After its successful launch yesterday atop the SpaceX Falcon 9 rocket, the Dragon spacecraft is currently in orbit making its way for a rendezvous with the International Space Station (ISS) on Friday morning at 8:06 a.m. at a distance of 2.5 km below the ISS. At that time, and before the capture and berthing take place, the Dragon spacecraft will perform a series of tests before it is allowed to approach the ISS.
During this “fly-under,” Dragon will establish UHF communication with the ISS using its
COTS Ultra-high frequency Communication Unit (CUCU). Dragon will perform a test of its Relative GPS (RGPS) system, which uses the relative positions of the spacecraft to the space station to determine its location. Also, using the crew command panel (CCP) on board the station, the ISS Expedition crew will briefly interact with Dragon, monitoring the fly-under and sending a command to Dragon to turn on its strobe light. This ability for the crew to send commands to Dragon will be important for the next day’s activity. Once the fly-under is complete, Dragon will fire its engines to begin a loop out in front, above and then behind the station in a racetrack pattern at a distance between 7-10 km. This will set the spacecraft up for a re-rendezvous with the station the next day.
For its final day of approach to the ISS, Dragon will perform another engine burn that will bring it 2.5 km below the station once again. A go/no-go is performed by the Mission Control Houston team to allow Dragon to perform another set of burns that will bring it to within 1.4 km of the ISS. Another go/no-go will take place from Mission Control Houston, and then Dragon will move from up to 250 meters from the ISS. The next set of Commercial Orbital Transportation Services program (COTS) milestone demonstrations will begin, the first of which is Dragon’s test of its LIDAR system. This test will confirm that Dragon’s position and velocity is accurate by comparing the
LIDAR image that Dragon receives against Dragon’s thermal imagers. A series of checkout maneuvers will commence. The Dragon flight control team in Hawthorne, California, will command the spacecraft to approach the station from its hold position. It will move from
250 meters to 220 meters below the station. The crew, using the CCP, will then command Dragon to retreat, and the spacecraft will move back down to the hold point. This test will ensure that Dragon’s range to the ISS is accurate, and that the flight control team sees the spacecraft’s acceleration and braking perform as expected. It will hold at 250 meters, and once again the Dragon flight team will command it to approach the station. At the 220 meter position, the crew will command the vehicle to hold.
Another go/no-go is performed in Houston, and then Dragon is permitted to enter inside the Keep-Out Sphere (KOS), an imaginary circle drawn 200 meters around the ISS that prevents the risk of collision with the orbiting complex. Dragon will proceed to a position 30 meters (98 feet) from the station and will automatically hold. Another go/no-go is completed, and then Dragon will proceed to the 10 meter (32 feet) position, which is the capture point. A final go/no-go is performed, and the Mission Control Houston team will notify the crew they are go to capture Dragon.
At that point, Expedition 31 crew member Don Pettit will use the station’s robotic arm, which measures 17.6 meters long, to reach out and grapple the Dragon spacecraft. Pettit, with the help of fellow crewmember Andre Kuipers, will guide Dragon to the bottom, Earth-facing side of the Harmony node, where it will be attached to the ISS. If the rendezvous and Dragon testing runs long, Mission Control could elect to leave Dragon grappled to the station’s arm overnight before berthing it the next day.
The crew will open the hatch between the Dragon and the ISS the following day, after performing an inspection of the air inside Dragon, a standard procedure for any visiting vehicle. The crew will spend about 25 hours over the next couple of weeks unloading the Dragon of the cargo that was flown up to the station. On this test flight, Dragon will transport 460 kilograms of cargo and will return 620 kilograms. Because this is a test flight, the cargo being brought to the station is considered non-critical and includes additional food, water and clothing for the station residents. It will supplement what was flown on the European Space Agency’s Automated Transfer Vehicle, which docked with the ISS on March 28.
Dragon will spend about two weeks attached to the ISS, at which point the crew will detach it from Harmony, maneuver it out to the 10 meter release point and then will ungrapple the vehicle. Dragon will perform a series of engine burns that will place it on a trajectory to take it away from the vicinity of the ISS. Mission Control Houston will then confirm that Dragon is on a safe path away from the complex and it will then begin its voyage home for a splashdown off the coast of California for recovery.
Canadarm2 to Catch SpaceX’s Dragon on its Maiden Voyage to the ISS – Part 1
Canadarm2 to Catch SpaceX’s Dragon on its Maiden Voyage to the ISS – Part 2