[time-nuts] ISS NTP operation problems.

[Magnus Danielson]

Warren,

On 2021-01-08 23:15, Warren Kumari wrote:
> On Fri, Jan 8, 2021 at 11:40 AM Lux, Jim <jim at luxfamily.com> wrote:
>> On 1/8/21 6:59 AM, Magnus Danielson wrote:
>> That is probably harder than it seems.  There's a lot of isolation among
>> systems on ISS - partly for safety, partly from history, partly from
>> institutional inertia. My payload on ISS (SCaN Testbed) had a
>> MIL-STD-1553 connection and a unidirectional Ethernet connection (out of
>> payload only). There's multiple GNSS receivers on ISS, but not all are
>> visible to an arbitrary payload - their output might get packaged up as
>> telemetry and store/forward sent to the ground via episodic
>> transmissions on the Ku-band system.  One of the experiments on my
>> payload was to actually try to measure the time and position offsets
>> between our radio(which had S-band Tx/Rx and GPS receiver) and the
>> various time sources on the Station.
> I must admit that I'm very surprised that GPS receivers worked and
> were able to compute a fix.
> The majority of GPS receiver chipsets have altitude and speed limits
> built in, both because of assumptions/discarding pathological results,
> but also because of ITAR and similar regulations. Were these special /
> licensed receivers which didn't have the "Erk, I think I'm on an ICBM"
> logic?

These receivers do not follow the ITAR rules for sure. Just being beyond
18 km is breaking one ITAR rule, being faster than 1 MACH is another
(don't recall the exact number for ITAR, but there aboutish).

But it works.

A fun special satellite measures the GPS satellite occulation behavior,
thus how the signal bends from below the horizon to just above. That is
an atmospheric measurement tool. For sure not ITAR compliant.

Cheers,
Magnus