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Transferring to Duna while staying in the Sun?


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I recently asked about transfer orbits to Duna using my small probe. I was informed that the optimal transfer orbit is a 'darkside' transfer and that this means the solar panels don't get power. That's no problem for a small probe, I can rebuild it with better propulsion.

Where this becomes an issue is my new MTV vehicle. It's intended as a manned Duna transfer vehicle based one the Copernicus MTV NASA conceived for the more distant part of the Constellation project. It relies on solar power and I want to keep it powered.

Is there a reasonable transfer orbit to Duna that will keep my solar panels lit? It might not be optimal, but it will be better?

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You'll be in the sun for 100% of any transfer orbit because there's nothing to block the sun out there in space.

If you mean that you want to make your transfer burn in the sun, that's harder because you need to increase your Sun apoapsis to go to Duna, which means accelerating in the direction of Kerbin's orbit, which means burning at night. But you're in dark for the same time (or less) than you would be in a single orbit of Kerbin so if your ship can't handle darkness for that long you may need some more batteries or RTGs.

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Thinking about it, it might work to launch retrograde around Kerbin and then burn in daylight to transfer to Duna. But that would take a lot more dV than a standard launch and transfer, and if your ship can't handle being in the dark for the transfer burn, it'll die as soon as it makes its first Duna orbit anyway.

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The vast majority of your transfer will be done in the sunlight, only the initial burn will be done in the shadow of Kerbin.

If you using Ion engines then that will be a bit of a problem, but if you are trying to boost something large with ion engines you are going to have issues anyway. My advice would be to switch to a nuclear stage, or if you really like long burns use the ion engine to spiral out without worrying about where your pe/ap are until you are nearly going fast enough to escape and then time your final burn to send you off into kerbol orbit in the right direction.

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As long as it doesn't have Ion engines you can add batteries to keep it powered on the dark side of a planet.

If it relies on Ion engines, no amount of batteries will allow it to make a 1000d/v ejection burn:(

As an alternate solution, you could try a moon slingshot if you want to keep it in the sun most of the time. Example below(not optimal, but you get the idea)

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that way, you do two burns, one as you come out on the daylight side of the planet, and another as you pass by the daylight side of the moon. as you can see in the second photo, that will get you to Duna orbit if you line up the phase angles right(mine aren't set up right now, so it won't show an intercept.)

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Yea, I think it was meant to be powered by nukes. . . in which case, if your ship is manned, you don't have to keep it powered to keep it under control. Only Ion engines will give you trouble on the dark side.

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Yea, I think it was meant to be powered by nukes. . . in which case, if your ship is manned, you don't have to keep it powered to keep it under control. Only Ion engines will give you trouble on the dark side.

I double down on that statement, shouldn't be an issue with NERVA's.

Increase your altitude further out from Kerbin, that way you spend a hell-of-a-lot less time in the shadow of the planet. Might work, might not.

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Assuming you're not using ion engines, there shouldn't be any problems. Manned capsules have fairly substantial power reserves of their own, and an extra battery pack or two will give you plenty of backup power unless you're also using some other system that imposes a constant strain on your power demands already.

The most power-consuing probe bodies, the new Remote Guidance Units, only consume electricity at a rate of 3 Electric Charge per minute. An RGU plus a Mk1-2 Command Pod have a total electric reserve of 165 EC, which will last you 55 minutes before going dry. Slap on a pair of Z100s for an extra 200 EC, and you can keep that thing running for just a hair over 2 hours in total darkness. Most (though not all) chemcial rockets also provide some power output while they're burning as well, although the LV-Ns don't.

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