How do you plan your launch windows in RSS?

[CitizenVeen]

Hi everyone, how do you plan your launch windows in Real Solar System?

I went to the moon, and did it by kinda estimating. About 18days to the moon, moon should be arround here. Then cape carnavaral should be around such and such, so that when I overspend my initial orbit (with a ~200km Pe, and a 3k AP, because of the many engines having only 1 ignition), my high AP should be arround the DN/AN node. It worked, after initial orbit I planed a manouvre node that raised my Ap on the DN node (which was somewhere near my Pe, but not really), and got a pretty good capture at the moon.

However, as I am planning to go to mars, I expect it wont be as much forgiving.

Questions:

1. Is there a launch window planner for RSS out there? Can only find stock ones.

2. Is there a good way to plan it without a launch window planner just telling you what to do where? As we can't see DN/AN nodes before we launched. Nor plan manouvre nodes before we are decently in orbit, its kinda hard to estimated imo.

3. What launch sites do you use?

Answers much appreciated. Thanks!

[Snark]

I'm not an RSS user, but in general it's not too hard to calculate Hohmann transfers between circular orbits. Let's say you're at Earth and want to go to Mars. You'd work out the window like this:

1. Calculate the orbital period of an elliptical orbit whose Pe is at Earth and whose Ap is at Mars.
   • Time for an orbit is 2 * pi * sqrt(a³ / GM), where G is the universal gravitational constant, M is the mass of the thing you're orbiting, and a is the semimajor axis of the orbit, i.e. the average of periapsis and apoapsis.
2. Take half of that. This is how long the journey takes.
3. Divide by the length of a Mars year, then multiply by 360. This will tell you how many degrees Mars will move while you're on your way.
4. Subtract your answer to step #3 from 180.

The answer you get in step 4 is how many degrees behind Mars the Earth should be when you launch. There's your window.

 

Edited January 6, 2016 by Snark

[NathanKell]

There's a great tool linked in the OP of the RSS thread.

[Gaarst]

Flyby Finder (program) and Transfer Window Planner (in-game mod) both work with RSS.

[UnusualAttitude]

If I understand correctly, part of your problem is launching into the correct inclination for an encounter with the Moon? One solution is to have a probe in Low Earth Orbit (at say 200 - 400 km) that is already on the correct plane (20-something degrees). You could do this via hyperedit or - if that feels cheaty - by launching a small probe with a ton of monoprop or a restarting engine, targeting the Moon and adjusting inclination until AN/DN are at 0°. You can then easily use this probe's orbit as a guide: when your launch site passes under the orbit's path it is time to launch into the same 20-something degree inclination.

For interplanetary, I haven't really found it essential to launch into the precise optimal inclination for the transfer (although Transfer Window Planner Gaarst cited above will tell you what this inclination should be).

I mainly use the equatorial sites. They give you the best dV-to-orbit reduction and allow you to reach almost any inclination you want, directly. Try Kourou (South America, 5° from Equator) or Omelek (Pacific Island, 9° from Equator).

[PLAD]

For getting to the planets I use Flyby Finder for RSS (*blush*) as mentioned above. For getting to the Moon I also wrote a little spreadsheet in which you enter your launch site and the search start time, and it tells you the next two launch opportunities for a transfer to the Moon using a due-East launch azimuth. It's available at the bottom of the first post in the FF for RSS thread.

[CitizenVeen]

Still having problems finding flyby's for planets.

I guess my main problem is that, because earth and mars have inclinations arround the sun that differ by ~2 degrees. I dont get an encounter at the Ap, when raised to fits mars Ap. (because I am either going 'over' or 'under' mars' orbit). No matter how I burn, from what inclination orbit from earth, I am pretty much getting the same results. The only thing I can find, is to do a mid course change (at the DN/AN towards mars mostly), but this costs me an easy extra 3000 deltaV. Is it even possible to get a direct encounter mars encounter, from a single burn from earth orbit? And if so, how the hell do you guys do it? Some help-the-noob instructions out there somewhere?

Also, when entering the exact information all the fly by planners out there give me, I dont get anything near an encounter (they all suggest something different anyways).

 

[Laie]

Gaarst linked the Transfer Window Planner above. That one's quite good to determine the launch window, but it assumes that you depart from an enter into an equatorial orbit, so the directions should be taken with a shovel of salt. Still, it's good for mission planning while at the space center -- somehow I feel more comfortable if I inspect the porkchop plot myself, instead of just trusting the date KAC comes up with.

MechJeb's maneuver planner has a tab "advanced transfer to another planet". I don't know what assumptions it makes about your destination (flyby? orbit? If the latter, what inclination?), but I do know that it starts it's calculation with the actual orbit you are in. The launch windows it comes up with typically fall a little earlier that those by the Planner above (on the order of 2 weeks for a Mars transfer). Anyway, it plots a maneuver for you: no need to carefully transpose pre-calculated data.

Here's how I make my interplanetary missions:

a) I have a spent satellite in LEO; even though it has long since run out of juice, MJ still works nicely on it. So I run Mechjeb on that satellite and let it determine a transfer for that satellite. If the transfer has an extremely large normal component, I'm not above using Hyperedit to adjust the satellite's "Longitude of Ascending Node" in 10-degree increments until the maneuver becomes mostly prograde. This may sound like an arcane art, but in fact it's easy to learn while doing it.

b) when the launch day comes, I select said satellite as a target: this gives me an inclination to launch into. Of course I never quite match the orbit, but getting the inclination about right is the one issue that matters most.

c) using the position and known magnitude of the satellite's maneuver node as a starting point, I like to set up the maneuver myself. Except when I'm lazy and just use MJ to plan the burn.

[CitizenVeen]

13 hours ago, Laie said:

Gaarst linked the Transfer Window Planner above. That one's quite good to determine the launch window, but it assumes that you depart from an enter into an equatorial orbit, so the directions should be taken with a shovel of salt. Still, it's good for mission planning while at the space center -- somehow I feel more comfortable if I inspect the porkchop plot myself, instead of just trusting the date KAC comes up with.

MechJeb's maneuver planner has a tab "advanced transfer to another planet". I don't know what assumptions it makes about your destination (flyby? orbit? If the latter, what inclination?), but I do know that it starts it's calculation with the actual orbit you are in. The launch windows it comes up with typically fall a little earlier that those by the Planner above (on the order of 2 weeks for a Mars transfer). Anyway, it plots a maneuver for you: no need to carefully transpose pre-calculated data.

Here's how I make my interplanetary missions:

a) I have a spent satellite in LEO; even though it has long since run out of juice, MJ still works nicely on it. So I run Mechjeb on that satellite and let it determine a transfer for that satellite. If the transfer has an extremely large normal component, I'm not above using Hyperedit to adjust the satellite's "Longitude of Ascending Node" in 10-degree increments until the maneuver becomes mostly prograde. This may sound like an arcane art, but in fact it's easy to learn while doing it.

b) when the launch day comes, I select said satellite as a target: this gives me an inclination to launch into. Of course I never quite match the orbit, but getting the inclination about right is the one issue that matters most.

c) using the position and known magnitude of the satellite's maneuver node as a starting point, I like to set up the maneuver myself. Except when I'm lazy and just use MJ to plan the burn.

Thanks alot! 

I only tried the mechjeb planner once. But then it gave me a suggestion wich was just a 60m/s burn or so from a LEO (so, naturaly, that only raised my AP with a couple km) so i assumed it was pretty bugged and useless, it did warn me that it doesnt work on al inclinations, so that might have been the problem. Ill try it again

[Aleksejev78]

You're all bunch of yappers, explaining things nonsense and complicating easy things. All you have to do, to launch to moon's right inclination in RSS, is select Moon as target and wait purple retrograde icon to move to 90 degress in kompas and launch your rocket. Just turn to 90 degrees orbit and you shouldn't miss orbit inclination more than 1 degree... I think that wasn't too hard to explain.

[Vanamonde]

6 minutes ago, Aleksejev78 said:

You're all bunch of yappers, explaining things nonsense and complicating easy things. All you have to do, to launch to moon's right inclination in RSS, is select Moon as target and wait purple retrograde icon to move to 90 degress in kompas and launch your rocket. Just turn to 90 degrees orbit and you shouldn't miss orbit inclination more than 1 degree... I think that wasn't too hard to explain.

Well, the yappers in this 3-year-old thread were trying to help, anyway. It is, after all, rocket science. 

[Lapis]

On 1/6/2016 at 4:10 PM, Snark said:

I'm not an RSS user, but in general it's not too hard to calculate Hohmann transfers between circular orbits. Let's say you're at Earth and want to go to Mars. You'd work out the window like this:

1. Calculate the orbital period of an elliptical orbit whose Pe is at Earth and whose Ap is at Mars.
   • Time for an orbit is 2 * pi * sqrt(a³ / GM), where G is the universal gravitational constant, M is the mass of the thing you're orbiting, and a is the semimajor axis of the orbit, i.e. the average of periapsis and apoapsis.
2. Take half of that. This is how long the journey takes.
3. Divide by the length of a Mars year, then multiply by 360. This will tell you how many degrees Mars will move while you're on your way.
4. Subtract your answer to step #3 from 180.

The answer you get in step 4 is how many degrees behind Mars the Earth should be when you launch. There's your window.

 

Just going to re-explain this but with images if that is ok.

Here  is step one as an expression(I may have done it wrong just going off of how I understood your explanation):

Step two(the answer to this will be the variable z):

step 4(Where y is the length of a mars year. this expression will now be z):

 

And your answer will be

Edit: always check the comment date before replying. Hope this will be able to help anyone else i guess

Edited December 7, 2019 by Lapis