Satellites provide information and other services that are critical for national security, economic vitality, and human well-being. Their owners are increasingly concerned about keeping them safe. As long as there have been satellites there have been plans for interfering with them. The act of destroying a satellite can damage the space environment by creating dangerous amounts of space debris. What’s more, the impairment or loss of an important satellite, such as one used for reconnaissance, can quickly escalate a conflict or generate other unpredictable and dangerous consequences. And short of an actual attack on a satellite, even the targeting of satellites or the construction of space-based weapons could precipitate an arms race with damaging and far-reaching consequences, including the diversion of resources from other pressing issues, or the hindrance of international cooperation on such important challenges as nuclear non-proliferation, climate change, and terrorism.
The space environment has changed over the last fifty years—especially rapidly over the last decade or two. For a large fraction of our history in space, space was primarily the domain of two actors, the United States and the Soviet Union, who mainly used it for strategic national security purposes, such as early warning of ballistic missile launches and intelligence support to verify arms control treaty compliance.
Both countries developed prototype anti-satellite weapons, including weapons that would propel shrapnel from an explosion near a satellite, weapons that would ascend on a missile launched from an airplane and then collide with the satellite, and ground-based laser weapons targeting the sensors and other vulnerable components of satellites. At the same time, both countries engaged in research and development of strategic missile defenses. Because intercontinental-range ballistic missiles reach similar speeds and altitudes as low-earth orbiting satellites, ballistic missile defenses can often be used as well (or better) as anti-satellite weapons.
In the spring of 1983, President Ronald Reagan gave his “Star Wars” speech, announcing that he intended to focus on developing a large scale missile defense system. The Strategic Defense Initiative (SDI) he created was expected to develop several types of space-based interceptors with anti-satellite capabilities. Though the systems that emerged from this program are mainly ground-based, small research projects dedicated to space-based missile defense still exist.
While there was interest in these technologies, the overall story was one of mutual restraint. Both states understood that unconstrained weaponization of space would lead to an arms race and dangerous instabilities in the nuclear relationship. And the Anti-ballistic Missile Treaty constrained strategic missile defense deployments.
In the early 2000s, the metaphor of mastering the “high ground” became a principle driving military thinking and planning for space, particularly in the United States. This was at least in part a response to the growing importance of space assets to the conduct of conventional military actions—providing the means for precision guided munitions, intelligence surveillance and reconnaissance, and for global communications.
Plans for dominating space proliferated, and included proposals for ground-based weapons aimed at satellites and space-based weapons aimed at space and ground objects.
Ultimately, the US plans foundered as they came up against technical and economic realities and because priorities shifted after the events of September 11, 2001.
Today, many more actors are now in space, trying to use it to develop economically, to pursue scientific goals, and to support national security. This has created a complex ecosystem that can bring great benefits, but which creates competition. Space is not insulated from conflict on earth, and can unpredictably escalate crises on the ground or be the spark that starts one.
In the last decades, numerous international efforts have aimed at getting a handle on these risks by negotiating constraints. These efforts have not led to substantive limits on space-based weapons, on anti-satellite weapons, or on behavior.
Within 24 hours of being sworn in this past May, Secretary of the Air Force Heather Wilson stated in testimony that “space is now a warfighting domain, similar to the more familiar air, land, and maritime domains our men and women are fighting in today.” This reflects the shift in thinking in the US government away from the idea that space has a special character, as indeed is reflected in the description of space as a peaceful domain in the Outer Space Treaty. It indicates that the US will work quickly to preserve its superiority in space. This is primarily due to the progress of other countries, particularly China, in establishing their own national security architectures in space as well as the proliferation of technologies useful for anti-satellite weapons.
Some of these technologies are expensive and sophisticated, but others are within the reach of less developed countries and could provide the ability to hold satellites at risk.
Directed energy weapons, such as lasers and microwave weapons, have a number of desirable features for an attacker. The beams reach their targets at the speed of light, and the delivered power can be tailored to produce temporary and reversible effects or permanent, debilitating damage. Directed energy weapons also have disadvantages relative to physical interceptors: they can only reach targets in their line of sight (unless relay mirrors are used) and simple shields of reflective, absorptive, or conductive material can be effective defenses.
Relatively low-powered lasers can be used to interfere with a satellite’s sensors by coupling them with mirrors that focus the light and can track the satellites as they move across the sky
Lasers can dazzle imaging sensors, making it difficult or impossible for them to see an area on the ground, but without creating lasting damage. Or at higher powers they could permanently damage sensors. This relatively low-tech weapon is expected to be within reach of a wide range of actors_even sub-state actors.
A more sophisticated system could be used to train high powers of energy onto a satellite’s solar panels or damage it. This is harder to do. As laser power increases, the lasers become larger and more complicated, since they require large power supplies, cooling, and, in some cases, exhaust systems. The testing and existence of such systems should be detectable and limits on them could be part of a verifiable arms control regime.
A more problematic technology is hit-to-kill interceptors. These are ground-launched (though could be air-launched) missiles which target ballistic missiles during midcourse (as they travel up above the atmosphere) and destroy them with the force of impact. This technology has been demonstrated by the US and China against orbiting satellites, and is within the reach of Russia, India, and Japan.
Because satellites and long-range ballistic missiles travel on similar paths through space with similar speeds, this technology can also be used to target satellites. In fact, it is probably easier to target satellites than ballistic missiles, since a satellite attack can be delayed until conditions are optimal, but ballistic missile launches come with little warning and may be accompanied by decoys and other countermeasures.
The data presented here shows the anti-satellite capability of the United States’ missile defense system based on Aegis ships. These ships carry interceptors, which are being gradually improved with respect to sensor capability and speed. In 2008, the United States used one such interceptor to destroy a failed intelligence satellite at about 250 kilometers altitude, an altitude at which the resulting debris would rapidly be pulled out of orbit by the atmosphere.
Figure 1. Maximum altitude reachable by SM-3 variants.
Figure 1 gives estimated burnout speeds for the two main types of SM-3 interceptors, Blocks I and II, as well as the altitude they could reach if launched straight up.
Figure 2. Number of satellites with perigee at or below altitude
The solid vertical line in Figure 2 is 600 km, the height limit for the Block I interceptor, and the green dashed line is the conservatively estimated height limit for the Block II interceptor. The blue curve is the approximate cumulative number of satellites with closest approach to earth at that altitude. These interceptors could reach all of the low earth-orbiting satellites. The SM-3 Block IIA interceptors are still under development, and it is not clear what the final procured numbers will be, but there may be several hundred of them—perhaps 5-600-and the 33 BMD capable ships may increase to perhaps 80. These ships can be deployed worldwide.
This technology already exists and is deployed, Because it has been demonstrated both against satellites and against missiles, and because the interceptors are expected to be so numerous, this system may become the greatest obstacle to satisfactory limits on anti-satellite weapons. (And it may also impede the reduction of global caches of nuclear-armed missiles.)
Such kinetic energy destructions leave enormous amounts of debris on orbit, which can make subsequent space operations risky and more expensive. This may contribute to self-limiting behavior by states that want to keep space working well into the future. However, under crisis conditions, this can’t be counted on.
Persistent space debris is inimical to the safe and secure use of space, so actors are increasingly interested in holding satellites at risk with less destructive types of weapons. For example, some satellites can approach an adversary’s satellite closely at low speeds while both are on orbit without the target’s cooperation. At sufficiently close ranges, other types of nondestructive methods to interfere with the target can be contemplated, such as electromagnetic attacks, spray painting sensors, even setting the satellite spinning. Such attacks could produce less debris. While the US has a great lead in this technology, other states are pursuing it as well, including China and Russia. Close approach technology is also dual use; it can be used to repair, inspect, or refuel satellites, for example.
Proximity operations may be either temporary or permanent and are technically sophisticated. While they may have some elements of stealth or unattributability, one cannot count on hiding in space indefinitely, and close approaches of this type are observable behaviors, and therefore could be subject to verifiable limits.
The main“blast from the past” must be space-based missile defense. In the last few years, a group of missile defense and space weapons advocates in the US Congress have been promoting the project of a space-based missile defense system to defend against both nuclear-armed ballistic missiles and direct ascent ASAT weapons.
It has been more than thirty years since the denouement of Ronald Reagan’s fanciful Star Wars concept and more than twenty since the cancellation of Brilliant Pebbles, its more limited but still space-based descendant. It has been fourteen years since the American Physical Society’s (APS) landmark analysis concluded that a system of space-based interceptors “would require a fleet of a thousand or more orbiting satellites just to intercept a single missile” and that “deploying such a fleet would require a five- to tenfold increase in the United States’ annual space-launch capabilities.” It has been eight years since the Obama administration set aside the George W. Bush era plan to build a Space-based Test Bed.
It has been five years since the US National Academy of Sciences released its report on boost-phase missile defense. It stated that an “austere” capability of 600 or so interceptors would cost $300 billion and that space-based missile defense will be at least 10 times as expensive as any other option.
One problem with space-based weapons that require timeliness is that objects in space are moving rapidly. A single satellite will generally not to be in the right place at the right time. If a weapon or surveillance asset needs to be available promptly, multiples will be necessary, and this gets expensive. For example, for the Global Positioning System, one needs a constellation of at least 24 satellites to have enough of them in view to make the system work.
Besides the fact that a great many enormously costly interceptors would be necessary, space-based missile defenses are vulnerable to being overwhelmed or defeated.
Unfortunately, members of Congress haven’t learned the lesson, and their new study will ask the Pentagon to go back again to get the same answers that we already know. The Ballistic Missile Defense Review is underway now.
For space security, this issue is of the highest importance. Although probably no full constellation would be built, it is likely there will be an effort to stage a test bed of a few interceptors. While the flaws of space-based missile defense will not be resolved with research and development, it’s important to note that even a “test bed” project could be destabilizing internationally. Space-based interceptors are inherently anti-satellite weapons, and putting prototype interceptors in space would be viewed by adversaries and allies alike as stationing the first dedicated space weapons in orbit. It would likely encourage development of similar technologies or other types of anti-satellite weapons by others.
The year 2017 marks the fifty-year anniversary of the Outer Space Treaty. This is once again an inflection point in space security. Technology is rapidly advancing and proliferating, but the strategic environment lacks a straightforward Cold War logic that drove the negotiation of agreements such as the Outer Space Treaty or the Anti-Ballistic Missile Treaty.
There are very good arguments that negotiated limits on technologies and behaviors in space would improve security, including lowering risks of crisis escalation, enhancing stability and the usability of space, and protecting the space environment for the generations to come. Even those countries with huge technical and economic advantages must recognize that they cannot remain protected from a determined adversary in space and cannot secure safe access to space unilaterally. Security and sustainability will need to be built cooperatively.
Laura Grego is a physicist working with the Union of Concerned Scientists.