Planing a big tour - with a probe ! slingshot advises needed

[Darth Lazarus]

good day everyone

currently, i'm planing a big tour to some planets with a probe. my goal is, to reach several planets (Jool in main focus) with only gravity assits by other plantes and the inertial depature burn from Kerbinorbit. visiting the planets (and maybe larger moons) will be done only in flybys. i don't want to establish orbits and i don't want to do hard aerobrakes, maybe some slightly touch the outerlayers without risikng to heat the space craft.

my question is now: is there a tool or tutorial or guide for planing such a mission? like giving hepful informations of when to start to which planet?

the spacecraft i want to use is a Voyager 1 replcia with only 400 m/s dV with RCS thrusters

thank you very much for help

little edit: i dont want to visit all the planets, but as much as possible. maybe Jool and Eve for sure

here a pic of my Voyager 1

Edited February 11, 2015 by Darth Lazarus

[Deadpangod3]

to visit ALL the planets? id say impossible, i mean, an error of .5 m/s at kerbin makes a difference at jool the size of laythes orbit, so youd have to be pretty much DEAD ON, and even then itd be iffy, because the planets would have to be aligned perfectly (which probably would take 10000 years of timewarping to find) plus with the floating point errors would mess your trajectory up, so i dont think its possible without course corrections.

+1 rep for cool replica though

[Darth Lazarus]

thanks Deadpangod for teh rep

i dont want to visit all planets, maybe i have to clarify it. but i want to visit as much as possible.

[Deadpangod3]

ah, okay, well, i guess you should try and see if you can get a few aligned so you can do flyby's, but if we're including moons it may add to the total if you happen to encounter one of the planets moons (unless said planet is Moho, Dres, or Eeloo.) especially at Jool (coughTylocough) if you can get lucky you can encounter a few of Jool's moons.

you can also just fire the probe off into a solar orbit and wait, maybe an orbit going below Moho's and around Eeloo's orbit, eventually youll get an encounter with something, and as long as you dont crash into whatever it is your encountering youll encounter another, then another, and another, until you hit something or quit the game

[NASAHireMe]

Arrowstar's Trajectory Optimization Tool is the best we have.

But a word of caution: many players have attempted to do what you are planning to do. It is not easy. Since floating-point errors and such are prevalent and unavoidable, even the best calculations will be wrong 99% of the time. You will have to make course corrections-- there's basically no way to do it in one go. And plus, planets like Moho and Eeloo and Dres don't have a lot of mass, so you'll have to do multiple passes on them to get somewhere else.

[Guest]

In case of the inevitable FP errors, bring along an ion drive and some xenon. If you plan right you shouldn't need all that much delta-V for corrections, but it will reduce imprecision headaches, I assume.

[CalculusWarrior]

A very ambitious mission you have there! I don't see why it couldn't be possible, as long as you're patient and careful about where you burn. Also, that's an awesome replica of Voyager!

For the gravity assist maneuver, mass is king. The larger the planet you slingshot around, the more your trajectory is affected. As such, this points at Jool as the obvious candidate to try to hit in order to make those large transfers. However, it's pretty far out in the system, so it's difficult to get to immediately from Kerbin. If your Kerbin Departure Stage lacks the delta-v to put you all the way out there, then you may want to shoot for a closer target: Eve, or even Kerbin itself (a la Rosetta).

However, I recommend including at least one engine on Voyager, as you will have to expend some delta-v en route; KSP is simply not accurate enough to allow you to complete a flyby of every body in the system with only one trajectory. Instead, consider using the gravity assists to take care of most of the heavy delta-v requirements, while using small burns to fine-tune your trajectory.

Visiting all the Joolian moons will be difficult, as the very nature of the gravity assist means that you cannot enter orbit around the body you're trying to slingshot around. That means you need to be very clever when it comes to flying around the system, perhaps using Tylo's influence for further gravity assists.

These are just my thoughts though; I've never actually launched a mission which primarily gets around via gravity assists, though you have inspired me to take a look at one for a future probe!

[Robotengineer]

Very good Voyager replica. The gravity assists would be difficult, given that the stock planets don't have much mass compared to real planets. Then when you enter Jool SOI you would have to be careful to not fling yourself out of the solar system or straight into Jool do to the moons. The way I would do it would be to go from Kerbin to Eve, then slingshot from Eve to Duna, and from Duna to Jool and out of the system, or into orbit.

[Darth Lazarus]

first of all: thank you very much everyone for your words and helpfull hints

Voyager already has RCS with around 400 m/s of dV. but after reading all your replies, i think i will boost it up slightly (or maybe adding an iondrive) ... we will see. and i will launch first a test mission with a regular probe with engines to test the slingshot maneuver.

an other question: any good part pack with large SRB's to build a Titan III E replica? i already have a stock version, but the boosters look terrible and real fairings would be awesome (and reduce teh partcount a lot)

[Robotengineer]

FASA has proper Titan SRB's. You might also want to look at KW or NovaPunch.

[Darth Lazarus]

yeah FASA, good idea to look at this mod pack. i tried it months ago for some Saturn V landings. hrm, a combination of FASA Titan parts and KW fairings (if FASA dont have any)

downloading now the packs. thanks for sugestion.

[Xavven]

Very good Voyager replica. The gravity assists would be difficult, given that the stock planets don't have much mass compared to real planets. Then when you enter Jool SOI you would have to be careful to not fling yourself out of the solar system or straight into Jool do to the moons. The way I would do it would be to go from Kerbin to Eve, then slingshot from Eve to Duna, and from Duna to Jool and out of the system, or into orbit.

Luckily, the shmelta-vee requirements are also much lower in KSP, and the distances between the bodies are also much, much smaller.

Don't be afraid to perform targeting maneuvers in deep space to ensure your gravity assist is lined up, seeing as we do this IRL. It's unrealistic to expect a single escape maneuver from Kerbin to result in a grand tour without, at minimum, fine tuning your approaches. I'm assuming that's what your 400 m/s of schmelta-vee is for.

As for what planets to use, I'd start with slingshots using Kerbin and Eve to get your orbit raised, and aim straight for Jool.

Duna and Dres are too small to help you so it's not worth the time trying to get energy out of them. However, that doesn't prevent you from lining up a flyby on your way to Jool.

[Darth Lazarus]

yes, i plan to use the 400 dV in the Voyager for cursecorrections. but i will see if i need more or less.

thanks for adviosing to start with Kerbin to Eve first and then go for Jool. what do you mean with targeting maneuvers? something like, adding teh planet as target to get a close encounter like i woudl "rondevous" with the planet?

a quick mockup of teh Titan III E with parts from FASA and Fairings from KW Rocketry ... locks awesome.

[Guest]

#centaurneigh

[cantab]

I did a flyby grand tour a while back. I had a fair bit more delta-V, but it was still a case of pulling a load of gravity assists.

The big catch compared to real life is there's only one big outer planet, Jool. There's nothing analogous to the Jupiter-Saturn-Uranus-Neptune trick. Duna can be useful but doesn't really have the punch to sling you out to Jool.

[r_rolo1]

Hum, that is a problem I've been working sporadically for a couple of months, the one of making some kind of multi-slingshot calculator ( in fact I have a nice 100 page ESA document about math for calculating that in a patched conic approach right next to me ATM waiting for a full read ) and while I still don't have any concrete results, I can say with some confidence that is possible to do with some ease a Kerbin->Eve->Duna->Dres->Jool->Eeloo slingshot with minimal corrections (the SoI transitions spoil all the fine tune stuff :/ ) and moderate fuel spendings. It is Moho that spoils the broth , though, being a small body with a somewhat eccentric and inclined orbit near the main body...

[Xavven]

yes, i plan to use the 400 dV in the Voyager for cursecorrections. but i will see if i need more or less.

thanks for adviosing to start with Kerbin to Eve first and then go for Jool. what do you mean with targeting maneuvers? something like, adding teh planet as target to get a close encounter like i woudl "rondevous" with the planet?

a quick mockup of teh Titan III E with parts from FASA and Fairings from KW Rocketry ... locks awesome.

http://i.imgur.com/Tuo9MD7.png

Yes, you've got it. A targeting maneuver is a small burn that puts you on an intercept course with a celestial body to get a gravity slingshot.

[quantumpion]

This guy did a grand tour in tier-0 parts with lots of gravity assists:

[bitbucket]

Seeing as the Kerbin system only has one big gas giant planet, if you want to pull a Voyager and not go inward before you go outward, the only reasonable slingshot is using Jool to get to Eeloo.

[cantab]

And I'm not sure if that's even possible with the orbital resonance, not if you want to do it in less than a complete solar orbit.

[Xavven]

And I'm not sure if that's even possible with the orbital resonance, not if you want to do it in less than a complete solar orbit.

That's really the main thing... If you're not a math whiz and calculating out the perfect trajectory, there's always the Kerbal way, which is to keep completing orbits until the planet you want to get to is in roughly the right place and perform a cheap targeting maneuver.

After playing around with gravity assists in some of my early games, I realized that getting around the Kerbolar system is all about expending delta-v vs. time. The more time you're willing to wait, the better opportunities you have to expend less delta-v. If you need to get somewhere NOW, prepare to use lots of fuel.

[cantab]

Just be warned that in the case of Eeloo it will be a long wait even at maximum timewarp. I actually edited the savefile one time to skip a full 50 Kerbin years on a trip there.

[BlkBltChemie]

Have you seen either of these posts? They offer a very robust method for planning gravity assists.

Gravity Assists by Stochasty

Multiple Grav Assists on a Body

Definitely keep us posted on your attempt; I for one would like to see how it turns out! (If it works well, you should consider adding a report in the Fan Works subforum.)

[Darth Lazarus]

thank you for the new links.

i will keep you all updated over the weekend, but first i have to recover from a visit at the local dentist ... wisdomteeth are no fun

my Titan III E replica ahs finished flighttests and i conmsider to update Voyager with a smal ion tug for worst case scenarios.

[merendel]

The more time you're willing to wait, the better opportunities you have to expend less delta-v. If you need to get somewhere NOW, prepare to use lots of fuel.

chuckle, I know how that goes. My most recent game I accidentally accepted a duna satellite contract and was way off window for it and didnt want to wait. I launched it now with a 5km/s departure burn that cuts down below moho's orbit to hit duna with another 5k in the tank to slow down since I know aerobreaking from that speed in duna's thin atmo isnt happening. Still its going to get there months before the actual launch window opens.