Difference between revisions of "Basic maneuvers"

Revision as of 10:01, 30 October 2013

This is a brief "cheat-sheet" of orbital maneuvers, low on details, math, background info or video content (these are all better provided by other pages and articles). This is instead meant as a quick reference while in-game.

Ascend to Orbit

1. Ascend straight up for at least 10 km. See table below for optimal ascent speed.
2. After 10km, begin your gravity turn by slowly leaning east (bearing 90 degrees on your navball, usually "right" from the standard launchpad). You can lean other directions as well but going east saves fuel by moving with Kerbin's own spin.
3. Continue to accelerate until your apoapsis (hit M and mouse over the Ap node) is greater than 70 km (the end of Kerbin's atmosphere) - ideally around 100km.
4. Cut your engines (hit 'x') and wait until you are getting close to the apoapsis point.
5. Accelerate prograde (i.e. the direction you are going, represented by a green circle on your navball) until your periapsis (also visible on your map) is also around 100km.

You can save fuel by being close to your terminal velocity during ascent. Lower velocity wastes delta-V on gravity, higher is wasted on air resistance:

Change Orbital Shape

In general, burning prograde will make your orbit "larger" and burning retrograde will make it "smaller".

Lower your apoapsis by burning retrograde (see navball) at your peripasis. Raise your apoapsis by burning prograde at your periapsis instead.

Lower your periapsis by burning retrograde at your apoapsis. Raise your periapsis by burning prograde at your apoapsis.

Match Orbital Inclination

If you want to orbit on the same plane as another object (planet, ship, etc) - set it as your target in the map view. You will see two green arrows labeled as the "ascending node" or "descending node" where the two orbital planes cross.

The direction the craft needs to burn depends on which direction the current orbit is off from the target orbital inclination. When hovering over the ascending or descending node, it will show the difference in degrees. Both show the same difference, but the descending node show the value as a negative number while the ascending node show the value as a positive one. If the craft is passing through the ascending node, where the angle is positive, it needs to burn antinormal (South from an equatorial orbit), while if it's passing through the descending node, and the angle is negative, it should burn normal (North from an equatorial orbit).

If you need several burns to get to your desired inclination, remember that if you burn "normal" on one node you need to burn "antinormal" on the other to keep going the same direction.

It might also help to plan your burns using the orbital maneuver planning system in the map view, where normal and antinormal directions are labeled with purple icons. Matching orbital inclination is a crucial first step in a rendezvous or docking procedure.

Docking / Rendezvous

An orbital rendezvous is one of the most challenging maneuvers, requiring a perfect match in orbit and position. Follow the steps below to get it right on your first try and feel like a space wizard. These steps also work for getting into orbit around planets and moons.

1. Go to the map view and use the maneuver tool.
2. Begin by matching your orbital inclination as described above. During the procedure below occasionally check to ensure that the inclination is exactly zeroed and make correction burns as necessary.
3. Bring one point on your orbit (ideally an apsis) tangent to the target orbit. You will see an orange/purple pair of arrows. Each colored arrow corresponds to the relative position of you and your target. The orange is the nearest encounter, and the purple is the next encounter after that.
4. At the point of nearest encounter maneuver to make:
   1. your orbits as close as possible to each other.
   2. the next encounter (probably right back here) to within 0.5km or so.
5. On reaching that encounter, burn to match velocity. To do this, go back to the staging or docking screen. Click on the "point of reference" on the Navball until it displays the relative target velocity. Rotate the "Level indicator" (which indicates the direction your vehicle is pointing) until it is aligned with "Orbit Retrograde" marker and burn until you bring the relative target velocity (displayed at the top of the Navball) close to zero (ideally less than 1-2m/s). At this point you have brought your vehicle close to the target and almost stationary relative to the target - your orbits and velocities should now be nearly identical, and position separated only by a fraction of a kilometer.
6. Now, rotate so that the the "Level indicator" is aligned with the "Target Prograde" marker . This points the nose of your vehicle towards the target. You should keep these markers aligned as you approach the target until you are within a few metres and ready to make the final docking maneuvers. Using the SAS may help with this.
7. Activate your RCS system, this gives you the finest control of your approach.
8. Press the "H" key to start moving towards the target. You should keep the relative velocity low as you approach (less than 10m/s when more than 500m away, slower as you approach). You should see the "Orbit Prograde" marker line up with the "Target Prograde" marker (check that you navball is still has the "Target" as its "Point of Reference"). Use the lateral thrust keys ("I","J","K" and "L") to adjust the "Orbit Prograde" marker as you approach, and keep it lined up with the "Target Prograde" marker.
9. As you get closer, use the "N" key to slow your approach. Slow down gradually to ~1m/s by the time you are within 50 meters or so. Eventually come to a stop (0 m/s relative velocity) close to the target.
10. Try not to bump into anything while you are docking. See the docking article for how to actually connect your vessels.