Marek Banaszkiewicz

The Ulysses neutral gas experiment: Determination of the velocity and temperature of the interstellar neutral helium

Abstract A new technique to directly detect low energy neutral helium has been developed and successfully used in space for the first time. It makes possible the in-situ measurement of the local angular distribution of the flow of interstellar neutral helium in the inner heliosphere. Based on the transformation of a velocity distribution, using Liouvilles theorem, a straightforward model has been developed to determine, from these measurements, the flow parameters of the interstellar helium at infinity. From twelve measurements at radial distances between 1 and 5 AU, average values of the flow parameters were determined, namely: υ ∞ = 26 ± 1 km s −1 , downstream direction: λ ∞ = 72 ± 2.4°, β ∞ = −2.5 ± 2.7°, temperature T ∞ = 6700 ± 1500 K. These values are in agreement with results found by completely different methods (such as, backscattered UV-light, pick-up ions), although in detail there are significant differences.

A soft solid surface on Titan as revealed by the Huygens Surface Science Package

The surface of Saturns largest satellite—Titan—is largely obscured by an optically thick atmospheric haze, and so its nature has been the subject of considerable speculation and discussion. The Huygens probe entered Titans atmosphere on 14 January 2005 and descended to the surface using a parachute system. Here we report measurements made just above and on the surface of Titan by the Huygens Surface Science Package. Acoustic sounding over the last 90 m above the surface reveals a relatively smooth, but not completely flat, surface surrounding the landing site. Penetrometry and accelerometry measurements during the probe impact event reveal that the surface was neither hard (like solid ice) nor very compressible (like a blanket of fluffy aerosol); rather, the Huygens probe landed on a relatively soft solid surface whose properties are analogous to wet clay, lightly packed snow and wet or dry sand. The probe settled gradually by a few millimetres after landing.

Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov-Gerasimenko

Thermal and mechanical material properties determine comet evolution and even solar system formation because comets are considered remnant volatile-rich planetesimals. Using data from the Multipurpose Sensors for Surface and Sub-Surface Science (MUPUS) instrument package gathered at the Philae landing site Abydos on comet 67P/Churyumov-Gerasimenko, we found the diurnal temperature to vary between 90 and 130 K. The surface emissivity was 0.97, and the local thermal inertia was 85 ± 35 J m−2 K−1s-1/2. The MUPUS thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength. A sintered near-surface microporous dust-ice layer with a porosity of 30 to 65% is consistent with the data.

Acceleration of the High Speed Solar Wind in Coronal Holes

We outline a theory for the origin and acceleration of the fast solar wind as a consequence of network microflares releasing a spectrum of high frequency Alfvén waves which heat (by cyclotron absorption) the corona close to the Sun. The significant features of our model of the fast wind are that the acceleration is rapid with the sonic point at around two solar radii, the proton temperatures are high (~ 5 million degrees) and the minor ions are correspondingly hotter, roughly in proportion to their mass. Moreover we argue that since the energy flux needed to power the quiet corona in closed field regions is about the same as that needed to drive the fast solar wind, and also because at deeper levels (< 2 × 105 K) there is no great difference in the properties of supergranules and network in closed and open field regions, the heating process (i.e., dissipation of high frequency waves) must be the same in both cases.

A NEW METHOD FOR THE DETERMINATION OF THERMAL CONDUCTIVITY AND THERMAL DIFFUSIVITY FROM LINEAR HEAT SOURCE MEASUREMENTS

The new algorithm of the thermal conductivity and thermal diffusivity determination from the transient hot-wire method has been applied to measurements performed in several solid materials. The algorithm makes use of the exact formula for the temperature variations, instead of its simple, asymptotic form that has been employed earlier. In the process of the least-square optimization of the residual function three parameters are obtained; thermal conductivity, thermal diffusivity, and the initial temperature. Two different variants of the method are presented: the classical one with the power kept constant during the measurements and the newly introduced constant current technique. The latter one has an advantage of requiring simpler conditioning electronics, and can therefore be recommended in space applications. The results of data processing show that thermal conductivity can be reliably determined even from the nonasymptotic part of the temperature measurements. The determination of thermal diffusivity...

Optimization of the Trajectory of a General Free - Flying Manipulator During the Rendezvous Maneuver

The paper is focused on the dynamics of a manipulator mounted on a free-flying satellite performing rendezvous and docking maneuver (RVD). The target satellite is assumed to be passive, without attitude control and telecommunication link. The servicing satellite performs, by means of thrusters, a fly - by maneuver, in which it approaches the target satellite on a non-collision path. In the last phase of the RVD maneuver, when the 6dof manipulator executes a predefined path towards the target, it can disturb the dynamics and, in consequence, the trajectory of the servicing satellite. The system (satellite + manipulator) is nonholonomic and its linear momentum and angular momentum are not conserved. The paper describes the algorithm of the manipulator trajectory planning, based on the calculus of variation, which can solve (n+6) dof problem. The cost functional trades off power use of the DC motor and additional conditions constraining the end-effector motion so that it reaches the final desired state expressed as the linear and angular position and velocity. The behavior of the system is described in the Lagrangian formulation and the collocation method is chosen to solve the boundary value problem. The initial trajectory is calculated using the Generalized Jacobian Matrix (GJM) approach that is extended to the system, in which linear and angular momentum is not conserved. An example is provided that shows the optimal trajectory of the LBR manipulator during the RVD maneuver to a tumbling satellite.

Unusual origin, evolution and fate of icy ejecta from Hyperion

Abstract We readdress the idea that Hyperion may act as an effective source of dust in the outer Saturnian system. Hypervelocity impacts of dust particles coming from the outer irregular moons (Phoebe and several others recently discovered) and, to less degree, bombardment by interplanetary micrometeoroids should eject surface material of Hyperion to planetocentric space. Unlike Hyperion, whose motion is stabilized by a strong 4 : 3 mean motion resonance with the neighbouring Titan, so that encounters with this satellite are prohibited, a significant fraction of the Hyperion debris should be fast enough to be out of resonance. For slower ejecta, resonant locking may be destroyed later by the plasma drag and solar radiation pressure forces. The orbits liberated from the resonance become unstable and experience multiple close approaches to Titan. Using numerical integrations, we performed a statistical study of the grain trajectories to construct a spatial distribution of dust in the Hyperion–Titan system and to find out the eventual fate of the debris. Particles locked in resonance form an arc-like structure along the Hyperion orbit centred on Hyperions position; this “Hyperion swarm” is populated by grains of tens of micrometres in size and might be dense enough to be detected by the Cassini spacecraft during its flyby of Hyperion. The whole dust cloud in the Hyperion–Titan system is tilted off the equatorial plane of Saturn and has a structure that depends on the particle radii. No particular dust concentration in the vicinity of Titan was found. Most of the grains larger than ∼5 μm in size finally collide with Titan, whereas smaller particles are either lost in the inner part of the Saturnian system or hit Saturn. Our estimates of the dust influx to Titan show that the incoming rate of Hyperion particles may exceed the direct influx of interplanetary dust particles. The influx of icy (H2O) particles from Hyperion might help to explain the observed abundance of CO and CO2 molecules in Titans atmosphere.

Dynamic Simulations of Free-Floating Space Robots

This paper focuses on the dynamics of a 6-dof manipulator mounted on a free-flying servicer satellite during final part of an on-orbit rendezvous maneuver. Determination of reaction torques induced by the manipulator on the servicer satellite is critical for the development of the Guidance, Navigation and Control (GNC) subsystem. Presented in this paper is a path planning algorithm for capturing a tumbling target satellite, as well as simulation results of the capture maneuver and folding of the manipulator with the attached target satellite. The second part of this paper is focused on the presentation of our work leading to the construction of a planar air-bering test-bed for space manipulators.

An instrument for in situ comet nucleus surface density profile measurement by gamma ray attenuation

The MUPUS experiment on the Rosetta Lander will measure thermal and mechanical properties as well as the bulk density of the cometary material at and just below the surface of the nucleus of comet 46P/Wirtanen. A profile of bulk density vs. depth will be obtained by measuring the attenuation of 662 keV gamma rays emitted by a ^(137)Cs source. Compton scattering is the dominant interaction process at this energy, the attenuation depending directly on the total number of electrons along the source–detector path. This in turn is approximately proportional to the column density. We report here on the design of the bulk density instrument and the results of related Monte Carlo simulations, laboratory tests and calculations of the instruments performance. The ^(137)Cs radioisotope source is mounted in the tip of the MUPUS thermal probe—a 10 mm diameter rod, to be hammered into the surface of the nucleus to a depth of ~ 370 mm. Two cadmium zinc telluride (CZT) detectors mounted at the top of the probe will monitor the count rate of 662keV photons. Due to the statistics of photon counting, the integration time required to measure column density to a particular accuracy varies with depth as well as with bulk density. The required integration time is minimised for a material thickness equal to twice the exponential attenuation length. At shallower depths the required time rises due to the smaller fractional change in count rate with varying depth, while at greater depths the reduced count rate demands longer integration times. The former effect and the fact that the first 45 mm of the source–detector path passes not through the comet but through the material of the probe, mean that the first density measurement cannot be made until the source has reached a depth of perhaps 100 mm. The laboratory experiments indicate that at this depth an integration time no less than 348 s (falling to 93.9 s at full penetration) would be required to measure a bulk density of 1000 kg m^(-3) to 5% accuracy, assuming a source activity of 1.48 mCi (decayed from an initial 2 mCi). Although solutions involving feedback of the measured bulk density into a time-budgeting algorithm are conceivable, a simple approach where equal time is spent per unit depth may be best, providing an accuracy in bulk density of around 5–20%, for 25 mm slices and the expected range of parameters.

Analytical Model of Eddy Currents in a Reaction Sphere Actuator

A recently proposed technique to control the satellite attitude using a magnetically levitated sphere requires the development of suitable models of its dynamics. One of the phenomena that can affect motion of the system are eddy currents induced in the stator of the actuator due to time variable magnetic field generated by rotational motion of a permanent magnet rotor. We present an analytical model of the eddy currents for the actuator with eight-pole rotor. The model is derived using a second-order vector potential-based approach, and the solution is obtained in terms of spherical harmonic functions. This model allows us to study rotor rotations with constant angular frequency around an axis arbitrarily oriented with respect to both rotor and stator of the reaction sphere actuator.