Main Engine Cut Off

Thoughts on XS-1

Jeff Foust, of SpaceNews, with some background on the selection of Boeing for phases 2 and 3 of the program:

Boeing will develop its “Phantom Express” vehicle for phases 2 and 3 of DARPA’s Experimental Spaceplane 1 (XS-1) program, which has the goal of performing 10 flights in 10 days to demonstrate responsive and low-cost launch. Phase 2 will cover development of the vehicle and ground tests though 2019, with a series of 12 to 15 test flights planned for phase 3 in 2020.

DARPA spokesman Rick Weiss said the value of the award to Boeing is $146 million. The award is structured as a public-private partnership, with Boeing also contributing to the overall cost of the program, but Boeing declined to disclose its contribution.

It’ll be powered by a single SSME, or at least a derivative of the SSME:

“As one of the world's most reliable rocket engines, the SSME is a smart choice to power the XS-1 launch vehicle,” said Aerojet Rocketdyne CEO and President Eileen Drake. “This engine has a demonstrated track record of solid performance and proven reusability.”

For the XS-1 program, Aerojet Rocketdyne is providing two engines with legacy shuttle flight experience to demonstrate reusability, a wide operating range and rapid turnarounds. These engines will be designated as AR-22 engines and will be assembled from parts that remained in both Aerojet Rocketdyne and NASA inventories from early versions of the SSME engines. Assembly and ground testing will take place at NASA's Stennis Space Center in Mississippi.

With a partially-reusable, flyback, two-stage-to-orbit vehicle operating today, the XS-1 concept is less impressive than it would have been a few years ago. It’ll still be interesting to follow along with, especially as someone who loves launch vehicles, but I can’t help but be a bit disappointed in the decision.

I was hopeful that the XS-1 program would be used as a good opportunity to invest in and develop new capabilities from younger players in the industry. Instead, Boeing is developing a bigger X-37B-like aircraft and putting an SSME on it.

Proactively widening the industry would do more to lower launch costs than working with Boeing on yet another project powered by an SSME-derived engine. “Boeing” and “low-cost launch” have rarely, if ever, been used in the same sentence.

I’ll also be very interested to hear what changes are being made to the SSME to encourage rapid turnaround and low maintenance.

From Foust’s SpaceNews article:

That engine represents an apparent switch in Boeing’s XS-1 concept. In phase 1 of the program, Boeing was partnered with Blue Origin, with the expectation Blue Origin would provide an engine for the spaceplane. “We selected the Aerojet Rocketdyne engine as it offers a flight proven, reusable engine to meet the DARPA mission requirements,” Sampson said.

Aside from the use of the term “flight proven,” which SpaceX gets a lot of shit for using, this may be the most curious part of the decision.

In the same way that the Air Force and NASA have a vested interest in keeping Orbital ATK around—thus prompting decisions to build new launch vehicles with crucial components built by Orbital ATK—there is a vested interest in keeping Aerojet Rocketdyne around.

It’s hard not to think that the switch to the AR-22 was prompted by two factors: AR-1 and SLS.

If and when Blue Origin’s BE-4 is selected for ULA’s Vulcan, Aerojet Rocketdyne would be effectively out of the first stage-class engine business, other than the RS-25E. They have a few more RS-68A engines to build, sure, but no new developments beyond that.

Additionally, Boeing, who is building the core stage of SLS, has a vested interest in helping Aerojet Rocketdyne get a new RS-25E production line spun up, since the existing supply of RS-25 engines will run out by SLS’ fourth flight.

In 2014, DARPA announced three phase 1 awards for initial studies of the XS-1 concepts. In addition to Boeing, DARPA provided awards to Masten Space Systems, working with XCOR Aerospace; and Northrop Grumman, working with Virgin Galactic.

It’s a bummer that Masten and XCOR lost out on this. I hope Masten continues work on Broadsword, since that could prove to be a very useful engine in the near future. And I’m not sure where this leaves XCOR. Their XR-8H21 engine is in the running for use on ULA’s ACES upper stage, but they’ve got tough competition in the RL10 and BE-3U.

Overall, I’m quite disappointed at the missed opportunity XS-1 presented to widen the industry. It’ll take a lot to convince me that a Boeing project of this sort will ever be affordable. Boeing doesn’t have the best reputation for cost-efficiency when it comes to launch vehicles—Delta IV and SLS being the two most recent examples—and their last small launch DARPA project didn’t end well.