Pluto, discovered by
Clyde Tombaugh in 1930, is an interesting target for planetary exploration, but Pluto presents significant challenges for exploration because of its small mass and great distance from Earth. In 1964,
Gary Flandro of the
Jet Propulsion Laboratory proposed a mission called
Grand Tour, taking advantage of the fact that an alignment of planets in the late 1970s would enable a single spacecraft to visit all of the outer planets, including Pluto, by using
gravity assists. Due to the cost, the mission was not funded, although the planetary alignment was used by the two probes of the
Voyager program, launched in 1977. One of many possibilities for the
Voyager 1 spacecraft after its
flyby of Saturn in 1980 was to use Saturn as a
slingshot towards Pluto for a flyby as early as March 1986. However, scientists decided that a flyby of
Titan during the Saturn encounter would be a more important scientific objective, making a subsequent flyby of Pluto impossible, because the close approach to Titan put it on a trajectory that slingshotted it out of the
plane of the Solar System. Because no mission to Pluto was planned by any space agency at the time, it would be left unexplored by interplanetary spacecraft for years to come. After the success of the Voyager program, planetary scientists looked to Pluto as the destination for a subsequent mission. In the 1980s,
Robert Farquhar proposed that a Pluto mission could be added to the proposed
Solar Probe mission, which at the time was proposed to fly by Jupiter on the way to its solar encounter. The mission was tagged "Fire and Ice." However, the proposal was not accepted.
The Pluto Underground, Pluto 350 and Mariner Mark II spacecraft. This was later ruled out in favor of a smaller, less expensive spacecraft similar to the "Pluto 350" concept. 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. 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. Doubts about the cost-effectiveness were raised by Farquhar's team as Pluto had just passed
perihelion, which would exponentially increase the mission duration before the launch date was finalized. Pluto's approximate axial tilt of 118 degrees meant that the southern hemisphere would not be able to be photographed as it entered decades-long darkness with the onset of winter. 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. The series featured a stamp for all planets, displaying an image of the planet and highlighting an associated spacecraft which was sent to it. The stamp for Pluto, however, depicted a featureless sphere, presented with the phrase "not yet explored" in place of the name of a spacecraft. The stamps were unveiled in a ceremony at the
Jet Propulsion Laboratory. Two scientists who attended the event, World Space Foundation president Robert Staehle and JPL scientist Stacy Weinstein, were inspired by Pluto's status on the stamp, such that they started to inquire about the feasibility of sending a spacecraft to Pluto. Engineers at the Jet Propulsion Laboratory, inspired by the "Not Yet Explored" status of Pluto, also started to put forward ideas about a mission to Pluto. In August 1992, Staehle telephoned Pluto's discoverer,
Clyde Tombaugh, requesting permission to visit his planet. "I told him he was welcome to it", Tombaugh later remembered, "though he's got to go one long, cold trip".
Pluto Fast Flyby That year, Staehle, with the help of JPL engineers and students from the
California Institute of Technology, formed the
Pluto Fast Flyby project. The mission heralded the same ideology as the Pluto 350 concept: small in size and cost-effective in scope, so that the spacecraft would be able to get to Pluto faster and be affordable to develop and launch. Described as a "radical" mission concept, the mission would see two spacecraft being sent to Pluto. Both spacecraft were to weigh only around 35-50 kilograms each (including 7 kg worth of scientific instruments), and the project would cost less than US$500 million to develop, excluding launch costs. The proposal was forwarded to Administrator Goldin, but he vetoed the proposal, recommending instead that the JPL look into the feasibility of Pluto Fast Flyby being launched aboard a smaller rocket, such as the
Delta II. In response to the backlash caused by the cancellation of Pluto Kuiper Express, it was decided to inaugurate a new class of missions that would fit between the big-budget
Flagship Program and the low-budget
Discovery Program, creating a compromise for missions such as the former Pluto Kuiper Express, which proved to be too expensive for the Discovery Program. A competition was held, in which NASA would select a mission concept to fund as part of the first mission of the
New Frontiers program.
Proposed exploration (2003) A Pluto orbiter/lander/sample return mission was proposed in 2003. The plan included a twelve-year trip from Earth to Pluto, mapping from orbit, multiple landings, a warm water probe, and possible
in situ propellant production for another twelve-year trip back to Earth with samples. Power and propulsion would come from the bimodal MITEE nuclear reactor system. ==
New Horizons ==