A.2.2.9 Battery Selection (Yaple)

The specifics for the battery we are using for the launch vehicle was chosen by looking at what is historically used in space applications and then finding the one that best fits our needs. Our first source of information was a NASA document “Battery SelectionPractice for Aerospace Power Systems”. This document went through the general qualities one should look at when they are picking a battery for an aerospace purpose. We determine that we need a primary battery type and not a secondary. Primary batteries are not rechargeable and are used for short durations like our flight. Secondary batteries are used more for long-term missions and satellites. In choosing a historically used primary battery we limit the battery choices to three; Lithium/Monoflouride (Li/CF), Lithium/Thionyl Chloride (Li/SOCl2), and Silver/Zinc (Ag/Zn).

Table A.2.2.8.1 Primary Battery Selection Criteria

LiCF / Li SOCl2 / AgZn
Watt-Hours/Kilogram / 130 / 185 / 110
Watt-Hours/Liter / 160 / 240 / 200
Discharge Rate / Low / Moderate / High
Failure Tolerance / Low / Low / High
Cell Voltage / 2.95V / 3.1V / 1.5V
Experience Level / High / Moderate / High
Costs / Low / Low / Low

As shown in the table above the Silver Zinc battery has the highest failure tolerance. The Lithium Monoflouride and Silver Zinc have similar energy densities (Watt-hour/kg and Watt-hour/liter). The Lithium/Thionyl Chloride battery is a fairly new battery with limited experience. Thus we rule that the Lithium/Thionyl Chloride would have had too great a start up cost and failure rate for just a slight improvement in performance.

So due to having a high discharge rate, a high failure tolerance, high experience level and relatively low cost we select using a silver zinc batteries as our primary batteries.The silver zinc batteries have been used on all the Apollo missions and the Delta Rockets.

Originally we had one battery placed on the top stage of the launch vehicle. This design idea was quickly discarded due to the fact that our battery outweighed the smaller payloads. Currently the design consists of two batteries, one that will be on the gondola to control the ignition of the first stage and a second one on the second stage which will be located with the CPU and Telecom systems in the skirt between the second and third stage. The additional cost of having a second battery was outweigh by the cut in cost by having less weight on the rocket.

In our battery selection process a lot considerations were taking into account. Yet we were not able to make a complete selection of a specific battery. Due to unknowns in the engines and other systems the full power need was only approximated and not exact. This is a limitation in our analysis. Also we only analyzed tradition space capable batteries. There may be a battery that would be lighter and/or cheaper that is not traditionally used in a space application.