Does getting to other planets require a lot of precision?

[Stealth2668]

Managed to land on Mun and Minmus manually which wasn't too hard (only 1 kerbal casualty) and today I managed to get to Duna using mechjeb just to get a feel for things. At one point my nearest approach to Duna was about 625 km and to fix this I used mechjeb (Hohmann transfer command) and that created an encounter but it only required 4.4 dV and pinpoint accuracy. With so little room for error how does anyone manage to go to other planets manually when you need to be super precise? Is mechjeb just doing something weird or the "hard" way?

[TwoHedWlf]

A lot of precision? Yeah. But it's not overly difficult. What I do is get out of kerbin's sphere of influence then you can just create a maneuver node and fiddle with it until you get it close. It can be really fiddly because a fraction of a meter per second can be the difference between a close pass and totally missing. Then after you've finished thrusting for that one do another manuever node about halfway there to tweak your course. Usually should be enough to get right where you want to go.

[Joe_Bender]

I find that playing while drinking too much beer tends to lessen the chances of a successful trans-orbital flight by a factor of ten.

[Stealth2668]

I tried setting up a manual node without using mechjeb but I just couldn't get an encounter. I was adjusting for like 10 minutes and when I used mechjeb, I had to wait for like 40 days before an encounter was possible. How would you even know that without helpful mods like mechjeb, protractor etc.?

[Vanamonde]

It is a small target to hit in proportion to the distance, but as TwoHedWif points out, you can mess with maneuver nodes and mid-course corrections until you bring the path of your ship to coincide with the path of the planet.

[Stealth2668]

^ True but getting that initial path is a pain.

[tuguley]

You could use protractor. It gives you a somewhat accurate indication, but it still requires you to do the burns manually and more often than not, perform mid-course corrections.

[Mercedoniusinter]

Short of using protractor or mechjeb to get the phase angles you can eyeball the trajectory if you memorized them. The trick is once you think the planet is in the right place, set up your burn initially where you align your escape trajectory with kerbin's orbit and burn until you hit the target planet's orbit. Once you see the closest approach you can either wait until the intercept aligns, if you are early, which will save delta v. If you are late you will have to expend more delta v burning past the optimal path to shift your apoapsis or periapsis to an intercept.

As for corrections the earlier you are the less delta V you need to make corrections, however, this also means it is difficult to make an optimal trajectory and fine tune the results. You can either use RCS or wait until later in the orbit where it is less sensitive to fine tune your approach.

Also another trick if you don't want to memorize and eyeball the phase angels at all is to burn until you are slightly outside or inside the target plant's orbit(Whichever uses less delta V) and circularize it. From there you wait until your spacecraft is at the same angle relative to kerbol as the planet is. Once there just burn either prograde or retrograde(Depending on whether you are inside or outside the orbit respectively) until you get an intercept with the planet. This method is a surefire way to get you to another planet regardless of your planetary alignment however it does use more delta v and it also usually takes a LONG time. This is the method I used to get to eve before we had maneuver nodes, since I couldn't get an intercept even with protractor.

[Exal]

It's not to hard if u just think about what a certain type of thrust does firmest make sure ur planes are the same then go prograde to reach the targets orbit then fiddle with moving the while node and prograde and retro grade till I get an encounter then use the blue use to fine tune ( don't know the name for them) that should get u at least a decent encounter

[Scotius]

And remember: you can drag open node circle along the trajectory by holding left mouse button. It will let you delay or speed up start of the burn. I found it very useful. Another useful trick is entering target's SoI in real time, with time warp disabled - this way your PA will stay roughly the same as was set. With time warp engaged it can jump around significantly.

[RoboRay]

Lots of precision or lots of corrections.

As you noted, tiny delta-v changes make big differences on interplanetary missions. Even if you're not planning to dock during the flight, you may want to bring along an RCS tank and a thruster or two to make the fine trajectory adjustments easier. You can pin-point a precise aerobraking pass from halfway across the solar system like that.

[Karriz]

Duna and Eve are fairly easy targets. You just need to know the angle that's between the planets, for example with Duna it's ~40 degrees ahead Kerbin.

With maneuver nodes you can see how to get inside the SOI, and then just do some corrections to lower the periapsis.

[simonh]

Small changes early in the journey are magnified enormously at the destination. Either you need to hit the nail bang on the head from the start, **Cough** Mechjeb **Cough**, or you'll need to wait until you're closer and make an easier, but more expensive corrective burn then.

Oh, and use Nuclear rockets.

Simon Hibbs

[MBobrik]

Set the planet as your target and then even when you have no encounter you will see whether the planet will be ahead or before you, above or bellow you at the point of closest approach. And then just fiddle with your velocity and direction and see how the markers move and you will soon discover that it is not very difficult to move them towards each other and when they are all close enough, you will get an encounter. Then you can fiddle with them some more to lower your periapsis. I usually get it down to a few dozen kilometers and then I adjust it just after entering the SOI.

[Elemental]

I have found if you first make sure you are on the same orbital angle, the encounter becomes fairly easy to get... that seemed to be the trick for me. Some have very small SOI's which make it all sorts of finicky though.

[Anglave]

I learned (manual) planetary transfers before Maneuver Nodes. The nodes make it almost trivial. It does help to understand what different vectors of thrust will do to your orbit, and to have some practice and "feel" for how much dV it's going to take to make a given change.

Yes, it requires some precision, but if you get your departure angles right it's really not that hard to set up a maneuver to encounter any planet in the system. The angles are forgiving enough that I figure them by eye, and if you mess up the maneuver while you're planning it, just scrap it and start again. This is much easier than the "perform the maneuver, then see if you got an encounter" method of 0.17 and before.

I do wish there were a "fine tune" mode to the maneuver nodes. Sometimes the smallest adjustment I can make is much too large. And the UI for adding and manipulating nodes needs improvement. All too often I have to zoom clear in to select the node, then clear out to adjust it, and after each adjustment it becomes un-selected, so I have to zoom clear in to select it...

Hitting a planet from half way across the system takes a lot of precision. But setting up a reasonable Hohmann transfer in-game really isn't overly difficult.

Edited May 14, 2013 by Anglave