Galileo spacecraft: Encyclopedia II - Galileo spacecraft - Galileo's atmospheric entry probe

Galileo spacecraft - Galileo's atmospheric entry probe

The 339 kilogram atmospheric probe measured about 1.3 meters across. Inside the heat shield, the scientific instruments were protected from ferocious heat during entry. The probe had to withstand extreme heat and pressure on its high speed journey at 47.8 km/s. The probe was released from the main spacecraft in July 1995, five months before reaching Jupiter, and entered Jupiter's atmosphere with no braking beforehand. It was slowed from the probe's arrival speed of about 47 kilometers per second to subsonic speed in less than 2 minutes.

It then deployed its 2.5-meter (8-foot) parachute, and dropped its heat shield. As the probe descended through 150 kilometers of the top layers of the atmosphere, it collected 58 minutes of data on the local weather. The data was sent to the spacecraft overhead, then transmitted back to Earth. Each of 2 L-band transmitters operated at 128 bits per second and sent nearly identical streams of scientific data to the orbiter. All the probe's electronics were powered by lithium sulfur dioxide (LiSO₂) batteries which provided a nominal power output of about 580 watts with an estimated capacity of about 21 ampere-hours on arrival at Jupiter. The probe included six instruments for taking data on its plunge into Jupiter. The instruments were: an atmospheric structure instrument group measuring temperature, pressure and deceleration; a neutral mass spectrometer and a helium-abundance interferometer supporting atmospheric composition studies; a nephelometer for cloud location and cloud-particle observations; a net-flux radiometer measuring the difference in flux upward versus downward in radiant energy flux at each altitude and a lightning/radio-emission instrument with an energetic-particle detector which measured light and radio emissions associated with lightning and energetic particles in Jupiter's radiation belts. Total data returned from the probe was about 3.5 megabits. The probe stopped transmitting before the line of sight link with the orbiter was cut. The likely proximal cause of the final probe failure was overheating, which sensors indicated before signal loss. The atmosphere as the probe descended was somewhat more turbulent and hotter than expected. The probe would have been melted and vaporized after a few hours of falling, completely dissolving into Jupiter's hot, dense lower atmosphere.

Adapted from the Wikipedia article "Galileo's atmospheric entry probe", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki