Finding efficient maneuvers with stock Kerbal X

[sixers2329]

Hi guys, bought the game a few days ago and have been flying the stock rockets to get a feel for the mechanics and I've been trying to land the stock Kerbal X rocket on the Mun (I know it doesn't have enough fuel for a return trip) and I seem to always run out of fuel trying to slow my orbital speed once I'm in orbit around the Mun. I feel like I'm not using maneuver nodes efficiently but I can't figure out a better way to do it. No matter what I try I end up burning relatively the same amount of fuel. Not sure if my initial Kerbal orbit is too low or if the Kerbal X just really wasn't designed to land on the Mun.

Any help would be appreciated

Edited July 17, 2013 by sixers2329

[stupid_chris]

The Kerbal X isn't the most efficient design to land on the Mun, but I think it's sufficient. How much fuel do you have left once in a stable orbit around the Mun? IF you use a bunch of fuel to get there, that might be your problem. Ideally you'd have over the 3/4th. First you want to start rather low, a 20km orbit is nice for landing on the Mun. Then you want to do a slight deorbit burn to start losing altitude and head to the ground. Don't set maneuver nodes, they'll distract you too much. Just look at the navball and burn at the retrograde marker. Then, when you're getting rather close to the ground, just start burning retrograde all along. Don'T let your speed go too low else you might end up going upwards again. Just slow down gradually until you're near the ground. Then try as much as you can to cancel out any horizontal speed by slightly burning retrograde until the retrograde marker is pointing directly up. Then, you just let yourself fall slowly to the ground and adjust the throttle to get a soft landing. It takes a lot of practice, but eventually you'll get it fine ^^ Quicksaves (F5) and quickloads (F9) are your friend here. Just practice, you'll get the hang of it eventually

[astropapi1]

I think the Kerbal X doesn't have enough deltaV to land on the Mun. It's more like an orbiter and an example of asparagus staging.

You should try to land a probe first, this reduces the mass of the lander and lets you make a smaller rocket. Just remember to pack an RTG.

[stupid_chris]

Well, it should have enough to get to the Mun, but maybe not back according to MechJeb:

I'll give it a test flight right now, I'll post the results soon.

[stupid_chris]

Bump!

Indeed, enough delta V to land, but not enough to come home:

had 250m/s left, so yeah, our friends are staying there. But it's a good start, just use your fuel wisely and you should be able to do it!

[sixers2329]

Wow that's pretty sweet you were able to do it! Yeah I definitely don't have 3/4 of my fuel left, more like 1/4th when I get to the Mun. The area I'm having trouble with is using the kerbal x and using the minimal amount of fuel to get orbit and then transfer orbit. Would you be able to describe those steps in your trial a little bit?

[stupid_chris]

Personally I used MechJeb. But I can still give out some information on how I did it:

Basically launching with the Kerbal X is easy, it has a really high TWR. However, it doesn't have enough delta V to get on a circular orbit without using the lander's fuel. I had to decouple the main stage during the circularisation burn, but that didn't eat up too much delta V. Then I just set a maneuver node to the Mun, just as usual, took about 840m/s of delta V. Then I circularized at an altitude of 20km, the lower the better. Landing from there wasn't so complicated, the lander has a ridiculous TWR on the Mun (about 15, really it's ridiculous). So you can do a small deorbit burn and come in really shallow, you'll be able to slow down don't worry. MechJeb got me very worried, and started the breaking burn at 1km from the ground. Really I was scared for a second. But it went perfectly well and clearly showed how ridiculous the TWR is. Basically, don't come down steep. You'll loose too much delta V fighting gravity. Come in shallow, and burn retrograde at around 2km from the ground (be careful, the altimeter gives you the sea level altitude, not the real one). If you slow below 100m/s, stop burning, you'll waste fuel. Really, the Kerbal X can do 100m/s to 0m/s in just above 5s, so don't be too scared. Just watch the ground and slow down when closer to the ground.

However, as you can see, it's really tricky. Really, you should consider using something else, the Kerbal X is uh, hard to use.

[capi3101]

I too attempted to use the stock Kerbal X to reach the Mun once. Whole reason why I have the Mun rescue cross on my salad bar...

Of course, most of the stock craft can't really do any of the things advertised in their default configuration. I think that's the point - they're there to give you ideas for your own designs and to fart around with. Take the X for example - if you take the booster off the lander portion and add another stage (say an X200-8 and an LV-N), that oughta give you enough extra delta-V to make it into orbit without burning any of the lander's fuel. Possibly enough to transfer to the Mun without using fuel either.

Granted, I haven't actually tried this. I should; if it doesn't work, it'd give me an excuse to deploy the Flying Dutchman 7 (my Munar rescue boat) again.

[stupid_chris]

I too attempted to use the stock Kerbal X to reach the Mun once. Whole reason why I have the Mun rescue cross on my salad bar...

Of course, most of the stock craft can't really do any of the things advertised in their default configuration. I think that's the point - they're there to give you ideas for your own designs and to fart around with. Take the X for example - if you take the booster off the lander portion and add another stage (say an X200-8 and an LV-N), that oughta give you enough extra delta-V to make it into orbit without burning any of the lander's fuel. Possibly enough to transfer to the Mun without using fuel either.

Granted, I haven't actually tried this. I should; if it doesn't work, it'd give me an excuse to deploy the Flying Dutchman 7 (my Munar rescue boat) again.

At small scales like those, an LVN is usually not worth the weight. An LV-909 would probably do a better job actually. But still, yes the Kerbal X is flawed, very flawed.

I could put together a failproof lander with it's launcher to get to the moon if you want to, it would be better than trying to work around the Kerbal X. Up to you!

[Johnno]

I've barely played with the stock rockets but after stupid_chris posted about landing on Mün I had an idea. What about Minmus? So, I loaded up the entirely stock Kerbal-X, no changes (no ASAS!), didn't add flight engineer or anything even, just launched.

Turns out, Minmus is doable. I had some fun and did an extreme EVA with Bill as well, landed from orbit using only his EVA pack and then got back up into orbit with the EVA pack fuel he had left. Jeb and Bob landed and then got back into orbit to pick up Bill before heading home.

Enjoy the pictures and give it a go.

Javascript is disabled. View full album

[sixers2329]

Ahh I see. Yea I originally wanted to try to land on the Mun with the kerbal X because I thought it was "realistic" and I didn't want to just start building über powerful rockets and get there no sweat I'm still having trouble burning too much fuel. I think my problem is I use the booster to push my apogee as far as I can, then use a bunch of my lander fuel to circularize the orbit. Would it be better to shoot for a higher elliptical orbit, or should you always try to circularize an orbit so if you want to get to another orbital body you can essentially have your apogee and perigee at any point of the circle?

[troyn123]

I think one thing some people overlook when trying to improve their efficiency is the atmospheric drag on Kerbin ascent itself. Take a look at the chart in the atmosphere section of the wiki for Kerbin: http://wiki.kerbalspaceprogram.com/wiki/Kerbin#Atmosphere

If you throttle back a bit during ascent and try to keep your ship's velocity under the terminal velocity as you rise, you'll save a little fuel, as you won't be pushing harder against the air than you need to.

[capi3101]

A good gravity turn is also essential. Go to 45 degrees on a 090 heading when you get up to about 10,000 m, and then lower that to around 20 degrees on the same heading when you get to around 25,000 m and see if that helps any. You might also try shooting for a higher initial orbit around Kerbin, say 150 km or so (this is one of those counter-intuitive things...a higher orbit has a lower orbital velocity requirement and therefore requires less delta-V overall. The booster stage of the Kerbal X has about 4330 delta-V available by stupid_chris's pic on the first page of this thread; that's a little less than what's required for a 150k orbit).

[stupid_chris]

Ahh I see. Yea I originally wanted to try to land on the Mun with the kerbal X because I thought it was "realistic" and I didn't want to just start building über powerful rockets and get there no sweat I'm still having trouble burning too much fuel. I think my problem is I use the booster to push my apogee as far as I can, then use a bunch of my lander fuel to circularize the orbit. Would it be better to shoot for a higher elliptical orbit, or should you always try to circularize an orbit so if you want to get to another orbital body you can essentially have your apogee and perigee at any point of the circle?

The lower and the more circular your orbit, the more efficient your transfer burn will be. Try to shoot as low as you can. 75km is a good altitude to go to the Mun.

[sixers2329]

The lower and the more circular your orbit, the more efficient your transfer burn will be. Try to shoot as low as you can. 75km is a good altitude to go to the Mun.

It's more efficient to transfer orbits when in a low circular orbit? I assumed it would be easiest in a high elliptical orbit because you have to fight less of the origin celestial body's gravity at a distance.

EDIT: Hrmm I still can't get to the Munar surface, it blows my mind you guys could get to minimus and back with that fuel. Whatever I try its about 800 delta v to get from Kerbin orbit to munar orbit, and is usually a 50 second-ish burn (which is like half my lunar lander fuel). I also use the entirety of the booster to get to about 100,000m. Where's my waste at?

Edited July 16, 2013 by sixers2329

[Johnno]

Hrmm I still can't get to the Munar surface, it blows my mind you guys could get to minimus and back with that fuel.

Well actually Minmus is easier to get to when it comes to delta-v because of its low gravity. The burn from Kerbin costs a bit more (around 100m/s extra I think) but getting into Minmus' orbit doesn't cost much, nor does landing and taking off. And the trip back doesn't cost much either, I went straight for aerobreak re-entry, otherwise it'd cost fuel to tweak your Kerbin orbit even if you aerobreak for capture.

I was merely demonstrating that even if Mün may not be a prime target for the stock KerbalX craft, Minmus is entirely possible.

Whatever I try its about 800 delta v to get from Kerbin orbit to munar orbit, and is usually a 50 second-ish burn (which is like half my lunar lander fuel). I also use the entirety of the booster to get to about 100,000m. Where's my waste at?

800 delta-v from Kerbin to Mün sounds about right. Also the booster on KerbinX will run out before you're in orbit pretty much. Even with a good gravity turn you have to use a bit from the 'lander' part. But to save fuel, try aiming for a 75x75km orbit, the atmosphere ends just after 69km so 75km usually gives enough leeway to be safe.

[sixers2329]

Would it be better to just shoot into mun orbit from kerbin, or establish an orbit around kerbin first? The latter seems like it requires excess fuel. I'm still getting to mun orbit with roughly 250 of my fuel left and seem to run out of it just before landing

EDIT: Grhhh I run out of fuel seconds before landing, I've tried this start to finish two dozen times now and I really don't think there's anyway you could be in a Mun orbit with 3/4 of the lunar lander fuel left.

Edited July 17, 2013 by sixers2329

[stupid_chris]

Would it be better to just shoot into mun orbit from kerbin, or establish an orbit around kerbin first? The latter seems like it requires excess fuel. I'm still getting to mun orbit with roughly 250 of my fuel left and seem to run out of it just before landing

EDIT: Grhhh I run out of fuel seconds before landing, I've tried this start to finish two dozen times now and I really don't think there's anyway you could be in a Mun orbit with 3/4 of the lunar lander fuel left.

You're probably wasting fuel during your ascent. Really, try with another rocket, the Kerbal X is a bit too tight on fuel.