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DARPA Funds Stage 2 of XS-1 Spaceplane Design Competition

A reusable spaceplane could be putting satellites into orbit every single day by 2018

3 min read

Evan Ackerman is IEEE Spectrum’s robotics editor.

DARPA Funds Stage 2 of XS-1 Spaceplane Design Competition
Image: Darpa

The Space Shuttle was originally intended to make getting to space easy, inexpensive, and routine, with an initial goal of a launch nearly every week. It didn't quite play out that way, and we’re now back to tossing things into orbit on top of massively expensive rockets that are good for only a single one-way trip. It’s a system that works (most of the time), but it's not a system that’s efficient.

Just because the Space Shuttle didn’t magically open orbit up to everyone doesn’t mean that getting to space through a reusable platform is a bad idea. In commercial spaceflight circles, the thinking is that reusability is the best way to help drive down costs. DARPA, the U.S. Defense Department’s blue-sky research arm, wants a piece of the action; but in typical DARPA fashion, the agency is looking for something even more futuristic. It has just awarded nearly $20 million to three aerospace companies to continue design work on a reusable spaceplane that will be able to launch a satellite into space every single day.

Here are DARPA’s totally reasonable requirements for the XS-1 spaceplane demonstrator, as of the initial 2013 announcement:

  • Fly 10 times in 10 days
  • Fly at Mach 10+
  • Launch a representative small payload (3,000 to 5,000 pounds) to orbit
  • Operate at less than $5 million per flight

That $5 million per flight figure is about an order of magnitude less than current launch costs for payloads of this mass, and ten flights in ten days is flying about an order of magnitude more frequently than anything else is currently able to. But hey, that’s DARPA for you—always wanting the impossible and quite often getting it.

DARPA has awarded $6.5 million each to three companies for developmental design work, including Boeing (in partnership with Blue Origin), Northrop Grumman (in partnership with Scaled Composites and Virgin Galactic), and Masten Space Science Systems (in partnership with XCOR Aerospace).

Here's a look at some concepts from the three companies involved in the competition:

Boeing / Blue Origin:

imgImage: Boeing

Northrop Grumman / Scaled Composites / Virgin Galactic:

imgImage: Northrop Grumman

Masten Space Science Systems / XCOR Aerospace:

imgImage: Masten

If these XS-1 concepts look familiar, it’s almost certainly because they remind you of the X-37B, Boeing’s own spaceplane:

imgPhoto: USAF

The X-37 started off as a collaborative project between Boeing’s Phantom Works and NASA in the late 1990s, and was classified and transferred to DARPA in 2004. In 2006, the US Air Force asked for its own version, and they now have two X-37B spaceplanes with the capability of placing small satellites in orbit and then staying up there for years at a time.

While the X-37B and the XS-1 concepts do look a lot a like, the big difference is how they get themselves to orbit. The X-37B is a passenger, sitting on top of a conventional rocket (an Atlas V) inside an aeroshell. Once the rocket puts the X-37B in orbit, the space plane can maneuver all by itself and then glide to a landing, but until it gets up there, it’s mostly helpless.

The XS-1, on the other hand, isn’t really intended to spend any time in orbit at all, but it is intended to get itself most of the way there without any help, trading conventional rocket stacks for a hypersonic propulsion system that can boost it to Mach 10, just over 12,000 kilometers per hour. 

DARPA envisions that the space plane will essentially act as a reusable first stage. Once it reaches hypersonic speeds at altitude, it’ll fire off a separate, expendable booster rocket to actually get the payload the final distance to low Earth orbit. Then, the spaceplane will fly itself back to base for a controlled gliding landing. 

Just exactly how this hypersonic propulsion will work in practice isn’t entirely obvious at this point, and at least initally, DARPA had a rather diverse set of potential ideas about how the XS-1 might get airborne:

imgImage: DARPA

I personally am a fan of the double-spaceplane-and-booster sandwich. Yummy.

Of these options, using a carrier aircraft has recently proved to be both realistic and cost-effective: Virgin Galactic has beeing using it for SpaceShipTwo for years; giant towed gliders are under active development at NASA; and Paul Allen is working on something crazy. This isn't to say that the XS-1 won’t ultimately launch horizontally or vertically on its own, but the strict requirements will likely be easier to meet if the XS-1 vehicle gets a free ride up to 15,000 meters or so.

By August of 2016, DARPA wants to see finalized designs, and it’ll choose one to develop into a prototype that could fly as early as 2018.

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