Sailing towards the stars close to the speed of light

The authors describe the general motion of radiation-pushed sails accelerated near the speed of light with directed energy propulsion. Practical applications of the model are also given, including the interstellar flyby mission to the Alpha Centauri star system envisioned by the Breakthrough Starshot program. Any misalignment between the driving light beam and the direction of the sail's motion is naturally swept away during acceleration toward relativistic speed, yet leads to a deviation of about 80 A.U. in the case of an initial misalignment of 1 arc sec for a sail accelerated up to 0.2c toward Alpha Centauri. Then, the huge proper acceleration felt by the probes (of order 2500 g), the tremendous energy cost (of about 13 kt per probe) for poor efficiency (of about 3 \%), the trip duration (between 22 and 33 years), the temperature at thermodynamic equilibrium (about 1500 K), and the time dilation aboard (about 160-days difference) are all presented and their variation with the sail's reflectivity is discussed. We also present an application to single trips within the Solar System using double-stage light sails. A spaceship of mass 24 tons can start from Earth and stop at Mars in about seven months with a peak velocity of 30 km/s but at the price of a huge energy cost of about $5.3\times 10^4$ GWh due to extremely low efficiency of the directed energy system, around $10^{-4}$ in this low-velocity case.Comment: 15 pages, 10 figures, constructive comments welcome. Open Access Published version in Physical Review Research (5 nov. 2020

Alicornops (Mammalia, Rhinocerotidae) dans le Miocène supérieur des Collines Bugti (Balouchistan, Pakistan) : implications phylogénétiques

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Suoidea (Mammalia, Cetartiodactyla) from the early Oligocene of the Bugti Hills, Balochistan, Pakistan

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Early Miocene mammals of Beaulieu (Bouches-du-Rhône, France), comparison with Wintershof-West and the problem of the MN3/MN4 boundary

[FR] Le niveau biochronologique de Beaulieu est défini par quatre localités, contemporaines du volcanisme daté de -17,5 ± 0,3 Ma. et dont deux sont en corrélation avec un dépôt marin daté des biozones N6 + N7. La microfaune (rongeurs et lagomorphes) indique un niveau élevé dans la période du «cricetid vacuum» (zone B d’AGUILAR (1982) ou MN 3 (DE BRUIJN et al., 1992), probablement plus jeune que Wintershof-West, tandis que la macrofaune indique un âge sub-contemporain. L’âge radiométrique et la polarité normale du basalte permettent une discussion sur la limite MN3/MN4.[EN] Beaulieu’s biochronological level is defined by four localities, contemporaneous of the volcanism dated -17,5 ± 0,3 My., among which two of them are in correlation with marine deposits dated in biozones N6 + N7. The microfauna (rodents and lagomorphs) indicates a high level in the time interval named the «cricetid vacuum « (zones B of AGUILAR (1982) or MN 3 (DE BRUIJN et al., 1992), probably younger than Wintershof-West, while the macrofauna is indicating their sub-contemporaneity. The radiometric age and the normal polarity of the basalt allow to discuss about the MN3 / MN4 boundary.[ES] El nivel biocronológico de Beaulieu está definido por cuatro localidades, contemporáneas del volcanismo cuya edad es -17,5 ± 0,3 Ma. y donde dos están correlacionadas con un depósito marino de las biozonas N6 + N7. La microfauna (roedores y lagomorfos) indican un nivel alto en el periodo del «cricetid vacuum» (zona B de AGUILAR (1982) o MN 3 (DE BRUIJN et al., 1992), probablemente más joven que Winthershof-West, aunque la macrofauna indica una edad casi contemporánea. La edad radiométrica y la polaridad normal del basalto permiten discutir la límite MN3/MN4.3/MN4.Publication ISEM 2002 - 029 UMR 5554 du CNRSPeer reviewe

New artiodactyl ruminant mammal from the late Oligocene of Pakistan

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A large crocodyloid from the Oligocene of the Bugti Hills, Pakistan

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Himalayan Forelands: palaeontological evidence for Oligocene detrital deposits in the Bugti Hills (Balochistan, Pakistan)

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