Capturing Asteroids. UPDATE: Mission Complete!

[Rocket In My Pocket]

So, as some of you may know I'm a bit of a habitual re-starter. Pretty much whenever a new update comes out I start a new Career save. Since it's been so long since 1.3.0 and 1.3.1 wasn't major enough to warrant a restart, I've actually almost finished the tech-tree for once! Lol.

So anyways, Asteroid wrangling was something I never really got into, and I've just accepted a contract to bring a Class-A back to Kerbin orbit; sounds easy enough. I designed a small/medium sized puller which I thought would be more than adequate for a one star Class-A Asteroid contract.

After a couple of preliminary test runs though, I'm a touch confused on the best way to go about this. Should I wait for the Asteroid to come to me and try to rendezvous with it while it's passing through Kerbins SOI? Just matching inclination takes a lot of Dv, more than I assumed I'd need to go grab such a small asteroid. Should I go out into solar orbit and nab it, then bring it back? How much Dv does an average Asteroid mission take? I kind of assumed it'd be less than an interplanetary mission, but it doesn't seem that way from the bit of experimenting I've done. What about timescale? Is this a quick "go grab it and be done" thing, or a multi-year mission? Is it a matter of brute forcing it regardless of what orbit the Asteroid is on, or should I wait for a more "viable" Asteroid? I'm not looking for a ton of specifics or ship designs; just the broad strokes of the best way to approach the problem and why. Appreciate any advice, thanks in advance!

[Aegolius13]

Scott Manley has a great tutorial on this.  

To get to the asteroid, you want to travel up the exact path it's coming down.  I.e., if it will take a vertical (perpendicular to the ecliptic) path through Kerbin's SOI, you'd want to launch into a polar orbit.  This can be pretty fussy to get right.  Then you want to do a Kerbin escape burn such that you follow the asteroid's trajectory as closely as possible.  Then you just keep iteratively adjusting to get a close rendezvous somewhere out in Kerbol orbit, and then do the normal docking thing.  

I would budget several thousand m/s of delta-v [from LKO], especially for the first time.  You're probably looking at a little over 1,000 for the escape burn, and a decent chunk more to rendezvous.  The good news is that Class A's are really light, so they won't impede your TWR or delta-v much after docking.  For bigger asteroids, standard practice is to bring ISRU stuff so you can mine it as you go.  In that case, you only need enough delta-v to reach the asteroid.

I usually launch when the asteroid is a couple months away from reaching Kerbin's SOI (if you're a reasonable distance out, you can adjust its Kerbin trajectory as desired for minimal delta-v).  Since you're not altering the asteroid's path too radically, the mission should be done more or less when the asteroid was originally supposed to show up near Kerbin. 

Edited December 20, 2017 by Aegolius13

[Corona688]

Just like any rocket, significant changes in DV mean expending a large fraction of the payload's own weight in fuel.  At a very rough cut, you can get 2km/s delta-V on a 10-ton asteroid from 10 tons of fuel.

If you intercept while very far away, you can fine-tune where it passes through Kerbin system for almost nothing, and maybe take advantage of a lucky moon mun intercept -- people have occasionally found asteroids captured for free.

Edited December 20, 2017 by Corona688

[Geschosskopf]

5 minutes ago, Rocket In My Pocket said:

After a couple of preliminary test runs though, I'm a touch confused on the best way to go about this. Should I wait for the Asteroid to come to me and try to rendezvous with it while it's passing through Kerbins SOI? Just matching inclination takes a lot of Dv, more than I assumed I'd need to go grab such a small asteroid.

It depends on the asteroid and what your ultimate goal for it is.  First off, there's the question of how much time you have before it enters Kerbin's SOI and what effect that encounter will have on the asteroid's subsequent trajectory.  These are constraints on your strategy.  If you don't have a lot of time to complete the contract, then you might have to finish the job during this pass.  OTOH, if you've got years and the Kerbin encounter won't put the asteroid into an inconvenient orbit, then you can work it into the desired position in solar orbit over several years.  Then there's the question of mass.  As and Bs aren't THAT expensive to wrangle inside Kerbin's SOI but Ds and Es seem cheaper to maneuver in solar orbit.  Cs are can go either way depending on your tech and how much you want to spend on them.

But the amount of maneuvering you need to do is a function of where you want or need the asteroid to end up.  If the contract is just to put it in ANY orbit, and you never plan on doing anything else with it once you've got it, then all you need to do is capture.  You don't need to change it's inclination or Ap/Pe afterwards.  If that's the case, then you can wait until they enter Kerbin's SOI.  But if you need to put them in a specific orbit, it's best to get them in solar orbit so you can make them enter Kerbin's SOI as close to the desired orbit as possible.

If you'll be catching it in Kerbin's SOI, the inclination change required for interception isn't that expensive.  Just launch with that inclination and go into a wide parking orbit.  Then just rendezvous with it once it's in Kerbin's SOI.  The best case for this is an asteroid whose closest approach to Kerbin is farther out than Mun.  Close to Minmus is even better.  This gives you plenty of time to rendezvous before the asteroid reaches is Pe, which is where you want to burn to capture it.

 

5 minutes ago, Rocket In My Pocket said:

Should I go out into solar orbit and nab it, then bring it back? How much Dv does an average Asteroid mission take? I kind of assumed it'd be less than an interplanetary mission, but it doesn't seem that way from the bit of experimenting I've done.

The dV required to reach a NKO asteroid in solar orbit is roughly the same as required to go to Duna or Eve, PLUS perhaps a fairly significant plane change.  And once you get there, you have another significant burn to match velocities with it, with no help from gravity, aerobraking, or Oberth.  And that's just getting there.  Then moving it requires a hefty chunk of dV as well (and the more massive it is, the more fuel this requires), and then you still have to capture it once you get to Kerbin.

For grabs in Kerbin's SOI, the dV to meet the asteroid isn't quite so much.  You get the necessary inclination from launch, then getting to your waiting orbit is about like going to and capturing at Minmus.  From there, it's not so much to get an interception, but you still have a fairly large burn to match velocities, and then of course the capture burn.  So it's still in the region of a Duna mission.

Speaking of fuel, you'll also need gobs of RCS.  As, Bs, and even Cs can be reoriented for burns by brute force, with sufficient RCS and torque.  With Ds and especially Es, however, it's often better to move your ship to the appropriate side of the asteroid instead of trying to rotate it.  Either way, you'll still use lots of RCS.

As far as physically making the rendezvous, the interface isn't too friendly when it comes to doing it in solar orbit.  I find that I have to make several correction burns along the way.  Get a closest approach within a couple hundred km, warp ahead a little, refine the closest approach to a few dozen km, repeat, until you get it down to 1km or less.  In Kerbin's SOI, however, the interface is no more difficult than when rendezvousing with a space station.

 

5 minutes ago, Rocket In My Pocket said:

What about timescale? Is this a quick "go grab it and be done" thing, or a multi-year mission?

For capturing a small roid in Kerbin's SOI, it's a few weeks to a month, about like a MInmus mission.  For grabbing a big rock in solar orbit and capturing it into any old orbit once you get to Kerbin, it's usually several months, like a trip to Eve.  For grabbing a big rock in solar orbit, matching planes with Kerbin so you come in at Kerbin's equator, and then fine-tuning your Kerbin Pe to capture into a low orbit, you're usually talking at least 1 year, usually 2.  This is because first you have to ride to the asteroid's AN or DN with Kerbin, do the plane change, then ride to a good spot to burn to set up your pass by Kerbin.

 

5 minutes ago, Rocket In My Pocket said:

Is it a matter of brute forcing it regardless of what orbit the Asteroid is on, or should I wait for a more "viable" Asteroid? I'm not looking for a ton of specifics or ship designs; just the broad strokes of the best way to approach the problem and why. Appreciate any advice, thanks in advance!

It's much more brute force if you do everything in Kerbin's SOI, but that should only be for small roids which don't weigh much more than a heavy capsule and attachments, so brute-forcing them isn't a real issue.  For big ones, waiting for one that's nearly in the same plane as Kerbin to start with is VERY important:  it saves you gobs of dV both going there and then getting it exactly in Kerbin's plane.  The less dV you need, the better, because with the big ones, it takes LOTS of fuel to produce a given amount of dV.

This brings up the question of power plant.  You can capture a small rock into any old orbit in Kerbin's SOI with a non-extravagant LFO ship.  You can do the same for a C with a slightly extravagant LFO ship or a non-extravagant LV-N ship.  But beyond that, you start getting extravagant with nukes, or have to use ions and accept REALLY LONG burns.  To put a big rock in a low equatorial Kerbin orbit might actually require 2 or 3 ships for different parts of the job.  Maybe an ion ship to go meet it in solar orbit, match its plane to Kerbin, and get its Kerbin Pe out near Minmus.  Then a nuke ship meets it before Pe to do the capture capture.  Then a monstrous LFO ship with high thrust (and possibly mining to refuel itself from the rock)) brings the Ap and Pe down.

[Rocket In My Pocket]

Thank you everyone for all the great advice! An extra thanks as well to @Geschosskopf for his especially detailed write up; that's a lot of keyboard mashing on my account, and I appreciate it!

You guys have confirmed what I suspected, which was that I had some serious misconceptions about the scale of this endeavor. (I built a ship with roughly enough Dv to go to Minmus...so I was low-balling it a touch I guess?) Luckily I have 2 A class on scope atm, and one is coming soon, the other much later; so I have plenty of opportunity to put your guy's advice to good use.

I'll be sure to let you know how it goes with some pics and stuff, thanks again! 

(If anyone's curious; here's the ship I designed originally; I haven't decided if I'll modify it or start over from scratch...I did sort of like the way it looked though.)

Spoiler

The actual Asteroid puller.

The launcher. (Ignore the Twin Boars lol. I just wanted to use them on something because I hardly ever find a reason to.)

 

Edited December 20, 2017 by Rocket In My Pocket

[Aegolius13]

8 hours ago, Rocket In My Pocket said:

The launcher. (Ignore the Twin Boars lol. I just wanted to use them on something because I hardly ever find a reason to.)

Heresy!  TwinBoars are awesome and should be used all the time.   (No joke,  they are my favorite launch engine).

[Geonovast]

8 minutes ago, Aegolius13 said:

 (No joke,  they are my favorite launch engine).

I stopped using them when I started doing asparagus staging, since for some reason using them would break fuel line rules.

 

Just be careful with those things.  I nearly gave up after my first attempt to harness an asteroid.  Turns out I found a hungry one and it ate my ship.

[Aegolius13]

1 hour ago, Geonovast said:

I stopped using them when I started doing asparagus staging, since for some reason using them would break fuel line rules.

Weird.  Though now with fuel flow priority, fuel lines might not even be needed.  

[Rocket In My Pocket]

9 hours ago, Aegolius13 said:

Weird.  Though now with fuel flow priority, fuel lines might not even be needed.  

Indeed, as you can see in my pick I have extra tanks feeding into the Twin Boars, no issues.

The fuel flow system not only took care of it, but did it automatically!

11 hours ago, Geonovast said:

Just be careful with those things.  I nearly gave up after my first attempt to harness an asteroid.  Turns out I found a hungry one and it ate my ship.

Lol, those pics are kind of creepy.

Like the Asteroid was alive and it was waiting for you in space...posing as an innocent rock...just lurking, and hoping for someone to come by that it could eat!

[Rocket In My Pocket]

So to keep you guys updated on the happenings; I decided to stick with the Ronin1 since I already launched it to orbit. (Jumped the gun a bit in hindsight lol.)

I figured since it was already set up to grab and tow asteroids, grabbing and towing fuel tanks should be no problem. So I sent some up! Money is no issue in my current career save after all.

I always build small/low part count because I've always had a potato computer, my new rig can handle large rockets with ease though!

Shogun1 is in position and waiting for contact with Ronin1. (I decided to go with a Samurai naming theme for my Asteroid rockets. Don't ask...I've been watching too many old black and white samurai movies lately. Lol!)

Success! I was actually only sending up one orange tank plus some side tanks worth but the launcher's orange tank had some fuel left, so I grabbed it by the engine and kept the whole thing for now, I'll decouple it later once it's drained, and re-dock Ronin to the payload tank.

That was all I had time for yesterday, but I'll be playing out the rest of the mission soon. I should have enough Dv to do it regardless of what approach I take now.

Edited December 21, 2017 by Rocket In My Pocket

[Rocket In My Pocket]

More updates and some cool(?) pics: Had some time to play this morning, so I've got myself all set up, inclination matched; plenty of fuel left, just waiting for my rock now.

Space truckin! (There was definitely some torque, but I got it pretty well lined up with the ol' Mk1 eyeball.)

Bonus points to anyone who get's the sci-fi movie quote reference. “Careful! That's not a load bearing structure!” “It is now.”

Tossing our spent extra lifter tank aside and re-grabbing our proper payload fuel stage as was originally intended.

33 days and counting! I've set up a maneuver node in advance for when the Asteroid arrives, then I plan to rendezvous and grapple it, then burn hard retrograde to capture it in Kerbins orbit. If something about what I've done (Or what I'm planning to do) doesn't look right to any of you, please tell me now! Lol. (Also I've got more fuel than KER implies, the entire orange tank is full, it just doesn't seem to count it since it has to be manually transferred over to the main tank through the grappler.)

Edited December 21, 2017 by Rocket In My Pocket

[Zhetaan]

Event Horizon, but in fairness, I didn't like it very much.  I've seen plenty of 'some things were not meant to be known' stories but wasn't really enthused about a picture that took that to the campy extreme of a literal 'have spaceship, go to hell' theme.  I get that that was part of the point (made painfully obvious by the picture's use of the 'saying it in Latin makes it scary' trope), but it's really not my cup of tea.  I prefer flinging space rocks in KSP.

Anyway, I'd suggest being very careful about your tug's engine placement.  Tugs are far and away better than pushers but they have a weakness:  if your engine exhaust impinges on the asteroid, you get zero thrust.  For a regular vessel, that just explodes the impinged part, but asteroids have an extremely high thermal capacity.  Most tugs I've seen either took the cosine losses and angled the engines or else built the Klaw onto the end of a long boom.

Edited December 21, 2017 by Zhetaan

[Rocket In My Pocket]

1 hour ago, Zhetaan said:

Event Horizon, but in fairness, I didn't like it very much.  I've seen plenty of 'some things were not meant to be known' stories but wasn't really enthused about a picture that took that to the campy extreme of a literal 'have spaceship, go to hell' theme.  I get that that was part of the point (made painfully obvious by the picture's use of the 'saying it in Latin makes it scary' trope), but it's really not my cup of tea.  I prefer flinging space rocks in KSP.

Anyway, I'd suggest being very careful about your tug's engine placement.  Tugs are far and away better than pushers but they have a weakness:  if your engine exhaust impinges on the asteroid, you get zero thrust.  For a regular vessel, that just explodes the impinged part, but asteroids have an extremely high thermal capacity.  Most tugs I've seen either took the cosine losses and angled the engines or else built the Klaw onto the end of a long boom.

I know, I know, it's so campy. I watched it originally when I was quite young so I have a certain nostalgic love for it. Lol. This was also around the same time as Jurassic Park so Sam Neil could just do no wrong in my eyes. It really is a pretty bad movie plot-wise. It's a lot of fun though I think, and has some great shots. They should have dialed back the actual gore a bit and made it more cerebral, I watched a making of thing where the director pretty much said he was going for "Hellraiser" in space. So he did atleast nail his vision. Lol.

Thanks for the tip, I already debug menu'd it out to the Asteroid in question when I was designing it to make sure it had engine clearance, those long struts the engines are mounted on were the result of said testing lol. It's only an A class so it didn't take much to get a clear thrust path. I'll certainly remember your advice for the next, bigger Asteroid though. First, I still have to go and get this one though!

[Cpt Kerbalkrunch]

I'm way late to this party (winter is our busy season, but Christmas week is freakin' brutal; no time to stalk the forum, or even play). Sadly, cuz I love asteroid grabbin'. Just wanted to say quick that your new rig is takin' some sweet screenshots. Looks like money well-spent. 

Edited December 21, 2017 by Cpt Kerbalkrunch

[Rocket In My Pocket]

1 hour ago, Cpt Kerbalkrunch said:

I'm way late to this party (winter is our busy season, but Christmas week is freakin' brutal; no time to stalk the forum, or even play). Sadly, cuz I love asteroid grabbin'. Just wanted to say quick that your new rig is takin' some sweet screenshots. Looks like money well-spent. 

Yeah, my brother is a manager at a large electronics type store, and he got me a sweet black-friday deal as well as his discount on a 4k TV and a new rig. (I7, Gtx1070, 16Gb Ram, SSD)

We're twins and our birthday is the 11th of December so it was sort of an early X-mas/late B-day gift from him. Lol.

Needless to say I'm very happy with it, I've always had potato computers to game on. I was just playing Destiny 2 at Ultra settings! Man, what a trip. I haven't played a AAA game like that on max settings in years, maybe decades (Since Half-Life 2 I guess?) Anyways, yeah KSP looks really nice at 4k, although text scaling with some mods is an issue. I'm not running anything too crazy as far as visual mods, I like KSP's stock clean, crisp look.

Edited December 21, 2017 by Rocket In My Pocket

[Geonovast]

4 minutes ago, Rocket In My Pocket said:

(I7, Gtx1070, 16Gb Ram, SSD)

Nice!  Makes my new "real computer" look like a potato...

[Cpt Kerbalkrunch]

47 minutes ago, Rocket In My Pocket said:

Yeah, my brother is a manager at a large electronics type store, and he got me a sweet black-friday deal as well as his discount on a 4k TV and a new rig. (I7, Gtx1070, 16Gb Ram, SSD)

This is the sound of me whistling. And wishing I had a brother who worked at Best Buy. 

[Rocket In My Pocket]

Hey guys just a quick update, It's been snowing a lot here and I've been quite busy so I haven't had any time to sit down and really play KSP.

On top of that I've seen a lot of mention lately about a bug involving Asteroids where they change size and Id number if you leave the scene, and they no longer give credit for the contract.

My plan at the moment is to do the rest of the mission in one extended sitting so I don't have to leave the Asteroid, but I'll need a good chunk of playing time for that to happen. Not that I think you guys are sitting around biting your nails over what happens or anything lol, but I just wanted to mention that I'm still working on it and I will let you guys know how it goes, because I appreciate all the help you offered when I was planning it.

Edited December 28, 2017 by Rocket In My Pocket

[Rocket In My Pocket]

So I finally got some free time to finish my ongoing Asteroid mission and I thought I'd update you guys who made it possible in the first place. Also an extra special thanks to @Tyko for the solution he posted to the Asteroid Id code generation issue!

Anyways; pictures!

Losing some of our extra fuel tanks after making our maneuver burn.

Same, I just liked this screenie. It makes space feel big and lonely.

A proud moment for my space program, our first asteroid has just appeared on screen!

We'd have visual confirmation if Ronin had eyes, but he's a robot so... (I should note it was at this point I saved, quit, and employed @Tyko's workaround for the Id code generation issue. So thanks to him again.)

Ejecting the main fuel tank so we can grab our rock! (Had 2/3 of it's fuel left...I may have been overzealous with the Dv lol.)

Ready for grapple!

More shots that I just like,  don't complain...it's my thread. Lol!

Close!

Closer...

Got it! (I left out the part where I bounced off it and had to try again. Shhhh....don't tell anyone.)

Now to bring it into orbit!

Contract complete!

 

A huge thanks to everyone who had suggestions and advice! You guys are the best. Seriously. 

(Also, If a moderator wanted to move this to Mission Reports or something it wouldn't hurt my feelings. I think it's prolly overgrown the initial scope of the question I was asking.)

Edited January 3, 2018 by Rocket In My Pocket

[Cpt Kerbalkrunch]

Excellent work and perseverance @Rocket In My Pocket. I don't know why, but everytime I close in on an asteroid it gives me a bit of that feeling I got the first time I rendezvoused 2 ships in orbit and I saw the other ship appear and then draw closer (you know what I mean, I'm sure). Seeing the big rock draw closer always gives me a thrill for some reason (I have a fondness for Class E's). And the big payoffs from those contracts certainly help as well. 

Edited January 4, 2018 by Cpt Kerbalkrunch