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View Full Version : Is it safe to point Cassini's antenna to the Sun directly?



yaohua2000
2004-Nov-30, 02:59 PM
According to JPL HORIZONS System, I found that there will be a transit of the Earth/Moon across the Sun as seen from Titan, just 3 hours before Huygens enters Titan's atomsphere. If the spacecraft transmit data to the Earth at that time, it has to point its main antenna to the Sun directly, is it safe? and because of this, I think the spacecraft will not receive command from the Earth, right?

kucharek
2004-Nov-30, 03:05 PM
As seen from Saturn Earth is always close to the sun, it should be no problem to point the antenna directly at it. This also happens during solar conjunction.
But while during solar conjunction two-way comm is a problem, in the case you describe it should be as you said: Cassini can't get us out of the sun's radio noise, but we have no problem to listen to Cassini.

Harald

PS: Are you sure there is really a transit? I guess, it must be a pretty rare event.

PPS: Yes, there is: http://en.wikipedia.org/wiki/Transit_of_Earth_from_Saturn and several other locations.

Ian R
2004-Nov-30, 08:44 PM
Cassini's high-gain antenna was built with its trajectory through the inner solar system in mind. During the Venus encounter, the high-gain was used as a shield to protect the scientific instruments from direct exposure to sunlight, which could potentially be very damaging at that distance from the Sun.

Hale_Bopp
2004-Dec-01, 07:34 PM
As seen from Saturn Earth is always close to the sun, it should be no problem to point the antenna directly at it. This also happens during solar conjunction.
But while during solar conjunction two-way comm is a problem, in the case you describe it should be as you said: Cassini can't get us out of the sun's radio noise, but we have no problem to listen to Cassini.

Harald

PS: Are you sure there is really a transit? I guess, it must be a pretty rare event.

PPS: Yes, there is: http://en.wikipedia.org/wiki/Transit_of_Earth_from_Saturn and several other locations.

You got the best of my curiosity, so I fired up Starry Night Backyard and went to Saturn to check it out.

Earth does seem to transit the Sun on January 13th, 2005, starting around 18:00 UT. It lasts almost 24 hours. You can also see the Moon trailing Earth in a transit across the Sun.

I just checked and Earth passes south of the Sun in late January of 2006, so there is no transit that year. There has to be an easy way to search and see how common it is...I am not in the mood to sit here and find all the possible transits in Starry Night!

Rob