Re: GPS under high acceleration

On May 29, 3:35 am, Sam Wormley <sworml...@xxxxxxxxx> wrote:
Sean Q wrote:
I was given the task of designing the GPS payload on a small sounding
rocket. Its task is to record the range/position of the rocket in all
phases of flight. It doesn't need to transmit the location, just store
it onboard.

The problem that I'm coming across is that it will be traveling at
very high acceleration/speed for a short period of time. In the first
few stages of flight it will be traveling at 70g and reaching a top
velocity of 680m/s, well outside the operational limits of the uBlox
GPS receiver.

I understand that I will lose lock with the satellites for a short
period of time. It will take around 6 seconds after launch to travel
at a speed/acceleration within the operational limits of the Ublox.
After this time would the GPS of traveled to far to reacquire the
satellites in Warm Start mode, or will it need to search for the
satellites again in Cold Start?

The research I have done said that It needs to travel several km
during the loss of satellites to require a restart in Cold Mode,
however because the rocket is still traveling at speed (between 180m/
s-400m/s)I am unsure how long reacquisition would take.

Also are you aware of any examples that I could peruse of GPS
receivers operating under similar conditions?

Thanks

Many GPS receivers are restricted in dynamics for military
reasons--dynamics not exceeding--

Dynamics:
Acceleration 4g (39.2 m/s^2)
Motional Jerk 20 m/s^3

Operational limits
Altitude < 18,000 m or velocity < 515 m/s
Either limit may be exceeded but not both (in non-military GPS
receivers).

These restrictions do not apply to the Space Shuttle or LEO satellites
making use of GPS signals. You can always build your own receiver
without restrictions of any kind.


When you say either limit may be exceeded, so you mean the receiver
can travel at 600m/s but as long as it is below 18,000m it will record
fine? May I ask where you got this infomation?

Also are you aware of what would happen to your readings and your
signal lock if you travel outside these limits (acceleration is my
main concern)

Thanks for the infomation!

.

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