Launching Directly to the Mun

[Midnight Star]

I was wondering if anyone could give me some information on how to do a launch which would require no transfer orbit.

While I\'m at it, any links to how to do this the hard way (actually doing math) would also be appreciated.

[DeltaBravo]

Boost straight up till your AP is about the same altitude as Munar orbit, cut engines and coast to AP, turn and burn till you\'re in orbit (either in same direction or opposite direction of Mun), and then do insertion as necessary.

[vexx32]

It is, however, highly dependent on timing if you want to boost straight into Munar orbit. There is no such thing as moving in a straight line when talking about space -- things always follow a curved trajectory, even if the curve is so slight it looks to be a straight line. Gravity\'s fault. It is possible to try to get directly to the Mun, but keep in mind that first it is very inefficient and would require you to design a craft that can apply thrust for much longer than most other craft and second that you are capable of basic orbital maneuvers to be able to correctly arrest your momentum when you get close to the Mun so as to avoid just flying directly into it at full speed.

[Midnight Star]

It is, however, highly dependent on timing if you want to boost straight into Munar orbit. There is no such thing as moving in a straight line when talking about space -- things always follow a curved trajectory, even if the curve is so slight it looks to be a straight line. Gravity\'s fault. It is possible to try to get directly to the Mun, but keep in mind that first it is very inefficient and would require you to design a craft that can apply thrust for much longer than most other craft and second that you are capable of basic orbital maneuvers to be able to correctly arrest your momentum when you get close to the Mun so as to avoid just flying directly into it at full speed.

Well yeah, what I meant is something like what I attached.

[vexx32]

It could work, but is by no means a foolproof method. I suspect a great deal of trial and error will be necessary, as the momentum imparted by kerbin\'s spin will not increase as depicted in the pic. I mean, the Mun moves at around 542m/s from memory, whereas the lateral momentum gained by the rotation of Kerbin will be much less than that. As such, it\'s highly likely you\'ll miss the Mun if you try to launch when it\'s overhead and go straight to it without applying further lateral thrust (i.e., not going directly up).

As stated, timing it is going to be a bit of a pain.

[Midnight Star]

As stated, timing it is going to be a bit of a pain.

Well yeah, that\'s kind of the point though. It takes fuel to make a circular orbit, wait and then burn towards the mun right? I\'m trying to figure out at which orientation of the mun will it take to lift off as if going into orbit (doing a gravity turn starting at about 15km and flattening it out at about 35km+) but instead of making a circular orbit, just keep burning until you hit 11kkm require to reach the mun.

I mean, in theory, you COULD burn directly up to 11kkm and hit the mun if you waited for the mun to be the right angle, but you would be fighting gravity the entire time and would be less efficient

The pic was a rough example that I did in 2 seconds >.> it isn\'t what I believe would be the actual method.

[vexx32]

Takes no fuel to wait, and it\'s easier to alter and established circular orbit than fight gravity by burning directly against it constantly all the time. Altering an orbit is just burning horizontally, which meets no real gravitational resistance. As such, it\'s more efficient to establish an orbit (eccentricity is largely irrelevant) outside Kerbin\'s atmosphere, and the general guide from there is to wait until the Mun rises over the horizon of Kerbin, then burn until your orbit\'s at about the Mun\'s altitude.

[Midnight Star]

Takes no fuel to wait, and it\'s easier to alter and established circular orbit than fight gravity by burning directly against it constantly all the time. Altering an orbit is just burning horizontally, which meets no real gravitational resistance. As such, it\'s more efficient to establish an orbit (eccentricity is largely irrelevant) outside Kerbin\'s atmosphere, and the general guide from there is to wait until the Mun rises over the horizon of Kerbin, then burn until your orbit\'s at about the Mun\'s altitude.

I think you\'re missing the point.... I know how to get to the Mun and Minmus. I\'ve done plenty of times. The point of this thread is that I\'m asking if anyone knows at what angle would it take so that I wouldn\'t have to make a circular orbit and just keep burning once I\'m burning at a pitch of 0 degrees or how I could find out using physics/math/etc.

[vexx32]

Hmm. I suppose... you could do a nice guess, check and refine method with some extra maths for optimal refining, but I suppose it\'d be possible to do with plain equations.

Here\'s me doing Physics in high school and I can\'t even be bothered to go get the relevant equations for this even though we did it last term... -.-

Ah well.

[Midnight Star]

Hmm. I suppose... you could do a nice guess, check and refine method with some extra maths for optimal refining, but I suppose it\'d be possible to do with plain equations.

Here\'s me doing Physics in high school and I can\'t even be bothered to go get the relevant equations for this even though we did it last term... -.-

Ah well.

Which is why I made this thread, I\'m wondering about what the math is involved unless someone has already done it. Moreover, I would like an educated guess rather than doing it 'the kerbal way' aka before I spent the next 5 hours launching ships up to orbit, getting it to 11kkm and seeing if an intersect vector appears.

I figured that if you launched x minutes earlier than when the mun would appear over the horizon, where x minutes is the amount of time it takes to an altitude of 80km or a velocity of ~2100 m/s, it would work but it\'s a bit hard to get it to work, especially since it\'s difficult to determine the correct angle the mun needs to be at.

[CanuckOverlord]

The obvious, kerbal way is to go up to Mun\'s orbit, miss it; then chase it down.

[honolululu]

If I\'m not mistaken, a fresh persistance file will present the Mun in such a position that a straight burn will have Munrise at the \'correct\' time.

That can\'t be right. Post or check first? Let\'s go Kerbal!

...how do you get a fresh persistance. Delete the old? Decided to search and found this.

This is I think where I heard it.

Post 5 http://kerbalspaceprogram.com/forum/index.php?topic=8359.msg122800#msg122800

Xivios

I\'ve also noted that a fresh persistance file will allow a fairly direct ascent with no Kerbin orbit if you pitch over about 30 degrees east and hold it there until apoapsis is at munar orbit. But that only works for your first launch, or a demo launch.

EDIT: Oops, forgot to add the I was only trying to help you reverse engineer the math from the right launch time without trial and error. Now to test.

[Atimed]

I was wondering if anyone could give me some information on how to do a launch which would require no transfer orbit.

- If you mean burning straight up until you reach the moons SOI..

- Go to orbital view, and wait until the Mun is 90° Right..(East, HDG 90°) from the launching pad..

- Launch and bur straight up..

- Wait for a intercept trajectory..

- Depending on your rocket wait around 20\'000m 35\'000m and burn Retrograde, and hope it works..

- Land..

---

- This consumes a load of fuel because of gravity drag..

- But is a quick and dirty way of getting there..

[Sky Visitor]

Well you could calculate the arclength with the differential displacement of the Mun along the curve of it\'s orbit, solving for the angle required between r1 and r2 within a plus or minus range consisting of the Mun\'s sphere of influence, all based on your velocity toward the curve which would get you captured by the Mun. As such it would be better to calculate using your distance and velocity on each launch, because there is no set 'angle' as you do not always launch at the same position relative to the moon; there is a constant difference between two radii but it moves around the curve with the Mun. Thus, your velocity is the variable. I\'m quite busy within the next couple weeks so I don\'t have any time to set up the equations but it seems like it would be fun (yes math is fun, I am an engineer )

[Zephram Kerman]

In the demo game version 0.13.3, we could launch immediately and interrupt the gravity turn at about 30° - 45° pitch. Just keep burning at that pitch angle until AP = 11 M km. Thanks to Oberth effect, the fuel penalty is not too bad.

I think the simplest way to know the correct launch time is to do the flight once, and measure the difference.