They would not return to Earth early on April 28, so why did NASA astronauts Michael Hopkins, Victor Glover and Shannon Walker, along with the astronaut Exploration Agency (JAXA), the astronaut Soichi Noguchi, climb up and get on board Crew dragon Resilience on April 5? Because a previously untested maneuver meant that, after closing the hatch between their spacecraft and the International Space Station, they had the chance that they would not return.
On paper, it seems easy to slide a capsule between coupling ports. Everyone Resilience had to do was to disconnect the International Docking Adapter 2 (IDA-2) that is in front of the Harmony module, self-connected to the Pressing Mating Adapter 2 (PMA-2) which was once the parking space for the spacecraft, and moved to the PMA-3 / IDA-3 on top Harmony. It was a short journey through the open space, and when the crew left their vessel and re-entered at the end of the station, they were only a few feet from where they had started about 45 minutes before.
What if the vehicle has a problem that prevented it from returning to the ISS? A relocation of this kind has never been attempted by an American spacecraft, much less a commercial one like the Crew Dragon. Although the chances of such an accident were slim, the crew still treated this short flight as if it could be their last day in space. Should the need arise, all the necessary investigations and preparations have been made to bring the occupants back to earth safely.
Fortunately, this was not necessary. The autonomous relocation of Crew Dragon Resilience without problems, and SpaceX had to add another “first” to their ever-growing list of achievements in space. But this first move of an American spacecraft to the ISS will certainly not be the last, as the advent and advancement of commercial spacecraft will only become more complicated in the future.
Unprecedented activity
During the Space Shuttle year, NASA did not have to worry about moving their spacecraft, as there was never more than one of the winged orbits in space at a time. But since the Shuttle could transport seven crew members and an incredible amount of cargo simultaneously, it was not a problem. All of NASA’s operational needs on the ISS were met by more than just one vehicle.
Of course, everything changed when the Shuttle retired in 2011. NASA has entered into business with its international partners, and eventually even commercial companies, to bring crew and cargo to the station on a wide range of smaller and operationally faster spacecraft. These vehicles occupy, in addition to the Russian Soyuz and Progress spacecraft, at any given time the most available plant and construction ports on the ISS. In the coming years, even more commercial spacecraft are expected to be brought online, which means that traffic will only get worse at the outpost.
As the US ISS segment is busier now than ever before, NASA faces a logistical challenge to which its Russian counterparts are already accustomed. It may have been the first time an American spacecraft had to move to another port during a mission, but so far 19 Soyuz capsules have had to make similar moves; of which the most recent pass took place on 19 March.
A complicated dance
Given that Resilience Eventually moving to a port that was just a few feet from the original origin, it’s easy to think that the whole thing was an experimental proof of concept. Perhaps as a test for future, more complex maneuvers. But in fact, the two international dock adapters are currently the only places on the ISS where commercial vehicles such as the Crew Dragon, Boeing’s Starliner capsule and finally the Dream Chaser spacecraft of Sierra Nevada can attach. In short, while the destination will vary, moving ports for U.S. spacecraft will always be a short jump.
But why? What difference can a ride of such a short distance make? The answer lies in the unique design of the Dragon’s Cargo variant, which can carry large bulky objects in the hollow “trunk” behind the capsule under pressure. Generally, the cargo brought into the rear of the Cargo Dragon is intended to be mounted on the outside of the station and is retrieved from the spacecraft using the robotic arm of the orbital laboratory. As it so happens, it is both IDA-2 and IDA-3 that were delivered to the station in 2016 and 2019.
The trick is that the station’s arm cannot reach into the dragon’s trunk when it is moored Harmony’s front port. This is not currently a problem Resilience carries no external load. But that will be in June when a Cargo Dragon delivers a new set of deployable solar power supplies for the station as part of the CRS-22 mission. To complicate matters further, four more astronauts will dock at the station at the end of April aboard the Crew Dragon. Try.
It meant Resilience needed to move to PMA-3 / IDA-3 Try can connect to PMA-2 / IDA-2 at the end of the month. Then once Resilience departure, the upper landing gate is free to accept CRS-22 in June, so that the solar arrays with the robotic arm can be removed from the trunk. After CRS-22 left, Try will have to make its own “up and over” jump to PMA-3 / IDA-3, as a Boeing Starliner will have to dock at PMA-2 / IDA-2 as part of its first test flight to the Station in July.
Sounds complicated? This is because it is so. Unfortunately for NASA, unless plans for a commercial expansion to the International Space Station go through, it is the game of revolution of ‘musical chairs’ with which they will be forced. With only two viable landing ports available for current and future spacecraft, the United States must quickly overtake its Russian counterparts when it comes to the fine art of juggling spacecraft. Except now, the shifts will be autonomous.