The SpaceX Dragon has safely returned to Earth after a 25 day mission to the ISS returning scientific samples to Earth for analysis and ISS hardware for repair and refurbishment.
SpaceX’s second commercial resupply mission has come to a successful conclusion after a problematic start. After the perfect launch on top of a SpaceX Falcon 9 rocket to orbit on March 1st Dragon’s computer system went into a passive abort mode leaving the spacecraft in a orbit that would bring the spacecraft back to earth in the next 30 to 48 hours. The computers cut out due to an issue in the Draco Thruster RCS system, 18 thrusters used for attitude and orbital speed control, as the pressure of three of the oxidizer tanks was too low for operational use. The problem was quickly traced to a blockage, either of a valve or something in the pipe, causing the helium pressurization gas to not flow to the oxidizer tanks.
Over the next few hours SpaceX, with help from the US Air Force allowing them access to their communications network, were able to start Dragons computer back up and deployed the solar arrays of the craft removing one of the issues of potentially running out of power. SpaceX software engineers wrote a program for Dragon to run that would “hammer the valves” of the helium tanks to clear the blockage. This approach worked and in sets of two, SpaceX brought all four of the Draco Thruster pods back online.
Elon Musk, CEO of SpaceX, later said during his keynote at SXSW that the issue was with a new valve that was on three of the four tanks as they had replicated the issue on the ground with the same hardware that was in the on orbit Dragon.
After arriving at the ISS on Sunday 3rd Dragon was grappled by the CanadaArm2 on station and then installed onto the Earth facing CBM port on the Harmony module. ISS crew worked hard on their rest day of Sunday to catch up on unloading the cargo Dragon brought up, including care packages from the farm of a SpaceX employee’s father that was local to SpaceX HQ in California.
Dragon berthed to the International Space Station
On the 26th March 2013 at 0806 UTC Dragon was un-berthed from ISS beginning the journey home to Earth. The departure day had been delayed by 24 hours due to high seas at the splashdown site. The CanadaArm2 then moved Dragon away from the station and moved it to the departure position. At 1058 UTC NASA Astronaut Tom Marshburn was given the go to release Dragon and move the robotic arm away from the spacecraft.
Dragon performed the first of three departure burns at 1059 UTC to move the spacecraft away from station safely. The second burn occurred at 1101 UTC. The Dragon the performed a yaw maneuver at 1105 UTC with the third and final departure burn happening one minute later at 1106 UTC.
“Sad to see the Dragon go, She performed her job beautifully” said astronaut Tom Marshburn aboard the space station. “heading back to her lair. Wish her all the best for the splashdown today.”
The rest of the flight home for Dragon included the closing of the GNC door on the spacecraft and performing the deorbit burn at about 1542 UTC. The burn lasts for 10 minutes and reduces Dragons speed by about 100 meters per second. After the burn was completed Dragon detached from the trunk section. The trunk and solar arrays burn up on re-entry while the Dragon carries on down into the ocean.
At 1629 UTC SpaceX confirmed that the drogue parachutes deployed correctly and one minute later confirmed that all three main parachutes successfully deployed. SpaceX confirmed at 1635 UTC that splashdown was successful and that recovery boats were moving into position to collect the Dragon.
The recovery boat radioed SpaceX to tell them they had secured the Dragon at 1701 UTC. The Dragon is due back in California within 30 hours of Splashdown to handover time sensitive cargo to NASA, after express cargo handover Dragon is then taken on a truck to SpaceX’s processing facility in McGregor Texas to be unloaded and to sign cargo off into NASA’s custody.
Later in the evening at 2350 UTC SpaceX said that the GLACIER freezers stowed inside the Dragon spacecraft never lost power after splashdown. On CRS-1 the power supply for the freezers had a sea-water intrusion after splashdown causing the freezers to lose power, while no samples were lost as the freezers kept their low temperatures well the reliability of the system was called into concern. SpaceX retrofitted this Dragon with better protection for the electronic systems of the spacecraft and have done a whole re-design of the system for the Dragon being constructed for CRS-3.
Featured Image: SpaceX
Dragon at ISS: NASA/CSA/Chris Hadfield
Recovery Boats and Dragon: SpaceX