Return to Newsletter Index

The Perils of Pluto

by Perry Pezzolanella

The dream of sending spacecraft to all of the planets began not long after the dawn of the Space Age. Back in those days the planets held many secrets. Venus was thought to be covered with a lush rain forest or a global ocean of seltzer, Mars was thought to have lichen and/or moss growing on its surface, and Jupiter was thought to have a solid surface wracked by massive hydrogen volcanoes, and there were many other theories, some quite wild. One planet was especially mysterious because it was so far away on the edge of the Solar System that it appeared as nothing more than a faint star. Scientists and the public alike yearned to know what it really looked like up close.

Pluto has always been the ultimate challenge in planetary exploration. Its distance, over 3 billion miles, has made it the Mount Everest of planetary exploration. In the early era of rocketry it was a feat in itself to send spacecraft past Venus and Mars. Sending a spacecraft to Pluto seemed impossible, but scientists during the 1960s calculated that by using gravitational assist of a large planet such as Jupiter it was possible to redirect and propel a spacecraft to another planet further out. A flight time to Pluto without gravitational assist could take over 20 years, but using Jupiter’s powerful gravity would cut the travel time down to hardly a decade. Even with this breakthrough in planetary exploration there was still one peril that everyone feared.

Flying through the asteroid belt was thought to be perilous as it was feared there were many unseen smaller asteroids and debris that could strike and destroy a spacecraft. It seemed impossible that any spacecraft could survive crossing it, thus making the missions to the outer planets seemingly hopeless. The Pioneer 10 & 11 spacecraft had the goal of flying past Jupiter and proving that it was possible to cross the asteroid belt without harm. Pioneer 10, launched March 2, 1972, successfully flew past Jupiter on December 3, 1973 and Pioneer 11, launched April 6, 1973, successfully flew past Jupiter on December 4, 1974, both proving that the asteroids were not a hazard. With this peril now put aside, it seemed that seeing Pluto up close was closer to reality. However, there was an even greater peril, Washington, D.C. The original plan for the Grand Tour mission involved launching four tried-and-true Mariner-class spacecraft that would explore the five outer planets: Jupiter, Saturn, Uranus, Neptune, and Pluto. They would be named Voyager and one of the four, most likely Voyager 4, was to fly past Pluto on March 9, 1986. Unfortunately, the need to fund the newly developed Space Shuttle and increased budget cuts forced two of the four spacecraft to be dropped from the plan. It was still possible to reach Pluto with one of the remaining two so it seemed that Pluto survived the peril of the budget ax.

Titan was proving to be a strange and exciting moon of Saturn. It has a thick atmosphere and hinted at the possibility of an ocean of liquid methane on its surface. Voyager 1 would fly past Jupiter for gravity assist so that it could be directed to Saturn in such a way that it would fly close to Titan. Unfortunately, this meant that Voyager 1 would arrive at Saturn too soon and too fast to be directed towards Pluto. The main goal for Voyager 2 after it flew past Saturn was for it to fly past both Uranus in January 1986 and Neptune in August 1989. Scientists did not want to risk an aging spacecraft on one distant unexplored world when it was possible for it to explore two poorly-known worlds. Voyager 2 could not fly to Pluto after leaving Neptune because it would have to fly deep within the atmosphere below Neptune’s cloud tops to get the proper gravitational assist, which meant the spacecraft would burn up. Pluto would have to wait.

The Voyager 2 discovery of nitrogen geysers on Triton in 1989 plus the discovery of small icy worlds beyond Pluto starting in 1992 reinforced the desire to send a spacecraft past Pluto. Five spacecraft designs would come and go with each one going over budget until the mission to Pluto was cancelled in September 2000. A young high school student started an online petition to save the Pluto mission. The results were so overwhelming that NASA and Congress reopened the opportunity to explore Pluto to the scientific community; however, it had to cost no more than $750 million. The New Horizons spacecraft, designed by the John Hopkins University’s Applied Physics Laboratory was approved in November 2001 as an affordable mission to explore Pluto and Charon. The peril of outright cancellation was finally history after one more threat in 2003. What else could possibly threaten the dream of seeing Pluto close up? Enter mechanics and Mother Nature.

CONTOUR, a multi-comet flyby mission, was launched during August 2002, but failed shortly afterwards. The cause may have been a faulty upper stage solid fuel booster rocket that may have overheated and destroyed the spacecraft. New Horizons was to use a slightly modified version of the same rocket, but ample testing put at ease any such risk of failure. Plutonium-238 was in short supply so it was feared there would not be enough to power the spacecraft, but enough was found and a highly energy efficient spacecraft, New Horizons, emerged. These two potential perils were dodged, but then Mother Nature took her turn. Hurricane Wilma blasted Florida during October 2005 with winds that damaged the Vehicle Assembly Building that housed New Horizons and one of the boosters on the Atlas rocket that was to launch New Horizons. The damaged booster was replaced, but then potential cracks were found in some of the Atlas boosters in NASA’s inventory. New Horizons was already mated to the booster stack and de-stacking would threaten missing the launch window that was hardly two months away. An x-ray was necessary to locate any potential cracks, but fortunately none were found. New Horizons had to launch during the second half of January 2006 to get to Pluto in less than ten years or face up to an additional five years of flight time.

January 17, 2006 was the target launch date but it was too windy at Cape Canaveral so they had to wait until the next day. The weather was better on the 18th, but not at the command center in Laurel, Maryland where a storm had knocked out the power. January 19 brought clouds back to Cape Canaveral, but the winds died down and the clouds parted enough in time for a flawless launch at 2 P.M. New Horizons was on its way to Pluto with all of its earthly perils left behind. The flyby of Jupiter on February 27, 2007 was a success; New Horizons worked flawlessly. The journey from Jupiter to Pluto was peaceful with New Horizons hibernating most of the way to conserve power, avoid wear and tear, and keep operating costs in check. Excitement was building on the 4th of July in 2015 as Pluto and Charon were coming into focus and the historic flyby was only ten days away. What could go wrong?

SAFE MODE! For a few hours during that 4th of July afternoon New Horizons fell silent. All science operations ceased as the spacecraft went into safe mode to await instructions from Earth. With only ten days until the Pluto flyby this was a frightening event. Fortunately, quick thinking and teamwork discovered a memory overload in the way the spacecraft was trying to process all of the data and commands. A fix was relayed to New Horizons and normal operations resumed on July 7. There was one more peril ahead and that was the fear of New Horizons striking a particle as it flew past Pluto. A grain of sand could disable the spacecraft and end the mission, but careful observation on approach plus having it fly between Pluto and Charon where it would most likely be clear of debris reduced the risk. The trajectory past Pluto was perfect. No harm came to New Horizons and history was made with the most detailed images of Pluto and its moons that will be seen for decades.

With the historic flyby now behind, there is still one final peril to deal with. New Horizons must remain functional until at least this November because it will take that long for it to transmit all of its Pluto encounter data and images to Earth. There is every reason to believe that everything will work as it has been a healthy, proven spacecraft. With all of the risks and challenges in trying to get to Pluto, it is hard to believe it was pulled off. Can anyone deny the determination of the human spirit to explore?