Power Analysis

Static Power Analysis

The power budget is calculated and the power generation with a solar cell configuration of 3S5P. They summarized below. Only worst-case is considered.

Component Orbit Average Power Consumption (W)

On board computer 1.38

Radio TX 0.367

Radio RX 0.202

Power Control Unit 0.525

Payload Camera 0.0135

Payload Controller 0.5

ADCS 0.67

Thermal 0.75

Deployment Mechanism 0.009 (5.12 W for 10 seconds)

Total 6.89 (with margin)

Power Generation

Maximum power per array 3.2 W

Worst-case pointing accuracy 21 deg

Total power from all arrays 16.02 W

Orbit average power generation 8.24 W

It is clear that the generation is greater than the consumption and the solar array configuration is suitable for our mission. The worst-case peak power consumption is 12.12 W while the instantaneous power generation is 13.96 W. To size the batteries, dynamic simulations are performed.

Figure. 1: Power Subsystem Simulator

The CubeSat has an estimated mission life of 2 years. The timeline is influenced by the power budget and the concept of operations. STK simulations are used to determine the eclipse and contact duration assuming an ISS orbit for the satellite.

• Duration of one orbit: 5560 s

• Worst-case Sun-pointing duration: 61.15% per orbit

• Worst-case eclipse: 2159 s, no payload imaging takes place, sun-sensors & attitude logging are off

• Longest contact duration with ground station: 400 s, 6 times a day

• Payload images are taken every 2 hrs during non-eclipse period

The power consumption timeline repeats itself every 3 orbits. The timeline is provided on the power design page under power budget. Some of the significant activities & their duration over 3 orbits are listed below.

• 3 orbit duration: 16680 s

• Worst-case eclipse: 3400-5560 s, 8960-11120 s, 14520-16680 s

• Worst-case communication: 1-400 s, 5560-5960 s, 7200-7600 s, 9000-9400 s, 11641-12041 s and 15402-15802 s

• Payload Imaging: 7200-7320 s (highest power consumption period), 14001 - 14120 seconds

• Highest power consumption takes place when communication and imaging take place simultaneously

Figure 2: Power consumption timeline over any three orbits

Figure 3: Simulation Results

From the SOC plot, it is clear that the battery doesn't significant degrade in over 100 orbits. The battery configuration found to be suitable is 2S3P. The static and dynamic analyses help conclude that the power subsystem design is suitable and sufficient.

Analysis for other operational modes

To optimize the power consumption on the CubeSat, load shedding is undertaken depending on the state of charge of the battery. The load shedding plan for different modes showing which systems on on and off during each respective mode can be seen on the Power Design Page. The following sections provide the power analysis for these modes.

Low-power mode

During the low power mode, attitude logging, torque rods and the payload controller and cameras are off. The low power mode power budget is given on the design page. The orbit average power consumption during low power mode is 3.83 W.

Survival-power mode

During the survival power mode, in addition to the components off during low power mode, attitude determination, C&DH, & Comms TX are off. The survival power mode power budget is given on the design page. The orbit average power consumption during this mode is 2.20 W.

Critical-hold mode

During the critical hold mode, only the battery charge controller and the power control unit are on. The critical hold power mode power budget is given on the design page. Orbit average power consumption during this mode is 0.75 W.

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