A GUIDE ON ORBITAL RENDEZVOUS
By Vincent McConnell.
There are few things one really needs to learn about the prospect of getting one spacecraft to link up with another that is 60 miles overhead and moving at nearly 3,000 meters per second, or 500 meters per second. The basic principles are something you can simply practice with different orbits. This guide will teach you how to orbit a spacecraft nearly perfectly and then to get another spacecraft to pull up to it.
ESTABLISHING A TARGET VEHICLE ORBIT
The first step is, of course, to put a target vehicle in place where it can be docked or rendezvous\'d with. I highly recommend that the average player on Kerbal Space Program gets very good with circular orbits and plane change maneuvers. Both of which are important to a successful link up. Launch into orbit the way you normally would, an eccentric orbit is fine for now. My best advice would be to use fairly weak RCS thrusters. This will ensure that you can bring an orbit down to a nearly exact number.
Let\'s assume for a moment that your orbit is 104x99 KM. The best thing to do is begin pro-grade thrusting with your RCS to turn the closest number into 100KM. In this case, it would be 99. A few pro-grade thrusts will put that up to 100KM. As you would do a circularization burn, you want to circularize this 104x100KM orbit. Wait until you hit the point in your orbit which is 100KM (probably your Periapsis) and begin retro thrusting so that you circularize the orbit from 104 to 100KM. The end result of this will be a 100KM orbit that is off by something in the neighborhood of only about 30 meters.
If your orbit is perfectly equatorial, pay no attention to this next part:
If you notice your orbit is tilted and looks like utter garbage, you are going to want to fix that. The best way to do this is a “plane change maneuverâ€. As you cross the equator of Kerbin or the Mun, you want to thrust either north or south, depending on which way you are moving. If your orbit is tilted downward and you are moving south, you will want to thrust NORTH.
The North and South indicators are directly in between pro and retro. North is characterized by an orange line. You will notice that your orbit begins to tilt back towards the equator. You can always use your main engine for a plane change maneuver if you\'d like.
If you have followed this correctly – there are plenty of guides elsewhere on how to get into orbit – you should be maintaining a circularized orbit of 100KM x 100KM that is near perfectly equatorial.
LAUNCHING YOUR DOCKING VEHICLE
Launching your docking vehicle is essentially the same maneuver. Here is the difference: Your docking vehicle will probably be at a lower altitude of orbit than your target vehicle. For Munar rendezvous, I recommend a rendezvous about 100KM above the Mun. For Kerbin rendezvous, I recommend 200KM. Circularize your docking vehicle\'s orbit at 90KM for the Mun or 190KM for Kerbin and make sure it runs along the same plane as your target vehicle. At this point, you will notice that your docking vehicle, being at a lower altitude, is moving faster than your target vehicle. It may take a few orbits for the two to begin to run along side each other, so engage time compression and wait.
ALIGNING YOUR ORBITAL ALTITUDE
Once your docking vehicle is running at a lower altitude, yet along the side of your target vehicle, it is time to RAISE your docking vehicle\'s orbit to the same orbit as the target vehicle. This will result in the two spacecraft at the same altitude, moving along side eachother at the same speed. To do this, begin prograde burning to put your AP or PE to the same altitude of orbit as your target vehicle. This requires what is known as a Hohmann transfer. A transfer from one orbit to another requires two or more burns. Once you have a PE or AP at the same altitude as your target, warp away until you reach that AP or PE and then pro grade thrust some more. Circularize your orbit to 100KM or 200KM so that you are at the same altitude as your target vehicle and are now running along side it. If this was done correctly, you will notice that your target is probably only a few kilometers away.
FINE CONTROL, FINAL APPROACH, RENDEZVOUS
It is important that you understand your RCS like the back of your hand. It will be your only assistance in this final phase. Point your docking vehicle at your target and begin thrusting towards it. This is a thing best done nice and slowly. You have plenty of time to approach it and the slower the better. There are THREE planes that you want to watch out for at this point. Side to side velocity, up and down and forward and backward velocity. Begin pushing slowly towards it, moving side to side as you do. Hopefully, you know about RCS at this phase, because the purpose of this guide is not to teach you how to control your spacecraft to the basics. As you drift closer towards the target, watch it\'s movement. You will not appear to move, although it is the other way around. The target is not moving, it is you who is moving. As you thrust backwards and forwards, side to side, up and down, the target will begin it\'s slow drift towards the center of your approach. You will notice it starting to get ever so closer. Within meters, you want this to be the slowest approach. Watch all three planes of movement so that you don\'t screw up. Hopefully, if you fine control this, much like a landing on the Mun, you will touch the two spacecraft together and prepare yourself for .15\'s update of docking.
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Here is my first lunar orbit rendezvous, which I just completed tonight!
http://kerbalspaceprogram.com/forum/index.php?topic=9058.0
