Atom interferometers have a multitude of proposed applications in space including precise measurements of the Earth’s gravitational field, in navigation & ranging, and in fundamental physics such as tests of the weak equivalence principle (WEP) and gravitational wave detection. While atom interferometers are realized routinely in ground-based laboratories, current efforts aim at the development of a space compatible design optimized with respect to dimensions, weight, power consumption, mechanical robustness and radiation hardness. In this paper, we present a design of a high-sensitivity differential dual species 85 Rb/ 87 Rb atom interferometer for space, including physics package, laser system, electronics and software. The physics package comprises the atom source consisting of dispensers and a 2D magneto-optical trap (MOT), the science chamber with a 3D-MOT, a magnetic trap based on an atom chip and an optical dipole trap (ODT) used for Bose-Einstein condensate (BEC) creation and interferometry, the detection unit, the vacuum system for 10 −11 mbar ultra-high vacuum generation, and the high-suppression factor magnetic shielding as well as the thermal control system. The laser system is based on a hybrid approach using fiber-based telecom components and high-power laser diode technology and includes all laser sources for 2D-MOT, 3D-MOT, ODT, interferometry and detection. Manipulation and switching of the laser beams is carried out on an optical bench using Zerodur bonding technology. The instrument consists of 9 units with an overall mass of 221 kg, an average power consumption of 608 W (814 W peak), and a volume of 470 liters which would well fit on a satellite to be launched with a Soyuz rocket, as system studies have shown.

The theory of general relativity describes macroscopic phenomena driven by the influence of gravity while quantum mechanics brilliantly accounts for microscopic effects. Despite their tremendous individual success, a complete unification of fundamental interactions is missing and remains one of the most challenging and important quests in modern theoretical physics. The spacetime explorer and quantum equivalence principle space test satellite mission, proposed as a medium-size mission within the Cosmic Vision program of the European Space Agency (ESA), aims for testing general relativity with high precision in two experiments by performing a measurement of the gravitational redshift of the Sun and the Moon by comparing terrestrial clocks, and by performing a test of the universality of free fall of matter waves in the gravitational field of Earth comparing the trajectory of two Bose–Einstein condensates of 85Rb and 87Rb. The two ultracold atom clouds are monitored very precisely thanks to techniques of atom interferometry. This allows to reach down to an uncertainty in the Eötvös parameter of at least 2 × 10−15. In this paper, we report about the results of the phase A mission study of the atom interferometer instrument covering the description of the main payload elements, the atomic source concept, and the systematic error sources.

The theory of general relativity describes macroscopic phenomena driven by the influence of gravity while quantum mechanics brilliantly accounts for microscopic effects. Despite their tremendous individual success, a complete unification of fundamental interactions is missing and remains one of the most challenging and important quests in modern theoretical physics. The spacetime explorer and quantum equivalence principle space test satellite mission, proposed as a medium-size mission within the Cosmic Vision program of the European Space Agency (ESA), aims for testing general relativity with high precision in two experiments by performing a measurement of the gravitational redshift of the Sun and the Moon by comparing terrestrial clocks, and by performing a test of the universality of free fall of matter waves in the gravitational field of Earth comparing the trajectory of two Bose–Einstein condensates of 85 Rb and 87 Rb. The two ultracold atom clouds are monitored very precisely thanks to techniques of atom interferometry. This allows to reach down to an uncertainty in the E¨otv¨os parameter of at least 2 × 10 − 15 . In this paper, we report about the results of the phase A mission study of the atom interferometer instrument covering the description of the main payload elements, the atomic source concept, and the systematic error sources.

The "Ice Giants" Uranus and Neptune are a different class of planet compared to Jupiter and Saturn. Studying these objects is important for furthering our understanding of the formation and evolution of the planets, and unravelling the fundamental physical and chemical processes in the Solar System. The importance of filling these gaps in our knowledge of the Solar System is particularly acute when trying to apply our understanding to the numerous planetary systems that have been discovered around other stars. The Uranus Pathfinder (UP) mission thus represents the quintessential aspects of the objectives of the European planetary community as expressed in ESA's Cosmic Vision 2015–2025. UP was proposed to the European Space Agency's M3 call for medium-class missions in 2010 and proposed to be the first orbiter of an Ice Giant planet. As the most accessible Ice Giant within the M-class mission envelope Uranus was identified as the mission target. Although not selected for this call the UP mission concept provides a baseline framework for the exploration of Uranus with existing low-cost platforms and underlines the need to develop power sources suitable for the outer Solar System. The UP science case is based around exploring the origins, evolution, and processes at work in Ice Giant planetary systems. Three broad themes were identified: (1) Uranus as an Ice Giant, (2) An Ice Giant planetary system, and (3) An asymmetric magnetosphere. Due to the long interplanetary transfer from Earth to Uranus a significant cruise-phase science theme was also developed. The UP mission concept calls for the use of a Mars Express/Rosetta-type platform to launch on a Soyuz–Fregat in 2021 and entering into an eccentric polar orbit around Uranus in the 2036–2037 timeframe. The science payload has a strong heritage in Europe and beyond and requires no significant technology developments.

One very cost-effective route into orbit is as an Auxiliary Microsatellite on the ASAP-5 structure. All planned flights of the ASAP-5 structure are into GTO. The Advanced Microsatellite Mission study carried out within the ESA General Studies Programme addressed the feasibility of a deep space mission starting from this point.One of the major configuration drivers in the ASAP-5 launch envelope is the available volume. Low density non-deployable equipment (tanks, star sensor baffles etc.) become design drivers. Optimisation for power and volume has led to an Attitude Control System architecture which is gyro-based (using the latest high performance MEMS devices) making use of opportunistic calibration by minimally baffled star sensors.Solar Electric propulsion appears the leading candidate for missions requiring large DeltaV. There has historically been a quest for every higher values of I-sp for SEP thrusters, but it is shown that a full mission-level tradeoff taking into account the restricted power availability on this class of spacecraft often leads to a lower value of I-sp in order to minimise operations costs and improve the timeliness of scientific observations.It is concluded that useful deep space missions can be performed by a spacecraft complying with the ASAP-5 constraints.

As the third medium-class mission in the ESA's Horison 2000 science programme, a Moon Orbiting Observatory (MORO) was proposed for global mapping of lunar topography, mineralogy, geochemistry and gravity. The growing need to reduce the cost of the space missions led the study team to look for several approaches to limit the costs. It was decided therefore to study in parallel to the baseline a smallsat version of MORO which would just address the most important scientific issues in complement to Clementine, Lunar Prospector and Lunar A, notably gravimetry and high accuracy stereo imaging, topography, mineralogy and some elemental composition detection capability. This resulted in halving the payload mass (4̃2 kg) and reducing substantially the spacecraft dry mass (≤300 kg). Such a small satellite can be placed into a lunar transfer orbit directly by a number of emerging new small-medium class launchers. The paper presents the mission and spacecraft design and describes the areas where the smallsat approach has allowed the largest cost reductions.

Entry of heated solar wind plasma into the magnetosphere is examined using electron distributions measured by AMPTE UKS and HEOS 2. In particular, the angular structure of the electron distributions is studied within the transition region separating the magnetosheath from the inner magnetosphere. The measurements suggest that electrons in the outer part of the transition region originate in the magnetosheath, whilst the population closer to the Earth consists of electrons from the magnetosphere combined with an energized magnetosheath component. This energized component contains “counterstreaming” electrons, which are confined to directions closely parallel and antiparallel to the magnetic field direction. The possibilities, that the energization of the counterstreaming electrons is cumulatively gained from either waves, electric fields perpendicular to the magnetic field, or quasi‐Fermi acceleration, are discussed. It is not possible to identify the topology of the magnetic fields of the outer part of the region, but there is strong evidence that the inner part is on closed magnetic field lines, which map to the day side auroral zone. The outer part of the transition region is a plasma depletion/magnetic field compression layer. The structure of the transition region is similar to that surrounding flux transfer events, which leads to the deduction that the plasma and field signatures of flux transfer events may be the result of displacement of the transition region earthward. Cases where the displacement is such that the field maximum of the depletion/compression region is encountered may well explain “crater” flux transfer event signatures.

The AMPTE barium ion release in the solar wind at 1232 UT on 27 December 1984 produced strong electric component plasma wave noise at frequencies below 3.9 kHz (amongst other emissions) which was detected at both the AMPTE-UKS and AMPTE-IRM spacecraft. In the region outside the magnetic cavity, this noise appears to be correlated with electron heating and changes sin the magnetic field. This paper compares data from the two spacecraft at high temporal resolution in order to identify the waves and the associated processes.

We present simultaneous measurements at high temporal resolution of flux transfer events (FTEs) earthward of the magnetopause using four instruments on the Active Magnetospheric Particle Tracer Explorers (AMPTE) UKS spacecraft. The seven events in our study are distributed in local time from early dawn to midafternoon over a GSM latitude range of ∼40°, from 24°N to 17°S. A multilayered structure is revealed with systematic behavior in fields and charged particle populations. The plasma pressure varies in anticorrelation with the field pressure, the total pressure in general exceeding that of the surrounding medium. While it is not the prime concern of this paper to discuss the validity of models proposed for FTEs, the new, detailed experimental results it contains make it clear that the Russell‐Elphic [1978] model needs, at the very least, more detailed development.

We present high resolution AMPTE-UKS data for a FTE signature in the magnetosphere. When the observations are confronted with the canonical model for such events, we find that we can substantiate clearly the existence of the two field regions (draping vs twisting) predicted from the model. In addition to these regions there is a separate, distinct region close to the expected boundary between open and closed field lines which we estimate to be of order ten ion gyroradii thick. This region is distinguished by a distinctive field and particle signature. The magnetic signature has not been reported before, but the electron signature bears a close resemblance to the electron heat flow layer reported in the ISEE data by Scudder et al. [1984 in Magnetic Reconnection in Space and Laboratory Plasmas (Edited by Hones E.W., Jr.), p. 153. AGU, Washington]. Other observations we report are the occurrence of a large flow burst and, in the central region of the FTE signature, the presence of magnetic field oscillations of period ∼ 3 s.

Active current sheets or diamagnetic cavities in the solar wind have been observed both by the AMPTE-UKS spacecraft on a number of occasions, and independently from ISEE by Thomsen et al /1/. Preliminary results from one of these UKS observations have been discussed recently by Schwartz et al /2/. In this paper we consider these phenomena in more detail. Results are presented for the position of five events. High resolution plasma data and plasma wave activity associated with these current sheets are examined.

UKS observations of the ionized barium and disturbed natural plasmas 170 km from the centre of the artificial comet release of 27 December 1984 lasted over 4 minutes. During this disturbance, solar-wind ions were retarded and deflected southwards and dawnwards, while barium was accelerated northwards. Substantial electron energization was seen throughout, varying with time and with the energy of the source electrons. Rapid electron and ion density changes were observed in later stages