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Solar Orbiter is scheduled to launch in January 2017, and will carry as part of its payload the Heavy Ion Sensor (HIS), one of the components of the Solar Wind Analyzer (SWA) instrument suite. Heavy ions of particular interest are Ne, Mg, Si, and S which have been difficult to measure in the past due to their similar mass per charge ratios in the solar wind. We have characterized the response of HIS to these species using a Monte Carlo simulation of the instrument. These simulations use a realistic count rate and account for lost energy and angular scattering of ions passing through a carbon foil, time-of-flight of the secondary electrons, and the pulse height defect within the solid-state detectors. Our results show that HIS is capable of resolving the masses and charge-states of solar wind ions, such as He, C, O, Ne, Mg, and Fe. Results also show that there is some overlap between S and Si, but it is likely that we will be able resolve these ions by integrating these measurements over longer time periods.

SERENA (‘Search for Exospheric Refilling and Emitted Natural Abundances’) is an instrument package that will fly on board the BepiColombo Mercury Planetary Orbiter (MPO); it will investigate the Mercury’s complex particle environment that surrounds the planet. Such an environment is composed by thermal and directional neutral atoms (exosphere) originating via surface release and charge‐exchange processes, and by ionized particles originated through photo‐ionization and again by surface release processes. In order to accomplish the scientific goals, in‐situ analysis of the environmental elements is necessary, and for such a purpose the SERENA instrument shall include four units: two Neutral Particle Analyzers (ELENA and STROFIO) and two Ion Spectrometers (MIPA and PICAM). The scientific merit of SERENA is presented, and the basic characteristics of the four units are described, with a focus on novel technological aspects.

The Interstellar Boundary Explorer (IBEX) mission will make the first global observations of the heliosphere’s interaction with the interstellar medium. IBEX achieves these breakthrough observations by traveling outside of the Earth’s magnetosphere in a highly elliptical orbit and taking global Energetic Neutral Atoms (ENA) images over energies from ∼10 eV to 6 keV. IBEX’s high‐apogee (∼50 RE) orbit enables heliospheric ENA measurements by providing viewing from far above the Earth’s relatively bright magnetospheric ENA emissions. This high energy orbit is achieved from a Pegasus XL launch vehicle by adding the propulsion from an IBEX‐supplied solid rocket motor and the spacecraft’s hydrazine propulsion system. IBEX carries two very large‐aperture, single‐pixel ENA cameras that view perpendicular to the spacecraft’s Sun‐pointed spin axis. Each six months, the continuous spinning of the spacecraft and periodic re‐pointing to maintain the sun‐pointing spin axis naturally lead to global, all‐sky images. Over the course of our NASA Phase B program, the IBEX team optimized the designs of all subsystems. In this paper we summarize several significant advances in both IBEX sensors, our expected signal to noise (and background), and our groundbreaking approach to achieve a very high‐altitude orbit from a Pegasus launch vehicle for the first time. IBEX is in full scale development and on track for launch in June of 2008.

The Interstellar Boundary Explorer (IBEX) is one of five Small Explorer (SMEX) missions undergoing Phase A study for NASA’s Office of Space Science. Around November 2004, NASA expects to select at least one of missions for development and flight. If selected, IBEX will provide the first global views of the Sun’s interstellar boundaries by taking a set of global energetic neutral atom (ENA) images at a variety of energies. Recent advances in ENA imaging have made it possible to remotely image space plasmas and ENA imaging is now poised to image the interstellar interactions and interstellar boundaries at the edge of our heliosphere. IBEX makes these exploratory ENA observations using two ultra‐high sensitivity ENA cameras on a simple spinning spacecraft. IBEX’s highly elliptical Earth orbit allows viewing of the outer heliosphere from beyond the Earth’s relatively bright magnetospheric ENA emissions. IBEX’s sole, focused science objective is to discover the global interaction between the solar wind and the interstellar medium. IBEX achieves this objective by answering four fundamental science questions: (1) What is the global strength and structure of the termination shock? (2) How are energetic protons accelerated at the termination shock? (3) What are the global properties of the solar wind flow beyond the termination shock and in the heliotail? and (4) How does the interstellar flow interact with the heliosphere beyond the heliopause? The IBEX objective is central to the Sun‐Earth Connection (SEC) theme as demonstrated by both the 2003 SEC Roadmap and 2002 NRC’s Decadal Survey and is specifically identified in the 2003 NASA‐wide Strategic Plan. In short, the IBEX mission provides the first global views of the Sun’s interstellar boundaries, unveiling the physics of the heliosphere’s interstellar interaction, providing a deeper understanding of the heliosphere and thereby astrospheres throughout the galaxy, and creating the opportunity to make even greater unanticipated discoveries.

Direct detection of interstellar neutrals is a powerful technique for enlarging our knowledge about the media surrounding our solar system. We present in this paper a combination of two telescopes and a pointing device that would enable precise and detailed measurements of the density, velocity, temperature, and composition of the neutral particles that penetrate through the heliospheric bow shock and the heliopause.

Interstellar Pathfinder (ISP), our first step into the interstellar medium, is a scientific investigation to study the outer boundary of our heliosphere and the interstellar matter that flows into it. A wind of interstellar neutral gas penetrates to within several astronomical units (AU) of the Sun, giving us a direct sample of present‐day galactic matter. ISP is a mission to this inner edge of the interstellar medium. Using highly sensitive instrumentation, ISP will determine the composition of our local interstellar environment. It will also take the first global images of the boundary region of the heliosphere at 100 to 150 AU. These measurements will allow ISP to answer fundamental questions about the origin of the solar system and the stars, about the evolution of our galaxy and of the universe, and about the characteristics of our local galactic environment and its influence on the heliosphere.

In the course of this decade, two NASA deep space mission to the inner and outer heliosphere, MESSENGER to the planet Mercury and New Horizons to the planet Pluto, will carry onboard energetic particle spectrometers. The combination of measurements near the Sun (0.3 AU), and from the outer heliosphere (up to almost 40 AU), will ideally complement the information available from Ulysses and from near‐Earth orbiting spacecraft, yielding boundary conditions on the processes that accelerate energetic particles. EPS is a hockey‐puck‐size Time‐of‐Flight (ToF) spectrometer that measures ions and electrons over a broad range of energies and pitch angles. Particle composition and energy spectra will be measured for H to Fe from 15 keV/nucleon to 3 MeV/nucleon and for electrons from 15 keV to 1 MeV. The ion section of EPS is a compact ToF telescope with two main components: a ToF section and a Solid State Detector (SSD) array to measure separately velocity and total energy of the incoming particles. Electrons are identified in EPS by the presence of an energy signal and by the absence of start or stop pulses, since energetic electrons have low efficiency for production of secondary electrons when passing through thin foils. For both ions and electrons the angle of arrival is determined by the position of the solid‐state detector that collects the particle.

We analyse three-dimensional distribution functions of solar wind alpha particles in velocity space and study their symmetry properties relative to the interplanetary magnetic field. We present convincing evidence for the occurrence of non-gyrotropic alpha-particle velocity distribution functions in the solar wind plasma. The three-dimensional distributions are obtained by measurements with high resolution (8 s for alpha particles and 2 s for protons) of the plasma experiment TAUS on the PHOBOS II mission to planet Mars. The measurements were made at heliocentric distances near 1.3 AU. In a detailed analysis of the distributions we show that non-gyrotropic features are related to a sizable fraction of phase space density in the alpha-particle distributions. These non-gyrotropic particles can be characterised as being gyro-phase bunched in velocity space. There are indications of a close relation between the non-gyrotropy of the core particles of a distribution and the large core temperature anisotropies (...