6.1 Introduction

The Neutral Interstellar gas Composition Experiment NICE is an instrument that would allow a direct measurement of interstellar neutral hydrogen and oxygen for the first time. Physical properties of the local interstellar gas (LISG), such as density, temperature, and velocity vector of oxygen and hydrogen, respectively could be measured. This would allow us to directly address questions such as

• What is the structure of the heliosphere?
• How do the sun and the galaxy affect the dynamics of the heliosphere?
• What is the nature of the nearby interstellar medium?
• How did matter in the solar system and the interstellar medium originate and evolve?

Different missions proposed under NASAs Quest 3 program - How do the Sun and Galaxy interact? - are suitable for such an instrument:

Mission	Start	Distance
Interstellar Pathfinder	2004	1-3AU
Interstellar Probe	2010	200AU (400AU)
Interstellar Composition Observatory	2020	300AU (500AU)

A NICE type instrument on the Interstellar Pathfinder mission would do sampling of the neutral interstellar gas from an orbit relatively close to the sun (see proposal in [34]). The other two missions will explore the interstellar medium directly. Using advanced solar sail propulsion these spacecraft are planned to be sent to distances of more than 200AU in less than 15 years. A NICE type sensor on these missions would allow for an in situ measurement of the neutral interstellar gas.

The main purpose of the test setup was to demonstrate the performance of a complete neutral particle instrument by doing an end-to-end test. Neutral oxygen atoms in the energy range of 30300eV were produced in a beam neutralization unit from ions provided by the CASYMS ion source. In the NICE sensor these neutrals were negatively ionized upon reflection from a conversion surface. The negative ions were then accelerated in an extraction lens into a time-of-flight section allowing for the unambiguous discrimination between intrinsic background, sputtered ions, and converted primary neutral particles.