does anybody else have to babysit mechjeb? and mun landing question.

[putnamto]

ive noticed that if i tell mechjeb to execute a burn, sometimes regardless of how long the burn is mechjeb just keeps going until im out of dv, i feel like i have to babysit him.

like just last night i tried to land on the mun, i set up my maneuver and it had an est. burn of four minutes and a i had a five hour time frame to get to the mun, so i told mechjeb to start the burn, went and got dinner and came back to find my ship out in the middle of god only knows where.  ive also noticed that the dotted orbits that show up after i set my node arent exactly where i would end up after using mechjeb, 90 percent of the time its spot on, other times its waaaaay off. like not even close to a munar orbit off.

another example i just watched while typing this, my projected mun pass said i would have a pe around the edge of the soi, i told mechjeb to execute, and now my orbit line is a crash course through the mun.
am i just trusting mechjeb to much? is it because im typing while he's burning the manuever?

and about the mun landing. i use smart A.S.S. to get rid of my horizontal speed, then i slart my vertical descent, but when i get anwhere from 10km-2km my retrograde marker shoots completely equitarial and my ship starts moving horizontally faster and faster, by the time ive corrected the sideways motion im either A crashed, or B gained enough vertical velocity that im moving away from the mun again just to have it happen again. 

i know i post alot of questions on this board, and i usually swear that i hate it, but i keep coming back, i guess i feel like im learning something.

oh another quick question, when making a kerbin orbit from launch, when im horizontal and mostly out of the atmosphere i hit my thrusters to circularize and sometimes my ap will start to get farther away, sometimes in will start to get closer, i know having an ap 30s to 1minute away is ideal and i usually try to keep in their but sometimes theirs just nothing i can do about it. what am i not understanding?(well alot of things really)

[ARS]

Using MechJeb to fully taking control of your mission is generally not a smart move, since it usually includes sensitive operations that could lead in mission failure if things going not the way you are intended. I'm using MechJeb, but only when the margin of error that could lead to mission failure is within tolerable limit, such as while in orbit, interplanetary transfer, etc (My rule is NEVER USE MechJeb while inside atmosphere or suborbital trajectory). Yes, I had to babysit MechJeb to ensure that my mission goes smoothly, I only manually override the control when there's operation that must be done ABSOLUTELY by me. For example: A common usage for MechJeb for me is sending station parts. During launch, ascent and orbit, the rocket is fully under my control. Then after the stable orbit achieved, I let MechJeb to take over control for rendezvous, but I watch the whole process to ensure that things goes smoothly and to make sure MechJeb did't use too much fuel than necessary. Once the craft and the station is within close proximity and close enough for docking, I turned MechJeb off and manually maneuver the station parts for docking since those operation is the one where I cannot afford to have anything going wrong

In short, use MechJeb for something that you cannot do, and don't use it for something that you can do

Edited March 24, 2018 by ARS

[Gargamel]

34 minutes ago, ARS said:

In short, use MechJeb for something that you cannot do, and don't use it for something that you can do

I kind of disagree with this.

I routinely use it for launch, as it has become cumbersome to do this repeatedly.  I can easily do it, but why not let MJ do it for me? If it fails to launch properly, it's usually due to my design rather than a MJ error.  First launches of new craft I'll observe, in particular to the launch angle for subsequent flights of identical craft to the same altitude.  That way I can send up repeated ships to the same station, usually within 10km upon completion of the circularization burn.  When I know MJ can handle a launch, I will frequently tab over to another window, but listen for any odds sounds from the speakers. 

I let MJ dock for me, but sometimes it does go wonky.  I have no problem stepping in and taking over the reins if needed.  Some craft just don't fly well with MJ's RCS algorythms.  But again, it's a routine cumbersome task that I let MJ do for me. 

Rendezvous on the other hand, I'm not that good at, so I let MJ do it.  The margin of error in this case is much lower as MJ will do it's best to stop the prescribed offset from the target.  I should do it more for the practice, but oh well. 

Landings are the only thing I really babysit MJ.  Sometimes, things just go sideways with MJ's landing algorythm, literally.  But by then it's usually too late to save it, so I have taken to quicksaving before every landing attempt.  

 

1 hour ago, putnamto said:

another example i just watched while typing this, my projected mun pass said i would have a pe around the edge of the soi, i told mechjeb to execute, and now my orbit line is a crash course through the mun.
am i just trusting mechjeb to much? is it because im typing while he's burning the manuever?

Learn what MJ can and can't do.

For transfers, let it do the burn for you.  Then when you switch SOI's, immediately change your inclination to the desired one, and then the periapsis.   As long as MJ sets you up with an encounter, don't worry about it, you can adjust things later.  Don't be afraid to add your own nodes into the flight plan if necessary.  Learn to do so to add small tweaks. 

 

Never change anything during a burn.  It's usually ok, but some bad data at the wrong time can have burn in a completely wrong direction. 

 

1 hour ago, putnamto said:

and about the mun landing. i use smart A.S.S. to get rid of my horizontal speed, then i slart my vertical descent, but when i get anwhere from 10km-2km my retrograde marker shoots completely equitarial and my ship starts moving horizontally faster and faster, by the time ive corrected the sideways motion im either A crashed, or B gained enough vertical velocity that im moving away from the mun again just to have it happen again. 

If you aren't going to use the landing autopilot, then just use the SAS.  But if you want to use MJ, then use the autopilot to do the landing.  There's plenty of good tutorials here on how to land, those may help you out.  There's nothing wrong with using Smart ASS, but the SAS buttons are easier to reach IMO. 

[Foxster]

MJ used to do a better job of just about everything but over time it has got more flakey. Perhaps due to the different contributors and the code churn. But a biggy was when the fuel routing changed and now MJ can get confused, especially if you don't have a straightforward rocket with fuel ducts. 

Most of the time it's a big help but it's no longer a good idea to leave it alone as it will do things like crash a simple craft into the Mun, plot a maneuver node with 500,000 dV for no apparent reason, miscalculate dV, etc. 

One thing to remember though is that MJ might not understand any mods you have installed. So before blaming MJ for something, try it without other mods installed. 

 

[putnamto]

im playing carreer so things like landing and taking off cant be controlled(atleast completely controlled) by mechjeb.

i do also use mechjeb for my Rendevous and most routine things like a mun transfer, ive done enough of them in the past two days because i strand a kerbal or crash and forget to quicksave before the burn.

as for the landing, i was trying to do that withought sas due to my mission structure and a slight, very slight, EXTREMELY slight oversight on the craft(probe cores go ABOVE the decoupler)

[Cpt Kerbalkrunch]

3 hours ago, putnamto said:

and about the mun landing. i use smart A.S.S. to get rid of my horizontal speed, then i slart my vertical descent, but when i get anwhere from 10km-2km my retrograde marker shoots completely equitarial and my ship starts moving horizontally faster and faster, by the time ive corrected the sideways motion im either A crashed, or B gained enough vertical velocity that im moving away from the mun again just to have it happen again. 

i know i post alot of questions on this board, and i usually swear that i hate it, but i keep coming back, i guess i feel like im learning something.

oh another quick question, when making a kerbin orbit from launch, when im horizontal and mostly out of the atmosphere i hit my thrusters to circularize and sometimes my ap will start to get farther away, sometimes in will start to get closer, i know having an ap 30s to 1minute away is ideal and i usually try to keep in their but sometimes theirs just nothing i can do about it. what am i not understanding?(well alot of things really)

I don't know anything about Mechjeb, so I can't be of any help there, but what you said about horizontal movement sounds like what happens when you come in for a landing with your Navball still set to "orbit" instead of "surface". I don't know if that's your issue or it really is a mod causing it, but it used to happen to me often on my early Mun landings. I wouldn't notice until I was near the ground that I was actually moving sideways. I would panic and end up crashing. Took awhile to get the hang of it. As I said, don't know if that's what's happening, just something to look out for.

For your launch, once you're horizontal, it depends on your speed and the power of your vessel. If you're going fast enough, and your ship is powerful enough, your Ap will keep rising as you burn because the curvature of Kerbin is basically making the ground fall away from you, while you continue straight into space. Sometimes you didn't build up enough speed during launch, and sometimes the stage you're using doesn't have enough oomph to keep rising when horizontal. You can raise your nose a bit to counter this, or start your circulation burn a little earlier. Then, of course, there's the launch that can be fine-tuned and the ship itself can pretty much always be optimized a bit more. Not sure if a design is ever really "done".

Anyway, hope all goes well.

[DerekL1963]

On 3/24/2018 at 1:10 AM, putnamto said:

ive noticed that if i tell mechjeb to execute a burn, sometimes regardless of how long the burn is mechjeb just keeps going until im out of dv, i feel like i have to babysit him.

Yes, MechJeb sometimes flakes out, the landing API being particularly buggy.  The best bet is to remember to quick save before executing a burn.  Heck, even when doing things manually it's a good idea to quick save before doing them, as the game itself sometimes flakes out. 

[Laie]

On 24.3.2018 at 9:10 AM, putnamto said:

a) ive noticed that if i tell mechjeb to execute a burn, sometimes regardless of how long the burn is mechjeb just keeps going until im out of dv, i feel like i have to babysit him.

b) like just last night i tried to land on the mun, i set up my maneuver and it had an est. burn of four minutes and a i had a five hour time frame to get to the mun, so i told mechjeb to start the burn, went and got dinner and came back to find my ship out in the middle of god only knows where.  ive also noticed that the dotted orbits that show up after i set my node arent exactly where i would end up after using mechjeb, 90 percent of the time its spot on, other times its waaaaay off. like not even close to a munar orbit off.

c) another example i just watched while typing this, my projected mun pass said i would have a pe around the edge of the soi, i told mechjeb to execute, and now my orbit line is a crash course through the mun.
am i just trusting mechjeb to much? is it because im typing while he's burning the manuever?

d) and about the mun landing. i use smart A.S.S. to get rid of my horizontal speed, then i slart my vertical descent, but when i get anwhere from 10km-2km my retrograde marker shoots completely equitarial and my ship starts moving horizontally faster and faster, by the time ive corrected the sideways motion im either A crashed, or B gained enough vertical velocity that im moving away from the mun again just to have it happen again.

letters added for easier answering, but first off: babysitting MJ isn't strictly necessary, but keeping half an eye on things is a good idea regardless.

a) how? Going in circles towards the end of the burn, perhaps?

b) I never tried to execute a maneuver before I was in the same SOI as the maneuver. Strange things happen at SOI transition, which might well upset MJ.

c) tough one to explain. A tiny bit of impulse near Kerbin easily makes for a 50km difference in munar PE. That's well within the +-0.1m/s precsion of default maneuver execution. However, missing the mun completely is a pretty large error... can it be that you had very low thrust and needed 10 minutes to do the burn?

d) it sounds as if you brake too hard, too early, and start going up again. SmartASS does as it's told: you want retrograde, and when you're going up, "retrograde" means pointing down.

[putnamto]

a. i dont realy know what its doing with the A situation, it might be user error, most of the time say if the node is prograde or whatever, he will continue going prograde long after the node, and continue doing so till im out of dv. this usually happens if i have to stage in the middle of the burn.

B. sorry i didnt explain this correctly, this was the burn in kerbin orbit that would set my mun trajectory, i would start the burn and get distracted to come back and find that its nowhere near what the burn said it would be, mechjeb is more than likely doing what he does in A

C. i dont know, ill get more info if/when it happens again.

D. another failure of communication on my part. i only use smart ass when im over 50-100km over the surface to get rid of my horizontal speed(according to KER) then i turn off smart A.S.S then when im coming down vertically im doing a small steady burn to continuously lower my vertical speed, and doing big thrusts occasionally when i feel like im going to fast. retro will stay on top of my navball until my height/vertical speed is roughly around 10km-15km/2ms-25ms but then any kind of throttle in my prograde shoots my retro marker horizontally and my ship starts to drift violently in a seemingly random direction.

the only way ive managed to land (referring to D) is to have my descent going faster than i think it should and doing quick full thrusts at lest then 100m off the surface, and this works maybe 10% of the time, usually tends to touching and doing a cartwheel.

[Kryxal]

Are you using orbit retrograde or SVEL-?  The second (on the Surface tab) is what you want once you're well suborbital, and as long as you keep a couple of m/s on the craft should lead to a clean landing.  Alternatively, you can align to UP once you're almost stopped horizontally.  By the way, see about bringing up the time to suicide burn, and don't let it go under 20 seconds for the initial part of the burn, and pitch up if it's dropping too much because you're scrubbing horizontal speed.  Once you're near-vertical, you can let it get a lot closer to 0.

[Laie]

21 hours ago, putnamto said:

until my height/vertical speed is roughly around 10km-15km/2ms-25ms but then any kind of throttle

Is your navball still showing orbital velocity, perhaps? Only explanation I can think of, sorry.

BTW, descending from 10km @25m/s takes a looong time (400 seconds to be precise). MJ also has a "Suicide Burn" timer somewhere, I'd suggest you try to use it.

Edited March 26, 2018 by Laie

[magnemoe]

On 24.3.2018 at 10:13 AM, Gargamel said:

I kind of disagree with this.

I routinely use it for launch, as it has become cumbersome to do this repeatedly.  I can easily do it, but why not let MJ do it for me? If it fails to launch properly, it's usually due to my design rather than a MJ error.  First launches of new craft I'll observe, in particular to the launch angle for subsequent flights of identical craft to the same altitude.  That way I can send up repeated ships to the same station, usually within 10km upon completion of the circularization burn.  When I know MJ can handle a launch, I will frequently tab over to another window, but listen for any odds sounds from the speakers. 

I let MJ dock for me, but sometimes it does go wonky.  I have no problem stepping in and taking over the reins if needed.  Some craft just don't fly well with MJ's RCS algorythms.  But again, it's a routine cumbersome task that I let MJ do for me. 

Rendezvous on the other hand, I'm not that good at, so I let MJ do it.  The margin of error in this case is much lower as MJ will do it's best to stop the prescribed offset from the target.  I should do it more for the practice, but oh well. 

Landings are the only thing I really babysit MJ.  Sometimes, things just go sideways with MJ's landing algorythm, literally.  But by then it's usually too late to save it, so I have taken to quicksaving before every landing attempt.  

Learn what MJ can and can't do.

For transfers, let it do the burn for you.  Then when you switch SOI's, immediately change your inclination to the desired one, and then the periapsis.   As long as MJ sets you up with an encounter, don't worry about it, you can adjust things later.  Don't be afraid to add your own nodes into the flight plan if necessary.  Learn to do so to add small tweaks. 

Never change anything during a burn.  It's usually ok, but some bad data at the wrong time can have burn in a completely wrong direction. 

If you aren't going to use the landing autopilot, then just use the SAS.  But if you want to use MJ, then use the autopilot to do the landing.  There's plenty of good tutorials here on how to land, those may help you out.  There's nothing wrong with using Smart ASS, but the SAS buttons are easier to reach IMO. 

Same here, launch is routine and MJ tend to fly better than me, MJ will also let you get the same result each time letting you optimize an common design:
Very low TWR upper stages will confuse mechjeb, they can usualy be done manual by lifting your nose above prograde marker this let you walk the Ap ahead of you and you will end up not having an real circulation burn, just an adjustment one as Pe might end up outside of atmosphere. 

Landing MJ is at least more accurate, it does not like high twr crashing stages like starting the landing burn on your transfer stage. 
On Mun its nice, on Minmus its has an 100-300 meter error margin, solution is to turn it off before it kills horizontal velocity  as it tend to mess up, switch it back to show landing indications and do an manual adjustment, I want down to 10-30 meter for kas refueling, I then let mechjeb land. 

Going to Mun I let it plot an course, then reduce it a bit so I get an nice Pe, usually a bit high as I do an rcs adjustment afterward. 
For minmus the same, but I tend to add 20 m/s dv to cut travel time to 3-4 days. Then move marker to get an good intercept again. 

Rendezvous i set up manual, let mechjeb do the burn and then let it adjust distance to target and match speed. 
Docking large ships I prefer mechjeb to handle because of lag. 

Just had one ship mechjeb could not handle at all, but SAS also had lots of problems with it. 

[DerekL1963]

12 minutes ago, magnemoe said:

Landing MJ is at least more accurate, it does not like high twr crashing stages like starting the landing burn on your transfer stage. 

I've had success using a crasher stage for the deorbit burn, then turning off the autopilot long enough to re-orient Normal+ to jettison it, then re-enabling the autopilot.  So long as the difference in TWR isn't too great, I've successfully ridden a crasher as low as 20km before jettisoning it.  The lower you go, the faster you have to be to re-orient to a no-reconcontact jettison orientation and then re-enable the autopilot though.  It took some practice to get it right.