DARPA has announced the second phase of its ambitious XS-1 program. The agency is seeking to make access to space more regular and affordable by employing an entirely re-usable high-speed, sub-orbital automated spaceplane as the first stage of its launch vehicle.

Upon reaching a designated height, an expendable upper stage would separate from the space plane, and insert a payload into low-Earth orbit (LEO). The spaceplane would then autonomously land and be serviced for the next launch.


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Phase 1 of the program saw DARPA award contracts to three companies, each of which was paired with a launch service provider. The teams were tasked with analyzing the feasibility of the project, and designing their own versions of the launcher.

"During Phase 1 of the XS-1 program, the space industry has evolved rapidly and we intend to take advantage of multiple impressive technological and commercial advances," states Jess Sponable, program manager for the XS-1. "We intend to leverage those advances along with our Phase 1 progress to break the cycle of escalating DoD space system launch costs, catalyze lower-cost satellite architectures, and prove that routine and responsive access to space can be achieved at costs an order of magnitude lower than with today's systems."

Phase 2 will integrate state-of-the-art technologies in combination with the advances made in Phase 1 of the program to design and fabricate a functioning launcher roughly the size of a conventional business jet. Whereas multiple contracts were offered in the first stage of the program, DARPA only envisions awarding a single commitment in Phase 2.

The second stage of the initiative will have four primary technical goals.

  • Fly 10 times in a 10-day period (not including weather, range and emergency delays) to demonstrate aircraft-like access to space and eliminate concerns about the cost-effectiveness and reliability of reusable launch.
  • Achieve flight velocity sufficiently high to enable use of a small (and therefore low-cost) expendable upper stage.
  • Launch a 900 to 1,500-lb (408 to 680-kg) representative payload to demonstrate an immediate responsive launch capability able to support both DoD and commercial missions. The same XS-1 vehicle could eventually also launch future 3,000+-lb (1,361-kg) payloads by using a larger expendable upper stage.
  • Reduce the cost of access to space for 3,000+-lb payloads, with a goal of approximately $5 million per flight for the operational system, which would include a reusable booster and expendable upper stage(s).

According to DARPA the final design will make use of advanced heat-resistant materials, cryogenic tanks and modular subsystems that will combine to lower the cost and reduce downtime. Conventional rocket-based launch providers can only offer a limited number of launch slots each year, and the launches are booked years before the launch time.

Even the Ariane 6, Airbus Safron Launchers' next-generation rocket, will offer only 12 launches per year. Employing a reusable spaceplane has the potential to provide cheaper, more flexible access to LEO. Beyond finding its uses in the commercial sphere, the XS-1 project will be used to assure American military satellites can be launched more frequently.

Source: DARPA