Economical descent profile for Mun landing?

[tavert]

I wasn't even caring about the parking orbit or the transfer from it, since that's so much less TWR-dependent. I do have my Mathematica code posted in the thread I linked earlier, though it's not the most readable and if you don't have Mathematica it doesn't do a lot of good. What language are you using?

You can take my delta-V numbers and pretty easily derive a payload mass fraction vs TWR curve for given engine stats. Not sure if that's what you had in mind, or something that would actually consider the discrete choices of engines and tanks and enumerate all the combinations. Perhaps if you take the continuous curves and find the closest discrete point that's actually achievable you'd get the right answer without too much difficulty?

And is this all going to be single-stage landers, fuel capacity for both landing and takeoff, or doing some dynamic programming to handle staged designs?

Edited July 29, 2013 by tavert

[Geschosskopf]

Efficiency schmiciency. It doesn't matter if you've still got 3/4 fuel in your tanks when you reach the Munar surface if those tanks are rolling down the hill by themselves from where your lander just tipped over. In fact, the more fuel in them, the more likely you are to tip over. Mun in 0.21 doesn't have a flat surface anywhere on it that I've found so far. So only take short, wide landers, don't land anywhere near a crater rim if you know what's good for you, and watch for and maneuver around microcraters all the way down. You can only do this from very low orbits. So take enough fuel to account for the resulting inefficiency.

[Frederf]

Wrong. because gravity drag loses are biggest near launch/landing position and decrease with speed. But on the way up your mass starts high and decreases and during landing your mass starts high and decreases. So you will spend more time in high gravity drag during ascent than during descent. This can be very significant for small craft with low TWR.

I think you missed the part where I said "negative propellant flow rate" meaning as you burn fuel is being added. This allows the ascent with magic adding fuel to be a time reversal of landing with normal disappearing fuel. I only forgot about the fact that the Mun spins the same way in both but it should be a minor effect.

[Nurph]

Did some testing with this ship and 498 units of fuel:

From a 20 km circular Mun orbit I did 3 runs each of 'kill orbital V and drop', 'gradual arc to target', and 'low periapsis suicide burn'.

For the straight drop from 20 km I got 227, 226, and 235 fuel units remaining and one failed landing after overestimating my TWR.

From a gentle arc from 20 km:

I got 267, 244, and 252 fuel units remaining. Of note there were no close calls or crashes with this method, probably the safer way to do a Mun landing.

From 20 km to a periapsis between 4600m and 4700 to landing I got 281, 267, and 278 fuel units remaining despite having to do some evasive manuevers once or twice and one failed landing.

I must say that low peri. landings are rather... exciting in 0.21. Oh and by the way, there is a ridge on the Mun that reaches nearly 6 km

The failed landing:

VERTICAL VELOCITY HOLY BEJEZZUS

Passing by the 6 km peak:

Note the shadow to the left of the Nav Ball:

So in short:

1. Don't drop straight from orbit, it's inefficent and dangerous if you don't have a feel for your TWR.

2. An arcing landing is not the most efficent, but usually a safer choice if you have the delta v to spare.

3. Low peri. landings are !!superfun!!/dangerous if you don't anticipate the terrain but usually are the most efficent.

BOOM SCIENCE IN ALL YO FACES

[Frederf]

Your empiricism as well as the cut of your jib are commendable.

[iPat]

I don't know if you guys have seen this, but it's a nice acceleration (or in this case, deceleration) calculator. You can enter your max acceleration according KER, and your orbit speed, and come up with a pretty good estimate of how long it will take to bleed off your horizontal velocity, and how much distance you'll cover in the process.

http://keisan.casio.com/exec/system/1224829579

[Snark]

This is an ancient thread, going back to 2013.  Not only has the game changed immeasurably in the meantime, but it's also fairly certain that all the participants have long since gotten their answers. 

Locking thread to prevent further confusion.