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Old 09-07-2018, 12:30 AM   #1
Marijn
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Default Glideslope - BaseSync low energy problem

For landings on earth, I've been using BaseSync and AeroBrakeMFD for most of my flights. This always worked quite well, but I wanted some more control over the final approach with a pre-planned circuit. So, I had a go with the BaseSync and Glideslope combo. But I am not getting the results I was expecting. In fact, I end up almost 3000km short of the base. So I must be doing something very wrong.

Glideslope is configured for runway 15 on Cape Canaveral using the default 'XR Series' GS, which should be fine for an almost empty XR5 I'd say. The starting orbit is 190kmx190km with one orbit to go before passing over the base. I target 'GS2' in BaseSync and everything seems fine. I let de autopilot of BaseSync do the burn.

After leveling the horizon, I let the XR attitude autopilot follow the reference values as indicated on the DATA screen of the Glideslope MFD. AoA is around 41 degrees. At first things seem ok, but after a short while Glideslope indicated an energy problem. It starts as a small difference, but this escalates out of control quite rapidly.

The dEngy value becomes many times bigger than the reference value. During the whole re-entry, I am losing energy. This already starts at 100km of altitude. I was not expecting that. Why would a plane loose so much energy in such thin air? AeroBrakeMFD is confirming that following the AoA as dictated by the Glideslope reference value is a bad plan which will end up short. Another thing wich caught my attention is that Glideslope shows a reference value for VAcc=0. At 70km of altitude. How is it possible not to decellerate while flying at 70km?

Any ideas on what I could be doing wrong? Thanks.

GS v2.7
BS v3.3
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Old 09-15-2018, 03:12 AM   #2
ADSWNJ
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Very interesting problem! I built the Glideslope XR series glideslope on the XR-5, and I have flown a BaseSync to Glideslope with the XR attitude AP many times. I always target approx a 200 x 200 km initial orbit, a 120 km entry interface, and a 0.7 degree glideslope. From there, you can ride the reference slope quite nicely.

On the VAcc - note it's VAcc, not Acc. Meaning: vertical acceleration. You can bring the vessel to a neutral climb position to flatten out the slope pre-HAC, and then just burn off horizontal speed.

Have a look at the docs, to see if they help. If not, set up a Ctrl-S scenario, and save your glideslope and I'll take a look.

One day, we may have a full AP to help you with this. Probably on a Tuesday several years from now
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Old 09-15-2018, 05:27 AM   #3
NukeET
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Quote:
Originally Posted by ADSWNJ View Post
 ...and I have flown a BaseSync to Glideslope with the XR attitude AP many times...
Quote:
Originally Posted by ADSWNJ View Post
 If not, set up a Ctrl-S scenario, and save your glideslope and I'll take a look.
I hope this isn't off topic, but I'm looking to brush up on my re-entry skills by finally trying Glideslope. Would you consider posting a scenario on this thread and/or making a video/text tutorial? But, to be honest. I haven't yet RTFM.
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Old 09-15-2018, 07:39 AM   #4
Marijn
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In the meantime, I had quite a bit of practice and I did re-read the manual. I am getting better results, but I still feel that I am not getting what GS has to offer.

Quote:
Originally Posted by Marijn View Post
 I let the XR attitude autopilot follow the reference values as indicated on the DATA screen of the Glideslope MFD
I was trying to keep the AoA as indicated by the reference value. The manual speaks about two ways to control the descend by focusing on the vertical speed:
1) fixed AoA and S-turns (hard)
2) changing AoA (simple)

So I was doing it wrong. Method 2 basicly is the way I always used before, by adjusting the AoA. I still get better results when following Aerobrake for the main descent and ignore the warnings of Glideslope. When closing in, the values in GS seem to settle down in green. But I want to do the whole descent without the aid of Aerobrake.

When I aim for a 200x200km orbit when returning from the ISS, I usually end up with 190x190km. Any idea how much of a difference this would make when using a profile inteded for a 200x200km orbit? Perhaps more than I think. Setting up a scenario so you can have a look is a great offer. I'll do that, thanks.
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Old 09-15-2018, 11:40 PM   #5
ADSWNJ
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@NukeET - have a look at the docs with this MFD. I have a tutorial in there.

@Marijn - the S-turns approach is really not too hard, and is way more authentic to the Shuttle's reentry. You just need to have the confidence to hold the nose at 40-43 AoA, and roll up to 135 degrees of bank. The pattern down the glideslope should be a decreasing bank on each roll reversal, gradually reducing the azimuth error each time (e.g. from 15 degrees to 5 degrees over 5 or 6 turns).

The reference Glisdeslope I offer is only my preference. You are welcome to fly a different profile, then save your run and convert it to your reference profile. I'm also happy to add it to the distribution if it's a different way to achieve the same goal.

My long term dream is to add the HUD nav boxes like in RV Orientation, plus heads-up data, so you can run a full virtual cockpit and no MFDs. But that's a long term goal.
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Old 09-26-2018, 07:12 PM   #6
Marijn
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Ok, I would like to use the scenario below for practicing with the Glideslope MFD. The ship is quite heavy with 40% fuel remaining. The orbit is 190x190km which is what I usually end up with when aiming for 200x200km. I'll have a bit more practice and I will post the glideslope of my best attempt and perhaps a video.

Code:
BEGIN_DESC
XR5 Moon to KSC after earth insert
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 51990.0204032957
END_ENVIRONMENT

BEGIN_FOCUS
  Ship XR5-01
END_FOCUS

BEGIN_CAMERA
  TARGET XR5-01
  MODE Cockpit
  FOV 40.00
END_CAMERA

BEGIN_HUD
  TYPE Orbit
  REF AUTO
END_HUD

BEGIN_SHIPS
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS -2537187.846 -5192619.864 3458235.388
  RVEL -6154.7775 4226.8929 1854.3241
  AROT -0.590 -60.448 151.754
  VROT -0.0832 -0.0846 0.0997
  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
XR5-01:XR5Vanguard
  STATUS Orbiting Earth
  RPOS -1303782.605 472243.838 6413724.408
  RVEL -7347.0479 2015.2422 -1643.1193
  AROT 128.514 70.669 125.939
  VROT 0.0311 0.0519 -0.0191
  RCSMODE 2
  PRPLEVEL 0:0.441333 1:0.915007
  IDS 0:199 100
  NAVFREQ 94 524 84 114
  XPDR 193
  SECONDARY_HUD 2
  LAST_ACTIVE_SECONDARY_HUD 0
  ADCTRL_MODE 0
  TAKEOFF_LANDING_CALLOUTS 7374.174524 142.526204 142.527013 0.000000 -1.200023
  APU_FUEL_QTY 0.977984
  LOX_QTY 1.000000
  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 Docking Port
  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
  DMG_32 1.000000 Bay Doors
  DMG_33 1.000000 Elevator
  IS_CRASHED 0
  MET_STARTING_MJD 51984.601786
  INTERVAL1_ELAPSED_TIME -1.000000
  INTERVAL2_ELAPSED_TIME -1.000000
  MET_RUNNING 1
  INTERVAL1_RUNNING 0
  INTERVAL2_RUNNING 0
  ACTIVE_MDM 1
  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 1 0 0.000000
  DESCENT_HOLD_DATA 0.000000 -3.000000 1
  AIRSPEED_HOLD_DATA 0.000000
  OVERRIDE_INTERLOCKS 0 0
  TERTIARY_HUD_ON 1
  CREW_DISPLAY_INDEX 0
  GEAR 0 0.0000
  RCOVER 0 0.0000
  DOCKINGPORT 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 0.000000
  LIGHTS 0 0 0
  PARKING_BRAKES 0
  CONFIG_OVERRIDE_MainFuelISP 1
  PAYLOAD_SCREENS_DATA 0.2 0 1 0
  PAYLOAD_BAY_DOORS 0 0.0000
  RCS_DOCKING_MODE 0
  ACTIVE_EVA_PORT 0
  CREW_ELEVATOR 0 0.0000
END
XR5-01_Bay:XRPayloadBay
  STATUS Orbiting Earth
  RPOS -1303759.386 472241.369 6413729.198
  RVEL -7347.0479 2015.2422 -1643.1193
  AROT 128.514 70.669 125.939
  VROT 0.0311 0.0519 -0.0191
  ATTACHED 0:36,XR5-01
  AFCMODE 7
END
CSA_XR5_ER_LOX-03-1:CSA_XR5_ER_LOX
  STATUS Orbiting Earth
  RPOS -1303783.248 472245.284 6413724.173
  RVEL -7347.0479 2015.2422 -1643.1193
  AROT 128.514 70.669 125.939
  VROT 0.0311 0.0519 -0.0191
  ATTACHED 0:2,XR5-01
  AFCMODE 7
  PRPLEVEL 2:0.981950
  NAVFREQ 0 0
END
END_SHIPS


---------- Post added at 09:12 PM ---------- Previous post was at 08:13 PM ----------

And a quicksave after the de-orbit burn at 133km with the attitude control enabled, Glideslope set-up and the radiator retracted, ready to hit the atmosphere.
Code:
BEGIN_DESC
Moon to KSC after earth insert - Entry interface
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 51990.0715037017
END_ENVIRONMENT

BEGIN_FOCUS
  Ship XR5-01
END_FOCUS

BEGIN_CAMERA
  TARGET XR5-01
  MODE Cockpit
  FOV 40.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE Glideslope
  Base Cape Canaveral
  Rway RWY15
  Page VSIT
  Unit METRIC
  ManZ FALSE
  HRad 10500
  FDst 17800
  Geom R-O
  APlt FALSE
  XTSv FALSE
  QARc FALSE
  Diag FALSE
  Deor FALSE
  GSlp XR
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE Glideslope
  Base Cape Canaveral
  Rway RWY15
  Page DATA
  Unit METRIC
  ManZ FALSE
  HRad 10500
  FDst 17800
  Geom R-O
  APlt FALSE
  XTSv FALSE
  QARc FALSE
  Diag FALSE
  Deor FALSE
  GSlp XR
END_MFD

BEGIN_SHIPS
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS 4256545.192 -5190765.291 -407826.775
  RVEL -4734.8531 -4229.1166 4359.4905
  AROT 15.122 -15.977 -171.585
  VROT 0.0151 -0.0923 0.0437
  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
XR5-01:XR5Vanguard
  STATUS Orbiting Earth
  RPOS 4599385.383 -1179579.168 4446124.236
  RVEL -5187.0203 1536.7965 5629.9174
  AROT 4.027 3.319 106.962
  VROT -0.0692 -0.0011 0.0029
  PRPLEVEL 0:0.436667 1:0.891028
  IDS 0:199 100
  NAVFREQ 94 524 84 114
  XPDR 193
  SECONDARY_HUD 2
  LAST_ACTIVE_SECONDARY_HUD 0
  ADCTRL_MODE 0
  TAKEOFF_LANDING_CALLOUTS 7395.234828 142.526204 142.527013 0.000000 -98.165887
  APU_FUEL_QTY 0.972373
  LOX_QTY 1.000000
  CABIN_O2_LEVEL 0.209000
  CREW_STATE 0
  INTERNAL_SYSTEMS_FAILURE 0
  COGSHIFT_MODES 1 0 0
  MWS_ACTIVE 0
  COOLANT_TEMP 31.894820
  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 Docking Port
  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
  DMG_32 1.000000 Bay Doors
  DMG_33 1.000000 Elevator
  IS_CRASHED 0
  MET_STARTING_MJD 51984.601786
  INTERVAL1_ELAPSED_TIME -1.000000
  INTERVAL2_ELAPSED_TIME -1.000000
  MET_RUNNING 1
  INTERVAL1_RUNNING 0
  INTERVAL2_RUNNING 0
  ACTIVE_MDM 2
  TEMP_SCALE 2
  CUSTOM_AUTOPILOT_MODE 1
  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 39.000000 0.000000 1 1 0.000000
  DESCENT_HOLD_DATA 0.000000 -3.000000 1
  AIRSPEED_HOLD_DATA 0.000000
  OVERRIDE_INTERLOCKS 0 0
  TERTIARY_HUD_ON 1
  CREW_DISPLAY_INDEX 0
  GEAR 0 0.0000
  RCOVER 0 0.0000
  DOCKINGPORT 0 0.0000
  AIRLOCK 0 0.0000
  IAIRLOCK 0 0.0000
  CHAMBER 0 0.0000
  AIRBRAKE 0 0.0000
  RADIATOR 0 0.0000
  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 0.000000
  LIGHTS 0 0 0
  PARKING_BRAKES 0
  CONFIG_OVERRIDE_MainFuelISP 1
  PAYLOAD_SCREENS_DATA 0.2 0 1 0
  PAYLOAD_BAY_DOORS 0 0.0000
  RCS_DOCKING_MODE 0
  ACTIVE_EVA_PORT 0
  CREW_ELEVATOR 0 0.0000
END
XR5-01_Bay:XRPayloadBay
  STATUS Orbiting Earth
  RPOS 4599390.342 -1179581.900 4446101.082
  RVEL -5187.0203 1536.7965 5629.9174
  AROT 4.027 3.319 106.962
  VROT -0.0692 -0.0011 0.0029
  ATTACHED 0:36,XR5-01
  AFCMODE 7
END
CSA_XR5_ER_LOX-03-1:CSA_XR5_ER_LOX
  STATUS Orbiting Earth
  RPOS 4599386.494 -1179579.446 4446125.355
  RVEL -5187.0203 1536.7965 5629.9174
  AROT 4.027 3.319 106.962
  VROT -0.0692 -0.0011 0.0029
  ATTACHED 0:2,XR5-01
  AFCMODE 7
  PRPLEVEL 2:0.981780
  NAVFREQ 0 0
END
END_SHIPS

BEGIN_DX9ExtMFD
END
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