...and hopefully at least as good, if not better. Clark Lindsey explains the significance of the successful UP Aerospace launch:

So why is this a big deal? Suborbital rockets have been launched at WSMR and elsewhere since the 1940s. This flight is significant because of the business model, not the altitude attained. The vehicle was designed to serve a consumer market rather than to carry out a task for the military or some other government entity. To do this profitably, the vehicle must be built for as low a cost as possible and must be cheap to fly. Spaceflight for the general public is new to the rocket world.

[Update a few minutes later]

Jon Goff has a very instructive post for those who buy into the mantra about how much more of a problem orbital is than suborbital with respect to energy.

As I note in his comments section, while these are great points when it comes to getting to orbit, the real issue is the energy that has to be dissipated to come home. I think that this will be the far greater challenge for orbital vehicle developers, at least if they're reusable (and despite progress that can continue to be made in dropping the cost of expendables, ultimately that's the only way to go for truly low costs, not to mention ability to bring the customers home).

Even Burt claims not to have a solution (though he may be sandbagging us). Certainly his current shuttlecock concept won't ever scale up to an entry from orbit. As I've noted before, though, Burt is not God, and just because he doesn't know how to do something, doesn't mean that it can't be done.

"the real issue is the energy that has to be dissipated to come home."

Ablative materials research could be a promising subject for a Centennial Prize, or heat shielding concepts in general. AFAIK, the serious players aren't looking at anything revolutionary on that front, but it could produce major weight savings if a breakthrough occurred.

"Even Burt claims not to have a solution"

Wouldn't surprise me -- genius in one field doesn't necessarily translate into another, and Burt is nothing if not a god of aviation. Also, his efforts have long been concentrated in a certain subset of aviation design (composites), whose prospects for scaleability are unknown. While there will probably be a strong role for composites in suborbital flight, and perhaps even in orbital destinations, it doesn't seem likely to be the answer for vehicles with extreme heating, stress, and other strength issues.

"(though he may be sandbagging us)"

Rutan doesn't strike me as coy, although it's not hard to imagine the directions he might take. If I had to guess, I would say any orbital system he develops would use a White Knight-derived carrier plane, but other than that it's difficult to speculate beyond agreeing that the vehicle itself wouldn't look much like SpaceShipOne or its descendents. He may simply open-source WK-# and let rocket entrepreneurs develop their own vehicles for high-altitude launch, perhaps make deals with Orbital to get its Pegasus costs down for additional revenue.

"and just because he doesn't know how to do something, doesn't mean that it can't be done."

Doesn't even mean that he himself won't figure it out, and I'm sure he relishes the impending challenge. Most people in this community would love to be involved in the Great Push in some substantive way, and he's right there on the eyewall of the brewing hurricane. And if VG turns out well, he'll have bottomless funding to pour into the effort.

Brian makes a very interesting comment here. Could the White Knight II carry a Pegasus or Pegasus XL to its drop altitude? This would certainly let Orbital drop the costs of that L1011 that sits about 800 yards to the east of Burt's shop.

You know, I'm not at all sure that dissipating energy is that big a deal, except perhaps we try to do it too fast. Now, I'm a logician and not a materials guy, but as I understand it the actual heating involved is proportional to wing loading, or more generally aerodynamic loading. It would seem then that either slower deceleration or a bigger surface area (like the Soviet's balloon re-entry scheme perhaps) could make it much less of an issue.

One word: inflatables.

Every new-generation commercial launch vehicle with payload space to spare should be taking up prototype inflatable reentry and descent vehicles to fly a dozen or two variations.

Starting NOW.

Rand,

I noted this over in Jon's comments, and I thought I'd note it over here as well.

I don't know exactly where (although I think it was a flight global article from 2005 or so) but Rutan talked a little about an orbital vehicle, he did say that he thought his shuttlecock woudl scale to orbital. Now, Im not claiming him to be god - he may have been sandbagging, he may have had an idea, but has since changed his mind, or he may still be planning on using it when he goes orbital. And I do understand the difficulties of it.

I do remember him saying that though

Dennis,
The altitude profile of WK1 is more than sufficient, so the real questions for WK2 are weight capacity and physical dimensions--which will, I imagine, depend on how SS2 requirements develop. I was just throwing the idea out there as speculation, since Rutan has often been critical of Orbital's decision to have a dedicated carrier plane instead of designing for commercial aircraft. He may very well have larger market considerations in mind while designing WK-2 than just serving SS2.

> Even Burt claims not to have a solution (though he may be sandbagging us).

I interpret this to mean he has not chosen a solution.

In a sense, the problem is not the lack of a solution but too many solutions. There have been quite a few solutions proposed over the years, but most have never been tested in actual flight vehicles.

If the 1960's x-planes had continued, we might know which ones work in the real world. Unfortunately, Apollo (and then the Shuttle) preempted that. Now, thanks to Orion, NASA doesn't even have the bandwidth to do laboratory research on new thermal protection systems.

You know, I'm not at all sure that dissipating energy is that big a deal, except perhaps we try to do it too fast.

The time required to decelerate from orbit is independent of the mass/area ratio of the vehicle. Instead, it depends (in an optimal trajectory) on the lift/drag ratio. So, you are advocating some kind of lifting reentry vehicle.

Also, prolonging the time over which reentry occurs can increase the heat absorbed by the vehicle, if I understand things correctly.

For reentry, cumulative heat load is important--thermal soakback may require an underlying structure which can take high temperatures, but peak heating rate is usually more challenging to handle. That is what leads one to exotic high-temp materials at the stagnation points. Peak heating rate has a strong dependence on the ballistic coefficient (similar to wing loading in aircraft), so a large, lightweight craft does better. Lift/drag ratio has a small effect on peak heating rate, but a large effect on the maximum deceleration felt. A good reentry design tries to achieve both low ballistic coefficient and high L/D. Hence the comments about inflatables, which are very promising (and always have been...). Deployable flexible (but not pressurized) heat shields offer similar benefits, and can have more benign failure modes. AMROC's SET-1 payload in 1989 was to be a test of such a system. Ah, if things had gone differently that October...

> The time required to decelerate from orbit is independent of the mass/area
> ratio of the vehicle.

The ratio (called the ballistic coefficient) makes a big difference. A parachute will come down much more slowly than a meteorite.

The ratio (called the ballistic coefficient) makes a big difference. A parachute will come down much more slowly than a meteorite.

No, the ballistic coefficient makes little difference in the time required to decelerate from LEO, on an optimal trajectory. The reason is the lower the ballistic coefficient, the higher altitude at which you do the deceleration. The air density and ballistic coefficient cancel out.

Eventually you decelerate so much that you're falling at terminal velocity (your parachute example), but by that time atmospheric entry is over.

If the ballistic coefficient is too large the altitude of that optimal trajectory comes out negative, so obviously you can't extend this argument indefinitely.

> No, the ballistic coefficient makes little difference in the time required
> to decelerate from LEO, on an optimal trajectory. The reason is the
> lower the ballistic coefficient, the higher altitude at which you do the deceleration.

Yes, you start to decelerate at a higher altitude. That's why the time does depend on ballistic coefficient. At higher altitudes, there's lower density and pressure so deceleration is more gradual. Fewer gees, deceleration takes place over a longer period of time.

That's why SpaceShip One put itself into a high-drag configuration for reentry.

> Eventually you decelerate so much that you're falling at terminal velocity
> (your parachute example), but by that time atmospheric entry is over.

What makes you think parachutes only operate at terminal velocity? If that were true, many common applications of parachutes would be impossible.

There are parachute designs for supersonic and even hypersonic velocities. See, for example, "A Hypersonic Parachute for Low-Temperature Re-entry."

http://www.ingentaconnect.com/content/els/00945765/1995/00000036/00000005/art00108

Yes, you start to decelerate at a higher altitude. That's why the time does depend on ballistic coefficient. At higher altitudes, there's lower density and pressure so deceleration is more gradual.

Do I have to repeat myself again, Ed? The time does *not* depend on ballistic coefficient. Nor does peak acceleration. The lower density and the lower ballistic coefficient cancel each other out.

Fewer gees, deceleration takes place over a longer period of time.

If you try to decelerate too gradually, you fall into denser atmosphere before slowing enough. You seem to think the deceleration can be made arbitrarily low by reducing ballistic coefficient. It pretty obviously can't. Think about it.

I will send you a reference to an aerodynamics book I have that devotes an entire chapter to this subject.

> Do I have to repeat myself again, Ed? The time does *not* depend on ballistic
> coefficient. Nor does peak acceleration.

No, you don't have to repeat yourself, Paul. Repeating yourself does not make you correct.

Talk to the engineers at TGV Rockets. Ask them why they have that big drag brake.

To quote from NASA Technical Memorandum 103544, Application of Low Lift to Drag Ratio Aerobrakes Using Angle of Attack Variation for Control, "An increase in the ballistic coefficient also results in a shift of the acceleration load limit boundary. This means that for a given target periapsis altitude, the peak acceleration load decreases as ballistic coefficient increases."

> If you try to decelerate too gradually, you fall into denser atmosphere
> before slowing enough. You seem to think the deceleration can be made
> arbitrarily low by reducing ballistic coefficient. It pretty obviously
> can't. Think about it.

I have thought about it, and so have many other people. What you overlook is the fact that you fall into denser atmosphere with *less* energy than you otherwise would have.

To quote from an August 2004 NASA Tech Brief on Inflatable Emergency Atmospheric-Entry Vehicles, "Due to very low mass-per-surface area, a large radius, and a large coefficient of drag, ballutes decelerate at much higher altitudes and with much lower heating rates than the space shuttle. Although the space shuttle atmospheric reentry results in surface temperatures of about 1,600 °C, ballutes can be designed for maximum temperatures below 600 °C."

> I will send you a reference to an aerodynamics book I have that devotes
> an entire chapter to this subject.

I'm sure the aerodynamicists at NASA have read some books, too, Paul. Maybe even written some. :-)

So, Ed, is it your claim that entry from LEO can be made arbitrarily long by reducing the ballistic coefficient? Assume the ballistic coefficient of the vehicle is constant, and the vehicle is non-lifting (although the last assumption isn't really needed).

Yes or no?

> So, Ed, is it your claim that entry from LEO can be made arbitrarily
> long by reducing the ballistic coefficient?

No, my claims are contained in the words that I typed.