Wednesday, September 26, 2012

Endeavor's Passing

Shuttle Endeavor above Golden Gate Bridge

I never got to see any of the Shuttles during their active service as spacecraft. Planned West Coast military launches from Vandenberg were scrubbed after the Challenger loss. I did hear the double sonic boom a couple of times  when Shuttles crossed the coast en route to landings at Edwards AFB.

And only by sheerest luck did I end up seeing Endeavor on its final piggyback flight last week: Paula happened to turn on local TV news half an hour or so before it overflew San Francisco en route to retirement in Southern California.

It was an impressive sight. But like the sight of USS Iowa passing under the same bridge, it was a somewhat melancholy occasion. What in my early adulthood was the spaceship of the future has become a spaceship of the past.

Will we see its like again?


The Shuttle program was star-crossed in multiple ways. Thus its experience does not provide a 'fair' test of reusable spacecraft. This is the good news.

First of all, it conflated the roles of experimental prototype and operational vehicle: a beta pushed into production. Its development costs were squeezed, compromising the design, and further compromised by demanding of it an enormous payload capacity.

Given all these fundamental shortcomings it is remarkable that it succeeded at all. It surely cost far more to operate over its service career than either a capsule atop a conventional rocket or a smaller, fully reusable spacecraft, refined from a prototype, would have cost - not to mention the greatest and most needless cost, two large crews. Spaceflight is dangerous, but the points of failure for both Challenger and Columbia were direct results of the flawed development process.

We cannot say how much a more robust Shuttle would have cost to operate, or how safe it would have been. All we can say is that it would have been cheaper and safer than the ones we actually flew.


Unfortunately, we can also say that a more robust Shuttle would have been - would still be - horrendously expensive to develop. The projected development cost of the original Shuttle design, circa 1969 - before the compromises mentioned above - was on order of $10 billion. This is equivalent to $60 billion in present-day dollars. Hear the deafening sound of wallets snapping shut.

And it gets worse. Assume a 30-year service lifetime, with monthly launches - less than hoped for, but a lot more human spaceflights than we have actually flown. The apportioned development cost - ignoring interest and such - thus comes to about $170 million per mission. Remember, this does not include any of the costs of actually flying the missions, or training the astronauts, or anything else: It is just the development cost leading up to the first operational flight.


There is also a line of argument, all too credible, that a truly viable reusable spacecraft - one that is cheaper in the long run than expendable rockets - is just not attainable at our techlevel. We know a lot about building large, lightweight structures, along with powerful engines able to drive them into the upper atmosphere or even into space. We can do significantly better at these things now than we could fifty years ago, but not dramatically better - an indication that our technology in these areas is pretty mature.

But getting into space is so intrinsically difficult that our normal technique involves large, expendable boosters or lower stages. Payloads are, at most, a few percent of launch weight. And the problem for reusable spacecraft is that they must carry heavy fittings, such as heat shields, along with wings and landing gear, that their expendable counterparts can do without.

A simple design burdened with these heavy fittings probably couldn't reach orbit at all. But a design refined to the point that it can reach orbit is liable to be so extreme in its specifications that it requires extensive  tear-down and inspection, and perhaps refurbishment, after every flight. Which defeats the whole point of being 'reusable.'


In all of this there is a glimmer of hope: We are not dealing here with 'cold equations' but with devils in the details, and the lines between not-quite-feasible and just-feasible are pretty fine. And even as the Shuttle rode off into the west, the US has begun operating another spaceplane, the X-37B.

This is in no sense a 'Shuttle replacement.' It is very much smaller, launched atop a conventional expendable rocket, and it is unmanned. It is also a classified DARPA project - even thought it began as a NASA project - meaning that not much is being said either about its performance or its missions. But it may well be more operationally robust than the Shuttle - in particular, safer during re-entry.

Incremental progress in mature technologies is glacially slow compared to the Moore's Law-style progress seen in tech revolutions. But in the course of this century we might (or might not!) gradually develop our launch capabilities to a level approaching what the Shuttle once hoped to achieve.

After which, things could get interesting.


Discuss.




Note: A recent, truly awesome XKCD comic has a relevant comment on space rocketry. You will have to look ... carefully ... to find it.




Another Note: Unrelated to this post, but a blog reader has done the service of converting my Planetary Climate Sim into Linux and Win32 object code.

The sim itself is designed primarily to test the effects on an Earthlike planet's climate of greater orbital eccentricity or different axial tilt. It also has some settings for different average locations within the habitable zone, greenhouse gas composition, differing proportions of ocean and land surface, and so on. But these things are far more complex, and pretty much above my pay grade.

 I don't warranty the results! And I haven't tested the Linux and Win32 versions at all - let me know how they work! I'll pass any bug reports along to the contributor.




The image of Endeavor and its 747 carrier above the Golden Gate Bridge comes, a bit paradoxically, via the Baltimore Sun.

248 comments:

«Oldest   ‹Older   201 – 248 of 248
Tony said...

Locki:

"I keep reading this and yet only 4 shuttles were built. Which is a bit confusing. What was the reason for this. If occurs to me there’s two completely contradictory explanations for the low number. Which is it?

1. If they had operated as promised (eg monthly space launches) would 4 always have been more than enough?

2. If they had operated as promised (eg cheap space launch) then they would have built a lot more to take the load."


The target turn-around time was two weeks. With a one month cycle time, four shuttles gets you 48 launches/year. Even with a two month cycle, four shuttles would have supported 24 launches/year.

"I think many of us were envisaging a Moonraker scenario with the cargo bay hold 20 astronauts in EVA and laser rifles duking it out around Drax’s space station"

Which -- no disrespect intended -- is completely ridiculous. Aside from the fact that laser rifles are magitech, nobody was going to put a Shuttle orbiter where it could even take one stray shot.

"It occurred to me that maybe the primary rationale for the huge cross range was a defensive requirement of the USAF. Eg it enables the shuttle to get the hell out of dodge if the bad guys come looking."

The rationale was as already stated -- once-around return-to-launch-site capability. It's in the public record.

"Which rather begs the question why you aren’t using expendable one shot launchers in wartime anyway …."

Because shuttle was supposed to be quickly configurable and have high dispatch reliability.

"Docking with a foreign station that is not compliant is going to be impossible I’d presume. For starters how are you even going to get in without depressurising the station?

Any clever lateral thinkers want to suggest how the Chinese may be able to get onboard the ISS if they were unwelcome?"


Enter through an airlock. It's not like the people inside have any effective means of resistance.

Tony said...

jollyreaper:

"The SpaceX commentary here isn't striking me so much as prudently conservative (which I am completely for) but old man stick in the mud."

Sometimes old men aren't sticks in the mud. They've seen the cow eat the cabbage and know how it has to be done.

"The real kicker here is that none of us personally have skin in this game aside from tax dollars we have no control over contracting for SpaceX services. This isn't like all of us in a room deciding on going in for a time-share and none of us are going to personally gain or lose regardless of what happens. At most we're like fans watching the team make a go for the championship and the thrills are vicarious."

Now that's an interesting analogy. Certainly the tax dollars are trivial, on a per capita basis. But I would argue that it's not about rooting for a team. It's about observing and coming to logical conclusions, based on the data. Maybe there's a personal interest in seeing one's opinions confirmed, but that's about the observer, not about the subject.

"They call it rocket science because it's tough. There are going to be mistakes. The rocket survived a pretty serious failure. I'm amazed that SpaceX has never lost a vehicle. That's a pretty rare record in the history of space travel."

"They" call it "rocket science" because they don't know what they're talking about. It's engineering, going all the way back to Goddard and von Braun. It is indeed tough engineering. But with all of the data available, building a rocket engine that doesn't fail in flight is actually pretty much a matter of good design principles, testing, and quality control. These days, you're supposed to have power head failures on the test stand, not on service vehicles.

WRT failures, SpaceX has had their fair share. Only 2/5 Falcon 1 flights were unqualified successes (one being an unqualified vehicle loss). Now only 3/4 of Falcon 9 flights.

Also, as previously pointed out, salvaging the vehicle for a continued few minutes of degraded service is not the objective. An unqualified success is the objective. The vehicle is expended anyway. Putting all of the payload(s) in the proper orbit is the only measure of success. Had the payload been monolithic, perhaps a heavier loaded Dragon, the mission would have been a complete failure for essentially the same reason that it was in the event -- NASA would not have been able to accept the risk of the second stage being safely disposed, WRT to ISS, and the payload would not have been boosted to its final orbit.

"SpaceX has set extraordinary goals but they've already done stuff along the way I never thought I'd see outside of fiction. Seriously. Private space flight? I'd given up on that around the same time I realized we'd never be seeing O'Neill colonies or a serious human presence in space in the PMF. The future we wanted was never going to happen. So this is a lot more than I'd ever expected. I'm grabbing the popcorn and watching with interest."

What definition of "private" are we using here? LockMart and Boeing are certainly private companies, and their rockets have all been used for commercial payloads. Perhaps you're referring to developed with private funds? Only up to a point. Falcon 1 was developed privately, but Falcon 9 was developed with NASA funding. Considering who the only likely customer is for even bigger rockets, they'll probably be developed with that particular customer's money as well. "Private" is pure hype.

Byron said...

Jollyreaper:
The SpaceX commentary here isn't striking me so much as prudently conservative (which I am completely for) but old man stick in the mud.
I resent the implication that I'm an old man. And what would you consider "prudently conservative"? It's probable that a piece just slipped through the cracks, but it's entirely possible that the same piece wouldn't have at, say, Rocketdyne. So how much blame does SpaceX as a whole bear?

They call it rocket science because it's tough. There are going to be mistakes.
Speaking as someone who is actually studying rocket science (in both the literal and colloquial senses), it's really not that much harder than building a high-performance jet. Everything is well-characterized, and there is a good-sized base of experience. A rocket engine is somewhat simpler than a jet engine, particularly given that it gets a lot more maintainence for a lot lower runtime. The margins are thinner, but the service life is a lot less. And the aerodynamics for aircraft are a lot worse than for rockets. So building the Falcon-9 is roughly akin to designing and building a business jet and engines for it in terms of technical complexity.

The rocket survived a pretty serious failure. I'm amazed that SpaceX has never lost a vehicle. That's a pretty rare record in the history of space travel.
As Tony noted, they lost Falcon 1s. And four flights is hardly statistically significant when compared to the launch numbers of other vehicles.

Thucydides said...

The limiting of the shuttle fleet to 4 operational units (technically there were 6; the Enterprise was never flight worthy and the Atlantis was assembled from "spare" parts, which implies a huge amount of "spares") mostly had to do with funding, which is really the story of the space shuttle from start to finish.

I have read somewhere that for another billion dollars, Rockwell could have opened an assembly line and built about 10 working space shuttles (plus the Enterprise and an unknown quantity of "spares"), which would have made most of the predictions about flight rates and military use somewhat viable.

Military space flight is really a different ball game, as a glance at an F-15 (or F-22 these days) compared to a 747 might imply. Military spacecraft should be small, rugged and cheap, and ready to fire at a moment's notice, so something like the X-37 mounted on a solid fulled booster is the current "best practice" for a truly militarized spaceship.

Byron said...

Thucydides:
The limiting of the shuttle fleet to 4 operational units (technically there were 6; the Enterprise was never flight worthy and the Atlantis was assembled from "spare" parts, which implies a huge amount of "spares") mostly had to do with funding, which is really the story of the space shuttle from start to finish.
No, there were only ever four. Originally, Enterprise (OV-101) was to be rebuilt as an operational orbiter, but it was cheaper to use STA-99 (a structural test article), which became Challenger (OV-99). Endeavour was built out of spares as a replacement for Challenger, not Atlantis.

I have read somewhere that for another billion dollars, Rockwell could have opened an assembly line and built about 10 working space shuttles (plus the Enterprise and an unknown quantity of "spares"), which would have made most of the predictions about flight rates and military use somewhat viable.
No doubt about this. The problem was that they tried to do too much with too little money. It still would have been more expensive than predicted, but the flights would have been cheaper.

Locki said...

Byron said...

I resent the implication that I'm an old man. And what would you consider "prudently conservative


=======

Didn't you post somewhere before that you were a 20yo aeronautical engineering student?

Man I can't believe it took me over 1000 posts to grind out an honourable stalemate against you on that last battleship thread.

I must be losing my touch.

Keep the good information coming.


Tony

Which -- no disrespect intended -- is completely ridiculous. Aside from the fact that laser rifles are magitech, nobody was going to put a Shuttle orbiter where it could even take one stray shot.


========

Surely you saw the irony in that comment of mine?

I've been arguing against weaponised energy weapons almost as hard as you have been this year.

Nope sleep easy. I know Moonraker was pure fantasy just as bad as Stargate. Even as a 12yo I knew suddenly spinning Drax's space station of doom wouldn't suddenly give you gravity everywhere/

================

The thing about these comment threads is I keep changing my mind like a top in the sea.

As soon as I find myself optimistically taking up someone like Jollyreapers point of view (spaceX may be capitalism at its best) and after reading a few more posts (byron/tony etc) I find myself suddenly changing my mind back to thinking they are naively idealistic at best and more probably vain glorious "type A" personalities with self aggrandizement problems.

I would have made a great politician ....

Anonymous said...

Locki:

As soon as I find myself optimistically taking up someone like Jollyreapers point of view (spaceX may be capitalism at its best) and after reading a few more posts (byron/tony etc) I find myself suddenly changing my mind back to thinking they are naively idealistic at best and more probably vain glorious "type A" personalities with self aggrandizement problems.

SpaceX is capitalism at its best because of good engineering and self aggrandizement. Their engineers have done a great job of getting Dragon into space, but there is still a lot of work to do to make Falcon as reliable as Atlas. Management and sales have done a great job of cheerleading to build up confidence for an eventual IPO to bring in more money. Making a good product and a good public image is capitalism at its best.

What we should be hoping for is a company like SpaceX becoming rocketry at its best.

Ron

Byron said...

Locki:
Didn't you post somewhere before that you were a 20yo aeronautical engineering student?
Indeed. So skepticism of SpaceX is not limited to old men.

The thing about these comment threads is I keep changing my mind like a top in the sea.

As soon as I find myself optimistically taking up someone like Jollyreapers point of view (spaceX may be capitalism at its best) and after reading a few more posts (byron/tony etc) I find myself suddenly changing my mind back to thinking they are naively idealistic at best and more probably vain glorious "type A" personalities with self aggrandizement problems.

I would have made a great politician ....

No, because you admit that you change your mind.

Part of the problem with this discussion is that all of us want SpaceX to succeed. I'd love to see their predictions on launch costs come true. I'm just skeptical that they will. Their current cost is very similar to that of the Proton, and is probably where they'll be long-term, if they succeed. The price might go up for the short term after the incident under discussion, but after a few years it should come down again.

Tony said...

Byron:

"Part of the problem with this discussion is that all of us want SpaceX to succeed. I'd love to see their predictions on launch costs come true. I'm just skeptical that they will. Their current cost is very similar to that of the Proton, and is probably where they'll be long-term, if they succeed. The price might go up for the short term after the incident under discussion, but after a few years it should come down again."

Proton is government subsidized in a funny-money economy. Nobody knows what it really costs in terms of material and effort.

While I don't want to see SpaceX go away, I also wouldn't expect any increase in tariff to be temporary. If they behave like a high reliability launch services provider, they're going to cost like one. That's even more true if they go public, because open market investors -- as opposed to angels and vehture capitalists -- aren't going to sit still for startup company operating procedures and risk taking.

Byron said...

Tony:
Proton is government subsidized in a funny-money economy. Nobody knows what it really costs in terms of material and effort.
Good point. The publicly-available numbers say the cost per pound to orbit is similar to that of the Falcon 9.

While I don't want to see SpaceX go away, I also wouldn't expect any increase in tariff to be temporary. If they behave like a high reliability launch services provider, they're going to cost like one. That's even more true if they go public, because open market investors -- as opposed to angels and vehture capitalists -- aren't going to sit still for startup company operating procedures and risk taking.
I'm not so sure. While I wouldn't rule out permanent increases (see law of accreting reliability above), they are still in the early stages of the process. There might well be some reduction with operational experience and volume production (even if not in absolute dollars, at least in inflation-adjusted dollars).

Tony said...

Byron:

"I'm not so sure. While I wouldn't rule out permanent increases (see law of accreting reliability above), they are still in the early stages of the process. There might well be some reduction with operational experience and volume production (even if not in absolute dollars, at least in inflation-adjusted dollars)."

Errrnh...I get that I may be too confident that traditional methods are the best ones. But I've been watching this industry as an adult for thirty years now,* and I can't escape the conclusion that if they could do it better (for any definition of "better"). There may not be a lot of competion, but there is enough.

*Not a slam on your youth, or anybody else's. It's just the factual context of my opinion.

Byron said...

Tony:
Errrnh...I get that I may be too confident that traditional methods are the best ones. But I've been watching this industry as an adult for thirty years now,* and I can't escape the conclusion that if they could do it better (for any definition of "better"). There may not be a lot of competion, but there is enough.
Yes, but I'm going to be an engineer. I have to believe there's a better way. Otherwise, I might as well pick some other career.

*Not a slam on your youth, or anybody else's. It's just the factual context of my opinion.
No offense taken. I'm not that sensitive about it, and mostly brought it up to point out to jollyreaper that age is not the cause of conservativism relative to SpaceX.

Tony said...

Byron:

"Yes, but I'm going to be an engineer. I have to believe there's a better way. Otherwise, I might as well pick some other career."

Hmmm...most engineers don't spend their lives building something better. They apply known principles to building more of the same, optimized for whatever the particular application is.

Byron said...

Tony:
Hmmm...most engineers don't spend their lives building something better. They apply known principles to building more of the same, optimized for whatever the particular application is.
Maybe I phrased that poorly. But I'm not going to accept that we really can't improve on what we did 50 years ago without a lot more research than I have done.

Tony said...

Byron:

"Maybe I phrased that poorly. But I'm not going to accept that we really can't improve on what we did 50 years ago without a lot more research than I have done."

THis brings us back to the mature technology discussion. My question would be: if we could make substantial improvements on the R-7 rocket (to speak of the most obvious example) why are we still using it? Sure, it's cheap and easy and damn near fully characterized as a dynamic system. But that's just the point. After fifty years of operation, we really can't supercede it for what it does best -- 7 tons to LEO.

Or, to make the point more, well...pointedly, our bright, shiny new super-heavy SLS is going to be built on 30 year old Space Shuttle external tank, solid rocket booster, and main engine technology. There are some political considerations built into that, but that's just another comfirmation of technological maturity. Nobody can point to an alternate means and conclusively say there's something really better. Nobody can walk into a congressional committee meeting and say, in effect, "You guys finanaced a '55 Edsel, when a '65 Mustang was available."

Anonymous said...

Tony:

Nobody can point to an alternate means and conclusively say there's something really better.

While it is true rocketry is a mature technology, that is not a reason to stop trying to improve it.

Now there might not be a lot of room for improvement as far as physics goes, but engineers could make advances improving designs for cost and reusability.

SpaceX is trying to reduce costs by doing most of the work in house. Better business practices and less government foolishness could also lower costs.

Of course, no one will know if any of this works if they don't try.

Ron

Thucydides said...

A wired interview with Elon Musk where he explains his vision in his own words. Your interpretation of his plan and ability is up to you, of course:

http://www.wired.com/wiredscience/2012/10/ff-elon-musk-qa/all/

jollyreaper said...

That's the SpaceX argument that makes sense to me. It's a variation of the Babylon 5 argument.

The show's creator and head writer said that he could put out a scifi show for $750k an episode. Miami Vice was something like a million bucks per in the 80's, same with Trek TNG. Nobody thought it was possible.

The creator said he could do it because there was a lot of waste and stupid involved in traditional production along with the other real and serious fixed expenses. For one thing, most shows have poor planning and execution with scripts coming in at the last minute, lots of unscheduled overtime and cost overruns.

So, did he prove it? Yes, he did.

B5 was averaging around $750k an episode and Voyager was more like $1.6 mil.

So, there's no more efficiency to be gained from rocket designs themselves? So what if production and management was streamlined instead of being a jobs program for giant aerospace companies? The Shuttle was a mess in part because of design by committee, in part because they had to farm out production around the country to satisfy politicians.

When I say old man stick in the mud attitudes, I'm talking about being crotchety like someone who is too cynical to realize when something actually is possible. Dismissing things out of hand is as much a mistake as believing everything you hear.

But again, none of us have money on the line here. Whether we are for or against really won't affect the world.

Tony said...

Re: Elon Musk and everything else

It turns out the Musk is -- as expected -- full of it.

Established aerospace companies are risk averse because they know what taking dumb risks cost.

The assertion that if it hasn't flown before, you can't fly it is a flat out lie. If it were true, there wouldn't be an Atlas V or a Delta IV.

I get why Musk likes vertical integration, but he's dead wrong that it saves all that much money in the long run. Even with two or three layers of profit tacked on -- five is an exageration, unless you're talking about things like fasteners and welding rod -- a lot of the time it just makes sense to farm out components to people that really know how to make them, and stick to your own knitting on system design and integration. You buy Rocketdyne and Pratt & Whitney engines because they know how to make them right, and you don't know any better -- as SpaceX has recently proven. The same goes for a lot of other things that go on a rocket.

Orbital's using the Russian engines because they're more efficient and have a higher thrust/weight ratio than anything they can buy anywhere else. I'm sorry if it ticks you off Elon, that Russian engineers in the 60s could do better than your boys and girls can do today, but that's how the cookie crumbles.

Finally, about not being willing to see another way. I've spent the last 30 years watching the "new world" of rocketry unfold, from the Shuttle to SpaceX. With that perspective, it's all too obvious that rocketry is just a mature technology. It's also obvious that doing it right has a price that one has to be willing to pay. An entire army of Elon Musks isn't going to change that. Mybe they'll incrementally shave a few pennies here, a dollar there, but their wilder fantasies aren't going to overcome the realities of physics and economics.

Rockets simply aren't computers, or cars, or even aircraft. Gotta get that through our collective heads when we look at operations like SpaceX. There isn't another way.

Anonymous said...

Tony:

Mybe they'll incrementally shave a few pennies here, a dollar there, but their wilder fantasies aren't going to overcome the realities of physics and economics.


They will be able to lower the cost, but I have to agree with you when they talk about order of magnitude savings. You are not going to cut 90% off the top just by being efficient.

It will take some impressive engineering, such as a Skylon that actually works instead of being a PowerPoint presentation, to cut cost by a factor of 10 or more. Maybe in the PMF, but I don't see it anytime soon.

Ron

Locki said...

I actually think Tony may have the right of this. We’ve pushed our engineering abilities – given our current theoretical base as far as we can. Sadly 1970’s era soviet rockets are the last word in efficient launches until a major breakthrough occurs.

Given, no evidence whatsoever, I think a radical breakthrough in our fundamental sciences is needed for the efficiency of space travel to jump an order of magnitude.

Which goes back to my point of setting achievable goals (unmanned missions to Europa I am looking at you) and plowing most of the discretionary spending into basic research into the basic sciences.

I’ve always thought the name of this blog is appropriate. Maybe we are all modern analogues of the steampunk visionaries, like Jules Verne, who looked at the moon and could only envisage a giant cannon to get there. They could only conceive of a giant manned cannon shell because they had no other context to plan in.

There is still hope in fundamental research . Afterall we don’t even have a theory of gravity yet (cue groans about wormholes etc)

Onto the original topic:

What are people’s opinions of the Venturestar X-33 project? What was needed to make this SSTO concept work? From what I can understand they thought 6 areas of innovation would enable them to leapfrog the shuttle and make safe SSTO travel a reality.

So from what I can understand the areas of extra efficiency were to be gained from:

1. Aerospike rocket engine.

Theoretically more efficient at more altitudes than a conventional rocket engine. But from a practical, engineering point of view could can it really be better (thrust, weight, ISP, reliability) than the SSME. Or is the SSME the last word In rocketry for the foreseeable future?

2. Lifting Body – saves a stack of weight from the wings

3. Vertical landing – again saves a stack of weight from the wings and parachutes

4. Carbon fibre fuel tank – it seems they may have actually got this to work

5. Computerised flight controls – I assume “flying” and vertically landing a giant, flammable lifting body is tricky. Are the computers up to it?

6. Metal heat shielding. Since you haven’t got a crazy cross range requirement I assume the venturestar can take a more gentle re-entry angle and not need ceramics. I also assume metallurgy has not advanced to the point of protecting something on a shuttle like steep reentry.

Which areas of advancement were achievable in the nearfuture given enough funds? Which areas requires another 10-20 years of research? And which areas require magitech pixie dust to past muster?

Byron said...

Locki:
1. Aerospike rocket engine.

Theoretically more efficient at more altitudes than a conventional rocket engine. But from a practical, engineering point of view could can it really be better (thrust, weight, ISP, reliability) than the SSME. Or is the SSME the last word In rocketry for the foreseeable future?

I'm not sure why they didn't use an aerospike for the shuttle. Somebody needs to bite the bullet and fly one.

2. Lifting Body – saves a stack of weight from the wings
Nothing new here.

4. Carbon fibre fuel tank – it seems they may have actually got this to work
Actually, I think this is where they had the big problems.

3. Vertical landing – again saves a stack of weight from the wings and parachutes

5. Computerised flight controls – I assume “flying” and vertically landing a giant, flammable lifting body is tricky. Are the computers up to it?

Both have been done on the DC-X. As there are no control systems people nearby, I can say that the flight controls aren't that big of a deal. Yes, they'd have to be dealt with, but it should be solvable with good engineering.

6. Metal heat shielding. Since you haven’t got a crazy cross range requirement I assume the venturestar can take a more gentle re-entry angle and not need ceramics. I also assume metallurgy has not advanced to the point of protecting something on a shuttle like steep reentry.
We've made some advances. They'd probably have a better ceramic for a new shuttle, but tossing the crossrange lets them go with metal, which is better overall.

All in all, it looks to be fairly plausible, so long as someone is willing to commit to doing it. That's my general impression of the whole SSTO concept. Physically, not too bad. Politically, not gonna happen.

Anonymous said...

“4. Carbon fibre fuel tank – it seems they may have actually got this to work
Actually, I think this is where they had the big problems.”

That is what killed the X-33. The composite cryogenic LH2 tank worked fine on the first test until they removed the hydrogen. When it warmed up the tank delaminated. Replacing the tank with good old aluminum would have increased the mass to the point a Venturestar probably couldn’t reach orbit, even without a payload.

The Venturestar would have been a very cool rocketpunk spacecraft. Maybe something like it will work in the future when we have better materials.

Personally, I’m not a fan of SSTO. You are lugging around a lot of dead weight to orbit. That reduces your payload, not a good thing. I like some of the early shuttle designs where it is a two stage vehicle. Both the orbiter and the booster are reusable and land on runways.

Skylon is a pretty good idea to get around the SSTO problem. Use atmospheric oxygen for the first part of the flight. That save a lot on the mass you have to haul upstairs. However, I am skeptical of the complex engine system. At least someone out there is trying and who knows, maybe they’ll get it right.

I don’t know why no one has tried an aerospike engine. Rocketdyne tested aerospike engines back in the 60s. For you youngsters, that’s when the big lizards roamed the Earth. :)

Ron

jollyreaper said...

The shuttle had the big, external tank pretty early on. They couldn't figure out a way to fit that much fuel inside the orbiter or split it with the manned booster craft.

Oddly enough, the GI Joe shuttle is somewhat like what the original idea would look like. The toy designers mined real and prototype weapons for ideas. This is the one they came up with I. The late 80's.

I do find the argument against wings as wasted mass compelling. I am a sucker for flying back to a runway feeling cooler than descending with a parachute. I know that's rule of cool thinking.

The spacex discussion about recoverable rockets remains interesting. It all comes down to what costs more at the end of the day. It's why repairing satellites in orbit seems like a good idea but its cheaper to just launch new ones. I'd wager we could have probably had a series of improved Hubble-class scopes lofted for the money we spent on shuttles to keep one in repair.

This is why I find the NASA and DARPA idea about repairing and refueling sats to be so interesting. If some space enthusiast suggested it I would shoot it down without a second thought. That the big boys are suggesting it makes me think they either know something I don't or are smoking something too rich for my blood. Damned curious to see how that idea will pan out. Sort of like the flying Hummer DARPA is funding. I suspect it will remain as impractical as easier attempts at flying jeeps. But if I'm wrong, wow!

Anonymous said...

Jollyreaper:

The shuttle had the big, external tank pretty early on. They couldn't figure out a way to fit that much fuel inside the orbiter or split it with the manned booster craft.

It made sense for a smaller shuttle, but not after they supersized the concept.

I do find the argument against wings as wasted mass compelling. I am a sucker for flying back to a runway feeling cooler than descending with a parachute. I know that's rule of cool thinking.

That's a good point, wings add a lot of extra mass. A lifting body design would not be as bad. Parachutes also add mass and are limited by what they can support. Powered landings like what SpaceX wants to do also add mass because of the extra fuel. It's all a tradeoff between capabilities and reduced payload. You pick the one you need, including good old expendable rockets to maximize payload.

So are you saying the Space Shuttle design was based on the rule of cool and not engineering?

Ron

Rob Lopez said...

Dumb question: what's this 'cross-range' business that keeps getting mentioned?

jollyreaper said...

The shuttle was more like false economies meets design by commitee. Fast, good, cheap, pick two, they ended up trying to do three. We've already discussed the extra Air Force requirements larded into the design. And everybody was fixated on the idea that reusable had to be cheaper than expendable but never ran the numbers to be sure that was the case. Now I can't tell you how seductive the space plane angle was in the planning process but I would not be surprised if capsules were seen as the past, not the future. The Air Force had a fetish for jet engines and a dislike of anything that wasn't, even if it made no sense to use jets instead of props.

Another good example, the Air Force hated the close-air-support role and did not want to build the a10 yet at the same time jealously defended tha Pentagon decree that the army could not operate fixed wing combat aircraft. At one point they were trying to retire the a10 and it would take three f16s to do the job and they were stoked because that's at least a proper jet that can go supersonic.

The stealth guys have a story about having mocked up a design for a radar-invisible aircraft carrier and showing it to the navy only to have it rejected. We don't build ships that look like that! Heh.

Byron said...

Rob:
Crossrange is simply how far off the original ground track a vehicle can land when entering the atmosphere. So the shuttle can land 2000 km to one side or the other of the original pat of its orbit.

Jollyreaper:
And everybody was fixated on the idea that reusable had to be cheaper than expendable but never ran the numbers to be sure that was the case.
They did and it was. First, there were some accounting changes that cost the shuttle big. Second, they just got it wrong.

The stealth guys have a story about having mocked up a design for a radar-invisible aircraft carrier and showing it to the navy only to have it rejected. We don't build ships that look like that! Heh.
An entirely reasonable response on the Navy's part. Stealth people try to design ships like they do airplanes, even though the environment is different. Also, stealth at sea doesn't work terribly well. See here for details.

Tony said...

Byron:

"An entirely reasonable response on the Navy's part. Stealth people try to design ships like they do airplanes, even though the environment is different. Also, stealth at sea doesn't work terribly well. See here for details."

Nothing to do with stealth carriers or stealth ships in general, but I find the following Stuart Slade comment (from the link) to be apropos of many discussions we have here about astronautics:

"When other simulations showed the Streetfighters being slaughtered by real warships under real conditions, he started a screaming campaign in the press, the usual nonsense about how his forward-thinking ideas were being suppressed by hide-bound admirals etc etc etc etc etc etc etc."

On the recent discussion in general, yes, you can get a single stage into orbit. Whether you can get it back is the real question, and if you can, could you deliver a useful payload? The answer, with current and foreseen materials science, is "no".

WRT aerospike engines in particular, the perceived advantage is in an engine intended for flight from the ground all the way up to a vacuum. For a single stage to orbit, that would be an advantage on fuel economy at lower altitudes. Of course, the fuel economy would not translate into larger payloads for a given GLOW. It would be used to help enable recovery and reuse. But, as was demonstrated with VentureStar, that wasn't enough.

When doing analysis for multi-stage expendables, it turns out that it's easy enough, and with less complexity -- and thus less engineering risk -- to specify operating altitude-optimized engines on each stage. So the aerospike turns out to be an engine fit for a niche application with no practical use.

Tony said...

Doing a little further research, it turns out that there's a really good reason aerospikes aren't used on expendables -- they just aren't efficient enough. Taking the RS-2200 linear aerospike that was being developed for the VentureStar, the Isp was 437v (vacuum) and 339sl (sea level). Well, in the Delta IV, which uses two stages, the RS-68 first stage engine has 410v and 365sl. Obviously it's optimized for lower altitude operation. But since that's exactly where it is operated, it's the better engine in that regime. Likewise, the second stage RL10B-2 engine has 462v, making it the better engine than the aerospike at the higher altitudes where it operates.

The aerospike, being a compromise, is only effective in an SSTO configuration. But there are other reasons that SSTO is a non-starter, whcih pretty much makes the aerospike a non-starter as well, if only for extrinsic reasons.

Byron said...

Tony:
On the recent discussion in general, yes, you can get a single stage into orbit. Whether you can get it back is the real question, and if you can, could you deliver a useful payload? The answer, with current and foreseen materials science, is "no".
And yet people keep trying to do it. Boeing offered the Air Force a fixed-price development contract for one (there was a rocket sled, but it was still basically an SSTO) in the late 80s. For about $2 billion, IIRC. That indicates some serious belief in the feasibility of the idea. And this is Boeing, who you hold as the standard for good practices.

When doing analysis for multi-stage expendables, it turns out that it's easy enough, and with less complexity -- and thus less engineering risk -- to specify operating altitude-optimized engines on each stage. So the aerospike turns out to be an engine fit for a niche application with no practical use.
At the moment, yes. Will that be the case forever? Probably not.

Tony said...

Byron:

"And yet people keep trying to [develop reusable SSTO]. Boeing offered the Air Force a fixed-price development contract for one (there was a rocket sled, but it was still basically an SSTO) in the late 80s. For about $2 billion, IIRC. That indicates some serious belief in the feasibility of the idea. And this is Boeing, who you hold as the standard for good practices."

I don't hold Boeing as the standard. They just have one of the best track records.

And you have to take the time into account. In the late 80s, there was still hope within industry circles for reusability. Also, Boeing, at that time probably thought they had a corner on the reusables market with their Shuttle orbiter participation. Finally, it was the Cold War, and a Cold War market for space launch. But I don't think a project over 20 years ago, in a very different economic and political environment, qualifies today's Boeing in the "keep trying" bracket.

"At the moment, [aerospike engines have no practical application]. Will that be the case forever? Probably not."

It's a simple exercise in design optimization. The aerospike can't, by it's very nature, be optimized for operating altitude. (Well, it can be, somewhat, by modifying spike geometry, but then what's the point?) A conventional bell nozzle engine can be. When working with staged launch vehicles, you use altitude-optimized engines. That rules out aerospike. Even an altitude-optimized aerospike is ruled out, on the basis of complexity alone (a lot of combustion chambers, and a lot of extra plumbing).

Aerospikes, like reusability, just appear to be an evolutionary dead end. Which is not their fault. It's just how things turned out.

Byron said...

Tony:
I don't hold Boeing as the standard. They just have one of the best track records.
My point was that they aren't a fly-by-night operation.

And you have to take the time into account. In the late 80s, there was still hope within industry circles for reusability. Also, Boeing, at that time probably thought they had a corner on the reusables market with their Shuttle orbiter participation. Finally, it was the Cold War, and a Cold War market for space launch. But I don't think a project over 20 years ago, in a very different economic and political environment, qualifies today's Boeing in the "keep trying" bracket.
The offered a fixed-price contract. That implies that they were certain they could do it. For less than the shuttle cost. Details are frustratingly hard to find, sad to say.

Aerospikes, like reusability, just appear to be an evolutionary dead end. Which is not their fault. It's just how things turned out.
Maybe. OTOH, the X-33 was started 15 years ago. Composites have made great strides since then, and if they got rid of the LH2, they could probably do it.
LH2 is massively overrated. Given the low density and handling problems, it really has no advantage over RP-1.

Thucydides said...

Probably the closest practical approach to SSTO technology would have been an evolution of the DC-X "Delta Clipper". Being VTOL eliminated the weight and complexity of wings, transitioning loads from vertical to horizontal and a host of other issues.

I was and am skeptical about the nose first reentry profile and trying to do a somersault at Mach 20 to orient the engines after re entry, but most of the rest of it seems well thought out; including the premise that the DC-X would be the first of a series of "x" rockets, many of which would be knowingly designed never to reach orbit, but only to bend metal and really test out concepts.

It seems very unfortunate and a bit premature that the DC-X program was terminated after so little flight time (and never followed on).

I also came across a NASA document attempting to forecast technologies; they had a chart suggesting that fullerine and carbon nanotubes could revolutionize transport by massive reductions in mass; a Space Shuttle launch stack would weigh only @ 500,000 lbs. Of course any reduction in mass on this scale would be self sustaining, less mass means smaller rocket engines, less fuel and oxidizer etc. Graphine is now the super nano carbon stuff of choice, and I suppose similar predictions can be made about it.

Locki said...

I don’t know why no one has tried an aerospike engine. Rocketdyne tested aerospike engines back in the 60s. For you youngsters, that’s when the big lizards roamed the Earth. :)

Ron


=========

I think I vaguely remember folk tales of the 50s-60s passed onto me by some of my revered ancestors of that epoch. :)

My dad tells me of punching cardboard cards and then spending hours feeding them in one by one to simulate pong or some sorta analogue computer. He also pulled his beers out of a kerosene powered fridge.

Optimising Rocket engines for different altitudes:

Thanks for explaining the problems with an aerospike engine Tony.

I seems to remember the dual mode air-breathing scramjets facing an altitude optimisation problem at least as great as the aerospike.

As everyone has pointed out non-air breathers quickly gain in efficiency as you reach higher altitudes. In addition each stage can be optimised for the altitude you are expected to operate at. So modern rockets aim to ascend as quickly as possible into thinner air.

A dual mode airbreather in comparison faces the problem that its engines work best where the air is relatively thick (so oxygen for fuel but relatively high drag). So to reach orbit it is deliberately ascending less quickly and doing most of its accelerating whilst in a high drag environment where there is sufficient oxygen.

I thought the jury was still out on whether the weight saved from using the oxygen from the atmosphere offsets:

1. The massively higher drag (remember drag is exponential ly related to velocity)

2. Higher weight and complexity of the engine

3. Not to mention you have to accelerate the rocket up to mach 3-ish so the scramjet starts working anyway.

I can see it being useful for high speed transport. Admittably, I don’t have the math, but it doesn’t sound like the greatest way of getting in to orbit.

I wonder why there is this fixation on reusability to lower costs? Virtually every aspect of our modern society shows us that to achieve the holy trinity of low cost, high reliability and high performance you build things disposable.

Cell phones are ditched after 18 months. Computers after 3 years. Cars ditched in 5yrs. No one rebuilds/repairs anything anymore.

addendum: The mighty B-52 as a glaring exception is already noted.

Jim Baerg said...

Locki:
Your claim that everything should be disposable seem at best exagerated to me. I bought my current car (Toyota Echo) in 2004 after owning my previous car (Nissan Micra) for 16 years. Ditching them after 5 years would have been wasteful.

When there is rapid progress in a technology it's likely not worthwhile to build a machine to last decades if the 5 year newer model will be much better. I recall that in _Democracy in America_ Tocqueville quotes an 1830's US ship captain as saying it's not worth it to build ships to last as long as Europeans do because of how fast ship technology was improving.

The economically optimum durability will vary a lot between different applications, but 5 years for cars strikes me as way too low.

Tony said...

Byron:

"My point was that [Boeing] aren't a fly-by-night operation."

Fair enough, though their products do fly well at night.

"The offered a fixed-price contract. That implies that they were certain they could do it. For less than the shuttle cost. Details are frustratingly hard to find, sad to say."

I'd have to see the particulars to render any further opinion.

"Maybe. OTOH, the X-33 was started 15 years ago. Composites have made great strides since then, and if they got rid of the LH2, they could probably do it.
LH2 is massively overrated. Given the low density and handling problems, it really has no advantage over RP-1."


It seems that all reusable SSTO schemes implicity rely on LH2. I'm not sure why, but I suspect it has to do with high altitude performance, where a LOX/LH2 rocket has all kinds of advantages. I'm just not convinced that SSTO -- particularly of the reusable type -- is anything other than a philosophical statement. With 55 years of space launch under our belts, we would know for a fact if we could do it or not. It wouldn't be subject to speculation and what-if.

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

Re: disposability

Expendability in launch vehicles has nothing to do with disposability in commercial products. It just turns out that you save a lot of mass for payload if you don't try to get the thing back. As far as reliability is concerned, the launch vehicle only has to operate for 8 1/2 minutes. But it has to operate near perfectly for that timespan. So launch vehicles are always going to be carefully prepped, checked, and monitored.

The interesting feature of launch vehicles is the longevity of design. The actual flight articles are expended in operation within months of being shipped from the plant. But they can be, and often are, built to designs originating in the 50s/60s/70s. Also of note is the capacity of expendable launch vehicles for evolution, while retaining core system features. Atlas, Titan, and Delta were all upgraded and repurposed over decades with the addition of SRBs, new upper stages, and payload accomodations. The new Space Launch System is really just a reconfiguration of the Shuttle stack for maximum payload to LEO. It actually makes a pretty fascinating study.

Byron said...

Tony:
I'd have to see the particulars to render any further opinion.
I haven't been able to find any, but I did find the NASA Access to Space Study. See this for an analysis of a similar H2O2/kerosene rocket.

The interesting feature of launch vehicles is the longevity of design. The actual flight articles are expended in operation within months of being shipped from the plant. But they can be, and often are, built to designs originating in the 50s/60s/70s. Also of note is the capacity of expendable launch vehicles for evolution, while retaining core system features. Atlas, Titan, and Delta were all upgraded and repurposed over decades with the addition of SRBs, new upper stages, and payload accomodations. The new Space Launch System is really just a reconfiguration of the Shuttle stack for maximum payload to LEO. It actually makes a pretty fascinating study.
The modern Atlas and Delta bear little resemblance to the original vehicles to bear those names. They're both relatively modern, and the Russians haven't had the money for new rockets.

Tony said...

Byron:

"I haven't been able to find any, but I did find the NASA Access to Space Study."

Predicated on developing and demonstrating speculative technologies that don't appear to have emerged in the intervening 18 years.

"See this for an analysis of a similar H2O2/kerosene rocket."

It's kind of hard to tell from what is written, but it appears to me that they weren't paying enough attention to altitude effects on engine performance, and hand-waving away the effects of G-limiting. And in the end, they couldn't get better performance than LOX/LH2, just a smaller vehicle -- though I suspect they made a lot of optimistic assumptions. I'm willing to bet that hydrogen peroxide as an oxidizer has issues at high volumes and pressures that LOX doesn't.

"The modern Atlas and Delta bear little resemblance to the original vehicles to bear those names. They're both relatively modern,"

Mmmhmm -- as I have pointed out myself on numerous occasions. It doesn't invalidate the point about the original Atlas and Delta systems anyway. Also, in order to market the EELVs as complete solutions through wide ranges of payload mass and target orbits, the new vehicles are highly configurable. So far, Atlas V has flown in 6 distinct configurations (basically 0-5 SRBs), while Delta IV has flown in 5 (through a combination of SRBs, LRBs, and 4 or 5 meter diameter second stages).

"and the Russians haven't had the money for new rockets."

Well, there is some question whether they really need them. Also, the Soviets/Russians haven't done a lot of booster-based vehicle configuration, opting instead for upper stage options

Byron said...

Tony:
Predicated on developing and demonstrating speculative technologies that don't appear to have emerged in the intervening 18 years.
Which ones, exactly? Most of the ones listed seem to be on the "nice to have" list, not the "absolutely required to make it work at all" list.
What they need to do is build an unmanned demonstrator that takes off SSTO, flies around once, and lands. It has basically no payload, and no other design drivers. Then we know it can be done, and can look at doing it for operational use. Total cost is probably fairly low.

It's kind of hard to tell from what is written, but it appears to me that they weren't paying enough attention to altitude effects on engine performance, and hand-waving away the effects of G-limiting. And in the end, they couldn't get better performance than LOX/LH2, just a smaller vehicle -- though I suspect they made a lot of optimistic assumptions. I'm willing to bet that hydrogen peroxide as an oxidizer has issues at high volumes and pressures that LOX doesn't.
You apparently didn't read the whole thing that closely. The main study was LOX/RP-1, not H2O2. There was some discussion of H2O2 earlier on, but I got confused as to which the main section discussed.
And can you go into more detail about these "bad feelings" you get? I know I'm coming across as sort of antagonistic, but you seem to be assuming that anyone who believes in SSTO is lying to themselves and others. A smaller vehicle is valuable because a lot of the costs scale with empty mass, and it's easier to recover. Also, I'm willing to bet that the person who wrote the report knows a lot more than you do about how rockets behave at altitude.

As to the need for liquid hydrogen, it's been greatly oversold as a fuel.

Tony said...

Byron:

"Which ones, exactly? Most of the ones listed seem to be on the 'nice to have' list, not the 'absolutely required to make it work at all' list."

"[A]dvanced materials". These were considered necessary for both the hybrid and rocket-only designs. Also, notice that the rocket-only design was as big as the entire Shuttle stack, and the hybrids were even larger. Knowing what we know about getting the Shuttle back to the ground and refurbishing it for reuse, do we really think anything that large is going to be efficient?

"What they need to do is build an unmanned demonstrator that takes off SSTO, flies around once, and lands. It has basically no payload, and no other design drivers. Then we know it can be done, and can look at doing it for operational use. Total cost is probably fairly low."

People have been saying that for decades. Build a "true" X-vehicle for technology development. When we fly it enough, we'll see what we can really do. The problem is that we can do some pretty sophisticaed dynamic analysis these days. We don't need to fly a brick, then shave it back to an elegant statue, to figure out what works.

"You apparently didn't read the whole thing that closely. The main study was LOX/RP-1, not H2O2. There was some discussion of H2O2 earlier on, but I got confused as to which the main section discussed."

You pointed to it for its discussion of H2O2/kerosene as an SSTO propellant combination. I read the whole thing, but I responded on the basis you introduced it.

"And can you go into more detail about these 'bad feelings' you get? I know I'm coming across as sort of antagonistic, but you seem to be assuming that anyone who believes in SSTO is lying to themselves and others. A smaller vehicle is valuable because a lot of the costs scale with empty mass, and it's easier to recover. Also, I'm willing to bet that the person who wrote the report knows a lot more than you do about how rockets behave at altitude."

I don't think you're being antagonistic at all. You just want to explore all of the possibilities.

And it's not bad feelings, per se. I'm just trying to establish a baseline of fact -- easily researchable and not all that hard to understand fact. I wouldn't even say that SSTO is a lie. It can be done -- expendably and inefficiently. When one tries to extend SSTO into reusability, then I align myself with John Shannon. He said resuability was "myth", in a public hearing of the Augustine Commission. I have to agree with him.

So what I'm doing is simple. I'm insisting that we take full notice of:

The state of the art, so we know where we really are),

The relationship of current art to prior art, in order to establish just how mature the technology really is, and

The history of SSTO and reusability as an established fact, not as mere speculation, so we understand just how far we really are from achieving it in any kind of practical form.

What's "bad" about that?

Tony said...

Byron:

"As to the need for liquid hydrogen, it's been greatly oversold as a fuel."

I don't know how we got on the track of a "need" for LH2. I just observed that it seems to be a reactant of choice. I speculated as to why, but I never purported to know all the reasons.

In any case, the arguments in the link have been invalidated by the Delta IV, which not only uses LH2 in a lower stage, but seems to do so safely and reliably. Now, it does use a little bit more hardware mass to get to orbit. The realtionship of vehicle dry mass to payload is 3.5 for the baseline version. The value for the same metric in Atlas V, using the baseline configuration, is 3.3.

I think the important thing to get here is that for reusability -- leaving SSTO totally aside -- you have to shoehorn every blessed bit of de-orbit propellant, thermal management, and landing hardware into a very light vehicle. Taking the hardware-to-payload ratio of the Atlas V, for example, and a nominal 10 mt payload capacity, you have to find room in 33 tons of tankage and engines to land two stages, one the size of a 737 fuselage, and the other the size of a semi trailer. Or you can start invading your payload mass to get the recovery capability. Or build a much bigger vehicle, that is just that much harder to safely and reliably recover.

And that's with two stages improving your overall mass ratio to begin with. Care to try that trick with a single stage?

Not trying to be patronizing or combative -- just pointing out the problem constraints.

Locki said...

Jim Baerg said...

Locki:
Your claim that everything should be disposable seem at best exagerated to me. I bought my current car (Toyota Echo) in 2004 after owning my previous car (Nissan Micra) for 16 years. Ditching them after 5 years would have been wasteful.


==========

Well that would be because you bought a good honest Toyota/Nissan instead of say a modern BMW/Mercedes. You too would be thinking the car was built to be disposable after the electric gremlins attack you at the 3yr mark.

But I take your point. Probably exaggerated.

My analogy is better for electronics and household appliances. I am constantly amazed when things like my washing machine/fridge/TV/vacuum cleaner break down.

If you can find even find someone to repair nowadays with a bit of bargaining its always cheaper just to buy a new one.

Byron said...

Tony:
"[A]dvanced materials". These were considered necessary for both the hybrid and rocket-only designs. Also, notice that the rocket-only design was as big as the entire Shuttle stack, and the hybrids were even larger. Knowing what we know about getting the Shuttle back to the ground and refurbishing it for reuse, do we really think anything that large is going to be efficient?
To quote Yoda, size matters not. Most of that size is empty tanks, which don't take that much babying. The rest is no worse than the shuttle, particularly if you put more emphasis on operational issues during the design. And materials have made a lot of improvements over the intervening two decades.

People have been saying that for decades. Build a "true" X-vehicle for technology development. When we fly it enough, we'll see what we can really do. The problem is that we can do some pretty sophisticaed dynamic analysis these days. We don't need to fly a brick, then shave it back to an elegant statue, to figure out what works.
So? Dynamic analysis doesn't catch everything. The point is to actually build the thing and demonstrate that it can be done. It may not have a payload, but it is doing the profile.

You pointed to it for its discussion of H2O2/kerosene as an SSTO propellant combination. I read the whole thing, but I responded on the basis you introduced it.
I thought the main section was H2O2/kerosene, not LOX/kerosene. Which is why I mentioned that. Either one works.

It can be done -- expendably and inefficiently. When one tries to extend SSTO into reusability, then I align myself with John Shannon. He said resuability was "myth", in a public hearing of the Augustine Commission. I have to agree with him.
That's not what the study said. It said that they could do it with a little bit of development. I'm not going to rule it out. And the fact that the head of the space shuttle program said that reusability couldn't work (and he's been deep in the work of the shuttle, which was a little too early) does not mean it's impossible. If we started over on a shuttle-type vehicle, 40 years later, I think we could do a bit better.

The history of SSTO and reusability as an established fact, not as mere speculation, so we understand just how far we really are from achieving it in any kind of practical form.
The last attempt with serious money tried to build an SSTO was cancelled a decade ago.

I think the important thing to get here is that for reusability -- leaving SSTO totally aside -- you have to shoehorn every blessed bit of de-orbit propellant, thermal management, and landing hardware into a very light vehicle. Taking the hardware-to-payload ratio of the Atlas V, for example, and a nominal 10 mt payload capacity, you have to find room in 33 tons of tankage and engines to land two stages, one the size of a 737 fuselage, and the other the size of a semi trailer. Or you can start invading your payload mass to get the recovery capability. Or build a much bigger vehicle, that is just that much harder to safely and reliably recover.
The thermal load is not as big of a problem as you think. The tanks reduce the sectional density, which in turn cuts the maximum heat load. This, plus better materials, makes it substantially easier. And on landing, the vehicle is much lighter than it was on takeoff. By a factor of, say, 15. Structurally, what was adequate to support the full stack on liftoff is pretty much adequate for landing.

Thucydides said...

The answer for LH2 over RP-1 is actually quite easy; you get a much higher ISP from using liquid hydrogen. IF everything else is equal, then the advantage of having an ISP in the 400's over one in the high 200's really cannot be argued with.

OTOH, LH2 has a very low energy density, is a deep cryogen, can pass through the pores in metal and has lots of other nasty issues making it difficult to use. RP-1 and similar hydrocarbon fuels have high energy density, are relatively non toxic, easy to handle at normal temperatures and are the products of a huge and well established infrastructure. This also explains why your car is powered by gasoline or diesel fuel rather than a hydrogen fuel cell.

Since SSTO needs to wring every possible advantage out of every system in order to work, anyone who is interested in the problem is attracted to the potential performance advantage of a LH2/LOX engine combination, hence the fascination with LH2.

Byron said...

Thucydides:
Since SSTO needs to wring every possible advantage out of every system in order to work, anyone who is interested in the problem is attracted to the potential performance advantage of a LH2/LOX engine combination, hence the fascination with LH2.
No, they aren't. The problem with LH2 is that it requires heavier tanks and heavier engines, is a lot more difficult to work with, and has some second-order effects that cut the required delta-V even more. It doesn't appear to be significantly more difficult to build one or the other at the moment. Read the link I posted.

Rick said...

A quick note that - at last! - a new post is up on the main page: A Planet of Alpha Centauri.

Tony said...

So, let's look at historical launch vehicle performance:

Launch Vehicle : LEO Payload (% of GLOW (Gross Lift Off Weight))
Saturn V : 3.91
Atlas V 541 : 3.66
Atlas V 401 : 3.65
Delta IV Heavy : 3.51
Atlas II : 3.41
Delta IV Medium : 3.32
Saturn 1B : 3.17
Falcon 9 : 3.04
Proton-K : 2.87
Titan 2 GLV : 2.39
Soyuz : 2.28
Delta 7920-8 : 2.17
Titan 3M : 2.04
Atlas/Mercury : 1.16

The Saturn V gains some advantage from being just so freakin' big -- the structure mass goes up (more or less) by a power of two, while the propellant mass goes up by a power of three.

Otherwise, more modern LVs get a higher percentage of their GLOW into orbit as useful payload. The Atlas II is the surprise here, but you'll see why in a bit.

Of particular interest to SSTO applications is Atlas/Mercury, which has a very low value. That's because it's about the closest thing to SSTO that anybody ever had -- and that came at the price of a very small payload, compared to overall vehicle size.

Now, let's look at things a slightly different way:

Launch Vehicle : Mass Ratio of Structure/Payload
Saturn V : 1.59
Atlas II : 1.92
Atlas V 401 : 1.96
Atlas V 541 : 2.16
Proton-K : 2.38
Titan 2 GLV : 2.54
Falcon 9 : 2.65
Saturn 1B : 2.93
Delta IV Heavy : 3.25
Soyuz : 3.38
Delta IV Medium : 3.44
Delta 7920-8 : 3.80
Atlas/Mercury : 3.97
Titan 3M : 6.61

Saturn V is, of course, the king, thanks to being big tanks and not much else.

Atlas is the real winner in the medium lift category, and overall. It should be. It's intentionally and emphatically a minimum-structure and maximum-payload approach. If you're wondering what the deal is with the relatively old school Atlas II, it's because it was the balloon tank's greatest hit. The Atlas V achieves almost the same performance with isogrid rigid tank structure and a much more efficient booster stage engine.

As expected, the Delta IV, thanks to it's LOX/LH2 propellant mixture, is much more heavily skewed towards launch vehicle structure, because it needs a lot more tankage and heavier engines.

One might ask why the Delta 7920-8 and Titan 3M come in so far down the list. Well, they both use solid rocket boosters, which are high thrust, but low efficiency, and just really heavy. The Atlas V 541 also uses solids, but they are a much smaller part of the overall package mass.

Atlas/Mercury is near the bottom of the list because it's essentially an SSTO with some disposable engine mass.

So, the big deal for SSTO? First, even the most modern structures and most efficient engines, using two stages for added efficiency, only get less than 4% of your GLOW into orbit as payload. And they do so with minimums of structural mass. Now, for SSTO, you're looking at 1% or so of GLOW as payload on orbit, and that's without any margin for reusability in the launch vehicle itself. Yes, modern engines are more efficient than those on the Atlas/Mercury. But we're presuming that we're not dropping any engine mass on the way up, and that the tankage is going to have to be rigid, not inflated. Also, the Atlas/Mercury was still less than 6% payload and structure, including the discarded booster engines. The rest was propellant. 1% GLOW as payload still seems about right, even with the most modern materials and systems.

So, for reusable SSTO, you're going to have to find your recovery margin in that 1% of payload. Say you can only get .5% GLOW into orbit as payload, if you want to recover the launch vehicle. Okay...that means that a reusable SSTO LV is going to have to fly seven times to equal the performance of a single expendable LV of the same size, using current technology. (Or any technology, really, because lighter tankage and engines are going to be adopted in expendables as well.) Or you have to fly a 7x larger vehicle to make up one payload of a comparable expendable LV.

Hmmm...seems like a big gap to bridge, considering that the cost of reusability in launch vehicles is a lot higher than originally presumed.

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