Explorer is a long and ongoing series of small American scientific spacecraft. Explorer 1, the first successful American satellite, discovered the Van Allen belts. Explorer 6 took the first photo of Earth from space. Subprograms of the Explorer series have included ADE (Air Density Explorer), AE (Atmosphere Explorer), DME (Direct Measurement Explorer), EPE (Energetic Particles Explorer), GEOS (Geodetic Earth Orbiting Satellite), IE (Ionosphere Explorer), and IMP (Interplanetary Monitoring Platform). Among the more recent Explorers are IUE (International Ultraviolet Explorer) and COBE (Cosmic Background Explorer). Subcategories of the modern Explorer program include SMEX (Small Explorer), MIDEX (Medium-class Explorer), UNEX (University-class Explorer), and Missions of Opportunity, while the themes of the program are the Astronomical Search for Origins and Planetary Systems, the Sun-Earth Connection, and the Structure and Evolution of the Universe.

 

Explorer 1.

 

The name "Explorer," designating NASA's scientific satellite series, originated before NASA was formed. "Explorer" was used in the 1930s for the US Army Air Service-National Geographic stratosphere balloons. On 31 January 1958, when the first US satellite was orbited by the US Army as a contribution to the International Geophysical Year (IGY), Secretary of the Army Wilbur M. Brucker announced the satellite's name, Explorer 1. The name indicated the mission of this first satellite and its NASA successor – to explore the unknown.

 

Explorer	launch date	launch vehicle	launch site	orbit	mass (kg)
1	Feb 1, 1958	Juno 1	Cape Canaveral	358 × 2,550 × 33°	5
2	Mar 5, 1958	Juno 1	Cape Canaveral	failed to reach orbit	5
3	Mar 26, 1958	Juno 1	Cape Canaveral	186 × 2,799 × 33°	5
4	Jul 26, 1958	Jupiter	Cape Canaveral	263 × 2,213 × 50°	8
5	Aug 24, 1958	Juno 1	Cape Canaveral	failed to reach orbit	17
6	Aug 7, 1959	Thor-Able	Cape Canaveral	237 × 41,900 × 47°	64
7	Oct 13, 1959	Juno 2	Cape Canaveral	573 × 1,073 × 50°	42
8	Nov 3, 1960	Juno 2	Cape Canaveral	417 × 2,288 × 50°	41
9	Feb 16, 1961	Scout X-1	Wallops Island	545 × 2,225 × 39°	7
10	Mar 25, 1961	Delta	Cape Canaveral	highly elliptical	35
11/Met. Sat 1	Apr 27, 1961	Juno 2	Cape Canaveral	486 × 1,786 × 29°	37
12/EPE-1	Aug 16, 1961	Delta	Cape Canaveral	790 × 76,620 × 33°	38
13/Met. Sat 2	Aug 25, 1961	Scout X-1	Wallops Island	wrong orbit	86
14/EPE-2	Oct 2, 1962	Delta A	Cape Canaveral	2,601 × 96,189 × 43°	40
15/EPE-3	Oct 27, 1962	Delta A	Cape Canaveral	300 × 17,438 × 18°	44
16/Met. Sat 3	Dec 16, 1962	Scout X-3	Wallops Island	744 × 1,159 × 52°	100
17/AE 1	Apr 5, 1963	Delta B	Cape Canaveral	254 × 891 × 57°	185
18/IMP-1	Nov 26, 1963	Delta C	Cape Canaveral	192 × 197,616 × 33°	62
19/ADE 1	Dec 19, 1963	Scout X-4	Vandenberg	597 × 2,391 × 79°	7
20/IE	Aug 25, 1964	Delta C	Cape Canaveral	855 × 1,001 × 80°	44
21/IMP-2	Oct 4, 1964	Delta C	Cape Canaveral	191 × 95,590 × 34°	62
22/BE 2	Oct 9, 1964	Scout X-4	Vandenberg	872 × 1,053 × 80°	52
23/Met. Sat. 4	Nov 6, 1964	Scout X-4	Wallops Island	463 × 980 × 52°	134
24/ADE 2	Nov 21, 1964	Scout X-4	Wallops Island	530 × 2,498 × 81°	9
25/Injun 4	"	"	"	524 × 2,349 × 81°	40
26/EPE-4	Dec 21, 1964	Delta C	Cape Canaveral	284 × 10,043 × 20°	46
27/BE 3	Apr 29, 1965	Scout X-4	Wallops Island	932 × 1,309 × 41°	60
28/IMP-3	May 29, 1965	Delta C	Cape Canaveral	229 × 261,206 × 31°	58
29/GEOS 1	Nov 6, 1965	Delta E	Cape Canaveral	1,114 × 2,273 × 59°	175
30/Solrad 8	Nov 19, 1965	Scout X-4	Wallops Island	667 × 871 × 60°	57
31/DME	Nov 29, 1965	Thor Agena A	Vandenberg	502 × 2,857 × 80°	99
32/AE 2	May 25, 1966	Delta C	Cape Canaveral	282 × 2,723 × 65°	225
33/IMP-4	Jul 1, 1966	Delta E	Cape Canaveral	85,228 × 481,417 × 41°	93
34/IMP-6	May 24, 1967	Delta E	Vandenberg	242 × 214,379 × 67°	75
35 IMP-5	Jul 19, 1967	Delta E	Cape Canaveral	n/a	104
36/GEOS 2	Jan 11, 1968	Delta E	Vandenberg	1,079 × 1,572 × 106°	209
37/Solrad 9	Mar 5, 1968	Scout B	Wallops Island	353 × 433 × 59°	198
38/RAE 1	Jul 4, 1968	Delta J	Vandenberg	5,835 × 5,861 × 121°	190
39/ADE 3	Aug 8, 1968	Scout B	Vandenberg	670 × 2,583 × 81°	9
40/Injun 5	"	Scout B	Vandenberg	677 × 2,494 × 81°	70
41/IMP-7	Jun 21, 1969	Delta E	Vandenberg	80,374 × 98,159 × 86°	174
42/SAS 1	Dec 12, 1970	Scout B	San Marco	521 × 570 × 3°	143
43/IMP-8	Mar 13, 1971	Delta M	Cape Canaveral	1,845 × 203,130 × 31°	288
44 Solrad 10	Jul 8, 1971	Scout B	Wallops Island	433 × 632 × 51°	118
45/SSS-1	Nov 15, 1971	Scout B	San Marco	272 × 18,149 × 3°	52
46/MTS	Aug 13, 1972	Scout D	Wallops Island	492 × 811 × 38°	136
47/IMP-9	Sep 22, 1972	Delta 1914	Cape Canaveral	201,100 × 235,600 × 17°	376
48/SAS 2	Nov 16, 1972	Scout D	San Marco	526 × 526 × 1°	185
49/RAE 2	Jun 10, 1973	Delta 1914	Cape Canaveral	1,053 × 1,064 × 56°	328
50/IMP-11	Oct 25, 1973	Delta 1914	Cape Canaveral	141,185 × 288,857 × 28°	371
51/AE 3	Dec 16, 1973	Delta 1914	Vandenberg	155 × 4,306 × 68°	658
52/Hawkeye	Jun 3, 1974	Scout D	Vandenberg	469 × 125,569 × 89°	27
53/SAS 3	May 7, 1975	Scout F	San Marco	498 × 507 × 3°	195
54/AE 4	Oct 6, 1975	Delta 2914	Vandenberg	151 × 3,819 × 90°	676
55/AE 5	Nov 20, 1975	Delta 2914	Cape Canaveral	154 × 3,002 × 20°	721
56/ISEE-1	Oct 22, 1977	Delta 2914	Cape Canaveral	436 × 137,806 × 13°	340
57/IUE	Jan 26, 1978	Delta 2914	Cape Canaveral	30,285 × 41,296 × 34°	672
58/HCMM	Apr 26, 1978	Scout D	Vandenberg	560 × 641 × 98°	134
59/ISEE-3	Aug 12, 1978	Delta 2914	Cape Canaveral	181 × 1,089,200 × 1°	479
60/SAGE	Feb 18, 1979	Scout D	Wallops Island	456 × 506 × 55°	147
61 Magsat	Oct 30, 1979	Scout G	Vandenberg	352 × 561 × 97°	181
62 DE-1	Aug 3, 1981	Delta 3914	Vandenberg	568 × 23,289 × 90°	424
63 DE-2	"	"	"	309 × 1,012 × 80°	420
64 SME	Oct 6, 1981	Delta 2914	Cape Canaveral	335 × 337 × 98°	437
65 AMPTE/CCE	Aug 16, 1984	Delta 3925	Cape Canaveral	1,121 × 49,671 × 5°	242
66 COBE	Nov 18, 1989	Delta 5920	Vandenberg	872 × 886 × 99°	2,265
67 EUVE	Jun 7, 1992	Delta 6925	Cape Canaveral	510 × 524 × 28°	3,275
68 SAMPEX	Jul 3, 1992	Scout G	Vandenberg	506 × 670 × 82°	158
69 RXTE	Dec 30, 1995	Delta 7920	Cape Canaveral	409 × 409 × 29°	3,200
70 FAST	Aug 21, 1996	Pegasus XL	Vandenberg	353 × 4,163 × 83°	187
71 ACE	Aug 25, 1997	Delta 7920	Cape Canaveral	halo	785
72 SNOE	Feb 26, 1998	Pegasus XL	Vandenberg	529 × 581 × 98°	120
73 TRACE	Apr 2, 1998	Pegasus XL	Vandenberg	602 × 652 × 98°	250
74 SWAS	Dec 6, 1998	Pegasus XL	Vandenberg	637 × 651 × 70°	288
75 WIRE	Mar 5, 1999	Pegasus XL	Vandenberg	540 × 590 × 98°	259
76 TERRIERS	May 18, 1999	Pegasus XL	Vandenberg	537 × 552 × 98°	120
77 FUSE	Jun 24, 1999	Delta 7925	Cape Canaveral	753 × 769 × 25°	1,400
78 IMAGE	Mar 25, 2000	Delta 7326	Vandenberg	1,000 × 45,922 × 40°	494
79/HETE-2	Oct 9, 2000	Pegasus	Kwajalein	598 × 641 × 1.9°	124
80/MAP	Jun 30, 2001	Delta 7425	Cape Canaveral	1,000 × 45,922 × 40°	840
81/RHESSI	Feb 5, 2002	Pegasus	Cape Canaveral	1,000 × 45,922 × 40°	293