The civil engineering Structures and Materials Laboratory, whose Fast Hybrid Test system has enjoyed a national reputation in the field of earth-quake engineering, played host to an unusual visitor over the winter holidays.
Just about the time that most students headed home for Thanksgiving, Sierra Nevada Corporation (SNC) in Louisville hauled its next-generation spacecraft, known as the Dream Chaser, up Regent Drive to the Engineering Center.
The vehicle, which is designed to carry up to seven people and vital cargo to the International Space Station after the retirement of the space shuttle this year, is being developed by SNC Space Systems as part of NASA's Commercial Crew Development initiative and competition.
The company received $20 million from NASA in 2010 to support the Dream Chaser's development as part of an innovative effort by NASA to foster entrepreneurial activity leading to high-tech growth in engineering, analysis, design, and research, and to promote economic growth.
About the size of a business jet, the 30-foot-long Dream Chaser is based on NASA's earlier HL-20 lifting body design. The vehicle is slated to launch vertically on an Atlas V rocket and land horizontally on conventional runways.
After carefully easing the spacecraft's structural core through the lab entrance, the CU-Boulder team commenced assembling the test set-up it designed with SNC to help ensure the spacecraft is ready for flight in two to three more years.
CU's structures lab houses high-performance hydraulic actuators with state-of-the-art controls and data acquisition systems. Of particular note is the capability for Fast Hybrid Testing, which combines real-time physical testing with computer simulation to achieve a complete structural analysis at a greatly reduced cost.
Led by civil engineering assistant professor Siva Mettupalayam, the CU-Boulder team used two high-speed actuators braced by concrete reaction walls to simulate thrust and landing loads of up to 35,000 pounds on each side of the spacecraft. Loads were applied to the rear of the spacecraft to simulate the thrust of its engines, and to the bottom of the spacecraft to simulate loads on its landing gear.
Mettupalayam, who also is working on an earthquake engineering simulation involving a partial building structure set upon a shake-table, noted that the forces applied in the Dream Chaser testing were relatively small as compared to those encountered in testing civil engineering structures.
"In principle, the testing is the same, but there are some differences in the types of fixtures we had to design," Mettupalayam notes. "For example, there are a lot of moving parts to these fixtures, which provide a mechanical advantage, but are also required due to the limitations of ceiling height."
Having developed experience with testing civil engineering structures, this project afforded the CU team a firsthand opportunity to understand test procedures and protocols in the aerospace industry.
About 200 strain gauges were placed on the vehicle structure to detect stretching of the carbon fiber composite—information that was fed into the lab's data acquisition software, and ultimately used to validate SNC's computer model.
Team members included engineer Eric Stauffer, whose association with the civil engineering department dates back to the engineering of its 400 g-ton centrifuge in the late 1980s through the development of the Fast Hybrid Test System, along with Nate Bailey and Kent Polkinghorne. All three are CU graduates. Students Graham Allen and Ryon Pax also helped out with the test setup.
"You can only afford to test so many of the load conditions, but you can run your model against all the other scenarios or situations and make sure you're going to be safe," says Jason Hinkle, a CU graduate (AeroEngr '89, MS '95, PhD '98) who now works for SNC as the structures lead on the Dream Chaser.
Hinkle noted that the structural tests on the multimillion-dollar aircraft required months of preparation, but only about 20 minutes each to run: "We all nervously placed our faith in Kent, Nate, and Eric, and they did a great job."
The next steps will be to build out the Dream Chaser with flight control instruments and "drop test" an unpowered glider version sometime in 2012, Hinkle says.
A five-foot-long, 15-percent scale model of the Dream Chaser that was designed, built, and operated by CU's Research and Engineering Center for Unmanned Vehicles in collaboration with SNC, was successfully drop-tested in December over NASA Dryden Flight Research Center.
Amounting to the very first flight test of the vehicle's design, the drop test of the scaled model helped to validate various aspects of the vehicle's configuration and performance, such as flight stability and aerodynamic data for flight control surface deflections.
"The success of the relationship between the University of Colorado Boulder and Sierra Nevada Corporation demonstrates how industry and academia can work together on a common project to achieve their own diverse goals," says Jim Voss, who is both a CU professor and vice president of Sierra Nevada Corporation.
"Working on the Dream Chaser human spacecraft provides students with an opportunity to apply classroom learning to a real-world project, and it allows professors to extend their research to assist with solving industry problems.
"For companies like SNC, it allows them to benefit from the energy and enthusiasm of students and the cutting-edge knowledge of the faculty. All benefit from working together, and in this case, our nation's space program benefits by gaining a way to transport humans into space."
This video was filmed in the Structures and Materials Laboratory by a Daily Camera photographer on the occasion of NASA Deputy Administrator Lori Garver’s visit to see the Dream Chaser spacecraft.