[WEB APP] Launch Window Planner

[Guest]

Did you just time it for exactly the UT specified, or did you adjust it to correct the ejection angle? (If the latter, I'd love to know how you worked it out, as I end up eyeballing them as often as not)

I timed it for the exact UT using the Maneuver Node Improvement mod. Theoretically that should result in the correct ejection angle because the node should be at that angle at that UT.

[Guest]

In my Moho trip I had to drag around my maneuver node (neglecting the whole "your ejection path must be parallel" stuff since I couldn't get even a close approach marker with that) for get an intersect, it was all good until I had to do the insertion burn, as I had to use like 4km/s more of what it was indicated by the app. It was the same launch window, with departure in day 10. Next time I will try to be more rigorous but it does seem that small errors in your initial burn create bigger ones later.

How do you not introduce slight flaws over a six minute burn? Is the app generating nodes for instantaneous burns? I suppose I could make an engine to test that theory... Either way, I wouldn't expect that large of a margin of error over a six minute burn.

Sorry for double posting, my phone is terrible for multi-quoting.

[Crater]

I timed it for the exact UT using the Maneuver Node Improvement mod. Theoretically that should result in the correct ejection angle because the node should be at that angle at that UT.

No, the correct UT will give you the correct phase angle (angle from Kerbin - Sun - Moho).

The ejection angle is where in your orbit around Kerbin you are at the time of your burn. Getting that wrong can make hundreds or even thousands of m/s difference to your orbital velocity around the Sun, which means you will be way off course. It is the difference between accelerating prograde out of Kerbin's SOI and adding your Kerbin-relative orbital velocity to Kerbin's Sun-relative one, down to dropping out retrograde, and subtracting the same, along with all of the options in between that would include a radial component.

[Guest]

No, the correct UT will give you the correct phase angle (angle from Kerbin - Sun - Moho).

So do you set the node at the correct ejection angle before or after the departure UT? Depending on your parking orbit, there's a pretty large window of time between those two nodes.

[skykooler]

So do you set the node at the correct ejection angle before or after the departure UT? Depending on your parking orbit, there's a pretty large window of time between those two nodes.

You should really have a parking orbit as low as possible; there's a rather large savings in required delta-v when launching from a low orbit due to the Oberth effect. So the window of time shouldn't be that long.

[Crater]

*grin* you time your launch so that you're in the right place at the right time, of course.....

Seriously, though.... you should be in a pretty low orbit anyway to take advantage of the Oberth effect, so you shouldn't be looking at more than an hour plus or minus on the departure time, and that's only a fraction of a degree on the phase angle, which is easily correctable for with just a little delta-V.

Mostly, you just have to go for whichever ejection point in your orbit seems closest to the correct phase angle.

Don't forget that the calculator gives stats for a single point-in-time implusive burn at the exact moment. If you're using a nuke engine and pulling 1/4 of a g, you're looking at something close to 10 minutes of burn per 1000m/s of delta-V, which you will NEED to bracket across the ejection burn point, and some people choose to do starting an orbit or two early, and do the burn in stages at ejection point, then at PE each time on successive orbits, and the fact that you don't get to make an impulsive burn is going to add a lot more error than one orbit earlier or later on your ejection.

[pina_coladas]

Quick suggestion: a bigger porkchop plot area! Maybe a fullscreen option or a zoom? It's kinda tiny. Also, it would be cool if the tooltip displayed more info than just the DV on mouse-over (maybe add flight-time). And the DV stats, it would be nice if the prograde/normal etc data was displayed by default and not just in a tooltip, for copy/paste purposes.

All around really cool little tool, thanks for making it.

[mic_e]

What about an option to ignore departure or arrival d-v (aerobraking etc...)

[tavert]

You can ignore arrival dv by leaving the arrival orbit altitude blank.

[Kerolyov]

Can someone clarify what these angles are and how they are defined?

1) Angle to intercept - is the angle between the where plane change burn occurs and intercept?

2) Ejection inclination - assume this is the angle from prograde in prograde-normal plane for an all in-one ballistic burn? So normal delta-V = sin(this angle) x Ejection delta-v?

3) Plane change angle - Assume this is just how much you change orbit plane by at plane change burn?

4) Insertion inclination -is this just the angle between your ship and target planets trajectories at intercept? If so how are -ve and + ve angles defined?

Thanks!

Edited October 19, 2013 by Kerolyov

[alexmun]

Can someone clarify what these angles are and how they are defined?

Sure!

1) Angle to intercept - is the angle between the where plane change burn occurs and intercept?

Yes, this angle only applies to the mid-course plane change trajectory and it is how many degrees before you get to your destination that you need to execute the plane change.

2) Ejection inclination - assume this is the angle from prograde in prograde-normal plane for an all in-one ballistic burn? So normal delta-V = sin(this angle) x Ejection delta-v?

It's not quite that simple. The ejection inclination is what you want the inclination of your hyperbolic ejection orbit to be after your maneuver. If you hover your mouse over the ejection delta-v value you'll get a tooltip with the prograde and normal components of the burn. The actual calculation requires you to know the velocity of your ejection orbit immediately after your burn, which I don't display. The formulas are:

normal delta-v = ejection velocity * sin(ejection inclination)

prograde delta-v = ejection velocity * cos(ejection inclination) - initial orbital velocity

3) Plane change angle - Assume this is just how much you change orbit plane by at plane change burn?

Yup!

4) Insertion inclination -is this just the angle between your ship and target planets trajectories at intercept? If so how are -ve and + ve angles defined?

It's the angle between the velocity of your ship and the velocity of the target planet at intercept. Another way of looking at it is that it is the inclination of your orbital plane around the planet relative to the planet's orbital plane around the sun.

[pina_coladas]

Oh hey you're back! What do you think about my suggestions for making the graph bigger, showing more detail on the graph mouseover tooltip (flight time?), and displaying delta v stats as selectable text instead of tooltips? Those few things would be a big improvement on an already very useful tool.

[Kerolyov]

Thanks Alexmun for the quick and helpful reply, great tool by the way . Had only just noticed the tooltip prograde and normal info. Maybe add some text to tell users to mouseover to see the prograde and normal as it isn't so obvious?

[flap]

Hello !

Nice tool ! It would also be really cool if the trajectory could be drawn when clicking a point.

[Ninja_Thomek]

Finally managed to get to Moho with your app Thanks a lot!

[quantumpion]

Is there any way to use this tool for non-parking orbits at departure for the purpose of planning multi-stage gravity assists (possibly powered)?

[jrandom]

Would it be possible to add support for those of use using the Real Solar System mod?

[sephirotic]

Is there any way to use this tool for non-parking orbits at departure for the purpose of planning multi-stage gravity assists (possibly powered)?

Would it be possible to add support for those of use using the Real Solar System mod?

+1 For these two questions!

If these two features were ever added, this would make this one of the most awesome and must have mods ever!

Btw, AFAIK RSS use J2000 for it's start point IIRC, I always wondered if real life launch window planning would work for RSS-KSP and vice-versa.

[alexmun]

A new version of the launch window planner is now live! Aside from some cosmetic upgrades, the main new feature for this version is the ability to edit the list of celestial bodies. You can now add new planets and moons to the list. You can also add your vessels, if you have their orbital elements from MechJeb, Kerbal Engineer, Telemachus, or the like. This allows you to do fun things like get a pork chop plot for transfers from any Kerbin orbit to the Mun or plotting a rendezvous with a stranded ship in solar orbit, or even just a simple rendezvous between two ships in Kerbin orbit.

Now to catch up on some old questions...

What do you think about my suggestions for making the graph bigger, showing more detail on the graph mouseover tooltip (flight time?), and displaying delta v stats as selectable text instead of tooltips? Those few things would be a big improvement on an already very useful tool.

The amount of time it takes to calculate the plot is directly related to the size of the graph. I've chosen the current size to give a good trade-off of speed vs detail. If you need more detail, you can always zoom in on an area of interest using the advanced settings.

You can read the flight time and time of departure (roughly) by looking at the Y and X axes of the graph, respectively. The new version does allow you to select the component delta-v's of your ejection burn after you click on the little info button.

Is there any way to use this tool for non-parking orbits at departure for the purpose of planning multi-stage gravity assists (possibly powered)?

If you enter 0 for your initial orbit, it will calculate a plot that ignores the origin planet's gravity which can give you an idea of what launch windows are open at what times for a given planet. The ejection delta-v that it gives you on that plot will represent the "hyperbolic excess velocity" you would need when leaving the planet's sphere of influence to get to your next destination. Actually calculating a gravity assisted trajectory is a much harder problem that is beyond what I plan to do with this tool.

Would it be possible to add support for those of use using the Real Solar System mod?

I've just released an update that allows you to edit the orbits and parameters of all the bodies in the system (except for the Sun). If you have the orbital elements of the Real Solar System bodies, you could enter them in and everything should work, except that you would also need to change the values for the Sun. That you would need to do from your browser's javascript console with the command:

CelestialBody.Kerbol.mass = mass
CelestialBody.Kerbol.gravitationalParameter = 6.674e-11 * mass
CelestialBody.Kerbol.radius = radius

Where mass is the mass of the Sun in kilograms and radius is the radius of the Sun in meters.

If somebody wanted to fork the project to provide the Real Solar System bodies by default, that would be very easy to do and fine with me.

[m4v]

Is it possible to add a feature for get plots similar to this? http://trajbrowser.arc.nasa.gov/traj_browser.php (just click search) ie, a single plot for several bodies.

[metaphor]

I love this web app!

Another suggestion, what about parking orbits that have a different inclination than equatorial?

[alexmun]

Is it possible to add a feature for get plots similar to this? http://trajbrowser.arc.nasa.gov/traj_browser.php (just click search) ie, a single plot for several bodies.

That is a very cool tool! Unfortunately, I don't think it's computationally feasible to calculate all those windows in real time. Someone has gone through and created a spreadsheet of launch windows which you could use to create a plot like that:

http://www.reddit.com/r/KerbalAcademy/comments/1qt764/a_compiled_list_of_optimal_interplanetary/

I love this web app!

Another suggestion, what about parking orbits that have a different inclination than equatorial?

Eventually, I would like to make it possible to calculate ejections from an arbitrary parking orbit, using the new features to add your vessel's orbital elements. No idea when I'll get around to doing that, however, because the current calculations take a lot of shortcuts based on the equatorial, circular assumptions.

[m4v]

That is a very cool tool! Unfortunately, I don't think it's computationally feasible to calculate all those windows in real time. Someone has gone through and created a spreadsheet of launch windows which you could use to create a plot like that:

http://www.reddit.com/r/KerbalAcademy/comments/1qt764/a_compiled_list_of_optimal_interplanetary/

I don't understand, is not going to be more computationally intensive than making 6 plots together, is kinda what I have been doing so far, I use the launch window planner once for each planet before deciding which one to visit. Just calculate the same porkchop for each planet, pick the transfer that uses the least dV in each, and display it in a single graph, isn't that right?

But the spreadsheet is useful too, not as pretty but it will work.

Edited January 29, 2014 by m4v

[Astronut25]

Would it be possible to include the prograde, normal, and radial Delta-v values in the transfer details?

[alexmun]

Would it be possible to include the prograde, normal, and radial Delta-v values in the transfer details?

If you click the blue info icon after the ejection delta-v value, it will give you a full breakdown of the delta-v components.