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Old 12-14-2014, 08:04 PM   #1
Thundersnook
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Default Accuracy of Base Approach

Hello Masters of the Universe!

I have a general Question with IMFD 5.5:

It happens to me, that the Base-Approach Part of IMFD is somewhat of inaccurate compared to the map-Part of IMFD. I uploaded a Screenshot for better understanding.

I've completed my course correction-burn for a (hopefully) nice reentry-path for some aerobreaking reentry from Mars. Looking at the Base-Approach Part of IMFD im pretty well on course with some very minor dV-variance. When looking on the Map Part of IMFD I'm almost hitting the ground with my periapsis. When using the standard Orbit-MFD the Periapsis is almost the same as with the Map-Part of IMFD, so I consider the Base-Approach calculation "wrong". (75k is my desired altitude with Base-Aproach ... map says around 5k altitude)

Is there a different approach in terms of calculation with the Base-Approach part which causes these huge differences or is there some kind of setting within the MFD I've overseen?

I already watched the great Video-Series of Dimitris and David for IMFD 5 and Ive learned a lot from that

Therefore I already use the suggested config-settings in Terms of Legs/Tolerances to get good results with the Map-Part.

But is there any other setting I've been overseeing? I know that the base approach works not very well when your not in the SOI of your target Planet but as you can see in my example I'm well inside the SOI

Any suggestion?

Thanks very much!

Edit: My IMFD-Config:

Code:
// Configuration file for BaseSyncMFD, I-MFD, AeroBrakeMFD

Color_01 0x0000DD00      // Current Ship orbit, Source Orbit [Bright green]
Color_02 0x00008800      // Additional Map lines [Dark green]
Color_03 0x0000BB00      // Base Text color [green]
Color_04 0x0000EEAA      // Hilighted text 
Color_05 0x0000CCFF      // Target orbit, Some Warnings [Orange]
Color_06 0x00EEEEEE      // Selected Item [White]
Color_07 0x00FF5555      // Planned trajectory [Blue]
Color_08 0x00666666      // Planets [Dark Grey]
Color_09 0x000000DD      // Warning lights [Red]
Color_10 0x00EEEEEE      // [White]
Color_11 0x00999999     // Headlines, Some planets [Grey]
Color_12 0x0000BB00    // Adjustable Items
  

// Multibody predictor configurations
Rectification 0.005    // Rectification constant for trajectory engine
NonSpherical 2          // Use Non spherical gravity on low orbit prediction in Map Program, 0=Disabled, 1=Auto, 2=Always ON
LegSize 1            // Legsize factor used in Multibody predictor
LegsPerFrame 64        // Number of legs calculated each time step
Celbody 1            // Use Orbiter's Celbody Interface to improve accuracy of the map  (1=On, 0=Off)
Adaptive 0            // Use Adaptive step-size control (1=On, 0=Off)
AdapTol 4            // Error tolerance (Lower value = higher accuracy)
Integrator 0        // Default Integrator 0=RK5(6), 1=RK6(7), 2=RK7(8)    


// General Configurations
RefAltitude 120e3        // Reference altitude for atmospheric entry interface
ReEntryAngle 6.2        // Default ReEntry in degrees 
DateFormat 0        // Default Date Format 0=MJD, 1=GET
UseRegres 1            // Use Nodel Regression Estimation (1=On, 0=Off)
IgnState 1            // Use numerical ignition state propagation
FastUpdate 1        // Use Fast Update of MFD Screens    

// Key Setup
BaseSyncKey 0x30        // StartUp key used by BaseSyncMFD
IMFDKey 0x17            // StartUp key used by IMFD
RotationKey1 0x26       // Rotation Key "L"
RotationKey2 0x2C        // Rotation Key "Z"

    
// Auto-burn options
AB_Rate 10.0        // AutoBurn MaxRate (degrees/s)
AB_RCS_Th 2.0        // RCS Level Treshold m/s
AB_Thr_Th 20.0        // Throttle Down Level Treshold m/s
Attached Thumbnails
IMFD55Accuracy.jpg  

Last edited by Thundersnook; 12-14-2014 at 08:12 PM.
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Old 12-15-2014, 01:18 AM   #2
boogabooga
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Please post scn. and I will try to reproduce. What spacecraft is that?
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Old 12-15-2014, 05:01 AM   #3
Thundersnook
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Hey boogabooga,

Its the XR2 Ravenstar

Greetings and thanks in advance!
Attached Files
File Type: scn Approach from Mars.scn (8.3 KB, 0 views)
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Old 12-15-2014, 09:09 AM   #4
BrianJ
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Hello,
I think you may have misunderstood the IMFD Base Approach "Target" parameter "Alt."
This is not your final periapsis altitude. It is your "start of reentry" altitude.
So, with your IMFD Base Approach settings, you will arrive at 75km alt. when you are 90deg away from your target, with your trajectory 6.2deg below horizontal.
Hope this helps :-)
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Old 12-15-2014, 09:23 AM   #5
Thundersnook
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Quote:
Originally Posted by BrianJ View Post
 Hello,
I think you may have misunderstood the IMFD Base Approach "Target" parameter "Alt."
This is not your final periapsis altitude. It is your "start of reentry" altitude.
So, with your IMFD Base Approach settings, you will arrive at 75km alt. when you are 90deg away from your target, with your trajectory 6.2deg below horizontal.
Hope this helps :-)
Indeed! That makes sense, as my final PeA is lower because of the Reentry angle ... Just for the understanding: does that mean that my Reentry-Alt is equal to my PeA when I set my reentry-Angle (trajectory) to 0?

Cant check it out right now as I'm at work ... *cough* but will try that when I'm home^^

But yeah that makes sense, I will try with the "standard" 120km Interface altitude which should lead my vessel not to deep in the atmosphere to burn up (I hope^^ .. had to do manuall corrections during inverted reentry anyways...) ... I will also experiment with the Anticipation, If I can go closer to the Base when returning from interplanitary journeys ... at the moment 90 works well, but I felt, that I can go a lot closer ... so maybe 120k/6.2/90 works, as this will leads my vessel closer to the Base compared to 70k/6.2/90 ... If I understand correctly :D

Last edited by Thundersnook; 12-15-2014 at 09:41 AM.
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Old 12-15-2014, 09:37 AM   #6
BrianJ
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"does that mean that my Reentry-Alt is equal to my PeA when I set my reentry-Angle (trajectory) to 0?"

I think that is correct(if you are approaching from a higher orbit). If you set your ReA to 0, you will arrive at 75km alt., 90 away from your target, with a horizontal trajectory.
(ignoring atmospheric drag).
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