Flight Question Slingshot problem

sorindafabico

sorindafabico

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I've already done a couple of slingshots around Mars, Jupiter and Titan, so, I thought I had understood the basic concepts of flybys.

I'm trying to do a tour around jovian moons using slingshots to save fuel, but something apparently weird is happening: it doesn't matter if I pass close to a moon being prograde (RInc < 1) or retrograde (RInc > 179), my orbit's semi-major axis decreases. I thought it would increase if my RInc was prograde.

I've tried this around Io (prograde and retrograde) and Europa (prograde). Am I doing something wrong?


Here's a scenario:

BEGIN_DESC
Orbiter saved state at T = 686672
END_DESC

BEGIN_ENVIRONMENT
System Sol
Date MJD 65702.0146309579
END_ENVIRONMENT

BEGIN_FOCUS
Ship GLRescue
END_FOCUS

BEGIN_CAMERA
TARGET GLRescue
MODE Cockpit
FOV 50.00
END_CAMERA

BEGIN_HUD
TYPE Orbit
REF AUTO
END_HUD

BEGIN_MFD Left
TYPE User
MODE Interplanetary
Scenario Old2
MapMFD V5
Reference Auto
Target Io
Center Io
Data 1 1 1.193423013922025e-007 0 0 1 0 0 1 0 0 0
MassLimit 1e+020
CMode 1
Config 1 1 1 1 0 0
ExtMode 0
Periapis Io
END
CorMFD V4
Reference Jupiter
Target Io
Source GLRescue
ActiveProg 1 1
DataA 1 3 0 1 0 0
DataB 38.443359375 1 65702.01462572224 0 0 0.3024329862586788 0 65702.90667993808 0
DVProg 0 0 0 1
AdvConf 6.126105674500098 0 9816536.540229349 1 0
Guidance 0
END
EjectMFD V5
Reference Auto
Data 0 1 3 0 1 65694.09697386767 10
Guidance 0
END
BaseAprMFD V2
Reference Auto
Target none
Source none
DataA 0 0 120000 0.10821 0.366519 1 1 65694.06878485183 65694.06878485183 0
DataB 0 3 0 1 0 1
END
SlingMFD V4
Reference Auto
Source none
Data 0 1 1 3 0 1 65694.06878485183 0
END
LaunchMFD V4
Target None
Data 0 1 1 3 0 1 0
END
CF1_DataA 0 0
CF1_DataB 65694.06703979291 10 120000 2 20 150000
CF1_SecTgt
mfdShare -1
mfdProgram 2
END_MFD

BEGIN_MFD Right
TYPE User
MODE Interplanetary
Scenario Old2
MapMFD V5
Reference Auto
Target Io
Center Io
Data 1 1 1.193423013922025e-007 0 0 1 0 0 1 0 0 0
MassLimit 1e+020
CMode 1
Config 1 1 1 1 0 0
ExtMode 0
Periapis Io
END
CorMFD V4
Reference Jupiter
Target Io
Source GLRescue
ActiveProg 1 1
DataA 1 3 0 1 0 0
DataB 38.443359375 1 65702.01462572224 0 0 0.3024329862586788 0 65702.90667993808 0
DVProg 0 0 0 1
AdvConf 6.126105674500098 0 9816536.540229349 1 0
Guidance 0
END
EjectMFD V5
Reference Auto
Data 0 1 3 0 1 65694.09697386767 10
Guidance 0
END
BaseAprMFD V2
Reference Auto
Target none
Source none
DataA 0 0 120000 0.10821 0.366519 1 1 65694.06878485183 65694.06878485183 0
DataB 0 3 0 1 0 1
END
SlingMFD V4
Reference Auto
Source none
Data 0 1 1 3 0 1 65694.06878485183 0
END
LaunchMFD V4
Target None
Data 0 1 1 3 0 1 0
END
CF1_DataA 0 0
CF1_DataB 65694.06703979291 10 120000 2 20 150000
CF1_SecTgt
mfdShare 0
mfdProgram 4
END_MFD

BEGIN_PANEL
END_PANEL

BEGIN_SHIPS
GLRescue:DeltaGliderIV
STATUS Orbiting Jupiter
RPOS -383113465.41 -19245839.57 -385498845.80
RVEL 10868.890 -188.395 -9468.023
AROT -50.94 57.26 -45.02
PRPLEVEL 0:0.824360 1:0.972930 2:0.983333
IDS 0:45 100
NAVFREQ 0 0
XPDR 0
;-------------------------- Skin parameters must contain directory name of skin (without space)
MeshSkin transworld
;-------------------------- Cargo payload must contain name of config file or "none".(see doc)
CargoPayload none
NOSECONE 0 0.00
GEAR 1 1.00
AllDoorsState 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00 0 0 0.00
But1Cockpit 0 0 0 2 2 2 0 2 2 2 2 2 2 2 2 1 1 2 1 1 1 4
But2Cockpit 0 0 0 0 0 0 0 0 2 2 2 2 2 0 50 0 0 0 2 0 0 0
TransEffect 0
LifeBut1State 0 2 1 2 1 2 2 2 2 2 2 2 2 0 3
LevelBatt 100.0213
Emergency_power 10000.0000
VoltageStartBus 0.0000
VoltageGen1 96.6059
VoltageGen2 96.3089
VoltageGenBus 96.0000
O2tankALevel 98.8194
N2tankALevel 100.0000
O2tankBLevel 100.0000
N2tankBLevel 100.0000
CabinO2Level 21.3986
CabinCO2Level 600.0002
CabinTempLevel 21.2000
CabinPressure 14.7000
CabinMoistLevel 36.0000
CabinDustLevel -0.0002
CabinO2Setting 21.4000
CabinTempSetting 21.2000
CabinPressSetting 14.7000
AntennaTarget no_target
O2ConsumptionSetting 4
FuelConsumptionSetting 0
MainenginePower 1
;------------------Crew parameters UMMUCREW Function-Name-Age-CardiacPulse-WeightKg (fonction of Pilot must be: Capt)
NoOneOnBoard 0
NoPilotOnBoard 0
UMMUCREW Capt-Robert_Gaitley-32-60-87
UMMUCREW Doc-Bradley_Banister-36-65-82
FailGearFailure 0
FailGearCollapse 0
FailLeftMainEngine 0
FailRightMainEngine 0
FailHoverEngine 0
FailRcs 0
FailSurfaceControl 0
FailComputer 0
FailComputerBlueScreen 0
FailAutopilot 0
FailExtRadiator 0
FailAirbrake 0
FailNoseCone 0
FailCanopy 0
FailAntenna 0
FailLeftTurbo 0
FailRightTurbo 0
FailCargoDoor 0
SpacesuitTimer 0
UCGO @@0,1,0,0,@@1,1,0,0,@@2,1,0,0,@@3,1,0,0,
END
END_SHIPS

BEGIN_ExtMFD
END
Click to expand...
 
Last edited:
dgatsoulis

dgatsoulis

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Slingshots are not just about getting your periapsis in the prograde or retrograde side of a planet/moon. The direction from which you encounter is more important. Adjusting the periapsis will set your exit direction and velocity.

In the scenario you posted, you need to perform a maneuver, in order to adjust your encounter direction, so that your departure is tangent to Io's orbit around Jupiter, in order to send you out to Europa's orbital altitude.

A good way to visualize this, is to imagine your trajectory without Io and see in which direction and when would you have to make a burn, in order to increase the SMa of your trajectory. That's the direction you must depart from the Io.

Then you adjust your encounter with Io and get the moon's gravity to make the "burn" for you.

Untitled-1-6.jpg


Code: 
BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 65702.0237357439
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GLRescue
END_FOCUS

BEGIN_CAMERA
  TARGET GLRescue
  MODE Cockpit
  FOV 50.00
END_CAMERA

BEGIN_HUD
  TYPE Orbit
  REF AUTO
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE Interplanetary
  Scenario Old2
  MapMFD V5
  Reference jupiter
  Target Io
  Center jupiter
  Data 0 1 1.391871078733039e-007 0 1 1 0 0 1 0 0 0
  MassLimit 1e+020
  CMode 0
  Config 1 1 1 1 0 0
  ExtMode 2
  Periapis Io
  END 
  CorMFD V4
  Reference Jupiter
  Target Ecliptic
  Source GLRescue
  ActiveProg 5 5
  DataA 0 3 0 1 0 0
  DataB 1 1 65702.02373514249 0 0 0.3024452796608887 0 65702.90667993808 0
  DVProg -322 0 -164.3000000000002 1
  AdvConf 6.126105674500098 0 9816536.540229349 1 0
  Guidance 0
  END 
  EjectMFD V5
  Reference Auto
  Data 0 1 3 0 1 65694.09697386767 10
  Guidance 0
  END 
  BaseAprMFD V2
  Reference Auto
  Target none
  Source none
  DataA 0 0 120000 0.10821 0.366519 1 1 65694.06878485183 65694.06878485183 0
  DataB 0 3 0 1 0 1
  END 
  SlingMFD V4
  Reference Auto
  Source none
  Data 0 1 1 3 0 1 65694.06878485183 0
  END 
  LaunchMFD V4
  Target None
  Data 0 1 1 3 0 1 0
  END 
  CF1_DataA 0 0
  CF1_DataB 65694.06703979291 10 120000 2 20 150000
  CF1_SecTgt 
  mfdShare -1
  mfdProgram 2
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE Interplanetary
  Scenario Old2
  MapMFD V5
  Reference jupiter
  Target Io
  Center jupiter
  Data 0 1 1.391871078733039e-007 0 1 1 0 0 1 0 0 0
  MassLimit 1e+020
  CMode 0
  Config 1 1 1 1 0 0
  ExtMode 2
  Periapis Io
  END 
  CorMFD V4
  Reference Jupiter
  Target Ecliptic
  Source GLRescue
  ActiveProg 5 5
  DataA 0 3 0 1 0 0
  DataB 1 1 65702.02373514249 0 0 0.3024452796608887 0 65702.90667993808 0
  DVProg -322 0 -164.3000000000002 1
  AdvConf 6.126105674500098 0 9816536.540229349 1 0
  Guidance 0
  END 
  EjectMFD V5
  Reference Auto
  Data 0 1 3 0 1 65694.09697386767 10
  Guidance 0
  END 
  BaseAprMFD V2
  Reference Auto
  Target none
  Source none
  DataA 0 0 120000 0.10821 0.366519 1 1 65694.06878485183 65694.06878485183 0
  DataB 0 3 0 1 0 1
  END 
  SlingMFD V4
  Reference Auto
  Source none
  Data 0 1 1 3 0 1 65694.06878485183 0
  END 
  LaunchMFD V4
  Target None
  Data 0 1 1 3 0 1 0
  END 
  CF1_DataA 0 0
  CF1_DataB 65694.06703979291 10 120000 2 20 150000
  CF1_SecTgt 
  mfdShare 0
  mfdProgram 4
END_MFD

BEGIN_SHIPS
GLRescue:DeltaGlider
  STATUS Orbiting Jupiter
  RPOS -374470577.27 -19389329.42 -392852156.51
  RVEL 11104.193 -176.393 -9226.217
  AROT -60.82 43.02 -48.41
  AFCMODE 7
  PRPLEVEL 0:0.824360 1:0.972290
  IDS 0:45 100
  NAVFREQ 0 0 0 0
  XPDR 0
  AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END
(I replaced the DGIV with a DG, because I don't have it installed in this PC).


If the trajectory on the right drops back towards Jupiter, re-adjust the outward velocity. Select Reference Io to see your departure after the encounter and then reset it back to Jupiter.

IMFD is great with the Map program, but my tool of choice for setting up and performing slingshots is TransX. You can then use IMFD to get a more precise trajectory prediction.
 
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