An SSTO as "God and Robert Heinlein intended".

[RGClark]

There are too many questionable (borderline nonsensical) assumptions in that post to even begin parsing them all.

Let's discuss them.

Bob Clark

 

[Urwumpe]

Let's discuss them.

Bob Clark

For example "However, with modern materials this probably can be cut to half that." Now you have two choices. We go through all the uncertainty the kindergarten way:

1. Which modern materials?
2. Is it really only because of the materials or are different structural solutions also required?
3. How probable?
4. Really half?

You could also just learn working methodically. Your self-references and unstructured postings are with very high certainty not even possible to be deciphered by yourself after some days. You try to scare opposition away by pure mass of words - a tactic popular on youtube. Who should give you criticism if this means spending one hours analyzing your text?


Seriously: If I would be the assistant of your university professor, such a homework or other written document would return to you with maximal a 10% score. Not because you are automatically wrong and your argumentations always lousy. I can't read your text in realistic time and gain an insight in your methodology. Your text is not really helping understanding your math, your math simply acts to increase the noise and make the text more confusing to read. a standard book on how to formulate scientific texts, especially regarding mathematics isn't expensive, I bought mine for 9 Euro. University courses for scientific method are free and usually even open to people with enough free time.



I don't even want to follow your references, if I already feel terribly betrayed by the arguments that refers to it. I know I can expect another thing from the ice in your text to conceal that you actually did not really bother thinking about your argumentation, but still prefer doing unstructured brain dumps.


Hell, I couldn't even take your unstructured brain dumps and turn them into proper technical articles myself. It is too much work filling the gaps (see above).

 

[T.Neo]

Now take the same ET put 2 RS 68 under it strap on 2 srb's and you have cheaper and much more capable rocket.

Small detail: such a vehicle won't make it to orbit, base heating will destroy the RS-68 engine ablative nozzles.

But your point still stands. There are plenty of ways to do it; if you assume tank length remains flexible, you could for example have something like a 2-3 RS-68 core stage with an upper stage powered by something like an RL-60 or J-2 that could lift the same amount of mass as the SSTO while being much smaller (shorter, less massive- cheaper). Or you could use 1.5 staging- it will be less efficient than a two stage vehicle, but it'll still be more efficient than an SSTO (especially with heavy engines like the RS-68).

With reusable SSTO you would need bleeding edge engines, structure, landing system, thermal protection, bleeding edge everything made by using most advanced production methods. That would not be cheap. And after every flight ecerything would have to be taken apart and inspected by army of technicians.

I don't think that is a fair way of putting it. Perhaps it would be better to say: reusable SSTO with current technology requires high performance propulsion and is very marginal in lift capability/responding to changes during development.

A lot of existing launchers use pretty (I guess one could say) advanced stuff; Centaur and Falcon's pressure stabilised tanks... even the H-IIB's core engine is staged combustion. Skylon may be at a definite physical advantage to a non-airbreathing SSTO, but still has very lightweight propellant tanks and high performance engines.

Ok, so the objective may be to use 'dumber' hardware outright to reduce costs. That can be a good idea. But TSTO does not automatically correlate to less costly technology- it's just that the physics gives you more leeway to play with your costs.

IMHO only way how to make reusable space plane is to use airbreathing engines or some sort of launch assist that would cut deltaV requirements by 1 km/s or more.

How about the space shuttle?

It was a reusable spaceplane, though perhaps not a very good one. It incorperated the payload fairing, payload mount, guidance system, second stage propulsion, and even a delivery system for the payload, but didn't incorperate the second stage propellant tank.

If you mean a reusable SSTO spaceplane, then that makes more sense. But neither spaceplane or reusable need to mean SSTO, and a spaceplane doesn't even have to be integral to the launch vehicle- see Buran.

However, here is a question: say we have a reusable spaceplane, the second stage of a TSTO, with propellant tanks integrated into the spaceplane itself (unlike with STS). Could it work, or would the center of mass/center of pressure difference created by the mass of the engines in the aft of the vehicle destabilise everything?

Let's discuss them.

I will, as long as you promise to respond to what I say...

1. My first issue is that you say the rocket equation is the first and foremost mathamatical equation in spaceflight. While I agree that it is important, I am inclined to say that dollars (or Euros or Rands, if you so choose) are more important a unit of measurement than meters per second, kilograms, seconds of ISP, or kilonewtons.

2. My second issue is that I feel you understimate (or misunderstand) the technical difficulty behind launch vehicle design and operations. You can't just switch engines and stages around. You can't just create new thrust chambers and you can't just create zombie-aerospikes. If it is possible to alter say an F9 first stage into an SSTO by bolting on different engines, there are still other changes that need to be made, for example.

3. My third issue is your enthusiasm for SSTO. Yes, I know why, and yes, I know why SSTO is attractive. But it has also been discussed at length here why SSTO is unattractive. You have always only done very simple analyses of things. Going back to my first post, for example: you have never done an analysis of a complete, operational system, as it would exist in reality (apart entirely from unbridled internet speculation). Neither have you done a complete analysis of two different systems- i.e. an SSTO and TSTO, and compared them.

4. Some of your methods of estimation just don't feel right to me. I don't know though; perhaps I'm just as bad, and I don't notice... :shifty:

I think the multiple-concepts-and-comparisons-between-them bit is a very interesting subject.

 

[Urwumpe]

Also, for making the formatting a bit easier...you can write:

[ table ]Heading 1|Heading 2|Heading 3
Value 1.1|Value 1.2|Value 1.3
Value 2.2|Value 2.2| Value 2.3[/table]

(Remove the blanks in the initial tag, needed it for circumnavigating a forum bug)
For getting this:

Heading 1|Heading 2|Heading 3
Value 1.1|Value 1.2|Value 1.3
Value 2.2|Value 2.2| Value 2.3

---------- Post added at 07:44 PM ---------- Previous post was at 07:31 PM ----------

And just to say the obvious: More important than that you write a text, is that somebody can read the text.

 

[Hlynkacg]

Let's discuss them.

Bob Clark

Ok, here are a few that jumped out at me.

better than the SSME's. With the advances in ceramics necessitated by the research and test flights with the hypersonic vehicles such high temperature lightweight ceramics should be further along now than they were with the VentureStar. For instance, the method of transpiration
cooling using ceramics should make rocket engine combustion chambers and nozzles lighter and more reusable[8]. So I'll assume the total engine weight remains the same with the aerospike.

This is a baseless and most likely incorrect assumption. Even if your aerospike made out of wonder-materials performs as advertised you do not appear to have accounted for the structural modifications that would need to be made to the stage itself to accomidate the spike and repositioned engines.

An SSTO is best utilized as a reusable though. Estimates of the added weight of reentry/landing systems are in the range of 28% [9]. However, with modern materials this probably can be cut to half that. Then the payload will be reduced to about 4.5 metric tons.

I'll repeat what Urwumpe said...

*Which modern materials?
*Is it really only because of the materials or are different structural solutions also required?
*How probable?
*Where are you getting "half"?

This example illustrates well the importance of altitude compensation. Using it we are able to increase our engine Isp by 10% or more, to the extent we can achieve an SSTO with significant payload

You do realize that altitude compensation does not increase ISP correct? It simply cuts your ambient pressure losses. Have you actually plotted out your thrust curve from sea-level up through MAX-Q and back?

The modifications to the aerospike nozzle should be relatively low cost compared to designing a whole new engine so the price should still be in this range.

Speaking as an engineering student, I stopped and laughed at this point. :lol: The modifications you propose would require signifigant structural changes and re-working of the engine's auxillary components. (Fuel-pumps, cooling, etc...) Depending on how much re-design is actually required it might actually be easier to start from scratch.

Another interesting possibility is suggested by the recent report of investigations of bringing back the shuttle as a commercial satellite launcher[15],[16]. My view is that the shuttle orbiter is too heavy for that role...

Mass has very little to do with cost. The chief driver of $ per Kilogram is the number of man-hours required per launch. (and in the case of a re-usable booster recovery/refurbishment as well)

 

[Sky Captain]

However, here is a question: say we have a reusable spaceplane, the second stage of a TSTO, with propellant tanks integrated into the spaceplane itself (unlike with STS). Could it work, or would the center of mass/center of pressure difference created by the mass of the engines in the aft of the vehicle destabilise everything?

Engines would probably have to be placed on wings like on Skylon to maintain stability with empty tanks and to avoid tendency to fly tail first when empty. Or maybe some sort of clever lifting dody besign had to be used.

How about the space shuttle?

Yeah, shuttle. Howewer it was more like rebuildable than reusable. Imagine how much your plane ticket would cost if a jetliner would have to be taken apart, inspected to last part and put back together by thousands of technicians after every flight. There isn't really much difference when that army of workers are used to rebuild the reusable launch vehicle or build a new expendable rocket for every flight.
Ultimate goal for spaceplane would be airplane like operations with little maintanance between flights and major sheduled maintanance happening only at predetermined intervals like it is with commercial aircraft.

 

[T.Neo]

Engines would probably have to be placed on wings like on Skylon to maintain stability with empty tanks and to avoid tendency to fly tail first when empty. Or maybe some sort of clever lifting dody besign had to be used.

How is it possible to mathematically figure out if a vehicle could be more or less stable throughout reentry and landing? I think this is what is needed here...

Yeah, shuttle. Howewer it was more like rebuildable than reusable. Imagine how much your plane ticket would cost if a jetliner would have to be taken apart, inspected to last part and put back together by thousands of technicians after every flight. There isn't really much difference when that army of workers are used to rebuild the reusable launch vehicle or build a new expendable rocket for every flight.
Ultimate goal for spaceplane would be airplane like operations with little maintanance between flights and major sheduled maintanance happening only at predetermined intervals like it is with commercial aircraft.

Since when was the STS orbiter rebuilt through every reuse cycle? "Taken apart, inspected to the last part and put back together"?

I'm pretty sure that while STS required a very extensive refurbishment, and that certain components (i.e. engines) needed to be stripped down and rebuilt after each flight, this sort of thing never happened on the total system level.

 

[RGClark]

Also, for making the formatting a bit easier...you can write:

[ table ]Heading 1|Heading 2|Heading 3
Value 1.1|Value 1.2|Value 1.3
Value 2.2|Value 2.2| Value 2.3[/table]

(Remove the blanks in the initial tag, needed it for circumnavigating a forum bug)
For getting this:

Heading 1|Heading 2|Heading 3
Value 1.1|Value 1.2|Value 1.3
Value 2.2|Value 2.2| Value 2.3

---------- Post added at 07:44 PM ---------- Previous post was at 07:31 PM ----------

And just to say the obvious: More important than that you write a text, is that somebody can read the text.

I separated the post into titled sections to improve readability. I wanted to be able to indent the beginning of each paragraph but the

function while it can indent the first line in a paragraph, it also inserts an extra line afterwards which is not what I wanted.
Anyone know how to do usual indenting of a paragraph?


Bob Clark​

 

[T.Neo]

Good. The formatting of your post has greatly improved, however, the quality of its content is still the same.

RGClark, I suggest (and not out of jest or sarcasm) that you do a simple cost comparison between a reusable TSTO and reusable SSTO. The conditions are that you have to show your work, and cite proper sources (i.e. NASA studies and technical papers, AIAA studies, etc) and not just things like space news websites. You cannot make baseless, referenceless and dubious claims (i.e. 'with modern materials, this can be reduced by half'). You have to show the reasoning behind the methods you use and your assumptions.

Good luck. And have fun!

 

[Hlynkacg]

How is it possible to mathematically figure out if a vehicle could be more or less stable throughout reentry and landing? I think this is what is needed here...

Oh it's possible, but I don't see anyone busting out 3D vector calculus on this thread. :lol:

 

[Urwumpe]

Oh it's possible, but I don't see anyone busting out 3D vector calculus on this thread. :lol:

It also depends on which demands you have on stability. A F-16 is very instable without FCS, but perfectly designed for its job.

The better question is: Which demands does the stability of a rocket put on its control systems and how does this reflect in mass?

 

[RGClark]

Good. The formatting of your post has greatly improved, however, the quality of its content is still the same.

RGClark, I suggest (and not out of jest or sarcasm) that you do a simple cost comparison between a reusable TSTO and reusable SSTO. The conditions are that you have to show your work, and cite proper sources (i.e. NASA studies and technical papers, AIAA studies, etc) and not just things like space news websites. You cannot make baseless, referenceless and dubious claims (i.e. 'with modern materials, this can be reduced by half'). You have to show the reasoning behind the methods you use and your assumptions.

Good luck. And have fun!

The cost comparisons to currently existing vehicles come on two fronts. (There is little debate that a reusable SSTO would have lower operational costs than a TSTO one if it exists. The debate is whether its lower payload would make it worthwhile.)
First, a key problem for reducing the cost of spaceflight is that it can only come from reusability. But, the argument goes, reusable spacecraft are more expensive to develop and you need many launches to make that expense worthwhile. Where's the market for that?
As I argued before for small SSTO's a large market would be for small privately owned manned SSTO's. In the examples in the post copied at the bottom of the prevous post, both the engines and the lightweight stage already existed. It is only required to marry them together. The cost? How much do you estimate to develop a launcher the size of a small business jet when the rocket engines and the primary structure already exists? How much do you estimate it cost to develop Falcon 1?
Furthermore for any estimates of rocket launchers it has to be kept in mind such estimates are based on the costs of government financed vehicles in the past.

The most important accomplishment of SpaceX may turn out to be they showed in stark terms that a privately developed spacecraft can be developed for 1/10th the cost of government financed ones.

The importance of this can not be overemphasized. So if you estimate a manned launcher may take $3 billion to develop, divide this by 10 to get an idea what it really should cost if privately financed.

Secondly, as mentioned in this thread a large portion of launch costs are because of operational costs due to the large labor costs as run as a government program. For the space shuttle this is literally thousands of people to run it. This has been recognized for a while. A key part of the proposal to cut launch costs for the VentureStar reusable launcher was to cut majorly this required labor force:

Lockheed Secret Projects: Inside the Skunk Works.
By Dennis R. Jenkins

One of the conclusions from the DC-X demonstration program was that it should not take a standing army to operate a launch vehicle. Almost 18,000 workers are employed to maintain and operate the space shuttle fleet, and it takes 60 to 70 days to prepare a shuttle for a new mission. By contrast, the X-33 will require only about 50 and have a 48-hour turnaround, and the VentureStar will require under 300 people and have a turnaround of less than one week. NASA and industry estimate the cost for each flight of a full-scale RLV will be about one-tenth as much as the space shuttle, or roughly $50 million each.

http://books.google.com/books?id=DU... venturestar&lr=&pg=PA106#v=onepage&q=&f=true

Elon Musk also recognized the need to cut the size of the ground crew:

The Rocketeers. How a Visionary Band of Business Leaders, Engineers, and Pilots is Boldly Privatizing Space.
by Michael Belfiore
HarperColins, 2007

Musk had identified five major drivers of launch vehicle costs and had set about bringing each one of those down. The first, and perhaps the biggest, was overhead. Looking around the Main Building I could see for myself that Musk ran a tight ship. He had fewer than a hundred employees, including all the engineers, machinists and associated support staff like the receptionists, administrative assistants, and a public relations officer."We are an extremely low-overhead company," said Musk. "If we simply handed our blueprints to a Boeing or Lockheed, I think the price would at least double if not more."
"There was the rocket itself, with three major components contributing to its cost: engines, structures (the actual body of the rocket as well as fuel and oxidizer tanks), and avionics - the sophisticated computers and software that controlled the other components to guide the rocket through the air to space and into orbit.
"And then there was the launch operation. Musk laughed as he told me how a Lockheed Martin representative boasted to him of his company's "lean" launch crew: only three hundred people. "Now what are those people doing? I can't tell you." Falcon 1's launch crew? Twelve to fifteen people sitting in a custom-made trailer at the launch site."

The Rocketeers, p. 175.
http://www.amazon.com/Rocketeers-Visionary-Business-Engineers-Privatizing/dp/B00381B7OG/


Bob Clark

 

[Urwumpe]

Can't tell that this impresses me a lot. The Falcon 1 did nothing more but reach orbit, something which the Scout rocket already did with a much smaller launch crew as the Falcon 1 needed. And the Russians use even less for their Dnepr launches.

If you don't need to do much, you don't need a big launch crew. And in case of the Falcon family, you can't even say that the small launch crew of it is really effective. Their big advantage is that they can afford letting their rockets catch rust on the launch pad for weeks before finally lifting off. They have no serious launch rate yet. And use NASA resources quite a lot during the launches.

 

[C3PO]

The fact SpaceX managed to develop a ELV at 1/10 of the "normal" cost doesn't guarantee that the same ratio will be possible with a manned craft, flyback stages, SSTOs, etc.
A lot of the hard lessons were learnt during those 10x$ programmes. But as SpaceX ventures into unproven methods, I bet they will run into some unexpected problems that will push up the cost.

Comparing the actual workforce for running a prototype like STS to a planned X-33 that has no final operational hardware built yet is a perfect example of nonsensical argument. I'm quite sure NASA didn't plan on that size of workforce for their once-a-week STS.

 

[RGClark]

The fact SpaceX managed to develop a ELV at 1/10 of the "normal" cost doesn't guarantee that the same ratio will be possible with a manned craft, flyback stages, SSTOs, etc.
A lot of the hard lessons were learnt during those 10x$ programmes. But as SpaceX ventures into unproven methods, I bet they will run into some unexpected problems that will push up the cost.
Comparing the actual workforce for running a prototype like STS to a planned X-33 that has no final operational hardware built yet is a perfect example of nonsensical argument. I'm quite sure NASA didn't plan on that size of workforce for their once-a-week STS.

That it was a government run program was a big reason for the run up in costs. To get support for the program you had to have all these NASA centers involved and you had to have these different subcontractors involved in all these different congressional districts that automatically drove up the labor costs. It is a major if not the major reason for the costs of the shuttle program that this veritable standing army of thousands of people still have to be paid whether you launch 1 shuttle flight in a year or 8. This is a well accepted failing of the shuttle program.
Elon Musk realized this and it was part of his business plan to do most of the work in house to have a lean operational system. It was not by accident he cut development costs by a factor of 10. It was by intent.

Bob Clark

 

[Pablo49]

Oh hello thread, outsider here. Every once and again I browse this whenever I have the patience. Just thought I would mention that your posts, RGClark, come across as silly. I really don't have much applicable knowledge regarding this so I could easily believe a well written post and yet be completely wrong, but your posts clearly come across as somewhat half-baked, sensational and in complete disregard to a lot of what others say (See above, you quoted TNeo's challenge to work out exact costs etc, and the only numbers you really mentioned were 1/10). I know you aren't trying to convince people like me who aren't knowledgeable to this, but if you can't lead a blind man, I don't think you can lead one who can see.

 

[RGClark]

Oh hello thread, outsider here. Every once and again I browse this whenever I have the patience. Just thought I would mention that your posts, RGClark, come across as silly. I really don't have much applicable knowledge regarding this so I could easily believe a well written post and yet be completely wrong, but your posts clearly come across as somewhat half-baked, sensational and in complete disregard to a lot of what others say (See above, you quoted TNeo's challenge to work out exact costs etc, and the only numbers you really mentioned were 1/10). I know you aren't trying to convince people like me who aren't knowledgeable to this, but if you can't lead a blind man, I don't think you can lead one who can see.

No offense, but I prefer to accept the opinion of the SpaceX professional engineers who have actually done it.
You are freely allowed to believe however it's just a coincidence SpaceX was able to cut development costs by a factor of 10 when that was their business plan all along.


Bob Clark

 

[Hlynkacg]

No offense, but I prefer to accept the opinion of the SpaceX professional engineers who have actually done it.
You are freely allowed to believe however it's just a coincidence SpaceX was able to cut development costs by a factor of 10 when that was their business plan all along.


Bob Clark

Annecdote does not equal data.

SpaceX was able to cut developement and launch costs by designing thier program by desinging their prgram to minimize overhead. This fact does not validate your post's other numerous flawed assumptions.

 

[RGClark]

Annecdote does not equal data.

SpaceX was able to cut developement and launch costs by designing thier program by desinging their prgram to minimize overhead. This fact does not validate your post's other numerous flawed assumptions.

The importance of their accomplishment is that they showed space costs do not have to be as expensive as commonly believed. One of the key cuts in overhead as Elon has admitted was by keeping labor costs low.
Elon also believes he can cut the costs to space to the $100 to $200 per kg range by reusability. Based on his track record I'd say it's a good bet he's probably right.


Bob Clark

 

[Hlynkacg]

The importance of their accomplishment is that they showed space costs do not have to be as expensive as commonly believed. One of the key cuts in overhead as Elon has admitted was by keeping labor costs low.
Elon also believes he can cut the costs to space to the $100 to $200 per kg range by reusability. Based on his track record I'd say it's a good bet he's probably right.


Bob Clark

That may be, but it has little to nothing to do with engineering challenges behind building a SSTO "as God and Robert Heinlein intended".