Skip to main content
8 events
when toggle format what by license comment
Aug 16, 2021 at 13:14 comment added PM 2Ring @J.G. Right. The vis-viva relation means that GPE gets converted into KE, which you then need to get rid of when you reach your destination. OTOH, you can save some energy if you don't mind ending up in an eccentric orbit.
Aug 16, 2021 at 12:55 vote accept J.G.
Aug 16, 2021 at 12:55 comment added J.G. OK. It looks like there's no way to turn lost GPE into angular-momentum KE to make a significant "nudging" saving.
Aug 16, 2021 at 12:52 comment added PM 2Ring I guess I should also to mention en.wikipedia.org/wiki/Delta-v#Delta-v_budgets "It is not possible to determine delta-v requirements from conservation of energy by considering only the total energy of the vehicle in the initial and final orbits since energy is carried away in the exhaust"
Aug 16, 2021 at 12:46 comment added PM 2Ring @J.G. Mine's a little smaller. ;) SE's $GMmr_i^{-1}/2$ is just the negative of the specific orbital energy of Earth, times $m$, the payload mass. My table gives that as ~443 million joules/kg. But we can reduce that by Neptune's $-\epsilon$ of ~14.7 MJ/kg to get the actual specific energy required, which is ~428.8 MJ/kg. (You get the same number if you add up the absolute values of the specific kinetic energy changes at the two burns). Sorry, I should've included that subtraction in my program & table. I'll update it tomorrow.
Aug 16, 2021 at 10:58 comment added J.G. How does this compare with the expense estimate in the other answer?
Aug 16, 2021 at 6:17 history edited PM 2Ring CC BY-SA 4.0
added 8 characters in body
Aug 16, 2021 at 6:11 history answered PM 2Ring CC BY-SA 4.0