NASA picked four missions today that later will be narrowed to two for its Small Explorer (SMEX) program and Missions of Opportunity (MO). These comparatively inexpensive missions can still provide a substantial science return. The four chosen today will study volatile stars, galaxies and cosmic collisions.

SMEX and MO are both part of NASA’s Explorer program, which is managed by Goddard Space Flight Center. Explorer dates back to the very beginning of the space program. Explorer 1, launched in 1958, led to the discovery of the Van Allen Belts of radiation that encircle Earth. More than 90 Explorers have been launched since then, including the Cosmic Background Explorer (COBE) that earned Nobel Prizes for NASA-Goddard’s John Mather and Lawrence Berkeley National Lab’s George Smoot for mapping the primordial hot and cold spots in the cosmic microwave background radiation.

SMEX missions are cost capped at $145 million and MOs at $75 million, not including launch. The two SMEX missions will each receive $2 million for 9-month mission concept studies, while each of the two MOs will get $500,000 for implementation concept studies. Then one of each will be selected for development.

NASA Astrophysics Division Director Paul Hertz said today that “With the high science rewards for low dollar amounts, Explorer missions successfully fill the scientific gaps in our current fleet of space observatories.”

The two SMEX missions and their Principal Investigators (PIs) are:

The Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) Mission. PI: Kevin France, University of Colorado at Boulder. ESCAPE would study rapid, strong ultraviolet flares from nearby stars.

PI: Kevin France, University of Colorado at Boulder. ESCAPE would study rapid, strong ultraviolet flares from nearby stars. The Compton Spectrometer and Imager (COSI). PI: John Tomsick, University of California, Berkeley. COSI would scan the Milky Way and measure gamma rays produced during stellar explosions.

The two MOs and their PIs are:

The Gravitational-wave Ultraviolet Counterpart Imager Mission. PI: Stephen (Brad) Cenko, NASA Goddard Space Flight Center, Greenbelt, Maryland. This mission would use two shoebox-size satellites in Earth orbit to scan the sky in ultraviolet wavelengths.

PI: Stephen (Brad) Cenko, NASA Goddard Space Flight Center, Greenbelt, Maryland. This mission would use two shoebox-size satellites in Earth orbit to scan the sky in ultraviolet wavelengths. LEAP – A LargE Area burst Polarimeter. PI: Mark McConnell, University of New Hampshire, Durham. LEAP would be mounted on the International Space Station to study the polarization of gamma ray bursts.

NASA Science Mission Directorate head Thomas Zurbuchen tweeted short videos with the PIs of each mission describing what they will do.

COSI would scan our Milky Way galaxy, measuring gamma rays from radioactive elements produced during stellar explosions to map the recent history of star death and element production. Congratulations John Tomsick and his team at @UCBerkeley! pic.twitter.com/Wb2MfFdYKz — Thomas Zurbuchen (@Dr_ThomasZ) March 16, 2020