Our research into a new GPS module for the Parachute System Control Computer (PSCC) led to a promising discovery; advanced GPS modules are available that utilize Real-Time Kinematic (RTK) data to determine position and altitude with an accuracy of a few centimeters. RTK data provides the GPS with information it needs to correct for the slight changes that occur to a GPS signal as it travels through the atmosphere. Normally these changes would create small inaccuracies in the GPS reading, but by using RTK, the GPS module adjusts for this and outputs a more accurate altitude reading.
While RTK equipped GPS modules are more expensive and complex then their non RTK counterparts, the enhanced accuracy that they offer is worth it, especially when an accurate reading is necessary to deploy the parachutes on time. Due to this, we purchased a RTK GPS and the related components to integrate it into the PSCC-2.
After the parts arrived we were faced with the task of assembling them and converting the PSCC-1 code into a version that would work with new PSCC-2. With the experience we had gained while building the first PSCC we were able to complete this task in only a few weeks and we ready to begin testing.
The first test we performed was a simple ground based test that would evaluate the accuracy of the PSCC-2 against a known source, a survey mark. Survey marks are areas that have had their altitude and location precisely measured, so that equipment of unknown accuracy, such as the one in our PSCC-2, can have their accuracy determined. We located a survey mark nearby, and acquired the published altitude value. At the site of the survey mark we powered on the PSCC-2 and collected an array of altitude readings (shown below).
When we compared this data with the published value of 1627532 mm, we found our PSCC-2 altitude readings had a discrepancy of approximately 1976 mm (2 m). Considering that we were unable to position the PSCC-2 directly on the beacon, this result is well within our accuracy requirements. Now that we have confirmed the performance of our system, we are ready to flight test the PSCC-2.