Mike Coslo wrote:

Lenover21 wrote in part:

Still going for 100,000 foot altitude? Start thinking in terms of
the balloon exapanding to something on the order of EIGHT times
in size at altitude maximum. That's visible on some of the high
altitude research balloon flights of the 1960s using lots and lots
of plastic sheet for balloon material.

An addition to my earlier post.....


Those large plastic balloons are not used solely to hold large amounts
of helium, although they do.

The zero pressure balloons, as they are called, are actually open at
the bottom. As the helium expands with the increase in height, the
balloon eventually reaches an equilibrium point where some of the helium
escapes through the bottom vent. At this point, the balloon levels off,
maintaining roughly the same altitude. These balloons are used for large
payloads, and/or a payload that is designed to stay up for a relatively
long time. Quite a simple and elegant solution.

For the purpose of Amateur near space science, we usually want to get
the payload up and down in a fairly short order. Latex balloons are the
ticket for that.

- Mike KB3EIA -