Delta V and the MUN

[vetrox]

Ages ago I saw a challenge to land on the mun and back with a spaceplane without refueling on stock parts. I've been trying this challenge for weeks on and off and to be honest have gotten pretty good at making some efficient and pretty genius spaceplane designs on stock parts.

However I finally have a good design that gets me to an 80km kerbin orbit with 2100m/s of dv.

Ok so using this delta v map I need 1710 ms to land on the mun. Now obviously using that map. Im not going to be getting it home however after landing i will have mabe 20m/s of dv left. So im already 400m/s behind!

Is there some magic trick that I'm missing here. Is it worth actually attaining a munar orbit or should i just aim to crash on the mun and skip the whole orbit thing? would this be more efficient? Im jsut stumped as I can seem to get close to the delta v that these maps seem to require!

Edited September 30, 2013 by vetrox

[blizzy78]

Im not going to be getting it home however after landing i will have mabe 20m/s of dv left. So im already 400m/s behind!

Not sure what the question is here. 2100 m/s is most definitely not enough to make it to the Mun, land, and come back again. So take more fuel with to begin with?

[vetrox]

According to that delta v map. From a munar orbit it should cost me 640 ms to land on the mun. However it costs me closer to 1000. So i was wondering the best way to go about landing. Do i do a retrograde burn from a higher orbit and drop straight down onto the surface and kill off my speed at the last possible moment? Do i do a gentle burn until touch down. I just cant seem to land on the mun using less than 1000dv and its really bugging me as it makes planning ahead difficult. I dont want any unessesary weight. Im trying to make it as efficient as possible so i dont want to take more than i need.

EDIT:Now that i read my own post back...the title of the thread isnt exactly relevant -.-

Edited September 30, 2013 by vetrox

[Moon Goddess]

1710 is optimal best case.

That's assuming you never translate horizontally you land perfectly always burning exactly the right amount to be exactly at the right speed you need to be at the right altitude at the right time.

Basically, always round up.

[vetrox]

Im pretty spot on at getting to the mun with that deltav map. But I just suck at the landing. What would be the best way to land and from what altitude. I have been trying all sorts from 20km to 5km with varying results.

Hmm...Google may well be my friend here! *scurries off to google and youtube*

[Specialist290]

In my experience, landing always takes a fair bit more delta-v than the map tells you because the map assumes a more-or-less perfect "reverse-launch" style landing, whereas for the most part you're actually going to be burning a fair bit more fuel on the final descent simply to ensure that you're coming down at a safe speed. Thus, I'd say pack enough delta-v that you have about half again the amount the charts tell you. Fortunately, you can generally take off again with a delta-v amount much closer to what the chart tells you.

Aiming for a direct impact is actually less efficient in the long run for the same reason that trying to launch straight up from Kerbin is, only in reverse -- you're fighting against gravity the whole way down. What you really want to do is aim for a trajectory that gives you a low (10-20 km) periapsis, then circularize there and begin your descent from that orbit.