The UK investment into Reaction Engines is drawing some hilarious stories. First, it should “keep Elon up at night“:
Skylon, thanks to BAE investment and backing, has the chance to become the first true space plane that can take off from an airport, fly into space, and then safely return to the atmosphere and land on the same tarmac where it took off. From there, the path to further space exploration can be achieved. For the time being, SpaceX has not yet been able to produce an effective disposable rocket.
This incident, together with the loss of the Progress rocket last April and Cygnus in 2014, are likely to cause some logistics problems for the ISS. Had SpaceX’s launch been successful, it would have marked a significant milestone for the future of space travel. However, this is not yet the case. Despite SpaceX’s reassurances, there is evidence the company may need to make significant changes or abandon ship.
And yet, interestingly, no such “evidence” is provided. #ProTip: A rocket that has successfully delivered payloads to orbit nineteen consecutive times, and which continues to sign up launch customers, is an “effective” rocket, disposable or otherwise.
This is what happens when airplane designers try to build a launch system (I saw this with North American people during the NASP program as well). They don’t understand how launch systems work, they don’t understand the source of the cost, and they think that the solution is to build an airplane, because everything look like a nail. No one actually familiar with the launch industry would write a silly article like this.
And then there’s this:
The 24-hour slog from Sydney to London might soon(ish) be a thing of the past, thanks to the UK government.
The Brits have just pumped £60 million (USD $92.40 million) into a next-generation engine that — its makers claim — will make low-cost space travel possible for commercial customers.
But you and I might not be stepping abroad this super-plane for a while yet. The new ‘Sabre’ engine — a hybrid rocket and jet propulsion system which theoretically allows travel anywhere on Earth in four hours or less — is still at least a decade away, the Independent reported.
And if and when it happens, tickets will be a million dollars each.
Agreed, the Profit Confidential thing is a silly hype piece with a sensational headline. A tiny critique to your commentary:
has successfully delivered payloads to orbit nineteen consecutive .
Falcon 9 got its primary payload to orbit 18 out of 19 times. #19 was CRS-7.
The Skylon concept has really unacheiveble mass fractions.
If you could build conventional rockets with the same mass fraction as skylon then it would be ssto reusable using high performance stages combustion rocket engines.
One of the highest hydrogen mass fraction stages ever built was the S-II ME ~11. If you removed the LOX and replaced it with H2 its mass fraction would be 3.16 Where the much more complex skylon is listed as having a mass fraction of 6.5 more than two times better than the best hydrogen stage EVER BUILT! Its utter B.S.
Google doesn’t immediately turn anything up for the ME variant of the S-II stage. Was that S-II, MF ~11? I’ll have to do some more digging into this; when I hear “high mass fraction hydrogen stage” I immediately think Centaur, not S-II.
Wikipedia claims that 92.4% of the S-II mass was fuel, so looks like the mass ratio was more than 11. If I remember correctly, the S-II was where most of the weight savings were made in the Saturn-V, as the mass of the rest of it kept growing during development.
That’s still just a mass fraction of ~13 which still puts the LH2 mass fraction around 3.8 which is still far short of 6.5.
For Apollo 17, “Apollo by the Numbers” (NASA SP-4209) gives a total S-II dry weight of 80,423 lb, against a total weight of 1,085,902 lb. The total includes 934 lb of “other” weight, which I’ll take as dead weight. The mass ratio is then 1,085,902/81,357 = 13.35.
How about the S-N NERVA-program nuclear 3rd stage (S-IVb) replacement for the Saturn rocket? That stage was a ginormous H2 tank mated to a nuclear-thermal rocket engine.
http://www.astronautix.com/craft/satsnc5n.htm
That Web site gives the mass-ratio (gross over empty weight) at about 5:1? Given that the S-N had a particularly heavy nuclear rocket on it, maybe the 6.5:1 of Skylon isn’t total dreaming, but then the SABRE multi-mode engine and the wings-and-wheels aren’t without a weight penalty either.
Yeah, yeah, S-N was a “paper rocket” in the sense that it never got built, but at least it gives you a sense of what another team considered achievable with a bulky tank carrying a very light reaction mass (LH2).
Centaur from Wiki has a MF of 9.13 the Saturn V stage 2 beats it.
I’d be interested to know more about your reasons for skepticism concerning airplane-style vehicles for space access. I’ve always regarded them as the long-term solution to getting into orbit, once ballistic missile-based vehicles had developed an initial market.
Stephen
Oxford, UK
I have never seen a design close on an airbreathing orbital system. The reason is that an airbreather has to spend too much time in the atmosphere to use its airbreathing engine, with associated drag, and rockets have much better T/W ratio. If you want to get to orbit, get the hell out of the atmosphere, ASAP, and that is done with a rocket. There is nothing about rockets that is intrinsically expendable.
“The reason is that an airbreather has to spend too much time in the atmosphere to use its airbreathing engine, with associated drag, ”
I went after them about that in particular when I visited in ’09. They were emphatic that they didn’t hang around in the atmosphere trying to use it to gain a lot of velocity, thus the drag/heating issue wasn’t an issue.
The obvious question is then: why bother with the added complexity of making that engine breath air in the first place? Best I can remember, they said it all had to do with being able to use advantages of HTOHL. But I think you can get that simpler ways…
Even if they don’t plan to hang around in the atmosphere very long, they will have to because an air breathing engine has a much lower T/W ratio (usually from about 4 to 12) than a rocket engine (50 to 150). That means the design can’t give the overall vehicle a high thrust to weight ratio or the engines become to large a fraction of the total mass. You either have to take a huge hit on mass ratio or limit the vehicle to low accelerations.
So whereas a rocket would happily be accelerating at 3 to 6 G’s, the air-breathing vehicle will be lucky to hit 1.5 G’s, and probably won’t see 1 G because of another issue, supersonic and hypersonic lift to drag ratios. If the L/D is 3 then a T/W ratio of 1.0 pans out to an acceleration rate as if T/W was only 0.666. That means that it will take quite a while to accelerate while the vehicle is burning fuel.just to overcome drag. A large fraction of the impulse is being spent to cover distance instead of building speed.
And a vehicle like Skylon is adding all that extra engine mass and only really gaining special benefits (over conventional jet engines) to cover the Mach 2.5 to Mach 5.5 range. What are 3 Mach numbers worth when you’re trying to get to orbit carrying a heavy air-breathing engine sized for the take-off weight?
I’ve seen this story before – or something like it…about every couple of years since the concept came out long ago.
Yes, in addition to a combined cycle engine that’s _really_ a plumber’s nightmare (compared even to your average rocket engine) they only have to build the lightest structural system in history. But as they told me when I visited in 09, that’s small potatoes compared to the engine. (They may be right about that…)
All that said, I do salute the progress they made in testing the LOX condensation-without-icing system. But I’m still a bit nervous about something that uses thousands of 1mm diameter tubes chemically milled to even smaller wall thickness after they arrive.
Orbital rockets are all about ISP* Mass fraction.
Using chemical propulsion anything going to orbit has to look like a gas tank with a tiny payload on top.
Wings, landing gear heat shields etc… don’t look like a tank they
have no place on a launch vehicle, they are parasitic weight that contributes nothing to the mission.
The one place where aircraft parts make sense is as a portable stage 0 launch platform for small to mid size vehicles.
Air has an incredible amount of drag and getting to orbit is all about going fast not going high. You can get to space with 1/25th the energy needed to get to orbit. Anything above Mach 5 or so in the atmosphere and anything real melts, so you limit your airbreather to contributing less than 7% of the energy needed to get to orbit. Much better to take the vehicle hight and slow and rocket straight up out of the drag, allowing lighter structures and better mass fraction…….
The Sabre is not a hybrid jet and rocket. It is a hybrid airbreathing/closed cycle rocket. There’s no jet in there.
And if it works as advertised, the Sabre will be a game changer. The secret is to get up to the stratosphere as quickly as possible then build up most of your speed there in airbreathing mode, just carrying enough Oxygen for the final 4 or 5 Mach and circularization and reentry.
Rand, I know you object to spaceplanes because so much of the flight profile is spent in the atmosphere, but consider: the entire 8.5 minute burn to orbit for Soyuz or Shuttle or Saturn occurred in the atmosphere, with only a small circularization burn actually in space.
Well, there’s a bypass ramjet baked into the current design. It’s there because they need more hydrogen for the precooler than they can burn in the rocket. So they burn the extra hydrogen in the bypass ram to reduce the parasitic drag they’d incur if they just dumped it. I don’t know how much net thrust it adds.
Clarification: They need more hydrogen to cool the helium for the precooler than they can burn.
Ed,
In the atmosphere as in dense enough atomphere for airbreathing horizontal flight, or in the atmosphere as in significant drag to rockets, they are not the same thing…
The space shuttle is over 150K ft by 2 minutes into launch.
Wait–Wikipedia says Skylon’s first test flight is projected to be 10 years from now, and at some point after that it might be reusable? When SpaceX hasn’t quite yet managed reusability now? Pull the other one, it’s got bells on.
Also, “For the time being, SpaceX has not yet been able to produce an effective disposable rocket” seems like it’s got the wrong second-to-last word.
From what I know of Skylon’s projected performance and payload, it may never be a serious threat in the cargo department. At the high end it can’t loft heavy payloads into orbit like the current Falcon 9 and the upcoming Falcon heavy. At the low end, by the time it finally becomes operational, how will it compete with small sat launch companies like Electric Rocket, and even Virgin Galactic’s small sat launcher. Skylon will be trying to bust into already established markets with already low prices. An when and if Space X achieves even first stage reusability launch prices will be even lower when Skylon become operational somewhere around 2025-2030 timeframe. It may turn out to be just a people mover with some cargo. As for cost, it could become a 21st century version of the Concorde.
An old post by Henry Spencer illuminates some of the problems with air breathing launch systems.
http://www.islandone.org/Propulsion/SCRAM-Spencer1.html
Like many here, I am very doubtful that Skylon has much of chance of succeeding. It does not surprise me that the UK government has put money into it. Nor do I think that’s necessarily a bad decision: it seems reasonable to me that governments fund a bit of long-shot research. But why is BAE putting money into this?
As I said, airplane designers don’t understand the design issues with launch systems. They really think that the problem is that they don’t breathe air, and have to carry an oxidizer.
A couple of questions for everybody:
1) What are the issues with using something like SABRE as a plain-ol’-vanilla hypersonic engine? RE is claiming T/W that’s a lot higher than a scramjet.
2) It seems as if this would be a nice ground-to-air platform for a HASTOL/rotating skyhook system. Any thoughts?
What’s the present use for a “plain-ol’-vanilla” hypersonic engine?
My guess is that it’s weapons for a while, but that’s kind of the question I’m curious about. It seems as if a hypersonic power plant with better T/W would grow some novel applications. I suspect that SSTO is more of a shiny object for Reaction Engines, and they’re really counting more on full- or mostly-air-breathing apps.
In future a need may arise to get Marines to a remote location – say Benghazi – tout de suite.
The closest application for hypersonic airbreathing engines is cruise missiles. But I doubt you need anything as fancy as RE’s engine for that — scramjets are probably closer (with hydrocarbon fuel reformed to H2 + CO by partial combustion before injection into the scramjet proper.)
More questions:
1) Are you saying that the undesirability of using LH2 in a weapons system outweighs the considerable T/W advantage that SABRE would have over a scramjet?
2) LH2 has less of a logistical problem in a strategic weapons system than in a forward-based tactical system. I’m hard-pressed to think of a hypersonic cruise missile as anything other than a strategic system. Do you disagree?
3) Do you have a pointer to how you’d use reforming in a flight system? Isn’t this the worst of all worlds wrt Isp? And what do you do with the CO? If you’re heating it for reaction mass, isn’t it easier just to burn it as kerosene or LNG and have done with it?
The key takeaway from your comment is that SABRE must use LH2 because it’s ultimately the heat sink for the precooler. So I agree that you absolutely need to factor in the LH2 logistical issues in your evaluation.
Not (just) logical considerations: the LH2 tanks would be too large. T/W might be higher, but drag would also be higher. Density is a very nice property to have in a fuel.
As for reforming: may not actually be necessary. The X-51 test program used JP7 as engine coolant and that heated it enough for injection and burning in the engine itself. That scramjet operated at speeds up to Mach 6. I don’t know if the fuel was chemically modified by the heating; if so, apparently coking wasn’t an issue.
If more heating is needed then some small portion of the airflow could be slowed to a near-stop and mixed with the fuel. I believe engines like this (or substantial parts of them) have been ground tested.
A winged rocket would be a good match for a rotating skyhook system. The Air breather doesn’t buy you much over a carrier aircraft and a winged rocket. (For a rotating tether you probably need significant cross range hence carrier aircraft.)
Aren’t all engines “Reaction Engines”?
Thanks for an interesting discussion. There seem to be both advantages and disadvantages to using a spaceplane as opposed to a missile. One possible advantage that nobody has yet mentioned is that, while the lower T/W ratio of the horizontal launcher’s engines limits its acceleration, this presumably also limits the vibration and general stress on the airframe, which could be important in prolonging its service life.
Ultimately, I suggest, both reusable spaceplanes and reusable rockets will need to be flown in practice before the true balance of advantage between them (for medium-sized payloads) becomes clear. Engineering is not an armchair pursuit. But it is regrettable that this is having to be done by the private sector, the space agencies having fixated on a preferred style of building and operating a single, prestige system as a socialist monopoly provider, rather than exploring the operational envelopes of a variety of different architectures.
Stephen