Dynamic Feasibility Study of a Tethered Coulomb Structure

Abstract

The Tethered Coulomb Structure (TCS) is a novel approach to generating a large deployable space structure. This concept uses electrostatic forces to repel a three-dimensional formation of spacecraft nodes interconnected through fine, lowmass tethers. This generates a near-rigid system that can be launched in a compact configuration and change its shape and size while on-orbit. The complex coupling between the close relative motion with electrostatics and tether dynamics is investigated. The TCS rotational stiffness characteristics are quantified through analysis of the TCS node attitudes. With a two-node configuration the rejection of angular rotation disturbances up to 50 deg/min are computed. The maximum absolute angular deflection is reduced as much as 75% by using a triple-tether over a single-tether. Further, the triple-tether setup can provide full three-dimensional stiffness even for a two-node system. However, the multi-tether configurations offer no benefit in preventing entanglement over the single-tether system due to the spread tether attachment points. Variations in TCS nodal mass distribution and radial dimension are simulated. Low inertia nodes with wide tether attachments significantly increase the rotational stiffness. Representative GEO plasma conditions are modeled to demonstrate that plasma shielding has minimal effect on TCS Coulomb inflation. Charging a TCS to negative potentials is advantageous in that only Watt levels of power are required to maintain quasi-rigid formations.

Optimal Microwave Radiation Field Parameters for Mercury Ion Microwave Frequency Standards

“…A trapping mercury ion microwave clock that has a long coherence time [1] and a relatively low second-order Doppler shift, [2,3] as well as being insensitive to environmental perturbations [4,5] and suitable for miniaturization, [6] is regarded as one of the main candidates as a space clock and for timekeeping standards. [7,8] The short-term stability of the helium buffer-gas-cooled linear trap mercury ion microwave frequency standard is extraordinary and has not yet been significantly surpassed by any passive frequency standard. [9] Short-term frequency stability as an important indicator used to characterize the performance of frequency standards, is usually defined by using the Allen variance, 𝜎 𝑦 (𝜅), where 𝜅 is the sampling time.…”