R. Reinhard

Diffusion coefficients of low-energy protons upstream of quasi-parallel interplanetary shocks

Abstract We present results of a study of the diffusion coefficient for low-energy protons upstream of three interplanetary shocks observed on ISEE-3. The intensity increase as the shock approaches can be fitted by a running exponential, the e-folding time t ★ of which is assumed to be a direct measure of the diffusion coefficient. The energy dependence of t ★ close to the shock (0–60 R e ) is derived from the four energy channels covering the range 35–238 keV. The t ★ in the low energy channels (less than 100 keV) increases with distance away from the shock. However t ★ decreases above 100 keV and roughly beyond 100 R e , so that the diffusion coefficient becomes independent of energy. We suggest that the energy-independence of t ★ in a region well upstream of the shock is the result of enhanced parallel scattering through 90° pitch-angles for higher energy (larger gyroradius) particles which are more sensitive to variations in the transverse direction of the magnetic field.

The Giotto mission to Halley's comet

Abstract ESAs Giotto mission to Halleys comet is a fast flyby in March 1986, about four weeks after the comets perihelion passage when it is most active. The scientific payload comprises 10 experiments with a total mass of about 60 kg: a camera for imaging the comet nucleus, three mass spectrometers for analysis of the elemental and isotopic composition of the cometary gas and dust environment, various dust impact detectors, a photopolarimeter for measurements of the coma brightness, and a set of plasma instruments for studies of the solar wind/comet interaction. In view of the high flyby velocity of 68 km/s the experiment active time is very short (only 4 hours) and all data are transmitted back to Earth in real time at a rate of 40 kbps. The Giotto spacecraft is spin-stabilised with a despun high gain parabolic dish antenna inclined at 44.3° to point at the Earth during the encounter while a specially designed dual-sheet bumper shield at the other end protects the spacecraft from being destroyed by hypervelocity dust impacts. The mission will probably end near the point of closest approach to the nucleus when the spacecraft attitude will be severely perturbed by impacting dust particles leading to a loss of the telecommunications link.

Interplanetary acceleration of low-energy protons as observed during the 25 september 1978 shock event

ISEE-3 observations of a long-lasting low-energy proton intensity increase during the 25 September 1978 shock event are presented as an example for interplanetary particle acceleration in association with shock waves. The observations are discussed in the light of current models for particle acceleration. The particular shape of the time intensity behaviour of the particle intensity increase, the existence of a shock spike and the observed particle distributions indicate that the particles are accelerated at the shock by the induced electric field E = −1c V × B.

The derivation of Halley parameters from observations

Abstract A set of nominal model parameters for P/Halley is derived from its light curve and spectra. In those cases where Halley observations are not sufficient, the average value derived from a large set of other comets has been used, or data from comet Bennett, Halleys best analogue has been taken. The derived parameters include nucleus mass, size, density, albedo, rotation period, axial inclination, and surface temperature, the composition of the parent molecules, the total gas and dust production rates, distributions for the dust size and bulk density as well as various other parameters.

Historical perspective on testing the Equivalence Principle

Abstract Few facts in science are more surprising and none has had a longer history than the apparent equivalence of the two kinds of mass in physics, gravitational and inertial. From Galileo and Newton to Eotvos and Einstein, it has been a compelling issue both theoretically and experimentally. Ground-based tests have now a precision of about 1 part in 10 12 . Even with this extraordinary agreement, there are profound theoretical reasons for carrying the measurements further. Our generation has the unique oppurtunity to make an advance of a factor of a million in testing the Equivalence Principle in space.

ESA's STEP assessment and phase a studies for M2 and M3

Abstract STEP (Satellite Test of the Equivalence Principle) was studied by ESA at Assessment and Phase A level as a candidate for the second medium-size project (M2) and, after its non-selection, again at Assessment and Phase A level for M3. During the M2 cycle, STEP was studied as an ESA/NASA collaborative project, during the M3 cycle as a European-only project. During both cycles, the payload consisted not only of several differential accelerometers to test the Equivalence Principle, but also of accelerometers to measure the Constant of Gravity, to test the inverse square law of gravity, to search for a hypothetical force between spin-polarised and ordinary matter, and to perform a high-precision geodesy experiment. In the end, STEP was not selected as M3 either. The studies carried out by ESA for M3 complemented similar studies performed at about the same time by NASA and by CNES. Over the last couple of years a variety of mission options was studied by the three space agencies with the result that a low-cost, cryogenic option that exclusively focuses on the Equivalence Principle test is the best way forward. This mission (MiniSTEP) is now under study as a NASA/ESA collaborative project.

Fundamental physics in space in ESA and COSPAR

Abstract In recent years, fundamental physics has emerged as a new discipline in European space science. This Symposium marks the topics entry into the COSPAR programme. There has been a small but important community active in the USA for many years. In Europe, the topics history goes back to the very origins of cooperative space science. After a decade of activity in the 1970s and a period of hibernation in the 1980s the topic has now re-emerged, triggered by the activities in the USA. Exciting projects are now being studied by ESA, such as testing the Equivalence Principle with unprecedented precision and the search for gravitational waves. In space, experiments in fundamental physics can often be carried out with much higher precision than on the ground because of the quieter gravitational background and the absence of the 1-g gravity. Some detections, e.g. gravitational waves at low frequencies, can only be made in space. Scientific objectives of fundamental physics missions are distinctly different (questioning the laws of Nature) from the objectives of astronomy and Solar System missions (taking the laws of Nature for granted and applying them). There is clearly now an active community of fundamental physicists in Europe in need of space flight opportunities, as there has been one in the USA for quite a while, and this is now being recognised by COSPAR. Consequently, on 21 July 1996, the COSPAR Council decided to set up a Scientific Commission for Fundamental Physics in Space (SC-H).

Electrostatic charging of test masses in Equivalence Principle experiments in low-Earth, near-polar orbits

Abstract Experiments to test the Equivalence Principle in space are typically suggested for flight in low-Earth, circular, Sun-synchronous orbits at 400–600 km altitude. In these orbits the spacecraft routinely traverses the South Atlantic Anomaly (SAA), where the fluxes of trapped charged particles are enhanced. These particles, together with energetic solar flare protons and galactic cosmic rays, will penetrate the spacecraft structure and develop into a shower of lower energy particles which deposit electrical charge, energy (heat), and momentum on the test masses. Of these, charge leads to the most serious disturbances. Estimates of the charging rates have been computed using the GEANT radiation transport code, in conjunction with realistic proton flux models.