Ariel 3, 4 (UK 3, 4)

Ariel 4 [NASA]

Ariel 3 a.k.a UK 3 (United Kingdom Research Satellite 3) was designed to continue and extend the previous UK satellite investigations in space. It was a small observatory with five experiments. The spacecraft consisted of a 57-cm-high, 12-sided prism with 69.6 cm between any pair of parallel sides. A 24.2-cm-high conical structure bearing various antennas was mated to the top of the prism. From the lower end of the prism, four paddles extended diagonally downward at an angle of 25 deg from the spin axis normal. Two sets of antennas were strung around the outer ends of these paddles. The paddles also served as mounts for some of the instrument sensors. Solar cells for power were mounted on both the sides of the prism and the paddles. The spacecraft was initially spin stabilized at about 31 rpm but slowed to about 12 rpm by the end of the first year in orbit. Attitude and spin were monitored by a combination of onboard sun sensors and by optical observations of solar reflection from a series of six mirrors mounted near the satellite equator. A tape recorder was included to obtain data for global surveys of observed variables. Experiment output for over one orbit could be recorded in a low-speed mode, with one complete set of sensor data each 0.9 s. A high-speed mode of observation provided for real-time telemetry with a complete set of sensor sampling 55 times per second. The data were dumped in 140 s in the high-speed mode. On October 24, 1967, the tape recorder began to malfunction. It operated sporadically until its complete failure on 6 February 1968. Real-time operation provided considerable data until a satellite power failure in December 1968 restricted operation to daylight hours only. By April 1969, operations had decreased to about 15 passes per week, and observations were made only from Winkfield, United Kingdom. At this time, the satellite spin had decayed to 1 rpm. The satellite was turned off in September 1969 and decayed on December 14, 1970.

The UK 4 (United Kingdom Research Satellite 4), a.k.a. Ariel 4 was a small observatory designed to investigate the interactions between electromagnetic waves, plasmas, and energetic particles present in the upper ionosphere. Experiments included observations of radio noise, electron density and temperature, very low frequency (VLF) and extremely low frequency (ELF) propagation, VLF impulses, and characteristics of low-energy charged particles. The satellite structure was similar to that of previous UK satellites, with four paddles extending out and downward from the base of the main satellite body. These paddles served as solar power cell mountings and as mounting for experiments. The satellite was a right cylinder attached to a right conical structure with solar cells placed on the cylindrical surface. The satellite was spin stabilized with an attitude control system that maintained the spacecraft's spin axis within 5 degrees of parallel alignment with the geomagnetic axis. With the particle experiment mounted at the apex of the cone, it looked at the northern geomagnetic pole. Tape-recorded data of global coverage were of low resolution, while the real-time observations taken within telemetry range of read-out stations were of high resolution. The satellite had a design lifetime of 1 yr.