Will Skylon Actually Fly?

[KerikBalm]

Correct me if I'm wrong, but isn't the idea of a reusable upper stage that the entire skylon doesn't make it to orbit?

You two stage it, so that the payload fraction is higher.

Its easier to make a small reusable upper stage that can handle reentry, than to make the entire skylon handle re-entry.

The upper stage is made heavier by making it able to reenter and be re-used, but the skylon is made lighter by not having to make it to orbit, and not having to withstand ~8km/s re-entry (instead, lets say it only reaches 3 or 4km/sec)

The sabre's are supposed to get to what, 2km/sec in airbreathing mode? that leaves another 6km/sec to get to orbit... why push the entire skylon another 6km/s? especially when its going to be so much more massive than the payload?

Push it another 2-3km/second using sabres in closed cycle and, then release the upper stage, leaving the upper stage with only 3-4 km/s to go.

A 5% payload fraction means its running right up against the limits of the rocket equation... the solution to that is staging.

You can stage and still be re-usable.

[magnemoe]

Yes one benefit of Skylon is that you have better margins than say Falcon 9, like the reusable attempt for Falcon 9 reusable upper stage will be an option then it can be uses.

One idea is to dump the fuel tank and recover engine and systems like ULA thing for the first stage, for an second stage this makes more sense, first you can do with an smaller heat shield, second the small engine would be practical to grab in the air with an pretty standard helicopter.

[prophet_01]

It's not just about how difficult it would be to design a second stage with a heat shield. It's about the weight which directly cuts into your payload. That stage would need to have way more fuel in order to return and to transport all the necessary equipment to remain operational on it's own after separation from the payload. That includes at least RCS, comm systems, avionics and batteries. The capability to reuse it also requires an engine that can be reignited multiple times (on multiple missions) which is expensive to develop and heavier than a disposable one. And of course you need something to recover or land it after returning from a higher orbit.

For conventional landings parachutes would do the job, but since you're planing to reuse it, diping it in salt water is a bad idea. So you likely also need retro rockets for the landing (something like super dracos or the system that soyuz uses).

Wings and landing gear could work as well, but would likely be even heavier. Both options would require it to be significantly more structurally stable and heavier compared to a regular 3rd stage.

If you want to recover it in space, you could skip that, but it now needs an attachement node and a canardarm instead (or something similar). The vehicle would also have to remain in space for quite some time which requires additional precautions. It would need to stay up there until the next skylon launches (assuming we still talk about suborbital skylon hop) and recovering something during on a suborbital trajeczory is already a stupidly difficult thing on it's own.

And remember, all of this is fairly heavy equipment that could as well be replaced by something that actually remains in space and that you get paid for.

From my point of view, skylon involves more than enough unproven technologies already. Does it realy need more concepts that may not work out as designed on paper?

Edit: That helicopter thing still requires you to land it fairly precisely. With winds involved you can easily miss by a couple of km and crash. As a result you need grid fins or engines to change course. I believe in those significant savings in weight when they complete a test.

Edited October 19, 2015 by prophet_01

[Kryten]

If you turn Skylon into a reusable lower stage, then you lose the entire point of the elaborate air-breathing rocket system. It moves it into an arena where it has to complete with more conventional rocket systems like the XS-1 contenders or probably Blue's orbital design, and in that context SABRE is just extra cost and complexity.

Edited October 19, 2015 by Kryten

[Rakaydos]

If you turn Skylon into a reusable upper stage, then you lose the entire point of the elaborate air-breathing rocket system. It moves it into an arena where it has to complete with more conventional rocket systems like the XS-1 contenders or probably Blue's orbital design, and in that context SABRE is just extra cost and complexity.

if I understand the argument correctly, they're not saying Skylon shoud BE an upper stage, the're saying it should HAVE an upper stage.

[Kryten]

Sorry, typo.

[Rakaydos]

Sorry, typo.

Considering how many kerbal SSTOs use air breathing first stages, I'm not sure your logic is sound. Oh, sure, the kerbal turbojet is OP, but the Rapier is supposed to be a direct expy of the Saber engine.

[KerikBalm]

If you turn Skylon into a reusable lower stage, then you lose the entire point of the elaborate air-breathing rocket system. It moves it into an arena where it has to complete with more conventional rocket systems like the XS-1 contenders or probably Blue's orbital design, and in that context SABRE is just extra cost and complexity.

It still operates from runways, not launch pads.. the SABRE spaceplane part would be made smaller, what it carrier would be made bigger... it could carry a small shuttle like some of the original shuttle concepts.

Now you don't need your Sabres to go through reentry... probably saving maintenence.

The air breathing stage doesn't go through reentry, saving maintenence.

Both the SABRe-plane and shuttle land right back at the runway.

It shouldn't add anything more complicated than a second guidance system, and re-attaching the orbiter -> which if designed right would be simple.

If you double the cost of operationg, but go from a 5% fraction to a 15% fraction, you come out ahead

A SSTO spaceplane that can cheaply get to orbit, but can't haul any payload up, is still very expensive per ton.

Staging can ensure you actually get a payload up there.

Even if a normal rocket has a 5% payload... its not using the benefits of airbreathing, and mostly not LH2+LOX fuel.

If it goes overweigh, you stick a smaller upper stage, and a smaller payload on top,

If the SSTO goes overweight... well then there's nothing you can do, it doesn't get to orbit...

When you consider how much less mass you'd have to take to orbit, how much lower velocity the SABRE stage would have to deal with... it seems to me that the added complexity of seperating a remounting an orbiter is worth the gain in performance.

Rakydos... SSTOs in KSP need to get to about 2,300 m/s... SSTOs in real life need to get to ~8,000 m/s

after switching to closed- cycle:

a SSTO in KSP needs to go about another 1,000 m/s

a SSTO in real life needs to go about another ~6,500-7,000 m/s

That's quite a difference!

you can't take what works for SSTOs in KSP and apply it to an argument about real life

Edited October 19, 2015 by KerikBalm

[Kryten]

I'm not comparing Skylon to expendable rockets, but to reusable systems that use normal rocket engines. Skylon only has the air-breathing system to hit the numbers required to hit SSTO; as a lower stage it doesn't provide much extra capability in return for the extra complexity.

It still operates from runways, not launch pads..

That's not going to make much difference. It's still going to have somewhere to be inspected, an integration facility, payload preparation and fuelling facilities, control rooms; most of the infrastructure of conventional launch.

[magnemoe]

I'm not comparing Skylon to expendable rockets, but to reusable systems that use normal rocket engines. Skylon only has the air-breathing system to hit the numbers required to hit SSTO; as a lower stage it doesn't provide much extra capability in return for the extra complexity.

That's not going to make much difference. It's still going to have somewhere to be inspected, an integration facility, payload preparation and fuelling facilities, control rooms; most of the infrastructure of conventional launch.

True, they will compete with falcon 9 reusable and similar systems. Note again that anything outside of LEO will need an second stage anyway.

Benefit of Skylon is that it might be able to take an decent payload to orbit, this depend on scale. The second stage will be smaller and simpler.

No need for aerodynamic, survive high g forces during launch or have much TWR.

Downside is an very expensive airframe and lots of new technology while something like falcon 9 reusable don't really uses new technology

[KerikBalm]

Presumably, the sabre spaceplane can fly right back to the launch point, unlike reusable boosters.

However, I do think reusable boosters may change the finances of getting to space, and make SSTO pointless altogether.

It's still going to have somewhere to be inspected, an integration facility, payload preparation and fuelling facilities, control rooms; most of the infrastructure of conventional launch.

Its going to have that whether or not its an SSTO...

Sure, the airbreathing part gets you to SSTO... but what is the point of SSTO at all?

If we imagine a situation where maintenence/inspection is cheap, but fuel is expensive, the airbreathing solution could be economical.

As it is, I don't expect Skylon to be competetive with reusable booster designs in the first place.

[Wolf Baginski]

The Skylon people have been working on the idea since the mid '80s.

We had supersonic airliners back then, and the maximum sustained speed was limited by the colour of paint used on the fuselage.The only thing the British government throws money at is the pockets of politicians. The only all-British satellite launch flew as Private Enterprise.

[Sanic]

The Skylon people have been working on the idea since the mid '80s.

We had supersonic airliners back then, and the maximum sustained speed was limited by the colour of paint used on the fuselage.The only thing the British government throws money at is the pockets of politicians. The only all-British satellite launch flew as Private Enterprise.

No Skylon then.

[Shania_L]

BAE seem to think Skylon will fly, they just bought a decent portion of Reaction Engines stock. Plus another UK government cash injection.

[Alias72]

This is a two part question.

1. Is Skylon physically possible.

Yes. Space planes are not, strictly speaking, over difficult to design. (the issue is are they worth it.)

2. Will Skylon get the support it needs to function.

ummmm...... not sure.

[_Augustus_]

Now that the UK govt. just gave them cash, my hopes are going up!

I really hope that Skylon flies, a fleet of them would be great for building space stations and setting up Mars missions.

My one question is though: Could Skylon be upgraded to fly to EML2?

[Kryten]

My one question is though: Could Skylon be upgraded to fly to EML2?

All those unproven technologies have to come out perfect for it just to reach LEO, same as most SSTO designs.

BAE seem to think Skylon will fly, they just bought a decent portion of Reaction Engines stock. Plus another UK government cash injection.

There are other applications for this tech than Skylon, and they're potentially much more practical. BAE has no interest in launch vehicles.

[Rakaydos]

Now that the UK govt. just gave them cash, my hopes are going up!

I really hope that Skylon flies, a fleet of them would be great for building space stations and setting up Mars missions.

My one question is though: Could Skylon be upgraded to fly to EML2?

You dont use a SSTO to go beyond low orbit. You lose the advantages of the air breathing engine by bringing extra dead weight.

Skylon + an ion tug, operating as a relay, however...

[Alias72]

One thing to understand is how pathetic Earths atmosphere truly is. The RSS mod gives you a pretty good sense of how low the altitude cutoff for jet engines is. It is also in a really bad place. Even if you get your speed up to a decent amount at the cutoff altitude your angle will be so shallow that most of the gains will be eaten up by atmospheric drag as you try and push yourself into orbit. There appears to be no good option when it comes to angle and velocity for spaceplanes.

[KSK]

The Skylon people have been working on the idea since the mid '80s.

We had supersonic airliners back then, and the maximum sustained speed was limited by the colour of paint used on the fuselage.The only thing the British government throws money at is the pockets of politicians. The only all-British satellite launch flew as Private Enterprise.

We had one supersonic airliner. It was a beautiful machine and a work of engineering art but it was also noisy and expensive to maintain and run. Turns out that most people didn't care about crossing the Atlantic in two hours - they wanted cheap flights to Spain to get some sun. I am intrigued about that paint colour assertion - compared to the other engineering challenges involved in building and running a supersonic airliner it sounds like a load of hooey to me, but I'm quite willing to change my mind if you provide a link.

And the all-British satellite launch. Presumably you're referring to Black Arrow, which was very definitely a government program. Sure it was built by private contractors - just like every other government run aerospace program out there.

[ment18]

https://en.wikipedia.org/wiki/Concorde

Concorde had livery restrictions; the majority of the surface had to be covered with a highly reflective white paint to avoid overheating the aluminium structure due to heating effects from supersonic flight at Mach 2. The white finish reduced the skin temperature by 6 to 11 degrees Celsius.^[93] In 1996, Air France briefly painted F-BTSD in a predominantly blue livery, with the exception of the wings, in a promotional deal with Pepsi.^[94] In this paint scheme, Air France were advised to remain at Mach 2 for no more than 20 minutes at a time, but there was no restriction at speeds under Mach 1.7. F-BTSD was used because it was not scheduled for any long flights that required extended Mach 2 operations.^[95]

I think that is what he was talking about.

[Van Disaster]

I wonder if this is BaE's attempt to get back into civil aviation - I suspect they're regretting selling off their part of Airbus.

Note that Reaction Engines specced out a hypersonic airbreathing engine with the same tech ( Scimitar ) so it's not necessarily *all* about orbiters. I'm surprised it's BaE and not RR though.

[Kryten]

I wonder if this is BaE's attempt to get back into civil aviation - I suspect they're regretting selling off their part of Airbus.

It's more likely an alternative to scramjets for hypersonic weapons systems.

[Van Disaster]

It's more likely an alternative to scramjets for hypersonic weapons systems.

UCAVs perhaps, they're very into UAV development - I suspect the Typhoon is probably the last manned fighter we'll see from BaE unless you count their share of the F-35. Skylon itself is a rather extreme UAV.

But still, no reason they couldn't get back into the civilian market.

[Nothalogh]

it was also noisy

Anyone who complains about aircraft noise deserves nothing short of a serenade by Slaanesh's finest Noise Marines