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The following photos are at the Northern Colorado Rocketry Atlas site near Ault, CO. The intended launch was subverted by a previously unflown, brand new, but seemingly defective backup altimeter. The altimeter seemed to have passed all the intial setup tests and responded correctly to the programming of the set points. However, after the altimeters were powered on and the shunts removed from the charges, about 30 seconds later we had a premature deployment of the backup charges. The drogue deployment went off first, the fin can section staying put on while the rest of the rocket left the rail. This psuedo launch, without a motor, was followed by the backup main charge being deployed (since we were obviously below 1000 feet elevation) for the final separation. Both chutes came out clean, an otherwise great deployment, not often seen this close by the spectators. We figured that maybe we had triggered the sensors by lowering the launch rails down while the altimeters were armed, so I went ahead and prepared additional charges, and reassembled the rocket for another try. We tested the avbay with the charges armed outside the rocket for over 30 seconds and the backup altimeter and charges seemed to be behaving properly. Once the rocket was back on the pad, I powered the altimeters on, and once we were getting the correct number of beeps (the shunts give the same beeps as the charges in this mode) we connected up the ignitor to the K560W. I enabled the charges and stepped away from the pad. While we were checking the continuity of the ignition system, The backup drogue charge went off again, followed by the main. Again the tail section stayed on the pad. I think the nose cone got to 30 foot elevation, the avbay and the rest of the airframe landing hard on the cement pad of the Atlas site. Wind speed was about 10mph in both instance, and the primary charges remained intact the whole time.I'm very thankful we had a slight delay in actually launching it, because if this rocket had separated during the thrust phase, instead of on the pad, it would have been destroyed. I'd like to thank Art, Bruce, John N., Tim, Joe, and all the other NCR members who helped get the pad setup and to help me get the rocket prepped. Back at home, I cleaned the black powder residue off the interior of the airframe, cut 1" off the middle airframe section and 2 inches of the forward airframe (nose cone end) section. I began testing the altimeter during the eveening hours with no failures.After I went to bed, at about 2 AM I had an epiphany, in realizing that my testing was done without the GPS/TX turned on. Sure enough, the transmitter was causing the problem by putting spurious currents into the altimeter which gave it a false launch signal and started the chain reaction of deployment charges going off. After several days of expirements and tests, I found that not all barometric altimeters are affected by the RF, having a ground plane helps the immumity. To keep from being affected, the GPS/TX needs to be more that 6" away from the altimeter. I have now moved the GPS/TX into the nose cone and reduced the length and number of wires in the avabay which act like an antenna. I continue to do more testing on other models of altimeters as I get them from the manufacturers. Event timers would not be affected since they deal with pure digital signals and not the low threshhold anaolog signals of the barometric sensors.

Avbay Shielding to prevent the above situation (and new schematic)

I performed a couple of tests to analyze the previous false launch problem initiated by the transmitter in the GPS/TX, here are two videos. The first shows how the proximity of the GPS/TX affects the altimeter. The altimeter seems unaffected until you are within 6 inches. The actual test moved the GPS/TX slowly toward the altimeter in 2" steps, letting it 'soak' for a 2 minutes before continuing on. (46MB) Proximity Test The second test was to see if the altitude is affected by the GPS/TX. (55MB) Altitude Reading Test Shielding the inside ofthe avbay protects the wiring from becoming antennas. Someone with a CB radio nearby could have the same effect since both frequencies are around 150 MHz. Before lining the inside of the avbay I tested the theory by wrapping kitchen aluminum foil around it. No false signals were encountered.