The 100/10/1 Rule.

kT wrote:

Henry Spencer wrote:
In article ,
Pat Flannery wrote:
We've read up on your "Brown Bess" booster concept; if you were going to
make an unmanned expendable SSTO, how would you go about it, and what
propellant combo would you use?

First, as Richard observed, I'd drop the "unmanned". If it's reliable
enough for expensive cargo, it's reliable enough for people. Like, for
example, me. :-)

(There are people who suggest building relatively unreliable rockets to
be
used for bulk cargo -- water, fuel, etc. -- only. I don't think this
actually works out well. You still need moderately good reliability,
say,
80-90%, if only to avoid being fined for littering :-). I don't see a
significant cost or complexity advantage to be had from the difference
between that and the 98-99% of conventional expendables. If you can
dependably get 80-90%, it should cost very little extra to hit 98-99%.)

(Getting to 99.9% is harder, as witness the fact that no existing
expendable has definitely achieved it -- there are a few uncertain cases
where moderate production runs simply had no failures -- with the
*possible* exception of the Soviet-era Soyuz launcher. It should be
feasible, given careful design, a high flight rate, and automated
production. Even 99.99% is probably not out of reach for expendables,
if you sweat hard on things like systematic process improvement. Beyond
that is strictly reusable territory.)

The real major dividing line is reusable vs. expendable. Here, by
definition, we're talking expendable.

After that is the big question of whether whoever's paying for it has
constraints to impose: use existing engines, no Russian subsystems, a
minimum payload size, etc. They also might have opportunities to offer,
e.g. use of shuttle-ET production facilities. Many of these things can
severely constrain the design. Assume none of this.

The major subsystem question is engines: buy or build? Buying means you
don't have to get into the engine-development business, which saves a lot
of trouble and may look less risky to potential investors. There are
some
downsides: (a) it's a lost dimension of competitive advantage, (b) the
choice of existing engines is somewhat limited and can severely constrain
design choices (in particular, ruling out many unconventional
approaches), and (c) buying engines tends to be expensive and to involve
a lot of
hassles. I'd favor build, if only to relax design constraints.

The major specs issue is, how much payload to what orbit? Orbital
inclination affects delta-V requirement by determining how much help you
get from Earth's spin. The big question for orbital altitude is whether
the orbit is low enough for a direct-ascent trajectory -- continuous burn
all the way up, like Gemini or Apollo -- or requires a Hohmann ascent
like the shuttle, injecting into an elliptical orbit and then doing a
final
insertion burn at apogee. Hohmann ascent would always be more efficient
if the atmosphere didn't get in the way. In real life, direct ascent
usually incurs little penalty up to 300-400km, but gets rapidly worse
thereafter. The nice thing about direct ascent is no engine restart.
And even with Hohmann ascent, you pay a price for higher orbits. Absent
outside constraints (e.g. cargo delivery to ISS), I'd favor direct ascent
to 250-300km, high enough to last a little while and give the payload
time to maneuver higher or be picked up by a tug.

As for how much payload... depends on whether there's a specific mission
constraint. If not, I would favor relatively small payloads, giving a
small launcher and frequent flights, and relying on orbital
infrastructure
(assembly base, tug, fuel depot) to assemble larger systems. Smallness
actually is not that important -- launcher cost scales much more strongly
with complexity, thinness of margins, and closeness to the leading edge
of technology than with sheer size -- but frequent flights are beneficial
in many ways.

*How* small depends on how much inconvenience you're willing to accept.
There are cutoff points where inconvenience rises sharply because you can
no longer launch particular objects in one piece, plus a general slow
rise in inconvenience as orbital assembly operations multiply.

If you want at least the option of launching people, that obviously sets
a
minimum size. For serious orbital operations, I see a high payoff for
being able to launch a two-man ferry spacecraft, sort of a stripped-down
Gemini, in one piece: it lets you have one pilot and one passenger, so
the passenger doesn't need exhaustive training in emergency procedures
for
the ferry. Gemini weighed a bit under 4t, with early-1960s technology
and
greater capabilities than the ferry really needs. An aggressive modern
design could come in quite a bit lighter.

For serious orbital operations, the other thing that it would be nice to
launch in one piece is a minimal habitation module. Perhaps
inflatable... but with an expendable SSTO, a "wet workshop" approach
using the spent
stages is also very attractive. Say: Launch #1 carries a life-support
module with consumables, integrated with the spent stage and with a
docking hatch at the top. Launch #2 carries a multi-hatch docking node
integrated with the spent stage, and a tug; the tug maneuvers it to mate
with #1, and sticks around to supply attitude control and reboost. A
ferry docks with one of the ports on the node, and you're in the
space-station business. (Actually berthing would be better than docking,
but that's a detail.) How much does each load have to weigh? That would
need more study, but it's interesting to note that the Apollo-Soyuz
Docking Module was about 2t.

Could this sort of scenario be done with payloads of 2t or less?
Probably, but it might get pretty tight. 5t should be lots. Let's be
mildly aggressive and set the payload at 3t. I'd want to look into
infrastructure issues -- size of manufacturing machinery, size of
facilities, etc. -- and if it didn't look like a slightly bigger launcher
would cross any boundaries that made things significantly harder or more
expensive, make it bigger just on general principles. Materials etc.
cost very little; the infrastructure issues are the main things that make
a launcher cost more just because it's bigger, and they mostly rise in
sudden jumps, not in a steady slope. And far more people have regretted
making a launcher a bit too small than have ever regretted making it
slightly too big.

Anyway, let's cut to the chase -- this has already taken rather longer
than I meant to spend on it :-) -- and look at the launcher. This is
based on some past thought but without rigorous calculation for this
particular design problem.

Shape: a plain cylinder with a cone on top, or possibly a two-slope cone
like the nosecone for Apollo 5 (which has lower drag and more usable
volume) -- simple to make, simple to analyze. More the proportions of
say, a Jupiter than a Delta -- the shorter, fatter shape has a bit more
drag but is a lot stiffer and less prone to bending problems. Very light
tanks, probably pressure-stiffened like the old Atlas. Likewise for the
nose -- that was done on Atlas for SCORE and some other flights. (Here
the nose stays on until reaching orbit, after which it hinges up and over
to expose the payload, staying on the rocket so it goes back down when
the
rocket deorbits itself.) Either aluminum alloy or composite -- that
would
need more investigation. Composites are stronger and lighter, but more
hassle to make, and there might be minimum-gauge issues with such light
sheets, and composite LOX tanks are still iffy.

Pressurization in the tanks is just enough for structural purposes, i.e.
not very much. Boost pumps at the bottom of the tanks, or possibly the
bottom of the feed lines, add enough pressure to prevent cavitation in
the main pumps. (This approach is out of fashion but it has been done
successfully in the past; it avoids having to make the tanks stronger and
heavier to permit higher pressures.) One interesting option is to make
the boost pumps jet pumps, recirculating a bit of the output from the
main
pumps to the jets in the boost pumps. (That too has been done.)

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.

Finally, for engines, I'm partial to the idea of an aerospike with a ring
of small individual chambers. The small chambers help keep the scale of
most engine-development facilities down. The aerospike provides altitude
compensation and also permits a light, compact nozzle with a very high
expansion ratio in vacuum. Expander or gas-generator cycle, preferably
the former if enough heat can be had. (It's been done with propane.)
Post-separation attitude control with propane cold-gas thrusters, and
deorbit by dumping residual propellants through the engines.

This is where hydrogen shines over the 'lesser fuels'.

With the lesser fuels, you just barely make it to orbit, and any fuel
you do have left over, you waste to deorbit the booster to then burn up
in the atmosphere, which is nearly 90% of your usable payload mass,
already delivered to 100 percent of orbital velocity. That's just nuts.

With hydrogen, you get there, and then some, with plenty to spare.

Lesser fuels make the hydrogen 100/1 rule look good.


Yes, the advantages are many for rockets and Atmospheric Flight to Orbit.
Double the energy in such a small package. Every performance curve in the
Atmosphere times 2, rockets less because of the square.

Post-separation attitude control with propane cold-gas thrusters, and
deorbit by dumping residual propellants through the engines.

This is where hydrogen shines over the 'lesser fuels'.

That's the popular myth, but it doesn't hold up on closer inspection.
High Isp and high vehicle performance are two different things, because
Isp is not the only variable in the rocket equation. What hydrogen gains
on high Isp, it loses on high dry mass, because of large heavy tanks,
inferior engine T/W, and added plumbing complexity. The required mass
ratio is lower, yes, but it's actually harder to achieve.

Stages with SSTO-class delta-V performance using "lesser fuels" appeared
several years *before* hydrogen stages with similar performance, and with
fewer development difficulties too. All three stages of the Saturn V had
near-SSTO performance, but the one that was closest to being a practical
SSTO was the first stage -- the one that *didn't* use hydrogen.

With the lesser fuels, you just barely make it to orbit...

Similar story with hydrogen, if not worse, given the greater difficulty of
achieving a given mass ratio with hydrogen.

and any fuel
you do have left over, you waste to deorbit the booster to then burn up
in the atmosphere, which is nearly 90% of your usable payload mass,
already delivered to 100 percent of orbital velocity. That's just nuts.

Not if you have no use for the booster. If you *have* a use for it, then
naturally you retain it in orbit. But if you don't, then whether it's 90%
or some other number, it's just dangerous space debris and you should
deorbit it. (Indeed, you may be required to do so; the regulatory
agencies are getting steadily more concerned about space debris. There
has already been one case of a rocket being grounded by government order
because debris concerns hadn't been addressed to everyone's satisfaction.)

There's nothing about this that depends on the fuel; the LOX/LH2 stages of
the Skylab crew launches were deorbited in exactly the way I described,
and for the same reason.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article ,
(Henry Spencer) wrote:

and any fuel
you do have left over, you waste to deorbit the booster to then burn up
in the atmosphere, which is nearly 90% of your usable payload mass,
already delivered to 100 percent of orbital velocity. That's just nuts.

Not if you have no use for the booster. If you *have* a use for it, then
naturally you retain it in orbit. But if you don't, then whether it's 90%
or some other number, it's just dangerous space debris and you should
deorbit it.

Well, it's only dangerous debris if it's uncontrolled. Even if you have
no immediate use for it, you might anticipate someone having some future
use for it (given that it's mass in orbit, and the great expense of
getting it there has already been paid). So, it might make sense to set
up an orbital scrap yard -- a crude space station that collects spent
stages and basically does nothing but keep them under control until
somebody wants to buy them.

None of which really invalidates your point, of course. But I agree
with the original poster, that wasting all that great mass already in
orbit seems nuts. At a minimum, we should be saving it for future use.
(But if you can't save it for future use, then of course you must
deorbit it.)

Best,
- Joe

Joe Strout wrote:
In article ,
(Henry Spencer) wrote:

and any fuel
you do have left over, you waste to deorbit the booster to then burn up
in the atmosphere, which is nearly 90% of your usable payload mass,
already delivered to 100 percent of orbital velocity. That's just nuts.
Not if you have no use for the booster. If you *have* a use for it, then
naturally you retain it in orbit. But if you don't, then whether it's 90%
or some other number, it's just dangerous space debris and you should
deorbit it.

Well, it's only dangerous debris if it's uncontrolled. Even if you have
no immediate use for it, you might anticipate someone having some future
use for it (given that it's mass in orbit, and the great expense of
getting it there has already been paid). So, it might make sense to set
up an orbital scrap yard -- a crude space station that collects spent
stages and basically does nothing but keep them under control until
somebody wants to buy them.

None of which really invalidates your point, of course. But I agree
with the original poster, that wasting all that great mass already in
orbit seems nuts. At a minimum, we should be saving it for future use.
(But if you can't save it for future use, then of course you must
deorbit it.)

Actually, if you buff it out with solar powered high Isp thrusters, it
may as well be a moving junkyard, as in moving on to geosynchronous
orbit. Then, for all practical purposes, it can remain there forever.

It would also be interesting to record the number of small 'hits' it
took on it's long leisurely ride up, too. It would be easy enough to
deck it out with impact detectors/recorders.

I can consider any number of things to do, but I'm particularly
interested in salvaging some old com sats, just for parts. Invention is
creativity applied to a pile of junk. However, I'm proposing designing
and building junk on the factory floor, which will be brand spanking new
once it reaches orbit. We have even begun to get creative with design,
it's all been brute force cave man ****, as far as I'm concerned.

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.

--
Get A Free Orbiter Space Flight Simulator :
http://orbit.medphys.ucl.ac.uk/orbit.html

In article ,
Joe Strout wrote:
Not if you have no use for the booster. If you *have* a use for it, then
naturally you retain it in orbit. But if you don't, then whether it's 90%
or some other number, it's just dangerous space debris...

Well, it's only dangerous debris if it's uncontrolled. Even if you have
no immediate use for it ... it might make sense to set
up an orbital scrap yard -- a crude space station that collects spent
stages and basically does nothing but keep them under control until
somebody wants to buy them.

Depends a whole lot on whether they're all going to the same orbit. The
problem is that in general, they aren't -- each customer wants a different
orbit, so there is no easy way to collect the spent stages together. The
major exception is if they're being used for something like space-station
resupply, in which case it might make sense to collect them.

Even then, it depends on whether they go all the way to the station, or
only to a low parking orbit where a tug picks up the cargo. If it's the
latter, spending the extra fuel to take them up to the station might not
be worthwhile. And the parking orbit and the station orbit won't stay
together -- their orbit planes will precess at different rates -- so even
launches to the same station won't all go to the same parking orbit.

There is also a general problem that *keeping* them up requires expending
stationkeeping fuel to fight air drag, and the amount can be significant
for big, light objects like spent stages. A collecting station can do
things to minimize the problem, but it doesn't entirely go away.

None of which really invalidates your point, of course. But I agree
with the original poster, that wasting all that great mass already in
orbit seems nuts. At a minimum, we should be saving it for future use.

It's definitely an appealing idea, but it's rather harder than it sounds.
Mother Nature isn't very helpful.

(But if you can't save it for future use, then of course you must
deorbit it.)

Exactly. So the launcher *has* to have a way to do that, even if
sometimes you won't use it.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Hi Henry,

I believe what your doing is extrapolating trade studies beyond there range
of usefulness. In some cases way beyond what the question being
investigated by the trade study. To some sort of global statement about
something else because certain aspects of the studies might indicate that.
Extrapolating outside the useful range of data can be very dangerous and
lead to false conclusion.

Trade Studies if done properly, are good for comparing this or that. This
and that being known quantities and done for the purposes of deciding which
is best. They are also probably good for identifying area were further
work, thought, consideration is required if you still want to do something
where the trade study indicated a negative outcome. Not, as good as the
other.

With a redesign, new concept, different materials and bit of clever
engineering the trade study may go the other way. This is true by orders of
magnitude if a large extrapolation outside the useful range has been made.
Even second order, third or fourth order effects can come into play
invalidating such an extrapolation.

An early example of this might be the ET to Orbit GN&C performance trade
study that I did for NASA after Reagan announced his "Free ETs in Orbit"
program. If I had done the obvious and simply looked at it as the deference
between the two, sure it's obvious, taking up more mass cost an appropriate
performance penalty. But, I liked the idea, and went about the study with a
positive attitude.

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. The question of the Trade Study change
from "how much" performance penalty to "how high" you can take it. Also,
the OMS engines could still point through the C.G., so from a
GN&C/Performance aspect there were no show stoppers.

Had NASA had a more positive attitude about taking ETs to Orbit, I don't
doubt that the overall outcome of the larger study would have been
different. We could possibly have had a 5-6 million pound station by now.
Attitude can have a lot to do with the outcome of a Trade Study.

In a more recent example with john hare's light weight jet engine, wanting
to build his engine, actually see it work, find a use for it. He starts out
wanting to dissuade me the Atmospheric Flight to Orbit is even possible,
really working against his stated goal. Then working on a Trade Study with
certain assumptions to show that it's not possible. 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.

If I had gotten a little more serious about entering the X-Prize, mine most
certainly would have been an air breathing solution with a "Fluid Variable
Intake". But, just about every turbojet in existence was developed by a
government entity not commercial, and what few reasonable worn out but
serviceable engine that are available are from the 50s maybe 60s. Where did
all the more modern worn-out engines go?

BTW john, the X-Prize which yielded a new venture by Sir Richard Branson and
Virgin Galactic company still has some very big problems with his business
plan/model (maybe/maybe, not, knowing what it is). At least the early part
with flying suborbital zero gee tourist flight. The biggest problem I see
has to do with recurring costs, turn around time, and size of his market
(number of customers). Which an air breathing solution could potentially
fix. Or, allow room for a competitor to undercut and take over market share
if it becomes a reality.

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

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

Henry Spencer wrote:

Post-separation attitude control with propane cold-gas thrusters, and
deorbit by dumping residual propellants through the engines.

This is where hydrogen shines over the 'lesser fuels'.

That's the popular myth, but it doesn't hold up on closer inspection.
High Isp and high vehicle performance are two different things, because
Isp is not the only variable in the rocket equation. What hydrogen gains
on high Isp, it loses on high dry mass, because of large heavy tanks,
inferior engine T/W, and added plumbing complexity. The required mass
ratio is lower, yes, but it's actually harder to achieve.

Stages with SSTO-class delta-V performance using "lesser fuels" appeared
several years *before* hydrogen stages with similar performance, and with
fewer development difficulties too. All three stages of the Saturn V had
near-SSTO performance, but the one that was closest to being a practical
SSTO was the first stage -- the one that *didn't* use hydrogen.

With the lesser fuels, you just barely make it to orbit...

Similar story with hydrogen, if not worse, given the greater difficulty of
achieving a given mass ratio with hydrogen.

and any fuel
you do have left over, you waste to deorbit the booster to then burn up
in the atmosphere, which is nearly 90% of your usable payload mass,
already delivered to 100 percent of orbital velocity. That's just nuts.

Not if you have no use for the booster. If you *have* a use for it, then
naturally you retain it in orbit. But if you don't, then whether it's 90%
or some other number, it's just dangerous space debris and you should
deorbit it. (Indeed, you may be required to do so; the regulatory
agencies are getting steadily more concerned about space debris. There
has already been one case of a rocket being grounded by government order
because debris concerns hadn't been addressed to everyone's satisfaction.)

There's nothing about this that depends on the fuel; the LOX/LH2 stages of
the Skylab crew launches were deorbited in exactly the way I described,
and for the same reason.

"Jorge R. Frank" wrote in message
...

Dense-propellant
SSTOs have lower gravity losses so they need a smaller fudge factor. (They
also typically have lower drag losses since the dense propellants allow
smaller tanks, but that's not as significant as the lower gravity losses.)


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.

Danny Deger

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 because of the higher mass ratio, which dense propellants allow.
The vehicles gets lighter faster, so acceleration increases more quickly.

Paul

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 Spencer wrote:

Depends a whole lot on whether they're all going to the same orbit. *The
problem is that in general, they aren't -- each customer wants a different
orbit, so there is no easy way to collect the spent stages together. *The
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. Many customers want to just take
as much as possible, this essentially includes anyone wanting to go to a
lower inclination than the latitude. The number of all flights out of KSC
to this inclination is most likely a much larger percentage of last stages
to Orbit than the Space Stations. Having an Orbital Junk Yard with Orbital
Space Tug Base here makes a lot of sense.