Which is a shame, it would be nice to believe there was some weight behind this article where Nextbigfuture believes the Reaction Engine Skylon Spaceplane will be fully funded as a result of SpaceX's potential dominance
It may be easier to obtain funding for a new class of engine that can be strapped to an existing vehicle
than to punt for a novel engine for a novel vehicle which requires novel infrastructure? or to put it anouther way QuoteAFRL officials views a single-stage-to-orbit Skylon space plane as "technically very risky as a first application [...]
AFRL officials views a single-stage-to-orbit Skylon space plane as "technically very risky as a first application [...]
Note for maximum cost reduction the engines and airframes must be identical.
Such a design needs 2 engines and 2 airframes to get funded, develop and test.
TSTO is the best bet if you don't want to solve the problems you're likely to uncover from both a dramatically new engine concept and an extremely good mass fraction airframe/TPS simultaneously.One miracle at a time.
Incorrect. This is the two-is-more-than-one myth again. A single design that can perform the two tasks is not necessarily going to be cheaper to develop than two designs that do one each.
In fact, given the demands of re-entry, the opposite is likely to be true. For a TSTO built around SABRE, a biamese may be the worse possible design possible.
With a TSTO, the upper stage engine would be a conventional rocket engine.
That will not be the same development costs as the first stage hybrid air-breathing engine. For the first experimental version of the system, you can even use a conventional upper-stage off an existing system. That reduces your development cost to just the first stage. Since the re-entry for the upper-stage is vastly more demanding than the first stage, deferring development of a reusable second stage saves a lot, and allows you to fly hardware sooner.
I'm not arguing that the USAF idea for TSTO is necessarily superior to Skylon, but two-is-more-expensive-than-one is not a valid argument against it.
Quote from: Robotbeat on 06/14/2016 11:59 pmTSTO is the best bet if you don't want to solve the problems you're likely to uncover from both a dramatically new engine concept and an extremely good mass fraction airframe/TPS simultaneously.One miracle at a time.If SABRE fully checks out on the ground you'll basically waste most of it's design features. If you just want precooled air inlets then it's not SABRE at all. It's jet engine with a heat exchanger up front. This should still generate significant revenue for REL, but it's not getting them anywhere near orbit. Regarding truss structure. NASA Langley did a study in 1969 comparing Aluminum with AlBe and Be tubing. The straight Al alloy structure (the "heavy" design) weighed 3lbs but could carry a 250lb load, roughly 83 1/3:1 load to mass.So I think a well designed truss structure can support very significant loads.
Quote from: Paul451 on 06/15/2016 01:03 amIncorrect. This is the two-is-more-than-one myth again. A single design that can perform the two tasks is not necessarily going to be cheaper to develop than two designs that do one each. Let me get this straight.A TSTO using 2 unique stage designs and engines will be cheaper to design and build IE the overall budget will be lower, than a biamese with a single structural and engine design
No one goes to a biamese design for performance.
You seem to be under the impression there is a shortage of space launch systems.
One thing that does worry me about the Skylon truss structure is something I saw in an interview with a crewman on the Wellington bomber, while he thought the framing was great, he recounted how flexible the Wellington's fuselage was, he said the plane virtually wriggled its way across the sky, with the fuselage continuously bending and twisting in flight.I imagine that the designers of Skylon will have to engineer a far more ridged frame structure given the rigidity that I assume the aeroshell will have.
Why would there be? We develop multistage rockets all the time. Something as sophisticated and high performance as Skylon and its airframe is FAR harder. It will be more expensive, by Reaction Engines' own estimates!
Build the aircraft equivalent of a "biamese" rocket. 2 Identicalaircraft with the same engines and airframe. SABRE sort of plays into this concept if your issue is you doubt REL's Skylon concept is infeasible. Note for maximum cost reduction the engines and airframes must be identical.
Yeah, I've heard that argument before, but Skylon is anything but bog standard.
I think Reaction Engines shouldn't let perfect be the enemy of the good, here. Far better to actually fly than to just talk about it because the initial investment step is simply far too high.
Following that train of thought, what are reasonable lower bounds on size for SABRE cycle designs, if you want to follow the minimum demo path with a mini-Skylon? What is the bricklifter equivalent, able to place a 3U cubsat in orbit? REL is loath to make anything less than full size, mostly due to LH2 turbine design issues, but AFRL is under no such constraint (though considering the recent demise of the air launch project again...)
Quote from: Robotbeat on 06/16/2016 03:37 pmYeah, I've heard that argument before, but Skylon is anything but bog standard.Only in areas where where it can't afford to be. Most of it's construction techniques have been suggested or used in other contexts, such as MLI and truss structures. Even the water cooled brake idea is SOP (in truck racing). Key risks are more in the materials area and structural interaction over the whole M0-23-0 range. QuoteI think Reaction Engines shouldn't let perfect be the enemy of the good, here. Far better to actually fly than to just talk about it because the initial investment step is simply far too high.Undoubtedly.The problem is moving to a 2 winged stage design, which is needed for full reusability. Skylons in rocket mode already has the best possible Isp and if you're worried about the structural design AFAIK all other are worse, requiring more of the mass to be set aside for the structure. I think it's fair to say most of the benefits of staging in other designs are simply delivered by the high Isp of SABRE.So if you can't design a 2nd winged stage with lower structural mass fraction than Skylon (the "safe" option because we're talking risk reduction here. Although at M5+ A lifting body design would be possible if you can figure out how to land it ) the only other option is the expendable rocket, IOW the XS-1 approach . Note this is the broad outline of the constraints and it's possible that at the margins an option for a fully reusable 2 stage vehicle exists. Perhaps Skylons structural design is actually conservative compared to some other approaches, allowing a heavier structure for the 2nd stage, rather than the straight propellant-tanks-with-engines-at-bottom which seems the only lighter weight option. Perceptions that a 2 stage winged system is somehow "safer" to design are just that, perceptions.Once you see the constraint map I can't help thinking "Let's go for broke. See what the budget is, build the smallest SABRE you can and the smallest Skylon around it you can. It might put 10Kg in LEO but it's a) fully reusable and b)can be returned to Earth after it's been in orbit. "This is still the USAF Research Laboratory. Research is about taking calculated risks.
You do NOT need wings or lifting bodies at all for reuse.
I would argue that three different wingless vehicles are much easier to design than a single winged vehicle that has to work from mach 0 to mach 25.
Quote from: Nilof on 06/20/2016 10:26 amYou do NOT need wings or lifting bodies at all for reuse. No, but it cuts the required takeoff thrust by your L/D ratio. IIRC the SABRE thrust in airbreathing mode isn't enough for vertical takeoff, without scaling the engine up considerably.
QuoteI would argue that three different wingless vehicles are much easier to design than a single winged vehicle that has to work from mach 0 to mach 25.Well yes, that's obvious. Is that actually what AFRL are proposing though?