Support TransX and docked vessels

[dougkeenan]

Is TransX OK to use with docked vessels, one pushing the other?

I used to "fake" the front vessel (as mesh-only with total mass added to the pushing vessel) until after TLI and stage separation. TransX would hit the target every time right on.

Now I've implemented the two separate docked vessels, one pushing another, and since then my burns as predicted are way off and resulting orbit a mess. (See picture.) I've also used Orbiter's body forces to check that the masses are indeed correct.

Is there anything wrong with doing it this way?

 

[Zatnikitelman]

Are you using the time to burn countdown in TransX and the burntime to engage/disengage the engine? I'm guessing TransX doesn't take into account the docked mass so those numbers would be off. About the only thing I know to do is get the Dv from TransX then use both Tsiolkovsky's equation and the burntime equation. Get the fuel mass you'll expend from Tsiolkovsky's equation, then plug that into burntime to get well...the burntime It won't be exactly exact because burntime doesn't take into account the changing mass of the stack.

 

[dougkeenan]

Are you using the time to burn countdown in TransX and the burntime to engage/disengage the engine? I'm guessing TransX doesn't take into account the docked mass so those numbers would be off. About the only thing I know to do is get the Dv from TransX then use both Tsiolkovsky's equation and the burntime equation. Get the fuel mass you'll expend from Tsiolkovsky's equation, then plug that into burntime to get well...the burntime It won't be exactly exact because burntime doesn't take into account the changing mass of the stack.

Right, I use the burn countdown / remaining deltaV indicators in TransX.

 

[2552]

I've used TransX to fly the Grand Tour with the JamesCook, with 10 Shuttle-A's with cargo docked to it and it worked just fine.

 

[agentgonzo]

Are you using the time to burn countdown in TransX and the burntime to engage/disengage the engine? I'm guessing TransX doesn't take into account the docked mass so those numbers would be off. About the only thing I know to do is get the Dv from TransX then use both Tsiolkovsky's equation and the burntime equation. Get the fuel mass you'll expend from Tsiolkovsky's equation, then plug that into burntime to get well...the burntime It won't be exactly exact because burntime doesn't take into account the changing mass of the stack.

No, TransX doesn't take into account the mass of docked vessels, so the "Begin Burn" feature of TransX won't give you an accurate time to start your burn. The remaining Delta-V will be accurate and the "T to Mnvre" will be accurate, so if BurnTimeMFD takes account of docked vessels, then you can use that to calculate the amount of time before "T to Mnvre" to begin your burn. Otherwise you have to break out the rocket equations and do it yourself :-(

 

[dougkeenan]

Thanks for the confirmation. I checked the BTC142 code, it does account for stack mass so there should be a workable solution in here somewhere.

Still ... can I haz new feature request of TransX pretty please?

eta: Spot on! Take DV value from TransX and feed it to BTC. Take DV/2 value from BTC and wait for that value at Time to Maneuver, then execute burn as usual. Awkward but reasonably accurate.

 

[agentgonzo]

Still ... can I haz new feature request of TransX pretty please?

I've coded up a new version which should take into account the mass of the whole stack, rather than just the current vessel.

However, I have no way to test it out at the moment as I don't have a working orbiter install.

Can you test it out for me please? The new files are here (v3.13.1.1). Can you check it out please? It should now calculate the mass of the vessel stack correctly. Can you check the following please:
A) The text in the bottom left corner correctly prints out the vessel stack mass for BOTH a lone-vessel AND a vessel docked to a stack
B) The burns work for BOTH an lone-vessel and a vessel docked to a stack.

Ta

 

[dougkeenan]

Instant CTD when I click to the "follow the X" page. Maybe a null handle somewhere?

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  J130-CEV-DHCUS
  FNumber 2
  Int 0
  Orbit True
  Vector  -6024218.72303 594890.818552 -2493535.57129
  Vector  2984.55867694 54.2836982752 -7238.29591296
  Double  3.98600439969e+014
  Double  58473.2705882
  Handle Earth
  Handle NULL
  Handle Moon
Select Target
 0 Moon
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  3133.74417785
Man. date
 5  58473.2896381
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
  Int 0
  Orbit True
  Vector  -252235521.771 31901017.3715 -274801178.725
  Vector  595.245015297 -76.399668647 673.41731371
  Double  4.90279493298e+012
  Double  58472.7245822
  Handle Moon
  Handle NULL
  Handle NULL
Select Target
 0 None
Autoplan
0 0
Plan type
0 1
Plan
0 0
Plan
0 2
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Base Orbit
0 0
Prograde vel.
 0  0
Man. date
 0  58473.2725829
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Finvars
  Finish BaseFunction
END_MFD
BEGIN_MFD Right
  TYPE User
  MODE TransX
END_MFD
 
BEGIN_SHIPS
J130-CEV-DHCUS:DIRECT\JUPITER_DHCUS
  STATUS Orbiting Earth
  RPOS -5383568.60 591612.42 -3684766.11
  RVEL 4390.937 -91.989 -6476.672
  AROT -179.18 -34.26 174.35
  VROT 0.00 0.07 -0.00
  PRPLEVEL 0:0.994
  DOCKINFO 0:1,J130-CEV-Orion
  NAVFREQ 0 0
  TGTALT 185
  TGTINC 2861
  CONFIG 11
  MET 2000
  PAYLOAD 3
END
J130-CEV-Orion:DIRECT\JUPITER_CEV
  STATUS Orbiting Earth
  RPOS -5383560.72 591612.25 -3684777.68
  RVEL 4390.937 -91.989 -6476.672
  AROT -179.18 -34.26 174.35
  VROT 0.00 0.07 -0.00
  PRPLEVEL 0:1.000
  DOCKINFO 1:0,J130-CEV-DHCUS
  NAVFREQ 0 0
  MET 194
  LUNAR 1
  AFTDOCK 1
END
END_SHIPS

 

[agentgonzo]

Bother. That's annoying. I'll see if I can spot it. If I can't do it by Friday, then you'll have to wait a week and a bit as I'm off on holiday come monday.

 

[dougkeenan]

That's OK, the workaround will do for now. Enjoy your holiday!

 

[Nemoricus]

Okay, my first test on my complex and messy Orbiter installation with Deepstar 2.0's Trans-Jupiter Injection was a CTD when I had the left MFD open to stage one of that plan, switching to maneuver mode. The right was open to stage 2, variables mode.

Given the complexity of my installation, it could be unexpected interactions, so I'm going to test it out on a fairly clean version later. However, that scenario did not crash under those circumstances before. Perhaps something is wrong in how the current version parses existing plans?

I'll let you know what I find out.

 

[agentgonzo]

It won't be anything to do with parsing existing plans, as it was just the VESSEL::GetMass calls that I replaced. It will only affect the burn-time stuff. It'll be a bug somewhere in there, but not having a place to install orbiter at the moment restricts the debugging that I can do. I'll post another tester tomorrow when I get back to the dev machine.

 

[Nemoricus]

Okay, more problems. I was able to plan a maneuver in the same scenario with the original plan deleted. However, when I went to the burn time and direction screen, it immediately crashed to desktop.

Same scenario, old plan deleted from the scenario file, first target Jupiter, second target Io, left screen open to stage one maneuver, switching to burn time and direction. The right screen was open to stage three, Jupiter encounter, with a target of Io.

A little request. Is it possible to make it so that multiple maneuvers can be planned simultaneously in each stage? If that's not possible, is it possible to make it so it would effectively be a separate stage? For example, in an Moon-Earth-Mars mission, there are several steps. First, lunar ejection. That's stage one. The second stage is the trans-Earth coast. Here there is no direct way to plan another stage. You aren't ejecting, and you're not maneuvering to any satellites of Earth. You're just maneuvering around Earth.

If there were a way to create another Earth-centric stage, you could then plan an eject burn to Mars as stage three. Stages four and five would be trans-Mars coast and Mars encounter as usual.

 

[agentgonzo]

OK, I called oapiGetVesselInterface twice by mistake (I'd already got the VESSEL pointer from the handle). Try this one.

 

[Nemoricus]

Okay, crashes are gone and it looks like this burns very accurately. I just did the Deepstar 2.0 TLI scenario with a planned periapsis of 173 km and 174 degree inclination. After the burn, I had a 1.3 Mm periapsis and 173.6 inclination, due to inaccuracies in making the burn. The older version was not this accurate in that scenario.

Nice job. I'll keep hunting around, see if anything else crops up. Let's see if I can get a good handle on slinging.

 

[dougkeenan]

Much better, thanks! I tested it on a two-vessel and a three-vessel inline stack (and agree with Nemoricus about improved accuracy). My only recommendation would be removing the debug string though it might be useful as another text field in the targeting view.

 

[Nemoricus]

I've done most of the Voyager slingshot route, passing Uranus and finetuning my approach to Neptune. It went very well indeed. The only problem that came up was of my own making in that I didn't have the Saturn-Uranus sling set up well. I spent a significant amount of energy fixing it.

It looks like TransX is working just fine. I'll keep looking, but I don't think that you'll find any major problems.

 

[Nemoricus]

Well, I find another crash. I was planning a Titan-Saturn-Mars route, adjusting variables in stage one when I moved to the burn view screen while docked to a wheel space station with a DGIV fuel payload docked to that.

I'm not sure what caused the crash.

 

[dougkeenan]

I've had unexpected CTD's when I leave TransX on in one stage (after TLI, for example) then try to activate it in another vessel for the next stage (like to plan escape). These were happening before the test release though.

 

[agentgonzo]

Well, I find another crash. I was planning a Titan-Saturn-Mars route, adjusting variables in stage one when I moved to the burn view screen while docked to a wheel space station with a DGIV fuel payload docked to that.

I'm not sure what caused the crash.

I've had unexpected CTD's when I leave TransX on in one stage (after TLI, for example) then try to activate it in another vessel for the next stage (like to plan escape). These were happening before the test release though.

Nemoricus, Doug, can you both set up the scenario that caused this and send me the scenario file, along with a brief instruction as to what you did to cause the crash. I'll take a look at it and see if I can fix them.

Thanks.