The engines could not reasonably be put anywhere except either at the back or out on the wings. Otherwise you have structure in the exhaust plume. You can't put them at the back because it kills your trim during reentry, so out on the wings it is.
Anybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.
Quote from: mlorrey on 04/19/2011 01:23 amAnybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.I'm not sure if its justified, but there's been concerns raised that the US won't give source code for the JSF to Britain despite a lot of the technology being developed in Britain.BAe systems in the USA is a US Company, and operates as such.
The original hotol had the engines integrated with the fuselage but had major issues with the COG changing as fuel was used. Mounting the engines in the middle and draining tanks fore and aft solves this.
Quote from: nacnud on 04/19/2011 07:42 pmThe original hotol had the engines integrated with the fuselage but had major issues with the COG changing as fuel was used. Mounting the engines in the middle and draining tanks fore and aft solves this.Also by having them out allows for cleaner airflow during lower atmosphere operation and enables simpler servicing.
Quote from: alexterrell on 04/19/2011 10:42 pmQuote from: mlorrey on 04/19/2011 01:23 amAnybody claiming ITAR about Skylon (or SS2 for that matter) are people who either dont know what they are talking about, or are not interested/too lazy to do the paperwork. The fact that a British company can be closely involved in development of SS2, which is at least as much an example of a similar-IRBM as Skylon is, disproves any ITAR claims about restraints on US involvement in Skylon.I'm not sure if its justified, but there's been concerns raised that the US won't give source code for the JSF to Britain despite a lot of the technology being developed in Britain.BAe systems in the USA is a US Company, and operates as such.Which source code and which technology in particular? If the technology you want the source code for was developed in Britain, then you should already have it in Britain. Is it that the British govt wants source code to American corps technologies too? Or that the US is keeping the BAe developed tech classified?
If this fails they should opt for fully-reusable two-stage, with full rocket propulsion on both stages.
Given 1350kN max airbreathing thrust and their max 14:1 T/W the Sabre engines are about 9800kg each and at minimum 6:1 airbreathing T/W produce about 580kN. (1800kN in rocket mode).At minimum T/W of 10 for the ramjet at Mach 1 (from "pocket ramjet reader"), and needing 580kN thrust a ramjet engine weighs about 5900kg. Add a 1800kN rocket engine with 60:1 T/W for another 3000kg, and there is still about 1000kg less than Sabre.
Wouldn't a ramjet-rocket solution have worse overall Isp than a Sabre engine unless the airbreathing regime was extended thus requiring higher TPS requirements and greater hypersonic lift?
Quote from: RobLynn on 04/20/2011 11:30 amGiven 1350kN max airbreathing thrust and their max 14:1 T/W the Sabre engines are about 9800kg each and at minimum 6:1 airbreathing T/W produce about 580kN. (1800kN in rocket mode).At minimum T/W of 10 for the ramjet at Mach 1 (from "pocket ramjet reader"), and needing 580kN thrust a ramjet engine weighs about 5900kg. Add a 1800kN rocket engine with 60:1 T/W for another 3000kg, and there is still about 1000kg less than Sabre.I don't think you are comparing like with like here. The BIS paper quotes LOX/H2 ramjet T/W you seem to be using LOX/Kero T/W from the primer.
Also the SABRE T/W is worst at high speeds (Mach 5.4), which it is difficult to get a ramjet to run at, due to high temperatures. The added mass for ramjet cooling would need to be taken into account.
Finally SABRE has an Isp in airbreathing mode of between 1500-3200 (best Isp at low speeds), while a LOX/H2 ramjet has an Isp range of 1000-1500 (best Isp at ~Mach 2).
As this is an acceleration mission T/W at low speeds (Mach 1) is important as that determines vehicle acceleration. So to get the same acceleration at low speeds the ramjet would need 1350kN of thrust, and thus mass 13700kg.
The lower Isp would mean more fuel and tankage, leading to a larger vehicle. This in turn would require more thrust from the ramjet and rocket. I really don't think that a ramjet+rocket combination will close for a reusable SSTO, even with a sledge assist. I assume the sledge assist is up to ~Mach 0.5, you aren't considering a supersonic sledge are you.
Kinda the point of a runway launch is to avoid having an expensive single-use launch infrastructure. IIRC, their current plan is just to use the runway at Kourou as-is (which was designed for Hermes, and is thus fairly long at 3.2 km).
Sabre ramjet is shut down at 5.14. All ramjets have thrust that tapers off at high speed as inlet air gets hotter and hotter allowing less fuel to be burnt under the dissociation limit (~2500K). That upper limit is jsut the same for Sabre as for a Ramjet and the pressure ratios at that speed are so high that there will be no appreciable difference between their exhaust velocities.
Quote from: simonbp on 04/20/2011 04:24 pmKinda the point of a runway launch is to avoid having an expensive single-use launch infrastructure. IIRC, their current plan is just to use the runway at Kourou as-is (which was designed for Hermes, and is thus fairly long at 3.2 km).Shaving a few billion of a 15 billion development effort for 100million in infrastructure would be massively cost effective and would reduce the $/kg to orbit substantially, but only if that infrastructure has low operating costs. I think that a launch sled would be cheap to maintain and operate.