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 fueland so has 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

Larry Gales wrote in message news:Pine.WNT.4.56.0308302326280.2728@homecomps. ..
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 fueland so has 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

We had a similar discussion here under "Low mass ratio SSTO" .

I think people just want to write papers and justify large RD budgets
that end up being spent on people who do not work. They need big
ticket buzzwords like SSTO or fusion reactors. They just take the
money, promise something that's hard to do like a non cylindrical fuel
tank or a SCRAM jet engine and later they just say, oh well we did not
succeed. Of course many times they do not need to say a thing because
they get lucky and the project is cancelled before they are supposed
to deliver hardware.

Of course it is easy to build SSTO.

Zoltan

A LOX/Kero SSTO would be fairly straightforward (I
hesitate to say easy only because any major project,
even just digging a big ditch (like the Suez canal)
has its own difficulties and complexities). I
perceive several reasons why such things aren't being
built now. First, is history. From the beginning,
orbital rocketry was pretty difficult. The engines
available were terrible, and were it not for the
fact that liquified gasses and the means to handle
them in bulk had been developed since well before
the turn of the 20th century it might have been even
worse. More so, building very strong structures
which are also very light is, and has been, a
substantial challenge. If it were not that the
aircraft industry had been working in the same
direction about a step ahead of rocketry in the early
days (since large scale aircraft preceded large scale
rocketry by only a few decades), it would certainly
have been much, much worse. Anywho, what all that
meant (poor engines, and clunky structures, even
when both were state of the art) was that SSTO was
impossible early on. The early liquid fueled rockets
had Isps about as high as the best solid rockets do
today. And especially in that Isp range with respect
to orbital rocketry any significant performance hit
bites pretty hard (an Isp of ~240s leads to a mass
fraction to reach orbital speed of *twice* that as
with an Isp of ~300s (which is the lower end of the
range of Isps for current Kero engines)). Factor in
the unfamiliarity both with building very large
rockets (e.g. Saturn V class, since you get a hefty
advantage in dry mass fraction as you scale up) and
with building very low dry mass fraction rockets and
that led to the result that staged rockets were the
only way to get to orbit. At the time.

Here's where the second point comes in, since rocketry
was so difficult early on and seemingly so fickle that
a kind of institutionilzed cult of accumulated
superstition arose. More like the shipwrights of old
than, say, the cpu designers of today, rocket builders
were enormously leery of from-scratch designs and
instead opted for evolving, modifying, and scaling
old designs to get what they wanted. And that led to
a whole host of ideas becoming fixed in the head of the
industrial and government aerospace establishment,
including things like LOX/LH2 being a superior fuel than
denser fuels, a fixation on minimizing GLOW in relation
to payload size, etc. As the rocket industry developed,
rather than getting rid of old preconceptions, mostly
they just added new ones (such as the "inherent"
advantages of winged RLVs over capsules). That inertia
has morphed itself into the hand-built, multi-stage
launch vehicles you see today and into the idea that
SSTO is a really difficult problem.

Third and finally, and this is the important point,
the launch vehicle business is already established and
current launch vehicles meet the needs of the customers
fairly well. Brand new vehicles, especially of different
designs, would have to develop rather quickly and mold
themselves (at leas initially) more to the common
characteristics of current launch vehicles (especially in
terms of g-loading and vibration). And that adds a
development burden to anyone wanting to do an SSTO that
would be commercially viable with existing markets.
Though there are emerging markets which may provide
useful niches. One of the biggest problems of SSTOs is
that they have too much thrust. When you take a single
stage with only a small payload and you take the engines
which are designed to lift it off the ground by brute
force with fuel tanks to the brim and you keep those
same engines on when the fuel tanks are empty (i.e. when
the vehicle plus payload weighs at most 1/7th as much
(for the best LOX/LH2 engines) or more likely less than
7% as much (for really good LOX/Kero engines)), you end
up with a hell of a lot of excess gees. In fact, for a
manned LOX/Kero SSTO, if the engines weren't throttled
down the g-load at engine burnout would be pretty close
to lethal. High g-loads are slightly more tolerable but
not all that much better for multi-million dollar pieces
of machinery, so it's a general problem. So a usable
SSTO needs to be able to throttle *very* deeply. And
that almost certainly means not just individual engines
with a large thrust range but being able to cutoff
engines as the vehicle depletes its fuel. And that
adds complexity, difficulty, and cost to the design and
construction.


For example, your Titan-II w/ NK-33 SSTO has a mass-
ratio of 17.1:1, which means that the peak thrust at
burnout would be around 17 gees, give or take. You
give a dry weight of about 7,000 kg, and one NK-33 has
a thrust in vacuum of abour 167,000 kg-f, so that gives
a max g-force of about 24 gees. According to this page:
http://www.spaceandtech.com/spacedat...33_specs.shtml

The NK-33 has a throttle range of 55 - 104% (the vac.
thrust data is from astronautix.com, FYI), so that gives
a minimum g-load at burnout of 12 gees.


As I said, fairly straightforward but not easy.

In article Pine.WNT.4.56.0308302326280.2728@homecomps,
Larry Gales wrote:
So it appears to me that we have had reusable SSTO capability for
dense fuel vehicles for a long time.

There is little doubt, among those willing to actually look at the facts,
that you can get a single-stage expendable into orbit -- at least, with
little or no payload -- and have been able to do so for some time.
Another example of that (without even exploiting the dense-fuels bonuses)
is what you get if you put six SSMEs on the base of a shuttle ET; that one
actually should be able to carry quite a substantial payload.

The "reusable" part can legitimately be questioned. The assumptions you
made about how much various things add to the dry mass are highly
debatable. For example, assuming that wings add only 7% is awfully
optimistic.

It is very difficult to actually *resolve* disagreements about basic
assumptions when the battle is viewgraphs vs. viewgraphs. Nothing short
of flying hardware will settle such disputes. Claims that LOX/LH2 rockets
are inherently difficult and complex to operate were quite persistent for
years, but quietly evaporated when DC-X started flying.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Larry Gales wrote:


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):

The problem is that the NK-33 is a russian engine. NASA would *never* build
a craft with a russian engine, and the russians themselves lack sufficient
funding to do something interesting with their huge stockpile of fantastic
engines. They also lack the technology to build very lightweight fuel
tanks. Private (or at least semi-private) entities such as Boeing and
LockMart have used russian engines very successfully (Sea Launch and Atlas
V), but they are too conservative to develop something revolutionary.

So if you can convince someone to build a simple cylindrical design with
NK-33 engines, then SSTO with significant payload is quite doable. Reusable
SSTO should also be doable if you use vertical landing. And even a VTVL
SSTO space transport with zero payload would be very useful since you could
use it as a testbed for various technologies and get a quite significant
payload by just adding a few booster rockets.

The problem is not technical but political. This is kind of sad since most
of us s.s.t regulars really enjoy technical discussions like Kerosene vs.
LH2, VTVL vs. VTHL vs HTHL, pure rocket vs. airbreather, SSTO vs. TSTO and
so on. But such discussions will not get us closer to CATS unless somebody
can pony up the money to actually build it. NASA will not do it for us.

Larry Gales wrote in message news:Pine.WNT.4.56.0309042104270.2228@homecomps. ..
On Wed, 3 Sep 2003, Anthony Q. Bachler wrote:

Date: Wed, 03 Sep 2003 06:51:48 GMT
From: Anthony Q. Bachler
Newsgroups: sci.space.tech, sci.space.policy
Subject: Why is a LOX/Kero SSTO not rather easy?

You cant just 'scale up' a launch vehicle like you scale up a pizza. There
are structural factors to consider that are not necessarily linear with
vehicle size or weight. You also cant just switch materials without
testing. I dont know what problems may or may not arise, but neither do you
and that's the whole point.

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

Yes I do: it is well known that mass ratios become significantly
easier as you scale a vehicle up: some things like TPS and insulation
scale
only as the square of the size, and some other things, such as avionics,
pilot, etc scarecly increase, and air resistance is proportionaly much
less for large vehicles. This is born out in comparisons of large
versus small rockets.

Know I *don't* know for sure if this could achive a practical reusable
SSTO, but I *do* know that the mass ratio would definitely be easier
for a scaled up version.

-- Larry

My 46-year-long pursuit of cheaper ways of getting
into space--born at a reception that I attended at
the Soviet Embassy reception during which Sputnik
was launched--supports Larry's assertions regarding
higher achievable mass ratios as gross mass increases.

I feel that current technology could enable a VTOHL
space transport having a gross mass of about
750 tonnes or more. But I think that TSTO makes
much more economic sense for the near future. TSTO
can be much smaller--with proportionately smaller
payload, of course. With some TSTO concepts, I think
that operations can also be superior to any SSTO that
is likely to be practical for a long time to come.

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

"Larry Gales" wrote in message
news:Pine.WNT.4.56.0308302326280.2728@homecomps...

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 fueland so has 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

Please review this thread for another, more detailed, SSTO concept using
NK-33s and a wet wing.

http://www.google.com/groups?hl=en&l...phi.com&rnum=1

I hope pasting this will work. If not, then I will paste in the entire
article. Thanks,

BobDL





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Larry Gales wrote in message news:Pine.WNT.4.56.0309042104270.2228@homecomps. ..

On Wed, 3 Sep 2003, Anthony Q. Bachler wrote:


Date: Wed, 03 Sep 2003 06:51:48 GMT
From: Anthony Q. Bachler
Newsgroups: sci.space.tech, sci.space.policy
Subject: Why is a LOX/Kero SSTO not rather easy?

You cant just 'scale up' a launch vehicle like you scale up a pizza. There
are structural factors to consider that are not necessarily linear with
vehicle size or weight. You also cant just switch materials without
testing. I dont know what problems may or may not arise, but neither do you
and that's the whole point.


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

Yes I do: it is well known that mass ratios become significantly
easier as you scale a vehicle up: some things like TPS and insulation
scale
only as the square of the size, and some other things, such as avionics,
pilot, etc scarecly increase, and air resistance is proportionaly much
less for large vehicles. This is born out in comparisons of large
versus small rockets.

Know I *don't* know for sure if this could achive a practical reusable
SSTO, but I *do* know that the mass ratio would definitely be easier
for a scaled up version.

-- Larry

I was under the impression TPS scaled linear with the mass of the
vehical. For a larger vehical, unless surface is proportional to mass,
it will plunge deeper into the atmosphere before slowing and take a
greater intensity of skin heating.

Larry Gales wrote in message news:Pine.WNT.4.56.0308302326280.2728@homecomps. ..
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 fueland so has 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

Please review this thread for another, more detailed, SSTO concept
using
NK-33s and a wet wing.

http://www.google.com/groups?hl=en&l...phi.com&rnum=1

I hope pasting this will work. If not, then I will paste in the entire
article. Thanks,

BobDL

On Tue, 9 Sep 2003, Christopher M. Jones wrote:

Date: Tue, 9 Sep 2003 00:59:16 -0500
From: Christopher M. Jones
Newsgroups: sci.space.tech, sci.space.policy
Subject: Why is a LOX/Kero SSTO not rather easy?

"Larry Gales" wrote:
I used that vehicle as a rough proof of concept, but it could never be
practical. But if you scale it up to a 3 engine vehicle, then the mass
ratio is easier to achive and the peak acceleration is about 4 gees

Oh, I'm already well sold on the concept. But it's the "sticky
bits" that you have to worry about if you actually want to do
it. A 3 engine vehicle won't really solve that due to symmetry
and redundancy issues.
--- cut/snip ---
LOX/Kero on
the otherhand has a lower Isp, so SSTOs using it as a propellant
have higher mass ratios, around 15 to 20 or so. Factor in the
existing throttle range and you're deep in the range of gee loads
thought suitable for few other than well trained fighter pilots.
And you need a good factor of 2 at least to bring it back to the
reasonable range, and that's, as they say, non-trivial.

But, it's not an insurmountable obstacle either. The main
difficulty right now is that because of the early technical
impossiblity of SSTO rocketry, all orbital rocketry has been
staged rocketry and the worldwide enterprise of orbital
rocketry has focused on solving the problems of staged
rocketry. So all the currently existing hardware and
experience in rocketry is biased toward staged rocketry.


============================
Oh, I guess the symmetry issue comes after you shut off one engine,
which I assume would be the middle engine, then to shut off the next
one you would be unbalanced. But can't gimbaling the remaining
engine take care of that? After all the shuttle starts off with a massive
imbalance due to the off-center location of the tank which chnages in
weight throught the flight.

-- Larry