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0something0

Best way to go from planet to moon

Question

So, we have two different mission profiles. 

  • Mission Profile 1
    • This mission profile involves waiting until the time is right,  than launch straight up to hit the satelite.
  • Mission Profile 2
    • This profile involves getting into orbit and hohmann-transferring into the satellite's sphere of influence

So, which one would cost less delta-v?

Edited by 0something0

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#2 is almost always the lowest dV, but the exact answer depends on your TWR.

However, the deltaV difference between #2 and #1 is not large, #1 is definitely faster to get to your destination, #1 is easier if you do not have manuever nodes unlocked, and #1 is easier if you do not have the "prograde hold" SAS mode available yet.

 

 

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1 hour ago, 5thHorseman said:

I'd like to see someone consistently get to Minmus using method #2. And I'd like to know how many kerbucks (I don't care about dV because you don't pay for dV. You pay for engines to give you more TWR, and fuel to lift those engines, which possibly won't increase your dV significantly or even at all) the rocket costs to deliver its payload.

I never use direct-launch, it's just too annoying to time correctly and is only suitable for one-shot missions.

In contrast, lauch-to-orbit then transfer is exactly the same for one-shot, orbital refuelling, orbital construction and reusable infrastructure.  It uses standard, dedicated, launch vehicles and space-only transfer vehicles so is as cheap as any other launch.

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Then again, if you're heading there to actually do stuff, I think #2 is going to make life easier on you since capture will be easier.  In both cases, there's going to be a "leave at the right time" component ... have people tested how much of a difference lower-TWR engines make on a straight-up ascent?

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I'd like to see someone consistently get to Minmus using method #2. And I'd like to know how many kerbucks (I don't care about dV because you don't pay for dV. You pay for engines to give you more TWR, and fuel to lift those engines, which possibly won't increase your dV significantly or even at all) the rocket costs to deliver its payload.

Edited by 5thHorseman

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There's another option.

  • Mission Profile 3
    • Perform a gravity turn during launch (i.e., not "straight up"), but burn continuously until your apoapsis reaches the target

This approach doesn't waste delta V on gravity losses and performs the transfer burn when the vessel is lower and moving faster, so it has the potential to be more efficient than both of the other two. But in practice any differences are likely to be too small to notice.

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I do #1 sometimes... I just build a bigger rocket to make up for the lost efficiency. #2 is harder but more efficient. 

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1 hour ago, HebaruSan said:

There's another option.

  • Mission Profile 3
    • Perform a gravity turn during launch (i.e., not "straight up"), but burn continuously until your apoapsis reaches the target

This approach doesn't waste delta V on gravity losses and performs the transfer burn when the vessel is lower and moving faster, so it has the potential to be more efficient than both of the other two. But in practice any differences are likely to be too small to notice.

While that does have the benefit of a slightly reduced dV on a perfect launch (and it's awesome to finish your launch burn with a Duna intersection) the other downsides are the same as with the straight-up approach: No rest period to plan, and any deviation from perfect will require a correction burn which eats into any savings you had on launch.

But I must reiterate that it is totally awesome to nail one of these, especially interplanetary.

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