How do I plot an ejection burn from the launch pad?

[birdog357]

I'm looking to launch to Jool direct from the pad with no parking orbit. How do I go about plotting the node so I have an aim point once I clear atmo? Mods are an option.

[Signo]

I will assume you will take off and simply go straight at the correct ejection angle and timing. If I were you I would send a small probe on the correct path the day before your actual mission launch to have a route traced on the map and to check the ejection speed.

Then I would launch (of course exactly six hours after) and eyeball the right path without a node trying to match the probe route. You can then choose the best place for a node and refine your approach to Jool SOI.

I know that it may sound barbaric but the first time I tried KSP there were no nodes. 

 

EDIT: you could actually just set up a node on your way before leaving Kerbin SOI, however the probe will give you a path to follow and if you are on the right trajectory you will just need to push prograde.

Edited September 17, 2019 by Signo

[birdog357]

32 minutes ago, Signo said:

I will assume you will take off and simply go straight at the correct ejection angle and timing. If I were you I would send a small probe on the correct path the day before your actual mission launch to have a route traced on the map and to check the ejection speed.

Then I would launch (of course exactly six hours after) and eyeball the right path without a node trying to match the probe route. You can then choose the best place for a node and refine your approach to Jool SOI.

I know that it may sound barbaric but the first time I tried KSP there were no nodes. 

I'm going to be flying a gravity turn because my booster(BDB Titan IV/B) has a t/w<1 at several points in it's ascent profile. My en route maneuvering budget is going to be very small. I'm trying to put Probes+ Cassini/Huygens into orbit using the proper booster but the Centaur will have bleed it's propellant off fairly quickly. Brute force probably won't work.

[Snark]

1 hour ago, birdog357 said:

How do I go about plotting the node so I have an aim point once I clear atmo?

You don't, at least not in stock.

Out of curiosity, though, any particular reason why you're not doing a parking orbit?  Navigation is a whole lot easier if you do, and you're not sacrificing any significant dV to do so.

[birdog357]

3 minutes ago, Snark said:

You don't, at least not in stock.

Out of curiosity, though, any particular reason why you're not doing a parking orbit?  Navigation is a whole lot easier if you do, and you're not sacrificing any significant dV to do so.

Because a parking orbit is not how it's done IRL with outer planet probes. Also the way the booster is designed and the fact that I have my reaction wheels nerfed to hell and back, I won't have near enough RCS to rotate anything but the Centaur and I will have wasted a fair bit of the second stage's propellant if I release the Centaur. I'm all for mods so if you've got a mod solution that will work, lay it on me. I already have KAC Mechjeb and KER BTW.

[Snark]

12 minutes ago, birdog357 said:

Because a parking orbit is not how it's done IRL with outer planet probes.

Sure, but it's also worth noting that IRL planet probes are carefully computer-controlled the whole way and "navigational concerns" simply aren't a thing in that regard, so (unlike KSP) they have no advantage in going to a parking orbit first.

Anyway, if that's how you like to play, makes perfect sense!    Was just curious.

I never use navigational mods myself, so am not in a position to offer any advice there-- maybe someone else will have ideas or suggestions.

[Superfluous J]

I do this fairly frequently. I do the starter probe thing that @Signo suggested, but launch my gravity turn to match its ejection.

It will take a few tries but after you get it a couple times you'll get a feel for it and future launches will be much easier. Like everything in KSP.

And leave that probe in orbit. You can use it to pre-plan all future ejections.

Edited September 17, 2019 by 5thHorseman

[birdog357]

3 minutes ago, 5thHorseman said:

I do this fairly frequently. I do the starter probe thing that @Signo suggested, but launch my gravity turn to match its ejection.

It will take a few tries but after you get it a couple times you'll get a feel for it and future launches will be much easier. Like everything in KSP.

And leave that probe in orbit. You can use it to pre-plan all future ejections.

I've got a station in a parking orbit. How do I see it's plotted trajectory from my launch vehicle?

[bewing]

3 hours ago, birdog357 said:

I've got a station in a parking orbit. How do I see it's plotted trajectory from my launch vehicle?

You have to "target" the station.

[birdog357]

I ended up using the station to plot the track, switched to the launch vehicle when it was below the node and then flew a gravity turn. When I was exo-atmospheric and closing in on a circular orbit I used mechjeb to plot the actual node and then flew that. I have a deep space correction burn of 185 m/s in a year or so that will plop me into an equatorial plane and drop my Jool PE to just above the clouds.

[k00b]

if you are leaving kerbin to the suns orbit; then why don't you just keep on burning prograde ? (i don't get it / thanks).

[birdog357]

11 minutes ago, k00b said:

if you are leaving kerbin to the suns orbit; then why don't you just keep on burning prograde ? (i don't get it / thanks).

I want to aim for Jool, thus I need to direct my trajectory appropriately. Since I'm flying a gravity turn my launch time is important too.

 

[k00b]

1 minute ago, birdog357 said:

I want to aim for Jool, thus I need to direct my trajectory appropriately. Since I'm flying a gravity turn my launch time is important too.

 

thanks; but as jool is so very very far away; don't you just burn prograde, when the launch pad is [a gravity turn] away from facing it's direction ? (- i.e. guess and then f9 if that doesn't work ?)

or am i being stupid ?.

[birdog357]

My Launch vehicle had just 100 m/s left after ejection so I had to get it very close to perfect or it would not work. I'm flying a BDB Titan IVB with a Probes Plus Cassini/Huygens on it with a 2.5x scaled system so it's very close to a perfect scaled model.

[Superfluous J]

4 minutes ago, k00b said:

thanks; but as jool is so very very far away; don't you just burn prograde, when the launch pad is [a gravity turn] away from facing it's direction ? (- i.e. guess and then f9 if that doesn't work ?)

or am i being stupid ?.

Not stupid at all if I'm reading you correctly. That's basically what he did, only he used a maneuver node on another ship as a guide to make sure he was doing it correctly, so as to not have to revert/restore a bunch of times.

[k00b]

4 minutes ago, 5thHorseman said:

Not stupid at all if I'm reading you correctly. That's basically what he did, only he used a maneuver node on another ship as a guide to make sure he was doing it correctly, so as to not have to revert/restore a bunch of times.

whats the point in the tracer ship launch ? - thanks

Edited September 19, 2019 by k00b

[birdog357]

Just now, k00b said:

whats the point in the tracer ship launch ?

To give me an idea of the vector to aim for at launch and to time my launch otherwise I have my original question. I just used a station in orbit. I didn't launch a new probe.

[k00b]

thanks, pretty sure that's what f9 is for; but i maybe mistaken!.

(on the basis, maneouvers in space UNLIKE getting into orbit in the first place, take negligable amount of fuel (i.e. "relatively speaking") vs. the extra "VAB work" = "f5, f9 combo FTW")).

 

[Superfluous J]

7 minutes ago, k00b said:

whats the point in the tracer ship launch ? - thanks

The same purpose of a tracer bullet firing. It's a super cheap* way to make sure your important thing is going exactly the right way.

*Even cheaper as there was no launch and a ship already in orbit was used.

[k00b]

...launching into orbit is not cheap.

[Superfluous J]

4 minutes ago, k00b said:

thanks, pretty sure that's what f9 is for; but i maybe mistaken!.

They're for whatever you want to use them for. If you prefer that, great. But others prefer planning and executing as close to the plan as possible. It's just that different people like different things. One of the plusses of KSP is that both types are rewarded.

 

 

2 minutes ago, k00b said:

...launching into orbit is not cheap.

I can do it for a couple hundred Kerbucks. That's cheap compared to the million+ I've spent on a Jool mission.

Edited September 19, 2019 by 5thHorseman