Please help for moon landing Delta V required

[XratedSippyCup]

Using the Most up to date engineer redux, it says i have 6,350dv and still require about 400dv to get home. How can people do this with ~5.2k dv? Im assuming its my lack of skill and knowledge of orbital mechanics which doesnt help meet that. What can i do to reduce dv back to even just 6k dv?

[Goro san]

1) Its Mun not Moon
2) Do launch directly into mun trajectory (without circulisation)
3) take care that its (barely) colision course
4) do sucide burn
5) remember to quicksave a lot XD

Its quite easy to go (one way) to Mun around 5500dV

[Chibbity]

Considering he has 800+ hrs played I'm gonna assume he's talking RSS or some other real universe mod and therefore the actual Moon.

[andylaugel]

That sounds about right to me. For a Mun landing and return, I'd budget 4k m/s dV to achieve 100 km circular LKO, 800 for Mun intercept, 250 Mun circularization, 750 Mun landing, 600 Mun orbit, 250 Kerbin atmosphere intercept, and plan to use aerobraking to land on Kerbin for a total of 6,650 dV used.

If you want to do with less, the best place to start is by making that gravity turn into LKO more efficient. The cheat sheet on the wiki suggests you only need 3,400 m/s dV to achieve an 80 km orbit. Design your ship with less drag, keep your acceleration below 2g, and steadily turn towards the eastern horizon until your altitude hits your desired altitude, and circularize a little before you get there. You really can't shave much dV from the other steps.

[RoofCat]

there is no way to go to Moon with 6k, since Earth has orbital velocity of close to 8ooom/s. You need a lot more to reach Moon, land and get back.


So it is rather Mun.

Mun needs:
~3400m/s for LKO (minimum ~3150, can save some)
857 transfer to Mun
270 to circulize at Mun
540+ to land on Mun (~700..800, but can save some with suicide burns)
540 (+some) to launch back (turn asap East and spend probably 580?)
270 to escape and transfer to Kerbin with ~40km Kerbin Pe


For the whole trip:
Unbelievable result is 5630m/s (supersuicide Mun landing with extreme TWR perfect Kerbin launch). Or even few m/s less with wheels or high impact margin parts for crash landing.
Great one would be somewhere around 5900m/s.
And anybody, who has done Training, should be able to do it with ~6100m/s with practice.
Or 6300m/s in "feeling lazy - I will get there somehow eventually" mode.


If you fly houses aka fat cows without nose cones, you may actually need 8ooom/s since KER has no idea about real delta v usage. All it can show is theoretical top values for that mass and engines.

[George Kerman]

It's not just the deltaV that matters. It also matters how much the rocket costs, how much leeway you give yourself for mistakes and inaccuracies, the TWR.... Why don't you do yourself a favor and allocate 7000 m/s dV for ships traveling in the Kerbin system anywhere (and back)? Once it's cruise control to land, get back and everything, then you can think about optimizing and minimizing your design. It's not like it's hard to achieve a ship with 7k dV.
And it's not like you need advanced orbital mechanics to reach the moon. Go east from launch, once in orbit do a maneuver with 850-860 m/s, if you don't hit the moon, move the maneuver node, it's that easy (grosso modo).

Oh and by the way, I've checked one of my rockets for the real Moon. It's got about 17.5 km/s dV but pretty low TWR on all stages, leftover is usually between 400 and 1000 depending whether I get the targeted landing correctly without hovering and where the moon is in its orbit for the return burn. Just one way, for probes for example, I allocate 15k, usual leftover of 1k (in case there's another biome nearby).

[Mightylink]

Since the moon has no atmosphere its better to be as low as possible, get your command module about 10k in orbit, and you wanna get your lander to be landing as sideways as possible just above the surface, that will use the least amount of fuel, just try not to crash into any hills :)

Same for takeoff, make your lander go almost 90 degrees sideways towards your command module, just keep it high enough to clear any hills ahead of you and that will use the least delta v possible.

[Crim]

When landing on Mind, pick a spot on the retrograde facing side. You can launch from there which will get you off the Mun and lower your periapsis into Kerbin's upper atmosphere. Don't dip too low; a few shallow passes is better than exploding when you are so close to home :)
You'll save a lot of DV using atmosphere in place of engine power. Don't forget to close PVPs before you hit turbulence too!

[George Kerman]

Originally posted by Byar:

When landing on Mind, pick a spot on the retrograde facing side. You can launch from there which will get you off the Mun and lower your periapsis into Kerbin's upper atmosphere. Don't dip too low; a few shallow passes is better than exploding when you are so close to home :)
You'll save a lot of DV using atmosphere in place of engine power. Don't forget to close PVPs before you hit turbulence too!

I don't believe he knows which is the retrograde facing side (by that meaning the point with 90 degrees to retrograde), but easier said: when your craft is between the Mun and Kerbin on your counterclockwise equatorial orbit. If you landed at the poles, it's easier to escape balistically, no orbit at all. 400 m/s escape is not entirely bad, but you should have 285m/s -ish if you were around a 10km circular equatorial orbit.

[RoofCat]

Originally posted by Byar:

When landing on Mind, pick a spot on the retrograde facing side. You can launch from there which will get you off the Mun and lower your periapsis into Kerbin's upper atmosphere. Don't dip too low; a few shallow passes is better than exploding when you are so close to home :)
You'll save a lot of DV using atmosphere in place of engine power. Don't forget to close PVPs before you hit turbulence too!

are you implying escaping straight up at 90° from tail side will be cheaper than using the usual orbital trajectory escape?

You do realize orbital/prograde direction launch happens in microgravity most of the time while straight launch experiences full amount of gravity (1.6m/s²) every second?

[killer_Foxy]

MOAR BOOSTERS

[Astronaut]

google ksp cheat sheet for delta-v. also install mechjeb if you really can't go to the mun. mechjeb will do it for you. also search youtube for some tutorials. Scott isn't the only good tutorial maker

[TinfoilChef]

Originally posted by Goro san:

1) Its Mun not Moon

Actually the body in question is a moon, it's name is Mün. The umlat on the letter u changes the pronounciation to something like "mewn" (note the spelling of "Mün or bust" on the side of a crashed ship that shows on one of the menu background screens when starting the game)

Originally posted by XratedSippyCup (Ehcks Dii):

Using the Most up to date engineer redux, it says i have 6,350dv and still require about 400dv to get home. How can people do this with ~5.2k dv? Im assuming its my lack of skill and knowledge of orbital mechanics which doesnt help meet that. What can i do to reduce dv back to even just 6k dv?

A very good tutorial is the Kerbal Space Academy "Boot Camp" that DasValdez does on his twitch channel. In it he walks new players though the start of a new save from starting up to the first flight to Mün and back.

This VOD is the most recent Boot Camp, done shortly after 1.2 was released and it's still valid today.

https://www.twitch.tv/videos/96679066

Yes it's 8 and a half hours long but thats because he explains everything in detail, answering viewer questions from the chat.

Das is without doubt, the best, most knowledgable KSP streamer out there and his channel is all about helping folks learn the game. I started playing in 0.13.3, bought the game in 0.16 and I still learn new tricks watching his streams.

[XratedSippyCup]

I appreciate all of the help and i am watching that boot camp vid in chunks. I probably havent gotten to the launch part yet ( im only 2.5 hours in).

When i look at the dV in Kerbal engineer in the VAB and it says 6,300 dV. Thats is not taking into consideration that half of that is burned in decreasing elvels of atmosphere. Essentially im asking if im reading Kerbal Engineer Redux incorrectly, and maybe I AM doing my gravity turn burns properly but reading KER incorrectly.

I hope is explained that well enough

[TinfoilChef]

Originally posted by XratedSippyCup (Ehcks Dii):

I appreciate all of the help and i am watching that boot camp vid in chunks. I probably havent gotten to the launch part yet ( im only 2.5 hours in), but a final quick question is why when Kerbal engineer shows 6.3k dv that by the time i get into LKO i have only 2.2k dv left. Ive tried different gravity turns and have varied ~ 100 dv.

If it takes 3200dv to get to LKO , why does my rocket use 6,300 - 2200 = 4,100 dv to get into LKO? How do you read dV when the Kerbal Engineer Redux says 6.3k when that shows the rocket working in atmosphere?

I hope that made sense... to you fellow armchair rocket scientists/ orbital mechanic math doctorate pros ;)

EDIT: and to those who truely are and earned those ranks, Im sincerely jealous D:

that 3200dv is more of an ideal number for a launch that is flown just right. Later in that VOD Das talks about how much dv that trip needs and advises taking more dv because most people, especially new players, are usually going to need more like 3600-4000 (or a bit more) to reach LKO.

Why? Because it takes a practice to gain skill flying a good flight profile all the way to orbit. Plus, every ship is going to have it's own idiosycracies.... like larger, heavier launches (especially those with large payloads in large fairings) will need different flight profiles.

Das typically advises new players have 7K+ dv on the pad when launching a trip to the moon. It's always better to have a bit more fuel than you need than to be short by even one drop.

[TinfoilChef]

As for how to read KER's dv .... the "in atmosphere" numbers you need to be concerned about is the TWR at launch, which should be around 1.5 on the pad. For numbers relavant to the rest of the flight, turn "atmosphereic" off and the last stage dv numbers are closer to what the whole flight has.

When reading that in the VAB I consider it as "under ideal conditions", if you have a KER part on the ship (attach it to the command pod), you'll see the dv numbers in the "vessel" tab of the main KER display. Those numbers reflect what the ship has at the current moment and are constantly updated as you burn fuel, jettison spent stages, etc.