What's the US Air Force up to now?

I've been watching the ongoing development of the Boeing X-37B reusable robotic space vehicle with considerable interest. It's preparing for its maiden flight later this month. Ares reports:

On April 19, the USAF/DARPA Boeing X-37B Orbital Test Vehicle (OTV) is due to be launched from Vandenberg AFB on an Atlas 501 rocket, wrapped in a supersized 5-meter payload fairing. It's a historic event because it is only the third known type of vehicle (after the Shuttle and Russia's Buran) to be launched into orbit with the intent of landing on a runway. The big mystery: what is it for and why is a cash-strapped air force supporting it? Nobody is saying too much about what the OTV is testing, or how long it's supposed to be in orbit before it tries to repeat Buran's feat of an autonomous re-entry and landing.

Resembling an elongated mini-Shuttle with V-tails, the X-37B traces its design to a black-world Rockwell project from the 1990s, known as Refly. Declassified later in the decade, it was renamed the Space Maneuver Vehicle (SMV).

The concept of operations was that the SMV could be launched and loiter on orbit for months at a time, carrying enough fuel to make several major orbital plane changes. It could then land, be refurbished, refuelled and even be fitted with a different payload before its next mission.

The big advantage was freedom to drive the vehicle all over the sky, compared with a satellite that is launched with all the fuel it will ever have. At one point the USAF was looking at hydrogen peroxide and RP rocket fuel - peroxide has its nasty habits but beats hydrazine.

There were a lot of potential uses, including surprise reconnaissance: a quick plane change on the other side of the world from your target, and you appear where you are not expected. Satellite inspection was another logical mission, and there were some breifings, videos and graphics which showed the SMV launching weapons.

. . .

Clinton-era squeamishness about the "weaponization of space" suppressed the MSP. The USAF and NASA's advanced launch community tried to get a joint project going in the 2001-2002 timeframe, but the loss of Columbia, and the subsequent NASA swerve into the Ares-Constellation dead end, killed that project too.

But somehow the OTV survived, through a number of airdrop and landing demonstrations with the subscale X-40 series - and the preceding history is probably why it keeps a low profile today. With the continued interest in the Prompt Global Strike program, however, and the apparent willingness of other nations to contemplate military operations in space, it may become less politically incorrect in the next few years.

There's more at the link.

The X-37B's first flight would be interesting enough: but now comes the news that the USAF is also interested in a reusable rocket booster, which would be the ideal launch vehicle for an operational X-37B or derivative. The official solicitation for proposals states in its detailed specification (link is to a .doc file):

The Air Force has identified the Reusable Booster System (RBS) concept as a promising approach to meet its future spacelift needs. The RBS consists of an autonomous, reusable, rocket-powered first stage with an expendable upper stage stack. The reusable first stage launches vertically and carries the expendable stack to the staging point. From the staging point, the reusable first stage returns directly to the launch base, landing aircraft-style on a runway.

To return the booster to the launch base, the Government is considering a rocket-back maneuver. The rocket-back maneuver consists of reorienting the vehicle so that it can use its main rocket engines to accelerate the vehicle back towards the launch site. The return to launch site maneuver is completed with an unpowered reentry and gliding flight and landing.

An important goal of the RBS Pathfinder program is to explore the feasibility and design space for the autonomous rocket-back maneuver. To the extent practical, the RBS Pathfinder program should also demonstrate other important technologies, processes and system attributes (TPSAs) that are expected to be included on the operational RBS.

Again, there's more at the link.

This has all kinds of interesting possibilities, from strike to reconnaissance, from robotic maintenance of satellites to the rapid launch of a constellation of micro-satellites to provide rapid coverage of a conflict zone (particularly if a technologically capable enemy has just shot down the permanent satellites on which the US depends). Both these programs will bear watching.

Peter