The Flight Captain introduced our speaker, our own Sam Ward, Laughlin class of 68H. He flew 130 missions in SEA in C-130s, and later the C-5.
He received a PhD in Aerospace Engineering with a major in orbital mechanics. He worked at Space Command at Colorado Springs and tracked
Santa Claus. He was involved with Navstar which is our Global Positioning System (GPS). Russia has one, China has about 3/4s of one, and
the European Union has about half of the needed satellites needed (about 24 for a full constellation). Our system was started in 1960 and
was fully operational by 1995. The first block consisted of 11 satellites with a 5-year life, but several are still in orbit. In 68
launches, there have only been 2 failures. Now the satellites last about 12 years and weigh about 2000 pounds. They are in a
semi-synchronous orbit at about 12,500 miles which has a period of 11 hours 58 minutes. They are in 6 planes at an inclination of 55 degrees.|
The Ground Segment Master Control Station is at Schriever AFB which is 25 miles east of Peterson Field. They track the satellites with radar and optics. There are six dedicated monitor stations at Cape Canaveral, Shemya, Hawaii, Kwajalein Atoll, Diego Garcia, and Accession Island. Using distance = rate x time and three satellite times, you can calculate lat-long. The fourth satellite will provide altitude. Corrections have to be made for the transmission times, clock errors, ionospheric, and satellite status, perturbations, earth's gravity, radiation pressure, and other bodies. They use 12 atomic clocks to calibrate the 2 or 3 atomic clocks in the satellites. They use Kalman filtering also known as linear quadratic estimation to make an estimate out of streams of noisy input data. This will generate positions within 33-feet at the 95% confidence level.
Differential GPS is an enhanced calculation that provides improved location accuracy down to 10 cm in the best implementations. Six meters would be more typical. The satellite calculates the estimated position of a known location and generates correction factors as needed. Wide Area Augmentation System (WAAS) was developed by the FAA to augment the GPS with improved accuracy, integrity, and availability. It uses measurements from reference stations to generate a received Deviation Correction to get an aircraft position within 1 meter. Airports have been using it since 2008, and there are now 600 ground stations. Besides using it for approaches, Australia, Iceland, China, Canada, and parts of Europe use it for situation awareness. Airplane location information is broadcast to all the airplanes in the area for their use. The system will be required in the US by 2020.
The Flight Commander thanked Sam for his excellent presentation. He closed the meeting with a note about the cost of our JROTC award program, ROTC scholarship and CFIP program. We will take donations any time.