Roton

In theoretical physics, a roton is an elementary excitation, or quasiparticle, in superfluid helium-4. The dispersion relation of elementary excitations in this superfluid shows a linear increase from the origin, but exhibits first a maximum and then a minimum in energy as the momentum increases. Excitations with momenta in the linear region are called phonons; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are sometimes called maxons.

The term "roton" is also used for the quantised eigenmode of a freely rotating molecule.

Models

Originally, the roton spectrum was phenomenologically introduced by Lev Landau. Currently there exist different models which try to explain the roton spectrum, with a different degree of success and fundamentality. The requirement for any model of such kind is that it must explain not only the shape of the spectrum itself but also other related observables, such as the speed of sound and structure factor of superfluid helium-4. Microwave and Bragg spectroscopy has been conducted on helium to study roton spectrum.

Roton (disambiguation)

Roton is the name of

Rotary Rocket

Rotary Rocket Company was a rocketry company that developed the Roton concept in the late 1990s as a fully reusable single-stage-to-orbit (SSTO) manned spacecraft. The design was initially conceived by Gary Hudson, who formed the company to commercialize the concept. The Roton was intended to reduce costs of launching payloads into low earth orbit by a factor of ten.

The company gathered considerable venture capital from angel investors and opened a factory headquartered in a 45,000-square-foot (4,200 m²) facility at Mojave Air and Space Port in Mojave, California. The fuselage for their vehicles was made by Scaled Composites, at the same airport, while the company developed the novel engine design and helicopter-like landing system. A full-scale test vehicle made three hover flights in 1999, but the company exhausted its funds and closed its doors in early 2001.

Rotary Rocket design evolution

Helicopter to orbit

Gary Hudson's and Bevin McKinney's initial concept was to merge a launch vehicle with a helicopter: spinning rotor blades, powered by tip jets, would lift the vehicle in the earliest stage of launch. Once the air density thinned to the point that helicopter flight was impractical, the vehicle would continue its ascent on pure rocket power, with the rotor acting as a giant turbopump.