How does rendezvous and docking work

[AverageUser54]

I know what rendezvous and docking are but I can not seem to grasp how they are obtained. What kind of burns are performed and compare to ksp how are they performed in real life?

In ksp you can perform a Homahn transfer and get a rendezvous in two burns. In real I heard spacecraft perform multiple burns could someone walk me through this. In real life how do they manage to stay so still and have a relative velocity of 0?

[ZooNamedGames]

In real life- there are more factors involved such as fuel decay, fuel ignition challenges, precision and navigation drift from such issues as gyroscopic precession.

Largely, it's similar, just with more steps involved. As the ISS is on a high inclination orbit, since it was launched from Russia, which has a high latitude inclination. As a result, most spacecraft must enter a similar orbit, however, it won't match its orbit completely, so they'll complete midcourse burns to get the proper orbit, then burn again for inclination, then again to close the encounter. Followed by a final deceleration burn if necessary.

[Bill Phil]

Essentially the goal is to meet the target (usually at a good distance to be safe) at the same place, at the same time, with a low enough relative velocity that the docking vehicle can achieve its goal.

To do this you need to adjust the trajectory the launcher put the vehicle into to a transfer trajectory, if it isn't already in such a trajectory.

Then you optimize the trajectory against all the limitations you have - delta-v, time, and so on.

An optimized trajectory might not look like it would in KSP. There are many reasons for this - the ISS isn't in a perfect vacuum, the high inclination of the ISS makes the Earth's bulge more likely to affect its trajectory, drag affects the active vehicle, and so much more.

The gravity model for Earth is much more complex than the gravity model for Kerbin. It includes mass concentrations, the Earth's bulge, and much more.

[ElWanderer]

Safety is also an important consideration. You can't just put yourself on a (near-)collision course with a view to matching velocities once close - what if your vehicle loses control in the meantime and can't change velocity? Approaches to the ISS are failsafe in that if the engines fail, there won't be a crash, but this means making multiple small correction burns to get close.

[Flibble]

4 hours ago, Bill Phil said:

The gravity model for Earth is much more complex than the gravity model for Kerbin. It includes mass concentrations, the Earth's bulge, and much more.

Don't forget the Moon as well. It's easy to forget other nearby bodies when you're used to KSPs two-body gravity, but the Moon being near (or far) can have a significant affect on orbits.

[AverageUser54]

When they get close to the iss are they not allowed to use rcs because the plume might shoot at the iss 

[mikegarrison]

6 hours ago, ElWanderer said:

Safety is also an important consideration. You can't just put yourself on a (near-)collision course with a view to matching velocities once close - what if your vehicle loses control in the meantime and can't change velocity? Approaches to the ISS are failsafe in that if the engines fail, there won't be a crash, but this means making multiple small correction burns to get close.

There are also other factors too. It is regulated which propellants you can use around the ISS -- they don't want corrosive chemicals getting onto their space station.

1 hour ago, PatelPratham said:

When they get close to the iss are they not allowed to use rcs because the plume might shoot at the iss 

I think cold nitrogen gas is allowed, although even that they don't want blasting the station with indiscriminately.