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Missions

Size: 4.38 X 2.75 X 1.5” (approx. 111 mm x 69 mm x 44 mm)

Weight: 7.37 ounces (209 grams)

• Operating Temperatures: -40°F to +185°F (-40ºC to +85ºC)
• Operating Altitude: -300 ft to +21,000 ft (-91 m to +6,492 m)
  
• Floats in water
• Waterproof to 1 meter for up to 30 minutes
• Humidity Rated:
  • MIL-STD-810E Method 507.3, 95% to 100% condensing
• Salt Fog Rated
  • Per MIL_STD 810E Method 509.3, 5% NaCl, 95% distilled water
• Vibration
  • Per SAE J1455
  • Random, 20 Hz to 2000 Hz, 0.04g2/Hz, one hour per axis
• Drop
  • Dropped twice on all six sides from one meter onto hard surface.

Battery Life: 14 days in SPOT tracking mode.

This is the backup GPS system we use now. We used to use the much more expensive (and heavier) PTT system. The SPOT is both cheaper to operate and lighter weight than the PTT (209 grams vs. 425 grams). We've disassembled a SPOT and could save about 100 grams by removing the hard case, but haven't needed to (yet).

Like the PTT, this serves as the last-chance backup tracking device that allows us to recover a payload in the event that either the communication payloads fail or we loose radio contact with the communication payloads. We are also considering using this device for tracking multiple payloads that descend under separate parachutes.

It works by transmitting the GPS location to the Globalstar satellite phone's constellation of satellites (i.e. good coverage). In the SPOT tracking mode, it automatically reports its position every 10 minutes. The location is viewable online nearly realtime (often less than 1 minute time lag).

We've used the SPOT on NBS-08-02 to an altitude of 100,351 feet. We were told that the unit will stop transmitting above 21,000 feet and should resume transmitting after the payload descends below 21,000.  During our test flight, it reported a position from 56,000 feet on the way up (it also reported a position from 61,000 feet, but it was an erroneous point). On the way down, it started reporting at an altitude of 37,000 feet and worked properly for the remainder of the mission.

On NBS-08-03 we used the SPOT as the only tracking system (this was a test of the SPOT device). On ascent, the last point the SPOT transmitted was around 25,000 feet. On descent, it started transmitting around 13,000 feet. Not as good as during NBS-08-02, but we also had a much higher ascent and descent rates for the balloon/parachute. Using the SPOT website, we were able to locate the payload after landing. The final position of the payload was within 10 feet of the reported position - much less than the accuracy of either the SPOT's GPS and the GPS we were using to locate the payload.

On NBS-08-04 we had a SPOT inside a dropped payload that was supposed to freefall for about a minute before deploying its parachute. The parachute deployed but got fouled. The SPOT (and LEGO NXT) fell from 82,000 feet with no more than a fouled parachute to slow them down. The SPOT survived without any problems and reported the position of the payload, which was successfully recovered. The main payload had a second SPOT which was also used to successfully locate and recover the rest of payloads.

As of August 2008, we've used a SPOT on 6 payloads and have never had a problem yet. We have decided that the SPOT device will now fly on all future missions, permanently replacing the PTT.

Pros

Cons

The lack of any display makes it hard to tell if it is actually working correctly and/or if it is in the SPOT tracking mode. The SPOT tracking mode also only works for 24 hours before it automatically shuts off. This should be long enough to locate a lost payload, but is far from the weeks that the PTT transmits.

The SPOT also does not function above 40,000 feet so it cannot be used to track the payloads during the majority of the mission (i.e. cannot be used as the primary tracking device).