Capturing Asteroids at Dres

[Wcmille]

I'm building a reusable craft that can capture asteroids in the Dres SOI. I've done this with small (class A & B) asteroids at Kerbin, but never elsewhere.

 

What advice do you have for me about the construction of the craft?

[Streetwind]

Mind the increased distance from the sun; you might need more solar panels. You're probably only getting something like 15% output that far out.

[Wcmille]

What engine are you using to capture asteroids?

[Streetwind]

I rarely bother, but when I do, it depends on my tech level. I have no problem with long burns (and I usually install BetterTimeWarp anyway), so I go for the highest Isp engines I can get. Ergo, Poodles and Rhinos, LV-N's, or even electric engines powered by reactors (those are modded parts, obviously - see signature link).

The thing you need to keep in mind that the total mass of your vessel has a large impact on your ability to capture asteroids. You can build a vessel weighing 50 tons that has 5,000m/s dV, and you can build a vessel weighing 500 tons that also has 5,000m/s dV. And if you attach them to similar asteroids, the small vessel will see its dV disintegrate to near-nothing, while the large vessel will lose much less. This happens because you're attaching extra payload in flight, and the rocket equation runs off of mass ratios.

As a result of this, while electric engines are great at downsizing the vessel while still obtaining big dV values, and they sometimes make for great tugs, they won't necessarily translate into always being the best option. Sometimes stupid amounts of liquid fuel and a couple of Nerv's is better, just because the mass difference between vessel and rock is so much smaller than with an ultralight electric space cruiser. Ideally, you would pre-plan this in the VAB by estimating - or even simulating - the potential extra mass you can expect the asteroid to add depending on the size class the tracking station gives you. Each class has a fixed range. They're probably in the KSPedia ingame, and if not, they most definitely are on the official KSP wiki.

[Pecan]

On 6/8/2016 at 10:45 PM, Wcmille said:

I'm building a reusable craft that can capture asteroids in the Dres SOI. I've done this with small (class A & B) asteroids at Kerbin, but never elsewhere.

 

What advice do you have for me about the construction of the craft?

Leave out the bar and recreation rooms; all the fun you need can be had at the Dres holiday resort ^^.

[Geschosskopf]

On 6/8/2016 at 4:45 PM, Wcmille said:

What advice do you have for me about the construction of the craft?

Well, the big question is, what are you going to do with the asteroids after you catch them?  The thing about Dresteroids is that they're already in stable, fairly equatorial orbits around Dres, whereas those at Kerbin are on interplanetary orbits.  Thus, if your ship is already at Dres, and you're going to use the Dresteroids at Dres, you don't need a whole lot of dV per trip.  There's no big interplanetary capture burn, all you're doing is adjusting the orbital altitude, and you don't need much thrust because the velocity is pretty low.

OTOH, if you're taking the Dresteroids elsewhere, then you've got a major task.  For starters, you have to make interplanetary round trips so the catcher ship needs the dV to get to Dres and capture there, then bring the Dresteroid back home with it and capture at the destination.  The timing of these trips depends on the normal progression of transfer windows to and from Dres, and the dV will vary depending on how far above or below the ecliptic Dres is at that point in its orbit.  So, you have a choice.  You can either build your ship for the worst-case scenario, lugging the biggest rocks at the worst time in Dres' year, or you can be less capable.  But if the ship is less capable, then there will be several Kerbin years at a time when it won't be able to operate, or can only get small rocks, due to Dres being way out of plane.  Also, if you're wanting to take the Dresteroids further out (like to Jool), these planets move so slowly that transfer windows between them only come around every 10 Kerbin years or so, so you might have to go when Dres is way out of plane or have to wait another decade or 2.

So in general, I find Dresteroids only useful at Dres.  But OTOH, a base at Dres isn't very useful as a stepping stone to further out because, as mentioned, transfer windows are so far apart.  But OTOH, Dres doesn't have much Ore and if you have a leper colony maximum security prison science outpost there, the Dresteroids make it pretty self-sufficient.  It's less of a bother to take Kerbin asteroids to Eve and Duna than it is to mess with Dresteroids.

HOWEVER, there's this cool mod called Custom Asteroids.  This adds populations of asteroids more or less like we have in real life, so there are mainbelt roids, centaurs, comets, KBOs, etc.  And if you don't want to chase those down (which takes many years), it's no biggie at all to write your own configs for CA to add Dresteroid-type things to, say Jool, which it kinda has in real life anyway.  IOW, bring the convenience of Dresteroids to planets you actually care about going to.

[Wcmille]

I'm actually not sure. My expectation is that I will get some number of career missions with them, and I'm putting a craft out there that can presumably do things with them.