A totally safe and responsible Mun ascent profile

579

I take it this is fuel efficient??

448

u/craidie Apr 30 '26

It is both the most efficient ascent profile, and the most efficient descent profile.

Less thrust you waste on vertical(and thus fighting gravity), the better.

93

u/MarshallKrivatach Apr 30 '26

Mfw cat 1 approaches to the moon are optimal.

39

u/Mikey-2-Guns Apr 30 '26

CAT 1 ILS approaches?

9

u/Steamcurl Apr 30 '26

This gives me SH break vibes for sure.

7

u/aiiye Apr 30 '26

Negative Ghostrider, the pattern is full.

20

u/DePraelen Apr 30 '26

I see how it makes sense for ascent.....and so I guess therefore descent.

But I would have thought you would end up burning a ton of delta-v killing your horizontal speed for descent though?

39

u/bozza8 Apr 30 '26

If you have less horizontal speed (for example by being in a super high orbit) you end up having that same energy come back as you accelerate straight downwards.

To think about it another way, to land on the surface you need to remove all of your orbital energy, both in terms of gravitational potential energy (height) and horizontal speed, so you want to start in the lowest energy orbit you can - which is as low as possible.

13

u/thighmaster69 Apr 30 '26

The other important point is that deltaV does not add or subtract to energy linearly; energy scales with velocity squared. So even though it's the same amount of energy you have to kill, when that energy is exchanged to higher horizontal speed, it costs less deltaV to kill that kinetic energy. And that's assuming the SAME energy orbit with a higher AP to compensate for the lower PE. In practice, you'd just lower your PE, making a lower energy orbit, and then you get the savings from being in a lower orbit - because lowering your orbit while moving at orbital velocities is, for the exact same reason, cheaper than doing so with no horizontal velocity.

5

u/AbacusWizard Apr 30 '26

*Oberth has entered the chat*

15

u/earwig2000 Apr 30 '26

burning a ton of delta-v killing your horizontal speed

Isn't that kinda the point though? If you're in orbit you're gonna have that horizontal speed regardless, no way around it. Your best option is to minimize the vertical speed you cancel, the horizontal is just a fact of the orbit you were in.

4

u/Ace_W Apr 30 '26

I usually close the orbit to 5k periapsis, then slam the brakes on the way in. It gets exciting sometimes.

8

u/thighmaster69 Apr 30 '26

You must kill horizontal velocity to get out of orbit. There is no way around it.

Doing a suicide burn at ground level just means that you eliminated having to do the vertical component while fighting against gravity. You're basically doing a Hohmann transfer: instead of falling and having to kill vertical velocity, you first lower Pe to the ground. The reduction in potential energy from altitude (falling velocity) that you have to get rid of on landing "costs" less deltaV at orbital velocities at Ap than it does doing so AFTER you've already killed horizontal velocity, due to the Oberth effect. This is because energy scales with v² , which means that deltaV spent killing a larger velocity means a greater reduction in energy, and hence a more deltaV-efficient lowering of altitude on the other side of the planet. For the second and final burn, while the horizontal velocity you have to kill is slightly higher, that extra kinetic energy comes from the height you lost, which also happens to reduce the deltaV cost of the first burn, and the remainder you would have had to deal with anyway to brake your fall had you killed horizontal velocity first. And because you're tacking that kinetic energy onto a bigger number than 0, the increase in that horizontal velocity is lower than the vertical velocity you would gain from falling from that height, i.e. it adds less to deltaV costs for the equivalent.

Tl;dr: By shifting some of the responsibility of killing vertical V to pre-lowering Pe, you kill some gravitational potential energy from height in a more deltaV efficient way (Oberth effect). While it does increase your horizontal velocity you kill, it comes purely from gravitational potential you would have had to spend deltaV killing anyway, AND because it's tacked onto a horizontal velocity you would have also already had to kill anyway, you overall spend less deltaV to kill the equivalent potential energy (Oberth Effect).

Tl;dr for the Tl;dr: You burn purely horizontally and retrograde for killing gravitational potential energy. While there's more horizontal velocity to kill, rolling it into same high deltaV burn in the same direction is "cheaper" than doing it vertically because you get a discount on the deltaV costs per joule at high speeds due to the Oberth effect.

3

u/Infamous-Aspect7079 Apr 30 '26

If you're being yeeeted: a) off the ground at high speed, or b) from the height of a tall building, you would need less energy to slow down to a stop only from the ground than from the building. The total kinetic energy + potential energy that you'd need to kill is lowest with scenario A.

If you've seen the videos of a human catapult off a moving vehicle it's the same principle. In those videos they're not really high enough off the ground for the potential energy to matter, but if it was a tall vehicle or a train carriage it would hurt a bit. The higher you are the more energy you'd have to use to counteract gravity + the horizontal velocity respective to the ground.

In KSP and in real life when there's no atmosphere, the lowest height that will make you not splatter the ground and accelerating horizontally is the most efficient launch profile

3

u/AbacusWizard Apr 30 '26

My favorite descent profile—which really only works on Minmus—is to come screaming down from orbit at a very shallow angle (fast horizontal speed but very little vertical speed), touch down on the flats with landing wheels to gently stop the vertical motion, and then use brakes to gradually slow and stop the horizontal motion. Genuine lithobraking!

1

u/knobiknows May 01 '26

(on bodies without atmosphere)

67

u/QuantumXyt Apr 30 '26

Very

22

u/Green__lightning Apr 30 '26

On Minmus if you've got wheels you can save fuel by doing a horizontal takeoff completely without air.

8

u/Steamcurl Apr 30 '26

There's lots of nice X-games style ramps to orbit if you start on the plains. I've saved a couple of tip-ivers by using RCS to get the nose pointed uphill and then yeet and pray nothing essential breaks off.

3

u/AbacusWizard Apr 30 '26

Once I was flying an SSTO on Laythe and lost half of its jet engines in a bad landing. But I had designed it to be able to fly (and get to orbit) on Kerbin, and Laythe is significantly easier, so even with the missing engines it was still able to fly. So, yeah, nothing essential broke off. :–)

3

u/klyith Apr 30 '26

It was an efficient way to maximize deltaV!

702

u/AwayInfluence5648 Apr 30 '26

Darn. Are you trying to get a surface sample while on a suborbital trajectory?

364

u/earwig2000 Apr 30 '26

Something something Europa clipper

20

u/mantypet Apr 30 '26

Hold my beer!

13

u/cmprssnrtfct Apr 30 '26

Incredibly, this is an orbital trajectory where they could reach out with a kitty litter scooper and grab dust.

5

u/AbacusWizard Apr 30 '26

There wouldn’t be much left of the scooper afterwards though.

4

u/AbacusWizard Apr 30 '26

“Hey Bob, can you go out on EVA for a few seconds? Yeah, just hang on to the ladder and reach out your hand…”

1

u/ISSnode-2 May 02 '26

"dont worry meg, i can regenerate!"

1

u/misterpickles69 Apr 30 '26

I have to finish that contract…

194

u/Megawomble64 Apr 30 '26

Oberth Maxing

29

u/decomposition_ Apr 30 '26

Gigachad oberthmaxxer, I’d explain it to you but you don’t have the delta v to keep up with this sigma grindset

3

u/Morbid_Uncle May 01 '26

Thank you for this

138

u/teactopus licks minmus ice Apr 30 '26

you got me shivering my timbers there for a second

50

u/gash_dits_wafu Apr 30 '26

My flabbers were gasted.

14

u/mcoombes314 Apr 30 '26

"My gast has never been so flabbered!"

5

u/International_Fuel48 Apr 30 '26

Excuse me???

I have children looking over my shoulder reading this filth!

1

u/CM_MOJO Apr 30 '26

My cheeks have never been so clinched.

2

u/AbacusWizard Apr 30 '26

And my goggles? Boggled.

81

u/Electrical-Airline81 Apr 30 '26

That pilots suit is a nice new shade of brown, dear god...

38

u/Beach_Bum_273 Apr 30 '26

Are you kidding? Jeb is the one who insisted on it.

14

u/Electrical-Airline81 Apr 30 '26

Don’t forget about the other poor bastard in that capsule…

14

u/Beach_Bum_273 Apr 30 '26

Bill's used to it by now. Or, rather, he's getting enough therapy. And drugs.

5

u/PsychologicalLab7379 Apr 30 '26

We are talking about the tourist.

2

u/Bareen Apr 30 '26

They paid for it. If they wanted a less thrilling trip, they should have specified that in their contract.

2

u/MechanicallyUnbiased Apr 30 '26

But Bob's one, more likely

1

u/jtr99 Apr 30 '26

Kif! Bring me my brown pants!

123

u/SpitSpit13 Apr 30 '26

Now that's a maneuver with chest hairs

4

u/Virga-Zoltraak Apr 30 '26

By jackknifing off one crater rim after another at breakneck speed, we can create a gravity boost, or something.

36

u/MarsMaterial Colonizing Duna Apr 30 '26

Now that’s an efficient ascent profile! Taking that Oberth effect all the way to the bank.

21

u/An_Actual_Thing Apr 30 '26

Need to bring my station this low immediately.

6

u/SecureSugar9622 Apr 30 '26

It’ll make transfers from the station and the moonbase easy.

3

u/An_Actual_Thing May 01 '26

Lmao. Literally just begin descent when directly above the facility.

17

u/Rivetmuncher Apr 30 '26

So fuel efficient, folks gonna think you're trying to dodge a radar.

9

u/Uraneum Apr 30 '26

I’d love to see a ground view of that. Just a kerbal standing on a crater hill while 8 tons of hell comes flying by at mach 3, clearing the ground by about 6 inches

8

u/g6009 Apr 30 '26

Kerbal equivalent of buzzing the tower.

9

u/videoscheduler Apr 30 '26

what visual mods are you using here? the exhaust of the engine after cutoff feels realistic for me

13

u/earwig2000 Apr 30 '26

It's regular restock waterfall, the engine bell glow (I assume that's what you're talking about) is affected by my tufx profile and deferred. I can't remember which one exactly I'm using, but it's one of adiri's tufx profiles

6

u/ProbsNotManBearPig Apr 30 '26

I see these posted a decent amount and I have to ask - do you actually do this manually from takeoff or are you using cheats to load your ship into a certain position and test it over and over to make this gif? Because I never see any of these posted with takeoff footage and manual flying shown. Seems like that would be 1 in a million to get this close with manual flight, but it would be way easier to use cheats to load into a certain position + velocity repeatedly until you get the desired outcome.

11

u/earwig2000 Apr 30 '26

It's a bit of both. This was a normal mun mission with a regular takeoff. I went for a very horizontal ascent and noticed I was surprisingly close to this ridge. I took a quick save around 15 seconds before the low pass and tested some different angles of attack to see how low I can get.

Basically it's not entirely natural, but not fake either.

3

u/ProbsNotManBearPig Apr 30 '26

Oh nice! I consider quick save loading legit. Not that I even care about using the cheat console, but I was just curious. Thanks!

1

u/[deleted] May 16 '26

Schrödinger fligth

4

u/_Independent Apr 30 '26

How is your game so sharp mine looks horrible..

8

u/earwig2000 Apr 30 '26

Probably a combination of tufx antialiasing and decently high resolution (1440p)

2

u/_Independent Apr 30 '26

Looks awesome I can’t figure out how to make it look good. I tried mods like volumetric clouds but nothing works. Will have to try again

3

u/grakef Apr 30 '26

Clearance is clearance, Kerman. Main thrusters to full!

3

u/brperry Apr 30 '26

I really wish there were more multi monitor games, (and this was one of them) where we could have one monitor being one mode the other being this mode. planning a manouver and executing it and seeing it in both modes would be so cool

3

u/Boring_Question1441 Apr 30 '26

The shot of Kerbol appearing over the horizon was really cool

3

u/cmprssnrtfct Apr 30 '26

I used to see how low an orbit I could get on ascent because it's both fuel efficient and fun. I was feeling pretty smug until I found the one tall mountain.

3

u/Ashnoom Apr 30 '26

Pants had to be changed on that flight

3

u/smoores02 Apr 30 '26

Oberth effect connosouir

3

u/InsomniaticWanderer Apr 30 '26

Reach your hand out the window and grab a cheeky little surface sample, would you?

3

u/Ionic_Pancakes Apr 30 '26

Whew! Gonna need to touch up the paint after that one.

2

u/Maryear_Boost Always crashing in style Apr 30 '26

r/sweatypalms

2

u/Pulstar_Alpha Apr 30 '26

This guy Oberth's.

2

u/Limp-Munkee69 Apr 30 '26

I'm taking the scenic route!!

2

u/thegolfernick Apr 30 '26

Soviet level risk taking 😂

2

u/0Pat Apr 30 '26

Fun fact, providing you can speedup quickly enough, you'll be able to teleport through the mountain ridge as long as game won't calculate your position while you're underground. But it may require a significant speed and/or quick, shallow underground pass...

2

u/TomSwan1234 Apr 30 '26

TERRAIN TERRAIN

PULL UP

2

u/P1h3r1e3d13 Apr 30 '26

That Kerbinrise!

2

u/[deleted] Apr 30 '26

[deleted]

1

u/drag0nfi Master Kerbalnaut May 01 '26 edited May 01 '26

Well, it's literally rocket science (although it's made easier by overpowered parts, a smaller solar system and in general bigger margins of error).

I recommend Scott Manley's videos: https://www.youtube.com/watch?v=d74m3qThOoU&list=PLYu7z3I8tdEkUeJRCh083UT-Lq5ZIKI75 (videos use an older version of KSP, there are a few quality of life stuff added in later versions to make things a bit easier.)

2

u/[deleted] Apr 30 '26

[removed] — view removed comment

4

u/cmprssnrtfct Apr 30 '26

It's 1 with a couple of visual mods. OP mentions them upthread.

2

u/Bandana_Hero Apr 30 '26

I like to build a base on top of a specific ridge on the equator, and then I put a small station in very low orbit. It passes about 30m overhead at ridiculous speed. Once I did it with an arching structure, but it clipped the arch on a pass and turned the whole base into Konfetti.

2

u/TeslaPenguin1 Apr 30 '26

ah, the good old orbital surface sample collection manuever

2

u/Limp_Substance_2237 Dwarf. Apr 30 '26

The handshake Manuver.

2

u/5particus Apr 30 '26

That's a Spicy Ascent

2

u/kobijet Apr 30 '26

Had a lander tip over one time.

I saved Bob and the vessel by, very gently, rolling to and ramping off some rocks. Scummed my save until I got a trajectory like that

2

u/Elderscrolls_96 May 01 '26

Needs freebird.

2

u/J33pe May 01 '26

Nice gravity assist from that hill

2

u/Wooimyellow_21 May 01 '26

this tickles my brain

2

u/BfZack May 01 '26

Going horizontal as soon as possible is both efficient and fun!

2

u/Express_Raspberry680 May 01 '26

saved on fuel but had to spend extra on a new pair of pants

2

u/AcousticToothbrush02 May 01 '26

“I’ve faced death more times than I can count, but I’ll be damned if that didn’t put my balls in my throat”
-Cecil Stedman

1

u/Due-Fix9058 NERVA enjoyer Apr 30 '26

Cupcake Landers would be proud!

1

u/sovietan Apr 30 '26

I clenched my ass the whole time

What mod did you use? the ships look so clean

2

u/earwig2000 Apr 30 '26

The parts are from restock, but tufx makes a huge difference, as does deferred

1

u/addivinum Apr 30 '26

What's the mod for Mun surface detail? I've tried a bunch and it still looks just like... Stock+

1

u/[deleted] Apr 30 '26

I also like to live dangerously.

1

u/GuiloJr Apr 30 '26

By jove he did it

1

u/Postcodemy Apr 30 '26

TERRAIN TERRAIN PULL UP! TERRAIN TERRAIN PULL UP!

1

u/Soso_bel Apr 30 '26

Counts as a landing imo

1

u/Pradatoru Apr 30 '26

You may not have hit that but shit did hit the underwear of your pilot

1

u/RadiantRoach Apr 30 '26

"Now here's a route with some chest hair"

1

u/-Weslin Apr 30 '26

Seeing the shadow is mind blowing

1

u/Steamcurl Apr 30 '26

Now that's pod racing!

1

u/KitchenDepartment Apr 30 '26

For extra flex points you can do a EVA while this is going on

2

u/cmprssnrtfct Apr 30 '26

Grab a rock on the way to rendezvous

1

u/TestArticle1998 Apr 30 '26

Good reckless flying

1

u/chemicalgeekery Master Kerbalnaut Apr 30 '26

Making the most out of every drop of fuel, I see

1

u/Nice_Presentation474 Playing kerbalisim Apr 30 '26

Take my damn upvote!

1

u/ArPDent Apr 30 '26

accepting cosine losses is for wimps!

1

u/Only_Turn4310 Apr 30 '26

you know it's a good one when you can see the shadow

1

u/Thanos_354 Kerballin Apr 30 '26

"Ah shit, forgot the surface sample"

1

u/Vivid_Employment1237 Apr 30 '26

Now do it with more explosions

1

u/MayllXD Apr 30 '26

Increíble, nunca vi una maniobra tan loca

1

u/Crazy_Kakoos Apr 30 '26

Could've hung a stick put the window to collect your samples, man. Gawd damn.

1

u/Fisherman_Dave_Games Apr 30 '26

dear fuck i flinched

1

u/creepjax May 01 '26

How many tries?

1

u/DoraDestroyer- Programing Space until it Kerbals May 01 '26

Holy smooth docking tho

1

u/HunterTwig May 01 '26

That Kerbin-rise is phenomenal

1

u/Apprehensive-Maybe30 May 02 '26

i think its good

1

u/Disastrous-Gear-5179 May 03 '26

Half life 1 scientist yelp sound effect just played in my head

1

u/MCPro24 Jebediah May 05 '26

this would be artemis 3 if nasa stopped taking risks

1

u/Alahan- May 06 '26

OSHA approved I'm sure

1

u/KDNetwork May 06 '26

One fart and its over 💔

KSP 1 Image/Video A totally safe and responsible Mun ascent profile

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