What, another Elcano challenge? Minmus my destination.

[damerell]

I've decided to have a crack at the Elcano challenge; circumnavigating celestial bodies at ground level. I'll start with a small one, Minmus.

Here's how I interpreted the challenge provisions:

1) Stay on the ground, brief jumps permitted. Well, Minmus has some pretty low gravity, so I might get some pretty big jumps, but the rover will be driven only by contact with the ground.

2) Kerballed missions; I use a life support mod, which should give some scope for irritation.

5) Mods are acceptable; I'm playing with the same mod package my career game uses, whether that's convenient or not. Mind you, that's a large mod package, and I'm doing the challenge in sandbox mode.

Rover designs can be freely tested on Kerbin, but only on Kerbin. Once the mission proper is underway, if I need to revise the design I'll have to fly a new rover to the crew before they starve (not a serious issue in Kerbin's SOI, of course).

I'm going to attempt the circumnavigation itself entirely in IVA, or looking through a Hullcam VDS camera, or in Hullcam's first-person EVA mode. (I'll take screenshots in conventional third-person mode if I want to, mind).

Here, then, is the Mk XI, the first design to be sent to Minmus (click through for full resolution):

It's largely built around the Kerbal Foundries parts. I'm not convinced by the rover body; radial parts don't attach to it neatly. If I were going for a complete redesign, I'd probably build the usual sort of girder shell. The tracks seem pretty effective, though.

Valentina Kermana (pilot) will drive from the Mk I pod, but Sally Kerman (science) will command from the foremost inline pod with its superior view. Valentina is, however, able to use an Aerocam under the nose of the pod and a fore-and-aft Boostercam on top of the rover. The rear pod is for Svetlana Kermana (engineer). The "top deck" of the rover also has two external command seats, which Sally and Svetlana may wish to use when Valentina has learned how not to roll it all the time.

Two Kerbal Foundries skids under the nose and stern of the rover let it traverse changes in terrain without scraping off the Aerocam or rear-mounted parts.

The rear part of the rover contains a reaction wheel, life support supplies, a docking port, a 4-wedge Universal Storage core, and a kOS processor.

The Universal Storage core has an Kerbal Inventory System wedge with spare parts for the more easily broken extremities, and also a hydrogen-oxygen fuel cell, a water electrolyser, and a supply of hydrogen.

The kOS processor is intended to serve two purposes. One is to detect and control rolls; if the rover tips beyond a certain angle, kOS will level it out with the reaction wheel. The second is to monitor the electricity supply, using the fuel cell when charge is needed and the electrolyser when there is an excess (and capacity for more hydrogen and oxygen). I hope this arrangement combined with the large battery capacity of the rover body will let me drive through Minmus's short nights.

The docking port will attach it to the Minmus landing stage, which will belly-flop to lower the rover to the ground - this should be a safe maneuver in Minmus's gentle gravity. The rover is not intended to return to Kerbin; Jebediah will bring a separate 4-kosmonaut return vessel to pick up the rover's crew when the mission is complete.

[Geschosskopf]

Snazzy ride Good luck with it!

Roving on Minmus has always been a huge challenge for me. The gravity so so weak that you just don't have much traction, so it's hard to get any speed, hard to turn, and hard to stop. A lot of folks mount an ion engine on the top to push the rover onto the ground better. I've never tried that myself, but it might save you some trouble.

[Squiggsy]

good luck on your challenge! yes Geschosskopf mentioned the main thing I would suggest, Ion engines firing downwards, should give you better traction , and enable you to steer without flipping, though I would assume getting them ballanced around your COM will be important or they may end up causing more problems...

[damerell]

I considered that, but I think I have to stay true to my intention to only use the tracks for any kind of propulsion. I guess I'll just accelerate carefully (the KF tracks have a variable power setting, which may help) and concentrate on landing well after enormous jumps.

Tonight's project will be to write the kOS scripts and/or to design a lifter.

[Starwhip]

In my experience, horizontal speed is much, much easier to survive than vertical speed... though on an airless body they are not so closely related. Just a tip.

Good luck!

[damerell]

Well, that took a while, but I've written my kOS script and gotten it off the ground. However, some combination of RPM and Hullcam seem to have got confused, and I can't see out of any camera except the forward Aerocam. I'm still driving in IVA - from Sally's cockpit for the vantage point, since Val can't use the forward facing cam on the central strut - but I'm not restricting myself from using third-person mode when necessary.

Here we are at takeoff:

The rover itself is enclosed in a fairing, with a standard command pod above it so that the kerbals can see where they are going - and more importantly, so that the abort switch can actually be able to save them. The SRBs are attached with Space-Y rocket decouplers, so even if the abort switch is pressed with them still burning, there's a good chance of getting away with it. The middle engine is a Modular Rocket Systems quad-LV-N - I've no wish for my transfer burn to take all week. When the boosters are lit, it's really, really loud.

The whole craft is a bit overengineered, really; VOID has the dV hilariously wrong. I got down to Minmus with about 3.5 km/s to spare, and I wasn't intending to use the lander for the return trip, to boot. Another issue is that the lander is not well-balanced; throughout burns, MechJeb was having to adjust the pitch to compensate.

Because the fairing is in two parts, ditchable independently, the crew transfer out of the command pod after the circularisation burn was easy - jettison one half to expose the rover, then the other. First error made; the crew's carefully selected KIS inventories were nowhere to be seen after the transfer. Hope I won't need those spare parts.

Here we are about to go to Minmus:

And here we are landed on Minmus - on the flats, obviously - with Sally Kerman planting our first flag:

One interesting development is that the RTG is overheating. I have no idea if it's going to explode or not. It provides just under 1 electriccharge a second - not a great deal, but it all helps.

I landed near the West edge of the Greater flats, and the first part of the mission did consist of little more than pressing forwards and waiting. The rover can get up to full speed (18 m/s) - while there's not much traction, presumably rolling resistance losses are small. I'm a bit concerned about running into things with no way of stopping, but I crossed the flats and got up the first line of hills without incident. Here's Svetlana planting another flag:

With any luck the next few screenshots will be in daylight.

[Geschosskopf]

Sounds like you're off to a good start, even with the problems. I've never seen RTGs overheat. Wonder what's doing that.

[B-STRK]

Sounds like you're off to a good start, even with the problems. I've never seen RTGs overheat. Wonder what's doing that.

Not sure about the RTG's heat dynamcs values, particularly the conduction vs. radiative values. I see however, that it's mounted on a US wedge. According to the documentation (and when I asked the mod authors about it once), those wedges are modeled in such a way that they treat the wedge structure as a radiator, particularly for their processors which have heat generation. So it could be that. Had a craft once that also had US wedges, mounted onto a structural adapter that was then mounted to a girder. First, the US core heated up, especially when I ran the fuel cell I had there, then the girder acted like damerell's RTG on his craft. So either there's a processor running there, or the wedges are soaking up and passing down heat from the rest of the craft into the RTG. And depending on the RTG's own heat dynamics values, it might be taking in the heat and finding no place else to put it in.

Hell, for a moment, I thought that my US-powered electric minichopper would blow up (the girder was the structural fuselage, and hence why I asked the US guys about it). She held, but I didn't want to gun the engines (which were also mounted to the girder, so it's like it's getting everything at once). If it gets tetchy, damerell, you might want to find an alternate mount point for the RTG.

[damerell]

I can see a few possibilities. At high timewarp, it (mysteriously) cools down again - it did each time I warped on the trip to Minmus. Ordinary KSP play doesn't involve hours of chugging around the surface of moons, so people might not have noticed it.

It's a JDiminishingRTG, which might have different, less desirable, heat characteristics.

Between this and B-STRK's suggestion (although the US processors are port and starboard, and don't run routinely), it's very possible I'm the lucky first person to trigger this particular combination of circumstances.

If it blows, it blows - it was an afterthought to the rover's main generation system. We shall see...

[damerell]

So, success already? Well, Minmus is really not very big; curiously, indeed, the circumference of Minmus is almost exactly the furthest I ever rode a bicycle in a day, so there was certainly time to zip around it in a rover. However, the trip was a bit of a comedy of errors. I've skipped some routine flag-planting pictures at the start to get straight to the things that went wrong.

First of all, the kOS script I wrote to manage the fuel cell and electrolyser worked perfectly. Hooray! It wasn't really necessary, though; the rover had huge reserves, the power demand was modest because of the low rolling resistance on Minmus and the ease of going uphill, and the solar generation capacity produced an overall surplus through a day-night cycle.

The part of the kOS script that detected excessive roll also worked nicely. The part that corrected it did not, even after a few pre-launch design iterations, producing the occasional catastrophic feedback roll. This scraped off the RTG (mind you, it was going to blow up anyway), the deployable solar panels (bother), and the docking port used to release the rover after landing (who cares). The right tool to use for this is the MechJeb rover autopilot's "stability control", which turns out to try and turn the underside of your rover towards the ground (accounting for the local topography) at all times. The one downside is that it won't let you put on the brakes (why not, we ask). After the second wild spin, I switched to using that, experimenting on the way with a "panic" MechJeb surface SmartASS system - heading 90, 0 pitch, 0 roll. The stability control is better, though - really good at keeping the tracks on the ground whenever possible.

A second interesting fact I learned was that when you see an odd grey patch in the ground that looks almost like a split in it, don't drive over it because it is in fact a split in the ground and will fire you into the air stripping a few more parts off your rover. Here I am going for a little flying lesson, having lost the electrolyser and nearly all the hydrogen for the fuel cell. Fortunately, life support supplies were plentiful, so I knew in the worst case I could always drive during the day and rest at night.

After this, I got nearly halfway round Minmus before driving off a cliff. That's Sally's cockpit view - not very interesting except if you click through to the full-res version you can see that the radar altimeter at bottom left reads around 900m.

I was going at 55m/s in the dark (while the rover tracks cap out at about 18m/s, it'll go a lot faster downhill), but I suspect I would have driven off it at any speed. My existing arrangement of headlights was woefully unsatisfactory, and also it's very hard to see what's on the other side of a crest in the ground with no real perception of distance. A camera mounted higher up (or even the one on the tower working properly) would have given more warning. However, KSP doesn't distinguish a grazing impact from a direct one, so although my vertical speed was not that high after falling 900m on Minmus, my overall speed was too high and the skids mounted under the forward pod did not protect it:

Regrettably, Valentina was killed. After this incident, MechJeb's stability control became distinctly balky about using the rover turn commands - I suspect because the CoG had shifted well to the rear of the tracks. From here on, I had to wrestle the rover around corners constantly. Svetlana and Sally would continue the mission without a pilot:

I realised an easy way to make a lot of ground was to come downhill onto the flats. There's no risk of driving off a cliff because the flats are at Minmus's sea level, so you can skim along at a really good clip. Most of the journey from here was on the flats at 40-50 m/s; there's some big wiggles in the later course where I'm going around mountains in the hope of finding a way through on the flat.

I may have driven off a cliff again. It wasn't even dark! The uniform texture and lack of depth perception really means you need a higher viewpoint.

Surely you are joking, Stability Control:

MechJeb did deign to turn us the right way up before impact, but nevertheless it was the turn of everything mounted on the rear of the rover to be destroyed, including all the life support supplies outside the cockpits. If the mission hadn't been so close to the pickup point on such a tiny world, there might have been cause for concern, especially since kerbals seem (understandably, if lazily) to consume whatever supplies are closest to them.

However, we did get some good out of the command seats on the top platform:

Given their delighted expressions, I can only presume Valentina was not popular with the two survivors, alas.

Now, the misgiving. The Kerbal Foundries tracks and rover body were robust enough to withstand the various en-route catastrophes. They might have been anyway (some stock wheels have very large crash resistance figures) but it turns out nearly all KF parts have crash and structural figures that make them basically indestructible. I'm happy enough with this circumnavigation - I didn't know that my tracks were indestructible when I set out - but before I do another I'll have to adjust them to something more reasonable.

Design notes on the rover:

The KF tracks performed well. The KF rover body was not so satisfactory. It holds a lot of electric charge, but anything sticking out its ends is practically asking to get snapped off, being almost flush to the ground. It's also an awkward shape, making it hard to attach equipment radially. That's one reason for the control platform. For a Mk II rover, I'd use a conventional assembly of struts and panels... with a rollcage, if possible.

kOS can detect critical rolls well enough; what it ought to do when it does is to retract equipment like deployable solar panels. It might not stow them in time, but it's worth a go, right?

The Universal Storage parts are particularly fragile and should be mounted somewhere better protected.

Setting off with non-working cameras was highly unsatisfactory. I thought I had removed every camera, saved the ship, reloaded, added cameras... but nothing seemed to help. This needs further investigation.

Infernal Robotics could be used to raise and lower a camera boom for a very high vantage point, and allow it to look around freely. Also, once I'd figured out the stability control, crew could and should have used the external command seats for a higher viewpoint.

IR could also provide self-righting for rovers on higher gravity worlds where you can't just roll over with reaction wheels.

More testing of headlights (particularly going up/down hills), and more action groups to control exactly which ones are on. Minmus's albedo varies dramatically; at times, two headlights were too many up close.

It's obvious in retrospect that before landing it's worth doing a complete SCANsat altimetry scan.

It's the cheap OX-STAT panels that survived the trip unscathed, not the deployable panels, the RTG, or the fuel cell - and provided enough electricity for the entire journey. Part count is obviously a concern, but fitting a few and having a few more in KIS storage can't hurt.

Don't forget your KIS inventory next time.

Don't charge around at 55m/s... or possibly, write some sort of kOS function for detecting we have driven off a cliff and taking appropriate action.

Edited June 8, 2015 by damerell

[stellarator]

I like very much that design... Im not able of combine functionality and that impressive design... Im always try to do a general design, wich don't require many changes between missions (my orbital labs, as example).

[damerell]

I like very much that design... Im not able of combine functionality and that impressive design... Im always try to do a general design, wich don't require many changes between missions (my orbital labs, as example).

You're too kind; much of the looks are down to the KF rover body part, and the functionality was not all it could be. :-/

[B-STRK]

You're too kind; much of the looks are down to the KF rover body part, and the functionality was not all it could be. :-/

Still, you were able to build on it. All the more where it could actually be run off kOS scripts, as your experiment proved (though not without casualties, e.g, Val. )

Not to mention, I thought the same as you, that a skid on the nose, when the track isn't long enough to cover it, would protect it from ground impacts. But now, after your trip, some of my dream designs may have to go back to the drawing board.

tl;dr: You still deserve credit for an awesome drill tank design.

[Geschosskopf]

Great job, damerll! I was rather worried at the lack of down-thrust but it turns out not to have mattered

[damerell]

What I needed was up-thrust and/or back-thrust for the big drops. The Mk II should have some.

[damerell]

I'm off to the Mun with my Mk II rover, a singularly ugly (but, I hope, less fragile) contraption.