Whats wrong with Skylon?

[sevenperforce]

7 minutes ago, cantab said:

As for in-air refuelling, I disagree. It's logistically complicated, rather hazardous, and demands extra pilot training. There's a reason that really only the military uses it. In the long run it will be simpler, safer, and cheaper to take off fully-fuelled from the ground.

It's been done thousands and thousands of times, and it's not terribly hazardous since you'd probably be transferring hydrogen peroxide.

[blowfish]

The main benefit to mid-air refueling would be lower takeoff mass, but it's at least questioning how much benefit that would bring ... as far as taking off goes you can always just build a longer runway.  The fuel mass required between takeoff and mach 1 isn't that large, and the refueling would have to take place at much higher dynamic pressure than usual (since the Skylon has stubby wings for good hypersonic performance).  This means that aerodynamic forces are a lot higher and the margin for error is lower.

[sevenperforce]

5 minutes ago, blowfish said:

The main benefit to mid-air refueling would be lower takeoff mass, but it's at least questioning how much benefit that would bring ... as far as taking off goes you can always just build a longer runway.  The fuel mass required between takeoff and mach 1 isn't that large, and the refueling would have to take place at much higher dynamic pressure than usual (since the Skylon has stubby wings for good hypersonic performance).  This means that aerodynamic forces are a lot higher and the margin for error is lower.

Oh, it would definitely have to be done with something more like the dedicated Black Horse. Though the SABRE engines would help, of course. 

[Nibb31]

9 hours ago, fredinno said:

yes. https://en.wikipedia.org/wiki/STS-51-A

" Palapa B2 and Westar 6, meanwhile, had been deployed during the STS-41-B mission earlier in the year, but had been placed into improper orbits due to the malfunctioning of their kick motors; they were both safely recovered and returned to Earth during STS-51-A."

The Shuttle could only retrieve those satellites because they had already been launched by the shuttle. They had grappling fixtures and cargo bay cradles especially designed for them.

Also, the Shuttle retrieval missions cost more than building replacement sats.

It never had anywhere near the capability to retrieve uncooperative military satellites. 

[DerekL1963]

28 minutes ago, Nibb31 said:

The Shuttle could only retrieve those satellites because they had already been launched by the shuttle. They had grappling fixtures and cargo bay cradles especially designed for them.

Those birds were released from cradles (not grappled), and the launch cradles were quite different from those they were brought back on (since the launch cradles were attached to the jettisioned kick motors).

[KSK]

11 hours ago, sevenperforce said:

It's been done thousands and thousands of times, and it's not terribly hazardous since you'd probably be transferring hydrogen peroxide.

Um, what? Unless that's a spellchecker gone wonky, SABRE is a hydrolox engine last time I checked. I suppose you could decompose the peroxide to generate hydrogen in-flight but you'd then need to liquefy it too. 

Besides, hydrogen peroxide is far from being 'not terribly hazardous' at the concentrations needed to be a useful propellant or source of hydrogen.

[Nibb31]

44 minutes ago, DerekL1963 said:

Those birds were released from cradles (not grappled), and the launch cradles were quite different from those they were brought back on (since the launch cradles were attached to the jettisioned kick motors).

Nevertheless, it was actually only possible because the sats were designed with attachment points that were compatible with the Shuttle, and because NASA had full details of the dimensions and weight distribution of those sats.

Bringing back a hostile military sat simply was never a serious option, although it was sold to the military at one point. To do so, they would have needed to have the fully detailed plans of the sat in order to build a proper cradle, and they would have needed to be sure there were no countermeasures on the satellite or that they could be safed. That would have meant that they already knew just about everything about the satellite, which would have made the whole operation pointless.

[mikegarrison]

8 minutes ago, Nibb31 said:

Nevertheless, it was actually only possible because the sats were designed with attachment points that were compatible with the Shuttle, and because NASA had full details of the dimensions and weight distribution of those sats.

Bringing back a hostile military sat simply was never a serious option, although it was sold to the military at one point. To do so, they would have needed to have the fully detailed plans of the sat in order to build a proper cradle, and they would have needed to be sure there were no countermeasures on the satellite or that they could be safed. That would have meant that they already knew just about everything about the satellite, which would have made the whole operation pointless.

Besides all that, it would be theft.

[fredinno]

2 hours ago, Nibb31 said:

The Shuttle could only retrieve those satellites because they had already been launched by the shuttle. They had grappling fixtures and cargo bay cradles especially designed for them.

Also, the Shuttle retrieval missions cost more than building replacement sats.

It never had anywhere near the capability to retrieve uncooperative military satellites. 

Well,Vivisat, the Orbital ATK satellite repair satellite is capable of attaching and moving satellites by attaching itself to the satellite's apogee/reboost motor./ It may have not been possible in 1985, but capturing satellites like this is definately possible IRL. The only problem would be trying to make sure the nozzle doesn't break, which is why this would likely never be used for very large satellites.

 

Also, these reterival missions were side missions, not primary missions, and were done on the side afer payload deployment.

Edited March 12, 2016 by fredinno

[DerekL1963]

8 hours ago, Nibb31 said:

8 hours ago, DerekL1963 said:

Those birds were released from cradles (not grappled), and the launch cradles were quite different from those they were brought back on (since the launch cradles were attached to the jettisioned kick motors).

Nevertheless, it was actually only possible because the sats were designed with attachment points that were compatible with the Shuttle, and because NASA had full details of the dimensions and weight distribution of those sats.

That's my point Nibb - they didn't have any 'specialized attachment points'.  What attachment points they did have were jettisoned along with the kick motor.  As recovered, they had no attachment points at all.  None.  Zip.  Nada.  That's why they had to design grappling fixtures that the astronauts attached while spacewalking.

And if the insurance company (who paid for the recovery) wanted NASA to have the relevant specs, you can bet the builder would pony them up.

[sevenperforce]

9 hours ago, KSK said:

Um, what? Unless that's a spellchecker gone wonky, SABRE is a hydrolox engine last time I checked. I suppose you could decompose the peroxide to generate hydrogen in-flight but you'd then need to liquefy it too. 

Besides, hydrogen peroxide is far from being 'not terribly hazardous' at the concentrations needed to be a useful propellant or source of hydrogen.

Hydrogen peroxide can't be decomposed to produce hydrogen; it produces oxygen. 

And yeah, the SABRE engine runs on LOX. I'm talking about the Black Horse project. The engine would have to be redesigned to use H2O2.

[wumpus]

2 hours ago, sevenperforce said:

Hydrogen peroxide can't be decomposed to produce hydrogen; it produces oxygen. 

And yeah, the SABRE engine runs on LOX. I'm talking about the Black Horse project. The engine would have to be redesigned to use H2O2.

You know how some posters have mentioned that you ignore the big picture to include your favorite details?  Here's a hint: there is simply *no* *way* you are getting a SSTO that uses H2O2 as a fuel (note that it won't even if you use an oxidizer, and your post implies a monopropelant which is absolutely hopeless).

There is no excuse for complicating the launch of a vessel that has turbojet engines just to get 250 or less m/s.  It will have enough problems with the issues that are handwaved away once it switches to "rocket mode", if it can't solve the 0-mach 6 issues on its own there is no possible future for SABRE.

[ModZero]

On 3 March 2016 at 7:43 PM, A35K said:

I don't see why this should be the case. Unless it lands exceptionally fast, there is no reason it shouldn't be able to land at most major airports.

It would need a special runway for take-off, because of the abort requirements, extra-high take-off weight (which a hefty part of it will shed almost immediately, by jettisoning the water that would be used for braking in an abort). I don't think I've read about any special requirements for landing (though it's kinda biggish, so it probably won't land on your local Cessna airfield). OTOH, because it needs water cooling for the brakes and jettisons the water, it's presumably be way worse at braking during landing (but also far lighter).

Of course guessing at it's landing gear is kinda silly, they need an engine first, then an airframe, then someone who's excited enough about 12t to LEO to pay for it. By the time it happens (if it happens, as right now it's at "why not?" level of funding) it might be a flying saucer, for all we know.

[Nibb31]

It's also much heavier than an A380. It will definitely need a reinforced runway for takeoff as well as a liquid hydrogen supply facility.

There is no way it will be using a standard airport.

[cantab]

On the contrary, Skylon's planned weight is considerably lighter than the A380. It's the undercarriage design on Skylon that puts higher loads on each wheel therefore demanding the special runway. That's not a huge drawback I'd say, considering rockets need specialised infrastructure too. It's also plausible that different wheel arrangements could permit use of other runways.

I expect that much like the Space Shuttle, Skylon would have various alternate landing sites. They would need to have a long enough runway, and also have the liquid hydrogen fuelling infrastructure put in place or capable or arriving to support the ferry flight back to base afterwards.

Edited March 12, 2016 by cantab

[sevenperforce]

On 3/11/2016 at 3:11 PM, wumpus said:

You know how some posters have mentioned that you ignore the big picture to include your favorite details?  Here's a hint: there is simply *no* *way* you are getting a SSTO that uses H2O2 as a fuel (note that it won't even if you use an oxidizer, and your post implies a monopropelant which is absolutely hopeless).

There is no excuse for complicating the launch of a vessel that has turbojet engines just to get 250 or less m/s.  It will have enough problems with the issues that are handwaved away once it switches to "rocket mode", if it can't solve the 0-mach 6 issues on its own there is no possible future for SABRE.

Black Horse wasn't my idea. Neither was using H2O2 for the oxidizer.  

Specifically, JP-1 and H2O2 with aerial propellant transfer (oxidizer only) and airbreathing up to around Mach 5 outperforms LH2/LOX SSTO.

 

Edited March 14, 2016 by sevenperforce
Corrected broken link.

[fredinno]

5 hours ago, Nibb31 said:

It's also much heavier than an A380. It will definitely need a reinforced runway for takeoff as well as a liquid hydrogen supply facility.

There is no way it will be using a standard airport.

THe Shuttle Landing facility should do nicely...right?

[AngelLestat]

Skylon really needs a big runaway as Nibb31 said.. but no sure why it needs more than one... 
 

[cantab]

11 hours ago, fredinno said:

THe Shuttle Landing facility should do nicely...right?

Possibly, if an American organisation ends up building Skylon. Which I think is quite likely actually, because (UK) Politics. Then again, a runway at the European space port in French Guiana would let it take more payload to orbit.

In the short term, indeed Skylon only really needs one launch facility. But I'd say that if we get any sort of Really Cheap Launch Method, then a choice of launch sites starts to become important because the logistics of shipping payloads to the site becomes relevant in cost and time.

[AngelLestat]

To land in a different runaway can be solve with aerobrake parachutes, to take off with full payload will be hard, it needs some boosters for acceleration.

But all those issues just to avoid payload transport to the right runaway seems silly, a 747 has an ISP of 6000s, skylon has 3600s, then risk a machine as skylon in inter country travel no sure if payoff.
You still need to transport the payload to the airport, the only good point that I see for this is that you save 1 step in the shipping, many steps can damage the payload.

But well, in the cases the payload is below 10t and the runaway is in the right latitude for the chosen orbit, yeah it will worth it, but you still need cryo fuels systems in that airport.
 

[blowfish]

On 3/12/2016 at 4:07 PM, sevenperforce said:

Specifically, JP-1 and H2O2 with aerial propellant transfer (oxidizer only) and airbreathing up to around Mach 5 outperforms LH2/LOX SSTO.

[citation needed]

Also what do you mean by "outperforms" ?  If you mean it has a higher payload fraction on takeoff, then that has nothing to do with H2O2 and everything to do with propellant transfer, since most of the mass burnt in rocket mode is oxidizer.  But takeoff mass hardly affects anything, particularly since the launch facilities have to be specialized anyway, and the propellant mass burnt from takeoff to mach 1 is tiny.

 

Re: Alternate takeoff sites: @AngelLestat is 100% correct that it's very easy to ship payloads and very difficult to ship spaceplanes ... not to mention all the infrastructure required for payload integration and fueling at each launch site.  The only justification I see for alternate launch sites is for highly inclined orbits for which an equatorial site isn't favorable.

Re: Alternate landing sites: The Skylon would weigh practically nothing on landing (most of the takeoff mass is fuel), so it could probably land just about anywhere, but you want to land back at the launch site if at all possible.  The only reason why the Shuttle had alternate sites was because weather conditions might be unfavorable at Cape Canaveral - something similar might be desirable for the Skylon, but only as a last resort - the Skylon could fly itself from site to site, but it would be both very risky and costly to do.

[Val]

10 hours ago, AngelLestat said:

To land in a different runaway can be solve with aerobrake parachutes, to take off with full payload will be hard, it needs some boosters for acceleration.

But all those issues just to avoid payload transport to the right runaway seems silly, a 747 has an ISP of 6000s, skylon has 3600s, then risk a machine as skylon in inter country travel no sure if payoff.

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.

4 hours ago, blowfish said:

Re: Alternate takeoff sites: @AngelLestat is 100% correct that it's very easy to ship payloads and very difficult to ship spaceplanes ... not to mention all the infrastructure required for payload integration and fueling at each launch site.

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.

Edited March 14, 2016 by Val
Typos. Sub-sonic. Manual

[sevenperforce]

10 hours ago, blowfish said:

[citation needed]

Also what do you mean by "outperforms" ?  If you mean it has a higher payload fraction on takeoff, then that has nothing to do with H2O2 and everything to do with propellant transfer, since most of the mass burnt in rocket mode is oxidizer.  But takeoff mass hardly affects anything, particularly since the launch facilities have to be specialized anyway, and the propellant mass burnt from takeoff to mach 1 is tiny.

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

Edited March 14, 2016 by sevenperforce
Fixed broken link

[blowfish]

3 hours ago, sevenperforce said:

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

That link leads nowhere for me.

[sevenperforce]

22 minutes ago, blowfish said:

That link leads nowhere for me.

Whoops, sorry. Fixed it.