2018-01-08
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The Soviet Union launched the first artificial satellite, Sputnik 1, in 1957. Two American physicists, William Guier and George Weiffenbach, at Johns Hopkins's Applied Physics Laboratory (APL), decided to monitor Sputnik's radio transmissions. Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit. The Director of the APL gave them access to their UNIVAC to do the heavy calculations required.The next spring, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem — pinpointing the user's location, given that of the satellite. (At the time, the Navy was developing the submarine-launched Polaris missile, which required them to know the submarine's location.) This led them and APL to develop the TRANSIT system. In 1959, ARPA (renamed DARPA in 1972) also played a role in TRANSIT.
The first satellite navigation system, TRANSIT, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour.
In 1967, the U.S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required by GPS.
In the 1970s, the ground-based OMEGA navigation system, based on phase comparison of signal transmission from pairs of stations, became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy.
While there were wide needs for accurate navigation in military and civilian sectors, almost none of those was seen as justification for the billions of dollars it would cost in research, development, deployment, and operation for a constellation of navigation satellites. During the Cold War arms race, the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded. It is also the reason for the ultra secrecy at that time. The nuclear triad consisted of the United States Navy's submarine-launched ballistic missiles (SLBMs) along with United States Air Force (USAF) strategic bombers and intercontinental ballistic missiles (ICBMs). Considered vital to the nuclear deterrence posture, accurate determination of the SLBM launch position was a force multiplier.Precise navigation would enable United States ballistic missile submarines to get an accurate fix of their positions before they launched their SLBMs.The USAF, with two thirds of the nuclear triad, also had requirements for a more accurate and reliable navigation system. The Navy and Air Force were developing their own technologies in parallel to solve what was essentially the same problem.
To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms (comparable to the Russian SS-24 and SS-25) and so the need to fix the launch position had similarity to the SLBM situation.
In 1960, the Air Force proposed a radio-navigation system called MOSAIC (MObile System for Accurate ICBM Control) that was essentially a 3-D LORAN. A follow-on study, Project 57, was worked in 1963 and it was "in this study that the GPS concept was born." That same year, the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS" and promised increased accuracy for Air Force bombers as well as ICBMs.
Updates from the Navy TRANSIT system were too slow for the high speeds of Air Force operation. The Naval Research Laboratory continued advancements with their Timation (Time Navigation) satellites, first launched in 1967, and with the third one in 1974 carrying the first atomic clock into orbit.
Another important predecessor to GPS came from a different branch of the United States military. In 1964, the United States Army orbited its first Sequential Collation of Range (SECOR) satellite used for geodetic surveying. The SECOR system included three ground-based transmitters from known locations that would send signals to the satellite transponder in orbit. A fourth ground-based station, at an undetermined position, could then use those signals to fix its location precisely. The last SECOR satellite was launched in 1969.Decades later, during the early years of GPS, civilian surveying became one of the first fields to make use of the new technology, because surveyors could reap benefits of signals from the less-than-complete GPS constellation years before it was declared operational. GPS can be thought of as an evolution of the SECOR system where the ground-based transmitters have been migrated into orbit.
3.What does GSM,Lock&Unlock Mean?
The term GSM means -Global System for Mobile Communications. It is the most popular standard for mobile phones in the world. GSM differs significantly from its predecessors in that both signaling and speech channels are Digital call quality, which means that it is considered a second generation (2G) mobile phone system. GSM is an open standard which is currently developed by the 3rd Generation Partnership Project (3GPP).
From the point of view of the consumer, the key advantage of GSM systems has been higher digital voice quality and low cost alternatives to making calls such as text messaging. The advantage for network operators has been the ability to deploy equipment from different vendors because the open standard allows easy inter-operability. Like other cellular standards GSM allows network operators to offer roaming services which mean subscribers can use their phones all over the world.To help you further understand, GSM is simply a standard used by phones to communicate with each other. It is a new standard that has been adopted to all new models of phones and is now so prevailant that it has become the 'norm' in the phone world.
Now to answer your other question, with respect to locked and unlocked phones. A phone is locked when it is attached to network. For example if you go to AT&T and purchase a phone from them then that phone is said to be locked unto the AT&T network and as such it cannot work on another network such as SPRINT or NEXTEL. Thus an unlocked phone is a phone that is bought, that is not locked to any network. And as such it can work on any network.
The network it will lock unto will depend on the SIM card you put into the phone. For example if you put a AT&T sim in an unlocked phone then it will work on the AT&T network. In the same way if you put a NEXTEL SIM card in an unlocked phone then it will work on the NEXTEL network.
However if the phone is locked to a particular network, like say for example AT&T then changing the SIM card in the phone to another SIM card from another network such as NEXTEL will not work. This is because the phone is locked unto to AT&T network and as such will not work on any other network.
Yes, you can use the prepaid SIM card on the phone once the phone is either unlocked or on the same network as the SIM card you are going to put into it. It should work just fine.
Unfortunatlyis isn't possible to have more than one phone on the same line. It is possible to have more to than one phone on the same account, in fact, some providers will allow many many lines on one account.
The reason why your unable to do this is that your phone has a ESN (electronic serial number) that assoicated with that line. What this does is allow your network to send the calls to your phone. If there is more then one ESN per line then it will cause problems receiving calls.
For example, I had a phone that i wasnt using anymore when i bought a new one, well my old phone was recieving text messages that my new one was supposed to get, but the new one would get all the calls. To resolve the issue that had to erase the programming on the phone.
