SpaceX faces key test of Dragon Spacecraft safety
Posted May 5, 2015
Updated May 6, 2015
On Wednesday, SpaceX will test their Dragon capsule’s ability to get astronauts out of a bad situation quickly. The Pad Abort Test will simulate an emergency escape from the launch pad in the unlikely case of the booster rocket failing at liftoff or other scenario that would threaten the crew inside the spacecraft. The Dragon Capsule, packed with test equipment rather than a crew, will blast off atop a simulated trunk module from the company's Space Launch Complex 40 (SLC-40) at the Cape Canaveral Air Force Station in Florida.
Built into the walls of the Dragon Spacecraft are eight 3D printed SuperDraco rocket engines. Those engines have quite a kick, each producing 120,000 pounds of thrust, allowing Dragon to reach a speed of 100 miles per hour in less than a second. Testing the required Launch Abort System (LAS) is a necessary step in proving the Dragon capsule safe for ferrying astronauts to the International Space Station.
LAS dates back to the late 1950s when powerful solid rocket motors were mounted on a tower above the Mercury and Apollo capsules. Today, Russian Soyuz and Chinese Shenzhou spacecraft as well as the upcoming NASA-designed Orion Capsule use a “tractor” LAS design to pull the capsule to safety from the launch pad.
Dragon uses a different design, mounting LAS engines on the capsule itself to urgently remove it from the booster. This enables “launch escape capability from the launch pad all the way to orbit” while the liquid-fueled engines also save on costs, according to SpaceX.
While similar tests have been performed over the years, a Pad Abort system has been used only once in an emergency. In 1983, Soyuz 7K-ST, bound for the Soviet Salyut 7 space station with cosmonauts Vladimir Titov and Gennady Strekalov aboard, was pulled at 14-17 times the force of gravity from a pad fire seconds before the fully fueled rocket exploded.
LAS systems have never been used in an emergency by NASA, through controllers were very close to employing it when the Apollo 12 mission was struck by lightning 36 seconds after liftoff causing the spacecraft to lose power and guidance control. Ground controller John Aaron recalled the odd telemetry pattern they were faced with and relayed a switch position to astronaut Alan Bean who saved the mission from abort and continued on to the moon.
The lone rider on Wednesday's Dragon mission is a test dummy. Despite rumors otherwise, this is not “Buster” of Mythbusters fame, but an unnamed but more technically capable test subject to record forces that human crews might expect during such a ride.
The test window opens at 7:00 a.m. and extends through 2:30 p.m Eastern and will air live on NASA TV. The entire test will last less than 2 minutes and follow this order:
- As the test begins, the eight SuperDraco engines ignite simultaneously propelling the capsule and trunk off the pad vertically to clear the rocket and lightning towers.
- A half-second in: The spacecraft pitches toward the ocean and continues its controlled burn. The SuperDraco engines throttle to control the trajectory based on real-time sensor readings.
- After 5 seconds: All propellant is consumed and Dragon coasts for just over 15 seconds to its highest point about 1500 meters (.93 mi) above the launch pad.
- After 21 seconds: The trunk is jettisoned and the spacecraft begins a slow rotation with its heat shield pointed toward the ground again.
- After 25 seconds: Small drogues parachutes deploy to stabilize the vehicle during a 4-6 second window following trunk separation.
- After 35 seconds: Once stabilized, three main parachutes deploy and further slow the spacecraft before splashdown.
- After 107 seconds: Dragon splashes down in the Atlantic Ocean about 2200 meters (1.4 mi) downrange of the launch pad. Crews will retrieve the capsule for further study.
Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.