What am I doing wrong in my Moho mission

[SalehRam]

Hey everyone...

For the past 2 months I have been raging, crying and doing everything related to anger because of Moho...

My own challenge: get THREE Kerbals on Moho by not using Apollo-style lander.

I have managed to build things with 10k dV, 11k dV, and landed successfully, but could not get to Kerbin again...

I have even installed MechJeb (only for few minutes) to watch the ascent profile, and the transfer burn being done automatically to see if I am doing things wrong, but my actions were all good...

I see people talk about capture burn in Moho SOI that requires only 2000-2500m/s of dV, and same goes for transfer burn that requires about 1600m/s for them. But for me the numbers I am seeing are far from these...

My major issue is the return trip as I consume all the fuel on the way to that little planet. My latest attempts is this (which is going on while I am writing this):

 

The total dV on that rocket on launchpad was 12.5k m/s, here is the full rocket (Mods in use: KER, RT2, TAC LS), about 287 parts.

So my question is, what is going on wrong with my actions from the images above? I have used the tool by Alex Moon to know the right time to launch, and I recently started using precise node to get more control over the nodes...

Edited February 6, 2016 by SalehRam

[Foxster]

One way is to have more dV on board. Here's how I do it:

Do the mission in three bits: The Kerbin lifter, the transfer+return stage and a disposable lander. 

The lifter has about 4500-5000 dV depending where your favorite orbit is at. I like 605km as I can max warp there. 

The lander is as light as possible so that it uses less fuel to get to Moho. You could even consider just a command seat. If you make it disposable then you won't need all the docking paraphernalia. Just EVA your crewman back to the transfer craft, which has a Kerbin-landing capable capsule. You lander doesn't need huge dV. 2500 should be fine and you can get that with one engine.   

It's hard to see what is making up your transfer stage but this is where you are going to put your dV so it needs to be good. Nukes are the obvious choice. A core LF tank, some LF drop tanks and 3 or 4 nukes should do it.  You want about 4000 outbound and 3000 back for a decent safety margin. Remember that you won't be bringing the lander back so your "MPG" will be better on the way back. 

I'll dig out the last craft I used or make a new one in a bit and re-check those numbers. 

Edit: Just spotted you want a crew of three. Not a problem. Just make sure to use the lightest capsules for that. I'll have to make a new craft to test that out and I'll get back to you. 

Another edit: I really must read more carefully. I see you don't want an Apollo-like mission. So I'm guessing you want a lander that can fly back to Kerbin. OK, that's cool. Give me a bit to make something and check the numbers. 

Edited February 6, 2016 by Foxster

[SnakyLeVrai]

2 hours ago, Foxster said:

The lifter has about 4500-5000 dV depending where your favorite orbit is at. I like 605km as I can max warp there. 

You can max warp but, unfortunately, high orbits require more dV to get out of a planet's SOI. Example: I am currently flying a mission to study Kerbol. It's a long burn out of Kerbin (I don't have a lot of thrust), so I burn in two times. starting from a 500km circular orbit. 1st burn gets me to a higly excentric orbit, then I wait uintil I get back to periapsis to burn my way out of Kerbin. Well, I've noticed that by lowering my periapsis to 90-100km will save me 200m/s dV. And Lowering the periapsis costs me only 7m/s because my apoa^psis is real high.

 

Theroretically, I'd save even more by lowering to 80, 70, ..... 0 km, but there is this atmosphere thing  Be careful not to lower to much, you don't want to hit the atmosphere this fast  

[Foxster]

11 minutes ago, SnakyLeVrai said:

You can max warp but, unfortunately, high orbits require more dV to get out of a planet's SOI. Example: I am currently flying a mission to study Kerbol. It's a long burn out of Kerbin (I don't have a lot of thrust), so I burn in two times. starting from a 500km circular orbit. 1st burn gets me to a higly excentric orbit, then I wait uintil I get back to periapsis to burn my way out of Kerbin. Well, I've noticed that by lowering my periapsis to 90-100km will save me 200m/s dV. And Lowering the periapsis costs me only 7m/s because my apoa^psis is real high.

 

Theroretically, I'd save even more by lowering to 80, 70, ..... 0 km, but there is this atmosphere thing  Be careful not to lower to much, you don't want to hit the atmosphere this fast  

200dV really is negligible for the extra bother. Great if you really like shaving things to the bone but personally I prefer a little comfort. 

Edited February 6, 2016 by Foxster

[juanml82]

I'd send a spare tanker as well, just in case. That way, you can refuel in Moho's orbit, after exploring the surface.

[Foxster]

I found a bit of time to have a go at this myself. Seemed harder than I remember from last time. I don't think not being able to find a particularly lean transfer was helpful.

Here are some pictures...

And a craft file: https://www.dropbox.com/s/nqzpz65iehls9kr/Moho%203.craft?dl=0

Total dV is 15,911. Lifter has  5064, so there is ~1,000+ left to get going to Moho. Transfer stage has 6017, so plenty for the rest of the transfer, braking, orbit and even landing on Moho. Lander has 4830, which is enough to get home and the heat shield means you can go straight for re-entry from inter-planetary speed with a Pe of ~25km. 

Hope it gives you at least of couple of tips. 

(PS - Just spotted that on your craft you have your nukes bolted to an S3-14400 and an S3-3600 tanks. They only have LF in right? You could use a Mk3 long LF fuselage instead to save a bit of weight. But it's better to use some smaller tanks and stage them to save dV

I also see that you used a Mk1-2 command pod. They are a very overweight way to convey three crew

You have also probably used too many nuke engines. Is that 6 or 8? Cutting it down to 4 or less will make the burns longer but save a LOT of mass). 

Edited February 6, 2016 by Foxster

[Snark]

Strong suggestion:  Ditch the Mk1-2 command pod.  It's extraordinarily overweight.  That pod looks nice, but it has FIVE TIMES the mass of a Mk1 pod, and you really can't afford to waste mass on a Moho mission.  Sticking a Mk1 pod on top of a Mk1 crew cabin may not look as nice as a Mk1-2 pod, but it has less than half the mass.  Saving a couple of tons of dead weight at the pointy end of the stack will really make a difference for a Moho trip.

 

So, the OP stated as a personal challenge

On 2/6/2016 at 1:56 AM, SalehRam said:

by not using Apollo-style lander

I'm not totally sure what is meant by that, but I'm guessing he meant "I don't want to leave a command stage in orbit and just go down to the surface."

That's going to cause you major grief, going to Moho.  The problem is,

• it takes a lot of dV to get from Moho down to the surface and back
• it takes a lot of dV to get from Moho orbit back home to Kerbin

However you get down to Moho's surface and back, you need a lot of dV to go home again after that.  Which means a whole lot of fuel.  And you really, really don't want to be sending that fuel down to the surface of Moho and back, because doing so would be really expensive since Moho itself has such a high escape velocity.

Furthermore:  the engineering needs for a transfer stage between Kerbin and Moho are very different from the engineering needs to go from Moho orbit to the surface and back.

• To transfer between Kerbin and Moho, you want the highest Isp possible, so that you can get maximum fuel efficiency.  In practice, that means using nuke engines.  But those have really low thrust, which means they're extremely unsuitable for landing on Moho (which has high gravity and needs a higher-thrust engine).  Nuke engines are also really massive, so you you don't want to be carrying them as dead weight down to the surface of Moho and back.
• To land and take off on Moho, you need an engine with really good TWR.  But those engines don't have the highest Isp, which means they're not such a good choice for transferring between Kerbin and Moho.

So:  I'd suggest a design that has a nuclear-powered transfer stage, and a lightweight disposable lander that has high-TWR engines.  You fly the whole shebang from low Kerbin orbit to low Moho orbit using only nuclear engines.  Use the nukes to get into a really low Moho orbit.  Then you transfer the kerbals to the lander, and it goes down with its high-TWR engines, does its thing, and takes them back to orbit.  Then you move the kerbals back to the transfer stage and send it back to Kerbin, leaving the lander in orbit around Moho.

Another option would be to make an ISRU miner, so that you can refuel at Moho.  That means your Kerbin-Moho transfer vehicle only needs enough juice for a one-way trip, since you can fill up at Moho before going home.  This strategy will take some engineering finesse of its own, since a drilling rig isn't lightweight, and Moho gravity makes hauling fuel up from the surface a challenge, but it's doable and I've done it.

Finally:  make sure you're flying right, and not doing anything that's costing you more dV than you need, because you don't have any to spare.

Specifically:

• What's your dV budget to get from Kerbin to Moho, or Moho to Kerbin?  Make sure you're using a good window, with a planner like http://ksp.olex.biz .  How much dV are you currently spending to do this?
• Make sure you're getting maximum use of Oberth effect upon arrival at Moho, and not doing something silly like circularizing in high orbit.  You want your initial approach to Moho to be toe-scrapingly low, with a Pe just high enough to avoid smacking into terrain, and do your circularization burn there, at low orbit.
• When you're landing the lander, make sure you have an efficient vacuum landing technique, i.e. have you mastered the art of "suicide burns"?  Moho's high gravity is unforgiving; if you don't use an efficient landing and takeoff technique, you'll waste scads of dV.

 

[Aethon]

When it comes to Moho forget transfer windows.  The best direct path there is to leave for Moho when Kerbin crosses it's Ascending node.  I'll quote myself from another thread and provide some links.  Read Macollos and Kashuas posts.  With this method I can land on Moho for about 6100m/sec dv from an 80km Kerbin orbit.

 

I landed on Moho last night using macollos' method and it's slicker than snot on a broom handle. Basically you leave LKO on Mohos' AN/DN.

The first time this occurs ( IIRC the AN ) is ( Earth ) Year 1 Day 21, on or about Hour 17. Set Moho as your target and drag a dummy Kerbin escape node out to see where the AN/DN is. I combined my Kerbin escape burn with my inclination burn at a total cost of 2300 dv. At my solar periapse ( which was also Mohos' solar periapse ) I burned 1800ms retro ( as Kashua suggests. See link ) to make sure I encountered Moho on my next orbit, which lowered my solar apoapse and slowed the eventual Moho encounter down dramatically. My capture burn at Moho was around 1000ms.

Didn't know this thread was going to pop up or I would have documented better.

Use it! Props to macollo.

 

 

 

http://forum.kerbalspaceprogram.com/index.php?/topic/55965-oh-bugger-injection-burn-at-moho/#post835667

http://forum.kerbalspaceprogram.com/index.php?/topic/24615-delta-v-to-reach-moho-orbit/&page=1

[SalehRam]

Well, thanks all for the useful input... I have came to a design that can do 13.1k m/s dV, so far it seems I am doing it well. Lifter has 4500+ m/s dv, and when I am in LKO, I get about 9000k+ m/s dV for the remaining trip, and I hope that is enough.

I am going to change the Mk2 Pod with what Snark said, as I completely forgot/missed the ability to do that. Also I check macollo's method... It seems easier to do and I hope it will give me more chances to success.

6 hours ago, Snark said:

Specifically:

• What's your dV budget to get from Kerbin to Moho, or Moho to Kerbin?  Make sure you're using a good window, with a planner like http://ksp.olex.biz .  How much dV are you currently spending to do this?
• Make sure you're getting maximum use of Oberth effect upon arrival at Moho, and not doing something silly like circularizing in high orbit.  You want your initial approach to Moho to be toe-scrapingly low, with a Pe just high enough to avoid smacking into terrain, and do your circularization burn there, at low orbit.
• When you're landing the lander, make sure you have an efficient vacuum landing technique, i.e. have you mastered the art of "suicide burns"?  Moho's high gravity is unforgiving; if you don't use an efficient landing and takeoff technique, you'll waste scads of dV.

For point 1: my dV consumption for getting into 100km orbit around Kerbin is around 4500-4700m/s depends on the ascent profile I make and the possibility to make quick actions while in the launch lag and fps drop.

For point 2: I can already get my PE on Moho encounter at around 20km to 15km.

For point 3: I have been doing suicide burns all the time after realizing KER can help me with that through calculations. and I am going to do this on Moho as well.

 

Currently, I have a design where I use Mammoths, Mainsails for my 2 lifting stages. Then for transfer, 1 central Rhino and 6 Mainsails, these 7 engines are separated on 2 stages. Then for capture and circularizing burns, I use 6 nukes connected to 1 S3-7200 and 1 S3-3600 tanks.

Lander, I am using 4 LV-909s, and combination of X200-16, and FL-T400, FL-T200 tanks...

 

I will see how the next attempt will work as I think I am getting there slowly.

[Geschosskopf]

14 hours ago, SalehRam said:

So my question is, what is going on wrong with my actions from the images above? I have used the tool by Alex Moon to know the right time to launch, and I recently started using precise node to get more control over the nodes...

First off, as others have said, ignore all transfer windows generated by various web pages, mods, and such.  There are only 2 reasonably sane ways to get to Moho and back, the bi-elliptic transfer (as well-described above) and using Eve for gravity assists.  I don't find much difference between the 2.

To use Eve, leave Kerbin on a transfer window to Eve.  When you get to Eve, tweak your approach for a low pass in a retrograde direction (IOW, passing on the sunny side instead of the dark side).  The idea here is that your orbit after the Eve fly-by will have a Pe down at or just inside Moho's orbit and your Ap will be up about Eve's orbit, all this gained for free.  While you're at it, adjust your Eve Pe up/down as needed so that after the Eve fly-by your orbit will be inclined as close as possible to Moho's.  Once you leave Eve's SOI, you'll have to do a plane change and, if you can't do a small burn to hit Moho soon after leaving Eve, you might have to wait an orbit or 3 to synch up at your Pe, but capturing at Moho will then be pretty cheap.

To get home, it's pretty much the reverse.  Leaving Moho as close as  possible to one of its AN/DN points with Kerbin helps, but you have to leave when you've got a window to Eve.

[Snark]

38 minutes ago, SalehRam said:

Currently, I have a design where I use Mammoths, Mainsails for my 2 lifting stages.

This sounds good.  Mammoths and Mainsails make great lifters.

38 minutes ago, SalehRam said:

Then for transfer, 1 central Rhino and 6 Mainsails, these 7 engines are separated on 2 stages.

Not good, unless you're just using them to reach circular LKO.

From the moment you reach circular LKO, you want every drop of fuel you spend to be emitted through nukes and nothing but nukes, to take maximum advantage of their Isp. You already have nukes on the ship.  If they're good enough for capture and circularizing at Moho, then they're also good enough to eject from LKO.

So drop the Rhino, drop the Mainsails.  That's 45 tons of dead weight you don't need.  Replace them (and their fuel supply) with LF-only drop tanks to feed the nukes.  It'll give you lots more dV for less mass.

43 minutes ago, SalehRam said:

Then for capture and circularizing burns, I use 6 nukes

Do you really need six of them?  That's a lot of mass.  Fewer can do the exact same job... it's just that the burns are longer.  If you can drop some, that'll save more mass and get more dV.

45 minutes ago, SalehRam said:

Lander, I am using 4 LV-909s, and combination of X200-16, and FL-T400, FL-T200 tanks...

This sounds good, the Terrier's a great lander engine.  If you can swing it, you could replace the four Terriers with a single Poodle.  It'll have slightly more thrust, 250 kg less mass, and a slightly higher Isp.

Or, if you stick with the Terriers:  rig them asparagus-style, so that you can jettison 2 of them (with their fuel tanks) on the way up, as soon as they're empty.

[SalehRam]

Thanks for all your great input (as usual ), Thanks to your advises, I have modified the rocket a little bit to this:

 

I have removed the Mainsail engines only form the lifter stage, and kept their fuel tanks to feed the Mammoth's

Also, added 4 Nukes for transfer stage, and 4 extra disposable fuel tanks (with LF only).

Same goes for capture and orbit stage, with 2 Nukes, and 2 disposable tanks.

I have surrendered to the fact that I need something in orbit to rendezvous with, so I added to large docking ports between the lander/final stage and the orbit stage, to be able to use whatever fuel left for the way home.

I got a total of about 14.4k m/s dV now, which is 1500 more than my previous work.

I'll test it and get you some feedback!

Regards

[Skylar']

use nose cones on the Kerbodyne tank's even if their not fit they reduce the drag. the k.e.redux will show less deltav,it but it works.

 

 

Edited February 7, 2016 by Skylar'

[Snark]

49 minutes ago, SalehRam said:

Thanks for all your great input (as usual ), Thanks to your advises, I have modified the rocket a little bit to this

What are you feeding the nukes?

Nuclear engines use LIQUID FUEL ONLY.  They don't use oxidizer. If you're including oxidizer for them, you're crippling your craft with many tons of unusable dead weight.

The only tanks that I see there for the nukes are LFO tanks, not LF tanks.  Also, it's kinda hard to read the teeny-tiny resource display, but as far as I can tell, you have a full load of fuel and oxidizer-- i.e. it looks like you're trying to feed the nukes LFO.

One "fix" for that is to simply adjust the content of all the fuel tanks that are feeding the nukes, and delete the entire oxidizer supply from them.  That would be enormously better than shipping dozens of tons of useless oxidizer.  However, it would still be far from the best solution, because it would mean you'd be launching a craft with many tons of half-empty fuel tanks, and fuel tanks are heavy.

Therefore, what you really should do is get rid of the LFO fuel tanks altogether, and replace them with (full) tanks that are LF-only.  If you're using stock parts, the Mk3 plane series has some large LF-only tanks.  Otherwise, you could use Porkjet's Stock Fuel Switch mod to convert the tanks in-place to be LF-only.

So, once you've got everything put together, your ship will look like:

1. lifter, powered by LFO & Mammoths
2. transfer, powered by LF & nukes
3. lander, powered by LFO & Terriers

Also:  I note that your lifter has a bunch of big Kerbodyne tanks that are exposing big flat front surfaces, which is terrible for aerodynamics.  You should consider putting nosecones on those.  An ADTP-2-3 adapter with a Mk7 nosecone should do the trick.

Edited February 7, 2016 by Snark

[SalehRam]

24 minutes ago, Snark said:

What are you feeding the nukes?

Nuclear engines use LIQUID FUEL ONLY.  They don't use oxidizer. If you're including oxidizer for them, you're crippling your craft with many tons of unusable dead weight.

The tanks around the Nukes are all containing LF only. I had to use these LFO tanks because the game becomes impossible to play at a certain part count, so I did not find anything to sacrifice other than these tanks...

I might even send a separate mission with mining module to permanently orbit Moho, as I am not planning to leave it easily once I break the wall of dV requirements

[Snark]

53 minutes ago, SalehRam said:

The tanks around the Nukes are all containing LF only. I had to use these LFO tanks because the game becomes impossible to play at a certain part count, so I did not find anything to sacrifice other than these tanks...

Good good. 

One of the major holes in the game is that there aren't any LF-only tanks that are rocket-friendly, other than the one dinky 2-ton one.  Everything else is hopelessly spaceplane-centric, which makes it awkward to build decent LV-N-powered rockets.  I really wish they'd fix that.

In any case:  if you'd like to have large LF-only tanks, you can use the big Mk3 airplane tanks.  Their form factor is roughly the same as the 3.75m rocket parts, so you could swap one of those in.  Or you could use a mod, like Porkjet's Stock Fuel Switch, to tweak them to be LF-only.

This is quite a pain point for me in my own games, since I use LV-N's a lot.  What I've done for my games is to mod up a few LF-tanks:  basically, just copy the 4-ton, 16-ton, and 32-ton LFO tanks, ModuleManager them to be LF-only, and gray out the textures enough to make them visually distinct from the LFO versions.  That gets the job done pretty well for me.

Edited February 7, 2016 by Snark

[Edax]

13 hours ago, Snark said:

Good good. 

One of the major holes in the game is that there aren't any LF-only tanks that are rocket-friendly, other than the one dinky 2-ton one.  Everything else is hopelessly spaceplane-centric, which makes it awkward to build decent LV-N-powered rockets.  I really wish they'd fix that.

In any case:  if you'd like to have large LF-only tanks, you can use the big Mk3 airplane tanks.  Their form factor is roughly the same as the 3.75m rocket parts, so you could swap one of those in.  Or you could use a mod, like Porkjet's Stock Fuel Switch, to tweak them to be LF-only.

This is quite a pain point for me in my own games, since I use LV-N's a lot.  What I've done for my games is to mod up a few LF-tanks:  basically, just copy the 4-ton, 16-ton, and 32-ton LFO tanks, ModuleManager them to be LF-only, and gray out the textures enough to make them visually distinct from the LFO versions.  That gets the job done pretty well for me.

Don't forget that that the large ore tank and large ISRU can function as a very large LF fuel tank.  The downside is that you can't actually use the ore during a burn or take-off, but the upside is that pound for pound, the large ore tank can store a very large amount of "potential" liquid fuel, more then the equivalent sized fuel tank (because ore is more dense.)  You just need to carry enough LF fuel tanks to complete a burn, then refine some more liquid fuel when your on the go.  Great for saving space when you need to use size 2 parts.

Edited February 8, 2016 by Edax

[Cornholio]

Porkjet's fuel switch is quite essential to the current version of the game. 

[Warzouz]

My solution for a Moho trip is not as refined as those presented before :

• I send a space station to Moho with a mining capacity
• The station depart with only useful fuel (not RCS, no oxydizer (interplanetary stage is mainly LVN)
• The station is supposed to arrive there nearly dry (it has only the fuel to go mining)
• The miner gets to the ground, mine an return to the station which will refine the fuel
• Science landing can start with a light lander
• Crew return home with a dedicated small ship
• The station stays in Moho orbit so it can be used again.

In my current design, Return vehicle and science lander  are part of a separate flight.

As I'm not too easy with multiple burns (especially for going to Moho), I prefer a medium TWR interplanetary stage at LKO.

(click to enlarge)

The station can refill the lander 4 times before needing to be refuels. Refueling the return vehicle drains a lot though...

(click to enlarge)

More here

[Gojira1000]

If you're willing to use ISRU you can brute-force it.

 

Edited February 9, 2016 by Gojira1000

[SalehRam]

New update:

Managed to get more dV out of the design thanks to your tips!

Spoiler

Got 15km/s dV now, and I really hope it is enough. I did a test run with a slightly different (less dV) design, and I managed to land on Moho, take off and dock with the passive half that I left there as a fuel tanker/storage, but could not burn back to Kerbin as I was low on fuel. This might get better with more dV for sure...

I would like to get some feedback about the shown burn times in KER window on top of the screen, are these normal? should they be shorter or this is what is expected from such a ship and destination?

I also got one more thing I never experienced before and I would like some advise on it:

Using LV-Ns will force me to do long burns, so how do I manage that while being in Kerbin SOI (transfer burn), and on Moho capture burn? because of the burn time, I will have to start the engines long before I reach the node, thus lowering my PE to the point where either I will crash, or get in atmosphere again...

Should I make several burns across several orbit cycles? or there is a method for that?

Thanks for the help

Edited February 9, 2016 by SalehRam

[Snark]

11 minutes ago, SalehRam said:

New update:

Managed to get more dV out of the design thanks to your tips!

Got 15km/s dV now, and I really hope it is enough. I did a test run with a slightly different (less dV) design, and I managed to land on Moho, take off and dock with the passive half that I left there as a fuel tanker/storage, but could not burn back to Kerbin as I was low on fuel. This might get better with more dV for sure...

Congratulations!

One question/suggestion-- I don't understand why you have two stages with nukes, there.  Looks like you have stage A with four nukes that will burn until it runs out of fuel, then you ditch it, then you have stage B with two nukes that uses its fuel.

That's inefficient, in that you're lugging around those two stage B engines as dead weight during the entire stage A burn.

Suggestion:

• Get rid of two of stage A's nuke engines-- specifically, the two that are directly below stage B's.
• Set up fuel lines so that stage B pulls fuel from stage A.
• Set up your staging so that stage A's engines and stage B's engines are activated together.

That way, you save six tons of dead weight (due to the discarded LV-N's), without sacrificing anything else such as TWR (since you could never run all six engines at the same time anyway).  When you activate the combined nuke stage, the four nukes are all running, and all pulling fuel out of stage A only.  When stage A runs out of fuel, you decouple it (along with its engines), leaving you with a full stage B that has two engines on it.

 

16 minutes ago, SalehRam said:

I would like to get some feedback about the shown burn times in KER window on top of the screen, are these normal? should they be shorter or this is what is expected from such a ship and destination?

I've never run KER itself, so I can't comment on that, but those burn times look typical for high-mass, low-TWR, nuke-powered interplanetary ejection burns.  So I'd say they look approximately right.

Yeah, they're slow.  Physics warp is your friend, there. 

 

21 minutes ago, SalehRam said:

Using LV-Ns will force me to do long burns, so how do I manage that while being in Kerbin SOI (transfer burn), and on Moho capture burn? because of the burn time, I will have to start the engines long before I reach the node, thus lowering my PE to the point where either I will crash, or get in atmosphere again...

Should I make several burns across several orbit cycles? or there is a method for that?

Yup, that's always an issue for those really low-TWR burns.

Typical approach is to split it across several burns, though there's a limit to that because you can only build up around 700-800 m/s of dV before you pretty much have to just go for the gusto and do the rest of your burn.

So a typical approach is:  do several burns, always in the same direction, always at Pe, one per orbit.  Each burn no longer than 3 minutes or so.

Each of those burns kicks your Ap up higher.  Eventually you'll get it up to the point where it's, say, halfway to the Mun, and there's not a lot of point in sending it much higher than that (lots of added orbit time for not lots of extra dV).

Then it's time for your final burn, which you have to do all in one go.  If it's a lot longer than 3 minutes (it probably is), you don't have to split it symmetrically across the node-- you can start it however long before the node you're comfortable with, and continue it past the node until it's done.

One thing you can do to help with that last burn, since it's likely to be so long, is don't try to stick pointed straight at the node the whole time.  When you start your burn, do it orbital prograde rather than node-prograde; this means your nose will be pointed somewhat higher than the node is.  You can stay like that until you're somewhat past Pe, then at some point you'll ease your orientation to point at the maneuver.

It's an art.  It's hard to "hit the bullseye" and is necessarily rather sloppy.  What I usually do, in the above technique, is to stop my final burn when I'm about 80% through its dV budget.  Then I delete the maneuver node and set up a new one a few minutes in front of me, re-zeroing it on my target, and then I do that burn holding straight on the maneuver node.  That helps me to adjust for any inaccuracy that crept into the first burn, without being too wasteful about it.  It does mean that I waste a little bit of Oberth benefit during those few minutes that I'm coasting up to the second node, but that's generally when I'm already at a high enough altitude anyway that the differential amount of Oberth benefit is pretty small.

[SalehRam]

Testing day!

I will have the latest design tested today in a flight, and I optimistic about it. Once I get it to work, and get the results, I will share the craft so other can use it and it might ease the days of someone like was tearing his hair because of Moho

On 2/9/2016 at 9:16 PM, Snark said:

Congratulations!

One question/suggestion-- I don't understand why you have two stages with nukes, there.  Looks like you have stage A with four nukes that will burn until it runs out of fuel, then you ditch it, then you have stage B with two nukes that uses its fuel.

That's inefficient, in that you're lugging around those two stage B engines as dead weight during the entire stage A burn.

Suggestion:

• Get rid of two of stage A's nuke engines-- specifically, the two that are directly below stage B's.
• Set up fuel lines so that stage B pulls fuel from stage A.
• Set up your staging so that stage A's engines and stage B's engines are activated together.

That way, you save six tons of dead weight (due to the discarded LV-N's), without sacrificing anything else such as TWR (since you could never run all six engines at the same time anyway).  When you activate the combined nuke stage, the four nukes are all running, and all pulling fuel out of stage A only.  When stage A runs out of fuel, you decouple it (along with its engines), leaving you with a full stage B that has two engines on it.

For the 2 LV-Ns stages, they are 2 separated stages, I tried to make the upper 2 engines use fuel from below tanks to increase TWR, but the total dV was also lowered, so I thought I stick with the shown design in the image...

All the previous work was on career mode to get a working craft. I just started new career and will put that design to use, however I am not sure how will be work in career specially with the game settings where money will matter now (that rocket costs about 730k credits), and the performance, as part count jumped to 400+...

But getting to 15km/s dV itself is a great achievement for me (even with many mission failures) as I never reached this limit before!

Also, worth to note that I only had Duna missions before as interplanetary missions, then I jumped to Moho after that... I'm sure this will make other planets much easier now after I had this fight with Moho...

I'll post back after today's test when I get back home (as I'm in work now )

Edited February 11, 2016 by SalehRam