Low Cost Shuttle Competition

Thus far, all U.S. liquid rockets for space boosters, anyway, have been
reusable to some extent.

True. I met an engineer who worked on one of the one-shot booster engine.
After assembly, since thrust output various with each engine, they test fire
it at given condition to get the thrust measurement. According to
measurement, tweak the fuel flow system to meet the engine thrust
specification. Fire it for the second time to verify the thrust. So all
engine gets fired at least three times counting real flight. The duty
cycle of the engine is far grater than its flight duration.

Emilio.

"Peter Stickney" wrote in message
...
In article ,
"Keith Willshaw" writes:

"NoHoverStop" wrote in message
...
"John Halliwell" wrote in message


Sadly "Horizon" has been noticeably "dumbed-down" of late, preferring
hyperbole to subtlety, relishing in constantly trotting out the same
"established scientists said it couldn't work/happen/exist, but these
renegades/upstarts/FSU-engineers have proven them wrong" line whether
the
programme is about dinousaurs, rockets, asteroids or aircraft. Rockets
are
not my field, but I am given to understand that the SSME (noticeably
American when I last checked) is a closed-cycle design.



The statement about the US having abandoned close cycle engines was
made by one of the US engineers who was involved with licensing
the rocket motor design from Energomash and in this instance I
dont recall any rubbishing of US efforts by the program maker.

The Channel 4 web site carries the same story by the way stating

http://www.channel4.com/science/micr.../timeline.html

Quote

US rocket scientists are taken to see stored NK33s.

Scientists from the US company Aerojet are amazed to find a store of
over 60
pristine engines, of a compact design that they had never seen before.
What
surprised them most was that the engines used the closed-cycle
technology
that had been rejected by American rocket scientists as being too risky.

/Quote

As does wired.com

http://www.wired.com/wired/archive/9.12/rd-180.html

It agrees that the SSME has a closed cycle engine but states that its
the exception and of course the SSME is quite unusual in being
a restartable engine. Most rocket engines are one shot devices.

That's not quite true, Keith. Thus far, all U.S. liquid rockets for
space boosters, anyway, have been reusable to some extent. They're
all proff-fired before use. Some, such as the RL-10 have demonstrated
(in ground testing) the ability to be restarted over 30 times.
We just haven't been using them that way.
Most booster engines, with the exception of upper stages for systems
that will need to change orbit, like, say, an Apollo leaving parking
orbit to go to the Moon, or a Mars Probe, or such, aren't restartable
in flight. Once they are lit, you can turn 'em off, but there's not
way to get them lit again.

I think there may be a bit of overstating the case here, too. It's
not so much that a closed-cycle engine is _that_ much more difficult,
but it does reflect a different design philosophy than most
U.S. rocket manufacturers have used. The again, nearly all
U.S. liquid fuelled rocket motor are either late 1950s designs, or
derivitives of designs from the late 1950s and the 1960s. There've
been plenty of incremental improvements, but not a lot of new
development.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

"Peter Stickney" wrote in message
...
In article ,
"Keith Willshaw" writes:

"NoHoverStop" wrote in message
...
"John Halliwell" wrote in message


Sadly "Horizon" has been noticeably "dumbed-down" of late, preferring
hyperbole to subtlety, relishing in constantly trotting out the same
"established scientists said it couldn't work/happen/exist, but these
renegades/upstarts/FSU-engineers have proven them wrong" line whether
the
programme is about dinousaurs, rockets, asteroids or aircraft. Rockets
are
not my field, but I am given to understand that the SSME (noticeably
American when I last checked) is a closed-cycle design.



The statement about the US having abandoned close cycle engines was
made by one of the US engineers who was involved with licensing
the rocket motor design from Energomash and in this instance I
dont recall any rubbishing of US efforts by the program maker.

The Channel 4 web site carries the same story by the way stating

http://www.channel4.com/science/micr.../timeline.html

Quote

US rocket scientists are taken to see stored NK33s.

Scientists from the US company Aerojet are amazed to find a store of
over 60
pristine engines, of a compact design that they had never seen before.
What
surprised them most was that the engines used the closed-cycle
technology
that had been rejected by American rocket scientists as being too risky.

/Quote

As does wired.com

http://www.wired.com/wired/archive/9.12/rd-180.html

It agrees that the SSME has a closed cycle engine but states that its
the exception and of course the SSME is quite unusual in being
a restartable engine. Most rocket engines are one shot devices.

That's not quite true, Keith. Thus far, all U.S. liquid rockets for
space boosters, anyway, have been reusable to some extent. They're
all proff-fired before use. Some, such as the RL-10 have demonstrated
(in ground testing) the ability to be restarted over 30 times.
We just haven't been using them that way.
Most booster engines, with the exception of upper stages for systems
that will need to change orbit, like, say, an Apollo leaving parking
orbit to go to the Moon, or a Mars Probe, or such, aren't restartable
in flight. Once they are lit, you can turn 'em off, but there's not
way to get them lit again.


Which in practise makes them one shot devices.

I think there may be a bit of overstating the case here, too. It's
not so much that a closed-cycle engine is _that_ much more difficult,
but it does reflect a different design philosophy than most
U.S. rocket manufacturers have used. The again, nearly all
U.S. liquid fuelled rocket motor are either late 1950s designs, or
derivitives of designs from the late 1950s and the 1960s. There've
been plenty of incremental improvements, but not a lot of new
development.


The US manufacturers concerned were clearly sold enough on the
case to license the design from Energomash and its was THEY
who made the claims referenced not the TV company (or me).

Keith

In message - Bradford Liedel
writes:


I find this stuff very interesting. I'm curious to see if (within the
next 30 years) space travel actually becomes a consumer industry
rather than a government only industry. With backstreet boys being
launched into space, towers into the atmosphere, corporations
competing on new shuttle designs, etc...who knows what this will all
bring.


I often see this type of thinking: "if only we'll start launching on
commercial scale things will be cheap". Well, things are not that rosy:
physical limits come to play. The classical rocket equation:

dv = Ve * ln((final mass) / (initial mass))

whe

Ve = exhaust velocity.
dv = change in velocity

The exaust velocity is more or less constant for chemical fuels. In F-1
engines of the Saturn-V first stage it was around 2.9 km/Sec in vacuum
(2.6 km/Sec at sea level). The required dv is about 8 km/Sec (to LEO).
Substitute the figures into the equation and you'll get that final mass
is only about 5% of the initial mass. That means: 95% of the rocket mass
is fuel and the WHOLE structure and payload and engines has the meager
5% of the mass budget. That'll dictate you engineering decisions very
uncomfortable to live with:

1) You can't make the spacecraft "sturdy as a buttleship", in fact
you'll be forced to make its structure rather flimsy (forget
about "belly landing" with shuttle) and therefore you'll have
to very thoroughly inspect it before EVERY flight to make sure
absolutely nothing is damaged and probability of slight damage
requiring repairs will be quite high. Such inspection by an army
of technitians adds cost.

2) The cryogenic fuels (LH2+LOX or Kerosine+LOX or other similar stuff)
are much mode dangerous to handle than ordinary jet fuel, therefore
in almost any event of unexpected pre-launch maintenance you'll need
to drain the tanks and refill them again and it's not as simple
as dealing with jet fuel - again you'll need many more people
which again adds to the cost.

3) Because of the tight mass budjet (5%) every equipment must be
on the cutting edge in terms of mass (materials used) which makes
it expensive to build and maintain.

I'm not saying you can't make launches cheaper than NASA does (if Shuttle
launch costs $19,000/kg and is equal to Saturn-V launch cost per kg than
clearly NASA missed something implementing the "reusable cheaper than
expandable" attitude) but there are inherent technical problems which can't
be solved in a cheap way when you'rr constrained by the 5% mass budget.

However, if you'll use nuclear propultion - that really opens the road to
cheap space access. All you need is LOTS of R&D money to restart programs
USAF conducted in 50-s and 60-s (and got as far as having working prototype
of nuclear rocket on a test stand) and solve the problems of engine life,
radioactive exhaust, worst case launch failure survivability of the
reactor, etc. And of corse, you'll need to re-educate the public (voters)
to allow polititians to make such decisions.


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* Arie Kazachin, Israel, e-mail: *
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