How to know when my satellite will be over the Welcome Back Island?

[Joontry]

Hello, I have a contract that requires me to do a gravity scan while in space over the Welcome Back Island biome in a JNSQ save. Is there a mod or a method that will allow me to predict when exactly my satellite will be over that biome? I believe it is a very small biome, so it would be difficult to just wait and watch for when I happen to be over the biome. Thanks

[jimmymcgoochie]

The easiest way to do this would be launching a small suborbital rocket just above the atmosphere from the Welcome Back Island launch site (which only appears with Kerbal Konstructs installed), though launching from the KSC into an equatorial orbit should bring you over WBI fairly regularly and you could use something like [x]Science to grab the gravity scan as soon as you were in the right place.

[Joontry]

14 minutes ago, jimmymcgoochie said:

The easiest way to do this would be launching a small suborbital rocket just above the atmosphere from the Welcome Back Island launch site (which only appears with Kerbal Konstructs installed), though launching from the KSC into an equatorial orbit should bring you over WBI fairly regularly and you could use something like [x]Science to grab the gravity scan as soon as you were in the right place.

Thanks for the reply. The thing is, the measurement has to be taken while high in space from this particular satellite that launched from KSC whose orbit is about 87 degrees inclined and is very eccentric. I know that eventually the sat will pass over WBI but that it could take hours or days and will only be over WBI for a few seconds, so I'm trying to predict when that will be. I guess the alternative is to use kerbalism, RO, or some mod that makes the science experiment continuously take readings, but I really don't want to do that.

[jimmymcgoochie]

Kerbalism won’t help you here- gravity scans take 14 days so it’ll take literally years to complete.

In this case, if you’ve fulfilled every other contract parameter I think it’s acceptable to use the alt+F12 cheat menu to complete the contract- trying to get an experiment done in space high over a biome that’s only a few square kilometres in total on a planet the size of JNSQ Kerbin is nearly impossible no matter how you go about it.

[Joontry]

Thank you. I'm running Principia also. Sure, I could just cheat to finish the contract. But then I'd miss a chance to learn something and I'm more interested in that than finishing the contract quickly. How exactly would you predict when a satellite in a near polar orbit will be directly over a particular set of coordinates in real life? I get that the math involved is probably quite difficult. Is it possible to make a mod that would apply that same method to solving a similar problem in KSP?

[jimmymcgoochie]

Principia?  You’re on your own…

Joking aside, SCANsat might help you- if you make a biome map of Kerbin, you could use that to see the probe’s trajectory over the surface and find a time when it crosses over Welcome Back Island that way; no idea if it works with Principia though.

Does the contract require that specific satellite to do the gravity scan, or can you just launch anything up there into an equatorial orbit with a much better chance of passing over WBI and get the scan done that way?

[Morphisor]

I concur with Jimmy, Scansat is your best bet. In this particular case however, WBI is an uncommonly tiny biome which is extremely frustrating to try and cover from high space.

Best bet would be to launch a satellite on a molniya orbit such that the highest part of the orbit crosses the latitude of WBI location.

[Joontry]

Thanks for the replies. I had already used the alt-shift-f12 and completed the contract though. But now that I have a complete biome scan with SCANsat and have used it a bit, I realize you are correct that looking at the trajectory on a SCANsat biome map and its zoomed-in map, warping until that trajectory crosses WBI, then trying to come out of warp and do the experiment right at the moment I'm over WBI, would be the closest thing to a best solution. Good call on the molniya orbit! That would make the mission take much less in game time. I think the contract required that the specific satellite do the scan and that it have a very polar orbit though (80-100 degrees ish, too polar for molniya). I've used the SCANsat biome map while running Principia to execute a few other experiments over small biomes like "shores" and it works fine. It seems like a possible new feature for SCANsat would be to tell you when your orbit's trajectory over the surface will come within a given distance of a particular set of coordinates, since it already seems to be doing much of the math required to answer that question. I wonder if SCANsat communicates with Principia well enough to make predictions far into the future about the trajectory the craft's orbit will trace over its maps of the surface.

[Morphisor]

2 hours ago, Joontry said:

Thanks for the replies. I had already used the alt-shift-f12 and completed the contract though. But now that I have a complete biome scan with SCANsat and have used it a bit, I realize you are correct that looking at the trajectory on a SCANsat biome map and its zoomed-in map, warping until that trajectory crosses WBI, then trying to come out of warp and do the experiment right at the moment I'm over WBI, would be the closest thing to a best solution. Good call on the molniya orbit! That would make the mission take much less in game time. I think the contract required that the specific satellite do the scan and that it have a very polar orbit though (80-100 degrees ish, too polar for molniya). I've used the SCANsat biome map while running Principia to execute a few other experiments over small biomes like "shores" and it works fine. It seems like a possible new feature for SCANsat would be to tell you when your orbit's trajectory over the surface will come within a given distance of a particular set of coordinates, since it already seems to be doing much of the math required to answer that question. I wonder if SCANsat communicates with Principia well enough to make predictions far into the future about the trajectory the craft's orbit will trace over its maps of the surface.

If you look closely at the Scansat big map with trajectories on, you'll notice there's not just the immediate next orbit, but a huge set of predictions on it, in the form of small 'dents' or short lines covering the map. You can use this to estimate when you'll make a close approach. Not sure how well this interacts with principia however.

If being alerted when over a specific biome is your aim, sciencealert or x science may do the trick, assuming there's an experiment to trigger. Coming out of high speed time warp has a tendency to overshoot, however, so don't rely on it too much.