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Author Topic: "Lesser" moons of Earth  (Read 2295 times)

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Offline GW_Simulations

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29 October 2005, 11:06:27
Are there any addons for the four "Lesser" moons of Earth, such as Cruithne?

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Offline BrianJ

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Reply #1 - 30 October 2005, 00:03:41
Hi, I haven't seen Cruithne or any other co-orbital asteroids available - although I can recomend Nighthawke's
asteroids add-on available at SpaceSimMods. But why not have a go at making it yourself? You could just re-name a
suitable mesh (and associated texture .dds file) - you could use the deimos or phobos mesh/textures that come with
Orbiter -  to Cruithne. Then you need to make the Cruithne.cfg file that contains the physical and orbital data - easiest
way is to copy another asteroid .cfg and adjust it to the correct values for Cruithne. And then add Cruithne to your
sol.cfg as another planet.

However, you won't see the interesting orbital behaviour (horseshoe orbits etc) - in Orbiter the orbit will not change
from the ellipse specified in the Cruithne.cfg. To see that, you would need to classify Cruithne as a "Vessel" rather
than a "planet" - it will then be subject to the various gravitational influences that cause Cruithne's orbit to change.

Having said all that, the time scales invloved are so long that even at max time accel, you will need to run the sim for
an awfully long time to see the "horseshoe orbit" phenomenon (I think).

If you haven't seen it already, Tony Dunn's "GravitySimulator" program is better suited to showing this kind of orbital
behaviour -

But if you want to fly there in a DeltaGlider, there's only one program that'll do that for you!

All the best,

Offline felixar90

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Reply #2 - 30 October 2005, 01:18:29
Orbital elements C
Epoch July 14, 2004 (JD 2453200.5)
Eccentricity (e)    0.515
Semi-major axis (a)    149.260 Gm (0.998 AU)
Perihelion (q)    72.415 Gm (0.484 AU)
Aphelion (Q)    226.104 Gm (1.511 AU)
Orbital period (P)    364.019 d (1.00 a)
Mean orbital speed    29.82 km/s
Inclination (i)    19.810°
Longitude of the
ascending node (Ω)    126.311°
Argument of
perihelion (ω)    43.719°
Mean anomaly (M)    190.171°
Physical characteristics
Dimensions    ~5 km
Mass    1.3×1014 kg
Density    2 ? g/cm³
Surface gravity    0.0014 m/s²
Escape velocity    0.0026 km/s
Rotation period     ? d
Spectral class     ?
Absolute magnitude    15.1
Albedo    0.15 ?
Mean surface
temperature    ~275 K

Found on wikipedia



Offline freespace2dotcom

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Reply #3 - 30 October 2005, 02:41:19
Now correct me if I'm wrong, but doesn't orbiter still use only static planetary orbits?

Orbiter calculates the orbital trajectory at startup and sticks with that regardless of gravitational influence, thus you
can't make objects with fancy orbits that require lots of secondary gravitational influence. so you can't make a
pluto/charon planetary system, in which pluto's orbit is mainly affected by the sun, but also secondly by it's satelite. (producing a kind of wobble effect) the earth-synrchronous asteroids follow this same pattern, just more extremely. in this case, it's primarily affected by the sun, but earth's gravity is secondary, as it alters the asteroid's course whenver they get close enough to do their thing. The only things that have dynamic orbits are objects like spacestations, ships, rockets, etc. :(

hope this helps.

Post Edited ( 10-30-05 02:42 )

Offline StarLost

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Reply #4 - 30 October 2005, 23:50:31
I reflected this question back to M6. Apparently the latest version of Orbiter can handle Cruithne's orbit and also for
similar orbits like Dione's. Only problem is, is that an ephemeris dll will have to written for it. To my knowledge, this has
not been done yet.

Sounds like a great project, though.

Editted: Reflecting the question turned out to be an interesting discussion on M6. You might want to follow this thread:

Tony was kind enough to include an animation of the orbit from his gravity simulator. Very fascinating orbit!

Post Edited ( 10-31-05 08:19 )

Offline GW_Simulations

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Reply #5 - 31 October 2005, 20:27:58
I might have a go at it, in a basic Earth orbit, but DLL programming is currently beyond me.

Are there any tutorials on writting such a DLL, or could somebody help me?

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Offline StarLost

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Reply #6 - 01 November 2005, 11:30:05
No such explicit tutorials that I am aware of. The second best way is to take an ephemeris dll from one of the planet addons
and seek the source code from the author and try to emulate it. It is possible to "back-engineer" such a dll but I have never
tried it.

Of course, you would need a good C++ compiler (Orbiter was/is written in VC++ 6) and the Orbiter SDK.

Would the project be worthwhile? Take a look at what tony said about the time period of the asteroids orbit. In real time,
you wouldn't see much difference from an ordinary eliptical orbit.  Time compaction cranked up to 100,000x you might, but
that would probably induce other problems.

That all said, I am now seriously out of my depth. I would highly recommend you join the conversation in M6, or (if you can
handle la vraie langue, français) slip over to the French Forum and see what they can add. Our colleagues de la pays de
Madeleine, usually have lots of surprises.

Offline StarLost

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Reply #7 - 06 November 2005, 08:19:02
Was just perusing some documentation tonight, and if you look in the OrbiterSDK documentation  API guide, Martin has included
a rather extensive section on doing planetary modules. Not a tutorial, persay, but it will be of great help.

« Last Edit: 06 November 2005, 08:19:02 by StarLost »