How to rendez-vous with an asteroid?

[goldenpeach]

I know how to make an interplanetary transfer(to some extant, if the planet in inclined it's really hard for me(=) but I have no idea on how I could do the same with an asteroid before it escape Kerbin making it impossible(or really hard) to send it on kerbin orbit.

Anyone have any idea on how I could do that(I use mechjeb if it can be of any help)?

Thank you for reading and have fun with the new update!

Edited April 2, 2014 by goldenpeach

[jztemple]

Boy, I'd love to see an answer for this as well, I'm so at sea without MechJeb I feel sometimes I should just keep launching rockets and hope one of them hits something solid

[kookoo_gr]

the devs have some tutorials at the scenario option menu. check them out.

[purpletarget]

A couple things you can work with:

1. Find an asteroid with a descent Pe around Kerbin. (ie: Not just a grazing pass, you'll have an easier time with something that has at least 1/3 an orbit, if not more)

2. Launch into a co-planar orbit with the Asteroid pass through the Kerbin SOI. (Adjust once in orbit to make your An/Dn close to 0 degrees.

3. Set a maneuver node to push the Ap of your s/c out to somewhere a little before the Pe of the roid. Take a note of the time it will take to get out to Ap.

4. Switch back to Tracking station, and allow asteroid to close with Kerbin. Stop timewarp when the Roid is a little longer to Pe than your Ap transfer time from Step 3.

5. Once within a day to hours, switch back to S/C, and setup a new maneuver (the node from Step 3 will be way out of date), this time target the asteroid and setup an RV. You want to intercept earlier than Pe, because you'll probably need some time to refine the RV and get setup for the capture and burn.

6. On reaching the Ap/intercept with the roid, you'll need to zero the relative target speed. Have lots of dV for this...it's generally at least as much as a circulation burn at the Pe altitude, plus escape velocity, plus the excess velocity the roid had when it came into the SOI.

7. RV is similar to any spacestation or s/c docking, except that you usually only get one shot to intercept before the roid leaves the SOI.

[Capt. Hunt]

I haven't tried it yet (I'm focusing on completing the mission I started before the update before I tackle any asteroids). Theoretically, it should work just like any rendezvous. Remember, the asteroids have no gravity, so think of it more like rendezvousing with a spaceship then with a mun.

By the way, Mechjeb has an unoffical hotfix that makes it work again, check the mechjeb thread.

[biohazard15]

Unless MJ doesn't have the dedicated module (or some additions to rendezvous autopilot code), do it the hard way, i.e. manually. Use the new "advance orbit" buttons to tune your burn time, try to aim at asteroid's Pe. It's hard, but not too hard.

You can use MJ to launch at asteroid's plane and to match inclination.

[Vanamonde]

I'd suggest not trying to rush out and meet one as it's whizzing by. Go out interplanetary and grab one where you have weeks to guide it to an aerobraking pass. Remember, the farther away you start, the easier it is to change the asteroid's trajectory.

[purpletarget]

I'd suggest not trying to rush out and meet one as it's whizzing by. Go out interplanetary and grab one where you have weeks to guide it to an aerobraking pass. Remember, the farther away you start, the easier it is to change the asteroid's trajectory.

Yes.... and solar RV is a whole 'nother conversation.

[Geschosskopf]

I second what Purpletarget says, but there are also other ways to do it. Not as smart or efficient, but they work.

I personally like to go for asteroids that will pass a fair distance from Kerbin, like out beyond Minmu's orbit. This means the roid will be moving pretty slowly so it'll be easier to match up with and you've got days to make it happen if you screw it up the 1st time. It goes like this.

1. Select the roid you want based on where it will pass through Kerbin's SOI and its size. The bigger the roid, the more ship you need to capture it. You also want one that won't enter Kerbin's SOI for a couple months at least.

2. Determine whether the roid will go above or below Kerbin. Then launch into a polar orbit when KSC is more or less in line with the roid's path. Depending on whether the roid is going above or below Kerbin, and whether KSC is facing its approaching or departing path, you'll launch more or less north or more or less south. The essential thing is to make sure you're going around Kerbin in the same direction the roid will be when it gets there. You don't have to match inclination perfectly at this point, just get reasonably close.

3. Get into a huge orbit straight from launch, like out as far as Minmus, and more or less circularize it. Once there, you can fine-tune your inclination to match the roid's. At that distance from Kerbin, this won't cost much. The thing is, though, you want to be a fair bit inside the roid's path so you complete an orbit faster.

4. Now you wait for the roid to enter Kerbin's SOI. Warp at high speed until it's close to entering, then slow down so it enter's Kerbin's SOI at no more than 10x warp. IOW, treat it just like it was one of your ships, because roids that cross SOI borders at high warp end up with altered orbits just like ships do.

5. Now make a node to rendezvous with the roid as best you can. At this distance, the roid will be in Kerbin's SOI for a couple months usually so you've got plenty of time. Just set up the burn so you'll come within about 500km of the roid. Closer is of course better, but anything less than 1000km will do.

6. Coast out to your closest approach and burn to match velocities with the roid. Then burn towards the roid. It's exactly the same as rendezvousing with a space station except the distances are much greater so you burn to a much higher speed towards the target. Like the 1st time you move towards it, get up to 150m's or so towards it. Periodically kill your relative velocity then burn towards the roid again, same as a normal rendezvous, using warp as needed to pass the time. Eventually, you'll get within a couple hundred meters and can finish off with RCS. And because the roid is moving so slowly, this will usually happen at least a little before the roid reaches its Kerbin Pe.

7. Arm the grabber, control from the grabber, target the roid's CoM, and ease up to it until the grabber sets. Because roid surfaces are highly irregular, you'll probably dock at an angle to the CoM. No worries, just release the grabber's pivot and pitch/yaw the ship as needed to line up with the CoM, then lock the pivot. The only real trick in this part is if you're going after a D- or E-size roid. With these, it's VERY difficult to reorient the ship/roid combo to line up for a burn; it's easier to move the ship to the other side of the roid. So when you 1st catch the roid and know you're going to burn retrograde to capture it around Kerbin, try to grab a big rock on its prograde side so you can at least do this capture burn without having to release and move the ship around.

8. You want to capture the roid into as big an orbit as possible, so the burn to change its plane down to Kerbin's equator is as small as possible. Once you've got the plane change done, shrink the orbit as desired so you can either park the thing around Mun or crash it into KSC as preferred .

[Geschosskopf]

Yes.... and solar RV is a whole 'nother conversation.

Definitely. It can be done but I've found it to be way more trouble than it's really worth. But that's because I probably am doing it wrong

[purpletarget]

Definitely. It can be done but I've found it to be way more trouble than it's really worth. But that's because I probably am doing it wrong

I find for the big ones, I find it's critical. Sending a small probe out for a solar SOI does a few things. (The new ION's are perfect for this, deep space has few shadows)

1. You can get the mass of the asteroid once docked.

2. You can use the probe to plane the capture burns with maneuver nodes in the Kerbin SOI. That will tell you exactly how much dV is required to get it where you want it.

3. Between the two, you can find out how much fuel you need on a capture ship to achieve that dV.

4. Then you can tack on the extra fuel you need to get the ship itself to the RV....and you are less likely to be surprised later by not having enough fuel.

(Trying to do all this during the Kerbin Encounter, is less likely to have time to build, launch and RV with a new ship)

....but maybe that's just me.

[goldenpeach]

Thank you for the answers!

Of course I forgot to check the new tutorials(I basically forgot they have been updated in this update)!

[Yarrula]

I managed it by setting up my orbit to match the inclination of the asteroid once it entered Kerbin's SOI. When you track an asteroid, set it as a target on a ship in orbit. You should be able to see the orbit the asteroid will take once it enters the system.

I then fiddled around with the maneuver node until I had an intercept as far out as possible. I didn't want to try and match orbits with the 'roid when it was at PE and traveling as fast as possible.

This worked very well as it gave me more time to use low thrust ion engines to capture it into a stable orbit.

[Kasuha]

In my opinion, meeting the asteroid while it is still interplanetary is in fact easiest.

Put your ship on launchpad, select the asteroid as target, and time warp till the asteroid is right on horizon of your navball.

Launch and gravity turn towards/from the target (whatever is more eastward). That will put you on roughly correctly inclined trajectory.

Circularize.

Place maneuver node on your orbit and add burn which will intersect the asteroid trajectory at about half the way between its current position and Kerbin intercept. Or sooner if you feel like it but that will mean you'll need to brake more.

After leaving Kerbin SOI perform standard rendezvous.

Edited April 2, 2014 by Kasuha

[GavinZac]

roids

Thank you! But, please, don't call them that

[keoki]

First rock was a cakewalk, almost regretted the work I put into the ship design.

The second rock had an off-set center of gravity, so pushing with my large engine was a no-go, just put me in a spin that took half an hour to damp, good thing it was a single axis spin... But my ship had a secret weapon, Reverse!

It is better to pull the asteroid than to push it, it seems. Same asteroid was easy to control in reverse. Just reserve enough fuel to do something useful. Both of my missions had to cheat on fuel to finish, so they don't count.

You may want to have a fleet of robotic craft in orbit and fueled up for quick intercepts. Get them to orbit, and park them, then ferry up fuel to fill em all up

Edited June 10, 2014 by keoki

[JackGruff]

The second rock had an off-set center of gravity, so pushing with my large engine was a no-go, just put me in a spin that took half an hour to damp, good thing it was a single axis spin...

I think you may have forgotten that you can right-click the asteroid, target center of mass. Then rotate the vessel so that it faces the new target. Then you can lock the clamp to make the connection between the asteroid and your vessel rigid.

[palioxis1248]

How I do solar rendezvous is the Zeno method. Inefficient, but hey, we've got ARM parts.

1. Burn for escape, while making sure your escape trajectory seems to be pointed in the general direction of the asteroid.
   
2. Once you're out of Kerbin's SOI, try and get a good camera angle that allows you to see both your trajectory and the asteroid's trajectory.
   
3. From here on in, assuming you've packed enough fuel, you can actually treat the two trajectories as straight lines. Then setting your maneuver nodes becomes somewhat more intuitive.
   
4. Now here comes the reason why this is called the Zeno method. On your first node, don't aim for a close pass any shorter than 100km.
   
5. After you've completed the burn, warp to close half the distance to your intercept. Set up another node, and this time you should be able to aim for a closer pass, ~50km.
   
6. Repeat ad infinitum until you've got <1km close approach.
   
7. Then it's just standard rendezvous.
   

[Duke23]

I've captured two (a class A and class , one was in Kerbol soi and one was near its PE to Kerbin somewhere between Minmus and Mun if I remember correctly... Neither was exactly easier to grab than the other because each had its own set of problems, except that I had to launch a ship specifically for that asteroid when I grabbed it near Kerbin as opposed to just leaving one fully fueled on high orbital standby for whatever I feel like going after. The other one I basically trailed it as it escaped from Kerbin's soi and caught up. I say that to say this... Bringing one back with you is (in my opinion) easier with a solar rendezvous because you have greater control over your Kerbin approach, inclination, etc and there's really no big rush to grab it and furiously burn retrograde while hoping you lined everything up just right. If you're not comfortable with being outside of Kerbin's soi yet though, well that's a different story.

As far as the actual methods to do either, it seems pretty well explained by others and I don't have anything to add.

[Claw]

While we appreciate the advice you all are giving, this request for help is 2 months old. I imagine goldenpeach has it figured out by now.

[goldenpeach]

More or less...

I watched a youtube video and achieved to grab an asteroid after several try(and a lot of time). However, I forgot to check the size of the asteroid before grabbing it, and when I did it, I realized my mistake. The asteroid was a class E asteroid, my delta-v dropped from several thousand m/s(I used the NERVA engine) to a few m/s.

I was disgusted and stopped any asteroid grabbing mission.

Maybe I should try again, first by grabbing it in solar orbit,just to have a feeling of achievement