Power
The primary purpose of the electrical power system (EPS) is
to generate, store and distribute power to all subsystems during all mission
phases. In order to achieve this objective, a satellite power subsystem must,
at the minimum, consist of the following three components:
-
A power generation
system,
-
An energy storage system, and
-
A power distribution system.
Due to the
nature of this project, the power generation system will be solar cells and the
energy storage system will be secondary batteries. The power distribution system
consists of a relatively simple design that will be constructed using modified
off-the-shelf DC-DC converters.
Based upon the nominal solar cell
design, it is possible to obtain approximately 26 W of average power from the
solar cell arrays. Degradation during the design mission lifetime is negligible.
The power calculations have been under the assumption that all surfaces of
Dawgstar are at least 85% covered with solar cells. When the solar cells are
integrated, bypass diodes will need to be installed in order to prevent power
loss due to shadowing effects.
The table below is the power budget for all UW Dawgstar subsystems.
The total power available is based upon calculations that were performed using
the available surface area and the geometry of the bus structure.
System |
Total budget (%) |
Power (W) |
Payload |
5 |
1.31 |
Propulsion |
10 |
2.62 |
Attitude Control |
10 |
2.62 |
Communication |
25 |
6.55 |
C & DH |
10 |
2.62 |
Thermal |
5 |
1.31 |
Power |
25 |
6.55 |
Structure |
0 |
0.0 |
Margin |
10 |
2.62 |
Total |
100 |
26.2 |
Solar Cells. The current design of the solar
arrays is to place cells over every possible increment of the satellite's surface area, after
all other components have been placed on the surface.
The Air Force is currently negotiating
with two companies to donate solar cells to all of the nanosatellite teams;
therefore the final verdict as to which solar cells the Dawgstar will be
receiving is not yet known. The two companies produce cells with slightly
different specifications. The power design for the Dawgstar nanosatellite cannot be
finalized until the choice for solar cells is made.
Battery.
To provide a steady source of power
for mission operations while in the earth’s shadow, the UW Dawgstar will
be equipped with a bank of secondary batteries. Acting as a power reservoir,
these batteries will be recharged for approximately 56 min each orbit, and
must be capable of providing power during the eclipse phases of the mission.
Power Distribution
System. One could consider the heart of the
power subsystem to be the solar cell power generators and battery storage
system. The power distribution system, however, plays a central role in the
overall design.
Due to the nature of the UW Dawgstar, mass, efficiency, and
design simplicity are all of critical importance to the power subsystem
design. Therefore, the series connected boost converter (SCBC) configuration has been selected for the power
distribution and regulation system.
The SCBC architecture will provide a
simple and reliable way to distribute electrical power to the main bus. Its
design is robust in that it provides the capability for fault isolation and high
efficiency power distribution.
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