How to get an encounter with another planet without a launch window

[MerlinsMaster]

Hey Guys,

I want to send a probe out to Duna. But I don't have a launch window anytime soon, but I've got a metric crapton of delta v. I've tried it a bunch of different ways, but every time I try to set a manuever node, I can never get an encounter. But there must be a way to do it.

Does anyone have a solution?

Edited October 20, 2014 by MerlinsMaster

[Lunaran]

http://alexmoon.github.io/ksp/

Tell it where you're going, when you want to leave, and click anywhere on the graph it generates. It'll tell you what it costs and what your ejection angle should be.

[Crown]

Tanuki described a method as "Hohmann transfer" (I wouldn't call it that but it might be the correct name for it). She used it to get back from Duna to Kerbin while there would have been a lot of time to wait for the transfer window. She had put the Periapsis between the orbit of Kerbin and Duna and then used a maneuver node near the periapsis to find an encounter with Kerbin. One restriction was that the time to wait for the next window was way shorter than the time that had passed since the last transfer window.

My attempt to reproduce this attempt would be:

1) you have to wait little: Put the orbit between Kerbin and Duna, and try to find an encounter using the maneuver node (just like with rendezvous in Kerbin orbit) near thee apoapsis

2) you have to wait a lot: put the orbit between Duna and Dres, and try the above

I haven't tried both myself. So I don't know if they would work.

[smart013]

http://alexmoon.github.io/ksp/

Tell it where you're going, when you want to leave, and click anywhere on the graph it generates. It'll tell you what it costs and what your ejection angle should be.

The latest dev version of mechjeb by the great sarbian has a point and click integration of this great helper as a experimental. Clicking on this graph automatically generates a manoever node with all the needed data and timing. This way flying to other planets is only a question of your available dv and not your window of opportunity, the same as by using alexmoons helper.

But of course my "look into the future" app tells me that there will come a "i do no mechjeb, i am leet and dis is cheeting!" Posting in 1-2....

Edited October 17, 2014 by smart013

[Riph]

How to get an encounter with another planet without a launch window

My solution is to do exactly the same thing you do when trying to make two spacecraft encounter each other, for example to dock a lander to an orbiter.

Here is a plan for Duna:

Step one: Escape Kerbin orbit. You are now in a circular orbit around the sun very similar to Kerbin's orbit.

Step two: Target Duna and match it's inclination (via the ascending and descending nodes.) DO NOT SKIP THIS STEP.

Step three: Burn prograde at your periapsis to push your apoapsis out until it is TANGENT TO DUNA's ORBIT. Observe that the 'next encounter position' markers have appeared in your orbit path and Duna's orbit path.

Step four: Watch the next encounter position markers. Since your apoapsis is tangent to duna, but your periapsis is not, you are on a SHORTER ORBIT than Duna, therefore you are circling the sun faster than it is. This means that your orbits will eventualyl SYNCRONIZE. Fast forward until your orbits are nearly syncronized.

Step five: Start using maneuver nodes AT YOUR APOAPSIS ONLY and find a prograde burn that simultaniously pushes your periapsis out to make your orbit match Duna's, and also encounter Duna. This may take several revolutions.

If any of this is baffling to you, practice docking orbiters and landers around Mun or Minmus. The procedure is essentially identical, and those moons are a much friendlier and more fuel efficient place to practice.

[Riph]

Also mechjeb is cheating

[ratchet freak]

using a parking orbit is probably easier:

get into interplanetary space in a matching orbit lower than the planet you want to encounter

make a maneuver node to raise the apo into the planet's orbit (aka standard Hohmann transfer)

move the node around until you have an encounter

execute node

then you will be on a collision course with the target's SOI

[SRV Ron]

Getting a transfer window at launch and using a Hoffman Transfer burn from Kerbal orbit will take slightly more Delta v then doing an escape from Kerbal orbit, not much more then getting a Minmus encounter. It will take about as much delta v to get the Duna encounter from a Kerbal escape parking orbit as it does to escape Kerbal itself. It make take a Kerbal year or two for that intercept window to show up. Otherwise, with massive amounts of delta V, you can try a direct approach.

Doing an aerobraking on Duna will aid getting you into orbit or direct to a landing using very little additional delta v. Go in at a shallow angle so you don't smash into the surface or end up with an unplanned landing. Aerobraking is very critical as to what altitude you aim for so save using F5 before executing the maneuver.

[Superfluous J]

I made a video of how to do this. I've got mods installed but it works 100% of the time with no mods.

But you should really have at least PreciseNode. And Kerbal Alarm Clock. They take away so much of the pain-in-the-arse from traveling around the Sunar system.

[Cannon]

Transfer windows aren't that hard, why avoid them?

[Sirrobert]

Transfer windows aren't that hard, why avoid them?

Thing is they don't stick around waiting for you to deceide you want to launch

[cantab]

Get into Low Kerbin Orbit.

Target the planet you want to get to.

Set a manouvre node with a prograde burn for the amount of delta-V you are able and willing to spend.

Drag that manouvre node *around* your parking orbit until you see a close approach to your target planet. You may need to fiddle with the camera orientation so you can see Kerbin in the foreground and your close approach markers in the background.

Refine that close approach into your proper encounter.

If you never see a close approach, it means you're trying to leave at a really bad time, such that it would take more delta-V than you have.

[DerekL1963]

Thing is they don't stick around waiting for you to deceide you want to launch

So, plan ahead. And use Kerbal Alarm Clock to let you know when a window is approaching.

[Pecan]

So, plan ahead. And use Kerbal Alarm Clock to let you know when a window is approaching.

You're right, of course, but there are times - life support mods, challenges, Bob's wife's birthday - when you just have to transfer outside an efficient window.

[EdFred]

Also mechjeb is cheating

I have better things to do than babysit a 25 minute burn.

[MerlinsMaster]

Doing an aerobraking on Duna will aid getting you into orbit or direct to a landing using very little additional delta v. Go in at a shallow angle so you don't smash into the surface or end up with an unplanned landing. Aerobraking is very critical as to what altitude you aim for so save using F5 before executing the maneuver.

That's why I always use this little beauty:

http://alterbaron.github.io/ksp_aerocalc/

[MerlinsMaster]

http://alexmoon.github.io/ksp/

Tell it where you're going, when you want to leave, and click anywhere on the graph it generates. It'll tell you what it costs and what your ejection angle should be.

Oh yeah...I forgot that's what porkchop plots are for. I also forgot it gives you the ejection angle. Thanks.

[Superfluous J]

I reread your first post, and thought you were trying to find a window but now see you don't want to wait for one.

First off, you should wait for one. You'll almost guaranteed get there quicker (both in wall-clock time and Kerbin time) if you do.

Secondly, if you really don't want to wait, do this:

1. Burn to get your apoapsis out to Duna, or whatever planet you're going to. I don't suggest this for Jool or Eeloo (or even Dres) because you'll be top-speed-time-warping a LOT and out there it's still SLOOOOOOOOOOW.
   
2. At your AN/DN, burn to get your orbit lined up with Duna.
   
3. Tweak until you see encounter markers. They likely won't be anywhere near each other but no biggie.
   
4. (Yes, so far this is exactly what you'd do to get to Duna if you started in a launch window. You're just doing it without the window.)
   
5. Time warp out until you pass your encounter marker. This will make the other marker jump somewhere else.
   
6. Burn prograde or retrograde (whichever makes Duna's marker get closer to yours) until the markers get really close. Eventually, you'll get an encounter.
   
7. Time warp until you get to that encounter.
   

EDIT: I also misunderstood. I figured you didn't want to use a window because you didn't want to use outside tools. I see I'm wrong about this as well.

In that case you should install the Transfer Window Planner mod. Does what Alexmoon's website does, but in the game. I love it.

Edited October 17, 2014 by 5thHorseman

[MerlinsMaster]

I reread your first post, and thought you were trying to find a window but now see you don't want to wait for one.

First off, you should wait for one. You'll almost guaranteed get there quicker (both in wall-clock time and Kerbin time) if you do.

Yeah...basically I was hoping there was a way to do a brachistochrone transfer as opposed to a hohmann transfer. But as I'm saying that I realize how silly it is.

Secondly, if you really don't want to wait, do this:

1. Burn to get your apoapsis out to Duna, or whatever planet you're going to. I don't suggest this for Jool or Eeloo (or even Dres) because you'll be top-speed-time-warping a LOT and out there it's still SLOOOOOOOOOOW.
   
2. At your AN/DN, burn to get your orbit lined up with Duna.
   
3. Tweak until you see encounter markers. They likely won't be anywhere near each other but no biggie.
   
4. (Yes, so far this is exactly what you'd do to get to Duna if you started in a launch window. You're just doing it without the window.)
   
5. Time warp out until you pass your encounter marker. This will make the other marker jump somewhere else.
   
6. Burn prograde or retrograde (whichever makes Duna's marker get closer to yours) until the markers get really close. Eventually, you'll get an encounter.
   
7. Time warp until you get to that encounter.
   

Basically a rendezvous. Unfortunately that would take longer and defeat the purpose for wanting to leave earlier.

EDIT: I also misunderstood. I figured you didn't want to use a window because you didn't want to use outside tools. I see I'm wrong about this as well.

In that case you should install the Transfer Window Planner mod. Does what Alexmoon's website does, but in the game. I love it.

That sounds pretty handy. I'm gonna have to get that. Thanks.

[MerlinsMaster]

I've got another related question. I tried installing Transfer Window Planner, but unsurprisingly, it doesn't work on 0.23. To save you the trouble of asking why I'm still on 0.23, one of the mods I'm running doesn't work on any later versions. My question is, how do I implement the numbers on Alex Moon's site into my maneuver node, particularly things like ejection angle, ejection inclination, and phase angle? Do I just have to keep adjusting the starting time of my burn until they work out, or is there an easier way?

[Higgs]

Also mechjeb is cheating

No. It is not cheating. Not in the slightest. It is a valuable TOOL that provides you with an immense amount of information that is otherwise occluded from you. It is also a wonderful teaching tool. It is MY OPINION (yes the caps are intended to show that I am speaking from a perspective of PERSONAL OPINION, and not in anyway, shape, form, function, fashion or thought being nasty, rude or otherwise inconsiderate or fight provocative) that those who call MechJeb cheating, are in fact ashamed that they cannot do in full, or with as much accuracy (when mechjeb isnt being kerbal about things) by hand. I also note that YES, KER does exist and can do SOME of what MechJeb does, BUT, MechJeb is also an autopilot, which is never a bad thing.

Now, speaking in dispassionate and factual terms, MechJeb in its AUTOPILOT function, is able to do repetitive tasks, dull, protracted tasks such as 25 minute burns that otherwise must be done constantly by hand, which, is not fun when for example, you are flying a mission to a space station to refuel it, take down science, change crew or what ever menial task that must be performed for the thousandth time. I further show you as example, not even NASA, ESA or JAXA fly 100% operator controlled missions up to the ISS each and every time something needs to either go UP or come back down from Station. MOST if not ALL those sorts of tasks are FULLY AUTOMATED, which by extension, is comparable to someone using MechJeb.

Now, that I have digressed to an extensive degree, I will address the OP's post. Check out KSP.OLEX.BIZ (caps are not mandatory) it is a good tool for manual burns. Also, just burn into a phasing orbit with your targeted destination and wait for the correct sync time to burn for it

[Kryxal]

MerlinsMaster, I think it's going to end up being adjusting of start time. I looked at PreciseNode, and it looks like it could incorporate what you're looking for easily enough (but doesn't). I could see just inputting an ejection angle and that being turned into a time for node, then maybe a +orbit button (though you'd have to be careful with that, +orbit maintaining ejection angle isn't EXACTLY an orbit).

[MerlinsMaster]

MerlinsMaster, I think it's going to end up being adjusting of start time. I looked at PreciseNode, and it looks like it could incorporate what you're looking for easily enough (but doesn't). I could see just inputting an ejection angle and that being turned into a time for node, then maybe a +orbit button (though you'd have to be careful with that, +orbit maintaining ejection angle isn't EXACTLY an orbit).

Well, I was able to get something close by adjusting the start time using PreciseNode. I can keep doing that if necessary.