Faster/More Interesting way to travel biomes on airless moons

[zetacross]

Disc: I have mods installed [McJeb/EL/KW/Interstellar/More planets etc]

So I have a tiny-ass rover (~4t) cramped full of scientific gear, with one scientist roving around Moho going to each of the 12 biomes collecting science in a box. That tiny rover will then shove it's way back to Kerbin with 200+ experiments. I did the same on Minmus and got like ~200k science. I'm using Kerbal Research & Dev mod(so i kinda do want science but the MPL way is kinda too cheaty)

Is there a faster way to travel/land/relocate rover with no air . McJeb doesn't do landing well(or it takes longer) so I'm doing them manually, which gets dull after a while.

-> Tried a large MK3 bus with huge wheels but the wheels crack and jam under pressure even on Minmus

-> Tried a ship with engines facing both ways but hilariously hard to balance properly and stop from flipping.

-> Landing fast on airplane landing wheels tend to make your ship flip someway when it touches the ground

 

-> Can I like make RCS fire downwards like some sort of harrier jet? Engines are way too hard to balance without ship flipping

-> Is there a mod/way I can calculate when to brake(burn) downwards to land softly enough?

Technically, I can just shove 8 MPLs into one mega ship and just spam experiments .... but where's the fun in that?

[Foxster]

You could make a bunch of little "science bombs". Each bomb to go to one biome. Consisting of a set of experiments to be left behind and a little return craft with just an Experiment Storage Unit as payload to return to Kerbin.

If that get's tedious flying them all back then you could just fly them to one spot on the body being researched, the science then being collected by a Kerbal, loaded into another ESU and return that to Kerbin.  

[Magzimum]

You could fly? If you don't mind ISRU, this can be done without any problems. I only use rovers for either really short distances, or when I do a really economical (low-budget) mission, and therefore refuse to use fuel to get from A to B. 

In my current Dres mission, I created a rather extravagant example of this flying-biome-hopping concept, but more economic options are of course possible too:

Basically, it is just a lander. Engines facing downwards. Landing legs. Reaction wheels to orient it retrograde on final approach of the landing spot. ISRU to fill the tanks. All stock. The engines are just much bigger than I needed... and that made it fun.

 

[Snark]

3 hours ago, zetacross said:

-> Can I like make RCS fire downwards like some sort of harrier jet? Engines are way too hard to balance without ship flipping

I've built some Duna airplanes that have trouble slowing down enough to land (due to the very thin air), and have had some good luck with mounting a couple of Vernor engines on the underbelly to provide RCS-based "lift" at landing.  Have never had any reason to do that on a vacuum world, though, since it's simplest just to build a lander that comes down on its tail, with landing legs.

3 hours ago, zetacross said:

-> Is there a mod/way I can calculate when to brake(burn) downwards to land softly enough?

Well, a mod that will help with vacuum landings (though not do them for you) is this one:

...when you're descending, and you're within a couple of minutes of hitting the surface, it displays a "time until impact" next to the navball (in the usual place where "time until maneuver" is shown), and also an "estimated burn time" (again, in the usual place) that gives you the estimated time you need to burn your engines to come to a halt when you're on the surface.

So, if you're doing suborbital hops, it comes in handy for landing.  Just set your navball to surface mode, set your SAS to "hold retrograde", wait until the "time until impact" is about 60-70% of the estimated burn time, then hit the throttle.  It'll slow you down in time-- it's not a precise autopilot, it won't take you to a dead halt right precisely at ground level, but it'll get you pretty close, so that the last few hundred meters of descent you can manage with just good old fashioned eyeballing and throttle control-- with the added benefit that as your velocity changes, it keeps updating the estimated time to impact.  Works pretty well. 

[bewing]

You can indeed make a hopping rover. But the real question is, how many hops can you get out of a reasonable amount of fuel, before you have to refill the tank? Even on the Mun, the answer is only about 3. On Moho -- a well-designed hopping rover may only be able to make 2 suborbital hops. Which won't get you to all 12 biomes. I think it's easier to do it with a 2-part system. A high Isp support ship that stays in orbit, and your rover. The rover has enough fuel and a nice enough engine to descend and ascend once only. The support ship slows to a halt over the target biome, drops the rover, and then reaccelerates into orbit. Then you switch back to the rover and land it. Drive around to visit all the biomes in easy reach, then fly back to orbit. Refuel the rover after you dock in orbit, and then repeat the process.

 

[Snark]

4 hours ago, bewing said:

I think it's easier to do it with a 2-part system. A high Isp support ship that stays in orbit, and your rover. The rover has enough fuel and a nice enough engine to descend and ascend once only.

^ This.  This right here.  It's much more efficient because the rover is much lighter (since it only needs enough fuel for one round trip) and therefore uses less fuel.

Think about it this way:  if you have a single rover that hops multiple times... then each kilogram of fuel in its tanks has to be accelerated by hundreds of m/s, multiple times.

4 hours ago, bewing said:

The support ship slows to a halt over the target biome, drops the rover, and then reaccelerates into orbit.

...why this, though?  The support ship is going to have a mass much higher than that of the rover.  Unless the support ship's Isp is insanely higher than the rover's, the rover will require a lot less fuel than the support ship to attain the same dV.  So I'd be inclined to leave the support ship completely inert (it just coasts in orbit, doesn't ever maneuver unless it needs to do a plane change to reach different biomes), and the rover handles deceleration from orbit, and acceleration back to orbit.

Also... slowing-to-a-halt at orbital altitude isn't particularly dV-efficient, in terms of Oberth effect.  If you're orbiting at some altitude H and want to end up on the surface, "slow to a halt directly over the target while at H, then drop down and brake at the surface" uses a lot of dV.  A more efficient approach that requires less dV is to do a much smaller burn at H, but on the opposite side of the planet from the target location, so that your long "fall" from orbit takes you halfway around the planet instead of straight down.  Less total dV.

[bewing]

13 hours ago, Snark said:

...why this, though?

Yeah, that part's probably a matter of taste. A biome (or really, the intersection of multiple biomes!) can be a very tiny target to hit from the other side of the planet. It can be a pretty small target even from almost overhead. Partly it depends on the TWR of your descent engine on your rover and how overbuilt your rover is. I just find that my support ships only mass a little more than twice my hoppers, and have a little more than twice the Isp. So that part comes out almost a wash. And some refueling for the support ship in orbit is usually very easy to come by. And that reducing the dV that my hopper needs, so that it doesn't have to counteract all the orbital velocity along with the gravitational acceleration with the puny rover engine simplifies my fuel/engine needs.

 

Edited December 23, 2016 by bewing

[fourfa]

If we're going to talk about hitting all biomes from orbit with a smaller vehicle that can only regain orbit once - now we need to talk about polar orbit rendezvous as well.  I mean, knock out all the equatorial biomes first, so it's as simple as possible.  But given the OP has exactly one post, let's give some detail about getting to the poles with this scheme.

[zetacross]

Thanks for all the recommendations, I have a larger mothership in orbit around Moho with all the refueling needs, in case the rover doesn't have enough fuel. I also can plonk in a miner->refinery ship on Moho if I really want; so fuel isn't really an issue. I also have a refinery on Minmus and a giant 600t fuel tank I can easily get into Minmus orbit. I'm also landing only small planets and moons, which won't take much to get into orbit. Big planets I can use liquid engine SSTOs instead.

Worst, I just need to land a 5 part rocket(from mothership) and stick the experimental data(KAS) on it and fly that home.

I kinda just want a faster way to land a tiny ship many times. I'd usually just target a spot on the map, aim my rover that direction and lift, later slowing down; This eats quite a lot of fuel but it is faster than driving, but it still is kinda dull after doing it so many times.

Or any suggestions/examples on what other people use to hop around airless planets. Or do you guys just science once then screw that planet?

Yes, it's my first post and I've played Kerbal for like 2 months and having fun, but only recently being able to get outside Kerbin

> What happens if a ship was made like a porcupine with landing struts. Does the rating on struts [10m/s,15m/s] represent how fast I can crash the thing without it breaking?

> Could you make a reasonably high speed hovercraft? Tried doing that but small bumps on the surface explode my ship into fireball going over 70m/s

> Could you make something like a star wars ball droid and roll that one direction?

> Is there another what I can brake in airless planets besides burning retro?

Thanks for all the comments!

[Foxster]

Crash-landing a ship doesn't work well. It is possible in some circumstances but usually you at least lose some parts and at worse explode horribly. 

You really have little choice but to de-orbit and land if you want to do it reliably. MJ will do this fine for you. 

There are three ways of doing this I can suggest:

Build a high dV craft with ions or nukes (depending on the gravity) that can hop between a lot of biomes and then return to orbit. You will need one scientist aboard to reset the experiments. 

Build a biome hopper with refuelling capabilities. This will add to the mission time and complexity, plus the mass of the lander will be much more but it will mean you can visit as many biomes as you like. 

As I suggested before: Build lots of probe-based mini landers...

Craft file: https://www.dropbox.com/s/141qhx21g8bbq80/Moho science bomb 1.craft?dl=0

Stack a bunch of those on a lifter/transfer craft behind a fairing and fly to Moho, along with a Kerbin-return-capable manned lander. Get the lander down. Drop a science bomb on each biome. Do the science and the return the bombs to the manned lander via orbit. Have the Kerbal collect the science from the bombs. Return to Kerbin. 

Edited December 23, 2016 by Foxster

[Loren Pechtel]

As long as you put enough torque on it an IRSU hopper works pretty well with MechJeb.  MechJeb will fare pretty horribly if you attempt to hop with a lander that turns like a pig, though.