It does seem that in flight refueling of the carrier and SLV should be early on the list of improvements. I believe some of the heavies are nearly 50% fuel on long haul flights, so the 50,000 pounds you mentioned is probably very conservative.

Did Mitch suggest LOX instead of peroxide in one of his papers? I seem to recall that he made a very good case for peroxide only in flight transfer. Non cryogenic and around 85% of total propellant loading.

You are right. As I recall the sensitivities, the most important attribute is altitude, followed closely by flight path angle and then airspeed.

That said, if you need to get over 30Kft to avoid weather, you’re probably dodging thunderstorms, which is pretty unhealthy to begin with. So the earlier comment about a ‘knee’ in the calculations at about 30Kft is either related to this, or conveniently close.

Without revealing Scaled details I can’t talk about, it is generically true that one can trade fuel weight down and range down and increase payload weight, up to a point where there are Cg or structural load issues on the airframe. Making such trades will oft times increase payload as much as 50%, we’ve found. And in the end, everything comes down to economics. Much of the sizing we did on custom aircraft was driven by what was available on the surplus market in the way of engines, landing gear, and actuators or other subsystems. The only affordable way to build a new custom aircraft for the space launch mission is to reuse that sort of item from a certificated airframe.

You reminded me of another booster idea a few of us discussed a few years back. I’ll add it to my list and post it sometime.

*Never* assume I’m right and you’re not; in fact, I really like a number of your engine ideas (perhaps since I’ve played with similar concepts for a decade or so). The way of progress is that we all question everything and from that questioning, innovation emerges! And being “right or wrong” in engineering is oft times tied to the assumptions with which one begins the debate.

I have to assume you are better informed than I am. I’m not in the business, and it will be at least two years before I will be able to afford to try to get back in again. One thing that concerns me is drifting into the Geatano/Mook mode where I assume I have all the answers and expect all to agree. That is dangerous to me and possible, partly because I could easily reach a point of not comprehending that I don’t even understand the argument I’m lecturing others about. My turbine based ideas lean heavily on the roton concept you and Bevin pioneered, so mostly I’m probably reverse engineering you.

I think an analogy I could use is to point out that it is harder to make a “just OK” sort of carrier aircraft than a good one. It’s a bit like building an expendable pump-fed rocket engine. You can’t build a “just OK” one that is good for only a flight or two, because in order to build it properly to survive that one cycle with high reliability, you end up putting in margin that yield relatively longer life. That’s why the RL-10 can handle a few hundred cycles right out of the box even though it is “expendable”.

Perhaps it might be better to suggest that the carrier aircraft should be optimized for heavy lifting and medium range, with low development costs. Higher fuel consumption and lower service ceiling being acceptable trades to hold development costs down.

As for altitude, I don’t think one needs 40-50K feet. We found the knee in the curve is about 25-30K. Higher is somewhat better, but once again, it is best to put the weight into the rocket than add altitude performance to the aircraft, once you have reached about 30K ft.

My assumptions seem to be mostly based on the Scaled high altitude units. It just seems to me that they are doing some things the hard way. I’m also influenced by the Space Van concepts Len wrote up in the late 1990s, especially the economic arguments.

One of these days I might write this up in more detail. Meanwhile, you can find a partly relevant paper at the AirLaunch website. It’s off line today as we transition to a new hosting service, but when it comes back I’ll give a proper pointer. Or I could send the paper to you or John by email.

I went through the half dozen or so AirLaunch papers I saw a few months back when Jon linked to them. They influenced my thoughts here. If there are more, I would like to read them. rdnktech@tampabay.rr.comspam

Both t/Space and AirLaunch LLC analysis contributed to my opinions.

t/Space is not doing anything at the moment; our experience with NASA has not been positive. Once Griffin is gone then maybe we can revisit matters but I don’t plan on holding my breath for real change…