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The 100/10/1 Rule.



 
 
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  #131  
Old March 18th 07, 02:38 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
Craig Fink
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Posts: 1,858
Default fun with expendable SSTOs (was The 100/10/1 Rule.)

Nothing wrong with that thinking.

Things to consider when trying to use Hydrogen/Oxygen SSME type engine on
your SSTO launcher:

Hydrogen, all that energy in such a small package, nice. Comparatively,
Oxygen much larger, allows large variations in the efficiency (ISP) vs
Thrust curve with large variations in mixture ratio. All with the same
engine.

Expansion ratio, make it huge, so the Hydrogen/Oxygen engine can really
shine where it does best. Shuttle SSMEs have a compromised expansion ratio,
so that they can operate at a low altitude.

At liftoff, using this engine will probably require a kick in the ass to get
it going. May as well fix the backflow problem caused by the huge expansion
ratio at the same time. Since it's going to be running at the extreme end
of it's mixture ratio ISP/Thrust curve, may as well do something simple and
relatively light weight.

The lightest and simplest thing I can think of to give it a kick in the ass,
is to drill a big hole right along the centerline of the engine. In the
hole, run a pipe going thru the injectors, thrust chamber, throat, and into
the bell. This give a simple nice clear path to inject lots of mass into
the supersonic flow inside the engine bell, to eliminate any backflow
problems.

What should the mass be? Well, since the engine is already running on the
extreme Oxygen rich side, probably any old heavy dense liquid that reacts
well with Oxygen would do. Since pressures are lower in the bell, maybe
even a pressure fed tank might work, even though turbines are alway nice to
have.

Heck, even make the pipe and Christmas tree (or, roots) in the bell out of
aluminum. That way when the extra mass is gone at a high altitude, it will
simply burn off clearing the thrust chamber/throat and bell of the
unnecessary fluid engine plug.

There are other cool things that could be done with a fluid engine plug,
huge expansion ratio LOX/LH2 engine. Don't like the third propellent, ok,
use the hydrogen instead of the the dense liquid.

Oversize the first stage compressor of the hydrogen compressor slightly,
this way some of the pressurized hydrogen can be bled off into that pipe
running down the centerline. Just after the throat, split the pipe into
many small pipes, branches of a Supersonic Christmas Tree. The small pipes
can then begin to diverge slowly to distribute the extra mass in the bell.
Crossing the flow lines in the engine at very small angles so that the
supersonic flow is not disturbed too much. Maybe split the flow again a
little further down. Smaller, but more total area pipes, gasifying and
heating the not so high pressure Hydrogen.

A exo-atmospheric SSTO with disposable Supersonic Afterburners. The
Afterburners themselves little Hydrogen dispersion rockets, to distribute
the not so high pressure hydrogen into the very low pressure Oxygen rich
supersonic exhaust.

Oh what fun, the development would be. The Trade Studies, at tweak here, a
tweak there. But, magnitudes more fun to actually watch it fly and
Magnitudes More to Ride.

I still think Atmospheric Flight to Orbit is the way to go, I kind of like
the extra payload to Orbit.

--
Craig Fink
Courtesy E-Mail Welcome @
--

kT wrote:

Expect for the shuttle, that was pretty darn clever. I want to take
everything that was good about the shuttle, and nothing that was bad
about it, and apply that experience to an SSME powered SSTO launcher.

At this point, a propane powered SSTO makes no sense to me at all.



  #132  
Old March 18th 07, 04:54 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
kT
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Default fun with expendable SSTOs (was The 100/10/1 Rule.)

alexterrell wrote:

On 11 Mar, 06:57, (Henry Spencer) wrote:

The oxidizer is LOX -- cheap and dense. The fuel is probably propane --
slightly better performance than kerosene, less tendency to leave oily
residues and otherwise misbehave, and it's still liquid and quite dense at
LOX temperatures.

Quick question, as an Economist might ask: If propane is better than
Kerosene, why doesn't everyone use it instead of kerosene? (apart from
the non budget constrained LH2 users).


Henry is somewhat isolated from reality.

--
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  #133  
Old March 18th 07, 05:59 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
Henry Spencer
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Posts: 2,170
Default fun with expendable SSTOs (was The 100/10/1 Rule.)

In article .net,
Craig Fink wrote:
major exception is if they're being used for something like space-station
resupply, in which case it might make sense to collect them.


The other orbit is the performance optimal orbit, for KSC 28.5 degree
inclination due to latitude of the site...


Unfortunately, that isn't one orbit. A 28.5deg orbit with a launch at
noon is in a different plane from a 28.5deg orbit with a midnight launch.
The former crosses the equator roughly at sunset heading south, while the
latter also has a sunset crossing, heading north -- the two directions are
57deg apart. And there's a full range in between. Yes, customers often
do care about which one they get, for reasons like sun angles, which is
why even 28.5deg launches usually have well-defined launch windows.

Mind you, sometimes the preferences aren't that strong. You might be able
to attract a modest fraction of the 28.5deg customers to a single orbit if
you offered a discount. But a fair number of them wouldn't bite.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #134  
Old March 18th 07, 06:06 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
Henry Spencer
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Posts: 2,170
Default fun with expendable SSTOs (was The 100/10/1 Rule.)

In article .com,
alexterrell wrote:
The oxidizer is LOX -- cheap and dense. The fuel is probably propane --
slightly better performance than kerosene, less tendency to leave oily
residues and otherwise misbehave, and it's still liquid and quite dense at
LOX temperatures.

Quick question, as an Economist might ask: If propane is better than
Kerosene, why doesn't everyone use it instead of kerosene? (apart from
the non budget constrained LH2 users).


Quick answer: it's not a lot better than kerosene; many designers are
constrained to use existing engines or simple derivatives of same; and
it's just unconventional enough to trip a cautious decision-maker's
risk-aversion reflex. (Despite its avant-garde reputation, spaceflight
these days is mostly a very conservative business.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #135  
Old March 18th 07, 06:15 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
Henry Spencer
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Posts: 2,170
Default The 100/10/1 Rule.

In article ,
Danny Deger wrote:
Can you explain this? I would have thought gavity loss fudge factor would
be a strong function of thrust/weight. I don't understand why it would be
function of density.


It's not a function of density, but of Isp -- lower Isp is *better* in
this respect!

Consider a couple of simple cases which are easier to visualize.

Vehicle X starts out being 1/4 fuel. Halfway through its burn, with half
the fuel gone, it has 7/8 of its takeoff mass. If thrust is constant,
that means it has 8/7 (circa 1.14) times its original acceleration.

Vehicle Y starts out half fuel. Halfway through its burn it has 3/4 of
its takeoff mass, so 4/3 (circa 1.33) times its original acceleration.
Because its less efficient engines gobble more fuel, its mass drops off
faster and its acceleration increases faster.

As I mentioned in my original posting, the difference is not huge -- about
300m/s out of 9000m/s or so -- but it's significant. By itself it would
not make lower Isp competitive, but it helps.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #136  
Old March 18th 07, 06:26 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
John Schilling
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Posts: 391
Default fun with expendable SSTOs (was The 100/10/1 Rule.)

On 18 Mar 2007 02:01:40 -0700, "alexterrell"
wrote:

On 11 Mar, 06:57, (Henry Spencer) wrote:


The oxidizer is LOX -- cheap and dense. The fuel is probably propane --
slightly better performance than kerosene, less tendency to leave oily
residues and otherwise misbehave, and it's still liquid and quite dense at
LOX temperatures.


Quick question, as an Economist might ask: If propane is better than
Kerosene, why doesn't everyone use it instead of kerosene? (apart from
the non budget constrained LH2 users).


Propane may be slightly better as a launcher fuel, but it's a cryogen
(albiet a soft one), which makes it much worse as a missile fuel. As
most everyone who has ever built a space launch vehicle has also been
in the missile-building business as well, they've understandably gone
and standardized on kerosene as their hydrocarbon fuel of choice.

There have been a few launcher-only design groups, but none of them
so lavishly funded that they could afford to develop *everything* from
scratch, and so far they've all found it expedient to borrow bits of
kerosene-rocket technology from the missile-based side of the industry
than build their own propane rockets from scratch.

The more ambitious your goals, though - and this is a fairly ambitious
hypothetical project - the more you are driven towards building stuff
from scratch rather than borrowing extant but inadequate technology,
and this opens the door to propane. Doesn't make it a no-brainer,
though. SpaceX, which did design its engines and propellant tanks
from scratch, still uses kerosene.


--
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  #137  
Old March 18th 07, 07:22 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
Henry Spencer
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Posts: 2,170
Default fun with expendable SSTOs (was The 100/10/1 Rule.)

In article nk.net,
Craig Fink wrote:
What should the mass be? Well, since the engine is already running on the
extreme Oxygen rich side, probably any old heavy dense liquid that reacts
well with Oxygen would do. Since pressures are lower in the bell, maybe
even a pressure fed tank might work...


If you're injecting into the supersonic flow, you might as well just use
water. There won't be *time* for any significant reaction; the exhaust is
moving *fast* at that point, and accelerating fiercely, and it just
doesn't stay in the nozzle for long. The usual rule of thumb is that
reaction rates even in the already-mixed combustion gases are effectively
zero after the throat.

Even just reasonable mixing -- which is what's needed if you want to bulk
out the exhaust this way -- is doubtful with just a straight pipe. You
need some kind of atomization, even if it's only plugging the end of the
pipe and drilling a bunch of holes in its side just above the end.

Some kind of non-trivial injector discharging into the chamber will work a
lot better. At which point, of course, you can start thinking about how
much hydrogen and how much dense fuel is appropriate. Interestingly
enough, you might find that the percentage of hydrogen keeps going down as
you analyze more carefully. Surprise, you've just discovered that dense
fuels are better for SSTOs than hydrogen...

I still think Atmospheric Flight to Orbit is the way to go, I kind of like
the extra payload to Orbit.


Odd that people who actually study this in detail quite consistently find
that it gives less payload to orbit. (E.g., the HOTOL team found that
going all-rocket, with other assumptions left unchanged, would more than
double their payload. Same story as dense fuels vs. hydrogen: lower Isp,
but also much lighter hardware bringing the mass ratio way up.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #138  
Old March 18th 07, 08:48 PM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
Henry Spencer
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Posts: 2,170
Default fun with expendable SSTOs (was The 100/10/1 Rule.)

In article . net,
Craig Fink wrote:
I believe what your doing is extrapolating trade studies beyond there range
of usefulness.


No, actually, I'm looking at real rocket stages that were actually built
and flown. Achieving high single-stage delta-Vs is consistently harder
with hydrogen than with dense fuels; that is actual experience, not trade
studies. Dense-fuel rocket stages with SSTO delta-V numbers were in
production for operational service in 1962. The first hydrogen stage that
came anywhere close was the S-II, whose development difficulties (notably
in dry-mass control) were severe.

Extrapolating outside the useful range of data can be very dangerous and
lead to false conclusion.


Quite so. For example, much of the belief in *hydrogen* comes from the
implicit belief that you can replace (say) kerosene with hydrogen without
making a large difference to the stage's dry mass. That was a common
assumption in early studies, but is verifiably false in actual experience.
Other propellant substitutions had made little difference in dry mass, but
the range of propellant temperatures and densities involved was relatively
modest, and so the impact of hydrogen's extremely low temperature and very
low density was grossly underestimated.

Taking it to Orbit wasn't just keeping it attached and doing a normal ascent
profile. It also freed up some "MECO ET disposal" constraints. Removing
those constraints also allowed a more optimal profile which resulted in the
a performance gain at MECO. The ET could to be brought to a fairly high
orbit with no performance penalty.


Was that for the original two-OMS-burn ascent, or the later "direct"
ascent? My understanding was that taking the ET to orbit originally
showed a net gain, but that turned into a loss when the more efficient
"direct ascent" trajectory became usual.

...I bring up "Fluid
Variable Intakes" which fits nicely with his engine and invalidating
certain assumptions of his trade study. His study just swung in a different
direction.


I don't believe you explained what "Fluid Variable Intakes" are. It's not
a term I'm familiar with either, although I don't keep up with the current
fads :-) on the airbreathing side.

I'm sure you presentation "But the Sim Said It Would Work!" will be quite
good.


Unfortunately, I'm not going to make Space Access this year, to my great
annoyance, so the talk won't appear. Deadline problems.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |
  #140  
Old March 19th 07, 12:51 AM posted to sci.space.history,sci.space.policy,sci.space.station,sci.space.shuttle
john hare
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Posts: 47
Default fun with expendable SSTOs (was The 100/10/1 Rule.)


"Henry Spencer" wrote in message
...
In article . net,
Craig Fink wrote:

...I bring up "Fluid
Variable Intakes" which fits nicely with his engine and invalidating
certain assumptions of his trade study. His study just swung in a
different
direction.


I don't believe you explained what "Fluid Variable Intakes" are. It's not
a term I'm familiar with either, although I don't keep up with the current
fads :-) on the airbreathing side.

It would have needed negative mass to counteract the engine weight
to a degree necessary to match pure rocket stage performance.
I lost interest somewhat in supersonic intakes when it became
clear that there could not be a cost advantage to them.

If I ever get started again, I have business reasons for a continuing
interest in some airbreathing cruise. If my business model matches
reality closely enough, The mass penalties will be acceptable. If
I get money, it will most likely come from pilot/businessmen. If
we ever fly, it will probably have to be from airports that have not
done the paperwork to become spaceports.

Fad maybe, but I hope to compete in a slightly different field
of my own choosing. This does not require that I be deluded
in thinking it performs better for real space missions.

I'm sure you presentation "But the Sim Said It Would Work!" will be quite
good.


Unfortunately, I'm not going to make Space Access this year, to my great
annoyance, so the talk won't appear. Deadline problems.
--

This eases the sting of missing two in a row for me. It is very annoying
to miss my mini vacation repeatedly.

spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |



 




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