The SpaceX mission to berth with the International Space Station has successfully passed the first set of demonstrations with NASA. Dragon completed a series of maneuvers early this morning to adjust its orbit as it prepared for the first flyby of the ISS, passing just 2.4 kilometers (1.5 miles) beneath the station. In addition to the maneuvering, a series of tests was completed to confirm Dragon‘s onboard navigation and communication equipment was working properly before moving closer to the ISS on Friday.
Over the course of several hours all of the demonstrations went well, according to SpaceX’s lead mission director John Couluris, “all Dragon systems checked out, we look good” he said in a press conference following the flyby. “Dragon‘s go for berthing day tomorrow.”
NASA’s ISS flight director Holly Ridings also said the first set of demonstrations was a success, comparing it to the numerous simulations completed by both SpaceX and NASA together. “Today went really very close to how we had trained it,” Ridings said. “There was no major deviation from our pre-flight plan.”
Today’s maneuvers were just the latest in several steps SpaceX has to make to to successfully demonstrate Dragon‘s capabilities as part of NASA’s Commercial Orbital Transportation System (COTS) before NASA will allow the company to deliver cargo to the space station.
as seen with its solar panels deployed from the ISS. Photo: NASA
Within hours of Tuesday morning’s launch, Dragon had successfully deployed its solar panels and opened the doors to its guidance, navigation and control sensors and began testing some of this equipment that will be used as the spacecraft approaches the space station.
On Wednesday, Dragon‘s GPS was shown to be working properly and the vehicle’s COTS UHF Communications Unit (CUCU, pronounced cuckoo) which will be used to communicate with the ISS was powered up and running.
In preparation for the maneuvers close to the ISS, some of Dragon‘s 18 Draco thrusters were demonstrated on Wednesday with both a series of short pulses, and a longer continuous burn simulating the vehicle’s ability to abort from its approach to the station.
A diagram of today’s flyby and the rest of the day’s flight as Dragon
makes a loop around the ISS. Image: NASA
All of the activities during the first two days took place as Dragon was chasing the ISS in an effort to be in position for today’s flyby. Before the first maneuver, Dragon was in orbit about 60 kilometers (37 miles) behind and 9.5 kilometers (6 miles) beneath the ISS. At 12:58 a.m. PDT, the Dragon team at SpaceX’s headquarters in Hawthorne, California, announced a successful “height adjustment burn” giving Dragon the vertical push closer to the space station (an orbit further away from the earth).
Forty-five minutes after the height adjustment burn at 1:43 a.m. PDT, Dragon performed a “co-elliptic burn” to effectively allow the capsule to level off at the desired distance beneath the station. Initially the altitude was to be 2.5 kilometers beneath the station, but this was changed to an actual distance of 2.4 kilometers. A few minutes later the crew on board the station sent a command to Dragon that turned on the capsule’s strobe light to confirm the CUCU communication link between the ISS and Dragon.
SpaceX’s John Couluris said Dragon‘s maneuvers around the ISS were successful, and it ended up using 36 kilograms (79 pounds) less propellant during the Draco burns than planned.
Couluris said the extra propellant offers a bit of a cushion if any part of the mission needs to be extended, “if we need to take more time and come back around a second time.”
While Dragon continued to close the distance horizontally to the ISS (remaining 2.4 kilometers beneath the station), SpaceX confirmed the capsule’s relative GPS was operational. The relative GPS is what will be used tomorrow as Dragon begins its approach to the station before laser and thermal imaging sensors guide it in the final meters.
View from inside the ISS’ Cupola where astronaut Don Pettit will grasp Dragon
with the robotic arm and berth it with the station. Photo: NASA
As Dragon approached the station, the ISS crew announced it could see it with a traditional “tally ho” while cameras onboard both the ISS and Dragon were able to capture the other.
At 4:26 a.m. PDT, Dragon passed directly beneath the ISS at the prescribed 2.4-kilometer distance before continuing in front of the station as part of the large loop it will fly over the next day before beginning its final close approach early Friday morning.
All of the Dragon operations are being controlled by the SpaceX team at its headquarters in Hawthorne, California. The company’s mission control center is located on the factory floor in a glass enclosure allowing employees to watch the entire mission projected onto large screens.
SpaceX’s Couluris says he has been working with NASA on this mission for more than five years. “We’ve been simulating for almost three years,” he said.
During that time, both teams have rehearsed the mission numerous times. “We have conducted almost 20 joint simulations with NASA” Couluris said, “and over 40 simulations internally here at SpaceX over the four shifts of operators we have working.”
Simulations are a mainstay of the aerospace community with everybody from airline pilots to spacecraft operators developing, practicing and refining all aspects of a flight on computers before flying the real thing for the first time.
“We fly by the mantra of, ‘train like you fly and then fly like you train,’” Couluris said, describing the long hours spent rehearsing. A former naval aviator, Couluris added the mantra is working, “so far the mission has been proceeding just like a regular simulation.”
Both Couluris and NASA’s Ridings reiterated the flight-test nature of the mission, adding that many difficult tasks still lie ahead. And despite all of the rehearsals and simulations there is still plenty that can go wrong with the massively complex systems involved, something SpaceX discovered after a small valve forced an abort of the first launch attempt as the rocket engines ignited on the launch pad.
Coverage of the next series of maneuvers will begin broadcast on our Open Space page beginning at 11 p.m. PDT today.
The crew aboard the ISS watches the launch of SpaceX’s Falcon 9 rocket Tuesday morning. Photo: NASA