MechJeb 1 Manual

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Orbital Operations

Orbit summary

At the top of the window is displayed a summary of your current orbit, showing its periapsis, apoapsis, and inclination.

PE - Change periapsis

Specify a new periapsis for your orbit and hit Burn, and MechJeb will automatically execute a burn to lower or raise your periapsis to the specified altitude. As this burn is preformed at the current position, the selected periapsis cannot be above the current altitude.

AP - Change apoapsis

Specify a new apoapsis for your orbit and hit Burn and MechJeb will automatically execute a burn to lower or raise your apoapsis to the speciified altitude. As this burn is preformed at the current position, the selected apoapsis cannot be below the current altitude.

AP+PE - Change both apsides

This lets you set both your periapsis and apoapsis at once. Specify a new periapsis and a new apoapsis and hit Burn and MechJeb will automatically execute a burn to achieve both simultaneously. As this burn is preformed at the current position, the selected apoapsis cannot be below the current altitude and the selected periapsis cannot be above the current altitude.

CIRC - Circularize

Hit Circularize and MechJeb will execute a burn to circularize your orbit at its current altitude. Note that if you are rising or falling rapidly you might be at a different altitude by the time MechJeb actually manages to circularize the orbit.

TRANS - Trans-munar injection

While in Kerbin orbit, specify a desired munar periapsis. Hit Transfer to the Mun and MechJeb will warp to the appropriate point in your orbit, then execute a trans-munar injection (TMI) burn. The burn will be calculated so that when you enter the Mun's sphere of influence, your periapsis will be the one you specified. Once it has made the TMI burn, MechJeb will also display your predicted Munar periapsis, enabling you to make manual course corrections while you are still in Kerbin's sphere of influence. Note: automatic trans-munar injection is likely to go wrong if you are in an orbit with an inclination greater than around 1 or 2 degrees, or a highly elliptical orbit. MechJeb assumes that you are starting from a zero-inclination, circular orbit around Kerbin.

WARP - Time warp

This lets you time warp to apoapsis, periapsis, or the next sphere of influence (SoI) switch. Select one of these three and hit Warp, and MechJeb will automatically ramp the time warp rate up and down to move you quickly to the specified point. When warping to periapsis or apoapsis you can specify a lead time. This lets you warp to, e.g. 15 seconds before periapsis. Note that when warping to the next SoI switch, MechJeb will not go above 1,000x warp, as often ramping down from the higher 10,000x warp carries you farther than you would like.

Abort

To immediately end any automatic operation, hit Abort.

Status

This will report what operation is currently being executed, or Idle if the orbital operations module is not currently doing anything.

Ascent Autopilot

MechJeb's ascent autopilot will fly a ship completely automatically from the launchpad to any desired circular orbit around Kerbin. Engage the autopilot on the launchpad to place it in the Awaiting liftoff state. Launch your ship as usual and the ascent autopilot will fly it to orbit and then automatically disengage. Disengage the autopilot at any time to regain manual control of the ship.

Flight modes

During flight, the autopilot operates in several sequential modes. They are:

  1. Vertical Ascent - The rocket first flies straight up until it reaches a certain altitude.
  2. Gravity Turn - The rocket then gradually pitches over and starts accelerating horizontally. This phase ends when the apoapsis reaches the desired orbit altitude.
  3. Coast To Apoapsis - Then the engines turn off while the rocket and the rocket coasts until it reaches apoapsis, at the desired orbit altitude.
  4. Circularization Burn - When the apoapsis is reached, the ship executes one final burn to make the orbit circular. The ascent autopilot will automatically disengage after the circularization burn is complete.

Inputs

Orbit Altitude

The altitude of the circular orbit into which the ascent autopilot will insert the rocket.

Inclination

The inclination of the orbit into which the autopilot will insert the rocket. Zero inclination gives a normal eastward equatorial orbit. +90 or -90 degrees inclination give a polar orbit starting out north or south, respectively. 180 degrees gives a westward equatorial orbit. Clicking Inclination will turn this input into a Heading input.

Heading

The heading of the desired orbit. When launching from the equator (where KSC is located), 90 heading is an eastward equatorial orbit, 0 is a northward polar orbit, 180 southward polar orbit, and 270 a westward equatorial orbit. Clicking Heading will turn this input into an Inclination input.

Auto-Stage?

By default the autopilot will automatically fire the next stage of the rocket when the current one burns out. This can be turned off by toggling Auto-stage?.

Auto-Warp Toward Apoapsis?

By default the autopilot will use time warp to speed the coast to apoapsis phase. This can be turned off by toggling Auto-warp toward apoapsis?.

Auto-Throttle?

By default the autopilot will seize exclusive control of the throttle while it is engaged. If you want to control the throttle during the vertcal ascent and gravity turn you can turn off Auto-throttle?. This will replace the orbit altitude input with a display of your current apoapsis and periapsis, and a Circularize button. When your apoapsis is at the desired height, you can press Circularize and the autopilot will again take control of the throttle for the coast to apoapsis and circularization burn at the apoapsis.

Time Launch To Rendezvous

The ascent autopilot can time your launch to approximately rendezvous with a target vessel. Properly used, you can end up about 1km from the target immediately after the circularization burn. This will only work if the target vessel is in a circular, equatorial (0 inclination/90 heading) orbit. First, you will need to do a practice launch so that the ascent autopilot can learn the timing of the ascent for you particular rocket and the particular descired altitude. For the practice launch, don't select Time launch to rendezvous?. Just enter the altitude of the target as the orbit altitude and launch as usual. At the end of each ascent (after the circularization burn), the autopilot calculates and remembers a launch phase angle (LPA). This phase angle lets the autopilot time future ascents of the same rocket to the same altitude. Note that changing the rocket, the orbit altitude or the ascent path will change the launch phase angle and you will have to do another practice launch.

After the practice launch, restart the flight or start a new one with the same rocket. Leave the ascent autopilot disengaged. Select Time Launch To Rendezvous?. The Known LPA field will already be filled in with the launch phase angle calculated on the previous launch. Click Choose target and then select the vessel you are trying to rendezvous with. Again, this vessel must be in a circular equatorial orbit or the rendezvous won't work well. Now hit Engage and the ascent autopilot will begin a countdown to launch. At T-0 seconds the autopilot will automatically ignite the first stage and begin the ascent. If all goes well, the circularization burn will end near the target vessel.

Note: To speed the countdown, the autopilot will use time warp. Many rockets respond poorly to time warping on the pad, and will fall apart when coming out of warp. If this is happening to your rocket, there's little you can do but try to build a sturdier rocket.

Customizing the ascent path

The Edit path button brings up a window that lets you customize the path the ascent will take through the atmosphere. The ascent path window includes a graph of the planned path, which will change to reflect changes in any of the parameters below.

  • Turn Start Altitude - the height to which the rocket will ascend vertically before starting to turn over.
  • Turn End Altitude - the height at which the rocket stops pitching over, above which the rocket will maintain the Final flight path angle
  • Final Flight Path Angle - The flight path angle is the angle the velocity vector makes with the horizon. The Final Flight Path Angle is the flight path angle the rocket will maintain above the Turn End Altitude.
  • Turn Shape - This slider adjusts a continuous parameter describing the shape of the pitchover trajectory. Try varying it to see its effect on the path.

Ascent stats

The Stats button brings up a window with some statistics about the ascent.

Time

this counts up from launch and will stop counting at MECO (main engine cut-off) at the end of the circularization burn, and so can be used to time the launch.

Total Δv Expended

a measure of the fuel cost of the launch. For a given rocket ascending to a given orbit, a more efficient ascent is one that expends less Δv. Gravity losses, drag losses, steering losses, and speed gained break down what the Δv was expended on.

Gravity Losses

a measure of how much thrust was spent fighting against gravity instead of accelerating the rocket. Gravity losses are high when the rocket is travelling straight up and zero when the rocket is travelling horizontally.

Drag Losses

a measure of how much thrust was spent fighting against atmospheric drag instead of accelerating the rocket. Drag losses are high when the rocket is travelling fast in the dense lower atmosphere and low when the rocket is travelling slowly or is above the dense lower air.

Steering Losses

a measure of how much thrust was spent turning the rocket instead of accelerating it. Steering losses are high when the rocket is thrusting at a significant angle to its current velocity, and zero when it is thrusting parallel to its current velocity.

Speed Gained

the net acceleration of the rocket during the launch. Note that this is computed in the rotating reference frame of the planet.

Launch Mass

the mass the rocket had at launch. This will display as 0 if you switch to an in-progress mission.

Current Mass/Mass to Orbit

the current mass of the rocket. Mass to orbit is another measure of the ascent's efficiency: a more efficient ascent of the same rocket will bring a greater mass to orbit, since less fuel will have been burned.

Launch phase angle

If the rocket had been launched this angle ahead of a another vessel that was already in the target orbit, the two ships would meet at the end of the circularization burn. This angle is used in timing launches to achieve orbital rendezvous.

Ascent from other bodies

The ascent autopilot can be used for ascent from bodies besides Kerbin, as follows. With the autopilot disengaged, first enter the desired orbit parameters and edit the ascent path to the desired path. (Note: if you're launching in vacuum, you can have a quite low turn start and turn end: as a suggestion, try a turn start altitude of 0km, a turn end altitude of 5km, and a final flight path angle of 0 degrees. This launch profile turns horizontal to thrust for orbit almost immediately, since there is no atmosphere to climb above.) When you are ready, engage the autopilot and it will immediately begin the ascent to orbit.

Landing Autopilot

MechJeb's landing autopilot can automatically fly you down to a landing on Kerbin or the Mun. Optionally, you may specify the coordinates to land at. The landing autopilot can also be used to predict the outcome of aerobraking maneuvers.

Untargeted Landings

If you want to do a powered landing, and don't want MechJeb to aim for a specific target, hit LAND. You can activate LAND at any point in your descent. If you are still in orbit, MechJeb will do a deorbit burn. LAND will manage your speed to fly you down to a soft landing. It will try to touch down at the vertical speed specified in the Touchdown speed field.

Targeted Landings

MechJeb can also land a specified target coodinates. Coordinates can be specified in two formats, decimal (DEC) and degrees-minutes-seconds (DMS), and you can switch to one or the other by pressing DEC or DMS.

First you need to set a target. There are several ways of doing this:

Entering coordinates by hand

You can type coordinates into the target coordinate text fields. For instance, if you want to land next to another vessel that has already landed, you can mouse over the ship in map view and the game will display its coordinates in DMS format. You can then enter these coordinates as your target coordinates, making sure you are in DMS mode.

Point-and-click

Hit Select target on map and you'll be taken to the map view. Now you can click any point on the surface of the body you are orbiting. The point you click will become the target landing site. MechJeb will display coordinates as you mouse over the surface, and will automatically paste these into the target coordinate text fields when you click on your desired landing site.

Target KSC

Hit Target KSC and MechJeb will automatically paste the coordinates of KSC on Kerbin into the target coordinate text fields.

Landing

Once you have set your landing target, hit LAND at target and MechJeb will initiate a completely automatic targeted descent to land at the target. The descent proceeds in several stages:

  1. Deorbit burn - If you are still in orbit, MechJeb will first warp to the appropriate point in the orbit and perform a deorbit burn.
  2. Course correction - MechJeb will do a correction burn culminating in fine adjustments to the trajectory so that it's aimed precisely at the target.
  3. On course for target - Once the trajectory is good enough, MechJeb will display the status On course for target (safe to warp). As indicated, it's now safe to increase time warp as much as you like to speed the descent. MechJeb will automatically unwarp when necessary. In addition, if you are going to stage during the descent it's best to stage now, rather than during deceleration burn, as staging during the deceleration burn will throw off MechJeb's predictions and cause you to over- or under-shoot the target.
  4. Deceleration - For Munar landings the next step is a deceleration burn. MechJeb will continue to make small corrections to the trajectory during this burn. MechJeb aims for the deceleration burn to end 200m vertically above the target. At the end of the burn, the ship will briefly come to a halt before dropping down on the target. For Kerbin landings, MechJeb simply allows the atmosphere to slow down the craft during this stage.
  5. Final descent - This is the final vertical powered descent, culminating in touchdown. MechJeb will try to touch down with the vertical speed specified in the Touchdown speed input.

Manual Targeted Landings on Kerbin

You can use the landing autopilot's landing prediction to do a targeted landing on Kerbin manual instead of under autopilot control. When you are on a landing trajectory, MechJeb will display your predicted landing site, taking into account atmospheric drag. It will also display how far that predicted landing site is from your target. By doing manual burns to bring the predicted landing site to the target landing site you can make sure you land at your target.

MechJeb will not display a predicted landing site on the Mun unless the LAND at target autopilot mode is active, so it won't help you do manual targeted landings on the Mun. This is because your landing site is highly dependent on the exact details of your deceleration burn, and MechJeb cannot predict how you will perform the deceleration burn.

Aerobraking predictions

If you are on an aerobraking trajectory--one that passes through the atmosphere but does not land--the landing autopilot will show a prediction of what your orbit (apoapsis and periapsis) will be after you exit the atmosphere. This lets you perform accurate aerobraking maneuvers.

Vessel Information

Coming soon.

  • Moment of Inertia, X Z Y
  • Angular Velocity, X Z Y
  • Angular Momentum, X Z Y
  • torqueThrustPYAvailable, Vector capable liquid fuel engine torque
  • torquePYAvailable, Pod + RCS (if enabled) torque
  • torqueRAvailable, Pod torque.

Surface Information

  • Altitude (ASL) Altitude at sea level.
  • Altitude (true) Altitude above the ground below the ship.
  • Pitch
  • Heading
  • Roll
  • Ground Speed
  • Vertical Speed
  • Horizontal Speed
  • Latitude +/- 90 degrees, negative values are south, positive are north.
  • Longitude +/- 90 degrees, negative values are east, positive are west.

Orbital Information

Orbiting

The current SoI the ship is in.

Orbital Speed
Apoapsis

Highest altitude during the currently projected orbital path

Periapsis

Lowest altitude during the currently projected orbital path

Period

The time taken to complete one orbit along the currently projected path

Time to Apoapsis

The time until the craft reaches the currently projected Apoapsis.

Time to Periapsis

The time until the craft reaches the currently projected Periapsis.

LAN Longitude of the ascending node

Horizontally orients the ascending node of the ellipse (where the orbit passes upward through the reference plane) with respect to the reference frame's vernal point (green angle Ω in diagram). <ref>http://en.wikipedia.org/wiki/Orbital_elements</ref>

LPe Longitude of the Periapsis
Inclination

The angle formed between the current orbital path and an orbit that is around the equator.

Eccentricity

The elliptical-ness of the orbit. A perfectly circular orbit has an eccentricity of 0, while an 'orbit' that is straight up/down has an eccentricity of 1.

Semimajor Axis Semimajor axis (a,!)

The sum of the periapsis and apoapsis distances divided by two. For circular orbits the semimajor axis is the distance between the bodies, not the distance of the bodies to the center of mass. <ref>http://en.wikipedia.org/wiki/Orbital_elements</ref>

Translatron

Velocity control for Jebediah Thrillmaster

The translatron controls the throttle of your spacecraft. Available modes:

  • KEEP OBT keeps orbital speed
  • KEEP VERT keeps vertical speed (climb/descent speed)
  • KEEP SURF keeps surface speed
  • Panic Mode Abort mission by seperating all but the last stage and activating landing autopilot

Please note that KEEP VERT is only used for controlling vertical speed (that is, rate of climb) If you set a pitch of 80 degrees and vertical speed of 100, your vessel will climb at 100 m/s and acellerate since to it's HDG because it's leaning at a 80 degrees. HOWEVER, if you use KEEP SURF, you total speed will be measure and not your climb/descent (vertical) speed.

Please keep in mind all values are integers and can contain a sign.

Panic Mode

  1. Kill Throttle
  2. Seperate everything but the last decoupler
  3. Engage landing autopilot, as if the Land button in the landing autopilot had been pressed.

Using any ship controls while panic mode is enganged will disengage panic mode.

Smart A.S.S. -- Smart Automatic Space Steering

Pitch controls for the rocketry impaired. Smart A.S.S. controls the pitch of your spacecraft.

These controls should be pretty obvious. Please note that the Smart A.S.S autopilot calculates it's pitch, bank and roll according to the orbital flight path and will not follow the flight path marker on the artifical horizon but will instead calculate it's own flight path marker from the orbital speed. NOT the surface or current speed mode selected or shown on the artificial horizon. Availables modes:

  • KILL ROT kills rotation
  • SURF is for setting a pitch relative to the horizon. * HDG sets the heading to follow * PTH sets the pitch
  • PRO GRAD for orbital Prograde
  • RETR GRAD for orbital Retrograde
  • NML+ for normal, useful to changing orbit inclination
  • NML- for anti-normal, useful to changing orbit inclination
  • RAD+ for radial outward (away from the SOI), will manuever the navball to the top of the blue hemisphere.
  • RAD- for radial inward (towards the SOI), will manuever the navball to the top of the brown hemisphere.

Extra modes available when a target is selected:

  • TGT+ points toward the target
  • TGT- points away from the target
  • RVEL+ points toward your relative velocity. Burning this direction will increase your relative velocity.
  • RVEL- points opposite youru relative velocity. Burning this direction will decrease your relative velocity.
  • PAR+ points parallel to the target's orientation. If the target is a docking node it orients the ship along the docking axis, pointing away from the node.
  • PAR- points antiparallel to the target's orientation. If the target is a docking not it orients the ship along the docking axis, pointing toward the node.

Instrument Landing System

The Instrument Landing System provides data and guidance to help you land a spaceplane at the KSC runway.

Navball guidance

When its window is active (even when it's minimized), the ILS makes the purple circle marker on the navball point toward the runway. Actually, if you are currently to the left of the runway the purple circle will point a bit right of the runway, and if you are are currently to the right of the runway, the purple circle will point a bit to the left. This way, if you keep your velocity vector (yellow circle) lined up with the purple circle, you'll maintain a steady descent toward the runway and land properly aligned with it.

If you find that the purple circle indicates a descent too steep for your liking, dive down a bit. The purple circle will come up toward the horizon. When it's at a nice descent angle, you can start following it again. Similarly, if you intend to make a steeper descent, you can keep your velocity vector above the purple circle for a bit, which will cause the purple circle to move down farther below the horizon.

Landing data

When maximized, the ILS provides some data readouts relevant to your landing approach. If you don't care about the data and only want the navball guidance, you can minimize the ILS window by clicking "Minimize."

Lateral speed

How fast you are drifting left or right of the runway.

Lateral displacement

How far you are currently offset left or right of the runway's centerline. When this is zero you are perfectly lined up for landing. If you are, say, displaced to the right, you want to get some leftward lateral speed to kill your offset.

Flight path angle

The angle your velocity vector currently makes with the horizon, i.e., the angle you are descending at. Will be negative when you are descending, and zero when you are flying perfectly horizontal.

FPA to runway

The flight path angle that would let you touch down at the runway. If your FPA is greater (less negative) than this, you are on course to overshoot the runway. If your FPA is lower (more negative) than this, you are on course to undershoot the runway. If you are making your final descent, you want your FPA to equal the FPA to the runway. Note that this value will start changing very rapidly when you get very close to the runway, since you will not be on course to land exactly at the start of the strip. At that point you should just maintain your steady descent and touch down, ignoring the "FPA to runway" value.

Distance to runway

The distance to the start of the runway, in kilometers.