Is it possible to create a 'target' from just orbital location information?

[drtedastro]

Is there any way to create a 'pseudo' point, just based on its orbital location, to be able to use as a target???

For instance, I wish to place a comms sat ahead and behind Mun, in Mun's same orbit just ahead and behind by xxxxx km's. I can do a hit or miss approach playing with nodes and pushing and pulling them, but there 'should' be a way to put in a desired location to be a target.

thanks for any info.

DrTedAstro.

[Panichio]

Sorry, you're going to need a ship in that location already if you want to have a target there.

Using the maneuver node, the navball will point to it, and with MechJeb, there might be some information you could use there to help.

[KerbMav]

Sounds like Lagrange points which are not in the game (yet)?

[maltesh]

To the best of my knowledge, no, there's no stock capability mod that allows you to target a user-specified position on an orbit where no object currently is.

My general tactic has been to teleport a marker object into the position I'm aiming for by editing the persistence file, and then rendezvous with the marker object for the real mission.

[Kimberly]

There's already a way to do this, if you have Kerbal Engineer to quickly tell you your orbital period:

Get into a circular orbit that's just outside the Mun's sphere of influence. Your orbital period will be shorter than the moon's, so you'll "catch up" after a bunch of orbits. Once you're orbiting next to the moon, find out where you want to go. Turn this into a fraction of the Mun's orbit, e.g. if you want to orbit 10,000 km away from the Mun, find out what fraction of the Mun's orbital circumference is. Then, burn prograde until your orbital period is the Mun's orbital period minus that fraction, e.g. if you want to be 1/8th ahead of the Mun, make your orbital period 7/8ths of the Mun's orbital period. One full orbit later, you'll be 1/8th ahead of the Mun, so burn until your orbital period is equal to that of the Mun. You should stay in the same relative position to the Mun now.

This strategy works for any time you want to get in the same orbit, at a specific location ahead of an existing satellite. It's just harder to do with bodies that have their own sphere of influence.

[drtedastro]

To the best of my knowledge, no, there's no stock capability mod that allows you to target a user-specified position on an orbit where no object currently is.

My general tactic has been to teleport a marker object into the position I'm aiming for by editing the persistence file, and then rendezvous with the marker object for the real mission.

I am not familiar with this method. if possible could you please explain in more detail. sounds like what I will need to try for now.

[drtedastro]

There's already a way to do this, if you have Kerbal Engineer to quickly tell you your orbital period:

Get into a circular orbit that's just outside the Mun's sphere of influence. Your orbital period will be shorter than the moon's, so you'll "catch up" after a bunch of orbits. Once you're orbiting next to the moon, find out where you want to go. Turn this into a fraction of the Mun's orbit, e.g. if you want to orbit 10,000 km away from the Mun, find out what fraction of the Mun's orbital circumference is. Then, burn prograde until your orbital period is the Mun's orbital period minus that fraction, e.g. if you want to be 1/8th ahead of the Mun, make your orbital period 7/8ths of the Mun's orbital period. One full orbit later, you'll be 1/8th ahead of the Mun, so burn until your orbital period is equal to that of the Mun. You should stay in the same relative position to the Mun now.

This strategy works for any time you want to get in the same orbit, at a specific location ahead of an existing satellite. It's just harder to do with bodies that have their own sphere of influence.

thanks for reply, but I already use this method for where and when it will work.

for other locations, I really need / want the ability to specify a navigational way point, orbital body and other orbit parameters, and then basically navigate to it.....

thanks to all for ideas and suggestions.

[Mr Shifty]

There's already a way to do this, if you have Kerbal Engineer to quickly tell you your orbital period:

Get into a circular orbit that's just outside the Mun's sphere of influence. Your orbital period will be shorter than the moon's, so you'll "catch up" after a bunch of orbits. Once you're orbiting next to the moon, find out where you want to go. Turn this into a fraction of the Mun's orbit, e.g. if you want to orbit 10,000 km away from the Mun, find out what fraction of the Mun's orbital circumference is. Then, burn prograde until your orbital period is the Mun's orbital period minus that fraction, e.g. if you want to be 1/8th ahead of the Mun, make your orbital period 7/8ths of the Mun's orbital period. One full orbit later, you'll be 1/8th ahead of the Mun, so burn until your orbital period is equal to that of the Mun. You should stay in the same relative position to the Mun now.

This strategy works for any time you want to get in the same orbit, at a specific location ahead of an existing satellite. It's just harder to do with bodies that have their own sphere of influence.

This works great, and you don't even need to do the fractions. Just get out to the Mun's orbit (11,400,000 meters) and circularize. Determine if you want to move your position clockwise or counterclockwise. Burn prograde for clockwise and retrograde for counterclockwise until your orbit is a few 10's of km bigger, then just wait until you're where you want to be relative to the Mun. Then burn the other way until your orbital period matches the Mun's. For satellites, you don't need to be in a perfectly circular orbit; you'll maintain your position relative to the Mun if the periods match. Note that you need to get them to match as closely as possible. I recommend trying to get it exact to the second. And even then, you'll have to do periodic station keeping.

[Kimberly]

This works great, and you don't even need to do the fractions. Just get out to the Mun's orbit (11,400,000 meters) and circularize. Determine if you want to move your position clockwise or counterclockwise. Burn prograde for clockwise and retrograde for counterclockwise until your orbit is a few 10's of km bigger, then just wait until you're where you want to be relative to the Mun. Then burn the other way until your orbital period matches the Mun's. For satellites, you don't need to be in a perfectly circular orbit; you'll maintain your position relative to the Mun if the periods match. Note that you need to get them to match as closely as possible. I recommend trying to get it exact to the second. And even then, you'll have to do periodic station keeping.

This works as well, of course, but using fractions is very useful if you want to evenly space out satellites.

[drtedastro]

Ok, for bodies that have their own SoI, you mentioned 'harder'..... What is the 'harder' method?

[Kimberly]

Ok, for bodies that have their own SoI, you mentioned 'harder'..... What is the 'harder' method?

It's the same method, it's just more difficult to do to. This is because the shorter orbit you use to catch up with the body can't intersect the body's sphere of influence, or its gravity will will alter your orbit. Similarly, the place you want to end up at relative to that body has to be outside of its sphere of influence, so you don't start orbiting it instead of the parent body. With artificial satellites, you don't have that problem.

[drtedastro]

It's the same method, it's just more difficult to do to. This is because the shorter orbit you use to catch up with the body can't intersect the body's sphere of influence, or its gravity will will alter your orbit. Similarly, the place you want to end up at relative to that body has to be outside of its sphere of influence, so you don't start orbiting it instead of the parent body. With artificial satellites, you don't have that problem.

Again, 'more difficult to do?'... so how, exactly, would you put something 3100 km's in front and behind Mun. Anyone can pick any spot on the orbit, away from the SoI and then wing-it until you are 'close', but how would you put a craft exactly at the desired point.

Your description is very 'general' to say the least. I have placed many sat's into equi-distance orbits for my comms and gps arrays, but just wanted to see if there was a method that was not based on 'hit or miss', or close enough approach, other than cheating, where SoI was in the way.....

[Kimberly]

Again, 'more difficult to do?'... so how, exactly, would you put something 3100 km's in front and behind Mun. Anyone can pick any spot on the orbit, away from the SoI and then wing-it until you are 'close', but how would you put a craft exactly at the desired point.

Your description is very 'general' to say the least. I have placed many sat's into equi-distance orbits for my comms and gps arrays, but just wanted to see if there was a method that was not based on 'hit or miss', or close enough approach, other than cheating, where SoI was in the way.....

If you use fractions of the orbital period, you can get a pretty exact result. Say you want to get into the same orbit as the Mun, 180 degrees apart from it. Get into the same (circular) orbit as the Mun, check what fraction of the Mun's orbit you need to move forward to get to the desired position, and then burn retrograde so your orbital period is the Mun's orbital period minus that fraction of the Mun's orbital period. In one orbit, you'll have moved up ahead just as much as you want, so when you reach apoapsis you can burn prograde and get the same period as the Mun again.

The added difficulty, compared to doing this with any old satellite, is that you can't enter the Mun's sphere of influence.

[drtedastro]

The "check what fraction of the Mun's orbit" part. is this just a visual guesstimate, or are you looking at some orbital parameter that I seem to be missing.

Thanks for help with this, I appreciate it.

DrTedAstro.

[Nao]

You could make a node on LKO for Mun encounter and just drag it around the LKO a desired number of degrees (15,58deg for 3100km before/after in Mun orbit. For 100km LKO its 84,7s before/after Mun transfer burn).

In reality its even easier using Mun as a target we make node with transfer orbit to reach Ap of 11400km (Mun orbit) and see closest approach markers, then just rotating the burn position on LKO we can change separation to desired 3100km or something similar. And make burns according to nodes. In testing I managed to get to Mun orbit ahead of it by 3278km in just two burns from LKO.

[Kimberly]

The "check what fraction of the Mun's orbit" part. is this just a visual guesstimate, or are you looking at some orbital parameter that I seem to be missing.

Thanks for help with this, I appreciate it.

DrTedAstro.

This is easier if you're releasing a network of satellites, because you can always work things out from your current position, where you release satellite #1... If you use the Mun as a target, though, I think Kerbal Engineer has some information on this. Otherwise, you do need to eyeball that part.

[Ralathon]

Ok, for bodies that have their own SoI, you mentioned 'harder'..... What is the 'harder' method?

He never said there was a harder method. Just that bodies with a SoI make it harder. This is probably because if you end up inside the SoI it'll mess up your orbit pretty badly.

[maltesh]

I am not familiar with this method. if possible could you please explain in more detail. sounds like what I will need to try for now.

To get around to answering this quesiton:

Step 1: BACK UP YOUR SAVE FILE, BY copying it to elsewhere on your hard drive. Failure to back up the save file will make it somewhere between difficult and impossible to fix things later if you screw things up.

Build your Marker Object in the VAB, and move it to the Launchpad.

Scott Manley has a tutorial on Persistence file editing here:

THe basics are:

Hit F5 to Quicksave.

Open the quicksave.sfs file in a text Editor such as notepad (but not Wordpad)

Find the your marker object's Vessel information in the persistence file. Within it will be the following attributes:

            sit = LANDED
            landed = True
            landedAt = LaunchPad

And you'll want to change them to

            sit = ORBITING
            landed = False
            landedAt = 

Which will make KSP ignore the surface information about the spacecraft and pay attention to the orbital information. Now you've got to modify the Orbit info to put it in the appropriate place.

In Kerbal Space Program, the Mun's orbit, and its position along it is defined by the following orbital Parameters (Converted to the Persistence File's Vessel format for clarity)

            ORBIT
            {
                SMA = 12000000
                ECC = 0.0
                INC = 0.0
                LPE = 0.0
                LAN = 0
                MNA = 0.9
                EPH = 0
                REF = 1
                OBJ = 0
            }

Since the Mun is a special case, with a circular orbit, and apparently the desired distance from its center is 3100 km. If the distance you want to place the marker object at is 3100km measured along the Mun's circular orbit, the calculation is fairly simple.

The Mun mover along its orbit at 542.5 m/s. It takes an object moving at that speed 5714.28571 seconds to cover 3100 km. So if you place an object on the Mun's orbit with the same Mean Anomaly at Epoch (MNA) such that its Epoch (EPH) is 5714.28571 seconds later, it will be 3100km behind the Mun.

            ORBIT
            {
                SMA = 12000000
                ECC = 0.0
                INC = 0.0
                LPE = 0.0
                LAN = 0
                MNA = 0.9
                EPH = 5714.28571
                REF = 1
                OBJ = 0
            }

Similarly if you set EPH = -5714.28571 , it will be 3100km ahead of the Mun. Note that the reason this particular edit works is because the Mun is in a circular orbit; There is no orbital position that maintains a fixed distance from a non-gravitating object in a non-circular Keplerian orbit.

Once you've adjusted the approapriate information, save the modified quicksave.sfs file, go back to the game, and hit F9.

Your marker object will be now teleported to a position on the Mun's orbit, 3100km away from the Mun, measured along its orbit, as requested.

You may now launch a real mission to rendezvous with the Marker Object, and delete the Marker Object when it gets there.

So yeah, that's basically how I'd do it. Hyperedit has a similar facility to teleport things off the pad, but I've not made use of it, so I don't know if it lets you modify your orbit's epoch. But if you have known, specific set of Keplerian orbital parameters that you want to guide a spacecraft to (such as what I had when setting up my Tetrahedral Configuration Challenge), I find the process fairly useful.

Edited July 20, 2013 by maltesh

[drtedastro]

To get around to answering this quesiton:

Step 1: BACK UP YOUR SAVE FILE, BY copying it to elsewhere on your hard drive. Failure to back up the save file will make it somewhere between difficult and impossible to fix things later if you screw things up.

Build your Marker Object in the VAB, and move it to the Launchpad.

Scott Manley has a tutorial on Persistence file editing here:

THe basics are:

Hit F5 to Quicksave.

Open the quicksave.sfs file in a text Editor such as notepad (but not Wordpad)

Find the your marker object's Vessel information in the persistence file. Within it will be the following attributes:

            sit = LANDED
            landed = True
            landedAt = LaunchPad

And you'll want to change them to

            sit = ORBITING
            landed = False
            landedAt = 

Which will make KSP ignore the surface information about the spacecraft and pay attention to the orbital information. Now you've got to modify the Orbit info to put it in the appropriate place.

In Kerbal Space Program, the Mun's orbit, and its position along it is defined by the following orbital Parameters (Converted to the Persistence File's Vessel format for clarity)

            ORBIT
            {
                SMA = 12000000
                ECC = 0.0
                INC = 0.0
                LPE = 0.0
                LAN = 0
                MNA = 0.9
                EPH = 0
                REF = 1
                OBJ = 0
            }

Since the Mun is a special case, with a circular orbit, and apparently the desired distance from its center is 3100 km. If the distance you want to place the marker object at is 3100km measured along the Mun's circular orbit, the calculation is fairly simple.

The Mun mover along its orbit at 542.5 m/s. It takes an object moving at that speed 5714.28571 seconds to cover 3100 km. So if you place an object on the Mun's orbit with the same Mean Anomaly at Epoch (MNA) such that its Epoch (EPH) is 5714.28571 seconds later, it will be 3100km behind the Mun.

            ORBIT
            {
                SMA = 12000000
                ECC = 0.0
                INC = 0.0
                LPE = 0.0
                LAN = 0
                MNA = 0.9
                EPH = 5714.28571
                REF = 1
                OBJ = 0
            }

Similarly if you set EPH = -5714.28571 , it will be 3100km ahead of the Mun. Note that the reason this particular edit works is because the Mun is in a circular orbit; There is no orbital position that maintains a fixed distance from a non-gravitating object in a non-circular Keplerian orbit.

Once you've adjusted the approapriate information, save the modified quicksave.sfs file, go back to the game, and hit F9.

Your marker object will be now teleported to a position on the Mun's orbit, 3100km away from the Mun, measured along its orbit, as requested.

You may now launch a real mission to rendezvous with the Marker Object, and delete the Marker Object when it gets there.

So yeah, that's basically how I'd do it. Hyperedit has a similar facility to teleport things off the pad, but I've not made use of it, so I don't know if it lets you modify your orbit's epoch. But if you have known, specific set of Keplerian orbital parameters that you want to guide a spacecraft to (such as what I had when setting up my Tetrahedral Configuration Challenge), I find the process fairly useful.

Maltesh, first thanks for a great reply. Sorry I have not been back to this sooner. I actually thought that it was dead issue. I see what you are doing and that will work perfectly for me at this time. Maybe, sometime in the future, there will the an option to 'create target' based on info like you have used....

again, thanks....