What's the most efficient way to perform suborbital hops on Mun?

[Zamolxes77]

I'm exploring the Mun, looking for biomes and doing experiments for science. I have a orbital laboratory, used to reset the experiments on my lander. The lander itself has 4 Science Jr, 4 goo canisters and all assorted science tools. It's a 7,000 or so delta-v craft with 4 nuke engines. In current trip, I managed to deorbit from my laboratory and do 3 hops, storing experiments and samples at each stop.

My conundrum is regarding how to perform these hops, what would be the most efficient way to save fuel.

Initially, after landing, next hop was one continuous arc, from point of origin to point of destination, with immense burns at start and arrival.

Atm, I proceed in following way:

1. Quicksave, after all experiments are stored and ready to bunny-hop.

2. Identify my next target and what heading I have to take.

3. Burn at max throttle, immediately after launch turning into the heading at 45 degrees from normal.

4. Burn until the apoapsis hits 10 km.

5. Cut engines and wait for Aps.

6. Point ship straight up.

7. When I'm 1 second away from Aps., I start burning, at very low setting, maintaining that countdown of 0.5 to 1 seconds until apoapsis.

Basically I "migrate" my apoapsis towards where I want to go.

Pro's:

- When my burn brings the apoapsis to 10 km, my surface speed is only around 150m/s, very little to kill off when you land, compared to 500 m/s I get when doing a parabola sub-orbit, from point of departure to point of destination.

- Easy to control surface speed and altitude.

- The angle of descent, when coming in for landing, is 45 degrees or more, usually over 60, coupled with relative low speed makes an easy landing.

Con's:

-I don't know, that's why I'm asking about the subject .

- fuel consumption?

I don't use Mcjeb nor do I intend to, all flights are done manually, I use Engineer redux for data display.

Please leave your input, I appreciate the help.

[EdFred]

Since there's no atmospheric drag on Mun, your most efficient way is going to be determine launch angle (someone just posted a formula for this a couple days ago) and basically point, fire engines, kill engines, coast, burn to stop.

[Kerba Fett]

I was also wondering about this. I use MechJeb and a couple of other mods so it's no problem for me to go to 1km up then set the ship to maintain altitude automatically and build up some surface speed. My lander has about 25 minutes of hover time and it uses pretty low throttle to maintain a constant altitude.

I just wasn't sure if it took less fuel to stay close to the ground or to use a high arc with a hard burn at each end.

[Kryxal]

You'll want to stay fairly close to the ground really ... 45 degrees for short hops, and the angle gets shallower the further you mean to go. You could probably do a fairly good job by noting how long you burn for initially, then reverse your angle and wait till that length of time before impact and do a full-power burn. You'll end up a ways above ground at pretty close to a standstill, then just ease yourself down, or ease off a bit earlier when you have the feel for it.

[Superfluous J]

I *think* you want to aim 45 degrees up from the line between you and your destination point. As was said above, 45 degrees over the horizon for short hops and increasingly shallow for longer ones until you'd in theory be burning into the planet for anything less than about 1/4 of the planet's circumference away.

Practically speaking though, I'd just go 30-45 degrees and pay very close attention to map view while burning. You'll probably waste more fuel trying to be exact than you would just going for it on a more relaxed but still semiefficient trajectory.

[Sirine]

http://forum.kerbalspaceprogram.com/threads/51610-Flying-around-on-the-Mun

For Your Reference.

[Geschosskopf]

If you've got the lab up in orbit to rearm the goo and material bays, and store all the data for eventual return to Kerbin, then IMHO you shouldn't be doing suborbital hops wit the lander. You need all 4 of the goos and materials in each bioime to get all the points from it. So what you do is go down to a new biome, get all the science, back up to the lab, store the science in it and rearm the experiments, then land on another biome. Repeat until all biomes are pillaged, you run out of fuel, then bring the lab home to land on Kerbin for thousands of science.

The only trick is to make sure you hit all biomes. Which is very easy to do if you put the lab in a polar orbit. Eventually, Mun's rotation will bring every one of its biomes under the path of your mothership on the daylight side. It might take a few weeks of gametime but it will happen eventually. Just hit the desired biomes as they come along.

[Laie]

If you've got the lab up in orbit to rearm the goo and material bays, [...] get all the science, back up to the lab, store the science in it and rearm the experiments [...]

I agree.

The lander itself has 4 Science Jr, 4 goo canisters [...] It's a 7,000 or so delta-v craft with 4 nuke engines.

Great gods! If you can build that, you can as well integrate the lab in your lander. Then you can clean out the experiments on the spot, without docking in-between.

The lab-rover-lander was my vehicle to harvest all mun biomes. I don't have savegames or pictures from the actual mission anymore, but if memory serves, it was capable of 3-5 suborbital hops before it needed to redock for fuel. The wheels saw little use, but still saved me 2-3 jumps.

It's quite overpowered, btw: a single engine would wholly suffice to lift it. The second one makes up for 10% of it's fueled weight. I wonder if the two Nervas actually save fuel on that ship.

The only trick is to make sure you hit all biomes. Which is very easy to do if you put the lab in a polar orbit. Eventually, Mun's rotation...

Integrating the lab into the lander solves that problem, too: you can make a series of hops from near-equator to polar lowlands to poles and so on; the trick is to plan your landings so that you will again be near the equator by the time you run short of fuel.

As to your original question: don't worry too much about the most efficient approach. Wasting some delta-V in order to play it safe / have it more convenient is definitely worthwhile. I for one found that I prefer my suborbital hops to be quite a bit higher than strictly nessary. Wasted quite some time and fuel, though I wouldn't say the time was wasted: I didn't need to quickload once. I don't think I could have pulled that off with the most fuel-efficient approach, where you tend to come in fast & low.

In your particular case, with 7000m/s for (at most) four munar landings, you could even afford to enter into a proper orbit each time. If you feel like it.

Edited July 1, 2014 by Laie

[tartley]

Ah, I can see I'm doing it wrong. Currently embarking on my first orbiting munar science lab plus lander. I only have one materials bay and two mystery goo containers (for balance) on my lander. So I'm only going to be able to visit one or two biomes before having to reorbit and dock with the lab to reset these experiments. Thought I was being clever having a small, lightweight lander. Back to the VAB for me.

[Duke23]

I pretty much do the same thing you described, Zamolxes, except usually below 5km depending on the vehicle and destination. Seems to work well enough. I had a small rocket rover design early in the tech tree that worked well for that within about 50km of the main lander, with a Rockomax 48-7S and landing gear. I'd just set the lander down near where two or three biomes meet and reap the benefits. The advantage was that if I was about to run out of fuel I could stay on the ground and use short bursts from the engine to coast along at ~30m/s almost indefinitely. And because it was basically a tiny rocket with wheels it was nearly impossible to crash if you were actually paying attention.

[Laie]

I only have one materials bay and two mystery goo containers (for balance) on my lander. [...] Thought I was being clever having a small, lightweight lander.

Well you definitely want *two* materials and goo reports from every biome you visit. A third won't hurt, four is becoming excessive. A set of two each will weigh 700kg; if you want to visit five biomes, that becomes 3500kg. Incidentally, a Lab + one Goo + one Science Jr weighs 3850kg and can create / store as many reports as you like.

I still slapped on several items of each experiment, for convenient batch processing: run 20 experiments, collect 20 results, and clean out the equipment while moving on. Bulk science collection is a pointy-clicky chore; the above landers are designed in such a way as to make that task less gruesome (all experiments are acessible from a single ladder &c).

Edited July 3, 2014 by Laie
got the lab's weight wrong...

[tartley]

Thanks Laie, that's very interesting to hear.

I think when I have N material bays and goo cannisters I'd rather hit N biomes, instead of getting multiple reports per biome. A single visit to each biome sounds like more points than I'll need to fill out the tech tree, while not driving me too pointy-clicky crazy. Am I misunderstanding much?

[EtherDragon]

Thanks Laie, that's very interesting to hear.

I think when I have N material bays and goo cannisters I'd rather hit N biomes, instead of getting multiple reports per biome. A single visit to each biome sounds like more points than I'll need to fill out the tech tree, while not driving me too pointy-clicky crazy. Am I misunderstanding much?

To avoid going pointy clicky crazy, group your experiments into Action Groups in the VAB. Then at the press of the "5" key (for example) you do a battery of experiments for a single biome. The next on "6" and again on "7" etc... that is if you have several experiments that can't be repeated - like 8 goo canisters or something.

[Zamolxes77]

Thank you all for input.

@Laie actually the Science lab weights 3.5 tons, 3500 kgs, adding that on top of my 45 ton empty Lander is (was) not possible. My last trip from the moon brought in 3500 science points, some 55 odd experiments, that allowed me to unlock the whole tree, less the grappling hook. 3500 kgs is a lot more than the extra canisters, to carry that much around will increase the size of the craft and fuel it has to carry. Here's what I used:

@Gescho I don't know what version you playing, but on .23.5 you can only use one canister and science module per biome. Well you can use as many as you want, but if you try to store multiple versions of same experiments, they get discarded when you board your capsule. Your suggestion doesn't work, that's why I put 4 of each on the Lander so I don't have to dock after every biome visit.

[Laie]

Thanks Laie, that's very interesting to hear.

See that star symbol under my post? (wink wink nudge nudge)

I think when I have N material bays and goo cannisters I'd rather hit N biomes, instead of getting multiple reports per biome. A single visit to each biome sounds like more points than I'll need to fill out the tech tree, while not driving me too pointy-clicky crazy. Am I misunderstanding much?

Don't know. IIRC, a materials study from the Mun's surface will yield 100-25-5.5 points for the first, second and third report you return (Edit: also see Kerba Fett's post below). Surface samples and goo follow the same basic pattern, but yield slightly more points (samples) resp. much less (goo). Seeing as most of the work consists of getting there in the first place, bringing some redundant equipment doesn't seem to be such a big deal.

Oh man, I completely forgot about surface samples. Command pods can hold many different samples, but if you want to collect n samples from the same site, you need n pods -- or one laboratory. When you put it into perspective, those 3.5 tons really are a bargain. You still want to bring a pod for the crew reports, though.

To avoid going pointy clicky crazy, group your experiments into Action Groups in the VAB. Then at the press of the "5" key (for example) you do a battery of experiments for a single biome. The next on "6" and again on "7" etc... that is if you have several experiments that can't be repeated - like 8 goo canisters or something.

Action groups go a long way -- you should definitely do that. But you still have to touch off every experiment when you collect the reports. Grouping them in one place means that you don't have to walk around the ship each time (in which case you should still be happy that you can walk and don't have to do this in space). Further, I found that Science Jr. containers are a bit nasty: Touching them with the helmet isn't close enough, your Kerbal's body has to be right next to them. That's how I came to employ ladders.

Oh, and one more thing: Try your design before you launch. Really. I mean it.

Edited July 3, 2014 by Laie

[LethalDose]

The ideal angle isn't always 45 degrees. It varies as a function of how many radians around the planet you want to travel. It's something like 0 degrees above the horizon to travel pi radians (180 degrees, 1/2 way 'round the body), and steeper angles as you reduce the distance traveled.

Someone on this forum page linked a fully scanned copy of Bate, Mueller & White's "fundamentals of Astrodynamics" to discuss the same issue. If you really want to dig into it, the relevant section starts on book page 277 (not pdf page 277).

The simpler answer is probably "45 degrees is fine to go less than 1/4 way around the globe, go lower if you're going further". Just understand that strategy isn't "optimal"

Also, mind the large rocks.

[Kerba Fett]

I did some experimenting with a lander that integrates a lab. I've got 3850 dV and a refueling base on the Mun.

At each biome I repeat 3 experiments. A material observation, a goo observation, and a surface sample.

The first time is to transmit. The lab helps with that. The second is to return and gets stored in the pod.

The third is also to return and gets stored in the lab.

The stuff in the pod goes back to Kerbin in 1 courier ship while the stuff in the lab goes back in a second ship.

After visiting 4 biomes and transmitting the first copy of the data for instant science, my first load of stored data was worth 906 points. The second load of stored data was only worth 260 points. A nice bonus for just going outside again at each site, but probably not worth an extra landing to get it.

Of course I also did crew reports and EVA reports at each site and transmitted those too.

[Laie]

@Laie actually the Science lab weights 3.5 tons, 3500 kgs, adding that on top of my 45 ton empty Lander is (was) not possible.

3.5t? Sorry, fixed that.

I'm usually not one to criticise other people's designs, but in this case... you maybe shouldn't pack as much fuel. A Munar landing/reorbit takes like, what, 1300m/s or so. If that thing really has 7000m/s (you said so in your first post, and the ship sure looks like it), you could enter a stable orbit after each of your four landings and would still have half your your delta-V left. Hell, you could *land* on Duna and return to LKO, *twice*.

In short: you've got much more fuel than you need, and it shows: The lander in the picture is all tanks and no payload. If you design a vessel for a "mere" 3000m/s, you'll find that you can move much more equipment.

Look at this one: http://forum.kerbalspaceprogram.com/threads/79215-A-convenient-career-mode-LabLander

I used it on Minmus and found 4500m/s to be excessive, it could have touched off every biome without refueling. I didn't try it on the Mun, though. My Munar lander had 2800m/s -- and if memory serves, it was good for three to five suborbital hops (depending on distance and skill).

@Gescho I don't know what version you playing, but on .23.5 you can only use one canister and science module per biome. Well you can use as many as you want, but if you try to store multiple versions of same experiments, they get discarded when you board your capsule.

You can't rearm your experiments before you meet up with the lab, so until then the results can as well stay on the equipment. After rendezvous and docking, have a kerbal touch off every container, collect the data and store it on the lab (which has limitless capacity). Taking two, three, many similar results to the lab is a question of how many containers you use in every single biome.

There comes a point where it's better to land a lab rather than a whole bunch of Science Jr's. Also, convenience: it's so much easier to collect the data on the ground.

[Geschosskopf]

@Gescho I don't know what version you playing, but on .23.5 you can only use one canister and science module per biome. Well you can use as many as you want, but if you try to store multiple versions of same experiments, they get discarded when you board your capsule. Your suggestion doesn't work, that's why I put 4 of each on the Lander so I don't have to dock after every biome visit.

You missed the part where I said you had a Mobile Lab in orbit. True, CAPSULES can only store 1 goo/material report per biome, but the Mobile Lab has no limits whatsoever. You can store multiple copies of everything in them. And the Mobile Lab, holding all this science, is what you eventually recover back on Kerbin.