A few hours ago, the SpaceX Dragon 2 spacecraft docked with the International Space Station’s Harmony module. Astronauts Kate Rubins and Victor Glover monitored the operation, but the cargo spacecraft, which blasted off last Sunday, completed the maneuvers automatically without any problem.

The Dragon spacecraft’s approach to the International Space Station follows a procedure that has become routine but remains long and delicate. The Station’s safety is the top priority so every little step of the Dragon gets checked. Only if all goes well in the spacecraft’s position and velocity they proceed with the next step and in case of any problems can be aborted at every step.

The difference from the previous missions is that the procedure continued until the Dragon 2 arrived at a few meters from the Station, the last step before the actual docking maneuver, whereas the first version stopped in the position where it was captured by the Station’s Canadarm2 robotic arm.

Now for the first time there are two Dragon spacecraft docked to the International Space Station as the Crew Dragon Resilience arrived on November 17 on the Crew-1 mission. The two Dragons are derived from the same project, adapted to different functions. From the outside, you can see the lack of windows in the Cargo Dragon and the presence of two fins instead of the four of the Crew Dragon, probably because the cargo doesn’t have the SuperDraco thrusters needed in the event of an emergency abort procedure, so it doesn’t need to stabilize the air flow in that type of maneuver. The big differences between the two versions are on the inside, where the Cargo Dragon has no life support systems nor some other systems.

The Dragon 2 space freighter is a little bigger and more massive than the first version. This allowed for 20% more cargo capacity, with the possibility to add payloads until the last moment thanks to the same launch pad structure used by astronauts in Crew Dragon launches. That’s a useful option to avoid leaving in the Cargo Dragon for days cargoes such as perishable food for astronauts or mice that are used in various medical experiments. On the return journey it will be possible to carry more cargoes as well, and in particular a greater amount of scientific experiments that require to be kept in freezers.

The direct docking by the Dragon space freighter allows to open the hatch a few hours earlier as moving the first Dragon version until it docked to the Station took hours. This time the Station crew just had to check that the automated procedures were working perfectly.

The CRS-21 mission will end in about a month. The first version of the Dragon spacecraft had limited resistance to open space conditions, so returning to Earth after about a month was mandatory. The Dragon 2 freighter can remain docked to the Station for up to 75 days, so we can expect future missions to last longer. Meanwhile, the first mission of the second contract with NASA is progressing smoothly.