On 3/8/11 1:45 PM, Magnus Danielson wrote:
Kevin,
On 03/08/2011 06:57 PM, Kevin Watson wrote:
Hi Jim,
<snip>
Do you, or anyone else, have a recomendation for the GPSDO? Jackson Labs'
(http://jackson-labs.com/) DROR seems like it might work, but I wonder if
there might be better alternatives.
First thing to consider is that standard GPSes will not meet your needs,
since they have to obey the height and speed limits for export rules.
OTOH, if you're building a rocket that's big enough to need something
like this, you can likely get the needed export licenses, or at least,
comply with the export control laws. But yes, the vanilla off the shelf
GPS probably has the "don't report over 60,000 ft or 1000 km/hr" lockouts.
The side-effect is that doppler frequencies may be much higher and both
tracking and acquisition needs to include these more extremer doppler
frequencies.
That would be my concern with GPS... the so called "high dynamic"
environment. LEO orbit is 7km/sec, so you'd think the Doppler would be
huge, but actually, that's not a big problem, since you already have to
deal with an even higher Doppler from the GPS SVs already. Whether
your receivers nav solution can work with a fast moving platform is
another story. It may assume that nothing can go that fast, and so it
doesn't track.
OTOH, if you're buying a GPS module from someone like Trimble or
Motorola or whoever, you can probably ask them.
Use of PTP within a rocket or spacecraft may or may not be a good thing.
NMEA + PPS may suffice and be less power-hungry. IRIG may also be an
option.
I would agree.. unless you're trying to minimize wire count and you
already have Ethernet. Spacecraft designs are very mass and pin count
sensitive (every pin in the connector needs to be tested, which costs
money, etc.)
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
