A linear formation-flying astronomical interferometer in low Earth orbit

Space interferometry is the inevitable end point of high angular resolution astrophysics, and a key technology that can be leveraged to analyse exoplanet formation and atmospheres with exceptional detail. However, the anticipated cost of large missions, such as Darwin and TPF-I, and inadequate technology readiness levels have resulted in limited developments since the late 2000s. Here, we present a feasibility study into a small-scale formation-flying interferometric array in low Earth orbit, which will aim to prove the technical concepts involved with space interferometry while still making unique astrophysical measurements. We will detail the proposed system architecture and metrology system, as well as present orbital simulations that show that the array should be stable enough to perform interferometry with <50 m s–1 yr–1 delta-v and one thruster per spacecraft. We also conduct observability simulations to identify which parts of the sky are visible for a given orbital configuration. We conclude with optimism that this design is achievable, but a more detailed control simulation factoring in a demonstrated metrology system is the next step to demonstrate full mission feasibility.

Investigation on a Flexible Tether Slackness Based on In- and Out-of Plane Libration Angles

Tethered Satellite Systems (TSS) have been used in various applications such as in performing space interferometry, orbit transfer and other relevant fields. As far as the operation system of a TSS is concerned, it is crucial to ensure that the tether will not go slack as its slackness would adversely affects the overall operation outcome due to an undesirable system dynamics. Therefore, it is important to investigate the types of conditions that will cause the tether slackness. Investigations on in-plane and out-of plane libration angles can be utilized to measure at what point that the tether will go slack. Based on previous research works, usually a rigid tether comprising of a uniformed mass is considered while the connecting two satellites are regarded as point masses in order to simplify the governing dynamics equation of motion. However, in order to develop a much more accurate modeling, a flexible tether is chosen by further incorporating the reeling mechanism, attitude dynamics of rigid bodies and tether deformations. Furthermore, a tether has a tendency to go slack if the in-plane and out-of plane libration angle exceeds 65° and 60° respectively regardless of the types of tether utilized whether it being a rigid or a flexible one. Thus, the tension of the tether will serves as a constraint and plotted against the in-plane and out-of plane libration motions that would be attained via the generalized forces. The results will then be analyzed to establish in-plane and out-of plane libration boundaries. Subsequently, the in-plane and out-of plane operation contrains are established for TSS corresponding to a reference mission.