[IMFD] James Cook HLV & IMFD Issue

[dkluempers]

I downloaded the James Cook & James Cook HLV spacecraft with the needed prequistes. I fired up the Lunar Base scenario and engaged the Prograde Auto-Pilot. It took quite awhile for the spacecraft to settle down and get oriented to the Prograde velocity vector. I understand it is a large ship with a great deal of mass so it will respond slower than a DGIV.

I fired up IMFD and plotted a course to the moon using Target Intercept and it dutifully plotted my course for me. When I use Auto Burn the RCS cannot seem to keep the velocity vector on track. As soon as it engages the main engines the bow of the ship swings heavily to the left (towards earth and soon the main engine cuts off and it take several minutes for the ship to reorient itself to the burn velocity vector and re-engage the main engines.

I found a thread that discusses the AB RCS Threshhold and AB Throttle Down values in the IFMD Configuration. I did not find any documentation on them but I could have missed it. I tried bumping them around remembering to keep AB RCS Threshhold below AB Throttle Down as suggested in the thread but had no luck. I am wondering if the spacecraft configuration needs to be changed to allow the RCS to have bit more power to allow IMFD to work properly. If so what parameters would I need to change. Here is the the current info on the James Cook (Just the first part):

[CONFIG]
MESHNAME="jamescook"
SIZE=100
CAMERA=(0,0,100)
EMPTY_MASS=350000
FUEL_MASS=2400000
MAIN_THRUST=18000000
RETRO_THRUST=12.3e4
ATTITUDE_THRUST=64e5
ISP=150000
TRIM=0.05
PMI=(15.5,22.1,7.7)
CW_Z_POS=0.09
CW_Z_NEG=0.09
CW_X=2.
CW_Y=1.4
CROSS_SECTION=(422,398,148)
COG=2.5
PITCH_MOMENT_SCALE=0.00005
BANK_MOMENT_SCALE=0.00005
ROT_DRAG=(0.43,0.43,0.29)

Thanks for any help you might be able to offer me on this. Orbiter has a steep learning curve and I have a great deal to learn.

DaveK

[liber]

Try changing...

ATTITUDE_THRUST=

...value.

[dkluempers]

I am reintalling from scratch to be sure I have not missed something. I discovered that when in the James Cook scenarios when I switch to another spacecraft Orbiter crashes. I can't seem to find an orbiter.log file to try an track down the problem. Once I have nailed that I will take shot a modifying ATTITUDE_THRUST.

THanks,

DaveK

---------- Post added at 07:17 PM ---------- Previous post was at 01:03 PM ----------

Well I bumped ATTITUDE_THRUST from 64e5 to 65e5, then 94e5, then 64e6 with no luck. I will keep at it.

Thanks again,

DaveK

---------- Post added at 10:06 PM ---------- Previous post was at 07:17 PM ----------

I tried using the Descartes and it worked just fine. I adjusted the ATTITUDE_THRUST to 64e7 on the James Cook and IMFD can now handle it. The Descartes uses ATTITUDE_THRUST of 95000. I can only guess as to the reason but perhaps the number and placement of the RCS thrusters could account for the need to have a large jump in thrust.

Anyway, thanks for the assistance - I learned a bit more about Orbiter today.

DaveK

[pattersoncr]

Descartes uses attachments for all the stuff attached to the main vessel rather than the docking ports. With attachments, Orbiter ignores the mass of the attached vessels. This makes attitude control much easier.

I vaguely remeber having issues with IMFD and James Cook in the past. IMFD didn't account for the mass of the docked vessels when computing how long to burn for and so my burns ended up too short. This was with an older version of IMFD and I believe it was corrected on this version.

[Tommy]

Look into the new IMFD manual, it has tips on how to adjust IMFD to work better with ships that rotate slowly.