Six NiH2
batteries support the Telescope’selectrical power needs during three periods:
when demand exceeds the Solar Array (SA) capability, when
the Telescope is in Earth’s shadow, and during
safemode entry. The batteries reside in Support System Module (SSM)
Equipment Section Bays 2 and 3. These units
have extensive safety and handling provisions
to protect the Shuttle and its astronauts. The design
and operation of these batteries, along with
special nondestructive inspection of each cell,
have allowed these units to be “astronaut-rated?
for replacement during a servicing mission.
To compensate for the effects of battery aging,
astronauts installed a Voltage/Temperature
Improvement Kit (VIK) on each of the batteries during the SM3A servicing mission. The VIK provides battery
thermal stability by precluding battery overcharge
when the HST enters safemode, effectively
lowering the Charge Current Controller
(CCC) recharge current.
The Solar Arrays (SAs) recharge the batteries every orbit
following eclipse (the time in the Earth’s
shadow). The recharge current is controlled by
the CCCs. Each battery has its own CCC that
uses voltage-temperature measurements to
control battery recharge.
Fully charged, each battery contains more than
75 amp-hours. This is sufficient energy to sustain
the Telescope in normal science operations mode
for 7.5 hours or five orbits. The batteries provide
an adequate energy reserve for all possible
safemode contingencies and all enhancements
programmed into the Telescope since launch. |