Space Shuttle External Tank Launchers

(Ben Klooterman) wrote in message . com...

Made another one ... SSME ISP is 453 in vacuum. It is much lower that
that at ground level ( cant remember but around the mid 300's ).

363 Sea Level Isp.

Also the thrust is quite low so it takes it a while to get
to less dense air .

179000kgf at sea level. Six SSMEs under a full ET and 20-30 tons of
cargo would produce 1.34Gs of thrust at the pad.

The average Isp for an SSME/ET combination from surface to orbit is
425, which is enough for SSTO work and avoids the headache of the
SRBs.

Why not just add two more SRBs to the stack.




-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

In article ,
Mike Miller wrote:
1) Would engine recovery in the form of a drop-off engine pod make the
ET/SSME-derived SSTO more economical?

..Maybe. Certainly recovering the SSMEs (and you'd put the electronics
in the same pod) would make the whole thing look a lot better; the ET
itself is not that costly. The big question is, how good is the pod?
It's one thing to bring the engines down fully protected in perfect
condition, but that's rather harder than approaches which might involve a
bit of wear&tear and a bit of salt water here and there.

As witness the shuttle SRBs, there comes a point where the recovered
hardware needs so much refurbishing that it's really not worth it.

2) Would there be much difference in R&D cost between an ET/SSME SSTO
with recoverable engine pod and a new, completely reusable SSTO with
6-7 SSMEs?

Yes, most notably because the engine pod has a much smaller heatshield
area and could use off-the-shelf technology there.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Joshua Barney wrote in message news:humhb.529944$Oz4.408471@rwcrnsc54...
I hear rumors that out at Thiokol (or whatever it is they call it now, think
they changed their name) they're working on a new design for the SRBs that
will enable 'em to push out 20% more thrust (yikes!). There's a test
coming up later this October I think. Gonna see if I can go to it.

If it works it could mean that the shuttle could dump the ET and get rid of
its main engine, as the two SRBs alone could launch the shuttle (and a
heavier payload) into orbit...

... well, if the shuttle flies again.

~ Joshua

WRONG.

SRB's are an extremely poor choice for providing all of the deltaV for
an oribtal rocket. They have a poor vacuum ISP (269), and a high
ratio of structural mass to fueled mass (14.6%), in addition to all
the drawbacks inherent to solid rockets (i.e. can't shut them down or
throttle them).

Reaching orbit using stages based on SRB technology would require at
least 3 and more probably 4 stages, since a SRB is good for less than
5000m/s of dV with ZERO payload. Getting an orbiter plus payload
sized mass into orbit would require something like two dozen standard
sized SRBs, and would be a very uncomfortable and dangerous trip.

All that a 20% increase in thrust for the SRBs would be good for is
maybe a 15% bigger ET, and perhaps a 40% bigger payload. But I
shudder to think how much NASA would charge to man-rate the Shuttle
XL.

Damon Hill wrote in message . 132...
(Mike Miller) wrote in
om:

1) Could the ET be converted to an (expendable) SSTO, or be used as
the basis for an SSTO in such a fashion?
2) What would be the ballpark payload to LEO?


SSTO via existing launchers has been in an on-going thread in
sci.space.history. I believe the payload for an ET SSTO [with
6 x SSMEs (Ed Kyle comment)] was estimated at around 60,000
pounds [Gary Hudson, 1991], but these SSMEs ain't cheap. I'd
like to see a 1 1/2 stage a la Atlas using a jettisonable ring
of RS-68s and a SSME sustainer. Probably some more mass savings
with elimination of Shuttle-specific structures and other tweaks.
I don't know if tank stretch or propellant scavenging would
help much.

An interesting exercise, but probably doesn't have much payload
advantage over existing EELV capability, which has some room for
growth.


I did this exercise and found that it might possible to better
the EELV LEO payloads by more than 1.6 times with such a scheme.
I assumed a ring of 3 jettisonable RS-68 engines and one SSME
sustainer, as follows.

Basic SLWT structure 26.06 metric tons
SSME 3.20 tons
SSME Thrust structure 6.60 tons
Avionics 0.23 tons
Residuals (0.25%) 1.81 tons
-----------------------------------------
Injected Mass (No P/L) 37.90 tons

3 x RS-68 20.10 tons
RS-68 thrust structure 7.00 tons
-----------------------------------------
Jettisonable Mass 27.10 tons

Propellant Mass 735.84 tons

Payload 39.00 tons
-----------------------------------------
Gross Liftoff Weight 838.03 tons

All four engines would ignite on the pad to produce a
total of 1,067 tons of sea-level thrust. The RS-68s
would burn for a full-throttle equivalent of about
205 seconds (in practice they would probably be
throttled and so would burn a bit longer than this).

During the first "stage" of flight, the RS-68s would
produce an average thrust of roughly 960 tons at an
effective ISP = 392 sec. The SSME would produce an
average thrust of 201 tons at an effective ISP = 425 sec.
Propellant consumption would be 2.922 tons per second
for a total of 599 tons. Total effective ISP would
be 398 sec. Ideal delta-v would be 4,895 m/sec.

During the sustainer phase, the single SSME would
burn for an additional full-throttle equivalent of
about 267 seconds at vacuum ISP = 453 sec, 232 tons
thrust. Sustainer phase ideal delta-v would be
4,503 m/sec.

With a 39 metric ton payload (86,000 lbs, 1.6 times
more than Delta IV Heavy), this machine could produce
9,398 m/sec ideal delta-v, enough for a 200 km x 27 deg
orbit from KSC/Cape Canaveral.

Boeing claims than an RS-68 costs 1/4 as much as an SSME,
so the propulsion cost would be equal to 1.75 SSMEs (versus
0.75 SSMEs + two RL10s for a Delta IV Heavy). So, while it
would be interesting to fly an ET into LEO this way, there
would not be a propulsion cost advantage compared to
Delta IV Heavy unless a lower-cost SSME (or alternative
equivalent engine) could be used.

- Ed Kyle

(ed kyle) wrote in
om:




With a 39 metric ton payload (86,000 lbs, 1.6 times
more than Delta IV Heavy), this machine could produce
9,398 m/sec ideal delta-v, enough for a 200 km x 27 deg
orbit from KSC/Cape Canaveral.

That's an encouraging result, as it could accomodate an
outsize payload or eliminate a double launch in some
cases vs. two heavy EELV launches.


Boeing claims than an RS-68 costs 1/4 as much as an SSME,
so the propulsion cost would be equal to 1.75 SSMEs (versus
0.75 SSMEs + two RL10s for a Delta IV Heavy). So, while it
would be interesting to fly an ET into LEO this way, there
would not be a propulsion cost advantage compared to
Delta IV Heavy unless a lower-cost SSME (or alternative
equivalent engine) could be used.

Delta IV Heavy uses a single RL10 (22klbs/thrust); it's planned
to go to a single MB60 (~60klbs/thrust), which should improve
payload somewhat by reducing gravity losses and/or enabling
larger propellant tanks. So cost should continue to favor
EELV in the future, but an ET sorta-SSTO looks interesting
nonetheless.

Some work is being done on lower cost SSME equivalents,
which could potentially favor either launcher by raising
average Isp and thrust:

http://www.pratt-whitney.com/prod_space_cobra.asp

http://www.boeing.com/defense-space/...ropul/SLI.html

--Damon

PS Of little particular relevance but of some interest,
Pratt and Whitney's redesigned their web page and added
new rocket propulsion products and information.

http://www.pratt-whitney.com/prod_space.asp

wrote:
... it might possible to better
the EELV LEO payloads by more than 1.6 times with such a scheme.
... assume a ring of 3 jettisonable RS-68 engines and one SSME
sustainer ....
With a 39 metric ton payload (86,000 lbs, 1.6 times
more than Delta IV Heavy), this machine could produce
9,398 m/sec ideal delta-v, enough for a 200 km x 27 deg
orbit from KSC/Cape Canaveral.


Replace the SSME sustainer with an RS-68 and adjust the
staging time down to the 145-150 second range and you'll
get 32 metric tons (more than 70,560 pounds) of payload
into the same orbit. The propulsion cost for this
vehicle (4xRS68) is about the same as for *one* SSME and
about 1.17 times the propulsion cost of a Delta IV Heavy.
Since the LEO payload is 1.33 times greater than that of
Delta IV Heavy, this particular stage-and-one-half ET
comes out ahead of EELV in terms of propulsion cost per
kg to LEO.

Even more payload should be possible by stretching the ET
tanks to carry 150 tons or so additional propellant. With
a GLOW of about 1,000 tons, a stretched RS-68 powered
ET stage-and-a-half vehicle should be able to hurl 38 tons
or so to LEO.

- Ed Kyle

"Damon Hill" wrote in message
32...
(ed kyle) wrote in
om:




With a 39 metric ton payload (86,000 lbs, 1.6 times
more than Delta IV Heavy), this machine could produce
9,398 m/sec ideal delta-v, enough for a 200 km x 27 deg
orbit from KSC/Cape Canaveral.

That's an encouraging result, as it could accomodate an
outsize payload or eliminate a double launch in some
cases vs. two heavy EELV launches.

Volume for me has always been the biggest draw for Shuttle derived vehicles
not the mass to orbit.



Boeing claims than an RS-68 costs 1/4 as much as an SSME,
so the propulsion cost would be equal to 1.75 SSMEs (versus
0.75 SSMEs + two RL10s for a Delta IV Heavy). So, while it
would be interesting to fly an ET into LEO this way, there
would not be a propulsion cost advantage compared to
Delta IV Heavy unless a lower-cost SSME (or alternative
equivalent engine) could be used.

Delta IV Heavy uses a single RL10 (22klbs/thrust); it's planned
to go to a single MB60 (~60klbs/thrust), which should improve
payload somewhat by reducing gravity losses and/or enabling
larger propellant tanks. So cost should continue to favor
EELV in the future, but an ET sorta-SSTO looks interesting
nonetheless.

Just my opinion but I think with the Delta IVs second stage is over large
already so they will go for a third stage rather then making the second
stage much bigger.
With the MB-60 they can easily fit a Delta II second stage on all Delta
IV's and even a Delta III second stage on the Heavy.
Only on a Shuttle derived would they go for a much bigger second stage.

Some work is being done on lower cost SSME equivalents,
which could potentially favor either launcher by raising
average Isp and thrust:

http://www.pratt-whitney.com/prod_space_cobra.asp

http://www.boeing.com/defense-space/...ropul/SLI.html

I really like the RS-84 a reusable Kerosene and Oxygen engine has great
potential as a first or booster stage.


--Damon

PS Of little particular relevance but of some interest,
Pratt and Whitney's redesigned their web page and added
new rocket propulsion products and information.

http://www.pratt-whitney.com/prod_space.asp

I greatly appreciate this I was about to give up hope on the RL-60.
Now if Boeing would just do the same and give more recent info on the MB-60.

(Henry Spencer) wrote in message ...

(SSMEs are just too
expensive for expendables.)

How about putting them into a capsule and recovering them ?

Boeing made and test flew a parachute, to recover a 139 tons S-IC
stage, and the whole Shuttle weighs less.

And there were schemes by McDonnell-Douglas to recover the S-IVB stage
from orbit.

There must be a solution in there somewhere.

Regards

Carsten Nielsen
Denmark

(Henry Spencer) wrote:
[...]
Even if you assume a generous addition of mass for structure, and no
reduction of existing structural mass -- heavier than needed in several
areas -- the ET is light enough that with six SSMEs, it could do the job
with a substantial payload. Some proposals have added one more SSME to
increase margins further.
[...]

Would the payload be a new beanie cap? Or would it go about where the
shuttle is? If you had to do a lot of trusswork to support the
payload on top, the requal costs would start getting up to new vehicle
range, and if you hang it on the side, you have payload protection
issues....


/dps