Manual/Maneuver Planner

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The maneuver planner can create maneuver nodes for a variety of orbital operations. It can also automatically execute maneuver nodes, whether they were created by MechJeb or created manually.

Automatically executing maneuver nodes

MechJeb can execute maneuver nodes automatically: just set up the maneuver node and then click "Execute next node." The maneuver node need not have been created by the maneuver planner: you can create a maneuver node manually and then tell MechJeb to execute it. MechJeb will automatically delete a maneuver node when it finishes executing it.

Mechjeb can also execute all maneuver nodes if you have set up more than one: just click "Execute all nodes."

Available maneuvers

Circularize

This maneuver will circularize your orbit. You can schedule the burn:

  • at a given time in the future
  • at the next apoapsis of your orbit.
  • at the next periapsis of your orbit.
  • whenever your orbit next passes through a given altitude.

If you want to get into a circular orbit at a particular altitude, say 100 km, there are several ways to do it:

  • If your orbit is currently below 100 km, raise your apoapsis to 100 km and then circularize at apoapsis.
  • If your orbit is currently above 100 km, lower your periapsis to 100 km then then circularize at periapsis.
  • If your orbit currently passes through 100 km, use the circularize maneuver's feature to circularize at a given altitude.

Change periapsis

This maneuver node will place your periapsis at a chosen altitude. You can schedule the burn:

  • at a given time in the future.
  • at the next apoapsis of your orbit.
  • at the next periapsis of your orbit.

Change apoapsis

This maneuver node will place your apoapsis at a chosen altitude. You can schedule the burn:

  • at a given time in the future.
  • at the next apoapsis of your orbit.
  • at the next periapsis of your orbit.

Change both periapsis and apoapsis

You will probably not need this maneuver much. If you want to achieve a particular elliptical orbit, with both your periapsis and apoapsis to particular values, this maneuver can do that. The given periapsis must be less than your current altitude, and the given apoapsis must be greater than your current altitude (otherwise it is impossible to achieve the desired orbit in one burn). You can schedule the burn:

  • at a given time in the future.

Change inclination

This maneuver will change your inclination to a given angle. For instance, you can set your new inclination to 90 degrees to get a polar orbit.

You can schedule the burn:

  • at a given time in the future.
  • at the equatorial ascending node: this is where your orbit passes above the equator, heading north.
  • at the equatorial descending node: this is where your orbit passes above the equator, heading south.

If you are in a circular orbit, the most efficient place to change inclination is at either the equatorial ascending node or the equatorial descending node. (If you are in a highly elliptical orbit, it may be more efficient to change inclination at apoapsis).

Note that it is impossible to change your inclination to be smaller than your current latitude. So for example if you want to achieve zero inclination, you need to burn at one of the equatorial nodes.

Match planes with target

This maneuver will put you in the same orbital plane as your target. You must have selected a target vessel or planet to use this maneuver. This is a useful for step for orbital rendezvous.

You can schedule the burn:

  • at the next ascending node with your target.
  • at the next descending node with your target.

The ascending and descending nodes are the two points at which your orbit passes through your target's orbital plane. KSP shows these points automatically on the map view.

Hohmann transfer to target

This maneuver is used to intercept a target. If you are orbiting below your target, it will do a prograde burn timed so that at the apoapsis of your new orbit, you will pass as close as possible to the target. If you are orbiting above your target, it will do a retrograde burn timed so that at the periapsis of your new orbit you will pass as close as possible to the target.

This maneuver assumes that you are starting from a circular orbit. If your starting orbit is highly elliptical the planned burn may not achieve a good intercept with the target. It is OK if the target is in a highly elliptical orbit.

This maneuver also assumes that you are orbiting in the same plane as your target. If you aren't in approximately the same plane, you probably won't achieve a good intercept. You can align your plane with the target using the "Match planes with target" maneuver.

There aren't any timing options for this maneuver: MechJeb computes the correct time to burn at to achieve an intercept.

After you execute this burn, you can improve the intercept with the target by using the "fine tune closest approach to target" maneuver.

Transfer to another planet

This maneuver will do a burn to put you in a solar transfer orbit from one planet to another one. You must select the destination planet as your target to use this maneuver. To start with, you must be in orbit around a planet (not a moon). Your orbit should be approximately circular and your inclination should be approximately zero: if these aren't true the maneuver may not work. MechJeb will plot a burn that will send you into a solar orbit that will pass near the target planet. If you are transferring to a higher planet, the intercept should occur near your transfer orbit's apoapsis. If you are transferring to a lower planet, the intercept should occur near your transfer orbit's periapsis.

Note that the patched conic prediction on the map view may not show an intercept with the target planet after you finish the burn. The biggest reason for this is that your destination planet usually has a slightly different inclination than your starting planet. To correct this, use the "fine tune closest approach to target" maneuver.

There aren't any timing options for this maneuver: MechJeb computes the correct time to burn at.

Beware: if the planned burn ends up being far in the future, it may be inaccurate by the time you reach the planned burn time. Over long periods of time, small changes in your orbit can compound to invalidate the predictions that MechJeb used to plan the burn. To guard against this, you can remove the maneuver node and have MechJeb recompute it a few hours before you are scheduled to burn. This should make sure the burn is accurate.

Fine tune closest approach to target

Use this maneuver when you are on course to pass near your target, but want to reduce the closest approach distance. The main uses for this are:

  • Transferring to a moon or a another planet
  • Orbital rendezvous

You must have a target selected to use this maneuver. MechJeb plans a burn that will tweak your orbit to put you on a more exact intercept course for your target. The time of the burn is automatically chosen to minimize the amount of delta-V that will be expended in the course correction.

A maneuver of this type is almost required during interplanetary transfers. Your initial burn will put you on a transfer orbit that approximately intercepts the target, and then you will need to do a course correction to actually achieve a good intercept. A similar course correction is often required when transferring to Minmus from Kerbin orbit, since Minmus has an inclined orbit.

Intercept target at chosen time

For this maneuver, you select a target and choose a time interval, and MechJeb computes a burn that will put you on a course to intercept that target after the given time interval. For example, if the "Hohmann transfer to target" maneuver is too slow for your tastes, you could use this maneuver to get to your target faster. You must select a target to use this maneuver.

For this maneuver, you set two times: when the burn, and how long after the burn to intercept the target. For example, you might schedule the burn 5 minutes from now, and choose to intercept the target 1 hour after your burn. Then MechJeb would create a maneuver node that lay 5 minutes in the future, with the burn calculated to intercept your target 1 hour and 5 minutes in the future: that is, 1 hour after the burn.

You must be orbiting the same body as your target. If your target is a planet, for instance you must be orbiting the Sun; if your target is a vessel in Kerbin orbit, you must also be in Kerbin orbit.

Match velocities with target

This maneuver will bring your relative velocity with your target to zero. It is useful as a final step in orbital rendezvous, once you have gotten near your target and wish to come to rest with respect to it.

You can schedule the burn:

  • at a given time in the future.
  • at closest approach to your target: this is the predicted point during your next orbit at which you will pass closest to your target.

An example: Using the Maneuver Planner for orbital rendezvous

As an example of how you might use the maneuver planner, here are some ideas on how to use it for orbital rendezvous.

If you are already close to your target

If you are already close to your target (under 100 km, perhaps), and in a similar orbit, orbital rendezvous is very simple. You can essentially just burn towards your target, then match velocities when you get close:

Intercept the target using the Intercept target at chosen time maneuver.

Match velocities using the Match velocities with target maneuver, setting the burn to occur at closest approach to the target.

If you are far away from your target

If you are starting far away from your target, orbital rendezvous is a longer process. You might proceed this way:

Align your orbital plane using the Match planes with target maneuver.

If necessary, circularize your orbit using the Circularize maneuver. This will make MechJeb more accurate in the next step.

Intercept the target using the Hohmann transfer to target maneuver.

Note: If your orbit has a similar altitude to the target's orbit, MechJeb will schedule the Hohmann burn a very long time in the future. This is because you are orbiting at almost the same rate as your target, so you will only catch up to your target (or vice versa) extremely slowly. To fix this, you need to start from an orbit that has a different altitude from that of your target. You can experiment with orbits of different altitudes to see how long you have to wait at different altitudes. You can change the altitude of your orbit with the Change apoapsis or Change periapsis maneuver followed by a Circularize maneuver at your new apoapsis or new periapsis.

Once you are on a course to intercept the target, match velocities with your target with the Match velocities with target maneuver, scheduling the burn at closest approach.

This should bring you to rest close to the target. If you aren't close enough, you can follow the steps above for rendezvous in the case where you are already close to your target.

Format for entering times

For many maneuvers you can "Schedule the burn ____ from now," where the blank is a text box that lets you enter a time. If you enter a number into this box, it will be interpreted as a number of seconds. You can also enter times in a more intuitive format. Here are some examples of valid times you could type into the text box:

  • 30s
  • 1m 5s
  • 5d, 3h, 20m


Creating vs changing maneuver nodes

Usually when you use the maneuver planner it will be to create a brand new maneuver node. But you can also tell the maneuver planner to reuse an existing maneuver node. The main reason to do this is that it lets you choose the time of the maneuver by manually placing a maneuver node at the desired point in your orbit. Then you can tell MechJeb to use the maneuver node you just placed. To do this, create a new maneuver node and then click "Create a new maneuver node" in the Maneuver Planner to toggle it to read "Change the last maneuver node." Then you need to "schedule the burn 0s from now." This tells MechJeb not to shift the time of the maneuver node.

For maneuvers where MechJeb automatically computes the burn time, such as transferring to another planet, you can't choose the burn time this way.

Chaining maneuvers

If you want, you can plan a sequence of burns using the maneuver planner. A common example is planning to raise your orbit and circularize it at a new altitude. To do this, you can use the "change apoapsis" maneuver to raise your apoapsis to the desired altitude of your new orbit. Then you can plan a second maneuver even before you have executed the first one. Leave the first maneuver node in place and plan a "circularize" maneuver, scheduled to burn at apoapsis. This will create a circularization burn maneuver node at the the first apoapsis after your first burn, which is right when you arrive at your target final altitude.

Note that if you have a sequence of more than one burn planned, any small errors in the execution of each burn will compound. If you need precision, it may be a good idea to recompute the second burn after executing the first. Even in this case, it can still be useful to plan out the sequence in advance, for instance to estimate how much delta-V the sequence will require.