The SpaceX Dragon spacecraft splashed down near California at 8:42 local time this morning, capping an almost flawless mission that went so smoothly that it was difficult to recognize its intricacy and incredible degree of difficulty.
Before Dragon left the International
The SpaceX Dragon spacecraft splashed down near California at 8:42 local time this morning, capping an almost flawless mission that went so smoothly that it was difficult to recognize its intricacy and incredible degree of difficulty.
Before Dragon left the International Space Station, the astronauts aboard used the new Special Purpose Dexterous Manipulator (Dextre) multi-armed robot to inspect Dragon's non-pressurized trunk. The trunk had no cargo for this demonstration mission, so the inspection was strictly a dry run and showed that there were no stowaways. Some material brought to the International Space Station will reside outside the station; that portion will be removed from future cargo craft by Dextre.
At about 4:07am ET Thursday morning, Don Pettit used Station's robotic arm to separate the spacecraft from its berth and released it about 40 minutes later. Dragon eased itself away using three quick departure burns, quickly falling below the Station's orbit.
A lot of eyes watched Dragon closely during the descent. Flight Engineer Don Pettit took a protective air toward the young spacecraft, calling Mission Control to ask whether it had splashed down correctly only a few minutes into the re-entry. Elon Musk, the company's founder, sat in the front row of the SpaceX mission control room, hunched over a desk to watch the monitors. Two NASA tracking aircraft circled below in the atmosphere, and NASA controllers followed the craft from Johnson Space Center, broadcasting updates on NASA TV.
Dragon's "trunk," the aft portion of the spacecraft, separated at approximately 11:09am ET, and quickly fell into the distance as the spacecraft completed a de-orbit burn. Entry interface, the time when atmospheric drag first takes a tight hold on the spacecraft, took place at 11:25. The two NASA tracking aircraft acquired Dragon as it developed a hot coat of plasma, which blocked communication. This time is known as the "blackout period," because of the lack of radio transmissions.
This last part of the mission, successfully bringing a spacecraft from 17,000 miles per hour to 0 in 19 minutes, is by no means the least difficult. The spacecraft must be oriented correctly before doing a deorbit burn to lower itself into the atmosphere, firing its thrusters in the opposite direction of its travel. Once the atmosphere catches the craft, deceleration occurs quickly, and there is no turning back if something looks wrong.
Reentry depends on the craft's heat shield and a good attitude (in this case, orientation, not positive thinking). Dragon uses a relatively new heat ablative shield material known as PICA-X that is machinable and much lighter than the AVCOAT coating used by the Apollo capsule. PICA stands for Phenolic Impregnated Carbon Ablator, developed by NASA Ames Research Center in the 1990s. SpaceX developed PICA-X themselves, and it has the advantage of being ten times less expensive to manufacture.
An ablative heat shield is designed to wear away as the spacecraft descends, carrying heat away with it and allowing very little through to the spacecraft. PICA-X is very tough though, and SpaceX says Dragon's heat shield could theoretically be reused many times without being replaced.
When friction has slowed the spacecraft down sufficiently, Dragon deploys two drogue chutes to slow itself further. About a minute later, at an altitude of 45,000 feet, the main chutes pop. Dragon has three main chutes, 116 feet in diameter apiece, and all three deployed without a hitch this morning. Once they opened, it took 6 minutes for the craft to fall slow