New Horizons style mission

[1of6Billion]

So I installed the Outer Planets mod pack... Now I want to do a New Horizons style mission to Plock. "So what about it?" I hear you ask.

First let me explain what I mean with New Horizons style mission: 

1. Launch
2. Coast a little to injection burn (so, no circularisation)
3. Fly top speed to Plock
4. Zip by at ridiculous speed
5. Be close enough to collect the "low orbit" science
6. Leave Kerbol forever

So no slingshotting at Jool or whatever.

I don't have a clue how to time this right. Is there a formula I could use? I guess it all depends on dV, TWR and whatnot.

[Evanitis]

40 minutes ago, 1of6Billion said:

Zip by at ridiculous speed

You know if that line wasn't there, I'd summon a math expert or started to wonder if MJ's advanced transfer function works with extra planets (pretty sure it does)..

But the regular methods for going to different planets such as hohmann transfer and launch windows are all based around the concept that you want to use the least amount of dV at the start and at the arrival. But I'm pretty sure inefficient ways result in more speed, so I'd try to brute force first. As in: make the most overbuilt craft you can get to orbit take out of Kerbin SoI, and just plot an intercept. If that needed a ridiculous amount of dV, wait 100 days and retry. And/or add moar boosters.

Well, that would be my first though. The other two options I could think of were hinted above.

Edited January 14, 2016 by Evanitis

[Streetwind]

What you want to do is called a "high energy transfer".

When you think of the concept of "launch windows", they are generally used to describe the optimal times to leave when you want to do a Hohmann transfer. Because you're not doing a Hohmann transfer, these classic launch windows are not useful to you. However, it is useful to realize that there are also launch windows that do work for you - they're just different ones. Because your transfer is different.

What you need to do, then, is to find your launch window. You do this exactly the same way you figure out launch windows for Hohmann transfers that cannot be eyeballed or do not happen to be preprogrammed into Kerbal Alarm Clock: you use a porkchop plotter. My favorite one is here: http://alexmoon.github.io/ksp/

It includes only stock planets, for now. We'll get to that part later. For starters, select something like Eeloo. It works as an example. Check the box for "no insertion burn", and just press "plot it" and let it spit out something. What you have just received is a standard Hohmann transfer window from Kerbin to Eeloo. It will be visible as a spot selected inside a blue zone in the colorful porkchop plot at the bottom. Blue means it costs the smallest amount of dV.

But "smallest amount of dV" is not your concern, is it? You want to fly a high energy transfer. You're willing to throw dV at the problem. What you're interested in is "shortest travel time". And in that porkchop plot, the travel time is the upright, vertical axis. If you want a shorter transfer, you can simply click anywhere in that plot, at a spot that is lower down than the spot the calculator preselected. The further it is down towards the bottom, the shorter your trip will be. Ideally, select a spot with a color that is also indicative of (relatively) low dV costs. You are still looking for the optimal moment in time to leave, after all. And the "moment in time to leave" is the bottom, horizontal axis in the plot.

Now, instead of clicking around in the plot and guessing, you can have the planner spit out a high energy transfer by default. Click the easily overlooked "show advanced settings" link above the "plot it" button, and you will get the ability to specify your minimum and maximum acceptable travel time. Set that to your desired values, set earliest and latest departure time based on where you are in your savegame and roughly when you want to fly this mission, and then, plot it again. The calculator now finds you the cheapest possible transfer window in the time period specified, which will not exceed your maximum acceptable travel time. It's common here, if you're aggressive, to find the calculated solution plastered against the very top of the porkchop plot, indicating that you're really flooring it and all the cheaper solutions are slower.

Up next, look at the list of "Selected Transfer Details". The entry for "Ejection dV" has a little blue info button right next to it. Click it. You get a little pop-down showing a prograde dV, a normal dV, and a heading. If you actually want to fly this transfer ingame, you launch your ship into orbit - the same orbit height you used for calculating the transfer in the planner! There, make a maneuver node, and give that maneuver node exactly the normal dV shown, and then add prograde dV until the node's total is exactly the value given for Ejection dV. Then, if the time of the transfer has come, all you need to do is to select your destination as a target, and move the node around in Kerbin's orbit until you get an encounter. (You could technically try and find the precise angle with a protractor, or use an addon like PreciseNode, but this method is simple and works for a stock install.)

If you don't want to circularize your New Horizons style mission, well, be prepared for trouble! Because the transfer window planner assumes a circular orbit, you will have to add additional dV to your planned node to offset the fact that you're not yet in orbit. (In other words, you don't save any dV in this approach. At all.) How much extra? I can't tell you, and neither can any calculator, because it depends on how you flew your ascent, and how much dV you would need for the circularization burn you are deciding to skip here. So yeah, I recommend against this. But if you absolutely must, then it's probably required that you use a different spacecraft - like a small probe in the correct orbit - to practice setting up the node and getting the encounter before you launch. Remember that you can shift your node forward in time in increments of one orbital period. You'll need to do this to accurately simulate a node for a craft that has not yet launched. A large problem here is that you must first find out where in orbit around Kerbin your ship actually needs to be to start the burn, because that informs how the planet must be rotated at the moment of launch so your non-circularized spacecraft is actually in space at the same location as the node after finishing the gravity turn.

 

Now you are perfectly capable of plotting and executing exactly the transfer you need to get to Plock. Except... how can you get a transfer planner that includes Plock?! Conveniently, alexmoon's transfer planner is also available as an ingame addon, called simply "Transfer Window Planner". It works exactly like the website, and unless I completely misremember here, it should automatically pick up on all planetary bodies present. Including those added by Outer Planets Mod, if you have it installed.

 

Go forth, and godspeed

 

Edited January 14, 2016 by Streetwind

[Snark]

You'll do just fine... except for

1 hour ago, 1of6Billion said:

(so, no circularisation)

for a very practical reason:

Any interplanetary mission is like trying to shoot a very small bullseye from a very long distance, especially when the target is something small like Plock.  Getting that intercept is very tricky, even if you have an unlimited dV budget.

That's what maneuver nodes are for, and they do great at that.  The problem is that:

1. setting up your high-speed transfer to Plock is going to require a lot of finicky fiddling with the maneuver node to get it just right
2. you can't set up the maneuver node until you have a trajectory (i.e. you can't do it while sitting on the launch pad)
3. if you're not circularizing, then you have only a minute or two of coasting during which you can set up your node

Is there some reason you don't want to circularize first?  It'll save you a lot of hassle, and it really doesn't cost you any significant dV to circularize in LKO first.

If your reason for wanting not to circularize is "role-playing" (i.e. "I want to do it just like NASA did"), then go to it, and good luck!    But be aware that NASA had an advantage that you don't, namely, they have way better software than you do and plan maneuver nodes before they've even built the rocket, let alone launched it.

If you don't have some role-playing reason for not circularizing, then I'd advise doing that just so you'll have the leisure to tinker with the maneuver node.

If you decide that you definitely don't want to circularize, then about the best you can do will be to figure out approximately the right burn before launching, do a big approximate burn, then do a fine-tuning burn a while after that in order to get your trajectory just right.  It'll be more finicky, more trial-and-error, and will likely cost you more dV that way.  If you do go that route, then you want to launch when Kerbin is between the 3 o'clock and 4 o'clock position around the Sun (if Plock is at 12 o'clock), with your craft at between 3 o'clock and 4 o'clock position around Kerbin.  That way you're adding both your ship's orbital velocity around Kerbin, and Kerbin's orbital velocity around the Sun, to your eventual interplanetary trajectory.

 

Edited January 14, 2016 by Snark

[1of6Billion]

Wow, great help all. @Evanitis, I use Mechjeb a lot for regular transfers and it does work with the extra planets. @Streetwind, your post made me understand *how* porkchops work. @Snark I think I don't have to be *that* OCD about not circularising, if that makes life more easy.

I'll launch, circularise and plot a transfer with all the dV I can bring to orbit. Thát will keep me busy tonight

[MagicFireCaster]

If you don't want to circularize you should try a high almost circular suborbital trayectory, also if you want a "New horizons" flight, you should try to do the fastest transfer possible, so i think your sun orbit shouldn't be too circular, it should be almost a straight trayectory i think 

[Kekkie]

So could you post some pics of the mission?

[cantab]

Nitpick: New Horizons *did* use a Jupiter gravity assist. That got it to Pluto about two years quicker than if it hadn't made the flyby. It also makes New Horizons our most recent probe to visit Jupiter (until Juno arrives this July), and it actually returned more data from there than it will about Pluto!