Eeloo and return mission

[steuben]

I've got a plan, with a kerbal in a can. Off to Eeloo, it's true. Send him there, through the air. Bring him back, for a snack.

I'm planning out a mission to Eeloo. I figure it will take about 5 k/s of dv to get there, 5 k/s to get back, 2 k/s to land and orbit Eeloo, and about 1 k/s to land back on Kerbin. I'm budgeting using the subway map off the wiki. I'm not budgeting for gravity assists. Yes I know they will save me m/s

Doing it with Dawns and Nervs is fairly easy. I'm thinking of doing it with only teir 5 tech.

I'm going with the fleet approach. The core ship consisting lander and "living" space for my lucky kerbal. Accompanied by 3 or 4 tankerships.

My ships, as always, are over build, over fueled, and over powered. My concern is about electrical, reading the wiki it looks like a factor 20 drop in solar power out there. If my math is right, two correctly oriented ox-stat panels should still power the octo core, correct?

Anything else I should be considering?

 

[Snark]

22 minutes ago, steuben said:

My concern is about electrical, reading the wiki it looks like a factor 20 drop in solar power out there. If my math is right, two correctly oriented ox-stat panels should still power the octo core, correct?

Solar power definitely a problem out there.  Normally I'd say to abandon solar cells entirely and rely on RTG's (they give more power per kilogram once you're past Jool, and are way more reliable), but they're top-tier tech and you said you wanted to do this low-tech.

So in that case, I'd say:  spam the solar panels.  Get the auto-sun-tracking ones, not OX-STAT; you need every erg of power you can get.

[Plusck]

I wouldn't rely on OX-STATs. I lost my first lander on Bop to that, and Eeloo is worse.

If you're planning to capture with Dawns, you are going to have to be very sure that you've got enough juice to run them when you get there. 8x 6-panel solar panels will let you get about 1/7th power out of your Ion engine.

So you really, really want to include an RTG on every ship just to be sure you don't die by getting stuck with panels not facing exactly the right way. Or lots of batteries with at least one locked off (though in 1.1, from what I've read locked batteries can't be unlocked if there is no power and no crew to flick the switch... so beware if the mission is still on-going when 1.1 comes out).

[Warzouz]

Well

• Go to LKO : 3400m/s
• Low Eeloo orbit : 3500m/s + 1000 for reasonable plane change if needed
• Land and orbit : 1240m/s
• Return to kerbin (direct reentry) : 2500m/s

So you should put a 7400m/s ship to LKO.

 

 

[Snark]

By the way, a word on the electricity math:

• An OKTO probe core requires 1.2 EC/minute
• An OX-STAT produces 21 EC/minute at Kerbin, if pointed straight at the sun
• Sunlight at Eeloo is about 44 times weaker than at Kerbin
• Therefore, two OX-STAT panels at Eeloo's distance will give you around 0.95 EC/minute, i.e. not quite enough to run an OKTO
• ...and that varies with Eeloo's orbit, since it's fairly eccentric.  Sometimes it'll be better than that, most of the time it'll be worse.
• ...and that assumes that the panels are pointed straight at the sun.

So you should bring a lot more solar panels than that.  Get the sun-tracking ones, and bring lots of 'em.

Or even better, use RTGs instead, if it's an option for you.

As an emergency backup solution, if you don't have RTGs:  make sure each ship has a "reserve" battery that you keep fully charged but turned off, and a fuel cell.  That way, if a ship ever runs out of power and goes dead, you can turn on the reserve battery to bring it back to life, then use the fuel cell to turn a little bit of fuel into quite a bit of electricity, hopefully enough to get you through the crisis.  It's an emergency recovery tool, not a way to power your fleet continuously (you'd run out of fuel pretty quick).

[Guest]

1 hour ago, steuben said:

My ships, as always, are over build, over fueled, and over powered. My concern is about electrical, reading the wiki it looks like a factor 20 drop in solar power out there. If my math is right, two correctly oriented ox-stat panels should still power the octo core, correct?

Solar power in KSP follows the inverse square law for light (I think?  Pretty sure, NathanKell never corrected me on that one).  Given Kerbin orbital SMA as 1 AU, and that solar power listing in the VAB/SPH is at 1 AU, we can easily calculate the power you'll receive at Eeloo.

Kerbin SMA: 13,599,840,256 m

Eeloo SMA: 90,118,820,000 m

That means Eeloo is at 6.626 AU.  The inverse square law for light is I/R^2 and since power is normalized at Kerbin we can treat I as 1 at R = 1 AU (1/1^2 being 1).  So out at Eeloo you'll be generating 1/6.626^2 power, or 1/43.9 of the power you would normally generate.  At the outer bounds of Eeloo apoapsis you'll be generating 1/69.7 of the power you'll receive at Kerbin, which is probably a better number for planning.

The OKTO core requires 1.2 EC/min or 0.02 EC/sec.  A 3x2 or 1x6 solar panel (the retractable ones) puts out 1.6 EC/sec, while an OX-STAT gives us 21 EC/min and a OX-STAT-XL gives 2.8 EC/sec.  Out at Eeloo apoapsis the numbers look like 0.023 EC/sec for a 1x6 or 2x3, 0.005 EC/sec for an OX-STAT, or 0.04 EC/sec for an OX-STAT-XL.

As you can see, a pair of 3x2 or 1x6 solar panels are perfectly adequate for powering a small probe at Eeloo, all other power considerations aside.  In fact, a single would be fine but I always prefer panels in pairs.  You now have the tools to figure out power collection requirements for, say, a Dawn engine.

Edited April 15, 2016 by regex