Ascent Guidance

The Ascent Guidance of Mechjeb allows to easily get a rocket into a stable, circular orbit with a variety of options. Launches can also be timed to rendezvous with a specific target or can simply be launched when ready.

Table of contents

• Launch process
• Main Actions
• Main Options
• Ascent Profile
  • Edit Ascent Path
    • Classic Ascent Profile Options
    • Stock-style GravityTurn
    • Powered Explicit Guidance
• Target Options

Launch process

There are four main parts to the launch process, and the exact altitudes at which they occur are customizable:

1. Initial ascent
2. Gravity turn
3. Coast to the edge of the atmosphere (if applicable)
4. Circularization burn at apoapsis

Main Actions

• Show navball ascent path guidance
  Creates a targeting reticule on the navball display to point towards while launching (NOTE: this creates a virtual target which will unset any target you currently have set)

• Engage/Disengage autopilot
  Engages the autopilot or (if engaged) disengages the autopilot

Main Options

• Orbit altitude [km]
  The desired altitude in kilometres for the final circular orbit

• Orbit inclination [°]
  The desired inclination in degrees for the final circular orbit

• Prevent overheats
  Limits the throttle to prevent parts from overheating

• Limit Q to [pa]
  Limits the maximal dynamic pressure. This avoids that pieces break off during launch because of atmospheric pressure. TODO: specify when to use it

• Limit acceleration to [m/s²]
  Never exceed the acceleration during ascent

• Limit throttle to [%]
  Never exceed the percentage of the throttle during ascent

• Keep limited throttle over [%]
  Never go below the percentage of the throttle during ascent

• Electric limit Lo [%] Hi [%]
  TODO

• Force Roll climb [°] turn [°]
  TODO

• Limit AoA to [°] (0.0°)
  TODO

  • Dynamic Pressure Fadeout [pa]
    TODO

• Corrective steering
  Will cause the craft to steer based on the more accurate velocity vector rather than positional vector (large craft may actually perform better with this box unchecked)

• Auto-stage
  The autopilot will automatically stage when the current stage has run out of fuel

  • Delays: pre: [s] post: [s]
    The autopilot will pause the actual staging before (pre) and after (post) for each stage.

  • Clamp AutoStage Thrust [%]
    TODO

  • Stage fairing when:
    Stage the fairing independently of the actual staging process, whenever all (or any? TODO) the following conditions are met:

    • dynamic pressure smaller than [kPa]
    • altitude greater than [km]
    • aerothermal flux smaller than [W/m²]

  • Stop at stage
    Staging will not occur beyond this stage number

• Auto-deploy solar panels
  Automatically deploy solar panels when safe (verify! TODO).

• Auto-warp
  Automatically use warp during ascent

• Skip Circularization
  Do not circularize when apoapsis has been reached

Ascent Profile

There are different ascent profiles available:

1. Classic Ascent Profile
   TODO Classic Ascent Profile should be more or less what you're used to.

2. Stock-style GravityTurn™
   This profile is similar to the gravity turn mod. It is a 3-burn to orbit style of launch that can get to orbit with about 2800 dV on stock Kerbin. If you want to have fun make a rocket that is basically a nose cone, a jumbo-64 a mainsail and some fairly big fins. Have the pitch program flip it over aggressively (uncheck the AoA limiter, set the values to like 0.5 / 50 / 40 / 45 / 1) and let it rip. Note that its not precisely the GT mod algorithm, and I didn't intend it to be -- I just didn't know what else to call it. It does not do any pitch-up during the intermediate burn right now (that's another TODO) so it won't handle low TWR upper stages.

3. Powered Explicit Guidance (RSS/RO)
   PEG is actual gravity turn algorithms from the Surveyor missions that properly integrates the trajectory. It will likely not be that useful on Kerbin since it does not know how to do two-burn to orbit (does not understand coast phases) so most Kerbin launch vehicles won't ever get locked guidance with it. So if you give a 100x100 orbit, then you need a rocket that will burn continuously, without throttling, until insertion where it will shut down right when it hits the 100x100 orbit. Example of it flying a 3-stage rocket to orbit: https://vimeo.com/224742550

Edit Ascent Path

Depending on the profile selection, the Edit Ascent Path button will open a new window with options on the respective profile.

Classic Ascent Profile Options

The options show the diagram of the rocket's idealized ascent. The following options can be edited, and the diagram will update as their values change:

• Turn Start Altitude
  The altitude at which the gravity turn should begin

• Turn End Altitude
  The altitude at which the gravity turn should end

• Final Flight Path Angle
  The final angle with respect to the prograde direction

• Turn Shape
  Varies the parabolic part of the trajectory

Stock-style GravityTurn

TODO

Powered Explicit Guidance

TODO

Target Options

Further options are available when a target is selected and the current ship is landed

TODO