Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Thu, 25 Oct 1990 02:17:09 -0400 (EDT) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Thu, 25 Oct 1990 02:16:37 -0400 (EDT) Subject: SPACE Digest V12 #486 SPACE Digest Volume 12 : Issue 486 Today's Topics: Re: You Can't Expect a Space Station to be Cheap Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 24 Oct 90 19:03:04 GMT From: hub.ucsb.edu!ucsbuxa!3001crad@ucsd.edu (Charles Frank Radley) Subject: Re: You Can't Expect a Space Station to be Cheap Thanks for your assistance. I would like to continue if you have time. >1 - Atomic oxygen, very few materials can survive thirty years >in the AO environment, Fred has a 30 year lifetime requirement. >That means we have to GUARANTEE 30 years, in reality it might >last much longer; what material is the inflatable habitat made > of ? Exterior surfaces must all be metallic to shield against >AO, does the LLNL design do this ? + The LLNL Earth station outer layer is PTFE-overcoated Kevlar. +They are designed to deal with vacume and temprature. ILC, the +company which has built all NASA space suits since Apollo has +done a preliminary design and say it will work [1]. As for +atomic oxygen, PTFE has exibited surface erosion when exposed to +atomic O2 of less than 3 microns/year [2] so a coating 100 +microns deep will do. I should also add that the LLNL station +is designed for a life of ten years not thirty. But since it +costs less than 5% of what Freedom costs this shouldn't be +viewed as a problem. Aha ! Ten years lifetime - that changes everything, do you have any idea how much cheaper Fred would be if it only had a ten year lifetime requirement ? I do not have any numbers, but it is a whole new ball game ! Seems LNNL and co are talking apples versus oranges..... As for the AO erosion rate of PTFE, yes I have heard it is about the only nonmetallic with reasonable resistance, my materials expert is out of town this week, but I will chat with him when he gets back. Note: atomic oxygen is not O2, it is O or AO. >2 - Radiation - need to guarantee to operate after a 30 year > > dose in LEO (crews rotated every 90 days) kinda restricts the > electrical design; + My sources do not say anything on this for the Earth Station, +just for the trip to Mars. However, in my readings of NASA +objections to the Great Exploration they make no mention of it. +It could be that LLNL presented an approach NASA accepted. + What special steps is Freedom taking? Rad-hard electronics generally makes use of expensive "limited edition" chips developed by the military. Then the boxes have heavy shielding which is another weight hit. >3 - orbital debris - need to have a Safe Haven configuration of > multiple interconnected nodes and modules with fast closing > hatches in between, to seal off the punctured section, can the > LLNL design do this ? +Yes, for details, see [1]. The Earth Station has an external +shield plus 24 spearate airtight compartments. +BTW, can Freedom do the same? From what I have seen the two main +modules are all open. What would the Freedom crew do if there +was a large breach in the main habitation module? Freedom Safen Haven is presently based on the following ten sealable compartments: 4 Nodes, 1 Lab, 1 Hab, 1 ESA, 1 JEM, 1 PLM, 1 AL interconnected like this: node4---lab---node2---jem | | | | node3---hab---node1----esa | | plm al >4 - Can LLNL assemble their Fred equivalent system using 22 > shuttle flights? This means weight is a big issue. +The LLNL Earth Station goes up in 1 HLV flight. This can be done +because the inflatable structures greatly reduce weight and +launch volume. In [1], ILC states that the packed volume of the +Earth Station would be 28.8 cubic meters for an all fabric +design and 31.6 cubic meters for a design with hard pressure +bearing floors. The total weight budget is 40.4 tons, but that +includes everything. Aha again ! Another case of apples and oranges. Does LLNL figure in the cost of developing HLV in their costing ? Seems kind of expensive to develop a whole new HLV then only fly it once. Cheaper to use a smaller SSX and take it up in several peices. >LLNL's_amorphous_silicon solar cells are certainly cheap to > manufacture, but for watts per pound they are inferior, and > heavy to launch. +They are claiming 1KW per kilo of silicon. NASA says that is an +order of magnitude better than the state of the art. (Dr. Wood +provided them with samples). Samples alone mean little. A lengthy qual and life test program is required for components to be added to the NASA Approved Parts and Materials List. Have the amorphous cells flown ? If so, for how long ? What was the end of life power output ? Can they last thirty years, or even ten ? NASA has learned that test data are required for reliability purposes. A solar cell which dies within a month on orbit is useless. Even super highly tested spacecraft solar cells sometimes fail when you least expect it. +Either way, this is a minor issue. The weight budget for power +is big enough to use what NASA says is the state of the art. Then why did they bother proposing amorphous Silicon ? >5 - LLNL's Nickel-hydrogen batteries are nothing new, Fred uses > the same type; + Interesting. The NASA assessment says these batteries won't +work [3]. Why is Freedom using batteries which NASA says won't +work? If they will work, why is NASA saying they won't? Could be a design detail. Maybe LLNL have some new exotic variant of NiH cells. NiH cells are already in orbit on several spacecraft, including some commercial commm sats. Space-rated batteries are extremely difficult to build and operate, again, extensive qual and life tests are required to obtain reliability data. I suspect LLNL are trivializing the process. >6 - What experience does LLNL have in the following areas of > space applications:- + Don't know in detail (why don't you call and ask?). Prefer to minimise my long distance calls. Do you have e-mail address for anybody there ? Any of those guys coming to southern California any time soon ? + They have however, done work in space based systems and have + experience running large complex technical programs. >The impression I have is that LNNL trades off safety and risk > versus cost. + And who doesn't? The only way for Freedom to avoid those trade + offs is to not build it. At first sight you can save an awful lot of money by accepting higher risks, but then again expensive spacecraft like Shuttles and Space Station, are very expensive and their replacement cost must be figured in the risk equation. > As a safety engineer that is anathema to me. +Tell me something, as a safety engineer on Freedom what are the +odds of a death due to a major breach of the habitation module? 100 %, except for those wearing EVA suits. Same for LLNL. >There is nothing clever about taking risks, any fool can do > that. +That implies that the people flying on Freedom are either not +taking any risks or are fools. Foolishness is proportional to degree of risk taken. + Yes this program is risky. It is about as risky as Apollo. The +Earth Station however, has an assured crew return vehicle as +part of its design so although the odds of a major failure are +high, the odds of loss of crew are much lower. NASA keeps asking for assured crew return vehicle, congress keeps deleting it from the budget. >However, they better be prepared for the bad press they get when > they have a Challenger style disaster. + They are. They are preparing by being up front with the risks +involved. Challenger was a disaster because people felt +betrayed. NASA told them the system was safe enough to send a +school teacher. Had they been more honest Challenger wouldn't +have been so big a deal. + NASA levels of safety will cost us half a trillion dollars to +get to Mars. We can't affoard that. Exploration has always been +very risky, there is no way around that. Dynamic research and +exploratory organizations thrive on this risk and look forward +to pushing the envelope. That spirit prevaded NASA during +Apollo. I don't think that spirit is dead, but it is dying. As the cost of aerospace systems escalates, the tendency to "push the envelope" naturally falls off. The B-2 test program made little if any attempt to "push the envelope" in the Chuck Yeager sense. Similarly, the purpose of Freedom and Shuttle is not to push the envelope, they are to acquire R & D data in the most risk effective manner. The taxpayer cannot afford to lose a Shuttle each time they want a new data point. In summary, I am not opposed to innovative ideas, I embrace them. I support SSX and would like to see a moonbase get higher priority. However, LLNL's plan to relax requirements, and reduce cost by increasing risk sounds fine, until the first one blows.....and the taxpayer has to replace it. ------------------------------ End of SPACE Digest V12 #486 *******************