TransX Earth to Phobos

[laukejas]

Hello,

I'm trying more advanced interplanetary traveling with TransX. Right now, I'm thinking about Earth - Phobos direct or via Mars transfer.

Question is, how should I plan it? I create plan for Mars, but upon arrival, I need to arrive on correct inclination and LAN, and on the right time, when I can intercept Phobos in PeA of Mars (I think it should be most fuel efficient).

However, even I don't understand it fully, I noticed that upon arrival to Mars, I can't enter some inclinations, there are limits dependent on my trajectory. So it means that going to Phobos should be planned very early.


How should I do it? How to enter correct inclination, LAN, and arrive on the right time, so I can intercept Phobos while passing PeA of Martian orbit? How to plan this?

I would prefer not to use any surrogate ship, if possible.

 

[dgatsoulis]

Hi,

Even though it is certainly possible to set up such a flight in TransX from the ground up - all you have to do, is to setup a maneuvre at Martian Pe- i wouldn't recommend it. It only adds complexity. Here is a scenario with a DG on pad 1 of KSC with such a TransX plan:

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 55809.7573726779
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  GL-01
  FNumber 4
  Int 1
  Orbit True
  Vector  -5576346.74191 2647431.13424 1576472.82578
  Vector  -28.6800358866 161.879029961 -373.297527844
  Double  3.98600439969e+014
  Double  55809.7573721
  Handle Earth
  Handle NULL
  Handle NULL
Select Target
 0 Escape
Autoplan
0 0
Plan type
0 0
Plan
0 1
Plan
0 0
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Base Orbit
0 0
Prograde vel.
 0  0
Man. date
 0  55809.7573721
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
Pe Distance
 0  6577819.54864
Ej Orientation
 0  -0.58643062867
Equatorial view
0 0
Finvars
  Finish BaseFunction
  Int 2
  Orbit False
  Handle Sun
  Handle Earth
  Handle Mars
Select Target
 0 Mars
Autoplan
0 0
Plan type
0 2
Plan
0 0
Plan
0 0
Plan
0 1
Select Minor
 0 None
Manoeuvre mode
0 0
Base Orbit
0 1
Prograde vel.
 0  0
Man. date
 0  55809.7559387
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
Prograde vel.
 2  3251.59860547
Eject date
 3  55882.5014082
Outward vel.
 2  28.2
Ch. plane vel.
 2  -785.3
Finvars
  Finish BaseFunction
  Int 0
  Orbit True
  Vector  5782507292.39 -346704849.04 907194111.114
  Vector  -4877.56218176 293.612101614 -758.927919192
  Double  4.28282991638e+013
  Double  56092.1609211
  Handle Mars
  Handle NULL
  Handle Phobos
Select Target
 0 Phobos
Autoplan
0 0
Plan type
0 1
Plan
0 0
Plan
0 0
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 1
Base Orbit
0 0
Prograde vel.
 2  -3282.75785751
Man. date
 5  56105.86421
Outward vel.
 1  281
Ch. plane vel.
 1  678
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Finvars
  Finish BaseFunction
  Int 5
  Orbit False
  Handle Phobos
  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 1
Prograde vel.
 0  0
Man. date
 0  55809.7550056
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
Draw Base
0 0
Finvars
  Finish BaseFunction
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE TransX
END_MFD

BEGIN_SHIPS
GL-01:DeltaGlider
  STATUS Landed Earth
  BASE Cape Canaveral:1
  POS -80.6797794 28.5998557
  HEADING 150.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 402 94 0 0
  XPDR 0
  GEAR 1 1.0000
  AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END

Instead of doing that, setup a normal Earth to Mars plan and add a maneuver once you are inside the Martian (weak) SOI (OrbitMFD, Ref Mars, G ~0.10)

Ideally you would want the Pe to coincide with one of the nodes where your orbit and Phobos' intersect. This way you can burn at Pe just enough so that you are captured by Mars, coast to Ap to align planes with Phobos and then sync orbits with the tool of your choice.
Here is an example of a DG that just entered Mars' SOI:

As you can see in OrbitMFD, the DG is coming in at an Inclanation of ~140 degrees, which means that it's on a Retrograde trajectory relative to Mars. The first thing to do, is to set up a maneuvre that will bring us in a Prograde trajectory, with a PeA above Mars' atmosphere and make the burn. (It usually takes a few meters of negative "Outward Vel" to do that). You can see that burn already set up on the left MFD.

After that, you need to setup another maneuvre, this time at Periapsis.

Here is the scenario with the maneuvre already set up. It will bring you within 50 km of Phobos, after one orbit.

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 56155.5867003595
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  GL-01
  FNumber 2
  Int 0
  Orbit True
  Vector  372924438.723 75120756.3908 32423706.0248
  Vector  -3037.00599584 -586.589415321 -208.14221834
  Double  4.28282991638e+013
  Double  56155.5861887
  Handle Mars
  Handle NULL
  Handle Phobos
Select Target
 0 Phobos
Autoplan
0 0
Plan type
0 1
Plan
0 0
Plan
0 0
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 1
Base Orbit
0 0
Prograde vel.
 3  -1681.20306986
Man. date
 5  56156.9652492
Outward vel.
 2  -6.48
Ch. plane vel.
 1  42.3
Intercept with
0 0
Orbits to Icept
0 2
Graph projection
0 2
Scale to view
0 1
Advanced
0 0
Finvars
  Finish BaseFunction
  Int 5
  Orbit False
  Handle Phobos
  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 1
Prograde vel.
 0  0
Man. date
 0  56155.5866994
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
Draw Base
0 0
Finvars
  Finish BaseFunction
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE TransX
END_MFD

BEGIN_SHIPS
GL-01:DeltaGlider
  STATUS Orbiting Sun
  RPOS -109719327546.43 -1399741748.34 -199382682416.78
  RVEL 19089.859 -1331.612 -9843.778
  AROT 22.72 9.32 -33.87
  RCSMODE 2
  AFCMODE 7
  PRPLEVEL 0:0.776504 1:0.989838
  NAVFREQ 402 94 0 0
  XPDR 0
  AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END

A better way to do this, is to setup your PeA inside the atmosphere, in order to use the friction to lower your ApA and eventually be captured by Mars, but it takes a little bit of practise.

Hope this helps.
Have fun, happy orbiting.

 

[Jarvitä]

You can't really orbit Phobos, so as I understand it, the whole affair is essentially about making sure you arrive into a correct Martian orbit to rendezvous with it. Check whether it takes less dV to areobrake yourself into an elliptical orbit with Phobos at apoapsis, or to brake straight into Phobos' orbit. I predict it is the former.

 

[laukejas]

Hello again,

First of all, thanks for your previous suggestion, dgatsoulis, it really helped.

However, with bodies of stronger gravitation (like Jupiter) and with spacecraft with little DeltaV budget (like the Probe ( )), this technique can sometimes not work, because even if I align Pe with node of a moon, it can still be necessary to use a lot of DeltaV for inclination change, because gravity can be very strong with bigger planets.

So I'm back to my original question - is it possible to arrive to a planet at the same inclination and LAN as the moon which is the final destination? How can I do that? (Maybe a 2 plane plan, that is departure from Earth, at some point make an inclination change, and then arrive at the planet at the same inclination as the moon?)

Is that possible? Can you suggest how should I plan such thing?

And sorry for digging up old topic, but it wouldn't be good idea to continue discussion in new topic when we have this one.


Edit:

For example, it could happen like this:

And now there is no way to make aerobraking in any of the nodes. So I have to arrive in good inclination and LAN to start with.

 

[dgatsoulis]

However, with bodies of stronger gravitation (like Jupiter) and with spacecraft with little DeltaV budget (like the Probe ( )), this technique can sometimes not work, because even if I align Pe with node of a moon, it can still be necessary to use a lot of DeltaV for inclination change, because gravity can be very strong with bigger planets.

Bigger planet=larger SOI. The same thing that I posted before applies.

So I'm back to my original question - is it possible to arrive to a planet at the same inclination and LAN as the moon which is the final destination? How can I do that? (Maybe a 2 plane plan, that is departure from Earth, at some point make an inclination change, and then arrive at the planet at the same inclination as the moon?)

Is that possible? Can you suggest how should I plan such thing?

Yes it is possible. The first scenario in my previous post does exactly that.
Another way to do it, is to setup your MCCs to arrive at your target planet in a trajectory that is coplanar with the moon you want to visit.

Please post a scenario here with your ship right after the TMI burn so that I can review it and try to setup some examples for you.