DLR launches latest round in decade-old Shefex program
German researchers are pleased so far with the results of their summer space launch of a rocket-boosted hypersonic demonstrator, which reached 11 times the speed of sound, even though it is now clear they will not be able to recover the vehicle payload from its resting place at the bottom of the Greenland Sea.
The Sharp Edged Flight Experiment (Shefex II) aimed to validate structures, systems and design technology for future spacecraft that will be more maneuverable for reentry and landing than the current generation of blunt-body designs. The flight followed a Shefex I test in 2005 and will pave the way for a more ambitious near-orbital reentry Shefex III demonstrator in 2016.
Although researchers hoped to recover the test vehicle from a shallower zone than the 3-km-deep (1.9-mi.) water in which it eventually impacted, they have plenty to go on. “We have all the data from the reentry and very interesting data from the ascent,” says Hendrik Weihs, Shefex II project manager at German aerospace center DLR.
The 7-ton Shefex II was launched on June 22 from a mobile facility at the remote Andoya rocket range in Norway at 21:18 p.m. local time and impacted an area 250 km away in the sea west of Spitzbergen, north of the Arctic Circle. Its 10-min. flight covered an arc 180 km to the northwest, reaching Mach 11 as it reentered the atmosphere. Although aircraft and a recovery ship stood ready, due to safety restrictions they were far from the landing site and unable to reach it before the payload was lost, Weihs says.
Even so, Shefex II's 300 sensors measuring temperature, pressure, heat fluxes, acceleration and other key data worked well, Weihs says. Data were collected on the performance of the launch and vehicle design as well as the ability of its tiles, insulation and cooling systems to be able to handle reentry heat of up to 2,500C (4,532F); and the ability of special canards to execute a controlled roll during flight.
Weihs laid down the first drawings for Shefex in 2001. The first craft flew from Andoya four years later, and designs for Shefex II got underway in 2007. The program is aimed at developing technology for a maneuverable spacecraft that can safely reenter the atmosphere and land. “Right now the shuttle or other winged vehicles have only high drag during the hypersonic phase—they are flying at the end of the trajectory at subsonic speeds. We want to fly in the hypersonic cross-range in the upper atmosphere, and then we intend to only have a lifting body for landing,” he says.
Distinguished by canard control fins and a faceted design, Shefex II consisted of flat triangular panels joined at sharp edges to form the nose. DLR believes the sharp edges add aerodynamic capabilities, and that the panels are easier and cheaper to produce than the rounded surfaces found on traditional space capsules.
Although Germany does not have an official hypersonic program, the technology under testing also applies to hypersonic aircraft. “The hypersonic community would like to develop a hypersonic aerospace plane that can replace conventional rocket launches into space,” notes Chris Goyne, director of the University of Virginia's Aerospace Research Lab. The low-cost Shefex faceted design shows promise “because developing a fully-functioning hypersonic aerospace plane will be expensive, initially,” he adds.
The sharp edges face challenges though, notes Sean O'Byrne, a physicist at Australia's University of New South Wales. “They allow for better aerodynamics—which is very desirable at high speed and altitude where lift is considerably lower than for conventional aircraft. But it means greater heating near the sharp edges, which poses greater challenges for the materials scientists and engineers designing the airframe.”
Johan Steelant, an aerothermodynamicist at the European Space Agency, says an edge-led design would have the effect of enlarging the “cross-range,” or ability to reach long distances to the left or right, meaning a reentry vehicle would have the possibility of returning to Earth at any time.