We’ve been hyping up this installment of This Week in Rocket History all episode. So what is it? Another foreign satellite launched on a U.S. Scout rocket, the U.K.’s Ariel 3.

Ariel was a British satellite program that made the United Kingdom the third country to operate a satellite. Ariel 1 was launched in 1962, 2 in 1964, and 3 in 1967. Ariel 1 and 2 had British-built experiments on an American satellite bus.

Development of Ariel 3 started in 1962 with a formal proposal of the instruments to NASA from British scientists. A year later, in 1963, all of the instruments were agreed to by the two teams, but for a variety of reasons, the satellite construction did not start until 1964.

Ariel 3 was the first satellite built in the U.K., and the British team was responsible for building a prototype, engineering models, and two flight satellites. The satellite’s orbit was changed from an originally-planned 50-degree inclination to 80 degrees, to give a molecular oxygen experiment access to other latitudes to collect data, important because the solar cycle was picking up at the time.

Ariel 3 had four solar panels and five experiments and weighed just under 90 kilograms. The main purpose of the satellite was to observe variable stars and galactic radio sources. Unlike the San Marco satellites we talked about last week, Ariel 3 was launched on a Scout A rocket from Vandenberg Air Force Base on May 5, 1967. It was originally planned to be launched from Wallops like San Marco 1 but was moved to Vandenberg because of the new orbit.

The satellite body had three paddles – which Gordon on our editorial team thought looked more like snowshoes – where solar panels and some of the instruments were mounted.

The terrestrial radio noise experiment was designed to quantify the radio noise at the satellite altitude by allowing scientists to more easily tell what was a terrestrial radio source and what was a galactic radio source. The experiment demonstrated that most of the noise came at frequencies just above the “ionospheric critical frequency”, where terrestrial transmissions at lower frequencies are blocked and reflected back toward Earth by the ionosphere. Additionally, the noise from higher frequencies was so spread out that it was easy to filter.

It also measured the density and temperature of electrons with a Langmuir probe and radiofrequency capacitance counter. The Langmuir probe measured the temperature of electrons by comparing the voltages of two different spheres on the spacecraft. The voltages were constantly changed in reaction to electron temperature to maintain a fixed ratio between the two spheres. The electron temperature was determined by comparing how the voltages actually changed compared to the fixed ratio.

The radiofrequency capacitance probe measured electron density by counting the change in current between two grids. Like the Langmuir probe, it operated by switching voltages rapidly. To properly measure the change in current, it needed to be at “space potential” – or the same arrangement of positively or negatively charged environment of space – for at least part of the sweep. This was enabled by changing voltages. The two experiments actually used the same probes, with the experiments switching every 5.2 seconds.

The last major experiment on Ariel 3 counted molecular oxygen, a hazard in low Earth orbit, which can damage spacecraft. It does this by chemically interacting with almost everything, breaking down materials exposed to UV radiation. Indeed, the experiment itself was damaged by this, and after twenty days the sensors were ruined. Fortunately, ground experiments predicted this would happen, so nothing was lost. All of the other experiments continued functioning through the end of the mission, exceeding their one-year design lifetime.

Ariel 3 operated nominally until its tape recorder failed in early 1968. In late 1968 its battery failed, meaning it could only be used when the satellite was directly lit by the Sun. In early 1969, it could only downlink to one ground station, and it was finally turned off in mid-1969. Ariel 3 re-entered the Earth’s atmosphere in 1970 when its orbit decayed.

More Information

“An Introduction to the Ariel III Satellite Project,” A. C. Ladd and J. F. Smith, 1969 August 12, Proceedings of the Royal Society of London

Terrestrial Radio (Thunderstorm) Noise experiment (NASA)

Galactic Radio Noise Sources experiment (NASA)

Langmuir Probe experiment (NASA)

Radio Frequency Capacitance Probe experiment (NASA)