Tests of ’s CST-100 commercial crew vehicle in a supersonic wind tunnel at ’s are focused on gathering data that will be needed to keep a four-person crew alive during a launch failure and return them to Earth safely.
The high-definition, 12-in.-dia. aluminum tunnel-test model includes pressure sensors and simulated thrusters to determine the aerodynamics of a launch abort. The work will involve “flying” the 1/14-scale model through more than 20 different positions and using the data to validate computer models of the way the capsule will handle in an abort.
“It’s a really high-def model,” says John Elbon, vice president and general manager for space exploration at. “They pipe it for thrusters so you can fire thrusters when it’s in the wind tunnel and measure the disturbances that you get.”
Engineers are moving the Boeing capsule toward preliminary design review next February or March, Elbon says. Also on the agenda are drop tests from a helicopter to assess the parachute/airbag combination Boeing plans to use in easing the capsule back to the ground if its Atlas V launcher fails on ascent. The company already has run low-cost tests from a moving tractor-trailer, dropping the capsule off the back to add lateral motion to the landing simulation.
“There’s a small airbag inside a larger one, and when you land there are flaps in the larger one, and there are explosive ties on those flaps, and at the right point in time the explosive ties cut the flaps open, and then the larger, outer airbag deflates and you settle on the smaller airbags, so it takes all the g-force out,” Elbon says.
The seven-person capsule carries four Pratt & Whitney Rocketdyne Bantam abort engines in the pusher configuration, instead of an escape tower that must be jettisoned if it is not used. That allows the abort fuel to be used for maneuvering if it isn’t needed to push the capsule off a failing launch vehicle, but it also raises future design issues for the Boeing team. While the 54,000-lb.-thrust nitrogen tetroxide/monomethyl hydrazine Bantam is built to burn for 10 min., an abort would require it to fire for only 3 sec.
“We can take a lot of weight out of it—it can basically be ablative—so we’re developing the lighter-weight version of that, and we’ll fire that version next spring,” Elbon says.
Boeing has selected the United Launch Alliance (ULA) Atlas V as its launch vehicle, largely on the grounds of reliability, according to Elbon. ULA already has usedcommercial crew development (CCDev) seed money to begin developing a vehicle health-monitoring system to trigger an abort, and Boeing will begin integrating the warning signals into its CST-100 avionics suite under its current round of CCDev funding.
“It’ll be automatic, or the crew can initiate [an abort] manually,” Elbon says. “Most likely—and we haven’t completed that design yet—they’ll also be able to override it. That’s a pretty complex scenario that’s got to be worked out, because we’ll have the control center for the launch vehicle, the control center for the spacecraft, range safety and the flight crew all involved in monitoring the ascent and making calls on the abort. Of course, those kind of scenarios happen so quickly that basically it has to be automated to be successful.”
Other issues that need to be resolved include selection of a material for the thermal protection system that will allow the capsule to reenter Earth’s atmosphere. The company has dropped for now its plans to use a material known as Boeing lightweight ablator, because of cracking and other production problems that arose when it was applied to the CST-100 shape. Instead, engineers are now evaluating more expensive, but proven materials, Elbon says. But there are no technical show-stoppers in sight for the overall vehicle.
“Technically it’s totally doable,” Elbon says. “There’s not a lot of new technology that has to be developed. As with all spaceflight programs, there’s risk that has to be managed.