Satellite Technology Feature Article
SpaceX Dragon is a 'Go' to Rendezvous, Berth with ISS
By Doug Mohney, Contributing Editor
In the early morning of May 24, the commercially built and owned SpaceX (News - Alert) Dragon spacecraft successfully completed a series of objectives it needed to berth with the International Space Station (ISS) on May 25. Key milestones include demonstrating its Absolute Global Positioning System (GPS) in good working order, two different abort procedures, "free drift" mode for capture by the space stations robotic arm and a successful communications link with the station.
NASA flight director Holly Ridings described operations "very successful up to this point," pointing out that SpaceX has been training with NASA for this event for "many years." Part of the testing and shakeout procedure is the ability of the commercial SpaceX team and NASA to work together to bring two dynamic spacecraft safely together in the same space.
About the only two deviations from the demonstration and setup plan today were about a 50-minute late start on Dragon's approach to 2.4 kilometers below the station and a glitch in the robotic arm setup. Ridings said the delay in approach was given to let the crew start their work a little later in the day and that tomorrow's activities leading up to berthing should start on time.
SpaceX confronted a number of systems during its approach to the station, including the all-important COTS UHF Communications Unit (CUCU), which allows the crew to command Dragon. It was expected to have a range between 23-28 kilometers and established communications at around 90 kilometers. The station crew was able to test the link by commanding Dragon to turn a strobe light on and off.
Other systems demonstrated onboard Dragon today included a pair of thermal imagers and LIDAR (Laser radar) used for close navigation.
The Dragon also has a number of onboard cameras to monitor spacecraft systems. SpaceX Mission Director John Couluris says a camera inside the SpaceX capsule should provide video of the astronauts opening the hatch on Saturday, May 26 if berthing is successful during the test flight.
Tomorrow morning, activities and emotions get kicked up another notch as Dragon will navigate a set of points in space as it closes with the ISS, first closing to a go/no-go point of around 250 meters with both spacecraft going into free drift.
Once it passes the 200 meter mark, Dragon will drift to within 10 meters of the space station where a robotic arm will grapple and pull the spacecraft up to a docking point on the Harmony node.
If all goes as planned on Friday, the crew will conduct about two hours of procedures early on Saturday morning to open Dragon's hatch at 5:30 AM ET. The "nominal" return of the Dragon cargo capsule back to Earth is expected to start on May 31, when the vehicle will undock, shed its service module and then reenter in the Pacific Ocean.
Successful completion of the mission opens the door for SpaceX to start fulfilling its Commercial Resupply Services (CRS) contract with NASA for at least 12 flights, to provide supply services and large amounts of "downmass" capability to return experiments and equipment back to earth.
Edited by Braden Becker