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And even if the unit costs end up being higher than predicted, that isn't a show stopper. Unlike the shuttle this will be designed to have a quick turnaround time allowing for far greater reusability than we've ever had, which reduces launch costs greatly over time.
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Que angelic choir.Originally Posted by aquitaine
Skylon definitely have that Ooohhh shiiiney factor going. the fact that it at least in theory is looking up to be the best thing since the moon landings is just groovy.
On a more serious note. skylon is not going to be some small step ahead technology wise when it comes to launchers. it's going to be a giant leap. and hence the development risks are far greater as well. I'm really looking forwards to seeing the biggest risk of them all, the pre cooler technology, properly tested and in working order this summer.
Exciting times ahead.
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The Shuttle was designed for a quick turnaround time. It didn't work out that way in practice; the original design was to support something like 25 flights per vehicle per year.
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too bad the shuttle didn't end up remotely resembling the original concept then.
What the shuttle did end up as was a somewhat reusable orbiter with a honking big single use fuel tank and a pair of oversized fireworks rockets mounted on the sides.
Let's be honest. The shuttle never met any of it's original design criteria. It's not really reusable in the proper sense as that word is normally employed (like a car is reusable, or a ship, even airliners operate reusable vehicles in the trues sense). the very fact that it needs to have a whooping big external fuel tank and it's attendant SRB's precludes it from ever operating in that manner. there is room for operating it tonnes more efficiently than they have been doing, but there is a hard limit to how efficient one can be with this system.
The skylon is different, there will never be added any honking big external throwaway components. if that becomes a requirement in order to make it capable of launching, then the program will be scrapped as a failure. The skylon either becomes reusable in the traditional sense, or it is going to be seen as a big failure.
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You mean original designs like these:
Space_Shuttle_concepts.jpg
Where the shuttle was an SSTO or a true TSTO? One of those might have achieved those turnaround times and flight rates but we will never know because that isn't what NASA got is it?
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Yes, keyword original. But that requirement ended up falling by the wayside in light of additional Air Force requirements being forced onto it. The shuttle had the following design problems that prevented it from being reusable:
1.) Dependence on an external fuel tank - This thing needed to be remanufactured after every flight, and at most they could make 24 a year, so that's 24 flights for ALL orbiters.
2.) Fragile ceramic tiles that needed constant replacing - Not only did some of them need to be replaced after every flight, when they were replaced they needed to be handcrafted.
3.) Overly complicated main engines - These needed to be completely disassembled after every flight, which is very time consuming considering that it was an integral part of the orbiter. I don't know to what extent the SABRE engines are modular, but since they are mounted on pods like an airplane's that makes me hope that it can be quickly replaced.
4.) The shuttle's maintanence staff - Each orbiter required a ground crew of 1,500 people, that's bigger than a full army battalion. The salaries of having that many support staff alone accounted for a great deal of the launch costs.
The Skylon has none of these problems.
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http://www.bbc.co.uk/news/science-environment-17864782
Pre cooler testing, perhaps the single most critical new element.
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Good article. One remark though: they say the engine will encounter intake air of 1000°C that needs to be cooled before compressing it. Well, that is before compressing it further in the active compressor. The very fact that it is 1000°C intake air means that it has already been significantly compressed by RAM deceleration in the intake.
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There is nothing wrong with having drop tanks. It reduces what you have to cover with TPS. Unlike airbreathers, pure rocket-planes don't have to get as hot going up to space as they do in returning.
Suppose you use denser propellants like hypergolics. Then external tankage is far less complicated than on the shuttle external tank.
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Just a shame pure rocket planes don't work as SSTO.
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They could, in theory. The Titan II first stage reportedly could be an SSTO with a small payload, modern engineering might allow reusable engines and some spray on ablative coating.
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Even for a lifting ascent the TPS is still going to be primarily dictated by the re-entry profile of the vehicle and not by any extra heating from flying somewhat faster trough the atmosphere. the only airbreather concepts that has issues with heat on the way up are ScramJet's. Mach 5.5 @28km alt. is not all that fast tbh, but it saves a huge amount of oxidizer nonetheless, but those precoolers dictate the use of a cryogenic as fuel. thus bringing us back towards liquid hydrogen again.
It's been mentioned before, but I'l mention it again. There are some bonus advantages to having huge internal fuel tanks that bloat the volume of the vehicle. Namely that of achieving a low vehicle density, thus allowing the vehicle to loose speed at a faster rate during the re-entry, at a higher altitude, thus lowering the max heat flux excperienced by the TPS system.
This is opens up the options for avoiding ablatives in favour of more reusability friendly TPS material.
If you build a rocket stage huge enough, it automatically becomes a SSTO. It's all about mass ratios. the bigger the rocket stage the more fuel it can carry per unit of dry mass, and thus the bigger it's effective DV budget becomes. volume increasing faster than surface area for a 3 dimensional object and all that.
A non airbreathing version of skylon would have to be much much larger vehicle than what skylon is going to be in order to have the same mass capacity as skylon is going to have. It has never been a question about physics, but about economics. It's not exactly clear that a winged reusable vehicle 4 times the size of skylon would be any cheaper than a quarter sized 2 stage non winged expendable system with a comparable payload capacity.
If it was reusable enough i guess it should be cheaper in theory at least, but only as long as you can match skylons projected turnaround capabilities. (Wings and landing gear mass may spiral out of controll tho. hard to tell without running some serious numbers)
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When someone says "not work" I tend to assume it is a matter of physics, not finances, my apologies.
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True, drop tanks is not an inherently a bad thing, but it is kind of cheating for an SSTO, as you are really retaining the stages of the conventional staged craft(the primary reason for staging is to carry the fuel needed but being able to drop the mass when the fuel is out), though you are probably saving a little mass by having the engine capacity on the main craft, Still, If you are going to have parts dropping of, why bother trying to approach a SSTO design?.
Also, when the advantages of SSTO are discussed, the lists tend to include the lack of parts that need to be recovered or that is expendable,
The use of hydrogen fuel is integral to the design and feasibility of the Skylon, it is not just the cooling in the engine, but also for the active thermal protection systems, and you need to have a craft that is relatively big compared to its mass during reentry if you do not want to have heat protection tiles or something that add to the cost and complexity.
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Last i heard it may be that there wont be any active cooling on skylon. Yes i know it was baselined for the C1 config, but they used some rather conservative numbers to keep a healthy margin for mass growth in the TPS system available. aparently the higher fidelity sim numbers they got from the company that did re-entry simulations are showing a more benign re-entry environment than first assumed. Also there have been some advances in material sciences for high strenght high temp tollerant materials.
The airframe is not really finalized tho. so more changes are to be expected still.
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My fault I should have been clearer. Yes you could in theory get one off the ground but the payload fraction is appalling. There was a long thread about this courtesy of Bob Clark and his various 'lego rockets'. Essentially you could get some conventional first stages to launch themselves into orbit. Problem was that by and large they couldn't carry any payload. In fact if you added any sort of systems to make them reusable they ceased being able to get to orbit. Now with a purpose designed vehicle like Venturestar using cutting edge technology you might get a small but usable payload fraction but it is probably going to still be an expensive ride in cost per kilo terms.
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Hmm... going by memory here, but wasnt one of the main reasons for why venturestar got cancelled, that is had so much mass growth in those cutting edge fuel tanks that their payload fraction got more than eaten up by the added mass?
I do remember that Bob kept gettign back to trying to shoehorn venturestar into working by swapping fuel from cryogenics into hydrocarbons. soemthing that would have changed the mass of the vehicle massively
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There seems to be a lot of conflicting material on Venturestar but even in the best version it's payload fraction would have been relatively small, it was never going to address the issue of lowering launch costs. Yes Bob's 'designs' were mindboggling.Hmm... going by memory here, but wasnt one of the main reasons for why venturestar got cancelled, that is had so much mass growth in those cutting edge fuel tanks that their payload fraction got more than eaten up by the added mass?
I do remember that Bob kept gettign back to trying to shoehorn venturestar into working by swapping fuel from cryogenics into hydrocarbons. soemthing that would have changed the mass of the vehicle massively
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A truly reusable SSTO could have other uses beyond being cheaper. For example, the infrastructure to support it could conceivably be less complex. I am imagining something that could go from Earth orbit to the lunar surface and back again, servicing a lunar facility the way Progress does the ISS, returning with samples and possibly even lunar hydrogen and oxygen, the Delta-V for lunar surface to Earth orbit being significantly less than it takes to get from Earth surface to Earth orbit, and low thrust, high ISP strategies can potentially be used.There seems to be a lot of conflicting material on Venturestar but even in the best version it's payload fraction would have been relatively small, it was never going to address the issue of lowering launch costs. Yes Bob's 'designs' were mindboggling.
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I was very surprised when NASA picked that design. There were so many advanced technology aspects that I assumed there must have been a black project where this stuff had been tested, but that they weren't talking about it publicly. As it developed, though, it became very clear that it was wildly untested. That was one of my major disappointments with NASA.
I think a second generation shuttle would have made a lot more sense (two stage, both stages reusable, advanced thermal protection system, the spacecraft designed for high reliability and low maintenance). Or failing that, at least the DC-X, which was intended as an SSTO, but at least there had been some work already done.
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
The Leif Ericson Cruiser
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Hmm... going by memory here, but wasnt one of the main reasons for why venturestar got cancelled, that is had so much mass growth in those cutting edge fuel tanks that their payload fraction got more than eaten up by the added mass?
I do remember that Bob kept gettign back to trying to shoehorn venturestar into working by swapping fuel from cryogenics into hydrocarbons. soemthing that would have changed the mass of the vehicle massively
There was an article a while ago detailing exactly what went wrong with that project, but basically it was this: The design called for alluminum fuel tanks, but the managers decided to go with graphite composites, even though the engineers told them it was doomed to fail. Not surprisingly it did fail, just as was predicted, and after wasting a bunch of time and money they went back to the aluminum tank. Unfortunately just as things were getting back on track a former NASA director testified in front of congress that it had to use composite tanks, which would require a complete redesign of the vehicle, and congress said no and canned the whole thing. Mismanagement at its finest.
The payload was 20,000 kg, which isn't too bad. What would have lowered launch costs was its various design features that would have dramatically lowered the amount of maintenence needed (which is where the inflating costs of the shuttle largely came from). Still, the Skylon in my opinion is a better design than this, but it is a worthy runner up and would have made a nice stopgap, and maybe even spurred more funding for the Skylon. Then we can have, you know, real competition. That would be nice.
Last edited by aquitaine; 2012-May-07 at 05:42 AM. Reason: url fail
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It does seem at times like NASA went out of their way to undermine launcher projects in the 90's though the apparently endlessly rising costs of the ISS had a lot to do with it.
Well there is competition to lower launch costs with ideas like Stratolaunch but yes SSTO is a one horse race at the moment.The payload was 20,000 kg, which isn't too bad. What would have lowered launch costs was its various design features that would have dramatically lowered the amount of maintenence needed (which is where the inflating costs of the shuttle largely came from). Still, the Skylon in my opinion is a better design than this, but it is a worthy runner up and would have made a nice stopgap, and maybe even spurred more funding for the Skylon. Then we can have, you know, real competition. That would be nice.
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IMHO, the space shuttle program demonstrated conclusively that rocket and/or aircraft launchers are not the way to go. The energy required to launch payloads into low Earth orbit means big rockets and big aircraft. They are inherently very dangerous. The U.S. has 14 dead astronauts to prove it. Rail guns, gas guns, big dumb boosters, space elevators, launch towers that reach into the stratosphere, we need to re-think all the launch options.
Ideas?
Regards, John M.
I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.
"Mainstream isn’t a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik
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Since those other things have not being built, we don't know their safety margins.
The things that killed the astronauts were not inherent in the design of the space shuttle, or of rockets in general, but because of safety problems in procedures, management ignoring problems that arose.
O-Ring problems showed up before Challenger and her crew met their doom for example.
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The dangers of space travel is rather inherent, you have a succession of hostile environments that only the most rigorous safety precautions and applications of high levels of ingenuity can make survivable, so unless some rather central factors change, there will always be some risk involved, regardless of launch system.
But, even though the immediate cause of the Shuttle disasters were technical problems with the craft and a bad combination of coincidental factors, the ultimate cause was problems with the way safety was handled in the design and use of the Shuttles.
If we assume that the projected specifications is relatively correct, a Skylon fleet(equipped with SPLMs) of the size of the Shuttle fleet at the times of the disasters would probably not have resulted in the death of the crew, even if the incidents were reproduced as near as feasible with such dissimilar systems. Still, the Skylon would, as far as possible, be operated as an unmanned craft, and I expect there would be many unmanned trips before any manned ones, and even then it would probably only be to carry crew to and from orbital facilities that it would be used as a crew carrier.
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The shuttle proved none of this. the shuttle only proved that the shuttle was unsafe, and nothing else. There are plenty of other launchers that have amply demonstrated how poor the shuttle success rate is in comparison. This lack of reliability is a failure that squarely rests on the shuttle design and the way it has been run, (human errors confounding technological weaknesses with the design), and is not an indication of rockets in general being more inherently dangerous than any other concieved launch system.
Rockets have the advantage of being technologically quite simple. (read cheap to build) and one of the main risk drivers is the performance maximizing that is done in the name of economics.
RLV's need to be built to maximize reliability first and payload capability second in order to achieve the economic benefits such an inherently more complex launch system entails. concepts like skylon will therefore have to be built with safe abort capability performance for all of the flight to orbit. this is because a loss of vehicle is an economic disaster for the operator. it not only destroys a single mission, but at the very least heavily delays future planned missions as well as causing the loss of a hugely expensive vehicle.
This inherrent economic driver towards ultra high reliability is a major reason for suporting RLV's in the first place. most alternative concepts like gun launchers etc lack this inherent driver as they too tend towards payload maximizing instead of reliability maximizing the payload delivery portion of the system.
Concepts like stratospheric launch towers and space elevators are so far beyond our current technological capability that they are for all intents and purposes irrelevant in a discussion about the next generation of launch systems. (10 to 50 years timeframe is considered next gen by this space enthusiast)
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The shuttle was too heavy to land on most of the runways of the world, so a similar design would need less payload capabilities to make it runway compatable.
Possibly the passenger airlines would convert to vertical take off and land except for the huge investment in the present system. Vertical does have some important advantages.
SSTO = single stage to orbit assumes LEO = low Earth orbit. Why do we want a stopover in LEO if we are going to solar sychonous orbit or almost anywhere else? Unless there is a good reason, let's forget LEO as craft designed for elsewhere can generally make a delivery to low Earth orbit, enroute to somewhere else. If the first stage leaves the atmosphere traveling vertically at 10 kilometers per second, won't a modest ion engine get us almost anywhere, by the shortest and quickest possible route, if it has enough ejection mass? Neil
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It would make sense if re-fueling in LEO.
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Space planes would probably use spaceports rated for such craft, not normal airports.
I expect that any SSTO craft would be a rather specialized craft, and that the designers would focus on making it as efficient as possible at carrying stuff between the surface and low earth orbit, and would not focus on long range space travel or fitting it with any scientific instrumentation suited for system exploration. There would most likely be separate modules or vessels for such work, similar to what REL have suggested.
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Read more aviation history. Until fairly recently, it was pretty common for experimental test pilots to die in the line of work. On that basis -- which is, in my opinion, the right one for comparison -- the US Manned Spaceflight Program has done quite well.
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