Mariner 2
Published on Jul 12, 2007 at 11:21 pm.
3 Comments.
Filed under space exploration, wonders.
My third candidate for being one of the Seven Wonders of Space Exploration is Mariner 2.
Launched August 27, 1962, Mariner 2 was the first successful mission to another planet. It was not the first spacecraft to leave Earth, though. Luna 1, a Soviet space probe launched January 2, 1959, flew past the Moon and into interplanetary space. To this day, it still orbits the Sun. But, Mariner 2 was designed to be an interplanetary spacecraft.
The United States made plans to launch two interplanetary spacecraft soon after the Luna 1 mission. These spacecraft were to be designated Mariner. However, these initial Mariner spacecraft were large and required a larger rocket than was currently available. Plans were to mate a new hydrogen fueled rocket, the Centaur, on top of an Atlas missile to provide the thrust needed to send these spacecraft to Venus and Mars. However, the Centaur was taking longer to develop than had been planned. So, a decision was made to use an Agena rocket as the upper stage for an Atlas for the interplanetary mission to Venus. The problem, though, was that an Atlas-Agena launch system was not powerful enough to launch the planned Mariner missions. NASA, though, was already at work designing the first American lunar missions, the Ranger spacecraft. The Rangers were small hexagonal spacecraft fitted with television cameras that smashed into the surface of the Moon, sending data back to Earth all the way until they were destroyed (This is called a “hard landing.”). So, two extra Ranger class spacecraft were modified to be interplanetary spacecraft. These became Mariner 1 and Mariner 2. They had a mass of about 203 kilograms and had an instrument mast on top with a directional antenna on the bottom. Twin solar panels provided a nominal 220W of power to operate scientific equipment. Instruments included a magnetometer, radiation detectors, and radiometers.
Mariner 1 was launched July 22, 1962, but a little over 4 minutes after launch a problem developed and the booster began to lose control. When it looked like the rocket might veer back over populated areas, the range safety officer send the destruct signal, causing it to blow up. The problem was traced to a software error. The error was fixed, and Mariner 2 launched just a few weeks later on August 27, 1962. On the way to Venus, controllers determined that a course correction was needed to make sure that the spacecraft actually made it to Venus. The on board engine had only a small amount of fuel, enough for only one course correction burn. Fortunately, that single course correction was all that was needed. Mariner 2 passed Venus on December 14, 1962, making three scans of Venus as it passed. The last signal received from the space probe was on January 3, 1963. It no longer functions, but it still circles the Sun.
Mariner 2 showed that Venus’ atmosphere was extremely rich in CO2 and very poor in O and H2O. Furthermore, Mariner 2 showed that the surface of the planet was much hotter than had been expected and had far higher atmospheric pressure than expected (astronomer Carl Sagan had previously shown that a greenhouse effect was likely active on the planet making the surface far hotter than it would otherwise be, but the actual greenhouse effect was even more than he had computed). Mariner 2 also showed that Venus rotates very slowly in a retrograde direction (backwards from the direction that the other planets orbit, and backwards from the direction of the planet’s orbit). Surprisingly, given that Venus is nearly the same mass and size as Earth, Mariner 2 found no magnetic field at Venus. We now know that this is likely due to the slow rotation.
In addition to the findings at Venus, Mariner 2’s instruments were working on the way to Venus, showing that interplanetary space was not empty as astronomers had expected. Mariner 2 found that there is a continual stream of material from the Sun (the solar wind), and that interplanetary space is permeated with changing magnetic fields, particles, and plasmas. Furthermore, Mariner 2 aided in refining measurements of the Astronomical Unit (the distance between the Earth and the Sun). Since Venus has no natural satellite, astronomers had no way to actually measure its mass until Mariner 2 passed by. Until that time, all anyone could do was to guess that it had a mass similar to Earth’s since it was similar in size.
So, Mariner 2, the first interplanetary spacecraft, is the next entry on my list of the Seven Wonders of Space Exploration.
-Astroprof
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