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Adiós, Space Fence

While most news outlets were freaking out about killer pythons, the Japanese helo carrier, or the 68th anniversary of the bombing of Hiroshima, the US Air Force was quietly preparing to shut down Space Fence, one of the oldest but most productive parts of its space surveillance network.

It’s also one of the few facilities that can provide 24/7 “uncued detection” capability… which is nerd-speak for the ability to find things in orbit that nobody expected to be there (ie. space junk).  Contrary to what Hollywood likes to show you, it’s impossible to track every single object of space debris.  There are over half a million distinct objects, some smaller than a penny, and no one nation (or even group of nations) has enough radar or visual coverage to follow them all.  In fact, the US Space Surveillance Network has only 6 facilities worldwide dedicated to on-orbit detection and tracking; Space Fence was the largest and most effective of them, spanning the continent at the 33rd parallel.


Space Fence is the red line stretching across North America

Why is the closure of this capability important, you ask?  It might be easier to have some visual reinforcement.


STS-7 window impact

This is what a mere fleck of paint did to a cockpit window on OV-099 Challenger during the STS-7 mission, back in June of 1983.  The pit you see there is only 1mm in diameter, but remember that paint is probably the most innocuous bit of debris one can run into when travelling 17,580 miles an hour.   During STS-59, OV-105 Endeavour experienced similar window damage, and the object actually penetrated half of the window’s total depth.  That’s kind of a big deal.  Other STS missions have seen micro-collisions where objects have punched right through the orbiter’s silvery radiator panels.  Objects like this paint fleck are too small for Space Fence to detect and track, but there are literally hundreds of thousands of larger objects.

Despite being several decades old, Space Fence is still relevant today because it has a longer reach than most other sensors, and because it can do its work un-cued.  In other words, it detects without being specifically tasked to look for a known or unknown object in a given region of orbital space.  It is responsible for around 40% of the observations on the 23,000 objects the Department of Defense currently tracks.

Though part of a broader surveillance network, the VHF Space Fence is crucial because it can track objects up to 24,000 kilometers away. Other sensors in the network generally track objects at altitudes lower than a few thousand kilometers, [Brian Weeden, technical adviser at the Secure World Foundation, a nonprofit organization dedicated to space sustainability] said.

“The Space Fence is very important as it gives an ‘uncued tracking’ capability,” Weeden said. “Because it’s constantly transmitting, it can detect objects without being tasked to do so. There are some other sensors in the network that can do uncued tracking to some degree, but the Space Fence is rather unique in the sheer size of the detection coverage it has.”

Gruss, Mike.  Shelton Orders Shutdown of Space Fence.  SpaceNews, 6 August 2013.

Granted, the current Space Fence is a little long in the tooth and suffers the additional handicap of being based on 1960s technology.  Thanks to sequestration, not only is the current capability being forced to close, but its future replacement is also stuck in limbo—waiting for the Pentagon to decide what projects it can reasonably afford.  Meanwhile, there are about 500,000 debris objects too small (from 1-10cm in diameter) for the current space surveillance network to keep tabs on.  And their numbers will only increase.


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GPS interference

…from a domestic source:

An analytical assessment performed by the Defense Department suggested that GPS receivers will be negatively affected if the [LightSquared 4G cellular network] is deployed. That analysis has now been confirmed by recent field testing, Air Force Gen. William Shelton, commander of Air Force Space Command, said during a May 11 hearing of the Senate Armed Services strategic forces subcommittee. Using actual LightSquared hardware at Kirtland Air Force Base, N.M., engineers detected interference to military, civilian and commercial GPS receivers, Shelton said.

“Although the data is still being analyzed, I would tell you that the empirical data appears to be consistent with the analytical data, so we have concerns for commercial applications, civil applications and military applications,”?he said.

— Brinton, Turner. “House Panel Slashes Funding for ASSIST.”, 13 May 2011.

The problem is, in essence, the proximity of the satnav and cellular frequency bands.  GPS satellites transmit their navigation signals in the 1559 to 1610 MHz band, and LightSquared’s proposed 4G network would operate in the adjacent L-band, from 1525-1559 MHz.  The 4G network would involve the erection of 40,000 new base stations, and manufacturers of satnav receivers are concerned that the large increase in base stations would create interference with GPS receivers, resulting in satnav dead zones all across the United States.  (The GPS industry’s January 2011 report to the FCC on interference and jamming effects has additional detail.)

According to a February 2011 article in New Scientist magazine, LightSquared characterises the problem as a fault in the GPS receivers themselves, since some have the ability to “see” into the L-band where the cellular network will operate.

The GPS industry’s testing appears to have taken place using L-band simulated transmissions, while USAF’s testing occured using actual LightSquared hardware.  According to Gen. Shelton’s May 11th testimony to the Senate Armed Services Committee’s strategic forces panel, the Air Force’s testing seems to have validated the earlier results; it will be interesting to see what this heralds for next-generation telecom networks and GPS receivers.

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High Frontier

First published 16 July 2004.

There’s an excellent article in this month’s [July 2004] issue of Air Force magazine, entitled “Securing the Space Arena“. American armed forces are utterly dependent on space-based assets to conduct modern warfighting, and the article examines the vulnerabilities of United States spacecraft and how U.S. Air Force Space Command is working to reduce those risks. One of the major problems is that at present, Air Force Space Command does not have the tools to determine whether a malfunctioning satellite is suffering from natural phenomena or a deliberate attack. In one case, the Air Force did not become aware until mid-April that a dormant Defense Meteorological Satellite Program (DMSP) spacecraft had broken into six pieces — cause unknown.

Western success, both commercial and military, depends heavily upon information dominance. Our economies have enjoyed a competitive advantage over the past few hundred years because of our ever-increasing technological advantages. Our businesses have been able to communicate, innovate, market, monitor and respond better and faster than anyone else. Likewise, Western armed forces are so effective because they attained and kept a technological edge. Today the West’s warfighters have access to critically important space systems that provide communication, navigation, weather forecasting, targeting and intelligence. If Western military forces were to lose those advantages, some of our warfighting capability would be degraded back to the Vietnam era.

Effective anti-satellite weapons do not have to be something expensive and exotic launched from Cape Canaveral, or an exo-atmospheric missile fired from fighter aircraft. An article titled “GPS Vulnerabilities” in the March-April 2001 issue of Military Review, written by Lieutenant-Colonel Thomas K. Adams, USA (Ret.) and published by the U.S. Army Combined Arms Center, describes how even a low-tech adversary can take out satellites:

It is not difficult to reach at least low-earth orbit with ordinary meterological sounding rockets that carry 50- to 100-pound payloads. If a rocket could carry 40 pounds of 00 steel buckshot — available in most sporting goods stores — it could kick the pellets out into an appropriate orbit with an explosive charge. Moving at relative velocities of about four miles a second, the tiny pellets would slam into and disable any satellite they encountered.

Most satellites are not protected against anything more exotic than temperature extremes, radiation exposure and use by unauthorized ground stations. Armour is not an effective answer since it adds weight and impairs the satellite’s functionality, and some satellite parts (such as solar panels) cannot be armoured at all. Using maneuvering fuel might save a satellite, provided that threat detection was timely, but the satellite may have reduced capability (or be completely useless) while it is out of its assigned orbit. Replacement is also an option, albeit an expensive and time-consuming one. Presently, the United States has concentrated on orbiting small numbers of very expensive satellites with extended longevity and exceptional capability. Replacing these satellites on short notice is not easy, as Lieutenant-Colonel Adams points out.

The time needed for countries such as China, India, Japan or North Korea to acquire significant space-denial capabilities is rapidly becoming less than the time the United States needs to replace existing satellites. During the Falklands War, the Soviet Union launched 29 small satellites within 69 days. In contrast, the United States took 113 days to replace a defense weather satellite after an emergency.

It’s also not that hard to exponentially increase the effectiveness of low-tech anti-satellite weapons, as Lieutenant-Colonel Adams goes on to illustrate in very humourous terms.

The effectiveness of these defense measures is limited; an attacker could increase his satellite lethality simply by using ball bearings instead of buckshot and attacking twice. Suppose the attacker has a little better lift capacity and is less fussy. Orbiting a thousand pounds of gravel could sweep parts of near-Earth space like a broom and provide history’s most spectacular meteor shower as millions of tiny rocks, bits of $500-million satellites and plans for information dominance all begin the long slide to earth.

But who would want to take out Western satellites, and why? Strategic rivals like China, certainly; probably regional aggressors like North Korea as well. For now, states are unlikely to wage that kind of war because they lack the strategic imperatives and political will to risk it all by putting a dent in the Western economy and encouraging a Western military response. But what about non-state actors, like al-Qaeda? Acquiring sounding rockets, or something better, would not be a tremendous challenge; acquiring something with a thousand-ton payload capacity might be. Considering that the X-Prize and SpaceShipOne are ushering in the era of private spaceflight, it is not inconceivable that a terrorist group might attempt to steal a privately-built spacecraft. SpaceShipOne’s payload capacity is undisclosed, but we do know that it can carry three persons, so we can estimate its payload capacity at somewhere between 540-750 pounds.  That’s enough to put a lot of gravel into orbit.

Whether or not Western civil populations would be willing to engage in war to avenge lost satellites is, in itself, an interesting question. Suppose all of those satellites were swept from our skies tomorrow; would we be willing to go to war even though no humans died in the assault against us?

In Canada our debate about space systems is stillborn; the Conservatives support Canadian involvement in ballistic missile defense (BMD) and the NDP wails that BMD will lead to an arms race, nuclear holocaust, and a worldwide Bushitler reign of terror. What is missing is the realization that Canada has her own small fleet of very expensive satellites up there, and Canadian policymakers are more concerned about scoring points with the electorate than thinking about how to protect our hard-earned investments.

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