Sputnik 1 was the first artificial Earth satellite. The Soviet Union launched it into an elliptical low Earth orbit on 4 October 1957. It was a 58 cm (23 in) diameter polished metal sphere, with four external radio antennae to broadcast radio pulses. It was visible all around the Earth and its radio pulses were detectable. This surprise success precipitated the American Sputnik crisis and triggered the Space Race, a part of the larger Cold War. The launch ushered in new political, military, technological, and scientific developments.
Sputnik itself provided scientists with valuable information, even though it wasn't equipped with sensors, by tracking and studying the satellite from Earth. The density of the upper atmosphere could be deduced from its drag on the orbit, and the propagation of its radio signals gave information about the ionosphere. Sputnik 1 was launched during the International Geophysical Year from Site No.1/5, at the 5th Tyuratam range, in Kazakh SSR(now known as the Baikonur Cosmodrome). The satellite traveled at about 29,000 kilometres per hour (18,000 mph; 8,100 m/s), taking 96.2 minutes to complete each orbit. It transmitted on 20.005 and 40.002 MHz, which were monitored by amateur radio operators throughout the world. The signals continued for 21 days until the transmitter batteries ran out on 26 October 1957. Sputnik 1 burned up on 4 January 1958, as it fell from orbit upon reentering Earth's atmosphere, after travelling about 70 million km (43.5 million miles) and spending three months in orbit.
The chief constructor of Sputnik 1 at OKB-1 was Mikhail S. Khomyakov. The satellite was a 585-millimetre (23.0 in) diameter sphere, assembled from two hemispheres that were hermetically sealed with o-rings and connected by 36 bolts. It had a mass of 83.6 kilograms (184 lb). The hemispheres were 2 mm thick, and were covered with a highly polished 1 mm-thick heat shield made of aluminium-magnesium-titanium AMG6T alloy ("AMG" is an abbreviation for "aluminium-magnesium" and "T" stands for "titanium"; the alloy contains 6% of magnesium and 0.2% of titanium). The satellite carried two pairs of antennas designed by the Antenna Laboratory of OKB-1 led by Mikhail V. Krayushkin. Each antenna was made up of two whip-like parts: 2.4 and 2.9 meters (7.9 and 9.5 ft) in length, and had an almost spherical radiation pattern, so that the satellite beeps were transmitted with equal power in all directions, making reception of the transmitted signal independent of the satellite's rotation.
The power supply, with a mass of 51 kg (112 lb), was in the shape of an octagonal nut with the radio transmitter in its hole. It consisted of three silver-zinc batteries, developed at the All-Union Research Institute of Current Sources (VNIIT) under the leadership of Nikolai S. Lidorenko. Two of these batteries powered the radio transmitter and one powered the temperature regulation system. The batteries had an expected lifetime of two weeks, and operated for 22 days. The power supply was turned on automatically at the moment of the satellite's separation from the second stage of the rocket. The satellite had a one-watt, 3.5 kg (7.7 lb) radio transmitting unit inside, developed by Vyacheslav I. Lappo from NII-885, that worked on two frequencies, 20.005 and 40.002 MHz. Signals on the first frequency were transmitted in 0.3 sec pulses (under normal temperature and pressure conditions on-board), with pauses of the same duration filled by pulses on the second frequency. Analysis of the radio signals was used to gather information about the electron density of the ionosphere. Temperature and pressure were encoded in the duration of radio beeps. A temperature regulation system contained a fan, a dual thermal switch, and a control thermal switch. If the temperature inside the satellite exceeded 36 °C (97 °F) the fan was turned on and when it fell below 20 °C (68 °F) the fan was turned off by the dual thermal switch. If the temperature exceeded 50 °C (122 °F) or fell below 0 °C (32 °F), another control thermal switch was activated, changing the duration of the radio signal pulses. Sputnik 1 was filled with dry nitrogen, pressurized to 1.3 atm. The satellite had a barometric switch, activated if the pressure inside the satellite fell below 130 kPa, which would have indicated failure of the pressure vessel or puncture by a meteor, and would have changed the duration of radio signal impulse. While attached to the rocket, Sputnik 1 was protected by a cone-shaped payload fairing, with a height of 80 cm (31.5 in). The fairing separated from both Sputnik 1 and the spent R-7 second stage at the same time as the satellite was ejected. Tests of the satellite were conducted at OKB-1 under the leadership of Oleg G. Ivanovsky.
The control system of the Sputnik rocket was adjusted to an intended orbit of 223 km (139 mi) by 1,450 km (900 mi), with an orbital period of 101.5 min. The trajectory had been calculated earlier by Georgi Grechko, using the USSR Academy of Sciences' mainframe computer. 19.9 seconds after engine cut-off, PS-1 separated from the second stage and the satellite's transmitter was activated. These signals were detected at the IP-1 station by Junior Engineer-Lieutenant V.G. Borisov, where reception of Sputnik's "beep-beep-beep" tones confirmed the satellite's successful deployment. Reception lasted for two minutes, until PS-1 fell below the horizon. The Tral telemetry system on the R-7 core stage continued to transmit and was detected on its second orbit.The Sputnik rocket was launched on 4 October 1957 at 19:28:34 UTC (5 October at the launch site) from Site No.1 at NIIP-5. Telemetry indicated the side boosters separated 116 seconds into the flight and the core-stage engine shut down 295.4 seconds into the flight. At shut down, the 7.5 tonne core stage with PS-1 attached had attained an altitude of 223 km (139 mi) above sea level, a velocity of 7,780 m/s (25,500 ft/s) and velocity vector inclination to the local horizon of 0 degrees 24 minutes. This resulted in an initial orbit of 223 kilometres (139 mi) by 950 kilometres (590 mi), with an apogee approximately 500 kilometres (310 mi) lower than intended, and an inclination of 65.1 degrees and a period of 96.2 minutes. The designers, engineers and technicians who developed the rocket and satellite watched the launch from the range. After the launch they drove to the mobile radio station to listen for signals from the satellite. They waited about 90 minutes to ensure that the satellite had made one orbit and was transmitting, before Korolev called Soviet premier Nikita Khrushchev. On the first orbit the Telegraph Agency of the Soviet Union (TASS) transmitted: "As result of great, intense work of scientific institutes and design bureaus the first artificial Earth satellite has been built". The R-7 core stage, with a mass of 7.5 tonnes and a length of 26 meters, also reached Earth orbit and was visible from the ground at night as a first magnitude object following the satellite. Deployable reflective panels were placed on the booster in order to increase its visibility for tracking. The satellite itself, a small, highly polished sphere, was barely visible at sixth magnitude, and thus more difficult to follow optically. A third object, the payload fairing, also achieved orbit. The core stage of the R-7 remained in orbit for two months until 2 December 1957, while Sputnik 1 orbited until 4 January 1958, having completed 1,440 orbits of the Earth.
Source :- https://en.wikipedia.org/wiki/Sputnik_1