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A balloon satellite, sometimes referred to as a "satelloon", is a satellite inflated with gas after it has been put into orbit.
The first flying body of this type was Echo 1, which was launched into a 1,600-kilometer (990 mi) high orbit on August 12, 1960, by the United States. It originally had a spherical shape measuring 30 meters (98 ft), with a thin metal-coated plastic shell made of Mylar. It served for testing as a "passive" communication and geodetic satellite.
One of the first radio contacts using the satellite was successful at a distance of nearly 4,000 kilometers (2,500 mi) (between the east coast of the US and California). By the time Echo 1 burned up in 1968, the measurements of its orbit by several dozen earth stations had improved our knowledge of the precise shape of the planet by nearly a factor of ten.[ citation needed ]
Its successor was the similarly built Echo 2 (1964 to about 1970). This satellite circled the Earth about 400 kilometers (250 mi) lower, not at an angle of 47° like that of Echo 1, but in a polar orbit with an average angle of 81°. This enabled radio contact and measurements to be made at higher latitudes. Taking part in the Echo orbit checks to analyze disturbances in its orbit and in the Earth's gravitational field were thirty to fifty professional earth stations, as well as around two hundred amateur astronomers across the planet in "Moonwatch" stations; these contributed around half of all sightings.
The Pythagorean theorem allows us to calculate easily how far a satellite is visible at such a great height. It can be determined that a satellite in a 1,500-kilometer (930 mi) orbit rises and sets when the horizontal distance is 4,600 kilometers (2,900 mi). However, the atmosphere causes this figure to vary slightly. Thus if two radio stations are 9,000 kilometers (5,600 mi) apart and the satellite's orbit goes between them, they may be able to receive each other's reflected radio signals if the signals are strong enough.
Optical visibility is, however, lower than that of radio waves, because
Despite this there is no problem observing a flying body such as Echo 1 for precise purposes of satellite geodesy, down to a 20° elevation, which corresponds to a distance of 2,900 kilometers (1,800 mi). In theory this means that distances of up to 5,000 kilometers (3,100 mi) between measuring points can be "bridged", and in practice this can be accomplished at up to 3,000–4,000 kilometers (1,900–2,500 mi).
For visual and photographic observation of bright satellites and balloons, and regarding their geodetic use, see Echo 1 and Pageos for further information.
For special testing purposes two or three satellites of the Explorer series were constructed as balloons (possibly Explorer 19 and 38).[ specify ]
Echo 1 was an acknowledged success of radio engineering, but the passive principle of telecommunications (reflection of radio waves on the balloon's surface) was soon replaced by active systems. Telstar 1 (1962) and Early Bird (1965) were able to transmit several hundred audio channels simultaneously in addition to a television program exchanged between continents.
Satellite geodesy with Echo 1 and 2 was able to fulfill all expectations not only for the planned 2–3 years, but for nearly 10 years. For this reason NASA soon planned the launch of the even larger 40-meter (130 ft) balloon Pageos. The name is from "passive geodesic satellite", and sounds similar to "Geos", a successful active electronic satellite from 1965.
Pageos was specially launched for the "global network of satellite geodesy", which occupied about 20 full-time observing teams all over the world until 1973. All together they recorded 3000 usable photographic plates from 46 tracking stations with calibrated all-electronic BC-4 cameras (1:3 / focal length 30 and 45 cm (12 and 18 in)). From these images they were able to calculate the stations' position three-dimensionally with a precision of about 4 meters (13 ft). The coordinator of this project was Professor Hellmut Schmid, from the ETH Zurich.
Three stations of the global network were situated in Europe: Catania in Sicily, Hohenpeißenberg in Bavaria and Tromsø in northern Norway. For the completion of the navigational network exact distance measurements were needed; these were taken on four continents and across Europe with a precision of 0.5 millimeters (0.020 in) per kilometer.
The global network enabled the calculation of a "geodetic date" (the geocentric position of the measurement system) on different continents, within a few meters. By the early 1970s reliable values for nearly 100 coefficients of the Earth's gravity field could be calculated.
Bright balloon satellites are well visible and were measurable on fine-grained (less sensitive) photographic plates, even at the beginning of space travel, but there were problems with the exact chronometry of a satellite's track. In those days it could only be determined within a few milliseconds.
Since satellites circle the earth at about 7–8 kilometers per second (4.3–5.0 mi/s), a time error of 0.002 second translates into a deviation of about 15 meters (49 ft). In order to meet a new goal of measuring the tracking stations precisely within a couple of years, a method of flashing light beacons was adopted around 1960.
To build a three-dimensional measuring network, geodesy needs exactly defined target points, more so than a precise time. This precision is easily reached by having two tracking stations record the same series of flashes from one satellite.
Flash beacon technology was already mature in 1965 when the small electronic satellite Geos (later named Geos 1 was launched in November 1965. With its companion, Geos 2, that was launched in January 1968, the GEOS system brought about a remarkable increase in measurement precision.
From about 1975 on, almost all optical measurement methods lost their importance, as they were overtaken by speedy progress in electronic distance measurement. Only newly developed methods of observation using CCD and the highly precise star positions of the astrometry satellite Hipparcos made further improvement possible in the measurement of distance.
| Satellite | Launch date (UTC) | Decay | Mass(kg) | Diameter(m) | NSSDC ID | Nation | Usage |
|---|---|---|---|---|---|---|---|
| Beacon 1 | 1958-10-24 03:21 | 1958-10-24 (launch failure) | 4.2 | 3.66 | 1958-F18 | US | ado |
| Beacon 2 | 1959-08-15 00:31:00 | 1959-08-15 (launch failure) | 4.2 | 3.66 | 1959-F07 | US | ado |
| Echo 1 | 1960-08-12 09:36:00 | 1968-05-24 | 180 | 30.48 | 1960-009A | US | pcr, ado, spc, tri |
| Explorer 9 | 1961-02-16 13:12:00 | 1964-04-09 | 36 | 3.66 | 1961-004A | US | ado |
| Explorer 19 (AD-A) | 1963-12-19 18:43:00 | 1981-10-05 | 7.7 | 3.66 | 1963-053A | US | ado |
| Echo 2 | 1964-01-25 13:55:00 | 1969-06-07 | 256 | 41 | 1964-004A | US | pcr, tri |
| Explorer 24 (AD-B) | 1964-11-21 17:17:00 | 1968-10-18 | 8.6 | 3.6 | 1964-076A | US | ado |
| PAGEOS 1 | 1966-06-24 00:14:00 | 1975-07-12 | 56.7 | 30.48 | 1966-056A | US | tri |
| PasComSat (OV1-8) | 1966-07-14 02:10:02 | 1978-01-04 | 3.2 | 9.1 | 1966-063A | US | pcr |
| Explorer 39 (AD-C) | 1968-08-08 20:12:00 | 1981-06-22 | 9.4 | 3.6 | 1968-066A | US | ado |
| Mylar Balloon | 1971-08-07 00:11:00 | 1981-09-01 | 0.8 | 2.13 | 1971-067F | US | ado |
| Qi Qiu Weixing 1 | 1990-09-03 00:53:00 | 1991-03-11 | 4 | 3 | 1990-081B | PRC | ado |
| Qi Qiu Weixing 2 | 1990-09-03 00:53:00 | 1991-07-24 | 4 | 2.5 | 1990-081C | PRC | ado |
| Naduvaniy gazovoy balloon | 1991-03-30 (?) | 1986-017FJ | RU | ||||
| Orbital Reflector | 2018-12-03 | US | sculpture | ||||
abbreviations:
Geodesy is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies, such as planets or circumplanetary systems.
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. These points are usually on the surface of the Earth, and they are often used to establish maps and boundaries for ownership, locations, such as the designed positions of structural components for construction or the surface location of subsurface features, or other purposes required by government or civil law, such as property sales.
The Transit system, also known as NAVSAT or NNSS, was the first satellite navigation system to be used operationally. The radio navigation system was primarily used by the U.S. Navy to provide accurate location information to 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 continuous navigation satellite service from 1964, initially for Polaris submarines and later for civilian use as well. In the Project DAMP Program, the missile tracking ship USAS American Mariner also used data from the satellite for precise ship's location information prior to positioning its tracking radars.
The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM). The standard is published and maintained by the United States National Geospatial-Intelligence Agency.
In geodesy, the figure of the Earth is the size and shape used to model planet Earth. The kind of figure depends on application, including the precision needed for the model. A spherical Earth is a well-known historical approximation that is satisfactory for geography, astronomy and many other purposes. Several models with greater accuracy have been developed so that coordinate systems can serve the precise needs of navigation, surveying, cadastre, land use, and various other concerns.
LAGEOS, Laser Geodynamics Satellite or Laser Geometric Environmental Observation Survey, are a series of two scientific research satellites designed to provide an orbiting laser ranging benchmark for geodynamical studies of the Earth. Each satellite is a high-density passive laser reflector in a very stable medium Earth orbit (MEO).
In satellite laser ranging (SLR) a global network of observation stations measures the round trip time of flight of ultrashort pulses of light to satellites equipped with retroreflectors. This provides instantaneous range measurements of millimeter level precision which can be accumulated to provide accurate measurement of orbits and a host of important scientific data. The laser pulse can also be reflected by the surface of a satellite without a retroreflector, which is used for tracking space debris.
Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, were metalized balloon satellites acting as passive reflectors of microwave signals. Communication signals were transmitted from one location on Earth and bounced off the surface of the satellite to another Earth location.
A geodetic datum or geodetic system is a global datum reference or reference frame for precisely representing the position of locations on Earth or other planetary bodies by means of geodetic coordinates. Datums are crucial to any technology or technique based on spatial location, including geodesy, navigation, surveying, geographic information systems, remote sensing, and cartography. A horizontal datum is used to measure a location across the Earth's surface, in latitude and longitude or another coordinate system; a vertical datum is used to measure the elevation or depth relative to a standard origin, such as mean sea level (MSL). Since the rise of the global positioning system (GPS), the ellipsoid and datum WGS 84 it uses has supplanted most others in many applications. The WGS 84 is intended for global use, unlike most earlier datums.
Satellite geodesy is geodesy by means of artificial satellites—the measurement of the form and dimensions of Earth, the location of objects on its surface and the figure of the Earth's gravity field by means of artificial satellite techniques. It belongs to the broader field of space geodesy. Traditional astronomical geodesy is not commonly considered a part of satellite geodesy, although there is considerable overlap between the techniques.
A geodetic control network is a network, often of triangles, that are measured precisely by techniques of control surveying, such as terrestrial surveying or satellite geodesy. It is also known as a geodetic network, reference network, control point network, or simply control network.
Ajisai is a Japanese satellite sponsored by NASDA, launched in 1986 on the maiden flight of the H-I rocket. It is also known as the Experimental Geodetic Satellite (EGS), as it carries the Experimental Geodetic Payload (EGP).
Stellar triangulation is a method of geodesy and of its subdiscipline space geodesy used to measure Earth's geometric shape. Stars were first used for this purpose by the Finnish astronomer Yrjö Väisälä in 1959, who made astrometric photographs of the night sky at two stations together with a lighted balloon probe between them.
PAGEOS was a balloon satellite which was launched by NASA in June 1966. It was the first satellite specifically for use in geodetic surveying by serving as a reflective and photographic tracking target, and at the time it improved on terrestrial triangulations by about an order of magnitude. The satellite, which carried no instrumentation, broke up between 1975 and 1976. One of the largest fragments of the satellite finally deorbited in 2016.
GEOS-3, or Geodynamics Experimental Ocean Satellite 3, or GEOS-C, was the third and final satellite as part of NASA's Geodetic Earth Orbiting Satellite/Geodynamics Experimental Ocean Satellite program (NGSP) to better understand and test satellite tracking systems. For GEOS 1 and GEOS 2, the acronym stands for Geodetic Earth Orbiting Satellite; this was changed for GEOS-3.
ANNA 1B was a United States satellite launched on October 31, 1962, from Cape Canaveral, on a Thor rocket.
The Geodetic Observatory Wettzell is located atop the 616 meter-high mountain Wagnerberg, west of the village Wettzell in the German district Cham in the Bavarian Forest.
Explorer 22 was a small NASA ionospheric research satellite launched 9 October 1964, part of NASA's Explorer Program. It was instrumented with an electrostatic probe, four radio beacons for ionospheric research, a passive laser tracking reflector, and two radio beacons for Doppler navigation experiments. Its objective was to provide enhanced geodetic measurements of the Earth as well as data on the total electron content in the Earth's atmosphere and in the satellite's immediate vicinity.
Explorer 29, also called GEOS 1 or GEOS A, acronym to Geodetic Earth Orbiting Satellite, was a NASA satellite launched as part of the Explorer program, being the first of the two satellites GEOS. Explorer 29 was launched on 6 November 1965 from Cape Canaveral, Florida, with a Thor-Delta E launch vehicle.
Explorer 36 was a NASA satellite launched as part of the Explorer program, being the second of the two satellites GEOS. Explorer 36 was launched on 11 January 1968 from Vandenberg Air Force Base, with Thor-Delta E1 launch vehicle.