Discovery Program

Header of the Discovery program website (January 2016)^[1]

NASA's Discovery Program (as compared to New Frontiers or Flagship Programs) is a series of lower-cost, highly focused American scientific space missions that are exploring the Solar System. It was founded in 1992 to implement then-NASA Administrator Daniel S. Goldin's vision of "faster, better, cheaper" planetary missions. Discovery missions differ from traditional NASA missions where targets and objectives are pre-specified. Instead, these cost-capped missions are proposed and led by a scientist called the Principal Investigator (PI). Proposing teams may include people from industry, small businesses, government laboratories, and universities. Proposals are selected through a competitive peer review process. All of the completed Discovery missions are accomplishing ground-breaking science and adding significantly to the body of knowledge about the Solar System.

NASA also accepts proposals for competitively selected Discovery Program Missions of Opportunity. This provides opportunities to participate in non-NASA missions by providing funding for a science instrument or hardware components of a science instrument or to re-purpose an existing NASA spacecraft. These opportunities are currently offered through NASA's Stand Alone Mission of Opportunity program.

History

In 1989, the Solar System Exploration Division (SSED) at NASA Headquarters initiated a series of workshops to define a new strategy for exploration through the year 2000. The panels included a Small Mission Program Group (SMPG) that was chartered to devise a rationale for missions that would be low cost and allow focused scientific questions to be addressed in a relatively short time.^[2] A fast-paced study for a potential mission was requested and funding arrangements were made in 1990. The new program was called 'Discovery' and the panel assessed a number of concepts that could be implemented as low-cost programs, with 'Near Earth Asteroid Rendezvous' (NEAR) as the first mission to be implemented.^[2] On February 17, 1996, NEAR became the first mission to launch in the Discovery Program.^[2] The Mars Pathfinder launched on December 4, 1996, demonstrated a number of innovative, economical, and highly effective approaches to spacecraft and planetary mission design such as the inflated air bags that allowed the Sojourner rover to endure the landing.^[2] Note that the two Mars rover Opportunity and Spirit of the Mars Exploration Rover mission were not a part of the Discovery Program, although they did re-use the overall landing system of Mars Pathfinder. Also, Phoenix and MAVEN were in the Mars Scout Program not Discovery program.

Launches and endings

Mars Pathfinder's Sojourner mini-rover takes its Alpha Particle X-ray Spectrometer measurement of the Yogi Rock (1997)

Discovery program launches 1996 Mars Pathfinder NEAR Shoemaker 1997 1998 Lunar Prospector 1999 Stardust 2000 2001 Genesis 2002 CONTOUR 2003 2004 MESSENGER 2005 Deep Impact 2006 2007 Dawn 2008 2009 Kepler 2010 2011 GRAIL 2012 2013 2014 2015 2016 2017 2018 InSight (planned launch)

Discovery program ended or active (2016) 1997 Mars Pathfinder 1998 1999 Lunar Prospector 2000 2001 NEAR Shoemaker 2002 CONTOUR 2003 2004 Genesis 2005 2006 2007 2008 2009 2010 2011 Stardust 2012 GRAIL 2013 Deep Impact 2014 2015 MESSENGER 2016 Dawn (active) Kepler (active) InSight (active)

Timeline of launched and active Discovery missions

Asteroid Eros regolith

Launched and active Discovery missions

Year
1996	2
1997	2
1998	2
1999	3
2000	2
2001	3
2002	3
2003	2
2004	3
2005	3
2006	3
2007	4
2008	4
2009	5
2010	5
2011	6
2012	5
2013	4
2014	3
2015	3
2016	2

Missions

Standalone missions

Asteroid 253 Mathilde

Mars Pathfinder's view

Animation of the rotation of 433 Eros.

• Mars Pathfinder (Mission #1), a Mars lander to deploy Sojourner rover on the surface. Launched in 1996, it landed on Mars on July 4, 1997. It has completed its primary and extended mission. The Principal Investigator was Matthew Golombek of NASA’s Jet Propulsion Laboratory.
• NEAR Shoemaker (Mission #2), a mission to study asteroid 433 Eros. Launched on February 17, 1996, the spacecraft entered orbit around Eros in 2000 and successfully touched down on its surface one year later. It has succeeded its primary and extended mission and is now complete. The Project Scientist was Andrew Chang of The Johns Hopkins University Applied Physics Laboratory.
• Lunar Prospector (Mission #3), a Moon orbiter to characterize the lunar mineralogy. Launched in 1998, it spent 1½ years in lunar orbit. It has completed its primary and extended mission and deliberately impacted onto the Moon's surface. The Principal Investigator was Alan Binder of the Lunar Research Institute.
• Stardust (Mission #4), a mission to collect interstellar dust and dust particles from the nucleus of comet 81P/Wild for study on Earth. Launched in 1999, it successfully collected samples between 2000–2004, then the sample return capsule returned to Earth on January 15, 2006. The capsule is on display at the National Air and Space Museum in Washington D.C. Scientists worldwide are studying the comet dust samples while citizen scientists are finding interstellar dust bits through the Stardust@home project. The spacecraft was assigned a new task, called Stardust-NExT to revisit Tempel 1 and observe the crater left by Deep Impact. Having completed its primary and extend missions, Stardust did a final burn to deplete its remaining fuel on March 24, 2011.^[3] The Principal Investigator was Donald Brownlee of the University of Washington.
• Genesis (Mission #5), a mission to collect solar wind charged particles for analysis on Earth. Launched in 2001, it collected solar wind between 2002–2003. In Sept. 2004, the sample return capsule's parachute failed to deploy, and the capsule crashed into the Utah desert. However, solar wind samples were salvaged and are available for study. Despite the hard landing, Genesis has met or anticipates meeting all its baseline science objectives. The Principal Investigator was Donald Burnett of the California Institute of Technology.
• Comet Nucleus Tour (CONTOUR) (Mission #6), was a failed mission to visit and study comets Encke and Schwassmann-Wachmann-3. It was launched on July 3, 2002. Six weeks after launch, after a planned maneuver that was intended to propel it out of Earth orbit and into its comet-chasing solar orbit, the spacecraft was lost. The investigation board concluded the probable cause was structural failure of the spacecraft due to plume heating during the embedded solid-rocket motor burn.^[2][4] Subsequent investigation revealed that it broke into at least three pieces, the cause likely being structural failure during the rocket motor burn that was to push it from Earth orbit into a solar orbit.

MESSENGER imaging Mercury's surface hollows at Sholem Aleichem.^[5]

• MESSENGER (Mission #7) (Mercury Surface, Space Environment, Geochemistry and Ranging) conducted the first orbital study of Mercury. MESSENGER's science goals were to provide the first images of the entire planet and collect detailed information on the composition and structure of Mercury's crust, its geologic history, the nature of its thin atmosphere and active magnetosphere, and the makeup of its core and polar materials. It was launched on August 3, 2004 and entered orbit around Mercury on March 18, 2011. The primary mission was completed on March 17, 2012. It achieved 100% mapping of Mercury on March 6, 2013, and completed its first year-long extended mission on March 17, 2013. The mission had two more extensions until the spacecraft ran out of propellant and was deorbited on April 30, 2015.^[6]
• Deep Impact (Mission #8), a mission in which a spacecraft released an impactor into the path of comet Tempel 1. Launched in January 2005, the impact occurred on July 4, 2005. After the successful completion of its mission, it was put in hibernation and then reactivated for a new mission designated EPOXI. The Principal Investigator was Michael A'Hearn of the University of Maryland.
• Dawn (Mission #9) was launched on September 27, 2007 to study the two most massive objects of the asteroid belt – the protoplanet Vesta and the dwarf planet Ceres. It reached Vesta in July 2011 and completed the study of Vesta by September 2012 and is currently orbiting Ceres, where it arrived in March 2015.^[7][8] It is using solar electric ion thrusters to orbit both asteroids in one mission, a feat that has not been attempted before. The Principal Investigator is Chris Russell of the University of California, Los Angeles.
• Kepler (Mission #10) is a space observatory tasked to explore the structure and diversity of exoplanet systems, with a special emphasis on the detection of Earth-size planets in orbit around stars outside our Solar System.^[9] The spacecraft was launched on March 7, 2009,^[10] and announced its first exoplanet discoveries in January 2010. The Principal Investigator is William Borucki of NASA’s Ames Research Center.
• Gravity Recovery and Interior Laboratory, (GRAIL) (Mission #11) provided higher-quality gravity field mapping of the Moon to determine its interior structure; launched in September 2011.^[11] The Principal Investigator is Maria Zuber of the Massachusetts Institute of Technology. GRAIL spacecraft impacted the Moon on December 17, 2012. MoonKAM was an education related sub-program and instrument of this mission (Moon Knowledge Acquired by Middle school students.^[12]

Insight lander in assembly (April 2015, NASA)

• InSight (Mission #12)– An Announcement of Opportunity for the 2016 Discovery mission was released by NASA on June 7, 2010. Twenty-eight proposals were submitted, and on May 5, 2011, three were chosen for further study.^[13] Following these one-year preliminary design studies, the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission was selected in August 2012. InSight (initially named Geophysical Monitoring Station or GEMS) will study the structure and composition of the interior of Mars and advance understanding of the formation and evolution of terrestrial planets.^[14] An Announcement of Opportunity for a Discovery mission was released by NASA on June 7, 2010. Out of 28 proposals from 2010,^[15] three finalists received US$3 million in May 2011 to develop a detailed concept studies.^[13] In August 2012, InSight was selected for development and launch;^[16] however, persistent problems with the vacuum seal on the seismometer meant that the payload was not ready in time for the mission to make the 2016 launch window.^[17]

Missions of opportunity

This provides opportunities to participate in non-NASA missions by providing funding for a science instrument or hardware components of a science instrument, or specific extended mission for spacecraft that may different from its original purpose. Some examples include: M3, EPOXI, EPOCH, DIXI, and NEXT.

• Moon Mineralogy Mapper is a NASA-designed instrument placed on board the ISRO's Chandrayaan orbiter. 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 Sept. 2009, one month after the mission ended. The Principal Investigator was Dr. Carle Pieters of Brown University.
• Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) was selected in 2007.^[18] 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. The Principal Investigator was Dr. L. Drake Deming of NASA's Goddard Space Flight Center.

Nucleus of Comet Hartley 2

• The Deep Impact eXtended Investigation of Comets (DIXI) mission used the Deep Impact mission's 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. Dr. Michael A'Hearn of the University of Maryland was the Principal Investigator.
• New Exploration of Tempel 1 (NExT) 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. Dr. Joseph Veverka of Cornell University is the Principal Investigator.
• 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 in June 2003, it has been orbiting Mars since Dec. 2003. The Principal Investigator is David Winningham of Southwest Research Institute.
• Strofio^[19] is a unique mass spectrometer that is part of the SERENA instrument package that will fly on board the European Space Agency's BepiColombo/Mercury Planetary Orbiter spacecraft. 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.

Examples of proposals

Possible configuration of a lunar sample return spacecraft

Mercury by Discovery's MESSENGER

However often the funding comes in, there is a selection process with perhaps 2 dozen concepts. These sometimes get further matured and re-proposed in another selection or program.^[20] 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,^[20] 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, space-observatory to detect Oort cloud by transit method
• Io Volcano Observer
• Comet Hopper (CHopper)
• Titan Mare Explorer (TiME)
• Suess-Urey, similar to the later Genesis mission.^[20]
• Hermes, a Mercury orbiter.^[21] (compare to 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.^[22] The concept was further matured and implemented as Juno in the New Frontiers program.^[23]
• Psyche — a mission to the metallic asteroid 16 Psyche.^[24]
• The Dust Telescope is a space observatory that would measure various properties of incoming cosmic dust.^[25] The dust telescope would combine a trajectory sensor and a mass spectrometer, to allow the elemental and even isotopic composition to be analyzed.^[25]
• OSIRIS (Origins Spectral Interpretation, Resource Identification and Security) was an asteroid observation and sample return mission concept selected in 2006 for further concept studies.^[26] It was further matured and launched September 8, 2016 as OSIRIS-REx in the New Frontiers Program.^[27]
• Hera is a mission concept for near-Earth asteroid sample return.^[28] Envisioned as the follow-on from the NEAR mission, the design was intended to collect three samples from three different asteroids.^[29] The initial proposal proposed 1999-AO10, 2000-AG6 and 1998-UQ asteroids, but this was later expanded to three of 40 different options.^[29]
• Small Body Grand Tour, an asteroid rendezvous mission.^[30] This 1993 concept reviews possible targets for what became NEAR— 4660 Nereus and 2019 Van Albada^[30] Other targets considered for an extended mission included Encke's comet (2/P), 433 Eros, 1036 Ganymed, 4 Vesta, and 4015 Wilson–Harrington(1979 VA).^[30] (NEAR did visit 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.^[31] (See also Stardust (spacecraft))
• Micro Exo Explorer would use a new form of micro-electric propulsion, called 'Micro Electro-fluidic-spray Propulsion' to travel to a near Earth object and gather important data.^[32]

Mars focused

Mars Geyser Hopper would investigate 'spider' features on Mars, as imaged by an orbiter. Image size: 1 km (0.62 mi) across.

• Pascal, a Mars climate network mission.^[33]
• MAUDEEE (Mars Upper Atmosphere Dynamics, Energetics, and Evolution)^[34] (compare to MAVEN of the Mars Scout program)
• Phobos Surveyor is an orbiter mission concept to the Mars moon Phobos, which would also deploy special rovers for the moon's low gravity environment.
• PCROSS, based on LCROSS but to Mars' moon Phobos.^[35]
• Merlin mission would place a lander on Mars' moon Deimos.^[36]
• Mars Moons Multiple Landings Mission (M4), would conduct multiple landings on Phobos and Deimos.^[37]
• Hall is a Phobos and Deimos sample return mission.^[38]
• Aladdin was a Discovery-class Phobos and Deimos sample return mission.^[39] It was a finalist in the 1999 Discovery selection, with a planned launch in 2001 and return of the samples by 2006.^[40] Sample collection was intended to work by sending projectiles into the moons, then collecting the ejecta.^[40]
• Mars Geyser Hopper is a lander that would investigate the springtime carbon dioxide Martian geysers found in regions around the south pole of Mars.^[41][42]
• MAGIC (Mars Geoscience Imaging at Centimeter-scale) is 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.^[43]
• Red Dragon, a Mars lander and sample return.^[44]

Lunar focused

• Lunar sample return from the South Pole–Aitken basin. No geologic model adequately accounts for all of the characteristics of the area and disagreements are fundamental.^[45]
• EXOMOON, in situ investigation on Earth's Moon.^[46]
• PSOLHO, would use the Moon as an occulter to look for exoplanets.^[47]
• Lunette, a lunar lander.^[48]
• Twin Lunar Lander, a geophysics mission to the Moon.^[49]

The Venus Multiprobe Mission involved sending 16 atmospheric probes into Venus in 1999.^[50]

Venus focused

• Venus Multiprobe, proposed for a 1999 launch, would have dropped 16 atmospheric probes into Venus, and fall slowly to the surface, making pressure and temperature measurements.^[20]
• Vesper was a concept for a Venus orbiter focused on studying that planet's atmosphere.^[51][52][53] It was one of three concepts to receive funds for further study in the 2006 Discovery selection.^[52] Osiris and GRAIL were the other two, and eventually GRAIL was chosen and went on to be launched.^[26]
• V-STAR (Venus Sample Targeting, Attainment and Return) is a Venus atmosphere sample return mission.^[54][55] While returning samples from the surface of Venus has noted difficulties, a Discovery-class sample return from the upper atmosphere is being proposed.^[54] Something along the lines of Stardust mission but using a free-return trajectory (it would not go into Venusian orbit).^[54]
• VEVA (Venus Exploration of Volcanoes and Atmosphere) is an in atmosphere probe for Venus.^[56] The centerpiece is a 7-day balloon flight through the atmosphere accompanied by various tiny probes dropped deeper into the planet's thick gases.^[56]
• Venus Pathfinder, a long-duration Venus lander.^[57]
• RAVEN, a Venus orbiter radar mapping mission.^[58]
• VALOR, a Venus mission to study its atmosphere with a balloon.^[59] Twin balloons would circumnavigate the planet over 8 Earth-days.^[59]
• Venus Aircraft, a robotic atmospheric flight on Venus' atmosphere using a long-duration solar-powered aircraft system.^[60] It would carry 1.5 kg of scientific payload and it must contend with violent wind, heat and a corrosive atmosphere.^[60]

Selection process

The first two Discovery missions were Mars Pathfinder and Near Earth Asteroid Rendezvous (Shoemaker)

Discovery 3

In February 1995 Lunar Prospector, a lunar orbiter mission, was selected for launch.^[61] NASA decided it was mature enough it could go directly to development without a final selection, which left three other missions to undergo a further selection later in 1995.^[61] Those three missions were Stardust, Suess-Urey, and Venus Multiprobe.^[61] There were 28 proposals submitted to NASA in October 1994.^[61] The announcement of opportunity was in August 1994.^[61]

A full list of proposals was released by NASA for this selection:^[61]

1. ASTER- Asteroid Earth Return
2. Comet Nucleus Penetrator
3. Comet Nucleus Tour (CONTOUR)
4. Cometary Coma Chemical Composition (C4)
5. Diana (Lunar & Cometary Mission)
6. FRESIP-A mission to Find the Frequency of Earth-sized Inner Planets
7. Hermes Global Orbiter (Mercury Orbiter)
8. Icy Moon Mission (Lunar Orbiter)
9. Interlune-One (Lunar Rovers)^[62]
10. Jovian Integrated Synoptic Telescope (IO Torus investigation)
11. Lunar Discovery Orbiter ^[63]
12. Lunar Prospector (Lunar Orbiter) (Chosen in February 1995 for Discovery 3)
13. Mainbelt Asteroid Exploration/Rendezvous
14. Mars Aerial Platform (Atmospheric)
15. Mars Polar Pathfinder (Polar Lander)
16. Mars Upper Atmosphere Dynamics, Energetics and Evolution
17. Mercury Polar Flyby
18. Near Earth Asteroid Returned Sample
19. Origin of Asteroids, Comets and Life on Earth
20. PELE: A Lunar Mission to Study Planetary Volcanism
21. Planetary Research Telescope
22. Rendezvous with a Comet Nucleus (RECON)
23. Suess-Urey (Solar Wind Sample Return) (Discovery 4 semi-finalist)
24. Small Missions to Asteroids and Comets
25. Stardust (Cometary/Interstellar Dust Return) (Discovery 4 semi-finalist, chosen in the fall of 1995 for selection)
26. Venus Composition Probe (Atmospheric)
27. Venus Environmental Satellite (Atmospheric)
28. Venus Multi-Probe Mission (Atmospheric)^[64] (Discovery 4 semi-finalist)

Lunar prospector was selected in early 1995 and Stardust later that year, becoming the third and fourth Discovery missions respectively.

Discovery 4

Stardust succeeded. Comet Wild 2 shown here

Stardust, a comet sample return mission was selected in November 1995 over two other finalists, Venus Multiprobe and Suess-Urey.^[65] These three mission were selected of 28 proposals submitted in October 1994.^[65] Stardust used an aerogel to capture particles of Comet Wild 2 and return them to Earth.^[65]

Discovery 5 and 6

In October 1997, NASA selected Genesis and Contour as the next Discovery missions, out of 34 proposals that were submitted in December 1996.^[66] The four previously selected missions at this time were NEAR, Pathfinder, Lunar prospector, and Stardust.

The five finalists were:^[67]

• Aladdin (Mars' moon sample return)
• Comet Nucleus Tour (CONTOUR)
• Genesis (Solar wind sample return)
• Mercury Surface, Space Environment, Geochemistry and Ranging mission (MESSENGER)
• Venus Environmental Satellite (VESAT)

Discovery 7 and 8

Deep Impact nails a comet nucleus

In July 1999, NASA selected Messenger and Deep Impact as the next Discovery program missions.^[68] Messenger was the first Mercury orbiter and mission to that planet since Mariner 10, and the Deep Impact sent a projectile into the comet Tempel 1.^[68] Both missions targeted a launch in late 2004 and the cost was constrained at about $300 million USD each.^[68]

In 1998 five semi-finalists were selected to receive $375,000 USD to further mature their design concept.^[69] The five proposals were selected out of perhaps 30 with the goal of achieving the best science.^[69] Those missions were:^[69]

• Aladdin
• Deep Impact
• MESSENGER
• Inside Jupiter
• Vesper

Aladdin and Messenger were also semi-finalists in the 1997 selection.^[69]

Discovery 9 and 10

Scale comparison of Vesta, Ceres, and the Moon

Kepler spacecraft art

26 proposals were submitted to the Discovery solicitation, with budget initially targeted at 300 million USD.^[70] The semi-finalists were downselected in January 2001 for a phase-A design study were three missions: Dawn, Kepler, and INSIDE Jupiter.^[71] INSIDE Jupiter was similar to a later New Frontier's mission called Juno; Dawn is an asteroid mission, and Kepler is a space telescope mission aimed to discover extrasolar planets. The three semi-finalists received $450,000 USD to further mature the mission proposal.^[72]

In December 2001 NASA selected the Kepler mission for launch.^[73] At this time only 80 exoplanets had been detected, and that was part of the mission of Kepler, to look for more exoplanets, especially Earth-sized.^[73] Kepler became the tenth Discovery mission selected for flight.^[74] Also in December 2001, the Dawn mission to asteroids Vesta and Ceres was selected.^[70] Both missions were initially selected for a launch in 2006.^[70]

The Discovery Program fell on hard-times after this, with several mission experiencing cost-over runs, and one mission exploded during launch. Although both Dawn and Kepler would become widely praised success stories, they missed their somewhat ambitious 2006 launch target, launching in 2007 and 2009 respectively. Kepler would go on to receive a mission extensions, and Dawn likewise successfully orbited both Vesta and Ceres. Nevertheless, the next selection would take longer than previous as the program selection of new missions slowed down. As the successes of the new missions enhanced the image of the Discovery Program, the difficulties began to fade from the limelight. Also, the number of active missions in development or active began to increase as the program ramped up.

Discovery 11

In November 2007 NASA selected the GRAIL mission as the next discovery mission, with a goal of mapping Lunar gravity and a 2011 launch.^[75] There were 23 other proposals that were also under consideration.^[75] The mission had budget of $375 million USD (then-year dollars) which included construction and also the launch.^[75]

The announcement of opportunity for this Discovery mission was released in April 2006.^[76] There were three semi-finalists for this Discovery selection including GRAIL (which won), OSIRIS, and VESPER.^[77] OSIRIS was very similar to the later OSIRIS-REx mission, an asteroid sample return mission to 101955 Bennu, and Vesper, a Venus orbiter mission.^[77] A previous proposal of Vesper had also been a semi-finalist in the 1998 round of selection.^[77] The three finalists were announced in October 2006 and awarded 1.2 million USD to further develop their propoals for the final round.^[78] The three missions of opportunity which were selected for study were EPOXI, EPOCH, and DIXI.^[78] Some concurrent events to this period was that the ESA Venus Express successfully entered Venus orbit in the Spring of 2006 and also Hayabusa achieved rendezvous with a small asteroid.

Discovery 12

This was an especially tough selection, coming on the heels of a successful Mars rover landing and the termination of the Mars Scout program (parent program of Phoenix and MAVEN), it meant that the proposals to the very popular red-planet competed with more obscure destinations. On the other hand, Titan had just been landed on by Huygens and Comets were getting the full-treatment by the flagship-class ESA Rosetta mission. The Advanced Stirling radioisotope generator was later cancelled.

Out of 28 proposals from 2010,^[79] Insight was one of the three Discovery Program finalists receiving US$3 million in May 2011 to develop a detailed concept study.^[80] In August 2012, InSight was selected for development and launch.^[16]

Huygens in situ image from Titan's surface

Same image with contrast enhanced.

The three semi-finalists:

• InSight, this Mars lander was selected for development, and will be launched on May 5, 2018.
• Titan Mare Explorer (TiME) spacecraft for landing in, and floating on, a large methane-ethane sea on Saturn's moon Titan. A Titan moon "lake" lander was previously considered Titan Saturn System Mission and other concepts, but have lost out to other missions which have themselves been cancelled.
• Comet Hopper (CHopper) study cometary evolution by landing on a comet multiple times and observing its changes as it interacts with the Sun.

According to the BBC, of the 28 first round mission proposals, 3 were for the Moon, 4 for Mars, 7 for Venus, 1 Jupiter, 1 to a Jupiter Trojan, 2 to Saturn, 7 to asteroids, and 3 to Comets.^[81]

Future mission

Discovery Mission 13

NASA is making the NEXT ion thruster technology available for the Discovery Program mission #13.^[82]

Concept art of VERITAS orbiter at Venus

Concept art of Pysche orbiter at 16 Pysche

On September 30, 2015, NASA selected five mission concepts for refinement during the next year, as a first step in choosing one or possibly two of the missions for development.^[83] Each mission received $3 million for a one-year study. The winner will be chosen around December 2016^[84] and must be ready to launch by the end of 2021.^[85][86]

The five semifinalists are:^[87]

1. Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) − it would study the chemical composition of Venus' atmosphere during a 63-minute descent.
2. Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy (VERITAS) — it would produce global, high resolution topography and imaging of Venus' surface and global surface composition.
3. Psyche Orbiter — it would explore the origin of planetary cores by studying the metallic asteroid 16 Psyche.
4. Near Earth Object Camera (NEOCam) — is a space infrared telescope designed to survey the Solar System for potentially hazardous asteroids.
5. Lucy — it would perform the first reconnaissance of the Jupiter trojan asteroids. Some possible reported targets would be 3548 Eurybates, 21900 Orus, 11351 Leucus, the binary 617 Patroclus with its companion Menoetius, and main-belt asteroid 52246 Donaldjohanson.^[88]

The budget is planned to be $450 million, but there are some optional technology and bonuses available beyond this:^[89]

• An additional $30 million available if it attempts to demonstrate laser communication in space (as opposed to radio communication) system at extra-Lunar distances^[89]
• An additional $10 million available if it demonstrates a 3D woven heat shield^[89]
• An additional $5 million available if it incorporates the miniaturized Deep Space Atomic Clock^[89]
• A xenon ion engine and a radioisotope heater unit are also available for the mission without additional incentives^[89]

Selection process

In February 2014, NASA released a Discovery Program 'Draft Announcement of Opportunity' for launch readiness date of December 31, 2021.^[90] As with previous Discovery missions such as Dawn, solar electric ion thruster propulsion may allow increased mission options if applicable.^[91] Technologies may include the NEXT ion thruster,^[92] laser communication,^[85] and/or re-entry technology.^[82] The main mission is budgeted for up to 450 million USD, with various conditions but also bonuses.^[82][93] For the first time, the $450 million cost cap will not include post-launch operations expenses.^[94]

The final requirements were changed later in 2014.^[95] In regard to the laser communication package: it is not required, but if included, could grant an additional 30 million USD bonus on top of the existing budget.^[95] That feature is the "Deep Space Optical Communications payload", and involves sending data with lasers beyond one lunar distance (distance from Earth to the Moon).^[96] The deadline for proposals was February 16, 2015 and may have included some of the following mission candidates:^[94][97]

Saturn system

• Enceladus Life Finder (ELF) — an astrobiology orbiter mission to assess Enceladus' habitability and search for biosignatures.^[98]
• Journey to Enceladus and Titan (JET) — an astrobiology orbiter mission to assess Enceladus' habitability and search for biosignatures in the plumes.^[99]
• Life Investigation For Enceladus (LIFE) — an astrobiology sample-return mission to assess Enceladus' habitability and search for biosignatures in a sample of a plume.^[100]

Jupiter system

• Io Volcano Observer — a mission to explore Io's active volcanism and impact on the Jupiter system as a whole by measuring its global heat flow, its induced magnetic field, the temperature of its lava, and the composition of its atmosphere, volcanic plumes, and lavas.^[101]
• Advanced Jovian Asteroid eXplorer (AJAX) — a mission to a single Jupiter trojan^[102]

Venus

• Radar at Venus (RAVEN) - High-resolution mapping of Venus^[103]
• Venus Atmosphere and Surface Explorer (VASE)— would measure the complete inventory of atmospheric noble gas and light stable isotopes and provide the first complete atmospheric structure profile from clouds to surface of temperature, pressure and wind.^[104]
• Venus Emissivity, Radio Science, InSAR Topography and Spectroscopy (VERITAS)

Mars system

• Mars-Moons Exploration, Reconnaissance and Landed Investigation (MERLIN) misson to flyby Deimos and then orbit and land on Phobos.^[105]
• Phobos And Deimos Origin Assessment (PANDORA), to orbit Deimos and Phobos^[105]
• Phobos And Deimos & Mars Environment (PADME)^[105][106]
• Icebreaker Life would use the Phoenix/InSight platform but would carry a payload to search for past extraterrestrial life on Mars.^{[107][108][109]}

Asteroid, comet, and lunar proposals

• Binary Asteroid in-situ Explorer (BASiX)— a mission to visit a binary asteroid and set off small explosions to see how they affect the movement of both objects.^[110]
• Comet Radar Explorer (CORE)
• Dark Asteroid Rendezvous (DARe)— a mission to visit up to nine asteroids using a spacecraft equipped with ion propulsion.^[111]
• Lucy — would tour Trojan asteroids^[112]
• Psyche Orbiter to 16 Psyche asteroid — the most massive metallic asteroid in the asteroid belt, thought to be exposed iron core of a protoplanet.^[113]
• Moon Age and Regolith Explorer (MARE)^[114][115]
• NanoSWARM — CubeSat mission to study space weathering, lunar magnetism, lunar water and small-scale magnetospheres.
• Near-Earth Object Camera (NEOCam)
• Proteus – mission to 238P/Read, a main-belt comet^[116]

Other

• Kuiper Telescope — this would target multiple objects, including the giant planets, their satellites, and small bodies with a 1.2-meter diameter mirror space telescope placed at Earth L2 point.^[117]

Summary

Discovery Program
NEAR 1996	Mars Pathfinder 1996	Lunar Prospector 1998	Stardust 1999	Genesis 2001	MESSENGER 2004
Deep Impact 2005	Dawn 2007	Kepler Observatory 2009	GRAIL 2011	InSight 2018

Mission insignias

This section includes an image of most of the Discovery missions' patches or logos where available, as well as the launch year

Discovery Program
NEAR 1996	Mars Pathfinder 1996	Lunar Prospector 1998	Stardust 1999	Genesis 2001	MESSENGER 2004
Deep Impact 2005	Dawn 2007	Kepler Observatory 2009	GRAIL 2011	InSight 2018

Launches

This section includes an image of most of the Discovery missions' rockets, as well as the launch year

Discovery Program
NEAR 1996	Mars Pathfinder 1996	Lunar Prospector 1998	Stardust 1999	Genesis 2001	MESSENGER 2004
Deep Impact 2005	Dawn 2007	Kepler Observatory 2009	GRAIL 2011	InSight 2018

See also

• Explorer program
• Mars Exploration Program
• Mars Scout Program
• New Frontiers Program
• New Millennium Program

References

1. "Discovery Program Official Website (January 2016)". National Aeronautics and Space Administration (NASA). January 15, 2016. Archived from the original on January 15, 2016. Retrieved January 15, 2016.
2. "A Look Back at the Beginning: How the Discovery Program Came to Be" (PDF). NASA. 2010. Archived (PDF) from the original on March 1, 2011.
3. "NASA's Stardust: Good to the Last Drop". NASA.gov. NASA. Retrieved April 17, 2016.
4. "CONTOUR Mishap Investigation Board Report" (PDF). NASA. May 21, 2003. Archived (PDF) from the original on January 3, 2006.
5. "High-resolution Hollows". MESSENGER Featured Images. JHU - APL. March 12, 2014. Archived from the original on March 14, 2014.
6. Farewell, MESSENGER! NASA Probe Crashes Into Mercury. Mike Wall. Space News April 30, 2015.
7. Aron, Jacob (September 6, 2012). "Dawn departs Vesta to become first asteroid hopper". New Scientist. Archived from the original on September 7, 2012.
8. "DAWN – A Journey to the Beginning of the Solar System". Dawn Mission Timeline. Jet Propulsion Laboratory. Archived from the original on October 19, 2013.
9. Koch, David; Gould, Alan (March 2009). "Kepler Mission". NASA. Archived from the original on March 6, 2014.
10. NASA Staff. "Kepler Launch". NASA. Archived from the original on November 7, 2013.
11. Harwood, William (September 10, 2011). "NASA launches GRAIL lunar probes". CBS News. Archived from the original on September 11, 2011.
12. "About GRAIL MoonKAM". Sally Ride Science. 2010. Retrieved April 15, 2010.
13. "NASA Selects Investigations For Future Key Planetary Mission". NASA. Archived from the original on May 7, 2011.
14. "New NASA Mission to Take First Look Deep Inside Mars". NASA. August 20, 2012. Archived from the original on August 22, 2012.
15. Agle, DC; Webster, Guy; Brown, Dwayne (August 20, 2012). "New NASA Mission To take First Look Deep Inside Mars". Mars Exploration Program. JPL, NASA. Archived from the original on October 5, 2012.
16. Vastag, Brian (August 20, 2012). "NASA will send robot drill to Mars in 2016". The Washington Post.
17. "NASA Suspends 2016 Launch of InSight Mission to Mars". December 22, 2015.
18. "Deep Impact Heads to New Comet". Space.com. October 31, 2006. Archived from the original on November 2, 2006.
19. "Discovery Program - Strofolio". NASA. Archived from the original on March 1, 2011.
20. "3 Proposed Discovery Missions". National Space Science Data Center, NASA. Archived from the original on March 1, 2014.
21. "1994LPI 25..985N Page 985". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics. Retrieved February 28, 2014.
22. "NASA announces Discovery mission finalists". Space Today. January 4, 2001. Archived from the original on September 16, 2003.
23. "Space Missions Roster". Lunar and Planetary Laboratory. The University of Arizona. Archived from the original on March 13, 2014.
24. Elkins-Tanton, L.T.; Asphaug, E.; Bell, J.; Bercovici, D.; Bills, B.G.; Binzel, R.P.; Bottke, W.F.; Jun, I.; Marchi, S.; Oh, D.; Polanskey, C.A.; Weiss, B.P.; Wenkert, D.; Zuber, M.T. "Journey to a Metal World: Concept for a Discovery Mission to Psyche" (PDF). 45th Lunar and Planetary Science Conference (2014). Universities Space Research Association. Archived (PDF) from the original on February 27, 2014.
25. "Cosmic Dust - Messenger from Distant Worlds" (PDF). University Stuttgart. Archived (PDF) from the original on February 24, 2014.
26. "NASA Announces Discovery Program Selections". News Release. NASA. October 30, 2006. Archived from the original on June 29, 2009.
27. "OSIRIS-REx Factsheet" (PDF). University of Arizona. Archived (PDF) from the original on July 22, 2013.
28. Bassett, S.; Sears, D. W. G. "The Hera Mission: Meeting Discovery Class Mission Precedents for Education and Public Outreach" (PDF). Arkansas Centre for Space and Planetary Sciences. Archived (PDF) from the original on December 28, 2005.
29. Sears, Derek; Allen, Carl; Britt, Dan; Brownlee, Don; Franzen, Melissa; Gefert, Leon; Gorovan, Stephen; Pieters, Carle; Preble, Jeffrey; Scheeres, Dan; Scott, Ed (May 19, 2003). "The Hera Mission : Multiple Near-Earth Asteroid Sample Return" (PDF). Planetary Geosciences Group, Brown University. Archived (PDF) from the original on June 24, 2010.
30. Farquhar, Robert; Jen, Shao-Chiang; McAdams, Jim V. (September 12, 2000). "Extended-mission opportunities for a Discovery-class asteroid rendezvous mission". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics.
31. Sandford, Scott A.; A'Hearn, Michael; Allamandola, Louis J.; Britt, Daniel; Clark, Benton; Dworkin, Jason P.; Flynn, George; Glavin, Danny; Hanel, Robert; Hanner, Martha; Hörz, Fred; Keller, Lindsay; Messenger, Scott; Smith, Nicholas; Stadermann, Frank; Wade, Darren; Zinner, Ernst; Zolensky, Michael E. "The Comet Coma Rendezvous Sample Return" (PDF). Lunar and Planetary Institute. Archived (PDF) from the original on June 28, 2010.
32. Riedel, Joseph E.; Marrese-Reading, Colleen; Lee, Young H. (June 19, 2013). "A Low-Cost NEO Micro Hunter-Seeker Mission Concept" (PDF). Low-Cost Planetary Missions Conference, LCPM-10. California Institute of Technology. Archived (PDF) from the original on March 1, 2014.
33. Haberle, R. M.; Catling, D. C.; Chassefiere, E.; Forget, F.; Hourdin, F.; Leovy, C. B.; Magalhaes, J.; Mihalov, J.; Pommereau, J. P.; Murphy, J. R. "The Pascal Discovery Mission: A Mars Climate Network Mission". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics. Retrieved February 28, 2014.
34. "MUADEE: A Discovery-class mission for exploration of the upper atmosphere of Mars". Netherlands: Delft University of Technology. Retrieved February 28, 2014.
35. Colaprete, A.; Bellerose, J.; Andrews, D. "PCROSS - Phobos Close Rendezvous Observation Sensing Satellite". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics. Retrieved February 28, 2014.
36. Rivkin, A. S.; Chabot, N. L.; Murchie, S. L.; Eng, D.; Guo, Y.; Arvidson, R. E.; Trebi-Ollennu, A.; Seelos, F. P. "Merlin : Mars-Moon Exploration, Reconnaissance and Landed Investigation" (PDF). SETI. Archived (PDF) from the original on February 28, 2014.
37. Lee, Pascal; Hoftun, Christopher; Lorbe, Kira. "Phobos and Deimos: Robotic Exploration in Advance of Humans to mars Orbit" (PDF). Concepts and Approaches for Mars Exploration (2012). Lunar and Planetary Institute. Archived (PDF) from the original on March 1, 2014.
38. Lee, Pascal; Veverka, Joseph; Bellerose, Julie; Boucher, Marc; Boynton, John; Braham, Stephen; Gellert, Ralf; Hildebrand, Alan; Manzella, David; Mungas, Greg; Oleson, Steven; Richards, Robert; Thomas, Peter C.; West, Michael D. "HALL: A Phobos and Deimos Sample and Return Mission" (PDF). 41st Lunar and Planetary Science Conference (2010). Lunar and Planetary Institute. Archived (PDF) from the original on February 27, 2014.
39. Pieters, C.; Murchie, S.; Cheng, A.; Zolensky, M.; Schultz, P.; Clark, B.; Thomas, P.; Calvin, W.; McSween, H.; Yeomans, D.; McKay, D.; Clemett, S.; Gold, R. "ALADDIN - Phobos-Deimos sample return". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics.
40. Pieters, C.; Calvin, W.; Cheng, A.; Clark, B.; Clemett, S.; Gold, R.; McKay, D.; Murchie, S.; Mustard, J.; Papike, J.; Schultz, P.; Thomas, P.; Tuzzolino, A.; Yeomans, D.; Yoder, C.; Zolensky, M.; Barnouin-Jha, O.; Domingue, D. "ALADDIN: Exploration and Sample Return of Phobos and Deimos" (PDF). Lunar and Planetary Science. Lunar and Planetary Institute. Archived (PDF) from the original on September 5, 2004.
41. Landis, Geoffrey A.; Oleson, Steven J.; McGuire, Melissa (January 9, 2012), "Design Study for a Mars Geyser Hopper" (PDF), 50th AIAA Aerospace Sciences Conference, Glenn Research Center, NASA, retrieved July 1, 2012
42. "Mars Geyser-Hopper (AIAA2012)" (PDF). NASA Technical Reports. NASA. Retrieved February 28, 2014.
43. Ravine, M. A.; Malin, M. C.; Caplinger, M. A. "Mars Geoscience Imaging at Centimetre-Scale (MAGIC) from Orbit" (PDF). Concepts and Approaches for Mars Exploration (2012). Lunar and Planetary Institute. Archived (PDF) from the original on October 29, 2013.
44. "Red Dragon", Feasibility of a Dragon-derived Mars lander for scientific and human-precursor investigations (PDF), SpaceX, October 31, 2011, archived (PDF) from the original on June 16, 2012
45. Duke, M. B.; Clark, B. C.; Gamber, T.; Lucey, P. G.; Ryder, G.; Taylor, G. J. "Sample Return Mission to the South Pole Aitken Basin" (PDF). Workshop on New Views of the Moon II. Lunar and Planetary Institute. Archived (PDF) from the original on November 9, 2004.
46. "Robotics Institute: EXOMOON - A Discovery and Scout Mission Capabilities Expansion Concept". Robotics Institute, Carnegie Mellon University. June 15, 2011. Archived from the original on February 28, 2014.
47. Clarke, T. L. "Planetary System Occultation from Lunar Halo Orbit (PSOLHO): A Discovery Mission". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics. Retrieved February 28, 2014.
48. Klaus, K (October 24, 2012). "Concepts Leading to a Sustainable Architecture for Cislunar Development" (PDF). LEAG. Lunar and Planetary Institute. Archived (PDF) from the original on March 1, 2014.
49. Neal, C. R.; Banerdt, W. B.; Alkalai, L. "Lunette: A Two-Lander Discovery-Class Geophysics Mission to the Moon" (PDF). 42nd Lunar and Planetary Science Conference (2011). Lunar and Planetary Institute. Archived (PDF) from the original on March 1, 2014.
50. "Discovery Missions Under Consideration". Goddard Space Flight Centre, NASA. Archived from the original on March 1, 2014.
51. "Deep Impact: Five Discovery Mission Proposals Selected for Feasibility Studies". Deep Impact. Press Releases. University of Maryland. November 12, 1998. Archived from the original on June 20, 2002.
52. "NASA - Vesper Could Explore Earth's Fiery Twin". NASA. Archived from the original on August 23, 2007.
53. "The VESPER Mission to Venus". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics.
54. "Venus Sample Targeting, Attainment, and Return (V-STAR)" (PDF). 2007 NASA Academy at the Goddard Space Flight Center. The Henry Foundation. Archived (PDF) from the original on March 15, 2012.
55. Sweetser, Ted; Peterson, Craig; Nilsen, Erik; Gershman, Bob. "Venus Sample Return Missions - A Range of Science, A Range of Costs" (PDF). California Institute of Technology. Archived (PDF) from the original on May 26, 2010.
56. Klaasen, Kenneth; Greeley, Ronald (March 31, 2003). "VEVA Discovery mission to Venus: exploration of volcanoes and atmosphere". Science Direct.
57. Lorenz, Ralph D.; Mehoke, Doug; Hill, Stuart. "Venus Pathfinder: A Stand-Alone Long-Lived Venus Lander Mission Concept" (PDF). 8th International Planetary Probe Workshop (IPPW-8). National Institute of Aerospace. Archived (PDF) from the original on February 27, 2014.
58. Sharpton, V. L.; Herrick, R. R.; Rogers, F.; Waterman, S. "RAVEN - High-resolution Mapping of Venus within a Discovery Mission Budget". Astrophysics Data System. Harvard-Smithsonian Centre for Astrophysics. Retrieved February 28, 2014.
59. Baines, Kevin H.; Hall, Jeffery L.; Balint, Tibor; Kerzhanovich, Viktor; Hunter, Gary; Atreya, Sushil K.; Limaye, Sanjay S.; Zahnle, Kevin. "Exploring Venus with Balloons: Science Objectives and Mission Architectures for small and Medium-Class Missions" (PDF). Georgia Tech Library. Archived (PDF) from the original on February 27, 2014.
60. Landis, Geoffrey A.; LaMarre, Christopher; Colozza, Anthony (January 14, 2002). "NASA TM-2002-0819 : Atmospheric Flight on Venus". American Institute of Aeronautics and Astronautics, The Pennsylvania State University. CiteSeerX 10.1.1.195.172.
61. Discover 95 : MISSIONS TO THE MOON, SUN, VENUS AND A COMET PICKED FOR DISCOVERY - NASA
62. "Interlune-One: A Scientific Mission Across the Surface of the Moon (PDF Download Available)". Researchgate.net. Retrieved January 11, 2016.
63. "UA scientist seeking big bucks from NASA - Tucson Citizen Morgue, Part 2 (1993-2009)". Tucsoncitizen.com. January 27, 1995. Retrieved January 11, 2016.
64. "NASA Technical Reports Server (NTRS) - Venus Multiprobe Mission". Ntrs.nasa.gov. Retrieved January 11, 2016.
65. "STARDUST Selected as Discovery Flight". Stardust.jpl.nasa.gov. Retrieved January 11, 2016.
66. "Missions to Gather Solar Wind Samples and Tour Three Comets Selected as Next Discovery Program Flights" (TXT). Nssdc.gsfc.nasa.gov. Retrieved January 11, 2016.
67. "News from Space - LPIB 82". Lpi.usra.edu. September 30, 2002. Retrieved January 11, 2016.
68. "NASA Selects Missions to Mercury and a Comet's Interior as Next Discovery Flights". Nssdc.gsfc.nasa.gov. Retrieved January 11, 2016.
69. "Five Discovery Mission Proposals Selected For Feasibility Studies" (TXT). Nasa.gov. Retrieved January 11, 2016.
70. Susan Reichley (December 21, 2001). "2001 News Releases - JPL Asteroid Mission Gets Thumbs Up from NASA". Jpl.nasa.gov. Retrieved January 11, 2016.
71. "NASA announces Discovery mission finalists". Spacetoday.net. January 4, 2001. Retrieved January 11, 2016.
72. Richard StengerCNN.com Writer. "Space - NASA selects finalists for next Discovery mission - January 5, 2001". CNN.com. Retrieved January 11, 2016.
73. "NASA". Nasa.gov. Retrieved January 11, 2016.
74. "Science Analysis Support for NASA Discovery Program's Kepler Extended Mission | SETI Institute". Seti.org. Retrieved January 11, 2016.
75. "NASA aiming to look inside the moon - Technology & science - Space - Space.com". NBC News. September 6, 2011. Retrieved January 11, 2016.
76. Cain, Fraser. "Back to Venus with Vesper". Universe Today. Retrieved January 11, 2016.
77. Paolo Ulivi; David M. Harland (September 16, 2014). "Robotic Exploration of the Solar System: Part 4: The Modern Era 2004 –2013". Books.google.com. p. 349. Retrieved January 11, 2016.
78. "NASA - NASA Announces Discovery Program Selections". Nasa.gov. November 2, 2008. Retrieved January 11, 2016.
79. Jpl, Nasa (August 20, 2012). "Mars Mobile". Marsmobile.jpl.nasa.gov. Retrieved January 11, 2016.
80. "NASA Selects Investigations For Future Key Planetary Mission". NASA. Retrieved May 6, 2011.
81. Hand, Eric (September 2, 2011). "Venus scientists fear neglect". Nature. Archived from the original on May 26, 2012.
82. Kane, Van (February 20, 2014). "Boundaries for the Next Discovery Mission Selection". Future Planets. Archived from the original on March 7, 2014.
83. Stephen Clark. "NASA might pick two Discovery missions, but at a price". Spaceflight Now. Retrieved January 11, 2016.
84. Clark, Stephen (September 7, 2016). "NASA official says new mission selections on track despite InSight woes". Spaceflight Now. Retrieved September 8, 2016.
85. Clark, Stephen (February 24, 2014). "NASA receives proposals for new planetary science mission". Space Flight Now. Retrieved February 25, 2015.
86. Kane, Van (December 2, 2014). "Selecting the Next Creative Idea for Exploring the Solar System". Planetary Society. Retrieved February 10, 2015.
87. Brown, Dwayne C.; Cantillo, Laurie (September 30, 2015). "NASA Selects Investigations for Future Key Planetary Mission". NASA News. Washington, D.C. Retrieved October 1, 2015.
88. Dreier, Casey; Lakdawalla, Emily (September 30, 2015). "NASA announces five Discovery proposals selected for further study". The Planetary Society. Retrieved October 1, 2015.
89. "The DAVINCI spacecraft". Phys.org. Retrieved January 11, 2016.
90. "NASA Discovery Program Draft Announcement of Opportunity". NASA Science Mission Directorate. SpaceRef. February 19, 2014.
91. "Evaluation of Solar Electric Propulsion Technologies for Discovery-Class Missions". American Institute of Aeronautics and Astronautics. Retrieved February 28, 2014.
92. Clark, Stephen (March 3, 2015). "NASA eyes ion engines for Mars orbiter launching in 2022". Space Flight Now. Retrieved March 4, 2015.
93. "NASA Discovery Program Draft Announcement of Opportunity". SpaceRef. February 19, 2014.
94. Clark, Stephen (April 6, 2015). "Diverse destinations considered for new interplanetary probe". Space Flight Now. Retrieved April 7, 2015.
95. "NASA Drops Laser Comm Requirement From Discovery Solicitation". SpaceNews.com. November 5, 2014. Retrieved January 11, 2016.
96. NASA Drops Laser Comm Requirement From Discovery Solicitation. Space News, Dan Leone. November 5, 2014
97. "NASA Sorting Through Latest Discovery Proposals". Spacenews.com. February 23, 2015. Retrieved January 11, 2016.
98. Enceladus life finder: the search for life in a habitable moon. Geophysical Research Abstracts. Vol. 17, EGU2015-14923, 2015 EGU General Assembly 2015.
99. Kane, Van (April 3, 2014). "Discovery Missions for an Icy Moon with Active Plumes". The Planetary Society. Retrieved April 9, 2015.
100. LIFE: Life Investigation For Enceladus: A Sample Return Mission Concept in Search for Evidence of Life. Astrobiology Volume 12, Number 8, 2012 DOI: 10.1089/ast.2011.0813
101. Io Volcano Observer (IVO). Geophysical Research Abstracts, Vol. 11, EGU2009-6448-1, 2009. EGU General Assembly 2009.
102. John F. Mustard; Scott L. Murchie; Andrew S. Rivkin; Douglas A. Eng; Elena Y. Adams; Patrick N. Peplowski; David J. Lawrence; Goestar Klingelhoefer (June 9–11, 2015). The Advanced Jovian Asteroid Explorer (PDF). 11th Low Cost Planetary Missions Conference.
103. RAVEN - High-resolution Mapping of Venus within a Discovery Mission Budget
104. Venus Atmosphere and Surface Explorer. American Astronomical Society, DPS meeting #46, #214.15 (2014)
105. MERLIN: The Creative Choices Behind a Proposal to Explore the Martian Moons (Merlin and PADME info also)
106. Phobos And Deimos & Mars Environment (PADME). 45th Lunar and Planetary Science Conference (2014).
107. McKay, Christopher P.; Stoker, Carol R.; Glass, Brian J.; Davé, Arwen I.; Davila, Alfonso F.; Heldmann, Jennifer L.; Marinova, Margarita M.; Fairen, Alberto G.; Quinn, Richard C.; Zacny, Kris A.; Paulsen, Gale; Smith, Peter H.; Parro, Victor; Andersen, Dale T.; Hecht, Michael H.; Lacelle, Denis; Pollard, Wayne H. (April 5, 2013). "The Icebreaker Life Mission to Mars: A Search for Biomolecular Evidence for Life". Astrobiology. 13 (4): 334–353. Bibcode:2013AsBio..13..334M. doi:10.1089/ast.2012.0878. PMID 23560417.
108. Choi, Charles Q. (May 16, 2013). "Icebreaker Life Mission". Astrobiology Magazine. Archived from the original on August 15, 2013.
109. McKay, C. P.; Stoker, Carol R.; Glass, Brian J.; Davé, Arwen I.; Davila, Alfonso F.; Heldmann, Jennifer L.; Marinova, Margarita M.; Fairen, Alberto G.; Quinn, Richard C.; Zacny, Kris A.; Paulsen, Gale; Smith, Peter H.; Parro, Victor; Andersen, Dale T.; Hecht, Michael H.; Lacelle, Denis; Pollard, Wayne H. (2012), "The Icebreaker Life Mission to Mars: A Search for Biochemical Evidence for Life", Concepts and Approaches for Mars Exploration (PDF), Lunar and Planetary Institute, archived (PDF) from the original on December 3, 2013
110. Binary Asteroid in-situ Explorer Mission (BASiX): A Mission Concept to Explore a Binary Near Earth Asteroid System. 45th Lunar and Planetary Science Conference (2014)
111. Dark Asteroid Rendezvous (DARe). 46th Lunar and Planetary Science Conference (2015)
112. jobs (March 16, 2015). "Five Solar System sights NASA should visit : Nature News & Comment". Nature.com. Retrieved January 11, 2016.
113. JOURNEY TO A METAL WORLD: CONCEPT FOR A DISCOVERY MISSION TO PSYCHE. (PDF) 45th Lunar and Planetary Science Conference (2014)
114. "Dating moon rocks accurately with new design mass spectrometer - News". SpectroscopyNOW.com. July 22, 2015. Retrieved January 11, 2016.
115. Hurlbert, Eric; Morehead, Robert; Melcher, John C.; Atwell, Matt (2016). Integrated Pressure-Fed Liquid Oxygen / Methane Propulsion Systems – Morpheus Experience, MARE, and Future Applications (PDF). NASA CASI. NASA Johnson Space Center.
116. "PROTEUS – A MISSION TO INVESTIGATE THE ORIGIN OF EARTH'S WATER: CREATING HABITABLE WORLDS" (PDF). Astrobiology Science Conference 2015. Retrieved January 11, 2016.
117. "Kuiper : A Discovery-Class Observatory for Outer Solar System Giant Planets, Satellites, & Small Bodies" (PDF). Lpi.usra.edu. Retrieved January 11, 2016.

External links

• Official NASA website for Discovery Program
• Official NASA website for Discovery & New Frontiers Programs Office