Quote from: KelvinZero on 11/22/2015 03:57 amThis certainly contradicts the optimism of those suborbital schemes that are effectively two stage with integration in flight Like SpaceShipTwo? Yeah, it's cool and I'd be glad to see it (or any suborbital tourism) succeed, but I don't think it's a particularly good idea.
This certainly contradicts the optimism of those suborbital schemes that are effectively two stage with integration in flight
It's a correct assumption. There is no turn-key SSTO capability that would be competitive with expendable launch systems.
The low hanging fruit right now is just making the first stage returnable. Even that is very hard to do.
I was being a bit facetious, referring to ideas where a sort of upper stage in orbit aerobrakes down to meet a suborbital vehicle and then pushes it to orbit.
Quote from: nec207 on 11/17/2015 09:21 amWhat technological breakthrough is needed to make space planes and or single-stage-to-orbit (or SSTO possible? What major problem holding back space planes and or single-stage-to-orbit?Two different questions a space plane does not need to be single stage to Orbit, see the Space Shuttle, X-37, Dream Chaser and SSTO does not need to be an space plane(however being some type of airplane could be helpful in terms of being capable of generating lift.)SSTO is possible now, but the problem is SSTO while carrying a practical payload and most SSTO concepts require re usability. The issue is with materials. Mathematically it is possible to get to orbit using chemical rocket in an single stage. It is just that the materials we have to build the SSTO out of are too heavy to allow this concept to work with current technology but technology changes. Lighter weight structures and heat shields would allow this concept to work as well as engines like the sabre(which could allow you to get much higher and faster without using on board oxygen and can double as both an jet and rocket engine.). We can build an SSTO now, but it won't be able to haul much into orbit and it won't be reusable. It simply would not be practical at the moment. Space planes are better suited than capsules for certain things. The return to the capsule is being driven by different dynamics. For Orion and CST-100 reusing Apollo's shape saves research and development(esp. for Orion). For Space X, wings don't fit the company philosophy. For Dream Chaser "wings" allow much more selection of places to land as well as reduced G-forces on the crew. In terms of BEO. Space planes could find an role as an mars mission as the earth reentry vehicle. There is debate on wither on not an the crew can survive the G-forces from that fast an reentry in an capsule. For lunar missions there was an interesting concept floated of using an version of dream chaser as an lunar craft or using the shuttle's cargo bay to haul up an capsule and crew and docking it with an pre-positioned stage launched by Titan in LEO. While wings can be useless in space, they can be handy at the end of the mission.
What technological breakthrough is needed to make space planes and or single-stage-to-orbit (or SSTO possible? What major problem holding back space planes and or single-stage-to-orbit?
Almost wish I could organize a superkickstarter to get billionaires to fund an independant research group to actually develope a working Lifting Body SSTO system.
"Big dumb whatever" works in a lot of areas, but in aerospace, you have the brutal exponential rocket equation. If you try "big dumb" you necessarily have to have several stages. It's still possible, though at the expense of needing more stages, which means more expense. And you still have a much higher GLOW for the same payload, which means a bigger launch pad (or launching at sea, with all the complications involved)."Big dumb" may be a valid first stage design criteria, I'm not sure. But for the upper stage, where your mass overhead directly eats into your payload, you are likely to be much better off with the typical approach of trying to lightweight the crap out of everything and picking the highest performing materials possible, especially for an RLV (which can be reused). Making everything out of silver or something just as expensive clearly makes sense (obviously silver isn't that strong for its mass, just using an example).
Incidentally Russian rockets, which have racked up 100s of launches without failure, follow some of the MCD principles, with a safety factor of 2, rather than the 1.25 of US ELV's (and SF of 1.5 for human rated ELV's).
Quote from: Robotbeat on 11/23/2015 12:04 am"Big dumb whatever" works in a lot of areas, but in aerospace, you have the brutal exponential rocket equation. If you try "big dumb" you necessarily have to have several stages. It's still possible, though at the expense of needing more stages, which means more expense. And you still have a much higher GLOW for the same payload, which means a bigger launch pad (or launching at sea, with all the complications involved)."Big dumb" may be a valid first stage design criteria, I'm not sure. But for the upper stage, where your mass overhead directly eats into your payload, you are likely to be much better off with the typical approach of trying to lightweight the crap out of everything and picking the highest performing materials possible, especially for an RLV (which can be reused). Making everything out of silver or something just as expensive clearly makes sense (obviously silver isn't that strong for its mass, just using an example).Before commenting further I suggest you read what the originator of the idea has to say for himself on the subject.http://www.sfo.org/library/schnitt/You should note his goal was minimum cost design. Being "big" and (relatively) "dumb" was the result.Incidentally Russian rockets, which have racked up 100s of launches without failure, follow some of the MCD principles, with a safety factor of 2, rather than the 1.25 of US ELV's (and SF of 1.5 for human rated ELV's).
Quote from: Robotbeat on 11/23/2015 12:04 am"Big dumb whatever" works in a lot of areas, but in aerospace, you have the brutal exponential rocket equation. If you try "big dumb" you necessarily have to have several stages. It's still possible, though at the expense of needing more stages, which means more expense. And you still have a much higher GLOW for the same payload, which means a bigger launch pad (or launching at sea, with all the complications involved)."Big dumb" may be a valid first stage design criteria, I'm not sure. But for the upper stage, where your mass overhead directly eats into your payload, you are likely to be much better off with the typical approach of trying to lightweight the crap out of everything and picking the highest performing materials possible, especially for an RLV (which can be reused). Making everything out of silver or something just as expensive clearly makes sense (obviously silver isn't that strong for its mass, just using an example).Before commenting further I suggest you read what the originator of the idea has to say for himself on the subject.http://www.sfo.org/library/schnitt/You should note his goal was minimum cost design. Being "big" and (relatively) "dumb" was the result.
To quote Arthur Schnitt himself, "The MCD analysis showed that first stages, as part of a multi-stage expendable SLV, should be the least sophisticated; and that the optimum degree of hardware sophistication increases with each successive, upper stage."
BTW, Musk just claimed that F9 first stage is a SSTO
Hey, you know that dumbish-idea of some massive infrastructure that catapults the rocket off the launch pad, saving the first few seconds of slowly building up speed which apparently uses a fair bit of fuel..
Quote from: Proponent on 11/24/2015 11:57 amTo quote Arthur Schnitt himself, "The MCD analysis showed that first stages, as part of a multi-stage expendable SLV, should be the least sophisticated; and that the optimum degree of hardware sophistication increases with each successive, upper stage."Exactly. Save the cutting edge, wafer thin margin tech for the uppermost stage. ...
Quote from: Proponent on 11/24/2015 11:57 amTo quote Arthur Schnitt himself, "The MCD analysis showed that first stages, as part of a multi-stage expendable SLV, should be the least sophisticated; and that the optimum degree of hardware sophistication increases with each successive, upper stage."Exactly. Save the cutting edge, wafer thin margin tech for the uppermost stage. Which sort of flips SX's plans on their head.
Quote from: john smith 19 on 11/24/2015 01:40 pmQuote from: Proponent on 11/24/2015 11:57 amTo quote Arthur Schnitt himself, "The MCD analysis showed that first stages, as part of a multi-stage expendable SLV, should be the least sophisticated; and that the optimum degree of hardware sophistication increases with each successive, upper stage."Exactly. Save the cutting edge, wafer thin margin tech for the uppermost stage. Which sort of flips SX's plans on their head.If you have a fully, rapidly reusable first stage, then yeah, Minimum Cost Design would lead you to use cutting edge tech on the first stage while relaxing the cutting-edge-ness on the (expendable) upper stage.Different assumptions give you different conclusions.
Quote from: Robotbeat on 11/25/2015 12:39 amQuote from: john smith 19 on 11/24/2015 01:40 pmQuote from: Proponent on 11/24/2015 11:57 amTo quote Arthur Schnitt himself, "The MCD analysis showed that first stages, as part of a multi-stage expendable SLV, should be the least sophisticated; and that the optimum degree of hardware sophistication increases with each successive, upper stage."Exactly. Save the cutting edge, wafer thin margin tech for the uppermost stage. Which sort of flips SX's plans on their head.If you have a fully, rapidly reusable first stage, then yeah, Minimum Cost Design would lead you to use cutting edge tech on the first stage while relaxing the cutting-edge-ness on the (expendable) upper stage.Different assumptions give you different conclusions.I suggest you read his articles again. His point is to do with what NASA have called the "exchange rates" IE 1 unit of extra mass means what do you lose from final payload. For the 1st stage not much. So go big (which is pretty cheap), go simple (to keep it cheap) and go expendable. But this was back when avionics were heavy and (very) expensive. So that changes things a bit. Likewise piston pumps are much simpler to make but Whitehead's team reckons the crossover point was only about 5000lbs, so we get back to turbopumps. OTOH CAD driving CNC changes the economics of that problem quite a lot. But his conclusion still says "pay mass to avoid cost."Trouble is that means you leave all the reusability in the upper stage, as well as the return from orbit issues.And just a reminder SX still does not have a reusable first stage. Currently I'm thinking it'll be available before Q417.