{"id":1126,"date":"2008-12-05T12:00:44","date_gmt":"2008-12-05T18:00:44","guid":{"rendered":"http:\/\/www.spaceelevatorblog.com\/?p=1126"},"modified":"2008-12-05T23:52:47","modified_gmt":"2008-12-06T05:52:47","slug":"how-strong-does-the-space-elevator-tether-need-to-be-part-2","status":"publish","type":"post","link":"https:\/\/www.spaceelevatorblog.com\/?p=1126","title":{"rendered":"How strong does the Space Elevator tether need to be – Part 2"},"content":{"rendered":"

<\/a>In my previous post<\/a>, I referred to Spaceward<\/a> CEO Ben Shelef\u2019s document (The Space Elevator Feasibility Equation<\/em>) as a basis for discussing how strong a Space Elevator tether really has to be and I wrote this; \u201cThe answer to this question relates to how strong the climber power system is.\u00a0 The stronger the power system is, the weaker the tether can be<\/strong><\/em> (and vice-versa).\u201d<\/p>\n

Why is this so?\u00a0 Well, let\u2019s look at an example.<\/p>\n

Say you have a tether which is rated at 30 tons.\u00a0 What this means is that you can have up to 30 tons of Climber\/Payload weight on the tether at any one time.\u00a0 Does this mean that you can only have one 30-ton Climber (or three 10-ton Climbers or six 5-ton Climbers) on the tether at one time?<\/p>\n

The answer is no \u2013 you can have more than 30 tons of mass on the Climber at one time and the reason for this is the Climber, as it ascends, weighs less and less (though its mass, of course, never changes).\u00a0 This is due to the force of gravity weakening as you get farther and farther away from earth.\u00a0 So, a Climber which weighs 30 tons at ground zero will only weigh only half as much (15 tons) when it gets to 2,624 kilometers in height (where the force of gravity is one-half that at ground level).\u00a0 When the Climber ascends to 6,400 kilometers, the Climber will weigh only one quarter as much (7.5 tons) and so on.\u00a0 So this means that when a 30 ton Climber ascends to 6,400 kilometers (and weighs only 7.5 tons), you can then launch another Climber weighing 22.5 tons.\u00a0 When that Climber gets to 6,400 kilometers (and the first one launched is now at 12,800 kilometers), the total Climber weight on the tether is now 10.8 tons (1\/4 of 30 tons plus 1\/9 of 30 tons) which means you can launch another 19.2 ton Climber (note that the Climbers will weigh even less than I\u2019ve indicated as they ascend due to centrifugal force, but that factor doesn\u2019t become significant until you get close to GEO and so I\u2019ve ignored it here).<\/p>\n

As you can see, one can play with these numbers in several different ways to get different launch schedules, but the bottom line is this; you can launch any number of Climbers you want to on this 30-ton rated tether as long as the total weight of these Climbers (as opposed to the total mass of these Climbers) does not exceed 30 tons.<\/p>\n

From this, it should be pretty clear that it is advantageous to have the Climbers ascend as rapidly as possible.\u00a0 The higher they ascend and the quicker they do so, the sooner you can launch another significant Climber.\u00a0 And this brings us back to the statement; \u201cThe stronger the power system is, the weaker the tether can be<\/strong><\/em>\u201d.<\/p>\n

The stronger your power system is (with all other things being equal), the faster your climbers can ascend (up to a limit, of course).\u00a0 So, if your goal is to get 20 tons to GEO every day, you need, say, a 30 ton rated tether with a power system strong enough to propel a 20 ton Climber at least 2,624 kilometers per day, or, you can have, say, a 60 ton rated tether with a weaker power system just able to propel a 20 ton Climber at least 1,312 kilometers per day.\u00a0 Both tethers will do the job, but it\u2019s certainly going to be easier (and faster) to build a 30-ton rated tether than a 60-ton rated one.\u00a0 And what if a 60-ton rated tether is just not possible?<\/p>\n

\u201cThe stronger the power system is, the weaker the tether can be<\/strong><\/em>\u201d.<\/p>\n

Not only would we LIKE to lift the maximum amount possible on any specific tether, it is also going to be NECESSARY to lift the maximum amount possible on any specific tether.\u00a0 This is because there are \u2018housekeeping chores\u2019 which will consume a very significant fraction of a Space Elevator\u2019s capabilities, housekeeping chores which, if not done, will mean a Space Elevator will simply not be viable.\u00a0 I will talk about these housekeeping chores in my next post.<\/p>\n

(Picture of Stone-Wales defect from here<\/a> – click on it for a slightly larger version)<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

In my previous post, I referred to Spaceward CEO Ben Shelef\u2019s document (The Space Elevator Feasibility Equation) as a basis for discussing how strong a Space Elevator tether really has to be and I wrote this; \u201cThe answer to this question relates to how strong the climber power system is.\u00a0 The stronger the power system […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,4],"tags":[],"class_list":["post-1126","post","type-post","status-publish","format-standard","hentry","category-news-announcements","category-spaceelevatorcompetitions"],"_links":{"self":[{"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1126","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1126"}],"version-history":[{"count":0,"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=\/wp\/v2\/posts\/1126\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1126"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1126"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.spaceelevatorblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1126"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}