Point of View

listen to your engineer

On 24 August 2007, theNational Aeronautics andSpace Administration(NASA) announced that it

had determined the cause of space shuttleexternal tank foam loss, during launch, aswell as its solution. The external tank car-ries liquid propellant for the launch and iscoated with a composite foam for heatdissipation and a lighter foam for high-insulation efficiency. Apparently,composite foam atop the metal bracketsthat hold fuel lines on the tank maydevelop microscopic cracks, which causethe lighter foam above it to fall during thestress of launch. On the basis of theresults of testing, NASA believes thatonly the lighter foam is required forbracket coating. This foam modificationwill be tested during the next Discoverylaunch on 23 October 2007 [1].

While the shuttle manager, N. WayneHale, Jr., believes that the foam lossproblem is solved, I prefer to wait fordata from the inevitable next dozenlaunches to support his conclusion. In1973, NASA’s original specificationsincluded a requirement that debris dur-ing launch be prevented.

3.2.1.2.14 Debris Prevention:

The Space Shuttle System, in-cluding the ground systems, shallbe designed to preclude the shed-ding of ice and/or other debrisfrom the shuttle elements duringprelaunch and flight operationsthat would jeopardize the flightcrew, vehicle, mission success orwould adversely impact turn-around operations. [2]

In 1980, the External Tank ComponentEnd Item Specification reiterated thisrequirement [3]. Nevertheless, the inau-gural 1981 flight of Columbia sustaineddamage from debris, causing 300thermal protection tiles to be replaced.Later, external tank foam struck the left

wing during Columbia’s launch on 16January 2003. During subsequent reen-try on 1 February, this breach in thethermal protection system led toprogressive melting of the aluminumstructure of the left wing, failure of thewing, and breakup of the Columbiaorbiter [4]. For the next two and one-half years, NASA researched andimplemented safety improvements fororbiters and external tanks to prevent

foam loss. However, when Discoverywas launched on 26 July 2005, fourpieces of foam still fell from the exter-nal tank. The largest chunk weighed0.9 lb, more thanhalf the weight ofthe foam thatdoomed Columbia.This chunk barelymissed hitting theorbital. During thisflight, Hale sent ane-mail to the Dis-covery crew con-fessing that he was‘‘absolutely morti-fied by the perfor-mance of the externaltank foam’’ and thatthey were not goingto fly again until itwas fixed [5]. After

this Discovery flight, space shuttlesflew five additional times, with externalfoam loss during each launch.

NASA does not understand riskanalysis. Even though it created itsOffice of Safety, Reliability, and Qual-ity Assurance per the recommendationof the Rogers Commission after theChallenger exploded during launch in1986, NASA’s culture continues tomaximize risk rather than let schedulessignificantly slip. After Discoveryflew again with foam loss in 2005,after two and one-half years of safetywork, seven of the 25 voting membersof the Stafford-Covey Task Group,tasked for certifying that the ColumbiaAccident Boards’ recommendationshad been met, issued a minority report.In this 19-page annex to the mainreport, they observed that ‘‘NASA’sleaders and managers must break thiscycle of smugness substituting forknowledge’’ [6].

Risk involves two components: theprobability of occurrence of harm andthe consequence of that harm. As shownin the classic risk chart (Figure 1), if therisk associated with a current productdesign occurs in the intolerable regionof high probability of occurrence and

Digital Object Identifier 10.1109/MEMB.2007.911013

Gail D. Baura

Increasing Severity of Harm

IncreasingProbability ofOccurrence

Intolerable Region

ALARPRegion

BroadlyAcceptableRegion

Fig. 1. Three region risk chart [7].

Risk involves

the probability

of occurrence

of harm and the

consequence of

that harm.

52 IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE 0739-5175/07/$25.00©2007IEEE NOVEMBER/DECEMBER 2007

high severity, then the design should bemodified to reduce risk to as low as rea-sonably possible.

Even though foam loss occurred duringthe inaugural flight, which demonstratedthat an external tank requirement was notbeing fulfilled, NASA classified and con-tinues to classify foam loss as being withinthe broadly acceptable region of risk.

When risk analysis is conducted in themedical device industry, developers andusers meet for endless hours to documentall known risks and to mitigate them.Development engineers are critical to thisprocess. Similarly, NASA should havelistened to engineer Roger Boisjoly whenhe tried to prevent Challenger from

launching during the coldest launchtemperature to date, which he believedwould cause O-ring failure. NASA shouldhave granted chief engineer RodneyRocha’s request to obtain a detailed videoof the Columbia launch to assess foamdamage before reentry. Finding a solutionin 2007 to a problem that first occurred in1981, against a specification requirementwritten in 1973, and after seven deaths in2003 remains unacceptable.

Gail D. Baura is a professor at KeckGraduate Institute of Applied Life Sci-ences in Claremont, California. She canbe reached at gbbook@mindspring.com.

References[1] W. E. Leary, ‘‘NASA believes it has found rea-son foam fell on shuttle,’’ NY Times, p. A3, 25 Aug.2007.[2] NASA National Space Transportation System,‘‘Space shuttle program description and require-ments baseline,’’ NASA, Houston, TX, NSTS-0700,vol. 1, book 1, 1973.[3] NASA National Space Transportation System,‘‘External tank component end item specification,’’NASA, Houston, TX, NAS8-30300, 1980.[4] G. D. Baura, Engineering Ethics: An IndustrialPerspective. Burlington, MA: Academic Press, 2006.[5] J. Schwartz and W. E. Leary, ‘‘Return to space:The overview; shuttle docks; shield damage is calledminor,’’ NY Times, p. A1, 29 July 2005.[6] Stafford-Covey Task Force, ‘‘Return to flighttask group,’’ NASA, Houston, TX, final rep., July2005, p. 197.[7] Association for the Advancement of MedicalInstrumentation, ‘‘Medical devices—Application ofrisk management to medical devices,’’ AAMI, Wash-ington, DC, ANSI/AAMI/ISO 14971:2000, p. 20.

Book Reviews (continued from page 11)

This text is divided into three broadsections. Part 1 is aimed at deliveringthe necessary nuts and bolts introduc-tion to relevant topics in biology, mathe-matics, and experimental techniques.The range of topics covered is relativelycomprehensive with corresponding con-cise and useful clarifications. The expla-nation of molecular bonds and forcescovers three pages, as does differentialequations and DNA libraries.

Part 2 introduces the fundamentaldetails that qualify the systems descriptorto this field. This includes descriptions ofprocesses, cycles, and expressions aswell as modeling tools and approaches.Many engineers will be comfortable withthe mathematics associated with compu-tational and modeling approaches, evenif they are not familiar with it. This maynot be the case, however, for the descrip-tions of biological systems. These in-clude applications to cellular processesand functions, including self-organizationand self-replication as well as geneexpression/regulation including timedelays. The authors specifically seek toexplain how different models are used toapproach distinct classes of simulations.

Particularly revealing is the use ofthese models and interpretations tocellular systems including regulation,cascades, oscillations, and even aging.The application of modeling to theunderstanding and explanation of theseintercellular and intracellular proc-esses is a familiar engineering approach.Part 2 concludes with examples of howsystems biology affects medical systemsand biotechnology, and it specificallyaddresses text mining, drug develop-ment, food production, ecology, nano-technology, and even the design of neworganisms.

Discussions and examples of Internetresources for information retrieval andexamination are the focus of Part 3. Theauthors focus more specifically onavailable modeling tools and the data-bases they use in their specific investi-gations, although all the prominentdatabases and modeling software arecovered. Specific databases addressedinclude KEGG, BRENDA, and othersfrom the National Center for Biotech-nology and European BioinformaticsInstitute. The modeling tools includegeneral purpose, mathematical, and

Math lab (including examples) toolsand specialized tools such as Gepasi,E-Cell, PyBioS, as well as the SystemsBiology Markup Language, and theSystems Biology Workbench.

Overall, this text successfullyachieves its goal of providing a surveyof contemporary systems biologyapproaches. The review materials areuseful as few individuals are adept atthe broad range of the topics presented.The treatment, or practice, of systemsbiology covers an extremely broadrange of cellular systems and potentialapplications. Computational Internettools are ever evolving in the number ofapplications and their complexity, andthis shared resource continues toprovide insight and holds great promise.Engineers other than those working inbioinformatics and computational biol-ogy may initially be uncomfortable andunfamiliar with some of the topics andapplications addressed. This resourcedoes an admirable job of bringing thereaders to a level where they can pursuemore advanced study and research.

—Benjamin S. KelleyBaylor University

Point of View (continued)

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