The Coming SSTO's.

[RGClark]

Recently announced:

---------------------------------------------------------------------
Boeing proposes SSTO system for AF RBS program.
The new issue of Aviation Week has a brief blurb about a Boeing
proposal for the Air Force's Reusable Booster System (RBS) program:
Boeing Offers AFRL Reusable Booster Proposal - AvWeek - June.13.11
(subscription required).
Darryl Davis, who leads Boeing's Phantom Works, tells AvWeek that they
are proposing a 3-4 year technology readiness assessment that would
lead up to a demonstration of a X-37B type of system but would be
smaller. Wind tunnel tests have been completed. Davis says the system
would be a single stage capable of reaching low Earth orbit and, with
a booster, higher orbits. The system would return to Earth as a
glider.
Davis says "that advances in lightweight composites warrant another
look" at single-stage-to-orbit launchers.
http://www.hobbyspace.com/nucleus/index.php?itemid=30110
---------------------------------------------------------------------

It is my contention that the reason why launch costs are so high, the
reason why we don't have passenger access to space as routine as say
trans-Pacific flights is that the idea has been promulgated that SSTO
is impossible. That is not the case. In fact it is easy, IF you do it
in the right way. The right way is summarized in one simple
statement:
If you use both weight optimized structures and highest efficiency
engines at the same time, then what you wind up with will be SSTO
capable whether you intend it to or not.
We all know that to get a good payload to space you want a high
efficiency engine. And we all know we want to use lightweight
structures so the weight savings can go to increased payload. So you
would think it would be obvious to use both these ideas to maximize
the payload to orbit, right?
And indeed both have been used together - for upper stages. Yet this
fundamentally obvious concept still has not been used for *first
stages*. It is my thesis that if you do this, then what you wind up
with will automatically be SSTO capable. This is true for either
kerosene fueled or hydrogen fueled stages.
Part of the misinformation that has been promulgated is that the mass
ratio for SSTO's is some impossible number. This is false. We've had
rocket stages with the required mass ratio's since the 60's, nearly 50
years, both for kerosene and hydrogen fueled. Another part of the
misinformation is that it would require some unknown high energy fuel
and engine to accomplish. This is false. The required engines have
existed since the 70's, nearly 40 years, both for kerosene and
hydrogen fueled.
What has NOT been done is to marry the two concepts together for
first stages. All you need to do is swap out the low efficiency
engines that have been used for the high mass ratio stages and replace
them with the high efficiency engines. It really is that simple.
This makes possible small, low cost orbital vehicles that could
transport the same number of passengers as the space shuttle, about 7,
but would have a comparable cost to a mid-sized business jet, a few
tens of millions of dollars.
Then once you have the SSTO's they make your staged vehicles even
better because you can carry greater payload when they are used for
the individual stages of the multi-staged vehicle.
In disseminating the false dogma that SSTO's are not possible it is
sometimes said instead that they are not practical because the payload
fraction is so small. Even this is false. And indeed this is just as
damaging as making the false statement they are not possible because
the statements are often conflated into meaning the same thing. So
when those in the industry make the statement they are not
"practical", meaning actually they are doable but not economical, this
becomes interpreted among many space enthusiasts and even many in the
industry as meaning it would require some revolutionary advance to
make them possible.
The fact that you can carry significant payload to orbit using SSTO's
can be easily confirmed by anyone familiar with the rocket equation.
To get a SSTO with significant payload using efficient kerosene
engines you need a mass ratio of about 20 to 1. And to get a SSTO with
significant payload using efficient hydrogen engines you need a mass
ratio of about 10 to 1. Both of these the high mass ratio stages and
the high efficiency engines for both kerosene and hydrogen have
existed for decades now.
See this list of rocket stages:

Stages Index.
http://www.friends-partners.org/partners/mwade/stages/staindex.htm

Among the kerosene-fueled stages you see that several among the Atlas
and Delta family have the required mass ratio. However, for the early
Atlas stages you have to be aware of the type of staging system they
used. They had drop-off booster engines and a main central engine,
called the sustainer that continued all the way to orbit. But even
when you take this into account you see these highly weight optimized
stages had surprisingly high mass ratios.
See for instance the Atlas Agena SLV-3:

SLV-3 Atlas / Agena B.
Family: Atlas. Country: USA. Status: Hardware. Department of Defence Designation: SLV-3.
Standardized Atlas booster with Agena B upper stage.
Specifications
Payload: 600 kg. to a: 19,500 x 103,000 km orbit at 77.5 deg inclination trajectory.

Stage Number: 0. 1 x Atlas MA-3 Gross Mass: 3,174 kg. Empty Mass: 3,174 kg. Thrust (vac): 167,740 kgf. Isp: 290 sec. Burn time: 120 sec. Isp(sl): 256 sec. Diameter: 4.9 m. Span: 4.9 m. Length: 0.0 m. Propellants: Lox/Kerosene No Engines: 2. LR-89-5
Stage Number: 1. 1 x Atlas Agena SLV-3 Gross Mass: 117,026 kg. Empty Mass: 2,326 kg. Thrust (vac): 39,400 kgf. Isp: 316 sec. Burn time: 265 sec. Isp(sl): 220 sec. Diameter: 3.1 m. Span: 4.9 m. Length: 20.7 m. Propellants: Lox/Kerosene No Engines: 1. LR-105-5
Stage Number: 2. 1 x Agena B Gross Mass: 7,167 kg. Empty Mass: 867 kg. Thrust (vac): 7,257 kgf. Isp: 285 sec. Burn time: 240 sec. Isp(sl): 0 sec. Diameter: 1.5 m. Span: 1.5 m. Length: 7.1 m. Propellants: Nitric acid/UDMH No Engines: 1. Bell 8081
http://www.friends-partners.org/partners/mwade/lvs/slvgenab.htm

Looking at only the gross mass/empty mass of stage 1, you would think this
stage had a mass ratio close to 50 to 1. But that is only including the
sustainer engine. The more relevant ratio would be when you add in the
mass of the jettisonable booster engines to the dry mass since they are
required to lift the vehicle off the pad. These are contained within the stage 0
mass at 3,174 kg. This makes the loaded mass now 117,026 + 3,174 =
120,200 and the dry mass 2,326 + 3,174 = 5,500 kg, for a mass ratio of
21.85.
But this was using the low efficiency engines available in the early
60's. Let's swap these out for the high efficiency NK-33 [1]. The
sustainer engine used was the LR-105-5 [2] at 460 kg. At 1,220 kg the
NK-33 weighs 760 kg more. So removing both the sustainer and booster
engines to be replaced by the NK-33 our loaded mass becomes 117,786 kg
and the dry mass 3,086 kg, and the mass ratio 38.2 (!).
For the trajectory-averaged Isp, notice this is not just the midpoint
between the sea level and vacuum value, since most of the flight to
orbit is at high altitude at near vacuum conditions. A problem with
doing these payload to orbit estimates is the lack of a simple method
for getting the average Isp over the flight for an engine, which
inhibits people from doing the calculations to realize SSTO is
possible and really isn't that hard. I'll use a guesstimate Ed Kyle
uses, who is a frequent contributor to NasaSpaceFlight.com and the
operator of the Spacelaunchreport.com site. Kyle takes the average Isp
as lying 2/3rds of the way up from the sea level value to the vacuum
value [3]. The sea level value of the Isp for the NK-33 is 297 s, and
the vacuum value 331 s. Then from this guesstimate the average Isp is
297 + (2/3)(331 - 297) = 319.667, which I'll round to 320 s.
Using this average Isp and a 8,900 m/s delta-V for a flight to orbit,
we can lift 4,200 kg to orbit:

320*9.8ln((117,786+4,000)/(3,086+4,000)) = 8,919 m/s. This is a
payload fraction of 3.3%, comparable to that of many multi-stage
rockets.
Note in fact that this has a very good value for a ratio that I
believe should be regarded as a better measure, i.e., figure of merit,
for the efficiency of a orbital vehicle. This is the ratio of the
payload to the total dry mass of the vehicle. The reason why this is a
good measure is because actually the cost of the propellant is a minor
component for the cost of an orbital rocket. The cost is more
accurately tracked by the dry mass and the vehicle complexity. Note
that SSTO's in not having the complexity of staging are also good on
the complexity scale.
For the ratio of the payload to dry mass you see this is greater than
1 for this SSTO. This is important because for every orbital vehicle I
looked at, and possibly for every one that has existed, this ratio is
going in the other direction: the vehicle dry mass is greater than the
payload carried. Often it is much greater. For instance for the space
shuttle system, the vehicle dry mass is more than 12 times that of the
payload.
This good payload fraction and even better payload to dry mass ratio
was just by using the engine in its standard configuration, no
altitude compensation. However, for a SSTO you definitely would want
to use altitude compensation. Dr. Bruce Dunn in his report "Alternate
Propellants for SSTO Launchers" [4] estimates an average Isp of 338.3
s for high performance kerosene engines when using altitude
compensation. Then we could lift 5,300 kg to orbit:

338.3*9.8ln((117,786+5,300)/(3,086+5,300)) = 8,906 m/s.

But kerosene is not the most energetic hydrocarbon fuel you could
use. Dunn in his report estimates an average Isp of 352 s for
methylacetyene using altitude compensation. This would allow a payload
of 6,300 kg : 352*9.8ln((117,526+6,300)/(3,086+6,300)) = 8,900 m/s.


Bob Clark


REFERENCES.
1.)NK-33.
http://www.friends-partners.org/partners/mwade/engines/nk33.htm

2.)LR-105-5.
http://www.friends-partners.org/partners/mwade/engines/lr1055.htm

3.)EELV Solutions for VSE.
Reply #269 on: 11/05/2007 09:20 PM
http://forum.nasaspaceflight.com/index.php?topic=10497.msg208875#msg208875

4.)Alternate Propellants for SSTO Launchers.
Dr. Bruce Dunn
Adapted from a Presentation at:
Space Access 96
Phoenix Arizona
April 25 - 27, 1996
http://www.dunnspace.com/alternate_ssto_propellants.htm

Disclaimer: the citing of a particular reference should not be
construed as an endorsement by the cited authors of the viewpoint
expressed herein.

 

[RGClark]

It would be a truly watershed moment just creating a SSTO even if it doesn't carry much payload. It wouldn't have to be anything extensive like perhaps what Boeing is planning with their X-37B derived SSTO.
A small one could be demonstrated by amateur science or technical organizations, for instance by the British Interplanetary Society, or the Planetary Society.
The Planetary Society is spending about $5.8 million total on their two attempts at solar sail demonstators:

Cosmos 1.
http://en.wikipedia.org/wiki/Cosmos_1

LightSail-1.
http://en.wikipedia.org/wiki/LightSail-1#Creation

A small SSTO demonstrator that could carry a few hundred pound payload could be developed for less than this amount and would be far more important for it would show that low cost SSTO's are possible.
In fact the organization developing it could even make money on it because they could use it to launch small scientific payloads.



Bob Clark

 

[sferrin]

Gotta start somewhere.

 

[Grey Havoc]

Perhaps something along the lines of the Delta Clipper? DCX did pave the way before NASA wasted it testing that infamous fuel tank, among other things, for the VentureStar program. Although Blue Origin is trying to build on the DCX technology, I'm not sure that they will be successful, at least not in the limited time they have left before the current administration is likely to be shown the road with the ensuing political and bureaucratic bloodbath.

 

[Orionblamblam]

It is my contention that the reason why launch costs are so high, the
reason why we don't have passenger access to space as routine as say
trans-Pacific flights is that the idea has been promulgated that SSTO
is impossible.

1: SSTO has been known to be possible since at least 1947.
2: The high cost of rocketry has nothing to do with SSTO. Any technlogy that would make SSTO practical would make a fully reusable TSTO substantially cheaper than the SSTO.

 

[archipeppe]

1: SSTO has been known to be possible since at least 1947.
2: The high cost of rocketry has nothing to do with SSTO. Any technlogy that would make SSTO practical would make a fully reusable TSTO substantially cheaper than the SSTO.

I fully agree with you.

NASA could have TSTO at least twice: the first time in 1969-71 timeframe during the STS early development phase, and the second time in 1985-88 timeframe during the Shuttle-II development phase. In both cases technology of that times could sustain such achievement.

 

[shockonlip]

...
Any technlogy that would make SSTO practical would make a fully reusable TSTO substantially cheaper than the SSTO.

If a SSTO is practical for a mission, why would I want a TSTO for it?

Ether part of the TSTO is not suitable by itself.

SSTO's will be thought of as aircraft are today, but to coin Gen. LeMay, TSTO's are a formation !

And it will be true that I can turn a SSTO into a TSTO. But I can't do the opposite.

 

[Grey Havoc]

Well, if it's just as a personnel ferry, with a secondary luggage/light cargo capability, then you can argue that the technology is already there (ie. Delta Clipper). For heavier, larger cargo, a TSTO such as the NASA-Langley/GRC 'Spacejet' (series of subsonic-staged parallel-lift launch vehicle designs) would seem to be viable in the current environment, while for outsized/higher mass cargo, a large shuttle/ shuttle tech derived design or other heavy lifter would appear to be best suited.

 

[Orionblamblam]

If a SSTO is practical for a mission, why would I want a TSTO for it?

Because for equivalent levels of technology, a TSTO would be cheaper and more reliable than an SSTO. SSTO will *always* require a greater mass ratio than either stage of a TSTO, meaning that SSTO will always have to be more of an eggshell than TSTO. This means that SSTO will always have to be built to finer tolerances and lower redundancy than TSTO. Meaning more expensive, more prone to damage.

Ether part of the TSTO is not suitable by itself.

So? That's like arguing that a cargo shipping system that requires a container ship across an ocean *and* a truck from the dock to the final customer has too many componants and what the world really needs is an amphibious cargo transport system that can go stright from Hong Kong to Kansas.

And if you build a TSTO and get hit with weight growth during the process, that's bad news. If you build an SSTO and get hit with weight growth, that's a *disaster.*

 

[shockonlip]

When we say that a SSTO is practical for a mission, that means (to me) that it is a done deal.

It is already developed and presented to the market as available for a specific mission or
missions and has been found "practical" for those mission(s).

So arguments that SSTO requires greater mass ratio, and SSTO will be more of an eggshell,
and SSTO has finer tolerances, while maybe true, are just statements describing the
"practical" SSTO.

And SSTO getting hit with disasterous weight growth is now moot as the SSTO is available
and practical for the mission. The weight for SSTO orbit is now placarded and known.

My point is, if such a SSTO is available for purchase for such a mission or missions, why would
I ever buy a TSTO instead for that mission or missions?

Plus as I said the SSTO could potentially also be designed to support different missions as
a TSTO.

I agree SSTO's are harder to make practical, but I agree with RGClark that it would be a
wonderful moment for one to actually perform the SSTO and back mission with even a toothbrush
as payload, and be that rocket or airbreather or a mixture of both (most probably), that would be
a GREAT and celebrated moment and the dawn of a new age.

 

[Orionblamblam]

I agree SSTO's are harder to make practical, but I agree with RGClark that it would be a
wonderful moment for one to actually perform the SSTO and back mission with even a toothbrush
as payload, and be that rocket or airbreather or a mixture of both (most probably), that would be
a GREAT and celebrated moment and the dawn of a new age.

Meh.

Shuttle and Pegasus both used reusable componants... and wound up being just about the most *expensive* ways of getting to space that mankind has yet devised. An SSTO that can orbit and return a toothbrush might be a wonderful technological achievment, but unless it can compete economically... it's a stunt.

Too many "space fans" are more interested in the technology than the mission. What's the *mission?* Is it to orbit and return a toothbrush as economically as possible... or is it to orbit and return a toothbrush with an SSTO?

For too many people, the future *must* be a VTOL SSTO. Or it *must* be an airbreathing HTOHL SSTO spaceplane. Or *this.* Or *that.* They've made a fetish of the *design,* rather than the mission.

Assume for the sake of arguement:
1) An SSTO-based space launch economy can orbit a billion tons of payload and ten thousand passengers per year at a cost of $1000 per kilogram
2) A fully-reusable TSTO economy can do the same for $500 per kilogram.
3) A partially expendable TSTO economy can do the same for $250 per kilo.

What's best? #1 is most elegant. #3 is downright ugly. But do you want elegance, or do you want to get the job done?

 

[RGClark]

Because for equivalent levels of technology, a TSTO would be cheaper and more reliable than an SSTO. SSTO will *always* require a greater mass ratio than either stage of a TSTO, meaning that SSTO will always have to be more of an eggshell than TSTO. This means that SSTO will always have to be built to finer tolerances and lower redundancy than TSTO. Meaning more expensive, more prone to damage.
....
And if you build a TSTO and get hit with weight growth during the process, that's bad news. If you build an SSTO and get hit with weight growth, that's a *disaster.*

The advantage of a reusable SSTO is low cost for a small launcher. For instance you could have small reusable SSTO's privately owned by corporations or wealthy individuals. Most national governments could also afford to buy one. I estimate the cost for one of these small launchers would be in the range of a mid-size business jet, a few tens of millions of dollars. Then you would really have space travel truly becoming common place.
It is true you could carry more payload by staging. However, you can carry even more payload if those individual stages of your multistage system are SSTO capable because that means each stage necessarily has to be both weight optimized and use the most efficient engines.
Then why not use one of those single stage to carry a small payload to orbit if you don't need the larger more expensive multi-stage system? You don't hire a tractor trailer to move a mattress and box spring. You hire a pick up truck.
Here's another way of looking at it. You can also carry more payload using three stages than two stages. But that certainly does not mean two stage systems can't have operational and cost advantages over three stage systems, as proven by SpaceX with their two stage launchers.
And here's another indication of this fact. Virgin Galactic is planning to use two stages for their suborbital tourism venture at a price point of $200,000 per passenger. But Xcor with the single stage Lynx vehicle is planning to offer suborbital flights at only $100,000 per passenger. The development costs and operational costs are lower for the smaller single stage system.

Bob Clark

 

[Orionblamblam]

The advantage of a reusable SSTO is low cost for a small launcher.

Then TSTO would be even better, since the launcher would be smaller for the same payload.

It is true you could carry more payload by staging. However, you can carry even more payload if those individual stages of your multistage system are SSTO capable because that means each stage necessarily has to be both weight optimized and use the most efficient engines.

Packing in every last milligram of paylaod performacne is the surest way to drive costs through the ceiling.

You don't hire a tractor trailer to move a mattress and box spring. You hire a pick up truck.

Actually, it's a safe bet that you *did* hire a tractor trailer to transport that mattress from the warehouse 1500 miles away to the store on the other side of town. And very likely hired a *ship* prior to that.

Virgin Galactic is planning to use two stages for their suborbital tourism venture at a price point of $200,000 per passenger. But Xcor with the single stage Lynx vehicle is planning to offer suborbital flights at only $100,000 per passenger. The development costs and operational costs are lower for the smaller single stage system.

Due in no small part to the fact that Xcor is *not* trying to create the most technologically advanced system. Xcor, in fact, endeavors to create the most *operational* systems. This means rockets that run all day long without exploding. This also means that their Isp isn't quite as high as it could be, and the dry weight is heavier than in could be. They trade performance for economics. Additionally, if Xcor of Scaled Composites fall 1% short of their performance goals... meh. Who'd notice a few seconds less freefall? But if they fell a percent short on trying to get to orbit...

In other words... you're making my point for me.

 

[shockonlip]

I agree SSTO's are harder to make practical, but I agree with RGClark that it would be a
wonderful moment for one to actually perform the SSTO and back mission with even a toothbrush
as payload, and be that rocket or airbreather or a mixture of both (most probably), that would be
a GREAT and celebrated moment and the dawn of a new age.

Meh.

Shuttle and Pegasus both used reusable componants... and wound up being just about the most *expensive* ways of getting to space that mankind has yet devised. An SSTO that can orbit and return a toothbrush might be a wonderful technological achievment, but unless it can compete economically... it's a stunt.

Too many "space fans" are more interested in the technology than the mission. What's the *mission?* Is it to orbit and return a toothbrush as economically as possible... or is it to orbit and return a toothbrush with an SSTO?

For too many people, the future *must* be a VTOL SSTO. Or it *must* be an airbreathing HTOHL SSTO spaceplane. Or *this.* Or *that.* They've made a fetish of the *design,* rather than the mission.

Assume for the sake of arguement:
1) An SSTO-based space launch economy can orbit a billion tons of payload and ten thousand passengers per year at a cost of $1000 per kilogram
2) A fully-reusable TSTO economy can do the same for $500 per kilogram.
3) A partially expendable TSTO economy can do the same for $250 per kilo.

What's best? #1 is most elegant. #3 is downright ugly. But do you want elegance, or do you want to get the job done?

You're giving the same old arguments for why you'd "design" a TSTO instead of a SSTO.
The original statement was that a SSTO is "practical". Therefore SSTO works already.
If SSTO works then there exists applications where I would say, I don't want all the other stuff I have to buy for TSTO.
Why should I need two sets of landing gear parts, and tires, two sets of different types of engines with attendant parts and spares,
two sets of airframe parts (one orbital capable and one not). Two sets of avionics (space capable and not) and attendant parts, plus
the training (space rated and not) and space to store all this stuff, and the time to maintain two sets of systems. Instead of one set
of systems that does it all. TSTO doesn't sound that cheap!
So you can hopefully see that if presented a practical SSTO, it makes sense, and will only continue to make more sense over time.
Thus it should be developed. Glad you thought of it !! Good work dude!

 

[Orionblamblam]

You're giving the same old arguments for why you'd "design" a TSTO instead of a SSTO.
The original statement was that a SSTO is "practical". Therefore SSTO works already.

And therefore a TSTO is even *more* practical.

A technology that makes SSTO cheap and reliable but somehow does not do the same and better for TSTO not only does not exist, it is counter-logical.

 

[sublight]

....meaning that SSTO will always have to be more of an eggshell than TSTO. This means that SSTO will always have to be built to finer tolerances and lower redundancy than TSTO. Meaning more expensive, more prone to damage.

I think this statement is the clincher. If its relevance isn't obvious then there is no point in continuing to argue.

Don't let it go to your head Scott. You're still wrong about that "other" issue.....

 

[GeorgeA]

Also, either stage has (conceptually) utility as an independent system, i.e., a TSTO first stage can be used for some types of in-atmosphere missions such as a boost-glide weapons launcher, or a TSTO second stage can be launched on an expendable booster.

 

[Orionblamblam]

You're still wrong about that "other" issue.....

I'll be deep in the cold, cold ground before I recognize Missouri.

 

[RGClark]

The advantage of a reusable SSTO is low cost for a small launcher.

Then TSTO would be even better, since the launcher would be smaller for the same payload.

So you're saying SpaceX would be better off building a three stage system since it would be smaller for the same payload?
And Xcor would be better off making their Lynx suborbital craft two stages since it would be smaller for the same number of passengers?


Bob Clark

 

[RGClark]

...
Packing in every last milligram of paylaod performacne is the surest way to drive costs through the ceiling.

The point is that it's not that hard. The Centaur upper stage has been doing what I'm suggesting for years. It is still the best upper stage on the market. It does this by using both weight optimized structures and most highly efficient engines at the same time.
If you do the same for a first stage then what you get will automatically be SSTO capable.


Bob Clark

 

[RGClark]

Virgin Galactic is planning to use two stages for their suborbital tourism venture at a price point of $200,000 per passenger. But Xcor with the single stage Lynx vehicle is planning to offer suborbital flights at only $100,000 per passenger. The development costs and operational costs are lower for the smaller single stage system.

Due in no small part to the fact that Xcor is *not* trying to create the most technologically advanced system. Xcor, in fact, endeavors to create the most *operational* systems. This means rockets that run all day long without exploding. This also means that their Isp isn't quite as high as it could be, and the dry weight is heavier than in could be. They trade performance for economics. Additionally, if Xcor of Scaled Composites fall 1% short of their performance goals... meh. Who'd notice a few seconds less freefall? But if they fell a percent short on trying to get to orbit...
In other words... you're making my point for me.

Actually it is precisely because the Xcor liquid fueled engine is more efficient than the hybrid engines of Virgin Galactic that it is able to to make its suborbital flights in a single stage.

Bob Clark

 

[Byeman]

This is just another example of Clark spamming a forum with his nonviable ideas. He has done it on Usenet, BAUT, NSF, etc. People prove that his ideas are wrong and he ignores them.

 

[Orionblamblam]

If you do the same for a first stage then what you get will automatically be SSTO capable.

A Centaur would not survive re-entry. A first stage modeled on Centaur design practices would not survive the freefall to the ocean, never mind splashdown or even deployment of chutes.

 

[Orionblamblam]

So you're saying SpaceX would be better off building a three stage system since it would be smaller for the same payload?
And Xcor would be better off making their Lynx suborbital craft two stages since it would be smaller for the same number of passengers?

Somehow I don't recall saying those things.

*Decades* of trade studies have tended to show that a two-stage system is optimal for orbital flight, based on various assumptions such as structural margins, safety margins, engine types and performance.

And Xcor *has* studied a two-stage Lynx. I believe they've looked at a three-stage. Each has a place for particular missions.

 

[Orionblamblam]

This is just another example of Clark spamming a forum with his nonviable ideas. He has done it on Usenet, BAUT, NSF, etc. People prove that his ideas are wrong and he ignores them.

I knew I'd seen his tagline before: Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.

Rather than doing the math again, I found this:
http://forum.nasaspaceflight.com/index.php?topic=23703.msg679069#msg679069

Titan 2 first stage:
Inert mass 9000 lb
Gross mass 269,000 lbs
Vacuum Isp 296 sec --> Delta V= 9860 m/sec
Sea level Isp 258 --> Delta V=8590 m/sec

With SSTO performance requiring something like 9500 m/sec, a Titan II first stage, with a *lot* of modifications, *might* be able to attain orbit with approximately *zero* payload. It would need:
1: A nosecone
2: A new avionics & control system
3: An attitude control system
4: Adjustments to the engines to throttle down and perform longer, and probably stop-restart capability

None of these would be mass-free. None of these would allow recovery.

So even if you did pull it off, what would you have? A launch vehicle that would be roughly as labor intensive to operate and launch as a Titan II, at perhaps half the cost to purchase... with a small percentage of the payload. What would be the point?

 

[Triton]

I agree SSTO's are harder to make practical, but I agree with RGClark that it would be a
wonderful moment for one to actually perform the SSTO and back mission with even a toothbrush
as payload, and be that rocket or airbreather or a mixture of both (most probably), that would be
a GREAT and celebrated moment and the dawn of a new age.

Meh.

Shuttle and Pegasus both used reusable componants... and wound up being just about the most *expensive* ways of getting to space that mankind has yet devised. An SSTO that can orbit and return a toothbrush might be a wonderful technological achievment, but unless it can compete economically... it's a stunt.

Too many "space fans" are more interested in the technology than the mission. What's the *mission?* Is it to orbit and return a toothbrush as economically as possible... or is it to orbit and return a toothbrush with an SSTO?

For too many people, the future *must* be a VTOL SSTO. Or it *must* be an airbreathing HTOHL SSTO spaceplane. Or *this.* Or *that.* They've made a fetish of the *design,* rather than the mission.

Assume for the sake of arguement:
1) An SSTO-based space launch economy can orbit a billion tons of payload and ten thousand passengers per year at a cost of $1000 per kilogram
2) A fully-reusable TSTO economy can do the same for $500 per kilogram.
3) A partially expendable TSTO economy can do the same for $250 per kilo.

What's best? #1 is most elegant. #3 is downright ugly. But do you want elegance, or do you want to get the job done?

Very well said. Many space evangelists and aerospace enthusiasts have become enamored by the technology or form of these vehicles and have lost sight of their true function or purpose.

 

[Orionblamblam]

Many space evangelists and aerospace enthusiasts have become enamored by the technology or form of these vehicles and have lost sight of their true function or purpose.

It's easy to do. In the days of the Delta Clipper, I would have swore up and down that the only way we could get a spacefarign civilization was with VTOL SSTO's. Then when I was hired to work on an HTOL TSTO... why, clearly *that* was the only way to go. And as I've matured and grown the hell up, the thing I've realized is... We Just Don't Know. Because nobody has actually build one of these things with the serious intent of low cost and high reliability.

Anybody who claims that Scheme XYZ is the best is... full of crap. We just don't know. What we *do* know is that some things are possible, because they've been done. Some things are almost certainly possible, because we've come close. Some things *might* work, and others are very much an open questions. Abandoning "what we know works" in favor of "what's almost certainly possible" might be sensible. But abandoning it in favor of "well, the math says it *might* work" is insanity. Abandoning chemical rockets in favor of scramjets all the way to Mach 25. Abandoning fission powerplants in favor of fusion.

Those things that are at the outer edge of "math sez yes" are perfectly fine things for organizations like NASA to devote efforts to by way of X-planes and the like. But they are *not* good ideas for actually *planning* purposes.

 

[shockonlip]

You're giving the same old arguments for why you'd "design" a TSTO instead of a SSTO.
The original statement was that a SSTO is "practical". Therefore SSTO works already.

And therefore a TSTO is even *more* practical.

A technology that makes SSTO cheap and reliable but somehow does not do the same and better for TSTO not only does not exist, it is counter-logical.

Yes, and you're Aunt Millie makes a fine cup of tea!

 

[shockonlip]

....meaning that SSTO will always have to be more of an eggshell than TSTO. This means that SSTO will always have to be built to finer tolerances and lower redundancy than TSTO. Meaning more expensive, more prone to damage.

I think this statement is the clincher. If its relevance isn't obvious then there is no point in continuing to argue.

Jeez! How is that a clincher ?

Given a SSTO. It's skin will be quite adequate, I guarantee you. Remember, it has to withstand Mach 25 reentry. And
if it's an airbreather, it will have to withstand even higher loads ! So does this sound like a weak structure/skin to
you?

The point is, if you develop a SSTO, it's structure/skin has to be adequate for the mission. If you mishandle it, then
that is your problem.

So bringing up being more prone to damage is spreading FUD. The TSTO must also be handled properly or it can be
damaged as well.

And if SSTO structure is an eggshell, it will be quite an advanced eggshell, as it has to handle air loads as well as high
temperatures. And such a thing is quite useful !

 

[shockonlip]

Very well said. Many space evangelists and aerospace enthusiasts have become enamored by the technology or form of these vehicles and have lost sight of their true function or purpose.

Yea, right!

I'm guilty of being a technology evangelist (I develop technology in my day job and am quite good at it - you and the aerospace
community are actually benefiting from it), and I am also an aerospace enthusiast. I thought that's what we all were here.

Just like I have this radar that guides me in my day job, that same radar is taking me towards SSTO technology in the future.

Fighting against it is fruitless.

At the very least it keeps me out of the strip clubs and therefore maybe more of a benefit to society.

Regards.

 

[sferrin]

Very well said. Many space evangelists and aerospace enthusiasts have become enamored by the technology or form of these vehicles and have lost sight of their true function or purpose.

Yea, right!

I'm guilty of being a technology evangelist (I develop technology in my day job and am quite good at it - you and the aerospace
community are actually benefiting from it), and I am also an aerospace enthusiast. I thought that's what we all were here.

Just like I have this radar that guides me in my day job, that same radar is taking me towards SSTO technology in the future.

Fighting against it is fruitless.

At the very least it keeps me out of the strip clubs and therefore maybe more of a benefit to society.

Regards.

And cost? The more you have to optimize and shave weight the higher the costs go. On the other hand, how many flights would a SSTO have to fly to make up for the expense of throwing all the expensive hardware into the Atlantic? (Even expendable stuff isn't cheap.)

 

[shockonlip]

I am having the hardest time explaining my point.

Look, part of Scott's original statement was:
" Any technlogy that would make SSTO practical would make a fully reusable TSTO substantially cheaper than the SSTO."

Notice that Scott said: "Any technlogy that would make SSTO practical". I thought this was interesting from an argument
standpoint. In other words say that SSTO are "PRACTICAL". Is the rest of his statement true? In other words, were not
arguing about whether a SSTO can be built. We're saying one HAS BEEN BUILT (because it's "practical" - they aren't
"practical" today).

So thinking about it:
1. I then asked. Well if SSTOs are practical, then would I still want a TSTO? I was thinking of a SSTO to carry a few people
on a joyride to orbit and back, not a large payload orbiter. Think of all the extra junk I'd have to have with a TSTO.
I mentioned two sets of landing gear parts, tires, two sets of different types of engines with attendant parts and spares,
two sets of airframe parts (one orbital capable and one not). Two sets of avionics (space capable and not) and attendant
parts, plus the training (space rated and not) and space to store all this stuff, and the time to maintain two sets of systems.
Instead of one set of systems that does it all. Is TSTO beginning to sound more expensive than my 2 people joyride SSTO?
It does to me ! Plus what if one part of my TSTO is down? I can't go then. I'd have to get it fixed. Of course my SSTO could
be down but then I'd also get it fixed. But with a TSTO I have two vehicles that can break. But the SSTO is individually more
complex than either part of the TSTO, true, but, it also depends on the complexity of the TSTO. And you know what? I then
realized SSTO's would drive certain changes to TSTO's for them to remain competitive. So SSTO's could be good for TSTOs.
But I didn't mention that.

2. I then realized that a SSTO can also be used as a TSTO (and I mentioned that). A TSTO can't. Therefore one can realize that
a SSTO can have some flexibility that a TSTO doesn't have. In fact, a SSTO may be a better TSTO if it can stage at a high enough
Mach number such that it can go all the way around the earth and return back to its launching base, where a TSTO may not
be able to do that (depending on certain factors), you may need a 2nd base for the TSTO booster to land at. Then ferry it back
to the launch site.

So I began to wonder if Scott's original statement:
" Any technology that would make SSTO practical would make a fully reusable TSTO substantially cheaper than the SSTO." is really
true. And I don't think it necessarily is, given the right conditions.

None of my points were responded to. Instead, this has been a discussion about developing SSTO's, not a discussion where, given
they exist, would you still want a TSTO for that mission. It's an interesting way of looking at the TSTO vs SSTO question. At least I
think so.

And you are essentially asking the same thing. Yes, SSTO development costs would be higher but once it's done, it's done.
And as stated above, this exercise assumed SSTO's are already available for at least one mission (my 2 person to orbit mission).

I'm not sure what the second part of your statement is saying about "make up for the expense of throwing all the expensive hardware
into the Atlantic?" Maybe you could explain further.

Did the above help any better with where I'm coming from?

 

[Orionblamblam]

Did the above help any better with where I'm coming from?

You seem to be trying to have a discussion about either some alternate reality, or some future date, where someone has already made an SSTO that works. Fine. What I'm pointing out is that in this alternate reality or future date with an already-build SSTO, someone *else* has built a reusable TSTO that orbits payload for less $$$ than your SSTO.

 

[Orionblamblam]

Given a SSTO. It's skin will be quite adequate, I guarantee you. Remember, it has to withstand Mach 25 reentry. And
if it's an airbreather, it will have to withstand even higher loads ! So does this sound like a weak structure/skin to
you?

Yes. "Just able to manage" is sadly going to be the design requirement for advanced launch vehicles for a long time to come, until after chemical propul.sion has been supplanted by somethign sci-fi like impulse engines or antigravity and shaving off every last gram doesn't matter anymore.

And if your SSTO is an airbreather... you're *really* doing it wrong.

And if SSTO structure is an eggshell, it will be quite an advanced eggshell, as it has to handle air loads as well as high
temperatures. And such a thing is quite useful !

Indeed it would be useful. Imagine how much better of a TSTO you could make once you've developed those neato new SSTO techs.

 

[RGClark]

The point of the matter is that the many small spacecraft and suborbital craft of lightweight composite design become high Mach suborbital, a la the X-33, when switched to using high efficiency engines. And moreover if they are scaled up by a factor of 2, then these larger versions become fully orbital vehicles.

I discuss this in regard to the Air Forces's X-37B and Sierra Nevada's Dream Chaser here:

Newsgroups: sci.space.policy, sci.astro, sci.physics, sci.space.history
From: Robert Clark <rgregorycl...@yahoo.com>
Date: Fri, 22 Jul 2011 15:09:14 -0700 (PDT)
Subject: Re: A kerosene-fueled X-33 as a single stage to orbit vehicle.
http://groups.google.com/group/sci.space.policy/msg/76507410efcbf1ea?hl=en

This is also true of the X-34 and SpaceShipOne: they become high Mach suborbital, as a single stage, when switched to high efficiency engines. And when scaled up twice as large with the high efficiency engines, they become now fully orbital single stage vehicles.
The case of SpaceShipOne is especially interesting because the twice scaled up vehicle is already built in SpaceShipTwo. Then swapping out the hybrid engines of SpaceShipTwo for high efficiency ones produces a SSTO.


Bob Clark

 

[Orionblamblam]

And imagine how useful a single stage to orbit Ford Pinto would be. All you need to do is dream up a sufficiently efficient engine.

Gah.

Sigh.

 

[RGClark]

This is just another example of Clark spamming a forum with his nonviable ideas. He has done it on Usenet, BAUT, NSF, etc. People prove that his ideas are wrong and he ignores them.

I invite responses on their viability. Some believe they will work. Some believe they won't.
The (very) near future will decide:

Boeing proposes SSTO system for AF RBS program.
The new issue of Aviation Week has a brief blurb about a Boeing proposal for the Air Force's Reusable Booster System (RBS) program: Boeing Offers AFRL Reusable Booster Proposal - AvWeek - June.13.11 (subscription required).

Darryl Davis, who leads Boeing's Phantom Works, tells AvWeek that they are proposing a 3-4 year technology readiness assessment that would lead up to a demonstration of a X-37B type of system but would be smaller. Wind tunnel tests have been completed. Davis says the system would be a single stage capable of reaching low Earth orbit and, with a booster, higher orbits. The system would return to Earth as a glider.
Davis says "that advances in lightweight composites warrant another look" at single-stage-to-orbit launchers.

http://www.hobbyspace.com/nucleus/index.php?itemid=30110


Bob Clark

 

[RGClark]

I knew I'd seen his tagline before: Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.

Rather than doing the math again, I found this:
http://forum.nasaspaceflight.com/index.php?topic=23703.msg679069#msg679069

Titan 2 first stage:
Inert mass 9000 lb
Gross mass 269,000 lbs
Vacuum Isp 296 sec --> Delta V= 9860 m/sec
Sea level Isp 258 --> Delta V=8590 m/sec

With SSTO performance requiring something like 9500 m/sec, a Titan II first stage, with a *lot* of modifications, *might* be able to attain orbit with approximately *zero* payload. It would need:
1: A nosecone
2: A new avionics & control system
3: An attitude control system
4: Adjustments to the engines to throttle down and perform longer, and probably stop-restart capability
None of these would be mass-free. None of these would allow recovery.
So even if you did pull it off, what would you have? A launch vehicle that would be roughly as labor intensive to operate and launch as a Titan II, at perhaps half the cost to purchase... with a small percentage of the payload. What would be the point?

I wanted to include a link in my sig file but I ran out of space for allowed number of characters. This is what I was referring to about the Titan II first stage:

Single-stage-to-orbit.
Examples.
http://en.wikipedia.org/wiki/Single_stage_to_orbit#Examples

It had this capability without having the lightweight materials we have now nor the high efficiency engines we have now. The point was not that it should have been made SSTO then but that the advances in materials and engines since then mean we could have a SSTO of the size of the Titan II first stage that does carry significant payload.
BTW, the 9,500 m/s delta-V is unnecessarily high. When you consider launches eastward from low latitude locations such as Cape Canaveral, you get an extra boost from the Earth's rotation. In that case the required delta-V is more like 9,200 m/s. Also there is the fact that dense fuels incur less gravity loss, so you might be able to subtract an additional 300 m/s off that for vehicles that use dense fuels such as the Titan II:

Single-stage-to-orbit.
Dense versus hydrogen fuels.
http://en.wikipedia.org/wiki/Single_stage_to_orbit#Dense_versus_hydrogen_fuels


Bob Clark

 

[shockonlip]

Did the above help any better with where I'm coming from?

You seem to be trying to have a discussion about either some alternate reality, or some future date, where someone has already made an SSTO that works. Fine. What I'm pointing out is that in this alternate reality or future date with an already-build SSTO, someone *else* has built a reusable TSTO that orbits payload for less $$$ than your SSTO.

Not an alternate reality, just the thought experiment I thought you proposed. As I now see from your comments,
that is not what you were thinking. But no matter, I think it was an interesting question.

And I disagree that just because something is cheaper it wins the competition. For example, I may not have the
facilities to support a TSTO, which is what I was arguing, because the thought experiment made such a thing readily
visible. So I would select the SSTO when the facility cost of TSTO actually makes the TSTO more expensive than
the SSTO !

 

[Orionblamblam]

And I disagree that just because something is cheaper it wins the competition.

Sure, if we're talking about government projects. But if we're talking about *actually* low cost space launch... then "low cost" seems rather important.

Let the market decide.

For example, I may not have the
facilities to support a TSTO, which is what I was arguing, because the thought experiment made such a thing readily
visible. So I would select the SSTO when the facility cost of TSTO actually makes the TSTO more expensive than
the SSTO !

But just as we can pull "practical SSTO" directly out of our ass, so can we with "dirt-cheap easy low maintenance TSTO." If you have the facilities gig worked out so that SSTO maintenance, refurb and general upkeep is cheap and easy, there's no good reason to assume that it'd be any harder for TSTO. At worst, you'd need to hire some union goon from down at the docks to run a crane to lift stage 2 onto stage 1.

Nobody has come within a few orders of magnitude of operating a launch vehicle as an inexpensive vehicle. So until there are actual examples, all we have to go on are educated guesses and math. And the math shows that SSTO is a more difficult, dangerous and expensive prospect than TSTO.