General, Research, Technology

Why does Soyuz dock with the ISS faster than Crew Dragon?

Long time to deliver peopleand cargoes to the International Space Station were used by the Russian Soyuz spacecraft. But in May 2020, SpaceX proved that its Crew Dragon spacecraft could do that too. It looks beautiful both inside and out, and sending astronauts is much cheaper for NASA than cooperation with Roscosmos. But in October, the Russian Soyuz 17 spacecraft docked with the ISS in just 3 hours, while the Crew Dragon takes 19 to 30 hours to do this. The question arises - why does a Russian-made ship reach the station much faster than Elon Musk's ship? The author of the Overlook Horizon YouTube channel recently started looking for an answer to this question. He came to some very interesting conclusions.

Crew Dragon docking with ISS

Docking of ships with the ISS

According to the author of the Overlook Horizon channel, three factors strongly influence the speed of docking of a spacecraft with the ISS. Firstly, during docking, the station should be on the sunny side - in the dark it will make docking very problematic. Secondly, there must be a stable connection between the Earth and the ship's crew, because the negotiations speed up and facilitate the docking. Thirdly, all members of the mission should sleep well the night before, because concentration in this matter is very important.

Good lighting is important during docking with the ISS

Also, the author of the channel drew attention to the fact that initially the ship did not fly directly to the station. First of all, it falls into a lower orbit, and only from there it passes through the so-called Homan trajectory... This is the name of the elliptical orbit, whichused by aerial technology to move from one orbit to another. Then the spacecraft needs time to catch up with the space station and carry out the docking process. And that also takes a lot of time. You can try to dock the ship with the station yourself using this simulator, which works right in the browser.

Spacecraft takes time to enter ISS orbit

Also, the author of the channel noted that during the sendingspacecraft on the ISS, the utmost accuracy is important. For example, if the rocket engine runs even for a second longer than required, the ship can lag behind the station or go off the trajectory with an error of 8 kilometers. That is why the SpaceX company and the state corporation "Roscosmos" often postpone the launch dates of the rockets. Sometimes they fear bad weather, and in some cases they miss the perfect moment to launch.

Docking speed is also affected by launch time

Also a very important parameter when launching a shipon the ISS is the start time of the mission. Depending on it, the angle at which the ship will fly to the station varies greatly. For example, at one time it can be 12-18 degrees, and at another - from 170 to 320 degrees. These indicators, of course, also greatly affect the speed of the spacecraft docking to the International Space Station.

See also: Roskosmos is developing its own version of the Crew Dragon ship. What's wrong with her?

Conditions for docking the ship

At the end, the author of the video highlighted four more factors,which affect the speed and success of the docking. First, they directly depend on the modernity of the technologies used in the ship. Secondly, the team must be completely confident in the operability of all systems, because if a malfunction is detected, the launch will have to be postponed. The third factor flows smoothly from the previous one - the ship must be fully operational. Well, the fourth factor says that the leadership of the mission must be very willing to quickly dock the ship with the station.

It turns out that the Soyuz spacecraft does notfeatures that allow him to dock with the station faster than Crew Dragon. If it was important for SpaceX to dock the spacecraft with the ISS as soon as possible, it would easily do it through precise calculations. And during the two launches, speed was clearly not a priority.

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The Crew Dragon ship has one important thingadvantage over Russian "Soyuz". It can accommodate four astronauts at once, while a maximum of three people can be placed in the Roskosmos spacecraft. SpaceX recently delivered four astronauts to the space station at once, and you can read about how this mission went in this article.