Saturday, July 15, 2017

China's quantum satellite Mozi 墨子 produces a successful result

Communication through quantum entanglement is impossible to crack.
Many nations are researching in the area of secure communication.
 In a paper published today in Science, researchers from the Chinese Academy of Sciences announced China's quantum satellite "Mozi" 墨子 had successfully distributed entangled photons between three different terrestrial base stations, separated by as much as 1,200 kilometers on the ground. The result is the longest entanglement ever demonstrated, and the first that spanned between the Earth and space. Researchers say the system "opens up a new avenue to both practical quantum communications and fundamental quantum optics experiments at distances previously inaccessible on the ground.”

The spacecraft was launched by a Long March 2D rocket from Jiuquan Launch Pad 603, Launch Area 4 on 17 August 2016. The satellite uses a crystal to produce pairs of entangled photons in orbit. The photons are then transmitted down to base stations in China, traveling as much as 2400 km through space. The mission costs around US$100 million in total.
In theory, entangled photons can remain linked across any distance, but in practical terms, it's often difficult to distribute photon pairs without disrupting entanglement. If entanglement can be maintained, the result is a communication channel that’s effectively impossible to intercept. The simplest application is what cryptographers call a quantum key distribution network, using the network to securely distribute long and complex encryption keys. Anyone trying to intercept those keys would be easy to detect, since it's impossible to observe the photons in transit without altering them.
Quantum networking has already shown promise in terrestrial fiber networks, where specialized routing equipment can perform the same trick over conventional fiber-optic cable. The first such network was a DARPA-funded connection established in 2003 between Harvard, Boston University, and a private lab. In the years since, a number of companies have tried to build more ambitious connections. The Swiss company ID Quantique has mapped out a quantum network that would connect many of North America’s largest data centers; in China, a separate team is working on a 2,000-kilometer quantum link between Beijing and Shanghai, which would rely on fiber to span an even greater distance than the satellite link. Still, the nature of fiber places strict limits on how far a single photon can travel.
According to ID Quantique, a reliable satellite link could connect the existing fiber networks into a single globe-spanning quantum network. "This proves the feasibility of quantum communications from space," ID Quantique CEO Gregoire Ribordy tells The Verge. "The vision is that you have regional quantum key distribution networks over fiber, which can connect to each other through the satellite link.”
China isn't the only country working on bringing quantum networks to space. A collaboration between the UK's University of Strathclyde and the National University of Singapore is hoping to produce the same entanglement in cheap, readymade satellites called Cubesats. A Canadian team is also developing a method of producing entangled photons on the ground before sending them into space.

Saturday, June 17, 2017

China successfully launches x-ray satellite 慧眼 using Long March 4B

China's first astronomical satellite,  慧眼, "insight" or "smart eye", an x-ray telescope that will search the sky for black holes, neutron stars, was placed into orbit today after an early morning launch from the Inner Mongolia Desert.

The 2.8-ton Hard X-ray Modulation Telescope (HXMT), dubbed Insight according to  Xinhua news agency, was carried aloft by a Long March-4B medium lift rocket from the Jiuquan Satellite Launch Center 酒泉衛星發射中心. The newest of several x-ray telescope in space, the HXMT will observe some of the most turbulent processes in the universe. The x-rays generated by those events cannot penetrate Earth's atmosphere; they can only be observed by high-altitude balloons or satellites. The HXMT carries three x-ray telescopes observing at energy ranging from 20 to 200 kilo-electron volts as well as an instrument to inspect the space environment, according to its designers. While orbiting 600 kilometers above the planet, the HXMT will perform a sky survey that is expected to discover many new x-ray sources. Over an expected operating lifetime of 4 years, it will also conduct focused observations of black holes, neutron stars, and gamma ray bursts.

This great achievement by China's space science program "is certainly welcomed" by the world community, says Andrew Fabian, a theoretical astrophysicist at the University of Cambridge in England. "It is very meaningful that they have launched their first astronomical satellite and this will pave the way for others,” he says. Fabian believes that the HXMT sky survey will prove particularly valuable for catching transient x-ray sources that emerge, flare up to tremendous brightness, and then just as quickly fade away. As yet, the processes behind x-ray transients are poorly understood. Other missions are also trying to catch transients in the act. But "any satellite looking at that phenomena is going to find interesting things and do good science," Fabian says.

The "Insight" is the last of the cluster of four space science missions covered under China 12th 5-year plan that were developed by the National Space Science Center (NSSC) of the Chinese Academy of Sciences in Beijing-the other three are a dark matter probe, a collection of microgravity experiments, and a test of long-range quantum entanglement. Funding constraints meant all four had to be developed simultaneously, and all four were launched over the course of 18 months. " This is not a sustainable way to have a science program," NSSC Director  told Science in a 2016 interview.

Monday, May 29, 2017

China's planned far side of Moon sample mission

A view of the far side of the Moon and the distant Earth, captured by the 2014 Change 5-T1 mission.

China is progressing with plans to launch an unprecedented attempt to collect samples from the far side of the Moon in 2020, as well as future polar missions, following a meeting of top lunar scientists and space officials in Beijing.

The ambitious and complex Chang'e-6 mission is part of wider plans outlined for the exploration of the Moon which will follow on from the original three-stage Chinese Lunar Exploration Project (中国探月工程).

Chang'e-6 would follow the first ever landing on the far side of the Moon by the Chang'e-4 lander and rover mission, scheduled for late 2018, and would likely also target the scientifically significant South Pole-Aitken Basin.

Probes to both lunar poles are also being developed for the decade of 2020, which tentatively involve surface exploration, resource development and related technology validation.

"The exploration of lunar poles is a significant innovation in human history, which has drawn great attention from around the world. It will also lay a solid foundation for deeper and more accurate Moon probes in the future," Tian Yulong, chief engineer at SASTIND, said in October.

Such missions will also be of interest to the European Space Agency (ESA), which has been discussing cooperation in and coordination of lunar exploration plans with China as part of ESA's 'Moon Village' concept.

In March, Mr Wu told Xinhua agency that Chang'e-6 would target a 2020 launch, but that the mission had not yet been officially approved.

Such a declaration could only realistically come after success of China's first, near-side lunar sample return mission, Chang'e-5, which will launch on a Long March 5 heavy lift rocket from Wenchang in November.

CLEP has so far involved two orbiters, Chang'e-1 and 2, and a lander and rover mission, Chang'e-3 in 2013, and will culminate in the Chang'e-5 lunar sample return mission.

The four-part probe involves orbiting, landing, collecting samples, ascending to lunar orbit, rendezvous and docking in orbit, high-speed return to Earth and a skip reentry into the atmosphere.

The mission, the first of its kind since Soviet's Luna 24 in 1976, could return by far the youngest samples of lunar material so far, and will also prove useful experience for human landings in the future.

If the complex Chang'e-5 mission succeeds in bringing 2 kg of lunar samples back to Earth, Chang'e-6 - the designated backup spacecraft - will then be tasked with the scientific and exploration first of retrieving material from the far side of the Moon.

The far side of the Moon is not visible to Earth due to 'tidal locking', meaning tracking and communicating with the probe directly is not possible.

Thus facilitating a landing on the lunar far side will be a communications relay satellite, stationed in a halo orbit around the second Earth-Moon Lagrange Point beyond the Moon.

This will be launched around six months before the launch of Chang'e-4, which itself is a re-purposed backup to the successful Chang'e-3 mission which involved the Yutu, or Jade Rabbit, rover.

SASTIND, which oversees the Chinese space programme, last autumn stated that it is developing a 20 year strategy for lunar and interplanetary exploration, including the above plans, missions to Mars and potential human landings on the Moon.

While such a goal has been often stated in the media, there is mounting evidence that China is working on the capabilities required for putting astronauts on the lunar surface and getting them home.

In June 2016 as part of the debut flight of the Long March 7 rocket, a scale version of a return capsule for crewed deep space missions was successfully tested.

China is working on two variants of a successor to the crewed Shenzhou spacecraft, with masses of 14 and 20 metric tonnes and capable of accommodating 4-6 astronauts.

And early research into a launch vehicle powerful enough to send the required mass toward to Moon, the Saturn V-class (and Russian failed N1 class) Long March 9 rocket, is already underway.

Long March 9. Long March 9 (LM-9, CZ-9, or Changzheng 9, Chinese: 长征九号) is a Chinese super-heavy carrier rocket that is currently in study. It is planned for a maximum payload capacity of at least 140,000 kg to LEO or at least 50,000 kg to Lunar Transfer Orbit.