I've finally landed on Minmus! Now, how do I get back?

[JackBush]

It's taken a long time but I've finally done it. I've collected my science and am ready to take it all back to Kerbin. But how. Here's my situation: [URL]http://imgur.com/DRsLQw9[/URL]

I've searched for how to do this but find it all confusing. [B]An[/B] I think I have too little fuel. So I'm looking, no, pleading for help on getting back. Or, if I should leave my Kerbal there and send a rescue party (with more gas) how do I do that?

Hope you can help.

[Snark]

Hard to say how much dV you have without knowing your ship mass, but assuming that you're around 2 tons, you should have just about enough dV to get home.

I'm assuming you're on or close to Minmus' equator, yes?

Take off at max thrust and [I]immediately[/I] crank it over so that you're pointing due east and only just slightly above the horizontal. Burn until you've raised your Ap up to something low, but high enough not to worry about mountain collision-- say, 12 km. Circularize at that altitude.

To head home to Kerbin, burn when you're heading Kerbin-retrograde (that is, on Minmus' near side, where your orbit around Minmus is in the opposite direction to Minmus' orbit around Kerbin. A maneuver node will help with this. Make the burn big enough so that it lowers your Kerbin periapsis down to about 30 km.

You should [I][U]easily[/U][/I] have enough dV to get to Minmus orbit, the only question is whether you can make it home to Kerbin. My guess is that you probably do. If you don't, you have a couple of options. One would be to send another ship to rescue your kerbal from Minmus orbit (be sure to have your kerbal retrieve any science you've gathered, to bring it home with you). Another option would be to burn all your fuel, then go EVA (don't forget to grab the science!) and use your kerbal's jetpack to complete the burn. Kerbal EVA packs have like 300 m/s in them, it's ridiculous, that's easily enough to get home to Kerbin. Of course, the kerbal won't be able to reenter without burning up-- you'd have to put up a rescue ship to grab the kerbal as he goes by.

[Reactordrone]

I estimate that the ship has just under 340m/s delta v left which should be just enough to get home but there's no margin. You'll want to get into a very low prograde orbit as efficiently as you can and them set up a manoeuvre node so that your ejection burn takes you in the opposite direction to the direction that Minmus is travelling in. It will take about 170m/s to get your periapsis into Kerbin's atmosphere. If you're short on fuel you can decouple the pod and get out and push for the last few m/s.

Should be similar to this,

[IMG]http://img.photobucket.com/albums/v499/swampmonster/Kerbal%20space%20program/MUN%20RETURN_zpsugtqm906.jpg[/IMG]

But with Minmus rather than the Mun.

[Foxster]

One tip for next time would be to take less 'chutes, which would save dv. One Mk16 would have been enough to land the capsule and heatshield at Kerbin.

[Harry Rhodan]

I can see MJ in the screenshot. It should be able to provide a delta-v readout.

[Plusck]

Agreed with everything said here except two things:
Forget about circularising your orbit - you'll simply waste a few precious delta-V and if you are that tight it could make all the difference.
And periapsis at 30km with that setup might be unmanageable.

No circularising:
You want to burn prograde at more-or-less exactly the point shown on Reactordrone's pics. If you are somewhere on the surface just west of there, simply prod the craft skywards then burn due east and level at max throttle until you have a very low suborbital arc that gives you time to plot your exit at Ap. Any distance you put between yourself and Minmus before burning back into Kerbin's SOI is a waste. You're already at over 5000m so most of the moon is lower than you anyway.

Periapsis at 30km:
The main problem that I see is your chutes. Heading back for a touchdown on the first pass back from Minmus is hot. I've tried but have always given up trying to get back with anything still attached under my pod (I'm sure I managed a materials suite thingy once or twice, but not an empty fuel tank). So quicksave before you lower your periapsis below about 40km, because you might find that you need to do several high passes to bleed off speed before you can survive reentry. It's a grind, I know. Edited November 26, 2015 by Plusck

[sardia]

To add to all this, Use EVA to push your ship, once to fix your orbit around minmus, and the next to fix your AP around Kerbin.

[Snark]

[quote name='Plusck']Forget about circularising your orbit - you'll simply waste a few precious delta-V and if you are that tight it could make all the difference.[/QUOTE]

I disagree with this-- I'd advise the OP to circularize (very low, like 12 km). The dV difference between "circularize at 12 km, then another burn to go home" versus "do a direct burn from the surface" will be negligible-- Minmus gravity is pretty darn low. Whereas if the OP circularizes first, it's much easier to take time to carefully set up just the right maneuver node, as opposed to trying to do it all in a hurry during a burn. My guess is that taking the time to get the maneuver node just right will more than make up for whatever small difference in dV it makes over a direct burn.


[quote name='Plusck']
Periapsis at 30km:
The main problem that I see is your chutes. Heading back for a touchdown on the first pass back from Minmus is hot. I've tried but have always given up trying to get back with anything still attached under my pod (I'm sure I managed a materials suite thingy once or twice, but not an empty fuel tank). So quicksave before you lower your periapsis below about 40km, because you might find that you need to do several high passes to bleed off speed before you can survive reentry. It's a grind, I know.[/QUOTE]

From the screenshot, it looks like he's got a heatshield directly under his command pod, with a decoupler below that. So he ought to be fine. Return from Minmus is no problem if you have a heat shield.

[Plusck]

[quote name='Snark']I disagree with this-- I'd advise the OP to circularize (very low, like 12 km). The dV difference between "circularize at 12 km, then another burn to go home" versus "do a direct burn from the surface" will be negligible-- Minmus gravity is pretty darn low. Whereas if the OP circularizes first, it's much easier to take time to carefully set up just the right maneuver node, as opposed to trying to do it all in a hurry during a burn. My guess is that taking the time to get the maneuver node just right will more than make up for whatever small difference in dV it makes over a direct burn.[/QUOTE]

Hmm. I'll accept the principle but at the stage the OP is at, will ultra-fine-tuned nodes be doable?

[quote name='Snark']From the screenshot, it looks like he's got a heatshield directly under his command pod, with a decoupler below that. So he ought to be fine. Return from Minmus is no problem if you have a heat shield.[/QUOTE]

True, but I'm supposing that the materials science suite thingy is meant to be going back too. So it comes down to a choice between a 30-32km quick return and loss of science points, or a higher science return and a number of grindy non-warpable passes through the upper atmosphere.

[Waxing_Kibbous]

It looks like the decoupler is going to blow off the Sci Jr. , if that's the case make sure you grab that science- you have chutes on it though so I'm not sure what the plan is (if it's a goof, I just returned from a Minmus mission where I forgot my landing gear haha, thankfully I landed on the second stage poodle engine a couple of times :P- Kerbals are forgetful engineers!). Like others have said, launch and immediately head sidewards so your orbital plane matches Kerbin's roughly (aka don't do a polar orbit), making sure to clear any mountains. I dare say you can go as low as 10km for a minmus orbit, heck maybe even 8km. You want every little bit of fuel for the approach- if you can get your return orbit into Kerbin's atmosphere you are golden.

From the wiki: [QUOTE]Minmus has very divergent elevations. Plateaus at around 5 km high are matched by "Flats" at datum altitude (0 m).[/QUOTE] Edited November 27, 2015 by Waxing_Kibbous

[Snark]

[quote name='Snark']I'd advise the OP to circularize (very low, like 12 km). The dV difference between "circularize at 12 km, then another burn to go home" versus "do a direct burn from the surface" will be negligible-- Minmus gravity is pretty darn low. Whereas if the OP circularizes first, it's much easier to take time to carefully set up just the right maneuver node, as opposed to trying to do it all in a hurry during a burn. My guess is that taking the time to get the maneuver node just right will more than make up for whatever small difference in dV it makes over a direct burn.[/QUOTE]

[quote name='Plusck']Hmm. I'll accept the principle but at the stage the OP is at, will ultra-fine-tuned nodes be doable?[/QUOTE]

Actually, that was the reason I was suggesting it-- I would contend that setting up a maneuver node (at your leisure, when there's no time pressure, and you can see how it is, and tweak it) is considerably easier than trying to get the burn just right, with no help from a maneuver node, just eyeballing it, burning straight from the surface. [I][U]Especially[/U][/I] for someone who's relatively new to KSP.

Doing things with maneuver nodes is [I]easier[/I] than doing without them. It's why the feature's in the game, and why unlocking patched conics is something people like to do. :)



[quote name='Plusck']True, but I'm supposing that the materials science suite thingy is meant to be going back too. So it comes down to a choice between a 30-32km quick return and loss of science points, or a higher science return and a number of grindy non-warpable passes through the upper atmosphere.[/QUOTE]

Well, yeah, he'd lose the materials bay. But there's no need to lose any science points at all, just grab the science out of the materials bay and stash it in the command pod. The only reason to bring back the instrument is to save a few funds in recovery cost, but it's not all that much.

[JackBush]

[quote name='Snark']just grab the science out of the materials bay and stash it in the command pod.
[/QUOTE]

First, thanks everyone for the excellent advice. Try as I might, the closest I can get the Kerbin periapsis is about 5 million meters. And that's from a Minmus orbhit of about 6-7 km. I squeezed the fuel as much as possisble and that was it.

Second, to Snark's quote: how do you grab the science and store it in the command pod. I lowered the Kerbal on a ladder and had him stop in front of the open materials bay, waiting for a message to store the data but saw nothing . What are the steps to doing that?

Third, I'm going to send up the same rocket minus the extra chutes as suggest above. Wish me luck.

[Plusck]

Yeah as Snark has pointed out I was being somewhat stupid earlier, confusing issues with science reports and bays...
To get science out of the materials bay, right-click on it when your kerbal is close. If close enough you'll get a "take data" button. Unfortunately it has to be pretty close for the materials bay. Since your kerbal is not a scientist, you'll get a warning that it will be unusable after that. Then when you get back in the pod it'll be added automatically (saying "deleted" from the Kerbal and "added" to the pod). You can also click on the pod from EVA and there will be "store experiments" button which does the same thing. You should do this often on EVAs to get multiple temperature and pressure reports (once unlocked) from different biomes.

[Snark]

What Plusck said.

Taking science from instruments is pretty important, because it greatly boosts your science yield. Let's say you're going to Minmus and you have a science instrument on the ship. When you enter the SoI, you take a measurement, and it's "in space high over Minmus." You send out your kerbal, retrieve the science from the instrument by right-clicking and choosing "Take Data", then send your kerbal back into the command pod. Then you wait until you're very close to Minmus: you can do it again, and get credit for a new science result, "in space near Minmus". Then you land on Minmus and do it again. If you have enough fuel, hop to a different biome and do it again.

In this fashion, one science instrument can give you many science results from a single trip, which greatly boosts your science return-- but you can only do that if you send out your kerbal to take the data from the instrument, thus freeing it up to be used again.

The one wrinkle to the above is that two of the instruments (Mystery Goo and Science Jr., i.e. the first two that you get in the tech tree) are single-use experiments. Once you take the data out of them, they become inoperable. [I][U]However[/U][/I], if your kerbal is a scientist (rather than an engineer or pilot), he/she can click on the used-up experiment and choose "Restore", which then lets you use it again.

So a really handy exploration strategy, once you've unlocked the OKTO probe core (which has SAS on it), is to send little single-kerbal exploration ships to Mun/Minmus where the crew is a scientist, and you rely on the probe core for SAS.

[ElWanderer]

On Fri Nov 27 2015 01:36:57 GMT+0000, JackBush said:

First, thanks everyone for the excellent advice. Try as I might, the closest I can get the Kerbin periapsis is about 5 million meters. And that's from a Minmus orbhit of about 6-7 km. I squeezed the fuel as much as possisble and that was it.

I did a quick manual calculation of the delta-v you had from your screenshot before the forums went down for maintenance and came up with 329m/s though I didn't include the mass of the solar panels (and I may have forgotten to include one of the parachutes). The delta-v maps I've looked at suggest 180m/s to get into Minmus orbit and 160m/s to escape back to Kerbin orbit, for a total of 340m/s. So it was always going to be difficult to get back.

One additional trick to try would be a gravity assist - plot an escape burn from Minmus that flies past the Mun (may be many days wait until it's in the right place) and fiddle with it until the resultant orbit drops you into Kerbin's atmosphere. A rescue mission may be quicker.

On rescue missions: to transfer fuel requires docking the old and new craft together (plus an upgrade to the R&D lab?) Pretty difficult if you don't have a docking port. Your best bet is to rendezvous in Minmus orbit and EVA the pilot (with the science data) over to the new ship.

[stormdot5]

One potential method of returning from this specific situation would be to wait until Minmus rotates to point you almost directly backwards in it's orbit. Then burn straight up. It's less effiecient to escape minmus SOI but every m/s spent will decrease your orbital speed round Kerbin, lowering your Periapsis. Also, it is a very simple technique.

Escape velocity of Minmus: 242.61m/s

Orbital speed of Minmus around Kerbin: 274.1m/s

You should have enough dV to escape this way, make sure to quicksave though and work out a good aerobraking periapsis, it may be lower than you expect.

[EuSouONumero345]

An engine would probably be the best option. With a fuel tank, you'd expect.