From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.tech
Subject: Re: TNT as propellant!?!?!?!?!?
Date: Thu, 20 Jul 2000 01:16:55 -0700

Aaron Smith wrote:
>
> I just came up with an idea:  I was reading about the "putt-putts" used
> for ORION research and thought of this:  TNT has a detonation velocity
> of almost 7500 m/sec.  That translates to an ISP of around 760.  Maybe
> feed solid TNT into a blast tube (kinda like a PDE, but with solid
> propellant) and detonate.  My question is this:  would the feed system
> mass undo preformance gains?  There are also explosives with higher
> Vdets, I'll look into them.

That's how fast the detonation shock front propagates through the
material, it is not the expansion velocity of the product gases.  The
energy per unit mass of TNT is only 4.5E6 J/kg, much less than even
peroxide/kerosene, and the molecular weight of its reaction products is
too high (it essentially burns too lean to achieve the best Isp, which
is typically well on the rich side of stochiometry). The Isp of TNT is
barely 300 s even for expansion from 10,000 psi to .1 psi- ok, but not
worth the hassle and hazard.

You aren't the first person to confuse Vdet with Vexhaust, don't be
embarrassed.  It would be great if true, though- NERVA performance from
a dense propellant would be unbeatable.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.tech
Subject: Re: TNT as propellant!?!?!?!?!?
Date: Thu, 20 Jul 2000 01:34:52 -0700

Doug Jones wrote:
>
>
> the molecular weight of its reaction products is
> too high (it essentially burns too lean to achieve the best Isp, which
> is typically well on the rich side of stochiometry).

I wrote that, then forgot to delete it. The shifting equilibrium
products have quite a bit of hydrogen and CO, so it certainly isn't too
lean.

From: zerog@aol.com (Zerog)
Newsgroups: sci.space.tech
Subject: Re: TNT as propellant!?!?!?!?!?
Date: 21 Jul 2000 18:43:28 GMT

>Vdetonation != Vexhaust.  Sorry.  Don't know the Isp of TNT off hand,
>but you're about 3X high.  What matters is the directed velocity of the
>final exhaust products, not the speed of propogation of the reaction.

As usual, your numbers are pretty close to reality.  Experimental Putt-Putt
research done back in the 80's for potential use in upper stages confirmed a
useful Isp of around 250 sec for TNT.

Bevin McKinney

From: gchudson@aol.com (GCHudson)
Newsgroups: sci.space.tech
Subject: Re: TNT as propellant!?!?!?!?!?
Date: 22 Jul 2000 19:02:28 GMT

>>Vdetonation != Vexhaust.  Sorry.  Don't know the Isp of TNT off hand,
>>but you're about 3X high.  What matters is the directed velocity of the
>>final exhaust products, not the speed of propogation of the reaction.
>
>As usual, your numbers are pretty close to reality.  Experimental Putt-Putt
>research done back in the 80's for potential use in upper stages confirmed a
>useful Isp of around 250 sec for TNT.
>
>Bevin McKinney

Yep.  The tests I ran in 1980 produced Isps in the 190 range, as I recall.  But
they were pretty crude, and slight optimization should give something like
230-250.

Gary C Hudson

From: "L.C." <lcurcio@bellatlantic.net>
Newsgroups: sci.space.tech
Subject: Re: TNT as propellant!?!?!?!?!?
Date: Sun, 23 Jul 2000 13:31:56 GMT

A related propellant was actually put into production. The agent wasn't TNT, but
ammonium picrate, which is
chemically close.


(Source _Solid Propellant Rockets_ by Afred J. Zaehrenger 1958)

NDRC propellant:
Ammonium Picrate            46.4%
Sodium Nitrate                  46.4%
Ethyl Cellulose Binder        7.2%

The listed Isp on this was 180 seconds.

One might consider an oxidizer like AP with TNT (rigorously excluding
yours truly from the county).  That would help burn the copious soot from
the TNT reaction. At the same time, it dilutes the TNT reaction. The
result would be some average of TNT Isp with AP/hydrocarbon Isp. That may
be what's happening here with sodium nitrate instead of Isp.

-Larry Curcio



GCHudson wrote:

> >>Vdetonation != Vexhaust.  Sorry.  Don't know the Isp of TNT off hand,
> >>but you're about 3X high.  What matters is the directed velocity of the
> >>final exhaust products, not the speed of propogation of the reaction.
> >
> >As usual, your numbers are pretty close to reality.  Experimental Putt-Putt
> >research done back in the 80's for potential use in upper stages confirmed a
> >useful Isp of around 250 sec for TNT.
> >
> >Bevin McKinney
>
> Yep.  The tests I ran in 1980 produced Isps in the 190 range, as I recall.  But
> they were pretty crude, and slight optimization should give something like
> 230-250.
>
> Gary C Hudson