how to spend less fuel to get to the munn

[ulujm]

Hi I was wondering what is the best way to set a path to orbit the munn with a minimum burn.

Also once land on the munn and nimnus, what is the next step. what Do I need to do.

thanks

[Jimbimbibble]

Get in a low Kerbin orbit, then burn prograde toward the mun when the mun comes over the horizon. Adjust your orbit so you get as close as possible. When you arrive, do your capture burn as close to the mun as you can (but don't run into a hillside).

[Pecan]

Once, or even before, landing on Mun and Minmus your next step is up to you. There's nothing you need to do, except have fun :-)

Getting back safely would be a good idea though. After that there are all the other planets to visit.

[sal_vager]

Best way to use/need less fuel to reach the Mun is to use a lighter craft, you don't need a monster to get there, land, take off and return

[SRV Ron]

Best way to use/need less fuel to reach the Mun is to use a lighter craft, you don't need a monster to get there, land, take off and return

While this design will do the job with plenty of fuel for landing and return;

This much smaller design worked just as well with plenty of fuel reserve for landing and return.

Mun takes less fuel to get to but more to land and return which this ship will easily do.

Practice on Minmus first, then go for Mun.

[Sirrobert]

If you are unsure of the 'burn when Mun comes over the horizon' thing (I know I used to be), and rather use manouver nodes:

Rotate the screen so that Mun is on the right side of Kerbin (3 o clock).

Now put a manouvernode at the bottom of the screen (6 o clock).

Pull the prograde marker until you get an encounter.

You can actualy start the burn a little earlier, which is slightly cheaper, but you'd have to experiment with that yourself.

As for landing: A full landing mission costs rhoughly the same for Minmus and Mun. Mun costs less to get to, while Minmus costs less to land on.

So if you need practice, I suggest you practice the get to part with Mun, and once you can get there, practice the landing on Minmus.

Remember that Minmus is in an inclined orbit, so you'll need to match your rocket's orbit if you want to go there.

To do that, select Minmus in the map. This will bring up 2 markers on your orbit. The Accending, and Decending node. Put a manouver node on either of those, and use the purple markers on the manouver to reduce the number of the Node.

After you matched the orbit, do the same thing to get to Minmus as you did with Mun (drag the manouver node around a little to get a good encounter)

[xcorps]

Hi I was wondering what is the best way to set a path to orbit the munn with a minimum burn.

Also once land on the munn and nimnus, what is the next step. what Do I need to do.

thanks

What you're looking for is called a Hohmann transfer. http://en.wikipedia.org/wiki/Hohmann_transfer_orbit

Use an optimized launch into a zero degree inclination circular orbit of about 75km. Then create a maneuver node that just barely intersects Mun's orbit and you'll see the target indicators pop up. Drag the node around until you get a capture point, then fine tune it to minimize Dv.

If it's a manned mission, do some science. Have your Kerbals do a few spacewalks on the way to Mun, then on the surface do an EVA and get a soil sample.

Then just leave. Head back to Kerbin. Burn straight up (in map mode) until you get the escape point, turn off your engine. Time warp until you escape, then time warp some more so you have some separation from the SOI of Mun, then burn retrograde until your orbit intersects Kerbin.

[LethalDose]

A simple Hohmann xfer is the best path to the moon really is the most efficient path to the Mun, because the Mun is in a circular orbit with zero inclinication around your launch site.

Because the Mun's orbit is so simple, there really aren't "tricks" to get there cheaper. The only other advice I could think to give to save fuel is to keep your LKO orbit really low. When launching to LKO, try to keep your Apoapsis below 80 km, and try to circularize with Ap and Pe between 75 km 100 km. Circularizing too high around Kerbin will lead to lower orbital speeds, which in turn lead to less efficient transfer burns. But this is seriously a minor issue.

[technicalfool]

See also the link here: http://imgur.com/a/AGQF5

The spiral can be used for transferring from planet to moon, or from planet to planet. A rather useful diagram!

[joekidd1992]

I don't know if this will help you, but if you can use the winglets for maneuver, do so. It helped me tremendously. If you're going to the Mun, get on a 90% heading, or as close as possible, because this will place your orbit on the same plane as the Mun's orbit. Then using the planned maneuvers using the proapsis and preapsis planners, it should be fairly easy to get there.

[magnemoe]

Use nodes, create one who take your orbit out to Mun orbit, now rotate it so it intercept, adjust it so you get 100 km or less from Mun at closed point, say you need a 3 minutes burn then start burn at one minute before node, after burn adjust so you get on inside of Mun orbit and say 50 km, next adjustment is as you enter Mun SOI.

[thescientist]

Remember: you need more engines to lift more fuel, but you need more fuel to power your engines.

The efficiency comes with practise and many, many kerbal error.

[michaelhester07]

Once you establish your orbit wait until the mun is at first quarter phase (prograde of kerbin's orbit aorund the sun). You can then design a burn that skips the capture phase and goes directly to landing. This saves you about 500 dV (1/5th of your lander's fuel tank) that would have been used for the capture burn. You wait for first quarter so you land in the sunlit side of the Mun and minimize the risk of a crash when using stock components.

[KerikBalm]

design a burn that skips the capture phase and goes directly to landing. This saves you about 500 dV (1/5th of your lander's fuel tank) that would have been used for the capture burn.

No it doesn't - the dV you use to decelerate for landing is greater.

Suppose we have a 200 m/s capture burn, and then need 200 m/s to go from low orbit to landing.... for 400 m/s total

If you skipped a capture burn, you'd be coming in even faster, and you'd need ≈400 m/s to land.

The only fuel savings are from the oberth effect, but that is miniscule assuming that you capture into a very low orbit

[allmhuran]

Skipping circularization can be cheaper, but it is not much cheaper - definitely not 500m/s cheaper. But it's also certainly not true that "the delta V you use to decelerate for landing is greater". Falling from, say, 20km is always going to speed you up by exactly the same amount, whether you start off heading directly at the ground (a straight in landing) or heading tangential to the ground (starting from orbit, ie, circularizing first).

The difference is *when* you pay the additional delta V charge. If you go into orbit before landing, then you had to spend delta V to capture. If you come straight in at the ground then your descent velocity will be vastly higher than if you started from orbit, where your vertical velocity is zero, so you pay for it there instead.

[joekidd1992]

While this design will do the job with plenty of fuel for landing and return;

http://i.imgur.com/vdlNdVm.jpg

http://i.imgur.com/rH78NoH.jpg

This much smaller design worked just as well with plenty of fuel reserve for landing and return.

http://i.imgur.com/BvSAte9.jpg

http://i.imgur.com/h669f6P.jpg

http://i.imgur.com/Yo1TNvB.jpg

Mun takes less fuel to get to but more to land and return which this ship will easily do.

Practice on Minmus first, then go for Mun.

Is that 4 under the coupler? I tried it with 3 and I can land on the moon, but I definitely don't have enough to get home.

[kidolvski]

You can use asparagus staging to do it more efficiently...

[KerikBalm]

But it's also certainly not true that "the delta V you use to decelerate for landing is greater"

Sorry if that was unclear, I meant the dV needed to land if you've done no circularization is greater than the dV needed to land after you've already circularized. Ie: 400 to land with no circularization vs 200 to circularize and 200 to land. 400>200, so although you skip circularization, you pay more for the landing, and basicallyend up spending the same amount of dV.

I did not mean to imply that doing it his way costs more dV.

I only meant to imply that the savings are miniscule and far far less than the 500 m/s claimed, and I think we can both agree on that

Edited May 20, 2014 by KerikBalm

[SRV Ron]

Is that 4 under the coupler? I tried it with 3 and I can land on the moon, but I definitely don't have enough to get home.

That one is 4 under the coupler. To do it with three, you need to add three SRBs boosters to launch it to the first 5000 meters. You want to have fuel enough in the intercept stage to crash it into Mun or Minmus using very little fuel from the lander for close circularizing prior to committing to landing.

The bigger design uses asparagus staging after the SRB boost.

[stormoffires]

do not add the little dome covers, at this time ive noticed the dome covers which should promote less drag actually ADD to the drag, right now the game identifies all objects by their drag stat, so there is no slip stream/aerodynamics. just an FYI endless someone else can show, but the several rocket tests ive done have shown that the added weight/drag does effect. run without for best results

i used the wings alot on my small crafts, just got back from a trip to the mum for the first time, 456 science points thank you very much took 2 science models (forgot goo!!! arg!)

Id also suggest if you cant make the returns with the hvy science pods and what not, send a couple of rockets trying to get the same landing zone, with science models/satellites then 1 rocket/pod to pick the data then return no need to lug everything back.

[KerikBalm]

Yea, you need FAR for the aerodynamic nose cones to actually be useful. I mod them so they act as small fuel tanks(same mass ratio as the other tanks), so they look better and are functional.

[allmhuran]

Sorry if that was unclear, I meant the dV needed to land if you've done no circularization is greater than the dV needed to land after you've already circularized. Ie: 400 to land with no circularization vs 200 to circularize and 200 to land. 400>200, so although you skip circularization, you pay more for the landing, and basicallyend up spending the same amount of dV.

Aye, that's clearer now, and yeah, despite the theoretical possibility of a direct landing being cheaper, I agree that it usually doesn't actually work out that way to any degree of significance.

[KerikBalm]

I'm not even sure there is a theoretical benefit, although I haven't done the math.

Consider a perfect sphere (or an attempted landing atop the highest poin on the surface) - in this case you can set your perapsis arbitratily low.

you can thus circularize into an orbit arbitrarily low over your landing site, while burning perpendicular to gravity the whole time, making your gravity drag essentially zero.

In this case from an arbitrarily low orbit, you need only to arrest horizontal velocity to land, no burning pointing at the surface required*

Meanwhile, if you come in on a trajectory perpendicular to the surface, you may lose significant amounts of dV to gravity drag, although the higher your TWR during the "suicide burn", the less this is.

* but, to pull off that horizontal landing, from very low orbit, you need a very very very high TWR, otherwise you will drop into the surface while you still have significant horizontal velocity. Of course, with an arbitrarily high TWR, the suicide burns dV lost to grav drag also approaches zero... so....

If you manually pilot (maybe mechjeb can pull it off better), getting the suicide burn right is pretty difficult - the sooner you have to start the suicide burn, the more likely you'll end up with too much of a margin of error and lose a lot of dV to gravity drag as you slowly descend, and the more likely you'll need too much "lithobraking".

For me, manually piloting everyting (I don't have mechjeb), I always end up using less dV by capturing into a low orbit, and then doing my suicide burn from a low altitude. I can get much more precision. I'f I'm coming in at a very shallow angle, and see I wont stop in time, I can point the thrust down a little bit (sure, losing some dV to grav drag there), to buy more time. When I do direct landings, I usually end up wasting a lot of fuel slowly descending from 1 km above the surface or something like that.

I'd say the maximum theoreticaly benefit is probably less than 10 m/s, and in practice, you'll end up spenidng more than that on landings due to a lack of precision and sufficient error margins, or crashing spacecraft due to a lack of precision and insufficient error margins.

Unless the body has an atmosphere, I always capture into a low orbit before landing.*

* also, assuming you want to get back to Kerbin, leaving the fuel you need to get back to orbit is much more efficient in many cases- ie doing it "apollo style".

Although in this case you must consider the dV needed for docking maneuvers and the docking port weight. For the two moons of Kerbin, its often not really worth it (but I still do orbital rendevous with an orbiting fuel depot + science lab to collect science from many biomes), but as one moves on to other bodies, like Tylo and Eve especially, you'll always want to capture first, and then use a lander and orbital rendevous.

[allmhuran]

It's an interesting thought experiment.

What we can say for sure is this: In order for circularization to be cheaper, it must be true that you circularize at an altitude no higher than the altitude you would otherwise require to perform a direct descent to the surface at 100% throttle the whole way. That's the high altitude limit for circularization efficiency.

But we also can't circularize at an arbitrarily low altitude, even given a perfectly spherical target: If we circularize at an infinitesimal altitude above the surface and then attempt to land, we will impact the surface as soon as our trajectory is suborbital, which will be immediately, because being suborbital means our trajectory dives into the terrain more quickly than the terrain dives away from us. Ie, we hit the ground with our horizontal velocity at value infinitesimally less than orbital velocity.

So our minimum altitude for circularization must be high enough that our vertical velocity can be brought to zero before this collision occurs.

If we take an example where we circularize with infinite thrust, then we can indeed circularize at an arbitrarily low altitude, because we kill all horizontal velocity instantly when we decide to land, and hit at zero horizontal velocity. But then this means we are firing our engines for an infinitesimally small amount of time at, essentially, zero altitude... which is the same as a direct vertical landing with infinite thrust, where we would kill all vertical velocity at zero altitude instantly instead! So at this theoretical limit, the two approaches converge to perfect efficiency.

Edited May 22, 2014 by allmhuran

[rennsport27]

It's an interesting thought experiment.

What we can say for sure is this: In order for circularization to be cheaper, it must be true that you circularize at an altitude no higher than the altitude you would otherwise require to perform a direct descent to the surface at 100% throttle the whole way. That's the high altitude limit for circularization efficiency.

But we also can't circularize at an arbitrarily low altitude, even given a perfectly spherical target: If we circularize at an infinitesimal altitude above the surface and then attempt to land, we will impact the surface as soon as our trajectory is suborbital, which will be immediately, because being suborbital means our trajectory dives into the terrain more quickly than the terrain dives away from us. Ie, we hit the ground with our horizontal velocity at value infinitesimally less than orbital velocity.

So our minimum altitude for circularization must be high enough that our vertical velocity can be brought to zero before this collision occurs.

If we take an example where we circularize with infinite thrust, then we can indeed circularize at an arbitrarily low altitude, because we kill all horizontal velocity instantly when we decide to land, and hit at zero horizontal velocity. But then this means we are firing our engines for an infinitesimally small amount of time at, essentially, zero altitude... which is the same as a direct vertical landing with infinite thrust, where we would kill all vertical velocity at zero altitude instantly instead! So at this theoretical limit, the two approaches converge to perfect efficiency.

An interesting point, I guess this shows the fallacies involved when thinking about hypothetical, perfect scenarios. Especially since in order to get "arbitrarily close" to these cases, you'd need a huge TWR, which limits you to very inefficient engines, and therefore undoes all the fuel savings.