How to target an asteroid v0.24.2

[DavidHunter]

Hi folks,

Figured I may as well get around to doing an ARM. Launched my rocket into LKO, then realised I can't actually target the asteroid I want to go for (when I right-click on it in the map view, it just says 'View in tracking station'; there is no option to 'set as target'). Kerbal Engineer Redux's target selection system also doesn't let me select the asteroid.

How am I meant to set the asteroid as a target?

Thanks in advance.

Dave

Edited August 15, 2014 by DavidHunter
Changed prefix to answered... thanks! :D

[AlexinTokyo]

You need to track the asteroid (from the tracking station) first.

That actually causes it to be physically present so it can be targeted.

[DavidHunter]

You need to track the asteroid (from the tracking station) first.

That actually causes it to be physically present so it can be targeted.

Ah, I see now. Got it working. Thanks for your help.

Next silly question... this asteroid is on a direct collision course for Kerbin. Periapse is at -454km... will this end my game if I allow it to hit?

[Pecan]

No (10 chars)

[DavidHunter]

No (10 chars)

For the record, I was only joking...

Anyway, I've got my ARM spacecraft in LKO, I have aligned the orbits, but I can't figure out how to intercept it... The asteroid is on its way toward Kerbin. How should I proceed?

[robopilot99]

Its best to catch it in interplanetary space so you can set up an arro braking maneuver. If you're uncomfortable with that just use maneuver nodes to get as close as you can. Experiment a lot missing the capture isn't a big deal.

[LethalDose]

How on earth would you 'aero-brake' to an asteroid? There's no atmosphere...

I've been wondering for some time how to intercept an asteroid efficiently. I'm picturing a GREAT deal of manual retro-burning, and adjustment to even get close.

You aerobrake the asteroid in Kerbin's atmosphere. You don't aerobrake the probe around the asteroid.

IMO, there are three ways to approach an asteroid:

1- Get on a kerbin escape basically going straight up the path the asteroid is going to take (180 degree inclincation) after it gets into Kerbin's Hill Sphere.

2- Go into a parking orbit in the same inclination as the asteroid, and then time a hohman x-fer to the asteroids Periapsis. I've found this best for asteroids with low periapses.

3- Same As 2, but you intercept the asteroid as it's coming down towards kerbin by timing an intercept during a big eliptical orbit that's tangential to the asteroid's path. It's kinda tricky, but it works well when you get the hang of it. Has dV costs between 1 & 2, and you usually won't catch it much more than a few hours before periapsis anyway. Best for the same ones as 2, but you can get the rock a little bit before periapsis.

I only really try to catch the little buggers high if I need to divert them from a colision with Kerbin. I usually get them low, burn retro at periapsis just enough to capture them into a highly eliptical stable orbit, then manipulate the orbit to what I want/need. Circularizing is the absolute last thing I do.

[DavidHunter]

Its best to catch it in interplanetary space

I'd like to, but it's already within Kerbin's SoI. So it's showing a parabolic orbital path at this point, and so I can't figure out how to do a Hohmann manoeuvre to it. :S

[DavidHunter]

This help explain my predicament?

[DavidHunter]

You aerobrake the asteroid in Kerbin's atmosphere. You don't aerobrake the probe around the asteroid.

IMO, there are three ways to approach an asteroid:

1- Get on a kerbin escape basically going straight up the path the asteroid is going to take (180 degree inclincation) after it gets into Kerbin's Hill Sphere.

2- Go into a parking orbit in the same inclination as the asteroid, and then time a hohman x-fer to the asteroids Periapsis. I've found this best for asteroids with low periapses.

3- Same As 2, but you intercept the asteroid as it's coming down towards kerbin by timing an intercept during a big eliptical orbit that's tangential to the asteroid's path. It's kinda tricky, but it works well when you get the hang of it. Has dV costs between 1 & 2, and you usually won't catch it much more than a few hours before periapsis anyway. Best for the same ones as 2, but you can get the rock a little bit before periapsis.

I only really try to catch the little buggers high if I need to divert them from a colision with Kerbin. I usually get them low, burn retro at periapsis just enough to capture them into a highly eliptical stable orbit, then manipulate the orbit to what I want/need. Circularizing is the absolute last thing I do.

Sorry, for some weird reason your post didn't show up until just now (despite multiple browser refreshes). Anyway, thanks for the suggestions. I'll give option #2 a try as I at least know how to do that.

[Sirrobert]

This help explain my predicament?

https://dl.dropboxusercontent.com/u/4446393/ARM.png

Ok at this point, it's might be to late to catch it.

It might be possible, but very difficult now. The asteroid has an orbital period of 17 days, so you probably have about 5 days to make all the required orbital tranfers and get an encounter. Note that the further away you encounter it, the easier it'll be to capture, and to redirect

First, you have to match inclination. Than you have to burn out until you get a rhough encounter. Don't try to finetune it, you won't have time for that.

Than, when you get close, match velocity and close the distance.

When you caught it, raise the periaps (by burning radial) until you get an aerocapther rather than a landing (Mechjeb landing autopilot as an option to show predicted orbit after aerocapture). After this, you can play around with it.

Alternativly you might wanna forget about this asteroid and pick an easier one, with more time to prepare

[ripvanlemon]

1- Get on a kerbin escape basically going straight up the path the asteroid is going to take (180 degree inclincation) after it gets into Kerbin's Hill Sphere.

Can someone try to explain this to me please? Techniques 2 and 3 make perfect sense because I'm arriving at the asteroid with roughly matched velocity. The only downside I can think of is that I can't rendezvous until it's in Kerbin's SOI. If I run straight out in the opposite direction like LethalDose suggests, how do I then set up a rendezvous?

[el_coyoto]

I have a limited experience in asteroid retrieval, but the only ARM I did happened to take place in Kerbin SOI, so I might help a little bit.

The first step is launching directly into the asteroid orbital inclination. I don't have good tips there other than doing the launch azimuth computation by hand (this resource for Orbiter I've used in the past or this video for KSP that I haven't watched yet) or using MechJeb to do it for you.

Once you have launched into the asteroid plane of inclination, things get much easier : it is a matter of setting up a node with some prograde dV then messing with the time of departure until I get close to it by turning the maneuver node around Kerbin (the time is important because it determines into which direction you will burn) . And then tweak the ejection burn, tweak the departure time until I get a good rendez vous (<2 km), like the usual docking procedure.

From my limited experience with Kerbin SOI interceptions, apart from the launch azimuth computation, the hardest part was kind of forgetting the asteroid had a hyperbolic trajectory, or trying to visualize it. For me, it ended like setting up a "direct" docking encounter (in one orbit) and making sure I intercepted it before PE.

Edited August 1, 2014 by el_coyoto

[DavidHunter]

Sorry, for some weird reason your post didn't show up until just now (despite multiple browser refreshes). Anyway, thanks for the suggestions. I'll give option #2 a try as I at least know how to do that.

Ok, ended up giving up. Too hard.

Ok at this point, it's might be to late to catch it.

It might be possible, but very difficult now. The asteroid has an orbital period of 17 days, so you probably have about 5 days to make all the required orbital tranfers and get an encounter. Note that the further away you encounter it, the easier it'll be to capture, and to redirect

First, you have to match inclination. Than you have to burn out until you get a rhough encounter. Don't try to finetune it, you won't have time for that.

Than, when you get close, match velocity and close the distance.

When you caught it, raise the periaps (by burning radial) until you get an aerocapther rather than a landing (Mechjeb landing autopilot as an option to show predicted orbit after aerocapture). After this, you can play around with it.

Alternativly you might wanna forget about this asteroid and pick an easier one, with more time to prepare

Yeah, decided to go for one that has a perikee of around 1,000,000m. That'll be easier and I at least know how to rendezvous with it.

Thanks for the tips.

I have a limited experience in asteroid retrieval, but the only ARM I did happened to take place in Kerbin SOI, so I might help a little bit.

The first step is launching directly into the asteroid orbital inclination. I don't have good tips there other than doing the launch azimuth computation by hand (this resource for Orbiter I've used in the past or this video for KSP that I haven't watched yet) or using MechJeb to do it for you.

Once you have launched into the asteroid plane of inclination, things get much easier : it is a matter of setting up a node with some prograde dV then messing with the time of departure until I get close to it by turning the maneuver node around Kerbin (the time is important because it determines into which direction you will burn) . And then tweak the ejection burn, tweak the departure time until I get a good rendez vous (<2 km), like the usual docking procedure.

From my limited experience with Kerbin SOI interceptions, apart from the launch azimuth computation, the hardest part was kind of forgetting the asteroid had a hyperbolic trajectory, or trying to visualize it. For me, it ended like setting up a "direct" docking encounter (in one orbit) and making sure I intercepted it before PE.

Yeah, tried that out but couldn't get a close encounter. Thanks anyway.

[Mr Shifty]

The first step is launching directly into the asteroid orbital inclination. I don't have good tips there other than doing the launch azimuth computation by hand (this resource for Orbiter I've used in the past or this video for KSP that I haven't watched yet) or using MechJeb to do it for you.

Kerbin rotates so slowly relative to orbital speed that you can usually just fudge it. Launch generally to 90°+inclination for descending node launches or 90°-inclination for ascending node and move a couple extra degrees away from 90° to account for Kerbin's rotation. If you can see the orbit-to-match on the map screen, you can visually adjust your heading during launch to get pretty close. I recently posted a [thread=88371]challenge that tried to highlight this skill[/thread], but got no takers. KSC's location on the equator makes this skill pretty obscure in KSP, otherwise, I'm sure we'd have our own version of LaunchMFD already. (Well I suppose MechJeb counts.)

Edited August 6, 2014 by Mr Shifty

[DavidHunter]

Ok, so yeah, I ditched the original rock I was aiming and went for another one. Had more warning time and built a replacement spacecraft with the atomic engines, was able to catch up with the asteroid just after it left Kerbin's SOI, then dragged it's sorry backside back to Minmus orbit for 800 sciences.

Swish.

Thanks guys.