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John Kermin

Plz Help me with Minmus ;(

Question

John Kermin    1
Posted (edited)

So i have been playing KSP for Years on and off and i have landed on Minmus a lot. But now that i have started again i can't seem to get into Minmus Orbit. And i am not sure what i am doing wrong.

So it goes like this:

1. Start from Kerbin

2. Reach 75 km and then Circularize.

3. Use Mechjeb to "Hohmann Transfer to Target" to Minmus, about 950 m/s seems fine.

4. Wait till i am past Mun and then use Mechjeb "Fine Tune closest approach to Target" to get to 10km around Minmus.

So far so good (there are probably some things already i could have done for the sake of efficiency though) but now this happens:

I tell Mechjeb to circularize at next periapsis and he tells me some ridiculous number like 2800 m/s whereas it should take only 160 according to http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet

My only guess is that i do something very wrong from the beginning. How do i do this correctly ?

(Also, yes i know Mechjeb is frowned upon. But apparently i am even to incompetent to use Mechjeb)

P.S: I am using the newest Versions of KSP and Mechjeb.

Thank you for your help!

Edited by John Kermin

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bewing    1274

Or you can just do it the old-fashioned way. Wait until you are at your Minmus Pe. Click SAS. Click "retrograde". Hit Z. When your orbit is low enough to satisfy you, hit X.

 

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Freshmeat    264

I am not a MechJeb user myself, so take this with a grain of salt. To answer your question, my guess would be that MJ tries to circularize with respect to Kerbin, not Minmus. Do you give the command in Kerbins SOI, or Minmus'? Again, I have no actual knowledge of MJ, but it might be worth a shot until someone shows up with a real answer.

Don't worry. MechJeb is like any other mod, use it if it is more fun to you. I used to go total godmode in DooM2.

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Spricigo    437
25 minutes ago, Brent Kerman said:

If you want to learn how to do simple (or complex) things without Mechjeb, I can recommend watching Scott Manley. He has some excellent tutorials.

Not only SM, there is other good tutorials (video and also text/pictures) around. Just be careful with outdated info.

If nothing else, is usefull to understand why MJ do what MJ do.

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Brent Kerman    236
Posted (edited)

The newest version of Mechjeb is not compatible with the newest version of KSP. You have to use 1.2.2. Mods very rarely work in prereleases.

But it sounds like its working better for you than it did for me.

Edited by Brent Kerman

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Brent Kerman    236

If you are actually using 1.2.2, which I almost suspect, as Mechjeb crashes 1.2.9 for me, then @Freshmeat is correct, Mechjeb is trying to circularize at Kerbin if you are still it its SOI.

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Spricigo    437

 

No problem in using MJ, but is always good to have a basic understanding of the orbital mechanics. So you can spot that kind of misbehaviour and know how to solve it.

I secound the suggestion of Bewing, doing the capture maneuver manually at Minmus periapsis. Also a good idea to do a mid-course correction maneuver at kerbin SoI to get into Minmus orbit with a good maneuver for what you want to do.

 

3 hours ago, John Kermin said:

But apparently i am even to incompetent to use Mechjeb

Who don't know can learn, who does know can teach. Don't be afraid to ask for help if you are in trouble and by all means don't just assume you are incompetent.

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Brent Kerman    236

If you want to learn how to do simple (or complex) things without Mechjeb, I can recommend watching Scott Manley. He has some excellent tutorials.

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mattssheep4    35
3 minutes ago, Brent Kerman said:

If you want to learn how to do simple (or complex) things without Mechjeb, I can recommend watching Scott Manley. He has some excellent tutorials.

Seconded.

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Daveroski    319

Mechjeb likes you to match planes with Mimnus before you do the "Hohmann Transfer to Target"

 

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I have been using MechJeb for a year.

It is very usefull and I enjoy it very much.

My approach to reach Minmus (Flats) is:

- Low Kerbin ecuatorial orbit (same as you mention)

- Hoffman transfer (same as you mention)

- As soon as my burn is complete I try Intercept target at a fixed time trying to minimize delta v with 40 to 54 hours. (To my humble understanding of orbital mechanics the difference depends upon the part of the orbit Minmus)

- Time warp to SOI Change.

- Once in Minmus SOI change inclination at a fixed time to 0,  (If you are going to another spot then another inclination would seem more convenient)

- Change periapsis at a fixed time to something between 15 and 30 Km depending upon TWR (the highest orbit for the lower TWR)

- Circularize at periapsis

- Launch Guidance

- Pick target on the intended Flat

- F5

- Land at target (controllig RCS does not desactivate for no apparent reason)

- Cross my fingers in anxiety

 

Best luck!

Ignacio

 

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Spricigo    437
31 minutes ago, Ignacio Urteaga said:

- Cross my fingers in anxiety

Doing the landing manually that is the step I feel most difficult to do.

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Starman4308    701
1 hour ago, Daveroski said:

Mechjeb likes you to match planes with Mimnus before you do the "Hohmann Transfer to Target"

 

It'll do the Hohmann transfer even if your inclination is off; it'll just miss Minmus, requiring a correction maneuver later.

To the OP: A, wait until you're in the correct SOI to plot a burn, and a hint. Go into the tracking station, and wait until KSC is directly beneath Minmus's orbital track. Then, launch six degrees north or south of east, and you'll be in approximately the right orbital plane for a trivial amount of delta V.

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PrathamK    6

A common MJ effect, it circulate around parent Body, use manual Maneuver, or wrap till you are in Minimus SOI and plan maneuvers, I too very anex when, i was about to lose dunatian PerisApsis. 

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Kryxal    142

Barring little quibbles about your transfer (such as using match plane after the hohmann transfer or some such ... or for that matter, just fine-tune earlier, MJ is willing to wait!) you just need to wait till you cross the SoI to set up your orbital insertion burn with MJ's maneuver planner.

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juvilado    94

MJ for Minmus? Really? 

Mun and Minmus are easy to reach even by eyeball! 

Just make a man node at kerbin orbit with prograde until you reach Minmus orbit. :)

And play with the timing of the node to make the maneouver cope with minmus SOI

 

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You are right, Juvilado!

But,

Several of us (me included) use MJ for each maneuver unless we are dissatisfied with its performance.

I agree it is somewhat easy to reach Minmus by hand set maneuver nodes.

I confess I use MJ on a regular basis just to work a little bit less.

Ignacio 

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Ty Tan Tu    231

For those that are interested, here is the link to the site Jenkins maintains with the latest MechJeb2 dev betas. Right now the most recent stable build is 2.6.0.0-698.Remember these are betas. :) (how that is a smiley face has always escaped me. But when in Rome, do as the Kerbins.)

https://ksp.sarbian.com/jenkins/job/MechJeb2-Dev/

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On 2017-5-17 at 3:53 PM, John Kermin said:

So i have been playing KSP for Years on and off and i have landed on Minmus a lot. But now that i have started again i can't seem to get into Minmus Orbit. And i am not sure what i am doing wrong.

So it goes like this:

1. Start from Kerbin

2. Reach 75 km and then Circularize.

3. Use Mechjeb to "Hohmann Transfer to Target" to Minmus, about 950 m/s seems fine.

4. Wait till i am past Mun and then use Mechjeb "Fine Tune closest approach to Target" to get to 10km around Minmus.

So far so good (there are probably some things already i could have done for the sake of efficiency though) but now this happens:

I tell Mechjeb to circularize at next periapsis and he tells me some ridiculous number like 2800 m/s whereas it should take only 160 according to http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet

My only guess is that i do something very wrong from the beginning. How do i do this correctly ?

(Also, yes i know Mechjeb is frowned upon. But apparently i am even to incompetent to use Mechjeb)

P.S: I am using the newest Versions of KSP and Mechjeb.

Thank you for your help!

Hi Like you i to have come back after a year off, I got Minmus straight away, I remember Scott M saying when your on the launch pad go to map fast forward, so Minmus is at 4oclock, sun at top of screen, then launch. dont know about mechjeb, but starting time Must be important.  hope this helps, dont want to teach you to suck eggs, iam sure your a capable astronaut.  good luck. 

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Starman4308    701
20 hours ago, juvilado said:

MJ for Minmus? Really? 

Not everybody picks up the game quickly. Heck, I use it to plot the actual Hohmann transfer to Minmus; while I could do it manually, it would take me a couple minutes of fiddling around with the maneuver node to get it just right, and it wouldn't be as precise as what MJ plots.

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Spricigo    437
21 hours ago, juvilado said:

MJ for Minmus? Really? 

Mun and Minmus are easy to reach even by eyeball!

Moot point.  OP never asked if MJ was necessary or how to do it without MJ.

As far as I'm concerned: he don't care how to do manually , so I shouldn't care also.  And if he change his mind and ask for help with manually plotting the trajectory I expected better advice than "just eyeball because is easy" 

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