SparkFun Forums

[mike whorley]

Here is some data from a flight to show the slow responce of the gps to altitude. This was not a high and fast flight either.

[mike whorley]

Here is the data from the flight to 32K.

Looking at the gps file shows the problem I had. The gps output the same sentence for around 14 seconds. I assume the gps would catch up again like it did on previous flights but it has never output the same sentence multiple times.

I beleive the loss of contact to ground station to be from the airframe. The airframe is carbon fiber with a fiberglass nosecone. The gps is located in the nosecone due to the inability for rf to go through carbon.

The current theory is the higher the rocket goes the farther away the ground station needs to be for the airframe not to get in the way.

[DavidCary]

the rule for altitude records (flawed as it maybe) states that flights over 30,000 ft altitude needs to be determined by gps.

According to Wikipedia: GPS,
"All GPS receivers capable of functioning above 18 kilometers (11 mi) altitude and 515 metres per second (1,001 kn) [3] are classified as munitions (weapons) ... These limits attempt to prevent use of a receiver in a ballistic missile. ... This rule applies even to otherwise purely civilian units ... Disabling operation above these limits exempts the receiver from classification as a munition. Vendor interpretations differ. ... This has caused problems with some amateur radio balloon launches which regularly reach 30 kilometers (19 mi)."

Is there any way to tell if your GPS is deliberately choosing not to work in an attempt to avoid the munitions classification, and is perhaps being excessively conservative?

[mike whorley]

Yes this is an issue but as I understand it most gps units OR velocity and altitude (meaning if one OR the other is over limits condition is true). The Lassen IQ uses AND ( altitude AND velocity need to be over limits for condition to be true)