The 100/10/1 Rule.

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.

On Sat, 17 Mar 2007 15:01:21 GMT, in a place far, far away, Craig Fink
made the phosphor on my monitor glow in such a
way as to indicate that:


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.

There is zero reason to believe this, despite your airbreathing
fetish.

Greg D. Moore (Strider) wrote:

"Rand Simberg" wrote in message
...
On Thu, 15 Mar 2007 17:09:34 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

In article ,
Neil Gerace wrote:
...and because cold metal is stronger than warm
metal and hence can take higher pressures.

Cold tin is definitely weaker than warm tin, though of course it's a bit
weird as metals go and there's none involved here so it doesn't count
:-) (I think cold 'grey' tin has the tetrahedral-covalent diamond
structure but
nothing like the bond strength, while warm 'white' tin is more like a
true
metal.)

I forget the exact story on tin, but yes, phase changes can mean that
you're not dealing with quite the same metal :-) at different
temperatures.

The other joker in the deck is that some metals -- notably ordinary
carbon steel -- become brittle when cold.

IIRC, this was a factor in the loss of the Titanic. Though only one
of many. And I don't always recall correctly...

Ayup, brittle fractures. The big surprise when they started to look at
the actual wreck was that it wasn't a single huge gash like they thought
but lots of small.

As I understand it, the problem wasn't so much the hull plates, but the
rivets that held them together. The shock of the collission sheared a lot
of rivets, and thus seams were started in areas not directly at the site of
the iceberg strike.

--
Pete Stickney
Without data, all you have is an opinion

"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

"Peter Stickney" wrote in message
...


As I understand it, the problem wasn't so much the hull plates, but the
rivets that held them together. The shock of the collission sheared a lot
of rivets, and thus seams were started in areas not directly at the site
of
the iceberg strike.

That was a big part of it, but IIRC if the plates had been made of the right
kind of steel they would have absorbed more of the impact instead of
transmitting most of it to the rivets.

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.

Craig Fink wrote:

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.

Except there's no reason to expect these launches to be to the same *plane*.

Paul