1/ Lots of buzz about the UK bidding to resurrect OneWeb as a GNSS system, short thread trying to unpack what I think is going on & the challenges in doing so (caveat is not a lot of public info on this right now)

2/ According to @FT ( https://www.ft.com/content/a1da90e8-8869-4740-b5eb-d8c6339d8e2f) the UK govt plans to put up £500M to help bring OneWeb out of bankruptcy and turn their system into some sort of GPS augmentation

3/ Apparently this is seen by the UK govt as a better alternative than the £5B (and more!) of building a completely independent UK GNSS, which was always an absurd idea anyways

4/ So what might this look like? Well, one option would be to have the OneWeb constellation broadcast the same signals as GPS, which is what the Japanese QZSS system does: https://qzss.go.jp/en/overview/services/sv03_signals.html

UGGH I hate it when Twitter chokes on an image and doesn't post the rest of your thread and you refresh the page and lose it all! Anyways, back to our story -

5/ QZSS was conceived because a high density of tall buildings blocks GPS, so the system broadcasts the same GPS signals from a highly inclined orbit

6/ QZSS is also in an orbit that stays over Japan, meaning they can provide good regional coverage with only a handful of satellites

7/ Another option would be to use OneWeb as an augmentation and enhancement system like the American WAAS or European EGNOS

8/ WAAS uses a system of ground stations to receive GPS, determine the errors caused by atmospheric interference, and broadcasts a GPS-like signal that can correct for those errors

9/ But either of these options pose big challenges. First and foremost they'd require broadcasting signals in L-band, which is very different from the Ka- and Ku-band signals OneWeb was designed and licensed for

10/ Theoretically OneWeb could get a new license for L-Band and redesign their payload to broadcast it, or potentially broadcast L-band GNSS and Ka/Ku broadband services. But would likely might require a redesign of the bus power system

11/ Another alternative would be to embed a navigation message into the Ka/Ku brodband signal, similar to what Satelles does with Iridium Next https://www.satellesinc.com/technology-2/ 

12/ That would be easier from a technology/power perspective and wouldn't require a new license, but it would mean end users need a whole new receiver as the signals couldn't be received by existing GPS or Galileo receivers. It would be a new service, not an augmentation

13/ Bottom line, turning OneWeb into some sort of GNSS augmentation/alternative is a better idea than the absolutely bonkers idea of an independent UK GNSS service but still has a lot of challenges /fin