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Authors: Joseph N. Pelton
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Space Debris and Other Threats From Outer Space (9 page)
BOOK: Space Debris and Other Threats From Outer Space
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Joseph N. Pelton
SpringerBriefs in Space Development
Space Debris and Other Threats from Outer Space
2013
10.1007/978-1-4614-6714-4_9
© Joseph N. Pelton 2013
SpringerBriefs in Space Development
Space Debris and Other Threats from Outer Space
2013
10.1007/978-1-4614-6714-4_9
© Joseph N. Pelton 2013
9. Protecting Against Comets and Potentially Hazardous Asteroids
(1)
40th St. North 4025, Arlington, 22207, USA
Abstract
We know that there are on the order of 40,000 so-called NEOs orbiting the Sun. At least these are the best calculations that come from a reasonable sample of the sky based on the observations and thousands of pictures taken by the WISE spacecraft.
From a wild weird clime…sublime, Out of Space
—
out of Time.
—
out of Time.
–Edgar Allen Poe (1845)
The Odds are with Us: Unless We Miscalculate
We know that there are on the order of 40,000 so-called NEOs orbiting the Sun. At least these are the best calculations that come from a reasonable sample of the sky based on the observations and thousands of pictures taken by the WISE spacecraft.
And these NEOs are just the ones that are 100 m or larger in size and have orbits that come within some 9 million miles (14.4 million km) of Earth. The ones that are truly potentially hazardous are fortunately significantly less in number.
Even with all the data collected by Earth observations and scientific spacecraft like the WISE vehicle, there is still a great deal that we do not know. In short, predicting those asteroids or comets that truly might collide with Earth is not as easy as it might seem. There are distortions in the Sun’s gravity that might make a much smaller and less massive object go through a so-called “keyhole” event such as portrayed in Fig.
8.2
. Also, a PHA that comes reasonably close to Earth on a particular orbit can clearly be disturbed by Earth’s own gravity so that when it returns some years later the impact becomes more likely. This is the case of Apophis, which will come past Earth in 2029 in such as way that it could come closer in 2036.
8.2
. Also, a PHA that comes reasonably close to Earth on a particular orbit can clearly be disturbed by Earth’s own gravity so that when it returns some years later the impact becomes more likely. This is the case of Apophis, which will come past Earth in 2029 in such as way that it could come closer in 2036.
Although this is even more unlikely it is also possible that the gravity from the Moon or even Venus or Mars could create a disturbance that results in a later collision with Earth many years later. There is further uncertainty about an asteroid’s path as a result of the so-called Yarkovsky effect. This effect is named after the Russian engineer who first identified in 2003 how the Sun affects an asteroid’s orbit other than just by gravitational pull. As an asteroid travels around the Sun it is heated by the solar rays. After a time the asteroid begins radiating energy away from itself in such as way that it very slightly alters its flight path. Although this is a very subtle phenomena it adds up over many years to become a real feature in orbital path prediction [34].
The NASA Safeguard Program and the European Space Agency NEO Shield Program are researching and developing strategies for protecting Earth against a future PHA or comet strike. Some of this research is geared to finding out what materials constitute the asteroid. This could be metallic, granite or stony or some other material that might be less massive and easier to divert. Another part of the research is geared to the shape of the asteroid and to determine if it might be more easily split or diverted by one or more means. In short some strategies for diversion of the orbit of an asteroid or comet depend a good deal on both the shape and the composition of the object in question.
Although there are a number of strategies that might be employed the top four strategies involve the following:
1.
Crashing a rocket with a heavy payload into the PHA or comet at a very high relative velocity.
This strategy is the simplest and likely the most cost effective one that might be employed. It would slightly alter the mass and gravitational pull on the threatening body so that over time the orbital trajectory would change. Of course there could be variations on the theme, such as to crash two rockets into the offending space object to double the gravitational effect. In order for this strategy to be successful precise navigation would be required to ensure that contact would be made and with sufficient impact so that the mass of the rocket and its payload would remain in contact over a period of months or even years so the orbital path would change.
This strategy is the simplest and likely the most cost effective one that might be employed. It would slightly alter the mass and gravitational pull on the threatening body so that over time the orbital trajectory would change. Of course there could be variations on the theme, such as to crash two rockets into the offending space object to double the gravitational effect. In order for this strategy to be successful precise navigation would be required to ensure that contact would be made and with sufficient impact so that the mass of the rocket and its payload would remain in contact over a period of months or even years so the orbital path would change.
2.
Tethering a rocket to a PHA or comet with sufficient chemical fuel or electronic propulsion to alter its orbit.
This strategy is actually a variation on the theme of the previous approach. In this case the harpooned space object would not only supply additional mass that would serve to change the asteroid or comet’s orbit, but the remaining chemical fuel could be expended to either push or pull the body into a less threatening orbit. In addition a long acting electronic ion engine could also add some propulsion to steadily move the body toward a safer orbit. The electronic thruster might also be used to maneuver the rocket into place for the harpoon firing to establish the link with the rocket. This approach would require even more precision guidance than the simpler approach of crashing the rocket into the threatening object, but the effect could be more substantial over the longer term.
This strategy is actually a variation on the theme of the previous approach. In this case the harpooned space object would not only supply additional mass that would serve to change the asteroid or comet’s orbit, but the remaining chemical fuel could be expended to either push or pull the body into a less threatening orbit. In addition a long acting electronic ion engine could also add some propulsion to steadily move the body toward a safer orbit. The electronic thruster might also be used to maneuver the rocket into place for the harpoon firing to establish the link with the rocket. This approach would require even more precision guidance than the simpler approach of crashing the rocket into the threatening object, but the effect could be more substantial over the longer term.
3.
Use of a nuclear weapon to divert the asteroid or comet.
This strategy would require much more knowledge of the asteroid or comet. In short one would need to know about the shape and composition of the object. Hopefully one would be able to place with some accuracy a shaped explosive or tactical weapon onto the threatening NEO in such a way that the nuclear device would generate a predictable new orbit and avoid simply creating several fragments that could also endanger Earth. The strategy could thus be quite crude and unpredictable in terms of a desperation action, or it could be a much more well-engineered plan. The more sophisticated approach might start with a smaller chemical charge first being detonated by robots at a predetermined location. This would be followed by a tactical nuclear device being put in place to create a second much more powerful shaped explosion that would initiate a pre-planned new orbit. This could be carried out as a mission with human crew aboard or perhaps conducted entirely with robots. In a sufficiently dire situation, there might be volunteers who would be willing to sacrifice their lives on a one-way mission.
This strategy would require much more knowledge of the asteroid or comet. In short one would need to know about the shape and composition of the object. Hopefully one would be able to place with some accuracy a shaped explosive or tactical weapon onto the threatening NEO in such a way that the nuclear device would generate a predictable new orbit and avoid simply creating several fragments that could also endanger Earth. The strategy could thus be quite crude and unpredictable in terms of a desperation action, or it could be a much more well-engineered plan. The more sophisticated approach might start with a smaller chemical charge first being detonated by robots at a predetermined location. This would be followed by a tactical nuclear device being put in place to create a second much more powerful shaped explosion that would initiate a pre-planned new orbit. This could be carried out as a mission with human crew aboard or perhaps conducted entirely with robots. In a sufficiently dire situation, there might be volunteers who would be willing to sacrifice their lives on a one-way mission.
4.
Use of reflective devices to vaporize the PHA or comet’s surface so as to create new thrust and shift the orbit.
The feasibility of this approach clearly needs to be tested, and certainly there is much that could go wrong in terms of deployment of metallic reflectors, the orientation of the reflectors so that the solar rays are properly oriented to the surface of the PHA or comet, and even the degree to which the ablated surface would create sufficient thrust to achieve the desired orbital changes. There is a new variation on this approach that would create a phased array of high powered lasers with enough strength to vaporize the asteroid from an Earth based location. This system known as DE-STAR for "directed energy solar targeting of Asteroids and exploRation" would use large scale solar reflectors to bombard and vaporize asteroids. This same system could also be used at the same time to generate energy that could power vehicles to travel within the solar system.
The feasibility of this approach clearly needs to be tested, and certainly there is much that could go wrong in terms of deployment of metallic reflectors, the orientation of the reflectors so that the solar rays are properly oriented to the surface of the PHA or comet, and even the degree to which the ablated surface would create sufficient thrust to achieve the desired orbital changes. There is a new variation on this approach that would create a phased array of high powered lasers with enough strength to vaporize the asteroid from an Earth based location. This system known as DE-STAR for "directed energy solar targeting of Asteroids and exploRation" would use large scale solar reflectors to bombard and vaporize asteroids. This same system could also be used at the same time to generate energy that could power vehicles to travel within the solar system.
The wisdom of Occam’s razor seems especially compelling in the field of space in advising that if there are several solutions then pick the simplest.
In all of the above possible solutions clearly time and forewarning is of the essence. The earlier the potential threat is identified the easier the diversion of the orbit is to achieve. If there can be years of early warning, then the very slightest change in orbital vectors can allow safe passage away from Earth. Conversely, if there should be just a very short period of warning, then the diversion becomes incredibly more difficult. Future satellite surveyors such as those similar in design to the WISE spacecraft can certainly aid in identifying possible threats to be cataloged and studied.
Today the greatest danger appears to come from the influences that can throw off orbital projections and perhaps convert a seemingly harmless NEO into a massive killer and possibly catching us off guard with too little time to respond. The so-called “keyhole gravitational affect” of the Sun on the massive 2011 AG5 or possibly the 1999 RQ36 asteroids are clearly potential “jokers in the deck” that could result in our not being warned in sufficient time. This “keyhole” gravitational phenomenon is to be closely watched and hopefully better understood. Yarkovsky effect also needs to be better understood. Finally we need to have a better sense of what techniques, under what set of circumstances, make the most sense to use on threatening NEOs.
Joseph N. Pelton
SpringerBriefs in Space Development
Space Debris and Other Threats from Outer Space
2013
10.1007/978-1-4614-6714-4_10
© Joseph N. Pelton 2013
SpringerBriefs in Space Development
Space Debris and Other Threats from Outer Space
2013
10.1007/978-1-4614-6714-4_10
© Joseph N. Pelton 2013
10. Top Ten Things to Know About Threats from Outer Space
(1)
40th St. North 4025, Arlington, 22207, USA
Abstract
Large and immanent threats that could result in large-scale death and destruction tend to dominate the news. Coming mega-disasters vividly capture the public attention because people and their loved ones are at clearly risk, and there is preciously little time to prepare for the worst.
In centuries when our population was smaller, our species could blithely pollute the air and water of the Earth and remain unscathed by the consequences. So too, for the last several decades we thought we left our space debris in orbits unlikely to collide. We are only slowly realizing the error of our ways.
–Paul S. Dempsey, Director, Institute of Air and Space Law, McGill University
Coping Strategies for Space Threats in the Near and Longer Term
Large and immanent threats that could result in large-scale death and destruction tend to dominate the news. Coming mega-disasters vividly capture the public attention because people and their loved ones are at clearly risk, and there is preciously little time to prepare for the worst.
These pending disaster events often tend to command major budget allocations either for prevention or recovery—perhaps both. This is the case whether one is talking about a volcanic eruption, a Category 5 hurricane just off shore, or even rapidly rising unemployment in an economy that is in a financial nosedive.
Other types of threats are more difficult to sort out and prepare for intelligently. Clearly minor threats that are very far away get virtually no attention at all. Medium term threats obviously rise in public awareness as they come closer to happening, and this is particularly so if the threat is clearly manifest and easy to understand. Forecasts of particularly high tides for a hotel on the Grand Canal in Venice, Italy, is taken most seriously as the day of the event draws near because the coming flood damage is quite real, and complete recovery may take weeks to accomplish before the hotel can reopen.
Perhaps the most difficult-of-all threat to cope with is the one that is hard to understand and visualize, seen to be far away, and yet if it occurs could be truly devastating to the future of humanity and its ultimate advancement. Yet such threats indeed do exist. It is possible that the buildup of orbital debris over time could threaten all future science and application satellite deployments. Runaway cascades of orbital debris could in time make it impossible to launch astronauts safely or to launch defense satellites to sustain national defenses.
Beyond space debris there are other “obscure threats” from space that could wipe out our modern electronic grids, disable millions of electronic processing devices such as those in cars, trucks, airplanes, and home and business computers. These are events such as super solar flares (or coronal mass ejections), a surge of solar or cosmic radiation, or cosmic events that could disturb Earth’s magnetosphere in a significant way. Finally the most unlikely (in a statistical sense) cosmic event, yet potentially the most devastating of all, is the risk of a huge NEO such as a comet or a potentially hazardous asteroid crashing into Earth with the force of millions of atomic bombs and wiping out human civilization and most animal and plant life along with it.
This book has attempted to acquaint the reader with the nature of these threats, the likelihood of their occurrence, the various strategies that might be undertaken to cope with these threats, and best steps forward. The following are some of the more important take away lessons from this book.
1. We are far from solving the problem of orbital space debris
.
.
Figure
2.1
shows just how dramatic the increase in orbital debris has become. Although tons of debris from LEO decays each year, the mass of satellites launched into Earth orbit each year far outweighs the de-orbiting debris. Although there have been reforms to eliminate elements of debris such as exploding bolts and such, there are still upper stage rocket motors, nose-cone fairings that cover satellites during ascent, etc., that are left orbiting as debris in space. Each launch, even with voluntary guidelines to control new debris, still creates perhaps 10–12 new debris elements. Satellites in LEO and Sun-synchronous polar orbits, where the greatest problems lie, are generally equipped so as to be actively de-orbited or launched to an altitude where relatively rapid orbital decay will naturally occur.
2.1
shows just how dramatic the increase in orbital debris has become. Although tons of debris from LEO decays each year, the mass of satellites launched into Earth orbit each year far outweighs the de-orbiting debris. Although there have been reforms to eliminate elements of debris such as exploding bolts and such, there are still upper stage rocket motors, nose-cone fairings that cover satellites during ascent, etc., that are left orbiting as debris in space. Each launch, even with voluntary guidelines to control new debris, still creates perhaps 10–12 new debris elements. Satellites in LEO and Sun-synchronous polar orbits, where the greatest problems lie, are generally equipped so as to be actively de-orbited or launched to an altitude where relatively rapid orbital decay will naturally occur.
But these de-orbit plans are not perfect. Problems can and do arise. In the case of the Iridium satellites for instance there were several problems. In some cases it was not possible to command a satellite to fire the jets to de-orbit. In one case Iridium officials indicated that they were asked not to de-orbit a satellite because of its risk of colliding with a U.S. defense department surveillance satellite.
If there are 10 new debris elements created with each launch and over 100 launches a year this could generate 1,000 new debris elements or 10,000 over a decade. But the debris accumulation occurs in many other ways. One collision between two large space objects or a satellite and a missile can generate 3,000 new debris elements. A fuel tank explosion can also generate hundreds of new debris elements.
All of these problems obviously mount up. Missiles hitting satellites, satellite or large rocket engine collisions, and fuel tanks exploding are the biggest source of problems. Experts have indicated that with no new launches the total number of debris elements will significantly increase over the next decade without active removal processes.
This is not a problem that is going to fix itself. The long-term sustainability of space is indeed at risk due to mounting orbital space debris. Although the prime concern is in the LEOs and particularly the Sun- synchronous polar orbits so key to meteorological and remote sensing satellites, there is a concern with mounting orbital debris in all orbits. The concern has increased to the degree that application satellite operators have formed the Space Data Association (SDA) to seek to avoid the collision of active satellites. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) has also formed a working group on the Sustainability of Space to seek solutions to orbital debris problems and other issues that might impair the future uses of space for all nations. Today only some ten to twelve countries can launch spacecraft into orbit, but all nations benefit from spacecraft and their uses for communications, navigation, remote sensing, meteorology, geodetics, scientific research, and national defense.
2. There is no internationally agreed mandatory system to prevent the buildup of space debris nor easy to administer international agreement under which removal of space debris can be easily achieved
.
.
Two international groups have now adopted voluntary guidelines to reduce the formation of new orbital debris. These groups are COPUOS and the Inter-Agency Space Debris Coordination Committee (IADC). The IADC is an international governmental forum of space agencies that are working together to mitigate and minimize the adverse affects of manmade and natural debris in space. Unfortunately, because of the complexity of international coordination it has taken 18 years to develop and get groups to agree to voluntary procedures to reduce debris. These voluntary procedures do not address the issue of nosecone fairings or upper stage rockets.
There is currently no obligation for those who launch satellites to ensure that space debris is removed, and the liability treaty actually represents a barrier to countries having others undertake to remove any such debris, since liability cannot be transferred.
There have been proposals that countries require launching organizations sign an “assured removal” clause as a condition for obtaining a license to launch and operate a satellite regardless of whether they were deployed by a national or foreign launch service. In the case of GEO debris removal this could mean placing the satellite in a “graveyard” orbit. Such a clause would apply not only to the satellite but the upper stage of the launcher and its fairings and also require that insurance be obtained if for some reason removal was not accomplished.
Alternatively it has been proposed that all launching organizations pay into a fund dedicated to orbital debris removal or mitigation of new debris being formed. For either one of these proposals to become effective a change in the international space liability treaty is necessary.
3. There is no clearly identified and tested technical/operational means by which orbital debris can removed from orbit
.
.
Further, any such means would be: (i) expensive to carry out; (ii) difficult to accomplish and administer under existing international law and (iii) lacking any attractive way to finance such a removal process, which will be expensive to execute under virtually any plausible scenario.
The change to international space liability convention is one of the steps needed to start cleaning up the various orbits in space. But the even larger hurdle appears to be the challenge of developing the technology that can allow the cost-effective and reliable removal of space debris from orbit, especially from LEO and Sun-synchronous polar orbits. The great variety of concepts that might be used for this purpose was outlined earlier in the book. Unfortunately none of these technologies or concepts are considered to be mature and ready for near-term implementation.
Any technologies that require a separate launch for each major debris element removed are obviously quite expensive. There are variations on the concept of electro dynamic-based systems that would utilize Earth’s magnetic field to derive electric propulsion to power such removal operations that might prove to be more cost effective. The Slingsat concept that would use momentum generated from the removal process might also prove to be less costly.
For any of these concepts to ultimately prove viable would require for the method to be broadly endorsed by the international community to remove a large number of satellites. To date no such broad agreement exists.
On top of all of the technical challenges, there is yet the further challenge that many of the space-based debris removal systems or the ground-based laser pulses could be considered to be “space weapons”. One of the innovative solutions suggested in this respect is to have the country of launch registration and “ownership” of the space debris assume direct operational control of the removal or avoidance process so that they directly oversee the removal activity.
4. There might be some new and innovative ways to address problems associated with orbital space debris that include using ground based lasers to avoid collisions of larger space objects and financing removal operations
.
.
Another approach that has been suggested as an interim solution, until effective removal processes are developed and tested, is to simply direct ground-based laser pulses to satellites or other large space objects on likely collision courses so as to avoid such collisions. Since these objects are moving at very considerable speeds, such as on the order of 25,000 km or (15,000 miles) per hour, relatively small pulses could slow the velocity of the satellite or space object a very miniscule amount to avoid the collision. The problem is sufficiently accurate tracking with laser-based systems to make sure that the pulses would indeed avoid the collision rather than actually causing the unwanted impact to occur.
A variation on this theme of active collision avoidance is already being conducted with regard to the International Space Station and other high value satellites such as surveillance or “spy” satellites. In this case on-board thrusters or, in the case of the ISS propulsion engines, can be fired to lift the space object above the orbit of the satellite or inert space object that is considered an impact threat. Experiments to test these concepts in terms of the accuracy of laser-based precision tracking and minute adjustments to space objects orbital speeds are now being conducted. The issue of whether such laser bursts might be considered a space weapon, however, remains an open issue.
5. Solar flares and coronal mass ejections (CMEs) could be much larger problems than previously thought with modern electronic and electrical systems particularly at risk
.
.
The documented evidence of the so-called “Carrington event” remains very much a reminder that very powerful solar flares or coronal mass ejections can zap Earth’s thin protective atmosphere shield with enormous force. When such a torrent of ions or high energy radiation head directly for Earth at great speed, the Van Allen belts serve to shift the impact toward the polar regions. The atmosphere that protects our planet can still be distorted and extended some ten to twenty times Earth’s diameter. In the case of the exceptionally powerful Carrington event this distortion might be as much as 30 Earth diameters and the remaining level of protection becomes very thin indeed until the atmosphere is pulled back by Earth’s gravity.
No such truly mega-event has socked Earth since 1859 although the March 1989 event was quite severe. The bottom line is that we have no way of knowing with any precision when the next such massive coronal mass ejection will occur and where this stream of super-charged ions would impact Earth’s atmosphere with the maximum velocity and destructive power. Fortunately, less massive CMEs do occur to provide useful data. During the solar max year in the 11-year cycle, particular experience is gained in how to power down satellites when the most powerful coronal mass ejections do occur. Despite some degree of radiation hardening, heavy duty switches and the powering down of satellites when alerts are received of the most violent space weather, failures of satellites still occur.
Here on Planet Earth dangers from the most severe CMEs also exist. Certainly power transformers have been disabled or destroyed by solar events within recent times, and concerns have increased that all sorts of computer processors and electrical systems in space and on the ground could be destroyed on a massive scale if something like the Carrington event were to occur today.
Even more effective protective strategies can be undertaken for space systems. Radiation hard electronic components and wiring, highly protective insulation coating, wide gap on/off switches and circuit breakers, component redundancy and even Faraday cage structures are all part of the strategy to protect spacecraft from coronal mass ejections as well as an electro-magnetic pulse (EMP) from an in-orbit nuclear explosion.
Satellites, perhaps most importantly, can be powered down when there are alerts of a powerful solar ejection. On the ground transformers can be built within Faraday cages and in critical situations could be powered down and again equipped with surge protectors and heavy duty circuit breakers.
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