The launch of Mariner G toward Mars, originally scheduled for 1:58 p.m. PST Monday, March 24, has been postponed for at least 3 days because of problems with the spacecraft's on-board computer and one of its science instruments. Project officials said the spacecraft will be de-mated from the Atlas Centaur vehicle tonight, and the two subsystems will be replaced.
Thursday, March 27, is now the earliest possible launch date for Mariner G, which will be re-designated Mariner 7 follow- ing successful injection into a Mars transfer orbit. On Thursday a one-hour launch window opens at 1:35 p.m. PST.
The decision to postpone the Mariner launch was made following a series of extensive tests to isolate the source of the problem which appeared during a pre-countdown spacecraft test on March 20. No definitive cause was determined.
The two subsystems being replaced are the central computer and sequencer, which performs timing and sequencing for Mariner functions, and the infrared radiometer which will provide temperature measurements of the surface of Mars.
Mariner G is identical to Mariner 6 launched February 24, and destined to arrive at Mars July 30. The second Mariner is targeted to arrive at the planet on August 4. Its launch period extends through April 9.
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The two 850-pound spacecraft will fly past Mars at an altitude of 2000 miles taking high resolution TV pictures and making other scientific measurements of the Martian surface and atmosphere.
Mariner 7 listed off its launch pad at Cape Kennedy at 2:22 p.m. PST today (March 27), beginning a 130-day journey to Mars.
The launch, by an Atlas-Centaur rocket combination, placed a second automatic scientific spacecraft on a flight path designed for a Mars rendezvous next summer. Mariner 6, twin to Mariner 7, was launched toward Mars on February 24.
The 850-pound Mariner 7 was boosted to escape velocity of about 25,000 miles per hour during 11 1/2 minutes of powered flight. Cutoff of the second stage Centaur engines and separation of the spacecraft from the Centaur occurred at 2:33 p.m. PST.
Launch was delayed 47 minutes from the planned liftoff time by an unscheduled hold and re-cycling of the countdown during the final one minute of count. The count was resumed when a ground support problem was resolved.
Mariner 7 is being tracked by stations of the Air Force Eastern Test Range in the Atlantic. The Deep Space Network station at Johannesburg, South Africa, will be in contact with the spacecraft at approximately 23 minutes after liftoff. Johannesburg shares the Mariner tracking and data acquisition duties with DSN stations in Woomera, Australia; Madrid, Spain; and Goldstone, California.
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Following the launch phase, control center for the mission is the Space Flight Operations Facility at the Jet Propulsion Laboratory in Pasadena, California.
Upcoming events during the first day of flight include sun acquisition which stabilizes the spacecraft on two axes and allows conversion of solar energy to electric power and acquisi- tion of the star Canopus for three-axis stabilization. Sun acquisition can occur as early as liftoff plus 42 minutes and Canopus acquisition is expected about four hours later. A mid- course maneuver is planned for approximately 12 days after launch.
With the successful launching of Mariner 6 and Mariner 7, the United States has, for the first time, two spacecraft enroute to another planet.
(Dual launchings in 1962 resulted in the successful mission of Mariner 2 at Venus, and in 1964-65 the first close-up scientific exploration of Mars by Mariner 4. A single planetary launch in 1967 sent Mariner 5 to Venus.)
At launch time for Mariner 7, Mariner 6 was 5.38 million miles from Earth and 76 million miles from Mars. It had completed more than 55 million miles of its 226-million-mile flight to Mars. Mariner 7 must fly approximately 195 million miles to reach the planet.
Mariner 6 will arrive at Mars at 10:18 p.m. PDT on July30. Mariner 7 is targeted to reach the planet at about the same time on August 4. The two spacecraft will fly past Mars at
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