From: "Jeff Greason" <jgreason@hughes.net>
Newsgroups: sci.space.policy
Subject: Re: Costs and The Need For Government Money
Date: Wed, 7 Feb 2001 17:59:26 -0800

Jim Benson <jim@spacedev.com> wrote in message
news:vsq18t0shfedbbvfrl9819gakvnvsk3tf5@4ax.com...
> Sub--orbital planes will not be financed if they use dangerous (liquid
> or solid) rocket motors. Planes like the Bristol space plane are
> impossible because of the rocket motor (e.g. RL-10) characteristics -
> expensive, non-reusable and uninsurable.

While I certainly agree that safe engines are the key to
commercial success, I believe Jim is overstating the case for
hybrids a little bit here.   That is understandable -- when all
you have is a hammer, everything looks like a nail.

From the SpaceDev web site, the AMROC data base includes
~300 test firings.  During that set of firings, there was one
uncontained energy release.  Speaking for myself, I don't
consider a data base of 300 test firings to be adequate
assurance of safe and reliable operation.  We've got over 600
firings since developing ignition interlocks, and none of these
have ever had an uncontained energy release.  And we have a
lot more testing to do before the engines are ready for use on
a manned vehicle.

(I'm using the phrase "uncontained energy release" because I
 don't want to get into an argument over whether a bursting
 hybrid rocket case counts as an explosion or not).

I think hybrids are a useful technology for some niches.
Their biggest advantage is minimum development cost in
large thrust applications.  If I needed a new strap-on booster
for a large vehicle, I'd think seriously about a hybrid, for
example.  But to claim that hybrids are intrinsically safe and
cannot pose a risk to the vehicle, just because they are
hybrids, is a bit off the mark.  Regardless of  technology,
safety and reliability are products of proper design and
thorough test.

----------------------------------------------------------------
"Limited funds are a blessing, not         Jeff Greason
a curse.  Nothing encourages creative      President & Eng. Mgr.
thinking in quite the same way." --L. Yau  XCOR Aerospace
   <www.xcor-aerospace.com>                <jgreason@hughes.net>

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: suborbital vehicle for X-Prize
Date: Fri, 16 Feb 2001 03:31:41 GMT

In article <0d0n8tcv15u4enikr52rs9ech644bniqkd@4ax.com>,
Jim Benson  <jim@spacedev.com> wrote:
>The biggest problem most of the space plane people are having is a
>safe motor.

Easy, buy one from the Russians.

>Liquid and solid motors are bombs waiting to go off, most liquid
>motors do not restart, and only a few can be throttled. Solid motors
>not only explode, they burn out of control, cannot be stopped, are
>toxic and fragile.

Solids are fireworks, but many liquid motors are safe and controllable.
In particular, although it's a neglected subfield compared to space, there
are liquid-fuel *aircraft* rocket motors which are qualified for long
service with maintenance by ordinary aircraft technicians.  (For example,
the design used in the Mirage III rocket-boost pack, apparently still in
service on the Swiss Mirages.)

All rocket motors are bombs waiting to go off, in the sense that they pack
a lot of power into a small container.  But some are more bomb-like than
others.

>The only safe motors for human sub-orbital flights seem to be hybrids
>like SpaceDev makes.

Although it was never mentioned in their pressure releases for some
reason, Amroc did have one of their big hybrids explode, on a USAF test
stand.  (A friend of mine was there.)  The throat got plugged somehow.
Hybrids are a lot safer than solids, and they arguably have some safety
advantages over liquids, but perfectly safe they are not.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

Date: Fri, 16 Feb 2001 13:42:50 +0100
From: Bruno Berger <bruno.berger@spl.ch>
Newsgroups: sci.space.tech
Subject: Re: suborbital vehicle for X-Prize

Henry Spencer wrote:
<snip>
> service with maintenance by ordinary aircraft technicians.  (For example,
> the design used in the Mirage III rocket-boost pack, apparently still in
> service on the Swiss Mirages.)

Not any more, they stooped using the rocket pack about 10 years ago.
They used the boosters for high altitude flights (20-25 km, ballistic).
This kind of flights were quite expensive, the handling of the nitric
acid was a nightmare, the green people had also their scruples about the
environmental impact and this type of flight profile is a bit dubious in
such a small country like Switzerland (but interesting :-) . 4 Years ago
they replaced the good old Mirage with F-18's (the IIIs were sold to
museums etc, the IIIr are still in use as a reconnaissance plane).

Bruno (who has maintained this plane during his military service)

--
Bruno Berger
Swiss Propulsion Laboratory
E-Mail: bruno.berger@spl.ch
WWW:    http://www.spl.ch

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: suborbital vehicle for X-Prize
Date: Fri, 16 Feb 2001 14:43:04 GMT

I wrote:
>...liquid-fuel *aircraft* rocket motors which are qualified for long
>service with maintenance by ordinary aircraft technicians.  (For example,
>the design used in the Mirage III rocket-boost pack, apparently still in
>service on the Swiss Mirages.)

Correction:  a friend tells me that the rocket packs were phased out in
the early 1990s.  The need for them was limited, the propellant handling
was a headache, and they just weren't quite worth it any more.

>Although it was never mentioned in their pressure releases for some
>reason, Amroc did have one of their big hybrids explode...

Oops, obviously that should have been "press releases"!
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

From: zerog@aol.com (Bevin McKinney)
Newsgroups: sci.space.tech
Date: 16 Feb 2001 20:19:55 GMT
Subject: Re: suborbital vehicle for X-Prize

>Although it was never mentioned in their pressure releases for some
>reason, Amroc did have one of their big hybrids explode, on a USAF test
>stand.  (A friend of mine was there.)  The throat got plugged somehow.
>Hybrids are a lot safer than solids, and they arguably have some safety
>advantages over liquids, but perfectly safe they are not.


The rupture of AMROC's first 250k motor had nothing do with plugging of the
throat.  It was the result of a flawed insulation design at the interface
between the engine case and forward dome.  Hot gasses leaked across the
interface and the forward dome unzipped in < 20 ms.  The insulation interface
was redesigned, tested in 18" diameter motors, and applied to subsequent
motors.   The problem was never seen again.

To say that it was an explosion is misleading.  If you're worried about the
effects of high-order chemistry, they are not present in classic hybrids.
However, the motor case is unavoidably a high-pressure vessel subject to
rupture.  The consequences of such a rupture can still be substantial.
Composite cases mitigate these effects to a great extent.  However, when one
instantaneously removes a 6 ft diameter dome from a 500 psi pressure vessel ...
you do the math.  The resulting near instantaneous force is roughly 2Mlb and
the pressure wave, even though subsonic, still carries quite a wallop.

BTW - In some early test motors, even big ones, we often passed stuff through
the nozzle that was considerably larger than the throat.  Most times it was
barely noticeable.  One large motor whose fuel grain had been inadvertently
frozen due to flooding with LOX several hours before, spit out an incredible
amount of fractured fuel chunks, some as big as auto tires.  The only way you
could tell that it was happening was to watch the flaming chunks of fuel set
fire to the sagebrush on an adjacent hillside.

We never popped a motor due to plugging of the throat.  In fact, although we
had burn-throughs, sometimes intentional, I don't think we ever popped one,
with the exception of the first 250k motor.

Bevin McKinney

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: suborbital vehicle for X-Prize
Date: Sat, 17 Feb 2001 05:20:19 GMT

In article <20010216151955.26762.00001059@ng-cq1.aol.com>,
Bevin McKinney <zerog@aol.com> wrote:
>>...Amroc did have one of their big hybrids explode, on a USAF test
>>stand.  (A friend of mine was there.)  The throat got plugged somehow...
>
>The rupture of AMROC's first 250k motor had nothing do with plugging of the
>throat.  It was the result of a flawed insulation design at the interface
>between the engine case and forward dome.  Hot gasses leaked across the
>interface and the forward dome unzipped...

Thanks for the correction!  My friend was on the USAF side, and evidently
didn't hear the details about what caused it.

>To say that it was an explosion is misleading...

Equally, to say that it was *not* an explosion is misleading. :-)  In a
technical sense, such a rupture isn't an explosion, but that word does
give the right general idea about the effects on the surroundings.
--
When failure is not an option, success  |  Henry Spencer   henry@spsystems.net
can get expensive.   -- Peter Stibrany  |      (aka henry@zoo.toronto.edu)

From: "Jeff Greason" <jgreason@hughes.net>
Newsgroups: sci.space.tech
Subject: Re: suborbital vehicle for X-Prize
Date: Fri, 16 Feb 2001 21:25:55 -0800

Bevin McKinney <zerog@aol.com> wrote in message
news:20010216151955.26762.00001059@ng-cq1.aol.com...
> >Although it was never mentioned in their pressure releases for some
> >reason, Amroc did have one of their big hybrids explode, on a USAF test
> >stand.  (A friend of mine was there.)  The throat got plugged somehow.
> >Hybrids are a lot safer than solids, and they arguably have some safety
> >advantages over liquids, but perfectly safe they are not.

> To say that it was an explosion is misleading.  If you're worried about
the
> effects of high-order chemistry, they are not present in classic hybrids.

While Bevin certainly knows this (after all, he explained it to me
in the first place), I thought this was a good point to clarify terms
for reference.

While often used interchangeably, "explosion" and "detonation" are
not synonymous.  A "detonation" is a supersonic shock wave
with energy release along the shock.  That's what happens in a
high explosive.  An "explosion" (from Webster's) is (neglecting
irrelevant cases):

explode:
(2): to burst or cause to burst violently and noisily
(3): to undergo a rapid chemical or nuclear reaction with
production of heat and violeng expansion of gas

(3) includes detonations, and hybrids don't do that.  However,
as a large pressure vessel, they clearly can do (2).  A bursting
pressure vessel is a "boiler explosion" in the literature on the
subject.

All detonations are explosions, but not all explosions are
detonations.  Hybrids don't detonate -- they can explode.  Of
course, given proper design, construction, and test, they
*won't*, and that's more important...
But then, that's true of other rocket types.  The trick is to
*do* the proper design, construction, and test, using
practices appropriate to your choice of technology.

----------------------------------------------------------------
"Limited funds are a blessing, not         Jeff Greason
a curse.  Nothing encourages creative      President & Eng. Mgr.
thinking in quite the same way." --L. Yau  XCOR Aerospace
   <www.xcor-aerospace.com>                <jgreason@hughes.net>