Galileo (spacecraft)

Galileo (spacecraft)
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Name	Galileo
Mission type	Jupiter orbiter / atmospheric probe
Operator	NASA / Jet Propulsion Laboratory
COSPAR ID	1989-084B
SATCAT	20298
Mission duration	Planned: 8 years, Final: 13 years, 11 months, 3 days
Spacecraft	Galileo
Manufacturer	Jet Propulsion Laboratory, Hughes Aircraft Company
Launch mass	2,223 kg (4,900 lb)
Power	570 watts
Launch date	October 18, 1989, 16:53:40 UTC
Launch rocket	Space Shuttle Atlantis, Inertial Upper Stage
Launch site	Kennedy Space Center, LC-39B
End of mission	September 21, 2003
Last contact	September 21, 2003
Decay date	September 21, 2003 (intentional atmospheric entry)
Orbit reference	Jupiter
Orbit regime	Highly elliptical
Apsis	jove

Galileo (spacecraft) was an American robotic space probe sent to study the planet Jupiter and its moons. Launched in 1989 aboard the Space Shuttle Atlantis, it was the first spacecraft to orbit Jupiter and to deploy an entry probe into its atmosphere. The mission, managed by NASA's Jet Propulsion Laboratory, revolutionized understanding of the Jovian system with numerous groundbreaking discoveries before its intentional destruction in 2003.

Mission overview

The primary objectives of the mission were to conduct long-term observations of the Jovian system, including detailed studies of the planet's atmosphere, magnetosphere, and its four largest Galilean moons. A key component was the Galileo Probe, which was released to make direct measurements within the atmosphere of Jupiter. The mission faced significant challenges, including a delayed launch following the Space Shuttle Challenger disaster and a failure of its main high-gain antenna, which required extensive reprogramming from JPL engineers to use its low-gain antenna. Despite these setbacks, the spacecraft vastly exceeded its planned mission duration, providing over a decade of scientific data.

Spacecraft design

The spacecraft consisted of two main segments: a orbiter and a descent probe. The orbiter was stabilized by spin-stabilization and powered by two radioisotope thermoelectric generators (RTGs), as solar panels were impractical at Jupiter's distance from the Sun. It carried a high-gain antenna for primary communication, which failed to deploy fully, and a robust low-gain antenna used as a backup. The probe was designed to withstand extreme heat and pressure during its descent into Jupiter's atmosphere, protected by a heat shield made of carbon phenolic. The orbiter's command and data handling system was reprogrammable from Earth, a feature critical to salvaging the mission.

Scientific instruments

The orbiter was equipped with a sophisticated suite of instruments, including the Solid State Imaging (SSI) camera, the Near-Infrared Mapping Spectrometer (NIMS), and the Ultraviolet Spectrometer (UVS). It also carried instruments to study plasma and dust particles, such as the Energetic Particles Detector (EPD) and the Dust Detection System (DDS). A magnetometer measured the strength and direction of Jupiter's powerful magnetosphere. The Galileo Probe contained six instruments, including an atmospheric structure instrument and a neutral mass spectrometer, to analyze the chemical composition and physical state of the atmosphere of Jupiter during its 57-minute descent.

Mission profile and major events

Launched on October 18, 1989, from Kennedy Space Center, the spacecraft used a VEEGA (Venus-Earth-Earth Gravity Assist) trajectory, flying by Venus once and Earth twice to gain sufficient velocity for the journey to Jupiter. During its interplanetary cruise, it made the first close-up observations of an asteroid, 951 Gaspra, and later 243 Ida, discovering its moon Dactyl. The Galileo Probe was released five months before arrival and entered the atmosphere of Jupiter on December 7, 1995. The orbiter fired its main engine to enter Jupiter orbit on the same day, beginning its primary tour, which was later extended through the Galileo Europa Mission and Galileo Millennium Mission.

Scientific discoveries

The mission provided transformative insights, revealing that the atmosphere of Jupiter was drier and windier than models predicted. It found evidence of a subsurface saltwater ocean on Europa, making it a prime target in the search for extraterrestrial life. Intense volcanism on Io was observed to be a hundred times more active than on Earth, driven by tidal heating. The spacecraft also detected a thin atmosphere on Ganymede and confirmed it possesses its own intrinsic magnetic field, a first for a moon. Data from the probe and orbiter drastically revised understanding of the structure and dynamics of the Jovian magnetosphere.

End of mission and legacy

To prevent any possibility of a future impact with and biological contamination of Europa, NASA commanded the spacecraft to perform a controlled de-orbit into the atmosphere of Jupiter on September 21, 2003. It was destroyed, with the final signal received at the Jet Propulsion Laboratory. The legacy of the mission is profound, having provided the foundational data for subsequent missions like Juno and the planned Europa Clipper. Its discoveries about potentially habitable environments on the Galilean moons have fundamentally redirected the goals of planetary science and astrobiology.

Category:Space probes Category:NASA spacecraft Category:Jupiter spacecraft