Letter from Robert O. Spiegel to B. R. Colson

Letter from Robert O. Spiegel to B. R. Colson. The one-page handwritten note is on Our Florida Friend letterhead and is dated 16 November 1912. There is a transcript of the correspondence included in the item PDF

Stained glass as a medium of religious education

Thesis (M.A.)--Boston University, 1939, no p. 19 in original

On the Blazhko Effect in RR Lyrae Stars

The Blazhko effect is a long term, generally irregular modulation of the light curves that occurs in a sizeable number of RR Lyrae stars. The physical origin of the effect has been a puzzle ever since its discovery over a hundred years ago. We build here upon the recent observational and theoretical work of Szabo et al. on RRab stars who found with hydrodynamical simulations that the fundamental pulsation mode can get destabilized by a 9:2 resonant interaction with the 9th overtone. Alternating pulsation cycles arise, although these remain periodic, i.e. not modulated as in the observations. Here we use the amplitude equation formalism to study this nonlinear, resonant interaction between the two modes. We show that not only does the fundamental pulsation mode break up into a period two cycle through the nonlinear, resonant interaction with the overtone, but that the amplitudes are modulated, and that in a broad range of parameters the modulations are irregular as in the observations. This irregular behavior is in fact chaotic and arises from a strange attractor in the dynamics.Comment: 5 pages, 3 figure

CubeSat Proximity Operations Demonstration (CPOD) Mission Results

CubeSat rendezvous and proximity operation (RPO) technology development is critical for improving the performance and economics of space debris remediation and the inspection, servicing, and assembly of larger space systems. The CubeSat Proximity Operations Demonstration (CPOD) is a program led by Terran Orbital and funded by NASA to achieve autonomous on-orbit RPO with two identical 3U CubeSats, thereby maturing CubeSat RPO technology. This article presents the CPOD RPO guidance architecture and its on-orbit outcomes. The architecture advances the autonomy, fuel-efficiency, and safety of CubeSat RPO through the synthesis of optimization-based control theory and orbital dynamics analysis, with different optimization techniques tailored to different stages of the mission. Fully autonomous stages frequently, regularly recompute optimization solutions onboard the vehicles, each time using new measured data to provide robustness to unmodeled force disturbances. RPO is supported by a unique docking magnet control scheme for angular momentum management, a thruster configuration yielding 3DOF translational control, and a data-driven intersatellite distance prediction method for advance (12-200 hours) RPO planning. Ultimately this framework yielded rendezvous of the vehicles from intersatellite distances up to 997 km, a minimum intersatellite distance of 361 m, and passively safe formation flying across 5 major on-orbit experiments