Forget supersonic: Hypersonic is the U.S. military’s new speed

By Justin Bachman, Bloomberg News

In the future, military dominance will depend partly on how fast you can fly and how quickly you can get into space. That’s one of the guiding principles behind an advanced Pentagon project to build a spacecraft able to launch smaller payloads into low-earth orbit on short notice, and at lower cost.

Boeing Co.’s XS-1 (Experimental Spaceplane), which the company dubs “Phantom Express,” got a green light this week by the Defense Advanced Research Projects Agency, or Darpa. The XS-1 is designed to quickly lift satellites as heavy as 3,000 pounds into orbit for $5 million or less, launching from the ground, deploying a small upper-stage module, and then landing like a traditional airplane-the key to reuse and lower operating expense. Darpa also has a separate program aimed at launching 100-pound satellites for less than $1 million per launch, using conventional aircraft.

“The XS-1 would be neither a traditional airplane nor a conventional launch vehicle but rather a combination of the two, with the goal of lowering launch costs by a factor of ten and replacing today’s frustratingly long wait time with launch on demand,” Jess Spoonable, a Darpa program manager, said in a May 24 statement.

“When most people think about hypersonic aircraft, many believe they would have to be large, expensive, and exotic.”

The Phantom Express will be powered with an Aerojet Rocketdyne Holdings Inc. AR-22 engine, a newer version of the main engine trio that served on NASA’s Space Shuttle. Boeing will design and build the aircraft through 2019, including 10 engine ground firings over 10 days, followed by 12-15 flight tests in 2020. A Boeing spokeswoman declined to comment on the project’s cost.

Beyond the military’s desire for a spaceplane, such a craft would likely carry immense appeal for commercial companies, many of which are planning to launch constellations of small satellites. These companies don’t need the weight capability, or large expense, associated with traditional payload launches sold by United Launch Alliance, the Boeing-Lockheed Martin Corp. joint venture, Arianespace, or Elon Musk’s SpaceX.

The XS-1 is also envisioned as a means to further engineering work on advanced airframe designs capable of hypersonic flight, generally five to 10 times above Mach 1, the speed of sound at sea level (approximately 767 miles-per-hour). Historically, these designs have been challenged due to the intense friction and heat generated by higher Mach speeds.