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The Cassini Spacecraft
Staff posted on October 16, 2006 |

The Cassini Spacecraft

While not a part of the spacecraft itself, the launch vehicle is definitely a part of the Cassini flight system. The Cassini spacecraft was launched on October 15, 1997 from the Cape Canaveral Air Force Station using a U.S. Air Force Titan IVB/Centaur launch vehicle. The function of the launch vehicle is to provide enough energy to inject the spacecraft into Earth orbit. While in orbit, the Centaur upper stage performed a maneuver to send the Cassini spacecraft on the first leg of a Venus-Venus-Earth-Jupiter Gravity Assist (VVEJGA) trajectory to Saturn. Since the spacecraft weighed more than 5600 kilograms (6 tons) at launch, it was be too heavy to be injected into a direct trajectory to Saturn--it simply would not generate enough speed to make the trip in an acceptable length of time or with enough propellant left over to allow braking for orbit insertion around Saturn. Thus, in addition to the boost from the Titan IVB/Centaur, the planetary gravity assists are absolutely necessary.

Titan IV is the nation's largest expendable launch vehicle. The Titan IV consists of two solid propellant stage "0" motors and a liquid propellant two-stage core. The system will be adapted to fly with a Centaur upper stage (8.8 meter, 29 foot) and a payload enclosure or fairing (20.1 m or 66 ft). At liftoff, the total mass of the launch vehicle and payload will be 941,658 kilograms (1038 tons). The solid rocket motors thrust at launch will be 3.4 million lbf (15.2 million Newton (N)). The first stage will provide 548,000 lbf (2.4 million N) of thurst and the second stage will provide 105,000 lbf (467,000 N). The upper stage Centaur, which is designed to fly atop the Titan IV second core stage, is 4.3 meters (14.1 feet) in diameter and 8.8 meters (29 feet) high, and provides 33,000 lbf (147,000 N) of thurst. Total stack height of the launch vehicle is 56 meters (184 feet), which is approximately the height of an twenty story building.

After launch, when the two Titan IV stages have burned out, the Centaur will separate from the second core stage and burn for approximately 2 minutes, placing the spacecraft into an elliptical "parking" orbit with an apogee (farthest point from Earth) of 445 kilometers (227 miles) and a perigee (point nearest to Earth) of 170 kilometers (106 miles). After 17 minutes in this orbit, the Centaur will fire for the last time and launch Cassini out of Earth orbit and onto its trajectory toward Venus, which will provide the first planetary gravity assist.

The Titan IVB/Centaur launch system will be procured from the U.S. Air Force by the NASA Expendable Launch Vehicle Office. The Launch Vehicle Project Office at NASA's Lewis Research Center in Cleveland, Ohio will oversee the integration of the spacecraft with the launch vehicle. The prime contractor to the Air Force for the launch vehicle system is the Lockheed-Martin Corporation.

The Titan IVB/Centaur Rocket

Titan IVB/Centaur Rocket

1. Payload Fairing (McDonnell Douglas)

Length: 20.1 m (66 ft)
Diameter: 5 m (16.7 ft)
Structure: Aluminum isogrid

2. Cassini Spacecraft (JPL)

3. Guidance and Navigation (Honeywell)

Guidance computer and control system, including ring laser gyroscope

4. Centaur Upper Stage (Lockheed Martin Astronautics)

Length: 8.8 m (29 ft)
Diameter: 4.3 m (14 ft)
Propulsion: 2 engines (Pratt and Whitney)
Propellant: Liquid hydrogen and liquid oxygen
Thrust: 147,000 N (33,000 lbf)
I_sp: 444 sec

5. Titan IVB Lower Stage

6. Liquid-Propellant Rockets (Stage I and Stage II) (Lockheed Martin Astronautics)

Length: 36 m (118 ft)
Diameter: 3 m (10 ft)
Structure: Aluminum skin (Stringer)

7. Stage I and Stage II Engines (Aerojet)

Propellant: N204-Aerozine 50
Thrust: Stage I: 2.4 million N (548,000 lbf, total for 2 engines), Stage II: 467,000 N (105,000 lbf)
I_sp: Stage I: 302 sec, Stage II: 316 sec

8. Solid-Propellant Rocket Motors (Alliant Techsystems)

Length: 34.3 m (112.4 ft)
Diameter: 3.2 m (10.5 ft)
Thrust: 15.2 million N (3.4 million lbf, total for 2 motors)
I_sp: 286 sec

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