Re: GAS team balloon stuff

Jared Smith

I thought that the uneven terrain and fast approach velocity (around 60 MPH) caused signal interference that caused the inaccuracies, but that doesn't align with the data.

Attached is a Google Earth view of the reported descent. You can see that it's rather linear from the near the top of the descent (by the way, it fell at 175 miles per hour after burst!) to where it should have hit the ground NE of Paradise. The problem is that the descent should have slowed as it got into thicker air and approached the ground.

Attached is a chart that compares altitude over time for the May 20 vs. June 17 flights. May 20 is normal, but today's flight increased its descent rate below around 15000 meters. Unless there's some other factor in play, this simply isn't possible. The red line indicates what I think was the actual altitude.

This suggests that the GPS was reporting inaccurate altitude for probably the last 15-20 minutes of flight - for every single position update until well after it was on the ground. I don't think that signal disruption could have caused that. I think this suggests a programming or internal issue, perhaps due to the cold temperatures.

I'd be happy to hear any other theories.


On Sat, Jun 17, 2017 at 8:38 PM, <ag1t@...> wrote:
Before 2000, the government degraded the signal (called Selective Availability).  Bill Clinton removed the limitation via Executive Order in 2000.

Most good GPS devices can be accurate within a meter now both vertically and horizontally.


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