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KonigVonMurmeltiere t1_iyalntk wrote

Reply to comment by NinjaLanternShark in Astronomers Worldwide Troubled by New 'Cell Phone Towers in Space' by IslandChillin

It won't affect communications with GPS satellites. But those satellites are only useful if they have a reference point on the earth to calibrate to. Those reference points are generated by radio observatories that observe distant quasars, similar to how sailors used to observe stars, to determining the Earth's precise position in space. But those radio observatories primarily use frequencies that are in the same range as cell towers, so they're in remote areas. AST SpaceMobile's plan is to basically flood the earth with these signals so these remote areas are no longer "quiet", rendering a large portion of the radio telescope's observations useless (exactly how much is TBD).

GPS satellites tell you where you are on the Earth. But how does the GPS satellite know where it is? Geodetic observatories tell the GPS satellites where they are relative to the Earth. Without that, it's all going to be inaccurate.

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egregiouscodswallop t1_iyawmha wrote

šŸ‘šŸ‘šŸ‘ Good explanation! Thank you for teaching me something cool today. Our little potato is clocking itself against galaxies to tell us how potato we are from day to day.

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tastycidr t1_iyayspn wrote

Analogies like this are what make the internet great

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mfb- t1_iyaxg35 wrote

Starlink has uncovered cells around major radio telescopes, i.e. it doesn't send direct signals in that direction. AST SpaceMobile could do the same. How much would that help?

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KonigVonMurmeltiere t1_iyb0jj2 wrote

It would help a lot, and thatā€™s exactly what radio astronomers are proposing. The FCC required Starlink to create those gaps, and they arenā€™t perfect. Enforcement is lax and the protected areas arenā€™t big enough so radio observations are still impacted by Starlink, but itā€™s still a big improvement. Basically radio astronomers are asking the FCC to treat 5g cell frequencies with the same care and consideration that other frequencies already get. The Government Accountability Office (GAO) wrote a recent report that could be interpreted as saying the FCC needs to be looking into this and other concerns.

Itā€™s important to note that the FCC has not granted permission for AST SpaceMobileā€™s plans yet, they only have an experimental license for one single satellite. So there is time to act and come to an agreement. But compared to SpaceX, Blue Origin, and others, AST Spacemobile has not been very cooperative about working with astronomers. They ignored dozens of invitations to meet and discuss the problem, various conferences on the topic, etc, and are only just now in the early stages of discussing it - but have made no public comments or promises.

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Born_Employment405 t1_iybfhic wrote

AST owns no spectrum. It has to have a local partner in country like Tmobile or Claro to operate. They use the partner's spectrum. If they transit without spectrum rights they'll be fined. If they receive without an MNO partner it's unlawful surveillance. They're only going to operate in places where their partner is currently permitted to operate. If there's a prohibition on transmission because of radioastronomy AST will need to observe that prohibition too. Also, GPS space segment clocks are hyperstable over long periods, they only need to be calibrated once every 10 years.

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KonigVonMurmeltiere t1_iybihpj wrote

Correct, they'll only be broadcasting in certain areas where the partners are permitted to operate, using their spectrum. At the moment there are few regulations on mobile providers in most places, as stated in the article. In the past that wasn't a big deal because most radio observatories are remote and many are typically situated in valleys or bowls so the terrain helps block the interference, but that may not be enough anymore.

The clocks may be stable but the Earth is changing all the time so it still has to be updated frequently, not just time offsets but position offsets to account for tectonic activity, changes in the Earth's rotation and precession, etc. It is all very small but over time the errors grow.

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toodroot t1_iyb3oe5 wrote

You can get Starlink at several EHT stations, so I'm not so sure how true that is. For example, Haystack.

Maybe that changed more recently?

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mfb- t1_iyb4s5g wrote

It can be a bit confusing, but if you check the map then it has gaps in these locations. I have a list of all of them, there are two holes without an explanation and something weird at the Polish border, but apart from that all holes are radio telescopes. It looks like actual signup is not always following the map 1:1.

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toodroot t1_iybalip wrote

OK so that changed. I had put in reservations for Owens Valley, Haystack, and the LMT in Mexico and was notified that the first 2 cells were opened... but that was quite a while ago now.

Other ones not there off the top of my head:

EHT: Kitt Peak and Mt. Graham AZ; IRAM 30m uphill from Grenada; NOEMA in the French Alps, and I know that Thule Greenland is using Starlink. The South Pole will likely want to use Starlink.

VLBA: Arecibo (the VLBA antenna didn't fall down)

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mfb- t1_iybh5uw wrote

Several radio telescopes don't have empty cells, indeed. I don't know how they decided on that list and it can change on short notice - it's just a software setting anyway.

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toodroot t1_iybjotr wrote

One nit is if they actually have customers in those cells -- no one lives near the LMT, NOEMA, or the IRAM30m, but actual people certainly do live near Haystack.

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ahecht t1_iybuwm4 wrote

Starlink currently has a gap over Haystack, as well as one over the nearby VLBA antenna in Hancock, NH.

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TK-741 t1_iyaubeg wrote

Wow, I hope that the proposal is rejected or shelved or something. These seem like issues that are absolutely not acceptable for anyone.

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Woody3000v2 t1_iybeaaa wrote

They've already approved testing and the launch was approved prior. The benefits of having global 5g coverage from an economic, environmental, national defense, and efficiency perspective outweigh brightness issues (which may be addressed) and interference issues (which is why they're testing with BW3 before launching 300 satellites).

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lew_rong t1_iybnmr6 wrote

When I visited the Very Large Array in New Mexico, visitors were asked to turn their phones off, even though there's no signal out there. The plaintive cries of your iPhone desperately trying to get back in touch with the rest of the world are something like a million times stronger than the signals the VLA is trying to observe.

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LegitimateGift1792 t1_iydtnme wrote

and it is going to drain the battery like crazy as it ups power to reach out harder.

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Woody3000v2 t1_iyb9nkz wrote

Thats ridiculous. They aren't flooding anywhere with the entire spectrum. They will get assigned spectrum just like everyone else. And it will have to be assigned in a non interference basis.

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HairyManBack84 t1_iyaybcj wrote

Man, you donā€™t obviously know how any modern connections work. It wonā€™t randomly blast areas. Itā€™s all beamformingā€¦ If it sent signals everywhere it wouldnā€™t work at all.

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KonigVonMurmeltiere t1_iyba1im wrote

Directional antennas still produce sidelobes. They arenā€™t laser precise. Keep in mind radio telescopes are very sensitive, a satellite like BlueWalker 3 would be far stronger than natural radio sources in the sky even if it isnā€™t directly aimed at itā€¦ and the goal is to have enough of them to maintain coverage of an area at all times. The point is to at least not directly aim the beam at a radio telescope, and provide a little extra buffer room to account for the sidelobes.

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toodroot t1_iyb469i wrote

I know VLBI very well, and there's still a problem even if you take beamforming into account.

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