Matt_W
1703
It’s more efficient to do it at the apoapsis because your velocity is lower there and the delta-V from your engines will have more effect. In fact, it’s actually best to raise the apoapsis way out toward the edge of the Hill Sphere, coast out there, change the inclination, and then recircularize. That will use less fuel than trying to do it near the planet.
Pod
1704
It’s best to do it at lift off ;)
Also, I always heard it was best at PE because of the Oberth effcet, but I have no idea if it applies here.
Do you use any mods to slow down time? I don’t know how people (Scott Manley lol) are able to make a maneuver node (yep finally unlocked it!) while on their initial ascent and launch.
With Kerbal Engineer Redux, I would like the live telemetry as well as I saw that in a video and it would be super useful. Can it be configured so it doesn’t crowd the screen with lots of other junk?
Matt_W
1706
Oberth effect only applies with thrust is applied in the same direction (or the opposite) as the velocity. Inclination changes require thrust normal to the vessel’s velocity and the amount of delta-V required is proportional to the velocity, thus is more efficient at slower speeds.
KER has a few toggle-able sections: surface, for ground speed and time to impact, among others; orbit, for orbital characteristics; vessel, for delta-V, mass, and stage burn times; and rendezvous, for meeting up with targets. You can turn each section on or off, but you can’t edit what’s in each one.
For making maneuver nodes during ascent, I haven’t worked that out either. I don’t use any time-slowing mods, but I also rarely need to put down a maneuver node right on launch. My rockets end up taking iffy flight paths to orbit most of the time anyway, so I usually have a minute or two of coasting up to apoapsis for my circularization burn.
Scott is obviously a KSP God. It can be a little frantic get the orbit burn working. If it looks like I’m running out of time I just burn petfograde until I achieve orbit. But honestly it’s the main reason I still use Mechjeb. I dont have restarts so Mech Jeb is my assistant.
Thanks for the info. OK another question. I have 3 ways to try and grab a Mun orbit. Which one is the best you think (uses the least amount of fuel for later Mun landing).
- Fling around back-side and grab orbit from there.
- Keep it super tight and decelerated when close to Mun periapsis.
- Wider capture.
CraigM
1710
Option 1, by far.
The reason is rotational. By using option 1 your trajectory is the same as the Mun’s Rotation. So the amount of delta V is less by twice the surface rotational speed (roughly).
And I mean twice, because options 2 and 3 require you to not only fully reverse direction but also match rotation.
Made up numbers, but if the Mun has a rotational speed of 100 m/s at the equator and your orbital speed relative to the mun at capture is 400, then to land (which requires matching your orbital speed to the ground speed to be safe) you need to shed 300 m/s in order to land in scenario 1 (plus any potential energy differences from orbital height). Options 2 and 3 require you to shed the 400 m/s then also gain another 100 in the opposite direction.
Now this is all assuming your diagrams are from a north orientation, which given the direction of your Kerbin orbit is the safe assumption, but needs to be specified.
CraigM
1712
But here’s the simple way to think of it, without requiring any specific answer.
When trying to land on a body, the optimal route is to approach intercept from the direction of rotation. So an object rotating clockwise, approach from the left side. Counterclockwise, approach intersect from the right.
As for high versus low orbit, that is largely immaterial. You are trading potential energy for velocity either way. A higher intercept has a lower speed, but ultimately requires roughly the same delta V to descend to the surface. However a lower intercept has a slight advantage due to Oberth effects, so intercepting at higher velocities does improve efficiency somewhat. So a lower intercept orbit is slightly preferable.
I’m having trouble getting all my science experiments down to the Mun’s surface. I just can’t seem to bring enough fuel to get there, land with it all, take off, and get back to Kerbin. I’ve looked all over for a a ship based on the parts I have and have found nothing that will work. People post their Mun Landers, but none with all the science stuff included. This is my current tech tree:
And this rocket got me there, I landed. But I ran out of fuel on the way back just 100km from the moon’s surface. The design was to try and maximize the amount of science I could do. Both around orbit, and on the surface.
Any suggestions would be awesome as I spent all day yesterday making a bajillion trips and different designs and they all failed. I’ve pretty much exhausted all the science I can do on Kerbin and in Kerbin orbit, and much of the Mun orbit stuff, which is why I want to land on the Mun to get lots more science to unlock things I should have focused on earlier (proper landing gear).
Consider it a Kerbal challenge :)
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If you’re having trouble getting the science components back to Kerbin, you can design your Munar lander to leave the science parts behind. Go EVA and interact with the science parts, and you can take the data to store in the command module. Then you only need a wee little spacecraft to get back to Kerbin—a command module and an engine, pretty much. It also saves you having to reenter with a Science Jr., which in my experience is very explosion-happy.
A there-and-back-again mission to the Mun will take about 6100m/s of vacuum delta-V if you’re nearly perfect, and that’s if you’re aerobraking going back to Kerbin. The built-in delta-V display starts, IIRC, in atmospheric mode, so I can’t tell, just looking at it, if you have enough or not.
Edit: you can also try Minmus or Duna. Minmus is pretty easy to get to seat-of-the-pants—put a maneuver node on a Kerbin orbit when it’s just over the horizon and add delta-V to raise your apoapsis to its orbital radius, then do a normal/antinormal burn midway out to correct your orbit. It’s actually easier, in terms of delta-V budget, to land on Minmus and return than it is to land on the Mun and return, because Minmus has such light gravity.
Duna is a bit harder, but reaching Duna is less delta-V than a Mun land-and-return, too. If you have the third-level tracking station, I think you have enough antenna power to send a Duna probe or two.
I don’t think dumping Science Jr on the surface will work as I was so far short of getting back to Kerbin. The Science Jr. is not very heavy at just .2 T.
I used the heavier command module as I wanted to bring my scientist so I could get all plus bonus science so I’d like to keep that if possible I think, as I also need a pilot as I can’t fly worth a crap without SAS.
So this is my new design and I installed KER.
When I switch KER to Mun it looks like the combined vacuum delta-V is not enough? I’m not sure how I can make this work.
Maybe I should have a command pod with enough fuel left over to get the group back to Kerbin? Though not sure how much fuel it would take to rendezvous with a command pod.
ohhhh wait, delta V is constant regardless of location. I see, the second pic is less because I had to add RCS tanks which I’d forgotten on the earlier screenshots.
I sometimes settle for getting my Kerbals back to Kerbin orbit. From there, I can set up a rescue/recovery mission. To that end, I almost always try to include a small docking port somewhere on the craft.
Sorry, I wasn’t clear—by vacuum delta-V I meant the whole rocket’s delta-V, unadjusted for atmosphere, including the booster.
How much is your lander doing? To go from low Munar orbit to the Mun to Kerbin, you need ~1200m/s to land from and take off to low Munar orbit, ~350m/s to escape from the Mun, and possibly 100-200m/s more to ensure you get a good trajectory for aerobraking at Kerbin, for about 1750 total. Add 1200 if your booster only gets you to orbit—that’s about what it takes to go from low Kerbin orbit to a low Munar orbit.
Delta-V maps are handy for mission planning, especially now that the base game has an indicator for your total dV.
Regarding getting all of the science experiments down. Breaking ground has a fairly early science experiment Go-ob ED Monitor, and you also need Probodobodyne Experiment Control Station to control all the breaking ground science experiement. They both need a solar panel so you need 4 components. But the storage box only has room for 3 experiments. Is that a mistake or is that WAS. Is Has anybody figured out a way to deploy the experiment without having to used two boxes?
My landers are already pretty tall and I hate adding more height
I think they did it on purpose to force you to take 2 boxes.
@Fishbreath I’m not sure. I’m not even sure if I can take off and fly properly with that mess on top. I’d like to get to the Mun with that lander contraption and only use the fuel on it for landing, take off, and coming all the way to Kerbin. Think there’s enough fuel and delta V for that?
Speaking of which it seems like my asparagus staging no longer works. As in - fuel is not flowing from one tank to another. For instance I just tried this monster, and no fuel is moving between tanks. Any idea why?
Yes I finally did it! First Mun landing. So exciting! Though it was scary as I landed on a slope and this crazy contraption still wanted to tip over.
EEK
SMILE!
And the big payoff (which was even better than I could have hoped for!)
Grats! Thats awesome! I gotta get back into this :)
Thanks. I had all of .5 seconds of fuel left on my slingshot back to Kerbin. The odds of my next trip running out are way too high lol.
