![]() ![]() The primary goal of the mission was to improve parallax measurements of the distances to stars inside and outside the Milky Way, with secondary goals being the study of the heliopause, measurements of conditions in the interstellar medium, and (via communications with Earth) tests of general relativity. It was a proposed nuclear electric rocket spacecraft that used a 1 MW fission reactor and an ion drive with a burn time of about 10 years and reach a distance of 1000 AU in 50 years. Studies continued into 1990, working with a launch in the 2005-2010 timeframe. One scientific purpose would be to measure the distance to other stars via stellar parallax. TAU ( Thousand Astronomical Units) was a proposed unmanned space probe to a distance of one thousand astronomical units (1000 AU) from the Earth and Sun by NASA/JPL in 1987 using tested technology. However, because of their short lifetime, the range of the tau is mainly set by their decay length, which is too small for bremsstrahlung to be noticeable: their penetrating power appears only at ultra high energy (above PeV energies).Īs with the case of the other charged leptons, the tau has an associated tau neutrino, denoted by. Because of their greater mass, tau particles do not emit as much bremsstrahlung radiation as electrons consequently they are potentially highly penetrating, much more so than electrons. Since their interactions are very similar to those of the electron, a tau can be thought of as a much heavier version of the electron. Tau leptons have a lifetime of and a mass of (compared to for muons and for electrons). ![]() ![]() Tau particles are denoted by and the antitau by. Like all elementary particles with half-integral spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the positive tau). Together with the electron, the muon, and the three neutrinos, it is a lepton. The tau (τ), also called the tau lepton, tau particle, or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of. ![]()
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