ScramSpace Grapples with Scramjet Testing Challenges

Yesterday, an Atlas V and an Antares rocket both roared off of the United States eastern coast and into space. However, in a remote area of Norway, another rocket launch didn’t go as planned. ScramSpace, a scramjet developed by researchers at the University of Queensland, disappeared over the Atlantic Ocean without sending back the hoped-for data. Scientists were left to clean up the two rocket sections that launched ScramSpace skyward and head home.

What’s the difference? How can complex orbital missions like the Atlas V and Antares be successful when a scramjet flight so easily goes awry? Part of the difference is the physics, which makes scramjets harder to test. While both rockets and scramjets are means of achieving high speeds, they differ in design. Scramjets squeeze high speed (greater than Mach 5) air into a small tube, compressing and heating it. Then a fuel is injected into the airstream. They only work above Mach 5. In contrast, rockets supply their own fuel and oxidizer (air is an example of an oxidizer, oxygen is another), mixing them to cause the explosive reaction that gets them moving. The physics of rockets is fairly well understood after years of launch. Scramjets have not had the luxury of so many tests, mainly because testing scramjets is difficult.

First of all, the testing setup for scramjets is tricky. Unlike rockets, which can be ignited at any speed, scramjets only work when they are already traveling at Mach 5 or greater. Since no research planes currently achieve these speeds, rockets are required. ScramSpace, the University of Queensland explains, uses a two-stage rocket to send the scramjet into space. Then the test is completed as the scramjet accelerates toward Earth (see graphic at top). Other projects, like the X-43 and X-51 projects in the US, launch the scramjet from a B-52 bomber, accelerate it with a rocket and then perform the experiment, according to NASA. These tests are not simple or easy to do.

Plus, once you get to Mach 5, the conditions are nasty. At high speed, aerodynamic heating causes the scramjet to experience extreme temperatures. This means that scramjets require high temperature alloys to simply maintain their structural integrity. The physics also get complicated at hypersonic (above Mach 5) speeds. Shockwaves bounce around inside the scramjet tube and must be “swallowed” correctly in order to achieve maximum thrust. In an ABC Catalyst special, a ScramSpace engineer explains that the air must also rush into the inlet at the right angle. Extensive ground tests help scientists determine these conditions, but they don’t depict how the vehicle will react in actual flight.

The test setup also leaves very little room for error. In the same ABC short video, a ScramSpace engineer explains how vital proper controls are to the experiment, demonstrating how reaction thrusters are used to properly align the craft in space. If improperly aligned, the ScramSpace vehicle would not work correctly. U.S. projects have also had difficulties controlling scramjets at high speeds. An X-51 WaveRider scramjet failed to ignite when one tiny fin (of four) became loose before the ignition, according to Zach Rosenburg. Controlling the vehicles is difficult and the conditions at Mach 5 and above leave little room for error.

Despite all these difficulties, scramjets have accomplished some amazing test flights. The third test of the X-43 still holds the world record for an air breathing engine (as opposed to a rocket engine, which carries its own “air” or oxidizer). According to NASA, it achieved a speed of Mach 9.6, and, theoretically, scramjets can go even faster, reaching Mach 14 or 15. That’s almost fast enough to reach space! The last test of the X-51 Waverider flew successfully for over 6 minutes, according to Space Ref. This was huge accomplishment for a test period that is typically 5-15 seconds.

Overcoming the difficulties of scramjet flight is difficult, not impossible. Perfecting scramjets is challenge worth taking on. Since scramjets use atmospheric air as the oxidizer, instead of carrying big oxygen tanks as rockets often do, they offer great weight savings over rockets. Yet, funding for scramjets is often limited. The ScramSpace team is heading back the University of Queensland, according to a recent report, not to begin building again, but to be disbanded. Once perfected, scramjets can become the transportation of the future, streaking through the skies at speeds above Mach 10, but they face many physical and budgetary challenges in the near future.

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NASA Has a History of Crashing Helicopters for Science

In a video reminiscent of Discovery Channel’s Mythbusters, NASA dropped a 45 ft long Marine CH-46E helicopter fuselage into the dusty ground at NASA’s Langley Research Center. NASA reports that the helicopter, having plummeted from 30 feet in the air, smashed into the ground at 30 mph. This was a simulation of a survivable crash, but the 15 crash-test dummies locked inside did not have a smooth ride. At the conclusion of the video posted by NASA, one almost expects to hear Mythbuster Adam Savage giggle.

Perhaps smashing things does make NASA engineers giggle; they have a history of crashing helicopters and other experimental aerial vehicles. In 2009, the U.S. Army donated an MD-500 helicopter to NASA, according to a NASA press release. What did NASA do with it? They crashed it (“for science”). The initial test had a “deployable energy absorber,” a Kevlar honeycomb design originally intended to cushion space capsules. Miraculously, the helicopter survived the first test relatively intact, thanks to the new technology.

Four months later, NASA explained that it had dropped the helicopter a second time. This time, however, the MD-500 had no honeycomb cushion. As a result, the helicopter was too damaged for further testing. Engineers had recorded over three times the “g” forces compared to the previous test with the cushion. The picture below shows the windscreen shattered and the skids bent. It was destructive testing, indeed.

However, unlike Mythbusters, NASA conducts the tests for more than the wanton destruction and cool video footage. In the 2009 and 2010 tests, NASA was able to demonstrate that the honeycomb cushion designed for space capsules could also increase the survivability of a helicopter crash. It worked so well that they were able to simulate another crash for comparison.

Last week’s crash test of the much larger CH-46E helicopter also provided useful crash data. Unlike the 2009-10 tests, this time NASA crashed the unmodified helicopter first. Although the test already had scientific use as a basis for which to compare a future test of a composite airframe, additional experiments abounded. The Navy, Army and FAA all contributed different crash test dummies. CONAX Florida Corporation DBA Cobham Life Support tested a restraint system in the cockpit. Unlike Mythbusters, NASA now has 350 different instrumentation points to analyze, as well as high speed camera data.

Destructive testing, like NASA’s recent helicopter crash, is not only fun and entertaining, but extremely useful. New technologies, like the honeycomb cushion, can be tested and vetted for future use. The cost, however, is high. Not everyone has the money available to conduct these necessary tests. With NASA facing flat budgets for the next few years, we wonder ‘who will crash our helicopters for us in the future?’

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Repurposing Spacecraft not a Novel Idea, but a Cost-Effective One

On August 15th, NASA officially issued a call for help, in the form of scientific white papers, in hopes of repurposing the crippled Kepler spacecraft. The telescope, which had led the charge in finding exoplanets, planets orbiting distant stars, has been unable to function due to issues with two of its four reaction wheels. These wheels, which, NASA explains, are used to point to distant galaxies, are vital to Kepler’s scientific mission, studying distant stars for the changes in light intensity that would signal a planet passing between Kepler and the star. Without the ability to point correctly, the spacecraft’s main mission is compromised. Rather than letting it drift in space, NASA is trying to repurpose the satellite to save money, a strategy that the space agency has used in years past.

NASA had success with repurposing two of the THEMIS spacecraft in 2010, according to an old press release. Originally intended to study the magnetosphere, the little understood magnetic field that surrounds the Earth, two THEMIS spacecraft were diverted toward the moon after finishing their original mission. Once in lunar orbit, the spacecraft began a new mission, ARTEMIS, studying the effect of solar wind on the moon’s surface. By simply sending the fueled spacecraft to another location, NASA scientists were able to get valuable new data, without spending much extra money.

“Using two repurposed satellites for the ARTEMIS mission highlights NASA’s efficient use of the nation’s space assets,” said Dick Fisher, director of the Heliophysics Division in NASA’s Science Mission Directorate at the agency’s headquarters in Washington. With its budget shrinking, NASA is doing all that it can to avoid the high cost of building and launching spacecraft.

NASA is not alone in trying to save money through repurposing satellites. John Keller reported in late January that the U.S. Defense Advanced Research Projects Agency, aka DARPA, is also looking to repurpose spacecarft, by recycling components from non-operational satellites. Defunct spacecraft often have still useful antennae and sensors. Building and launching these components is costly, in terms of both manufacturing and fuel. By recycling parts already up there, DARPA can lower the cost of a new satellite.

Using new ideas and clever innovations to repurpose or recycle spacecraft is both cost effective and a strong move toward sustainability. The junkyard of decommissioned satellites can instead become a useful tool shop for those with innovative ideas.