v3.0.3 / chapter 2 of 2 / 01 feb 08 / greg goebel / public domain
* The Soviet Union followed the American lead in navigation satellites, fielding a system known as "Parus / Tsikada" comparable to Transit in the 1970s and then developing a GPS-like system named "GLONASS" in the 1980s. Other nations are now getting into the navigation satellite business, with Japan and China now operating their own "navsats" and Europe now working on the "Galileo" system to compete with GPS.
* The Soviets set up a network of navigation satellites similar to the US Transit system, using Doppler location technology and with comparable accuracies. As with the US Transit system, the primary rationale was to provide navigational data to ballistic-missile submarines. Investigations began in the late 1950s, leading to start of a formal development program in 1962. Launch of an initial series of "Tsyklon" experimental satellites began in 1967, with a total of 29 launched into 1978, not counting at least two launch failures.
The development program was protracted because it proved difficult to obtain
the required location accuracy. Meeting specification required launch of
geodetic studies satellites to obtain a more precise gravity map of the
Earth. The last 13 Tsyklons were operational prototypes, close to production
spec, and were also called "Zaliv".
_______________________________________________________________________
15 may 67 Cosmos 158 -- dummy payload
27 sep 67 Tsyklon dummy payload launch attempt -- failure
23 nov 67 Cosmos 192
07 may 68 Cosmos 220
14 aug 69 Cosmos 292
21 oct 69 Cosmos 304
11 apr 70 Cosmos 332
20 aug 70 Cosmos 358 -- went into unusual, possibly wrong, orbit
12 oct 70 Cosmos 371
12 dec 70 Cosmos 385
22 may 71 Cosmos 422
15 dec 71 Cosmos 465
25 feb 72 Cosmos 475
06 may 72 Cosmos 489
16 aug 72 Cosmos 514
26 jan 73 Cosmos 546
25 may 73 first Zaliv launch attempt -- failure
20 jun 73 Cosmos 574
14 sep 73 Cosmos 586
29 dec 73 Cosmos 627
17 jan 74 Cosmos 628
27 jun 74 Cosmos 663
19 oct 74 Cosmos 689
23 apr 75 Cosmos 729
03 feb 76 Cosmos 800
03 jun 76 Cosmos 823
29 jul 76 Cosmos 846
20 jan 77 Cosmos 890
28 oct 77 Cosmos 962
15 mar 78 Cosmos 994
27 jul 78 Cosmos 1027
_______________________________________________________________________
The Tsyklon series was followed by the fully operational "Tsyklon-B" or
"Parus" system. Unlike the wildly varying Transit satellites, the Tsyklon
and Parus satellites had similar configurations. Both were in the form of a
drum covered with solar cells, with a weighted mast on top for
gravity-gradient stabilization, and a what appears to have been an antenna
hung off one side near the bottom. They were all launched from the Plesetsk
Northern Cosmodrome by the standard Soviet Kosmos 3M medium-lift booster, one
satellite per shot, though a few did include small secondary payloads. The
developed Parus satellites had a launch weight of about 810 kilograms (1,785
pounds), and were placed into a near-circular orbit of about 1,000 kilometers
(620 miles) at a near-polar inclination of 83 degrees.
95 Parus satellites have been launched since 1974, not counting two failures.
The system was formally accepted into service in 1976, but it appears that
the full constellation required 22 satellites and that wasn't achieved until
1980. The Parus satellites also provided a "store-dump" communications relay
service for Red Navy surface vessels and submarines. Parus satellites
continue to be launched, and some suspect that military communications is now
the primary rationale for the constellation.
_______________________________________________________________________
26 dec 74 Cosmos 700
11 apr 75 Cosmos 726
14 aug 75 Cosmos 755
04 nov 75 Cosmos 778
20 jan 76 Cosmos 789
29 oct 76 Cosmos 864
28 dec 76 Cosmos 887
21 feb 77 Cosmos 894
13 jul 77 Cosmos 928
13 sep 77 Cosmos 951
23 dec 77 Cosmos 971
17 jan 78 Cosmos 985
28 feb 78 Cosmos 991
28 mar 78 Cosmos 996
23 may 78 Cosmos 1011
20 dec 78 Cosmos 1064
16 jan 79 Cosmos 1072
21 mar 79 Cosmos 1089
07 apr 79 Cosmos 1091
31 may 79 Cosmos 1104
16 oct 79 Cosmos 1141
14 jan 80 Cosmos 1150
25 jan 80 Cosmos 1153
20 may 80 Cosmos 1181
05 dec 80 Cosmos 1225
12 feb 81 Cosmos 1244
04 jun 81 Cosmos 1275
12 aug 81 Cosmos 1295
18 sep 81 Cosmos 1308
14 jan 82 Cosmos 1333
24 mar 82 Cosmos 1344
08 apr 82 Cosmos 1349
18 jun 82 Cosmos 1380
07 jul 82 Cosmos 1386
19 oct 82 Cosmos 1417
12 jan 83 Cosmos 1428
30 mar 83 Cosmos 1448
06 may 83 Cosmos 1459
24 may 83 Cosmos 1464
08 dec 83 Cosmos 1513
11 jan 84 Cosmos 1531
02 feb 84 Cosmos 1535
11 may 84 Cosmos 1550
27 jun 84 Cosmos 1577
13 sep 84 Cosmos 1598
11 oct 84 Cosmos 1605
15 nov 84 Cosmos 1610
01 feb 85 Cosmos 1627
14 mar 85 Cosmos 1634
23 oct 85 Launch failure.
28 nov 85 Cosmos 1704
19 dec 85 Cosmos 1709
16 jan 86 Cosmos 1725
23 may 86 Cosmos 1745
18 jun 86 Cosmos 1759
24 nov 86 Cosmos 1802
17 dec 86 Cosmos 1808
18 feb 87 Cosmos 1821
06 jul 87 Cosmos 1864
14 oct 87 Cosmos 1891
23 dec 87 Cosmos 1904
22 mar 88 Cosmos 1934
18 jul 88 Cosmos 1959
22 feb 89 Cosmos 2004
04 apr 89 Cosmos 2016
07 jun 89 Cosmos 2026
25 jul 89 Cosmos 2034
20 mar 90 Cosmos 2061
20 apr 90 Cosmos 2074
14 sep 90 Cosmos 2100
26 feb 91 Cosmos 2135
16 apr 91 Cosmos 2142
22 aug 91 Cosmos 2154
27 nov 91 Cosmos 2173
17 feb 92 Cosmos 2180
15 apr 92 Cosmos 2184
01 jul 92 Cosmos 2195
29 oct 92 Cosmos 2218
09 feb 93 Cosmos 2233
01 apr 93 Cosmos 2239
02 nov 93 Cosmos 2266
26 apr 94 Cosmos 2279
22 mar 95 Cosmos 2310
06 oct 95 Cosmos 2321, did not reach operational orbit
16 jan 96 Cosmos 2327
05 sep 96 Cosmos 2334*
20 dec 96 Cosmos 2336
17 apr 97 Cosmos 2341
23 sep 97 Cosmos 2346*
24 dec 98 Cosmos 2361
26 aug 99 Cosmos 2366
08 jun 01 Cosmos 2378
28 may 02 Cosmos 2389
04 jun 03 Cosmos 2398
22 jul 04 Cosmos 2407
20 jan 05 Cosmos 2414*
11 sep 07 Cosmos 2429
_______________________________________________________________________
(*) Indicates other payloads in launch.
Parus was a secret military system, but it was followed into service by a
simplified system for civilian use, known as "Tsikada", also launched by the
Kosmos 3M booster. Parus is sometimes referred to as "Tsikada Military" or
"Tsikada-M". The Tsikada system was accepted into service in 1979 and
reached its full complement of satellites in 1986. Tsikada was heavily used
by the Soviet merchant marine. A few launches involved secondary payloads;
in particular, the Tsikada satellite Cosmos 2123 was also fitted with two
Russian amateur radio communications transponders.
_______________________________________________________________________
15 dec 76 Cosmos 883
08 jul 77 Cosmos 926
31 mar 78 Cosmos 1000
12 apr 79 Cosmos 1092
18 mar 80 Cosmos 1168
10 dec 80 Cosmos 1226
04 sep 81 Cosmos 1304
18 feb 82 Cosmos 1339
26 oct 83 Cosmos 1506
17 may 84 Cosmos 1553
30 may 85 Cosmos 1655
23 jan 86 Cosmos 1727
13 nov 86 Cosmos 1791
29 jan 87 Cosmos 1816
23 jun 87 Cosmos 1861
05 feb 91 Cosmos 2123*
10 mar 92 Cosmos 2181
12 jan 93 Cosmos 2230
24 jan 95 Tsikada*
05 jul 95 Cosmos 2315
_______________________________________________________________________
(*) Indicates other payloads in launch.
Although the last Tsikada satellite as such was launched in 1995, the
constellation continues to be replenished with a slightly different type of
spacecraft. A series of Tsikada-type satellites were fitted with an
auxiliary COSPAS-SARSAT rescue beacon locator payload, described in more
detail at the end of this chapter, and were given the name "Nadezhda (Hope)".
An evaluation prototype was launched in 1982, followed by the first launch of
an operational satellite in 1983. From the mid-1990s the Nadezhdas were
fitted with an improved "Kurs" rescue locater system, and these improved
satellites were designated "Nadezhda-M".
_______________________________________________________________________
30 jun 82 Cosmos 1383 (evaluation prototype)
24 mar 83 Cosmos 1447
21 jun 84 Cosmos 1574
04 jul 89 Nadezhda 1
27 feb 90 Nadezhda 2
12 mar 91 Nadezhda 3
14 jul 94 Nadezhda 4
10 dec 98 Nadezhda 5 (Nadezhda M)*
28 jun 00 Nadezhda 6 (Nadezhda M)*
26 sep 02 Nadezhda 7 (Nadezhda M)
_______________________________________________________________________
(*) Indicates other payloads in launch.
BACK_TO_TOP
* Although both the Parus and Tsikada / Nadezhda systems are still in operation, the Soviets went on to develop a GPS-like system, with the English name of "Global Navigation Satellite System (GLONASS)". Like GPS, the full GLONASS network includes 24 satellites, consisting of 21 operational satellites and three spares.
All the satellites transmit identical codes but at different frequencies, exactly the reverse of the scheme used for GPS. Actually, some satellites do transmit on the same frequencies, but they are placed in "antipodal" orbits so they can't be picked up by a receiver at the same time. The GLONASS satellites provide a "High Precision (HP)" signal for military location purposes and a "Standard Precision (SP)" signal for civil location purposes. The orbits are at an altitude of 19,100 kilometers (11,865 miles), slightly lower than that of the GPS satellites, with the satellites placed in three orbital planes, each containing eight satellites and with the planes separated by 120 degrees. Each satellite completes an orbit in 11 hours 15 minutes. The planes have orbital inclinations of 64.8 degrees. GLONASS is supposed to have location accuracy capabilities roughly similar to those of GPS.
GLONASS satellites, also known by the name "Uragan (Hurricane)", are launched in triplets by Proton heavy-lift boosters. They have a configuration roughly along the lines of that of US GPS Navstar satellites, with a central module carrying antenna arrays and twin solar panels. GLONASS launches began in 1982, apparently with prototype launches into 1985. An Etalon geodetic satellite was launched in place of one of the GLONASS triplets in two launches in 1989 to validate the GLONASS orbit.
The improved GLONASS-M / Uragan-M spacecraft has now been introduced,
featuring better signal characteristics and a design lifetime of seven years,
instead of the three year design lifetime of the original series. Older
GLONASS satellites were launched along with GLONASS-M spacecraft for a time,
apparently to burn up existing inventory.
_______________________________________________________________________
12 oct 82 Cosmos 1413:1415 dummy GLONASS x 3
10 aug 83 Cosmos 1490:1492 GLONASS prototype x 3
29 dec 83 Cosmos 1519:1521 GLONASS prototype x 3
19 may 84 Cosmos 1554:1556 GLONASS prototype x 3
04 sep 84 Cosmos 1593:1595 GLONASS prototype x 3
18 may 85 Cosmos 1650:1652 GLONASS prototype x 3
25 dec 85 Cosmos 1710:1712 GLONASS prototype x 3
16 sep 86 Cosmos 1778:1780 GLONASS x 3
24 apr 87 Cosmos 1838:1840 GLONASS x 3, launch failure
16 sep 87 Cosmos 1883:1885 GLONASS x 3
17 feb 88 Cosmos 1917:1919 GLONASS x 3, launch failure
21 may 88 Cosmos 1946:1948 GLONASS x 3
16 sep 88 Cosmos 1970:1972 GLONASS x 3
10 jan 89 Cosmos 1987:1989 GLONASS x 2, Etalon
31 may 89 Cosmos 2022:2024 GLONASS x 2, Etalon
19 may 90 Cosmos 2079:2081 GLONASS x 3
08 dec 90 Cosmos 2109:2111 GLONASS x 3
04 apr 91 Cosmos 2139:2141 GLONASS x 3
30 jan 92 Cosmos 2177:2179 GLONASS x 3
30 jul 92 Cosmos 2177:2179 GLONASS x 3
17 feb 93 Cosmos 2234:2236 GLONASS x 3
11 apr 94 Cosmos 2275:2277 GLONASS x 3
11 aug 94 Cosmos 2287:2289 GLONASS x 3
20 nov 94 Cosmos 2294:2296 GLONASS x 3
07 mar 95 Cosmos 2306:2309 GLONASS x 3
24 jul 95 Cosmos 2316:2319 GLONASS x 3
14 dec 95 Cosmos 2323:2225 GLONASS x 3
30 dec 98 Cosmos 2362:2364 GLONASS x 3
13 oct 00 Cosmos 2374:2376 GLONASS x 3
01 dec 01 Cosmos 2380:2382 GLONASS x 2, GLONASS-M x 1 (COSMOS 2382)
25 dec 02 Cosmos 2394:2396 GLONASS x 3
01 dec 03 Cosmos 2402:2404 GLONASS x 2, GLONASS-M x 1 (COSMOS 2404)
26 dec 04 Cosmos 2411:2413 GLONASS x 2, GLONASS-M x 1 (COSMOS 2413)
26 dec 04 Cosmos 2411:2413 GLONASS x 2, GLONASS-M x 1 (COSMOS 2413)
25 dec 05 Cosmos 2417:2419 GLONASS x 1 (COSMOS 2417), GLONASS-M x 2
24 dec 06 Cosmos 2424:2426 GLONASS-M x 3
26 oct 07 Cosmos 2431:2433 GLONASS-M x 3
25 dec 07 Cosmos 2435:2437 GLONASS-M x 3
_______________________________________________________________________
Launches of GLONASS spacecraft have been spotty, not surprising considering
the unsettled nature of the Russian state in the wake of the collapse of the
USSR, and the constellation still remains incomplete. However, the Russians
have been bringing in money with oil sales and finally have had the funds to
get moving on GLONASS. They managed to get 18 operational spacecraft into
orbit by the end of 2007, bringing the constellation up to a minimal
operating capability, and want to have a full constellation of 24 operational
spacecraft in orbit by 2010.
The Russians are now working on a third-generation GLONASS spacecraft, the "GLONASS-K", which will be smaller and will have a design lifetime of ten years. First launches are expected in 2008. India has signed a partnership deal with the Russians for a share in the GLONASS-K development program, with the Indians performing some GLONASS-M and GLONASS-K launches.
* Both Japan and the European Space Agency (ESA) are now working on GPS augmentation systems, with the main function of both networks being air traffic control.
The Japanese system is known as "MTSAT (Multifunction Transport SATellite) Space-based Augmentation System" or "MSAS", and is being implemented by the Japanese Meteorological Agency and the Japanese Ministry of Transport, hence the name of the satellite. The MTSAT spacecraft are a combination meteorological and communications satellite, and are being placed in geostationary orbit over the eastern Pacific.
The satellites provide voice and data links between aircraft and ground controllers; hand off relay GPS augmentation and integrity data to aircraft; and provide ground controllers with precision aircraft location. They replace the long-standing Japanese "Himawari (Sunflower)" or "Geostationary Meteorological Satellite (GMS)" series in the weather surveillance role, using a observation payload to track clouds and storms, and a relay system to pass data from surface stations on to central weather analysis centers.
The first MTSAT was launched by a Japanese H-2 booster on 15 November 1999, but the spacecraft failed to reach orbit. A replacement spacecraft, designated "MTSAT-1R", was successfully launched by an H-2A booster on 26 February 2005, with a second satellite designated "MTSAT-2" following on 18 February 2006. MTSAT-1 and MTSAT-1R were built by Space Systems / Loral, were based on standard Loral satellite buses, and had a launch weight of 2,900 kilograms (6,400 pounds). MTSAT-2 was built by Mitsubishi Electric with assistance from Boeing Satellite Systems and Alcatel Space, and had a larger launch mass of 4,535 kilograms (10,000 pounds).
* The ESA network is known as the "European Geostationary Navigation Overlay System (EGNOS)". Like MSAS, EGNOS transmits augmentation and integrity data to aircraft through geostationary communications satellites. It went into service in July 2005, using the INMARSAT AOR-E and IOR commercial communications satellites, along with the European Space Agency Artemis experimental communications satellite. The satellites provide coverage of subpolar areas ranging from the east coast of the United States to Japan, using 43 ground stations in 22 countries. It is being used as an approach and landing system comparable to WAAS.
* There has been some effort towards building receivers that can obtain signals from both GPS and GLONASS, providing substantially greater accuracy than would be possible from either by itself. Use of two satellite systems also gives users a "backup" operational capability if one of the systems is disabled. The European Community is now implementing the "Global Navigation Satellite System 1 (GNSS-1)", which will integrate services from GPS, GLONASS, and various augmentation networks.
One of the problems in combining use of GPS and GLONASS is that they use different global coordinate systems. GPS uses a coordinate system named "WGS-84", in which the precise location of the North Pole (which drifts a bit) is fixed at its location in 1984. GLONASS uses a coordinate system named "PZ-90", in which the precise location of the North Pole is given as an average of its position from 1900 to 1905. Trying to link the two coordinate systems has proven difficult, particularly because there are far fewer GLONASS receivers than GPS receivers.
GNSS-1 is supposedly a stepping stone to a completely independent European "GNSS-2". GNSS-2, or "Galileo" as it has been named, is to be based on an entirely new satellite constellation, consisting of 30 satellites, including three on-orbit spares, placed in three orbital planes at an altitude of 26,616 kilometers (16,530 miles). The orbital system will be integrated from the start with ground augmentation networks. The Galileo satellites will also carry COSPAS-SARSAT search and rescue payloads.
Unlike GPS, Galileo will be under complete civilian control. It is being implemented through a cooperative relationship between the ESA and the European Union (EU) organization. European military forces have expressed interest in making use of Galileo, but so far have not offered to help with funding. India bought into a share of the program in late 2003.
The Galileo group plans to offer four types of service packages: an "open" service available to all at no cost; a "safety of life" service that provides alerts when the system's accuracy or integrity is compromised; a commercial service using encrypted signals; and a public regulated service for government users. The Galileo system uses a different scheme from the US GPS system, but work was done to make sure the two systems dovetailed well enough to prevent mutual interference and allow users to pick up both systems with a single receiver.
The green light for the demonstration-validation ("dem-val") phase was given in the summer of 2003. Current plans envision flight of two "Galileo Test-Bed Satellites (GTBS)", with the spacecraft known more specifically by the name of "Galileo In-Orbit Validation Element (GIOVE), followed by launch of four dem-val spacecraft.
The contract for the first testbed satellite, GIOVE A, was issued to Surrey Satellite Technology LTD in the UK in July 2003. GIOVE A was launched from Baikonur by a Soyuz-Fregat booster on 28 November 2005; the satellite had a launch mass of 600 kilograms (1,327 pounds). Galileo Industries, a European consortium led by Astrium, Alcatel Space, and Alenia, is developing the larger GIOVE B satellite, with this spacecraft to be launched by a Soyuz booster from Baikonur in the spring of 2006. A contract for the four dem-val or "In-Orbit Validation (IOV)" spacecraft was signed in 2006 with Galileo Industries. Initial launch of an IOV satellite will be in 2008, with the full 30-satellite constellation in orbit by the end of 2010 and introduction to operational service in 2011. Galileo was designed to provide locations with a meter of error.
However, Galileo has suffered from delays and cost overruns, partly due to persistent bickering over the program among the member states. Critics have blasted the program, calling it a classic "Euro-boondoggle", based on a completely bogus business model and amounting to little more than an overpriced attempt to acquire a "me-too" GPS system. There have been loud calls for its cancellation, though for the time being the program remains alive.
* China is now operating their own first-generation satellite navigation
system, named "Compass". The first "Beidou" satellite, where "Beidou" is the
"North Dipper", the Chinese name for the constellation of the Big Dipper, was
launched in the fall of 2000, with five satellites launched to date:
___________________________________________________
31 oct 00 Beidou 1 Long March 3
21 dec 00 Beidou 1B Long March 3
25 may 03 Beidou 3 Long March 3
02 feb 07 Beidou 4 Long March 3
14 apr 07 Beidou 5 AKA Compass 1M Long March 3
___________________________________________________
The first four satellites were labelled as experimental, with the fifth being
the first operational spacecraft. The satellites were based on the Chinese
DFH-3 geostationary communications satellite and had a launch weight of 1,000
kilograms (2,200 pounds) each. The first two geostationary satellites
provided navigational coverage over the entire country. There was some
impression initially, partly because the spacecraft looked so much like
communications satellites, that they provided error corrections of GPS
signals much as did MTSAT, but as it turned out, they provided locations
without use of other navsat systems.
The scheme is referred to as the "TwinStar" system; it was demonstrated using two DFH-2A communications satellites in 1989, leading to authorization of full development of the Compass system in 1993. The developed system involves a ground-based control center sending an interrogation signal to a user's ground-based navigation receiver through the Beidou satellites, with the receiver then sending back a response through two satellites. The "time delay of arrival (TDOA)" of the response signal back to each satellite allows the position of the receiver to be determined by triangulation, with the position estimate refined at the control center by cross-referencing to a China terrain altitude database. The position data is relayed back to the receiver using an encrypted channel -- of course, Compass was designed with military applications in mind, just as were US and Soviet navsat systems -- and users can also send text messages with up to 120 Chinese characters through the spacecraft.
The system operates in a band around 2.491 GHz. There was an ambiguity in the use of two satellites, in that the position might be north or south of the Equator, but since all of China is well north of the Equator and Compass was intended at least at the outset as a national system, that's not a problem. Accuracy is only about 100 meters (330 feet), though it can be improved to 20 meters (66 feet) or better using ground-based augmentation systems. Since two-way communications are required, the Compass receivers are generally bigger than GPS / GLONASS receivers, and the maximum number of users runs to about 540,000 over the course of an hour.
Military users began to utilize the Compass system in late 2001, with civilian users getting on board in April 2004. Compass was clearly designed to provide a useful navsat system under Chinese control at much lower cost than fielding a full GPS / GLONASS-type global navsat constellation. Only five satellites will be needed to provide a low-resolution global satellite network, with a high-resolution system under consideration that would use 30 medium-orbit satellites. China is also cooperating on development of the Galileo system, possibly as an alternate plan.
* Robot and human explorers visiting other worlds in the Solar System such as the Moon or Mars would find a navigation satellite system useful to find their away around. While Earth-based tracking systems can do an amazingly good job of tracking a spacecraft in flight to or in orbit around another world, navigating around on the surface of the world requires a less cumbersome approach.
GPS is used for navigation on Earth orbiting spacecraft, but these vehicles are only in low orbit and so they might as well still be on the ground as far as the GPS constellation far above is concerned. Since GPS satellites point their antennas toward the Earth, once a spacecraft flies beyond the orbit of the constellation the signals start to become difficult to pick up. The best reception would be from satellites just coming over the Earth's horizon, but that would limit the number of satellites that could be observed at any one time for a position fix.
Furthermore, GPS signals are already weak, and at the distance of the Moon they would be so weak as to be very hard to pick up; in addition their triangulation angles would be narrow, limiting positioning accuracy. NASA researchers have had has some ideas for setting up a network of lunar ground stations to provide augmentation, though of course that would be a useless exercise on the Moon's far side, where there is no line of sight to the Earth or anything orbiting close to it.
Earth-based GPS signals would be impossible to pick up on Mars. NASA has rejected the idea of trying to duplicate a GPS constellation around Mars because of the cost and the difficulty of maintaining the timing system. Since Mars rovers don't move very fast, there would be no need to obtain continuous accurate positioning coordinates anyway. NASA sees that orbiters providing communications relay services to Mars ground stations and rovers could do the job, using a system similar to the classic DME aircraft navigation aid: the orbiter would send a short signal to the station or rover, which would immediately shoot it back, with the round-trip time giving the distance between the two. Since the position of the orbiter can be precisely determined by Earth stations, several such ranging transactions could give the precise ground location of the station or rover. Nobody envisions the number of ground stations or rovers as being very large, not remotely in the same league as the number of GPS receivers on Earth, and so the scheme would be manageable.
NASA and DARPA have been worked together on a particularly exotic notion for a space navigation system: mapping the positions of X-ray pulsars (XRPs) in the sky. An XRP is a superdense, rapidly spinning neutron star that produces bursts of X rays on a well-defined period that changes little on a human timescale, with different XRPs in different positions in the sky having different periods. Although the Earth's ozone layer prevents X rays from reaching the ground, the atmosphere of Mars presents little obstacle to X rays and the airless Moon presents no obstacle at all, allowing a map of known XRPs to be used to get a position fix. The trick to design an X-ray detector system that is compact and cheap enough to be practical, since traditionally an X-ray telescope is a hefty, complicated, and expensive piece of gear.
* As mentioned, the Soviet-Russian Nadezhda satellites carry an auxiliary "COSPAS-SARSAT" payload for search and rescue operations, which is an interesting technology in its own right. The "SARSAT" in the name stands for "Search And Rescue Satellite-Aided Tracking", which describes exactly what it is. (The "COSPAS" part is a Russian acronym for "Space System for the Search of Vessels in Distress".)
The US got interested in the use of civil radio rescue beacons in 1970, when a light aircraft carrying two US congressman disappeared over the wilds of Alaska. Given the vast uninhabited regions of the state, the search was like hunting for a needle in a haystack, and the plane and its passengers were never found. In response, the US Congress passed a law requiring that all aircraft operating in the United States carry a "Emergency Locator Transmitter (ELT)". The ELT would be activated in a crash and broadcast a distress signal at 121.5 MHz, the international aircraft distress frequency band.
The original ELT scheme was workable but far from satisfactory. Not only did the ELT have limited range, but its radio band was cluttered and noisy, and none of the signals operating on the band provided an identification feature to allow search and rescue (SAR) teams to sort between them. As a result, the US began to consider a space-based system that overcame these limitations. Other nations were interested in the same idea, and the US, Canada, and France banded together to work on the SARSAT concept. The USSR was working along a separate track on the COSPAS concept, but in 1979 the Western and Soviet groups decided to band together to form the COSPAS-SARSAT collaboration.
The new COSPAS-SARSAT rescue beacons operated on a band around 406 MHz that was reserved strictly for their use, and provided a coded digital ID signal so that a specific beacon could be identified. The digital ID signal was normally 112 bits in length and provided a country code, an ID code, and a field for supplementary data. An optional 32-bit data field could be added, extending the ID signal to 144 bits.
Satellites were fitted with secondary payloads that would monitor the rescue band and determine its location with enough accuracy to allow SAR teams to fly into the area and home in on the beacon signal. The satellites also monitored the old 121.5 MHz band, since the old ELTs were still in widespread use. The first satellite with a COSPAS-SARSAT payload was launched in 1982 and the network was fully operational by 1985. Dozens of countries eventually signed on to the effort.
* There are three different classes of homing beacons:
There are two classes of EPIRBs. A "Category I" EPIRB is carried in a special rack on board a vessel. If the rack goes underwater to a certain depth, the beacon is released to bob to the surface and start transmitting. It can be manually activated as well. A "Category II" EPIRB is manually activated only.
The signals emitted by the beacons are picked up by transponders on satellites that relay them to a ground station. Transponders for beacons are carried on three classes of satellites:
The TIROS and Nadezhda satellites are referred to as "Low Earth Orbit SAR (LEOSAR)" satellites. They can determine the location of a beacon using Doppler processing, something like the old Transit navigation scheme turned on its head. The satellites travel in a known orbit, and the Doppler shifts of a rescue beacon due to the motion of the satellite can be used to provide the general location of the beacon, allowing SAR teams to get close enough to pick up the beacon.
As the satellite moves towards the beacon, the Doppler shift increases the received frequency of the beacon signal; when the satellite passes over the beacon, there is no Doppler shift; when the satellite moves away from the beacon, the Doppler shift decreases the frequency of the beacon signal. If the beacon is offset to one side of the satellite's orbital path the same pattern of frequency shifts occur -- but over a decreasing range of frequencies as the sideways distance between the beacon and the orbital path increases.
There is an ambiguity here in determining which side of the orbital path the beacon is on with a single pass of a satellite, but two satellite observations along nearby tracks can cross-bracket the signal to a specific location. 406 MHz beacons result in greater location accuracy than the old 121.5 MHz beacons because the 406 MHz beacons are designed to tighter frequency specifications. Interestingly, even with observations from only one satellite, the system can give a "best guess" for which side of the flight track the beacon was on that often proves accurate. If the satellite were simply flying in a straight line over a flat immobile surface that would be impossible, but the real world is not flat and it is rotating under the satellite track, "skewing" the position vectors so that the change in angle of the vectors as the satellite passes is compressed slightly on the "correct" side of the track and expanded slightly on the "wrong" side of the track.
The GOES satellites, which are referred to as "Geostationary SAR (GEOSAR)" satellites, do not move relative to the Earth's surface and so cannot provide location information on their own, but they can relay alerts to the ground SAR network. In 1997, a new generation of 406 MHz beacons was introduced that could transmit Global Positioning Satellite coordinates as part of their coded signal, allowing precision location using any class of COSPAS-SARSAT satellite.
As mentioned, the European Galileo navigation satellites are supposed to carry COSPAS-SARSAT payloads. These spacecraft will be in medium Earth orbit, so it is a bit unclear what class of services they will provide for the COSPAS-SARSAT system.
* The ground stations of the COSPAS-SARSAT network are known as "Local User Terminals (LUTs)". They relay their information to a regional "Mission Control Center (MCC)", which deciphers the ID code on the beacon signal and correlates the event with other useful information, which is then passed on to the proper regional "SAR Point of Contact (SPOC)" or "Rescue Coordination Center (RCC)", which dispatches SAR teams to deal with the emergency.
Incidentally, apparently some numbers of 243 MHz beacons, like the 121.5 MHz first-generation beacons but operating at twice frequency, were built and some satellites in the COSPAS-SARSAT network can pick up 243 MHz signals. 243 MHz is the military emergency band and so these beacons are used by military forces.
* Sources include:
Launch histories and some details were obtained from Mark Wade's online ENCYCLOPEDIA ASTRONAUTICA, and Gunter Kreb's GUNTER'S SPACE PAGE in Germany. The Russian military maintains a GLONASS page, but at least the English materials are sketchy. ESA's pages on Galileo provided a fair update on the current status of a program that has been a moving target. The China Defense website gave the only explanation I could find of the Compass system.
* Revision history:
v1.0 / 05 dec 96 / gvg / Introduced as "The Global Positioning System".
v1.1 / 07 dec 98 / gvg / Minor cosmetic update.
v2.0 / 01 jun 99 / gvg / GNSS, Y2K problems, general rewrite.
v2.1 / 01 jun 01 / gvg / More details on WAAS & so on, plus GPS jamming.
v2.2.0 / 01 nov 01 / gvg / Added updates, data on other systems, new title.
v2.2.1 / 01 mar 02 / gvg / Minor fixes.
v2.2.2 / 01 jul 02 / gvg / GPS III comments.
v2.2.3 / 01 dec 02 / gvg / Comments on GPS constellation degradation.
v3.0.0 / 01 dec 04 / gvg / Split into two chapters, overall update.
v3.0.1 / 01 jan 05 / gvg / Minor cleanup, Galileo fixes.
v3.0.2 / 01 apr 06 / gvg / Various updates.
v3.0.3 / 01 feb 08 / gvg / Minor updates, some rearrangement.
BACK_TO_TOP
