DV for LKO -> Pol Surface

[SkyFall2489]

For a mission I'm planning, I need to get from Low Kerbin Orbit to the surface of Pol. Due to mass constraints, I might have a tight delta V budget, and want to know how much delta V I'll need. I think I can pull off a capture assist with Tylo or Laythe, but a full KEKKJ chain on the way to Jool is gonna be too risky. (especially because I'm doing it on an LMP server where I can't quicksave/quickload.)

[Superfluous J]

You can "plan" it pretty easily if you have control of a ship in LKO. Make a maneuver node that intersects Jool, set up a mid-course correction that encounters Pol, and then at Pol set up a maneuver that stops you. Landing at Pol won't cost appreciably more than stopping in space next to it would.

Add those 3 maneuvers up,  add 10% margin or so, and there's your fuel budget.

Oh, one more thing. Make sure you encounter Pol when it and your ship are traveling as close to the same direction as possible.

And yes, you can try to encounter Tylo or Laythe to save some dV but I'm not sure how much you'll save over a direct encounter. It will take more maneuver nodes but if you've got the time (and conic patch limits in settings) why not give it a shot?

Edited April 25, 2023 by Superfluous J

[jimmymcgoochie]

Google “KSP delta-V map”.

[s_gamer101]

10 hours ago, SkyFall2489 said:

For a mission I'm planning, I need to get from Low Kerbin Orbit to the surface of Pol. Due to mass constraints, I might have a tight delta V budget, and want to know how much delta V I'll need. I think I can pull off a capture assist with Tylo or Laythe, but a full KEKKJ chain on the way to Jool is gonna be too risky. (especially because I'm doing it on an LMP server where I can't quicksave/quickload.)

If you want to do a Tylo or Laythe flyby, watch out for stuff like Vall moving in the way and compromising the entire flyby route. The trajectory on the map screen isn't perfectly precise when it comes to SOI changes (which is by the way not something the game can be blamed for, because it is mathematically impossible to exactly solve the Kepler equation and I'm pretty sure this is essential for the way KSP predicts SOI changes) so you always have to watch out for unwanted flybys in the Jool system. If you have trajectorys installed and you have faith in the heath resistance of your ship, you could attempt aerobraking at Jool, but I do not even remember if I have ever tried that myself to be honest and I don't know if it is safe.

[SkyFall2489]

1 hour ago, jimmymcgoochie said:

Google “KSP delta-V map”.

That won’t help me with a Tylo assist, and without one, it tells me I likely wont have enough fuel. However, the ship making the journey still needs enough adjustments that Im not sure what its range will be.

1 hour ago, s_gamer101 said:

If you want to do a Tylo or Laythe flyby, watch out for stuff like Vall moving in the way and compromising the entire flyby route. The trajectory on the map screen isn't perfectly precise when it comes to SOI changes (which is by the way not something the game can be blamed for, because it is mathematically impossible to exactly solve the Kepler equation and I'm pretty sure this is essential for the way KSP predicts SOI changes) so you always have to watch out for unwanted flybys in the Jool system. If you have trajectorys installed and you have faith in the heath resistance of your ship, you could attempt aerobraking at Jool, but I do not even remember if I have ever tried that myself to be honest and I don't know if it is safe.

A Jool aerobrake might be possible, but it would mean major modifications to the ship, increasing mass, and Im working with some tight mass limits.

[fulgur]

A capture assist will get you into an elliptical and/or inclined orbit of Jool. If you're lucky, you can make a radial/normal burn to get to Pol with a few hundred meters per second. If you're not so lucky you can adjust future encounters to reduce your inclination and get your orbit just crossing Pol, at which point it's just a matter of time until you get a close encounter.

If you were to leave from Minmus orbit (image shows a trip to Eve, but the same principle applies) rather than LKO (refuelling at Minmus), you could then decrease the dV to Jool by a few hundred as well. That might help depending on how tight your margins are.

[king of nowhere]

12 hours ago, SkyFall2489 said:

For a mission I'm planning, I need to get from Low Kerbin Orbit to the surface of Pol. Due to mass constraints, I might have a tight delta V budget, and want to know how much delta V I'll need. I think I can pull off a capture assist with Tylo or Laythe, but a full KEKKJ chain on the way to Jool is gonna be too risky. (especially because I'm doing it on an LMP server where I can't quicksave/quickload.)

well, as you yourself recognize, it depends greatly on the mission profile. if you can get to jool with gravity assists, you can spend as little as 900 m/s to get there - starting with using Mun to get out of kerbin's SoI. Otherwise, a direct mission will cost at least 2100 m/s.

Once you get to Jool, I recommend to not use the direct injection method suggested by @Superfluous J; that method works well with big moons, where you can get Oberth effect from the moon itself, but not on something as small as Pol. I definitely recommend using Tylo for a gravity assist instead. If you place your gravity assist correctly, you can achieve for free a Jool orbit with an apoapsis touching Pol's orbit and a periapsis somewhere around Vall. From there, it takes roughly 500 m/s to intercept on Pol - a lot less than you could achieve in other ways. And then you need 100 m/s to land on Pol.

So, 2700 m/s total. Make it 3000 for safety. Could be as little as 1500 m/s by reaching Jool with gravity assists.

EDIT: Aerobrake at Jool is not a good idea. You may do it with a very good heat shield, but even if you are successful, you end up in a orbit with a low periapsis, so intercept speed on any of the moons will be more expensive. Aerobrake at Laythe is possible, actually it could save some fuel if you can partially aerobrake on Laythe but without getting captured, instead using that to enter a trajectory intercepting Tylo, from where you could get to Bop with a lower intercept speed. but it's extremely difficult to control your trajectory out of an aerobraking passage. And if you use Laythe for a gravity assist to Pol, you will have a higher intercept speed than if you did it from Tylo.

 

Edited April 25, 2023 by king of nowhere

[SkyFall2489]

12 hours ago, king of nowhere said:

well, as you yourself recognize, it depends greatly on the mission profile. if you can get to jool with gravity assists, you can spend as little as 900 m/s to get there - starting with using Mun to get out of kerbin's SoI. Otherwise, a direct mission will cost at least 2100 m/s.

Once you get to Jool, I recommend to not use the direct injection method suggested by @Superfluous J; that method works well with big moons, where you can get Oberth effect from the moon itself, but not on something as small as Pol. I definitely recommend using Tylo for a gravity assist instead. If you place your gravity assist correctly, you can achieve for free a Jool orbit with an apoapsis touching Pol's orbit and a periapsis somewhere around Vall. From there, it takes roughly 500 m/s to intercept on Pol - a lot less than you could achieve in other ways. And then you need 100 m/s to land on Pol.

So, 2700 m/s total. Make it 3000 for safety. Could be as little as 1500 m/s by reaching Jool with gravity assists.

EDIT: Aerobrake at Jool is not a good idea. You may do it with a very good heat shield, but even if you are successful, you end up in a orbit with a low periapsis, so intercept speed on any of the moons will be more expensive. Aerobrake at Laythe is possible, actually it could save some fuel if you can partially aerobrake on Laythe but without getting captured, instead using that to enter a trajectory intercepting Tylo, from where you could get to Bop with a lower intercept speed. but it's extremely difficult to control your trajectory out of an aerobraking passage. And if you use Laythe for a gravity assist to Pol, you will have a higher intercept speed than if you did it from Tylo.

 

Previously, I've reached Pol with around 2.7 km/s from low kerbin orbit, but it was some time ago and I don't exactly remember the route I took. I think I used a Tylo assist to capture.
If I depart from Minmus, burning until I have a low kerbin periapsis and then doing an escape burn there, I might be able to save around 600-700 m/s. This would result in needing 2.1 - 2.3 km/s, which I think I can achieve given the other mission constraints.

[king of nowhere]

8 hours ago, SkyFall2489 said:

Previously, I've reached Pol with around 2.7 km/s from low kerbin orbit, but it was some time ago and I don't exactly remember the route I took. I think I used a Tylo assist to capture.
If I depart from Minmus, burning until I have a low kerbin periapsis and then doing an escape burn there, I might be able to save around 600-700 m/s. This would result in needing 2.1 - 2.3 km/s, which I think I can achieve given the other mission constraints.

yes, exactly; if you refuel on minmus, the way to leave is to lower periapsis first, to get oberth effect.