International Journal of Space Science and Engineering (5 papers in press)
Synthesizing of Reactionless Flexible Mechanisms for Space Applications
by Bin Wei
Abstract: Often, one achieves the dynamic balancing condition by resorting to counter-devices approach, however, by doing this, one adds extra weight and therefore the inertia are increased inside the whole system, which is not cost-effective when the system is sent into space and later used in space. In this study, it is suggested one is able to achieve the reactionless condition through combining the self-balanced system. For example, the dynamic balancing condition can be realized via the reconfiguration concept. Extra counter-mass is not employed but through reconfiguring the whole structure, in this way, the system will not get to be heavy and therefore, reduce the energy costs and make the system more applicable and flexible for space applications. Based on this concept, first and foremost, one needs to balance a single component through the reconfiguration approach (i.e. decomposition process) and after that integrate the above balanced components to build the entire system (i.e. integration process). Finally, with the mechanical reconfiguration, the control laws governing the operation of the mechanism also need to be changed, so as to make whole systems more flexible when they are used in space.
Keywords: reactionless; reconfiguration; integration; space robot.
Saturn Ice Ring Exploration Network (SIREN) Mission Platform
by Eric Shear, John Moores
Abstract: SIREN is a proposed mission concept that would demonstrate the use of small spacecraft at the rings of Saturn to quantify the ring environment and study the composition of the ring particles. Many existing small spacecraft technologies are leveraged to make this mission possible. SIREN consists of several daughtercraft deployed from and networked to a mothership in hover-orbit over the ring plane. The mothership is based on the Saturn Ring Observer spacecraft (Nicholson et al, 2010). This paper details the mission objectives, the science requirements, the overall mission design, and the science payloads of the daughtercraft.
Keywords: mission concepts; CubeSats; spacecraft networks; small spacecraft; Saturn; rings; planetary science;.
Experimental Investigation of Optimal Positional Relation between RF Antenna and Magnetic Cusp for Thrust Performance of RF Plasma Thruster
by Yuya Oshio, Tomohiro Shimada, Hiroyuki Nishida
Abstract: The electrodeless radio-frequency (RF) plasma thruster, which avoids the risk of electrode failure, is likely to be a highly appealing electric propulsion system. Although this type of thruster has achieved notable thrust performance in high-power conditions of several hundred kilowatts, it falls short in low-power conditions of several kilowatts. To improve the thrust performance at low power, an RF plasma thruster has been proposed that involves a magnetic cusp. This study aimed to reveal the optimal positional relation between the RF antenna and the magnetic cusp. The performance of an RF plasma thruster with a magnetic cusp was characterized experimentally using a torsion-pendulum thrust stand for six positional relations between the RF antenna and the magnetic cusp. The maximum thrust performance (4.4 mN, 443 s at 1000 W, and 1.2 mg/s of Ar) was obtained with the RF antenna located downstream of the magnetic cusp. The proposed optimized positional relationship of the thruster components is with the RF antenna located downstream of the magnetic cusp and close to the thruster exit.
Keywords: Electric Propulsion; Electrodeless; RF discharge.
Solar Array Degradation on Geostationary Communications Satellites: The Quantification of Annual Degradation and Degradation over Solar Proton Events
by Whitney Lohmeyer, Raichelle Aniceto, Kerri Cahoy
Abstract: Solar array telemetry from eleven geostationary communication satellites, launched between 1990 and 1998, was analyzed and used to quantify solar array degradation of gallium arsenide (GaAs) and silicon (Si) solar cells. GaAs cells had an average annual percent degradation ranging between 0.44% and 1.03%, while Si cells had an average annual percent degradation ranging between 0.71% and 1.69%. The decrease in degradation rates for Si cells to ~10% over a 10 year mission suggests an update to the Si solar cell degradation design rule of thumb 25% over a 10 year mission. Degradation during solar particle events (SPEs) of 10 MeV proton flux > 10,000 pfu was analyzed and used to create a preliminary functional relationship between degradation experienced over SPEs and the accumulated fluence of these SPEs.
Keywords: Solar cell degradation; solar proton events; space weather; space environment; radiation environment; gallium arsenide solar cells; silicon solar cells; geostationary communication satellites.
Design of a variable ISP Space Engine
by Samanvay Karambhe, Xiaofeng Wu, Rishi Verma
Abstract: An existing propulsion system is modified to obtain variable ISP capabilities that could be used to modulate thrust. This created an engine that is able to use low thrust and high ISP setting for interplanetary travel and use high thrust and low ISP setting for attitude control and compensating for atmospheric drag. A cold gas thruster (CGT) was created by using the body of a charge exchange thruster (CXT) effectively producing a dual mode CXT with CGT capabilities. The dual mode CXT was capable of a maximum thrust of 94 μN in electric engine mode. Experimentations showed that using Argon, the dual mode CXT in CGT mode produced a thrust of 4 mN, a 43-fold improvement. A convergent divergent nozzle was designed and validated via ANSYS Fluent for use with the dual mode CXT, it showed a 16 fold improvement in CGT performance at low mass flow rates < 50 sccm.
Keywords: Vacuum Chamber; neutralisation; cold gas thruster; con-di nozzle; charge exchange thruster; variable isp;.