Permanent use of spice kernels

[CAP-Team]

Yesterday I was trying to rebuild the solar system using spice kernels (de421.bsp) by implementing it into solarsys.ssc (and timelines).
Problem is that the spice kernel isn't used when placed in the data directory or the celestia directory.

Only when the extras directory is used and the spice kernel is put there, it can be used.
Is this built in behaviour?

After some testing (Mercury, Venus, Earth + Moon), I began working on Mars. Mars itself wasn't very hard, but using a different spice kernel for Phobos and Deimos didn't seem to work.

So my basic question is, what are the limits of using spice kernels for permanent use, or are there some things I should do before this can be implemented succesfully?

[cartrite]

I began working on Mars. Mars itself wasn't very hard, but using a different spice kernel for Phobos and Deimos didn't seem to work.

What kernel are you using for Phobos and Deimos? de421 does not contain those bodies. You probably wnat to download the spice toolkit from NAIF.
ftp://naif.jpl.nasa.gov/pub/naif/toolkit/C
In it will be a program called brief. You can use that to see what bodies are covered by a kernel.
There is also a program called spkmerge. You can use that program to combine kernels together.
The kernel mar063.bsp contains Phobos and Deimos but there is no solarsystem barycenter and those moons probably have the sun as the origin or maybe Mars. I'm not sure. You can combine mar063 with de421 with spkmerge.
cartrite

[CAP-Team]

I used mars063.bsp for Phobos and Deimos, and the kernel does contain the Mars barycenter (I know the brief command )
Anyway, it did work when I copied both moons to phobos_spice and deimos_spice (in stead of modifying them), but the positions between Phobos and Phobos_spice were different from the keplerian elements I got from the Horizons system at 1-1-2000.

I thought I'd create the inner planets first (if successfully working), and later the outer planets with their moons

[cartrite]

I just started to use mar063 with ISIS to project the Phobos image from HiRise. And although it uses a barycenter for Deimos, Phobos and Mars, it doesn't use the solarsystem barycenter as the origin. It uses the Sun as the origin. Something that is causing me headaches. I wanted to see if you found a different kernel with data for Phobos.
I haven't tried to create a spice solarsystem for Celestia. I did a couple of addons. Deep Impact, Near, and Galileo. It was my understanding that the kernels needed to be in the data dir of the addon but that may have changed or I may have misunderstood. I just started to play with them again.
cartrite

[chris]

I used mars063.bsp for Phobos and Deimos, and the kernel does contain the Mars barycenter (I know the brief command )
Anyway, it did work when I copied both moons to phobos_spice and deimos_spice (in stead of modifying them), but the positions between Phobos and Phobos_spice were different from the keplerian elements I got from the Horizons system at 1-1-2000.

That could indicate that the HORIZONS elements were in the wrong coordinate system. How different are the positions?

I thought I'd create the inner planets first (if successfully working), and later the outer planets with their moons

A lot of the outer solar system work has already been done by volcanopele: the Galileo and Cassini SPICE add-ons take care of Saturn and Jupiter. My New Horizons add-on covers Pluto. Adding the Uranus and Neptune systems and packaging it all together would be very worthwhile.

--Chris

[CAP-Team]

That could indicate that the HORIZONS elements were in the wrong coordinate system. How different are the positions?

Well, other side of the planet or about 90 degree difference. I could post a screenshot.

A lot of the outer solar system work has already been done by volcanopele: the Galileo and Cassini SPICE add-ons take care of Saturn and Jupiter. My New Horizons add-on covers Pluto. Adding the Uranus and Neptune systems and packaging it all together would be very worthwhile.
--Chris

Yes I know, I used volcanopele's addon as an example Uranus and Neptune (planets) shouldn't be that hard, it's just the moons and their ephemerides.

I'd still like to know why .bsp files aren't read when placed in Celestia's data directory.
Essentially I now use the regular (with some adjustments) solarsys.ssc and use separate .ssc files in the extras directory to adjust the trajectories to use spice kernels.

[chris]

That could indicate that the HORIZONS elements were in the wrong coordinate system. How different are the positions?

Well, other side of the planet or about 90 degree difference. I could post a screenshot.

A lot of the outer solar system work has already been done by volcanopele: the Galileo and Cassini SPICE add-ons take care of Saturn and Jupiter. My New Horizons add-on covers Pluto. Adding the Uranus and Neptune systems and packaging it all together would be very worthwhile.
--Chris

Yes I know, I used volcanopele's addon as an example Uranus and Neptune (planets) shouldn't be that hard, it's just the moons and their ephemerides.

I'd still like to know why .bsp files aren't read when placed in Celestia's data directory.
Essentially I now use the regular (with some adjustments) solarsys.ssc and use separate .ssc files in the extras directory to adjust the trajectories to use spice kernels.

Are you sure there's not a typo somewhere? Does anything odd appear in the console log (~ key) when loading the solar system add-on?

--Chris

[CAP-Team]

No, at least no errors in loading textures.

Also funny thing (bug?) is that if I modify or replace Phobos or Deimos to use spice kernels, it seems as if the changes are ignored, but when I rename Phobos and Deimos in my extras directory, to create separate moons, they do show up.

Difference between kepler elements and spice kernels.

spice.jpg

Compared to David Seals solar system simulator the spice moons' positions are correct.

Weird lines are drawn for the orbits of Phobos and Deimos

spice2.jpg

[chris]

No, at least no errors in loading textures.

Also funny thing (bug?) is that if I modify or replace Phobos or Deimos to use spice kernels, it seems as if the changes are ignored, but when I rename Phobos and Deimos in my extras directory, to create separate moons, they do show up.

Difference between kepler elements and spice kernels.

spice.jpg

Compared to David Seals solar system simulator the spice moons' positions are correct.

Weird lines are drawn for the orbits of Phobos and Deimos

spice2.jpg

The strange lines are probably a result of not specifying the orbital period of the SpiceOrbit properly--without this field, Celestia's doesn't know what time range to use when displaying the orbit. Can you post your Phobos and Deimos definitions?

--Chris

[CAP-Team]

Sure, here it is.
It's placed in the extras directory.

Code: Select all

"Phobos_spice" "Sol/Mars"
{
  Class            "moon"
  Texture          "phobos.*"
  NormalMap        "phobos-normal.*"
  Mesh             "phobos.cmod"
  Radius                  13.1         # maximum semi-axis
  MeshCenter       [ -0.233 -0.156 -0.168 ]
  Albedo                   0.06
 
  Beginning        "1962 12 04 00:00"
  Ending           "2050 01 03 00:00"
  OrbitFrame { EclipticJ2000 { Center "Sol/Mars_bary"}}
  BodyFrame { EquatorJ2000 { Center "Sol/Mars" } }
 
  SpiceOrbit {
    Kernel     "mar063.bsp"
    Target     "401"
    Origin     "4"
    Period                 0.319142643586394
    BoundingRadius      1e10
  }

  UniformRotation {
    Inclination            0.0
    MeridianAngle        354.2
  }
}

# -----------------------------------

"Deimos_spice" "Sol/Mars"
{
  Class            "moon"
  Texture          "deimos.*"
  NormalMap        "deimos-normal.*"
  Mesh             "deimos.cmod"
  Radius                   7.8         # maximum semi-axis
  MeshCenter       [ -0.299 -0.284 0.369 ]
  Albedo                   0.06

  Beginning        "1962 12 04 00:00"
  Ending           "2050 01 03 00:00"
  OrbitFrame { EclipticJ2000 { Center "Sol/Mars_bary"}}
  BodyFrame { EquatorJ2000 { Center "Sol/Mars" } }

  SpiceOrbit {
    Kernel         "mar063.bsp"
    Target         "402"
    Origin         "4"
    Period                 1.26258716573443
    BoundingRadius      1e10
  }

  UniformRotation {
    Inclination            0.9
    AscendingNode        183.0
    MeridianAngle        214.7
  }
}


I've added a period in the spice orbit now. The orbits of Phobos and Deimos look fine now, but Mars still seems to be on some kind of highway

spice3.jpg

[Ajaja]

CAP-Team
I've been making Mars system using SpiceOrbits few days ago.
Looks very accurate.
View Phobos from Deimos: http://space.jpl.nasa.gov


Celestia:


There is my mars.ssc:

Code: Select all

Modify "Mars" "Sol"
{
    OrbitFrame {
       EclipticJ2000 { Center "Sol" }
    }
    SpiceOrbit
    {
        Kernel "mar063.bsp"
        Target "MARS"
        Origin "SUN"
        BoundingRadius 2
        Period 1.8809
    }
    BodyFrame {
       EclipticJ2000 { Center "Sol" }
    }
    SpiceRotation
    {
        Kernel              "pck00008.tpc"
        Frame               "IAU_MARS"
        BaseFrame           "eclipj2000"
        Period              24.622962
    }
}

Modify "Phobos" "Sol/Mars"
{
    OrbitFrame {
       EclipticJ2000 { Center "Sol/Mars" }
    }
    SpiceOrbit
    {
        Kernel "mar063.bsp"
        Target "PHOBOS"
        Origin "MARS"
        BoundingRadius 2e4
        Period 0.318910
    }
}

Modify "Deimos" "Sol/Mars"
{
    OrbitFrame {
       EclipticJ2000 { Center "Sol/Mars" }
    }
    SpiceOrbit
    {
        Kernel "mar063.bsp"
        Target "DEIMOS"
        Origin "MARS"
        BoundingRadius 3e4
        Period 1.262441
    }
}


Few notes. Latest spice library allows to use names instead of numbers ("MARS" instead of "499" for example). And I don't use barycenters. What is the sense to use them? It seems like spice library makes all required conversions by itself...

[CAP-Team]

I've tried this, the weird lines are gone, and it seems to work like this.

The barycenters are used for systems like Earth. The center of the Earth/Moon system, the point where Earth and Moon are rotating around is not the center of the earth but a point more at the surface of the earth.

Nevertheless, if it's true you don't have to use barycenters, it would simplyfy things a lot!

[Ajaja]

The barycenters are used for systems like Earth. The center of the Earth/Moon system, the point where Earth and Moon are rotating around is not the center of the earth but a point more at the surface of the earth.
Nevertheless, if it's true you don't have to use barycenters, it would simplyfy things a lot!

Nevermind, in Mars system or in Earth-Moon system, spice calculate correct coordinates of target relative to origin (planet, barycenter, anoter moon - it is not important). You need only specify corresponding center of orbit frame in Celestia *.ssc.