More on Galileo

Aerospace

DN Staff

March 3, 1997

7 Min Read

Determine the temperature and pressure of the atmosphere

Determine the chemical composition of atmosphere

Determine the physical structure of cloud layers

Measure the atmosphere's helium to hydrogen ratio

Measure the velocity and depth of Jupiter's winds

Measure the upward and net radioactive flux in Jupiter

Measure the occurrence rate and energy of lightening

Characterize high energy particles near Jupiter
Some results of the mission
- The probe entered on target but went through a hole in the cloud structure.
- The entry deceleration load was 238 g's.
- Wind speed in excess of 400 mph were detected.
- The probe descended 100 miles vertically on the main chute and drifted 300 miles laterally.
- Lightening was 10 less than on Earth and the RF frequency was much lower.
- The abundance of helium was less than the sun.
- A new intense radiation belt between Jupiter's ring and uppermost atmospheric layers was found.
- Upper atmospheric temperatures were higher than predicted.
- Atmosphere relatively dry, about a 10th of what was expected.
- Temperature structure indicates atmosphere below cloud levels neutrally stable. Upper atmospheric temperatures greater than expected.
- There was only one cloud layer, not multiple ones and the cloud is made up of ammonium.
The Galileo Mission Overview
- Probe was released on July 13, 1995 and entered the planet's atmosphere on December 7, 1995.
- Launched during the STS 34 flight of the Atlantis orbiter, the two spacecraft were pushed out of Earth orbit by an inertial upper stage rocket
- The trajectory that the spacecraft followed was called a VEEGA (Venus-Earth-Earth Gravity Assist) The craft headed first toward the sun for a gravity assist from Venus before encountering the Earth twice (spaced two years apart). This allowed Galileo to gain enough velocity to get out to Jupiter.
- Galileo had a front seat view of the Comet Shoemaker-Levey 9 fragments that impacted onto the planet Jupiter.
- Discovered a satellite of an asteroid - Dactyl, the satellite of Ida.
The Probe Spacecraft
Deceleration Module
2.8 feet high with rounded top above conical base angling down to a blunted tip. At widest point, diameter is 4 feet.

Ablative heatshield bonded to aluminum ring-stiffened monocoque structure. The conical forward shell was carbon phenolic, the aft cover phenolic nylon.

Two-stage parachute system, the canopy and shroud lines of the main parachute are made of Dacron, the riser of Kevlar. The parachute was 8.2 feet in diameter.

Thermal control system included mylar insulation; internally mounted 1 W radioisotope heater units; partial gold tape on nose

Descent Module

Titanium fairings with 3 spin vanes

Thermal control with thermal blankets and passive internal airflow restrictions

Titanium interface ring provided load path between DCM and other structural elements

Main equipment shelf composed of aluminum honeycomb with aluminum facesheets bolted to the titanium ring at forward surface.

Scientific instruments laid out around the decent modules circular interior with sensors extending through titanium walls. Instruments weighed 66 pounds.

Probe Instruments

Neutral Mass Spectrometer - determined the chemical constituents of Jupiter's atmosphere and their distribution
Helium Abundance Detector - determined the ratio of helium to hydrogen in Jupiter's atmosphere
Atmosphere Structure Instrument - measured the temperature and pressure of the lower atmosphere
Nephelometer - determined the location of cloud layers and characteristics of cloud particles
Net Flux Radiometer - measured energy radiated by Jupiter and Sun
Lightning and Radio Emissions Detector - measured electromagnetic waves generated by lightning flashes and detected light and radio transmissions from the flashes
Energetic Particle Instrument - measured fluxes of protons, electrons, alpha particles and heavy ions
Relay Radio Hardware - determined Doppler wind determination and atmospheric absorption

Galileo Timeline

1977 - Congressional approval
1978 - Contract awarded to Hughes Space and Communications
Early 1980's - Stretch-outs and reschedulings
1986 - Challenger accident
1989 - Launch October 18 from Shuttle Atlantis
1990 - February Venus fly-by, December Earth 1 fly-by
1992 - December Earth 2 fly-by
1993 - August Ida fly-by
1994 - Comet impacts
1995 - February ground battery tests, March probe checkout
1995 - July Probe release
1995 - December encounter
1996 - May complete data return
1996 - September, final report

Deployment sequence of the Galileo probe for entry into the atmosphere of Jupiter

As probe approached Jupiter, LiSO2 battery turned on by a time six hours before encounter.
Probe arrived at Jupiter
1.8 minutes, pilot parachute deployed
1.9 minutes, aft cover removed
1.9 minutes, main parachute deployed
2.1 minutes, heat shield dropped off
Begin telemetry of data through the atmosphere to the orbiter
61 minutes, probe mission terminated

Jupiter facts

Largest planet in our solar system. Named for the Roman god.
Jupiter has more mass than all the planets combined. It is 300 times the mass of the earth.
It is composed of a thin skin of winds and clouds -- 88% hydrogen, 11% helium with small amounts of methane, ammonia and water.
The great red spot visible on Jupiter is 16,000 miles wide, large enough to encompass two earths. It was first discovered in 1664 by British scientist Roger Hook who was using Galileo's telescope.
Some scientist believe the sun and Jupiter began as unequal partners in a binary star system. For a brief period of its formation, scientists believe that Jupiter was hotter and more luminous and 10 times larger than it is now.
It emits twice as much heat as it receives from the sun.
Jupiter spins faster than any planet in the solar system; twice as fast as Earth.