Multi-Flyby Kerbin -> Eeloo Mission

[Arrowstar]

Hi everyone,

I'm the author of the KSP Trajectory Optimization Tool, a Windows application designed to help KSP pilots execute efficient missions. The other day, I was having a conversation with some other folks over in the Tools and Applications section of the Add-On Showcase forum and we got to talking about a Kerbin -> Eve -> Kerbin -> Jool -> Eeloo mission a a possible "cheap" way to get out to Eeloo.

During our conversation, I used KSP TOT to try and find a cheap flight plan that hits those bodies. I ended up with something like this:

Here's the text in the boxes on the right:

Hyperbolic Departure Orbit from Kerbin
---------------------------------------------
Semi-major Axis =               -1428.959 km
Eccentricity =                  1.4899
Inclination =                   16.316 deg
Right Ascension of AN =         230.666 deg
Argument of Periapse =          180.000 deg
---------------------------------------------
Inbound Hyperbolic Flyby Orbit to Eve
---------------------------------------------
Semi-major Axis =               -4605.609 km
Eccentricity =                  1.83
Inclination =                   8.546 deg
Right Ascension of AN =         30.442 deg
Argument of Periapse =          61.484 deg
Periapse Radius =               3822.526 km
---------------------------------------------
Outbound Hyperbolic Flyby Orbit from Eve
---------------------------------------------
Semi-major Axis =               -1148.588 km
Eccentricity =                  4.328
Inclination =                   8.546 deg
Right Ascension of AN =         30.442 deg
Argument of Periapse =          61.484 deg
Periapse Radius =               3822.526 km
---------------------------------------------
Inbound Hyperbolic Flyby Orbit to Kerbin
---------------------------------------------
Semi-major Axis =               -157.364 km
Eccentricity =                  6.5234
Inclination =                   170.798 deg
Right Ascension of AN =         351.817 deg
Argument of Periapse =          69.888 deg
Periapse Radius =               869.181 km
---------------------------------------------
Outbound Hyperbolic Flyby Orbit from Kerbin
---------------------------------------------
Semi-major Axis =               -157.379 km
Eccentricity =                  6.5229
Inclination =                   170.798 deg
Right Ascension of AN =         351.817 deg
Argument of Periapse =          69.889 deg
Periapse Radius =               869.181 km
---------------------------------------------
Inbound Hyperbolic Flyby Orbit to Jool
---------------------------------------------
Semi-major Axis =               -84396.910 km
Eccentricity =                  1.2991
Inclination =                   142.676 deg
Right Ascension of AN =         344.707 deg
Argument of Periapse =          137.053 deg
Periapse Radius =               25247.139 km
---------------------------------------------
Outbound Hyperbolic Flyby Orbit from Jool
---------------------------------------------
Semi-major Axis =               -421944.420 km
Eccentricity =                  1.0598
Inclination =                   142.676 deg
Right Ascension of AN =         344.707 deg
Argument of Periapse =          137.053 deg
Periapse Radius =               25247.139 km
---------------------------------------------
Inbound Hyperbolic Orbit to Eeloo
---------------------------------------------
Hyperbolic Excess Vel. =        0.195 km/s

Phase 1 Transfer Orbit (Kerbin -> Eve)
---------------------------------------------
Semi-major Axis =             12019385.493 km
Eccentricity =                  0.20265
Inclination =                   2.195 deg
Right Ascension of AN =         32.917 deg
Argument of Periapse =          41.188 deg
Period =                     7646766.1128 sec
Departure True Anomaly =        138.812 deg
Arrival True Anomaly =          31.865 deg
---------------------------------------------
Phase 2 Transfer Orbit (Eve -> Kerbin)
---------------------------------------------
Semi-major Axis =             21741305.543 km
Eccentricity =                  0.54778
Inclination =                   2.138 deg
Right Ascension of AN =         26.878 deg
Argument of Periapse =          77.458 deg
Period =                    18602993.7241 sec
Departure True Anomaly =        1.630 deg
Arrival True Anomaly =          282.542 deg
---------------------------------------------
Phase 3 Transfer Orbit (Kerbin -> Jool)
---------------------------------------------
Semi-major Axis =             41677342.400 km
Eccentricity =                  0.72441
Inclination =                   0.759 deg
Right Ascension of AN =         26.878 deg
Argument of Periapse =          50.954 deg
Period =                    49374696.2892 sec
Departure True Anomaly =        309.046 deg
Arrival True Anomaly =          181.725 deg
---------------------------------------------
Phase 4 Transfer Orbit (Jool -> Eeloo)
---------------------------------------------
Semi-major Axis =             91419511.542 km
Eccentricity =                  0.25572
Inclination =                   6.860 deg
Right Ascension of AN =         74.533 deg
Argument of Periapse =          226.980 deg
Period =                   160403099.1772 sec
Departure True Anomaly =        318.077 deg
Arrival True Anomaly =          196.703 deg
---------------------------------------------
Kerbin Departure Date = 
                Year 1, Day 117 06:56:48.164
                       (10047408.164 sec UT)
Eve Arrival Date = 
                Year 1, Day 181 01:39:11.554
                       (15557951.554 sec UT)
Kerbin Arrival Date = 
                 Year 2, Day 16 19:24:33.158
                       (32901873.158 sec UT)
Jool Arrival Date = 
                Year 2, Day 324 08:39:33.237
                       (59474373.237 sec UT)
Eeloo Arrival Date = 
                 Year 6, Day 60 06:06:09.230
                      (162799569.230 sec UT)

Burn Information to Depart Kerbin
---------------------------------------------
Total Delta-V =                 1.525 km/s
Prograde Delta-V =              1155.385 m/s
Orbit Normal Delta-V =          -995.675 m/s
Radial Delta-V =                0.000 m/s
---------------------
Burn True Anomaly =             50.666 deg
---------------------------------------------
Burn Information to Depart Eve
---------------------------------------------
Total Delta-V =                 0.915 km/s
Prograde Delta-V =              915.283 m/s
Orbit Normal Delta-V =          0.000 m/s
Radial Delta-V =                -0.000 m/s
---------------------
Burn True Anomaly =             0.000 deg
---------------------------------------------
Burn Information to Depart Kerbin
---------------------------------------------
Total Delta-V =                 0.000 km/s
Prograde Delta-V =              -0.189 m/s
Orbit Normal Delta-V =          -0.000 m/s
Radial Delta-V =                -0.000 m/s
---------------------
Burn True Anomaly =             0.000 deg
---------------------------------------------
Burn Information to Depart Jool
---------------------------------------------
Total Delta-V =                 0.271 km/s
Prograde Delta-V =              -271.235 m/s
Orbit Normal Delta-V =          0.000 m/s
Radial Delta-V =                -0.000 m/s
---------------------
Burn True Anomaly =             0.000 deg
---------------------------------------------

---

The challenge is thus: Execute the above flight plan as closely as possible. Closely in this case involves matching the UT of the various body arrival dates shown in my second box, above, as closely as possible. I'm not worried about the departure date from Kerbin because that will vary some with your initial orbit (could be +/- an orbital period or so). One additional rule: no "deep space maneuvers." All burns must take place near periapsis of your hyperbolic flyby orbit. Your initial orbit should be a circular, equatorial orbit around Kerbin at 100 km altitude.

This challenge is just for fun, so I won't be keeping a leader board or anything, but I'm curious to see how good you pilots are. Have at it and post pictures of your flybys with the UT displayed in the picture somewhere. PreciseNode and MechJeb both have windows with the UT in them.

Let me know if you have any questions. Happy Orbiting!

[Kobymaru]

So here's the problem with the challange:

It's next to impossible to create a perfect orbit in KSP, even with MechJeb help. Therefore, for the given departure time, the orbital phase will be wrong, and the departure burn will also be wrong.

In fact, I tried to enter the numbers for the Kerbin departure into the MechJeb maneuver node editor, and it didn't even produce an encounter (not even after moving the departure node forward/backward).

So, I had to modify the node to get an encounter with Eve at all. The problem is: I do not know how this encounter has to look like, so I have no idea how to correct the burn in such a way that it produces the right encounter I guess the information required for a correct fly-by is contained somewhere here:

---------------------------------------------
Inbound Hyperbolic Flyby Orbit to Eve
---------------------------------------------
Semi-major Axis =               -4605.609 km
Eccentricity =                  1.83
Inclination =                   8.546 deg
Right Ascension of AN =         30.442 deg
Argument of Periapse =          61.484 deg
Periapse Radius =               3822.526 km

But a) I have no idea what half of those values mean and even if I knew, I have no Idea how to look them up. MechJeb only displays orbital properties of the current, *real* orbit but not those of a hypothetical orbit after a planned maneuver.

So in short: i do not know how to correct the burn, therefor I cannot make the burn precise enough.

Also, about the "no deep space maneuvers" rule: that's not realistic. No real burn can be perfect. There can be human errors, floating-point errors and every burn takes a finite amount of time (TWR is not infinity). And if the burn can't be perfect, you have to do the correction burns in deep space - no way around it.

[Mr Shifty]

The other day, I was having a conversation with some other folks over in the Tools and Applications section of the Add-On Showcase forum and we got to talking about a Kerbin -> Eve -> Kerbin -> Jool -> Eeloo mission a a possible "cheap" way to get out to Eeloo.

I may actually try your flight plan; it would be interesting to see if it works. But it's not a 'cheap' way to get to Eeloo. Your plan requires a total delta-V of about 2.9 km/s (not including Eeloo insertion.) You can do direct ascent from Kerbin to Eeloo for a little over 2 km/s. It's probably a cheap way to visit all those other planets on the way though.

EDIT: It would be interesting to use your tool to generate a mission that could visit as many planets as possible given a fixed delta-V budget, like this old challenge:

http://forum.kerbalspaceprogram.com/threads/37974-Optimal-gravity-assisted-grand-tour-%28AKA-Voyager-like-mission%29-challenge

Edited June 26, 2014 by Mr Shifty

[PLAD]

I have found that I can follow a plan like this to within +/-8 hours or so, at least for the inner planets. See my old mission report '1051 m/s KLO to Jool Orbit'. By the time I get to the outer planets the error is often several days though. You do have enough information to follow the plan in the challenge, all we really need is the dates and planets, one can figure out the rest. It's nice to have the total start velocity and normal component though, and especially the altitude and thrust magnitude of the flyby periapsis burns, that makes finding the path much easier. And you've got those but they are spread out through the various screens.

But there was a good point- I always have to do small course corrections far from any planet to execute a mission like this, because KSP cannot accurately do a thrust to better than about +/-.1 m/s and you would need better than that to set up a second flyby while doing a first flyby. There are also errors when changing your SOI, often 10m/s or more depending on your time warp when you cross the SOI. So 'no deep space maneuvers' would have to go.

TOT is the best tool I've seen for finding a low-dV path from Kerbin to Eeloo but I know I could do much better than this particular path so I would rather not fly it.

[MarvinKitFox]

no "deep space maneuvers." ?

In one word: impossible.

why?

The sheer floating-point inaccuracy inherent in KSP's calc will throw off your resultant vector by a margin larger than the needed accuracy.

After the flyby of Kerbin, you will hit Jool easily enough. But with a time inaccuracy of +- several hours. At 4km/s of orbital motion by Jool, this translates to many hundreds of thousands of km positional error at Jool.

After such a bad start at Jool slingshot, hitting Eeloo's tiny SOI after a thousand-day coasting is... pure luck.

[immelman]

Not to blow my own trumpet, but I've done a Kerbin - Eve - Kerbin - Kerbin - Jool - Eeloo slingshot already for my 75 ton grand tour:

http://imgur.com/a/Nm2wN#25

1983 m/s to close Eeloo 22x22km orbit

Edited June 27, 2014 by immelman

[MarvinKitFox]

Not to blow my own trumpet, but I've done a Kerbin - Eve - Kerbin - Kerbin - Jool - Eeloo slingshot already for my 75 ton grand tour:

http://imgur.com/a/Nm2wN#25

1983 m/s to close Eeloo 22x22km orbit

Quite believable.

Am I bet you needed to use the occasional mid-course trajectory maneuver?

With a well-planned trip, these can be kept below 50m/s each, but try doing it *without any*, as this challenge requires.

[Mr Shifty]

Not to blow my own trumpet, but I've done a Kerbin - Eve - Kerbin - Kerbin - Jool - Eeloo slingshot already for my 75 ton grand tour:

http://imgur.com/a/Nm2wN#25

1983 m/s to close Eeloo 22x22km orbit

My god, that grand tour is simply jaw dropping. Never seen anything like it. Well worth blowing your trumpet for.

[Kasuha]

Gravity slingshots are most effective if you can climb them like a ladder. I Kerbin system, Jool is almost on the same level as Eeloo and Dres and Duna are worthless. In this case slight inefficiency is that the trajectory to Jool has low periapsis, lower than Kerbin orbit. So what we got by slingshotting off Eve, we almost lost there.

[Kobymaru]

Not to blow my own trumpet, but I've done a Kerbin - Eve - Kerbin - Kerbin - Jool - Eeloo slingshot already for my 75 ton grand tour:

http://imgur.com/a/Nm2wN#25

1983 m/s to close Eeloo 22x22km orbit

This is truly amazing. How did you set up this grand tour? Did you plan ahead, or did you just go made up the encounters as you went?

What strategy did you follow?

Could you write a mini-tutorial on how to do such a thing?

Right now, I use slingshots only "if they happen" and tweak a bit to get a better orbit but I would be really interested in including them in mission planning as a reliable tool.

[immelman]

This is truly amazing. How did you set up this grand tour? Did you plan ahead, or did you just go made up the encounters as you went?

What strategy did you follow?

Could you write a mini-tutorial on how to do such a thing?

Right now, I use slingshots only "if they happen" and tweak a bit to get a better orbit but I would be really interested in including them in mission planning as a reliable tool.

Planned and flew it all while posting here:

http://forum.kerbalspaceprogram.com/threads/73203-Who-Needs-Command-Seats-a-minimalist-Grand-Tour-*IT-IS-FINISHED*

If you want to start using slingshots you need not look no further than Arrowstar's own TOT, I use it extensively. Plad's super cheap Jool flyby is very cool, as is Kasuha's Eve-Moho

For an excellent primer "howto gravity" by Stochasty was very helpful: http://www.reddit.com/r/KerbalSpaceProgram/comments/1oqp6z/psa_how_to_gravity_introduction/

[Kobymaru]

Planned and flew it all while posting here:

http://forum.kerbalspaceprogram.com/threads/73203-Who-Needs-Command-Seats-a-minimalist-Grand-Tour-*IT-IS-FINISHED*

If you want to start using slingshots you need not look no further than Arrowstar's own TOT, I use it extensively. Plad's super cheap Jool flyby is very cool, as is Kasuha's Eve-Moho

For an excellent primer "howto gravity" by Stochasty was very helpful: http://www.reddit.com/r/KerbalSpaceProgram/comments/1oqp6z/psa_how_to_gravity_introduction/

Thanks a lot, that's exactly what I needed!