Docking two Class E asteroids together

[Sharpy]

I had that dream for a long time.

I wasn't sure how to do it. I made a fine tug, but it wasn't nearly maneuverable enough... Probably everyone already knows my Claymore, because I brag about it left and right.

So, after revival of KSP, as soon as I could afford it, I pulled up Claymore out of old save folder, and quickly grabbed a Class E asteroid. One afternoon, and I had it in LKO. At first I planned a base around it, but first, orbit of 100km is terrible for any large projects because not only night lasts 50% of the time, there's no good time acceleration and my early base designs were... um, faulty to say the least. Plus asteroid physics is really, really glitchy. Things get... explodey around them.

Then... the game refused to spawn another class E for a long time. I launched a bunch of missions and occupied myself with other stuff, draining the one captured asteroid dry in the process.

Well, at last the game spawned another one. Not crossing Kerbin SOI so I had to send Claymore on a chase in Sun orbit, but it's a fine craft, the job wasn't a problem.

I parked the new asteroid in 250km orbit, and began plotting...

I need to dock it, like one docks a craft. I can't just do the trick with turning around to get the flight direction right. I need a true, fully-featured RCS. But what RCS can do a thing like this?? Lots and lots of vernors? No, that's an awful idea. Monoprop is right off. It's a goddamned asteroid, and it needs asteroid-sized RCS.

And thus, the asteroidal RCS project was born.

First, I made a thruster block.

Aerospikes are small enough so that the thing doesn't grow huge, they have a decent ISp, decent thrust...

I clipped a small tank, probe core and a battery inside (they are actually attached to the node at the tip of the top-most thruster...) Klaw, a bunch of surface lights which I had planned to use as indicators until I realized with them mounted on the thruster blocks all over the asteroid I won't be able to read anything out of them. So the ones that would be toggled had to go, but the color ones stayed - as labels. And I knew I'd need a control hub...

Then came the trickiest part. Instead of switching the computer on, that evening I spent with a pencil and a sheet of paper.

Upper left - action groups. 3 translations, 3 rotations, each in two directions - that's 12 action groups. I used all 10 for the more immediately needed ones, and gear and abort for roll, which wasn't as necessary.

Four thruster blocks around the asteroid. Hub in front. A fuel tank in the rear, because the first asteroid was depleted - later I planned using ISRU.

Then I planned the markings for the thruster blocks. Each of the thruster blocks is unique. I named them for colors on the top thrusters - Blue, Cyan, Purple and Orange. All engines with blue light point up. All purple point down. Orange point left, Cyan point right. Red is for Forward, Green is for Back. Except each thruster was 90 degrees from the neighbor. I planned their locations in the carrier craft, then I wrote which action groups assign to which color engine on which thruster.

Also, I planned the hub.

It started with MK1 inline cockpit, due to its excellent visibility. And I built a hud of the surface-mounted lights offset from the surface.

The one lit shows "Pitch Down" active. The one below it is "Translate Down". I'll post a screenie with all lit later.

Then the thing grew. It would need to be able to connect the asteroids. It would be very inelegant if it was not reusable after the operation. It also needed the ISRU, and not the toy one, because maneuvering for an encounter we're operating on a tight schedule and we need the fuel fast.

The resulting form factor was... uh, so ugly it was pretty. I called the thingy Ugly Duckling.

So, this is the Ugly Duckling carrying a crossbar, gripping it with airbrakes. (to align length-wise)

I packed the thrusters onto a rocket...

Then I made a rather simplish fuel carrier, and began the arduous work of docking it all to the asteroid.

Night was my bane. I didn't think of wide-area lights for Ugly Duckling or the carrier. I docked the carrier at night, and since without the booster it flies on monoprop RCS only, I barely did it before running out of monoprop, so the alignment was poor. I decided to follow up with the rest aligning it to the carrier.

But day was too short again, so I just docked the thrusters haphazardly and deorbited their carrier. Luckily, they *were* color-coded, and after resupplying their fuel, I was able to dock them roughly at compass points respective to the fuel carrier.

Then I moved the duckling to the center opposite, and began testing the system.

It worked fine... with one exception.

Crossfeed. The fuel just wouldn't flow up the Klaws. Aerospikes would drain the tiny tanks clipped in in matter of seconds.

So, I asked how to solve this...

And while now I have solemn thanks to @Palaceviking, at one point I wanted to curse him to hell.

He told me to use KAS ports and pipes.

But that's a Class E asteroid! The stuff is too far apart for single segments of pipe!

At first, I sent a KIS box of CB1 Ground Bases and KAS ports. Did you know you can attach the Ground Base to a planet, but NOT to an asteroid?

So instead, I sent a carrier of tiny "nodes" - probes, each equipped with two ports, Oscar B, HECS, two spiders and some solar panels.

Did I say asteroid physics is buggy? It is.

The probes were quite agile, able to stop and hover right where needed above the asteroid, and the Kerbal engineer easily built the pipelines, sometimes three segments long.

Then, as night came, I sent the engineer back to the cockpit... and before reaching it, I heard explosions.

Load. Explosions again. Load and checking what happens.

Pipelines shaking wildly, throwing orange tanks ripped off the carrier.

I retried it several times over. Time warp would calm the shaking for a couple seconds, so the kerbal managed to reach the cockpit with several segments of time warp. I went to the tracking station, saved my game and left it for another day.

Next day, the infrastructure would still explode seconds after loading the ship... but I noticed it takes good 30s from game load to explosions. So, the kerbal goes EVA, save, load. The kerbal flies a bit ahead, save, load. The kerbal reaches the pipelines, save, load. The kerbal approaches the thruster block rapidly, save, load. The kerbal crashes into the asteroid, sent spinning. Meanwhile, everything explodes. Load. The kerbal crashes into the asteroid... Load, and brake hard. The kerbal crashes into the asteroid...

Then I realized I didn't make any real progress since the tests of the asteroidal RCS, for which I have a named save. All I did were the pipelines, and they were a failure!

So, I went to the KSC, and just loaded that save, a good two game days earlier.

I upgraded the "nodes" with Klaws tweakscaled to MK0. I sent them again. I repeated the work, docking each node to the asteroid first. I didn't draw all the fuel lines to the carrier, instead drew them to one thruster, and then branched off to the remaining ones.

The plumbing looked quite impressive... and it didn't explode!

Then I saved, set up the encounter, used the Pitch and Yaw action groups to get the node right, and when the time to perform the node burn came... I sent the asteroid into a wild spin.

The thrusters were misaligned relative to the CoM.

I tried thrust limiter to reduce the spin. It wasn't very effective, but it worked... kinda. I botched the first maneuver badly, good 30km away from my encounter.

Still, correction after correction, node after node, I was learning to handle the asteroid.

Remembering to switch off an action after I finish the burn. Increasing throttle just a little instead of pressing Z. Switching control back to the goddamned cockpit after the game decided to pass control over everything to one of the HECS on the fuel line nodes (ARGH!)

The breakthrough came when I switched normal RCS on.

The thruster blocks were adequately supplied with Vernors, just to be able to maneuver them into place and dock where needed on the asteroid. I didn't expect the vernors to do much once docked. But they did. As I set SAS to "Node", and started a burn, I saw the Vernors fight a losing battle to keep the asteroid from spinning, as the thrust limiter was set "by hunch" on the off-center engines.

So, I'd slide the thrust limiter until Vernors on that block would nearly switch off - and with the engines finally balanced, Vernors were all that was needed to retain that balance and adjust for all errors and imprecisions! Aerospikes provided the power needed to move the asteroid - Vernors were that "last mile" needed for truly precise RCS.

At last, regretfully, I saw that I had finally mastered the asteroidal RCS, and I was left with 30m/s of delta-V to correct my past mistakes, make the encounter and dock. No way I could do this.

Then even before that, the aerospikes sputtered out.

A sour note after the success. Oh well. I'll need to send another tanker, dock it, fix the piping, by that time the semi-decent encounter I had would be long gone...

Where the heck do I still have that 30m/s of fuel if the aerospikes are starved?

(Truth of the matter - in Duckling's tanks and its single Terrier, but I realized that much later...)

So I did the easy thing. Opened the Resources, and hovered over the Fuel bar... noticing it's depleted roughly halfway. What?! I hovered harder.

The carrier has three orange tanks. The pipe is connected to one. The others were hardly touched, only as much as the Vernors pulled out of them.

That really made my day. I began pumping fuel, and soon my delta-V was well over 200! I turned to the node, performed the burn, prepared a node for the encounter, and warped there. A neat retrograde burn, and save! The final approach began!

I approached at some 3m/s, then braked to 2...

I keep struggling with the navball to rotate the Klaw to target's COM and... crashed. Surprisingly, no explosions.

I switched time warp 5x to arrest rotation of the two asteroids, left it and unsurprisingly... explosions.

I loaded and began the approach again. This time I switched SAS off, and used RCS manually to turn. I'd no longer use the aerospikes - the very precise movement was done purely through Vernors. Only one short aerospike burn retrograde...

Aaaand... Docked! For a celebration I lit up all the HUD lights.

And here it is. Two class E asteroids docked together!

It's been two weeks since I began working on the Thruster Blocks and the Ugly Duckling. And practically every day I'd do something towards docking the asteroid. Not counting the capture and bringing them into LKO. It's been a two-week project.