U.S.-Russian Team Studying a Joint Solar Probe Mission

A group of U.S. scientists and engineers are traveling to Moscow the week of March 27, 1995 for technical discussions with their Russian counterparts interested in the Mars Together and Fire and Ice missions. The group includes five JPL employees, who will exchange information on the current status and future study plans for the Fire/Solar Probe study.

NASA and the Russian Space Agency (RSA) recommendations on several solar system exploration cooperative studies for robotic missions were endorsed at the December, 1994, Gore-Chernomyrdin Commission meeting in Moscow. In particular, NASA and the RSA were directed to continue studying the feasibility of cooperating on robotic missions to explore the solar system, "solar system together," and to report their findings at the next joint Commission meeting to be held again in Moscow in the June-July, 1995, timeframe.

The first of the potential cooperative programs under study is a possible joint robotic missions for Mars exploration. The second is a concept in which the two countries would explore together the extreme ends of the solar system: the Sun at the center and Pluto at the outer boundary, ÒFire and Ice.Ó The two sides agreed that all such planning should take into consideration the appropriate budgetary and financial constraints.

The initial findings from the Mars Together and Fire and Ice technical study teams were presented on October 25, 1994 to Dr. Wes Huntress, Associate Administrator for Space Science at NASA. The presentation included the recommendation from the Fire and Ice Team that the study of a joint solar probe mission with Russia should be continued, with a near-term focus on instrument concept/feasibility studies, a near-Sun environment workshop, a near-sun science workshop, and a joint engineering development study team.

The report was based on the findings from an intense, six-month assessment of the technical feasibility of joint U.S.-Russian Fire (solar probe) and Ice (Pluto Flyby) missions. The study team was co-chaired by Dr. Charles Elachi of the Jet Propulsion Laboratory (JPL) and Academecian Albert Galeev of the Institute for Space Research (IKI) in Moscow. It was chartered by Huntress and Dr. Yuri Milov, Deputy Director of the Russian Space Agency in April, 1994, when Huntress led a delegation of U.S. space planners to Moscow for the purpose of reacquainting the Russians with NASA interest in possible joint missions to Mars, Pluto, and the Sun. The Russian side, led by Milov, was also anxious to explore joint mission possibilities with the U.S. The vision that emerged was of the U.S. and Russia, long rivals in space, joining forces to explore Mars and the ends of the solar system.

The Fire and Ice missions will for the first time explore two extreme regions of our solar system. The dual-spacecraft Fire (Solar Probe) mission will provide both in-situ and imaging measurements near the Sun, whereas the Ice mission (to Pluto) will Òfly byÓ the last unexplored planet at the outer limit of our solar system. The scientific goal of the solar probe is to investigate the origin of both the solar corona and the solar wind. The solar wind outflowing from the corona creates the heliosphere and influences the entire solar system, including the Earth. The processes of solar coronal heating and the solar wind acceleration have defied explanation by remote sensing observations, but in-situ measurement of the plasma characteristics at small distances from the Sun should identify the responsible physical mechanisms.

Fire will perform measurements along two quasi-parabolic polar trajectories around the sun: both have perihelion near the solar equator, one at four solar radii and the other at ten solar radii. These trajectories will provide crucial in-situ measurements, as a function of both latitude and distance from the sun, in the polar coronal hole regions where the fast solar wind is accelerated, across boundaries of the holes (plumes?), and in the streamer belt. Close imaging of the corona and disk at high latitude angles should untangle the projection effects that plague us here in the ecliptic when we try to understand the solar corona. The in-situ-imaging combination would provide a "ground truth" for physical interpretations of high-resolution solar observations from earth. Perihelion is planned to be over the west limb.

The currently preferred option for the Fire mission is two spacecraft, one Russian and one American, launched by a single Russian Proton with a U.S. Star 48 final stage. After launch the two spacecraft separate and independently use a Jupiter gravity assist to place them on their trajectories to perihelion at, respectively, four solar radii for the U.S. spacecraft and ten solar radii for the Russian spacecraft. The payload on the U.S. spacecraft will emphasize in-situ plasma measurements and coronal imaging excluding the solar disk, while those on the Russian spacecraft will emphasize in-situ plasma measurements and remote disk imaging to provide the global context for the two-level in-situ measurements.

The ground rules established by the Huntress-Milov agreement were that: (1) these would be strictly cooperative projects with no exchange of funds; (2) the collaboration would advance the established goals of each country; and (3) on the U.S. side, the Mars Together activity must stay within the approved budget line item of the Mars Surveyor program. Each country is developing a backup plan to pursue the solar probe objectives alone if the other side is unable to carry out its mission. A US-only option would have to be a very focussed, small, and inexpensive pathfinder-type spacecraft.