Sign in to follow this  
Avo4Dayz

Mechjeb atmospheric landings

Recommended Posts

I have been making some Space X styled re-useable rockets using various parts. Some are just stock with Kerbal reusability legs or as much as the full SapceY set up. But every time I try to get MechJeb to do a powered landing it consistently overshoots the Pad at KSP by the same amount (talking like 20km, not sub 100m). It's almost as if it isn't factoring drag or something. I mean it shows how much drag etc, but I can't for the life of me work out why it is consistently over shooting.... They at least come down with adequate speed to land properly...in the water

Any experts out there have a better understanding of what's happening?

Share this post


Link to post
Share on other sites

Overshooting should happen if the vessel loses drag, such as jettisoning the inflatable heatshield or airbrakes being destroyed or undeployed.  Anything that would cause the vessel to be smaller can cause this.  Undershooting is the main problem i have, that's what happens when drag isn't correctly factored in such as inflating the inflatable heatshield.

Share this post


Link to post
Share on other sites

Interesting points, however no changes for me.... maybe I'll add airbrakes and see if it uses them to advantage.

Share this post


Link to post
Share on other sites

The best way to do powered landings IMO is to use the Trajectories mod. The mechjeb one usually misses the target and probably doesn't take into account the atmospheric model very well. 

Share this post


Link to post
Share on other sites

I've found that if my ships have KRE grid fins, I need to deploy them before pressing the Land at Target button. It seems that MechJeb needs to have all aero devices in deployed position in order to make an accurate landing calc. MechJeb will usually land the ship a little short, so I manually open/close the grid fins to adjust the landing point.

Share this post


Link to post
Share on other sites

I agree that trajectories is the more accurate for non-powered targeting. Either way they need deployed and correctly faced craft.

Machine aided I find that splitting the descent into three phases for powered landings is the best way to handle regime changes.  Use trajectories/MJ to plot a somewhat overshooting path for retro firing.  As you begin your re-entry probably with fins and airbrakes stowed (deployed aero surfaces work too), make corrections to bring your overshoot to >10km, at this point Mechjebs landing prediction is more helpful.  After peak heating deploy the brakes and wait to kill your overshoot as you get to 10km or so.  Having a marker craft at KSC targeted is very helpful, one at each end of the runway can give you great night assist too. (I call mine *KSC East*, *KSC West* ).  Final phase you have aimed, hit [land somewhere].  MJ crashes you into ground, reload and try again, voila landed.

Or I have an easy manual method for powered  LKO equitorial de-orbit.   As you fly over the beach on the side opposite KSC, drop velocity to 1900, as you pass over the mountain range drop it to 1500, then halve the curve a few times.  That is to say, reduce your overshoot to your current arc distance to KSC, do that 3 times and your right on top of KSC, light maneuvering, open chutes or powered land to at least 97% recovery.

Share this post


Link to post
Share on other sites
This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this