[time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem

[Jim Lux]

On 9/21/13 11:03 PM, Hal Murray wrote:
>
> albertson.chris at gmail.com said:
>>> What stops working when things get cold? >
>>> On Mars, the solar cells are pointed in the right direction.  Why doesn't
> it
>>> recover when the sun comes back in the Spring?
>
>> They run out of power for running the battery heaters, then the battery
>> freezes and fails.  The batteries get to such a low temperature that they
>> are unable to be charged.  The rover was never designed so that it could
>> move and operate under solar power.  It is really battery powered and uses
>> the panel for charging.
>
> We are talking about running computers and radio gear rather than motors.
>
> I can see running motors in bursts from batteries, but computers and radios
> generally run continuously so they shouldn't need a battery when the sun is
> up.


The computers and radios and instruments actually take more power than 
the motors.  MER doesn't have very big motors.  It only moves a few cm/sec.

For instance, to fire up the radio to talk to earth, either via the 
relay link or direct on X-band, is probably around 50 watts.

MER has maybe 1 square meter of solar panels, it's farther from the sun, 
etc.
It probably has positive energy balance when the sun is shining in the 
summer and running the flight computer and radios.

The problem is running the heaters in the cold. In the winter, it gets 
colder AND there's less solar energy from the panels.