Introduction

On December 14, 1962, Mariner II reached Venus and became the first spacecraft to operate in the immediate vicinity of another planet and return useful scientific information to the Earth. This milestone was reached after Mariner II was designed and built in a relatively brief 11 months using proven technology from the Vega, the Ranger lunar series, and the canceled Mariner A. The following sections characterize the Mariner II mission in terms of mission objectives, hardware used, mission constraints, mission sequence of events, trajectory, and design strengths and weaknesses.

Mission Objectives

The over-all mission objectives of the Mariner II mission were:

1. The investigation of interplanetary space between the Earth and Venus, measuring such phenomena as the cosmic dust, the mysterious plasma or solar winds, high-energy cosmic rays from space outside our solar system, charged particles from the Sun, and the magnetic fields of space
2. Perform experiments near Venus ( 21,150 miles from the surface) in an effort to understand its magnetic fields, radiation belts, the temperature and composition of its clouds, and the temperature and conditions of the surface of the planet.

The Spacecraft

The Mariner II spacecraft was designed using previous technology because JPL had only 11 months to produce the spacecraft. The result was a spacecraft that had a gross weight of 447 pounds. In its launch configuration, the spacecraft was 5 feet in diameter and 9 feet 11 inches in height. In cruise configuration, the spacecraft was 16 feet 6 inches wide and 11 feet 11 inches high. The cruise configuration of Mariner II is shown in Figure 1.

Mariner II had basic, non complex subsystems. The structure of Mariner II consisted of a hexagonal frame made of magnesium and aluminum attached to an aluminum superstructure. The spacecraft's power system consisted of solar panels that could generate up to 222 watts and a silver-zinc battery which had a capacity of 1000 watt-hours. The Central Computer and Sequencer (CC&S) performed certain computations and provided the basic timing control for the subsystems which required a sequenced programming control. The CC&S was also designed to initiate the 3 "modes" of the spacecraft which were: the launch mode, the midcourse propulsion mode, and the encounter mode. The communications subsystem consisted of a data encoder unit, an omni-directional antenna, a high-gain directional antenna, and two command antennas. Mariner's attitude control system consisted of a system of gas jets and valves, three gyroscopes, and Sun sensors. Mariner II performed its midcourse correction with a hydrazine fueled rocket engine capable of developing 50 pounds of thrust for up to 57 seconds. For thermal control, Mariner II used passive techniques such as thermal shields, paint patterns, thin gold plating, etc., and active techniques such as louvers.

Mission Sequence of Events

The following is a chronological list of the sequence of events that occurred during the Mariner II mission:

1. The Atlas carrying Mariner II lifted off from Cape Canaveral at 01:53:14 EST on August 27, 1962.
2. The Aegena upper stage and Mariner II separate from the spent Atlas at 1:58 a.m. EST.
3. The Aegena is fired from 1:58:53 to 2:01:12 a.m. to put itself and Mariner II into orbit at an altitude of 116.19 miles.
4. Aegena fired again to inject Mariner II into its transfer orbit at 2:19:19 a.m. The Aegena separated from Mariner at 2:21 a.m.
5. The solar panels and radio dish were deployed at 2:27 a.m.
6. The attitude control system was turned on at 2:53 a.m.
7. On August 29, the cruise scientific experiments were turned on.
8. On September 3, an Earth acquisition sequence was performed to determine the orientation of the spacecraft with respect to the Earth.
9. On September 4, the midcourse maneuver was performed to put Mariner II on the proper trajectory.
10. On September 8, the spacecraft lost its attitude control for approximately three minutes for an unapparent reason.
11. On October 31, the output from one solar panel failed causing the entire load to be carried by the other panel. To lighten the load on the one panel, the cruise scientific instruments were turned off. A week later, the malfunctioning panel returned to normal operation and the science instruments were turned back on.
12. On November 15, the solar panel failed again, but Mariner II was close enough to the Sun so that one panel supplied enough power.
13. On December 9, telemetry measurements of the angle of the antenna hinge, the fuel tank pressure, and the nitrogen pressure in the midcourse and attitude control systems were permanently lost.
14. On December 14 at 5:35 a.m., a radio signal was sent to Mariner II to command it to start its encounter sequence after it failed to start the sequence on its own.
15. At 11:59:28 a.m. on December 14, Mariner II was 21,598 miles from Venus, the point of closest approach.
16. During the Venus encounter, Mariner II performed three scans: one on the dark side, one across the terminator, and one on the sunlit side. Good data were received on Earth from the experiments during these scans.
17. At 2 a.m. on January 3, 1963, communication with Mariner II was lost and never recovered.

The start of Mariner II's trajectory was the 116.19 mile parking orbit around earth in which Mariner II was traveling 18,000 miles per hour. Mariner II was then injected into a transfer orbit at a speed of 25,420 miles per hour. In order for the scientific instruments aboard Mariner II to operate within their design ranges, it was necessary to correct Mariner's trajectory to an approximate 8,000 to 40,000-mile "fly-by". The result of this midcourse maneuver was a 59 mile per hour decrease in speed relative to the Earth and a 45 mile per hour increase in speed relative to the Sun (from 60,117 to 60,162 miles per hour). As Mariner II continued its journey, its speed relative to the sun kept increasing until, at the point of closest approach to Venus, Mariner II was traveling about 88,400 miles per hour. The complete trajectory of Mariner II is depicted in figure 2.

Strengths and Weaknesses

The Mariner II mission had many strengths and very few weaknesses. Considering it was built in 11 short months, it had an impressive performance record which included:

• It performed the first and most distant trajectory-correcting maneuver in deep space.
• The spacecraft transmitted continuously for 129 days, sending back to Earth 90 million bits of information while using only 3 watts of power.
• Useful telemetry measurements were made at another record distance from the Earth: 53.9 million miles.
• Mariner achieved the longest continuous operation of a spacecraft attitude-stabilization system in space, and at a greater distance from Earth than any previous spacecraft: 129 days, 53.9 million miles from Earth.
• Mariner II was the first spacecraft to operate in the immediate vicinity of another planet and return useful scientific data to the Earth.

Last Modified: Sun Aug 01, 2004
CSR/TSGC Team Web