The possibility of maintaining a group of picosatellites in a bounded formation using very low-power electric propulsion (less than 2 W) is presented. A model predictive controller is used to develop a simple control scheme that avoids the need for an online orbit determination system. The control law, verified using a high-fidelity propagator, is capable of maintaining pairs of picosatellites within a range less than 1500 km with an average [ ] of [ ] per month. To reduce power demands, a combined thruster-based orbit and attitude control system is used. Attitude accuracy is shown to be better than 0.5 deg. A suitable vacuum arc thruster propulsion system is presented, designed specifically for a one-unit CubeSat. The combined attitude-orbit control, the simplicity of the control law, and the proposed propulsion system provide an important advantage for implementation in a picosatellite with extremely limited resources.

Non-equilibrium conditions in plasma are often achieved by pulsed power delivery, where the pulse shape and repetition rate determine the properties of the plasma constituents and thus its chemical reactivity. The evaluation of the latter is becoming increasingly important to understand the observed effects, especially when new application fields are targeted. The composition of the plasma and the occurring chemical reactions can be calculated using various models. Thereby, the temperature of the electrons, the electron number density, as well as the heavy particle temperature are usually required as the basis of such calculations. In this work, the influence of pulse amplitude and repetition rate on these plasma parameters is determined by laser scattering for a low-current, high-voltage discharge operated with nitrogen at atmospheric pressure. In particular, the characteristic parameters regarding the plasma free electrons in such discharges have not yet been experimentally determined to this extent. The results are validated by spectroscopic measurements, i.e., the electron density is estimated from the Stark broadening of the hydrogen beta line and the heavy particle temperature is estimated by fitting the spectrum of nitrogen molecular transitions. Depending on the operating frequency, a pure nitrogen discharge with an input power of about 650 W displays an electron density between $1.7\times {10}^{21}{\mathrm{m}}^{-3}$ and $2.0\times {10}^{21}{\mathrm{m}}^{-3}$ with electron temperatures in the range of 40,000 K and heavy particle temperatures of about 6000 K in the core of the discharge channel. Furthermore, a relatively slow electron recombination rate in the range of 20 µs is observed.

Schlieren diagnostics of cathodic arc flows in air are presented. Three important processes are observed: (1) a luminous hemispherical region near the cathode with a radius of ≈1 mm, identified as the cathodic metallic plasma; (2) a luminous plasma jet extending ≈10 mm from the cathode, termed as the cathodic air jet (CAJ); (3) a background gas pushed to expand at subsonic velocities ≥100 m/s. The gas is accelerated in the direction of the CAJ. The main collisional processes in the CAJ are identified using optical emission spectroscopy and mean free path analysis. The CAJ plasma is shown to be composed of ${\mathrm{N}}_2^{+}$ and Cu⁺ ions. It is concluded that the CAJ length is determined by the dissociative recombination of ${\mathrm{N}}_2^{+}$ . With external magnetic field, the CAJ rotates according to the Lorentz force direction. Observing the CAJ motion and its affect on stationary and flowing background gas, it is concluded that the CAJ has significant directed thrust.