![]() So the crux of the problem is that we are producing an emitting surface with a temperature in the range of 100,000 K. If we suppose that the photons take the form of black-body radiation and that there is 1 sq metre of radiating surface available per tonne of vehicle mass then we can obtain the necessary surface temperature from the Stefan-Boltzmann law…ĥ.7 x 10 -8 T 4 = 3 x 10 12 watts/metre 2 …a photon rocket accelerating at 1 g would require to dissipate power in the exhaust beam at the fantastic rate of 3 million Megawatts/tonne. Let me quote Shepherd on this, as the problem is serious: This stems from the fact that the matter/antimatter annihilation is so mind-bogglingly powerful. Producing and storing antimatter were known problems even then, but it was Shepherd who saw that “The most serious factor restricting journeys to the stars, indeed, is not likely to be the limitation on velocity but rather limitation on acceleration.” But Shepherd saw that even if it could be made to function, antimatter propulsion ran into other difficulties. ![]() Remember that neither of these scientists knew about the antiproton as anything other than a theoretical construct, which meant that a ‘photon rocket’ in the Sänger mode just wasn’t going to work. This was published just a year before Sänger explained his antimatter rocket ideas to the 4th International Astronautical Congress in Zurich, later published in Space-Flight Problems (1953). A specialist in nuclear fusion, his activities within the International Academy of Astronautics (he was a founder) and the International Astronautical Federation (he was its president) were legion, but this morning I turn to “Interstellar Flight,” a Shepherd paper from 1952. Shepherd isn’t as well known as he should be to the public, but within the aerospace community he is something of a legend. Because even as Sänger labored over the idea, one he had been pursuing since the 1930s, Les Shepherd was looking at the antimatter prospect, and coming up with aspects of the problem not previously identified. With that in mind, and in a ruminative mood anyway, let me turn back to the 1950s, as I did yesterday in our look at Eugen Sänger’s attempt to create the design for an antimatter rocket. Hawking’s name will, of course, continue to resonate in these pages - he was simply too major a figure not to be a continuing part of our discussions. How on Earth did he live so long with an illness that should have taken him mere years after it was identified? In my family’s case, the ALS diagnosis turned out to be mistaken, but there was no doubt about Hawking’s affliction. I want to finish up my thoughts on antimatter from the last few days, but I have to preface that by noting how stunning Hawking’s non-scientific accomplishment was. My family has had a closer call with ALS than I would ever have wished for, so the news of Stephen Hawking’s death stays with me as I write this morning.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |