Mun Problems

[Spaced Out]

Ok so I need some help. I have been sending lots of missions to the Mun (R.I.P. Valentina Kerman), and I keep tipping my lander over. I use a service bay to fling me back up, but how do I avoid tipping it in the first place? Also, on re-entry to Kerbin my first mission worked but the second one I almost instantly exploded. Any help on that?

[bewing]

Probably a screenshot of your lander would be helpful. Are you landing with sideways velocity? Or is it just that even on a relatively flat spot on the Mun, your lander is tippy?

Fixing horizontal velocity is tricky -- but fixing a tippy lander is easy (just spread your landing legs out wider).

For reentry: it's a matter of having a lot of drag, having a heat-resistant part facing the airflow, maybe encouraging your RV to tumble, and maybe using aerodynamic surfaces to create lift.

 

 

[Aegolius13]

To avoid tipping, you want your lander as wide and low as possible.   For instance,  the flat 800 fuel tank works a whole lot better than the tall narrow 800 tank.   You also want to put the heavier parts of the lander further down,  and the light stuff on top.   

Using four landing legs will also give you a bigger base of support than three.

[Spaced Out]

How do you add a picture

[Cunjo Carl]

@Spaced Out Mun's a tricky one! There's precious little flat ground, and it's very difficult to tell from orbit how slopey your landing site will be. The good news is there's a half-dozen solutions, but none of them are magic bullets. Hopefully they'll give you a starting point for thoughts on new designs! Also, unless you have a play-style reason against, I'd say don't be afraid to test your craft ideas in a sandbox mode with cheats to get a feel for things. Making the idea-design-test-result cycle quicker can make a surprisingly big impact.

No-tip lander options

1. Scout ahead. Send out comsats and rovers to scout out landing sites in advance. Finding flat-ish ground can really make all the difference

2. Broaden the leg-base of your lander. Depending on the size of your craft, you can replace taller fuel tanks with a few more stout tanks attached radially near the bottom. You can then put legs on these to make a squat, stout craft which will stay upright even on the steep slopes. These tanks will typically need aerodynamic cones for launch, but you can place your legs directly on these cones, so it's generally not a big deal during construction.

3. Increase springs on legs. If you're on a slantly slope, a higher spring constant will keep your rocket more orthogonal to the surface, rather than sagging downhill and tipping off balance. They also make you sproing off the surface like a super ball when you're trying to land, but you can't win 'em all!

4. Add tons of maneuvering. With enough reaction wheels (anywhere) or manuevering jets near your rocket top, you can just let your rocket lay flat to land and then sit up off the surface when you're ready to go. This works better on smaller, stouter craft, where the 1.25m reaction wheel really works lovely for its size, and the torque required isn't too vast. On larger craft, a couple jettisonable twitches near the top can serve a similar role.

5. Use airplane landing gear rather than legs. They naturally stick out, rather than almost straight down so it's much easier to get a broad base with them! Just make sure to account for the added weight, and pull them out of the tank like they want to be when you first place them. It looks a little silly, but it works nicely. Don't forget to apply the brakes!

6. Go to Minmus instead. *cough* It's got lots of nice flat places for easy landing, and is generally a much nicer trip. It's harder to get into its SOI, though.

 

Reentry from Mun options

1. Multi-pass through the upper atmosphere ~35-45km. This will bleed off the speed slowly, and create less heating all at once. The downside, of course, is it'll bleed off the speed slowly. I tend to put my final pass in the 22-28km altitude ballpark.

2. Lots of empty fuel tanks can help slow you down if your trajectory isn't too steep; this works well with the multi-pass. In this case, it's best to fly 'broad side of the barn' style to catch all the wind you can to slow down. For this, make sure to bring plenty of batteries, or have a way to recharge between passes (solar panels). Especially in this case, you can use body lift from your craft to control your trajectory. Making your craft a front-slash into the wind will make it lift up.

3. Retro-boost before entering the atmosphere. By bleeding off a few hundred m/s, you can often make easy work of an otherwise tricky reentry, or save yourself a couple passes. It wastes deltaV of course! If you happen to have extra fuel in the tanks, I'd say no harm done.

3. Use heat shields. In this case, you wouldn't so-much need to use them for their ablator, but instead for their high thermal tolerance. By removing most of their ablator, you can reduce their impact on your deltaV budget. The downside of the heat shields is they're very slippy aerodynamically, so you won't get much upper-atmosphere slowing with them. This can actually turn into a downside.

4. Put your kerbal in the service bay... There, I said it! Command chairs in service bays are so effective at reentry, that many consider them cheaty. I consider it funny! To be honest, it's probably best to avoid this for your first journey, but be aware that it exists.

5. Use fins as makeshift airbrakes. While this doesn't work with basic fins, structural D wings can be used as makeshift airbrakes from Mun return velocities. It's considerably more difficult than the other options, though.

6. If you're in the lower atmosphere but lawn-darting down to Kerbin, you often have a better chance of survival out of the craft than in. Bail! This will always work over water, and works maybe half of the time over land.

 

 It's KSP, so there's of course other options for all these, too. Hopefully something sounds fun and useful for your case. Best of luck! Let us know how it goes.

edit: woops, didn't notice others posted while I was typing in little bits here and there.

You can post images by:

1. Press the Print Screen button (or your computer's equivalent) while looking at your craft in KSP.
2. Alt-tab out and open Paint (or your computer's equivalent). In paint, press ctrl+v to paste in the photo.
3. Save it as a jpg.
4. Go to an image hosting service (imgur is this board's favorite, but I like Postimage for its simplicity)
5. Upload your photo to this site, and it'll provide you a link.
6. Paste that link into your post, and it'll appear as a photo like magic!

Edited June 8, 2017 by Cunjo Carl

[Kryxal]

For pictures, many people use Imgur or the like, then insert the image link and the forum shows it nicely if you do it right.

For landing, at the end consider using SAS set to retrograde for the final part of the descent, and if you're using a single engine, maybe dial it back for more fine control.  If you're using multiple engines, you don't want to adjust them on the fly, but action groups and at least 4 small engines could allow you to quickly shut only some down.

[Wanderfound]

To demonstrate what is meant by "wide and low" for landers:

 

Or

 

Wide-spaced landing legs, a bit of torque and a gentle landing on the flattest spot you can find.

[Spricigo]

2 hours ago, Wanderfound said:

To demonstrate what is meant by "wide and low" for landers:

For some reason,  it seems to be a widely used idea.