I don't have time to answer this email query, but perhaps some of the other readers do, in comments:

I loved your article about the Hyper X 43 and scramjets in genral, it was amazingly informative. As an amatuer space enthusiast I try to keep up, some of the stuff is completely out of my league. I had some questions, even if a singlestage could be built, would it be able survive re-entry? Second, even though Rutan's Spaceship one did in fact go to 62k up, didn't all the x-15's do the exact same thing? Could the feathering device that Spaceship one uses be applied to a space craft coming in from low-orbit or is that type of system restricted forever to sub-orbital manuevering? if not is the composite material shell of the Spaceship as effective or even in the same league as Shuttle's tiles? and finally, with the weight of turbofans and some kind of orbital manuevering system and reaction control system, could the design or anything like the design of the Spaceship One work off taking us to the runway to low orbit system that we only dream of in science fiction.

I'll try a couple of them.

While thirteen X15 flights went over 50 miles (80 km), only two went over 100 km and none went as high as SpaceShipOne did on its second X-Prize flight. The two flights over 100 km high were a little over a month apart, so SpaceShipOne beats the X15 on that count too, though perhaps the X15 never really tried for short turn-around times. Those two 100 km high flights were consecuitive flights, but I don't know whether they were in the same aircraft.

The X15 program cost far more than SpaceShipOne, but of course it was pioneering and was doing things other than altitude (e.g. the Mach 5+ runs).

IANAAE (I am not an aerospace engineeer), but my understanding is that the SS1 composite skin is definately not in the same league as the shuttle TPS. I believe that this is because the thermal loads encountered on the SS1 mission profile were much lower than a space shuttle descent from orbit.

SpaceShipOne's importance is that it was a private effort, privately financed and privately executed. It proved that space travel, albeit a briefm sub orbital jaunt, could be done by an entity other than a government. This is of great importance for the future.

According to Wiki, both X-15 100km flights were flown by X-15 #3.

Could the feathering device that Spaceship one uses be applied to a space craft coming in from low-orbit or is that type of system restricted forever to sub-orbital manuevering?

The feathering system might be useable if the entry velocity is low enough and the mass to surface ratio was low enough. What you would be trading is the mass of the structure needed to hold the wings on against the dynamic pressure and heating from the air. My feeling is that the trade would show that feathering is not feasible from orbital velocity.

if not is the composite material shell of the Spaceship as effective or even in the same league as Shuttle's tiles?

Not even close in heat rejection, but it didn't need to be.

and finally, with the weight of turbofans and some kind of orbital manuevering system and reaction control system, could the design or anything like the design of the Spaceship One work off taking us to the runway to low orbit system that we only dream of in science fiction.

Right now I don't think we know enough about scramjets, etc. to do such a vehicle. A vertical takeoff/vertical landing rocket such as DC-X or an X-33ish VTHL craft might be possible.

The key problem for commerical use of such a vehicle is making the system robust enough to survive failures and have a reasonable payload to orbit (as the hosts here have pointed out recently).

With all the hype about SpaceShip One, you'd think we're a few months from orbital trips. However, the mainstream press has downplayed the cautionary statements that the SS1 team has made that going to and from orbit is a lot harder and will take a lot of R&D. (Empahsis on the D, IMHO.)

Without in any way denigrating Burt Rutan's achievement, the problems of reentry from orbital flight are several orders of magnitude more difficult than those faced by SpaceShip One. Reentry heating is a function of the square of the velocity. SS 1 was essentially at zero velocity at the top of it's trajectory. The feathering operation served to put SS 1 into a very high drag configuration so the velocity would not exceed the limits of the design during descent. These limits are both structural and thermal.

Probably the highest thermal stresses were in the launch phase during the early-to-mid engine burn at the highest dynamic pressure. One of the reasons for using a flyback first stage (White Knight) was to get SS 1 above most of the atmosphere so as to reduce the dynamic pressure as SS 1 accelerated. (half of the atmosphere is below 18,000 ft, about 3/4 is below 33,000 ft)

The structure of SS 1 was probably some sort of carbon composite with thermal characteristics such that the relatively mild heating did not degrade the strength below the structural requirements. The shuttles thermal tiles have no structural requirement beyond staying together themselves under launch and recovery loading. Their primary function is to insulate the shuttle structure from reentry heating so that structure does not fail, for reasons more obvious since Columbia came apart.

Single-stage-to-orbit is certainly possible, but it may not be very efficient in terms of payload fraction. More likely in my view is the use of a high performance flyback first stage, perhaps launching a hybrid scramjet/rocket at 70-80,000 feet and around Mach 3-5.

In theory, you could kill off your orbital velocity before entering the atmosphere and use something like the high drag feather configuration to reduce reentry heating. The problem is to have enough fuel to perform that retrograde burn AND avoid falling like a rock until you were adequately slowed down to your desired velocity and low enough to not accelerate (due to gravity) too much before entering the atmosphere.

So, I guess the answer to the last question is that something vaguely resembling the White Knight/SpaceShip One combination is possible, but it would compare in the same way that White Knight compares to the B-70 or SR-71, which is to say, not much!

The big reason for the feathering was to allow for a combination of passive stable re-entry and high-crossrange (to make it possible to glide back to a landing at an airport, instead of, say, splashing down into the water). I can see this feature surviving into an orbital craft, but not by itself. While SS1 needed no real TPS, that will not be true of an orbital ship.

I suspect that what would be needed would be something like a combination of engines/propellant load capable of both de-orbiting, and then (firing more nearly vertical) slowing the descent; a high surface area design to absorb thermal loads and contribute to slowing the descent; a TPS - either built-in or plastered on, because the Shuttle system has proven far too costly - capable of resisting medium thermal loads; and a feather mode for once the ship is low enough and slow enough to take the dynamic load of deploying it. That would give a good margin of safety for a re-entry from orbit, though if an ablative TPS is used, it might slow the flight rate enough to be uneconomical.

The trick is to do this with as little weight and cost as possible.

SpaceShipOne made money.

More at "X-15 and today's space planes,"
http://www.thespacereview.com/article/204/1