DMC-FX7
ƒ/5.6
5.8 mm
1/400
80
They have a different sound from the standard solid fuel rockets, and they burn brightly into the sky like a shooting star.
10 responses to “Nitrous Oxide Hybrid”
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Mmmmm. Home-built rocketry porn.
Has the folks from Homeland Security given you guys any problems?
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They shut the high power motors down for a while, but then they mellowed out.
They also leave some undocumented regulatory gems to discover… e.g., GPS chip sets have embeddded code so that they stop operating when they notice that they are going real fast. So you can’t use an un-hacked chip set to build a cruise missile…
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Wow, that’s the first time I’ve heard about that feature of the GPS chip sets. Very interesting… and smart.
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To my knowledge GPS chip sets do not have embedded code to fail at high speed. What does happen is that most consumer grade systems rely on receiving the same (or nearly the same) reading several times in a row from the satellites to ensure that it’s not a corrupted or garbled reading. The value of "nearly the same" is calibrated so that it works right in most consumer applications, like walking or in a car (less than 100 mph or so). When you move faster than that, then the consumer grade GPS never thinks it got good data from the satellites and never gets a lock on it’s current position.
Most HPR rockets move much faster than that.
You can argue whether this is a bug or a feature, but it’s certainly not a "regulatory gem". It’s much harder to design a GPS unit that can track satellites correctly while moving at mach speeds or better, so the vendors don’t bother unless the application requires it. When was the last time you were mountain biking at Mach 1?
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thanks! The GPS limits make sense. But I wonder if both phenomena are true. I am not an expert on this, so I double checked with my source from this weekend. Here are the specifics from the GPS FAQ archive:
"1.8 What are the speed and altitude limitations?
The system has no inherent speed or altitude limitations (GPS has
been used on satellites for position determination), but the US
requires that commercial receivers be limited to operate below
about 900 knots and 60,000 ft. It is apparently possible to get
permission to bypass these limits for specific applications
(research rockets, etc.).Garmin used to limit their non-aviation models (40 and 45 at least) to
operation below 90 knots. Above this speed, the receiver displays
an error message and stops updating the position. This is
apparently a marketing decision to force aviators to purchase the
more expensive aviation models which incorporate an aviation
waypoint database. They discontinued this practice with the
advent of their 12 channel parallel units (GPS 12/12XL/II+/III). "
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The U.S. limitations come from Item 11 of the US missile technology control regime.So, if I try to piece this together, sat lock drift comes from cheap correlators on the chip set, but there is also a limitation placed on commercial units where they report an error if the limits have been passed. Make sense?
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Yeah, the GPS firmware basically looks at the readings, goes "that can’t be right" and ignores ’em.
There’s a guy with Portland State Aero Society who wrote a new GPS firmware as his Master’s project.
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