Quote from: mlorrey on 12/23/2008 06:18 amThats debatable, and not that simple. I doubt the 15 second figure. Prior experience people go by for example is the plasma damage X-15 suffered on one flight when a test scramjet cause some serious damage simply from the shock wave plasma at hypersonic speed. The X-15 was an inconel airframe was it not? Not titanium...
Thats debatable, and not that simple. I doubt the 15 second figure. Prior experience people go by for example is the plasma damage X-15 suffered on one flight when a test scramjet cause some serious damage simply from the shock wave plasma at hypersonic speed.
Drag losses are much worst with small vehicles.
A small RLV is even more difficult.
Also it should be a lot easier to raise the money for a big RLV, once a small RLV has demonstrated regular operations and retired most of the technical risk.
Quote from: indaco1 on 12/22/2008 12:01 amDrag losses are much worst with small vehicles. Depends on how you do it. As it is, drag losses are roundoff errors on typical launch vehicles (I think I was hearing ~200m/s for a typical EELV). There are options like air launch or other things that can help deal with that. Or you can just bite the bullet and deal with it. Admittedly if you get *too* small, drag losses get truly heinous, but I'm not talking about a 5kg to orbit vehicle, a 1000kg to orbit vehicle is still a respectable sized craft, but small enough to keep the development cost cheap enough to be feasible.QuoteA small RLV is even more difficult.But it's easier on the one dimension that matters most--the financial one. Raising hundreds of millions or billions of dollars for a bigger RLV is a lot harder than raising a smaller sum for a vehicle that is a lot smaller. There still are technological challenges with small RLVs (especially if you try to go too small), but if you don't overcome the financial challenge, you don't get to even try on the technical side. And quite frankly, I have higher confidence in being able to solve the technical issues than the financial ones.~Jon
3) Thrust reduction (throttling)
The key to a gas-and-go SSTO RLV IMO is airbreathing engines-somewhat like the Forerunner V business jet proposed somewhere on the forum (afterburning ultra-high-bypass turbofan to Mach 8, then LNG scramjet to Mach 15, then switch to LH2 to Mach 20), with a small rocket added for EOI. A metallic TPS should be used.
What about borane fuels? They were supposed to offer the performance of hydrogen at the density of kerosene, but I believe that their was a problem.
Quote from: tnphysics on 01/03/2009 04:24 pmThe key to a gas-and-go SSTO RLV IMO is airbreathing engines-somewhat like the Forerunner V business jet proposed somewhere on the forum (afterburning ultra-high-bypass turbofan to Mach 8, then LNG scramjet to Mach 15, then switch to LH2 to Mach 20), with a small rocket added for EOI. A metallic TPS should be used.That is really too complex.
The key to a gas-and-go SSTO RLV IMO is airbreathing engines-somewhat like the Forerunner V business jet proposed somewhere on the forum (afterburning ultra-high-bypass turbofan to Mach 8, then LNG scramjet to Mach 15, then switch to LH2 to Mach 20), with a small rocket added for EOI.
Quote from: tnphysics on 01/03/2009 04:24 pmThe key to a gas-and-go SSTO RLV IMO is airbreathing engines-somewhat like the Forerunner V business jet proposed somewhere on the forum (afterburning ultra-high-bypass turbofan to Mach 8, then LNG scramjet to Mach 15, then switch to LH2 to Mach 20), with a small rocket added for EOI.The gravity and air resistance losses would be much greater than for a standard rocket trajectory. But those are known weaknesses. Perversely, using the rocket to accelerate the vehicle to viable scramjet speeds may be better than adding a turbofan. It still means that a majority (as above) of your delta v comes from the scramjet. And you are carrying fewer systems as a result.
Quote from: kkattula on 12/26/2008 03:41 pm3) Thrust reduction (throttling)Only if it is manned. People also see SSTO, RLV, and assume manned.......
As far as the dream of having a fully reusable SSTO that enables aircraft like opperation I think that is likley 50 years out, the rocket equation is a harsh mistress and as long as you are married to it it almost totally preclude a realistic SSTO RLV....
What you need to do is change the equation. i.e. Create a launch vehicle or booster system that weighs nothing and has flyback capability for reuse. Impossible say's you?see the "Airlaunch Using Hybrid Air Vehicles" post under Advanced Concepts.Quote from: PurduesUSAFguy on 08/22/2006 11:13 amAs far as the dream of having a fully reusable SSTO that enables aircraft like opperation I think that is likley 50 years out, the rocket equation is a harsh mistress and as long as you are married to it it almost totally preclude a realistic SSTO RLV....
Quote from: kevin-rf on 12/28/2008 01:13 pmQuote from: kkattula on 12/26/2008 03:41 pm3) Thrust reduction (throttling)Only if it is manned. People also see SSTO, RLV, and assume manned.......I still wonder why the designers of the Shuttle did't just cut off one of the three main engines at a certain point of the launch instead of require a 66% thrustability that is equivalent..... I probably miss something.Thrust reduction is not the worst problem to design a SSTO, anyway.