Chapter 19. heritage of earth orbit   orbital debris - its mitigation and cultural heritage
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    Chapter 19. heritage of earth orbit   orbital debris - its mitigation and cultural heritage Chapter 19. heritage of earth orbit orbital debris - its mitigation and cultural heritage Document Transcript

    • 19 Heritage of Earth Orbit: Orbital Debris—Its Mitigation and Cultural Heritage Alice GormanCONTENTSIntroduction ............................................................................................................ 381Orbital Debris......................................................................................................... 382Managing Orbital Debris ...................................................................................... 385 Design and Operational Mitigation ............................................................. 385 Earth-Based Removal Programs .................................................................. 385 Intervention Missions .................................................................................. 385Archaeology and Heritage of Orbital Objects ...................................................... 386Vanguard 1 ............................................................................................................. 387 Aesthetic ....................................................................................................... 388 Historic ......................................................................................................... 388 Scientific ....................................................................................................... 389 Social ............................................................................................................ 389Survey of Early Satellites in Orbit ......................................................................... 390Risk Assessment .................................................................................................... 391Conclusions ............................................................................................................ 394Further Reading .................................................................................................... 395References .............................................................................................................. 396INTRODUCTIONSince the launch of Sputnik 1 in 1957, human material culture in the form of satellites,launch vehicle upper stages, mission-related debris, and “space junk” has prolifer-ated in Earth orbit. There are now significantly more than 10,000 trackable objectscircling the Earth between low Earth orbit at around 200 km and the “graveyardorbit” around the geostationary ring at 35,000 km above the surface of the Earth. 381© 2009 by Taylor and Francis Group, LLC
    • 382 Handbook of Space Engineering, Archaeology, and HeritageOnly a small portion of this material is operational spacecraft; the rest is classed asorbital debris. Space industry is now at the stage where collision with orbital debrisis a serious threat for the continued provision of satellite-based services, such asnavigation, telecommunications, meteorology, and earth observation. This situation constitutes an environmental management problem for space indus-try. In the short term, measures to control the proliferation of debris have includedchanging mission design and operation practices as recommended the U.S. NationalAeronautics and Space Administration (NASA), the European Space Agency (ESA),and the United Nations.1,2,3 However, it is widely recognized that more active mea-sures to remove debris from orbit will be required in the future. Proposals haveincluded the destruction of debris using ground- and space-based lasers and inter-vention missions by specialized spacecraft. While the necessity of some active management is accepted by all, the problemis slightly more complex than a consideration of the technical difficulties suggests.As discussed in Chapter 16, orbital space constitutes an organically evolved culturallandscape as defined by the World Heritage Convention.4 Objects now classed asorbital debris may have social, historical, aesthetic, and scientific significance fornations, communities, groups, and individuals who will have an interest in decisionsmade about their long-term survival. It is not just the threat of collision that needs tobe managed: proposals for orbital debris cleanup must also consider how to managethe cultural values of the orbital spacescape. This does not mean that everything must be saved. In this chapter, I look at someof the issues that can help us make well-grounded decisions about what to preservein situ and what to let go. There are two facets to this: an assessment of the risk posedto space operations by different debris classes, and the assessment of the significanceof orbital objects according to the categories of the Burra Charter, Australia’s pri-mary heritage management document.5 The Charter, while designed specifically forAustralia, has been recognized as a simple and powerful set of heritage managementguidelines that sets standards worthy of being emulated at an international level.To demonstrate how significance can be assessed as the basis for sound manage-ment decisions, I look at the oldest surviving human object in orbit: the Vanguard 1satellite.ORBITAL DEBRISOrbital debris has been defined as any human-manufactured object in orbit thatdoes not currently serve a useful purpose and is not anticipated to in the foreseeablefuture.6 Approximately 4,200 launches have occurred since 1957, leaving more than10,000 trackable objects larger than 10 cm in orbit (Figure 19.1).7 Only 7% of theseare operation spacecraft; 52% are decommissioned satellites, upper stages, and mis-sion-related objects, and 41% are debris from the fragmentation of orbital objects. Operational and decommissioned spacecraft include scientific and telecommu-nications satellites, weather and earth observation satellites, navigation and surveil-lance satellites, satellite constellations, and military satellites. Upper stages includethe durable Agena, in use from the time of the Gemini program to the mid-1980s,and those of the Ariane family of rockets, first launched in 1979.© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 383FIGURE 19.1 This computer-generated image shows the thousands of satellites, spentrocket stages, and breakup debris in low Earth orbit. (Courtesy of NASA.) Mission-related debris derive from deployments and separations of spacecraft,which typically involve the release of items such as separation bolts, lens caps, fly-wheels, nuclear reactor cores, clamp bands, auxiliary motors, launch vehicle fair-ings, and adapter shrouds.8 Solid rocket motors used to boost satellite orbits havecontributed other objects, such as motor casings, aluminum oxide exhaust particles,nozzle slag, motor-liner residuals, solid-fuel fragments, and exhaust cone bits result-ing from erosion during the burn, to the debris population. Fragmentation debris are derived primarily from the explosion of satellites andlaunch vehicle upper stages, both of which tend to remain in orbit after the comple-tion of their mission.9 Explosion can occur when residual liquid fuel componentsaccidentally mix, or when fuel or batteries become over-pressurized. There are alsocases where spacecraft have been deliberately detonated, to prevent reentry and/orto conceal their presence or purpose. More than 124 breakups have been verified sofar, and the rate of breakup increases each year. Another major source of debris ismaterial degradation from a range of environmental effects, resulting in the produc-tion of particulates, such as flakes of paint and insulation. Figure 19.2 shows the“energy flash” when a projectile launched at speeds up to 27,000 km/h impacts asolid surface at the Hypervelocity Ballistic Range at NASA’s Ames Research Centerin Mountain View, California. This test is used to simulate what happens when apiece of orbital debris hits a spacecraft in orbit. Debris is concentrated in the orbital configurations most commonly used in spaceoperations, defined by altitude above the earth’s surface, inclination, and eccentric-ity. The orbit employed depends on the purpose of the satellite and the location of thelaunch site. Most objects are in the nominally circular orbits, low Earth orbit (LEO)© 2009 by Taylor and Francis Group, LLC
    • 384 Handbook of Space Engineering, Archaeology, and HeritageFIGURE 19.2 Energy flash of an orbital debris hit. (Courtesy of NASA.)or geosynchronous Earth orbit (GEO).10 Medium Earth orbits are less widely used,to avoid the Van Allen radiation belts. In low Earth orbit, aerodynamic drag acts as a “natural cleansing mechanism,”causing objects to reenter the atmosphere and (mostly) burn up.11 At 400 km or belowin altitude, it may take only a few months for objects to reenter. However, above 600km, objects can remain in stable orbits for a few decades up to thousands of years.Satellites in GEO are beyond the reach of atmospheric affects although still subjectto the vagaries of the space environment. Within these orbital regimes, there are areas of higher debris density. In low Earthorbit, debris builds up near polar inclinations from sun-synchronous satellites and ataltitudes near 800, 1,000, and 1,500 km.12,13 There are an estimated 70,000 pieces ofdebris about 2 cm in size at the 850–1,000 km altitude.14 Objects in geosynchronousand Molniya orbits and constellations of navigation satellites cause another peak indensity at 25,000 km. The highest peak is at 42,000 km, consisting of objects at ornear the geostationary ring.15 Within the GEO region, peaks of debris occur at thefollowing: • The equatorial inclination • 28.5°, due to the latitude of the main U.S. launch site at the Kennedy Space Center • 63°, from Molniya and GLONASS satellitesModeling the debris environment is reliant on data collected from optical and radartracking. Debris over 10 cm is tracked by U.S. Space Command (USSPACECOM),using twenty-five land-based radars and optical telescopes in the Space SurveillanceNetwork. Over the former USSR’s territory, debris is tracked by the Russian Space© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 385Surveillance Centre,16 ESA maintains the DISCOS database of space debris. Onlydebris above a certain size can be tracked in this way, and visibility depends onaltitude: in GEO, an object must have a diameter of 1 m to be visible, while in LEO,radar can detect pieces as small as 5 mm. The population of debris below this size isestimated on the basis of impacts on returned spacecraft surfaces.17MANAGING ORBITAL DEBRISMitigation strategies for orbital debris can be broadly divided into three types: (1)design and operational solutions, (2) Earth-based removal programs, and (3) inter-vention missions.DESIGN AND OPERATIONAL MITIGATIONThis strategy is aimed at controlling the amount of new debris that enters the systemby designing spacecraft and missions to minimize mission-related debris and thepotential for fragmentation. Design solutions include using tethered lens caps andbolt catchers, shielding or augmenting components to withstand impact, and the useof operating voltages below arc thresholds. Operational measures include postmission maneuvers to place the spacecraftwithin the range of aerodynamic drag or in a graveyard orbit and expelling remain-ing propellants and pressurants to prevent accidental explosion.18 The NASA guide-lines for limiting orbital debris recommend that an object should not remain in itsmission orbit for more than 25 years.19,20EARTH-BASED REMOVAL PROGRAMSOther proposals have examined the prospect of removing debris between 1 and 10 cmin diameter in LEO by ground-based lasers (e.g., NASA’s Project Orion and Electro-Optical Systems).21,22 The laser ablates particles from the surface of the debris, creat-ing enough thrust to edge it into reentry.23 Space-based laser removal has also beenconsidered, for example, to move debris out of the path of the International SpaceStation, but is considered too costly in time and energy to be feasible at this stage.INTERVENTION MISSIONSIntervention missions include the use of specialized spacecraft that actively removeobjects from orbit. A study undertaken by QinetiQ investigated scenarios for remov-ing decommissioned satellites in GEO using a reorbiting spacecraft, concluding thatthis was plausible if not yet feasible.24 For LEO, a Royal Melbourne Institute ofTechnology group has proposed the use of space-based electrodynamic tethers tocapture and remove debris. At this point in time, only design and operational mitigation is used on space mis-sions. Before any active debris mitigation measures are implemented, the question ofwhether spacecraft currently classed as debris have any cultural heritage value needsto be addressed. What do we want to save for future generations? Should significant© 2009 by Taylor and Francis Group, LLC
    • 386 Handbook of Space Engineering, Archaeology, and Heritagespacecraft be left in situ or removed to Earth for curation and display? If we acceptthat orbital space is a cultural landscape, the most appropriate management responseis to leave spacecraft where they are. But this raises a critical question: can culturalheritage values be managed without compromising safety or service delivery?ARCHAEOLOGY AND HERITAGE OF ORBITAL OBJECTSThe primary concern of archaeology is to understand role of material culture inhuman social and environmental engagement. Despite popular perceptions, archae-ology is not necessarily concerned only with the ancient: there is much to be learntfrom contemporary material culture, particularly as it brings with it the added dimen-sions of extensive documentation and personal memories. It is often in the disjunc-tions between these that the most interesting stories wait to be told. Space objects fall into the field known as historical archaeology or postmedi-eval archaeology, which is concerned with the global expansion of industrializedEuropean nations, the growth of capitalist economies, and interactions with indig-enous people in the colonies. Within this broad field, there are subdisciplines, suchas military archaeology and contemporary archaeology, which have useful theoreti-cal perspectives. Spacecraft can be regarded as archaeological artifacts, the material record of aparticular phase in human social and technological development. They have researchpotential in terms of understanding human interaction with the space environment.But they also more than this. Material culture can be regarded as heritage: objectsfrom the past that have meaning in the present and that are important to the identityand well-being of communities. We know that people see the material culture of space exploration as important:for example, of all the Smithsonian institutions in Washington, D.C., the most popu-lar is the National Air and Space Museum. The attraction is actually seeing theartifacts such as the Gemini capsule, spacesuits, and pieces of Skylab.25 One canread books and documents, watch film footage, and view photographs, but nothingcan convey the same information or meaning as the actual object itself. So we knowthat at least some people in some places value these objects. The question we needto address in managing heritage values during orbital debris mitigation is for whomare they significant, and why? The significance of space material culture is often assumed to be self-evident. Oneof the most commonly cited rationales for space exploration, referred to in countlessbooks, documentaries, and museum displays, is that space exploration is the naturaloutcome of an innate human urge to explore. Thus, space objects are perceived tohave a globally understood meaning that appeals to our common human nature.26Space exploration is seen as the most recent manifestation of a fundamental curiositythat led humans out of Africa, across the seas from the Old World to the New World,and inevitably into space. Another popular model for understanding the significance of space materialculture is what I have called the Space Race model.27 In this formulation, objectsand places have significance for their contribution to the Cold War confrontationbetween the United States and the USSR. This model focuses on these two states,© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 387ignoring the achievements of other countries, such as France, Britain, China, Japan,and Australia, and the contributions made by “developing” nations who often hostedlaunch sites, ground stations, and so forth. The Space Race model emphasizes com-petitiveness rather than cooperation in space, with an implicit Darwinian overtone:spacefaring nations (mostly imperial, industrial, and white) demonstrate technologi-cal fitness by their success in space enterprises. The relationship of space explora-tion to inequalities between the developed and developing world is unexplored, andindeed unproblematic, in the Space Race scenario.28 Of course, these approaches do capture something meaningful about the sig-nificance of space material culture, but it is far from the whole story. To obtaina deeper and more inclusive understanding of heritage significance, I turn to theguidelines adopted by the Australian National Committee of the InternationalCouncil on Monuments and Sites in the Burra Charter.29 As well as providinga methodology for assessing significance, the Burra Charter sets out principlesfor preservation and conservation. Its main tenet is “Do as much as is necessaryand as little as possible” in order to retain the cultural significance of a place orobject. The Burra Charter outlines four different categories of significance: 1. Aesthetic: considerations of form, scale, color, texture, material, smells and sound, and setting 2. Historic: association with historic figures, events, phases, or activities 3. Scientific: importance in terms of rarity, quality, representativeness, and the degree to which a place can contribute further substantial information 4. Social: the qualities for which a place has become a focus of spiritual, polit- ical, national, or other cultural sentiment to a majority or minority groupThe Burra Charter also stresses that significance may be multivocal, and Article 6.3states that the “co-existence of cultural values should be recognized, respected andencouraged, especially in cases where they conflict.” These kinds of significance are used successfully as the basis for museum col-lections of space artifacts around the world and have been used in nominating spacesites on Earth for heritage listing. In the next section I want to apply them to the old-est artifact in Earth orbit: the Vanguard 1 satellite.VANGUARD 1The Vanguard 1 satellite, launched successfully on March 17, 1958, is now the old-est manufactured object in orbit (Figure 19.3). It is in a highly stable LEO orbit withevery prospect of remaining there for perhaps another 600 years. Unlike Sputnik 1 and Explorer 1, Vanguard was launched using scientificsounding rockets rather than missile technology to avoid a military “taint.” As thelaunch was part of the International Geophysical Year program, the Vanguard teamrecruited a network of volunteers across the world to carry out visual tracking inProject Moonwatch.30 This community involvement played an important role in con-figuring the project as scientific, cooperative, and inclusive.© 2009 by Taylor and Francis Group, LLC
    • 388 Handbook of Space Engineering, Archaeology, and HeritageFIGURE 19.3 Vanguard 1 satellite. (Courtesy of NASA.) In terms of the Burra Charter’s categories of significance, we might attempt anassessment along the following lines.AESTHETICIn design, Vanguard 1 is spherical, with antennae attached at right angles to thebody, made of silver aluminum. It was renowned for its small size, being dubbedthe “grapefruit satellite” by Khrushchev. The size and the design reflect the cost ofplacing material in orbit and perhaps also mutual influence with USSR designs—Vanguard and Sputnik are remarkably similar. Satellites are no longer manufacturedto a spherical design, so this shape is indicative of an early phase, where satelliteswere seen not so much as an earth-circling spaceship as a miniature moon (bébélune, or baby moon). The spherical shape continued to be used in the USSR forcrewed shariks (descent capsules), but by 1960 this design was becoming rare.HISTORICVanguard 1 is associated with the Cold War and the International GeophysicalYear of 1957–1958. It was the third satellite to be successfully launched and thesecond U.S. satellite. It represents the first experimental phase of space explora-tion. Analysis of Vanguard’s orbital perturbations revealed that the Earth was “pear-shaped.” Vanguard represents the conflicting motivations and rationales for spaceexploration in the critical period of the 1950s, when the United Nations also firstmoved to set up the principles of the Outer Space Treaty. Although it was designedas a peaceful scientific satellite, it was also an ideological weapon, a “visible display© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 389of technological prowess” aimed at maintaining the confidence of the free worldand containing Communist expansion.31,32 Vanguard’s design and mission reflect thecompeting models of cooperation and confrontation in space, at a time when therewere no rules, laws, or guidelines to structure the human-orbital interaction.33SCIENTIFICThere are three aspects to the scientific significance of Vanguard 1. • Representativeness: Vanguard 1 is the sole survivor of all satellites launched in 1957–1958, and one of the 23% of satellites remaining in orbit from 180 launches between 1957 and 1963 (the first successful geosynchronous launch, Table 19.1). As such, it is unique: there is no equivalent satellite if Vanguard should be destroyed. • Relevance to space research: There is no other object that has been in space as long as Vanguard 1; hence it is the only artifact that can inform us of the long-term impact of the space environment on human materials. • Relevance to archaeological research: Although there is extensive docu- mentation about the history of Vanguard 1, this does not convey the same information as the object itself and its relationship to other artifacts in Earth orbit. A recording of the physical features of Vanguard 1 (when this is pos- sible) may reveal discrepancies between documentation and reality, and aspects of technological processes that are not longer in use.SOCIALThe satellite represents the expectations that the United States would be first inspace, and its failure to be so caused nationwide doubt and panic. At the time, thecommunity esteem in which Vanguard was held was very low, and it was the butt ofjokes in both the United States and the USSR. Nevertheless, the staff of the NavalResearch Laboratory responsible for the project and the international network ofProject Moonwatch volunteers must have had considerable emotional investment inTABLE 19.1Satellites in Earth Orbit (1957–1963)Year Number of Launches Number of Satellites Remaining Country of Origin1957 2 0 USSR1958 8 1 United States1959 13 3 United States1960 23 7 United States1961 38 9 United States1962 61 10 Canada, United States1963 59 14 United States© 2009 by Taylor and Francis Group, LLC
    • 390 Handbook of Space Engineering, Archaeology, and Heritageits success. With the passage of time, Vanguard’s social significance has changed.Later assessments have acknowledged as Project Vanguard as “the progenitor of allAmerican space exploration today.”34 The satellite has Internet-based fan groups,including one that tracks its location in real time. It is now actually considered to bea “vanguard.” It is esteemed at an international level as the oldest human artifact inspace, at a national level as oldest U.S. artifact in space, and at the local level by thespace-buff communities who follow its progress. This cursory significance assessment demonstrates how the Burra Charter prin-ciples can be applied to orbital objects. Following the guidelines, significance assess-ment should then be used as the basis for management. So what then is the bestmanagement policy to preserve the cultural significance of this satellite? Optionsinclude destruction as part of an active debris mitigation program, removal to thesafekeeping of a terrestrial museum as soon as practicable, or—simply nothing. As is clear from the assessment of significance above, Vanguard does have highcultural significance, so destruction is not an appropriate option. It is also clear thatpart of Vanguard’s scientific and social significance is its presence in orbit. TwoBurra Charter principles can be applied here: first, that we should do as much asis necessary and as little as possible, and second, that the setting of an object orplace should be retained as part of its cultural significance. Removal to Earth woulddiminish the cultural significance of the satellite and should not be considered appro-priate management unless this would prevent its destruction.SURVEY OF EARLY SATELLITES IN ORBITVanguard 1 is not the only satellite that may have heritage significance from the earlyyears of space exploration. The following is a brief survey of other whole satellitesstill in low and medium Earth orbits from the period between the launch of Sputnik1 in 1957 to the launch of the first geosynchronous satellite, Syncom 1, in 1963. Data come from a publicly available database of objects tracked by USSPACECOM.The information presented here focuses on satellites that had been launched intention-ally into Earth orbit rather than toward the Moon, sun, or other planets. Spacecraftthat have been lost or deliberately deorbited, landed, or decayed, as well as rocketbodies, mission-related debris, and fragmentation debris, have been excluded. Of 180 satellites launched between 1957 and 1963, 41 remain in Earth orbit (23%).All except the Canadian Alouette 1 originated from the United States (Figure 19.4;Table 19.1). They occupy low Earth orbit at both equatorial and polar inclinations,sun-synchronous orbits, and medium Earth orbit. The function of the satellites is notalways clear-cut: many scientific and other missions were undertaken for militaryapplications, and information about others is still classified, but even in this earlyperiod, the satellites cover the range of functions that are still predominant today,with a fairly even distribution among scientific, meteorological, navigation, commu-nications, and defense-related missions.35 There are only a small number of satellites still in orbit from this early period, andeach one could be argued to demonstrate an aspect of developing space technology.They include Vanguard 1, 2, and 3; Explorer 7; TIROS 1, the first weather satellite;Transit 4A and 4B, which carried the first nuclear power sources on a spacecraft;© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 391FIGURE 19.4 Alouette 1. (Courtesy of NASA.)Telstar 1, the first active telecommunications satellite (Figure 19.5); and the Westfordneedles and their release capsule.36 In this range we can see technological trajecto-ries: from nuclear power to solar power, from passive telecommunications to active,from spherical baby moons to more diverse designs, increasing size, and increasingheight above Earth’s surface.37 The material is dominated by U.S. spacecraft: howmight this be interpreted by archaeologists of the future? What can we learn aboutthe early space programs by what is left in orbit, as opposed to the documentaryrecord? We cannot anticipate future research directions, but one day orbital objectswill tell their own stories, if they survive.RISK ASSESSMENTIf significant spacecraft are left in orbit, does this merely contribute to the orbitaldebris problem? The next step is to assess the actual risk posed by heritage space-craft to operational spacecraft. This involves a consideration of the damage causedby different size classes of debris, and the actual probability of collision. Orbital debris can be divided into three size classes. • Large: diameter greater than 10 cm. Large debris can be optically tracked. • Medium: diameter between 1 mm and 10 cm. Tracking depends on size and altitude. • Small: diameter less than 1 mm. This is the largest population of orbital debris, and these items cannot be tracked.© 2009 by Taylor and Francis Group, LLC
    • 392 Handbook of Space Engineering, Archaeology, and HeritageFIGURE 19.5 Telstar 1. (Courtesy of NASA.)The results of collision with a piece of debris include mechanical damage, materialdegradation, and, occasionally, catastrophic breakup of operational spacecraft. Eventiny particles can cause significant damage because the impacts occur at hyperve-locity (i.e., when the magnitude of the impact velocity is greater than the speed ofsound in the impacted material).38 In LEO, the average relative velocity of spacedebris at impact is 10 km/s (36,000 km/h).39 Average relative velocities in GEO aremuch lower, about 200 m/s (720 km/h), but collisions at this speed can still causesignificant damage. In terms of impact, a 10-cm fragment in geosynchronous orbithas roughly the same damage potential as a 1-cm fragment in LEO. A 1-cm geosyn-chronous fragment is roughly equivalent to a 1-mm low Earth orbit fragment.40 Collision with an object in the large size class (>10 cm) can cause fragmentationand breakup, a significant source of new orbital debris. Impact from the mediumdebris class, 1 mm to 10 cm, can cause significant damage and mission failure.41Penetration by a debris fragment 1 mm to 1 cm in size, through a critical component,can result in the loss of the spacecraft. Fragments greater than 1 cm can penetrateand damage most spacecraft.42 Although objects in the small size class rarely causecatastrophic breakup, they can erode sensitive surfaces, such as payload optics.43 However, it is also necessary to consider the frequency with which such collisionsoccur for the different size classes. There is a direct relationship between the num-bers of debris in each size class, the relative velocities in different orbital regimes,and the probability of impact.© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 393TABLE 19.2Mean Time between Impacts on a Satellite with a Cross-Section Area of10 m2 in Low Earth Orbit Mean Time between Collisions (Years)Height of CircularOrbit (km) Objects 0.1–1.0 cm Objects 1–10 cm Objects >10 cm 500 10–100 3,500–7,000 15,0001,000 3–30 700–1,400 20,0001,500 7–70 1,000–2,000 30,000Source: Courtesy of United Nations, Technical Report on Space Debris, United Nations, New York, 1999. In LEO, the population of large debris is much lower than the medium and smallclasses, but the severity of impact is much greater when collision does occur becauseof the high relative velocity.44 Despite this, collisions with large objects over 10 cmare rare, and there are only a few recorded breakups due to catastrophic collisions.45The density of the small debris class, however, is such that spacecraft in LEO experi-ence continuous bombardment by very small particles. Lower relative velocities and greater distances between objects in GEO signifi-cantly reduce the probability of collision.46 Because of the increasing use of disposalorbits after mission completion, the rate of debris accumulation is slower than inLEO. Approaches between operational spacecraft and tracked objects can be pre-dicted and evasive maneuvers undertaken to avoid collision. Because most objects inthe geosynchronous ring move along similar orbits, objects in GEO are more likelyto collide with a meteoroid than with debris.47 However, untracked debris in GEO isnot as well modeled as that in LEO.48 Table 19.2 illustrates the mean time between collisions with objects in thethree size classes in different orbits. This table also demonstrates that the great-est risk of impact derives from the small debris size class in LEO. The larger thepiece of debris and the higher the orbit, the less likely it is that a collision willoccur. However, the medium debris class, 1 mm to 10 cm, is the most destructive.Medium debris are far more numerous than the large class, have a higher riskof collision, and can cause significant damage and mission failure.49 Apart fromindicating that any active orbital debris mitigation program should target this sizeclass rather than large objects, this also suggests that costly intervention missionsaimed at removing large decommissioned spacecraft will have minimal impact onthe debris problem. In the first instance, then, preserving orbital debris larger than 10 cm, whichincludes whole but defunct satellites, upper stages, and mission-related debris suchas the famous glove lost by Edward White in 1965 (currently tracked by Electro-Optical Systems50) in their orbital locations can be done without compromisingthe safety and operation of crewed and uncrewed missions. If an object, such as© 2009 by Taylor and Francis Group, LLC
    • 394 Handbook of Space Engineering, Archaeology, and HeritageVanguard 1, has been identified as having heritage value, then it can be excludedfrom any future debris mitigation projects that involve deorbiting. Potentially cata-strophic approaches can be avoided by on-orbit maneuvers. As any active debrismitigation proposal must be designed to exclude operating spacecraft, it should sim-ply be a matter of appropriate planning to avoid objects of cultural significance. It is also possible that debris in other size classes may have cultural significance,particularly with regard to its representativeness. An initial reaction may assumethat any significance will be extremely low, but this cannot be determined without asystematic investigation, which I will not attempt here.CONCLUSIONSEarly conceptions of the Space Age imagined it as technological utopia, constructedof clean, metallic surfaces buffering the population from the disorder of a messy,organic past. In the contemporary world, it is acknowledged that continuity andconnection to the past are vital in maintaining the well-being of communities, asthe world becomes increasingly globalized. The destruction of cultural heritage hasaccelerated with the growth of population, development, and industrialization, andUNESCO, through the World Heritage Convention, recognizes that “that deteriora-tion or disappearance of any item of the cultural or natural heritage constitutes aharmful impoverishment of the heritage of all the nations of the world.” There is also a growing interest in the archaeology and cultural heritage of the morerecent past, covering events and phases such as the two world wars, the nuclear indus-try, and the Cold War.51,52 Heritage authorities around the world are now protectinglandscapes shaped by these events. It would be wrong to assume that simply because aplace or object is “recent” we know all about it: rapid technology change and militaryand commercial secrecy may, in some cases, mean that we understand even less abouta Cold War site than an Iron Age hill fort. Space places and objects are no exception. To date, all considerations of the orbital debris problem have focused on the riskposed to satellite services and crewed missions. The potential for space debris miti-gation to impact on cultural heritage values has not been examined. In this discus-sion, I have argued that orbital debris can have cultural heritage significance, andpreserving significant orbital objects in the large size class in situ does not add tothe risk posed by orbital debris to space missions. From this, it follows that theimplementation of active debris mitigation strategies, such as deorbiting into theatmosphere or into graveyard orbits, should consider what impact this will have onthe cultural landscape of orbital space and on the object as part of that landscape. In the absence of legal instruments, cultural heritage in orbit could be protectedby agreed guidelines. In 1999, an environmental symposium at the UNISPACEconference recommended that the concept of international environmental impactassessments be developed for all proposed space projects “that might interfere withscientific research or natural, cultural and ethical values of any nation.”53 Althoughcultural impacts were identified primarily as affecting the night sky as seen fromEarth, this could apply equally to orbital debris. Following terrestrial models such as those used in Australia, an environmentalimpact assessment for an orbital enterprise might include the following:© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 395 • Identification of objects of significance at international, national, and agency levels • Identification and consultation with stakeholders (designers, scientists, gov- ernment, industry, clients, and users of the service) • Significance assessment, including aesthetic, historic, scientific, social, or spiritual value for past, present, or future generations54 • Identification of impacts on orbital heritage (e.g., damage, destruction, alteration of current orbit, increased risk of collisions)Management options may include undertaking no active measures, monitoring of theposition of significant objects, changing the orbit of the significant object to reduce therisk of damage, or redesigning the mission to avoid impacts on the significant object. Before active debris mitigation strategies are implemented, there is an opportu-nity to assess the nature of the material record in orbit and ensure that objects ofsignificant cultural heritage value are not lost. What would future generations ofspace tourists think if they found that Vanguard 1 was destroyed needlessly throughlack of forethought?FURTHER READINGBelk, C.A., Robinson, J.H., Alexander, M.B., Cooke, W.J. and Pavelitz, S.D. 1997 Meteoroids and Orbital Debris. Effects on Spacecraft. NASA Reference Publication 1408. Huntsville, AL: NASA.Campbell, J.W. 1996. Project Orion: Orbital Debris Removal Using Ground-Based Sensors and Lasers. NASA-TM-108522. Huntsville, AL: NASA.Centre for Orbital Reentry and Debris Studies. http://www.aero.org/capabilities/cords.Chapman, S. 1959. IGY: Year of Discovery. The Story of the International Geophysical Year. Ann Arbor, MI: University of Michigan Press.Clark, P.S. 1994. Space Debris Incidents Involving Soviet/Russian Launches. Journal of the British Interplanetary Society 47(9): 379–391.Cocroft, W., and Thomas, R. 2003. Cold War: Building for Nuclear Confrontation 1946–1989. London: English Heritage.Crowther, R. 1994. The Trackable Debris Population in Low Earth Orbit. Journal of the British Interplanetary Society 47(4): 128–133.European Space Agency. 2006. Robotic GEostationary orbit Restorer (ROGER). http://www. esa.int/TEC/Robotics/SEMTWLKKKSE_0.html.European Space Operations Centre. 2003. Space Debris Spotlight. http://www.esa.int/ SPECIALS/ESOC/SEMHDJXJD1E_0.html.Gorman, A.C. 2005. The Cultural Landscape of Interplanetary Space. Journal of Social Archaeology 5(1): 85–107.Gorman, A.C. 2007. Leaving the Cradle of Earth: The Heritage of Low Earth Orbit 1957– 1963. Paper presented at the Australia ICOMOS Conference: Extreme Heritage, July 19–21, Cairns, Australia.Gorman, A.C., and O’Leary, B.L. 2007. An Ideological Vacuum: The Cold War in Space. In A Fearsome Heritage: Diverse Legacies of the Cold War, ed. J. Schofield and W. Cocroft, 73–92. Walnut Creek CA: One World Archaeology, Left Coast Press.Green, C.M., and Lomask, M. 1970. Vanguard: A History. NASA SP-4204. The NASA Historical Series. Washington DC.Hypervelocity Impact Test Facility. http://www.wstf.nasa.gov/Hazard/Hyper/Default.htm.ICOMOS Australia. 1999. Burra Charter. http://www.icomos.org/australia.© 2009 by Taylor and Francis Group, LLC
    • 396 Handbook of Space Engineering, Archaeology, and HeritageNASA. NASA Management Instruction 1700.8—Policy for Limiting Orbital Debris Generation. Washington, DC: Office of Safety and Mission Assurance.NASA. NASA Safety Standard 1740.14—Guidelines and Assessment Procedures for Limiting Orbital Debris. Washington, DC: Office of Safety and Mission Assurance.Osgood, K.A. 2000. Before Sputnik: National Security and the Formation of US Outer Space Policy. In Reconsidering Sputnik: Forty Years since the Soviet Satellite, ed. R.D. Launius, J.M. Logsdon, and R.W. Smith, 197–229. Amsterdam: Harwood Academic Publishers.Smith, B. 2004. It’s the Artifacts, Stupid! The Mineralogical Record 35(2): 106–107.Sullivan, W. 1999. Report on the Special IAU/COSPAR/UN Environmental Symposium: Preserving the Astronomical Sky (International Astronomical Union Symposium 196). http://www.iau.org/IAU/Activities/environment/s196rep.html.United Nations. 1999. Technical Report on Space Debris. New York: United Nations.UNESCO Intergovernmental Committee for the Protection of the World Cultural and Natural Heritage. 2005. Operational Guidelines for the Implementation of the World Heritage Convention. World Heritage Centre. http://whc.unesco.org/archive/opguide05-en.pdf.Woodford, J. 2004. A Blast from the Past. Sydney Morning Herald, July 10.REFERENCES 1. NASA. NASA Management Instruction 1700.8—Policy for Limiting Orbital Debris Generation. Washington, DC: Office of Safety and Mission Assurance. 2. NASA. NASA Safety Standard 1740.14—Guidelines and Assessment Procedures for Limiting Orbital Debris. Washington, DC: Office of Safety and Mission Assurance. 3. United Nations. 1999. Technical Report on Space Debris. New York: United Nations. 4. UNESCO Intergovernmental Committee for the Protection of the World Cultural and Natural Heritage. 2005. Operational Guidelines for the Implementation of the World Heritage Convention. World Heritage Centre. http://whc.unesco.org/archive/ opguide05-en.pdf. 5. ICOMOS Australia. 1999. Burra Charter http://www.icomos.org/australia/. 6. Crowther, R. 1994. The Trackable Debris Population in Low Earth Orbit. Journal of the British Interplanetary Society 47(4): 128–133. 7. European Space Operations Centre. 2003. Space Debris Spotlight. http://www.esa.int/ SPECIALS/ESOC/SEMHDJXJD1E_0.html. 8. Belk, C.A., Robinson, J.H., Alexander, M.B., Cooke, W.J., and Pavelitz, S.D. 1997 Meteoroids and Orbital Debris. Effects on Spacecraft. NASA Reference Publication 1408. Huntsville, AL: NASA. 9. Crowther 1994 (note 6). 10. Crowther 1994 (note 6). 11. Crowther 1994 (note 6). 12. Crowther 1994 (note 6). 13. Belk et al. (note 8). 14. Centre for Orbital Reentry and Debris Studies. http://www.aero.org/capabilities/cords/. 15. Crowther 1994 (note 6). 16. Clark, P.S. 1994. Space Debris Incidents Involving Soviet/Russian Launches. Journal of the British Interplanetary Society 47(9): 379–391. 17. Belk et al. (note 8). 18. Osgood, K.A. 2000. Before Sputnik: National Security and the Formation of US Outer Space Policy. In Reconsidering Sputnik: Forty Years since the Soviet Satellite, ed. R.D. Launius, J.M. Logsdon, and R.W. Smith, 197–229. Amsterdam: Harwood Academic Publishers. 19. NASA (note 1). 20. NASA (note 2).© 2009 by Taylor and Francis Group, LLC
    • Heritage of Earth Orbit 397 21. Woodford, J. 2004. A Blast from the Past. Sydney Morning Herald, July 10. 22. Campbell, J.W. 1996. Project Orion: Orbital Debris Removal Using Ground-Based Sensors and Lasers. NASA-TM-108522. Huntsville, AL: NASA. 23. Ibid. 24. European Space Agency. 2006. RObotic GEostationary orbit Restorer (ROGER). http:// www.esa.int/TEC/Robotics/SEMTWLKKKSE_0.html. 25. Smith, B. 2004. It’s the Artifacts, Stupid! The Mineralogical Record 35(2): 106–107. 26. Gorman, A.C. 2005. The Cultural Landscape of Interplanetary Space. Journal of Social Archaeology 5(1): 85–107. 27. Ibid. 28. Ibid. 29. ICOMOS Australia 1999 (note 5). 30. Chapman, S. 1959. IGY: Year of Discovery. The Story of the International Geophysical Year. Ann Arbor, MI: University of Michigan Press. 31. Green, C.M., and Lomask, M. 1970. Vanguard: A History. NASA SP-4204. The NASA Historical Series. Washington DC. 32. Osgood 2000 (note 18). (see specifically p. 216). 33. Gorman, A.C., and O’Leary, B.L. 2007. An Ideological Vacuum: The Cold War in Space. In A Fearsome Heritage: Diverse Legacies of the Cold War, ed. J. Schofield and W. Cocroft, 73–92. Walnut Creek CA: One World Archaeology, Left Coast Press. 34. Ibid. 35. Gorman, A.C. 2007. Leaving the Cradle of Earth: The Heritage of Low Earth Orbit 957–1963. Paper presented at the Australia ICOMOS Conference: Extreme Heritage, July 19–21, Cairns, Australia. 36. Ibid. 37. Ibid. 38. Hypervelocity Impact Test Facility. http://www.wstf.nasa.gov/Hazard/Hyper/Default. htm. 39. Belk et al. (note 8). 40. Crowther 1994 (note 6). 41. Belk et al. (note 8). 42. Crowther 1994 (note 6) (see specifically Fig. 11). 43. Crowther 1994 (note 6). 44. United Nations 1999 (note 3). 45. Crowther 1994 (note 6). 46. United Nations 1999 (note 3). 47. Belk et al. (note 8). 48. United Nations 1999 (note 3). 49. Belk et al. (note 8). 50. Woodford 2004 (note 21). 51. Gorman and O’Leary 2007 (note 33). 52. Cocroft, W., and Thomas, R. 2003. Cold War: Building for Nuclear Confrontation 1946–1989. London: English Heritage. 53. Sullivan, W. 1999. Report on the Special IAU/COSPAR/UN Environmental Symposium: Preserving the Astronomical Sky (International Astronomical Union Symposium 196). http://www.iau.org/IAU/Activities/environment/s196rep.html. 54. UNESCO 2005 (note 4).© 2009 by Taylor and Francis Group, LLC