Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Putting down Compton Gamma-Ray Observatory by Shuttle ?
Date: Tue, 28 Mar 2000 17:37:19 GMT

In article <8bpogj$cj4$1@supernews.com>,
Richard Ireson <richard_ireson@dknet.co.uk> wrote:
>Looking at all it's 'interesting' properties what is is about hydrazine that
>makes it so suitable for its use?

There are few good "storable" rocket fuel combinations, which can be
stored indefinitely in sealed tanks at more-or-less room temperature.
Hydrazine is about the only halfway-safe monopropellant that qualifies.
There is also only one good halfway-safe storable oxidizer (N2O4), and
hydrazine and various derivatives of it are about the best fuels for use
with it.

(As bad as hydrazine and N2O4 are, they still qualify as "halfway-safe"
compared to alternatives like divinyldiacetylene and ClF5.)

>Is there something else, more desirable,
>that could be used?

The choices are really very limited when you start asking for storability,
good performance, and hypergolic ignition (propellants ignite on contact,
so no ignition system is required).  Safe storable monopropellants and
oxidizers are especially hard to come by; hydrogen peroxide is about the
best in both categories, but it suffers from slow decomposition, so it's
not indefinitely storable and its tanks need to be vented.

There has been considerable interest lately in non-toxic propellants.  For
example, it would save considerable time in shuttle processing if its OMS
and RCS systems didn't use hydrazine (more precisely, monomethyl
hydrazine) and N2O4, because any time the OMS/RCS plumbing is worked on,
everyone else has to stop work and evacuate the building.  The leading
candidates, last I heard, are alcohol as fuel and either peroxide or LOX
as oxidizer.  This has been on the shuttle-improvements wishlist forever,
but there is no commitment to doing it yet.

(The reason for using alcohol rather than kerosene is that alcohol
reliably and completely boils away in vacuum, ensuring no residues in the
plumbing, whereas kerosene doesn't.  Peroxide got an undeservedly bad
reputation a while back, from which it is only slowly recovering, so its
acceptability depends on who's making the decisions; LOX is rather more
orthodox but has the disadvantage of being cryogenic.)
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Russian solid rockets (was Re: Discussion. Man rating of entire 
	vehicle.)
Date: Thu, 22 Oct 1998 13:15:02 GMT

In article <E6uX1.1007$4%.16273943@fozzy.nit.gwu.edu>,
Dwayne Allen Day  <wayneday@gwis2.circ.gwu.edu> wrote:
>...For instance, Korolev wanted to use liquid oxygen in
>his rockets.  But it is not storable.  So, to justify its use, he had to
>come up with a way of rapidly fueling a rocket using LOX.  He developed a
>system that could fuel an ICBM in 8 minutes.

The US did similar sorts of work, in the days before it had its act
together on big solids.  (I once ran into a comment, in an old book on
cryo technology, that one has to be careful to minimize particulate
contamination in fluids, because otherwise very-high-flow-rate systems
become sandblasting machines.  It was obvious just what application they
had in mind.)

For that matter, LOX actually *is* storable, if the storage in question is
within a well-equipped silo.  Right at the end of the Atlas program, the
Atlas guys had pretty much figured out how to keep an Atlas fueled and
ready, including a full load of LOX.  But by that point, the hypergolics
were clearly in the lead, with solids coming up fast behind, and the idea
was never pursued.

>...But military applications demand solids.
>Anything else is very difficult to work with.

That's a *slight* exaggeration.  What the military is really intensely
averse to is having to fuel their rockets just before launch.  Packaged,
sealed liquids that just sit in the rocket until use are not so bad, and
there have even been a few relatively recent systems using them -- Lance
used liquid fuel, for example.

However, navies in particular *do* prefer fuels that won't leak in the
event of accident or battle damage, because fire is the single biggest
threat to warships.  In liquid days, this motivated a lot of work on
difficult technical problems like gel fuels; big solids became viable
partly because the naval missile people were pushing for them.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Russian solid rockets (was Re: Discussion. Man rating of entire 
	vehicle.)
Date: Fri, 23 Oct 1998 01:59:25 GMT

In article <M6IX1.1022$4%.16439792@fozzy.nit.gwu.edu>,
Dwayne Allen Day  <wayneday@gwis2.circ.gwu.edu> wrote:
>: For that matter, LOX actually *is* storable, if the storage in question is
>: within a well-equipped silo.  Right at the end of the Atlas program, the
>: Atlas guys had pretty much figured out how to keep an Atlas fueled and
>: ready, including a full load of LOX...
>
>But LOX is not storable in the missile for long periods of time.  It also
>boils off, meaning that you constantly have to keep tweaking it.

With silo-based support equipment, it *is* storable in the missile for
long periods of time, despite common belief otherwise.  I repeat, this is
something the Atlas guys had solved, in hopes of keeping their bird in
service longer.

I don't know the details of what they planned to do, but I can think of at
least three ways to handle the boiloff problem, ranging from just pouring
fresh LOX in as fast as it boils off, to eliminating the boiloff entirely
by circulating the LOX through a refrigeration system.  (People have built
zero-boiloff cryo systems; it would have been absolutely necessary for use
of fluorine as an oxidizer, so the necessary technology was developed and
demonstrated back in the 1960s.  References on request.)

>: ...sealed liquids that just sit in the rocket until use are not so bad, and
>: there have even been a few relatively recent systems using them -- Lance
>: used liquid fuel, for example.
>
>Lance was a solid.

Nope.  There was a later upgrade proposal -- I'm not sure if it ever went
into service -- that converted it to a solid, but the original operational
Lance used storable liquids.  They might have preferred a solid, but the
odd guidance system they used demanded a throttlable engine.  (The main
burn put it into the desired trajectory, and then the sustainer burn was
throttled to keep an onboard accelerometer precisely at zero, so it flew
a pure, clean ballistic trajectory regardless of air resistance.)

>But solids are ideal for all kinds of military applications, not simply at
>sea.  If you have a mobile missile, like Pershing II or Scud, you want to
>keep launch preparation time to a minimum.  With a solid you simply stop,
>raise the rocket, and shoot.  With a liquid you have to fuel the thing.

Dwayne, please listen carefully:  it is possible to build liquid-fuel
missiles which have fuel and oxidizer packaged up in the missile at the
factory, so they are just about as hassle-free as a solid, and in
particular they have the same minimal reaction time.  Great efforts were
put into developing this technology in the 1950s, and several operational
US missiles (e.g., Lance) used it.  Solids are generally preferred,
because they're simpler and they can't leak, but only the Navy considered
the latter an extremely high priority.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Russian solid rockets (was Re: Discussion. Man rating of entire 
	vehicle.)
Date: Fri, 23 Oct 1998 14:25:53 GMT

In article <Gm%X1.1035$4%.16693814@fozzy.nit.gwu.edu>,
Dwayne Allen Day  <wayneday@gwis2.circ.gwu.edu> wrote:
>: Dwayne, please listen carefully:
>
>I thought this was a relatively civil discussion, but if you want to
>resort to condescension, feel free...

Sorry about that, but you were persistently equating "liquids" with "must
be fueled just before launch", despite explicit comments to the contrary
from me and others.

>: it is possible to build liquid-fuel
>: missiles which have fuel and oxidizer packaged up in the missile at the
>: factory, so they are just about as hassle-free as a solid...
>
>Name an American ballistic missile developed in the last three decades
>that used liquids.  There are none.  This in itself should demonstrate the
>overwhelming superiority of solids for military use.

Superiority, yes.  Overwhelming?  I'm less convinced of that.  Note that I
never said solids aren't better, and in fact I repeatedly said they *are*
better.  But you are overestimating the problems of liquids, apparently by
assuming that the major problems found in early liquid systems were never
solved, which is not true.

To take us back to the original topic, the primary reason that the Soviets
stuck with liquid-fuel missiles for so long was, indeed, that they had
trouble developing large solids... but a contributing factor was that once
they had storable liquids sorted out, a good bit of the incentive went
away.  Not all of it, especially for naval applications, but a lot of it.
Once you've got "wooden round" missiles -- haul it out of a storeroom, put
it on a launcher, and push the button -- then whether the stuff inside
them is solid or liquid is a secondary issue.

>: Solids are generally preferred,
>: because they're simpler and they can't leak, but only the Navy considered
>: the latter an extremely high priority.
>
>The Navy considered it a higher priority from about 1956 to 1958.  At that
>point the Air Force saw that they were workable and began its own program.
>To imply that services other than the Navy did not see the superiority of
>solids early on ignores the fact that they developed them as soon as it
>became practical and abandoned liquids.

Again, you don't seem to be reading my comments carefully -- I agree that
solids are superior, and that everyone saw this early, but disagree that
everyone considered this of overwhelming importance.  The Navy did, at
least for its strategic missiles. But not everyone was in such a hurry.
The Army started development of the liquid-fuel Lance in 1962, and
continued it to service entry in 1972; evidently they were in no great
hurry to abandon liquids.  And the original solid-fuel Bullpup was
replaced in both USAF and Navy service by liquid-fuel versions in the
early 60s.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)

From: jimdavis2@primary.net
Newsgroups: sci.space.history
Subject: Re: Russian solid rockets (was Re: Discussion. Man rating of entire 
	vehicle.)
Date: Fri, 23 Oct 1998 21:07:57 GMT

Henry Spencer wrote:

> Superiority, yes.  Overwhelming?  I'm less convinced of that.  Note that I
> never said solids aren't better, and in fact I repeatedly said they *are*
> better.  But you are overestimating the problems of liquids, apparently by
> assuming that the major problems found in early liquid systems were never
> solved, which is not true.
>
> To take us back to the original topic, the primary reason that the Soviets
> stuck with liquid-fuel missiles for so long was, indeed, that they had
> trouble developing large solids... but a contributing factor was that once
> they had storable liquids sorted out, a good bit of the incentive went
> away.  Not all of it, especially for naval applications, but a lot of it.
> Once you've got "wooden round" missiles -- haul it out of a storeroom, put
> it on a launcher, and push the button -- then whether the stuff inside
> them is solid or liquid is a secondary issue.

What seems to be missing in this discussion is an appreciation of the very
different roles the US and USSR envisioned for their SSBNs. The US SSBN force
was intended as a deterrent, with great emphasis being placed on maximizing
time spent on station. This led to the blue and gold double crew concept and
made a very reliable, low maintenance (i.e. solid fuel) missile
indispensable.

The Soviets on the other hand envisioned their SSBNs as a first strike
resource where the superior performance of the liquid fuel missile outweighed
its disadvantages. Since the Soviets anticipated striking first having as
great a fraction of resources available at any given time was far less
important.

But with the introduction of the Typhoon class another role for an SSBN was
established. The Typhoon was to be able to stay on station for up to a year
or more to continue attacks on the US in a protracted nuclear war. Thus the
Typhoon had to have solid fuel missiles.

The missiles arming the latest Soviet SSBNs are:

Missile          Range  Weight Throw weight Intro  SSBN    Fuel
R-39   (SS-N-20) 8300km 84t      2550kg     1983  Typhoon  Solid
R-29RM (SS-N-23) 8300km 40.3t    2800kg     1985  Delta IV Liquid

Note that for the traditional (first strike) Delta IV subs higher performing
liquid fuel is preferred while the Typhoon is equipped with solid fuel
missiles. Whether the strategic concepts dictated the technology selected or
technological capabilities dictated the strategy adopted is a very
interesting question that I hope someone can definitively answer. For my part
I accept that the Soviets had difficulties developing large solid rockets but
I don't think that the lack of them proves the point. I also think that
assuming that Soviet strategic concepts paralleled our own and the Soviets
had the same pressures to develop solids as the US is dangerous.

Jim Davis

Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Escape Velocity Stuff (NOT shuttle to moon!)
Date: Mon, 30 Nov 1998 16:22:05 GMT

In article <36622696.144CEBB0@worldnet.att.net>,
Ryan Butke  <butke@worldnet.att.net> wrote:
>     P.S. Ways to inject into Lunar/Martian orbit other than hypergolic
>rocket engines? Can't use cryo's. (Not in my little game, too volatile)
>Would solids work? I guess they would need to be darned accurate...

No, you can use the same approach solid-fuel ICBMs and space launchers
use:  a little hypergolic final stage to clean up the errors introduced
by the solids.

Do note, by the way, that you can get better hypergolic performance than
N2O4/hydrazine.  In particular, replacing the N2O4 with ClF5 adds about
50s of Isp, at the cost of greater handling hassles.

Note also, most cryogenics can be stored in space using only passive
cooling.  Carefully-designed passive cooling systems -- just radiating
heat to black space, with good insulation and pointing away from the Sun
and any nearby planets -- can get you down to 40-50K, maybe even lower.
If you aren't obsessed with LH2 -- which *is* somewhat of a headache --
then there is no great problem with long storage of cryogenics in space.
For example, LOX/methane should work fine.  If you're really pushed for
performance, use FLOX, adding some fluorine to the LOX (a modified RL10
has been fired with FLOX/methane, so you don't even need new engines).

>Would solids fire well in
>microgravity (PAM's work, but are they rough engines?) ?

Solids work just fine in microgravity.  Solid upper stages are in free
fall when ignited, e.g. the great big Castor 120 that's the second stage
on an Athena 2.  Nobody has yet tried to light a *really* big solid in
free fall, but there's no reason to think it wouldn't work.
--
Mass-market software technology has |  Henry Spencer   henry@spsystems.net
been deteriorating, not improving.  |      (aka henry@zoo.toronto.edu)