Forget about 'spaceplane economics'. Just get the SABRE engine out of the door already, then people can start talking about economics. Apparently the engine design has been complete for years and they just need additional funding.
Should a production SABRE engine prove to be low maintenance enough, it won't just be a matter of "stacking up", this will be huge. However, if the maintenance is costly, then it's the Space Shuttle all over again. In contrast to the shuttle, tho, there's no costly thermal protection system, the skin and some water cooling should be enough. Also, no astronauts, Skylon is supposed to be fully automated.
A fully reusable spaceplane for small payloads and a big dumb booster (SpaceX) should complement each other very well.
"Because it will use a low-density fuel, liquid hydrogen, a great volume is needed to contain enough energy to reach orbit. The propellant is intended to be kept at low pressure to minimise stress; a vehicle that is both large and light has an advantage during atmospheric reentry compared to other vehicles due to a low ballistic coefficient.[44] Because of the low ballistic coefficient, Skylon would be slowed at higher altitudes where the air is thinner. As a result, the skin of the vehicle would only reach 1,100 Kelvin (K).[45] In contrast, the smaller Space Shuttle was heated to 2,000 K on its leading edge, and so employed an extremely heat-resistant but fragile silica thermal protection system. The Skylon design does not require such a system, instead opting for using a far thinner yet durable reinforced ceramic skin.[2] However, due to turbulent flow around the wings during re-entry, some parts of Skylon would need to be actively cooled.[42]"
Point of note: some of the design constraints of the Shuttle were imposed by the USAF, whose proposed mission for it was to retrieve KH-11 class spysats from polar orbit for refurbishing/relaunch. (This mission was never actually carried out, but probably seemed like a Good Idea circa 1968-74. NASA needed USAF lobbying support to get funding for the STS program past Congress, so they deliberately tailored the shuttle design to suit speculative Air Force requirements.)
A corollary of the Shuttle being designed to transport classified payloads during re-entry was that at no stage during re-entry must the shuttle overfly "hostile" (Soviet or Chinese) territory, lest a disintegration result in classified payload fragments falling into the wrong hands.
Consequently the shuttle was designed with that outsized (spysat-friendly) payload bay which seldom got used to maximum effect, and with a short, fast, hot re-entry profile (so that it could commence and complete re-entry after leaving hostile airspace). Hence the need for an exotic, high-specification thermal protection system.
(This mission requirement probably contributed to the loss of the Columbia as well.)
Random Question: What is the altitude of "enemy airspace"? Is there some cutoff or threshold recognized by the UN or some other int'l protocol? (Presumably one isn't infringing on enemy airspace in actual earth orbit.)
"There is no international agreement on the vertical
limit of State sovereignty, the boundary between
territorial airspace and outer space. The need for
defining this boundary has been debated for over 50
years."
Thanks! As a datapoint, the order of magnitude [10km -100km] range seems like the focus of his recommendation:
More and more States are developing their own domestic space launch capability. Few of these new space powers will be able to freely access space, or utilize the most efficient launch azimuths, if neighboring States can claim
sovereignty up to even 62 miles (100 km). They will have even more difficulty returning objects to Earth if the boundary is set at that altitude. Even the U.S. and
Russia are facing limitations on their ability to freely access space. Setting a low vertical limit on State sovereignty will ensure all States have equal access to
space. (p81).
The last one was sent up on Decemember 2012 and its still up there. Probably not as cost-efficient, but, there is an unmanned spaceplane in production, but its a secretive DoD project so we don't know too many details nor will it be used for non-military applications.
X-37 is launched on a traditional expendable rocket and only glides to a landing. SABRE is an air-breathing SSTO spaceplane that takes off from a runway. They're completely different beasts.
I'm currently reading "The Space Shuttle Decision" by T.A. Heppenheimer, which discusses the planning in the late 1960s for a reusable successor to the Saturn rockets.
One interesting thing is that they then envisioned this to happen in phases: a "type I" partially reusable vehicle (with expendable fuel tanks and maybe expendable boosters), then a type II fully-reusable rocket-propelled vehicle (probably two winged stages which both fly back), and finally a type III air-breathing vehicle (Skylon-style air liquefaction was talked about already then).
The more advanced concepts cost a lot of money to develop, but reduce the per-launch cost. So the hope was to start with a type I vehicle (the eventual Space Shuttle) to reduce launch cost and grow the market, until there are plans for so many launches that it makes sense to fund the advanced types.
In hindsight, the Space Shuttle unfortunately kind of botched the reuseablity. But with SpaceX we finally seem to be on track to having a working partially resuable launch vehicle. Maybe this will "unfreeze the future"---with a bigger launch market and commercial pressure people might be tempted to go for something like Skylon rather than more of the same in follow-up Arianes...
No, it's single stage to orbit; it's a poorly written article. It goes to mach 5.4 with atmospheric air before switching to liquid oxygen. The article makes it sound like it only ever reaches mach 5.4.
It's by Jonathan Amos, who generally knows his stuff and whose articles are usually well above most bbc tech articles in quality. It's an unfortunately worded paragraph I'd say.
it is lost on me why Skylon would be noticeably better than a Mach 5-6 plane boosting a second stage. Such 2 stage system would have obviously less trade-offs and thus would be easier/cheaper to design and build.
Staging isn't free. While true that the second stage vehicle will be simpler, the combined second and first stage together could be more complicated/heavier than the Skylon.
Noticeably, the point of the Skylon and SABRE is that it's possible to use a common engine core in airbreathing and pure rocket mode, thus potentially generating weight savings.
I'm sure someone sat down and did the calculations. I have this feeling that a lot of the times when you actually sit down and work out the math for a range of assumptions, you generally come down to 'eh, maybe A, maybe B, so may as well try A'.
No. It's a plane that can go into low orbit. You need an additional booster to bring stuff into high orbits. For smaller satellites, this study concludes that it is economical to recover that booster.
"power units that work like jet engines at low altitudes and slow speeds, but then transition to full rocket mode at high altitudes"
and
"Skylon itself is designed only to go a few hundred km above the Earth, so it would need an additional "upper-stage" module to push the satellite into its final, 36,000km-high orbit."
The technical risk has to be factored in. Nobody has ever done such heat exchangers and how to keep them free of ice is a secret sauce they are not sharing. Without peer review or open discussion the engine might as well not exist.
Spaceplanes are ludicrously hard to get right in KSP. The aerodynamics model is not very good and the process whereby fuel is taken from the frontmost tank first tends to make the plane flip halfway through the ascent.
I've occasionally considered writing something with a better aerodynamics sim in ...
You need real money to develop aerospace technology. The SABRE engine is in its final stage of development, and according to the articles linked from the main article, just finishing the final stage will cost about 200 million pounds ($330 million dollars). That's about thirty times what the largest project in Kickstarter history has ever raised.
The article pegs the total development cost of the plane at the cost of developing an Airbus plane. That's about $10-15 billion, or more than an order of magnitude more than all of the money that has ever been raised in Kickstarter history. Probably more than all the money that has ever been raised by crowd funding period.
Sorry for the naive question, but any ideas on why it costs so much? Wouldn't putting 100-200 top engineers on it for a few years be enough? What do they need 300 million for?
You don't merely need engineers to design the thing. You also have to actually build what you design, custom manufactured out of exotic materials in small batches, and then test those components (often to destruction) before building a slightly-more ambitious prototype. A test or launch also involves a large land area for safety, significant support staff handling hazardous material, and miles of red tape to secure the firing range and airspace.
This build-test-debug loop costs millions and may take months or years, and a single spectacular failure can sink the entire project (e.g. DC-X).
Most engineering is not like software! For example, most of the cost of a bridge is not the civil engineering to design the structure...
Not just that, but original R&D is much more expensive than implementation of proven designs. Not knowing which designs will work, or whether the overall idea will even work at all, greatly increases the number of design/build/test/debug cycles needed to build a product.
$300 million to cover "a few years" arguably isn't that much - even basic stuff as the loaded costs of staff is going to be a significant proportion of that.
To maybe put that in perspective, $100 million a year is the budget of one of the smaller F1 teams.
A fully reusable single stage to orbit "plane" completely changes the dynamics of putting stuff in orbit both on cost and turn around time.
The Falcon 9 is privately funded as is the Merlin engine it uses however pretty much all the materials science, initial engineering etc required to design and build a merlin was publicly funded.
There are times when a public/private partnership makes sense and this is one of them.
SpaceX received a subsidy from Elon Musk. The financial case for the company wasn't clear at the start - it was only because they had significant financial backing for the initial development period that they could get to where they are now. They may now be profitable, but if you'd tried to make a case a decade ago for funding you'd get nowhere. There are all sorts of high-capital technology developments that simply aren't immediately profitable or low risk enough for VC funding. Why should we as a society rely on the whims of a few wealthy people? This kind of technology, should it be realised, has a value to everyone.
The UK isn't supporting Skylon "for the hell of it", either. Their taxpayers would likely be pretty happy to have the next Boeing/Airbus live on their soil.
Both situations involve someone with money taking a bet on a currently non-profitable venture hoping it'll pay off in the future. SpaceX wasn't profitable when Musk put money in.
The 'subsidy' is less than a non-SpaceX launch would cost and peanuts for a R&D project, specially one with this potential. And it's about the same amount the US military is currently spending to certify SpaceX for military launches. What about the NASA contracts? These are done with taxpayer money too.
I find it fascinating that Elon Musk hasn't chipped in since even though it's a competitor to SpaceX it is ultimately a step in the right direction for his goal of putting people on Mars and into space.
Hell he could take the engine and build a new spacecraft based on it.
I'm baffled. How does the need for public financing make a project "loose before the match even beings"? The project needs public financing because private investors wouldn't shoulder the risk.
Most significant leaps of technological innovation in the history of civilization required public support. And as we move on the leaps will become harder and riskier still which means even less willingness of the private investors to put up the money. So brace yourself :P
They are completely different designs, with different technology and applications. The Falcon is 1940s technology updated; the Skylon is new; there has never been anything else flown using the same engine concept before.
Should a production SABRE engine prove to be low maintenance enough, it won't just be a matter of "stacking up", this will be huge. However, if the maintenance is costly, then it's the Space Shuttle all over again. In contrast to the shuttle, tho, there's no costly thermal protection system, the skin and some water cooling should be enough. Also, no astronauts, Skylon is supposed to be fully automated.
A fully reusable spaceplane for small payloads and a big dumb booster (SpaceX) should complement each other very well.