Mario L. Cosmo

Two-Bar Model for the Dynamics and Stability of Electrodynamic Tethers

Previously a new dynamic instability that affected electrodynamic tethers in inclined orbits was studied, with a simple one-bar model that neglected the contribution of the tether lateral dynamics. The e exibility of the tether (lateral dynamics ), however, plays an important role in the overall motion of the system as shown by numerical simulations of a bare-tether generator in a circular inclined orbit. The same analytical techniques of the previous work arenow applied to investigate the dynamics and stability of an electrodynamic tether system modeled by two articulatedbarsthat accountforthelowestlateralmodesof thetether. Theanalysis,whichcanbedirectly extended to any electrodynamic tether system, has been focused on two particular, but important cases: the combination of a conductiveand a nonconductive leadertether (as in the Propulsive Small Expendable Deployment System )and a homogeneous, conductive tether. The lateral dynamics is extremely rich, with skip rope motion, instability peaks, and chains ofbifurcationsfor differentregions ofthe parameter space. The sameenergy pumping mechanism that destabilizes the rigid model (one bar) is found to drive an even faster instability of the lateral modes. Damping, which has not been included in the analysis, could change this unstable behavior.

Low altitude tethered mars probe

Abstract A long tether connects a Martian orbiter to a small probe orbiting in the dense atmosphere of the planet. The minimum altitude reachable by the probe is estimated based upon considerations of dynamic stability, tether temperature, resistance of the tether material, and propellant consumption required to maintain a constant orbital altitude. The results obtained by means of a static-force model are then verified by dynamics simulation carried out by using a lumped-mass computer code. The scientific applications of this tethered system include probing of the Martian upper atmosphere and gravity mapping of the planet carried out by collecting gradiometric data from the probe. Another application involves the release of Martian rovers and penetrators from the probe at low altitude.

Dynamics and control of the tether elevator/crawler system

This paper investigates the dynamics and acceleration levels of a new tethered system for micro- and variable-gravity applications. The system consists of two platforms tethered on opposite sides to the Space Station. A fourth platform, the elevator, is placed in between the Space Station and the upper platform. Variable-g levels on board the elevator are obtained by moving this facility along the upper tether, while microgravity experiments are carried out on board the Space Station. By controlling the length of the lower tether the position of the system center of mass can be maintained on board the Space Station despite variations of the systems distribution of mass. The paper illustrates the mathematical model, the environmental perturbations and the control techniques which have been adopted for the simulation and control of the system dynamics. Two sets of results from two different simulation runs are shown. The first set shows the system dynamics and the acceleration spectra on board the Space Station and the elevator during station-keeping. The second set of results demonstrates the capability of the elevator to attain a preselected g-level.

Test of the weak-equivalence principle in an Einstein elevator

SummaryA technique for testing the weak-equivalence principle is presented. This technique involves the measurement of differential accelerations between two test masses of different materials (e.g., aluminum and gold) free falling inside a 3 m long cryostat dropped from a 40 km altitude balloon. The free-fall duration is 30 s for a non-propelled cryostat. The falling test masses are part of a high-sensitivity differential detector with a foreseeable sensitivity in detecting differential accelerations of about 1.5·10−13

Balloon-released gravitation experiments in free fall

g/\sqrt {Hz}

Using the Global Positioning System to Study the Atmosphere of the Earth: Overview and Prospects

(at the liquid-nitrogen temperature of 77 K) and 1.5·10−14

The Weak Equivalence Principle (WEP) and the General Relativity Accuracy Test (GReAT) with an Einstein Elevator

g/\sqrt {Hz}