The Navigation Satellite Timing and Ranging Global Positioning System
GPS) has been operational, incredibly, for almost three decades.
The first satellite in the originally planned 24-member constellation
was launched on July 14, 1974. A total of 11 Block I satellites (built
by Rockwell) were launched into 10,900 nautical mile orbits between
1978 and 1985 on the Atlas-Centaur booster rocket. In 1982, the DoD
decided due to budget cuts to reduce the constellation number from 24
to 18, but by 1988, the number was back to 21 plus three orbiting spares.
In 1989, the first of the Block II NAVSTAR satellites was launched.
28 were scheduled for construction and launch because of attrition from
old technology and malfunction. By 1991, 24 satellites were in orbit
and commissioned. Mission accomplished.
Until 1997, the most
accurate GPS signal, the L2, was made available to the public only on
a sporadic basis. The L2 signal was closely guarded by the military
for use in their critical aircraft, spacecraft and munitions guidance
systems. Advances in technology that most people outside the highly
classified DoD community will never know about, and pressure brought
on by civilian groups to make the L2 signal available full-time are
credited for the policy change. Since that occasion, GPS devices and
products that incorporate GPS have grown exponentially.
GPS really got its launch (no pun intended) during the first Gulf War,
when concerned parents and spouses bought GPS units by the caseload
to send to their husbands and children in the deserts of Iraq. In those
days, the GPS receivers and computational engines were the size of a
cigarette pack, often took minutes to acquire and compute signals, and
drew large amounts of current. Since only the less accurate L1 signal
was available for these units and many had only a couple receiver channels,
the accuracy was limited to around 10-20 meters (good enough for a desert
in a sand storm). The military was enjoying accuracies as good as 5
meters with the L2 signal and many channels. Block III satellites will
generate a new
L5 signal, a higher power (roughly 4x), modified version of the
L2 intended for civilian use to provide better coverage with less sensitive
receivers. Now, GPS receivers are integrated onto a single slab of silicon
and routinely provide 12 to 16 channels and achieve positional accuracies
unfathomable in the early 1990s. Their current draw is measured in tens
Today, GPS receivers can and are integrated into
just about any kind of device that is not bolted down (and some that
are): cell phones, automobiles, boats, watches, vending machines, shopping
carts, full-size airplanes and model airplanes, and even the new
Gizmondo, GameBoy-like controller (for location-based gaming). Map
software can be had that, when combined with a solid state magnetic
compass (ala the
Nokia 5140 phone), provides the operator with directions that are
detailed enough to allow navigation instructions like, “Go straight
ahead for 200 feet and turn left at Main Street, then proceed 50 feet
to the Starbucks on the right.” “Real” GPS devices like those available
from Trimble, Garmin and Magellan provide even more amazing features.
GPS is now a technology that the folks at Aerospace Corporation,
when beginning their study in 1963 on the development of a space system
as the basis for a navigation system for vehicles moving rapidly in
three dimensions (leading directly to the concept of GPS), could never
have dreamed would be at such an advanced state of maturity forty years
later. Those who are still around can take pride in the system to which
they gave birth. Why, without their foresight, for instance, the people
involved in the frontier-advancing concept of GPS art would never have
been able to indulge in their craft. What is GPS art, you might ask?
It is the process of using a GPS tracking program to record an operator’s
path along the ground (or in the air or water) in a shape that results
in an outline of a pre-planned, recognizable object. As you might expect,
there are websites dedicated to chronicling the ample talent out there.
One of such websites is
There, you will find not only a large collection of GPS art that includes
tic-tac-toe games, pictures of whales and text messages, but also instructions
on how to generate such masterpieces yourself. Isn’t technology wonderful?
A huge collection of my 'Factoids' can be accessed from my 'Kirt's Cogitations'
table of contents.
Topical Smorgasbord, another manifestation of Factoids,
are be found on these pages:
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26 | 27
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31 | 32
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34 | 35 |
All pertain to topics that are related to the general engineering and science theme
of RF Cafe.
Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas
and reference material while performing my work as an RF system and circuit design engineer.
The Internet was still largely an unknown entity at the time and not much was available
in the form of WYSIWYG
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