Solar sail
The awning (also solar sail, English SSP -. Solar -sail propulsion ) is a concept for propulsion of space probes, in which the very low radiation pressure of sunlight to be used. Ideas about it already existed in the 1920s by the German engineer Hermann Oberth (1923 ) or the Russian space pioneer Konstantin Tsiolkovsky ( 1924). The term solar sailing ( eng. "solar sailing" ) was only coined later by Richard Garwin (1958).
The possible through a solar sail acceleration is very low compared to other drives. Therefore see concepts in the use of solar sailing mission durations of many years. The technological challenge is to develop films in space and maneuvering, which are very easy and very large.
While NASA temporarily stopped the development, testing 2010 Japan IKAROS successfully: During six months caused by light pressure change in velocity was 100 m / s Now NASA is planning a similar project for 2014.
Concept
At the awning of the solar radiation pressure is to be used as a drive source. With the solar constant of 1.367 kW / m² (radiant power density of the sun in Erdentfernung ) a radiation pressure yields of 9.1 ìN / m² - with complete, vertical reflection, on interplanetary orbits does not make sense though. Typical is the oblique sailing position, in which a tangential force component occurs, with which the web energy can be increased or decreased. The force acting on a square meter sail area force is then about
There are therefore very large areas and long times needed to accelerate even small masses appreciably. That is, the sail must be very thin. In a mass coating of 10 g / m², fully laden, the acceleration would be at 0.4 mm / s ² and an increase in speed of 10 km / s would take almost a year.
The intensity of sunlight is inversely proportional to the square of the distance. Close flybys of the sun could exploit this in order to achieve greater acceleration.
Practical tests
System components
The drive concept " solar sail " requires extremely thin foils that are including reflection and aufspannendem scaffold ten to one hundred times lighter than paper and simultaneously tear-resistant enough to be deployed from a compact package to multiple football field size can.
Design
NASA paper distinguishes between the following three types:
In addition to these, also still exist solutions that result in part from combinations of the above three types. For example, IKAROS has a square sail, but the Entfaltmechanismus based on centrifugal force, which meant that the satellite has a spin stabilization. Consequently, must on the one hand between the Entfaltmechanismen (centrifugal force utilization, mechanical extension, ...), the satellite stabilization (spin stabilization, three-axis stabilization, ...) and the leaflet geometry ( square, circular, blade -like, ... ) can be distinguished.
Material
An awning is usually a support layer, usually PET / Mylar, Kapton or Kevlar, and is metallized different on the two sides in order to obtain the corresponding emission and reflection values . A thin chromium layer is used to achieve a high emissivity on the side facing away from the sun, to dissipate the absorbed energy, and a thin aluminum layer is intended to generate a high reflectivity.