Nevada Space Grant
Weight: 7.37 ounces (209 grams)
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
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.
ProsLightweight and relatively inexpensive. Guests can log into the findmespot.com website and view the location of the SPOT. This can be useful for letting remote participants track the balloon in near realtime (similar to using FindU.com or APRS.fi).
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
The SPOT also does not function above 40,000 feet so it cannot
used to track the payloads during the majority of the mission (i.e.
cannot be used as the primary tracking device).