International Space Station (ISS) - $150 billion A joint project between the United States, Russia, Europe, Japan, and Canada, the ISS is a research facility in orbit around the Earth.
Space Shuttle Program - $209 billion The Space Shuttle Program was a US government project that developed and operated human spaceflight from 1981 to 2011.
Hubble Space Telescope - $10 billion The Hubble Space Telescope is a space-based observatory that has been in operation since 1990.
Cassini-Huygens Mission to Saturn - $3.26 billion A joint project between NASA, the European Space Agency, and the Italian Space Agency.
James Webb Space Telescope - $9.7 billion The James Webb Space Telescope is a space-based observatory set to launch in 2021 that will study the early universe, stars, and exoplanets.
Mars Curiosity Rover - $2.5 billion The Mars Curiosity Rover is a robotic vehicle launched by NASA in 2011 to explore the surface of Mars and search for signs of life.
Mars 2020 Mission - $2.7 billion The Mars 2020 mission, launched by NASA in 2020, includes the Perseverance rover and the Ingenuity helicopter.
Kepler Space Telescope - $600 million The Kepler Space Telescope was a space-based observatory launched by NASA in 2009 to search for exoplanets, planets outside of our solar system.
Gravity Probe B - $750 million Gravity Probe B was a mission launched by NASA in 2004 to test Einstein's theory of general relativity.
Chandra X-ray Observatory - $1.5 billion The Chandra X-ray Observatory is a space-based telescope launched by NASA in 1999 that observes X-ray emissions from objects in space.