A better Mun landing approach

[MPDerksen]

Thanks to the great responses to my first question(s).  Now for #2....

I landed on Mun, but forgot that the science was all BELOW the heat shield.  So I got the surface sample and the EVA etc, but missing all the rest.  So I added a probe brain and boarded my Scientist, rather than a Pilot.  I also had upgraded the landing legs!  However, I've tried my final landing approach from 20K meters above the surface 6 times so far.  half the time, I end up bouncing, but landing on my side (no, I can't launch that way, tried it....), or landing hard enough that I blow up the engine, and THEN fall onto my side.  I have a list of questions, but at the point of my quicksave, I'm at 20K altitude, doing about 250m/s.  My issues seem to come from the fact that I have a yellow "Limited Crew Control", which makes holding retrograde really tough.  Remember as I ask my questions that I've only had the sim for about a week or so (in other words, use small words).  Also, while there might be helpful mods, I'd like to get advice assuming I have none.

1.  When I first launch and get into Kerbin orbit, I typically end up having to do a Normal/Anti-Normal burn, since my inclination relative to Mun is around 5 degrees.  Not a big deal, but is this step a fuel waster?  Or a wise practice?  Current mission it took 25 seconds of burn to correct 4.7 degrees.
2.  I try to end up leaving my Pe opposite of Mun, and then burn prograde from there to create my Mun intercept.  When I create a maneuver point, all of a sudden the screen fills with lines and data that I can make little sense of.  I have my regular Blue, current line, right?  But there are Orange lines, and also Purple ones.  They seem to intersect and change direction.  Often, I end up dragging my Prograde/Retrograde and Normal/Anti-Normal bars on the marker, just trying to get something logical.  But since I'm not sure why I'm off, I then have no solid idea what to change!  On the last play, I needed 56 seconds of burn to get to a reasonable intersect with Mun.  That seems like a large amount!  Once I'm close, I can set myself into Mun orbit easy enough, but I do end up in a vastly different inclination.  This becomes evident if I try to get back to Kerbin.
3.  When I fly with a Pilot I get some additional SAS buttons, like "Prograde".  I thought using a probe core was my "pilot replacement unit"..... lol.  But since I'm over Mun now, and I have what I have, any advice for a softer landing?  On this play, I was at 600m/s at 70K above the surface.  I slowed to 250m/s at 20K and did a quicksave.  Now, here I am.  

Michael

[steuben]

You need to do it in threes. After the first one falls over, the second will explode and fall over, the third will stay upright. And that's what you'll have, my boy, the stablest lander in all the lands.

Not all cores have all the features. 

You'll have to feather the engine a bit when you get close.

Kerbnet will give you the altitude of the terrain above average "sea" level. So you'll want to be around 10 m/s surface speed for that last 100 -200 meters of decent.

Since you don't have hold pro-grade/retrograde you'll have to do it yourself. When your a good 1 to 2 km above ASL you'll want to be on a nearly vertical decent. and then drop down. Bounce the thrust every once in a while to keep your speed in control.

[GoSlash27]

1 hour ago, steuben said:

After the first one falls over, the second will explode and fall over, the third will stay upright. And that's what you'll have, my boy, the stablest lander in all the lands.

*Golf clap*...

-Slashy

[MPDerksen]

Pretty sure it burned down, fell over and THEN sank into the swamp.  However, the 4th one did NOT stay up, so other than, "get better at it", what is a recommended m/s as I'm coming in?  I'm using my shadow to estimate the ground, since I seem to be landing around 3K, and don't see any other gauge of how far off the ground I really am.

[klesh]

1.  Unless you have a specific target you're shooting for at the Mun which your mildly inclined Kerbin orbit prevents you getting to, I would consider it a waste.  If you're able to plot a course that still intercepts the Mun without leveling your inclination, then there's really no need.

2. The additional lines you're seeing are your trajectory being plotted after you leave the encounter with the Mun.  The initial burn to the Mun is most usually going to be a flyby (unless you plan to crash into it directly) so the game is calculating what will happen when you leave Mun sphere of influence.  I believe dotted-purple is the next one, and orange is probably after another SOI change.

Having no idea what to change and just pulling at the maneuver node to see what happens is essential to learning the game.  Pay attention.  Pull in different directions until you start to see the movement you want. Right click a PE or AP to have it display its numbers while you fiddle.  Look for the changes you want to see.

3.  You get extra options like those prograde  depending on the type of probe core, and or your experience level of your pilot.  What to do in this situation depends alot on the engine you have, your fuel ammounts etc.  I like to come across the surface low, kill my lateral velocity, and float slowly down to the surface.   Were I you, I would wait till 5k alt maybe, and start killing the sideways velocity.  Mun will pull you down towards it, and you now only have to manage that downward acceleration. Its not the most efficient, but it minimizes what you have to pay attention to at any given time.

[klesh]

33 minutes ago, MPDerksen said:

Pretty sure it burned down, fell over and THEN sank into the swamp.  However, the 4th one did NOT stay up, so other than, "get better at it", what is a recommended m/s as I'm coming in?  I'm using my shadow to estimate the ground, since I seem to be landing around 3K, and don't see any other gauge of how far off the ground I really am.

 

Yes, you want to use the shadow to gauge your distance to the ground.  Inside the capsule there is a radar altimeter, which will tell you your actual distance above the ground, but its kinda useless if you cant see it from outside IVA.

For final touchdown, I like to be going less than 5m/sec.  I do not maintain that 5m/sec though, throughout the entire fall from 5k as detailed above.  It would be a supreme waste of fuel fighting gravity the entire time.  I try to keep it manageable based on my engine thrust and TWR, perhaps in the 35 m/sec range until I am quite close, a hundred meters maybe, then I slow the whole operation down for final descent.

Edited March 26, 2018 by klesh

[MPDerksen]

10 minutes ago, klesh said:

 

Yes, you want to use the shadow to gauge your distance to the ground.  Inside the capsule there is a radar altimeter, which will tell you your actual distance above the ground, but its kinda useless if you cant see it from outside IVA.

For final touchdown, I like to be going less than 5m/sec.  I do not maintain that 5m/sec though, throughout the entire fall from 5k as detailed above.  It would be a supreme waste of fuel fighting gravity the entire time.  I try to keep it manageable based on my engine thrust and TWR, perhaps in the 35 m/sec range until I am quite close, a hundred meters maybe, then I slow the whole operation down for final descent.

Closer.  I'm upright, but popped the engine (so no way to get home).  Seems "practice" is in order.

Second try sank into the swamp, but the third one landed soft and stable.  Thanks all.

[klesh]

Nice work, homie.  Congrats.  

[MPDerksen]

Right.  So I'll get a bit more practice.  Seems I forgot the heat shield.....

 

[Snark]

4 hours ago, MPDerksen said:

When I first launch and get into Kerbin orbit, I typically end up having to do a Normal/Anti-Normal burn, since my inclination relative to Mun is around 5 degrees.  Not a big deal, but is this step a fuel waster?

Yes, it certainly is a fuel-waster.  My question, though, is... why do you have a 5-degree inclination relative to the Mun?  The Mun is in a perfectly equatorial orbit, and KSC is right smack dab on Kerbin's equator.  If you launch eastward from KSC, you ought to be ending up in an equatorial orbit to start with.  How do you end up inclined?

Correcting 5 degrees of inclination in LKO is nearly a couple of hundred m/s, which is significant.

4 hours ago, MPDerksen said:

When I fly with a Pilot I get some additional SAS buttons, like "Prograde".  I thought using a probe core was my "pilot replacement unit"..... lol

Different probes have different levels of pilot skill.  The OKTO just has "hold orientation".  The HECS adds hold and .  The OKTO2 gives you the ability to hold , and the 1.25m and 2.5m probe cores add .  Generally, the only ones you really want are , so focus on getting the HECS as soon as you can.

Until that happens, though... just use good ol' keyboard presses to hold your craft as close to as you can while landing.  Just takes practice.

4 hours ago, MPDerksen said:

On this play, I was at 600m/s at 70K above the surface.  I slowed to 250m/s at 20K and did a quicksave.

For maximum dV efficiency (i.e. landing with the least amount of dV required), you want to take maximum advantage of Oberth effect.  You can read all about it on the wiki link, but the executive summary is that you want to do as much of your burn as possible at the minimum altitude possible.

In practical terms, what this means is that when you're doing your ejection burn from LKO, aim to get the lowest Mun periapsis you can-- say, somewhere in the 10-15 km range (low enough to get good Oberth benefit, high enough that you won't accidentally smack into any inconvenient mountain ranges).  Then, to capture to the Mun, set a maneuver node right at your (very low) Pe to capture into a low circular orbit.

Once you're in a very low circular Mun orbit, it's time to land on the surface.  The most efficient technique is something aptly named a "suicide burn".  The idea is, you do a small braking burn in orbit, just enough to lower your Pe into the terrain so you're on a suborbital trajectory.  Then, wait until the last possible instant before slamming on the retro-thrust at 100%, such that you brake to a halt perfectly at the moment you reach the surface.

Easy, right?    (not)

The reason it's called a "suicide burn" is because of the difficulty of judging that "last possible instant".  Leave it even a little too long before you start braking, and you faceplant.  Start the burn too early, and you waste fuel because you end up hovering while still high above the surface.

So, given how tricky it is, how to do it?

Well, first of all, bear in mind that you don't have to be perfect.  I'm simply describing what "perfect" looks like so at least you have a general idea of what you're aiming for, so when you end up burning a lot of fuel or a little, it's easier to understand why, which tends to make practice more effective.

There are mods that can help with suicide burns, but there's also a handy technique you can use with maneuver nodes that doesn't require any mod at all.  It goes like this.  Let's say you're already in low Mun orbit, and you've already done your braking burn so you're on a suborbital trajectory.  Here's what you do:

1. Go to map view and zoom all the way in.
2. Place a maneuver node right exactly at the place where your projected trajectory hits the surface.
3. Drag the node's handle, until your projected trajectory shrinks to a point right at the node's location.

There you go.  Now, the "time until node" display on the navball tells you how long until you hit the surface.  And the "estimated burn time" tells you how long you need to burn to reduce your speed to zero at the surface.  So, you just wait until the "time until node" is about 60-70% of the estimated burn time, then burn at max throttle while holding as close to as you can.  Example:  after you do the fiddling with the maneuver node, you see that your estimated burn time is 10 seconds.  So, you wait until you're about 6-7 seconds from impact and then hit the gas.

Highly recommended to do a quicksave before you begin your descent, as you may need a bit of practice. 

 

Assuming you survive the landing, the next thing you'll need is an efficient way to go home.  An efficient trip home from the Mun consists of the following:

• Go from surface to very low Mun orbit
• From Mun orbit, do a burn to go home to Kerbin

Getting to low Mun orbit efficiently is simple.  Immediately upon takeoff, crank it over until you're accelerating nearly horizontally, right from the surface.  You want to be only slightly above horizontal-- just enough that you won't smack into any mountains while you're accelerating.  Having cranked it over so you're just a few degrees above horizontal, just burn until you see your Ap get up to an altitude of, say 12 km or so.  Coast to Ap, then circularize.  Now you're ready to go home.

Heading home is just a single burn in your low orbit, placed appropriately.  A bit of fiddling with maneuver nodes will find the right placement.  You want to eject from the Mun going exactly opposite the direction of the Mun's orbit around Kerbin.

 

4 hours ago, MPDerksen said:

half the time, I end up bouncing, but landing on my side (no, I can't launch that way, tried it....), or landing hard enough that I blow up the engine, and THEN fall onto my side.

Yep, common problems with landers.  Some suggestions:

• Blowing up when landing:  keep your surface-relative speed under 7 m/s when landing.
• Tipping over when landing:  make the lander as low and squat as possible.  If you've unlocked the "Baguette" fuel tanks, for example, you could put some of them around your central core and mount the legs to them to give your lander as wide a stance as possible.  When you're building your lander in the VAB, turn on the CoM display and look at where the CoM is, relative to how far apart the legs are planted.
• Bouncing:  In the VAB, you can tune the springs in the landing legs.  You can set the spring strength and the damper strength.  To avoid bouncing, tune the damper strength way up (specifically, set it higher than the springs).

 

[invision]

heres a super easy no thinking about it way to go to the Mun

from the start pitch slightly east (thats the 90 degree marker on nav ball) towards the ocean.

once the atmosphere arrow is in the dark blue area pitch 45 degrees on the navball

continue to fly at 45 degree's and press M for map. when our AP reaches 60km we pitch to 30 degree's

when our AP is just under 70k pitch 90 degree's and bring AP to 75k-80k

we time warp to about 15 seconds to top of AP and burn for orbit

now we time warp and let the mun pop out from behind kerblin and click prograde on navball and burn engines. go to map and target Mun.

we burn engine until intercept and click the mun and choose "focus view" to see exactly where our orbit is

now i very gently low thrust in prograde until the PE is where i want it.  DO NOT GO LOWER THAN 10K 

when close to PE choose "retro grade" on navball and slow down until orbit is reached

......................................................................

 

and thats all there is to it. now you just have to land. hope this helps.

Edited March 26, 2018 by invision

[wolfschwarzmond]

I've been playing KSP for long time, some things I've learned.
1 When you build your rocket, you'll forget something, put something in the wrong place, or generally foul it all up. Revert is your friend when you 1st start. Build your planned rocket and if you have revert Launch it and TEST IT without going anywhere other then orbit.

2 The only way to learn to land on airless moons/planets is to learn how not to crash, practice.

3 The fact that you fouled up and stranded a Kerbal somewhere is not the end. Its a new mission!!! We have to bring him home!! Less its Eve, then he's screwed. Least he can plant flags for Money.

4 Explosions...are very cool.

5 I can't fly a Space Plane worth anything. Which is odd, given how much I love flight sims.

6 Thank you to all Modders. 

7 Its a game, if you're not having fun, find something else to do.

8 Its rocket science, its not supposed to be easy. 

 

[pandaman]

Another simple tip...

Place a spotlight or two on your lander pointing down at the ground.  Even in daylight they illuminate the ground when within about 500m (and in the dark they are a life saver).  That makes it much easier to judge your altitude visually.

[RizzoTheRat]

11 hours ago, steuben said:

After the first one falls over, the second will explode and fall over, the third will stay upright. And that's what you'll have, my boy, the stablest lander in all the lands.

This is so true

 

Spotlights and shadows are a good way to help judge it by eye, but if you're interested in mods at all the Kerbal Engineer Redux (KER) mod not only helps massively when designing your craft by showing you the TWR and dV in the VAB, but it also has a HUD which can show you the radar altitude (from the centre of mass I believe so it's usually a few meters out) at the top of the screen which is a massive help.

For the actually landing, if you reduce the speed from orbital height you'll fall down and have a lot of vertical speed to kill in order to land safely.  If you think how you'd take off from an airless moon, you'd thrust vertically upwards for a very short time and then burn sideways as hard as you can.  For landing you want to do the opposite, set as low a PE as you dare somewhere near your target area and aim to stop your horizontal speed at as low an altitude as you can, without building up too much vertical speed.  Usually the vertical component is so small that burning prograde is within a few degrees of horizontal for most of the burn.  Then it's just a simple job of controlling your descent speed to make sure you hit at speed slow enough for your landing gear to cope with.  If you don't have a core capable of locking to prograde you'll need to watch your horizontal speed though as that could cause you to topple over on landing.   Again KERs HUD can show you the horizontal and vertical components of velocity which is very useful.

Also don't forget when designing your ship that landing legs are intended to compress, so make sure there's enough clearance under the engine. 

 

[MPDerksen]

All very helpful and makes a lot of sense.  

I don’t know why, but my ship, at launch, tends to roll slightly North each time.  I know about, and try to, launch due East and follow the steps above.  I’m using a fairly standard rocket with 3 sets of 2 boosters and asparagus staging.  I just dump 2 at a time as I go up, but the roll is happening before I let go of the first set.  I have 6 wings at the bottom to keep it straight.  Does a picture help?  Anyway, that’s why I have AN and DN once I get into orbit.

I’m really glad Invision posted those pics.  Referencing the one with the target orbits at Mun:  I see the DN, which I am very familiar with  and the blue Ap, which I get is my current Apoapsis around Kerbin.  Then I see a Purple Ap, and the Brown Pe.  All very cluttered in my head.  Taking the advice above, I believe the one I care about is the Brown Pe (assuming that’s my Mun Periapsis post maneuver).  Often, mine ends up 0.5-1.0M miles from Mun, and then I spend a tremendous amount of fuel to make that my Mun Ap, and bring around a Mun Pe.  I need to get much closer, but get lost HOW to get it closer.  I understand the Prograde and Retrograde, and how they effect my orbit.  I also understand Normal and Anti-Normal, I think.  The “light blue ones” are basically my swing to the left and right, yes?  

Last, as posted by Wolf, #3 above, I DID leave a Kerbal stranded.  I ran out of fuel orbiting Mun, tumbling terribly.  When I realized I had launched my Engineer instead of my Scientist, I moved on, thinking it would be a fun rescue mission later.  

I think I primarily need 2 things.  1.  Slow down, and make sure my craft and crew are right for the mission.  2.  Practice and enjoy it

[wumpus]

13 hours ago, Snark said:

Yes, it certainly is a fuel-waster.  My question, though, is... why do you have a 5-degree inclination relative to the Mun?  The Mun is in a perfectly equatorial orbit, and KSC is right smack dab on Kerbin's equator.  If you launch eastward from KSC, you ought to be ending up in an equatorial orbit to start with.  How do you end up inclined?

Correcting 5 degrees of inclination in LKO is nearly a couple of hundred m/s, which is significant.

Is this ideal for correcting inclination?  My understanding is that GSO satellites burn *past* GTO, then change inclination, and finally circularize into GSO.

I'd consider doing a 400 m/s burn (while lining up a munshot), fixing inclination at perikee, and then setting up a maneuver node to Mun (actually I nearly always fix it in LKO orbit.  I'm lazy that way, but if I knew that I was low on delta-v there are options).  Doing it this way is also more efficient with low powered engines (low TWR that take require a burn that takes a larger angle away from Pe).

[Snark]

1 hour ago, wumpus said:

Is this ideal for correcting inclination?

No, it isn't.  LKO is, in fact, the worst possible place to make a plane change, in terms of dV.  But for a new player who may not be fully expert in navigation, it's simpler to navigate that way, which I assume is why @MPDerksen was doing it.

But that misses the point of my advice, which was this:  there's no reason to be doing any plane change at all.  The cheapest inclination change is "none".    Just launch to an equatorial orbit from the get-go.

[Johnny Wishbone]

For what its worth, all the landing legs have an impact tolerance of 12m/s except the micro ones, which have a tolerance of only 10m/s. So you need to be going slower than that when you hit the surface to avoid breaking/blowing up your legs. 

https://wiki.kerbalspaceprogram.com/wiki/Landing_leg

 

[CrashyMcCrashFace]

As a beginner (take note I said beginner) SAS retrograde has really been my friend for Mun landings. I've had pretty good luck. I get into a decent orbit between 15K and 20K just so I have time to think and can pick a landing spot. I don't care about where Ap or Pe are when I start decent as long as they're close to the same height. I won't give you my speeds because I'm afraid I might be misleading you with my ignorance. But retrograde the whole time until you're very close to vertical and then optionally switch to heading hold.

Also as somebody that crashed a lot. If using the single person capsule you can use the next diameter up fuel tank and attach legs to that. The 800 (at work and can't check) I think. Also 4 legs not 3. Yes it will be ugly but both will help you not fall over in less than perfect landings.

Edited March 26, 2018 by CrashyMcCrashFace
Poor grammar

[Pthigrivi]

2 hours ago, MPDerksen said:

Often, mine ends up 0.5-1.0M miles from Mun, and then I spend a tremendous amount of fuel to make that my Mun Ap, and bring around a Mun Pe.  I need to get much closer, but get lost HOW to get it closer. 

Yeah you're much too high on your initial Mun Pe (snark is right that 10-15k is best). Any burn toward the Mun should really just be a prograde burn--no radial and no normal. So if you're having trouble getting a closer approach all you have to worry about are how long you're burning and when you're starting your burn. You should be able to drag the prograde marker out far enough to encounter the Mun and then swivel the node around your orbit until you get a nice close approach. Make sure though that you're entering Munar orbit prograde to its rotation. If you're looking down on the Mun the 'brown' encounter arc should be passing counterclockwise around it.  

If you're finding that you have any inclination on approach its probably because you're ever so slightly inclined from your initial ascent to orbit and that angle is getting magnified by the distance to the Mun. Don't worry about that when you make your transfer burn toward the Mun. Instead, you can usually fix it with a very small correction burn halfway between Kerbin and the Mun. After the brown encounter arc there will be a bigger purple ellipse. If you pan back and look side on you should be able to tweak the correction maneuver normal or anti-normal until this purple arc is perfectly level with the Mun's orbit. If you need to you can also create another small correction burn prograde or retrograde to adjust your Mun Pe just where you want it.

[MPDerksen]

starting to all make sense.  I concur that a perfectly aligned launch (no inclination) is the goal, but I still struggle with staying true East.  

I also think I'm making sense of all that data I see on the screen, from Blue to Brown.  But what is the Purple arcs I see?

Last, if I post a picture of the rocket I'm using, does that provide more information than if I just list out the components?  I like my design, which I stole, then tweaked.  For a lander, i have an LV-909 terrier under a Rockomax X-200-8 fuel tank, with SIX LT-1 landing legs.  Spring and Damper strength were both set to "1", but I've raised the Damper to 1.5 and lowered the Spring to .75.  On that I have the service bay for my OKTO and science equipment.  Then a Science Jr, Decoupler, Heat Shield (for once...) and the MK1.  I have solar panels and batteries, 3 each, around the fuel tank.  Maybe that's over kill and I should move just 1-2 batteries inside the service bay to reduce the drag on liftoff?

SO much to learn, but yes, this is still VERY fun.

[Waxing_Kibbous]

Just to add to the tip concerning creating an adjustment maneuver node halfway to the Mun: these will generally be very short burn times, I find it helps to adjust the thrust limiter on the engine  to about 10% before the burn. Just remember to set it back to 100% afterwards!

[invision]

if anyone wants to learn how to land ill be playing for a bit and you can see how to go about it

 

Edited March 27, 2018 by invision

[Snark]

1 hour ago, MPDerksen said:

Last, if I post a picture of the rocket I'm using, does that provide more information than if I just list out the components?

Absolutely.  Picture worth a thousand words, and all that.  Very often it's the case that simply posting a picture of a craft will let folks instantly spot all kinds of potential problems, suggested tweaks, what-have you.  It's immensely useful.

Posting inline pictures is easy.  Post your pic to some third-party image hosting site such as imgur.com, then copy the image URL (i.e. right-click on it and choose "copy image location"), then paste that URL here and it'll get automagically converted into an inline image.

1 hour ago, MPDerksen said:

I concur that a perfectly aligned launch (no inclination) is the goal, but I still struggle with staying true East.

It may be that there's some asymmetry or floppiness to your rocket design that makes it bend to one side.  Hard to say without seeing a picture.  Ideally, it shouldn't "pull" to either side.

In any case, unless a rocket design is seriously borked, then a slight tendency to go north or south can be corrected without too much trouble.  Just keep an eye on the navball and make sure that your marker is perfectly dead-on the "90" line, i.e. due east.  If it's skewed a little bit left of 90 (north), briefly steer a bit right to correct.  If it's skewed a little bit right of 90 (south), briefly steer a bit left to correct.

[MPDerksen]

Okay, let's give this a go then.  I don't believe I used "Toggle Snap" to a hexagon so my six boosters might not be aligned perfectly.  I figured that doing them as sets of 2 was sufficient.  Feedback most welcome.