Grant Hutchison's Contributions for Celestia v1.2.5

0: Introduction.
1: Corrections of rotation elements and surface maps.

1.1: Solarsys.ssc
1.2: newtextures.zip

2: Revised surface maps for Phobos and Deimos.
3: Galileo's flyby of Gaspra and Ida.
4: NEAR's flyby of Eros.

4.1: High resoultion model of Eros.
4.2: Lower resoultion model of Eros.
4.3: Topography texture maps of Eros.

5: Saturn's moons.

See also:

• Placing objects at defined locations on planetary surfaces
• An Empty object for mutual orbits
  (includes a binary asteroid definition; not needed for Celestia v1.3.0)
• Zubrin Statites to Terraform Mars
• Corrections for Celestia v1.3.0

0: Introduction.

1.1: solarsys.ssc

solarsys.ssc (32KB; February 2003)
This annotated version of solarsys.ssc has been updated to include additional orbital and rotational corrections for asteroids and other bodies that have been posted to the Celestia Web Forum during January and early February, 2003. These new revisions include the revisions to Gaspra, Ida, Dactyl and Eros, detailed in sections #3 and #4 below.

A small number of revisions to solarsys.ssc are still required to improve the accuracy of Celestia 1.2.5. Copy this file over the original solarsys.ssc in the Celestia data directory in order to correct the orientation of some planets and moons, and to fully utilize the altered textures in newtextures.zip. Solarsys.ssc is not included in newtextures.zip.

If you have already customized solarsys.ssc and do not wish to overwrite, there follows a list of the revisions I've made to the major planets and moons. (Gaspra, Ida, Dactyl and Eros revisions appear in sections #3 and #4 below.)

1. Added Venus surface texture and clouds (contained in newtextures.zip).

   
    Texture "venussurface.jpg"           #added Venus surface texture
    # BumpMap "venusbump.jpg"
    HazeColor [ 0.5 0.35 0.2 ]
    HazeDensity 0.35
    Radius 6052
   
    Atmosphere {
     Height 60
     Lower [ 0.8 0.8 0.5 ]
     Upper [ 0.6 0.6 0.6 ]
     Sky [ 0.8 0.8 0.5 ]
     CloudMap "venus.jpg" #
     CloudHeight 50           #Venus clouds using revised original Venus texture
     CloudSpeed  90          #
    }
   
   

2. Revised Jupiter's RotationOffset in order to position Great Red Spot correctly in default jupiter.jpg texture.

    RotationPeriod       9.927953 # System II (for GRS)
    # RotationPeriod    9.924920 # System III (radio emissions)
    Obliquity                2.222461
    EquatorAscendingNode -22.203
    # RotationOffset    305.40 #System III prime meridian
    RotationOffset 16 #revised to correctly align GRS in jupiter.jpg
   
   

3. Corrected RotationOffset for Galilean satellites, now that their orbits have been revised.

   Io

   RotationOffset 219
   

   Europa

   RotationOffset 53
   

   Ganymede

   RotationOffset 60
   

   Callisto

   RotationOffset 282
   

4. For completeness, provided RotationOffset for Saturn System III.

    RotationPeriod               10.65622 # System III - magnetic field
    Obliquity                        28.049
    EquatorAscendingNode 169.530
    RotationOffset                358.922 #correct System III prime meridian
   

1.2: newtextures.zip

newtextures.zip (700KB)

This file should be unzipped into your Celestia directory - it will over-write the Celestia textures in the lores and medres directories which require replacement.

These textures are provided in order to correct a number of orientation errors in the standard Celestia 1.2.5 texture maps.

Three types of texture correction are required, for various bodies:

1. A longitude adjustment, to bring the prime meridian to the centre of the map.

2. A north-to-south rotation, to correct the orientation of some maps which are applied to retrograde-rotating bodies.

3. A north-to-south mirror, to compensate for the unusual behaviour of texture maps when applied to Celestia's *.3ds mesh objects.

The following textures are adapted from existing Celestia textures:

Longitude adjustment:
europa.jpg

North-south mirror:
phobos.jpg
deimos.jpg (a higher-resolution texture than provided with Celestia)

North-south rotation:
venus.jpg
ariel.jpg
umbriel.jpg
titania.jpg
oberon.jpg


Longitude adjustment + North-south rotation:
miranda.jpg

In addition, I've produced a surface map of Venus, from public domain USGS imagery:
venussurface.jpg

Also included is a revised texture for Saturn's rings, produced by Selden E Ball Jr, which corrects a mismatch between the transparency and reflected-light image supplied in Celestia.

Grant Hutchison, January 2003

Note: Corrected lower resolution maps of Phobos and Deimos are included in newtextures.zip above, but these two higher resolution versions are not.

Deimos surface texture Celestia currently mirror-reverses textures applied to its 3DS shape models. This north-south reflected map of Diemos corrects that problem.

Phobos surface texture Celestia currently mirror-reverses textures applied to its 3DS shape models. This north-south reflected map of Phobos corrects that problem.

Celestia currently handles textures applied to 3ds mesh objects in an unusual way - instead of wrapping around the surface of the mesh, the texture appears to pass through the centre of the mesh object and be pasted onto the inside of the opposite surface. The resulting east-west mirroring effect can be offset by keeping the applied texture 180 degrees out of alignment with the orientation of the mesh object, but the north-south mirroring must be compensated for by pre-mirroring the applied texture, so that it appears the right way up within Celestia.

This effect occurs in all the 3ds objects in Celestia: Phobos, Deimos, Amalthea, Proteus, Hyperion and various asteroids and comet nuclei. All require their applied textures to be mirrored north-south for a correct Celestia appearance.

The above high-resolution maps of Phobos and Deimos have been correctly reorientated. They are derived from the public domain maps by Phil Stooke available at http://www.psi.edu/pds/maps.html.

Grant

ida-gaspra.zip

This file provides a replacement shape model for the asteroid Ida - the version provided with Celestia is a mirror image of the true asteroid shape. I generated the underlying mesh object from the shape data provided by Peter Thomas, which appears on Phil Stooke's Cartography of Non-Spherical Worlds website at http://publish.uwo.ca/~pjstooke/plancart.htm. "Praesepe" then smoothed and shaded my generated mesh object to give the final result.

This file also adds two texture maps to the medres folder:

idamosaic.jpg

gaspramosaic.jpg

These are public domain photomosaic maps prepared by Phil Stooke, and obtained from his Small World Atlas at http://www.ssc.uwo.ca/geography/spacemap/. They were created from images taken during the Galileo encounter, and necessarily provide mixed coverage - some high resolution, some very low resolution, and some absent coverage. They are therefore unsatisfactory maps for general use, but very interesting to use when following the Galileo encounter within Celestia, when it becomes clear why the mosaic coverage is as it is.

To accurately reproduce the Galileo encounters, you must also edit solarsys.ssc, pasting in the appended definitions for Gaspra, Ida and Dactyl. (The orbit I've defined for Dactyl is just one of several plausible, non-chaotic orbits consistent with the Galileo observations - see the URL I reference below for much interesting detail.)

Grant Hutchison January 2003

---

"Gaspra" "Sol"

{

	Class "asteroid"

	Mesh "gaspra.3ds"

	#Texture "asteroid.jpg"

	Texture "gaspramosaic.jpg" #Phil Stooke

	Color   [ 0.52 0.47 0.42 ]

	BlendTexture true



	Radius 9.5



	EllipticalOrbit

	{

	Epoch           2448559    #1991 Oct 29 - Galileo encounter

	Period          3.2837     #average

	SemiMajorAxis   2.2096348  #at epoch

	Eccentricity    0.1738752  #at epoch

	Inclination     4.0975771  #at epoch

	AscendingNode   253.445592 #at epoch

	ArgOfPericenter 129.045896 #at epoch

	MeanAnomaly     280.769206 #at epoch

	}



	RotationPeriod       7.042073

	EquatorAscendingNode 109.59

	Obliquity            69.28



        RotationOffset       238.865



	Albedo 0.1

}



"Ida" "Sol"

{

	Class "asteroid"

	Mesh "ida.3ds"

	#Texture "asteroid.jpg"

	Texture "idamosaic.jpg" #Phil Stooke

	Radius 45



	EllipticalOrbit

	{

	Epoch		2449228      #1993 Aug 28: Galileo encounter

	Period          4.8417       #average

	SemiMajorAxis   2.863731     #at epoch

	Eccentricity    0.043109     #at epoch

	Inclination     1.137110     #at epoch

	AscendingNode   324.586055   #at epoch

	ArgOfPericenter 113.017101   #at epoch

        MeanAnomaly     131.594945   #at epoch

	}



	RotationPeriod       -4.633632

	EquatorAscendingNode  172.77

	Obliquity	      23.04

	RotationOffset        0.54



	Albedo 0.24

}



"Dactyl" "Sol/Ida"

{

	#Data for Dactyl taken from: 

	#Petit et al.: The Long-Term Dynamics of Dactyl's Orbit

	#(Icarus 1997: 130; 177-197)

	InfoURL "http://www.lpl.arizona.edu/~hurfordt/research/papers/Icarus130.pdf"



	Class "asteroid"

	Texture "asteroid.jpg"

	Mesh "roughsphere.cms"

	Radius   0.7



	EllipticalOrbit

	{

	Epoch	         2449228.2028 #1993 Aug 28 16:52:05

	Period           -0.96534 #stable 5:1 resonant orbit (Petit et al.)

	SemiMajorAxis    83.5     #stable 5:1 resonant orbit (Petit et al.)

	Eccentricity     0.13     #stable 5:1 resonant orbit (Petit et al.)

	LongOfPericenter 230      #stable pericenter at 90ºE Ida longitude (Petit et al.)

	AscendingNode    90       #VERY approximate - chosen to place Dactyl north 

                                  #of Ida's equator, as seen at time of Galileo encounter

	Inclination      8        #estimated at 7-9 degrees (Petit et al.)

	}



	RotationPeriod  -23.16816 #enforce synchronous rotation

	RotationOffset  57        #place prime meridian facing Ida



	Albedo 0.2

}

---

The shape model of Eros provided with Celestia is mirror-reversed, perhaps because the original NEAR data use east longitude, rather than the more conventional west longitude. The files below provide a corrected shape model for Eros, prepared from the NEAR Laser Range Finder data accessible at http://pdssbn.astro.umd.edu/NEARdb/nlr/#shape.

4.1: High resoultion model of Eros.

eros.zip (370KB)

The original data are at one-degree resolution - this model has a resolution of two degrees - enough to show considerable detail without becoming too large. The colour of the model is taken from Celestia's original specification, which was sampled from NEAR colour photographs. This model does not accept textures in Celestia, but I have not so far encountered a texture for Eros that does more than obscure the surface features that are evident in the shape model. However I hope to provide a 5-degree resolution model that can use surface textures soon, as a separate download.

When you unzip this file in the Celestia root directory, it will place eros2.3ds in the models directory, and install a sampled orbit for the NEAR spacecraft - a file called NEAR-eros1998.xyz in the data directory and a file called NEAR1998.ssc in the extras directory. This recreates the position of the NEAR spacecraft during the fly-by of 22-24 December 1998 - look for NEAR1998 in Solar System Browser.

To correctly orientate the 2-degree model, paste the following specification into your Celestia solarsys.ssc file, replacing the original Eros definition.

---

"Eros" "Sol"

{

	Class "asteroid"

	Mesh   "eros2.3ds"

	# Color sampled from true color photo taken by NEAR

	Color   [ 0.52 0.47 0.42 ]

	BlendTexture true

	Radius 16.5



	EllipticalOrbit

	{

	Epoch           2451171 #23 Dec 1998 NEAR fly-by

	Period            1.761 #average

	SemiMajorAxis     1.458261 #at epoch

	Eccentricity      0.222885 #at epoch

	Inclination      10.830143 #at epoch

	AscendingNode   304.430882 #at epoch

	ArgOfPericenter 178.613184 #at epoch

	MeanAnomaly     208.403434 #at epoch

	}



	RotationPeriod         5.270

	Obliquity             78.70

	EquatorAscendingNode 107.23

	RotationOffset       158.165



	Albedo            0.16

}

---

This produces a good encounter for the 1998 NEAR fly-by: the orbital elements are incorrect for the later orbit and landing in 2000, but this encounter is so complex I expect that it will require xyz sampled orbits for spacecraft and asteroid. Grant Hutchison January 2003

4.2: Lower resoultion model of Eros.

eros-texture.zip (380KB)

The original data are at one-degree resolution - this model has a resolution of five degrees. I provided the mesh and the texture mapping, and "Praesepe" smoothed and tinted the result. This provides an alternative to the 2-degree, untextured mesh that I created earlier, since this one *will* accept a texture in Celestia.

Because there seem to be no useful Eros textures available, I have made my own, which is also included in this zip file. It is a 2k shaded relief map, prepared from the one-eighth-degree elevation data available at at the NEAR site mentioned above, and correctly orientated for the behaviour of mesh objects within Celestia.

(If anyone out there would like to take on the task of uniting this texture with the hi-res shape model, I'll be very happy indeed - contact me at the address indicated in the .ZIP file.)

To correctly orientate the 5-degree model, paste the following specification into your Celestia solarsys.ssc file, replacing the original Eros definition.

---

"Eros" "Sol"

{

	Class "asteroid"

	Mesh   "eros5.3ds"

	Texture "eros2k.jpg"

	# Color sampled from true color photo taken by NEAR

	Color   [ 0.52 0.47 0.42 ]

	BlendTexture true

	Radius 16.5



	EllipticalOrbit

	{

	Epoch           2451171 #23 Dec 1998 NEAR fly-by

	Period            1.761 #average

	SemiMajorAxis     1.458261 #at epoch

	Eccentricity      0.222885 #at epoch

	Inclination      10.830143 #at epoch

	AscendingNode   304.430882 #at epoch

	ArgOfPericenter 178.613184 #at epoch

	MeanAnomaly     208.403434 #at epoch

	}



	RotationPeriod         5.270

	Obliquity             78.70

	EquatorAscendingNode 107.23

	RotationOffset       158.165



	Albedo            0.16

}

---

This zip file should be Unzipped in your Celestia root directory, to install eros5.3ds in the models directory, and eros2k.jpg in the textures\medres directory.

Grant Hutchison January 2003

4.3: Topography texture maps of Eros.

Eros topography	Eros shaded topography
.
(The snapshots below were generated by Selden)
Eros 5-degree w/ topography	Eros 5-degree w/ shaded topography
Eros 5-degree w/ texture map	Eros 2-degree w/ no texture map

saturnmoons.zip

This file should be unzipped in your Celestia root directory. It provides shape models and textures for three inner moons of Saturn, adapted from public domain data and images provided by Phil Stooke at his "Cartography of Non-spherical Worlds" website http://publish.uwo.ca/~pjstooke/plancart.htm and his "Small World Atlas" website http://www.ssc.uwo.ca/geography/spacemap/contents.htm

I generated the 3ds mesh objects and modified and applied the texture maps. Smoothing of the resulting objects was done by "Praesepe".

All of these satellites depart markedly from simple elliptical orbits - Janus and Epimetheus interact strongly with each other during close approaches, as do Prometheus and the satellite Pandora. MeanAnomaly values provided in the Celestia add-on file minormoons.ssc have therefore been chosen arbitrarily. However, all these moons are in synchronous rotation with their orbital periods, so it adds realism if the shape models are rotated to align their prime meridians with Saturn.

To display them in their correct orientations in Celestia you should either add the relevant RotationOffsets to minormoons.ssc (if you have downloaded that add-on file), or create a new *.ssc file in the extras directory, containing the following definitions:

---

"Prometheus" "Sol/Saturn"

{

	Texture	 	"prometheus.jpg"

	Mesh		"prometheus.3ds"

	Radius		50



	EllipticalOrbit

	{

	Period		0.612986

	SemiMajorAxis	139350

	Eccentricity	0.0024

	Inclination	0

	MeanAnomaly     97 #arbitrary value taken from minormoons.ssc

	}



	RotationOffset  97 #set equal to MeanAnomaly to orientate prime meridian



	Albedo 0.1

}





"Epimetheus" "Sol/Saturn"

{

	Texture	 	"epimetheus.jpg"

	Mesh		"epimetheus.3ds"

	Radius		59



	EllipticalOrbit

	{

	Period		0.694590

	SemiMajorAxis	151422

	Eccentricity	0.009

	Inclination	0.34

	MeanAnomaly     140 #arbitrary value taken from minormoons.ssc

	}



	RotationOffset  140 #set equal to MeanAnomaly to orientate prime meridian



	Albedo 0.1

}



"Janus" "Sol/Saturn"

{

	Texture	 	"janus.jpg"

	Mesh		"janus.3ds"

	Radius		89



	EllipticalOrbit

	{

	Period		0.694590

	SemiMajorAxis	151427

	Eccentricity	0.007

	Inclination	0.14

	MeanAnomaly     136  #arbitrary value taken from minormoons.ssc

	}



	RotationOffset  136 #set equal to MeanAnomaly to orientate prime meridian



	Albedo 0.1

}

---

Grant Hutchison February 2003

Contents

1: Corrections of rotation elements and surface maps.

1.1: Solarsys.ssc
1.2: newtextures.zip

2: Revised surface maps for Phobos and Deimos.
3: Galileo's flyby of Gaspra and Ida.
4: NEAR's flyby of Eros.

4.1: High resoultion model of Eros.
4.2: Lower resoultion model of Eros.
4.3: Topography texture maps of Eros.

5: Saturn's moons.

• Placing objects at defined locations on planetary surfaces
• An Empty object for mutual orbits
  (includes a binary asteroid definition; not needed for Celestia v1.3.0)
• Zubrin Statites to Terraform Mars
• Corrections for Celestia v1.3.0

• Selden's List of Celestia Resources

---

The content of this Web page was provided by Grant Hutchison.

This Web page is maintained by Selden Ball at Wilson Lab.
Please send any comments or corrections to seb1@cornell.edu