Difference between revisions of "Maneuver node"

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| [[File:Maneuver.svg|thumb|107px|Maneuver marker on navball]]
 
| [[File:Maneuver.svg|thumb|107px|Maneuver marker on navball]]
 
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A maneuver node is a planed velocity change along an orbit. Multiple maneuver nodes can be added which will effect the following maneuver nodes. After adding a node it shows the velocity change needed to reach the next new orbit. It doesn't show a combination of all maneuver nodes, so after using a maneuver node it needs to be deleted manually and the system can showing the following maneuver node if any.
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A '''maneuver node''' is a planned velocity change along an [[orbit]]. Multiple maneuver nodes can be added which will affect the following maneuver nodes. After adding a node it shows the velocity change needed to reach the next new orbit next to the [[navball]]. If multiple maneuver nodes have been planned, only the velocity change needed for the first node will be displayed on the navball - once that node has been completed it should be deleted so that the next velocity change becomes visible.
  
== Adding a Maneuver Node ==
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In [[career mode]], maneuver nodes are unavailable at first. Using them requires upgrading both the [[Tracking Station]] and [[Mission Control]].
 +
<span id="Adding a Maneuver Node"></span>
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== Adding a maneuver node ==
 
[[File:ManeuverNodes.PNG|thumb|Two maneuver nodes with one in edit mode]]
 
[[File:ManeuverNodes.PNG|thumb|Two maneuver nodes with one in edit mode]]
Click on the vessel's orbital line and will show the option to add a new maneuver node. Once created, selecting and right-clicking the node gives the option to delete it. Selecting a node which the vessel has already passed, brings up the delete interface immediately.
 
  
Hovering over a node displays the time of arrival and the [[w:Delta-v|Delta-V]] needed to perform the maneuver.
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Click on the vessel's orbital line and a popup will give the option to add a new maneuver node. Once created, selecting and right-clicking the node gives the option to delete it. If the maneuver node has been passed, selecting it immediately puts it in "delete" mode.
  
== Directions ==
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Hovering over a node displays the time of arrival and the [[w:Delta-v|delta v]] needed to perform the maneuver.
Because movements in space or air are three dimensional there are three basic axes to burn. For each axis there are two opposite directions. So any movement could be described with a combination of up to three separate directions.
 
  
=== Prograde and retrograde ===
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After the node is created, it can also be dragged along the orbital path at any time. This is very useful when planning an orbital rendezvous and the placement was a bit off. When the view is focused on the maneuver node, dragging it can be difficult to control. It's much easier when moving a maneuver node to place a temporary node nearby and focus the view on that one while dragging.
{| style="float: right;"
 
| [[File:Prograde.svg|32px|Prograde]]
 
| [[File:Retrograde.svg|32px|Retrograde]]
 
|}
 
These vectors are directly changing the speed of the craft. Burning prograde will burning to the craft's velocity vector and raising the altitude of the orbit on the other side. They are colored green like the pro- and retrograde vectors on the [[navball]]. This is the most efficient way to change the orbital shape, so whenever possible these vectors should be used.
 
  
=== Normal and anti-normal ===
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== Directions ==
{| style="float: right;"
 
| [[File:Normal.svg|32px|Normal]]
 
| [[File:Anti-normal.svg|32px|Anti-normal]]
 
|}
 
The normal vectors are orthogonal to the orbital plane. Any burning normal or anti-normal will change the orbital inclination. On the navball it is between the pro- and retrograde marker on the equator line.
 
  
In most cases these vectors are needed to match the orbital inclination to another celestial body or craft. When the orbit crosses the other object's orbit burning normal or anti-normal is most efficient. To match the orbital inclination a normal burn is needed at the ascending node. At the descending node an anti-normal burn will move the inclination closer to the target's inclination.
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<gallery widths=64px heights=64px>
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File:Prograde.svg|Prograde
 +
File:Retrograde.svg|Retrograde
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File:Normal.svg|Normal
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File:Anti-normal.svg|Anti-normal
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File:Radial-in.svg|Radial (in)
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File:Radial-out.svg| Anti-radial (out)
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</gallery>
  
=== Radial in and radial out ===
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Because there are three dimensions of movement in space (or air), there are three basic axes on which to burn, with two directions per axis; thus, all maneuvers can be described as a combination of movement in three separate directions. All six of these directions are marked on the [[navball]], using the symbols above.
{| style="float: right;"
 
| [[File:Radial-in.svg|32px|Radial in]]
 
| [[File:Radial-out.svg|32px|Radial out]]
 
|}
 
The radial in vector is pointing to the orbited body while the radial out points away from the orbited body. When burning radially the orbit will rotate around the craft. At the beginning of the ascent from the launch pad the craft is burning in the same direction as radially out.
 
  
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The relationship between these three orbital vectors - prograde, radial and normal - is defined by the right hand rule. If you hold the first three fingers of your right hand at right angles to each other in the most natural way, the index finger points forwards representing prograde, the middle finger points towards the orbital focus representing the radial, and the thumb points "upwards" represents the normal. For a prograde equatorial orbit around Kerbin (following Kerbin's rotation, i.e. eastward), normal will be north, prograde will be east, and radial will be down.
  
== Using ==
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=== Prograde and retrograde ===
There are six symbols on the newly created node. Each symbol can be clicked on (while holding) and then pulled or pushed to change the desired orbit. Pushing a symbol is equivalent to pulling the symbol on the opposite side. Pushing or pulling further increases the speed the orbit is changed.
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These vectors directly change the speed of the craft. Burning prograde will increase velocity, raising the altitude of the orbit on the other side, while burning retrograde will decrease velocity and reduce the orbit altitude on the other side. To raise a craft from a lower orbit into a higher orbit using a [[Hohmann transfer orbit|Hohmann transfer]] two prograde burns are executed; while lowering an orbit two retrograde burns are used.
 
 
After adding a maneuver node there are three values shown next to the naval:
 
# Velocity change needed in meters per second
 
# Time to maneuver node or time since the craft passed the maneuver node
 
# Estimated burn time
 
  
Because a maneuver node assumes a instantaneous velocity change a perfect burn is in many cases impossible, as longer burns are required. To get the best results it is recommended to burn a half of the time exactly before the actual change and the other half directly afterwards.
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This is the most efficient way to change the orbital shape (specifically the most common case, raising or lowering apsides) so whenever possible these vectors should be used. When the craft is powerful enough it is possible to switch the orbital inclination by 180° when burning retrograde to cancel out all orbital velocity and then build it back up, which is faster and more efficient than using the normal vectors.
  
With maneuver nodes it is possible to reach a specific orbit, without checking the orbital map continually. When performing an [[aerobraking]] a previously placed maneuver node is showing the needed deceleration and will automatically updating the needed velocity change while decelerating in the atmosphere. If the aerobraking is outside the wanted deceleration this allows performing correcting maneuvers.
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=== Normal and anti-normal ===
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The normal vectors are perpendicular to the orbital plane. Burning normal or anti-normal will change the orbital inclination. On the navball the normal and anti-normal vectors are located on the equator line directly between the prograde and retrograde markers.
  
 +
These vectors are generally used to match the orbital inclination of another celestial body or craft, and the only time this is possible is when the current craft's orbit intersects the orbital plane of the target - at the ascending and descending nodes. To match the orbital inclination, either perform an anti-normal burn at the ascending node or a normal burn at the descending node. When the relative inclination at the nodes will reach 0° and they will start to move rapidly toward each other's positions.
  
=== Prograde ===
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<span id="Radial in and radial out"></span>
This is the direction of your velocity (velocity=speed+direction) and is symbolized by a yellow circle with three little wings at a 90 degree angle from each other.
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=== Radial and anti-radial ===
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These vectors are parallel to the orbital plane, and perpendicular to the prograde vector. The radial (or radial-in) vector points inside the orbit, towards the focus of the orbit, while the anti-radial (or radial-out) vector points outside the orbit, away from the body. Performing a radial burn will rotate the orbit around the craft like spinning a hula hoop with a stick. Radial burns are usually not an efficient way of adjusting one's path - it is generally more effective to use prograde and retrograde burns. The maximum change in angle is always less than 90°; beyond this point the orbit would pass through the center of mass of the orbited body and the ship would traverse a slow spiral in towards the orbited body.
  
Burning in this direction will increase your apoapsis or periapsis depending on where you are in your orbit. Think of it as increasing what your height above the ground will be on the opposite side of your orbit. This has other applications but this should help you get the gist of it.
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=== Effects on orbit ===
 +
<gallery widths=200px heights=117px>
 +
File:ManeuverNodePrograde.PNG|Increasing the opposite point's height of the orbit using a prograde burn.
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File:ManeuverNodeRetrograde.PNG|Decreasing the opposite point's height of the orbit using a retrograde burn.
 +
</gallery>
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<gallery widths=200px heights=117px>
 +
File:ManeuverNodeOrbitNormal.PNG|Tilting the orbital plane counter-clockwise using a normal burn.
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File:ManeuverNodeOrbitAntiNormal.PNG|Tilting the orbital plane clockwise using an anti-normal burn.
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</gallery>
 +
<gallery widths=200px heights=117px>
 +
File:ManeuverNodeRadialIn.PNG|Rotating the orbital plane corresponding with the orbiting direction using a radial-in burn.
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File:ManeuverNodeRadialOut.PNG|Rotating the orbital plane opposite with the orbiting direction using a radial-out burn.
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</gallery>
  
[[File:ManeuverNodePrograde.PNG|250px|thumbnail|none|Increasing the apoapsis.]]
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== Using ==
 +
Upon selecting a maneuver node six symbols will appear, each corresponding to the vectors above. Each symbol can be clicked and dragged to adjust the amount of velocity change desired on each axis. Pulling a symbol away from the center of the node increases the speed change along the selected axis, and pushing a symbol toward the center of the node is equivalent to pulling the symbol on the opposite side. The further the symbol is pushed or pulled, the more rapidly the adjustment will be made. Adjustments to an axis can be made also by hovering over one of its nodes and scrolling the mouse wheel.
  
 +
After adding a maneuver node three new values will appear next to the [[navball]]:
 +
# Velocity change required, in meters per second
 +
# Estimated burn time
 +
# Time to maneuver node (or time since the node was passed)
  
=== Retrograde ===
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Because a maneuver node assumes an instantaneous velocity change, a perfect burn is impossible; to get the best results, it is recommended to burn half of the time before the node and the other half directly afterwards.
This is the opposite direction of your velocity and is symbolized by a yellow circle with a cross in it as well as three wings at a 120 degree angle from each other.
 
 
 
Burning in this direction will decrease your apoapsis or periapsis depending on where you are in your orbit. Think of it as decreasing what your height above the ground will be on the opposite side of your orbit.
 
 
 
[[File:ManeuverNodeRetrograde.PNG|250px|thumbnail|none|Decreasing the apoapsis.]]
 
 
 
 
 
=== Normal ===
 
This direction is both perpendicular (i.e. forming a 90 degree angle) to the orbital plane ( the plane formed by one complete orbit along a particular orbital path or line) and perpendicular to the orbited body's radial direction or parallel to the surface (i.e. in the same direction as). It is symbolized by the pink triangle with a dot in the center.
 
 
 
This direction has two major uses. Primarily this maneuver is used to change the orbital plane by rotating it in the counter clock-wise direction (viewed from the side) around the point at which the burn takes place.
 
The secondary use is to rendezvous with an orbiting object (ship, moon or planet). This is done by burning in this direction at the ascending node (i.e. the point at which the orbiting body's orbit you wish to rendezvous with crosses the orbit of your ship and the orbit of the orbiting body will be above the orbit of your ship beyond this point in the direction of travel.) This is the descending node from the orbiting body's perspective.
 
 
 
[[File:ManeuverNodeOrbitNormal.PNG|250px|thumbnail|none|Tilting the orbital plane counter-clockwise.]]
 
 
 
 
 
=== Anti-normal ===
 
This direction is both perpendicular to the orbital plane and perpendicular to the orbited body's radial direction or parallel to the surface. It is also 180 degrees from Orbit Normal or in the opposite direction. It is symbolized by the pink triangle with little wings on two of the sides.
 
 
 
This direction has two major uses. Primarily, changes to orbital plane of the orbit by rotating in the clock-wise direction the orbit around the point at which the burn takes place. The secondary use is to rendezvous with an orbiting object (ship, moon, or planet); this is done by burring in this direction at the descending node (descending node= the point at which the orbiting body’s orbit you wish to rendezvous with crosses the orbit of your ship and the orbit of the orbiting body will be below the orbit of your ship beyond this point in the direction of travel.) By the way this is the ascending node from the orbiting body's perspective.
 
 
 
[[File:ManeuverNodeOrbitAntiNormal.PNG|250px|thumbnail|none|Tilting the orbital plane clockwise.]]
 
 
 
 
 
=== Radial in ===
 
This direction points in the direction of the orbited body, i.e. it is perpendicular to the surface of the orbited body. It is also perpendicular to the direction of travel and Orbit Normal. It is symbolized by a blue circle with what looks like a four leaf clover in it (actually 4 inward wings).
 
 
 
This direction is used to rotate the orbit about the point of burn without changing the orbital plane. (Think spinning a hula hoop with a stick.) This direction will rotate the orbit counter clock-wise with a maximum change in angle of less than 90 degrees. (The orbit will pass through the center of mass of the orbited body at maximum change of angle. The ship would traverse a slow spiral in towards the center of mass of the orbited body.)
 
 
 
This is primarily used in rendezvous to line up two irregular orbits.
 
 
 
[[File:ManeuverNodeRadialIn.PNG|250px|thumbnail|none|Rotating the orbital plane counter-clockwise.]]
 
 
 
  
=== Radial out ===
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Maneuver nodes can be used to reach a specific orbit without needing to continuously monitor the orbital map. When performing an [[aerobraking]] maneuver the current maneuver node will automatically update the needed velocity change as the craft's velocity decreases; this can be used to perform manual corrections if the aerobraking turns out to be insufficient or excessive.
This direction points away from of the orbited body; also, it is perpendicular to the surface of the orbited body. It is also perpendicular to the direction of travel and Orbit Normal. It is symbolized by a blue circle with a dot in the center and four wings at 90 degrees from each other.
 
  
This direction is used to rotate the orbit about the point of burn without changing the orbital plane. This direction will rotate the orbit clock-wise with a maximum change in angle of less than 90 degrees. (The maximum angle can never approach 90 degrees unless you perfectly cancel all horizontal momentum. This not possible in real life however it is possible in Kerbal Space Program. Normally the ship would traverse a slow spiral away from the center of mass of the orbited body.)
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[[File:TwoBlue.jpg|thumbnail|left|The Orbit Buttons]]
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==== Orbit buttons ====
  
This is primarily used in rendezvous to line up two irregular orbits.
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In {{version|0.23.5}} two small buttons were added when right-clicking a maneuver node. These buttons move the maneuver between future passes of the orbit without changing its position relative to the parent body, allowing maneuvers to be planned much further ahead of time. The right '''+''' button will move the maneuver to the next subsequent orbit, and the left '''-''' button will move it to the previous one.
  
[[File:ManeuverNodeRadialOut.PNG|250px|thumbnail|none|Rotating the orbital plane clockwise.]]
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{{clear|left}}
  
 
== Burning ==
 
== Burning ==
[[File:ManeuverNodesNavBall.PNG|200px|thumbnail|right|The nav ball at the bottom shows the blue marker the vessel has to be oriented to to perform the desired maneuver during the burn.]]
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[[File:ManeuverNodesNavBall.PNG|thumb|The nav ball at the bottom shows the blue marker the vessel must be oriented to in order to perform the desired maneuver during the burn.]]
To perform the desired maneuver, you have to initiate a burn at the time indicated. This is true for short burns. For long burns you want to get approximately ½ of your burn done before you actually hit the node.
 
  
If you are using SAS you can line up your nave ball indicator and the blue burn direction indicator as soon as you are done setting up the maneuver node (see screenshot).
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For best results the burn should be initiated roughly half of the duration of the burn before the indicated burn time. For instance, if the burn duration is 20 seconds the burn should be started around t- 10 seconds.
  
The reason the marker moves as you approach the end of the burn is because you did not have your burn perfectly lined up with the center of the marker. This can be ignored since it is usually a small error rather than a large one.
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[[SAS]] can help line up the level indicator with the blue burn direction indicator as soon as maneuver node is set up - once the maneuver has been defined, the burn direction will not change regardless of the craft's position. [[Pilot]]s of [[Experience#Levels|experience level]] 3 stars or higher enable the maneuver marker [[direction selector]] option when [[S.A.S.]] is enabled. This can automatically establish and maintain the vessel orientation throughout a maneuver burn. The more expensive, higher research level [[Probe]] cores can also do this.
  
Stop burning (key "x") once the change in velocity is close to approaching zero. After zero is reached the blue marker becomes meaningless and you can then delete the node marker since by this point you should be past it. This is even more important if you have set up multiple maneuver nodes since it will not go to the next nodal maneuver until the passed one is deleted.
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On completion of the burn the marker may begin to move away from the current heading; this is merely because it was not perfectly lined up. This can generally be ignored since it is usually a small error rather than a large one. The craft can be rotated to refine the burn direction and reduce such heading errors during long burns since they will be much more apparent, although care should be taken not to over-correct. If the craft is over-correcting with the smallest burn, it may be best to wait to make a small correction burn later, when the orbit will be less sensitive to applications of thrust. Alternatively engines with lower thrust, like [[RCS]] engines or engines with adjusted thrust level tweakable, could be used.
  
 +
Once the desired velocity change approaches zero the throttle should be reduced to avoid overshooting; once it reaches zero (or reaches a sufficiently small value) the burn should be stopped (press {{key press|X}}). Once the maneuver is completed the node should be deleted to clear the blue directional marker. This is especially important if multiple maneuver nodes are set up since the next node values will not show up until the last one is deleted.
  
 
[[Category:Control]]
 
[[Category:Control]]

Latest revision as of 14:58, 24 October 2018

Maneuver node in orbital view
Maneuver marker on navball

A maneuver node is a planned velocity change along an orbit. Multiple maneuver nodes can be added which will affect the following maneuver nodes. After adding a node it shows the velocity change needed to reach the next new orbit next to the navball. If multiple maneuver nodes have been planned, only the velocity change needed for the first node will be displayed on the navball - once that node has been completed it should be deleted so that the next velocity change becomes visible.

In career mode, maneuver nodes are unavailable at first. Using them requires upgrading both the Tracking Station and Mission Control.

Adding a maneuver node

Two maneuver nodes with one in edit mode

Click on the vessel's orbital line and a popup will give the option to add a new maneuver node. Once created, selecting and right-clicking the node gives the option to delete it. If the maneuver node has been passed, selecting it immediately puts it in "delete" mode.

Hovering over a node displays the time of arrival and the delta v needed to perform the maneuver.

After the node is created, it can also be dragged along the orbital path at any time. This is very useful when planning an orbital rendezvous and the placement was a bit off. When the view is focused on the maneuver node, dragging it can be difficult to control. It's much easier when moving a maneuver node to place a temporary node nearby and focus the view on that one while dragging.

Directions

Because there are three dimensions of movement in space (or air), there are three basic axes on which to burn, with two directions per axis; thus, all maneuvers can be described as a combination of movement in three separate directions. All six of these directions are marked on the navball, using the symbols above.

The relationship between these three orbital vectors - prograde, radial and normal - is defined by the right hand rule. If you hold the first three fingers of your right hand at right angles to each other in the most natural way, the index finger points forwards representing prograde, the middle finger points towards the orbital focus representing the radial, and the thumb points "upwards" represents the normal. For a prograde equatorial orbit around Kerbin (following Kerbin's rotation, i.e. eastward), normal will be north, prograde will be east, and radial will be down.

Prograde and retrograde

These vectors directly change the speed of the craft. Burning prograde will increase velocity, raising the altitude of the orbit on the other side, while burning retrograde will decrease velocity and reduce the orbit altitude on the other side. To raise a craft from a lower orbit into a higher orbit using a Hohmann transfer two prograde burns are executed; while lowering an orbit two retrograde burns are used.

This is the most efficient way to change the orbital shape (specifically the most common case, raising or lowering apsides) so whenever possible these vectors should be used. When the craft is powerful enough it is possible to switch the orbital inclination by 180° when burning retrograde to cancel out all orbital velocity and then build it back up, which is faster and more efficient than using the normal vectors.

Normal and anti-normal

The normal vectors are perpendicular to the orbital plane. Burning normal or anti-normal will change the orbital inclination. On the navball the normal and anti-normal vectors are located on the equator line directly between the prograde and retrograde markers.

These vectors are generally used to match the orbital inclination of another celestial body or craft, and the only time this is possible is when the current craft's orbit intersects the orbital plane of the target - at the ascending and descending nodes. To match the orbital inclination, either perform an anti-normal burn at the ascending node or a normal burn at the descending node. When the relative inclination at the nodes will reach 0° and they will start to move rapidly toward each other's positions.

Radial and anti-radial

These vectors are parallel to the orbital plane, and perpendicular to the prograde vector. The radial (or radial-in) vector points inside the orbit, towards the focus of the orbit, while the anti-radial (or radial-out) vector points outside the orbit, away from the body. Performing a radial burn will rotate the orbit around the craft like spinning a hula hoop with a stick. Radial burns are usually not an efficient way of adjusting one's path - it is generally more effective to use prograde and retrograde burns. The maximum change in angle is always less than 90°; beyond this point the orbit would pass through the center of mass of the orbited body and the ship would traverse a slow spiral in towards the orbited body.

Effects on orbit

Using

Upon selecting a maneuver node six symbols will appear, each corresponding to the vectors above. Each symbol can be clicked and dragged to adjust the amount of velocity change desired on each axis. Pulling a symbol away from the center of the node increases the speed change along the selected axis, and pushing a symbol toward the center of the node is equivalent to pulling the symbol on the opposite side. The further the symbol is pushed or pulled, the more rapidly the adjustment will be made. Adjustments to an axis can be made also by hovering over one of its nodes and scrolling the mouse wheel.

After adding a maneuver node three new values will appear next to the navball:

  1. Velocity change required, in meters per second
  2. Estimated burn time
  3. Time to maneuver node (or time since the node was passed)

Because a maneuver node assumes an instantaneous velocity change, a perfect burn is impossible; to get the best results, it is recommended to burn half of the time before the node and the other half directly afterwards.

Maneuver nodes can be used to reach a specific orbit without needing to continuously monitor the orbital map. When performing an aerobraking maneuver the current maneuver node will automatically update the needed velocity change as the craft's velocity decreases; this can be used to perform manual corrections if the aerobraking turns out to be insufficient or excessive.

The Orbit Buttons

Orbit buttons

In version 0.23.5 two small buttons were added when right-clicking a maneuver node. These buttons move the maneuver between future passes of the orbit without changing its position relative to the parent body, allowing maneuvers to be planned much further ahead of time. The right + button will move the maneuver to the next subsequent orbit, and the left - button will move it to the previous one.

Burning

The nav ball at the bottom shows the blue marker the vessel must be oriented to in order to perform the desired maneuver during the burn.

For best results the burn should be initiated roughly half of the duration of the burn before the indicated burn time. For instance, if the burn duration is 20 seconds the burn should be started around t- 10 seconds.

SAS can help line up the level indicator with the blue burn direction indicator as soon as maneuver node is set up - once the maneuver has been defined, the burn direction will not change regardless of the craft's position. Pilots of experience level 3 stars or higher enable the maneuver marker direction selector option when S.A.S. is enabled. This can automatically establish and maintain the vessel orientation throughout a maneuver burn. The more expensive, higher research level Probe cores can also do this.

On completion of the burn the marker may begin to move away from the current heading; this is merely because it was not perfectly lined up. This can generally be ignored since it is usually a small error rather than a large one. The craft can be rotated to refine the burn direction and reduce such heading errors during long burns since they will be much more apparent, although care should be taken not to over-correct. If the craft is over-correcting with the smallest burn, it may be best to wait to make a small correction burn later, when the orbit will be less sensitive to applications of thrust. Alternatively engines with lower thrust, like RCS engines or engines with adjusted thrust level tweakable, could be used.

Once the desired velocity change approaches zero the throttle should be reduced to avoid overshooting; once it reaches zero (or reaches a sufficiently small value) the burn should be stopped (press X). Once the maneuver is completed the node should be deleted to clear the blue directional marker. This is especially important if multiple maneuver nodes are set up since the next node values will not show up until the last one is deleted.