Joseph N. Pelton
Executive Board, International Association for the Advancement of Space Safety, Arlington, USA
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© Joseph N. Pelton 2013
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What Space Threats Should Concern Us Most?
Have you ever wondered if you might be hit by a piece of space junk falling out of the sky? Well not to worry. The chances of being hit by a piece of orbital debris or a meteorite are fewer than your getting the world’s rarest disease or being killed by a falling coconut if you only visited a tropical paradise for only 1 h in your entire lifetime. In over a half century of space activities there is perhaps one instance of a cow being killed in Africa and that was many decades ago. More recently in 1997 a woman was reportedly brushed on the shoulder by a lightweight fragment of space debris falling from the skies.
But there is still a very good reason for you to read this book. In fact, there are serious threats from space that are actually of mounting concern that you should know about and what actions could be taken to forestall these threats. The growing amount of space debris in the skies could make it difficult in the future to access space for many crucial applications, such as communications, navigation, remote sensing, weather forecasting, military surveillance, nuclear monitoring, or even space exploration. A surprising amount of the world scientific, economic and military activities are now based on spacecraft operations. Solar radiation that penetrates the ozone layer can and indeed does cause skin cancer, and currently occurring changes to the ozone layer are elevating this concern. The most intensive cosmic radiation from gamma rays if unchecked and sustained can also trigger harmful and even bizarre mutations of our genes so as to prevent healthy and normal reproduction.
Solar flares or coronal mass ejections could kill astronauts or wipe out our electrical grids in a powerful and instantaneous way, as happened as recently as March 1989. Although very unlikely, a massive and potentially harmful near-Earth asteroid could destroy much of life on Earth, as was the case with the so-called K-T event (i.e., the Cretaceous Tertiary Mass Extinction Event) that fortunately occurred some 65 million years ago. This single calamitous cosmic occurrence caused between 65 and 70 % of all species on Earth to be killed—including the dinosaurs—in what is known simply as a mass extinction event . On the scale of bad things to happen, this would be very, very bad indeed.
However, let’s start at the beginning to recap what has happened since the Space Age began. Let’s quickly review why today we know much more about cosmic threats than we ever did before, and why in learning about space through sending probes aloft we have managed to create some serious new problems of our own making.
At the Beginning of the Space Age
The age of spaceflight began well over five decades ago on October 4, 1957, with the launch of
When this first spacecraft was launched into Earth orbit, it was hailed as a major advance in human scientific and engineering achievement . The stark realities of the Cold War between the Soviet Union and the United States, however, also painted this first space launch in a vivid military context as well. This Soviet coup in space jolted a vibrant American space program into action. In just a few years there were a number of spacecraft and missile launches occurring in both the United States and the U.S.S.R. .
Back in 1957 little thought was given to what might be the risks associated with
many spacecraft launches. Over a half century later, however, the accumulation of human-built space debris in orbit is now a quite real problem. “Space junk” is now increasingly seen as a creditable threat to humanity’s longer term ability to access and utilize space. In literally dozens of ways humanity is dependent on satellites to communicate, to navigate, to track killer storms, and to provide an effective military defense capability. “Space junk” every day and in every way is becoming a true threat.
If we could effectively stop the creation of all new space debris, we would still not have solved the problem. In fact, the accumulation of debris, just due to collisions from existing space junk, 50 years hence would still be significantly worse. But in fact we are still launching more and more satellites, and space debris continues to mount.
Visionary Ideas are Easy to Often Easy to Dismiss
About a quarter of century ago the possibility that space debris might constitute a tangible threat to our longer term space programs was raised by space scientists and especially by Donald Kessler. Unfortunately at the time this was largely treated as simply a laughable idea. No one is laughing now. Figure2.1
, later in the book, shows rather graphically how this problem seemed to sneak up on us over the past few decades. Human skepticism often serves us well, but sometimes it smothers the most important new ideas. In the area of space this has often been the case.
Robert Goddard, the father of modern rocketry, and other innovators have taught us that there is often a thin line between longer-term vision and what are generally considered as outlandish or quixotic ideas.
In 1919 the Smithsonian Institute published a report by Robert Goddard outlining his plans to launch liquid-fueled rockets. In this treatise he indicated how such rockets could eventually reach the Moon. In 1920 the
New York Times,
with more arrogance than scientific knowledge, responded by running a derisive editorial to call Robert Goddard “The Moon Man” for his audacious claim that one day rockets would carry human adventurers to the lunar surface. Goddard persevered and successfully launched his first liquid-fueled rocked on March 26, 1921. Goddard famously said: “Every vision is a joke until the first man accomplishes it. Once realized, it becomes commonplace.” But it was not until a day after the Apollo Moon landing in 1969 that the
New York Times
ran a correction and an apology for its errors in the 1920 editorial—albeit some 49 years late .
Today space debris is no longer a “laughable idea” More and more people will have the opportunity to fly into space on governmental and commercial spacecraft in the twenty-first century. Up until the end of 2012 only about 500 people have flown into space. As twenty-first century commercial space industries mature, we will actually see more and more “citizen astronauts” flying on sub-orbital flights or even going into orbit. Unfortunately, for all future astronauts, whether government or private spacefarers, the risks to them from space debris will mount as they ride on rockets or live aboard space stations. For most people who will never venture into space, there are still areas of concern. The space debris actually does come down and sometimes at unfortunate times and places.
The Mounting Problems of Space Debris
Right now the biggest risk is that vital communications satellites or other key spacecraft can be destroyed by space debris traveling at speeds in excess of Mach 20. The ability of space debris to knock out spacecraft or injure or kill astronauts in space must now be taken seriously. There is also a concern that falling debris could cause property damage or even kill, but this probability fortunately is very, very small. The point is that now is the time to address all of these concerns.
How was this problem created? Over a period of time more and more space launches occurred. With these launches various types of debris began to accumulate. There are now explosive bolts, exploded fuel tanks, paint chips, upper stage rockets, rocket fairings that covered satellites that were being deployed in higher orbits, defunct satellites, and finally—in the last few years—debris from colliding satellites and even debris from a defunct satellite deliberately being hit by a ground-based missile.
At first there was only a minor amount of debris. But over the decades the debris accumulated. In time scientists began to understand that all this debris was beginning to pose a serious risk and a spreading “pile of space rubble” was accumulating—particularly in certain orbits. This now huge amount of space junk has now begun to threaten human longer-term access to space. Just as we now worry about the “sustainability” of life on Earth due to greenhouse gases and over population, we are worried about the “sustainability” of access to space due to space debris.
An enormous quantity of human-made debris is swirling around Earth, particularly in low Earth orbit (LEO). Scientists have determined that there are literally millions of debris elements in Earth various orbits—primarily LEO, but also Medium Earth Orbit (MEO) and geosynchronous earth orbit (GEO)—all of which have begun to fill up with space junk.
Many of these elements—literally millions of them—are of microscopic size and involve things such as chips of paint. It is currently estimated, however, that there are between 500,000 to 750,000 objects in orbit that are on the order of 1 cm in size. The first reaction of most people is something like, whew, those are really little guys that surely cannot do much harm.
shows a 1-cm puncture in the high gain antenna on the Hubble Space Telescope. A chip of paint traveling at 17,000 mph or over 28,000 kmph can put a serious crack in the window of a space shuttle or rupture an astronaut’s spacesuit. An element as large as 1 cm can do substantial harm, and something as large as 10 cm (4 inches in size) could potentially destroy a communications or remote-sensing satellite or some other valuable space resource. Shielding or armor on satellites against debris is really effective only up to about 1 cm.
Puncture in Hubble Space Telescope array cause by space debris (Image courtesy of NASA)
The Challenge of Tracking Space Debris
In 1980 there were just fewer than 5,400 sizeable objects (i.e., greater than 10 cm in size spinning around in low-Earth orbit) that were being actively tracked. By 2010 the number of large space debris objects had increased to 15,639. Today there are some 22,000 objects that are 10 cm or larger being tracked by the U. S. Air Force Space Surveillance Systems (AFSSS). This is a combination of ground-based plus several satellite-based tracking systems.
The current Very High Frequency (VHF) radar is being upgraded by a new “space fence” radar system operating in the S-band that will provide much greater resolution. (See Fig. 1.2
) The Air Force Space Surveillance System which was first implemented in 1961, in part as a missile tracking system that is now aging. Thus the Air Force has now contracted for a debris tracking system that is to be fully implemented by 2017. Tests carried out in March 2012 confirmed the new tracking capabilities and the effectiveness of the overall design of this so-called Space Fence by accurately tracking space debris elements. The details of this system will be discussed in greater detail inChap. 2
U. S. Air Force satellite used for space debris tracking (Graphic courtesy of the U. S. Air Force)
Of the 22,000 objects being tracked by the current AFSSS about 1,000 objects represent functional satellites, but the rest are “defunct” satellites or other forms of space junk.
The largest pieces of debris are most important to track for at least two reasons. First, these bigger objects can literally destroy the International Space Station (ISS) or other billion-dollar space facilities because of their huge kinetic energy, equivalent to large bombs. Secondly the collision of large space objects—regardless of their operational status—can create perhaps many thousands of major new debris elements. Big space objects colliding with each other is the number one problem we must seek to avoid, although it is imperative to find ways to reduce the formation of any type of new debris as well as a way to remove orbital debris from orbit in a systematic way regardless of size.
Over 6,300 Tons of Debris in Earth Orbit
The build-up various sized debris elements over the past two decades has now become alarming. The following chart from NASA explains the size of the various types of debris and their relative distribution. Fortunately most of the hundreds of millions of debris elements now in Earth orbit represent microscopic elements such as chips of paint. These microscopic elements are just the size of a grain of salt, but when traveling at speeds of perhaps 28,000 kmph (or about 17,500 mph), still pack quite a wallop, a wallop sufficient to penetrate the spacesuit of an astronaut or perhaps pit or even penetrate a window on a space vehicle (See Fig. 1.3
Breakdown of the 6,300 tons of mass in Earth orbit (Graphic courtesy of NASA.)
The nature of this problem, i.e., big objects colliding, has been vividly demonstrated within the past decade. First there was the collision of the operational Iridium 33 mobile communications satellite and the defunct Russian Cosmos 2251 weather satellite. Then there was the occasion when a Chinese anti-missile deliberately hit a defunct Chinese weather satellite. In both events on the order of 3,000 new tracked debris elements were created and resulted in a new level of threat to the International Space Station. In short these two events led to an impulse increase in “trackable” space debris objects by some 6,000. The Fig. 1.4
creates a representation of the debris created by the missile hit on the Feng-yun weather satellite and how this new swarm of debris relates to the orbit of the International Space Station as represented by the “white orbit” in the illustration.
Artist representation of orbital debris created by the destruction by missile of the Feng-yun weather satellite (Graphic courtesy of NASA Space Debris Program Office)
The greatest concern with regard to space debris is the so-called “Kessler Syndrome”. This is a condition whereby colliding space junk creates a deadly ongoing avalanche of more and more debris elements. Space scientist Donald Kessler in 1978 wrote a paper that warned that this type of problem could actually occur .
His paper explained how an ongoing series of collisions of space debris could lead to a cascade effect whereby the problem would become worse and worse once a “tipping-point” had been reached. Kessler’s warning—now known as the Kessler Syndrome—explained that once this tipping point was reached the problem would grow out of control. His early predictions of this effect, however, were not taken too seriously.
The truth is that important forecasts about space, from those of Sir Arthur Clarke concerning global satellite communications to those of Robert Goddard about lunar vehicles with human crews, were ridiculed or ignored when first made. Now, as the space debris problem has grown just as Kessler forecast, this problem is widely acknowledged around the world . In fact, a report by the U. S. National Research Council in September 2011 concluded that the problem was “worse than had been early thought” .
Currently, the only mechanism for removal of debris is orbital decay through atmospheric drag and Earth’s gravitational attraction, which ultimately leads to re-entry. Unfortunately, such gravitational removal of debris only works effectively for low-Earth orbits. For satellites in medium Earth orbit above the Van Allen Belts, it takes hundreds to thousands of years for objects to re-enter Earth’s atmosphere. For geosynchronous orbits, that are essentially one-tenth of the way to the Moon and where the pull of gravity is only 1/50th of that at Earth’s surface, the gravitational decay process for debris elements is essentially negligible. For a geo satellite to come down would literally take many millions of years. Consequently, there is currently no effective removal mechanism for MEO or GEO debris elements unless there were to be active rockets designed for controlled de-orbit.
As noted in Fig. 1.3
the build-up of debris elements in Leo orbit particularly in the polar area has now reached the incredibly high number of 2,700 tons, which far exceeds the gravitation degradation of a few tens of tons a years. Figure 1.5
shows that Leo polar orbits in particular are now extremely congested. This figure shows in some detail the debris that is being tracked in LEO by the U. S. tracking system.
Debris elements in LEO pictured over South America and Africa (Image courtesy of NASA Space Debris Projects Office)