Celestia Forums

Posted: **01.06.2003, 17:24**

Hey all

Here's a model of ESA's Infrared Space Observatory, which was the predecessor of the soon-to-launch Space Infrared Telescope Facility. It orbited earth from 1995-98, at a very large high eccentricity orbit.

Download from http://homepage.eircom.net/~jackhiggins/celestia/ (number 20) but first-

Here are a few screenshots:

I have an xyz for this model, but since it's in an earth orbit, an xyz doesn't work very well... I haven't been able to find any orbital elements anywhere, and Horizons wont allow me to get Earth centred elements.
I need your help!! If anyone can get good orbital elements for this craft, i'll be very grateful.

Thanks!

Posted: **01.06.2003, 18:52**

Jack,

I'm not sure what you mean by "good", but I had no troubel getting earth-centered Keplerian orbital elements for June 30, 1998:

Code: Select all

2450994.500000000 = A.D. 1998-Jun-30 00:00:00.0000 (CT)
 EC= 8.149526336541361E-01 QR= 5.215292311177972E-05 IN= 2.378672299975047E+01
 OM= 1.744584358535704E+02 W = 1.196470304113497E+01 Tp= 2.450994391607464E+06
 N = 3.610135642500096E+02 MA= 3.913117581335943E+01 TA= 1.420067408389750E+02
 A = 2.818355329321632E-04 AD= 5.115181427525467E-04 PR= 9.971924482889853E-01

I used Horizons' telnet interface.

Code: Select all

Symbol meaning [1 AU=149597870.691 km, 1 day=86400.0 s]:

    JDCT     Epoch Julian Date, Coordinate Time
      EC     Eccentricity, e
      QR     Periapsis distance, q (AU)
      IN     Inclination w.r.t xy-plane, i (degrees)
      OM     Longitude of Ascending Node, OMEGA, (degrees)
      W      Argument of Perifocus, w (degrees)
      Tp     Time of periapsis (Julian day number)
      N      Mean motion, n (degrees/day)
      MA     Mean anomaly, M (degrees)
      TA     True anomaly, nu (degrees)
      A      Semi-major axis, a (AU)
      AD     Apoapsis distance (AU)
      PR     Orbital period (day)

Posted: **01.06.2003, 19:01**

and here are the km/day elements around the earth-moon barycenter

Code: Select all

2450994.500000000 = A.D. 1998-Jun-30 00:00:00.0000 (CT)
 EC= 8.399821287888486E-01 QR= 8.524468037397823E+03 IN= 2.295419437950456E+01
 OM= 1.742678044060470E+02 W = 1.628463870879305E+01 Tp= 2.450994378370037E+06
 N = 2.557476708691096E+02 MA= 3.110657968825960E+01 TA= 1.401241053972481E+02
 A = 5.327197501677411E+04 AD= 9.801948199615041E+04 PR= 1.407637452871452E+00

Code: Select all

Symbol meaning [1 day=86400.0 s]:

    JDCT     Epoch Julian Date, Coordinate Time
      EC     Eccentricity, e
      QR     Periapsis distance, q (km)
      IN     Inclination w.r.t xy-plane, i (degrees)
      OM     Longitude of Ascending Node, OMEGA, (degrees)
      W      Argument of Perifocus, w (degrees)
      Tp     Time of periapsis (Julian day number)
      N      Mean motion, n (degrees/day)
      MA     Mean anomaly, M (degrees)
      TA     True anomaly, nu (degrees)
      A      Semi-major axis, a (km)
      AD     Apoapsis distance (km)
      PR     Orbital period (day)

Does this help?

Posted: **01.06.2003, 19:51**

Thanks!!

I've tried to use Horizons telnet several times in the last few weeks to get Earth centred elements, but it wouldn't let me specify the Earth as an orbit centre...

I'll put up these elements on my site for anyone who wants to use this model.

Posted: **01.06.2003, 20:44**

Ok i have those elements in a zip file on my site now. After comparing them both to the xyz file, the Earth centred one seems to be the more accurate, but the ISO's orbit seems to have changed a few times, from an eccentric near polar orbit, to the one in the ssc file.

Posted: **01.06.2003, 21:03**

Jack,

For the earth centered coordinates, all I did just now was type
earth
when it asked for the corrdinate system center. It didn't complain.
Maybe they changed something.
Of course "earth" is not the same as "earth-moon barycenter" (3).

Celestia Forums

New Infrared Space Observatory model- need an ssc!

New Infrared Space Observatory model- need an ssc!