Can you dock a spacecraft with the International Space Station?
SpaceX’s ISS Docking Simulator
One of the key tasks for a spaceship is to dock with another spaceship or a space station. In my YA SF book series Noctilucents this happens many times as our heroes travel around the Solar System, starting with Mars in Martian Blood.
At the end of this month, SpaceX’s Dragon capsule will hopefully be the first crewed mission for nearly 10 years to launch from the US heading for the International Space Station (ISS).
The two crew members will join others on the ISS, and to do that they will have to match orbits and then dock the Dragon capsule. And you can get a feel for this difficult manoeuvre using the SpaceX ISS Docking Simulator, available online here.
I managed to dock on my first attempt - as did none other than astronaut Buzz Aldrin!
Anyone wanting some tips as to how to dock, look below the following image for step-by step instructions. For those that want work it out for themselves - head over to the SpaceX ISS Docking Simulator!
Slowly approaching the ISS
So how to successfully dock? Well the top tip they give is to go slowly, and that is certainly true. Don’t try to do this in a few minutes - it took me a good half an hour.
And try to do it in stages:
Get the roll / pitch / yaw angles down to zero in each case
Get the Y and Z vector offsets down to zero, keeping the X value unchanged at about a safe 200m offset
Only when the (roll, pitch, yaw) angles and (Y, Z) vector components are all close to zero, then very slowly approach the ISS - I never went over 0.2 m/s
You’ll notice that as you slowly glide in the Z offset will slowly change and require constant adjustment. This is an example of how orbital dynamics in action, as it relates to the fact that whenever you fire your engines, you change your velocity and hence alter your orbit.
Orbit Modelling in Visualyse Professional
If the Dragon starts off in a circular orbit 200m away from the ISS and it fires its engine to go faster, it goes into a higher, elliptical orbit, so its Z component increases.
On the other hand, if the Dragon starts off in a circular orbit 200m away from the ISS and it fires its engine to go slower, it goes into a lower orbit (also elliptical), so its Z component decreases.
In this case we can see the latter is occurring. The solution is to let it drift down (e.g. to about -0.1 m) and then fire the Z-thruster until the Z = +0.1 m and then fire in the opposite direction to stop the drift: the orbital change will be sufficient to bring it back down and so the cycle continues until you reach the station.
Success! Time for that congratulatory cup of tea
Good luck!
