This invention relates to instrumentation for collecting particles in space, and more particularly to a particle collecting device for such instrumentation.
Particle analyzers are a type of instrumentation, used to measure the particle flux and other parameters of particles in free space. A common use of particle analyzers is in the field of space physics, where particles in space are collected and analyzed.
For collecting particles for space physics applications, there is a need for having a large collection area so as to collect as many particles as possible. The medium is tenuous and a large collection area increases sensitivity of the instrumentation and permits shorter integration times. For example, the density of the solar wind decays with the radial distance, r, from the sun by the inverse square, l/r2. For an instrument in the outer solar system to have the same sensitivity as one at one astronomical unit (the mean distance from the Earth to the Sun), its collection area must be increased by a similar factor. Also, the solar wind consists largely of ionized hydrogen mixed with about four percent helium and some minor constituents. Presently, long integration times are needed to obtain good counting statistics for minor ions. A large collection area increases the number of observed particles for a given particle flux.
There is also a need for space particle analysis instrumentation to be as small and lightweight as possible. This reduces constraints on the load capacities of the rockets that carry the instrumentation into space.
One aspect of the invention is an electrostatic mirror type deployable particle collector. An electrostatic mirror has a reflection grid and at least one reference grid, the grids being typically curved and concentric. An electrically conductive particle reflection grid is held at an electrical potential for reflecting electrically charged particles. At least one electrically conductive reference grid has a radius slightly smaller than that of the reflection grid, and is held at a ground reference electric potential. The reflection grid and the reference grid have a common focus point for reflecting electrically charged particles. A deployment mechanism is used to reconfigure the mirrors from a stowed state to a deployed state. For example, the deployment mechanism may be a radial rib type mechanism that deploys the mirror in an umbrella like manner.
An advantage of the invention is that it increases the particle collection area, while maintaining a small launch volume. Through the use of a deployable collector, on-board instrumentation can achieve greater sensitivity without increasing launch volume.
Various embodiments of the invention provide unfoldable, unfurlable, or inflatable collectors in front of a conventional particle analyzer. By analogy to optics, the front-end collector acts like a magnifying glass to a camera. A reflective (electrostatic mirror) design of the collector is analogous to an optical mirror telescope, whereas a transmissive (parallel plate) design is analogous to a Fresnel lens.