Discoverer 21
Encyclopedia
Discoverer 21, also known as RM-2, was an American
satellite
which was launched in 1961. It was a technology demonstration spacecraft, based around an Agena-B
.
The launch of Discoverer 21 occurred at 22:58 UTC on 18 February 1961. A Thor DM-21 Agena-B
rocket was used, flying from Launch Complex 75-3-5 at the Vandenberg Air Force Base
. Upon successfully reaching orbit, it was assigned the Harvard designation 1961 Zeta 1.
Discoverer 21 was operated in a low Earth orbit
, with a perigee
of 243 kilometres (151 mi), an apogee
of 1026 kilometres (637.5 mi), 80.7 degrees of inclination
, and a period
of 97.4 minutes. The satellite had a mass of 1110 kilograms (2,447.1 lb), and was used to demonstrate an engine restart, and to test infrared sensors for the Midas
programme. It remained in orbit until 20 April 1962, when it decayed
and reentered the atmosphere
.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
which was launched in 1961. It was a technology demonstration spacecraft, based around an Agena-B
RM-81 Agena
The RM-81 Agena was an American rocket upper stage and satellite support bus which was developed by Lockheed initially for the canceled WS-117L reconnaissance satellite program...
.
The launch of Discoverer 21 occurred at 22:58 UTC on 18 February 1961. A Thor DM-21 Agena-B
Thor-Agena
Thor-Agena was a series of orbital launch vehicles. The rockets used Thor first stages and Agena second stages. They are thus cousins of the more famous Thor-Deltas, which founded the Delta rocket family. The first attempted launch of a Thor-Agena was in January 1959...
rocket was used, flying from Launch Complex 75-3-5 at the Vandenberg Air Force Base
Vandenberg Air Force Base
Vandenberg Air Force Base is a United States Air Force Base, located approximately northwest of Lompoc, California. It is under the jurisdiction of the 30th Space Wing, Air Force Space Command ....
. Upon successfully reaching orbit, it was assigned the Harvard designation 1961 Zeta 1.
Discoverer 21 was operated in a low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
, with a perigee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
of 243 kilometres (151 mi), an apogee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
of 1026 kilometres (637.5 mi), 80.7 degrees of inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
, and a period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
of 97.4 minutes. The satellite had a mass of 1110 kilograms (2,447.1 lb), and was used to demonstrate an engine restart, and to test infrared sensors for the Midas
Missile Defense Alarm System
The Missile Defense Alarm System was an American system of 12 early-warning satellites that provided limited notice of Soviet intercontinental ballistic missile launches between 1960 and 1966...
programme. It remained in orbit until 20 April 1962, when it decayed
Orbital decay
Orbital decay is the process of prolonged reduction in the altitude of a satellite's orbit.This can be due to drag produced by an atmosphere due to frequent collisions between the satellite and surrounding air molecules. The drag experienced by the object is larger in the case of increased solar...
and reentered the atmosphere
Atmospheric reentry
Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line,...
.