dV needed to go from equatorial duna orbit, to poles, and back

[KerikBalm]

So my 0.24 Duna mission is underway, and I'm using a good old fashioned orbital rendevous plan -> LV-N tug + fuel depot stay in orbit, a lander goes down for Science!

I plan on installing custom biomes, which gives me more reason to visit the poles.

However.. My lander is just a modified Mun lander... and my Mun lander was a bit tight on dV going from an equatorial mun orbit, to the poles, and then back to equatorial. My duna lander does have some more dV built into it... but... I'm not sure it can do it.

As I figure it, obviously my lander saves a lot of dV coming down due to the atmosphere, a round trip from Mun orbit and back is 640*2 = 1280 m/s

A round trip on duna consists of ~50 m/s deorbit and cushion burn, and then 1380 m/s ascent... call it 1430 m/s vs 1280...

So for a plane change, I really only need to stick my apoapsis out a bit, then burn a bit to change it to polar, and aerobrake for a landing, then to launch into a polar orbit, stick my apoapsis out, change it to equatorial, and then aerobrake to circularize. (what I did for the Mun polar landing, except without the aerobraking).

Then, additionally, I can interact with Ike, and try to use its gravity for the plane change maneuver.

So basically, I'm asking how much dV I need to go from duna equatorial orbit, land on the poles of duna, and then rendevous again with a ship in equatorial orbit, assuming use of aerobraking and ike gravity assists.

Is it greater than the dV for doing the same at the mun?

I need to decide if I insert everything into a polar orbit, or equatorial.

I don't like polar orbits so much because the rendevous get a bit complicated if your lander spends too much time on the surface (ie, as the body rotates, for example, a surface stay of half of a duna day-month)

Or maybe I'll just visit the poles with an airplane (using modded ducted electric fans, or maybe just gliding there - using the NEAR mod fyi)

Edited September 10, 2014 by KerikBalm

[Jovus]

Have you considered the possibility of going directlly from your equatorial landing spot to the pole, and then back, and only then launching to orbit? I don't know if your lander will have that capability, but it might overall take less delta v than the plane change (while, admittedly, requiring you to frontload all the fuel into the lander.)

Beyond that, you might also investigate the idea of not just using Ike for an assist, but actually entering a highly elliptical orbit around Ike to change your inclination there. (It might take less dv due to the patched conic gravity model.)

[Empiro]

As a general rule of thumb, if you're in a circular orbit and not using gravity assists, it takes 0.414 * your current orbital velocity worth of delta-v to get into a highly elliptical orbit that's close to the edge of the SOI. (You're basically burning just under the escape velocity which is square-root of 2 times your current velocity). You can then make an arbitrary plane chance at the AP with very low cost. You then need to burn back to your original circular orbit, though with Duna, you can just aerobrake.

So to answer your question, assuming no gravity assists, around Duna it would take about 400-500 m/s delta-v to make any arbitrary plane change by going to the edge of the SOI.

Edited September 9, 2014 by Empiro

[cantab]

If you've yet to arrive, I'd just capture into a polarized orbit. Ascending after landing isn't that tricky, just wait until the lander is under the orbit, and make sure you head the right way!

[kahlzun]

To answer your question: as duna is larger and has higher gravity, it will probably need more fuel.

However, the aerobraking you can do to land saves a LOT of fuel.

It might end up being a wash, but it's hard to know for sure..

[Kryxal]

I'd say the best idea is to split off the lander early, burn to set up a polar aerobrake of lander + 10-15 minutes of delay, set up an aerobrake of your main craft, and hit the polar site first. I'd probably do a pass to capture and land on the second pass, but that's your choice.

[KerikBalm]

"Have you considered the possibility of going directlly from your equatorial landing spot to the pole, and then back, and only then launching to orbit? I don't know if your lander will have that capability, but it might overall take less delta v than the plane change "

To go to the edge of duna's SOI, for a cheap plane change, is 370 m/s, aerobraking basically takes care of the rest, I estimate the dv cost to be about 400 to get to the poles, and 400 to get from the poles back to equatorial. I doubt I could do a suboribtal hop from the equator to the poles for 400 m/s... maybe...

"To answer your question: as duna is larger and has higher gravity, it will probably need more fuel.

However, the aerobraking you can do to land saves a LOT of fuel.

It might end up being a wash, but it's hard to know for sure.. "

To answer my question, you repeat my question

Those are basically exactly the considerations I mentioned in my question.

"You can then make an arbitrary plane chance at the AP with very low cost. You then need to burn back to your original circular orbit, though with Duna, you can just aerobrake"

Yes, I know all that... its bascially what I described (although I used the dV maps for the SOI intercept calculations) - what I don't know is if I can use Ike to get a more efficient plane change, and how much dV that would save.

"but actually entering a highly elliptical orbit around Ike to change your inclination there."

Inclination doesn't work like that, I may be in a polar orbit around ike, but when I eject, I'm still in a more or less equatorial orbit around Duna, as I was in orbit around a body in an equatorial orbit.

"I'd say the best idea is to split off the lander early, burn to set up a polar aerobrake of lander + 10-15 minutes of delay,"

Yea, I guess I should hit the poles first, that way I only have to do 1 plane change with the lander instead of 2, it should save me about 300-400 dV (since I don't know what the dV cost is if I use Ike to change my inclination)

[Pecan]

Use the tug to get the lander into the right plane - uses efficienct LV-Ns, maintains full fuel in the lander. On the way back use it again to bring the lander home.

I know it doesn't answer your 'how much' question but I'm rushing off to work ...

[KerikBalm]

the laner, being for Duna, is also LV-N powered.

I ran the calculations, given the extra weight carrying 2 kerbals, 1 pair of radial chutes (also 1 pair of radial drogues, which really should be a stock part), etc, it is the "fuel optimal" engine to use given that the ISP is over double that of any other rocket engine, but it doesn't double the dry mass - even if I drop the science juniors and goo, for a dV requirement of 1,000 m/s, it uses less fuel than a 48-7s or a lv-909. I haven't checked if its mass optimal, but as I want it to do many landings and returns to orbit, I want it to use the least fuel per trip, so I don't need to send tankers out to refuel the depot so often.

The new stats for the structural fusalages means for only .2 tons, I can extend stacks low enough to accomodate the length of the central LV-N.

I see to go from orbit to an ike encounter is 270 m/s, whereas to the edge of the SOI is 370... so if I can perfectly use Ike... I might get away with a plane change for ~550 m/s

Edited September 10, 2014 by KerikBalm

[Laie]

I like cantab's suggestion the most: if you are in a polar orbit, you can land on the equator, too. And if you take up from the equator, you can as well ascend into a polar orbit.

So just approach with a polar orbit and do everything from there.

[Endersmens]

Inclination doesn't work like that, I may be in a polar orbit around ike, but when I eject, I'm still in a more or less equatorial orbit around Duna, as I was in orbit around a body in an equatorial orbit.

Well, actually it can work that way. If you eject from Ike retrograde in terms to Ike's orbit, with an equatorial speed of around 298 to 316 m/s (orbital speed of Ike) Along with some Polar momentum (IE you are going retrograde to the orbit, but at an angle so that you pop out at an angle) then your orbit around Duna will be somewhat polar. It'll be really precise, and tedious, but with careful manuever node planning it should definitely be possible.

Here are two pictures, kinda showing what I mean. The first one it top down, showing what the orbit will look like from the poles.

A standard escape burn, with at least 835 m/s of velocity (escape velocity+orbit velocity of Ike) So your burn delta-v should be around 835 (may be different depending on starting orbit height)

Here is a picture from the equator, showing your plane.

when you escape this way (it may be more of an angle than i drew) It will leave your Duna orbit somewhat polar. It will take a lot of finesse and tinkering with maneuever nodes, but it's defintely possible.

Disclamer: My art is bad, and my instructions may be hard to follow, so I'm sorry if it doesn't work because of that.

Edited September 10, 2014 by Endersmens

[Kasuha]

I'm with the polar parking orbit group here, if you're planning to visit multiple places on the planet, park in polar orbit and let the planet rotate below you. The same for any kind of surface scanning. You can park in polar orbit regardless of direction from which you'll come, there's onyl slight problem with phasing the ejection. but for that, all you need is a bielliptic plane change directly to the inclination in which you need to eject, and if you're lucky and do it right that change already comes with great deal of your ejection burn.

[KerikBalm]

Endersmens... yes it can work like that, but you don't need to go polar in ike orbit to do that. Jovus's suggestion was to go really eliptical at ike to do a plane change at Iki Apoapsis, instead of at duna apoapsis - if I understood him correctly.

Basically what you're showing is what I was planning, setting my Ike escape trajectory to be retrograde to ike's orbit around Duna... then just a nudge north or south will put me over duna's poles. I don't think its worth it to do any changing of the plane of my ike orbit, nor do I really plan to orbit Ike at all, I will enter the SOI, and I don't plan on using a capture burn.

Yes, it would be easier to just stick with a polar orbit, but that wasn't the question

Though I am open to the idea of sending my lander on a polar aerobraking, getting the pole visit out of the way, and doing the rest from an equatorial (or nearly equatorial) orbit

[SRV Ron]

An actual maneuver to do a 90* plane change using Ike as a slingshot;

The results;

With the new aids out there, that maneuver can be made more precise.

[Endersmens]

Endersmens... yes it can work like that, but you don't need to go polar in ike orbit to do that.

Wait, what? I wasn't suggesting a polar plane change. The first picture is top down, showing an equatorial orbit. When you perform your escape burn you just add a small plane change to put yourself in a polar orbit around Duna.

Basically what you're showing is what I was planning, setting my Ike escape trajectory to be retrograde to ike's orbit around Duna... then just a nudge north or south will put me over duna's poles. I don't think its worth it to do any changing of the plane of my ike orbit, nor do I really plan to orbit Ike at all, I will enter the SOI, and I don't plan on using a capture burn.

Yeah that sounds sort of like what I mean, and yeah you don't have to capture, you just have to plan your SIO changes correctly.

Also, yeah, if you use Ike to slow down, Your orbit would be really elliptic, so a polar plane change would be easy to accomplish after escaping Ike. Either way works.

[KerikBalm]

"Wait, what? I wasn't suggesting a polar plane change. The first picture is top down, showing"....

Yea, I get it, you weren't suggesting that, but I think that's what Jovus was suggesting, and thats what my comment was referring to.

SRV Ron- thats basically what I'm considering, I just wanted to know how much dV is needed to execute that manuever from low Dunar orbit... but I guess its pretty much what is needed to get an ike encounter+ a little adjustment.

[tomf]

To answer the original question I calculate that to do a 90 degree plane change by boosing to the edge of Duna's SOI doing the plane change there and then aerobraking back down will cost ~405m/s. 368 to boost the AP, 13.5 to change the inclination and then 22 to raise the PE back out of the atmosphere after the aerobraking.