RSP - Being able to land on every point of a planet/moon

[Jackissimus]

I am running a reusable space program, which means I don't waste any stages after I get things out of Kerbin atmosphere. That in turn means that I have to always have an infrastructure in place if I want to fly somewhere. I fly up to Kerbin Space Station, take a bus to Mun Space Station, then take a dedicated Mun Lander to the surface. The Mun Space Station gets refueled by a Fuel Shuttle from a Kethane Base on the surface.

So far I've been doing all this in equatorial orbits and equatorial landing sites. What if I wanted to land anywhere on Mun, though? I would need a space station on polar orbit. But that creates a problem that I can only take my bus from Kerbin twice per month. That's because I need to approach Mun at such an angle that will reach the space station without needing large burns to correct my longitude of ascending node. I might reach Mun polar orbit, but with a longitude of ascending node 90 degrees off in relation to the Mun space station. Correct me if I am wrong here.

That's not a big problem though, I can wait half a month (well not really a month, but it's tedious to call it "a time it takes Mun to do one full orbit"). The real problem comes when I want to do the same with Dres for example. Then I have to not only always wait for a transfer window for Dres, but also wait when the transfer window is aligned with the right approach angle for the polar space station. This might take many years and I don't like huge time warps.

So what's the best way to reach every point on Dres then? I thought of many things:

1. The first option is the one I just described - as far as I understand it involves a lot of waiting.
   
2. I could wait for the usual transfer window to Dres, then enter a really high equatorial orbit when I reach Dres. Then I need to wait for the right time to do a 90 degrees inclination burn to align my LAN with the station. The inclination burn should be cheap because I am in a high orbit, but I don't know how much waiting this involves (probably much less than option one).
   
3. I could just set up everything equatorially and then always land at the equator and perform a short suborbital hop to my base at higher latitude. This could be the fastest, but I don't know how much deltaV this involves.
   
4. Maybe there is a possibility to set up some maneuver nodes during the flight to Dres in such a way that will allow me to approach the polar space station at the right angle no matter when I come to Dres? I am not sure about this, what do you think?
   

This is interesting to me especially because it's sort of realistic. I know NASA had plans for a station around Earth, Moon and a tug between them, before the budget cuts in 60s/70s.

EDIT: This is a picture of option 1:

Edited August 12, 2013 by Jackissimus

[Monkeh]

To hit a certain spot on the Mun I got a low almost circular orbit. Pick the point you want to land and then add a maneuver node somewhere before it on your trajectory. Play with the little green and pink nodes and watch where you end up. Make sure you're heading a good bit past your intended point so you have the room to slow down. The pink nodes move you up and down the planet, green forward and back. (My terminology is terrible, sorry).

When almost exactly above the right place turn retrograde and burn baby, burn. Halt all horizontal movement. Use the 'set as target' button and then push the pink marker towards the green marker on your descent burn down.

I can get within a kilometer or so so far, getting closer with every attempt though.

[lunait]

Off the top of my head, I would probably choose option 2. You get to use the regular transfer windows, and you avoid the extra deltaV required to land and lift off again to adjust your position on the target celestial body. I haven't done the calculations or anything, but I would expect that adjusting the orbit while in... orbit, takes less effort (but maybe more time) than landing and then hopping along the surface.

Also, I propose the word "munth" (or "münth", depending on how you spell Mun/Mün) for the time it takes Mun to do one full orbit. Very imaginative, I know.

Edited August 12, 2013 by lunait

[Jackissimus]

Off the top of my head, I would probably choose option 2. You get to use the regular transfer windows, and you avoid the extra deltaV required to land and lift off again to adjust your position on the target celestial body. I haven't done the calculations or anything, but I would expect that adjusting the orbit while in... orbit, takes less effort (but maybe more time) than landing and then hopping along the surface.

Also, I propose the word "munth" (or "münth", depending on how you spell Mun/Mün) for the time it takes Mun to do one full orbit. Very imaginative, I know.

What a wordsmith! I hope "munth" lives on, it's a great word

Yeah I was guessing option 2 as well. It's the golden middle way. It's faster than option 1 and probably cheaper than option 3. I still wonder if there is an option 4 though ...

[Mr. Scruffy]

Hmmm... i am pondering these problems right now as well (well i just started pondering them, so...).

2. seems the best option, with the added detail of bringing your station in a high orbit to start with. That will make incliniation adjustments for your lander cheap. If you can spare the fuel or know exactly when to catch your fall, it also makes aiming for your target easier, once your lander has its desired inclination: Since your horizontal v will be rather low, burning it off is easy and then you fall straight down (except for the planet´s rotation). I´d probably go with a (nigh) equatorial orbit for the station, because the landers will be light (and thus correcting their inclination is cheap) compared to the ships coming in and out of the system, which will predominantely be on equatorial courses and rather costly to have their inclinination fixed.

[Scotius]

If i want to get into polar orbit, i aim for a very elliptic equatorial orbit first. When you are at apoapsis far away from a low gravity body, planar change is dirty cheap. Burn lasting mere couple of seconds is enough to flip your orbit plane by 90 degrees. Then you can do braking burn and go straight for landing. Unfortunately it means this method is best suited for long range transfers, when you can set such eccentric orbit from the get-go. Attempting polar landings from equatorially orbiting space station will cost a lot of dV.

[Boris_T_Roach]

Why not put your mun station at a 60 degree inclined orbit, then you''ve got 2 chances a month to get a ship to it, plus it covers more of the mun surface so you can easily land/launch anywhere within its track and maybe only a bit more Dv if you land near to the poles

Boris

[Jackissimus]

Hmmm... i am pondering these problems right now as well (well i just started pondering them, so...).

2. seems the best option, with the added detail of bringing your station in a high orbit to start with. That will make incliniation adjustments for your lander cheap. If you can spare the fuel or know exactly when to catch your fall, it also makes aiming for your target easier, once your lander has its desired inclination: Since your horizontal v will be rather low, burning it off is easy and then you fall straight down (except for the planet´s rotation). I´d probably go with a (nigh) equatorial orbit for the station, because the landers will be light (and thus correcting their inclination is cheap) compared to the ships coming in and out of the system, which will predominantely be on equatorial courses and rather costly to have their inclinination fixed.

I think this wouldn't work. When you kill your horizontal velocity in a high orbit, you come hurtling towards the planet at much higher speed because you are falling from higher altitudes, so it doesn't save you much delta-v. Also about the landers vs buses mass - it's actually the other way around. I have heavy surface lander shuttles that are meant to lift up a lot of fuel from my kethane bases and resupply the station. I want to have as much fuel left in them as possible when I reach the station. But the interplanetary bus mostly carries passengers, sometimes some base or station modules. The buses are relatively light, because they refuel all the time at the planetary orbital stations, so they are mostly payload mass.

If i want to get into polar orbit, i aim for a very elliptic equatorial orbit first. When you are at apoapsis far away from a low gravity body, planar change is dirty cheap. Burn lasting mere couple of seconds is enough to flip your orbit plane by 90 degrees. Then you can do braking burn and go straight for landing. Unfortunately it means this method is best suited for long range transfers, when you can set such eccentric orbit from the get-go. Attempting polar landings from equatorially orbiting space station will cost a lot of dV.

Exactly, you can easily go into a polar orbit when you arrive at a planet. The problem is that I need to randezvous with my station then, because my buses are not equipped for landing. And then I have a problem because my longitude of ascending node (LAN) can be very different than my station's.

Why not put your mun station at a 60 degree inclined orbit, then you''ve got 2 chances a month to get a ship to it, plus it covers more of the mun surface so you can easily land/launch anywhere within its track and maybe only a bit more Dv if you land near to the pole. Boris

As I said, what do you do when you want to do the same with Dres? It involves a lot of waiting.

[Mr. Scruffy]

Ahhh, yeah, i dont do kethane, so i thought the landers would be much lighter than the base. On the high-altitude for the base: I think i said ´ If you can spare the fuel or know exactly when to catch your fall´ - i didnt mean to say it was cheaper fuel-wise, just possibly be easier to aim for your target.

Well, if your landers are heavier than the station, than it ought to be the station switching incliniations according to the landers need. In other words, the station should move towards the lander, not vice versa, whenever possible. For decending it makes not much of a difference, so here it is the lander who has to move anyways, and there seems little point draging the station along at this point. But upon return, any inclination change should be done by the station and only the station, if possible and needed.

[SRV Ron]

If you want to do a polar orbit on Mun to land at the pole, or any other planet or moon, do a correction burn well before reaching the SOI to place the paragee directly above or below the target. Then, when you burn retrograde under the SOI, you will be in polar orbit. That same correction burn can be used to get an orbital plane on any angle that you need. The correction burn is far more efficient at changing orbital plane then doing so while in orbit.

[Jackissimus]

Ahhh, yeah, i dont do kethane, so i thought the landers would be much lighter than the base. On the high-altitude for the base: I think i said ´ If you can spare the fuel or know exactly when to catch your fall´ - i didnt mean to say it was cheaper fuel-wise, just possibly be easier to aim for your target.

Misunderstood, sorry. Anyway, without Kethane I have no motivation to build the station or the fuel lander whatsoever. I think without kethane I would just build one station around Kerbin and that's it.

Well, if your landers are heavier than the station, than it ought to be the station switching incliniations according to the landers need. In other words, the station should move towards the lander, not vice versa, whenever possible. For decending it makes not much of a difference, so here it is the lander who has to move anyways, and there seems little point draging the station along at this point. But upon return, any inclination change should be done by the station and only the station, if possible and needed.

The station is heavy too. It holds a lot of fuel itself. I was really hoping to just leave it on a polar orbit, and use the lander the shuttle back and forth whenever the station flies over the surface base (basically twice every planetary day).

[Jackissimus]

EDIT: Double post

[Jackissimus]

That same correction burn can be used to get an orbital plane on any angle that you need.

Really? That's great! That is what I was hoping for option 4.

Let me just see if I understand this. So I am approaching Dres. At the time of arrival the polar orbital station has an orbital plane tangential to the velocity vector of the planet. How can I set up the correction burn to align myself with the orbital plane? Should I basically burn to get in front of the planet?

I really need to learn to change the conics mode for this, I just don't understand my orbits before I reach the SOI.

Edited August 12, 2013 by Jackissimus

[chaos_forge]

I'm slightly confused here . . . why do you need a polar orbital station? You just need a better lander. A lander with 2 LVN's and a rockomax 16's worth of fuel has enough thrust-to-weight and delta-v to land anywhere on an airless body from equatorial orbit and then get back to equatorial oribt. And since the lander is reusable, you don't have a problem with radioactive materials falling back to kerbin.

[aNewHope]

Let me just see if I understand this. So I am approaching Dres. At the time of arrival the polar orbital station has an orbital plane tangential to the velocity vector of the planet. How can I set up the correction burn to align myself with the orbital plane? Should I basically burn to get in front of the planet?

I really need to learn to change the conics mode for this, I just don't understand my orbits before I reach the SOI.

Changing conics mode is fairly easy: Just open the settings.cfg file in your KSP directory and change the "CONIC_PATCH_DRAW_MODE" to 0. Then you can see your approach with the targeted planet in focus. For a polar orbit you want your periapsis above the north pole. To move it up/down you need to burn normal/antinormal and to move it left/right you need to burn counterradial/radial (prograde/retrograde can have similar effect).

Simply place a maneuver node halfway to Dres and test which direction you need to burn. When you have done it a few times, it gets very easy.

[LameLefty]

Changing conics mode is fairly easy: Just open the settings.cfg file in your KSP directory and change the "CONIC_PATCH_DRAW_MODE" to 0. Then you can see your approach with the targeted planet in focus. For a polar orbit you want your periapsis above the north pole. To move it up/down you need to burn normal/antinormal and to move it left/right you need to burn counterradial/radial (prograde/retrograde can have similar effect).

Simply place a maneuver node halfway to Dres and test which direction you need to burn. When you have done it a few times, it gets very easy.

There's also a mod called (I think) Maneuver Nodes that gives you a GUI to change conics mode on the fly, along with text entry fields to fine-tune the delta-V of your planned burn along all three axes. For those of who who really like planning and executing orbital maneuvers, it's a great addition to the game.

EDITED TO ADD: Here it is: Maneuver Node Improvement.

http://forum.kerbalspaceprogram.com/showthread.php/42716-0-21-1-Maneuver-Node-Improvement-v1-2b?highlight=Maneuver+Node

[Horn Brain]

All you have to do is put your periapsis in/near the line of intersection of your incoming trajectory with your station's orbit, then capture yourself into a highly elliptical orbit (apoapsis just below the SoI radius). You can then do the correction for very cheap, because the AN/DN of your orbit will be near apoapsis. This is actually pretty easy to do because you can rotate your periapsis in a circle around the planet just by doing tiny course corrections a few days before the encounter. Even if it isn't perfect, it is usually reasonably cheap, and you can sometimes do smaller normal/anti-normal burns to move your nodes out towards apoapsis before you do the big plane change.

Also, note that, if your incoming vehicles are going to be running low on fuel, they won't use as much fuel for the same amount of dV, so the cost of this whole maneuver is low in terms of mass, even if it's high in dV.

[arq]

If you put your station in a very high Munar orbit, it will be much cheaper to make the changes to match it. However, this makes trips to the surface very expensive, so it would prob be better to be in a low Munar orbit.

I would suggest go to Mun as normal, brake there just enough to capture in its SOI, coast back to Apo, make your inclination change, and then lower your Apo for a station rendezvous. Make sure that you capture such that your Peri/Apo are aligned with the polar orbit you want. This is probably easier if you start out in a more polar orbit in the first place.

[Jackissimus]

I'm slightly confused here . . . why do you need a polar orbital station? You just need a better lander. A lander with 2 LVN's and a rockomax 16's worth of fuel has enough thrust-to-weight and delta-v to land anywhere on an airless body from equatorial orbit and then get back to equatorial oribt. And since the lander is reusable, you don't have a problem with radioactive materials falling back to kerbin.

Inclination changes are very expensive, it's certainly not a very efficient way. Try to do a 90deg inclination changes in LKO. It will cost you more than twice the cost of getting to the Mun. It's interesting that it's actually cheaper to get to the Mun than to change inclination. Sometimes it's even better to fly to the Moon to make your inclination changes - check out this article: http://en.wikipedia.org/wiki/HGS-1.

I'm not sure I understand your last sentence.

[Mr Shifty]

And then I have a problem because my longitude of ascending node (LAN) can be very different than my station's.

Seems like it's possible to have the same problem with equatorial orbits as well. Imagine you approach a planet from the direction of its north or south pole. How do you get into an equatorial orbit in that case? You're going to have to tune your approach while you're in interplanetary space so that you come in tangent to the desired orbital plane.

[Kerbart]

So far I've been doing all this in equatorial orbits and equatorial landing sites. What if I wanted to land anywhere on Mun, though? I would need a space station on polar orbit. But that creates a problem that I can only take my bus from Kerbin twice per month. That's because I need to approach Mun at such an angle that will reach the space station without needing large burns to correct my longitude of ascending node. I might reach Mun polar orbit, but with a longitude of ascending node 90 degrees off in relation to the Mun space station. Correct me if I am wrong here.

That's not a big problem though, I can wait half a month (well not really a month, but it's tedious to call it "a time it takes Mun to do one full orbit"). The real problem comes when I want to do the same with Dres for example. Then I have to not only always wait for a transfer window for Dres, but also wait when the transfer window is aligned with the right approach angle for the polar space station. This might take many years

It's called a schedule. Most liner transport companies (ships, airlines) have one. You have a shipment for Dres? Well you're in luck! The stars align (well, kinda) and we have a vessel lined up for y... oooh, wait. We're booked full and it looks like we're going to roll your cargo for the next shipment, 14 munths from now...

Of course there's the express service, but it's a bit more expensive as we're burning insane amounts of fuel to get there...

*Hands you the "Dres Express" service guide. The "tariff" section simply says "if you need to know, you can't afford it anyway"*

[Jackissimus]

So I just got home and got some time to test the idea of approaching at the right angle to have the same orbital plane as the station, as SRVRon suggested. BTW I used the term LAN before, but saying "orbital planes" is easier to understand I think.

I was testing on a craft getting from LKO to Mun. I quickly noticed that yeah, I can fine tune my approach angle, but I can only approach the Mun from the front, not from the behind. And that I can do mostly in about 90 degrees range there, I cannot approach the Mun perpendicularly to its orbit for example. And then it hit me that I cannot approach the Mun from behind, I always have to come from the front, because I have much lower orbital velocity than Mun at that point, so it has to catch up to me. Opposite situation would be a transfer to Moho, I cannot approach Moho from the front, I am always going much faster than it is. But basically yeah, I can always overshoot the Mun orbit or undershoot it and end up in different orbital planes, that's what I learned ... the 90degrees range is a bit worrying though, maybe I can improve this.

Mechjeb has a great tool for quickly changing conics mode, I didn't even know, I already use its info screens.

[Jackissimus]

All you have to do is put your periapsis in/near the line of intersection of your incoming trajectory with your station's orbit, then capture yourself into a highly elliptical orbit (apoapsis just below the SoI radius). You can then do the correction for very cheap, because the AN/DN of your orbit will be near apoapsis. This is actually pretty easy to do because you can rotate your periapsis in a circle around the planet just by doing tiny course corrections a few days before the encounter. Even if it isn't perfect, it is usually reasonably cheap, and you can sometimes do smaller normal/anti-normal burns to move your nodes out towards apoapsis before you do the big plane change.

Also, note that, if your incoming vehicles are going to be running low on fuel, they won't use as much fuel for the same amount of dV, so the cost of this whole maneuver is low in terms of mass, even if it's high in dV.

I didn't get you in the beginning - how can you rotate your periapsis before the actual SOI change? Maybe a little, but not like 180 degrees, which is what I might need.

The last sentence is complete nonsense to me. It's the same dV as before. If you spend very little fuel at this stage, you still have to add a huge fuel tank at Kerbin ascent. DeltaV is the same no matter where you burn.

If you put your station in a very high Munar orbit, it will be much cheaper to make the changes to match it. However, this makes trips to the surface very expensive, so it would prob be better to be in a low Munar orbit.

I would suggest go to Mun as normal, brake there just enough to capture in its SOI, coast back to Apo, make your inclination change, and then lower your Apo for a station rendezvous. Make sure that you capture such that your Peri/Apo are aligned with the polar orbit you want. This is probably easier if you start out in a more polar orbit in the first place.

How do you change you orbital plane? Not inclination, longitude of ascending node.

Seems like it's possible to have the same problem with equatorial orbits as well. Imagine you approach a planet from the direction of its north or south pole. How do you get into an equatorial orbit in that case? You're going to have to tune your approach while you're in interplanetary space so that you come in tangent to the desired orbital plane.

No, this is not the same. Equatorial orbits you can always get into, there is just one single equatorial orbit and you can always reach it easily. However, there are 360degrees worth of polar orbits and it's difficult to reach the one you want exactly.

It's called a schedule.

Well it turns out I might not need to wait so many years, just wait for the transfer window. But there are still some unresolved issues.

I am getting a bit frustrated because my words maybe cannot really explain the problem. So I made a simple picture with all the mspaint power skills I could muster

[Mr Shifty]

No, this is not the same. Equatorial orbits you can always get into, there is just one single equatorial orbit and you can always reach it easily. However, there are 360degrees worth of polar orbits and it's difficult to reach the one you want exactly.

Ah, you're right, but for the wrong reasons. Equatorial orbits are only special because they (typically) lie near the plane of the ecliptic. I wonder if you can achieve what you want this way:

- Enter the planet's SOI; your trajectory will be hyperbolic.

- Burn normal/anti-normal to adjust the periapsis so that it lies over a pole. (This should be possible for cheap, but I'm not at KSP, so can't test it.)

- Do your capture burn at periapsis, but stop the burn as soon as the orbit closes. The orbit should now be a highly elliptical orbit with periapsis over one pole and apoapsis over the other.

- Coast to apoapsis and rotate the orbit to the desired longitudinal plane.

[SRV Ron]

Ah, you're right, but for the wrong reasons. Equatorial orbits are only special because they (typically) lie near the plane of the ecliptic. I wonder if you can achieve what you want this way:

- Enter the planet's SOI; your trajectory will be hyperbolic.

- Burn normal/anti-normal to adjust the periapsis so that it lies over a pole. (This should be possible for cheap, but I'm not at KSP, so can't test it.)

- Do your capture burn at periapsis, but stop the burn as soon as the orbit closes. The orbit should now be a highly elliptical orbit with periapsis over one pole and apoapsis over the other.

- Coast to apoapsis and rotate the orbit to the desired longitudinal plane.

You should set this up well before the encounter using the up and down translation handles on the maneuver tool when planning your correction burn. You have to place map view on the orbital plane to see those changes take place. Also, adjust the prograde, retrograde, so that the periapsis is directly over the pole of the target. Then, when you get the capture, burn at periapsis to circularize.