Some news on the NASA Front

[MultimediaMan]

No Fair...the (addled) boys and girls running Ariane have had a great run...after they got their Gyro problem solved with Ariane 5.

Specific Impulse is very important at any point: It pretty much determines how big your spaceship will likely be based on mission parameters: How much mass you will have to earmark for fuel, etc...

I'm not against using a "mothership" for launching spacecraft at all, that is an idea well-worth persuing. What I am preaching here is that whatever the orbiter's launching scheme is, it should use Liquid propulsion for better efficiency.

Rutan's design is great for a suborbital hop, but the propulsion scheme it is using is too limited for sustained use. Rutan's people could have used a hydrazine engine and have had the check for the X-prize in their back pocket a few months ago, if they had the money for one.

[K6-III]

No, no, no....

Trust me, noone wants to be using hydrazine. Far too toxic for a tourist vehicle.

I really like the configuration of the hybrid motor using nitrous oxide and rubber.

The White Night will be the first stage both for SpaceShip one and for the Streaker microsat launcher from SpaceDev, based on the same hybrid motor. (You can read the news at www.spacedev.com)

Note that making a spacecraft larger doesn't make it more expensive. Expense is your biggest enemy. Expense comes from people-hours and complexity adds people hours.

Hence, it is better to go pressure-fed and bigger than a higher-performance fragile pump-fed system.

[Dr Mordrid]

Hydrazine is toxic and LOX is extremely explosive even with a small leak. Wonderful choices

Rutans is suborbital, but given it's a minimalist design to the 100km requirements of the X-Prize that doesn't mean that's the limit of its potential. IMO if one can achieve what he's done with an early hybrid design the planes got real potential.

What intriques me more than anything is SPOnes re-entry profile, which could address a lot of the problems with both capsules and the shuttle. It also harkens back to some of the pre-Mercury single passenger proposals that also used the shuttlecock effect. Another was a stripped-down X-15.

Ariane: a faulty valve sent it off course so it had to be blown up. All this because of the need for liquid fuel to be preheated and provide nozzle colling in the process. Gotcha

Dr. Mordrid

[K6-III]

Well, regeneratively cooled nozzles are pretty common and not that hard to do....

Turbopumps, however, are VERY hard to do...

That reentry profile is only good for suborbital, assuming my thinking is correct.

You need atmosphere for the effect to work.

[K6-III]

Now, if Rutan wanted to go liquid biprop, a more reasonable choice may have been 90% hydrogen peroxide for oxidizer and kerosene for fuel.

[K6-III]

Personally, I'm cheering Carmack for the X-Prize with his mono-prop 90% Peroxide VTVL approach.

Let's hope his peroxide supply issues are resolved.

BTW, if any of you know of a good foreign or domestic source of HTP peroxide, let Carmack know.

[Dr Mordrid]

The X-Prize will require re-entry from 327,360 feet (62 miles or 100 km). The density of the atmosphere at 100 km is about 1,000,000/th that at sea level, and is well above the altitude at which Colombia broke up ( 200,700 ft).

Rutan comments on his reentry profile in his FAQ:

Why do you "fold" the wings to come back down?

In space, the wings are folded up to provide a shuttle-cock or "feather" effect to give the ship extremely high drag for reentry. This allows the reentry deceleration to occur at a higher altitude and greatly reduces the forces and heating on the structure. Also, the ship, in the feathered configuration, will align itself automatically such that the pilot has a less-critical flight control task. We refer to this as "care-free reentry". The atmosphere orients the vehicle to a belly-first attitude without pilot input. Another benefit is that, since the altitude is higher, the pilot can glide further after the entry deceleration. A SpaceShipOne pilot can glide more than 60 miles after he converts back to the non-feathered glider shape.

Looks like Rutans profile may not be so dependent on air density as you presume.

Dr. Mordrid

[K6-III]

Per this page, it is described as a stable, high-drag configuration, meaning that it would depend on air density:

http://www.scaled.com/projects/tierone/data_sheets/html/lith_space_one_p2.htm

[Dr Mordrid]

Dunno about that. If you read the quotes above he depends on a high drag configuration to slow the craft in the thin atmosphere at high altitudes.

This slows SPOne down before it hits the thicker air where the shuttle ran into trouble, reducing the thermal loading on the structure once it gets there.

Dr. Mordrid

[K6-III]

Again, at no point during its flight profile does the SpaceshipOne go far above Mach 3.

At that velocity and altitude, it scarcely has to worry about TPS.