584:(with two low-voltage, 0.5- and 3.2-kHz sinewave forms impressed upon it) provided a profile of voltage versus ion current. The change in slope of the voltage versus ion current profile, gives the energy distribution profile, which, for thermal ions, is a function of ion mass and satellite velocity. Thermal ion velocities broaden the mass peaks somewhat and thereby degrade mass resolution slightly, but this broadening effect was used to determine the ion temperature. Analysis of current variations resulting from the two sinewave forms on the sweep voltage, provided the required slope change data for analysis of the profiles. The probe was mounted at the positive end of the spin (Z) axis on a short tubular support. With the nominal spin axis, perpendicular to the orbit plane, this arrangement eliminated spin modulation of the observations. Although this experiment functioned properly, the occurrence of a large plasma sheath about the spacecraft, prevented acquisition of scientifically useful data.
1719:
559:
transmitter-receiver that recorded the time delay between a transmitted and a returned radio pulse. Six specific frequencies from 1.5 to 7.22-MHz were sampled in sequence once every 0.105-second. Several delay times were often observed for each frequency due to plasma resonances, birefringence of the ionosphere, nonvertical propagation, etc. Delay time was primarily a function of distance traversed by the signal, electron density along the signal path, and the mode of propagation. A total of 1450 hours of data was acquired. Most of these data were of adequate quality to prepare ionograms. Since only time is noted on each ionogram, satellite position and other related information must be obtained from world maps.
92:
633:
617:. Data were recorded for periods of 1/2 hour to over 4 hours per day depending upon available power. The experiments operated satisfactorily for about 16 months, despite problems with telemetry and interference. The ion probe was rendered useless due to large spacecraft plasma sheath that developed around the spacecraft, and efforts to compensate proved fruitless.
906:
874:
842:
787:
464:
Explorer 20 was a short cylinder capped at both ends by truncated cones. The satellite's primary experiment was a six-frequency ionospheric sounder: six sounding antennas (three dipoles) extended from the satellite equator, one pair of 18.28 m (60.0 ft) antennas forming the dipole used for
620:
The satellite's responses to command signals became undependable after 20 December 1965, and the satellite transmitter often spuriously turned on. Though equipped with a one-year automatic satellite turnoff, this device was disconnected just prior to launch. Explorer 20 did not respond to a turnoff
469:. An ion mass-spectrometer, mounted on a short boom, extended from the upper cone and measured ion concentrations and temperatures in the satellite's immediate vicinity. Explorer 20 also measured cosmic emissions using the noise signal from the sounder receivers. This experiment was provided by the
500:
of 864 km (537 mi), an inclination to the equator of 79.90°, and a period of 104.00 minutes. Upon reaching orbit, the antennas extended from the spacecraft, and tests of the primary and secondary experiments were completed within the first orbit. The satellite was spin stabilized at 1.53
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in the altitude range 300 km (190 mi) to 1,000 km (620 mi). The experiment was most useful for the study of irregularities in the electron density distribution and for the investigation of fine structure in the plasma resonances. The fixed-frequency ionosonde was a radio
571:
on
Explorer 20 was a spherical retarding potential instrument from which ion mass spectra and ion temperatures could be determined. It consisted of a spherical inner electrode, 9 cm (3.5 in) in diameter, surrounded by a spherical, gridded (0.5-mm holes),
460:
concentration is at its highest. This data could then be compared and correlated with ionospheric data collected from the ground. In addition, Explorer 20 would measure electron distribution, ion density, and temperature, and to estimate cosmic noise.
29:
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Explorer 20 was not equipped with a tape recorder, so data were only received when the satellite was in sight of ground telemetry stations, located to provide primary data coverage near 80° West plus areas near
542:
frequency range. The measurements were in rough agreement with previous observations of cosmic noise. The receiver calibration, however, was not sufficiently accurate to yield new scientific results.
1750:
580:
effects. The more massive ions passed through the grid to form an ion current dependent upon the voltage condition of the inner electrode. A slow-sweeping sawtooth potential from about -2 to +10
456:. Its primary purpose was to measure ionospheric emissions from above ("topside-sounding"), between the satellite and about 320 km (200 mi) above the Earth's surface, where ionospheric
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465:
low frequencies, the other two dipoles consisting of four 9.14 m (30.0 ft) antennas. The principal investigator for this experiment was the
Central Radio Propagation Lab of the
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1507:
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It was expected that information gathered from
Explorer 20 would help in the study of long-range radio transmissions, particularly the cause of periodic radio black-outs.
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just after antenna extension, with the spin axis initially very close to the orbit plane. After a year in orbit, the spin had slowed to 0.45 rpm.
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696:"Letter dated 12 October 1964 from the Permanent Representative of the United States of America addressed to the Secretary-General"
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covering, 10 cm (3.9 in) in diameter and 0.1-mm thick. A negative charge was maintained in the grid to remove
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booster's harness and subsequent pad requirements resulted in five months of delay. On 25 August 1964, at 13:43
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100:
79:
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experiment utilized the noise signal from the sounder receiver to investigate cosmic noise in the 1.5- to 7.2
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Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated in
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551:
1800:
Symbol indicates failure en route or before intended mission data returned
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2006:
1923:
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457:
484:
Originally planned for launch in March 1964, electrical issues with the
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2173:
1991:
1898:
1628:
1442:
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2062:
1996:
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1413:
1324:
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573:
246:
2516:. Payloads deployed from other spacecraft are denoted in (brackets).
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1104:
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Explorer 20 was a 44.5 kg (98 lb) satellite designed by
325:
315:
909:
This article incorporates text from this source, which is in the
877:
This article incorporates text from this source, which is in the
845:
This article incorporates text from this source, which is in the
790:
This article incorporates text from this source, which is in the
1966:
1463:
581:
449:
421:
72:
1813:
922:
492:, Explorer 20 was launched into a near-perfect orbit, with an
428:. Its purpose was two-fold: long-term investigation of the
448:'s Airborne Instrument Laboratory under the management of
436:
investigation of ion concentrations and temperatures.
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740:. McGraw Hill Publishing Company. 31 August 1964
1589:
701:. COMMITTEE ON THE PEACEFUL USES OF OUTER SPACE
1593:
1364:
621:command after its performance became erratic.
2512:. Uncatalogued launch failures are listed in
1825:
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892:"Experiment: Spherical Ion-Mass Spectrometer"
8:
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20:
767:
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860:"Experiment: Fixed-Frequency Ionosonde"
773:"Display: Explorer 20 (IE-A) 1964-051A"
657:
16:NASA satellite of the Explorer program
496:of 1,025 km (637 mi) and a
7:
804:McDowell, Jonathan (21 July 2021).
550:The purpose of the fixed-frequency
959:List of Explorers Program missions
738:Aviation Week and Space Technology
14:
1785:indicates active current missions
1717:
904:
872:
840:
785:
631:
27:
1797:indicate missions yet to launch
563:Spherical Ion-Mass Spectrometer
520:Spherical Ion-Mass Spectrometer
368:Spherical Ion-Mass Spectrometer
424:satellite launched as part of
102:
1:
734:"Explorer 20 Launch Succeeds"
1791:indicates cancelled missions
556:ionospheric electron density
471:University College of London
467:National Bureau of Standards
2534:Spacecraft launched in 1964
672:. Mark Wade. Archived from
454:Goddard Space Flight Center
330:1,025 km (637 mi)
2560:
828:"Experiment: Cosmic Noise"
2506:
1864:
1778:
1715:
956:
808:. Jonathan's Space Report
670:Encyclopedia Astronautica
546:Fixed-Frequency Ionosonde
517:Fixed-Frequency Ionosonde
372:
366:Fixed-Frequency Ionosonde
363:
354:
320:864 km (537 mi)
285:
281:
264:
260:
197:
193:
175:44.5 kg (98 lb)
126:
122:
54:
26:
894:. NASA. 28 October 2021
862:. NASA. 28 October 2021
830:. NASA. 28 October 2021
775:. NASA. 28 October 2021
210:25 August 1964, 13:43
44:Ionospheric Explorer-A
402:Ionosphere Explorer-A
295:Reference system
131:Spacecraft properties
33:Explorer 20 satellite
1848:Orbital launches in
147:Ionospheric Explorer
118:16 months (achieved)
63:Ionospheric research
2544:1964 in spaceflight
2468:Surveyor Mass Model
554:was to investigate
116:12 months (planned)
23:
1135:25 (Injun 4, IE-B)
639:Spaceflight portal
290:Orbital parameters
2539:Explorers Program
2521:
2520:
1807:
1806:
1774:
1773:
1713:
1712:
1220:42 (Uhuru, SAS-A)
950:Explorers Program
395:
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2551:
1909:Jupiter Nosecone
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647:Explorer program
641:
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432:from above, and
426:Explorer program
418:Topside Explorer
375:Explorer program
316:Perigee altitude
299:Geocentric orbit
277:20 December 1965
202:Start of mission
113:Mission duration
104:
95:
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88:
50:Topside Explorer
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2128:Atlas-Centaur 3
1935:Zond 3MV-1 No.2
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676:on 21 June 2002
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326:Apogee altitude
309:Low Earth orbit
253:Entered service
144:Spacecraft type
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2079:Molniya-1 No.2
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1415:85–89 (THEMIS)
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269:End of mission
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2375:Strela-1 No.8
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2368:Strela-1 No.7
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2361:Strela-1 No.6
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400:, also known
399:
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382:Explorer S-66
380:←
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2478:Transit 5E-5
2445:
2373:
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2326:Dragsphere 2
2321:Dragsphere 1
2263:
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2032:Transit 5E-4
2030:
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2016:
1979:
1972:
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1794:
1783:Green titles
1702:
1695:
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1681:
1629:82 (CHIPSat)
1573:
1566:
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1462:
1455:
1448:
1441:
1210:40 (Injun 5)
1109:
1105:S-66A (BE-A)
896:. Retrieved
886:
864:. Retrieved
854:
832:. Retrieved
822:
810:. Retrieved
806:"Launch Log"
799:
777:. Retrieved
742:. Retrieved
737:
703:. Retrieved
690:
678:. Retrieved
674:the original
669:
660:
619:
591:
566:
549:
536:cosmic noise
533:
530:Cosmic Noise
514:Cosmic Noise
483:
475:
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417:
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397:
396:
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364:Cosmic Noise
274:Last contact
162:Manufacturer
59:Mission type
18:
2493:Explorer 26
2483:San Marco 1
2431:Explorer 25
2426:Explorer 24
2416:Explorer 23
2338:Explorer 22
2301:Explorer 21
1789:Grey titles
1617:79 (HETE-2)
1533:93 (NuSTAR)
1508:81 (RHESSI)
1483:68 (SAMPEX)
1325:61 (Magsat)
1300:56 (ISEE-1)
1190:36 (GEOS-B)
1155:29 (GEOS-A)
574:nickel foil
525:Experiments
509:Instruments
398:Explorer 20
387:Explorer 21
359:Instruments
336:Inclination
229:Launch site
207:Launch date
184:Solar cells
172:Launch mass
139:Explorer XX
22:Explorer 20
2528:Categories
2463:Titan 3A-1
2265:Titan 3A-2
2159:Elektron 4
2154:Elektron 3
1919:Elektron 2
1914:Elektron 1
1513:83 (GALEX)
1493:73 (TRACE)
1457:HelioSwarm
1408:84 (Swift)
1390:78 (IMAGE)
1275:53 (SAS-C)
1260:50 (IMP-J)
1255:49 (RAE-B)
1250:48 (SAS-B)
1245:47 (IMP-H)
1235:45 (SSS-A)
1225:43 (IMP-I)
1215:41 (IMP-G)
1200:38 (RAE-A)
1185:35 (IMP-E)
1180:34 (IMP-F)
1175:33 (IMP-D)
1165:31 (DME-A)
1150:28 (IMP-C)
1140:26 (EPE-D)
1125:23 (S-55C)
1115:21 (IMP-B)
1095:18 (IMP-A)
1085:16 (S-55B)
1080:15 (EPE-C)
1075:14 (EPE-B)
1070:13 (S-55A)
1065:12 (EPE-A)
980:Explorer 1
898:7 November
866:7 November
834:7 November
812:7 November
779:7 November
705:5 December
653:References
440:Spacecraft
430:ionosphere
243:Contractor
233:Vandenberg
136:Spacecraft
2510:underline
2458:Kosmos 51
2447:DS-2 No.2
2436:Mariner 4
2411:Mariner 3
2396:Kosmos 50
2391:Kosmos 49
2350:Kosmos 48
2344:Voskhod 1
2311:Kosmos 47
2296:Kosmos 46
2276:Kosmos 45
2259:Kosmos 44
2254:Kosmos 43
2249:Kosmos 42
2244:Kosmos 41
2229:Kosmos 40
2224:Kosmos 39
2219:Kosmos 38
2204:Kosmos 37
2194:Kosmos 36
2169:Kosmos 35
2134:Kosmos 34
2115:Kosmos 33
2105:OPS 4467B
2100:OPS 4467A
2090:Kosmos 32
2085:Kosmos 31
2053:Kosmos 30
2043:Kosmos 29
2002:Kosmos 28
1987:Kosmos 27
1961:Kosmos 26
1941:Kosmos 25
1894:OPS 3367B
1889:OPS 3367A
1879:SOLRAD 7A
1734:Proposals
1727:Proposals
1607:72 (SNOE)
1554:97 (IXPE)
1540:94 (IRIS)
1526:91 (IBEX)
1503:75 (WIRE)
1498:74 (SWAS)
1488:70 (FAST)
1436:96 (ICON)
1429:95 (TESS)
1422:92 (WISE)
1395:80 (WMAP)
1385:77 (FUSE)
1373:69 (RXTE)
1355:67 (EUVE)
1350:66 (COBE)
1335:63 (DE-2)
1330:62 (DE-1)
1320:60 (SAGE)
1310:58 (HCMM)
1285:55 (AE-E)
1280:54 (AE-D)
1265:51 (AE-C)
1205:39 (AD-C)
1170:32 (AE-B)
1145:27 (BE-C)
1130:24 (AD-B)
1120:22 (BE-B)
1110:20 (IE-A)
1100:19 (AD-A)
1090:17 (AE-A)
1050:11 (S-15)
1035:9 (S-56A)
973:1958–1992
744:28 August
611:Australia
603:Singapore
569:ion probe
552:ionosonde
486:Scout X-4
222:Scout X-4
188:batteries
86:1964-051A
80:COSPAR ID
46:NASA S-48
2498:OPS 3762
2488:OPS 3358
2473:OPS 6582
2453:OPS 4439
2421:OPS 3360
2406:OPS 3062
2401:OPS 5434
2386:OPS 5063
2381:OPS 4384
2355:OPS 3559
2332:OPS 4036
2316:OPS 5798
2306:OPS 3333
2291:OPS 4262
2281:OPS 3497
2239:OPS 2739
2234:Syncom 3
2214:OPS 3216
2209:OPS 3802
2199:OPS 3042
2189:Ranger 7
2164:OPS 3491
2149:OPS 4923
2144:OPS 3684
2139:OPS 3395
2110:OPS 3754
2095:OPS 3236
2073:OPS 3483
2068:OPS 4412
2058:OPS 3592
2048:OPS 2921
2038:OPS 3743
2012:Polyot 2
2007:Gemini 1
1981:OPS 3467
1956:OPS 3435
1951:OPS 3722
1946:OPS 2423
1929:OPS 3444
1924:Ranger 6
1623:INTEGRAL
1519:90 (AIM)
1379:71 (ACE)
1345:65 (CCE)
1340:64 (SME)
1315:59 (ICE)
1305:57 (IUE)
1240:46 (MTS)
1015:7 (S-1A)
966:Missions
625:See also
578:electron
458:electron
420:, was a
224:(S-134R)
69:Operator
2514:italics
2179:Vela 2B
2174:Vela 2A
1992:Ariel 2
1899:Relay 2
1884:SECOR 1
1869:Poppy 3
1795:Italics
1741:FINESSE
1690:SunRISE
1568:TRACERS
1443:SPHEREx
1010:6 (S-2)
588:Results
498:perigee
434:in situ
101:SATCAT
2441:Zond 2
2184:ERS-13
1997:Zond 1
1904:Echo 2
1874:GGSE-1
1857:1965 →
1842:← 1963
1766:ESCAPE
1761:EXCEDE
1651:Hitomi
1639:Suzaku
1602:HETE-1
1295:DADE-B
1290:DADE-A
680:9 June
615:Africa
613:, and
595:Hawaii
494:apogee
480:Launch
346:Period
340:79.90°
305:Regime
247:Vought
218:Rocket
2271:OGO-1
1756:ASTRE
1751:OHMIC
1746:Arcus
1677:GUSTO
1671:XRISM
1657:NICER
1645:TWINS
1634:CINDI
1561:PUNCH
1365:MIDEX
1055:S-45A
1020:S-46A
699:(PDF)
582:volts
414:TOPSI
237:SLC-5
180:Power
108:00870
48:TOPSI
39:Names
2121:ESRS
1967:BE-A
1850:1964
1704:CASE
1697:EZIE
1664:GOLD
1586:UNEX
1575:COSI
1547:GEMS
1475:SMEX
1464:UVEX
1450:MUSE
1401:FAME
1060:S-55
1040:S-45
1030:S-56
900:2021
868:2021
836:2021
814:2021
781:2021
746:2019
707:2022
682:2018
666:"IE"
567:The
534:The
450:NASA
422:NASA
416:and
410:S-48
406:IE-A
186:and
73:NASA
42:IE-A
1683:AWE
1005:S-1
601:),
540:MHz
503:rpm
490:GMT
452:'s
212:GMT
153:Bus
103:no.
2530::
1590:MO
1045:10
754:^
736:.
715:^
668:.
609:,
605:,
473:.
412:,
408:,
404:,
235:,
157:IE
1833:e
1826:t
1819:v
1594:I
1592:/
1588:/
1025:8
1000:5
995:4
990:3
985:2
942:e
935:t
928:v
913:.
902:.
881:.
870:.
849:.
838:.
816:.
794:.
783:.
748:.
709:.
684:.
597:(
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
