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Radio transmissions to/from Webb

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09-07-2022 , 04:35 PM

JayKon

Pooh-Bah

Join Date: Jan 2003 Posts: 4,487

The James Webb telescope is in L2. L2 is always on the other side of the moon. The moon is made of rock. Radio doesn't go through rock very well. Clearly, communication with the telescope is robust.

Where am I wrong?

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09-07-2022 , 05:18 PM

BrookTrout

old hand

Join Date: Jul 2007 Posts: 1,808

L2 isn't always on the other side of the moon. Webb uses the Deep Space Network, like the Voyager probes.

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09-08-2022 , 07:19 AM

Kalaea

grinder

Join Date: Apr 2021 Posts: 494

It's in a halo orbit around L2, and far enough away (1.5M km) that it would be out of the umbra anyway.

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09-08-2022 , 12:33 PM

JayKon

Pooh-Bah

Join Date: Jan 2003 Posts: 4,487

Quote:

Originally Posted by Kalaea

It's in a halo orbit around L2, and far enough away (1.5M km) that it would be out of the umbra anyway.

So, Webb isn't actually at L2, but is orbiting around L2?

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09-09-2022 , 02:13 PM

BrookTrout

old hand

Join Date: Jul 2007 Posts: 1,808

L2 is a location in space that's moving relative to the Earth and the Sun, so Webb is moving with it.

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09-10-2022 , 12:55 PM

JayKon

Pooh-Bah

Join Date: Jan 2003 Posts: 4,487

Quote:

Originally Posted by BrookTrout

L2 is a location in space that's moving relative to the Earth and the Sun, so Webb is moving with it.

If that were strictly true, then the moon would block radio signals. As stated earlier, L2 is, by definition, on the other side of the moon. In fact, it would be dead center on the other side of the moon and Webb doesn't just sit there. I've seen the animations where it goes in circles and heard that it uses fuel to maintain that orbit.

Based on previous replies, it seems that orbit around L2 is what keeps it in view of earth and out of the umbra of the moon.

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09-11-2022 , 03:01 AM

Kalaea

grinder

Join Date: Apr 2021 Posts: 494

I see the confusion now. Webb is at the Sun-Earth L2 point, not the Earth-Moon L2. This keeps the Sun, Earth and Moon on the same side of the telescope at all times, enabling the telescope to be shaded from radiation from all three sources by one sunshield.

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09-11-2022 , 11:53 AM

JayKon

Pooh-Bah

Join Date: Jan 2003 Posts: 4,487

Quote:

Originally Posted by Kalaea

That makes sense. I think I got confused by the news reports that said it was beyond the moon. Thanks. Did a search with that distinction and found the following.

https://www.youtube.com/watch?v=6cUe4oMk69E

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09-11-2022 , 12:43 PM

Kalaea

grinder

Join Date: Apr 2021 Posts: 494

Nice explanation here: https://www.youtube.com/watch?v=ybn8-_QV8Tg

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09-12-2022 , 01:00 AM

#10

JayKon

Pooh-Bah

Join Date: Jan 2003 Posts: 4,487

Quote:

Originally Posted by Kalaea

Nice explanation here: https://www.youtube.com/watch?v=ybn8-_QV8Tg

Very cool, thanks.

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