International Guidelines for the Preservation of
Space as a Unique Resource

Phillip D. Anz-Meador, Ph.D., Dept. of Physics
Embry-Riddle Aeronautical University

Introduction

The non-benign nature of spaceflight had been recognized well before the first on-board sensors detected the van Allen radiation belts about the Earth or piezoelectric sensors, meant to measure strain and flexure within the structure of a rocket or spacecraft, first noted the impacts of micrometeoroids on the craft (Explorer 1, Alexander, personal comm.). Indeed, the recognition that meteoroids were “burning” in the upper atmosphere implied the requirement of a source of particles to burn, hence the studies of both photographic and radar/radio meteors. Observations of the sun, as well as such terrestrial phenomena as the Aurora Borealis and Australis, and such celestial phenomena as comets, asteroids, and the faint reflection provided by the meteoroid complex (the so-called “Zodiacal light”), provided further evidence, if needed, as to the significant constituents (and potential hazards) in the space environment.

Means of protecting spacecraft from this natural environment were required, and a significant amount of laboratory and on-orbit testing was conducted in order to protect and preserve spacecraft functions. Almost all measures were passive in nature, e.g. shielding was deployed to protect electronics from cosmic rays and micrometeoroids, designs were optimized to prevent static discharge, and “rad-hard” (radiation hardened) electronics were developed to cope with the ambient radiation environment. Time passed, and space became a place to explore, to do business, and to protect global security.

During that time, an appreciation of the many and varied components of the space environment grew. A large body of literature developed to characterize, explain, and predict the effect of the ambient environment upon spacecraft and space materials. It is not the intent of this paper to review that portion of the environment.

The near static nature of some of the components was noted, as well as the dynamic nature of others. Yet this was not the only categorization possible. For example, some (notably Mr. John Gabbard) noticed oddities in the catalogs of space objects tracked by the North American Aerospace Defense Command (NORADCOM). Certainly it wasn’t common knowledge that not only had we launched the LANDSAT 1 spacecraft aboard a Delta rocket, but evidently hundreds of other small objects with this launch. Further analysis indicated that these objects were debris associated with the accidental fragmentation of the Delta’s second stage. Again, time passed. Military tests were conducted in space, including intentional explosions and collisions, and the list of accidental explosions grew.

Debris began to accumulate and, with a maturity of thought not present at the dawn of the Space Age, scientists and engineers in the United States came to realize that spacecraft must not only be protected from the “natural” environment on-orbit, but also the induced, or “man-made” environment. Finally, a burgeoning sense of environmental stewardship led to the modern international consensus that not only must spacecraft be protected from their environment, but that same environment must be protected from spacecraft.

This, then, is the subject of this paper: what is being done to protect spacecraft from the macroparticle (to include both anthropogenic debris and meteoroids) environment, and what is being done to protect the environment from man’s presence. Only a holistic view of these processes can ensure a future environment safe for its navigation and capable of sustaining continued growth and exploitation of the unique natural resource offered us by space. Thus, in this paper we shall review the international guidelines being formulated to protect both spacecraft and the environment. To place these in context for the general reader, we shall start by providing an overview of the current space environment and environmental effects upon spacecraft.

Environmental Overview

The man-made space environment

The man-made component of the overall space environment is usually categorized into five types of objects, and as well by the object’s active or inactive status. The five types are spacecraft or payloads, rocket bodies or rocket boosters, operational debris, fragmentation debris, and anomalous debris. To be more explicit, we may define the types as follows:

• Spacecraft or payloads: active or inactive (in storage, or derelict) vehicles or objects whose purpose was the primary goal of their respective launch. While the term “spacecraft” is usually reserved for relatively complex vehicles, the broader term “payloads” describes all levels of sophistication, including such inert objects as calibration spheres and dipoles.
• Rocket bodies (or boosters; usually abbreviated as “R/B”): these vehicles provide the means of launch, orbital transfer, and orbital insertion to the payloads. Thrust is provided by liquid fuel engines, solid fuel motors, or gaseous and/or electric/ionic thrusters. Size ranges from over ten meters in length (e.g. the Commonwealth of Independent State’s [CIS] Zenit, or SL-16 [US Dept. of Defense designation], R/B) to small ullage motors used to settle liquid propellants and ejected by the CIS Proton’s (SL-12) fourth stage.
• Operational debris: debris released during stage separation, payload deployment, or payload operations. These may include, respectively, straps and bolts; adapters, clamp bands, and spin/de-spin weights (“yo” weights); and retention or hold-down straps and radiator or sensor covers.
• Fragmentation debris: debris created during the planned or accidental explosion of, or collision between, payloads and/or R/B. Though not cataloged due to their size, debris produced by collisions of small objects with large targets could logically fit into this category.
• Anomalous debris: debris created by unknown means, usually long after payload deployment or end-of-mission. While the majority of instances have produced one or two anomalous objects, some (such as the Cosmic Background Explorer [COBE] or the SNAPSHOT nuclear reactor-powered test satellite). It has been suggested (Johnson, N., personal comm.) that while fragmentation debris are a measure of space traffic’s effect upon the environment, anomalous debris may be a measure of the environment’s effect upon resident space objects.

The approximate distribution of objects by type is depicted in Fig. 1; the reader should note that these objects are exclusively 10 cm (approximately) and larger in size, and are cataloged using ground-based sensors.

Such time-sequenced events may have been observed by the Long Duration Exposure Facility’s Interplanetary Dust Experiment [8] and the SkiYMET meteor radars (Ref. X3) as well. Both exhaust products and paint pigments have been identified by scanning electron microscopy and elemental analysis in impact crater residue. Human biological wastes have also been identified by this technique [9], though these particulates should normally be confined to altitudes below about 400 km, the maximum altitude of most manned missions.

Degradation debris have also been measured on-orbit. Also referred to as local contamination, these debris tend to be most prevalent during the first weeks or months of operations; as such, they are similar to “out gassing” effects (Ref. X2).

Once classified by general type, a second objective method of characterizing the man-made population is by size and mass. The following table (after Ref. X4, with updated information) portrays the gross distribution of resident space objects in size and mass.

Table I. A statistical breakdown of the on-orbit man-made population. The total percent mass represents that fraction of a total estimated mass loading of 1,400,000 kg; this figure is based upon the NASA space traffic model and the Dept. of Defense Space Control Center (SCC) catalog.

The categorization by size is not coincidentally broken out in decades of size; objects greater than approximately 10 cm (in low Earth orbit, or LEO) are observed by ground-based sensors, tracked and correlated, and cataloged by agencies performing the space surveillance mission worldwide. Those between 1 and 10 cm may be observed by special radars during statistical data collection campaigns, while those smaller are rarely observed. Rather, objects smaller than 1 mm are typically assessed by counting the number of impact features on surfaces exposed to, and returned from, space.

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