Mariner 2 and The First Mission to Planet Venus
Space probes are launched more and more frequently as the years go by. We are sending these scouts to the far corners of the solar system in search of scientific knowledge. Like many accomplishments in science, a first mission to a planet had to occur. That triumph was the Mariner 2 space probe launched by the US in 1962.
To say that the road to Mariner 2’s launch was rough would be an incredible understatement. At the time, based on NASA’s history with probe launches up to that point, many wondered how we could be successful at getting a rocket off the ground, much less to another planet. To understand why the skepticism was high, we need to look at the track record that NASA had at the moment Mariner 2 launched. Brace yourself. It is rough.
By the time Mariner 2 was scheduled to launch, 8 Pioneers and 4 Rangers failed to complete their missions, most because of Jet Propulsion Laboratory (JPL) control issues, 5 because of launch problems. Ranger 1 had launched in August of 1961 but failed because the upper stage of the Agena rocket failed to refire, causing the probe to enter low-Earth orbit for 8 days before burning up in our atmosphere. Ranger 2 also had a problem with its Agena rocket in November of 1961. In January of 1962, Ranger 3 escaped Earth but missed the Moon by 22,860 miles after its Agena rocket gave it too much velocity and it overshot its target. And in April of 1962 Ranger 4 crashed into the moon after its solar panels failed to extend and provide the juice needed for the electronics onboard (Gerbis 34, O’Donnel 5).
Of course, Russia had many mishaps also, but it could afford to because of the frequency of its launches. This led them to having many firsts in space. Amongst those was the first lunar probe to successfully land on the moon on September 14, 1959 and also the launch of Venera 1 in February of 1961. Its mission was to study Venus, but a radio error prevented any science from being accomplished, although it did get within 62,000 miles of Venus (Gerbis 34, O’Donnel 5).
NASA wanted to have a first, and it was always behind in the so called “Space Race.” It assigned JPL, which had focused exclusively on Air Force ICBMs until the 1958 launch of Explorer 1, to construct 3 probes, 2 for Venus and 1 for Mars. This would be the Mariner program. They put Jack James in charge, namely because of his success in getting Pioneer 5 off the ground. That mission had launched in September of 1960 and was sent into a solar orbit between Earth and Venus where it discovered the interplanetary magnetic field. Jack James also had experience with getting the Corporal and Sergeant guided missiles on track. Many of his techniques from those programs would be used on the Mariner project (Gerbis 34-5; O’Donnell 2, 4).
Initially called Mariner A and B, they were both to be 1,250 pounds and would launch aboard a Centaur rocket. But in the summer of 1961, the Air Force announces that the upper stage to the Centaur rocket would not be ready in time for the launch. JPL comes up with a quick solution: swap out the old upper stage with an Agena upper stage. The cost, however, was that the Mariner probes would have to be decreased in weight by 2/3. Also, the program would need to be designed around the existing Ranger technology and would have to be designed within a week. Some were concerned about this last requirement because of the failure of the Rangers, but since those missions failed primarily because of rockets the concern was minimal (O’Donnel 2, 3, 5).
Another difficulty that needed to be overcome was a “midcourse correction” which had never been done before. It meant that Mariner would have to undergo a pitch maneuver to get rocket into an appropriate firing position, fire, and then reorient the craft so it could talk to Earth and absorb light from the Sun for its solar panels. If this maneuver was not done correctly, it would miss its target range to Venus and most of the science onboard would not be possible. Fortunately, 250 JPL employees worked it out with 34 subcontractors and 1,000 parts suppliers to get the necessary gear and after 2,360 work-years and $47 million 1961-dollars (about $554 million 2014-dollars), Mariners 1 and 2 were ready (3,4).
These probes were built with a lot of science to be done. Amongst the instruments on board were a magnetometer, some particle detectors, a cosmic ray detector, a cosmic dust detector, a solar plasma spectrometer, a microwave radiometer, and an infrared radiometer. Interestingly, no camera was brought with because it was determined that it would reveal little scientifically and that it would take up room that another science package could be in. The goal of these instruments was to measure the mass of Venus, its atmosphere and magnetic field, any ions near it, and also observe how the interplanetary medium changes as the flight progresses (Grazeck “Mariner 2”).
All of this was fit into a hexagonal base that was 1.04 meters long from vertex to vertex and was 0.36 meters thick, to help protect it. A mass of skeleton framework on top of this base also contained some science instruments, bringing the total height of the probe to 3.66 meters. Solar panels were attached to the bottom of the base along with an antenna, bringing the width from the end of one panel to the other 5.05 meters. While the panels were not deployed, the probe would draw power from a 1000 watt-hour silver-zinc cell batter that could be recharged by the panels once they were activated. The Mariner probes talked to home by using a 3 watt transmitter and moved about by using 10 small jets around the craft full of nitrogen gas. These jests would fire for 1/10 of a second every hour to ensure that the panels were optimally pointed towards the Sun. The main engine, for the midcourse correction, could fire up to 225 Newtons of force using hydrazine as fuel for up to a minute. Sadly, because of the timetable, redundancy was not able to be developed. If something failed, that was it, all gone. James also made sure to put small U.S. flags with each probe (Grazeck “Mariner 2,” O’Donnell 5).
Mariner 1 Blows Up Over the Blue Marble
With all the specifics of the probe detailed and construction complete, the Mariner 1 probe was all set to depart Earth and go to Venus. A 56-day window opened on July 18, 1962 and after a few scrubs on July 22, 1962 Mariner 1 launches. Unfortunately, shortly after lift-off the rocket developed some issues with its flight path and for safety reasons JPL did not want the rocket to crash into anything that could cost civilian lives. They therefore activated the self-destruct feature and blew up the rocket. Later, it was found that a coding error that did not block noise from other communications caused JPL to gather misinterpreted data from the rocket. The error was corrected quickly and James gets his back-up ready to go (O’Donnel 5, Gerbis 35).
Mariner 2 Departs the Blue Marble
On August 27, 1962, the 202 kilogram Mariner 2 launched aboard an Agena-Atlas rocket (since the Centaur-Agena was used on Mariner 1) after a few scrubs. It looked like it too would be doomed to failure after one of the stabilizing rockets does not respond to JPL commands. The rocket begins to roll, but the scientists at JPL determine it will not pose a risk and continue on. Amazingly, one minute after the glitch started, the problem resolved itself and the rocket was stabilized. After achieving a height of 118 kilometers above the Earth’s surface over a 980 second span, the second stage ignites. Upon completing this burn, Mariner 2 separates and enters a hyperbolic escape path towards Venus. 44 minutes later, the solar panels are extended. On August 29, the science packages are turned on and 5 days later begin transmitting data back to Earth at about 8 bits (not bytes!) per second (O’Donnel 6, Gerbis 34, Grazeck “Mariner 2”).
Problems, Problems, Problems
On September 4, Mariner 2 performs the midcourse correction at about 1.5 million miles from Earth. The entire maneuver takes just 34 minutes to complete and should have allowed Mariner 2 to fly within 9000 miles of Venus. Scientists at JPL discovered that once the burn was done, the valve stopping the gas was not working, but after sending a command to close again it responds. This was one of the many interesting problems that Mariner 2 encountered (O’Donnel 6).
Shortly after the midcourse correction, Mariner 2 began to have a hard time finding Earth. It was getting dimmer faster than it should have been. If Mariner 2 could not keep a link on Earth then the data it was transmitting would be lost. But shortly after the problem was found, it resolved itself without help from JPL. It is possible that something shiny on the spacecraft goofed up the sensors (6).
On September 8, just 4 days after the midcourse correction, the probe loses altitude control for 3 minutes when the gyroscopes activate without prompt. Then just as suddenly as they turned on, they are deactivated. It may have resulted from a collision with a small object, but a few weeks later a repeat of the incident occurs. On October 10, during a press conference for Mariner 2, JPL announced that instead of the projected 45 mph increase the midcourse correction was to supply was actually 47 because of that valve mishap. This meant that Mariner 2’s closest approach to Venus would be about 20,900 miles instead of 9000 miles. It would still be close enough for the science packages to be effective, fortunately (O’Donnell 7, Grazeck “Mariner 2”).
On Halloween, one of the solar panels begins to underperform and many instruments have to be turned off to conserve power. A week later, the panel begins to work again and the science instruments are resumed but by November 15 the panel fails permanently. Fortunately, the probe was close enough to the Sun that the remaining panel would provide sufficient power for the science instruments (O’Donnell 7, Grazeck “Mariner 2”).
As Mariner 2 got closer and closer to Venus, more and more concerns seemed to grow. The radiometer has a partial fritz and will not operate at 100%. This meant that any temperature readings would not be as reliable. Temperature readings from sensors inside Mariner 2 also indicated that the craft was getting hotter and hotter, approaching critical levels above 200 degrees Fahrenheit. Scientists wonder if it could handle it and even survive anything else going wrong. They had made it this far and wanted to complete the mission, not see all their hard work go to naught as the finish line approached them (O’Donnel 7, Gerbis 35).
Arrival at Venus and The End
December 14 was the magic date: the flyby. As JPL gears Mariner 2 up, the increased temperatures had caused the lynchpin microwave and infrared radiometers to partially fail and also caused the command protocols in the probe to fail to turn on automatically. Thankfully, JPL was ready and manually told Mariner 2 to begin data transmission. It ended up within 21,607 miles of Venus during the 30 minutes it was near the planet. After December 25, it was no longer close enough to Venus for any more science to be gathered and two days later it made its closest approach to the Sun. The final transmission from Mariner 2 occurred on January 3, 1963 as it began its heliocentric orbit, where it is today (O’Donnell 7, Gerbis 34-5, Grazeck “Mariner 2”).
The Legacy of Mariner 2
The science that Mariner 2 revealed about Venus was impressive, especially considering how much nearly went wrong. The magnometer did not find a magnetic field at the distance it was from Venus, meaning that if it had one it was very weak, at most 5-10% the strength of Earth’s. The comic dust collector managed to snag 1 measly particle during its months-long journey, indicating that space debris isn’t a major problem. The radiometer functioned and found Venus to be between 300 and 400 degrees Fahrenheit (actual is 900). It also discovered that the heat was near the surface and not high up in the 60 kilometer-high clouds, evidence for the greenhouse effect. Pressure was measured to be at 20 atm (actual is 90). Venus was also found to be a slow rotator and had its mass revised to 81.485% of Earths with a percent error of 15/1000 of 1%. Scientists were also able to refine the AU (O’Donnel 7-8, Grazeck “Mariner 2, Gerbis 35).
Just as important as the science was the boost it gave the American space program. Finally, they had a first in space. No one else had made it to another planet before successfully. It allowed the focus to shift back to the Ranger series and help improve them and also led to the successful Mariner mission to Mars. With Mariner 2 a success, JPL also proved it deserved more funding for even more ambitious programs (O’Donnel 8, Gerbis 34). But the most important result was that Mariner 2 proved that the US space program was on track and would deliver. It could overcome defeat and would herald a new era in space exploration.
Gerbis, Nicholas. “50 Years Later: How Mariner 2 Broke NASA’s Losing Streak. as Astra Winter 2012-13: 34-5. Print.
Grazeck, Dr. Ed. “Mariner 2.” NASA.gov. 16 Aug. 2013. Web. 18 Aug. 2014. http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1962-041A.
O’Donnel, Franklin. “The Venus Mission.” JPL. 19 Aug. 2014.
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© 2014 Leonard Kelley
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