Transit (satellite)

The Transit System, also known as NAVSAT or NNSS (for Navy Navigation Satellite System ), was the first satellite navigation system to be used operationally. The system has been used by the US Navy to provide accurate information on its polaris ballistic missile submarines , and it was also used as a navigation system by the Navy’s surface ships , as well as for hydrographic survey and geodetic surveying . Transit provided by the Department of National Defense.

History

The Transit Satellite System, sponsored by the Navy and jointly developed by DARPA and the Johns Hopkins Applied Physics Laboratory , under the leadership of Dr. Richard Kirschner at Johns Hopkins, was the first satellite-based system. [1] [2] [3] Just days after the Soviet launch of Sputnik 1 , the first man-made earth-orbiting satellite on October 4, 1957, William Guier and George Weiffenbach The radio signals that would be emanating from the satellite. They were able to determine Sputnik’s orbit by analyzing the Doppler shift of its radio signals during a single pass . [4] Frank McClure, the chairman of APL’s Research Center, suggested in March 1958 that if the satellite’s position was known and predictable, the Doppler shift could be used to locate a receiver on Earth, And propose a satellite system to implement this. [5]

Development of the Transit system Began in 1958 and has satellite prototype, Transit 1A , Was lancé in September 1959. [6] That satellite failed to reach orbit. [7] A second satellite, Transit 1B , was successfully launched April 13, 1960, by a Thor-Ablestar rocket. [8] The first successful tests of the system were made in 1960, and the system entered Naval service in 1964.

The Chance Vought / LTV Scout rocket was selected as the dedicated launch vehicle for the program because it delivered to orbit for the lowest cost per pound. However, the Scout decision imposed two design constraints. First, the weight of the previous satellites was about 300 lbs each, but the Scout launch capacity to the. A satellite mass reduction had to be achieved, despite a request for more power than APL had previously designed into a satellite. The second problem concerned the increased vibration that affected the payload during launching because the scout used solid rocket motors. Thus, electronic equipment that was shorter than before and rugged enough to withstand the increased vibration of had had to be produced. Meeting the new demands was more difficult than expected, but it was accomplished. The first prototype operating satellite (Transit 5A-1) was launched into a polar orbit by a Scout rocket on December 18, 1962. The satellite was a new technique for deploying the solar panels and for separating from the rocket. Because of trouble with the power system. Transit 5A-2, launched on 5 April 1963, failed to achieve orbit. Transit 5A-3, with a redesigned power supply, was launched on June 15, 1963. A malfunction of the memory occurred during navigation and stability. Thus, 5A-3 could not be used for navigation. HOWEVER, This satellite was the first to achieve gravity-gradient stabilization , and its other subsystems performed well. [9]

Surveyors Transit used to locate remote benchmarks by averaging Dozens of fixed Transit Producing sub-meter accuracy. In fact, the elevation of Mount Everest was corrected in the late 1980s by using a Transit receiver to re-survey a nearby benchmark.

Thousands of warships, freighters and private watercraft used Transit from 1967 up to 1991. In the 1970s, the Soviet Union started launching Their Own Satellite navigation system Parus (military) / Tsikada (civilian), qui est still in use today Besides the next generation GLONASS . [10] Some Soviet warships were equipped with Motorola NavSat receivers. Citation needed ]

The Transit system was made obsolete by the Global Positioning System (GPS), and ceased navigation service in 1996. Improvements in electronics. GPS used many more satellites than was used with Transit, allowing the system to be used continuously, while Transit provided a fix only every hour or more.

After 1996, the satellites were kept in use for the Navy Ionospheric Monitoring System (NIMS). [11]

Description

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Satellites

The satellite (known as OSCAR or NOVA satellites) used in the system was placed in low polar orbits , at an altitude of about 600 nautical miles (1,100 km), with an orbital period of about 106 minutes. A constellation of five satellites was required to provide reasonable global coverage. While the system was operational, at least ten satellites – one spare for each satellite in the basic constellation – were usually kept in orbit. Note That thesis OSCAR satellites Were not the Saami have the OSCAR series of satellites That Were Devoted to use by amateur radio operators to use in satellite communications .

Transit-1-Satellite Prototype

The orbits of the Transit satellites were chosen to cover the whole Earth; They crossed over the poles and were spread out at the equator. Since only one satellite was usually visible at any given time, fixed could be made only when one of the satellites was above the horizon. At the equator this delay between fixes was several hours; At mid-latitudes the delay decreased to an hour or two. SLBM launch, Transit sufficed, since submarines took periodic fixes to reset their inertial guidance system , purpose Transit lacked the ability to provide high-speed, real-time position measurements.

With later improvements, the system provided single-pass accuracy of roughly 200 meters, and also provided time synchronization to roughly 50 microseconds. Transit satellites also broadcast encrypted messages, although this was a secondary function.

The Transit satellites used arrays of magnetic-core memory as mass data storage up to 32 kilobytes. [12]

Determining ground location

The basic operating principle of Transit is similar to the system used by emergency locator transmitters , except that the transmitter is in the ground and the receiver is in orbit.

Each transit system satellite broadcast two UHF carrier signals That Provided precise time hacks (every two minutes), plus the satellite’s six Orbital Elements and orbit disturbance variables. The orbit ephemeris and clock corrections were uploaded twice each day to each satellite of the four-way Navy tracking and injection stations. This broadcast information allows a satellite receiver to calculate the location of the satellite at any point in time. Use of two carrier frequencies permitted by ionospheric refraction. The Transit system also provides the first world-wide timekeeping service, which allows users to synchronize with 50 microsecond accuracy.

The Transit satellite broadcast on 150 and 400 MHz. The two frequencies were used to allow the refraction of the satellite radio signals by the ionosphere to be canceled out,

The critical information that the receiver was able to compute was a single frequency curve caused by the Doppler effect . The Doppler Effect has caused an apparent compression of the carrier’s wavelength as the satellite receives, and stretching of wavelengths as the satellite receded. The spacecraft traveled at about 17,000 mph, which could increase or decrease the frequency of the received carrier by as much as 10 kHz. This Doppler curve was unique for each location within the satellite. Doppler shift for approach and recession, allowing the receiver to determine whether it was a satellite orbit, a non-symmetric satellite,

Calculating the most likely receiver location was not a trivial exercise. Doppler curve, based on an initial ‘trial’ location for the receiver. The software Would Then perform a least squares curve fit for Each two-minute section of the Doppler curve, recursively moving the trial position up to the trial Doppler curve ‘most étroitement’ matched the actual Doppler received from the satellite for all two-minute curve segments .

If the receiver was also moving relative to the earth, this would cause mismatches with the idealized Doppler curves, and degrade position accuracy. However, in the case of a slow-moving ship, even with two-minute Doppler curve. This was the US Navy, since American submarines would normally expose their UHF antenna for only 2 minutes to obtain a usable transit fix. The US submarine version of the Transit system also included a special encrypted, more accurate version of the satellite’s orbital data. This enhanced data allowed for considerably enhanced system accuracy [not Unlike Selective Availability (SA) under GPS]. Using this enhanced mode, LORAN C and GPS. LORAN C and GPS. Certainly, Transit was the most accurate navigation system of its day.

Determining the satellite orbits

A network of ground stations, whose locations were accurately known, continuously tracked the satellite Transit. They measure the Doppler shift and transfer the data to 5-hole paper tape. Applied Physics Laboratory in Laurel, Maryland using commercial and military teleprinter networks. The data from the fixed ground stations provided the information on the Transit satellite orbit. Locating a Transit satellite in earth orbit from a known ground station using the Doppler shift is simply the reverse of the known location of the satellite in orbit to locate an unknown location on the earth, again using the Doppler shift.

A typical ground station occupied by a small Quonset hut . The accuracy of the ground station was accurate. INITIALLY quartz oscillator in a temperature controlled oven Was used as the master clock. The master clock was checked daily for drift using a VLF receiver tuned to a US Navy VLF station. The VLF signal had the property that the phase of the VLF signal did not change from day to day at noon along the path between the transmitter and the receiver and thus could be used to measure oscillator drift. Later rubidium and cesium beam clocks were used. Ground stations had number names; For example, Station 019 was McMurdo Station, Antarctica. For many years during the 1970s this station was staffed by a graduate student and undergraduate student, typically in electrical engineering, from the University of Texas at Austin. Other destinations were located at New Mexico State University, the University of Texas at Austin, Sicily, Japan, Seychelles Island, Thule Greenland and other locations. The Greenland and Antarctica resorts have every pass of every satellite transit because of their polar orbiting satellites.

Vestibule and Quonset hut housing Transit satellite tracking station 019. 1. Triad satellite magnetometer down load antenna. 2. Fluid pole in background, 4 Revolving light temperature alarm, 5 VLF antenna, 6-9 Doppler satellite tracking antennas, 10 stove pipe for heater, 11 Flood light for low visibility conditions, 12 fuel tank.
Some of the equipment inside Transit satellite tracking station 019. 1. timer-counter, 3. time burst detector, 4. time conversion chart, 5. satellite ephemeris, 6. tracking receiver, 7. time display, 8 header-tailer programmer, 9. Digitizer and main clock, 10. master oscillator, 11. strip chart recorder, 12. paper tape punch, 13. short wave receiver. Out of sight: VLF receiver, refraction correction unit, backup battery system, power supplies, AC voltage regulators.

Portable Geoceiver

A portable version of the ground station was called a Geoceiver and was used to make field measurements. This receiver, power supply, punched tape unit, and antennas could fit in a number of padded aluminum cases and could be shipped as extra cargo on an airline. Data was taken over a period of time, typically a week, and sent back to the Satellite Control Center for processing. Therefore, unlike GPS, there was not an accurate rental of the Geoceiver rental. A Geoceiver was permanently located at the South Pole Station and operated by the United States Geological Survey staff. Since it was located on the surface of a moving ice sheet, its data was used to measure the ice sheet movement. Other Geoceivers were taken out in the field in Antarctica during the summer and were used to measure locations,

The AN / UYK-1 Computer

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Since a computer computer has been designed, the AN / UYK-1 has been developed. It was built with rounded corners to fit the hatch and was about five feet tall and sealed to be waterproof. The main design engineer was then-UCLA-faculty-member Lowell Amdahl, brother of Gene Amdahl . The AN / UYK-1 was built by the Ramo-Wooldridge Corporation [13] (later TRW) for the Lafayette class SSBNs. It was equipped with 8,192 words of 15-bit core memory plus parity bit , threaded by hand at their Canoga Park factory. Cycle time was about one microsecond .

The AN / UYK-1 was a microprogrammed machine with a 15-bit word length that lacked hardware to subtract, multiply or divide, but could add, shift, form one’s complement, and test the carry bit. Instructions to perform standard and floating point operations were subroutines and programs. For example, the “subtract” subroutine had to complement the subtrahend and add it. Multiplication required successive shifting and conditional adding.

The most important feature of the AN / UYK-1 instruction was that the machine-language instructions could have simultaneously manipulated the arithmetic registers. It also has a single-cycle indirect addressing ability.

During a satellite pass, a GE receiver would receive the orbital parameters and encrypted messages from the satellite, as well as the Doppler-shifted frequency at intervals and provide this data to the AN / UYK-1 computer. The computer would also have a reading of the latitude and longitude. Using this information the AN / UYK-1 ran the least squares algorithm and provided a location reading in about fifteen minutes.

Other satellites

There were 37 other satellites in the Transit series that were assigned to the Transit name by NASA. [14]

Transit 3B demonstrated uploading programs into the onboard computer’s memory whilst in orbit.

Transit 4A, launched June 29, 1961, was the first satellite to use a radioactive power source (RTG) (a SNAP-3 ). [15] Transit 4B (1961) also had a SNAP-3 RTG. Transit 4B was among several satellites which were inadvertently damaged or destroyed in a nuclear explosion, specifically the United States Starfish Prime high-altitude nuclear test on July 9, 1962 and subsequent radiation belt . [16]

Transit 5A3 and Transit 5B-1 (1963) each had SNAP-3 RTG . [17] [18]

Transit 5B-2 (1963) had a SNAP-9A RTG. [19]

Transit-9 and 5B4 (1964) and Transit-5B7 and 5B6 (1965) have had a nuclear power source.

The US Air Force also periodically launched short lived satellites equipped with radio beacons of 162 MHz and 324 MHz at orbital drag . Citation needed ] The Transit ground tracking stations tracked these satellites as well, locating the satellites within their orbits using the same principles. The Earth’s gravitational field. The Earth’s gravitational field.

References

  1. Jump up^ Helen E. Worth and Mame Warren (2009). Transit to Tomorrow. Fifty Years of Space Research at The Johns Hopkins University Applied Physics Laboratory (PDF) .
  2. Jump up^ Catherine Alexandrow (Apr 2008). “The Story of GPS” . Archived fromthe original on 2011-06-29.
  3. Jump up^ DARPA: 50 Years of Bridging the Gap . Apr 2008. Archived from the original on 2011-05-06.
  4. Jump up^ Guier & Weiffenbach (1998). “Genesis of Satellite Navigation” (PDF) .
  5. Jump up^ The Legacy of Transit: Guest Editor’s Introduction by Vincent L. Pisacane, Johns Hopkins APL Technical Digest, Vol 19, Number 1, 1998. (PDF) .
  6. Jump up^ “Navy Navigation Satellite System” . APL.
  7. Jump up^ “Transit 1A – NSSDC ID: TRAN1” . NASA NSSDC.
  8. Jump up^ “Transit 1B – NSSDC ID: 1960-003B” . NASA NSSDC.
  9. Jump up^ “An Overview of Transit Development, by Robert J. Danchik. Johns Hopkins APL Technical Digest, Volume 19, Number 1 (1998), pages 18-26” (PDF) .
  10. Jump up^ Encyclopedia Astronautica: Tsikada
  11. Jump up^ “Computerized Ionospheric Tomography, by Arnold J. Tucker, Johns Hopkins APL Technical Digest, Volume 19, Number 1 (1998), pp. 66-71″(PDF) .
  12. Jump up^ Ronald K. Burek. “The NEAR Solid-State Data Recorders”. 1998.
  13. Jump up^ AN / UYK-1 Machine Reference Manualat Bitsavers
  14. Jump up^ NSSDC Master Catalog[1]Search for ‘Transit’
  15. Jump up^ David, Leonard “50 Years of Nuclear-Powered Spacecraft: It All Started with Satellite Transit 4A” (June 29, 2011) Space.com’s Space Insider ColumnRetrieved July 30, 2011
  16. Jump up^ “Transit 4B – NSSDC ID: 1961-031A” . NASA NSSDC.
  17. Jump up^ Transit-5A3
  18. Jump up^ Transit-5B1
  19. Jump up^ Transit-5B2

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