Using the attitude response of aerostable spacecraft to measure thermospheric wind

Abstract

In-situ measurements of the thermospheric wind can be obtained by observing the attitude response of an aerostable spacecraft. In the proposed method, the aerostable spacecraft is left uncontrolled, freely reacting to the aerodynamic torques, and oscillating around its equilibrium attitude. The wind's magnitude and direction is determined by combining the attitude observations with estimates of the other perturbing torques, atmospheric density, and spacecraft's aerodynamic properties. The spatial resolution of the measurements is proportional to the natural frequency of the attitude's oscillation. Spacecraft with high aerodynamic stiffness to inertia ratios operating at low altitudes exhibit higher natural frequencies, making them particularly suited for this method. A one degree-offreedom case is used to present and illustrate the proposed method as well as to analyze its performance.

Attitude Stabilization of Spacecraft in Very Low Earth Orbit by Center-Of-Mass Shifting

“…In the orbital environment (>200 km in altitude) the residual atmosphere can no longer be considered as a continuum but, given its low density, needs to be considered as a rarefied-gas (Bird, 1994 ). The mean free path λ of an atmospheric gas particle is, in general, much greater than a representative spacecraft dimension (λ>100 m at 200 km altitude; Virgili-Llop, 2014 ). Consequently, it can be assumed that the interactions between gas particles (collisions) are very rare, and thus they can be safely neglected.…”

“…For radar payloads, either the antenna size or the transmission power can be reduced. Furthermore, a given launcher can usually deliver more payload at lower altitude orbits or, for a given spacecraft mass, a less capable and potentially more cost-effective launcher can be used (Virgili-Llop, 2014 ; Virgili-Llop et al, 2014a ).…”

“…The interaction of spacecraft with the residual atmosphere results in aerodynamic forces that, at low altitudes, can become major orbit and attitude perturbations (Fortescue and Stark, 1995 ). As the aerodynamic forces are only dominant in the lower part of the Low Earth Orbit (LEO) range the term Very Low Earth Orbit (VLEO) is used in this paper to make clear that the considered orbit range extends only up to ~450 km in altitude (Virgili-Llop, 2014 ; Virgili-Llop et al, 2014a ).…”

“…Although these aerodynamic perturbations are usually perceived as drawbacks, they can also be seen as an advantage (Virgili-Llop, 2014 ; Virgili-Llop et al, 2014a ). As the orbital lifetime is reduced, there is no need to de-orbit spacecraft at the end of their operational life.…”

Dual Quaternion Framework for Modeling of Spacecraft-Mounted Multibody Robotic Systems

“…The toolbox uses a recursive Newton-Euler approach, method further explored by Carignan and Akin ( 2000 ). Other open source toolboxes available online include SPART by Virgili-Llop et al ( 2017 ), developed specifically for spacecraft-mounted manipulators, and DART by Lee et al ( 2018 ), which is aimed for general multibody systems, among many others. Commercial software packages also exist.…”