Tutorial: Orbital Rendezvous

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An Orbital Rendezvous is an orbital maneuver in which a spacecraft changes its orbit to approach another spacecraft at a close distance and match their orbits.[1] It often involves docking after a successful rendezvous.

Usages

An orbital rendezvous is mostly used and prequisite for docking two craft together. By docking craft you can build a space station or a giant ship impossible to launch in one piece. Important goal of rendezvous can be refueling of a ship. One can also rendezvous with an asteroid and use the Advanced Grabbing Unit (commonly known as the 'claw') to clamp it and change its orbit.

Designing a rocket

A very important part of everything in KSP is of course the rocket, if you are at this page and don't know how to build a rocket capable of doing this, you should probably watch some videos, read some tutorials about it. But there are some things that are necessary for docking which should always have on your rocket:

  • Docking ports: a docking without a docking port is usually pretty hard to accomplish. A docking port is required on ALL ships to be attached. I usually use 2 around the center perfectly opposite each other to balance themselves out but it is also common to put multiple ports for the attachment of multiple pieces and/or shuttlecraft (The coolest thing you can have on a space station). This is only useful for complex stations though so don't worry about that now.
  • Solar panels: don't wanna run out of power and explode? well you'll need solar panels. Alot of power is not usually required so if you just want to not die you can use OX-Stat Photovoltaic Panels or small unfolding ones, However, if you want your station to look super cool, use the gigantors! they're awesome (but heavy) ***Note! if you put gigantors just above a docking port and unfold it then they will hit any ship docked there! it is important not to put solar panels on the same side as the docking ports!
  • Electric lights: if you have alot of power then lights can really help you out, you have a 50/50 chance of docking without any sunlight whatsoever so if you can afford it,lights may be a good investment.
  • RCS: a reaction control system is required for docking, to move your ship in place and to get it to the other port, Remember to conserve, docking can take alot of monopropellant so if you're using an RCS to stabilize your ship keep track of your reserves One time I was ready to dock and I realized I had no RCS system, don't be like me.

Completing the rendezvous

It can be challenging at beginning, but after few tries this can be simply mastered. Quicksave often. It is a good idea to read this as you do the procedure, not just read this all the way then take it from the top.

Assuming are in a stable orbit similar to your target's. For first attempts a circle orbit at 100 km above Kerbin could work nicely. First click the target and select "Set target", this will cause a whole variety of symbols to appear, such as your target's Ap and Pe, the Ascending and Descending nodes, your next encounter, and the next encounter after that.

Check the Ascending or Descending node. If it is more than 1°, plan a maneuver in AN or DN and go Normal/Antinormal until the nodes are bellow 1°. Now you are prepared to time the manuever.

Object in lower orbit moves faster than object in higher orbit. By Prograde/Retrograde maneuvers go to orbit which closes you to your target. If your target is ahead of you, burn Retrograde and go for lower orbit (Target has AP/PE=100/100, you aim for AP/PE=90/90). Time acceleration can help if fuel is precious.

If you are close enough, make one side of your orbit intersecting the target's orbit. (if target has AP/PE=100/100, have have AP/PE=105/90). New symbols (intersect) appear and more information is visible when hovering over them. There are two closest intersections and if you go through one, another appear. The closer the better, but above Kerbin, 10 km distance from target is fine. Use Prograde/Retrograde maneuvers. Radial in/out maneuvers can be also used but it is recommended for advanced users in planning mode.

Slowing down

When near the closest intersection, it is very easy if you know what to do. Click to top of navball and set it to the "Target" mode. Now, you see your relative speed and prograde/retrograde vectors are aligned against your target. Burn retrograde and set relative speed near 0. Make sure you are burning retro, not anti-target as most beginners do that.

Good work, we are almost there! Find a target on a navball (pink "circle") and burn Prograde. Remember, all the fuel your using now you'll need to use again to stop (relative to the target). Move the camera so you see the target and it's distance. As it is below 1 km, 10 ms are safe. Once near or if you start moving away, burn retrograde to 0, aim for your target, and burn prograde again.

Within 100 m, burn retrograde last time and celebrate your rendezvous :-)

Tips

  • it is possible to make moves more effectively, but you will self-learn them when repeating
  • targets at low orbits are difficult to catch if ahead (do not go to atmosphere), instead go for much higher orbit and wait for them
  • mastering this will help you a lot in inter-planetary transfers, as it is just orbital randezvous above Kerbol (Sun).
  • for inter-planetary transfers, it is very similar but good position of planets when start is a key to save a lot fuel
  • for catching asteroids, this can be also used but as inter-planetary transfer, a lot of fuel

Docking

Now it is time to dock. Most people go into docking mode for this but I don't because it changes many controls. Just know that WASDQE changes attitude and IJKLHN changes position (with RCS thrusters). So activate your RCS and orient yourself to the position you need to be in to dock, THEN start moving towards the target. Things move slow and you may need to use time warp for the approach but don't go above 5x, once you are very close, approach the docking port and slowly move towards it. Face the entire thing from the side, and adjust yourself to be perfectly lined up, then face from a 90° angle to that, making sure you can still see both ports, you may notice that although from the other angle you looked dead-on, from this angle you do not. So adjust this one until you look dead-on again and switch back to the other view angle. keep switching and adjusting the angle until you dock. You don't have to be perfect, just close. Once you get close the automatic magnetic docking thingy will activate, you'll notice that once you're very close to the target, you'll start accelerating towards it quickly until your ports hit each other. If you weren't to good then the ports will slide back and forth a while so if that happens, just be patient, a failed docking is very rare. It may dock instantly as well, if so, good job! Either way, you just docked. Cool right?

References

  1. w: Space rendezvous. Wikipedia. April 15 2015.