[Tutorial Video] Mission to the Mun and Back

[Kosmo-not]

This is an uncut video of my most recent mission to the Mun and back using the Koalemos II. Some special thanks goes to sjwt for asking for a video featuring this rocket.

Please, if you have any questions about a segment of the mission, ask them.

http://youtu.be/GzEEcNnBxqM

*correction on TKI velocity*

The ideal velocity is 839.5m/s (assuming a perfect trajectory), and not the 846m/s stated in the video.

[grovest4life]

Good video it answered some of the questions I had about direct Mun decent vs establishing an orbit and also how to escape the moon with a close periapsis to Kerbin for reentry.

[BillWiskins]

Now that is a useful video. Makes the beefy, six thousand fuel tank monsters everyone else (I) use seem a little silly by comparison.

I have a question, though it is not a particularly difficult one (and not specifically related, either). I would really like to know how to enable flight controls in the map screen. It\'s obviously so much easier, but whether it\'s through lack of observation, general stupidity, eddies in the space-time continuum, whatever - I just can\'t figure it out.

Anyway, lovely video and some lovely music on there, as well.

[Endeavour]

Great video. Could you explain why you reduced throttle at takeoff further? You said the Goddard Problem, but i\'m not sure how to apply it.

[Kosmo-not]

I have a question, though it is not a particularly difficult one (and not specifically related, either). I would really like to know how to enable flight controls in the map screen. It\'s obviously so much easier, but whether it\'s through lack of observation, general stupidity, eddies in the space-time continuum, whatever - I just can\'t figure it out.

You need to raise the navball on the map screen. Click the tab on the bottom center of your screen to bring it up.

Could you explain why you reduced throttle at takeoff further? You said the Goddard Problem, but i\'m not sure how to apply it.

If there is no air resistance, the obvious amount of thrust to use to maximize fuel economy is as much as possible. Air resistance is why there\'s an optimal thrust to weight ratio. The force do to air resistance is proportional to velocity to the second power. If you want to double your velocity, you need to quadruple your power (not including power to overcome gravity). You would probably agree that going too fast chews up a lot of power, while having a very small marginal return of velocity gain. You would also agree that not using enough power to leave the launchpad (because of gravity) is also very bad on your fuel economy. There has to be somewhere between the two that fuel economy is maximized.

The Goddard Problem is finding the most fuel efficient way to vertically ascend through an atmosphere. If you do the algebra, you will find that the most fuel efficient vertical ascent is one in which drag equals weight.

[sjwt]

Thanks for this, a nicely done how to, with good tips!

[UmbralRaptor]

Very impressive. Can you explain a bit more about what you did to raise your periapsis at the end there? (What direction you want to burn and why?)

[Kosmo-not]

Very impressive. Can you explain a bit more about what you did to raise your periapsis at the end there? (What direction you want to burn and why?)

At the time, I just knew that changing my velocity vector direction would be more effective than just burning prograde. I did some calculations just before typing this reply, and it seems the most ideal angle to thrust at in the particular case of this video was around 73° above the local horizon. I burned at about 55° in the video. Due to the cosign effect nature of this situation, my burn was very close to optimal.

Looking more at the spreadsheet I had made, it seems that, for a given delta-V, the most effective direction to burn in to maximize periapsis is one that minimizes your velocity vector\'s elevation angle (the angle between it and the local horizon). An easier way to think about it is to change your vector until it it level with the horizon, and then add velocity prograde after that if needed.

P.S.

Thanks for asking this question. You made me learn something.

[Rico88]

Now this is what I call fuel efficiency, great tutorial. It made me realise some of my mistakes.

[BillWiskins]

You need to raise the navball on the map screen. Click the tab on the bottom center of your screen to bring it up.

I knew it would be right in front of me. Cheers, sir.

[Zephram Kerman]

Very nice encapsulation of many concepts. Of course, to completely cover orbital mechanics and rocket science in one short video would be utterly impossible. But you\'ve picked out the most urgent ones, and squeezed them into a remarkably brief nutshell.

Most of these concepts are relatively advanced, and less useful to someone searching for an actual step-by-step tutorial. There are plenty of those, so maybe change the name to something more accurate, like 'Intermediate Rocket Science for Dummies Kerbals' or some such.

The music makes me think of cinematic 'happy moments' flashback scenes, with giggling white-clad children frolicking in slo-mo sprinklers and a hazy lens. : It doesn\'t fit your stern demeanor, but at least it isn\'t trite or cliche.

[Kosmo-not]

I\'m thinking about making more tutorial videos. Any requests?

[Endeavour]

Could you do a tutorial on a quick orbital rendezvous?

[Kosmo-not]

Could you do a tutorial on a quick orbital rendezvous?

I was planning on doing one about orbital rendezvous. What would you define as quick?

[Endeavour]

I\'d say within a few orbits would be quick so long as the method works at any altitude. Under 150km time warp is pretty slow, so if it can be done in an orbit or two I would consider that quick.

[Caleb1]

At the time, I just knew that changing my velocity vector direction would be more effective than just burning prograde. I did some calculations just before typing this reply, and it seems the most ideal angle to thrust at in the particular case of this video was around 73° above the local horizon. I burned at about 55° in the video. Due to the cosign effect nature of this situation, my burn was very close to optimal.

Looking more at the spreadsheet I had made, it seems that, for a given delta-V, the most effective direction to burn in to maximize periapsis is one that minimizes your velocity vector\'s elevation angle (the angle between it and the local horizon). An easier way to think about it is to change your vector until it it level with the horizon, and then add velocity prograde after that if needed.

P.S.

Thanks for asking this question. You made me learn something.

Great job man. Props for you lol. I know I would just use alot of trail and error. Thank you

[closette]

At the time, I just knew that changing my velocity vector direction would be more effective than just burning prograde. I did some calculations just before typing this reply, and it seems the most ideal angle to thrust at in the particular case of this video was around 73° above the local horizon. I burned at about 55° in the video. Due to the cosign effect nature of this situation, my burn was very close to optimal.

Cosine I think, unless someone needs to cosign your loan for the spacecraft

OK I always seem to be the one to ask - how did you calculate that? I can see how to do so in principle - at a given position, a change in velocity vector delta-v will change the orbital energy and angular momentum, related to semi-major axis a and eccentricity e , and the periapsis is just a(1-e), but it seems like an involved calculation to find the direction (and magnitude) of the minimum delta-v required. (And i could not find any version of this already worked out online).

Even a brute-force search over magnitude and angle (with a spreadsheet) would be quite impressive, but you\'d have to do it for each situation.

Care to share how you did it?

This comes up a lot when entering Kerbin\'s SOI on the way back from the Mun.

Thanks in advance?

[Kosmo-not]

Cosine I think, unless someone needs to cosign your loan for the spacecraft

OK I always seem to be the one to ask - how did you calculate that? I can see how to do so in principle - at a given position, a change in velocity vector delta-v will change the orbital energy and angular momentum, related to semi-major axis a and eccentricity e , and the periapsis is just a(1-e), but it seems like an involved calculation to find the direction (and magnitude) of the minimum delta-v required. (And i could not find any version of this already worked out online).

Even a brute-force search over magnitude and angle (with a spreadsheet) would be quite impressive, but you\'d have to do it for each situation.

Care to share how you did it?

This comes up a lot when entering Kerbin\'s SOI on the way back from the Mun.

Thanks in advance?

Good catch on the typo.

What I did was give myself a starting altitude, elevation angle, velocity, and a delta-V. I calculated the resulting periapsis for a range of delta-V elevation angles. I could change any of the fixed values and observed that periapsis was highest for delta-V angles which brought the resultant elevation angle closest to zero.

[Cykyrios]

Very good tutorial! I don\'t have much trouble going to the Mun and back anymore, but your video made me realize that my ascent was far from optimal (and my rocket\'s far too big), while the rest was probably okay.

As for a rendezvous tutorial, I\'d suggest a 200-ish km orbit, or at least something over 150 km so time warp isn\'t too much of an issue.

[ChronicSilence]

Great vid! Sounds awfully like that soundtrack used on the 'Most Astounding Fact' video. Coincidence?? I THINK NOT!!

If you\'re going to do another video, I\'d really like to learn more about:

1) properly changing orbital planes, i.e. what effects different types of burns (angles) will have

2) how to calculate how to land at the space center (or just off the coast) when de-orbiting (or coming back from Mun)

[Apotheosist]

Superb video and tutorial! You would benefit the KSP community hugely by continuing with more tutorials. I personally have recently been researching into the physics of the game. I finally know how to calculate delta-v. Although I don\'t fully know how to integrate. I\'ll be studying that next at school. For now I use an online dV calculator to do that bit. I did manage to work out the exhaust velocity of the stock engines. They are all the same at 5681.82m/s. I\'m also trying to find the thrust and exhaust velocity of RCS, to see which is most efficient. I was thinking it would be useful to know approximately how much delta-v is needed to get to certain places in ksp. I was, in fact going to use your craft, knowing you fly it efficiently, and work out the approximate minimum delta-v needed to get into orbit, to the mun, and so forth. A delta-v map for the kerbol system would be handy. Perhaps you could make a tutorial about change in velcoity calculations, and how one can use this to design craft. I know this would certainly help me a lot. Or you could just tell me. But then there wouldn\'t be a very well made video tutorial for everyone else to learn from

[Guest]

Can\'t get it right controlling the lift off at 10,000m 12,000m its way to hard to control it.

[hubbazoot]

Kosmo-not, I mean this in the best way possible... you\'re disgustingly good at this. What sort of background has given you this 'knack?'

I\'m going to an engineering school, but there\'s no aerospace study here, so I don\'t have much of a background in that.

I\'m mostly curious about your orbital burns. I find that when I turn sideways as quick as you did, it doesn\'t work for me.

My general approach is 90deg (straight up) until end of lower atmosphere, then 70deg through the next layer, then 45 deg until I reach my target Ap, I do my acceleration burn at my Ap to 'round it out.'

[Kosmo-not]

Kosmo-not, I mean this in the best way possible... you\'re disgustingly good at this. What sort of background has given you this 'knack?'

I\'m going to an engineering school, but there\'s no aerospace study here, so I don\'t have much of a background in that.

I\'m mostly curious about your orbital burns. I find that when I turn sideways as quick as you did, it doesn\'t work for me.

My general approach is 90deg (straight up) until end of lower atmosphere, then 70deg through the next layer, then 45 deg until I reach my target Ap, I do my acceleration burn at my Ap to 'round it out.'

I\'m a student in mechanical engineering. I got addicted to KSP back in January with no more than a very basic understanding of orbital mechanics. My curiosity on how things work on a fundamental level has led me to the knowledge I have now. If there\'s one thing I love to do, it\'s to analyze things (hence, why I chose engineering). It only requires a couple basic principles to derive a lot of this stuff.

As for ascending out of an atmosphere: I\'ve developed a 'feel' for it through repetition. The goal is to minimize your energy loss due to gravity drag and air resistance. I don\'t yet have any mathematical solution for this.

Here are two principles that will get you going if you want to derive some orbital mechanics for yourself:

Conservation of angular momentum.

Conservation of orbital energy.

[hubbazoot]

I\'m a student in mechanical engineering. I got addicted to KSP back in January with no more than a very basic understanding of orbital mechanics. My curiosity on how things work on a fundamental level has led me to the knowledge I have now. If there\'s one thing I love to do, it\'s to analyze things (hence, why I chose engineering). It only requires a couple basic principles to derive a lot of this stuff.

As for ascending out of an atmosphere: I\'ve developed a 'feel' for it through repetition. The goal is to minimize your energy loss due to gravity drag and air resistance. I don\'t yet have any mathematical solution for this.

Here are two principles that will get you going if you want to derive some orbital mechanics for yourself:

Conservation of angular momentum.

Conservation of orbital energy.

I have enough background knowledge to be conceptually comfortable with doing it. I was really wondering what your 'ascension curve' looked like as you climbed through different altitudes. (I.E. what you\'re looking for at each altitude.)