Like the sea and air before it, space has become a critical enabling domain for global military operations. And the terrain of earth orbit, like geography, is a fixed reality central to understanding larger geopolitical issues. One important lesson is that gravity, velocity and the limited ability to maneuver — as well as orbital debris — place very real constraints on the freedom of action in orbit.

Analysis

Space has become a pivotal domain for enabling military operations around the world, particularly for the United States. It is how the national command can communicate with its deployed forces on the other side of the earth and it is how those forces can navigate and communicate with each other. Space-based assets provide the intelligence, surveillance and reconnaissance that help enable the use of precision strike weapons. These and other assets in orbit have come to play a central role in a variety of military operations around the globe.

Other nations and potential adversaries are keenly aware of the advantage the United States has gained through its exploitation of space and are seeking ways to exploit these advantages themselves — and to deny the Pentagon their utility in a crisis.

The Basics

“Weightlessness gives us the illusion of freedom. In reality, space is a realm in which gravity and the laws of motion rule with an iron hand.” — Dr. George Friedman, The Future of War: Power, Technology and American World Dominance in the Twenty-first Century

Like fixed-wing aircraft, objects orbiting the earth are continually moving under the influence of gravity — indeed, they must in order to maintain their position. In the atmosphere of earth, were a fixed-wing aircraft to come to a halt mid-flight, air stops flowing over its wings and the lift created by the flow of air ceases to exist. Similarly, a spacecraft’s motion is an inescapable component of its position above the surface of the earth. Forward motion combines with the earth’s gravity so that, while a satellite is constantly being pulled toward the earth’s surface, its velocity allows it to essentially fall around the earth, following the path of a circle or an ellipse. This path is called an orbit.

The velocity that keeps satellites in orbit is first provided when they are launched and inserted into orbit. Precise velocity is critical. Too slow and the orbit quickly decays, allowing the satellite to slip slowly back to earth; too fast and the satellite breaks free of the orbit. Over time, due to a number of influences including friction, orbits decay anyway. The International Space Station (ISS), for example, must regularly be boosted into higher orbit to counteract this decay. This requires considerable energy.

The fuel for this energy, like every other manmade object above the earth, must also be launched into orbit. This is expensive, although the price for boosting payloads into orbit is falling, and there are several private firms like SpaceX that are trying to make a generational leap to reduce the high cost of a space launch. But weight considerations will continue to be a matter of fundamental significance for spacecraft design in the foreseeable future. And there are very strict limits to the amount of fuel a spacecraft can carry to maintain its orbit and maneuver within it over time.

The problem is that spacecraft do not have a thick atmosphere to push against in order to maneuver as aircraft do — indeed, if they did, their velocity would be quickly slowed and the orbit would decay. The only way for spacecraft to change direction or orientation is to burn fuel. So any alteration to an orbit must be carefully calculated, and factors such as gravity, velocity and available fuel must be constantly taken into account.

Debris

There is also the problem of orbital debris. This can be anything from the discarded upper stages of a launch vehicle to a tool dropped by an astronaut working on the ISS. More than 18,000 pieces of orbiting debris can be tracked from earth. All are traveling at phenomenal speeds, and even a collision with an object as small as a screw can have catastrophic consequences. Spacecraft are also constantly being peppered by a microscopic assortment of cosmic debris, be it natural or man-made.

The debris problem is most pronounced where human activity has been the heaviest, in the most densely populated bands of low earth orbit (LEO). And the problem is only getting worse. It is thought that as few as several dozen highly energetic anti-satellite events like the Chinese ASAT test in January 2007 could render whole swaths of LEO unusable for years or even decades.

The problem is widely recognized, though just what to do about it remains unclear. In the meantime, debris-mitigation measures are increasingly standard practice for satellite insertions, and every space-faring nation has a great incentive to avoid devastating wars in space that could greatly multiply the amount of debris in LEO.

Basic Orbits

Essentially, LEO begins where the friction of the atmosphere is low enough that an orbit can be maintained — from about 500 kilometers to 2,000 kilometers above the earth’s surface. This is where the bulk of the earth’s satellites reside, including the Hubble Space Telescope and the ISS — as well as most orbital debris. Where atmosphere ends and space begins is a little fuzzier. Satellites can be found orbiting as low as 200 kilometers above the earth’s surface, well within the thermosphere — the second highest layer of the earth’s atmosphere — where the friction of the atmosphere is not prohibitively intense.

Less powerful launch vehicles can boost small payloads to LEO, making it the most accessible — and the most crowded. To maintain altitude at this level, orbital objects move very fast in relation to the ground beneath them, often orbiting the earth many times in a single day. Generally, to maintain constant coverage over a single point on earth, a constellation of satellites is necessary. Being closer to the earth in LEO can be beneficial for several reasons. Optical spy satellites can achieve better imagery resolution, signals intelligence satellites can achieve greater sensitivity and communications satellites can broadcast a stronger signal with lower power requirements.

The next major mark is geostationary orbit (GSO), about 36,000 kilometers above the equator. At this altitude, along the equatorial plane, satellites can be placed into orbit where they can remain stationary in relation to a specific point on the surface of the earth. Unlike LEO, GSO is limited to the equatorial plane, not the entire sphere of orbit over the surface of the earth. GSO is home to, among other things, the U.S. Defense Support Program satellite constellation that provides a constant, global infrared launch-detection capability.

Though definitions can vary, medium earth orbit (MEO) is usually distinguished as the space between LEO and GSO. Consisting of trillions of cubic kilometers of open space, MEO is an enormous area much less densely packed than LEO. The dozens of satellites that comprise the GPS constellation are in MEO.

Orbits can also be defined by their inclination (the angle relative to the equatorial plane) or their eccentricity (how closely the orbital path resembles a circle). A common example of the former are highly inclined orbits generally classified as polar orbits because they go over the poles. Both the Iridium satellite and the Russian satellite that collided in February 2009 were in polar orbits; they hit over Siberia as they passed near the North Pole in LEO. (That this had not happened before is a testament to the enormous — although increasingly cramped — volume of empty space above the earth.)

There are also more eccentric orbits known as highly elliptical orbits (HEO), which can take many different shapes and inclinations. This kind of orbit has a much greater difference between the apogee (the point in the orbit that is the greatest distance from the earth’s center) and the perigee (the point in the orbit that is nearest to the earth’s center) than a less eccentric (more circular) orbit. Velocity will also vary more in an HEO. There can be specific considerations that make this kind of orbit desirable, especially long loiter time over a certain point of geography without having to boost a large satellite all the way out to GSO. HEO orbits are particularly beneficial for Russia, since even satellites in GSO provide poor coverage of Russian territory, which lies at too great an angle for optimal coverage from an equatorial orbit.

Lagrange Points and the Moon

Far beyond even GSO is the orbit of the moon, which varies from around 365,000 kilometers to more than 400,000 kilometers. The moon does not rotate relative to the earth, so the view of the surface of the moon is always the same from earth (notwithstanding the phases of the moon, which vary according to the alignment of the earth, moon and sun).

Together, these two orbiting bodies — the earth and moon — create Lagrange (or libration) points, as does the sun-earth system. Lagrange points are positions in space where all gravitational forces are equal. The sun-earth system also creates these points. (The graphic below shows the five Lagrange points of the sun-earth system. The points would be in the same pattern for the earth-moon system, though on a smaller scale.) In both cases there are five points in space where the gravitational effects of the two bodies create areas of equilibrium. NASA research satellites already orbit the sun-earth system’s L1 and L2 points, which exist in a sort of gravitational “saddle” and are dynamically unstable, meaning that fuel must be expended for station keeping and course correction. (L3 has this same dynamic instability, but over a longer period than L1 and L2; L4 and L5, however, are considered stable.)

The potential scientific, economic and military utility of the Lagrange points and the moon are not yet well understood. Like the geography of the earth’s surface, however, they are fixed realities and bear watching as the United States tries to find the funding and political will to continue manned spaceflight and as China expands its manned program (with India following in its footsteps) and more and more countries employ satellites for strategic purposes.

But understanding geography is only the first step. Recognizing where the high ground is does not mean having the ability to claim and defend it. As the theory and practice of utilizing strategic assets in orbit evolve, the powers in space must learn how to deal with their adversaries’ assets. This is not to say that space should be “weaponized”. It is STRATFOR’s belief that it already has been — and that countries interested in global military operations on earth have nowhere to go but up.

This article is published at Lebanonwire by agreement with www.stratfor.com, the world's leading private intelligence provider.

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