I have 2 questions about achieving orbits with Mechjeb

[Turk_WLF]

I’m not sure where I should post this posting due to nature of the questions.

1)I need help with achieving orbit use Mechjeb, I’m trying to land on the Mun. I got to the point where I’m heading towards the Mun but my Apoapsis is within the core of Mun & I have to circularizing my orbit (anywhere from 19 Km to 50Km) & I still crash into the surface Mun.

2)I was able to land on the Mun twice but I’m not sure how I did it, but I have 3 Kerbals Stranded on Mun without enough fuel to dock with the Space Station waiting in orbit. Therefore are there any tricks of landing another Lander within a few meters of the Stranded Lander & her Crew?

I’m using KSP 25.0 & MechJeb2 2.4.0.0

Thanks,

Edited May 14, 2015 by Turk_WLF

[Taki117]

2)

1) Mechjeb has a landing guidance feature, also, if you want to land you need to perform a slight deorbit burn (A picture of what you are doing would help here) and then decrease your horizontal velocity as much as possible and vertical velocity to less than 10m/s.

[Tokay Gris]

I need help with achieving orbit use Mechjeb, I’m trying to land on the Mun. I got to the point where I’m heading towards the Mun but my Apoapsis is within the core of Mun & I have to circularizing my orbit (anywhere from 19 Km to 50Km) & I still crash into the surface Mun.

I assume you have all features of Mechjeb unlocked (or are playing Sandbox) and I also assume you mean your periapsis is below Muns surface and not your apoapsis.

As soon as you enter Muns SOI (sphere of influence), you need to change your periapsis, so it is above the surface.

To do this using Mechjeb, use "change periapsis" and "after a fixed time" (default is "at next apoapsis"). Ususally 10 to 30 seconds.

After that, it is just "circularize" and "at next periapsis" (default is "at next apoapsis").

Another way is to use "finetune intercept with target" after the Hohmann-burn in LKO. If the target is a celestial body, you get to type in a desired periapsis. This usually is about 50 km off (no idea why). So, if you type in "100" you usually get something like 30km entering Mun SOI. This burn will take place somewhere along the Hohmann orbit to Mun. If you chose the "correct" number (which, as I said, somehow never is the really correct one), your periapsis will be above Muns surface.

I was able to land on the Mun twice but I’m not sure how I did it, but I have 3 Kerbals Stranded on Mun without enough fuel to dock with the Space Station waiting in orbit. Therefore are there any tricks of landing another Lander within a few meters of the Stranded Lander & her Crew?

MechJeb has a landing autopilot.

Go to the map view, target one of your stranded Kerbals, preferably if he is a little bit away from the others (maybe move him a bit beforehand), note the coordinates he is at. I think they are displayed in mapview.

Move that Kerbal again. MechJebs autopilot is very accurate at times, depending on vessel, so you don't want to be at those coordinates.

Go to your rescue vessel. Select the landing autopilot. Choose "pick target from map". Pick one. Any one. Change the coordinates to the ones you noted down before (where our unlucky Kerbal was). Mind "East"/"West" and such...

(There was a bug in MechJeb a while back, not sure if it is there anymore. If you typed in the coordinates directly, MechJeb did weird stuff...)

Execute...

Depending on your vessel, MechJeb should land at the coordinates or pretty close by.

Edited January 18, 2015 by Tokay Gris

[Orange_Slime_]

For me, I have to use mechjeb for landings and such, I just don't have the ability to land a ship, or sometimes even make an orbit in career, so If I want to get anywhere, mechjeb is key. I know there are haters saying its all cheat, but I only use it when I have tried a maneuver or landing at least twice. Now to figure out why my ship keeps pushing the apopasis up on the circulization burn...

[Geschosskopf]

1)I need help with achieving orbit use Mechjeb, I’m trying to land on the Mun. I got to the point where I’m heading towards the Mun but my Apoapsis is within the core of Mun & I have to circularizing my orbit (anywhere from 19 Km to 50Km) & I still crash into the surface Mun.

I'm assuming you mean your Mun periapsis (not Ap) is underground?

This is very easy to fix without MJ, or with it, take your pick, assuming you do this as soon as you enter Mun's SOI. The further out you do it, the better.

Manual method: Rotate the ship to point to Radial + and burn very slightly for a very short time (like tap SHF, then X in rapid succession) while watching your trajectory. Keep doing this until you get your Pe above the surface at the desired altitude.

MJ Method: Select Maneuver Planner. Select "Change Periapsis". Enter the desired Pe altitude. Select "at a time" and enter 30s (meaning 30 seconds from now). Hit "Create and Execute".

Once you have your Pe where you want it, then you just need to circularize once you're there. The MJ method is as follows:

Select Maneuver Planner. Select "Circularize". Select "At next Periapsis". Select "Create and Execute".

2)I was able to land on the Mun twice but I’m not sure how I did it, but I have 3 Kerbals Stranded on Mun without enough fuel to dock with the Space Station waiting in orbit. Therefore are there any tricks of landing another Lander within a few meters of the Stranded Lander & her Crew?

MJ has a Landing Guidance mode. All you need to do is give it a target and it will bring your ship down within a few meters of that point. In the version you're using, normally it would land about 10-20m due west of the target. However, sometimes it would come down right on top of it, so be sure to quicksave before starting the descent so you can try again if bad things happen .

Anyway, it goes like this:

First off, have your ship in an orbit about 100km up. MJ likes that better. Then select Landing Guidance. Go to the map view and select your stranded ship as the target. Make sure all the checkboxes in the Landing Guidance screen are where you want them (desired final speed, MJ operates landing gear, etc.). Then just hit the "Land at Target" button and watch the show.