TransX DV drift

[emery]

Help!
I am attempting to meet up with Iss using Trans X. from an orbit below. But unable to do so.
1- orbital planes aligned
2- DV for pro grade established to raise orbit to intersect Iss path
3- date established for burn initiation
The problem occurs during fast forwarding to the actual burn date, the DV
value drifts by huge amounts, up to several hundred percent.
Question, why is the drift? ( non spherical sources, radiation pressure are disabled)
:facepalm:

additional notes:
i was doing the burn after several orbits, in fact in about one full day delay.(minimum orbit height at about 250 km)
- One other thing, if i fine tune the ejection DV and ejection time just before the planned burn, the final burn mfd will still show the same insanely drifted DV value and not the DV value that has just been adjusted to. In other words, the drifted DV value gets "stuck" in the system and can not be corrected. I must be doing something wrong! Am I?

 

[IronRain]

What spacecraft are you using?

 

[agentgonzo]

2- DV for pro grade established to raise orbit to intersect Iss path

I would expect that this is due to a combination of Non-spherical gravity sources (as you say and TransX doesn't model) and also atmospheric drag that your vessel is experiencing (which TransX also doesn't model). Varying by over 100% is odd though (unless you are doing the burn in many orbits' time rather than within the current orbit)

 

[IronRain]

Some add-ons are not as stable as others. Time warp with the [ame="http://orbithangar.com/searchid.php?ID=5160"]Soyuz 7K series[/ame] add-on (not criticizing, this is one of the best add-ons out there for me) and your orbit will change.

 

[emery]

..it happens with all types of crafts, the accumulation of large errors is after several orbits but in comparison there is no accumulation of errors on the video tutorial I found on the net depicting an Iss intersect.

---------- Post added at 06:09 PM ---------- Previous post was at 01:45 PM ----------

-Yes, i was doing the burn after several orbits, in fact in about one full day delay.(minimum orbit height at about 250 km)
- One thing though, if i fine tune the ejection DV and ejection time just before the planned burn, the final burn mfd will still show the same insanely drifted DV value and not the DV value that has just been adjusted to. In other words, the drifted DV value gets "stuck" in the system and can not be corrected. I must be doing something wrong! Am I?

---------- Post added at 06:10 PM ---------- Previous post was at 06:09 PM ----------

---------- Post added at 06:14 PM ---------- Previous post was at 06:10 PM ----------

I would expect that this is due to a combination of Non-spherical gravity sources (as you say and TransX doesn't model) and also atmospheric drag that your vessel is experiencing (which TransX also doesn't model). Varying by over 100% is odd though (unless you are doing the burn in many orbits' time rather than within the current orbit)

/COLOR]-Yes, i was doing the burn after several orbits, in fact in about one full day delay.(minimum orbit height at about 250 km)
- One thing though, if i fine tune the ejection DV and ejection time just before the planned burn, the final burn mfd will still show the same insanely drifted DV value and not the DV value that has just been adjusted to. In other words, the drifted DV value gets "stuck" in the system and can not be corrected. I must be doing something wrong! Am I?:facepalm:

 

[lizardkilr]

Easy answer

Just use the scenario editor and dock your vessel to 1 of the 5 docks. Just simple. But if you're actually trying, use the spherical gravity. It helped me. Good luck!

 

[flytandem]

Can you post a scenario of the maneuver set up but not yet warped ahead to burn time?

 

[emery]

where do i post the scenario...I am new to this site...thanks

 

[agentgonzo]

where do i post the scenario...I am new to this site...thanks

Open the .scn file in notepad (it's just at text file). Then copy the contents and post it in this thread in

 tags:
[code]Your .scn contents here

 

[emery]

BEGIN_DESC

END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 51982.9189168924
END_ENVIRONMENT

BEGIN_FOCUS
  Ship XR1-01
END_FOCUS

BEGIN_CAMERA
  TARGET XR1-01
  MODE Cockpit
  FOV 40.00
END_CAMERA

BEGIN_HUD
  TYPE Orbit
  REF AUTO
END_HUD

BEGIN_MFD Left
  TYPE Map
  REF Earth
  BTARGET Cape Canaveral
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE TransX
  Ship  XR1-01
  FNumber 1
  Int 0
  Orbit True
  Vector  3654591.85602 5023956.91744 -2147543.75365
  Vector  6307.17885791 -4569.10230878 41.6104698229
  Double  3.98600439969e+014
  Double  51982.9162781
  Handle Earth
  Handle NULL
  Handle ISS
Select Target
 1 ISS
Autoplan
0 0
Plan type
0 0
Plan
0 0
Plan
0 0
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 1
Base Orbit
0 0
Prograde vel.
 4  81.34
Man. date
 6  51984.475838
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 1
Scale to view
0 0
Advanced
0 0
Finvars
  Finish BaseFunction
END_MFD

BEGIN_SHIPS
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS 1392491.51 6258840.93 -2047794.10
  RVEL 7389.648 -1948.865 -914.789
  AROT 158.41 -76.00 33.94
  AFCMODE 7
  PRPLEVEL 0:1.000000
  IDS 0:588 100 1:586 100 2:584 100 3:582 100 4:580 100
  NAVFREQ 0 0
  XPDR 466
END
Mir:Mir
  STATUS Orbiting Earth
  RPOS -5935939.65 -208556.53 -3044165.28
  RVEL 3533.982 -406.025 -6858.360
  AROT 1.91 -0.09 83.96
  AFCMODE 7
  IDS 0:540 100 1:542 100 2:544 100
  XPDR 482
END
Luna-OB1:Wheel
  STATUS Orbiting Moon
  RPOS -546454.92 -2171545.75 31.21
  RVEL 1434.954 -361.101 0.049
  AROT -0.00 -0.00 116.06
  VROT 0.00 0.00 10.00
  AFCMODE 7
  IDS 0:560 100 1:564 100
  XPDR 494
END
XR1-01:DeltaGliderXR1
  STATUS Orbiting Earth
  RPOS 4942670.03 3812724.62 -2060317.26
  RVEL 4923.408 -5991.417 718.890
  AROT -91.07 -56.81 19.97
  PRPLEVEL 0:0.127801 1:0.986852 2:0.074000
  IDS 0:199 100
  NAVFREQ 94 524 84 114
  XPDR 193
  SECONDARY_HUD 5
  LAST_ACTIVE_SECONDARY_HUD 0
  ADCTRL_MODE 0
  TAKEOFF_LANDING_CALLOUTS 7505.790864 24.097000 24.102000 0.000000 1.523304
  APU_FUEL_QTY 0.778854
  LOX_QTY 0.982196
  CABIN_O2_LEVEL 0.209000
  CREW_STATE 0
  INTERNAL_SYSTEMS_FAILURE 0
  COGSHIFT_MODES 0 0 0
  MWS_ACTIVE 0
  COOLANT_TEMP 31.200000
  DMG_0 1.000000 Left Wing
  DMG_1 1.000000 Right Wing
  DMG_2 1.000000 Left Aileron
  DMG_3 1.000000 Right Aileron
  DMG_4 1.000000 Landing Gear
  DMG_5 1.000000 Nosecone
  DMG_6 1.000000 Retro Doors
  DMG_7 1.000000 Top Hatch
  DMG_8 1.000000 Radiator
  DMG_9 1.000000 Airbrake
  DMG_10 1.000000 Left Main Engine
  DMG_11 1.000000 Right Main Engine
  DMG_12 1.000000 Left SCRAM Engine
  DMG_13 1.000000 Right SCRAM Engine
  DMG_14 1.000000 Fore Hover Engine
  DMG_15 1.000000 Aft Hover Engine
  DMG_16 1.000000 Left Retro Engine
  DMG_17 1.000000 Right Retro Engine
  DMG_18 1.000000 Forward Lower RCS
  DMG_19 1.000000 Aft Upper RCS
  DMG_20 1.000000 Forward Upper RCS
  DMG_21 1.000000 Aft Lower RCS
  DMG_22 1.000000 Forward Star. RCS
  DMG_23 1.000000 Aft Port RCS
  DMG_24 1.000000 Forward Port RCS
  DMG_25 1.000000 Aft Star. RCS
  DMG_26 1.000000 Outboard Upper Port RCS
  DMG_27 1.000000 Outboard Lower Star. RCS
  DMG_28 1.000000 Outboard Upper Star. RCS
  DMG_29 1.000000 Outboard Lower Port RCS
  DMG_30 1.000000 Aft RCS
  DMG_31 1.000000 Forward RCS
  IS_CRASHED 0
  MET_STARTING_MJD 51982.669219
  INTERVAL1_ELAPSED_TIME -1.000000
  INTERVAL2_ELAPSED_TIME -1.000000
  MET_RUNNING 1
  INTERVAL1_RUNNING 0
  INTERVAL2_RUNNING 0
  ACTIVE_MDM 3
  TEMP_SCALE 2
  CUSTOM_AUTOPILOT_MODE 0
  AIRSPEED_HOLD_ENGAGED 0
  SCRAM0DIR 0.000000 0.000000 1.000000
  SCRAM1DIR 0.000000 0.000000 1.000000
  HOVER_BALANCE 0.000000
  MAIN0DIR 0.000000 0.000000 1.000000
  MAIN1DIR 0.000000 0.000000 1.000000
  GIMBAL_BUTTON_STATES 0 0 0 0 0 0
  ATTITUDE_HOLD_DATA 0.000000 0.000000 0 0 0.000000
  DESCENT_HOLD_DATA 0.000000 -3.000000 0
  AIRSPEED_HOLD_DATA 0.000000
  OVERRIDE_INTERLOCKS 0 0
  TERTIARY_HUD_ON 1
  CREW_DISPLAY_INDEX 0
  GEAR 0 0.0000
  RCOVER 1 1.0000
  NOSECONE 0 0.0000
  AIRLOCK 0 0.0000
  IAIRLOCK 0 0.0000
  CHAMBER 0 0.0000
  AIRBRAKE 0 0.0000
  RADIATOR 1 1.0000
  LADDER 0 0.0000
  HATCH 0 0.0000
  SCRAM_DOORS 0 0.0000
  HOVER_DOORS 0 0.0000
  APU_STATUS 0
  EXTCOOLING_STATUS 0
  TRIM 0.030000
  LIGHTS 0 0 0
  XR1UMMU_CREW_DATA_VALID 1
  UMMUCREW XI0-Michael_Samuel-37-72-68
  UMMUCREW XI1-Nikita_Simone-29-72-68
  UMMUCREW XI2-Madeline_Dolenc-36-72-68
  UMMUCREW XI3-Seymore_Birkoff-24-72-68
  UMMUCREW XI4-Katherine_Quinn-28-72-68
  PAYLOAD_SCREENS_DATA 0.2 0 1 0
END
SH-03:ShuttleA
  STATUS Landed Earth
  BASE Habana:4
  POS -82.3982414 23.0005396
  HEADING 70.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 0 0
  XPDR 0
  PODANGLE 0.0000 0.0000
  DOCKSTATE 0 0.0000
  AIRLOCK 0 0.0000
  GEAR 0 0.0000
  PAYLOAD MASS 0.0 0
END
PB-01:ShuttlePB
  STATUS Landed Earth
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  HEADING 22.00
  AFCMODE 7
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  NAVFREQ 0 0
END
GL-02:DeltaGlider
  STATUS Landed Mars
  BASE Olympus:3
  POS -135.4300000 12.7366196
  HEADING 0.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
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  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
SH-01:ShuttleA
  STATUS Landed Moon
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  HEADING 0.00
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  NAVFREQ 0 0
  XPDR 0
  PODANGLE 0.0000 0.0000
  DOCKSTATE 0 0.0000
  AIRLOCK 0 0.0000
  GEAR 0 0.0000
  PAYLOAD MASS 0.0 0
END
END_SHIPS

BEGIN_ReFuelMFD
  SCENARIO_TREE 
    NAMED Computers
    END_NODE 
  END_NODE 
END

Note:I chose the dv somewhat higher than minimally needed, I now realize that the large dv drift is really due to trying to give a normal acceleration component during the burn as the original coordinates for burn initiation have changed during time forward. The program is still properly correcting to intercept the Iss, only that efficiency is lost because of the normal acceleration component....Am i correct here?

---------- Post added at 07:12 PM ---------- Previous post was at 03:39 PM ----------

-Thank You very much for all those who replied to my questions. It led to a much better understanding of the problem on my part.
- Indeed it looks like atmospheric drag was the main cause of the DV drift and its very large magnitude seems to be the consequence of the program attempting to correct the trajectory by introducing a normal acceleration (burn) component which of-course raises the DV vector greatly but not the magnitude of the velocity vector of the craft.
Thank You again :thumbup:

 

[flytandem]

I noticed that the craft is losing orbital height during the long wait for the maneuver. That would have an effect on the maneuver. I suspect atmospheric drag is the cause. You have set it up about 25 orbits ahead of the actual burn. If you need to set up the maneuver that far ahead, consider it just a test maneuver to get a rough idea of when it will happen. In time you will be able to eyeball when you are within a couple of orbits of the required maneuver even without this test maneuver setup. If you do set up a maneuver far ahead, about 1 orbit before you get there, toggle the maneuver off then on and set it up again. It will be far more precise. I usually will limit to a couple or 3 orbits in setting up a maneuver that I plan on burning. More often than not I set up the maneuver just 10 minutes before the actual burn time. Doing maneuvers and planning them far ahead, around airless worlds, is far less of a drag.

 

[emery]

Thank you Fly Tandem!

---------- Post added at 02:30 PM ---------- Previous post was at 01:14 PM ----------

One other observation: These DV drift effects also happen when interplanetary gravitational effects become significant, for example in high orbits about the Earth. I suspect that Trans X does not model the gravitational influence of more than one planetary body at one time. :hello:

 

[flytandem]

Yes TransX does not have great accuracy when high above the Earth mostly due to the effects of the moon I think. I have been playing with the backflip trajectories recently and it is turning out more art than science. Even the far more accurate IMFD is having trouble predicting the moon to moon inclined plane sling. :facepalm:

 

[emery]

Thank You Flytandem,
-A good feature of Trans X is that even though the DV can drift, the burn itself when executed will still be fairly accurate because the final trajectory is rotated by that normal component of the burn...this was obviously well thought out it seems.
-one question, do You know if there is a utility which can time a burn, so that we can enter the duration and then perform the burn at the proper moment?

---------- Post added at 08:26 PM ---------- Previous post was at 04:14 PM ----------

I have been experimenting with trans x burns with significantly drifted DV values. It seems that the burn is not that accurate when the drift is very large. Perhaps the algorithm used for determining direction and duration of the burn could be optimized further so that any burn regardless the DV drift will be more accurate. In my opinion (at the moment) this should be possible to achieve.
Any thoughts on this Flytandem, AgentGonzo,...

 

[agentgonzo]

Yes TransX does not have great accuracy when high above the Earth mostly due to the effects of the moon I think.

Correct. TransX treats everything as a two body problem (body + vessel) and so will ignore the gravitational effects of the moon - which for high orbits are significant.

 

[emery]

Thanks Agent Gonzo!
-I would add that the Sun's gravitational effect is sometimes overlooked in this situation. True, its field is more uniform near Earth but its magnitude is generally far greater than the Moon's field.
-The same high orbit intercept can be performed on moonless Venus with high resulting DV drifts. :facts:

 

[Tommy]

-one question, do You know if there is a utility which can time a burn, so that we can enter the duration and then perform the burn at the proper moment?

BurntimeCalcMFD may be what you are looking for. It won't help with orientation - but it will calculate the burn time (user inputs dV and selects engine) and perform the burn precisely.
[ame="http://www.orbithangar.com/searchid.php?ID=1407"]BurnTimeCalcMFD (BTC) 1.5[/ame]

It's also handy when landing on airless bodies - it will show you how far you will travel during the burn.

 

[emery]

Thanks Tommy, I am getting it right away...:tiphat: