[aprssig] Does GPS work in space ?

Home Andy kg6rwo at comcast.net
Sun Apr 23 09:27:01 CDT 2006

"Da problem" with operating above the GPS consellation is that its antenna clusters are pointed the wrong way, towards the ground.  As with any antenna, however, there is a potion of the pattern behind the antennae that exists at a weak level.  There have even been studies of using "weak signal" GPS on the moon rather than establishing a new constellation there.

The software in receivers operating above the constellation would have to know to discard any solution that is below the constellation, just as receivers now discard any solutions that are above the constellation. 
  ----- Original Message ----- 
  From: Wes johnston 
  To: vk4tec at tech-software.net ; TAPR APRS Mailing List 
  Sent: Sunday, April 23, 2006 6:42 AM
  Subject: Re: [aprssig] Does GPS work in space ?

  Yes and no.... 

  Yes, with the proper GPS receiver.  "Da Rules" say that a gps unit can give position reports if it is >18Km (I forget the exact number) as long as it is not moving faster than 500m/s.  You can do one or the other, but not too high and not too fast at the same time.  So since it impossible to go into orbit at less than 17,000mph, when your garden variety GPS gets to 18Km altitude, it will stop reporting positions.  Note that most GPS manufacturers read the rules as EITHER 18km or 500m/s, hence there are MANY MANY gps units that won't go higher than 18k/m... the GPS18 from garmin interprets the rules correctly thrus is good for balloon use over 18km up.

  PCSat has a GPS on board and for a while did report it's position because it had an exempted GPS receiver.  Even though it's in orbit, it's in a lower orbit than the GPS satellites, so they are still overhead relative to PCSAT.  

  Anyone know if these rules apply to the new european gps system?

  Does anyone know if the GPS system will work when a receiver it higher than the GPS satellites?  Seems like it should from a purely mathematical standpoint.

    ----- Original Message ----- 
    From: Andrew Rich 
    To: TAPR List 
    Sent: Sunday, April 23, 2006 5:44 AM
    Subject: [aprssig] Does GPS work in space ?

    Andrew Rich
    Amateur radio callsign VK4TEC
    email: vk4tec at tech-software.net
    web: http://www.tech-software.net
    Brisbane AUSTRALIA 


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