The Gravity Assist Derby

[Yakky]

This one is simple: Show off your amazing feats of interplanetary hop-scotching using gravity assists to boost you from point to point! You are also allowed to use rocket thrust, but it will reduce your score the more you use (beyond a certain point), so be sparing with those engines!

Setup: It is accepted Kerbal folklore that once you can get to Eve's SOI, you can get yourself pretty much anywhere using mainly gravity assists. So our challenge begins with you in Kerbol (solar) orbit, on your way inbound to Eve's Sphere of Influence. Set your delta-V counter to zero before you arrive at Eve. Eve's SOI will be your jumping-off point. Once you enter Eve's SOI, every meter per second of delta-V must be carefully conserved!

Scoring: You get 20 points for each unique celestial Sphere of Influence you can reach. A second visit to the same SOI (after going elsewhere) is awarded 10 points, and a third visit gets 5 points. No additional points for 4th and subsequent visits to the same SOI. Your total score is the sum of all your points, divided by the total delta-v used on your mission. BUT, if you use less than 100 total delta-V, you still divide by 100... in other words, everyone is encouraged to use at least 100 m/s delta-V. (This is to prevent scores from blowing up due to a vanishing denominator, and also to incentivize creative and elaborate multi-planet trajectory design by awarding everyone some "free" delta-V.)

For example, if you visit four unique SOIs (80 points) and burn 160 m/s delta-V doing it, your score is 80/160 = 0.5. If you visit two SOIs (40 points) and burn no delta-V, your score is 40/100 = 0.4, since the delta-V floor is defined by the rules to be 100 m/s.

Rules:

1. Stock solar system. No modding the celestial bodies or adding more of them. This goes for orbital alignments and conjunctions as well.

2. No mods, cheats, or exploits that give you "free" delta-V. Modded parts are fine as long as they allow correct computation of actual delta-V used. Hyperedit is OK to get your craft into position (as long as it's something that could have reasonably been achieved naturally), but not OK after your run starts.

3. Use something to display your delta-V (such as Kerbal Engineer), and sufficiently document your voyage with screen caps that show where you've gone and how much delta-V you used to get there. Also be sure to get screen grabs of your cool elaborate gravity assist trajectories!

4. You don't have to land on the celestial bodies, just pass through their SOI's.

5. Aerobraking is allowed and encouraged!

6. Kerbol (sun) does not count as a SOI for scoring purposes.

7. You can have whatever speed and trajectory you'd like before you start your run by entering Eve's SOI, and it doesn't count against your Delta-V budget. So plan your entry trajectory appropriately!

8. Exiting an SOI into a parent SOI doesn't count as a new SOI visit. So for example, exiting the Mun's SOI back into Kerbin's SOI doesn't add more points to your score for visiting Kerbin again.

9. "The mercy rule" as suggested by PLAD: time limit of 20 years once you start your mission (although you can choose whatever starting date you want). This is to avoid situations where people just wait in orbit endlessly for something interesting to happen. If you have some really cool trajectory that takes a little longer than 20 Y to complete, let me know and I might make an exception.

Bonus Points (added to your raw point score before dividing by delta-V):

1. Two bonus points for each (detachable) lander you land on each celestial body, limit one per body. Once the probes separate from your main craft, their delta-v's don't count against your score. If you do this, make sure to note your delta-v before and after you separate your lander from your main craft, as the separation event might throw off your delta-V counter.

2. 30 bonus points if you end with a safe landing on Kerbin. Thus, if you make Kerbin your final planet and you land safely there, you'd get 50 points instead of 20 for the Kerbin leg.

Max possible score (if I've done my math right) is 6.2 if you hit all the SOIs three times, land a probe on each one except Jool, and finish with a safe Kerbin landing, all with 100 m/s or less of delta-V spent. I very much doubt that's possible. But in case of a tie, lowest actual delta-V wins!

Standings:

1. PLAD, score of 1.3. See post #5 below. (I'm temporarioly on a bandwidth-limited iPad so this is not thoroughly vetted for the moment. If anyone disagrees with his score, let me know.)

2. von Ziegendorf, score of 1.0. See post #9 below.

3.

4.

5.

Edited October 18, 2014 by Yakky

[Pds314]

One word: JOOL.

[Pds314]

Also, question: if I do this:

Go to Duna's SOI: + 20

And then:

Go to Ike's SOI: +20

And then

Leave Ike's SOI, now under primary influence of Duna,

Does that count as an extra +10 from visiting Duna twice? Or must I go outside of the SOI, and not just to another one inside it?

[Pds314]

Calculated max score, it agrees with yours at exactly 6.20.

Also, question, when you are say that we can choose our trajectory before entering Eve's SOI, can we also choose the time and date, as well?

I'm imagining something involving the planets and moons being aligned at some point in a particular way to allow an almost straight shot at considerable speed.

[PLAD]

A very interesting challenge. For a quick opener I would like to submit my SSTO to Eeloo entry for this challenge as well, though it shows the earlier and later parts of the trip. I entered Eve's SOI at the 13th frame and this challenge would end when I entered Eeloo's SOI.

Javascript is disabled. View full album

If I understand the scoring right it would go like this:

Entered Eve's SOI +20 points

Entered Kerbin's SOI. +20 points

Passed through Mun's SOI. +20 points

Left Kerbin's SOI.

Re-entered Kerbin's SOI 213 days later. +10 points

Passed through Minmus' SOI. +20 points

Passed through Jool's SOI +20 points

Entered Eeloo's SOI +20 points

Total dV used between entering Eve's SOI and entering Eeloo's SOI: 27m/s. Round up to 100m/s.

Total score: 130/100 =1.30

I agree with pds314, the key to a high score is Jool and it's 5 moons. There's up to 222 points to be found there and then Tylo or Laythe could fling you to another planet.

I have a suggestion for a mercy addition to the rules. You might put a total time limit on the mission, say 15 or 20 'Earth years'. I imagine the craft's electronics are degraded by exposure to the interplanetary radiation levels or something. This would prevent someone from being tempted to circle the sun for 100 years waiting for a chance encounter with another planet. After all as long as you are near the plane of a planet there will always be another encounter eventually.

[Yakky]

You raise an excellent point. It shouldn't count when you exit a smaller SOI into the parent SOI. I will revise th rules to make this clear.

[Yakky]

I have a suggestion for a mercy addition to the rules. You might put a total time limit on the mission, say 15 or 20 'Earth years'. I imagine the craft's electronics are degraded by exposure to the interplanetary radiation levels or something. This would prevent someone from being tempted to circle the sun for 100 years waiting for a chance encounter with another planet. After all as long as you are near the plane of a planet there will always be another encounter eventually.

That's a good idea. Mercy rule adopted: 20 year limit on missions. If someone objects strongly, let me know and I will reconsider. Happy to have a discussion on this one.

[Yakky]

Calculated max score, it agrees with yours at exactly 6.20.

Also, question, when you are say that we can choose our trajectory before entering Eve's SOI, can we also choose the time and date, as well?

I'm imagining something involving the planets and moons being aligned at some point in a particular way to allow an almost straight shot at considerable speed.

Yes, you can choose whatever time and date suits you. Feel free to mine the future for that optimal orbital conjunction. Just mention what your starting date was when you post your entry so that others can verify it.

[von Ziegendorf]

Here is my favourite stock mission - Triple Flyby:

Javascript is disabled. View full album

First Eve flyby - 20

Duna flyby - 20

Second Eve flyby - 10

Kerbin landing - 50

RCS dV in Eve SOI - 412.4m/s

RCS dV before reentry - 329.2m/s

412.4-329.2=83.2m/s

So the score is (20+20+10+50)/100=1

[Yakky]

A couple nice entries to kick things off. Who's going to step it up with a really creative set of Jool system transfers?