Kerbal Space Program (KSP) challenges players to build rockets, explore the solar system, and master orbital mechanics. While manual control is rewarding, the learning curve can be steep. MechJeb — an autopilot and flight assistance mod — bridges that gap by automating launch, ascent, orbital transfers, and landings. Whether you are new to KSP or a veteran looking to streamline routine missions, MechJeb gives you a powerful set of tools for precise, repeatable maneuvers. This guide covers everything from installation to advanced planning, helping you get the most out of this indispensable mod.

Installing MechJeb in KSP

Before you can automate flights, you must install MechJeb. The mod is widely available and works with most versions of KSP. Follow these steps:

  • Download the latest release from a trusted source. The most reliable options are the official KSP forum thread or the mod repository on GitHub. You can also find it on SpaceDock.
  • Install using CKAN (recommended). The Comprehensive Kerbal Archive Network handles dependencies and updates automatically. Search for "MechJeb2" in CKAN and click install.
  • Manual installation: Extract the downloaded ZIP file and copy the MechJeb2 folder into your KSP GameData directory. Ensure you also install ModuleManager if it is not already present — MechJeb relies on it for configuration.
  • Verify the installation: Launch KSP. On the main menu, check for a new toolbar icon (the MechJeb icon) or look under "Addons" in the settings. In the Vehicle Assembly Building (VAB) or Space Plane Hangar (SPH), the MechJeb part should appear in the "Control" category.

If you are playing in Career or Science mode, you may need to unlock the MechJeb functions through the tech tree (typically under "Flight Control" or "Advanced Flight Control"). By default, all features are available in Sandbox mode.

Adding MechJeb to Your Craft

MechJeb comes in two flavors: a physical part and an integrated "MechJeb for all" configuration. The part method requires you to attach the MechJeb AR202 case to your vessel. The integrated method adds functionality to any probe core or command pod using ModuleManager patches.

  • Physical part: In the VAB/SPH, look under "Control" for the MechJeb part. It resembles a small computer case. Attach it anywhere on your craft (it does not need to be on the root part).
  • ModuleManager patch: Some mod packs include a patch that adds MechJeb to all command modules. You can also install the "MechJeb for All" add-on separately. This eliminates the need to clutter your craft with the physical part.
  • Career mode note: If you use the integrated patch, be aware that career progression may still lock features. You can adjust the "MechJeb TechTree.cfg" to allow early access or use a sandbox save for testing.

Once the part is attached and your vessel is on the launchpad, click the MechJeb icon in the toolbar (or right‑click the part) to open the main interface.

Understanding the MechJeb Interface

The MechJeb window has multiple tabs, each dedicated to different automation tasks. The most commonly used tabs are:

  • Flight Computer: Contains autopilots for launch, ascent, and maneuver execution. Also includes attitude control and landing guidance.
  • Maneuver Planner: Generates and executes orbital maneuvers, including Hohmann transfers, plane changes, and rendezvous.
  • Rendezvous: Automates the process of meeting another vessel in orbit, from phasing to final approach.
  • Landing: Provides autopilot for landing on planets and moons with atmosphere or vacuum.
  • Utilities: Displays delta‑V stats, surface information, orbital predictions, and transfer window calculators.
  • Settings: Customize autopilot behaviors, throttle limits, and steering aggressiveness.

Using MechJeb for Automated Flight

Ascent Autopilot

The most popular feature is the Ascent Autopilot, which flies your rocket from the launchpad to a target orbit. To use it:

  1. Open the Flight Computer tab and select the "Ascent Autopilot" subsection.
  2. Configure your target orbit: set desired apoapsis, periapsis, inclination, and altitude. For a standard orbit around Kerbin, you might set 80 km x 80 km at 0° inclination.
  3. Choose an ascent profile:
    • Stock: Mimics the KSP stock ascent guidance.
    • PVG (Powered Explicit Guidance): More efficient but requires fine-tuning.
    • Gravity Turn: Smooth, realistic turn based on acceleration.
    • Custom: Manually define turn shape via waypoints.
  4. Set throttle limits (e.g., 100%) and enable "Auto Throttle" to prevent over‑acceleration.
  5. Click Engage Autopilot. MechJeb will ignite the engines, steer the rocket, stage automatically, and circularize at the specified apoapsis.

You can override any phase by toggling the autopilot off and resuming manual control. MechJeb logs all actions in the console, which you can review later.

Customizing the Ascent Profile

For advanced users, the "Ascent Profile Editor" allows you to define waypoints by altitude or velocity. This is useful for heavy lifters, SSTOs, or non‑standard launches. For example, you can program a steep ascent to avoid terrain, then lower the pitch after clearing mountains. Save your profile for reuse across similar craft.

Maneuver Planning with MechJeb

The Maneuver Planner Tab

MechJeb simplifies the calculation and execution of orbital maneuvers. To plan a transfer from low Kerbin orbit to the Mun, follow these steps:

  1. Open the Maneuver Planner tab.
  2. Under "Target," select the body you want to reach (e.g., Mun).
  3. Choose a maneuver type:
    • Hohmann Transfer: Most efficient for circular orbits.
    • Bi‑elliptic Transfer: Useful for very high orbits or large distance changes.
    • Plane Change: Adjust inclination without changing orbital energy.
  4. Adjust parameters such as periapsis altitude (for capture) or transfer angle. MechJeb calculates the required delta‑V and shows the ejection angle.
  5. Click Create Node — a maneuver node appears on the map view.
  6. To execute, switch to the "Flight Computer" tab under "Maneuver Node Editor" and click Execute Next Node. MechJeb will align the vessel and burn the exact amount of delta‑V, compensating for throttle lag and pointing accuracy.

You can also plan multiple nodes in sequence. For example, a Mun mission could include: a burn from Kerbin orbit to the Mun, a capture burn at periapsis, and then a circularization burn. Each node is listed in order, and MechJeb can execute them one after another if you enable "Auto‑Warp" and "Auto‑Execute."

Fine‑Tuning Node Execution

MechJeb offers several options when executing a maneuver node:

  • Warp to Burn: Warps time until 30 seconds before the node, then stops time warp.
  • Limit Acceleration: Caps throttle to avoid breaking the craft or exceeding structural limits.
  • Align Procedurally: Automatically points the ship toward the burn vector, even if you rotate manually during the burn.
  • Copy to another vessel: Useful in multi‑vessel missions — you can apply the same node to another ship if it has MechJeb installed.

Automating Rendezvous and Docking

Rendezvous and docking are some of the most difficult tasks in KSP. MechJeb handles the entire process:

  1. From the Rendezvous tab, select the target vessel. MechJeb will plot a phasing orbit to bring you close (within ~1 km).
  2. Once close, click Match Velocities with Target — MechJeb zeroes out relative speed.
  3. For docking, use the Docking Autopilot (under Flight Computer). It aligns docking ports, approaches slowly, and makes the final connection. You can choose between a "Direct" approach (forward onto the port) or a "Rendezvous" approach that first matches direction.

You can adjust safety margins, approach speed, and rotation alignment in the docking autopilot settings. For beginners, we recommend setting the approach speed to 0.5 m/s and enabling "Auto‑Rotor" to keep the docking port aligned.

Landing Autopilot

MechJeb’s landing autopilot can land on any solid surface or in an atmosphere. It uses predictive guidance to pick a landing site, control descent speed, and compensate for drift.

  • Landing Guidance: Open the "Landing" tab. Select a target (e.g., the KSC runway, a biome, or a specific latitude/longitude). Choose "Autoland" for fully automated landing. MechJeb will de‑orbit, perform a suicide burn, and touch down with low vertical speed.
  • Settings: You can limit the touchdown speed, enable/disable parachutes at the correct altitude, and choose deployment altitude. For atmospheric bodies, MechJeb will manage parachute staging if you have deployed chutes.
  • Rover Autopilot: If you have wheeled vehicles, the "Rover Autopilot" drives them to waypoints while avoiding steep slopes and adjusting speed for terrain.

Tips for Effective Use of MechJeb

To maximize the benefits without losing understanding of orbital mechanics, keep these tips in mind:

  • Learn the basics first: Spend time flying manually to understand how thrust, gravity, and orbital energy interact. MechJeb will make more sense when you know what it is automating.
  • Use delta‑V readouts: The Vessel Info tab shows current delta‑V per stage and across the entire craft. This helps you verify that you have enough fuel for the planned maneuvers.
  • Check the mod compatibility: Some other mods (e.g., Real Solar System, Realism Overhaul, FAR) require tweaks to MechJeb’s ascent profiles. Look for configuration files or community patches on the KSP forum.
  • Monitor the console: MechJeb logs every action. If something goes wrong — such as overshooting a burn or failing to pitch over — the console provides clues.
  • Save custom profiles: After tuning an ascent profile that works well for a particular rocket design, save it. This saves time on repeat launches.
  • Do not rely solely on the autopilot: Use MechJeb as a co‑pilot. For precision maneuvers like docking with a spinning station, you may need to take manual control for the final approach.
  • Stay updated: MechJeb receives patches and improvements. Check the official KSP forum thread for the latest version and known issues.

Troubleshooting Common Issues

  • MechJeb does not show up: Ensure you have ModuleManager installed. Check that the part is added to the craft and that you are not in “Space Center” view (MechJeb only works with a vessel loaded).
  • Ascent autopilot fails to pitch over: Increase the “Start Turn Altitude” in the ascent profile. Low‑thrust rockets need a later turn.
  • Maneuver node execution drifts: Reduce the “Throttle Smoothing” or increase “Precision Factor” in the autopilot settings.
  • Landing autopilot crashes: The landing guidance may not account for terrain if your body has no atmosphere. Use the “Landing guidance” window to set a touchdown altitude above terrain height.

Conclusion

MechJeb is an incredibly versatile tool that can transform your KSP experience. Whether you are automating a routine launch to orbit, planning a complex interplanetary transfer, or executing a precision landing, the mod saves time and reduces frustration. By understanding each feature — from the Ascent Autopilot to the Rendezvous Planner — you can focus on the creative aspects of mission design while letting the software handle the math. Install it, experiment with settings, and soon you will be flying the cosmos with the help of your own on‑board flight computer.