Using GPSFlight Technology to Track Rockets - real telemetry..

Originally designed to track high-power rockets in extreme conditions, the ST900 can provide excellent telemetry data at extreme altitudes - at ranges exceeding 20 miles. 

	A 2.5" rocket with a J-350 rips off the pad in Eastern Washington.  This 160 lbs of thrust absolutely RIPS the 3 lb rocket off the pad!! GPSFlight telemetry is mounted in the nose-cone area sending GPS and Digital Altimeter data during the flight. On this particular day, EVERYONE lost the rocket because it went so fast, and so high.. Nobody even saw it land! GPSFlight tracked it the whole way! This was using the older STXe device. DOWNLOAD THIS DATA FILE (play it backwith GPSTeam Pro to see it) See DUAL ST900 Test Flight
View of real-time telemetry using GPSTeam Pro
The top-down view in real-time shows the track of the rocket flight...                   The GPSTeam Pro 'Distance Measure' tool showed exactly how far we would have to go     The altitude plot showed the GPS and Baro altitude readings all the way up and all the way down!
Back in the camper, we could see EXACTLY where it was, and what it was doing.... It was just UP about 5,000ft over our heads, and a 2.5" diameter rocket at that altitude is too small to see.  We watched it on the PC all the way to the ground, and then used a second GPS to find it.  Above, we see the yellow dot "TOM" as it drifts down. To the right is the alt plot. You can easily see that the chute has deployed - even if you can't see the darn rocket!!
	Our second GPS showed the position reported to be 5 FEET away from exact!! We recovered the rocket about 1/2 mile away over a draw, and lying nicely in a farmers field.
The J-350 pulls at least 15 Gs off the pad with this little rocket. Thanks to Bubble-wrap, we had good data the whole way!

MOUNTING CONSIDERATIONS

This section discusses how to mount the GPSFlight ST900 into a high power rocket in the optimum fashion for reception, GPS coverage, and elimination of negative effects of G-forces on the GPS.  As you know, the GPS is rated for 6 Gs only, so in many rockets the GPS will go 'silent' during the boost phase.  However,  mounted correctly, your ST900 can provide continuous data during your entire flight even at more than 15Gs, and you will KNOW exactly where it is because it will be telling you the whole time.  If you seek to provide position data under these high thrust conditions is your objective, then read on.

There are several factors to consider when using a GPSFlight ST900 flight telemetry unit in a high power rocket.  They are:

1. What to expect from your ST900

2. Mounting the unit to eliminate or reduce the effect of sharp G-force on the GPS unit.

16 things to EXPECT from your ST900:

1. Expect on a fully charged 2000mah battery pack (AA) to get 5 hours of run time at 1-per-second update rates. Likely this will be more like 12 hours, but be conservative

2. NEVER REVERSE VOLTAGE OR YOU WILL FRY THE UNIT AND HAVE TO BUY A NEW ONE!

3. Expect to have a range of up to 20,000ft using only the internal 'wire' antenna, even farther with a higher gain antenna on the ground (like a Yagi).  We have data tracks from these units to over 58 miles line of sight using gain antennas on the RXBase.

4. Expect the barometric altimeter to provide pressure and temp data regardless of the GPS having lock, and to be able to update as fast as every 250ms with fresh data.

5. Expect the temperature to read high. It is reading BOARD temp, not air temp.

6. Expect the data to stop when the unit lands on the ground or goes over a hill.  This breaks the line of sight.  However, even if it looses sight at 500 ft, the last known coordinates will be very close.

7. Expect the GPS data position from last known coordinates on a flat area (brush, trees, etc) to be within 30'.  Set your second GPS and BELIEVE it. Sometimes you won't think you are in the right area. YOU ARE.

8. Expect that if you mount the GPS firmly to the airframe, YOU WILL LOSE LOCK during the boost phase of flight, but to recover during decent.  Use bubble wrap method for best results.  Expect the GPS to blank out during periods of high thrust, but it will come back online after they are over.

9. Expect the unit to short out, and be damaged if you mount it with other metal touching the case, or the PCB.  If you choose to cram it in somewhere, you should protect the PCB and GPS case from connection with other metal.

10. Expect that if you mount the GPS using the 'bubble-wrap' technique, to maintain lock, even under 15G flights or possibly higher.

11. Expect it to fit in a 54mm tube, but nothing smaller.

12. Expect it to report over 1,000 mph speeds under 60,000 ft, and report over 60,000 ft while under 1,000 mph.  (Also expect that under extreme conditions like this the actual Max Speed values may be a bit off - esp if the GPS loses lock for a second or two)

13. Expect the GPS to SHUT DOWN if you exceed 5,150mph.

14. Expect the range of the radio to be 20 miles with standard antennas line of sight. Moving the 2db dipole RXBase unit antenna around a metal reflector like the side of a car can sometimes bring in far-off 40+mile signals - actually acting like a higher gain antenna.

15. Take care to be sure the power connection, battery pack, and radio components cannot come apart under thrust.

16. Face the GPS patch antenna sideways or up if you can. Remember tho - facing up going up, may be facing down coming down so think it through..

MOUNTING THE ST900

The Bubble-wrap technique is the ONLY way to do this.  We have tested this over and over, and the GPS (rated to 6Gs) does not handle the 'jerk' of a rocket launch well if mounted to the airframe.  With flights of 6+ Gs, your GPS will stop reporting valid position data (or report just the last one from the pad) until the high G-forces stop.  If the G-forces are REALLY high, it may take 10 minutes for it to recover.  But don't worry!!!  Bubble-wrap works wonders!

Note - we used just the integrated wire antenna on this flight.  It was facing down, and it was within about 1" of the GPS antenna - tho it was facing out the side.  Note the GPS patch was not facing UP, but OUT. That way when under chute, the patch still can see the sky - if even from the side.

   

 

Above you can see the ST900 with bubblewrap removed. The unit was rolled in a layer of wrap, and slid into the nosecone.  Above it was more bubble wrap to prevent it from getting stuck in the narrow section.  A wad of bubblewrap was below it to absorb the shock of the launch.  The GPS antenna (patch) was taped facing out, and the 4xAAA cell pack sat at the bottom of the nose cone.  In this case, it was a 'field fit' job - we cut the hatch in the side of the nose cone in the field, and slid the unit in while powered.  There was no on/off switch. 

Important:

Do not wrap the unit so tightly the ST900 cannot  'breathe'  it needs air pressure to give you a pressure reading.  Also, ensure there are vent holes to allow pressure inside to change.  This nose cone had two small holes one on either side of the cone.