Pratt & Whitney Canada announced today that Virgin Galactic has picked its PW308 engine for use on the White Knight 2 aircraft that will be the carrier aircraft for SpaceShipTwo. The engine, which generated up to 30,700 newtons (6,900 pounds) of thrust, has been used on a number of bizjets; the press release doesn’t indicate how many such engines WK2 will use. The release does state that P&WC will work with Virgin on the potential use of “advanced biofuels” to reduce engine emissions, reducing the system’s overall carbon footprint by up to 50 percent.

In his speech at the ISDC in May, Jim Benson said that the reentry forces that his company’s redesigned suborbital spacecraft would be less than the 6 Gs that SpaceShipTwo will experience. He wasn’t more specific then, but this week the company announced that their vehicle will subject passengers to no more than 3 Gs during reentry by spreading the deceleration forces over a wider range of altitudes. The vehicle will accomplish this through something called “Variable Ballistic Coefficient” slowing, which involves a number of vehicle configuration changes, most notably the dive brakes; the company has filed a patent application for this approach.

Something like this could prove to be a good differentiator over time: lower G forces will result in a more comfortable experience for passengers and perhaps allow people that for health reasons can’t tolerate higher G forces to fly at all. It may be less of an issue in the near-term, though, since people who are the most eager to fly (and have the means to pay for the flight) will probably be willing to put up with the inconvenience of a momentary surge of G forces.

The trade publication High-Performance Composites offers this news about the development of SpaceShipTwo:

Advanced Composites Group Ltd. (ACG, Heanor, Derbyshire, U.K.) will supply a new generation of out-of-autoclave prepregs for the project, featuring MTM45-1, a variable-cure temperature, high-performance, toughened epoxy matrix developed for resin film infusion and prepreg processing. It was designed for low-pressure vacuum bag processing and, in addition to resin film and prepreg formats, is available in partially or selectively impregnated formats to reduce layup time, surface defects and internal voids. After a freestanding postcure, the system is capable of 150°C (302°F) wet Tg and reportedly exhibits good damage tolerance. Initial cure can be as low as 80°C/176°F, which ACG says allows for the use of lower cost tooling materials.

But you all knew that already.

In an article in this week’s issue of The Space Review, Richard Speck of Micro-Space Inc. proposed a radical approach to human orbital spaceflight: to keep launch costs low, make the spacecraft as simple and as lightweight as possible. He proposes a spacecraft that is little more than a spacesuited astronaut strapped into a heat shield and thruster system, enough to get into orbit, maneuver to a space station, and then reenter and parachute to a landing. Speck goes through the technical details with such an approach, which could allow people to fly for just a few million dollars even at today’s relatively high launch costs.