When a high-voltage charged tether is put into streaming space plasma, the tether’s electric field disturbs the flow of plasma ions and thereby taps momentum from the plasma flow [1-4]. The effect is called electrostatic Coulomb drag. One application is the electric solar wind sail which uses the solar wind to generate interplanetary propulsion [1, 2]. Another application is the Plasma Brake [3, 4] which uses the ionospheric ram flow to generate Coulomb drag that slowly de-orbits the satellite. Both positive and negative tether polarities work. The plasma physics is different, but the net effect is a transfer of momentum in both cases. The reasons are somewhat complicated, but there is good motivation to select positive polarity in the solar wind case and negative polarity in the ionospheric Plasma Brake case. Measurement of Coulomb drag in Low Earth Orbit and testing deployment of tether is to be carried out by ESTCube-2 cubesat [5] which is scheduled for launch in spring 2023, and forthcoming Foresail cubesat scheduled for launch later in 2023-2024.Project DragLiner is ongoing and funded by ESA to define requirements and a preliminary design of a passive Coulomb Drag based deorbit system capable of bringing down LEO spacecrafts in an order of magnitude shorter time than the current regulations of re-enter time for the spacecraft (25 years). Other main requirements for the deorbiting system are low mass and independence from the spacecraft resources. The project will also create a TRL 4 prototype of a Plasma Brake module that can be used to deorbit a few hundred kilogram satellite or launcher upper stage from Low Earth Orbit. The module deploys ~5 km long tether that is made of four 25-50 micrometre diameter conductive wires. In addition to aluminium wires used previously in Cubesat projects we will also evaluate more advanced carbon fibre composite wires. The redundant multi-wire tether structure is used so that the tether does not break even when micrometeoroids cut some of its wires. The tether is deployed from a storage reel. The tether is kept at -1 kV voltage by an onboard high-voltage source. A ~100 m long metal-coated tape tether is used as an electron-gathering surface that closes the current loop. Alternatively, conducting parts of the debris satellite could be used for electron gathering. The power consumption is a few watts. Project Dragliner uses basic Space Plasma Physics to solve a practical and important problem of keeping satellite orbits clean for future generations and preventing a catastrophic Kessler syndrome scenario.[1] Janhunen, P., Electric sail for spacecraft propulsion, J. Prop. Power, 20, 763-764, 2004.[2] Janhunen, P. and A. Sandroos, Simulation study of solar wind push on a charged wire: basis of solar wind electric sail propulsion, Ann. Geophys., 25, 755-767, 2007.[3] Janhunen, P., Electrostatic plasma brake for deorbiting a satellite, J. Prop. Power, 26, 370-372, 2010.[4] Janhunen, P., Simulation study of the plasma-brake effect, Ann. Geophys., 32, 1207-1216, 2014.[5] Iakubivskyi, I., et al., Coulomb drag propulsion experiment of ESTCube-2 and FORESAIL-1, Acta Astronautica, 177, 771-783, 2020.

We compare the predictions of the GUMICS$-$4 global magnetohydrodynamic model for the interaction of the solar wind with the Earth's magnetosphere with Cluster~SC3 measurements for over one year, from January 29, 2002, to February 2, 2003. In particular, we compare model predictions with the north/south component of the magnetic field ($B_{z}$) seen by the magnetometer, the component of the velocity along the Sun-Earth line ($V_{x}$), and the plasma density as determined from a top hat plasma spectrometer and the spacecraft's potential from the electric field instrument. We select intervals in the solar wind, the magnetosheath, and the magnetosphere where these instruments provided good-quality data, and the model correctly predicted the region in which the spacecraft is located. We determine the location of the bow shock, the magnetopause, and the neutral sheet from the spacecraft measurements and compare these locations to those predicted by the simulation. The GUMICS$-$4 model agrees well with the measurements in the solar wind however its accuracy is worse in the magnetosheath. The simulation results are not realistic in the magnetosphere. The bow shock location is predicted well, however, the magnetopause location is less accurate. The neutral sheet positions are located quite accurately thanks to the special solar wind conditions when the $B_{y}$ component of the interplanetary magnetic field is small.

Rapid magnetic fluctuations are known to be closely linked to the high‐latitude geomagnetic activity, in particular, to geomagnetic pulsations and subtorms. Increasing amount of commercial activity in the arctic regions requires better monitoring capability and improved understanding on the effects of geomagnetic hazards to infrastructure. In this study, we analyze rapid, 1‐s fluctuations in Greenland. To measure high‐frequency geomagnetic fluctuations in the auroral oval and polar cap, we use high time resolution data of 1 s from 12 stations covering a large latitudinal range of 64 to 84 quasi‐dipole geomagnetic latitude (QDGMlat). We found out that the large magnetic field fluctuations exceeding 0.2 nT/s are observed 10–30% of the time in auroral oval latitudes, depending on the solar cycle phase and station location. The latitudinal differences are much larger in fluctuation coverage (fractional derivative rate, FDR) than in fluctuations amplitude (dH/dt). The highest |dH/dt| and FDRs at noon are observed at the northern stations from 72 to 84 QDGMlat, while in south Greenland from 72 to 65 QDGMlat, the highest |dH/dt| and FDRs are recorded at midnight. The largest differences in seasonal variation between noon and midnight are observed in the polar cap, where a summer increase is seen at noon and almost flat seasonal profile at midnight.

In this paper, we propose a CubeSat mission for mapping Moon remnant magnetic field and discuss various technical aspects and difficulties, such as instrumentation for weak magnetic field measurement, magnetic cleanliness of the CubeSat platform, orbit and orbital maneuvers. The mission would give information about the history of the Moon and possibly help to better plan lunar bases and manned missions.