{"id":3126,"date":"2012-07-11T22:43:31","date_gmt":"2012-07-12T03:43:31","guid":{"rendered":"http:\/\/helian.net\/blog\/?p=3126"},"modified":"2012-07-12T19:05:04","modified_gmt":"2012-07-13T00:05:04","slug":"interstellar-transport-freeman-dyson-and-hydrogen-bomb-propulsion","status":"publish","type":"post","link":"https:\/\/helian.net\/blog\/2012\/07\/11\/nuclear-weapons\/interstellar-transport-freeman-dyson-and-hydrogen-bomb-propulsion\/","title":{"rendered":"Interstellar Transport: Freeman Dyson and Hydrogen Bomb Propulsion"},"content":{"rendered":"

And you thought I was crazy…\u00a0 Check out this article by Freeman Dyson in the October 1968 issue of Physics Today entitled “Interstellar Transport<\/a>.”\u00a0 Dyson was an active participant in Project Orion<\/a>, a program to build interplanetary space vehicles propelled by nuclear bombs.\u00a0 After the program was ended by the 1963 nuclear test ban treaty, he decided to write a paper for a high visibility journal to insure that the idea was kept alive and people were aware of its potential.<\/p>\n

People thought big in those days, and Dyson’s notional interstellar transports certainly reflected the fact.\u00a0 The first was designed to absorb the blast of one megaton deuterium fueled bombs in a gigantic copper hemisphere with a radius of 10 kilometers weighing 5 million tons.\u00a0 The fully loaded ship would have weighed 40 million tons, including 30 million of the one megaton bombs.\u00a0 Assuming each bomb would require 10 pounds of plutonium (or about 60 pounds of highly enriched uranium), a total of 150,000 tons of plutonium would be required for the mission.<\/p>\n

Dubious assumptions were made, as, for example, that 100% of the bomb\u2019s energy would go into the kinetic energy of debris, even though it was known at the time (and certainly known to Dyson), that the actual fraction is much less than that.\u00a0 The cost was calculated to be one 1968 gross national product, based entirely on the projected cost of the necessary deuterium fuel (3 billion pounds at $200 per pound in 1968 dollars, for a total of $600 billion.)\u00a0 In other words, the cost of the plutonium, copper, and other building material wasn\u2019t even factored in, nor was the cost of getting it all into earth orbit prior to launch.\u00a0 In spite of all this, the massive ship, carrying about 20,000 colonists, would still take about 1300 years to reach the nearest stars.\u00a0 Barring a \u201cNoah\u2019s ark\u201d forlorn hope escape from a dying world, even Dyson considered this impractical for human travel, writing,<\/p>\n

As a voyage of colonization a trip as slow as this does not make much sense on a human time scale.\u00a0 A nonhuman species, longer lived or accustomed to thinking in terms of millennia rather than years, might find the conditions acceptable.<\/p><\/blockquote>\n

To obviate some of the objections of this \u201cconservative\u201d design, Dyson also proposed an \u201coptimistic\u201d design, which allowed some ablation of the surface of the vehicle nearest to the explosions, rather than requiring all the energy to be absorbed in solid material.\u00a0 After removing this energy limitation, the main limitation on the ship\u2019s performance would be imposed by momentum, or, as Dyson put it, \u201cthe capacity of shock absorbers to transfer momentum from an impulsively accelerated pusher plate to the smoothly accelerated ship.\u201d\u00a0 Basing his reasoning on the optimum performance of practical shock absorbers, Dyson calculated that such a ship could be accelerated at a constant one g, enabling it to reach the nearest stars in centuries rather than millennia.\u00a0 The cost, again based solely on the value of the deuterium fuel, would be only $60 billion 1968 dollars, or a tenth of the GNP at that time.\u00a0 The weight of the ship would be \u201conly\u201d 400,000 tons, a factor of 100 less than that of the \u201cconservative\u201d design.\u00a0 Dyson concluded,<\/p>\n

If we continue our 4% growth rate we will have a GNP a thousand times its present size in about 200 years.\u00a0 When the GNP is multiplied by 1000, the building of a ship for $100B will seem like building a ship for $100M today.\u00a0 We are now building a fleet of Saturn V which cost about $100M each.\u00a0 It may be foolish but we are doing it anyhow.\u00a0 On this basis, I predict that about 200 years from now, barring a catastrophe, the first interstellar voyages will begin.<\/p><\/blockquote>\n

I suspect Dyson wrote most of this paper \u201ctongue in cheek.\u201d\u00a0 He\u2019s nobody\u2019s fool, has remarkable achievements to his credit in fields such as quantum electrodynamics, solid state physics, and nuclear engineering, and remains highly regarded by his peers.\u00a0 Nobel laureate Steven Weinberg said that the Nobel Committee had \u201cfleeced\u201d Dyson by never awarding him the prize.\u00a0 The objections to his designs are obvious, but for all that, bomb-propelled space vehicles are by no means impractical. \u00a0I suspect Dyson realized that other scientists would recognize ways they could improve on his \u201cconservative\u201d and \u201coptimistic\u201d designs as soon as they read the paper, and start thinking about their own versions.\u00a0 Project Orion might be dead as a budget line item, but would live on in the minds and imaginations of his peers.\u00a0 And so it did.<\/p>\n

\"\"<\/a><\/p>\n

\n\t\t\t\t\tTweet<\/a>\n\t\t\t\t<\/div><\/div>","protected":false},"excerpt":{"rendered":"

And you thought I was crazy…\u00a0 Check out this article by Freeman Dyson in the October 1968 issue of Physics Today entitled “Interstellar Transport.”\u00a0 Dyson was an active participant in Project Orion, a program to build interplanetary space vehicles propelled by nuclear bombs.\u00a0 After the program was ended by the 1963 nuclear test ban treaty, … Continue reading “Interstellar Transport: Freeman Dyson and Hydrogen Bomb Propulsion”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[78,77,23,10,118,45],"tags":[],"class_list":["post-3126","post","type-post","status-publish","format-standard","hentry","category-fusion-energy","category-interstellar-travel","category-nuclear-energy","category-nuclear-weapons","category-project-orion","category-space-travel"],"jetpack_publicize_connections":[],"jetpack_shortlink":"https:\/\/wp.me\/pwEq0-Oq","jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts\/3126","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/comments?post=3126"}],"version-history":[{"count":4,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts\/3126\/revisions"}],"predecessor-version":[{"id":3131,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/posts\/3126\/revisions\/3131"}],"wp:attachment":[{"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/media?parent=3126"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/categories?post=3126"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/helian.net\/blog\/wp-json\/wp\/v2\/tags?post=3126"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}