JIMO, Prometheus, and Geospace

John F. Cooper
Space Physics Data Facility
Laboratory for Solar and Space Physics
NASA Goddard Space Flight Center

In 2002 the National Research Council's Solar System Decadal Survey 
identified Europa as the highest priority destination for a flagship 
mission. NASA created the Prometheus program to implement nuclear-powered 
spacecraft for deep space missions with a main initial focus on the outer 
solar system, and the Jupiter Icy Moons Orbiter (JIMO) was defined as the 
first Prometheus mission to meet the science consensus on Europa as the 
highest priority. The JIMO Science Definition Team considered the new 
capabilities to be provided by the unprecedented power, data rate, and mass 
available for the science payload of the JIMO spacecraft. Overarching 
objectives were the definitive survey of subsurface oceans and related 
surface composition on the icy Galilean moons,  the search for signs of 
life on Europa, and, very importantly for space physics, the study of 
relations between these moons and the Jupiter system including 
gravitational, magnetospheric, atmospheric, and ionospheric interactions. 
Beyond the more limited capabilities of orbital tour missions such as 
Galileo and Cassini/Huygens, the Prometheus-class spacecraft offered this 
prospect of full surveys for moon and ring systems of giant planets from 
Jupiter to Neptune, as well as of  extended tours for small interplanetary 
bodies from asteroids to the Kuiper Belt. Two Goddard teams within the 
now-designated Laboratory for Solar and Space Physics have been involved in 
development of high capability instruments intended for Prometheus 
missions, and such instruments will certainly be needed to fulfill the 
science promise and justify the high cost of such missions. High power ion 
propulsion could also offer the very practical benefit of saving the Earth 
from future catastrophic impacts, and future Prometheus missions might be 
used to test such capabilities. Although engineering and budget realities 
have deferred a mission to Europa by JIMO, the Prometheus program goes on 
and is now focused on a precursor mission, that would operate partly or 
wholly in geospace. Such a mission might properly be called the Prometheus 
Geospace Explorer and could, in an analogous manner as planned for JIMO at 
Jupiter, investigate the Earth-Moon-Magnetosphere system and the local 
interplanetary environment with higher capability instruments than 
previously available on geospace missions, while also testing new 
engineering and science technologies for exploration of the solar system. A 
suborbital test of one such instrument, the Planetary Advanced Radio 
Sounder, is now suggested for a high-altitude balloon flight over 
Antarctica during the International Polar Year. Another, a neutral atom and 
pickup ion imaging spectrometer, could measure compositional abundances of 
Earth atmospheric outflow, the lunar surface, the local solar wind 
environment, and distant heliospheric sources at high resolution. 
Revolutionary advances could also be expected for planetary x-ray 
spectroscopy, laser-based systems for compositional analysis, and other 
high capability measurements in geospace and beyond.