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Gravity-Mapping Satellite’s Communications Glitch to Be Fixed Soon
Ground controllers are gradually raising the orbit of Europe’s GOCE gravity-measuring satellite in preparation for a series of procedures they hope will permit the satellite to recover its data-transmission function, which failed in July.
The procedures, designed by a team of engineers from the European Space Agency (ESA) and GOCE’s industrial contractors, had not been approved for use as of Aug. 24. But Mark R. Drinkwater, head of ESA’s Earth observation mission science division, said some variant of the proposed data-restoration plan would be approved, and that by mid-September, GOCE controllers should have an idea of whether the plan is working.
GOCE, or the Gravity and steady-state Ocean Circulation Explorer, was launched in March 2009 on a two-year mission. It has produced its first global maps of the minor differences in gravitational attraction of different parts of the Earth. ESA officials say GOCE is the first satellite to produce such maps.
The satellite has already performed two-thirds of its mission assignments. Its managers nonetheless had hoped to continue the mission beyond 2011 given the fact that the relatively low solar activity in the past year has permitted GOCE to fly at an exceptionally low orbit and use relatively little fuel to eliminate the atmospheric drag that inhibits flight at GOCE’s 256-kilometer operating altitude.
“We have four of a planned six mappings completed, and we have fuel in the bank,” Drinkwater said in an Aug. 24 interview. “There is no reason we couldn’t operate until the end of 2012, if our member states grant us approval.”
GOCE’s main computer failed in February in what mission managers describe as a rare and still-unexplained failure of a computer chip that has flown many times on satellite missions.
With the main computer out of service, the July failure prevented GOCE from sending science data altogether. A board of inquiry has been established to examine the July incident, but Drinkwater said it is already clear that it bears no relation to the February computer chip failure.
“The present anomaly manifests itself in a different manner from the previous problem, as the processor itself remains healthy,” ESA said in a statement on the GOCE telemetry issue.
It remains unclear exactly what component suffered the glitch that stopped the flow of science data. The 18-nation ESA, in July 22 and Aug. 3 statements about GOCE’s status, said the problem appears to reside either in the backup computer’s processor board or in the satellite’s telemetry module. Several attempts to reboot the backup computer have not overcome the data-transmission problem.
The proposed work-around includes returning GOCE’s nominal computer to partial service, and combining that capacity with similar capacity available on the backup computer despite the July glitch.
Drinkwater said GOCE continues to respond to commands and shows no sign of having lost any of its data-generating ability.
Ground teams have sent software commands to GOCE that have forced the satellite to deliver more telemetry than it normally does, enabling controllers to verify the status of all the satellite’s systems in preparation for the recovery operation.
As part of that preparation, GOCE’s orbit is being raised by about 9 kilometers, to 265 kilometers, in anticipation of the fact that during the recovery, it may lose the use of its xenon-ion electric propulsion system, which permits GOCE to compensate for atmospheric drag as it flies. Also helping the satellite fly is its peculiar aerodynamic design, resembling an arrowhead.
The temporary loss of the propulsion system would cause GOCE to lose altitude almost immediately.
Many of its components have never flown before, including its gradiometer payload, composed of three pairs of accelerometers that will produce a global map of gravity’s differing pull in different regions of Earth, which were built by France’s Onera aerospace research institute, and its xenon-ion thrusters, built by Qinetiq of Britain. But it is not these systems that have caused GOCE’s problems so far.
China’s secure communications quantum leap
A team of 15 Chinese researchers from Tsinghua University in Beijing and the Hefei National Laboratory for Physical Sciences, a government-directed research center, in May published a research paper announcing a successful demonstration of “quantum teleportation” over 16 kilometers of free space.
These researchers claimed to have the first successful experiment in the world. The technology on display has the potential to revolutionize secure communications for military and intelligence organizations and may become the watershed of a research race in communication and information technology.
Although much of the science behind this technology is still young, quantum technologies have wide-ranging applications for the fields of cryptography, remote sensing and secure satellite communications. In the near future, the results from this experiment will be used to send encrypted messages that cannot be cracked or intercepted, and securely connect networks, even in remote areas, with no wired infrastructure, even incorporating satellites and submarines into the link.
Roots in quantum physics, applications in intelligence
Rather than transporting matter from place to place, quantum teleportation’s most practical applications currently involve using photons for instantaneous, almost totally secure data communication. Using the term “teleportation” to describe this effect can be justified by what Albert Einstein called “spooky action at a distance”: after two particles are linked together through quantum entanglement, any change in the state of one particle immediately alters the other, even from kilometers away. In effect, the state of the particle at the sender’s end is destroyed and reappears as an exact replica at the receiver’s end, with a negligible chance of undetected third-party interception.
While the teleportation of physical matter remains science fiction at this point, quantum teleportation could be immediately implemented as a means for secure communications and cryptography. Current encryption techniques are based upon mathematical functions involving very large prime numbers and secure key management and distribution, but this strategy has a number of drawbacks and is nearing the end of its shelf life.
In particular, as computing power continues to double every year and computer bits speed up through the use of quantum particles, the cryptographic keys used for encoding and decoding must now be changed more often to prevent encrypted data from being cracked. As a result, it has become very difficult to “future proof” the encryption of data, and were any major breakthrough in quantum computing to be achieved in the near future, current encryption techniques could become obsolete and encrypted data could suddenly become unprotected.
The security of using quantum teleportation to distribute cryptographic keys, on the other hand, is upheld by the laws of physics and has a seemingly infinite time horizon. These keys cannot currently be detected and cracked even with the help of the most powerful computers. Owing to the Heisenberg Uncertainty Principle, the quantum states of photons cannot be observed without changing the state of the particle, which has the result of immediately informing the sender and receiver of any eavesdropping. Quantum communication can thus be used to send the most sensitive information, including keys to decode encrypted data sent over less secure means.
Significance of the China’s achievement
As a result, the issue has found itself at the center of a rapidly developing geopolitical race to apply quantum technology to military and intelligence work. Since secure quantum key distribution (QKD) provides a much higher level of security between communication networks, employing quantum teleportation over a satellite network allows for completely secure communications, even in sensitive and remote areas, without fiber optic infrastructure, as long as all parties are able to maintain line of sight with a satellite. This could have wide applications in communications and intelligence for ground troops, aircraft, surface ships and submarines, and fits into China’s current plans to grow its satellite network even further.
Using quantum teleportation to send this type of information has been technically possible for several years, but according to the Chinese research paper, it had been previously demonstrated experimentally only over an enclosed fiber optics network and then only over a distance of several hundred meters.
The Chinese experiment appears to shatter these records by claiming to be the first to use a high-powered blue laser to exchange quantum information over a free space channel, and to demonstrate the principle over a distance as great as 16km. This distance is significant because it displays approximately the same degree of light distortion as is seen in communication from the earth’s surface to a satellite, and so would allow for quantum communication using satellites. If this experiment were indeed the first of its kind, it would appear that China has succeeded in leapfrogging the West, and gained a significant edge in next-generation communications and cryptography.
A quantum space race?
The Chinese claim to be the first may not be entirely accurate, although certain elements of their experiment were unique and innovative. In 2005, a group of universities and defense corporations under a Defense Advanced Research Projects Agency (DARPA) grant and led by BBN Technologies, the company responsible for developing the precursor to the Internet, succeeded in transferring cryptographic keys over a free-space link of 23 km in Cambridge, Massachusetts.
Well beyond the single link employed by the Chinese, the BBN program has developed an expanding, multi-node web of secure quantum communication that will be able to further expand and link seamlessly with existing Internet technology. There are a few differences in the physics of their experiment that still make it notable and may not technically disqualify the Chinese from claiming their status as first, but nonetheless American researchers seem to have had a five-year head start in demonstrating the principles of the technology.
However, one notable difference between the Chinese and American experiments is that the Beijing experiment used a blue laser for their teleportation experiments while the BBN team had been employing infrared. Both have advantages and disadvantages in range and power, but the primary difference in their applications seems to be that blue and blue-green lasers penetrate further into water and so have wider applications for sub-surface communications. China is currently modernizing its submarine fleet as a way to project force further past its coastal waters to deter any US naval response to a potential invasion of Taiwan as well as doing significant research into laser communications in submarines.
Quantum laser links with satellites would allow sub-surface communication without most of the traditional downsides of radio communications and allow subs to operate with even greater autonomy and silence [7]. Judging from the interest in blue lasers for underwater communication and the interesting choice of a blue laser for the teleportation experiment, it would be safe to venture a guess that applications for quantum communication are already beginning to find their way into Chinese military research and development.
Because of its security level and applications for satellite and submarine communications, quantum communication technology figures centrally in the objectives of the Chinese military to upgrade their growing command and control capabilities. A functional satellite-based quantum communication system would give the Chinese military the ability to operate further afield without fear of message interception.
However, Chinese researchers must also be aware of the potential for the United States to employ the same technology and may be seeking ways to counter this eventuality. While it is still almost impossible to intercept quantum messages without being detected, it may be feasible to jam the laser signals that send them with “optical noise” or other lasers. Understanding the ways in which quantum cryptography functions may also eventually expose further weaknesses in the network that can be exploited by a savvy adversary.
China’s continuing cutting-edge quantum cryptography, lasers and optics research thus seems as much a reaction to the same research in the United States and an attempt to counter it as it is to develop its own indigenous network.
Atlas V rocket delivers satellite from launch at Cape Canaveral
A satellite designed to keep the president and top military commanders in contact even if nuclear war breaks out is safely in orbit after launching Saturday atop an Atlas V rocket.
The spacecraft is the first in a series intended to upgrade and replace an aging constellation reserved for transmitting the most protected military satellite communications around the world under any conditions.
Technical problems and changes in the scope of the $6.5 billion Advanced Extremely High Frequency satellite program, or AEHF, delayed its first launch by almost two years.
But Saturday’s countdown proceeded without a hitch.
The United Launch Alliance Atlas V blasted off from Cape Canaveral Air Force Station’s Launch Complex 41 at 7:07 a.m., rising into a clear sky with the sun low on the horizon.
As the rocket arced east over the Atlantic Ocean, sunlight illuminated the top of its plume of smoke and steam in a brilliant white and cast a long shadow behind it.
Three solid rocket motors fell away almost two minutes into the flight, followed soon by the payload’s protective cover and then the first stage booster.
Launch controllers applauded when the Lockheed Martin Corp.-built spacecraft separated from the rocket’s Centaur upper stage less than an hour after liftoff.
The spacecraft called AEHF-1 will take several months to settle into its final orbit 22,300 miles above the planet. There it will undergo months more of testing before being moved to an operational location.
The satellite – the size of a small school bus and weighing 13,500 pounds at launch — joins five that make up the aging Milstar constellation, offering more capacity than all five combined. The system covers the area between latitudes 65 degrees north and 65 degrees south of the equator.