Phantom Express: The Spaceplane That Never Was

Even for those of us who follow space news closely, there’s a lot to keep track of these days. Private companies are competing to develop new human-rated spacecraft and assembling satellite mega-constellations, while NASA is working towards a return the Moon and the first flight of the SLS. Between new announcements, updates to existing missions, and literal rocket launches, things are happening on a nearly daily basis. It’s fair to say we haven’t seen this level of activity since the Space Race of the 1960s.

With so much going on, it’s no surprise that not many people have heard of the XS-1 Phantom Express. A project by the United States Defense Advanced Research Projects Agency (DARPA), the XS-1 was designed to be a reusable launch system that could put small payloads into orbit on short notice. Once its mission was complete, the vehicle was to return to the launch site and be ready for re-flight in as a little as 24 hours.

Alternately referred to as the “DARPA Experimental Spaceplane”, the vehicle was envisioned as being roughly the size of a business jet and capable of carrying a payload of up to 2,300 kilograms (5,000 pounds). It would take off vertically under rocket power and then glide back to Earth at the end of the mission to make a conventional runway landing. At $5 million per flight, its operating costs would be comparable with even the most aggressively priced commercial launch providers; but with the added bonus of not having to involve a third party in military and reconnaissance missions which would almost certainly be classified in nature.

Or at least, that was the idea. Flight tests were originally scheduled to begin this year, but earlier this year prime contractor Boeing abruptly dropped out of the program. Despite six years in development and over $140 million in funding awarded by DARPA, it’s now all but certain that the XS-1 Phantom Express will never get off the ground. Which is a shame, as even in a market full of innovative launch vehicles, this unique spacecraft offered some compelling advantages.

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DARPA Challenge Autonomous Robot Teams To Navigate Unfinished Nuclear Power Plant

Robots might be finding their footing above ground, but today’s autonomous robots have a difficult time operating underground. DARPA wanted to give the state of the art a push forward, so they are running a Subterranean (SubT) Challenge which just wrapped up its latest round. A great review of this Urban Circuit competition (and some of the teams participating in it) has been published by IEEE Spectrum. This is the second of three underground problem subdomains presented to the participants, six months apart, preparing them for the final event which will combine all three types.

If you missed the livestream or prefer edited highlight videos, they’re all part of DARPAtv’s Subterranean Challenge playlist. Today it starts with a compilation of Urban Circuit highlights and continues to other videos. Including team profiles, video walkthrough of competition courses, actual competition footage, edited recap videos, and the awards ceremony. Half of the playlist are video from the Tunnels Circuit six months ago, so we can compare to see how teams performed and what they’ve learned along the way. Many more lessons were learned in the just-completed Urban Circuit and teams will spend the next six months improving their robots. By then we’ll have the Caves Circuit competition with teams ready to learn new lessons about operating robots underground.

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Astra Readies Secretive Silicon Valley Rocket; Firm Exits Stealth Mode, Plans Test Launch

After the end of the Second World War the United States and the Soviet Union started working feverishly to perfect the rocket technology that the Germans developed for the V-2 program. This launched the Space Race, which thankfully for everyone involved, ended with boot prints on the Moon instead of craters in Moscow and DC. Since then, global tensions have eased considerably. Today people wait for rocket launches with excitement rather than fear.

That being said, it would be naive to think that the military isn’t still interested in pushing the state-of-the-art forward. Even in times of relative peace, there’s a need for defensive weapons and reconnaissance. Which is exactly why the Defense Advanced Research Projects Agency (DARPA) has been soliciting companies to develop a small and inexpensive launch vehicle that can put lightweight payloads into Earth orbit on very short notice. After all, you never know when a precisely placed spy satellite can make the difference between a simple misunderstanding and all-out nuclear war.

More than 50 companies originally took up DARPA’s “Launch Challenge”, but only a handful made it through to the final selection. Virgin Orbit entered their air-launched booster into the competition, but ended up dropping out of contention to focus on getting ready for commercial operations. Vector Launch entered their sleek 12 meter long rocket into the competition, but despite a successful sub-orbital test flight of the booster, the company ended up going bankrupt at the end of 2019. In the end, the field was whittled down to just a single competitor: a relatively unknown Silicon Valley company named Astra.

Should the company accomplish all of the goals outlined by DARPA, including launching two rockets in quick succession from different launch pads, Astra stands to win a total of $12 million; money which will no doubt help the company get their booster ready to enter commercial service. Rumored to be one of the cheapest orbital rockets ever built and small enough to fit inside of a shipping container, it should prove to be an interesting addition to the highly competitive “smallsat” launcher market.

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DARPA Subterranean Challenge Urban Circuit Now Livestreaming

Currently underway is the DARPA Subterranean Challenge (SubT) systems competition for urban circuits streamed live on YouTube now through Wednesday, February 26th.

The DARPA Grand Challenge of 2004 kicked research and development of autonomous vehicles into high gear. Many components on today’s self-driving vehicles can be traced back to systems developed for that competition. Hoping to spur further development, DARPA has since held several more challenges focused moving the state of the art in autonomous robotics ahead.

To succeed in this challenge, robots must handle terrain that would confuse today’s self-driving cars. Cluttered environments, uneven surfaces of different materials, even the occasional flooded section are fair game. These robots also lose access to some of the tools previously available, such as GPS. The “systems track” denotes teams building physical robot systems versus a separate “virtual track” for simulation robots. “Urban circuit” is the second of four phases in this competition, environments of this phase are focused on man-made underground structures. (Think subway station.) For more details on this competition as well as description of various phases, see our introductory post or the competition site.

Those who rather not watch robots tentatively exploring unknown territory (and occasionally failing) may choose to wait for summaries published after competition rounds are complete. The first phase (tunnel circuit) from August-October 2019 was summarized by IEEE Spectrum here. Or you can go straight to DARPA for details on the systems track and virtual track with overall results posted on the competition site.

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3D Printing May Be The Key To Practical Scramjets

The first scramjet, an airbreathing jet engine capable of pushing an aircraft beyond Mach 5, was successfully flown in the early 1990s. But while pretty much any other technology you could imagine has progressed by leaps and bounds in the nearly 30 years that have passed, the state-of-the-art in hypersonic scramjets hasn’t moved much. We still don’t have practical hypersonic aircraft, military or otherwise, and any missiles that travel at those sort of speeds are rocket powered.

NASA’s X-43 hit Mach 9.6 in 2004

This is somewhat surprising since, at least on paper, the operating principle of the scramjet is simplicity itself. Air rushing into the engine is compressed by the geometry of the inlet, fuel is added, the mixture is ignited, and the resulting flow of expanded gases leaves the engine faster than it entered. There aren’t even any moving parts inside of a scramjet, it’s little more than a carefully shaped tube with fuel injectors and ignitors in it.

Unfortunately, pulling it off in practice is quite a bit harder. Part of the problem is that a scramjet doesn’t actually start working until the air entering the engine’s inlet is moving at around Mach 4, which makes testing them difficult and expensive. It’s possible to do it in a specially designed wind tunnel, but practically speaking, it ends up being easier to mount the engine to the front of a conventional rocket and get it up to speed that way. The downside is that such flights are one-way tickets, and end with the test article crashing into the ocean once it runs out of fuel.

But the bigger problem is that the core concept is deceptively simple. It’s easy to say you’ll just squirt some jet fuel into the stream of compressed air and light it up, but when that air is moving at thousands of miles per hour, keeping it burning is no small feat. Because of this, the operation of a scramjet has often been likened to trying to light a match in a hurricane; the challenge isn’t in the task, but in the environment you’re trying to perform it in.

Now, both Aerojet Rocketdyne and Northrop Grumman think they may have found the solution: additive manufacturing. By 3D printing their scramjet engines, they can not only iterate through design revisions faster, but produce them far cheaper than they’ve been able to in the past. Even more importantly, it enables complex internal engine geometries that would have been more difficult to produce via traditional manufacturing.

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Go Subterranean With This DARPA Challenge

Whether it comes to rescuing people from a cave system or the underground maze of sewers, tunnels and the like that exist underneath any major city, having accurate maps of the area is always crucial to know what the optimal routes are, and what the expected dangers are. The same is true for combat situations, where such maps can mean the difference between the failure or success of a mission. This is why DARPA last year started the Subterranean Challenge, or ‘SubT’ for short.

This challenge seeks new approaches to map, navigate, and search underground environments during time-sensitive combat operations or disaster response scenarios, which would allow for these maps to be created on-demand, in the shortest amount of time possible. Multidisciplinary teams from the world are invited to create autonomous systems that can map such subsurface networks no matter the circumstances.

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DARPA Goes Underground For Next Challenge

We all love reading about creative problem-solving work done by competitors in past DARPA robotic challenges. Some of us even have ambition to join the fray and compete first-hand instead of just reading about them after the fact. If this describes you, step on up to the DARPA Subterranean Challenge.

Following up on past challenges to build autonomous vehicles and humanoid robots, DARPA now wants to focus collective brainpower solving problems encountered by robots working underground. There will be two competition tracks: the Systems Track is what we’ve come to expect, where teams build both the hardware and software of robots tackling the competition course. But there will also be a Virtual Track, opening up the challenge to those without resources to build big expensive physical robots. Competitors on the virtual track will run their competition course in theĀ Gazebo robot simulation environment. This is similar to the NASA Space Robotics Challenge, where algorithms competed to run a virtual robot through tasks in a simulated Mars base. The virtual environment makes the competition accessible for people without machine shops or big budgets. The winner of NASA SRC was, in fact, a one-person team.

Back on the topic of the upcoming DARPA challenge: each track will involve three sub-domains. Each of these have civilian applications in exploration, infrastructure maintenance, and disaster relief as well as the obvious military applications.

  • Man-made tunnel systems
  • Urban underground
  • Natural cave networks

There will be a preliminary circuit competition for each, spaced roughly six months apart, to help teams get warmed up one environment at a time. But for the final event in Fall of 2021, the challenge course will integrate all three types.

More details will be released on Competitor’s Day, taking place September 27th 2018. Registration for the event just opened on August 15th. Best of luck to all the teams! And just like we did for past challenges, we will excitedly follow progress. (And have a good-natured laugh at fails.)