Good 'Tater Catcher Designs

[capi3101]

Howdy all.

Quick question for y'all with more than a slight degree of laziness on my part: does anybody out there have a good design that you use for catching asteroids? The bigger the better.

What kind of elements do y'all usually put into your 'tater catchers anyways? Claw obviously. What else? Basically just seeing if I can make my current design any better.

[Alshain]

Your going to need either a lot of fuel or a lot of fuel efficiency. Most I've seen use the LV-N engines. I've never bothered to go catch one, I was never really interested.

[Taki117]

Howdy all.

Claw obviously.

I BEG TO DIFFER!

I used KAS winches and the radial mount point. It didn't get it into a nice circular orbit, but it did get it into a stable orbit. Like Alshain says, you either needs lots of fuel or lots of efficiency if you want to do 'roid wrangling.

That's also a Class D by the way.

Edited September 25, 2014 by Taki117

[capi3101]

I had actually given some thought to using the KAS winches. I just figured the mass of the rock would strain the lines a bit too much. Do you have radial connector ports on the rock or do you have grappling hooks/anchors deployed there?

By "lots of fuel", about how much are we talking about, roughly? My current rock catcher utilizes a single Jumbo-64 tank with 4 nukes. Steering is a serious issue; that's really where I'd like to try to improve things the most.

[MisterFister]

In particular, launch / intercept windows seem to be peculiarly important, especially on limited dV budgets -- especially because even with MJ / KER, you'll never know your full dV (due to mass calculations) until AFTER you've mated.

YouTuber iKerbals runs a, STS mission series. https://www.youtube.com/user/iKerbals/videos At STS-171, he manages a modded capture and begins developing an asteroid colony in circular LKO christened "Kerpophis." Kethane, Asteroid Resources, FusTek, KAS, and a few other mods feature prominently. Notably, he works exclusively with Helldiver Shuttle launches.

[cantab]

The Macbeth missions in my albums are all asteroid tugs. But my basic design suggestion is as follows:

Main section with a claw up front, a big fuel tank, and a cluster of engines. Using an engine cluster gives the advantage that you can set thrust limiters differently to counter minor imbalances. Don't put too many reaction wheels or RCS ports on this main section, its job is to provide the forward thrust.

Capability to add extra fuel.

Detachable "control sections", each with their own claw, some reaction wheels, and some RCS. Dot them about the asteroid and they'll really help keep it under control. I've had 500-ton D-classes be easy, if a little slow, to turn this way.

Also, I'm a firm proponent of solar orbit intercept. It takes more delta-V to get there but that's "cheap" delta-V expended without an asteroid in tow. Once you meet the asteroid you need only make a small correction for aerocapture. Or since asteroids in LKO are ten-a-penny, why not set up the ante with a gravity assist on to Eve or Duna.

[Taki117]

I had actually given some thought to using the KAS winches. I just figured the mass of the rock would strain the lines a bit too much. Do you have radial connector ports on the rock or do you have grappling hooks/anchors deployed there?

By "lots of fuel", about how much are we talking about, roughly? My current rock catcher utilizes a single Jumbo-64 tank with 4 nukes. Steering is a serious issue; that's really where I'd like to try to improve things the most.

It's the Radial Connector port, I hadn't unlocked the anchor yet, so I had to improvise.

[capi3101]

Yeah, I saw Claw's tutorial for asteroid capture outside Kerbin's SOI today; I might give that a shot next time out. Especially if I get another 'tater on a collision course.

[Moonfrog]

this might be relevant, it wasn't a design I came up with. But I saw a person use a modular ship design with docking ports, he first attached a ship to the asteroid, then after figuring out the mass, he then launched the fuel and engine section to dock with the craft. Its more complicated, but Its an option.

[mhoram]

I created this one a while back.

- ~9200 m/s after reaching LKO at a mass of 571 ton

- If I assume that I need 3000 m/s to rendezvous with a 5000 ton Class-E asteroid, I still have ~320 m/s left for steering the asteroid with a (Kerbin-Sealevel-) TWR of ~0,04

- Puller design, because pulling is easier

- Nuclear Engines for High-I_SP efficiency

- Large distance between engines and asteroid to make steering easier and don't get exhaust on the asteroid

- Lots of SAS for decent rotation

- Lots of RCS for docking with the asteroid

- 214 parts

Javascript is disabled. View full album

I really have to test this ship sometimes.

Edited September 26, 2014 by mhoram
Corrected dV and TWR

[capi3101]

I created this one a while back.

- ~9200 m/s after reaching LKO at a mass of 571 ton

- If I assume that I need 3000 m/s to rendezvous with a 5000 ton Class-E asteroid, I still have ~320 m/s left for steering the asteroid with a (Kerbin-Sealevel-) TWR of ~0,04

- Puller design, because pulling is easier

- Nuclear Engines for High-I_SP efficiency

- Large distance between engines and asteroid to make steering easier and don't get exhaust on the asteroid

- Lots of SAS for decent rotation

- Lots of RCS for docking with the asteroid

- 214 parts

http://imgur.com/a/7Wk9y

I really have to test this ship sometimes.

Interesting design. Not sure I'd go with the huge fuel tanks (though that's a personal preference; I don't like the 8.2:1 fuel ratio of the things as compared to the 9:1 of the Rockomax and FL-series tanks). Can't really get a good look at the boosters either - is this thing an SSTO? I'm assuming the need to hold the boosters in place is why you've got all those structural panels.

That's two puller designs y'all have posted up here so far - what are the advantages of pullers versus pushers when it comes to 'tater catching? Vice versa? My own design so far is a pusher, though that's more because of the way I've done things traditionally; I've had little success with pullers.

[mhoram]

Neither do I like the worse fuel ratio, but in this case partcount was if importance.

It is not a SSTO... the Lifter was my Lopac 52. And the structural panels are from the lifter to keep the Booster in place and provide places to strut the payload - in this case the Asteroid-Catcher-Ship.

Pusher designs are more prone to deviate from the direction of the burn, so more SAS-modules would be needed.

Regarding Pullers, it should be noted that the gimbaling might cause problems, because they steer the vehicle in the wrong direction, so "Toggle Gimbal" is your friend.

Edit: I might overhaul this ship and replace RCS with Vernor-Engines - should be good for the partcount and docking abilities.

Edited September 26, 2014 by mhoram

[Kryxal]

I have a pusher design, myself, and the first thing I do once I set the claw is turn off all the forward RCS ports ... you get much better leverage out of using the rear ports only, and it's not like you're going to shift direction that much. This is especially useful because I've had turning with SAS do some odd things, seemingly depending on asteroid size. Actually, that could be an advantage to pullers, your control point doesn't get confused by the CoM shifting to the other side...

[Sirrobert]

Regarding Pullers, something I've never tried but do wonder:

Could you just set the Claw to free gimbal and start pulling? Would it automaticly pull the asteroid in line with the COM?

I imagine it'd be next to impossible to properly line up the Asteroid's COM with the ship if it's that big

[cantab]

I believe it would, but you might have it swinging around, I think it'd be rather underdamped. I can also see there being problems rotating the asteroid, and maintaining a precise heading on your burns.

An advantage to pushers is you can make a more compact ship overall, because you don't need the engines on big outriggers or miles from the claw. Generally nothing more than an aesthetic issue in stock, but I can see it mattering in FAR.

[MarvinKitFox]

By "lots of fuel", about how much are we talking about, roughly?

If you plan to catch a rock, and *rocket* (not aerobrake) it into about a Mun-distance circular orbit..

And if you are using Nuke rocket...

You need about 1/10th the mass of the rock, in fuel.

[capi3101]

I might overhaul this ship and replace RCS with Vernor-Engines - should be good for the partcount and docking abilities.

Had Vernors on my first 'tater catcher design in lieu of RCS blocks. Forgot that the Vernors only shoot in a single direction at a time - when it comes to docking, you have to make sure you set a few to make prograde/retrograde burns. Guess who didn't realize that until the time came to hook onto the rock...