[AR] Re: Way OT question: degerate matter thrusters?
- From: Nathan Mogk <nm8911@xxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Wed, 18 Feb 2015 21:09:37 +0000
You are suggesting an infinite mass ratio. If you plug that in to the
rocket equation, it becomes clear that with such a tank, you can gain up to
an infinite amount of delta-v, regardless of your specific impulse. A
better question to ask is what mass ratio would be required for propulsion
system x to achieve orbit. If we assume 9.4km/s dv to get to orbit and an
Isp of 60 (generous for cold gas thrusters), then you would need a mass
ratio of 8,766,000. I believe the current state of the art for tank design
is slightly lower than a mass ratio of 6. Engineering feasibility really is
the limiting factor.
I didn't actually address the compressed air propulsion. The results of
that analysis would be a more accurate estimation of Isp, which will depend
on the temperature of the gas as it leaves the nozzle.
On Wed Feb 18 2015 at 1:55:16 PM 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
> <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 <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 <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
>
>
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