Electric Power Systems

Question 1

Primary Energy Sources: (4)

Answer 1

• Used for generating power supply during sunlight periods (continuously)
• Photovoltaic
• Heat Conversion using a thermoelectric generator
• For short times: Fuel cell and battery

Question 2

Secondary Energy Sources: (Def, 3 examples)

Answer 2

• Used mainly for power storage
• Ex:
  • Rechargeable batteries
  • Regenerative fuel cells
  • Solar dynamic generator

Question 3

Primary Energy Sources Characteristic: Photovoltaic (4):

Answer 3

• Sunlight freely available
• Around Earth: ~1360 W/m^2
• Reduces with ~ r^2 (distance from Sun)
• Mars/Jupiter is informal “boundary” for the usefulness of solar cells

Question 4

For a given solar cell, the power output depends on: (4)

Answer 4

• Illumination level (distance from the sun)
• Projected area
• Level of degradation (radiation)
• Temperature

Question 5

Radiation - Lifetime limiting factors (5):

Answer 5

• Main Reason for degradation
• Si-based cells have a lower sensitivity to radiation than others. GaAs is even better!
• n-type is always on top since less sensitive to radiation
• Thin cells are less sensitive to radiation
• Use glass covers for radiation and environmental protection

Question 6

When sizing a solar array one has to keep in mind of: (3)

Answer 6

1. End of Lifetime (EOL) power generation is lower than the Begin of Lifetime (BOL)
2. Spacecraft might move in areas with higher or lower illumination
3. Power Consumption of a spacecraft might change during the mission

Question 7

Primary Sources: Solar Dynamic Generators [Def, Pro, Con]

Answer 7

-> Any power sources working with Stirling, Rankine, or Brayon cycles.
• PRO: Higher specific power generation, smaller deployment structures
• CON: Moving parts & Dependence of Sun alignment

Question 8

Primary Sources: Radioisotope Thermoelectric Generator (RTG) [Def, Pro, Con]

Answer 8

-> Use radioactive decay to generate heat
• PRO: No sun dependency, no moving parts
• CON: Low efficiency (5-7%), huge initial energy dissipation

Question 9

Primary Sources: Nuclear Reactor [Def]

Answer 9

-> Fission of heavy elements like uranium‐235 creates heat which is
converted to electricity
• Used as a propulsion mean
• Generates contamination and space debris

Question 10

Secondary source: Batteries [Def]

Answer 10

-> Storage of electrothermal energy to release electrical power
• Preferred for photovoltaic primary sources
• Short supply time

Question 11

Secondary source: Fuel Cells [Def]

Answer 11

-> Converts H2 and O2 into H20 – releases electrical power
• Water can be consumed by astronauts
• More complex than batteries

Question 12

Power Management - Voltage and power output can be regulated by (5):

Answer 12

‐ Maximum Power Point Tracking (PPT or MPPT)
‐ Pulse‐width modulation
‐ Sequential Switching Shunt Regulation (S3R)
‐ Direct Energy Transfer (DET)
‐ Individual DC‐DC transformer are also standard

Question 13

Power Management - EPS Components (6):

Answer 13

• Solar Power Assemblies (SPA)
• Mode Control Unit (MCU)
• Power Control and Distribution Unit (PCDU)
• Battery Management Unit (BMU)
• Battery Charge Regulator (BCR)
• Battery Discharge Regulator (BDR)