Cannot get to the Mun and back without running out of fuel.

[Deseoso]

I have been trying to learn this program by watching Scot Manley's tutorials he did on YouTube. I am completely stuck on the fourth one though. Can anyone help?

In this tutorial Scott alters a rocket to get to the Mun. He then launches and enters an orbit of approx 105K above Kerbin. He then does a burn to leave Kerbin and enter an orbit around the Mun.

Up to this point I can copy him almost exactly and everything is fine. I run into problems trying to do what he does exactly 20 minutes into the video. When Scott sets up a maneuver node so that he can escape the Mun's orbit he sets up a trajectory that not only escapes the Mun but also puts the Apoapsis of his new trajectory to within Kerbins atmosphere so that he can land on the planet without the need for another burn.

When I place a maneuver node on my orbit around the Mun I cannot achieve the same trajectory regardless of where on the orbit I place it or how long I set to burn for. The closest I can get the Apoapsis of the new trajectory to Kerbis is about 500k. This means that I need to do another burn as I approach Kerbin in order to change my trajectory so I can land but then I always run out of fuel.

I tried to add more fuel but that also adds more mass which means I have to burn more fuel to achieve orbit in the first place so I still run out of fuel. Anyone have any ideas? I'm stumped.

[diomedea]

I would bet you entered in orbit around Mun at an angle (above or below the equatorial plane) so resulting in an inclined Munar orbit. Leaving a highly inclined Munar orbit, you may never have a viable solution for a return trajectory just burning prograde, you also need to correct inclination.

[EdFred]

Change WHERE your maneuver node is. If your maneuver node is too early, or too late, your periapsis for Kerbin will be off. Once in Munar orbit, make a maneuver node of around 300dV. Now hold your mouse over the maneuver node circle and it should change to a more white color. When it does this, click and drag the maneuver node around the orbit of the Mun. You will see how where you burn affects your Kerbin orbit. Slide it until you get a periapsis that's inside Kerbin's atmosphere.

However, you do have you make sure that your orbit is near the Mun's equator for this to work well. If it isn't, still do what I mentioned above, but you will have to also use the pink markers on the maneuver node to get your periapsis close to Kerbin.

[monophonic]

If you can't get the return to happen by dragging the maneuver node around, remember that the farther away from Kerbin you make your correction burn the less fuel you need for it. So in case you still need to do it, it's best done right after you leave Mun's SOI.

Personally, my first time visiting Mun I had to wait a quarter month before returning because I didn't pay attention and took off into a near polar orbit. I didn't have the skill to correct inclination nor enough fuel to brute force my way home, so my only option was to wait until the Munar cycle brought Kerbin into my orbital plane. Thanks to time acceleration that wasn't as painful or boring (to me, poor Bob might disagree) as it may sound.

[Geschosskopf]

I would bet you entered in orbit around Mun at an angle (above or below the equatorial plane) so resulting in an inclined Munar orbit. Leaving a highly inclined Munar orbit, you may never have a viable solution for a return trajectory just burning prograde, you also need to correct inclination.

I have to disagree here. You don't need to change your inclination when heading home from a polar orbit at Mun. Just burn prograde on the inside of your orbit to escape Mun. This will put you into a highly eccentric polar orbit of Kerbin but with a Pe still pretty far from Kerbin. Once in Kerbin's SOI, burn a little retro at or near your new Ap to bring the Pe at Kerbin into the atmosphere and you're golden. I find this cheaper than doing a plane change and not significantly more expensive than coming home from an equatorial Munar orbit.

[Mr Shifty]

I have to disagree here. You don't need to change your inclination when heading home from a polar orbit at Mun. Just burn prograde on the inside of your orbit to escape Mun. This will put you into a highly eccentric polar orbit of Kerbin but with a Pe still pretty far from Kerbin. Once in Kerbin's SOI, burn a little retro at or near your new Ap to bring the Pe at Kerbin into the atmosphere and you're golden. I find this cheaper than doing a plane change and not significantly more expensive than coming home from an equatorial Munar orbit.

You can also just wait. A polar orbit where the plane of the orbit is parallel to the Mun's orbit around Kerbin is as easy to return from as an equatorial one.

[Wanderfound]

I had an absolutely glorious Minmus return tonight; used a Munar encounter in order to cut my orbit by half and drop my periapsis into the atmosphere, then smoothly aerobraked to a landing in a single pass. Didn't touch the controls once between leaving Minmus orbit and popping the parachutes.

This has minimal relevance to this thread, but I wanted to brag.

[Reactordrone]

Check where your escape trajectory from the Mun is pointing, you want it to be pointing back almost along the Mun's orbital path. If it isn't, move the node around until it is (as others have suggested). Moving the node might bring your periapsis inside the planet so just readjust your burn to get the desired altitude. It may also be that you're using too much fuel obtaining your initial orbit around Kerbin. I just flew the profile and had about half my fuel left when I got into Munar orbit and about 50 fuel left when I got back to Kerbin so there is a bit of excess fuel to play with.

[Deseoso]

Okay so I tried again a few times and I'm getting the same result. I have definitely not changed my inclination at all. I should be fully in line with the Mun's equator yet I still cannot get a decent escape trajectory. One thing I am confused by is why when Scott Manley does it in his video the projected orbit around Kerbin that he gets is elongated yet when I do it I get this big circular orbit. What am I doing wrong? See the pictures below.

The return trajectory that Scott Manley achieves:

The return trajectory I achieve:

[MarvinKitFox]

All i see wrong with that return trajectory of yours is... not enough speed.

You need to slap at least 80, maybe 120m/s more oomph on that munar ejection burn.

Your angle is, to a first glimpse, just about right on target. You just need more oomph.