Celestia Forums

Celestia 1.6 1995 Dez 07 18:00:00 UTC

After that time, galileo goes inside jupiter...

I don't understand the problem, could you explain more?

Hi friends!
http://yfrog.com/0tgalileopj
Here is a snapshot of the passage of galileo spacecraft inside Jupiter!!
Celestia 1.6.0

Ciao
Pierluigi

piellepi wrote:Hi friends!
http://yfrog.com/0tgalileopj
Here is a snapshot of the passage of galileo spacecraft inside Jupiter!!
Celestia 1.6.0

Ciao
Pierluigi

celestia 1.6.0

cel://Follow/Sol:Jupiter/1995-12-07T18: ... rc=0&ver=3

Ephemeris Type [change] : VECTORS
Target Body [change] : Galileo Spacecraft [-77]
Coordinate Origin [change] : Sun (body center) [500@10]
Time Span [change] : Start=1989-OCT-19 01:29:33.2605, Stop=2003-SEP-30 12:00, Step=1 d
Table Settings [change] : output units=KM-S; quantities code=2; CSV format=YES; object page=NO
Display/Output [change] : default (formatted HTML)


*******************************************************************************
Ephemeris / WWW_USER Sat Sep 19 17:15:21 2009 Pasadena, USA / Horizons
*******************************************************************************
Target body name: Galileo Spacecraft (-77) {source: dpfil-000221-od281-i27-e}
Center body name: Sun (10) {source: DE405}
Center-site name: BODY CENTER
*******************************************************************************
Start time : A.D. 1989-Oct-19 01:29:33.2605 CT
Stop time : A.D. 2003-Sep-30 12:00:00.0000 CT
Step-size : 1440 minutes
*******************************************************************************
Center geodetic : 0.00000000,0.00000000,0.0000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: 0.00000000,0.00000000,0.0000000 {E-lon(deg),Dxy(km),Dz(km)}
Center radii : 696000.0 x 696000.0 x 696000.0 k{Equator, meridian, pole}
Output units : KM-S
Output format : 02
Reference frame : ICRF/J2000.0
Output type : GEOMETRIC cartesian states
Coordinate systm: Ecliptic and Mean Equinox of Reference Epoch
*******************************************************************************
JDCT , , X, Y, Z, VX, VY, VZ,
*******************************************************************************



http://img193.imageshack.us/i/imageig.png/

Here's an updated Galileo ssc and xyzv trajectory that is much more accurate and completely free of collisions:

http://www.celestiaproject.net/~claurel/celest ... update.zip

The old Galileo is moved to galileo-old.ssc to make it easy to compare the trajectories. The updated trajectory should be accurate to within 2km of the SPICE trajectory. For those interested, here's the xyzv information from the header:


--Chris

Chris,

is this version the same as the one you gave me by email, this morning ? (which contains a collision against Europa). I'm not home right now, so I can't check my personal home emails for the moment.

Since the xyzv file is relatively small (about 500 KB), maybe a 1 km resolution would be a good thing to try ? (if data is available, of course).

Cham wrote:Chris,

is this version the same as the one you gave me by email, this morning ? (which contains a collision against Europa). I'm not home right now, so I can't check my personal home emails for the moment.

Since the xyzv file is relatively small (about 500 KB), maybe a 1 km resolution would be a good thing to try ? (if data is available, of course).

The xyzv file is fine. It's the position of Jupiter that's off. The default VSOP87 model of the orbit of planetary orbits is only accurate to an arcsecond (as used in Celestia.) At Jupiter's distance from the Sun, this is over 3000km! Some possible solutions are:

- Use another semianalytic series with more terms for the orbits of the planets. The drawback is that the hundreds or thousands of trigonometric terms are expensive to evaluate.
- Use a table based ephemeris like DE405. Much faster than series, but a lot of data is necessary to cover a long time range (~200MB for the reduce precision DE406 ephemeris -3000 BCE to 3000 CE)
- Use a hybrid approach--tables covering 1950-2100, VSOP87 outside that range

To just get the Galileo mission right, I propose a solution similar to what's done for Cassini: split the mission into a heliocentric cruise phase and a Jupiter-centric orbital phase. Since the in the orbital phase the position of the spacecraft is given relative to Jupiter, inaccuracies in the position of Jupiter wouldn't cause troubles. Additionally, the orbit of Galileo would be shown relative to Jupiter after the cruise phase, which is a more helpful for understanding the geometry of encounters with the moons.

--Chris

chris wrote:To just get the Galileo mission right, I propose a solution similar to what's done for Cassini: split the mission into a heliocentric cruise phase and a Jupiter-centric orbital phase. Since the in the orbital phase the position of the spacecraft is given relative to Jupiter, inaccuracies in the position of Jupiter wouldn't cause troubles. Additionally, the orbit of Galileo would be shown relative to Jupiter after the cruise phase, which is a more helpful for understanding the geometry of encounters with the moons.

I agree with this proposition. It would be consistent with our representation of Cassini's mission.

Here's a new version of the Galileo mission with the trajectory split into a cruise and orbit phase:

http://www.celestiaproject.net/~claurel/celest ... pdate2.zip

The Moon encounters now match up pretty well with this timeline:

http://www.dmuller.net/realtime/mission ... on=galileo

The distances aren't spot on, but they seem to be within 100km or so. The difference is a limitation of the accuracy of the default orbits of the Galilean satellites. Making them more accurate involves the same tradeoffs as with planetary orbits.

I also updated the ending time for Galileo so that it actually hits Jupiter.

--Chris