karn@thumper.bellcore.com (Phil R. Karn) (06/08/88)
> >So, just what are Lithium batteries, and why would they be prohibited on > >a space flight, when I am allowed to take one in my watch and mingle > >around thousands of people in public places? Are they radioactive? What > >about a leak? > > I'm no battery expert, but I have a feeling that for powering a satellite there > might be a size or weight issue at stake here... Yes, there is a size/weight issue, but it strongly favors lithium batteries. That's why everybody wants to use them. The cell voltage is about 3 volts (twice that of most primary batteries) and they put out considerably more watt-hours/kilogram. This is inherent in lithium's high electronegativity (i.e., it likes to release electrons) and its small atomic number (which means you waste relatively little mass carrying protons and neutrons, in contrast to other battery anodes like zinc, cadmium and especially lead.) Lithium batteries also have an unusually long shelf life, which would be especially useful given the long delays and slips a typical Shuttle payload encounters. The reason NASA bans them from the shuttle is because they have been known to explode when shorted. They can usually tolerate a short lasting a few seconds (typically 5), which is how they can be wave-soldered to PC boards. No, they are not radioactive. Phil
jwm@stdc.jhuapl.edu (Jim Meritt) (06/11/88)
In article <1139@thumper.bellcore.com> karn@thumper.bellcore.com (Phil R. Karn) writes: }> >So, just what are Lithium batteries, and why would they be prohibited on }> >a space flight, when I am allowed to take one in my watch and mingle }> >around thousands of people in public places? Are they radioactive? What }> >about a leak? } }The reason NASA bans them from the shuttle is because they have been }known to explode when shorted. They can usually tolerate a short }lasting a few seconds (typically 5), which is how they can be }wave-soldered to PC boards. No, they are not radioactive. They don't like getting wet much, either. Is this a consideration for something launched over an ocean that spends most of its time (when it is not in a warehouse) above water? Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5 (James W. Meritt)