[time-nuts] More from the obsolete gps file: oncore nmea

Ralph Smith ralph at ralphsmith.org
Mon May 31 13:18:38 UTC 2010

We're diverting from time-nuttery a bit here, but I think this is still of interest to a large part of the group.

On May 31, 2010, at 6:00 AM, Hal Murray wrote:
> ralph at ralphsmith.org said:
>> The Vienna (Virginia) Wireless Society has had several balloon launches. Our
>> last, on May 1, 2010 reached 117,877 ft. We use a Garmin GPS-18, which works
>> at these altitudes. Information on our flights can be found at <http://
>> www.viennawireless.org/balloon/missions/>, and some pictures from the latest
>> flight are at <http://www.wherry.com/photos/2010-05-01-balloon-vws8/>. 
> Neat.  Thanks.
> Do you let it run continuously or do you do something to save power?

It runs continuously through the course of the flight. The GPS itself doesn't pull much current.

> What's the total payload weight?   One of the people I talked to at 
> Maker-Faire said the FAA doesn't care if it's under 4 pounds.

This last flight had a payload of 3.75 pounds. I was not involved with the payload team, but the payload contained the GPS; two transmitters: a 2 meter transmitter transmitting once every 70 seconds at 350 mW, and a BigRedBee transmitting at 15 mW on the 430 MHz band; and a camera. We were optimizing for altitude so we flew a lighter payload than we have in the past. Previous flights have included multiple cameras, or an iPhone which logged the accelerometer data.

The FAA regulations covering balloon flights such as this are in FAR 101 <http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&rgn=div5&view=text&node=14:>. There are restrictions on the strength of the payload suspension rope. In brief, you are exempt from most restrictions if you meet the breakaway limit and your payload weight is below 4 pounds. From four to six pounds you are exempt if you are below a weight to size ratio of 3 ounces per square inch on the smallest surface of the payload.

You can find a lot of useful balloon-related info at <http://www.eoss.org/>.


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