Problem 1: LEO Spacecraft Power Analysis

Using a spreadsheet model, determine the power requirements for a spacecraft mission with the following characteristics:

The space vehicle (SV) is launched unpowered into a 700 km polar low earth orbit. The solar β angle is 0° which maximizes the eclipse for this altitude. The orbit period is 98.77 minutes with a 35.29 minute umbra.

Upon separation from the launch vehicle the SV powers up, and operating on batteries, orients itself to a sun-pointing attitude, taking the entire first orbit period. It is controlled by the C&DH subsystem. Attitude determination uses sun sensors and a magnetometer, while magnetic torquers, with 30% duty cycle, control the SV attitude (reaction wheels and star tracker are not used and powered off). The SV receiver is receiving this entire time, and heaters operate with 30% duty cycle. At the end of the 1st orbit, the SV deploys two solar array panels, which are pointed toward the sun and begin producing power; during the 1st orbit the solar array produces no power. Since the SV is sun-pointing, the solar array drive assembly (SADA) is not used after the initial array pointing; the SADA and the deployment devices have such short operation time that the energy requirement is not significantly affected. The heaters operate at 30% duty cycle.

During the 2^nd orbit, the spacecraft is idle with the solar array deployed and able to produce full power. The SV sun-pointing attitude is maintained with sun sensors, magnetometer and magnetic torquers, as during the 1st orbit. The SV is pointed at the sun, as is the solar array, so the SADA is not used (powered). The heaters continue to operate at 30% duty cycle.

At the beginning of the 3^rd orbit the SV makes contact with the Earth, and is commanded to slew to a nadir-pointing attitude, using the star tracker for attitude knowledge and reaction wheels for control. Communication occurs when the SV is sun lit, and is full duplex (can transmit and receive simultaneously). Pass time (visibility to the ground station) is 10 minutes for this contact, and the transmitter has 10% duty cycle during this pass. The solar array uses the SADA to point the solar array, with 2% duty cycle. The reaction wheels' average power is half their peak power, and the torquers operate with 10% duty cycle to unload momentum from the reaction wheels; the magnetometer is powered ON. The heaters operate at 20% duty cycle.

At the start of the 4^th orbit, the SV turns on the payload instrument and begins observations. Data collected raises the transmitter contact time with the Earth to 90% of a 10 minute pass, which occurs when the spacecraft is sun lit. The solar array continues to track the sun. The reaction wheels and star tracker control the spacecraft, and torquers continue to operate at 10% duty cycle and the magnetometer remains powered ON. The heaters operate at 10% duty cycle.

 The components, and their CBE power, maturity factor, and MEV power are as follows:

The powers listed are the power when operated at 100% duty cycle, i.e., the peak power.

Using the included spreadsheet as a template (note that the spreadsheet is set up to analyze sunlit and umbra power separately), and for the four modes listed, answer the following:

a. Determine the peak and average power required for each mode.

b. Determine the orbit average power required, for each of the four orbits.

c. Determine the energy needed from the battery for the 1^st and the 4^th orbit.

d. Determine the net power (after all generating and conditioning losses), needed from the power generator (solar array) at the spacecraft power bus, for the 4th orbit.

Assume 90% battery recharge efficiency.

Use a filename that includes your name, and put it in the blue box on line 1.

Problem 2: Solar Cell Analysis

Pick any space solar cell (other than the Emcore ZTJ); SolAero (Emcore), Spectrolab and Azur Space are three suppliers of these. Using the data sheet (and include it in your submittal):

a. Calculate and plot, for temperatures between 0 and 80°C, the beginning of life (BOL) power/square centimeter) and voltage at the peak power point, Pmp and Vmp. Assume the temperature coefficients are valid from 0 to 80°C.

b. For a radiation fluence of 1 E+15 e/cm², calculate Vmp and Pmp at 80°C (without any cover glass). Compare these with the BOL values at 80°C.

NOTE: The radiation degradation factors are first applied to the BOL parameters, and then the radiation-affected temperature coefficients applied to determine performance at temperature.

Assignment File - https://www.dropbox.com/s/6z9vhonc2j6biqr/Assignment%20Files.rar?dl=0