Why is a LOX/Kero SSTO not rather easy?

I am not a particular fan of SSTO, but it appears to me that SSTO has
long been within our grasp.

The best figures that I could get for the Titan II 1st stage
(based on Rusty Barton's reply to my earlier post) are a
GLOW 0f 258000 lbs, and a dry weight of 10900, giving it a mass ratio of
23.7. Now comparing it to a LOX/kero vehicle powered by something like
the Russian NK-33, I see the following plus and minus factors affecting
its mass ratio (I am not including a payload in these calculations):

On the minus side, the Titan II 1st stage is not a complete vehicle. It:

(a) lacks a nose cone
(b) lacks most avionics
(c) lacks a cargo bay
(d) has 6% denser fuel so a slightly smaller fuel tank

On the plus side:
(a) the NK-33 is 420 lbs lighter than the Titan II engine
yet it is sufficient for a vehicle nearly 10% heavier
(b) the structure does not have to support the 32 ton 2nd stage
and so can be significantly lighter.

My guess is that those factors mostly cancel out. I also assume that
making a vehicle reusable adds about 40% to its dry weight:
Wings add 7%
Landing gear add 3%
TPS add 15%
Other add 15%

So if we crank those factors in:
Dry weight = 10900*1.4 = 15300 lbs
Glow = 258000 + (15300 - 10900) = 262400
MR = GLOW/(GLOW-Dry weight) = 262400/15300 = 17.15

Now for the NK-33 we have an average Isp of 331, and given a required
dV of 9200 m/s (300 m/s less than a LH2/LOX rocket due to less air
resistance, lower back pressure losses, and earlier peak acceleration)
we get a required MR of 17.01, which is slightly less than what we
can achieve. So we can make orbit with a single stage using very old
technology.

Of course, this is without payload, but given the fact that the Titan II
1st stage was not optimized for weight (you would not normally optimize a
1st stage) and we have lighter materials today, such as aluminum-lithium
and carbon fiber, I would think we would have the necessary margin
for a significant payload.

We also might fly with a wet wing and eliminate the kerosene tank
altogether. And of course if we scaled it up by a factor of 3
we would gain a substantial economy of scale.

So it appears to me that we have had reusable SSTO capability for
dense fuel vehicles for a long time.

-- Larry

Hi Larry!

Well, I'd like to add a few nitpicks. I removed a lot of the text where
I do not disagree.

Larry Gales wrote:
[...]
My guess is that those factors mostly cancel out. I also assume that
making a vehicle reusable adds about 40% to its dry weight:
Wings add 7%
Landing gear add 3%
TPS add 15%
Other add 15%

I do not think wings could be done for only 7% of the weight, especially
if one takes into account the added structure needed for a winged
vehicle. However I am partial to wingless vehicle and I did the following
calculations: The spaceship has in the earth a terminal velocity of
50...100 m/s (example: cw=1, 10 m diameter, 50t weight = 60m/s)
Say you want 200m/s fuel including reserves, so you would need 6-7%
mass depending on Isp - and the engines and structure needed are already
there.

Question: which items do you include among "other"? I see only
restfuel and a bit more avionics, but this should not amount to 15%.
However, I might easily miss something...

So if we crank those factors in:
Dry weight = 10900*1.4 = 15300 lbs
Glow = 258000 + (15300 - 10900) = 262400
MR = GLOW/(GLOW-Dry weight) = 262400/15300 = 17.15

Now for the NK-33 we have an average Isp of 331, and given a required
dV of 9200 m/s (300 m/s less than a LH2/LOX rocket due to less air
resistance, lower back pressure losses, and earlier peak acceleration)
we get a required MR of 17.01, which is slightly less than what we
can achieve. So we can make orbit with a single stage using very old
technology.

I notice most modern rockets are more "fat" than Titan. However, I am
not sure how much weight could be saved if the tanks have more diameter
and less length, and there is some delta-V loss due to additional air
resistance. Additional advantage to the fat version: I want a lot of
drag for breaking during descend.

Of course, this is without payload, but given the fact that the Titan
II 1st stage was not optimized for weight (you would not normally
optimize a 1st stage) and we have lighter materials today, such as
aluminum-lithium and carbon fiber, I would think we would have the
necessary margin for a significant payload.

You can optimize a RLV a bit more than a ELV: increased construction
costs for the airframe would be spread over a high number of flights.
However, initially you would *have* to keep down development costs,
so this might not be possible for the first generation.

We also might fly with a wet wing and eliminate the kerosene tank
altogether. And of course if we scaled it up by a factor of 3
we would gain a substantial economy of scale.

As befo I think you underestimate the weight of a wing.

So it appears to me that we have had reusable SSTO capability for
dense fuel vehicles for a long time.

Well, I agree. I just do not think a winged vehicle would be the way to
go.

Robert Kitzmueller

On Tue, 2 Sep 2003, Robert [ISO-8859-1] Kitzm=FCller wrote:

Date: Tue, 02 Sep 2003 18:49:47 +0200
From: "Robert [ISO-8859-1] Kitzm=FCller"
Newsgroups: sci.space.policy, sci.space.tech
Followup-To: sci.space.policy
Subject: Why is a LOX/Kero SSTO not rather easy?

Hi Larry!

Well, I'd like to add a few nitpicks. I removed a lot of the text where
I do not disagree.

Larry Gales wrote:
[...]
My guess is that those factors mostly cancel out. I also assume that
making a vehicle reusable adds about 40% to its dry weight:
Wings add 7%
Landing gear add 3%
TPS add 15%
Other add 15%

I do not think wings could be done for only 7% of the weight, especially
if one takes into account the added structure needed for a winged
vehicle. However I am partial to wingless vehicle and I did the following
calculations: The spaceship has in the earth a terminal velocity of
50...100 m/s (example: cw=3D1, 10 m diameter, 50t weight =3D 60m/s)
Say you want 200m/s fuel including reserves, so you would need 6-7%
mass depending on Isp - and the engines and structure needed are already
there.

Question: which items do you include among "other"? I see only
restfuel and a bit more avionics, but this should not amount to 15%.
However, I might easily miss something...

--------------------------------------------------

I am not wedded to the idea of a winged vehicle, and Henry Spencer also
thought that wings would be more than 7%.

What I would like to see is an annular aerospike for the engine for it
not only provides superior ISP but would also act as a heat shield and
would simpilfy landing as you could use but a few nozzles rather than
having to throttle large engines down.

Also all the stresses would be along the same line and in the same
direction throughout the flight making strucutre easier and lighter.

-- Larry

Larry Gales wrote:
What I would like to see is an annular aerospike for the engine for it
not only provides superior ISP but would also act as a heat shield and
would simpilfy landing as you could use but a few nozzles rather than
having to throttle large engines down.

It certainly looks like a workable concept. However, aerospikes were
never used for propulsion, neither for ELV nor RLV, so there might be
unknown problems. I see possible problems also in the aerospike
exhaust flow if there are only a few chambers (of a whole lot)
used: It will spread to the sides, and it might become turbulent.
(I say might, since I am not to sure about this. Has anybody ever looked
at this closely?)

Also all the stresses would be along the same line and in the same
direction throughout the flight making strucutre easier and lighter.

This would be the main attraction of a base-reentry base-landing RLV.

Larry Gales :

Yes. The only useful thing that might have come out of the X33 was
whether or not aerospikes would work throughout the flight path -- but we
never did learn that. In fact did we learn *anything* from the X33 other
than that the approach was a big mistake?

As far as I can tell, zero useful information was learnt from X-33 while over
a billion dollars was spent.

A cheap aluminium rocket could have been built to test the aerospikes - it
was not done because it was not a high tech enough way to doing the test.

A cheap solid fuel rocket (Orbital?) could have been used to test the
metallic TPS - again it was not done because it was not a high tech enough
way to doing the test.

A small scale tank could have been built and tested a hundred times with fill
and empty cycle and the problem found, or they could have given the contract
to someone who does know something about composite tanks like Scaled
Composite - but thier ego demanded building full scale tanks before they did
all the needed tests.

Doing it the low tech way probably would have cost less money than was spent
and would have given us good test data on two of the three techonologies.

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

Larry Gales wrote:

On Fri, 5 Sep 2003, Robert [ISO-8859-1] Kitzmüller wrote:

Date: Fri, 05 Sep 2003 17:48:06 +0200
From: "Robert [ISO-8859-1] Kitzmüller"
Newsgroups: sci.space.policy
Subject: Why is a LOX/Kero SSTO not rather easy?

Larry Gales wrote:
What I would like to see is an annular aerospike for the engine for it
not only provides superior ISP but would also act as a heat shield and
would simpilfy landing as you could use but a few nozzles rather than
having to throttle large engines down.

It certainly looks like a workable concept. However, aerospikes were
never used for propulsion, neither for ELV nor RLV, so there might be
unknown problems. I see possible problems also in the aerospike
exhaust flow if there are only a few chambers (of a whole lot)
used: It will spread to the sides, and it might become turbulent.
(I say might, since I am not to sure about this. Has anybody ever looked
at this closely?)
-------------------------
Yes. The only useful thing that might have come out of the X33 was
whether or not aerospikes would work throughout the flight path -- but we
never did learn that. In fact did we learn *anything* from the X33 other
than that the approach was a big mistake?
----------------------------------

-- Larry


Also all the stresses would be along the same line and in the same
direction throughout the flight making strucutre easier and lighter.

This would be the main attraction of a base-reentry base-landing RLV.



There was some *cold* flow data on the SR-71 mounted scaled-down
engine (the H2 leaked too much to fire LASRE in flight, if I understand
correctly), and plenty of hot firings of a static engine. Also, some
good work on more robust, weather-resistant (from samples tested on an
F-15 flying under various conditions) thermal protective materials.

But yeah, that, and how *not* to make a composite tank, were about
all we really got out of it....

Earl Colby Pottinger wrote in message ...
Larry Gales :

Yes. The only useful thing that might have come out of the X33 was
whether or not aerospikes would work throughout the flight path -- but we
never did learn that. In fact did we learn *anything* from the X33 other
than that the approach was a big mistake?

As far as I can tell, zero useful information was learnt from X-33 while over
a billion dollars was spent.



Are you trying to tell us that something stinks at the Skunkworks? ;-)



-Rusty

(Rusty B) wrote in message . com...
Earl Colby Pottinger wrote in message ...
Larry Gales :

Yes. The only useful thing that might have come out of the X33 was
whether or not aerospikes would work throughout the flight path -- but we
never did learn that. In fact did we learn *anything* from the X33 other
than that the approach was a big mistake?

As far as I can tell, zero useful information was learnt from X-33 while over
a billion dollars was spent.



Are you trying to tell us that something stinks at the Skunkworks? ;-)

If it's a high profile, high-cost program like the X-33,
then it ain't a skunkworks. The Skunkworks--when it
existed--was not a place, it was a way of doing business.
As Norm Nelson (Kelly's succesor) used to say: "You have
to get the project done, before the hyenas find out about
it."

Best regards,
Len (Cormier)
PanAero, Inc. and Third Millennium Aerospace, Inc.
( http://www.tour2space.com )


-Rusty

Len wrote:

(Rusty B) wrote in message . com...
Earl Colby Pottinger wrote in message ...
Larry Gales :

Yes. The only useful thing that might have come out of the X33 was
whether or not aerospikes would work throughout the flight path -- but we
never did learn that. In fact did we learn *anything* from the X33 other
than that the approach was a big mistake?

As far as I can tell, zero useful information was learnt from X-33 while over
a billion dollars was spent.



Are you trying to tell us that something stinks at the Skunkworks? ;-)

If it's a high profile, high-cost program like the X-33,
then it ain't a skunkworks. The Skunkworks--when it
existed--was not a place, it was a way of doing business.
As Norm Nelson (Kelly's succesor) used to say: "You have
to get the project done, before the hyenas find out about
it."

Best regards,
Len (Cormier)
PanAero, Inc. and Third Millennium Aerospace, Inc.
( http://www.tour2space.com )


-Rusty

From everything I have read lately, the only relationship that
the recent Lockheed-Martin "Skunkworks" has with the old
one formed by Kelly Johnson is the name.

The demise of the X-33 is much more a result of bad
management than either technical failure
(composite LH2 tanks) or even a bad selection of
the winning X-33 concept.

Mike Walsh

On Mon, 15 Sep 2003 00:39:01 GMT, in a place far, far away, Michael
Walsh made the phosphor on my monitor glow in
such a way as to indicate that:

The demise of the X-33 is much more a result of bad
management than either technical failure
(composite LH2 tanks) or even a bad selection of
the winning X-33 concept.

I disagree. The selection was awful, on a number of counts as (I
don't hesitate to point out) I pointed out at the time.

--
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