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Energy Power System
Electricity
• Electricity is the flow of electrons through a conductor
• Electricity will only move through a closed circuit, if the circuit is broken the flow of electrons stops
Electricity (cont.)
• Voltage - Electric potential or potential difference, provided by the battery, expressed in volts
• Amperage - The strength of an electric current, flows through the conductors to the load, expressed in amperes
• Resistance - Is present in any load, expressed in ohms
Light to Power
• Solar Panels collect sunlight and convert them into electrical power
• For maximum power solar arrays need to be perpendicular to the light rays hitting them.
Orbit Cycle
• During the 30 minute eclipse period the batteries supply power
• While in insolation period the solar arrays provide power while the batteries charge for the next eclipse period
Primary and Secondary power
• Primary power is high voltage power generated at a centralized source
• Before power is delivered to users it is stepped down by a transformer to a set voltage (secondary power)
• Secondary power is then delivered to the user
System Overview
• Internal and external systems– Internal system distributes
secondary power
– External distributes primary power
• 8 identical channels of power (1-4 A/B)– Each channel supplies 100
amps of current
Internal EPS
• Loads, RPDA, SPDA, DDCU, MBSU, ICC
• Converts primary power to secondary power
• Routes secondary power to any internal systems
Loads
• A load is anything that needs electricity to function.
• Computers, Lights, Pumps, etc.• Each load requires a certain current (amps)
which is specific to that device• Not all loads are physically inside the
station, but all are supplied by the same internal distribution network
SPDA/RPDA/DDCU
• Secondary Power Distribution Assembly– Supports a single channel of power
• A is even channel B is odd channel
– Routes power to one RPDA and six loads
• Remote Power Distribution Assembly– Routes power to six loads
• Direct current to Direct current Converter Unit– This is the unit that converts primary power (~160 V
dc) to secondary power (~124 V dc)
MBSU/ICC
• Main Buss Switching Unit– Each support 2 channels of power with a total
of 200 amps– Routes power to two SPDAs
• Interconnecting Cables– Create a bridge for two or more MBSUs to
share power across them
External EPS
• SARJ, IEA, ECU, SSU, PCU, BGA, PVA
• Produces primary power from the solar arrays, and stores power in batteries for eclipse phase
SARJ
• Solar Alpha Rotary Joint
• Rotates 4 channels of power at one time– Controls rotation
parallel to the main station truss
IEA
• Integrated Equipment Assembly
• Battery Charge Discharge Unit (BCDU)– When signaled by the ECU the BCDU begins
charging or discharging the batteries
• Batteries (BAT)– Batteries store power for use during the eclipse
phase of the station’s orbit
IEA (continued)
• Direct Current Switching Unit (DCSU)– Routes power from BGA to batteries, IEA, and
Internal system
• Direct current to Direct current Converter Unit (DDCU) – Provides Secondary power for all components.
IEA Thermal control system
• IEA has a self contained thermal control system for each channel
• Small radiators under each IEA dissipate heat from the SSU as well as batteries and other IEA components
• This system functions in the same manner as the main TCS for the station
• Pump and Flow Control Subassembly (PFCS) and Photovoltaic Radiator (PVR)
ECU/SSU
• Electronic Control Unit– Manages when to charge and discharge the
batteries
• Sequential Shunt Unit– Shunts any excess power generated as heat– Small radiator beneath each PVA radiates heat
Grounding
• To prevent electricity from arcing across the station all electrical devices are grounded to the main truss.
• Plasma Contractor Unit (PCU)– Emits a stream of plasma to ground the space
station’s main truss to space– Prevents arcing to any external spacecraft
during docking or EVA
BGA/PVA
• Beta Gimbal Assembly– Rotates one channel of power per BGA– Controls rotation perpendicular to the main
station truss
• Photovoltaic Array– Collects sunlight and converts it into electrical
power
Warning Signs of a SOBE
• Red indicator light on the system wall
• Loss of Power (I.e. lights or computer unexpectedly shut down)
• Warning through HAL or other system
• Contingency of another SOBE
Things to check during a SOBE
• For maximum power the panels must be perpendicular to the sunlight, if misaligned they may not produce enough power
• There are many points were power can be stopped, be sure to check them all