page_title: Exploration of Pluto
section_title: The Pluto Underground, Pluto 350 and Mariner Mark II
hierarchical_section_title: Exploration of Pluto / Early mission proposals / The Pluto Underground, Pluto 350 and Mariner Mark II
caption_attribution_description: A diagram of Pluto 350.
context_page_description: The exploration of Pluto began with the arrival of the New Horizons probe in July 2015, though proposals for such a mission had been studied for many decades. There are no plans as yet for a follow-up mission, though follow-up concepts have been studied.
context_section_description: In May 1989, a group of scientists and engineers, including Alan Stern and Fran Bagenal, formed an alliance called the "Pluto Underground". It was named in homage of the Mars Underground, another group of scientists that successfully lobbied for the restart of missions to Mars, following the lack of such since the Viking program. The group started a letter writing campaign which aimed to bring to attention Pluto as a viable target for exploration. In 1990, because of pressure from the scientific community, including those of the Pluto Underground, engineers at NASA decided to look into concepts for a mission to Pluto. At the time, it was thought that the atmosphere of Pluto would freeze and fall to the surface during winter, and so a lightweight spacecraft was desirable, as it would be able to reach Pluto before such an event would occur. One of the earliest concepts was for a 40-kilogram spacecraft that would reach Pluto in five to six years. The idea was shortly scrapped, however, because of the infeasibility of miniaturizing scientific instruments aboard such a spacecraft to that size.
  Another mission concept, known as Pluto 350, was developed by Robert Farquhar of the Goddard Space Flight Center, with Alan Stern and Fran Bagenal of the Pluto Underground, who both served as study scientists for the project. Pluto 350 aimed to send a spacecraft, weighing 350 kilograms, to Pluto. The spacecraft's minimalistic design was to allow it to travel faster and be more cost-effective, in contrast to most other big-budget projects NASA were developing at the time, such as Galileo and Cassini. Pluto 350, however, would later become controversial among mission planners at NASA, who considered the project to be too small and too high-risk. An alternative plan which was considered at one point was to send to Pluto a configuration of the Mariner Mark II spacecraft, which would weigh 2,000 kilograms and cost US$3.2 billion, in sharp contrast to Pluto 350's $543 million cost. While both projects competed for approval, Pluto 350 was more favored by NASA mission planners, who were starting to adopt smaller missions such as Mars Pathfinder and NEAR Shoemaker.
caption: A diagram of Pluto 350.
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