Orion crack repair under scrutiny in loads testing
BY STEPHEN CLARK
Posted: May 12, 2013
Engineers are putting NASA's first space-bound Orion capsule, set to fly in orbit in 2014, through tests to stress the capsule's structural shell and check repairs to cracks in the pressurized module's aluminum bulkhead.
The pressure shell of the Orion spacecraft, comprised of welded olive-green aluminum-lithium metal panels, is being put through the tests to verify the capsule can withstand loads it will encounter during launch, re-entry and splashdown in the Pacific Ocean.
The capsule's first unmanned spaceflight, called Exploration Flight Test-1, is scheduled to launch on a United Launch Alliance Delta 4-Heavy rocket in September 2014. The Orion spacecraft will launch into a 3,600-mile-high elliptical orbit and plunge back into Earth's atmosphere at more than 20,000 mph, exposing its Avcoat ablative heat shield to temperatures greater than 4,000 degrees Fahrenheit.
One of the test flight's primary purposes is verifying the heat shield's ability to withstand re-entry, which will be faster than any human-rated spacecraft since the Apollo moon program.
The Orion spacecraft is designed to ferry astronauts to destinations beyond low Earth orbit. It would be instrumental in NASA missions to retrieve and study an asteroid, journey to Mars and visit manned laboratories in deep space.
The 16.5-foot-diameter spacecraft, built by Lockheed Martin Corp., was delivered to Kennedy Space Center in June 2012. Engineers put the capsule through its first test at KSC in November, when they pressurized the Orion crew module to check its integrity.
The test was halted after technicians heard audible cracking sounds, and inspections showed three small cracks in the aft bulkhead on the lower half of the Orion spacecraft's pressure shell. The cracks materialized in three adjacent radial ribs of the aluminum bulkhead, according to NASA.
Engineers designed structural braces to resolve the problem, and those repairs are being tested now.
Mark Geyer, NASA's Orion program manager, said the cracks were about a half-inch long, but the fractures did not penetrate the spacecraft's pressure vessel.
NASA opted to install "doublers" and custom brackets over the cracked area to ensure the craft can sustain loads from pressure, launch and landing. The structural aids are similar to repairs often used on airplanes.
The loads testing was planned before the cracks appeared, but the stresses will double-check the repairs.
NASA and Lockheed Martin added more than 1,600 strain gauges to measure the effects of the loads testing on the spacecraft, which sits in a 20-foot-high test fixture inside the O&C Building at Kennedy Space Center.
The loads test, divided into eight phases, will first impart forces and stresses the spacecraft will experience during launch. The re-entry and landing portion of the test occurs last.
"We will start off with some tension and compressive load cases, and then we'll also put some pressure combination in there, too," said Dan Dumbacher, associate administrator of exploration systems at NASA Headquarters.
Hydraulic cylinders will slowly apply pressure to different parts of the Orion spacecraft to simulate the flight, according to NASA.
After the loads test, engineers will add avionics and computers to the Orion crew module, then turn on the spacecraft for the first time in late summer for further testing.
The spacecraft's heat shield, now being prepared by Textron Defense Systems in Massachusetts, will be delivered to Florida this summer, Dumbacher said in April.
Once engineers attach the heat shield, finish construction of a dummy Orion service module, and receive a launch vehicle adapter, the Orion spacecraft will be ready for fueling and integration with the Delta 4-Heavy rocket in March or April 2014, Dumbacher said.
That is about three months later than previously scheduled, but Dumbacher said there is still "some margin" in the schedule to meet the September 2014 launch date.