[AR] Re: Way OT question: degerate matter thrusters?
- From: "Troy Prideaux" <GEORDI@xxxxxxxxxxxxxxxx>
- To: <arocket@xxxxxxxxxxxxx>
- Date: Thu, 19 Feb 2015 08:59:24 +1100
Depends a lot on the *ambient* pressure the system is working in. At sea level
– the chamber pressure can contribute significantly to the Isp via nozzle
expansion. In the vacuum of space, high chamber pressures are virtually a waste
of mass and effort as they don’t contribute much at all and as Ian rightly
pointed out – you’re limited by multi phase flows with high expansions of cold
gas. Only *gas* can contribute to nozzle propulsion. Once it freezes, it
doesn’t contribute to the thrust coefficient or Isp.
Troy
_____
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of rsteinke@xxxxxxxxxxx
Sent: Thursday, 19 February 2015 8:41 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Way OT question: degerate matter thrusters?
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" <ian.woollard@xxxxxxxxx>
To:
<arocket@xxxxxxxxxxxxx>
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 <galejs@xxxxxxxxxx>
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 [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of rsteinke@xxxxxxxxxxx
Sent: Wednesday, February 18, 2015 3:40 PM
To: arocket@xxxxxxxxxxxxx
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" <galejs@xxxxxxxxxx>
To:
"arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
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 [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Monroe L. King Jr.
Sent: Wednesday, February 18, 2015 3:20 PM
To: arocket@xxxxxxxxxxxxx
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" <galejs@xxxxxxxxxx>
> Date: Wed, February 18, 2015 1:10 pm
> To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
>
>
> So why is supercritical steam "better" than air?
>
> -----Original Message-----
> From: arocket-bounce@xxxxxxxxxxxxx
> [mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of Monroe L. King Jr.
> Sent: Wednesday, February 18, 2015 3:01 PM
> To: arocket@xxxxxxxxxxxxx
> 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" <galejs@xxxxxxxxxx>
> > Date: Wed, February 18, 2015 12:55 pm
> > To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
> >
> >
> > Supercritical steam does not require heavy tankage?
> >
> > -----Original Message-----
> > From: arocket-bounce@xxxxxxxxxxxxx
> > [mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of Monroe L. King Jr.
> > Sent: Wednesday, February 18, 2015 2:47 PM
> > To: arocket@xxxxxxxxxxxxx
> > 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" <galejs@xxxxxxxxxx>
> > > Date: Wed, February 18, 2015 12:35 pm
> > > To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
> > >
> > >
> > > 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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