The Drag-Free Control system forces the satellite to follow the proof mass in order to generate a low disturbance free-fall environment.
Higher requirements for the thruster performance are made due to the demand for the drag-free control system and real-time compensation for non-conservative forces.
In order to achieve this very low disturbance environment (for some missions <10−14 g) the drag-free control system has to be optimized.
The experimental set-up consists of two ultrastable Nd YAG lasers, three crossed optical resonators (monolithic cavities), an ensemble of atomic clocks, an optical comb generator, laser tracking devices and a drag-free control system.
Unlike the co-sorption experiments, the experiments conducted with HA-precoated Al-oxide appear to be at or near Fe(II) sorption equilibrium after 120 days (Fig. 1a), enabling comparison to the equilibrium [Fe(II)]aq of the HA-free control system to determine whether HA impacts Fe(II)–Al-LDH solubility.
Evidence is provided by the XAS results (Fig. 2), from the comparison of the 7-day sorption sample of the HA-free control system (spectrum a, in Fig. 2) versus the 7-day co-sorption samples (spectra b, d in Fig. 2).
The Fe(II) sorption equilibrium in the 1-wt% HA system is very similar to that of the HA-free control system (Fig. 1a), which indicates that HA has essentially no impact on the stability of Fe(II)–Al III -LDH in this sAl III -LDH
The MiniSTEP drag-free control system must reduce the atmospheric drag forces acting on the spacecraft by seven orders of magnitude, to yield an average residual acceleration of less than 3·10−14 m s−2 averaged over the measurement bandwidth.
The various elements of a drag-free control system are discussed: proof mass design considerations; optical, capacitive and SQUID sensing of the displacements between the proof mass and the satellite; gas and electrical thrusters as actuators; and design considerations for drag-free control laws.
This paper will present approaches for in-orbit calibration of drag-free control systems.
Differences in reactivity between γ-Al2O3 and clay towards aqueous Fe(II) are evident from the results of the organic-free control systems.
