I am sure that they will initially charge whatever they can get away with for launches - undercut the competition but only just. But ultimately the recurring costs of a sled launch should be less than $100k, so the economics will continue to pay off.
Quote from: MikeAtkinson on 04/21/2011 05:57 pmI also think you grossly underestimate how difficult a supersonic sled is going to be. The Bloodhound SSC uses at least two techniques (negative lift and a very small clearance to the ground) that are inappropriate for a spaceplane.The sonic boom will probably make co-locating with any current facility infeasible as well.Bloodhound SSC cannot be positively located on a rail, and is running on an unprepared surface. As it stands this is pretty well developed technology as rocket sleds have been operated up to mach 8.5The Skylon on sled is clamped down and released once engines are lit.I agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and rails
I also think you grossly underestimate how difficult a supersonic sled is going to be. The Bloodhound SSC uses at least two techniques (negative lift and a very small clearance to the ground) that are inappropriate for a spaceplane.The sonic boom will probably make co-locating with any current facility infeasible as well.
I agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and rails
Quote from: MikeAtkinson on 04/22/2011 08:09 pmI agree noise will be an issue, but there are a lot of uninhabited desert areas are available for landing strips and railsSo, you have to have a very complex sled, like noone's ever built before, located in a remote location, and all sorts of waivers for supersonic (nay, hypersonic) overlight of land?How is that better than just slapping a few small solids to it and launching from Cape Canaveral (a la Snark)? Seems to have all the advantages of your sled, but dramatically cheaper...
Again, Reaction Engines do not intend to operate Skylon's. They intend to sell them to independant operators. The competition will be between Virgin Galactic Skylon's and British Airways Skylon's and if they collude over prices they get fined, again.
So, you have to have a very complex sled, like noone's ever built before, located in a remote location, and all sorts of waivers for supersonic (nay, hypersonic) overlight of land?How is that better than just slapping a few small solids to it and launching from Cape Canaveral (a la Snark)? Seems to have all the advantages of your sled, but dramatically cheaper...
even if the latter makes better economic sense
So what happens to the supersonic shocks from Skylon while on the sled?
You're proposing something completely different (on several important axes). May I respectfully suggest you start a new thread to discuss 'Rob's proposed ramjet/sled launcher', leaving this one for skylon related discussion?
Quote from: 93143 on 04/21/2011 05:25 pm4 tonnes of water1200kg water according to that spreadsheet and other literature I've seen
4 tonnes of water
my crude analyses suggest to me that in some ways their choices don't seem optimal.
With regard to re-entry temperatures; most of the discussion matches our understanding of the issues involved. The importance of low ballistic coefficient and high L/D is often missed but it means direct Shuttle or capsule comparisons do not work. We do have local CSiC for tips and leading edges, and there is a sweat cooling system at the canard interface with the body.One point the thread seems to have missed is that the most important issue for the wing nacelle configuration is the shock/shock interaction that hits the wing and would defeat any passive RCS. This heating is very local and is handled with an active cooling loop.
The shock / shock heating is very localised and does not involve too many actual joules. The active cooling just spreads the heat over the rest of the wing where it is radiated away from the upper surface.
Quote from: sb on 07/17/2010 09:12 amI seem to remember Skylon was thinking of liquid metal cooling (with MHD pumping?) to deal with the local heat flux on re-entry where the shock from the nacelle impinges on the wing. Is that still the case or was there a "nicer" way round it?At the moment we still have that solution in a small area on the wing leading edge close to the engine nacelle. Whether we will still need this in the D1 revision is not yet clear. Recent work by DLR has given us much more detail of the re-entry heating and we may be able to get a nicer solution.
I seem to remember Skylon was thinking of liquid metal cooling (with MHD pumping?) to deal with the local heat flux on re-entry where the shock from the nacelle impinges on the wing. Is that still the case or was there a "nicer" way round it?
heating on the way up is also an issue it is why the medium temperature TPS extends over the whole airframe rather than just the re-entry areas as on the Shuttle. This is another reason why Mach 5 is looking like a good transition point. In the end it is difficult to firmly establish whether it is the journey up or down that is driving the SKYLON temperature control.
Quote from: 93143 on 04/21/2011 05:25 pmSkylon's landing gear has an interesting feature - 4 tonnes of water as a heat sink, that gets dumped right after a successful takeoff. This is for a fully-loaded abort. Coming down after a mission, the gear can be light.As for the sled, HOTOL had one. Skylon doesn't. I can't recall whether I've seen a detailed rationale for this change, but it seems clear to me that there was one. Perhaps you should be a little less confident...One thing that strikes me immediately is that a launch sled is a pain logistics-wise...1200kg water according to that spreadsheet and other literature I've seen, but yes a good idea - although what is the mass penalty of that water cooling system? the brakes still have to be able to arrest a 50000kg vehicle on landing.I can't see why a sled would be a pain for logistics - the vehicle is precisely positioned in a cradle for fuelling and servicing, the landing gear does not need to be lifted in flight, simplifying that system. If driven by a winch the sled should be very low maintenance - though a steam rocket might be similarly simple, (150 Isp).
Skylon's landing gear has an interesting feature - 4 tonnes of water as a heat sink, that gets dumped right after a successful takeoff. This is for a fully-loaded abort. Coming down after a mission, the gear can be light.As for the sled, HOTOL had one. Skylon doesn't. I can't recall whether I've seen a detailed rationale for this change, but it seems clear to me that there was one. Perhaps you should be a little less confident...One thing that strikes me immediately is that a launch sled is a pain logistics-wise...
I also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.
Quote from: alexterrell on 04/26/2011 09:16 pmI also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.Last I heard, the runway at Kourou (designed for Hermes) was more than sufficient. And in no way is a multi-purpose long/reinforced runway going to be more expensive than a high-tech rocket sled...
Quote from: simonbp on 04/26/2011 11:16 pmQuote from: alexterrell on 04/26/2011 09:16 pmI also read it needs a strengthened runway for take-off. The runway might be 50m wide. That will be expensive.Last I heard, the runway at Kourou (designed for Hermes) was more than sufficient. And in no way is a multi-purpose long/reinforced runway going to be more expensive than a high-tech rocket sled...Generally any runway built for USAF strategic bombers is about as strong as you need. As I recall, the runways built for B-36 Peacemakers had concrete that was 6 feet thick (and yeah, wide enough) and 10,000+ ft long. This includes Chanute AFB, Loring AFB, Fairchild, DFW, Roswell, Ellsworth AFB, Nellis, Sheppard, Guam. I would not be surprised if at least one British runway was similarly built, as well as the runways at Ascension and Diego Garcia.The B-36 originally had single 3 meter diameter wheels on the main landing gear struts. with 357,000 lbs, thats a lot of mass per square inch of tire footprint. They later replaced them with four wheel carriages so they could fly from more bases.I doubt Skylon will need anything tougher than this.
