Can't get to asteroid [Noob & Using Mechjeb]

[NateDaBeast]

Okay so this is what I'm doing.

Going to launch pad

Using Ascent Guidance on MechJeb to get myself at 100km

Maneuver Planner I use "Hohmann transfer to target" after selecting the asteroid as target

Maneuver Planner then says "target for Hohmann transfer must be in the same sphere of influence"

It also sometimes says something about the hyperbolic curve or something

Example - http://i.imgur.com/LDfxnob.png

So what exactly do I need to do to get near or try to land on the asteroid using mechjeb ?

Thanks for reading!

Edited August 30, 2015 by NateDaBeast

[The_Rocketeer]

The issue is caused by you being in the planet Kerbin's gravity sphere (SOI, sphere of influence) whereas the asteroid is in the Sun's SOI. Mechjeb can't plan how your burn will affect your path relative to the Sun until you've left Kerbin's gravity.

The quick fix is to just accelerate until you have an escape trajectory from Kerbin's SOI, and then use Mechjeb to get to the asteroid once you're out into a solar orbit.

There are details that could help you do this much better (read more efficiently), but I wouldn't want to deprive you of the fun of figuring that out for yourself.

[Nansuchao]

Are you looking for a simple way to reach your asteroid?

Go to the Launchpad, target the asteroid, if possible when this is still some days out of Kerbin SOI. Wait until the marked orbit of the asteroid is roughly over the KSC, launch and point directly to the target, obvious control that there is no planet or moons in the trajectory. After a while, you'll have your first "Interplanetary Rendez-Vous". Travel a while far from Kerbin and begin, slowly, to create maneuvers nodes to have you rendezvous as close as possible. At the end, when you're near the target, cancel the relative velocity and grab your asteroid. Now you just have to be careful and wait until the asteroid cross the Kerbin SOI, then burn until it is more or less in a stable orbit.

This is not the best way, but it's surely successful.

Don't forget to bring with you a lot of fuel...

[Gaarst]

Don't use MJ and learn to do orbital rendez-vous by yourself...

Seriously now, the issue is that the asteroid's trajectory is hyperbolic (ie: it is escaping Kerbin's SOI), and for some reason, you cannot use MJ to have a rendez-vous with it with this kind of trajectory.

From then, you have two options:

- either you roughly follow it into interplanetary space (outside Kerbin's SOI) and then, it will have an elliptical orbit around the Sun so MJ will be able to set up a rendez-vous with it. I don't know how MJ handles rendez-vous, but due to orbital periods being around 1 Kerbin year, you might have to wait a long time to meet it, and then, you'll have to setup another rendez-vous with Kerbin to go back home (if you wish to, of course)

- or you do the rendez-vous by yourself, setting up an hyperbolic trajectory to make the rendez-vous within Kerbin's SOI and, either try to slow down the asteroid into an elliptical orbit around Kerbin (not gonna work with a large one) or, if you want to go back home, you meet with it really fast (understand: very precise rendez-vous not to lose time to approach it) to leave it and go back to Kerbin before leaving its SOI (you can still go back there outwith its SOI but it is a bit more complicated). This solution might not be easy if you're not experienced in rendez-vous.

I'll add (and recommend) a third option which is:

First: forget about this asteroid.

Second: learn how to master rendez-vous in LKO with two ships of yours (or probes or whatever), you can use MJ but the risk is that letting MJ do everything may prevent you from learning how to do an orbital rendez-vous by yourself.

Third: get to the tracking station and find a better asteroid to meet. Some asteroid actually spawn with an elliptical orbit around Kerbin, these are the ones you're looking for: a rendez-vous in an elliptical orbit, even with high eccentricity, is way easier than one in parabolic or hyperbolic orbits.

And then, when you feel comfortable with rendez-vous with asteroids within Kerbin's SOI, you can go and meet whatever asteroid you want wherever you want however you want.

Anyway, good luck with your rendez-vous !

EDIT: and I almost forgot: welcome to the forums !

Edited August 31, 2015 by Gaarst

[Sirine]

Wait till some asteroid enter Kerbin SOI.

[cantab]

There are two basic approaches to asteroid rendezvous. Meet it in Kerbin's SOI, or meet it in solar orbit. I prefer to meet them in solar orbit, and there's a simple trick to getting a close encounter: leave Kerbin's SOI in the direction the asteroid is projected to enter. Doing that puts you on a course good for intercepting the asteroid. Once in solar orbit it's much like a normal orbital rendezvous except everything's bigger; whereas around Kerbin you'd want to get within a few km then match speeds, around the Sun you can get within a few hundred km then match speeds then approach straight.

[NateDaBeast]

The issue is caused by you being in the planet Kerbin's gravity sphere (SOI, sphere of influence) whereas the asteroid is in the Sun's SOI. Mechjeb can't plan how your burn will affect your path relative to the Sun until you've left Kerbin's gravity.

The quick fix is to just accelerate until you have an escape trajectory from Kerbin's SOI, and then use Mechjeb to get to the asteroid once you're out into a solar orbit.

There are details that could help you do this much better (read more efficiently), but I wouldn't want to deprive you of the fun of figuring that out for yourself.

I'm guessing I have escaped from Kerbins SOI once it says I'm orbiting the sun or whatever correct ?

How would I then use Mechjeb to get to the asteroid like what features would I use ?

And don't worry about depriving the fun of figuring it out for me, I've been ticked off for the past 2 days every time I launch KSP and can't get to the asteroid.

[The_Rocketeer]

I'm guessing I have escaped from Kerbins SOI once it says I'm orbiting the sun or whatever correct ?

How would I then use Mechjeb to get to the asteroid like what features would I use ?

And don't worry about depriving the fun of figuring it out for me, I've been ticked off for the past 2 days every time I launch KSP and can't get to the asteroid.

Yes correct. Then you can use a hohmann maneuvre, the same as you would for getting to Mun/Minmus/your space station from LKO.

Also, as others have observed the hyperbolic trajectory is when the asteroid is currently in Kerbin's SOI but isn't going to stay there (it's moving too fast to be captured), so again Mechjeb can't plan the trajectories for changing gravity effects. You need an asteroid that's either in a true orbit of Kerbin, OR in orbit of the Sun and not entering Kerbin's SOI before you complete your intercept burn.

Of course, that's only true if you're using Mechjeb as a crutch. It's entirely possible to make any intercept anytime you want as long as you know how to plot a manoeuvre node and have enough dV, and are prepared to take the pilot seat for a while. Still, ur game, play it how u want.

Edited August 31, 2015 by The_Rocketeer

[mrclucks]

Rendezvous in solar orbit is much much easier than in a planets orbit.

First step is to just get into solar orbit. Then set a manuver bode ten or so minutes ahead and start tweaking your manuver node till you get a close encounter in a couple days or so. Then you want to have similar speeds and repeat previous step untill you get an encounter only a hundred or so km. At that point you'll want to match velocities and then burn straight at the target. Use RCS to move laterally if you need to. Eventually you'll see your target and just need to coast to your target.

RCS on and using the ijkl keys are a lifesaver btw

[Mastikator]

Wouldn't it be easier to put your rocket into a circular orbit that is aligned with the asteroids flyby trajectory and when it comes just do an intercept burn?

[mrclucks]

Wouldn't it be easier to put your rocket into a circular orbit that is aligned with the asteroids flyby trajectory and when it comes just do an intercept burn?

IMHO it takes more skill due to having to time it better and being more precise with your burns and manuver nodes, but is more efficient. Solar orbit rendezvous is much more forgiving as long as you have a bit more time. You also have alot more time to change the orbit it will take (especially if it's a larger astroid and you don't have a high twr).

I think that beginners should first do their rendezvous in solar orbit before they try any in a much smaller soi

[Nansuchao]

Not so easy, usually asteroids passes in the Kerbin SOI at high relative speed, so you need to be in the perfect point of your orbit to accelerate to rendezvous in those few minutes the asteroid is there. Doable, but difficult.

[eddiew]

Wouldn't it be easier to put your rocket into a circular orbit that is aligned with the asteroids flyby trajectory and when it comes just do an intercept burn?

MJ certainly can't tell you how to intercept something on a hyperbolic curve, although it is possible to meet an asteroid at it's periapsis as you describe.

I pulled this off on a 'roid that had a ~200km PE; that was relatively easy to engineer since my orbit was tight and fast and I had lots and lots of time to plan the intercept. With a high altitude flyby however, your orbit is weeks long, and the burn required for the intercept can be very expensive. If you're lucky with an LKO visitor, your orbit is minutes and you only need a few delta-v here or there to arrange meeting it.

[cantab]

Wouldn't it be easier to put your rocket into a circular orbit that is aligned with the asteroids flyby trajectory and when it comes just do an intercept burn?

It's an option. Advantage is you may find it easier with everything in one SOI. Drawbacks include the need to get your timing right, and if you want to capture the asteroid you lose the opportunity to course correct it and especially to aerocapture it.

[The_Rocketeer]

Wouldn't it be easier to put your rocket into a circular orbit that is aligned with the asteroids flyby trajectory and when it comes just do an intercept burn?

What your describing would be pretty advanced for a newish player who depends heavily on MechJeb for piloting and navigating their craft. Whatever anyone's views on that, there's no right or wrong way to play the game. The OP wants to know how to get MechJeb to do this, so that's the question I'm answering.

[NateDaBeast]

Yes correct. Then you can use a hohmann maneuvre, the same as you would for getting to Mun/Minmus/your space station from LKO.

Also, as others have observed the hyperbolic trajectory is when the asteroid is currently in Kerbin's SOI but isn't going to stay there (it's moving too fast to be captured), so again Mechjeb can't plan the trajectories for changing gravity effects. You need an asteroid that's either in a true orbit of Kerbin, OR in orbit of the Sun and not entering Kerbin's SOI before you complete your intercept burn.

Of course, that's only true if you're using Mechjeb as a crutch. It's entirely possible to make any intercept anytime you want as long as you know how to plot a manoeuvre node and have enough dV, and are prepared to take the pilot seat for a while. Still, ur game, play it how u want.

Okay so once in the suns orbit I would then use MechJebs maneuvre planner to hohmann transfer over to the asteroid ?

Rendezvous in solar orbit is much much easier than in a planets orbit.

First step is to just get into solar orbit. Then set a manuver bode ten or so minutes ahead and start tweaking your manuver node till you get a close encounter in a couple days or so. Then you want to have similar speeds and repeat previous step untill you get an encounter only a hundred or so km. At that point you'll want to match velocities and then burn straight at the target. Use RCS to move laterally if you need to. Eventually you'll see your target and just need to coast to your target.

RCS on and using the ijkl keys are a lifesaver btw

Well I'm in solar orbit now so could I use MechJebs rendezvous planner or rendezvous autopilot to get to the asteroid ?

[The_Rocketeer]

Yeah you're getting it. Trust your instincts, Luke.

The reality is to get right to the asteroid and grab it u'll probably need to use a few of the MechJeb functions as well as a bit of hands-on control. MechJeb is, after all, a corner-cutting tool for saving time and effort for the mundane jobs, not a precise implement for remotely accomplishing everything that's possible in the game. Sooner or later you'll probably have to get your hands dirty.

Also, as much as the community could give u step-by-step instructions for everything, isn't part of the fun muddling thru on your own? I promise you'll remember it better for next time if u found it out for yourself than if someone walked you thru it. In other words, it's time to start up the game and try a few things, see what works

[NateDaBeast]

Yeah you're getting it. Trust your instincts, Luke.

The reality is to get right to the asteroid and grab it u'll probably need to use a few of the MechJeb functions as well as a bit of hands-on control. MechJeb is, after all, a corner-cutting tool for saving time and effort for the mundane jobs, not a precise implement for remotely accomplishing everything that's possible in the game. Sooner or later you'll probably have to get your hands dirty.

Also, as much as the community could give u step-by-step instructions for everything, isn't part of the fun muddling thru on your own? I promise you'll remember it better for next time if u found it out for yourself than if someone walked you thru it. In other words, it's time to start up the game and try a few things, see what works

Okay so I use hohmann transfer with the maneuver planner on MechJeb and then it says this :

"Warning: Recommend starting Hohmann transfers from a near-circular orbit (eccentricity < 0.2).

Planned transfer is starting from an orbit with eccentricity 0.38 and so may not intercept target properly."

So what should I do with MechJeb when I'm getting this ?

Some pictures I took ingame of what was going on.

This is my ships location and the asteroid I'm trying to land on before doing anything.

Once using the hohmann transfer thing this is the maneuver it puts on the map and gives me that message.

After completing the maneuver it then shows this and it never took me to the asteroid or if I wait and speed up time it never does.

[Claw]

This doesn't use MechJeb, but perhaps a couple pictures will help you out. It uses the method Cantab offered, ejecting from Kerbin's SOI on the asteroid's inbound track.

http://forum.kerbalspaceprogram.com/threads/75759

Good luck, and welcome to the forums!

Cheers,

-Claw

[NateDaBeast]

This doesn't use MechJeb, but perhaps a couple pictures will help you out. It uses the method Cantab offered, ejecting from Kerbin's SOI on the asteroid's inbound track.

http://forum.kerbalspaceprogram.com/threads/75759

Good luck, and welcome to the forums!

Cheers,

-Claw

Thanks for welcoming me

Wish there was one for MechJeb tho, I'm new to KSP so I want to take my time understanding how everything works and watch mechjeb and try to do what it does I guess and compare my skills to mechjeb or something.

[radonek]

My 2 cents:

1) Find an asteroid on intersection course with Kerbin SOI.

2) Target it. Map view will show its trajectory around kerbin - parabolic.

3) Get on as close orbit as possible. You dont want to shoot out of Kerbin system just now, so you keep your PE inside Kerbin SOI, but you can match inclination and argument just fine. Obviously, launching right into right orbit is the thing here.

4) Now wait until asteroid is close…

5)… and just raise your PE away. You should get pretty close encounter (<2000km)

6) Once on your way, few small adjustments (<80m/s in my case) can get your encounter dead on.

Idea here is that parabola-by-kerbin is where asteroid will be in future, so you start with that and retrace it back

[Pax Kerbana]

Treat it like a fast moving station in an eccentric orbit. Get to LKO with aligned orbit. Set node and adjust to cross asteroid path. Then advance the node forward by clicking the +1 orbit button until you get or of the intercepts close to target. Burn out at the right time and adjust the course along the way. Get to asteroid and switch on target mode nav ball, kill relative V and burn to target. Pretty easy once you get it once.

You'll be better of learning to do it first, MJ not needed really. Watch a vid, it took me days to get it too but it's not all that hard.

[NateDaBeast]

My 2 cents:

1) Find an asteroid on intersection course with Kerbin SOI.

2) Target it. Map view will show its trajectory around kerbin - parabolic.

3) Get on as close orbit as possible. You dont want to shoot out of Kerbin system just now, so you keep your PE inside Kerbin SOI, but you can match inclination and argument just fine. Obviously, launching right into right orbit is the thing here.

4) Now wait until asteroid is close…

5)… and just raise your PE away. You should get pretty close encounter (<2000km)

6) Once on your way, few small adjustments (<80m/s in my case) can get your encounter dead on.

Idea here is that parabola-by-kerbin is where asteroid will be in future, so you start with that and retrace it back

Could you explain your steps with using mechjeb possibly ?

[The_Rocketeer]

Ok, my strong impression here now is that you understand very little about how to plan orbital manoeuvres in KSP and are looking for a very in-depth explanation of how it's done. I recommend you forget asteroids for now and use one of the tutorials for intercepting another planet (of which there are many on youtube, google and here) and then try to apply that knowledge to intercepting an asteroid (which is actually much more difficult because asteroids are so tiny).

Also, while I totally defend your choice to play using MechJeb for everything, as I've tried to explain, there are limits to what it can do. You may find that forgetting MechJeb and learning the old fashioned way is much more enlightening.

Also, if you get a report that says some gibberish you don't understand, try looking up the key terms, e.g. eccentricity. This, for example, basically means how circular your orbit is (more eccentric is less circular). A simple solution: if MechJeb gives that warning, would be to circularise the orbit first and then try for the intercept/transfer.

While the forum community will be happy to help with specific problems, I can't help but feel you're asking for a lot of help with things that you'd probably work out on your own with a bit more practice.

Edited August 31, 2015 by The_Rocketeer

[radonek]

Could you explain your steps with using mechjeb possibly ?

Sorry, no idea, I do not use mechjeb. However, point (3) is similar to nonequatorial sattelite contracts and everything else is pretty simple.