Proton (satellite program)

Proton 1: 16 July 1965 11:16 &nbsp; ( 1965-07-16UTC11:16Z ) &nbsp; UTC
Proton 2: 2 November 1965 12:28 &nbsp; ( 1965-11-02UTC12:28Z ) &nbsp; UTC
Proton 3: 6 July 1966 12:57 &nbsp; ( 1966-07-06UTC12:57Z ) &nbsp; UTC
Proton 4: 16 November 1968 11:40 &nbsp; ( 1968-11-16UTC11:40Z ) &nbsp; UTC

*Proton 1*, 2, 3, and 4
	A Proton satellite
Mission type	Astronomy
Operator	Soviet Union
COSPAR ID	1965-054A (Proton 1); 1965-087A (Proton 2); 1966-060A (Proton 3); 1968-103A (Proton 4);
Spacecraft properties
Manufacturer	OKB-52
Launch mass	12,200 kg (26,900 lb) (Proton 1); 12,200 kg (26,900 lb) (Proton 2); 12,200 kg (26,900 lb) (Proton 3); 17,000 kg (37,000 lb) (Proton 4);
Start of mission
Launch date	Proton 1: 16 July 1965 11:16 UTC; Proton 2: 2 November 1965 12:28 UTC; Proton 3: 6 July 1966 12:57 UTC; Proton 4: 16 November 1968 11:40 UTC;
Rocket	UR-500 (1–3), Proton-K (4)
Launch site	Baikonur Cosmodrome Site 81/23 (1–3), Baikonur Cosmodrome Site 81/24 (4)
End of mission
Disposal	De-orbited
Decay date	Proton 1: 11 October 1965; Proton 2: 6 February 1966; Proton 3: 16 September 1966; Proton 4: 24 July 1969;
Orbital parameters
Reference system	Geocentric
Eccentricity	.030 (1–3), .017 (4)
Perigee altitude	Proton 1: 183 kilometres (114 mi); Proton 2: 189 kilometres (117 mi); Proton 3: 185 kilometres (115 mi); Proton 4: 248 kilometres (154 mi);
Apogee altitude	Proton 1: 589 kilometres (366 mi); Proton 2: 608 kilometres (378 mi); Proton 3: 585 kilometres (364 mi); Proton 4: 477 kilometres (296 mi);
Inclination	63.5° (1–3), 31.5° (4)
Period	~92 minutes (1–4)

Proton (Russian: протон) ('proton') was a Soviet series of four cosmic ray and elementary particle detecting satellites. Orbited 1965–68, three on test flights of the UR-500 ICBM and one on a Proton-K rocket, all four satellites completed their missions successfully, the last reentering the Earth's atmosphere in 1969.