In the first step of a two step process, NASA has selected five proposals for detailed study as candidates fir the next mission in the Agency’s Discovery Programme of lower-cost, highly focussed scientific spacecraft.

In a unique step for this programme, NASA has also decided to fund a co-investigator to provide part of an instrument to study the interaction between the solar wind and the atmosphere of Mars. It is scheduled to fly aboard the European Space Agency’s Mars Express spacecraft in 2003. NASA plans to consider such investigations, categorised as "Missions of Opportunity" in all future Discovery and Explorer programme Announcements of Opportunity.

The mission proposals selected for further study would send spacecraft to orbit Mercury, return samples of two small moons of Mars to Earth, study the interior of Jupiter, excavate and study material from deep inside a comet nucleus and investigate the middle atmosphere of Venus.

The five missions were among 26 full mission proposals submitted to NASA. "The degree of innovation in these proposals climbs higher each time we solicit ideas," says Dr. Ed Weiler, Acting Associate Administrator for Space Science at NASA Headquarters. "Deciding which one or two of these exciting finalists will be fully developed will be a very difficult choice -–any one of them promises to return unique insights into our Solar System. Meanwhile, the solar wind instrument will fill in some critical gaps in our understanding of water on Mars."

Following detailed mission concept studies, which are due for submission by March 13, 1999, NASA intends to select one or two of the mission proposals in June 1999 for full development as the seventh and possibly eighth Discovery Programme flights.

The selected proposals are judged to have the best science value among 30 total proposals submitted to NASA in response to the Discovery Announcement of Opportunity (AO-98-OSS-04) issued on March 31,1998. Each will now receive $375 000 to conduct four-month implementation feasibility studies focused on cost, management and technical plans, including small business involvement and educational outreach. As stated in the AO, the initial mission cost estimates will not be allowed to grow by more than 20 percent in detailed final proposals.

The selected proposals are:

Aladdin, a mission to gather samples of small Martian moons Phobos and Deimos by firing projectiles into the moons’ surfaces and gathering the ejecta during slow flybys. It would then return the samples to Earth for detailed study. Aladdin would be led by Dr. Carle Pieters of Brown University in Providence, RI, at a total mission cost to NASA, including launch vehicle and operations, of $247.7 million

Deep Impact, a flyby mission designed to fire a 1 100 pound (500 kg) copper projectile into the comet P/Temple 1, excavating a large crater more than 65 feet (20 meters) deep, in order to expose its pristine interior ice and rock. Deep Impact would be led by Dr. Michael A’Hearn of the University of Maryland, College Park, at a total cost of $203.8 million.

The Interior Structure and Internal Dynamic Evolution of Jupiter, or INSIDE Jupiter, an orbiter spacecraft to study the giant gas planet’s interior, and its relationship to the atmosphere, through intensive measurements of Jupiter’s gravitational and magnetic fields. INSIDE Jupiter would be led by Dr. Edward Smith of NASA’s Jet Propulsion Laboratory, Pasadena, CA, at a total cost of $227.3 million.

The Mercury Surface, Space Experiment, Geochemistry and Ranging mission, or Messenger, an orbiter spacecraft carrying seven instruments to globally image and study the closest planet to the Sun. Messenger would be led by Dr. Sean Solomon of the Carnegie Institution, Washington, DC at a total cost of $279.3 million.

the Venus Sounder for Planetary Exploration, or Vesper, an orbiter with four instruments to measure the composition and dynamic circulation of the middle of the middle atmosphere of Venus and its similarities to processes in the Earth’s atmosphere. Vesper would be led by Dr. Gordon Chin of NASA’s Goddard Space Flight Centre, Greenbelt, MD, at a total cost of $195.8 million.

Aladdin and Messenger were finalists in the previous round of Discovery Programme mission selections in 1997.

The solar wind science hardware to be built as part of the selected Mission of Opportunity is intended for an instrument called the Analyser of Space Plasmas and Energetic Atoms, or ASPERA-3. The principal investigator for this instrument is Dr. R Lundin of the Swedish Institute of Space Physics in Kiruna, Sweden. The co-investigator being funded by NASA is Dr. David Winningham of the Southwest Research Institute, San Antonio, TX. NASA will provide approximately $5.3 million for the electron and ion spectrometer to be prepared for launch in 2003 aboard the Mars Express mission.

The investigations proposed in response to this AO were required to address the goals and objectives of the Office of Space Science’s Solar Exploration theme, or the search for extrasolar planetary systems element of the Astronomical Search for Origins theme. The missions must be ready for launch no later than Sept. 30, 2004, within the Discovery Programme’s development cost cap of $190 million in Fiscal 1999 dollars over 36 months, and a total mission cost of $299 million.

The next launch of a Discovery mission is scheduled for Feb. 6, 1999, when the Stardust mission will be sent on its wayto gather a sample of comet dust and return it to Earth in January 2006. The first Discovery mission, the Near Earth Asteroid Rendezvous (NEAR) spacecraft, is due to arrive at its target asteroid, 433 Eros, on Jan. 10 1999, for at least a year of close-up observations from an orbit around the Manhattan-sized body.