The Galileo Probe Mission Events Timeline

The Galileo Probe Mission Events Timeline

OCTOBER 18, 1989: LAUNCH
The Galileo Orbiter and Probe are launched on the Space Shuttle Atlantis. The Probe was attached to the Orbiter and two-way communication occured between the two spacecraft via an umbilical cable. Three status checks of the Probe and a system function test were conducted during the approximately six year cruise together.

JULY 13, 1995: 5:29 GMT: PROBE SEPARATION FROM ORBITER
DISTANCE FROM JUPITER: 81,520,000 km (50,660,000 miles).
SPEED RELATIVE TO JUPITER: 20,448 km/hour ( 12, 706 mph )
The Galileo Orbiter/Probe was spun up to 10.5 rpm to provide rotational stabilization of the Probe. The spin axis was precisely aligned with its trajectory. The separation velocity of the Probe was chosen so the gravitational pull of the Sun and Jupiter alone would successfully guide it into Jupiter's atmosphere on December 7, 1995. The Probe has no rocket engines for course corrections. It will enter Jupiter's atmosphere at an angle of 8.3 degrees to the horizontal. A 1.5 degree shallower angle would cause the Probe to skip off back into space; a 1.5 degree steeper angle would overheat the spacecraft and destroy it. During and after separation the Galileo Probe remains in a dormant state with only a Coast Timer operating. No communication from the Probe until after atmospheric entry.

DECEMBER 7, 1995 GALILEO PROBE ATMOSPHERIC ENTRY
All the times listed below are relative to the time of atmospheric entry (E). All altitudes listed below are relative to the level in Jupiter's atmosphere where the atmospheric (barometric) pressure equals Earth's sea level atmospheric pressure ( 1 bar of pressure, 14.7 lbs/square inch ). Atmospheric entry for the Galileo Probe is defined to occur at an altitude of 450 km. At the atmospheric entry level, the atmosphere is becoming thick enough to influence the Probe's motion.

ATMOSPHERIC ENTRY TIME (E): 22:04 GMT ( 2:04 PM PST )

E - 6 hours: COAST TIMER INITIATES PROBE OPERATION
DISTANCE FROM JUPITER = 600,000 km ( 373,000 miles )
SPEED RELATIVE TO JUPITER = 76,700 km/hour ( 47,600 mph )
HIGHLIGHTS: Warm-up and calibration of Probe scientific and engineering instruments begins. "g-switches" are used to sense the deceleration of the Probe by atmosphere as backup for timer malfunction.

E - 3 hours: MEASUREMENTS OF JUPITER'S INNER RADIATION BELTS BEGIN
DISTANCE FROM JUPITER = 360, 000 km ( 224,000 miles )
SPEED RELATIVE TO JUPITER = 97,200 km/hour ( 60,400 mph )
HIGHLIGHTS: The Energetic Particles Investigation begins measurements of the energetic electrically charged particles trapped in a part of Jupiter's intense radiation belts/ magnetic field not previously explored. Four minute sample sets are taken at E-180 minutes, E-140 minutes, E-96 minutes, E-60 minutes, and continuing sample sets are acquired thereafter until entry.

E: ATMOSPHERIC ENTRY
ALTITUDE = 450 km ( 280 miles )
VELOCITY = 170,700 km/ hour ( 106,100 miles/hour )
INCIDENCE ANGLE= 8.3 degrees below horizontal.
LATITUDE = 6.5 degrees North (planetocentric)
LONGITUDE= 4.4 degrees West.
HIGHLIGHTS: Atmospheric Structure Instrument begins continuously recording deceleration of Probe due to upper atmosphere. Atmospheric density, pressure, and temperature can be inferred from such data.

E + 56 seconds: PEAK AERODYNAMIC STRESS
ALTITUDE = 100 km ( 62 miles )
VELOCITY = 99,200 km/hour ( 61,600 miles/hour )
ATMOSPHERIC PRESSURE = 0.007 bar
ATMOSPHERIC TEMPERATURE = -119 degrees Centigrade (C)
HIGHLIGHTS: As the Probe enters Jupiter's atmosphere, aerodynamic forces quickly decelerate the Probe. The Probe experiences a force equivalent to 230 times the strength of gravity at Earth's surface. Largest aerodynamic force ever on a spacecraft entering the atmosphere of a planet.

E + 112 seconds: PILOT PARACHUTE DEPLOYED
ALTITUDE = 50 km ( 31 miles )
VELOCITY = 3,200 km/hour ( 1,990 miles/hour )
ATMOSPHERIC PRESSURE = 0.07 bar
ATMOSPHERIC TEMPERATURE = -160 C

E +114 seconds: MAIN PARACHUTE DEPLOYED
ALTITUDE = 50 km ( 31 miles )
VELOCITY = 3,120 km/hour ( 1,940 mph )
ATMOSPHERIC PRESSURE = 0.07 bar
ATMOSPHERIC TEMPERATURE = -160 C

E + 122 seconds: DECELERATION MODULE JETTISONED
ALTITUDE = 48 km ( 30 miles )
VELOCITY = 1,630 km/hour ( 1,010 mph )
ATMOSPHERIC PRESSURE = 0.09 bar
ATMOSPHERIC TEMPERATURE = -160 C

E + 126 seconds: DIRECT SCIENTIFIC MEASUREMENTS BEGIN
ALTITUDE = 48 km ( 30 miles )
VELOCITY = 1,540 km/hour ( 960 mph )
ATMOSPHERIC PRESSURE = 0.09 bar
ATMOSPHERIC TEMPERATURE = -160 C

E + 135 seconds: RADIO TRANSMISSION TO ORBITER BEGINS
ALTITUDE = 40 km ( 25 miles )
VELOCITY = 890 km/hour ( 550 mph )
ATMOSPHERIC PRESSURE = 0.1 bar
ATMOSPHERIC TEMPERATURE = -160 C
HIGHLIGHTS: Data stored in memory up to this point in the mission is transmitted along with the new measurements. To provide a backup to the communications link with the Orbiter, the data is radioed to the Orbiter in two nearly identical transmissions produced by separate electronics and transmitters on the Probe.

E + 4 minutes (approximate): VISIBLE CLOUD TOPS OF JUPITER REACHED
ALTITUDE = 26 km ( 16 miles )
VELOCITY = 454 km/hour ( 282 mph )
ATMOSPHERIC PRESSURE = 0.3 bar
ATMOSPHERIC TEMPERATURE = -150 C
HIGHLIGHTS: The visible clouds of Jupiter are believed to be made of frozen ammonia crystals.

E + 8 minutes: ATMOSPHERIC PRESSURE SAME AS EARTH'S SEA-LEVEL PRESSURE
ALTITUDE = 0 km ( 0 miles )
VELOCITY = 295 km/hour ( 183 mph )
ATMOSPHERIC PRESSURE = 1.0 bar
ATMOSPHERIC TEMPERATURE = -107 C

E + 13 minutes (highly uncertain): A SECOND MAJOR CLOUD DECK IS ENCOUNTERED
ALTITUDE = -21 km ( -13 miles )
VELOCITY = 234 km/hour ( 145 mph )
ATMOSPHERIC PRESSURE = 2.0 bar
ATMOSPHERIC TEMPERATURE = -67 C
HIGHLIGHTS: The existence and nature of these clouds is highly uncertain.

E + 24 minutes (highly uncertain): ENTER CLOUDS OF WATER
ALTITUDE = -57 km ( -35 miles )
VELOCITY = 170 km/hour ( 106 mph )
ATMOSPHERIC PRESSURE = 5.0 bar
ATMOSPHERIC TEMPERATURE = 0 C

E + 30 minutes: TEMPERATURE EQUALS ROOM TEMPERATURE ON EARTH
ALTITUDE = -71 km ( -44 miles )
VELOCITY = 154 km/hour ( 96 mph )
ATMOSPHERIC PRESSURE = 6.7 bar
ATMOSPHERIC TEMPERATURE = 25 C

E + 42 minutes: SUNSET OCCURS AT PROBE ENTRY SITE
ALTITUDE = -100 km ( -62 miles )
VELOCITY = 126 km/hour ( 78 mph )
ATMOSPHERIC PRESSURE = 11.7 bars
ATMOSPHERIC TEMPERATURE = 79 C

E + 60 minutes: END OF BASELINE MISSION
ALTITUDE = -135 km ( - 84 miles )
VELOCITY = 104 km/hour ( 65 mph )
ATMOSPHERIC PRESSURE = 20 bars
ATMOSPHERIC TEMPERATURE = 140 C
HIGHLIGHTS: Below this level, effects of pressure and temperature on Probe systems, limited battery capacity, and difficulty of radio signal transmission through dense atmosphere and clouds may lead to degraded Probe operation and data.

E + 75 minutes: END OF PROBE DATA RECEPTION BY ORBITER
ALTITUDE = -159 km (-99 miles)
VELOCITY = 92 km/hour (57 mph)
ATMOSPHERIC PRESSURE = 28 bars
ATMOSPHERIC TEMPERATURE = 185 C
HIGHLIGHTS: Determined by need to prepare Orbiter for Jupiter Orbit Insertion.

Site Last Modified: November 30, 1995

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