If it's
simply compressed very hard, but at room temperature, then the exhaust
velocity is basically no better than a party balloon; as it expands in
the nozzle it cools and then stops expanding. In order for it to work
well you have to have it stored at very, very, very high temperature.
On 18 February 2015 at 20:54, Galejs, Robert - 1007 - MITLL wrote:
Maybe I can ask my question once again, very precisely…
Is it theoretically possible, assuming I give you a magical tank with
zero weight and arbitrarily high tensile strength, to put an object
into orbit using highly compressed air (think giga-atmospheres of
pressure or more)? Or is there some physics limitation (like the
tank freezing from the air expanding or some other thermodynamic
gotcha) that would make this theoretical rocket not work?
- Robert
FROM: arocket-bounce@xxxxxxxxxxxxx [2]
[mailto:arocket-bounce@xxxxxxxxxxxxx [3]] ON BEHALF OF
rsteinke@xxxxxxxxxxx [4]
SENT: Wednesday, February 18, 2015 3:40 PM
TO: arocket@xxxxxxxxxxxxx [5]
SUBJECT: [AR] Re: Way OT question: degerate matter thrusters?
The engineering issue of tank weight is what would keep it from
getting to orbit. Compressed air rockets work fine except that you
just can't get very good mass ratio from a tank of air. Going to
higher pressures doesn't help because the tank has to get heavier to
hold the higher pressure. The reason that liquid fuels are better is
that they are higher density than air at the pressures that generally
make sense inside rocket propellant tanks.
----- Original Message -----
FROM:
"Galejs, Robert - 1007 - MITLL"
TO:
"arocket@xxxxxxxxxxxxx [7]"
CC:
SENT:
Wed, 18 Feb 2015 20:30:15 +0000
SUBJECT:
[AR] Re: Way OT question: degerate matter thrusters?
I believe that that's a bad example. If I understand things properly,
I
believe that the ISP of the air alone is higher, but the mass flow
with water
is much better.
But you missed my point entirely... I wasn't trying to optimize
anything, I
was just trying to see if using hyper-compressed air at some
arbitrarily high
pressure could be used to get something into orbit theoretically,
ignoring
obvious engineering issues like tank weight.
- Robert
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [9]
[mailto:arocket-bounce@xxxxxxxxxxxxx [10]] On
Behalf Of Monroe L. King Jr.
Sent: Wednesday, February 18, 2015 3:20 PM
To: arocket@xxxxxxxxxxxxx [11]
Subject: [AR] Re: Way OT question: degerate matter thrusters?
Here's a simple experiment to show you. Go down to the toy store and
buy
yourself one of the old pump up water rockets. Pump it up with air and
let her
rip. Then fill it with water and try again at the same pressure.
Monroe
> -------- Original Message --------
> Subject: [AR] Re: Way OT question: degerate matter thrusters?
> From: "Galejs, Robert - 1007 - MITLL"
> Date: Wed, February 18, 2015 1:10 pm
> To: "arocket@xxxxxxxxxxxxx [13]"
>
>
> So why is supercritical steam "better" than air?
>
> -----Original Message-----
> From: arocket-bounce@xxxxxxxxxxxxx [15]
> [mailto:arocket-bounce@xxxxxxxxxxxxx [16]] On Behalf Of Monroe L.
King Jr.
> Sent: Wednesday, February 18, 2015 3:01 PM
> To: arocket@xxxxxxxxxxxxx [17]
> Subject: [AR] Re: Way OT question: degerate matter thrusters?
>
> Well so does HP air. Unless your using just a plain ol jet engine
like
> a ramjet. That would be HP air also.
>
> > -------- Original Message --------
> > Subject: [AR] Re: Way OT question: degerate matter thrusters?
> > From: "Galejs, Robert - 1007 - MITLL"
> > Date: Wed, February 18, 2015 12:55 pm
> > To: "arocket@xxxxxxxxxxxxx [19]"
> >
> >
> > Supercritical steam does not require heavy tankage?
> >
> > -----Original Message-----
> > From: arocket-bounce@xxxxxxxxxxxxx [21]
> > [mailto:arocket-bounce@xxxxxxxxxxxxx [22]] On Behalf Of Monroe L.
King Jr.
> > Sent: Wednesday, February 18, 2015 2:47 PM
> > To: arocket@xxxxxxxxxxxxx [23]
> > Subject: [AR] Re: Way OT question: degerate matter thrusters?
> >
> > I think Supercritical steam would be better than air. High
> > pressures require heavy tankage.
> >
> > Monroe
> >
> > > -------- Original Message --------
> > > Subject: [AR] Way OT question: degerate matter thrusters?
> > > From: "Galejs, Robert - 1007 - MITLL"
> > > Date: Wed, February 18, 2015 12:35 pm
> > > To: "arocket@xxxxxxxxxxxxx [25]"
> > >
> > >
> > > 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
--
-Ian Woollard
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