# Electrical power system of a spacecraft mission to a comet

## Homework Statement

Calculate the solar array power capacity required at the start of the mission
• Mission duration is 10 years
• Distance from the Sun at end of mission is 4.8x[/8] km
• The power requirement for the spacecraft at the end of life is 510 W
• Solar array degradation over mission life = 30%
• Sun angle off normal = 45°
• Silicon solar cell efficiency at the spacecraft operating temperature = 12.5%
• Total power output from the Sun = 3.8x[/26] W
• The mass per unit area of a solar array is 2 kg [m][/-2]

## Homework Equations

Could only think of P(t) = [P][/o][e][/(-0.693t/[τ][/(1/2)])]
where P(t) is power at any given time, P_o is initial power, t is duration of mission and τ_1/2 is the time required for half of the power to be used up.

## The Attempt at a Solution

No real progress :(
help please

## Answers and Replies

donpacino
Gold Member
You know the power requirement at the end of the mission.
Figure out how much power from the sun will be delivered per solar area at the end of the mission.
Then figure out how much solar area you will need at the end of the mission.
Then use your degradation and mission duration to find how much you need at the beginning, such that the cells are sufficient at the end.