October 2, 2004
Guanaco Camp, Atacama Desert, Chile
Agenda
• Navigate and operate instruments autonomously
• Work on sun tracker and spectrometer
• Tested Li-Polymer battery controller
Status and Progress
Executed combined navigation and science. Today we ran tests of Zoe’s
autonomy software to confirm its performance planning and executing
both navigation and science tasks. Zoe traveled between goal locations
and stopped to collect panoramic images, high-resolution images, and
record spectra with the VNIR spectrometer. The Fluorescence Imager is
fully automated but a few details remain to fully integrate it the
high-level autonomy software; that should come in the next few
days. The mission planner generates time and energy optimized sequences
of navigation and science actions and these are communicated to the
rover executive which tracks progress against the plan and commands the
rover navigator and instrument manager.
Refining sun tracker. We worked to analyze the performance of the sun
tracking system both in tests with Zoe running in circles so that the
sun would cycle around, and stationary to confirm that the estimated
orientation remains constant as the sun moves. After correcting for
initial offset the sun tracker is producing precise estimates to within
several degrees.
Tested lithium-polymer batteries. Zoe has been operating thus far with
lead-acid batteries with approximately 250Whr capacity. These are
adequate to provide for peak draw during locomotion and under two hours
of run time with no input from solar energy. The lithium-polymer
batteries have more than four times the capacity, at the same
mass. However, they require a dedicated controller to monitor current,
voltage and temperature levels and when these bounds are exceeded the
batteries shut down. We found minor problems that we will work to
correct before we conduct further tests. During storage the cells have
moved out of balance, mean each is charged by a slightly different
amount, but because of the way the battery works, it charges until the
highest voltage cell reaches its higher limit and discharges until the
lowest voltage cell reach it lower limit so the effect of the imbalance
is to limit the total capacity of the battery. We also found that a
resistor in the safety circuit was 130C, hot even for the desert, and
will work to improve the design. We did conduct limited trials and
found that battery performance was excellent, in the end we turning on
everything we could on Zoe, turned off the solar array, and at the end
of our 1.5 hour test, had just started to move appreciably down the
discharge curve for these batteries. We are excited about the prospect
for overnight hibernation, and even nighttime science observations that
these batteries will provide. It has been a challenge to design,
build, and test our own batteries but it looks like it will be worth
it.
Upcoming
• Move Zoe to the field investigation site
• Install environmental monitoring station
Weather
Morning: Clear, calm, cool 10C, humidity 20%
Afternoon: Clear , warm 22C, humidity 35%
Evening: Clear, cool 10C, calm, humidity 30%
Quote of the Day
"So you’ve tried the reason, now you have to try the force."
