Discovery Program

The Discovery Program is a series of Solar System exploration missions funded by the U.S. National Aeronautics and Space Administration (NASA) through its Planetary Missions Program Office. The cost of each mission is capped at a lower level than missions from NASA's New Frontiers or Flagship Programs. As a result, Discovery missions tend to be more focused on a specific scientific goal rather than serving a general purpose.

The Discovery Program was founded in 1990. Existing NASA programs had specified mission targets and objectives in advance, then sought bidders to construct and operate them. In contrast, Discovery missions are solicited through a call for proposals on any science topic and assessed through peer review. Selected missions are led by a scientist called the principal investigator (PI) and may include contributions from industry, universities or government laboratories.

The Discovery Program also includes Missions of Opportunity, which fund U.S. participation in spacecraft operated by other space agencies, for example by contributing a single scientific instrument. It can also be used to re-purpose an existing NASA spacecraft for a new mission.

As of June 2021, the most recently selected Discovery missions were VERITAS and DAVINCI, the fifteenth and sixteenth missions in the program.

History

In 1989, NASA's Solar System Exploration Division began to define a new strategy for Solar System exploration up to the year 2000. This included a Small Mission Program Group that investigated missions that would be low cost and allow focused scientific questions to be addressed in shorter time than existing programs. The result was a request for rapid studies of potential missions and NASA committed funding in 1990. The new program was called "Discovery".

The panel assessed several concepts that could be implemented as low-cost programs, selecting NEAR Shoemaker which became the first launch in the Discovery Program on February 17, 1996. The second mission, Mars Pathfinder, launched on December 4, 1996, carried the ''Sojourner'' rover to Mars.

Missions

File:(253) mathilde crop.jpg, alt=An image of a rocky asteroid, Asteroid 253 Mathilde
File:PIA02406.jpg, alt=A view of the rocky Martian surface, ''Mars Pathfinder''s view of Ares Vallis
File:Eros rotation Dec. 3-4 2000.gif, alt=An animation of the rotation of an asteroid, Animation of the rotation of 433 Eros.
File:Hollows in Sholem Aleichem.jpg, alt=The surface of Mercury, ''MESSENGER'' imaging Mercury's surface hollows at Sholem Aleichem.
File:PIA19664-MarsInSightLander-Assembly-20150430.jpg, alt=InSight being built, InSight lander in assembly (April 2015, NASA)

Standalone missions

Missions of opportunity

These provide opportunities to participate in non-NASA missions by providing funding for a science instrument or hardware components of an instrument, or for an extended mission for a spacecraft that may differ from its original purpose.

* ASPERA-3, an instrument designed to study the interaction between the solar wind and the atmosphere of Mars, is flying on board the European Space Agency's Mars Express orbiter. Launched on 2 June 2003, it has been orbiting Mars since 30 December 2003. The Principal Investigator is David Winningham of Southwest Research Institute.
*A NASA contribution to the joint ESA - CNES NetLander Mars meteorological mission was planned, consisting of meteorological, seismic, and geodetic instruments; however, the mission was terminated prior to its 2007 launch.
* Moon Mineralogy Mapper (M3) is a NASA-designed instrument placed on board the ISRO's Chandrayaan orbiter selected in February 2005. Launched in 2008, it was designed to explore the Moon's mineral composition at high resolution. M3's detection of water on the Moon was announced in late September 2009, one month after the mission ended. The Principal Investigator was Carle Pieters of Brown University.
* Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) was selected in July 2007. It was a series of two new missions for the existing '' Deep Impact'' probe following its success at Tempel 1:
** The Extrasolar Planet Observations and Characterization (EPOCh) mission used the Deep Impact high-resolution camera in 2008 to better characterize known giant extrasolar planets orbiting other stars and to search for additional planets in the same system, as well as to investigate possible moons and ring systems of said exoplanets. A secondary science goal was to better observe the earth in both infrared and visible light, in order to create better computer models of exoplanets. The Principal Investigator was L. Drake Deming of NASA's Goddard Space Flight Center.
** The Deep Impact eXtended Investigation of Comets (DIXI) mission used the Deep Impact spacecraft for a flyby mission to a second comet, Hartley 2. The goal was to take pictures of its nucleus to increase our understanding of the diversity of comets. The flyby of Hartley 2 was successful with closest approach occurring on November 4, 2010. Michael A'Hearn of the University of Maryland was the Principal Investigator.
* New Exploration of Tempel 1 (NExT) was selected in July 2007 together with the EPOXI extension. It was a new mission for the '' Stardust'' spacecraft to fly by comet Tempel 1 in 2011 and observe changes since the Deep Impact mission visited it in July 2005. Later in 2005, Tempel 1 made its closest approach to the Sun, possibly changing the surface of the comet. The flyby was completed successfully on February 15, 2011. Joseph Veverka of Cornell University is the Principal Investigator.
* Strofio is a mass spectrometer that is a part of the SERENA instrument package on board the Mercury Planetary Orbiter component of the ESA's BepiColombo mission. Strofio will study the atoms and molecules that compose Mercury's atmosphere to reveal the composition of the planet's surface. Stefano Livi of Southwest Research Institute is the Principal Investigator.
* MEGANE (Mars-moon Exploration with GAmma rays and NEutrons) is an instrument planned to fly aboard the Martian Moons Exploration (MMX), a Japanese Aerospace Exploration Agency (JAXA) probe to Phobos and Deimos launching in 2026. MEGANE includes a gamma-ray spectrometer and a neutron spectrometer. David J. Lawrence of Johns Hopkins University is the Principal Investigator.
* VenSAR (Venus Synthetic Aperture Radar), is an instrument planned to fly aboard ESA's EnVision Venus orbiter. The principal investigator is Scott Hensley, Jet Propulsion Laboratory NASA/California Institute of Technology.
* In addition, the Lunar Reconnaissance Orbiter was temporarily managed under the Discovery Program from the termination of the Lunar Precursor Robotic Program until the creation of the Lunar Discovery and Exploration Program.

Mission timeline

Proposals and concepts

However often the funding comes in, there is a selection process with perhaps two dozen concepts. These sometimes get further matured and re-proposed in another selection or program. An example of this is ''Suess-Urey Mission'', which was passed over in favor of the successful '' Stardust'' mission, but was eventually flown as Genesis, while a more extensive mission similar to INSIDE was flown as '' Juno'' in the New Frontiers program. Some of these concepts went on to become actual missions, or similar concepts were eventually realized in another mission class. This list is a mix of previous and current proposals.

Additional examples of Discovery-class mission proposals include:
* Whipple, a space-observatory to detect objects in the Oort cloud by transit method.
* Io Volcano Observer, was proposed for missions 15 or 16, a Jupiter orbiter designed to make 10 flybys of the volcanically active moon Io.
* Comet Hopper (CHopper), a mission to comet 46P/Wirtanen that would've utilised multiple short flights to repeatedly land on the comet's nucleus in order to map various geological processes such as outgassing.
* Titan Mare Explorer (TiME), a lander mission to explore one of the methane lakes found in the north polar region of Titan, a moon of Saturn.
* Suess-Urey, similar to the later Genesis mission.
* Hermes, a Mercury orbiter. (similar to the MESSENGER Mercury orbiter)
* INSIDE Jupiter, an orbiter that would map Jupiter's magnetic and gravity fields in an effort to study the giant planet's interior structure. The concept was further matured and implemented as Juno in the New Frontiers program.
* The Dust Telescope, a space observatory that would measure various properties of incoming cosmic dust. The dust telescope would combine a trajectory sensor and a mass spectrometer, to allow the elemental and even isotopic composition to be analyzed.
* OSIRIS (Origins Spectral Interpretation, Resource Identification and Security), an asteroid observation and sample return mission concept selected in 2006 for further concept studies. It further matured and launched September 8, 2016, as OSIRIS-REx in the New Frontiers Program.
* Small Body Grand Tour, an asteroid rendezvous mission. This 1993 concept reviews possible targets for what became NEAR 4660 Nereus and 2019 Van Albada. Other targets considered for an extended mission included Encke's comet (2P), 433 Eros, 1036 Ganymed, 4 Vesta, and 4015 Wilson–Harrington (1979 VA). (NEAR Shoemaker visited 433 Eros and Dawn visited 4 Vesta)
* Comet Coma Rendezvous Sample Return, a spacecraft designed to rendezvous with a comet, make extended observations within the cometary coma (but not land on the comet), gently collect multiple coma samples, and return them to Earth for study. (Similar to ''Stardust'')
* Micro Exo Explorer, a spacecraft that would've utilised a new form of micro-electric propulsion, called 'Micro Electro-fluidic-spray Propulsion' to travel to a near Earth object and gather important data.

Mars focused

* Pascal, a Mars climate network mission.
* MUADEE (Mars Upper Atmosphere Dynamics, Energetics, and Evolution), an orbiter mission designed to study Mars's upper atmosphere. (similar to MAVEN of the Mars Scout program)
* PCROSS, similar to LCROSS, but directed towards Mars's moon Phobos.
* Merlin, a mission that would place a lander on Mars's moon Deimos.
* Mars Moons Multiple Landings Mission (M4), would conduct multiple landings on Phobos and Deimos.
* Hall, a Phobos and Deimos sample return mission.
* Aladdin, a Phobos and Deimos sample return mission. It was a finalist in the 1999 Discovery selection, with a planned launch in 2001 and return of the samples by 2006. Sample collection was intended to work by sending projectiles into the moons, then collecting the ejecta by means of a collector spacecraft flyby.
* Mars Geyser Hopper, a lander that would investigate the springtime carbon dioxide Martian geysers found in regions around the Martian south pole.
* MAGIC (Mars Geoscience Imaging at Centimeter-scale), an orbiter that would provide images of the Martian surface at 5–10 cm/pixel, permitting resolution of features as small as 20–40 cm.
* '' Red Dragon'', a Mars lander and sample return.

Lunar focused

* Lunar sample return from the South Pole–Aitken basin, current geological models don't adequately describe the area and this mission would have attempted to solve this issue.
* EXOMOON, ''in situ'' investigation on Earth's Moon.
* PSOLHO, would use the Moon as an occulter to look for exoplanets.
* Lunette, a lunar lander.
* Twin Lunar Lander, a double lander mission to better understand the Moon's evolution and geology.

Venus focused

* Venus Multiprobe, proposed for a 1999 launch, would have dropped 16 atmospheric probes into Venus, which would fall slowly to the surface, taking pressure and temperature measurements.
* Vesper, a concept for a Venus orbiter focused on studying the planet's atmosphere. It was one of three concepts to receive funds for further study in the 2006 Discovery selection. Osiris and GRAIL were the other two, and eventually GRAIL was chosen and went on to be launched.
* V-STAR (Venus Sample Targeting, Attainment and Return), a Venus sample return mission with a goal of understanding Venus's evolution. The mission would have consisted of a Venus orbiter with an attached lander. The lander would fall through the Venusian atmosphere, collecting samples along the way, as well as after landing through the use of a "mole". Said lander would launch those samples into a low orbit, where they would rendezvous with the orbiter, returning the samples to Earth.
* VEVA (Venus Exploration of Volcanoes and Atmosphere), an atmospheric probe for Venus. The main component is a 7-day balloon flight through the atmosphere accompanied by various small probes dropped deeper into the planet's thick gases.
* Venus Pathfinder, a long-duration Venus lander.
* RAVEN, a Venus orbiter radar mapping mission.
* VALOR, a Venus mission to study its atmosphere with a balloon. Twin balloons would circumnavigate the planet over 8 Earth-days.
* Venus Aircraft, a robotic atmospheric flight on Venus's atmosphere using a long-duration solar-powered aircraft system. It would carry 1.5 kg of scientific payload and would contend with violent wind, heat and a corrosive atmosphere.
* Zephyr, a rover concept that would be propelled by the wind force on its vertical wingsail. Conceived in 2012, the project has since made progress in developing electronic components that would allow the vehicle to operate for 50 days on the surface of Venus without a cooling system.Mars Pathfinder