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Trouble On Tutorial: To The Mun, Part 1


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Hello everyone! After asking on here for some advice about good goals, most people said to go to the Mun/Minmus. I decided to do this, and I was going to do the in-game tutorial 'To the mun, part 1' I do the part where you plot your maneuver and do the burn, but this pretty much uses up all my fuel! I do not have enough to burn prograde near the Mun in order to get into Munar orbit. I tried it many times, and I barely have any more fuel. How can I save fuel and actually complete the tutorial? Thanks!

Edited by CaptainApollo
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I have just tried that tutorial again to see what they give you to do it with. The supplied ship has enough fuel on board to do the burn to get you to Mun, and also to burn retrograde when you get there to establish an orbit. Once in orbit, you should still have fuel left, though I found it wasn't quite enough to actually land on the surface, though with slightly better flying it might just be possible.

Having said all that, you say you are virtually running out of fuel after your first burn. I found that with a correctly positioned manoeuvre node, with the prograde handle pulled out far enough to get a good Mun intercept, the indicated burn was less than 800 m/s. If yours is showing a lot more than that, then you need to juggle the manoeuvre node to give you a more favourable burn. I can't imagine that there is anything you are doing during the burn itself that would waste fuel unnecessarily, so have a play with the node, and let us know how you get on.

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I haven't bothered with the tutorials - unless you get some reward from them, they seem poorly produced and don't explain things that well. I learned plenty watching Scott Manley's latest beginners guid on youtube and then trying things out myself.

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I will play with the node later on when I do more KSP, and I will tell you the results.

- - - Updated - - -

At the moment, my burn is 1886 m/s. I suppose this is too much, and I am trying to correct it, but having trouble..

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I do not have enough to burn prograde near the Mun!

Surely you mean retrograde here :P

You are likely coming in too hot. An ideal Hohmann type transfer is an wide ellipse whose apoapsis just barely touches the sphere of influence of the body right as it arrives in that same spot. This saves you fuel both accelerating as you leave and decelerating as you arrive.

At the moment, my burn is 1886 m/s. I suppose this is too much, and I am trying to correct it, but having trouble..

Yeah, way too much. For the Mun you only need to wait in time to leave orbit at the right phase angle. For other bodies, you will usually need to also wait for the right time window due to the relative inclination change. Another way to judge when to leave for the Mun, is that the right time is just after Mun rise over Kerbin when you are in LKO.

Edited by cybersol
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You don't see your maneuver go into Mun's SoI, so no, it's not good.

Try put the maneuver at the place where prograde points to the Mun's current location (i.e. if you eyeball, burn when Mun is rising from Horizon). Expected dV is ~860 if you're in LKO, and maybe less if you're higher.

Try make your maneuver touch Mun's SoI first, and then fine tune so that Pe is 10km~20km

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The updated trajectory will get you an encounter, but there is still room for improvement, if you play around with the maneuver position and delta-v a bit. Ideally you want an angle between Mun's current position and your projected encounter position of around 90 degrees.

The plotted maneuver will acutally get you on a collidion course with Mun: See how the purple part of your trajectory does not have a periapsis value. You can improve with very small adjustments of the maneuver to get a nice close encounter.

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I updated my previous post, is this better?

- - - Updated - - -

I believe I have an intercept now.

Much, though not ideal. You are passing over, and then coming back to, the Mun's SoI. Ideally you want the Mun to capture you as you head out, not when you start to fall back. Lower your apoapsis (by pulling the retrograde handle) and move your node around until you get an encounter, if your Mun periapsis is too high you can burn radially just inside the SoI to fix it for only a few m/s of dV, which would still leave you plenty for the capture burn.

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Taki, I posted yet another image above, I think it's better now. Or no?

Still have the same issue I'm describing. Whether you have a periapsis or not is irrelevant since it is an easy adjustment to make once you are just inside the Muns SoI and a radial burn will fix it. (The radial burn is generally no more than 5m/s)

Ideally you want something that looks like this:

ZgKcn4p.png

Disclaimer: Not my pic.

Edited by Taki117
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This will get you to the Mun, mission accomplished!

There is still room for improvement in your future attempts, as Taki mentioned you overshoot the target, which is not the most efficient way to go. This will not matter in the tutorial, but when you build your own rocket and delta-v is in short supply, being more efficient helps a lot.

Keep it up and play around with the maneuvers a bit if you like. This can be very delicate because tiny changes in the maneuver can change your encounter a lot.

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Taki, I posted yet another image above, I think it's better now. Or no?

You're burning almost 180° away from the mun so you're having to raise your apoapsis beyond the Mun's orbit in order to slow down and wait for the Mun to catch up. You want to be closer to 90°, so if your orbit is extending out to the top of the screen (12 o'clock position) the Mun should be to your right (3 o'clock position).

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Still have the same issue I'm describing. Whether you have a periapsis or not is irrelevant since it is an easy adjustment to make once you are just inside the Muns SoI and a radial burn will fix it. (The radial burn is generally no more than 5m/s)

If you are on a collision course the correction burn is a lot more expensive for Mun in my experience. It is rather cheap for planetary encounters, but because Mun's SOI is comparably small while you are going fast, you can burn a lot of fuel if you do it after you enter SOI.

It's always best - and cheapest - to set it up correctly as early as possible, in this case a single digit amount of delta-v will always do the trick.

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I will follow this, as I used too much fuel. I will try, try again!

- - - Updated - - -

Thanks everyone, in am now in a perfect Munar orbit, and I will attempt a landing with the little fuel I have!

- - - Updated - - -

Unfortunately no landing, due to loss of fuel... But just look at these happy and proud Kerbals!

screenshot10.png

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  • 1 year later...

Your node is in the wrong place ... that's twice what you need to escape Kerbin's SoI and you'll go screaming by the Mun.  Reduce your burn so it just touches Mun's orbit, then slide the node till you get an intercept.

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