Whats wrong with Skylon?

[AngelLestat]

7 hours ago, Val said:

You don't really need a 747 to carry a 15 t payload, though. The latest Skylon user manual (pg. 6) list airbreathing Isp as ~4000-9000s.

I just mention 747 because it is the most common airplane, of course you can use another airplane that will fit better in cost for the payload size.
Thanks for the link..  but I am shocked with that new ISP number.. I thought that a jet turbine engine designed for lower speed would be more efficient. Maybe that isp depends on speed and altitude. 

 

7 hours ago, Val said:

Barring issues with noise and LH2 supply, Skylon can takeoff from any regular airport, when it's not loaded with LOX (~150 t lighter). Mark Hempsell says so here.

remove lox will help a lot.

7 hours ago, Val said:

It is actually one of the intended usage modes for Skylon, that you can have the payload integration in any airport that supports it. Fuel the Skylon with just enough LH2 and have it self-ferry sub-sonic in airbreathing mode to an equatorial launch site, where it's filled with LOX and LH2 before leaving for orbit.

It's probably not how it will be done at the beginning. Lack of infrastructure, I guess. But that is how it's envisioned to work when there's many Skylon owners.

If in the future if we see more cryo fuel airplanes as it should if we want to solve the co2 planet issue, then it may had more sense..  but we would still need lox.

[blowfish]

7 hours ago, Val said:

You don't really need a 747 to carry a 15 t payload, though. The latest Skylon user manual (pg. 6) list airbreathing Isp as ~4000-9000s.

Barring issues with noise and LH2 supply, Skylon can takeoff from any regular airport, when it's not loaded with LOX (~150 t lighter). Mark Hempsell says so here.

It is actually one of the intended usage modes for Skylon, that you can have the payload integration in any airport that supports it. Fuel the Skylon with just enough LH2 and have it self-ferry sub-sonic in airbreathing mode to an equatorial launch site, where it's filled with LOX and LH2 before leaving for orbit.

It's probably not how it will be done at the beginning. Lack of infrastructure, I guess. But that is how it's envisioned to work when there's many Skylon owners.

I don't doubt that this is possible, but I fail to see the use case.  In addition to LH2 fueling infrastructure, you would need dedicated payload integration and maintenance facilities.  The Skylon is not intended to land and then immediately take off again like an airliner - there is going to be significant maintenance between flights, even non-orbital flights.  So you could build all that infrastructure, deal with the cost and liability of an additional flight, and not actually get the payload to space any faster.  Or you could just put the payload on a cargo plane and fly it to the launch site.  Seems like a solution in search of a problem for me.

[FreeThinker]

I don't think the Skylon would work very well. The main problem is that LiquidHydrogen lack of density. Instead they should put a NUclear Ramjet, which could switch to Ammonia once in space, it would significantly improve it's effecte load.

[mikegarrison]

I am boggled by how many people can't seem to understand that these guys are developing an engine. The spaceplane idea is just a wrapper around the engine. All the suggestions to replace their engine with something else really, really miss the point.

[cantab]

1 hour ago, blowfish said:

I don't doubt that this is possible, but I fail to see the use case.

It's there when (if?) space launch becomes common enough. We're way off that now, and probably Skylon itself won't get us there, but I hope it gets that way before I die. Space hotels, Moon colonies, all the cool stuff we were imagining in the 1960s.

[blowfish]

11 minutes ago, FreeThinker said:

I don't think the Skylon would work very well. The main problem is that LiquidHydrogen lack of density. Instead they should put a NUclear Ramjet, which could switch to Ammonia once in space, it would significantly improve it's effecte load.

And why does fuel density even matter?  A larger tank means somewhat more drag, but remember that most of the delta-v is in rocket mode anyway.  Nuclear ramjets and rockets are going to have low TWRs anyway - not suitable for propelling a craft to orbit.

13 minutes ago, cantab said:

It's there when (if?) space launch becomes common enough. We're way off that now, and probably Skylon itself won't get us there, but I hope it gets that way before I die. Space hotels, Moon colonies, all the cool stuff we were imagining in the 1960s.

I still don't see the use case.  Shipping payloads is easy and cheap.

[wumpus]

5 hours ago, sevenperforce said:

I provided the citation above; it's this MIT study.

If you read to the end of the paper, you will note that it is a solution in search of a problem.  The whole point of providing a spaceplane that can takeoff and land in most airports in the world is to provide a plane for suborbital hops.  The catch is that suborbital flight requires only 3/4 of the fuel loaded up, while a vastly more common trip 1/4 around the world requires only 60% of the fuel.  One key that the authors aren't remotely serious is that they never make the obvious decision to take off with all necessary H2O2 (which was slightly more than the dry weight of the spaceplane.  Having an unmodified fueling plane plus only a single system of re-fueling would presumably lower logistics costs tremendously (H2O2 is an incredibly caustic, although probably not nearly as nasty as LOH, you would want to avoid refueling with it and keeping it out of your refueling planes if at all possible).

I also suspect that they are really pushing the numbers of the dry weight of the spaceplane.  With SABRE (and a free flight up to mach 5.5) you need 184,250 lbs of fuel.  With a standard SSTO rocket, (cheating by using the same dry weight), it only takes 224,250 lbs of methane (hyrdrogen's density means the numbers won't line up at *all*) to go from 0-orbital (cheating again by ignoring drag (worse for so small a craft)).  Do you really think you can get 3 passengers into orbit on a SSTO *smaller* than a Falcon?

Oh yes, in case you missed it: 184,250 lbs of fuel (and note that due to H2O2's listed cost, it should cost twice that in lbs of kerosene to the buck) for 440lbs of passengers.  Seriously expensive flight, even with "thousands of Skylons".  Don't forget to pay for the entire crew of the fueling plane and all the pre/post flight maintenance.

 

[blowfish]

6 hours ago, sevenperforce said:

I provided the citation above; it's this MIT study.

Thanks for fixing the link, but I still don't see where you're getting "better performance" from.  The Blackhorse concept they suggested has a lower payload fraction even at takeoff (i.e. before refueling) than the Skylon.  To get up to the Skylon's payload to orbit (15t), it would need to weigh 750t at takeoff, and nearly 2.5 Mt after refueling.  That's considerably larger than any plane that has ever flown.

[sevenperforce]

29 minutes ago, blowfish said:

Thanks for fixing the link, but I still don't see where you're getting "better performance" from.  The Blackhorse concept they suggested has a lower payload fraction even at takeoff (i.e. before refueling) than the Skylon.  To get up to the Skylon's payload to orbit (15t), it would need to weigh 750t at takeoff, and nearly 2.5 Mt after refueling.  That's considerably larger than any plane that has ever flown.

Better performance was vs VTHL SSTO pure rocketplanes.

[Emperor of the Titan Squid]

Skylon would revolutionize space travel, and is necessary to make it available to the masses. However, the SABER tech is unproven. Rockets are more versatile and skylon would only be effective if flown 100 times per year, but it can fly that much. Also, what does skylon stand for? What would be a good abort system? I thought pyros on payload bay doors and srbs on the crew module.

[ModZero]

14 hours ago, Emperor of the Titan Squid said:

Skylon would revolutionize space travel, and is necessary to make it available to the masses. However, the SABER tech is unproven. Rockets are more versatile and skylon would only be effective if flown 100 times per year, but it can fly that much. Also, what does skylon stand for? What would be a good abort system? I thought pyros on payload bay doors and srbs on the crew module.

Skylon has way too little payload to revolutionize anything on its own, it's not really all at necessary either. 

It doesn't have an abort system, because it's not a crewed vehicle. If it were to carry people, it would just go back to the airstrip – it dumps quite a bit of mass right after liftoff (water for the brakes), and could possibly jettison the oxidizer. 

[magnemoe]

50 minutes ago, ModZero said:

Skylon has way too little payload to revolutionize anything on its own, it's not really all at necessary either. 

It doesn't have an abort system, because it's not a crewed vehicle. If it were to carry people, it would just go back to the airstrip – it dumps quite a bit of mass right after liftoff (water for the brakes), and could possibly jettison the oxidizer. 

Yes it could do an in flight abort like other planes by dumping oxidizer and most fuel and do an landing, this will also work in unmanned mode and is an benefit with spaceplanes over rockets. On the other hand an engine out at hypersonic speed with engines on the wing tips will probably make confetti of the plane unless the system kills the other engine very fast. 

An future crewed version will likely use an crew module in the cargo hold, this can be ejected but don't think it could survive an reentry, so you need to ride plane down to mach 2 or something before ejecting. 

[Steel]

1 hour ago, magnemoe said:

Yes it could do an in flight abort like other planes by dumping oxidizer and most fuel and do an landing, this will also work in unmanned mode and is an benefit with spaceplanes over rockets. On the other hand an engine out at hypersonic speed with engines on the wing tips will probably make confetti of the plane unless the system kills the other engine very fast. 

An future crewed version will likely use an crew module in the cargo hold, this can be ejected but don't think it could survive an reentry, so you need to ride plane down to mach 2 or something before ejecting. 

Let's not talk about "future crewed versions" of a design that is not even finalised for an unmanned prototype. And that's overlooking the fact that the engines haven't even been fully designed, built or tested and probably won't be for some time.

[FreeThinker]

Only a nuclear powerered Skylon would make any sence to me, as  it would alllow free travel in the atmosphere, reducing the total develta V to get in space by 2000 km. After leaving the atmosphere, thanks to double the Isp, you need only half the fuel to get in low earth orbit, which would effectively increase effective paylood by more than a factor of 10. It would also be a big advantage when landing where the vessel won't behave like heavy glider, making landing a lot safer.

Edited April 12, 2016 by FreeThinker

[sevenperforce]

 

12 minutes ago, FreeThinker said:

Only a nuclear powerered Skylon would make any sence to me, as  it would alllow free travel in the atmosphere, reducing the total develta V to get in space by 2000 km. After leaving the atmosphere, thanks to double the Isp, you need only half the fuel to get in low earth orbit, which would effectively increase effective paylood by more than a factor of 10. It would also be a big advantage when landing where the vessel won't behave like heavy glider, making landing a lot safer.

And by "nuclear powered skylon" I assume you mean "not skylon at all, but a HTHL spaceplane powered by a hydrogen-precooled supercharged nuclear thermal turborocket"?

[FreeThinker]

1 hour ago, sevenperforce said:

 

And by "nuclear powered skylon" I assume you mean "not skylon at all, but a HTHL spaceplane powered by a hydrogen-precooled supercharged nuclear thermal turborocket"?

Yes, that would be the same yes, a nice bonus would be it can be converted to a intercontinental bomber, where it can bomb/nuke any location on earth within 30 minutes and repeat.

Edited April 12, 2016 by FreeThinker

[sevenperforce]

14 minutes ago, FreeThinker said:

Yes, that would be the same yes, I nice bonus would be it can be converted to a intercontinental bomber, where it can bomb/nuke any location on earth in within 30 minutes and repeat.

The precooler would still drink a considerable amount of liquid hydrogen...just saying. 

[FreeThinker]

Just now, sevenperforce said:

The precooler would still drink a considerable amount of liquid hydrogen...just saying. 

 we could get around this be creating a refrigeration with radiators build into the top wings, that way, no hydrogen has to be lost

[sevenperforce]

3 minutes ago, FreeThinker said:

 we could get around this be creating a refrigeration with radiators build into the top wings, that way, no hydrogen has to be lost

Eh, there is no way to dump that much heat that quickly. You've got to just go ahead and accept the coolant losses if you want a SABRE-style precooler to work. Project Pluto got around this by using SRBs for launch and having a fairly low velocity, but a launch vehicle needs to be able to accelerate well up toward orbital speed. 

[FreeThinker]

41 minutes ago, sevenperforce said:

Eh, there is no way to dump that much heat that quickly. You've got to just go ahead and accept the coolant losses if you want a SABRE-style precooler to work. Project Pluto got around this by using SRBs for launch and having a fairly low velocity, but a launch vehicle needs to be able to accelerate well up toward orbital speed. 

Orbital speed in an atmosphere? That just way to fast. I assumed the vehical only accelerated up to 2000 m/s in the upper atmosphere, the rest would be done by heating propellant to 2500K

Edited April 12, 2016 by FreeThinker

[Scotius]

1 hour ago, FreeThinker said:

Yes, that would be the same yes, I nice bonus would be it can be converted to a intercontinental bomber, where it can bomb/nuke any location on earth in within 30 minutes and repeat.

We have plenty of ICBM's just for that. No need to build a big, suborbital bomber that can do essentially th same, but at greater cost and risk.

[FreeThinker]

 

1 hour ago, Scotius said:

We have plenty of ICBM's just for that. No need to build a big, suborbital bomber that can do essentially th same, but at greater cost and risk.

Well the trouble with ICMB is they are self defeating, as any succesfull launch will automaticly trigger Mutualy assured destruction. a NUclear Sub Orbital Bomber can be used to do conventional bombing runs at safe height and speeds.

Edited April 12, 2016 by FreeThinker

[sevenperforce]

2 hours ago, FreeThinker said:

Orbital speed in an atmosphere? That just way to fast. I assumed the vehical only accelerated up to 2000 m/s in the upper atmosphere, the rest would be done by heating propellant to 2500K

No, not up to orbital speed; up toward orbital speed. A nuclear thermal ramjet is limited to lower cruise velocities. Launch vehicles have to be optimized for acceleration rather than cruise. 

[p1t1o]

1 hour ago, FreeThinker said:

Well the trouble with ICMB is they are self defeating, as any succesfull launch will automaticly trigger Mutualy assured destruction. a NUclear Sub Orbital Bomber can be used to do conventional bombing runs at safe height and speeds.

There hasn't been such a thing as a "safe height and speed" for quite some time, it will be far easier to shoot it down than to intercept a ballistic missile or a satellite for example.

[tater]

NTRs are a considerably more mature technology than REL's engine as a reality check. VASIMR is a considerably more mature technology. Heck, em-drive is more mature than the skyline engine, as is any engine type that has ever been tested in any way, at all.