When NASA was preparing its mission to the moon -- a rock that is 239,000 miles from Earth -- it ate up an enormous portion of the federal budget. In 1964, NASA consumed 3.52 percent of the budget. In 1965, it was 4.31 percent. And in 1966, NASA spent $5.9 billion -- $43.5 billion in 2015 dollars -- in the effort to beat to Soviets to the closest body to Earth. (Here's the original 1966 budget document.)

This year, comparing NASA's budget request to CBO spending estimates, the agency's budget will be less than one-half of 1 percent of federal spending -- a ratio that's dropped over the length of time that the New Horizons spacecraft has been making its 4.67-billion-mile journey to Pluto.

Gorgeous Pluto! The dwarf planet has sent a love note back to Earth via our New Horizons spacecraft, which has traveled more than 9 years and 3+ billion miles. This is the last and most detailed image of Pluto sent to Earth before the moment of closest approach, which was at 7:49 a.m. EDT Tuesday - about 7,750 miles above the surface -- roughly the same distance from New York to Mumbai, India - making it the first-ever space mission to explore a world so far from Earth. This stunning image of the dwarf planet was captured from New Horizons at about 4 p.m. EDT on July 13, about 16 hours before the moment of closest approach. The spacecraft was 476,000 miles (766,000 kilometers) from the surface. Images from closest approach are expected to be released on Wednesday, July 15. Image Credit: NASA/JHUAPL/SwRI #nasa #pluto #plutoflyby #newhorizons#solarsystem #nasabeyond #science

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One of the motivations for the trip to Pluto was a postage stamp. Released in 1991 as part of a series documenting our solar system, the stamp showed a picture of a barren sphere, underneath which was written, "Pluto: Not yet explored." (One of the stamps is included on New Horizons.) That stamp spurred interest in a mission to document the then-planet, and after two cancelled attempts, the current mission was put together in 2000. In 2006, the craft was launched from Cape Canaveral. And this morning, it arrived.

When that stamp was issued, NASA's budget was more than $24 billion in 2015 dollars. When the team was formed, the budget had shrunk to about $18 billion in 2015 dollars. At launch, another dip, albeit a smaller one.

As a percentage of the ballooning federal budget, the decrease is more pronounced.

Getting an unmanned craft deep into outer space is a much different challenge than getting a manned one even somewhere nearby. The former is much cheaper, if history is any guide. And given the declining appetite for spending federal dollars on space travel, it seems unmanned missions will continue to be the norm for the foreseeable future.