4.1.2 Power Architecture

The power and electrical systems running the MMVS are one of the most important issues in the entire design.  They will be needed to insure that the mission is success.  They will help to do everything from keeping the astronauts alive to providing power so that the astronauts can heat their food and dispose of their wastes.  As such, attached are charts that delineate the power requirements for the MMVS and further expanded are the Computer System and the Communications System Power Requirements.   To help accomplish the role of power generation, we will be using four separate systems.  On each system, there will be a solar  generation array, an equal number of radioisotope thermoelectric generators and batteries.  This  was done so that even if one part of the system crashes, the other parts of the system will still  provide power throughout the system.

The peak system Power Consumption was ascertained to be 22377 Watts for the entire MMVS.  As the MMVS will be using Photo-Voltaic Arrays to provide most of the power, we need to determine the size of the arrays.  Two assumptions are made in this determination: a) At the Beginning of Life (BOL), they produce 100 W/m2; b) At the End of Life (EOL), the arrays will produce 25% less power.

As the solar arrays will be needed to provide most of the power, we decided to have them provide the peak power.  Therefore, the size of the arrays at BOL will be:
(22377 Watts)/ (100Watts/m^2)  = 223.77 m^2.

After ramping this up, we get a total of 224 m^2.  These four arrays will then be 4 m wide by 14 m long.    Hence at EOL with a 25% reduction in power the arrays will provide a total power of:
        (224 m^2) * (75 Watts/m^2)  = 16800 Watts.
The arrays will add a total mass of approximately 413.5-kg to the weight of the MMVS.

In order to make up the remaining power, we will be using Radioisotope Thermoelectric Generators.  These RTG's emit quite a bit of power and radiation and as such will be attached behind the heat shield in order to protect the crew.  By adding 20 RTG's which each provide a total of 285 W each, we get a total of 5700 Watts.  This will help in the EOL to provide the peak power whenever it is needed.  At the other times, the RTG's will be used to help charge the batteries, which back the entire system up.  The RTG's will provide a total mass of 1100 kg.

The batteries are nickel-hydrogen batteries.  These batteries were chosen for their relative power to weight ratio and the fact that they are extremely stable, have long lives and have very few cons.  Their main con is the fact that they are a little more costly than their nickel- cadmium cousins.  However, their pros clearly outweigh their cons.  We decided by looking at the charts provided to us by the Handbook of Batteries, to go with the 50-Ah high-pressure nickel-hydrogen batteries.  They come standard with 27 cells each and provide a total of 1944-Watt hours (Wh).  So we decided that the batteries must provide at minimum a Keep Alive power of approximately 5000 Watts for a total of 72 hours (this giving them enough power to keep them alive long enough to fix any of the electrical problems that they might have).  This gives us:
5000 Watts * 72 hours = 360000 Wh.
  This can then be divided by the 1944 Wh for a 50 Ah battery to give an approximate total number of 185 batteries.  As each battery also weighs approximately 40.4 kilograms, this gives a total weight of 7474 kg.  They will also take up the most space with a total volume of 12.0824 m^3 for all 185 batteries.

Therefore the total mass of the power generation system will be 413.5+1100+7474= 8987.5 kg