Landing on the Mun

[Monkey Taylor]

I can get to the Mun, I can even land on it, but, I never have enough fuel to return. Can anyone help. Oh, and maybe if someone can tell me at what height to do suicide burns.

          

 

Thanks

Edited December 9, 2016 by Monkey Taylor

[bewing]

Are you in career mode, or sandbox mode? To land on the Mun and return to Kerbin without refueling takes a lot of deltaV. Are you choosing your engines to be extremely efficient? Are you willing to refuel either at the Mun, or in Kerbin orbit? There are many possible problems you could be facing here, and many possible solutions -- but we are going to need more details: a craft file, and readouts of the amount of fuel you have in LKO, in LMO, and landed at the Mun.

[WanderingKid]

1 hour ago, Monkey Taylor said:

I can get to the Mun, I can even land on it, but, I never have enough fuel to return. Can anyone help. Oh, and maybe if someone can tell me at what height to do suicide burns.

 

Thanks

Welcome to KSP.  

Suicide Burns are not done by eyeball, you die.  You want KER or some other mod that will let you know when to start them.  The problem is that there are a few dozen variables involved to know when to start them so there is no default height.  There are, however, default techniques you can use.

What follows is a conservative method:

First, and foremost, landing is easiest near the dawn/dusk line.  What this does is let you find your shadow when you're coming down.  Get yourself low to the Mun for your braking burn.  Gravity doesn't take over quickly.  I typically get my periapsis around 5,800 over my target LZ.  Watch out for East Farside, that's a high rim, go 6,500 there, and the poles are evil, 8,500 or bust.  From there I setup a maneuver node for 550 d/v retrograde and aim myself for the target.  You CAN eyeball it without maneuver nodes, but it takes a lot of practice.

Once you've negated your horizontal speed (the Retrograde marker is at the top of the blue of the navball) you'll be landing wherever you are.  Until you see your shadow, keep yourself at/under 100 m/s.  Once you see your shadow you can get a better idea of your inbound speed, but at this point you want to get under 50 m/s.  From here, you have to judge the TWR on your ship.  It might take a few tries, but I generally let my shadow get 'halfway' to me, and gradually drop to 10 m/s as I approach, then once the shadow is 'close' I'll drop under 5 m/s for the landing.

If you use IVA (Internal View) there's a radar altimeter in the ship, which you can't see from outside.  It'll tell you your height from ground, not sea level, which can help as well.

Now, getting home, that's a different issue.  Do you know how to calculate Delta V (if you're not using a mod for it)?  If you don't, you should probably grab a calculator and learn, else it's just guess work and experimentation, which can get frustrating.

You want ~6,500 vacuum d/v from Launchpad to land on and return from the Mun.  That's 3,500 to orbit (if you're aerodynamic), 860 for the Mun injection burn, ~300 orbital insertion, 550 braking burn, ~100-150 d/v for landing, another 550 to re-orbit, and ~280 to get home.  The rest is for corrections and over-burns and landing miscalculations.

So, to help you with returning, we'd need to see what you're sending up.

[Streetwind]

2 hours ago, Monkey Taylor said:

I can get to the Mun, I can even land on it, but, I never have enough fuel to return. Can anyone help. Oh, and maybe if someone can tell me at what height to do suicide burns.

 

Thanks

- Assume a 10 km circular orbit around the Mun.
- Land on the Mun.
- Take off into the same circular 10km orbit again.
- Perform an ejection burn retrograde to the Mun's orbit.

If you follow those steps, then your problem can be reduced to simply "build a spacecraft that has enough dV to pull it off". And that, in turn, simply means that you have to bring more fuel and less everything else. You might want to learn about mass fractions at this point.

[Magzimum]

Sounds like you need to install KER (that's a mod that gives you a lot of data, including the dV of a ship, but won't do anything else). After that, follow @Streetwind's advice in the post right above this one.

KER should be stock.

[tab]

Just add a Little tank of fuel in your last stage

Edited December 9, 2016 by tab

[Firemetal]

50 minutes ago, tab said:

Just add a Little tank of fuel in your last stage

Yes! Moar fuel! 

Could we have a picture of the lander? Would be much easier to help then.

Fire

 Edit: as an alternative to KER, you can calculate DV using this equation.

gravity * ISP(Find this in an engines description) * ln(mass with full fuel/dry mass) Keep in mind to drain only that stage's fuel rather than the whole rocket when just calculating one stage's DV. However, as a beginner, KER is an easier choice. 

Edited December 9, 2016 by Firemetal

[Aegolius13]

For suicide burns, the mod BetterBurnTime also has a nifty little indicator that shows how long you'd need to burn to stop, versus how long until you hit the ground.  Very simple and intuitive.  But it does not account for changes in the terrain, so you generally want to leave a margin if you're in a hilly area.  

[Kerbinchaser]

I struggled with this early too. I recommend you use rockomax parts.

[Snark]

Just to add to the chorus... if you'd like something much lighter-weight than KER (and without a potentially bewildering array of UI options), you may also find BetterBurnTime helpful:

...it's got basically no UI, but one of the things it does for you is this:  when you're on a collision course with the ground on a vacuum world, it displays a "seconds until impact" display next to the navball (in the same place that the navball usually displays "time until maneuver node"), and also a burn-time-to-come-to-a-halt-at-ground-level (in the same place that the navball usually displays "estimated burn time" for a maneuver node).  Simple and intuitive.  So all you need to do for a suicide burn is to set your SAS to "hold surface retrograde", wait until the time-until-impact is around 60-70% of the estimated burn time, then burn.

 

[tab]

Oh c'mon, don't use mod for a simple thing like this. I'm the One here Who plays stocked?

[WanderingKid]

1 hour ago, Lo Var Lachland said:

I struggled with this early too. I recommend you use rockomax parts.

What the heck does Rockomax have anything to do with suicide burn times or returning from the Mun?  Other than over-engineering the craft, that is.

12 hours ago, Monkey Taylor said:

Thanks

Some clarifications for your photos.

Mk1: Those are TT70's you used to connect up the outer engines with the T-30s, and a T-45 in the middle, right?  Additionally, that's a Terrier sitting on the last FL-T400 under the pod, correct?

Staged correctly, and with some additional strutting for the outer engines, that craft comes in with 6,726 delta V.  More than enough for a Mun landing and return.

Mk2: This is a curious design, and not one I'd use in general.  Chasing a Terrier with another pair of Terriers can be useful, but not in this setup.  Try looking at the Spark for your lander engine, it's got more than enough TWR for Mun/Minmus use if you're not landing anything massive.

the MK2 comes in at 6,167 d/v on the pad, nowhere near enough for returning from Mun as it stands.  Swapping the upper Terrier to a Spark brings you in at 6,462, which is close but you'd need to be perfect.  Where you finish getting the d/v is... the landing gear.  Pushing the Spark with the offset nearly inside the FL-T400 gives you a flat base to land the craft on the gas tank.  This (along with stripping off the ladders you don't need) gets you up to 6,690 d/v.  More than enough for a Mun visit and return.

When trying to improve delta V, the more you strip off the payload (in this case, your lander) the more everything else works more efficiently.  By removing .4 tons of engine (Spark for the Terrier), 0.15 tons of landing gear, and 0.02 from the ladders (this is kind of moot, I know), everything under it improves significantly.

[Ozymandias_the_Goat]

11 hours ago, WanderingKid said:

Suicide Burns are not done by eyeball, you die.

I agree. You can survive by eyeballing it, but you will use more fuel. KER can help, but it really shines when landing something with a low TWR. The LV-909 you are using as your landing engine has a high TWR. I think you can easily eyeball it without losing too much fuel.

About your craft, I don't think you need that heat shield. They are quite heavy, and a  mk. 1 capsule can survive a reentry without one. That could help shed a lot of weight. The other piece of advice i have is quite timeless; that being "moar" boosters!

[DD_bwest]

propulsion systems can make mun landings alot easier. you can make a smaller lander, which opens the possibility of using a stage meant for getting there, orbitting and cancelling out most of your speed at a very low altitude, then release the lander for a simple landing.  youd be surprised how much delta v you can get from some oscars and sparks.  

say on your lander, replace the tank with a materials bay, surface attach 3or 4 stacks of oscar Bs tanks 3 tall around it and put some sparks on it.   then make a stage with the terrier, it can be longer now since you arent landing it, use a delta V calc, or calculate it yourself to plan 1500-1700 deltaV.  then all you need to do is get that into orbit.

no mods required

[IncongruousGoat]

1 hour ago, WanderingKid said:

the MK2 comes in at 6,167 d/v on the pad, nowhere near enough for returning from Mun as it stands.  Swapping the upper Terrier to a Spark brings you in at 6,462, which is close but you'd need to be perfect.  Where you finish getting the d/v is... the landing gear.  Pushing the Spark with the offset nearly inside the FL-T400 gives you a flat base to land the craft on the gas tank.  This (along with stripping off the ladders you don't need) gets you up to 6,690 d/v.  More than enough for a Mun visit and return.

That's odd. I calculated the dV for the Mk. 2 and got 6,532 on the launchpad, even accounting for atmospheric efficiency loss. I even went as far as to build it and test it, and was able to successfully complete the mission, albeit with a fuel margin of around 6 units LF. The real problem with the Mk2 is the first stage. I had to change the fin arrangement to make it flyable in the first place, and even then loss of control authority in the upper atmosphere led to a steep, inefficient, and unpleasant launch.

[WanderingKid]

13 minutes ago, IncongruousGoat said:

That's odd. I calculated the dV for the Mk. 2 and got 6,532 on the launchpad, even accounting for atmospheric efficiency loss. I even went as far as to build it and test it, and was able to successfully complete the mission, albeit with a fuel margin of around 6 units LF. The real problem with the Mk2 is the first stage. I had to change the fin arrangement to make it flyable in the first place, and even then loss of control authority in the upper atmosphere led to a steep, inefficient, and unpleasant launch.

Okay, I was being lazy here, using KER.  The only way I can come close to those numbers is swapping the upper Terrier for a Spark.  I also added two struts for sanity.

The lander: 4.225t

• MK 1 pod, Mk 16 cute, Heat shield, Tr-18A, FL-T400, 4 ladders, 3 solar panels, 3 landing legs, 1 Terrier
• D/V: 2,170 ( ln(4.225/2.225) * 345 *9.81 )

Circularlization Stage: 9.925t

• TR-18A, TVR-200 Bi, 2xFL-T400, 2xTerrier
• D/V: 1,745 ( ln( 9.925 / 5.925) * 345 * 9.81)

Lifter Stage: 31.525t

• 2xTR-18A, 4xFL-T800, 2xT30, 4xAV-R8
• D/V: 2,204 ( ln( 31.025 / 15.025) * 310 * 9.81 )

Total: 6,119 d/v with no changes

KER and I disagree by a single point of D/V on the Lifter Stage, I get 2,205.  What's different between how I built what was presented and what you came up with?  I'd forgotten to put the AV-R8's on earlier which accounts for the 50 d/v difference from my earlier numbers.

[Waxing_Kibbous]

You could cut some weight by using only 3 of the smallest landing legs and ditching the ladders. I generally don't mess with Mun landings until I get at least fuel lines unlocked, and they get really easy once you get the 2.5m Poodle and Skipper unlocked. My advice: take this rocket to Minmus first and science the heck out of it, then get some beastier parts.

[IncongruousGoat]

2 minutes ago, WanderingKid said:

Okay, I was being lazy here, using KER.  The only way I can come close to those numbers is swapping the upper Terrier for a Spark.  I also added two struts for sanity.

The lander: 4.225t

• MK 1 pod, Mk 16 cute, Heat shield, Tr-18A, FL-T400, 4 ladders, 3 solar panels, 3 landing legs, 1 Terrier
• D/V: 2,170 ( ln(4.225/2.225) * 345 *9.81 )

Circularlization Stage: 9.925t

• TR-18A, TVR-200 Bi, 2xFL-T400, 2xTerrier
• D/V: 1,745 ( ln( 9.925 / 5.925) * 345 * 9.81)

Lifter Stage: 31.525t

• 2xTR-18A, 4xFL-T800, 2xT30, 4xAV-R8
• D/V: 2,204 ( ln( 31.025 / 15.025) * 310 * 9.81 )

Total: 6,119 d/v with no changes

KER and I disagree by a single point of D/V on the Lifter Stage, I get 2,205.  What's different between how I built what was presented and what you came up with?  I'd forgotten to put the AV-R8's on earlier which accounts for the 50 d/v difference from my earlier numbers.

Ah, now I see the problem. That's a bicoupler there, not a tricoupler. Whoops. This is what I get for rushing things. Yeah, in its current configuration the Mk. 2 should not have enough dV.

Edited December 9, 2016 by IncongruousGoat

[WanderingKid]

10 minutes ago, IncongruousGoat said:

Ah, now I see the problem. That's a bicoupler there, not a tricoupler. Whoops.Yeah, in its current configuration the Mk. 2 should not have enough dV.

I feel you, considering the Mk1.  The only way I was sure was because I could see bits of the wall in between the two tanks.  A tri-coupler would have blocked that out.

10 minutes ago, Waxing_Kibbous said:

You could cut some weight by using only 3 of the smallest landing legs and ditching the ladders. I generally don't mess with Mun landings until I get at least fuel lines unlocked, and they get really easy once you get the 2.5m Poodle and Skipper unlocked. My advice: take this rocket to Minmus first and science the heck out of it, then get some beastier parts.

While I disagree with wanting Rockomax parts for... well... anything inside Kerbin SOI besides lifting massive space stations up, Smaller landing legs and ladders are definitely preferable.  An example of one of my typical early landers for Mun (33 parts (strip off the landing legs to get to 30), 32.008 tons), in case the OP wants an alternate approach:

Edited December 9, 2016 by WanderingKid

[Snark]

10 minutes ago, Waxing_Kibbous said:

You could cut some weight by using only 3 of the smallest landing legs and ditching the ladders. I generally don't mess with Mun landings until I get at least fuel lines unlocked, and they get really easy once you get the 2.5m Poodle and Skipper unlocked. My advice: take this rocket to Minmus first and science the heck out of it, then get some beastier parts.

Definitely +1 for the smaller landing legs and no ladders.  Extra parts add drag; the tiny landing legs are plenty; and ladders really aren't needed on the Mun, ever, given how easy it is for kerbals to fly around with EVA thrusters in munar gravity.

I'm a fan of using fuel ducts for my first manned Mun landing.  Usually I'll send a single unmanned lander first, because compared with the science you get from Kerbin, even a single set of science results from the Mun can be a huge boost to early career.  Easily enough to get the fuel ducts. 

Nice choice of Mk1 pod + 2-ton LFO + Terrier for your lander stage-- that's an excellent combo in KSP, I use it all the time, for practically everything.  Available at low tech, cheap, light, has scads of dV.

Here's an example munar lander from early career that I used recently-- note the fuel ducts.

Spoiler

This lands and returns fairly handily, with a reasonable amount of dV safety margin.  Like your design, my top stage is Mk1 + 2-ton LFO + Terrier (though I've got a Science Jr in there).  Also like yours, the stage below that has 4 tons LFO (though I do it with one Swivel rather than two Terriers).  After that is where it gets different-- you have 24 tons of LFO, I've got 8 tons LFO in asparagus drop-tanks, backed up by ~30 tons of SRBs.

I'm not holding this up as any particular sort of "ideal" design-- there are a lot of ways to put together a low-tech Mun mission.  This just happens to be one that works reasonably well.  The SRBs give it a nice, solid, high-TWR boost off the pad.  By the time they burn out, it's already tipped over past 45 degrees and doesn't need much TWR, so the Swivel plus two Terriers provide sufficient TWR, and it doesn't need to spend much mass on engines.  (The SRBs burn out above 10km, so the Terriers do just fine-- they're practically in vacuum by that point.)  

[Kerbinchaser]

6 hours ago, WanderingKid said:

What the heck does Rockomax have anything to do with suicide burn times or returning from the Mun?  Other than over-engineering the craft, that is.

Some clarifications for your photos.

Mk1: Those are TT70's you used to connect up the outer engines with the T-30s, and a T-45 in the middle, right?  Additionally, that's a Terrier sitting on the last FL-T400 under the pod, correct?

Staged correctly, and with some additional strutting for the outer engines, that craft comes in with 6,726 delta V.  More than enough for a Mun landing and return.

Mk2: This is a curious design, and not one I'd use in general.  Chasing a Terrier with another pair of Terriers can be useful, but not in this setup.  Try looking at the Spark for your lander engine, it's got more than enough TWR for Mun/Minmus use if you're not landing anything massive.

the MK2 comes in at 6,167 d/v on the pad, nowhere near enough for returning from Mun as it stands.  Swapping the upper Terrier to a Spark brings you in at 6,462, which is close but you'd need to be perfect.  Where you finish getting the d/v is... the landing gear.  Pushing the Spark with the offset nearly inside the FL-T400 gives you a flat base to land the craft on the gas tank.  This (along with stripping off the ladders you don't need) gets you up to 6,690 d/v.  More than enough for a Mun visit and return.

When trying to improve delta V, the more you strip off the payload (in this case, your lander) the more everything else works more efficiently.  By removing .4 tons of engine (Spark for the Terrier), 0.15 tons of landing gear, and 0.02 from the ladders (this is kind of moot, I know), everything under it improves significantly.

He said he was never able to return because of fuel shortage.

Rockomax gives you a lot more fuel.

 

[Reactordrone]

The mk1 and 2 are both capable of landing on the Mun and returning (the Mk2 only just). I'd agree with ditching the ladders, they're not much use on the Mun and I'd also reduce the ablator on the heatshield by at least 50% and drain all of the monoprop to save weight.

If you're flying it right that mk1's core booster should take you all the way from LV-T30 booster burnout to Mun suborbit. A full tank on the lander should give you way more delta-v than you need from that point.

[Monkey Taylor]

Thanks!  I'll try doing this, Mk1: add struts 50% drain MP, Use less ladders, Reduce 25% ablator. If this doesn't work I'll change landing legs.

Mk2 is probably useless, that will be on my 6^th attempt.

[mystik]

Why don't you go with a lander with 3 or 4 legs (each with 2 large fuel tanks that you use now) with 909 engines at the end? Sure, this is expensive, but it helps with stability and allows for shorter burns and prevents you smashing into the ground. Look for the shadow when landing. My first Mun mission lander had lots of fuel and was made with 9 tanks and 3 engines. Found Minmus easier to land on and take off multiple times on the same mission. The Mun is hard to land but easy to get to.

Edited December 10, 2016 by mystik

[NSEP]

I suggest adding an extra stage on top of the lander for extra Delta-V.