QUESTION:
The Pathfinder mission is certainly as great success and credit to all those
who worked on it.  I am certain that the Pathfinder team is as frustrated
about the loss of contact as the rest of us.  The Sagan Memorial Station was
equipped with solar panels that would have enable it to operate in a "No
Battery" mode.  Reports by the Mars Rover team attributed their inability to
contact the Sagan Memorial Station to a loss of accurate time-keeping by the
Station.  My question therfore relates to the power supply of the
time-keeping mechanism.  Was that the time-keeping mechanism connected to
the main "battery" power supply or did it have its own independent power
unit?  If the time keeping mechanism was powered by the main battery, what
were the reasons for not giving it an independent power supply?

ANSWER from David Mittman on January 14, 1998:
Thank you for your kind words regarding the Mars Pathfinder Project. Yes, we
are terribly proud of what we were able to accomplish and a bit sad and
nostalgic about the end of the mission.

In spite of the eventual loss of communications, we were able to return more
science data in the 83 days of the mission than we could have hoped. It is
still not entirely clear that the loss of communication is due to either a
failed battery or loss of time reference.

The question of an independently powered clock (similar to a battery backup
operated clock on a computer motherboard) was considered as an option early
in the lander design. However, it is my understanding that appropriate
hardware did not exist to implement this option in the space environment in
which the spacecraft was to be operating. Additionally, a program to develop
the appropriate hardware was too costly and would have taken too long.

The mission was designed to operate in a no-battery mode; in case the
battery failed on landing, we would still be able to carry out our prime
objectives. The timekeeping mechanism designed for this mission involved
associating a specific rise in voltage from a solar cell on one of the
lander petals to a specific time of day. As the sun rises in the morning it
eventually provides the computer with enough power to boot up. During the
boot-up process the computer reads a time from non-volatile memory to
determine the approximate time.

David Mittman
Jet Propulsion Laboratory