hybrid rockets
Bruce Dunn
propellant rockets. Perhaps a better comparison is between a pressure fed
liquid using a liquid hydrocarbon fuel, and a pressure fed hybrid using a
solid hydrocarbon fuel.
1) Assuming helium pressurization, the pressurization system complexity is
the same for the two rockets. The liquid rocket needs a larger system
since it needs to pressurize both the oxidizer and the fuel, but this
doesn't affect the complexity of the system.
2) The oxidizer tank structure and contents are essentially identical
between the two rockets, and operate at essentially the same pressure.
This is true whether LOX or a storable oxidizer is used.
3) The hybrid fuel pressure vessel, and the liquid hydrocarbon propellant
tank are of roughly comparable size (the solid hydrocarbon fuel is denser
than the liquid, but is full of combustion passages which lower its
effective density).
4) The hybrid rocket has the advantage of having a slightly lower pressure
for the fuel compartment (the solid hydrocarbon is stored at chamber
pressure, while the liquid hydrocarbon is stored at somewhat higher than
chamber pressure to allow for injector pressure drop).
5) The liquid rocket has the advantage of a fuel compartment which remains
at or near room temperature and does not require thermal insulation - the
required insulation mass for the hybrid rocket tends to counteract the mass
savings from its lower operating pressure.
6) Propellant valving, piping and tank venting is simpler for the hybrid,
which has only one liquid propellant.
7) Rocket throats and nozzles for both liquid and hybrid vehicles can be
made with similar ablative technology so there is essentially no difference
in cost here.
8) The liquid rocket requires a combustion chamber, but with suitable
ablative technology this is simply an extension of the ablative nozzle and
throat assembly and does not present a large additional cost item. The
hybrid has a case to nozzle joint which requires ablative protection.
9) The hybrid rocket has an injector which is simpler than bipropellant
injectors. However, there may not be a large difference in cost if it is
assumed that the liquid rocket uses a low cost injector design such as the
TRW coaxial pintle injector, or one of several large thrust per element
designs.
10) The pressure vessels for both types of rockets are likely to be very
reliable under normal flight operation. They lack the joint problems that
have given trouble with large solid rockets, can be hydrostatically tested
before use.
11) The hybrid rocket can't blow up. Neither can the liquid rocket unless
both pressure vessels fail, allowing fuel and oxidizer to mix. Liquid
rockets will explode if they lose thrust and fall to the ground, or are
destroyed by range safety commands. However, in these cases the launch has
already failed for other reasons, and that fact that the hardware
subsequently blows up rather than creates an impact crater is probably not
a major issue.
12) The specific impulse of the liquid rocket is higher than that of the
hybrid rocket, due to better combustion efficiency and better mixture ratio
control.
13) The hybrid rocket's burnout mass suffers from leaving a minimum of
several percent of its fuel unburnt. The liquid rocket burns virtually all
of its fuel, but its burnout mass suffers from the higher mass of the
hardware for its pressurization system.
14) There is a far larger base of experience with liquid rocket engines
than with hybrids.
Overall, I can't see that a hybrid offers any great advantage over a
pressure fed liquid, when you are comparing a similar level of technology.
The question that would-be hybrid builders need to answer therefore is "why
bother".
Note: I am shortly going on holidays, and probably won't be seeing any
followups to this posting - E-mail me if you have comments please.
--
Bruce Dunn Vancouver, Canada Bruce...@mindlink.bc.ca
Paul Dietz
> Overall, I can't see that a hybrid offers any great advantage over a
> pressure fed liquid, when you are comparing a similar level of technology.
> The question that would-be hybrid builders need to answer therefore is "why
> bother".
The only real advantage I could think of would be that metallizing
the fuel is easier in a hybrid.
Paul
Steve Ratts
: This thread has been generally comparing hybrid rockets to pump fed liquid
: propellant rockets. Perhaps a better comparison is between a pressure fed
: liquid using a liquid hydrocarbon fuel, and a pressure fed hybrid using a
: solid hydrocarbon fuel.
I think it's not a good idea to place any constraints on either design.
We should compare the best that liquids can do to the best that hybrids
can do (realizing that we have yet to launch a large hybrid and all our
experience so far with hybrid motors of any realistic scale is ground
tests). Any other comparison is, I think, a waste of time for reasons I
will elaborate.
<many technical comparisons between hybrid and presure-fed liquid deleted>
: Overall, I can't see that a hybrid offers any great advantage over a
: pressure fed liquid, when you are comparing a similar level of technology.
: The question that would-be hybrid builders need to answer therefore is "why
: bother".
Why bother? Simple. Hybrids are potentially *much* cheaper to build.
Sure, either technology can work. Yes, we have more experience with
liquids and solids. Nevertheless, the bottom line will be $$. True,
initially hybrids won't be cheaper to build because the production base
does not yet exist to build hybrid launch vehicles, but in the long run
they will be cheaper. A cheap solution is always preferable to an
otherwise equivalent but more expensive solution. Hybrids will be
preferable to equivalent liquid or solid boosters.
The facilities needed to build hybrids are not free, but they will be
cheaper than the equivalent liquid or solid production facilities (were
they built from scratch today). Hybrids are simpler than liquids and
*much* safer to build than solids, and thus their production facilities
will be less costly than either of the current alternatives. Hybrids are
also safer to store and transport.
Furthermore, the exhaust gasses from hybrids will be *much* nicer to the
environment than those of either solids of liquids. Yes, you can
introduce some nasty things into hybrid exhaust in the quest for higher
Isp or quicker burning rate, but I doubt we'll use much of that
considering the direction our nation is taking with respect to the
environment. I suspect it will be cheaper (both economiclly and
environmentally) to simply take a small performance loss (due to the
omision of performance enhanceing addatives from hybrid fuel) and build a
bigger (but cleaner burning) booster.
Over the course of time, the facilities used to build hybrid motors would
eventually be "bought and paid for" as Brian Wygle pointed out is already
the case for solids. At that time the real cost of a hybrid booster
designed to place payload X into orbit Y will be significantly cheaper
than the cost of an equivalent liquid or solid.
Given that we are not about to stop launching payloads into space, and
that no better alternative is readily available, I think hybrids are the
way to go to reduce our launch costs. I also think that composites have
a bright future in the launch vehicle industry.
: Note: I am shortly going on holidays, and probably won't be seeing any
: followups to this posting - E-mail me if you have comments please.
I'm posting this to the news groups because this topic appears to be of
interest to lots of people.
Cheers,
Steve.
******************************************************************************
Rocket Ratts | "Ignorance killed the cat, sir, curiosity
| was framed."
ra...@scorpio.aml.arizona.edu | -- Sabrina Perrault-Cadiz
GE/CS/S d-- -p+ c++ l-(+) u+ e++ m++(*) s+/- !n(-) h f+ g+++ w+ t+ r+ y++(--)*
******************************************************************************
Jeff Norr
(Bruce Dunn) wrote:
<comparison deleted>
>
> Overall, I can't see that a hybrid offers any great advantage over a
> pressure fed liquid, when you are comparing a similar level of technology.
> The question that would-be hybrid builders need to answer therefore is "why
> bother".
>
> Note: I am shortly going on holidays, and probably won't be seeing any
> followups to this posting - E-mail me if you have comments please.
>
>
>
>
>
> --
> Bruce Dunn Vancouver, Canada Bruce...@mindlink.bc.ca
This may seem a relatively stupid reason to pursue hybrids, but we
should try to maintain all options. Whether hybrids are better than either
solid or liquid systems is very debatable. However, if they can offer the
same performance as either systems, with performance meaning both thrust
Isp Cost etc, then why not persue them. If we do may they will grow in
performance, or some other aspect to make them more desirable than a
competing system. Developing hybrid technology prevents the trap of
putting all the eggs in one basket. I know there liquids and solids so the
basket is a little bit bigger, but why not increase its size.
A second reason to persue hybrids, but necessarily on the launcher
sized scale is for teaching. At the University level trying to do work
with experimental fuel combinations or designs with solids or liquids is
almost impossible to due, because of safety. At the high school level it
is impossible excluding the "estes" model rocket type work. Thus, the
hybrid offers a unique ability to be used as teaching tool for rocketry.
Just a couple of ideas,
------------------------------------------------------------------------------
Jeff Norr | A man said to the universe:
Hybrid Rocket Project | "Sir , I exist!"
Dept. of Aero & Astro Engineering | "However," replied the universe,
University of Illinois | "The fact has not created in me
e-mail: j-n...@uiuc.edu | A sense of obligation."
Office: (217) 244-1448 | - Stephen Crane
Lab: (217) 244-1395 |
WWW: http://www.cen.uiuc.edu/~jn8168/ |
------------------------------------------------------------------------------
--
Jeff Norr
j-n...@uiuc.edu
Geoffrey A. Landis
Bruce...@mindlink.bc.ca wrote:
> Overall, I can't see that a hybrid offers any great advantage over a
> pressure fed liquid, when you are comparing a similar level of
technology.
> The question that would-be hybrid builders need to answer therefore is
"why
> bother".
In article <40ocar$a...@news.ccit.arizona.edu> Steve Ratts,
ra...@News.CCIT.Arizona.EDU writes:
> Why bother? Simple. Hybrids are potentially *much* cheaper to build.
>...
If you followed Bruce Dunn's argument, what he said was that a
pressure-fed hybrid is *not*, in principle, "much" cheaper to build than
an equivalent pressure-fed liquid. He said that hybrids are much cheaper
than *pump* fed liquids, and noted that this is a biased comparison.
It's an interesting comparison, and one I've never seen argued before.
If you would go back and read his technical comparison between liquids
and hybrids, I would be interested in hearing your counterargument.
>...
> Furthermore, the exhaust gasses from hybrids will be *much* nicer to the
> environment than those of either solids or liquids.
Solids, maybe. The exhaust of a hydrogen-oxygen rocket is water vapor.
>...
____________________________________________
Geoffrey A. Landis,
Ohio Aerospace Institute at NASA Lewis Research Center
physicist and part-time science fiction writer
Blair Patric Bromley
>In article <76163-8...@mindlink.bc.ca>, Bruce...@mindlink.bc.ca
>(Bruce Dunn) wrote:
><comparison deleted>
>>
>> Overall, I can't see that a hybrid offers any great advantage over a
>> pressure fed liquid, when you are comparing a similar level of technology.
>> The question that would-be hybrid builders need to answer therefore is "why
>> bother".
>>
>> Note: I am shortly going on holidays, and probably won't be seeing any
>> followups to this posting - E-mail me if you have comments please.
>> --
>> Bruce Dunn Vancouver, Canada Bruce...@mindlink.bc.ca
> This may seem a relatively stupid reason to pursue hybrids, but we
>should try to maintain all options. Whether hybrids are better than either
>solid or liquid systems is very debatable. However, if they can offer the
>same performance as either systems, with performance meaning both thrust
>Isp Cost etc, then why not persue them. If we do may they will grow in
>performance, or some other aspect to make them more desirable than a
>competing system. Developing hybrid technology prevents the trap of
>putting all the eggs in one basket. I know there liquids and solids so the
>basket is a little bit bigger, but why not increase its size.
> A second reason to persue hybrids, but necessarily on the launcher
>sized scale is for teaching. At the University level trying to do work
>with experimental fuel combinations or designs with solids or liquids is
>almost impossible to due, because of safety. At the high school level it
>is impossible excluding the "estes" model rocket type work. Thus, the
>hybrid offers a unique ability to be used as teaching tool for rocketry.
>Just a couple of ideas,
As others have pointed out, one of the key advantages of the hybrid system
is that is relatively safe compared to both liquids and solids. And this allows
the design and the infrastructure to launch it to be much cheaper. Much cheaper.
And since one of the primary goals is cheaper access to space, hybrids make
a lot of sense. And as I notice that Mr. Dunn is from Canada, he may appreciate
the idea that if Canada wants to develop its own launching capability aside from
a few sounding rockets, it will want to pursue the cheapest and fastest approach. Hybrids are clearly a worthwhile option.
Blair
Steve Ratts
: If you followed Bruce Dunn's argument, what he said was that a
: pressure-fed hybrid is *not*, in principle, "much" cheaper to build than
: an equivalent pressure-fed liquid. He said that hybrids are much cheaper
: than *pump* fed liquids, and noted that this is a biased comparison.
: It's an interesting comparison, and one I've never seen argued before.
: If you would go back and read his technical comparison between liquids
: and hybrids, I would be interested in hearing your counterargument.
Hybrids are cheaper than bi-propellant liquids (and much safer than
monopropellant liquids or *any* solids) for several reasons. They only
have half of the plumbing and pumps of a liquid system. They use much
simpler (read: cheaper) injectors. They are much cheaper to test than
liquids (which are known to explode taking a great deal of test equipment
with them when they do. Hybrids *can't* explode, tails of hybrid
explosions have recently been exaggerated). I thought that I had made
these points quite clearly in the posts I've made to the hybrids threads
on this news group over the past few days, but perhaps you missed one of
them.
I think the reasons why hybrids are inherently cheaper to build than
equivalent liquids is therefore quite obvious. Half the plumbing and
pumps, simpler (and therefore cheaper) plumbing components, and much
cheaper testing (worst case: you damage your motor and need to re-paint
the test stand and repair your motor. You should see the results we've
got when we deliberately caused motor failures. Amazingly benign!). All
other things being equal, hybrids will come out cheaper every time.
Unfortunately, all other things are not equal at this time. As Brian
Wygle so aptly pointed out in the comparison of hybrids to solids, we have
a built up ("bought and paid for" were his words if I recall)
infrastructure for producing solids. The same sort of argument can be
applied to the production of liquids I expect. It will take time to build
up an equivalent infrastructure for hybrids, but the potential cost
savings will be significant therefore it will eventually take place. The
accountants will see to it.
: >...
: > Furthermore, the exhaust gasses from hybrids will be *much* nicer to the
: > environment than those of either solids or liquids.
: Solids, maybe. The exhaust of a hydrogen-oxygen rocket is water vapor.
Alas, not all bipropellant liquids use hydrogen and oxygen, and when they
do they generally never use it in stoichiometric quantities. Check again.
Russell John Panter
: Geoffrey A. Landis (GLA...@lerc.nasa.gov) wrote:
: : If you followed Bruce Dunn's argument, what he said was that a
: : pressure-fed hybrid is *not*, in principle, "much" cheaper to build than
: : an equivalent pressure-fed liquid. He said that hybrids are much cheaper
: : than *pump* fed liquids, and noted that this is a biased comparison.
: : It's an interesting comparison, and one I've never seen argued before.
: Hybrids are cheaper than bi-propellant liquids (and much safer than
: monopropellant liquids or *any* solids) for several reasons. They only
: have half of the plumbing and pumps of a liquid system. They use much
: simpler (read: cheaper) injectors. They are much cheaper to test than
: liquids (which are known to explode taking a great deal of test equipment
: with them when they do. Hybrids *can't* explode, tails of hybrid
: explosions have recently been exaggerated). I thought that I had made
I beg to differ. I have a photograph of a hybrid exploding. HOWEVER, this
motor commited the deadly sin of mixing LOX and grease. It was an
experimental hybrid burning tar paper and roofing cement in an oxygen
atmosphere. The petroleum products adsorbed the O2, forming explosives
that soon did what they did best.
: I think the reasons why hybrids are inherently cheaper to build than
: equivalent liquids is therefore quite obvious. Half the plumbing and
: pumps, simpler (and therefore cheaper) plumbing components, and much
: cheaper testing (worst case: you damage your motor and need to re-paint
: the test stand and repair your motor. You should see the results we've
: got when we deliberately caused motor failures. Amazingly benign!). All
: other things being equal, hybrids will come out cheaper every time.
You're forgetting an important benefit of going hybrid. This comes from
the fact that pretty much anything can serve a fuel in a hybrid motor.
By selecting the right fuel, the designer can use the same material for
fuel and the combustion chamber. IOW, a monolithic block can be cast
that serves as both fuel and structure. An ablative nozzle is cast in
place.
For even more simplicity (and less plumbing), use self-pressurizing
propellants. N2O is a popular oxidizer, and a hybrid can be made of
literally three parts - a fuel grain/combustion chamber/nozzle, an
injector, and an oxidizer tank. The rest would stay on the pad.
Jeff Greason
> pressure fed liquid, when you are comparing a similar level of
> technology. The question that would-be hybrid builders need to answer
> therefore is "why bother".
>
the reasons to pursue hybrids is to use alternative solid fuels. We're
going to want Lunar-fueled rockets one of these days, and I think
a hybrid is a nice way to build an Al-LOX or Si-LOX rocket. You don't
need outstanding T/W for Lunar applications, so you've avoided one
problem. You don't have to worry about pumping liquid metals, so
you've avoided another worry. And the comparative simplicity (vs.
pump-fed liquids) is another advantage.
(There's room for different opinions on this; when I discussed this
with Henry Spencer, he thought it superior to melt and pump the
metals in a pump-fed liquid.)
However, I've not found a combination that I think gets over 280s of
Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
think they're worthy of more work than they're getting.
Disclaimer: While I am an Intel employee, all opinions expressed are my own,
and do not reflect the position of Intel, NETCOM, or Zippy the Pinhead.
============================================================================
Jeff Greason "We choose to go to the Moon in this decade,
<gre...@ptdcs2.intel.com> and do the other things, not because they
<gre...@ix.netcom.com> are easy, but because they are hard." -- JFK
Blair Patric Bromley
>In article <76163-8...@mindlink.bc.ca> Bruce Dunn,
>Bruce...@mindlink.bc.ca wrote:
>> Overall, I can't see that a hybrid offers any great advantage over a
>> pressure fed liquid, when you are comparing a similar level of
>> technology. The question that would-be hybrid builders need to answer
>> therefore is "why bother".
>>
>It hasn't come up yet, so I thought I'd mention that, IMO, one of
>the reasons to pursue hybrids is to use alternative solid fuels. We're
>going to want Lunar-fueled rockets one of these days, and I think
>a hybrid is a nice way to build an Al-LOX or Si-LOX rocket. You don't
>need outstanding T/W for Lunar applications, so you've avoided one
>problem. You don't have to worry about pumping liquid metals, so
>you've avoided another worry. And the comparative simplicity (vs.
>pump-fed liquids) is another advantage.
The solid Al / LOX hybrid engine would be a very important technological
development for making transportation to and from the moon economical. And
this is something I have been wondering about in the past. What I recall
from discusssions with some professors working on the combustion of metals
is that it very, very problematic, and developing a workable engine may
be impossible. Still, these current technogical hurdles may be overcome
within hte next 10 years.
>(There's room for different opinions on this; when I discussed this
> with Henry Spencer, he thought it superior to melt and pump the
> metals in a pump-fed liquid.)
>However, I've not found a combination that I think gets over 280s of
>Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
>hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
>think they're worthy of more work than they're getting.
Even if it can get 200s of Isp, it would still worthwhile. Consider
the alternative: Bringing in propellant from Earth. Granted, water
has been found at the poles of the Moon, but it is of a limited supply,
and it is not exactly conveniently located.
Blair
David L Burkhead
[ 8< Major clip >8 ]
>
>Solids, maybe. The exhaust of a hydrogen-oxygen rocket is water vapor.
>
Uhh, Geoffrey, while I agree with most of what you said (and the
guy you were agreeing with), but this one isn't _quite_ right.
Hydrogen-oxygen may only directly produce water vapor, but the exhaust
is energetic enough that it will interact with the atmosphere to
produce nitrogen oxides on top of that water vapor.
RP-1/LOX will produce the same as the above, with the addition of
carbon dioxide and some (probably _very_ little) carbon monoxide.
In either case, the results are better than solids wrt unpleasant
exhaust products, and _neither_ case is _worse_ than hybrids. Thus,
dispice this nit, the basic point remains.
David L. Burkhead
r3d...@dax.cc.uakron.edu
d.bur...@genie.geis.com
76435...@compuserve.com
--
Spacecub - The Artemis Project - Artemis Magazine
Box 831
Akron, OH 44309-0831
Nick Strauss
these things (hybrid rockets, that is).
But I've got some questions...they may have been answered already, before I was
paying attention, so apologies if I bring back ugly memories...
1) There has been talk about how environmentally "good" hybrids are, how there
exhause is cleaner than both liquids and solids. If LOX is the liquid oxidizer
component in a hybrid, what are the fuels being considered? What would their
exhause products be, and how exactly does this compare with LOX/Kerosene or
such?
2) Can hybrid's be throttled? Seems possible to me, reduce the LOX flow and
you reduce the burn rate, but I'm far from a rocket scientist (sorry, had to do
that!).
3) It has been said hybrid's can't explode. Why? Do they just burn really
fast (deflagarate is the word, right?)
Any way, thanks.
--Nick
Steve Ratts
: I beg to differ. I have a photograph of a hybrid exploding. HOWEVER, this
: motor commited the deadly sin of mixing LOX and grease. It was an
: experimental hybrid burning tar paper and roofing cement in an oxygen
: atmosphere. The petroleum products adsorbed the O2, forming explosives
: that soon did what they did best.
I'd like to see your picture! I've personally assited in the test firing
of hybrids here at the U of A. We have deliberately *tried* to make them
fail. We have deliberately started them back up and continued to run
them *after* we have experienced nozzle failure. We honestly cant make
them explode. But then, we use HTPB (essentially tire rubber) with a
little carbon black and trace amounts of a cureing agent as our fuel. I
suppose if we had selected the fuel you described above we would have
experienced similar results. To my knowlege, all serious large hybrid
designs today are calling for HTPB as the fuel.
: You're forgetting an important benefit of going hybrid. This comes from
: the fact that pretty much anything can serve a fuel in a hybrid motor.
: By selecting the right fuel, the designer can use the same material for
: fuel and the combustion chamber. IOW, a monolithic block can be cast
: that serves as both fuel and structure. An ablative nozzle is cast in
: place.
: For even more simplicity (and less plumbing), use self-pressurizing
: propellants. N2O is a popular oxidizer, and a hybrid can be made of
: literally three parts - a fuel grain/combustion chamber/nozzle, an
: injector, and an oxidizer tank. The rest would stay on the pad.
Yes, I've read about such designs in the May 1995 issue of High Power
Rocketry. Apparently the amatures are already building and selling two
different designs along these lines. For under $1000 you too can be
flying your own hybrid rocket. If it's cheaper for the amatures to build
hybrids, then why should it not be cheaper for the pros?
Geoffrey A. Landis
rj...@zimmer.CSUFresno.EDU writes:
> You're forgetting an important benefit of going hybrid. This comes from
> the fact that pretty much anything can serve a fuel in a hybrid motor.
> By selecting the right fuel, the designer can use the same material for
> fuel and the combustion chamber. IOW, a monolithic block can be cast
> that serves as both fuel and structure.
I don't see how you gain from doing that. There must still be a
combustion chamber at the end of thrust. That combustion chamber must
have enough strength to be able to hold in the chamber pressure. The
only difference is that the combustion chamber is made of the same stuff
that the fuel is made of. I would think it would be better to make the
combusion chamber out of something that has a high strength to weight
ratio, and the fuel out of something that burns evenly and has a high
specific impulse, instead of compromising on both.
> For even more simplicity (and less plumbing), use self-pressurizing
> propellants. N2O is a popular oxidizer,
Nice for model rockets, but the specific impulse isn't very good.
> and a hybrid can be made of
> literally three parts - a fuel grain/combustion chamber/nozzle, an
> injector, and an oxidizer tank. The rest would stay on the pad.
Steve Ratts
: However, I've not found a combination that I think gets over 280s of
: Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
: hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
: think they're worthy of more work than they're getting.
During the 60's, when the search for very high specific impulse reached a
high pitch, lithium/lithium hydride HTPB (a hydrocarbon
polymer-hydroxyterminated polybutadiene, read: enhanced tire rubber)
fuels and fluorinated liquid oxygen hybrids deliverd over 400 seconds.
Swithcing to beryllium fuel pushed the specific impulse over 500
seconds. Impresive numbers, but you can toss out all claims about benign
hybrid exhaust products if you select either of these combinations!
Perhapse these would be usefull on the moon, but even then you have to
deal with some of the same dangers in production that solids face.
Paul Dietz
>>However, I've not found a combination that I think gets over 280s of
>>Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
>>hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
>>think they're worthy of more work than they're getting.
>
> Even if it can get 200s of Isp, it would still worthwhile.
There is some extractable sulfur in the lunar regolith. Sulfur/oxygen
rockets can have a vacuum Isp around 200 seconds. Sulfur melts at
reasonable temperatures, so it can be used in an all-liquid engine.
In space, one would want to use some sort of non-chemical engine.
Paul
Steve Ratts
Nick Strauss (nstr...@murrow.corp.sgi.com) wrote:
: 1) There has been talk about how environmentally "good" hybrids are, how
: there exhause is cleaner than both liquids and solids. If LOX is the
: liquid oxidizer component in a hybrid, what are the fuels being
: considered? What would their exhause products be, and how exactly does
: this compare with LOX/Kerosene or such?
Provided you are not going to try to eek out the last margin of
performance at the expense of increasing the environmental dammage due to
exhaust products, hybrids produce cleaner exhaust than any solid I know of
and even cleaner than some liquids. LOX-H2 is somewhat cleaner than
LOX-HTPB (the typical hybrid oxidizer-fuel combination), and LOX-kerosene
is only equivalent to LOX-HTPB. Liquids are also a lot more expensive.
LOX-HTPB produce exhaust fundamentally similar to automobile exhaust.
After all, you are burning a hydrocarbon in the presence of oxygen.
LOX-HTPB produces the same carbon dioxide, carbon monoxide and water
vapor of a LOX-kerosene motor.
It is possible to realize an Isp over 500 seconds from a hybrid motor, but
you have to use nasty things like beryllium. Isp's over 400 seconds can
be achieved with the use of lithium/lithium hydride HTPB. However, I
don't think anyone will seriously suggest the use of either of these
combinations due to the environmental impact. It is alos possible to
hike the temperature and density impulse by mixing powdered aluminum
with the HTPB prior to cureing. Even this will result in some nasty
stuff in your exhaust, so I don't think it would be a good idea. AMROC's
Aquila design (capable of placing 2500 lbs into low polar orbits, or 3200
lbs into low 28 degree orbits) utilized unenhanced HTPB.
: 2) Can hybrid's be throttled? Seems possible to me, reduce the LOX flow
: and you reduce the burn rate, but I'm far from a rocket scientist (sorry,
: had to do that!).
Absolutely! This is one of the meny stong points about hybrids. They
can not only be throttled, they can be stoped and restarted numerous
times as well. It *is* possible to conduct a test firing on the pad
prior to launch.
: 3) It has been said hybrid's can't explode. Why? Do they just burn
: really fast (deflagarate is the word, right?)
The burn rate of hybrids is one of the things that we would like to see
increased, but never the less a hybrid can never explode the way a liquid
or solid can.
In a hybrid motor the solid fuel is burned only after the temperature and
pressure rise above the point at which the solid sublimes to vapor. So
the burning takes place where the fuel vapor meets the gaseous oxidizer.
This burning interface is called the flame sheet and part of the heat
produced in the flame sheet goes toward vaporizing more fuel.
In a solid rocket motor the fuel and oxidizer are mixed as very fine
particles such that around each fuel particle are several smaller oxidizer
particles. Once a solid rocket starts to burn there is almost no way to
put out the fire. With a hybrid rocket you can simply shut off the flow
of oxidizer and the burn will stop.
With a liquid the problem is similar to a hybrid, but a bit trickier
because you have two liquids to control instead of just one. You
therefore have to worry about leaks from the fuel tank in a liquid, which
cannot happen in a hybrid. If you get leaks from the fuel and oxidizer
tanks in a liquid, may very well explode, but such explosions are fairly
rare these days. The main advantages a hybrid has over a liquid are
lower cost and higher reliability (fewer pumps and less plumbing to fail)
Those were some good questions, Nick. I hope you stick around to ask and
learn more.
Jeff Greason
Blair Patric Bromley <bro...@ux4.cso.uiuc.edu> wrote:
>gre...@ptdcs2.intel.com (Jeff Greason) writes:
>
>>It hasn't come up yet, so I thought I'd mention that, IMO, one of
>>the reasons to pursue hybrids is to use alternative solid fuels. We're
>>going to want Lunar-fueled rockets one of these days, and I think
>>a hybrid is a nice way to build an Al-LOX or Si-LOX rocket. You don't
>
>development for making transportation to and from the moon economical. And
>this is something I have been wondering about in the past. What I recall
>from discusssions with some professors working on the combustion of metals
>is that it very, very problematic, and developing a workable engine may
>be impossible. Still, these current technogical hurdles may be overcome
>within hte next 10 years.
I really don't see what the big technological hurdle is (unless it's
ignition). Once ignited, Si or Al should burn just fine. (my present
favorite candidate is a few% alloy of P in Si, which should improve
ignition and burn rate, and tend to depress the melting point of the
exhaust products).
I favor Si or Al because the Isp comes out about the same, but Si is
easier to come up with (Fe/Si is a byproduct of magma electrolysis, one
of the candiate lunar oxygen production methods).
>>However, I've not found a combination that I think gets over 280s of
>>Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
>>hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
>>think they're worthy of more work than they're getting.
>
> Even if it can get 200s of Isp, it would still worthwhile. Consider
>the alternative: Bringing in propellant from Earth. Granted, water
>has been found at the poles of the Moon, but it is of a limited supply,
>and it is not exactly conveniently located.
Correction: Water has *NOT* (yet) been found at the poles of the moon.
(Maybe we should add this to FAQ)
* There are theoretical predictions that water could collect
in lunar polar "cold traps"
* Something has been found, which looks, by radar, very much
like ice, at MERCURY's poles. That raises hopes that
it might be found at Luna's poles.
* Clementine found that the southern polar region of the moon
contains a large basin, which is permanently shadowed
at present lunar inclination. (It's an open question
whether it stays shadowed over the 22Kyr precession
cycle)
* One of three bistatic radar passes by Clementine (reported
in 12/94 Science) found *small* shifts in radar
reflection. This could be ice, but it's very, very
ambiguous data. As of 12/94, the other two passes
had not yet been analyzed.
Lunar surface to lunar orbit, round trip, is ~4km/s assuming
conventional vertical landing (Apollo style). At Isp of 280s, that's
a mass ratio of 4.3 (not too bad, probably reachable with a craft built
primarily of local materials). You can get this with ~100atm chamber
pressure and an O2-rich mix with Si or Al fuel -- exhaust (in the
case of Si) is SiO2, SiO, and O2. (Nothing that's going to create
a persistent volatiles problem if you don't do too much of it, which
is one of the nice things about it)
At Isp of 200s, that's a mass ratio of 7.7, which is getting tough to
do without pushing mass margins or materials, (at which point more of
your spare parts are coming from Earth).
Neither of these combinations is that attractive for Lunar-based round
trips to LEO. Either you're doing a lot of staging (expensive) or a
lot of on-orbit refueling (still expensive). However, if you combine
this with a high Isp LEO-LLO shuttle (nuclear-thermal, solar-thermal),
or (for cargo), solar-electric, you've got a pretty nice system:
Earth to LEO round trips: H-rich fuel/oxidizers going up,
mostly aerobraking going down
LEO-Lunar Orbit round trips: H2 reaction mass, solar-thermal or
nuclear-thermal for fast trips (people)
(cargo can go with O2 reaction mass, solar-electric)
Luna-Lunar Orbit round trips: Al-LOX or Si-LOX, low mass ratio
craft.
Well, I've rambled on longer than intended. The point is that there
*are* situations, in the (hopefully) foreseeable future, where Si-LOX
or Al-LOX rockets are going to be very useful, so it would be nice to
get started on them.
John Childers
>I just started getting into this Hybrid debate, and am now really interested in
>these things (hybrid rockets, that is).
>
>
>3) It has been said hybrid's can't explode. Why? Do they just burn really
>fast (deflagarate is the word, right?)
Rockets explode when the presure in the combustion chamber gets too high
and ruptures the chamber.
In a solid fuel rocket the fuel and oxidizer are premixed and any
exposed 'fuel' surface burns. If the 'fuel' is cracked it has a
larger exposed surface and burns faster. That over presures the
combustion chamber, BOOM! Or, chunks of fuel can break off and
block the nozzle, BOOM!
Since a hybrid rocket has no oxidizer in the solid fuel, the burn
rate depends on the input of liquid oxidizer and cracks in the fuel
are less of a problem. However, if chunks of fuel block the nozzle,
they will go BOOM!
---
John Childers | ===+========:+:
UNC Charlotte | _/ \_ |
Internet? Try | |\ /| -);
jech...@uncc.edu | | X |
--------------------------| __________|/_\|___ .^.
Disclaimer? Does anyone | |Caution Spacecraft| /|=|\
on the net ever officially| |Under Construction| |_____|
speak for their computer? | |/\/\/\/\/\/\/\/\/\| / ^ ^ \
--------------------------------------------------------------
Nick Strauss
>
>Nick Strauss (nstr...@murrow.corp.sgi.com) wrote:
>
>: 1) There has been talk about how environmentally "good" hybrids are, how
>: there exhause is cleaner than both liquids and solids. If LOX is the
>: liquid oxidizer component in a hybrid, what are the fuels being
>: considered? What would their exhause products be, and how exactly does
>: this compare with LOX/Kerosene or such?
>
>Provided you are not going to try to eek out the last margin of
>performance at the expense of increasing the environmental dammage due to
>exhaust products, hybrids produce cleaner exhaust than any solid I know of
>and even cleaner than some liquids. LOX-H2 is somewhat cleaner than
>LOX-HTPB (the typical hybrid oxidizer-fuel combination), and LOX-kerosene
>is only equivalent to LOX-HTPB. Liquids are also a lot more expensive.
>
>LOX-HTPB produce exhaust fundamentally similar to automobile exhaust.
>After all, you are burning a hydrocarbon in the presence of oxygen.
>LOX-HTPB produces the same carbon dioxide, carbon monoxide and water
>vapor of a LOX-kerosene motor.
What exactly is HTPB...I've heard it referred to as something like tire rubber,
but what exactly is inside that set of initials.
[Mod Note: Hydroxyl-Terminated PolyButadiene, a slight variant on a very
common synthetic rubber... -gwh]
I'll bet the H stands for High, and that the P stands for Poly, and i might
even lay it on the line to say the T is Test, but with out that mysterious B,
its all for naught.
>It is possible to realize an Isp over 500 seconds from a hybrid motor, but
>you have to use nasty things like beryllium. Isp's over 400 seconds can
>be achieved with the use of lithium/lithium hydride HTPB.
Is there a good standard reference of the potential Isp's of various
fuel/oxidizer combinations, or do you have to do lots of complex calcualtions
that I haven't done for years now?
>AMROC's
>Aquila design (capable of placing 2500 lbs into low polar orbits, or 3200
>lbs into low 28 degree orbits) utilized unenhanced HTPB.
How was Aquila set up...stages, etc? Was it all hybrid, or did they use solid
upper or lower stages or strap ons? How was attitude control
performed...vectoring and catalytic hydrazane jets?
>Those were some good questions, Nick. I hope you stick around to ask and
>learn more.
Don't worry, I'm asking more already...now you'll never stop me!
--Nick
Blair Patric Bromley
>In article <40ttaj$t...@vixen.cso.uiuc.edu> bro...@ux4.cso.uiuc.edu wrote:
>>>However, I've not found a combination that I think gets over 280s of
>>>Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
>>>hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
>>>think they're worthy of more work than they're getting.
>>
>> Even if it can get 200s of Isp, it would still worthwhile.
>There is some extractable sulfur in the lunar regolith. Sulfur/oxygen
>rockets can have a vacuum Isp around 200 seconds. Sulfur melts at
>reasonable temperatures, so it can be used in an all-liquid engine.
>In space, one would want to use some sort of non-chemical engine.
Well of course, but we're talking about getting to and from the lunar
surface. One thought is that if a suitable NTR lunar SSTO could be developed,
LOX extracted from the lunar regolith could serve as a liquid propellant,
although the engine design would be terribly difficult. Plus, the extraction
of LOX would leave a lot of metallic ore left over that could better be used
as a solid fuel in a hybrid system. I wasn't aware of the availability of
sulphur in the regolith. The key question I have is: How much of it is
there? Enough to warrant the development of a fuel production infrastructure
based upon sulfur and oxygen? It all comes down to what propellants can
be extracted from the regolith for a long time at a very low cost.
Why bother developing an engine to run on sulfur/oxygen and the infrastructure to manufacture these propellants on the moon if the sulfur is going to run out in say, 10 years?
Blair
> Paul
Russell John Panter
: I'd like to see your picture! I've personally assited in the test firing
: of hybrids here at the U of A. We have deliberately *tried* to make them
: fail. We have deliberately started them back up and continued to run
Deletions...
: Rocketry. Apparently the amatures are already building and selling two
: different designs along these lines. For under $1000 you too can be
Oops, cut too much out. That picture, BTW, is in High Power Rocketry, the
February, 1995 issue. For those who haven't cheked it out, I suggest
picking up HPR. Recently, they devoted almost and entire issue to the
small hybrids now available in the hobby. It also covers eperimental
rocketry. You can find it in hobby shops, Tower Records, and barnes and
Noble.
I like experimantal rocketry. I for one am fed up with the slow pace of
space development. The experimental rocketry groups are now poised on the
brink of sub-orbital flights into space. They may not be high tech, but
low tech worked for the Soviet Union for many years. I can easily see
this experimental rocketry taking hobbyists into a better position than
the government. Oh, My. I'm talking like a *.politics poster, better
quit while I'm ahead.
Russell John Panter
: rj...@zimmer.CSUFresno.EDU writes:
: > fuel and the combustion chamber. IOW, a monolithic block can be cast
: > that serves as both fuel and structure.
: I don't see how you gain from doing that. There must still be a
: combustion chamber at the end of thrust. That combustion chamber must
: have enough strength to be able to hold in the chamber pressure. The
Very true if you try to use P-BAN or HTPB based propellants. Stronger
polymers will work as rocket fuel, too. I've seen ABS fuel grains. I'm
building my own acrylic-burning hybrid.
: > For even more simplicity (and less plumbing), use self-pressurizing
: > propellants. N2O is a popular oxidizer,
: Nice for model rockets, but the specific impulse isn't very good.
Well, a 700 newton-second "J" motor is not exactly for model rockets.
Hypertech's three thrust corves (from the same amount of oxidizer and
fuel) peak at 120 pounds, 100 pounds, and 90 pounds - depending on the
burn time. I know that the isp sucks on these. So does the system
mass. Neither of these problems from hybrids making the first stage
of a BDB, though. The booster will be bigger, but mabye we'll win
in the cost of production. Hybrids would also ease refurbishment of
the boosters. Just toss out the expendable nozzle and combustion
chamber (cheaply made as part of the fuel grain), and refuel.
Mabye it won't work - I don't know. I just think the idea hasn't
met its demise yet. I could be wrong.
Russell John Panter
: Nick Strauss (nstr...@murrow.corp.sgi.com) wrote:
: : 2) Can hybrid's be throttled? Seems possible to me, reduce the LOX flow
: : and you reduce the burn rate, but I'm far from a rocket scientist (sorry,
: : had to do that!).
: Absolutely! This is one of the meny stong points about hybrids. They
: can not only be throttled, they can be stoped and restarted numerous
: times as well. It *is* possible to conduct a test firing on the pad
: prior to launch.
Ever hear a hybrid throttle? Way cool. Pressure waves and a tuned length
make it sound like a combination of that sound paper makes as a vacuum
cleaner tries to suck it up, but it flops quickly in the airstream, a rocket
motor burning, and a fart.
: particles. Once a solid rocket starts to burn there is almost no way to
: put out the fire. With a hybrid rocket you can simply shut off the flow
Pretty much the only way to stop a burning solid is to vent the case. You
must use a big vent to avoid merely providing another nozzle. Works most
of the time, I can assure you.
: Those were some good questions, Nick. I hope you stick around to ask and
: learn more.
So do I. This is the stuff I read sst to find.
Paul Dietz
: Nick Strauss (nstr...@murrow.corp.sgi.com) wrote:
: : 2) Can hybrid's be throttled?
: Absolutely! This is one of the meny stong points about hybrids. They
: can not only be throttled, they can be stoped and restarted numerous
: times as well. It *is* possible to conduct a test firing on the pad
: prior to launch.
Steve carefully glosses over the problems here. Sure, you can test
fire your hybrid on the pad. However, you've now just used up some of
your fuel, and the hybrid, unlike a liquid fueled engine, cannot be
refueled outside of the factory. Your propellant mass fraction has
just gone down.
You can also throttle a hybrid. But can you maintain the proper
fuel/oxidizer ratio while doing so? I understand this has been
a problem with hybrids in the past; the mixture typically shifts
to more fuel-rich as the oxidizer flow rate is reduced. Again,
this cuts into performance.
I don't see any substantial advantage of the hybrid over a dumb
pressure-fed liquid engine.
Paul
Steve Ratts
: What exactly is HTPB...I've heard it referred to as something like tire rubber,
: but what exactly is inside that set of initials.
: [Mod Note: Hydroxyl-Terminated PolyButadiene, a slight variant on a very
: common synthetic rubber... -gwh]
Thanks, George. I should have spelled that out.
: Is there a good standard reference of the potential Isp's of various
: fuel/oxidizer combinations, or do you have to do lots of complex calcualtions
: that I haven't done for years now?
It may be possible to do theoretical calculations for Isp based on
chemistry, physics, and engineering but the only real numbers that count
are from test firing the motors. People have been doing such tests on
hybrids for something like 50 years now (or there abouts). I'm not aware
of any authoritative, comprehensive reference which tabulates this data.
The figures I know I've found by digging through numerous articles and
papers about hybrids.
: How was Aquila set up...stages, etc? Was it all hybrid, or did they use solid
: upper or lower stages or strap ons? How was attitude control
: performed...vectoring and catalytic hydrazane jets?
Well, it's never been build, and unfortunately may never be built, because
AMROC is at a pretty low point from what I've heard. I've never seen the
plans, but the drawings I've seen show three large engines strapped
together with what looks like another stage on top. I understand that
all the stages would have been hybrid. As for the control, I would
expect it to use thrust vectoring to steer the rocket. Hydrazine jets
are more like what you might expect a satelite or spacecraft to use for
attitude control and minor maneuvers once it's clear of the final stage
of the booster.
: Don't worry, I'm asking more already...now you'll never stop me!
Good! And always remember: A mind is like a parachute, it doesn't
function properly unless it's open.
Paul Dietz
> I wasn't aware of the availability of
> sulphur in the regolith. The key question I have is: How much of it is
> there? Enough to warrant the development of a fuel production infrastructure
> based upon sulfur and oxygen?
The following abstracts were found by searching NASA RECONselect
(http://www.sti.nasa.gov/casitrs.html):
------------------------------------------------------------
Title: Lunar sulfur - Abstract Only
Authors: KUCK, DAVID L.
Published: 1991
Corporate Source: Kuck (David L.), Oracle, AZ.
NASA Subject Category: LUNAR AND PLANETARY EXPLORATION
Major Subject Terms: CEMENTS, CONCRETES, LUNAR BASES, PLANETARY
COMPOSITION, SULFUR, SULFUR DIOXIDES
Minor Subject Terms: BASALT, EXOTHERMIC REACTIONS, IGNITION
TEMPERATURE, ILMENITE, MAGNETITE, MARIA, OXYGEN
PRODUCTION, TROILITE
Abstract:
Ideas introduced by Vaniman, Pettit and Heiken in their 1988 Uses
of Lunar Sulfur are expanded. Particular attention is given to uses
of SO2 as a mineral-dressing fluid. Also introduced is the concept of
using sulfide-based concrete as an alternative to the sulfur-based
concretes proposed by Leonard and Johnson. Sulfur is abundant in high
-Ti mare basalts, which range from 0.16 to 0.27 pct. by weight.
Terrestrial basalts with 0.15 pct. S are rare. For oxygen recovery,
sulfur must be driven off with other volatiles from ilmenite
concentrates, before reduction. Troilite (FeS) may be oxidized to
magnetite (Fe3O4) and SO2 gas, by burning concentrates in oxygen
within a magnetic field, to further oxidize ilmenite before
regrinding the magnetic reconcentration. SO2 is liquid at -20 C, the
mean temperature underground on the Moon, at a minimum of 0.6 atm
pressure. By using liquid SO2 as a mineral dressing fluid, all the
techniques of terrestrial mineral separation become available for
lunar ores and concentrates. Combination of sulfur and iron in an
exothermic reaction, to form iron sulfides, may be used to cement
grains of other minerals into an anhydrous iron-sulfide concrete. A
sulfur-iron-aggregate mixture may be heated to the ignition
temperature of iron with sulfur to make a concrete shape. The best
iron, sulfur, and aggregate ratios need to be experimentally
established. The iron and sulfur will be by-products of oxygen
production from lunar minerals. Author
CASI Accession Number: 91N26049 Pages: 00001
Report Number: none
Contract Number: none
Sales Agency & Price: Avail: CASI HC A01/MF A01
------------------------------------------------------------
Title: Total sulfur content and distribution in the lunar samples - Ph.D.
Thesis
Authors: CRIPE, J. D.
Published: 1976
Corporate Source: Arizona State Univ., Tempe, AZ.
NASA Subject Category: LUNAR AND PLANETARY EXPLORATION
Major Subject Terms: APOLLO FLIGHTS, APOLLO LUNAR SURFACE EXPERIMENTS
PACKAGE, LUNAR ROCKS, LUNAR SOIL, SULFUR
Minor Subject Terms: APOLLO PROJECT, CHEMICAL PROPERTIES, LUNAR
EXPLORATION, LUNAR SURFACE, ROCKS
Abstract:
The total sulfur content of representative samples from the six
Apollo lunar missions was determined using a combustion iodate
photometric titration technique. The technique was developed for rock
samples of less than 500 mg, with minimum preparation to minimize for
possible contamination. Total sulfur abundances were measured in 217
different Apollo lunar basalts, breccias, and fines to characterize
the abundance of sulfur in lunar samples. A sampling of 195
terrestrial basalts was measured for comparison. Lunar basalts were 2
to 3 times higher in sulfur content than terrestrial basalts.
Dissert. Abstr.
CASI Accession Number: 77N15959 Pages: 00182
Report Number: none
Contract Number: none
Sales Agency & Price: Avail: Univ. Microfilms Order No. 76-27268
------------------------------------------------------------
Title: Uses of lunar sulfur
Authors: VANIMAN, D.; PETTIT, D.; HEIKEN, G.
Published: September 1992
Corporate Source: Los Alamos National Lab., NM.
NASA Subject Category: LUNAR AND PLANETARY EXPLORATION
Major Subject Terms: LUNAR MARIA, LUNAR RESOURCES, LUNAR SOIL, SULFUR,
SULFUR COMPOUNDS
Minor Subject Terms: BIOCHEMISTRY, ELECTRICAL PROPERTIES, EXTRACTION,
LUNAR MINING
Abstract:
Sulfur and sulfur compounds have a wide range of applications for
their fluid, electrical, chemical, and biochemical properties.
Although known abundances on the Moon are limited (approximately 0.1
percent in mare soils), sulfur is relatively extractable by heating.
Coproduction of sulfur during oxygen extraction from ilmenite-rich
mare soils could yield sulfur in masses up to 10 percent of the mass
of oxygen produced. Sulfur deserves serious consideration as a lunar
resource. Author
CASI Accession Number: 93N13981 Pages: 00007
Report Number: none
Contract Number: none
Sales Agency & Price: Avail: CASI HC A02/MF A03
------------------------------------------------------------
Title: Sulfur abundances and distributions in the valley of Taurus-Littrow
Authors: GIBSON, E. K., JR. (NASA, Johnson Space Center,
Houston, Tex.); MOORE, G. W. (Lockheed Electronics
Co., Inc., Houston, Tex.)
Notes: In: Lunar Science Conference, 5th, Houston,
Tex.,, March 18-22, 1974, Proceedings. Volume 2.,
(A75-39540 19-91) New York, Pergamon Press, Inc.,,
1974, p. 1823-1837.
Published: 1974
NASA Subject Category: LUNAR AND PLANETARY EXPLORATION
Major Subject Terms: ABUNDANCE, APOLLO 17 FLIGHT, LUNAR COMPOSITION,
LUNAR ROCKS, LUNAR SOIL, SULFUR
Minor Subject Terms: BASALT, BRECCIA, GEOCHEMISTRY, LUNAR LANDING
SITES, MAGMA
Abstract:
Total sulfur abundances have been determined for 36 Apollo 17 soil,
breccia and crystalline rock samples. Sulfur concentrations range
from 550 to 1300 micrograms S/g for soil samples, with the orange
soil containing the lowest amount of sulfur. Noritic breccias contain
between 720 and 950 micrograms S/g, while the anorthositic rocks have
sulfur contents of 270 and 368 micrograms S/g. The dunite 72415
contained the lowest sulfur content (44 micrograms S/g) of any Apollo
17 sample studied. Apollo 17 basalts have unusually high sulfur
contents (1580-2770 micrograms S/g) as compared to Apollo 12 and 15
basalts and terrestrial basalts. Sulfur abundances for the Apollo 17
basalts are almost identical to those from Apollo 11 basalts. A
negative correlation between percent metallic iron and total sulfur
for the Apollo 17 and 15 basalts was found and suggests that a
portion of the metallic iron in lunar basalts may result from
desulfuration of the melt prior to crystallization from the lunar
magma. (Author)
CASI Accession Number: 75A39653 Pages: 00015
Report Number: none
Contract Number: none
Sales Agency & Price: copyright
Steve Ratts
: Steve carefully glosses over the problems here. Sure, you can test
: fire your hybrid on the pad. However, you've now just used up some of
: your fuel, and the hybrid, unlike a liquid fueled engine, cannot be
: refueled outside of the factory. Your propellant mass fraction has
: just gone down.
Actually, you *can* refuel on the pad, at at least in the vacinity of the
pad. It is not necessary to return to the factory at least. You can
simply remove the fuel core and replace it. It is not an especially
difficult task to design the fuel core to be easily removed and
replaced. However, this may tend to invalidate your test firing so I'm
not sure if you would want to do something like this. The usuall
scenario which has been discussed for replaceing a hybrid's fuel core is
one in which the motor has failed for some reason and it is therefore
necessary to remove and replace the fuel core. This is seen as something
of an advantage in hybrids. You can't do that with solids, and handeling
the liquid components of a bi-propellant liquid is more dangerous due to
the potential for fuel leaks.
: You can also throttle a hybrid. But can you maintain the proper
: fuel/oxidizer ratio while doing so? I understand this has been
: a problem with hybrids in the past; the mixture typically shifts
: to more fuel-rich as the oxidizer flow rate is reduced. Again,
: this cuts into performance.
Actually, the mixture ratio tends to change as the fuel is burned because
the ratio is a function of the exposed surface of the fuel. This is part
of the reason that hybrid motors have an efficiecy of 93-97% which is
lower than that for either liquids or soilds (for which the mixture ratio
is easier to control). A 93-97% efficiency is not what I would call a
big disadvantage.
: I don't see any substantial advantage of the hybrid over a dumb
: pressure-fed liquid engine.
Does cost come into your picture at any time? Once again: Hybrids have
half the number of pumps (or less), half the plumbing, and are
considerably safer (and therfore cheaper) to build and test than liquid
(pressure-fed or otherwise).
In my opinion, cost will play a big role in the selection of future
launch systems. Saftey and environmental impact will also play large
roles I think. Hybrids have advantages in *all* these areas with the
exception that some liquids (ther prefered ones) are somewhat more
environmentally freindly. Nevertheless, hybrids are on a par with LOX -
kerosene as far as environmental impact goes.
Steve Linton
>It hasn't come up yet, so I thought I'd mention that, IMO, one of
>the reasons to pursue hybrids is to use alternative solid fuels. We're
>going to want Lunar-fueled rockets one of these days, and I think
>a hybrid is a nice way to build an Al-LOX or Si-LOX rocket. You don't
>need outstanding T/W for Lunar applications, so you've avoided one
>problem.
>However, I've not found a combination that I think gets over 280s of
>Isp, so it's nice for Luna-LLO round trips and for point-to-point Lunar
>hops; not so nice for Luna-LEO round trips or Earth launch. Still, I
>think they're worthy of more work than they're getting.
Two comments:
1) You could improve your ISP (say for your upper stages) by shipping
a relatively small amount of hydrogen (or methane) out to the moon (or
minimig from regolith, polar ice or the solar wind) and making (some
of) your alumnium into a hydride.
2) What is the delta-V for LLO to Earth atmosphere-grazing (the Apollo
return maneouver)? I am thinking of a system where lunar cargoes are
dumping into aero-braking orbits, lose most of their excess energy in
the upper atmosphere (possibly in several passes a la Magellan) and
then make a small circularization burn to finish up in LEO.
Steve
Jacob M McGuire
Steve Ratts wrote:
>Actually, you *can* refuel on the pad, at at least in the vacinity of the
>pad. It is not necessary to return to the factory at least. You can
>simply remove the fuel core and replace it. It is not an especially
>difficult task to design the fuel core to be easily removed and
>replaced. However, this may tend to invalidate your test firing so I'm
>not sure if you would want to do something like this.
I am unsure as to how the fuel core may be replaced easily, perhaps
I am missing something? The only way I can see is either out the top
or the bottom, because the fuel core itself will not be load-bearing,
so it will have to be contained in a relatively strong structure (in
fact, the entire structure holding the fuel core must be strong enough
to withstand the chamber pressure, which has a pretty direct impact on
the rocket perfomance (chamber pressure, that is). So either you have
to take the oxidiser tank and pumps off the top of the rocket, and
lift the fuel core out, or you have to take the nozzle and such out of
the bottom, and lower it out, this however, requires that the rocket
be raised substantially off the ground, which might be hard.
>The usuall
>scenario which has been discussed for replaceing a hybrid's fuel core is
>one in which the motor has failed for some reason and it is therefore
>necessary to remove and replace the fuel core. This is seen as something
>of an advantage in hybrids. You can't do that with solids, and handeling
>the liquid components of a bi-propellant liquid is more dangerous due to
>the potential for fuel leaks.
If the motor fails to ignite, or before liftoff, it is not a problem
for liquids, you just shut it down. If it is a solid, you are hosed.
If it is a hybrid, you shut it down. Liquids come out ahead, because
refueling them is a damn sight easier than replacing the fuel core is
going to be. In general, if your motor fails in flight, you are
hosed. Solids tend to have more spectacular failure modes than
liquids, hybrids will probably also have more spectacular failure
modes as well. Either way, you are certainly in serious trouble.
>: You can also throttle a hybrid. But can you maintain the proper
>: fuel/oxidizer ratio while doing so? I understand this has been
>: a problem with hybrids in the past; the mixture typically shifts
>: to more fuel-rich as the oxidizer flow rate is reduced. Again,
>: this cuts into performance.
>Actually, the mixture ratio tends to change as the fuel is burned because
>the ratio is a function of the exposed surface of the fuel. This is part
>of the reason that hybrid motors have an efficiecy of 93-97% which is
>lower than that for either liquids or soilds (for which the mixture ratio
>is easier to control). A 93-97% efficiency is not what I would call a
>big disadvantage.
I don't know, the composition of the exhaust has a pretty
significant effect on specific impulse, and when your fuel is large
hydrocarbons, slight percentages of unburned fuel will dramatically
cut exhaust velocity and specific impulse; 5% changes in specific
impulse are important.
>: I don't see any substantial advantage of the hybrid over a dumb
>: pressure-fed liquid engine.
>Does cost come into your picture at any time? Once again: Hybrids have
>half the number of pumps (or less), half the plumbing, and are
>considerably safer (and therfore cheaper) to build and test than liquid
>(pressure-fed or otherwise).
How exactly are they safer to build than liquids? And how are they
safer to test? Liquids can explode, this however is relatively rare.
It is impossible to test a hybrid though, the engine is not even
remotely the same after you run it at all. They way I see it, hybrids
get the worst of both worlds. Not only do you have the turbopumps and
complicated machinery of liquids, but you have the "one-use-only"
effect of solids.
>In my opinion, cost will play a big role in the selection of future
>launch systems. Saftey and environmental impact will also play large
>roles I think. Hybrids have advantages in *all* these areas with the
>exception that some liquids (ther prefered ones) are somewhat more
>environmentally freindly. Nevertheless, hybrids are on a par with LOX -
>kerosene as far as environmental impact goes.
Saftey in flight equates to failure rate... being able to shut down
helps little at 50,000 feet. Hybrids just do not have the precise
control over combustion that liquids do. Hybrids are less
environmentally friendly than LH2/LOX, and are the same as RP-1/LOX.
Even including cost, how much of the cost of a given rocket is the
engine?
+------------------------------------+-----------------+
| Small towns in western Germany are | Jake McGuire |
| usually about ten kilotons apart | mcg...@cmu.edu |
+------------------------------------+-----------------+
Paul Dietz
>: I don't see any substantial advantage of the hybrid over a dumb
>: pressure-fed liquid engine.
>
>Does cost come into your picture at any time? Once again: Hybrids have
>half the number of pumps (or less), half the plumbing, and are
>considerably safer (and therfore cheaper) to build and test than liquid
>(pressure-fed or otherwise).
I read those claims before. I simply don't believe them.
Pumps: the hybrid is not going to half the pumps of a dumb
liquid rocket, since the latter has no pumps.
Plumbing: it's not clear the liquid is much more complex. You need a
fuel line, valves to control fuel flow, and a fuel pressure regulator.
Both the hybrid and the liquid engine will need much additional
plumbing for thrust vector control (either to gimbal the nozzles or
for fluid injection in the nozzle); they also each will use a single
source of pressurant. So "half the plumbing" is misleading. I also
suggest that plumbing for hydrocarbons is pretty much off-the-shelf,
while plumbing for LOX is more expensive. The extra cost for the
liquid should not be large.
Testing: a dumb liquid engine is smaller than a hybrid of equal
thrust. It should be possible to fabricate and test it for a fraction
of the cost. TRW did this years ago, with simple engines made with
what amounts to shipyard technologies. Dumb liquid engines, like dumb
hybrids, do not need fancy injectors or expensive and elaborate
regenerative cooling systems.
Safety: the liquid engine should be considerably safer to test than
the hybrid. Why? Because the propellant tanks are remote from the
engine itself; only a small pressurized volume is actually at the
engine. With the hybrid, the stored energy at the engine is
considerably larger, so any explosion will be considerably larger.
The cost of the test will depend on the consequences of the
maximum accident, not (strongly) on its likelihood, so any
putative advantage in the rate of explosions for hybrids
will count for little.
Let's also not forget that hybrid rockets, due to their poor
performance, may need more stages than a liquid booster. TRW's cost
optimized booster concept used two or maybe three stages. Aquilla
was, I believe, a *four* stage concept (with a N2O/ HTPB upper stage,
for crying out loud). More stages means more parts and more
complexity. I'm not surprised Aquilla never flew.
Paul
Blair Patric Bromley
>In article <UkCcVFW00...@andrew.cmu.edu> jm...@andrew.cmu.edu wrote:
>> In general, if your motor fails in flight, you are
>> hosed. Solids tend to have more spectacular failure modes than
>> liquids, hybrids will probably also have more spectacular failure
>> modes as well. Either way, you are certainly in serious trouble.
>This is yet another advantage of liquid engines. If you
>are feeding the engines from a common set of propellant tanks,
>failure of one engine need not mean failure of the vehicle;
>one can divert the propellant to the other engines. You
>can't do that with the fuel of a hybrid rocket.
True, but the type of failure that is being discussed here is
less likely to happen with a hybrid engine anyways.
As analogy to the redundant engines, one could have redundant
injectors or redundant oxidizer lines. One could have a hybrid
systems where there is a cluster of 5 engines; 4 boosters, one
sustainer. There is only one LOX tank that is stacked on top
of the sustainer. The four boosters draw from the common Lox
tank. But, I see your point whereby the hybrid system doesn't
have the flexibility in propellant transfer that the full
liquid system does; however, how many missions have there been
where a full liquid system was able to compensate for an
engine failure (unmanned missions)? It still comes down to
cost, and the hybrid overall could come out on top of liquids.
Blair
Paul Dietz
> tank. But, I see your point whereby the hybrid system doesn't
> have the flexibility in propellant transfer that the full
> liquid system does; however, how many missions have there been
> where a full liquid system was able to compensate for an
> engine failure (unmanned missions)?
I don't know about unmanned missions, but there have been at least two
manned missions in which this happened (Apollo 13 and one of the
Spacelab shuttle launches that aborted to orbit after a premature
shutdown of one of the SSMEs.)
The NLS (or ALS, or whatever they were calling it) was to have
single engine-out capability to improve reliability.
Paul
Thomas J. Frieling
>> how many missions have there been
>> where a full liquid system was able to compensate for an
>> engine failure (unmanned missions)?
>I don't know about unmanned missions, but there have been at least two
>manned missions in which this happened (Apollo 13 and one of the
>Spacelab shuttle launches that aborted to orbit after a premature
>shutdown of one of the SSMEs.)
The Saturn 1/1B also had engine-out capability on the first stage and it was
demonstrated successfully on two flights--one intentional (SA-4), the other
not (SA-6).
Henry Spencer
>...how many missions have there been
>where a full liquid system was able to compensate for an
>engine failure (unmanned missions)?
Most liquid systems don't have enough engine redundancy to handle such a
failure -- when you only have one or two engines, losing one is usually
an unacceptable performance shortfall. However, the shuttle, the Saturn V,
and the Saturn I (twice) have lost engines during ascent and carried on
with the mission.
The shuttle is kind of marginal in this regard, with only three engines,
but the loss happened very late in the burn. The Saturn V, with five
engines in each of the two lower stages, had fairly good engine-out
capability, as Apollo 13 showed when a second-stage engine was shut down.
And the Saturn I hardly noticed losing one first-stage engine out of
eight, which was done once deliberately as a test and then once
unintentionally due to a real engine failure.
--
The problem is, every time something goes wrong, | Henry Spencer
the paperwork is found in order... -Walker on NASA | he...@zoo.toronto.edu