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Autumnal equinox

September 22

Autumnal equinox

The autumnal equinox is one of two points in Earth’s orbit where the sun creates equal periods of daytime and nighttime across the globe. Many mark it as the first day of the fall. See what it looks like from space here.

NASA’s Osiris-Rex spacecraft could try to collect a sample from the asteroid Bennu NASA/Goddard/University of Arizona

October 20

NASA’s Osiris-Rex spacecraft could try to collect a sample from the asteroid Bennu


This NASA spacecraft has been orbiting an Empire State Building-sized near Earth asteroid for more than a year. It will attempt to collect a sample during a brief touch down on its surface, and eventually return it to Earth. Read about Osiris-Rex’s landing site here.

The Orionids meteor shower will peak Petar Petrov/Associated Press

Starting October 21

The Orionids meteor shower will peak

Starting in the evening of Oct. 21, through the next day’s dawn, you might get your best chance to catch a glimpse of the Orionids meteor shower. Learn more about the major meteor showers and how to watch them here.

SpaceX could launch more astronauts to orbit in its Crew Dragon capsule Joe Raedle/Getty Images

October 23

SpaceX could launch more astronauts to orbit in its Crew Dragon capsule

In May, SpaceX carried two NASA astronauts to the International Space Station. Now that those astronauts have safely returned to Earth, NASA is preparing for Crew Dragon to transport a team of four, including a Japanese astronaut, on the capsule’s second piloted trip. Read more about how NASA became SpaceX’s customer here.

The Leonids meteor shower will peak James S. Wood/Arizona Daily Star, via Associated Press

Starting November 16

The Leonids meteor shower will peak

Starting in the evening of Nov. 16, through the next day’s dawn, you might get your best chance to catch a glimpse of the Leonids meteor shower. Learn more about the major meteor showers and how to watch them here.

A lunar eclipse will be visible in the Americas, Australia and parts of Asia and Europe. Romeo Ranoco/Reuters

Starting November 29

A lunar eclipse will be visible in the Americas, Australia and parts of Asia and Europe.


This will be a subtle, penumbral lunar eclipse much like the one in July, but shifted to the East. Moon gazers in the Americas and Australia can try to detect the change, as can people throughout East Asia. Read about forthcoming lunar astronomy events here.

Japan’s Hayabusa2 spacecraft could return a sample from the asteroid Ryugu to Earth JAXA, via Associated Press

December 6

Japan’s Hayabusa2 spacecraft could return a sample from the asteroid Ryugu to Earth


Throughout 2019, this Japanese probe collected multiple samples from this near Earth asteroid, including a memorable operation that blew a hole in the space rock’s surface. After returning to Earth, it will eject a sample capsule that will attempt to touch down in the Australian outback. Read more about Hayabusa2 here.

The Geminids meteor shower will peak Ethan Miller/Getty Images

Starting December 13

The Geminids meteor shower will peak

Starting in the evening of Dec. 13, through the next day’s dawn, you might get your best chance to catch a glimpse of the Geminids meteor shower. Learn more about the major meteor showers and how to watch them here.

A total solar eclipse will be visible in parts of South America Toni Greaves for The New York Times

December 14

A total solar eclipse will be visible in parts of South America

Darkness will fall during daytime in parts of South America as the moon obscures the sun. See last year’s total solar eclipse in Chile and Argentina, here.

The Ursids meteor shower will peak Ian Webster and Peter Jenniskens

Starting December 21

The Ursids meteor shower will peak

Starting in the evening of Dec. 21, through the next day’s dawn, you might be able to catch a glimpse of the Ursids meteor shower. Learn more about the major meteor showers and how to watch them here.

Winter solstice Robert Simmon/NASA

December 21

Winter solstice

It’s the scientific start to winter in the Northern Hemisphere, when this half of the world tilts away from the sun. Read more about the solstice here.

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When Voyager 2 Calls Home, Earth won’t Be Able to Answer for next 11 months

When Voyager 2 Calls Home, Earth Soon Won’t Be Able to Answer

NASA will spend 11 months upgrading the only piece of its Deep Space Network that can send commands to the probe, which has crossed into interstellar space.

Antennas belonging to the Deep Space Network complex in Canberra, Australia.
Antennas belonging to the Deep Space Network complex in Canberra, Australia.Credit…Canberra Deep Space Communication Complex



Voyager 2 has been traveling through space for 43 years, and is now more than 11 billion miles from Earth. But every so often, something goes wrong.

At the end of January, for instance, the robotic probe executed a routine somersault to beam scientific data back to Earth when an error triggered a shutdown of some of its functions.

“Everybody was extremely worried about recovering the spacecraft,” said Suzanne Dodd, who is the Voyager project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

The mission’s managers on our planet know what to do when such a fault occurs. Although it takes about a day and a half to talk to Voyager 2 at its current distance, they sent commands to restore its normal operations.


But starting on Monday for the next 11 months, they won’t be able to get word to the spry spacecraft in case something again goes wrong (although the probe can still stream data back to Earth). Upgrades and repairs are prompting NASA to take offline a key piece of space age equipment used to beam messages all around the solar system.

The downtime is necessary because of a flood of new missions to Mars scheduled to leave Earth this summer. But the temporary shutdown also highlights that the Deep Space Network, essential infrastructure relied upon by NASA and other space agencies, is aging and in need of expensive upgrades.


On any given day, NASA communicates with an armada of spacecraft in deep space. These long distance calls require the most powerful radio antennas in the world. Luckily NASA has its own switchboard, the Deep Space Network or DSN.

The DSN is one of space exploration’s most valuable assets. It comprises one station in the United States — in Goldstone, Calif. — and two overseas in Canberra, Australia, and Madrid. It has been in operation nonstop for 57 years, and without it, spacecraft that traveled beyond the moon couldn’t communicate with Earth. It is used not only by NASA, but also the European Space Agency and the space programs of Japan, India and soon even the United Arab Emirates.


This summer, four missions are scheduled to launch to Mars. When the spacecrafts arrive at the red planet next year, three of them will need additional bandwidth to speak to Earth (China will use its own dishes for its Mars mission).

Each station on Earth is outfitted with three 34-meter antennas and one 70-meter antenna. They switch back and forth depending on where a spacecraft is in relation to our planet, and you can see which spacecraft are talking to Earth in real time by visiting NASA’s DSN Now website.

Because of Voyager 2’s trajectory relative to Earth, it can talk to only one station and one antenna in the network: Canberra’s 70 meter dish, also known as DSS 43. And that dish will need to be improved for the new Mars missions, prompting a shutdown and temporary dismantlement.

“Frankly, there’s never a good time to take down an asset and never a good time to fix the potholes in the road,” said Ms. Dodd, who is also director of the group that manages the Deep Space Network for NASA. “But you know you’re going to do the work at the airport, not during the Christmas rush. You’re going to do it when it’s less busy.”

Engineers at work on the Voyager spacecraft in November 1976.
Engineers at work on the Voyager spacecraft in November 1976.Credit…NASA/JPL-Caltech

Because Voyager 2 is considered a “geriatric” spacecraft, losing contact with it for any length of time is risky. And for the next 11 months, Earth’s ability to communicate with the probe, now in what’s considered interstellar space, will be limited.

“There is risk in this business as there is in anything in spaceflight,” said Glen Nagle, NASA’s outreach and administration lead for the station in Australia. “It’s a major change and the longest downtime for the dish in the eighteen years I’ve been here.”


One of the biggest risks is keeping Voyager 2’s communication antenna pointed at Earth. To do this, the probe fires its thrusters more than a dozen times a day to stay oriented. The mission’s managers have to trust that the automation on board will be executed relatively flawlessly for nearly a year.

Staying warm enough is another major concern. The Voyager team has been slowly shutting off instruments in order to use their heaters to keep the spacecraft’s fuel lines at a balmy 32 degrees Fahrenheit.

“We’ve done the analysis to show that we can get through the downtime,” with some margin for error, said Todd Barber, the propulsion engineer for the twin Voyager spacecraft. (Voyager 1 is able to communicate with other dishes.)

While the team won’t be able to command Voyager 2, they will still be listening to the spacecraft. By combining the power of the other antennas in Canberra, they will be able to collect its scientific observations.

“The Canberra site will still be getting data back from the spacecraft,” Ms. Dodd said. “The science data will still be coming down.”

Being able to only listen could prompt some anxiety. While Voyager 2 will keep collecting and sending back science data, should something go wrong, members of the team will be powerless to help it, and will just have to watch with their hands tied.

“We’ve been planning on this for over a year,” Ms. Dodd said. “I think like any good planning, we’re prepared for it. And we’ve done our best, you know, we’ve done the best that we can.”


And the operations to restore Voyager 2 during its recent troubles may highlight how much more life it could have in deepest space, Ms. Dodd said. Never before had all of the spacecraft’s instruments been shut off in this manner. Much to the mission managers’ delight and surprise, they were all brought back to life.

“They also came back on, which is actually pretty remarkable,” she said.

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An earlier version of this article misstated the distance of Voyager 2 from Earth. It is more than 11 billion miles from Earth, not 13 billion. (Voyager 1, the spacecraft’s twin, is more than 13 billion miles from Earth.)


A version of this article appears in print on

March 6, 2020

, Section A, Page 7 of the New York edition with the headline: Earth to Voyager 2: Phone’s Broken. Call Home by Monday or Wait 11 Months.Order Reprints | Today’s Paper | Subscribe



The Lenovo computers were manufactured under a Chinese government program to provide cheap labor from persecuted Uyghurs.

THE ONGOING PERSECUTION by the Chinese government of Uyghur Muslims is far from a distant problem. Recent reporting has identified Uyghur forced labor in the supply chain of major global brands, including BMW, Ralph Lauren, Samsung, and Sony.

Now, as school districts scramble to obtain electronic devices for a school year that may be primarily virtual, some children may end up using computers assembled by Uyghurs working in inhumane conditions. Shipping records show that since the start of the pandemic, Lenovo has imported an estimated 258,000 laptops from a Chinese manufacturer that has participated in a troubling labor scheme and been singled out by the U.S. government for violating human rights. The revelations serve as a reminder of how much of the supply chain is tied to forced labor and how many products that will aid us through the Covid-19 pandemic may be manufactured under duress.


The Lenovo computers were made by the manufacturer Hefei Bitland, which participates in a Chinese government program to provide factories with cheap labor from persecuted Uyghurs. Some of the computers included lightweight Chromebooks bound for public schools in the U.S. — and some were delivered even after the company was placed on a government list restricting trade. After they arrived at port, sources say, Lenovo apparently removed a portion of the computers from distribution; over the past few weeks, multiple school districts have reported holdups in their orders of Lenovo Chromebooks. But other computers shipped since the start of the pandemic made it through to American customers, according to a distributor and to labor advocates who analyzed shipping data for The Intercept. Lenovo did not respond to request for comment.

“Whatever happens with the recently arrived shipments, hundreds of thousands of notebooks made for Lenovo by Hefei Bitland, and produced while transported Uyghur labor was present at its production facility, have already been bought by individuals and institutions in the U.S.,” said Scott Nova, executive director of the Worker Rights Consortium, based on a review of the Import Genius shipping records.

EVIDENCE OF Hefei Bitland using forced labor first appeared in an August 2018 article in Xinjiang Daily, a state newspaper. The article explains that the plant uses Uyghur workers who are overseen by Communist Party minders and police. The Australian Strategic Policy Institute, or ASPI, a think tank in Canberra, included Hefei Bitland in a report on Uyghur forced labor published in March, as the novel coronavirus was spreading through the world. The U.S. Tariff Act prohibits companies from importing goods manufactured using forced labor, which is defined by the International Labor Organization as involving several possible indicators including intimidation, restricted movement, and abuse of a vulnerable population.

In the months that followed the ASPI report, schools and companies around the United States moved online and competed to cheaply purchase devices. Since March, Lenovo has imported nearly 1.3 million pounds of computers made by Hefei Bitland. If every boxed computer weighs 5 pounds, that would be the equivalent of 258,000 laptops.

On July 20, the U.S. Commerce Department’s Bureau of Industry and Security added Hefei Bitland and eight other Chinese companies to the Entity List for using forced labor performed by Uyghurs and other oppressed Muslim minority groups. (BIS also listed two subsidiaries of the gene sequencing powerhouse BGI, for the repressive use of genetic technologies in the traditional Uyghur home region of Xinjiang.)

Lenovo’s shipments continued even after Hefei Bitland’s July Entity List addition, which threw the weight of the U.S. government behind allegations of forced labor and rattled U.S. supply chains. Following the designation, other U.S. firms that rely on Chinese contractors accused of employing forced Uyghur labor said they intend to change suppliers. Lenovo has not made a public statement about the forced labor finding. A cached version of the website for Hefei Bitland’s Shenzhen-based parent company, Bitland, says that its other clients include Google and Intel. The list of customers has since been removed.

Customs records show that at least 16 separate shipments containing 355,982 pounds of Hefei Bitland-manufactured Lenovo laptops arrived in the Port of Los Angeles since the Entity List designation. The records, obtained via sea vessel cargo disclosures, were compiled by Import Genius, a technology company that tracks trade-related data. There are gaps in the disclosure system, however, potentially concealing other deliveries. Air freight cargo does not follow the same disclosure laws as shipments sent by sea.

At least some of those shipments are now in limbo. Multiple deliveries of Hefei Bitland laptops have been delayed, affecting school districts around the country. Nearly 4,000 laptops destined for Etowah County, Alabama, schools were held up earlier this month. The Etowah County school district, which ordered the laptops in June from Trinity3 Technology, a Lenovo distributor, canceled the order earlier this month when it became clear the delivery would not be resolved until October.

Similar delays over Hefei Bitland-made laptops were reported for schools in New Jersey and North Carolina. School district officials in Paterson, New Jersey, told the Paterson Times that the holdup was due to Lenovo trying to bring three additional factories online to produce Chromebooks, in order to replace laptops made by Hefei Bitland.

Trinity3 did not respond to repeated requests from The Intercept for comment. Scott Gill, the chief executive of Trinity3, told the News & Observer that Lenovo was in the process of “socially responsible sourcing and ongoing auditing processes for all production facilities to safeguard against the use of forced labor.” But some laptops Hefei Bitland shipped this summer have been distributed to school districts. Gill said that the company first learned of delays on July 27, and that before then, other shipments of Hefei Bitland laptops had made it to school districts across the country. One district in North Carolina recently received 7,650 Chromebooks from Trinity3, according to the paper.

HEFEI BITLAND’S campus spans 60 acres in an industrial quarter of Hefei, the capital of Anhui province in eastern China. The company makes laptops, graphics cards, and PC motherboards. Bitland, its parent company, says on its website that in 2019 Lenovo, which is headquartered in Hong Kong, awarded it the label “Diamond supplier.”

Two thousand miles away, in Xinjiang, the Chinese government interns as many as 1.5 million Uyghurs, Kazakhs, and other ethnic minorities in inhumane detention camps. In the internment camps, detainees are separated from their children, prevented from exercising their religion, and subjected to political indoctrination. Uyghurs have also been forcibly sterilized or made to use intrusive birth control methods — a treatment that some are now calling genocide.

Over the past few years, the internment camps have been joined by an institutionalized forced labor program in which workers are transferred from Xinjiang — in some cases directly from the camps — to factories in the east. Under a scheme called Xinjiang Aid, the Chinese government has placed an estimated 80,000 Uyghurs at factories, where they live in segregated dormitories, sometimes surrounded by brick walls, tall fences, or guard stations. Among the beneficiaries of this program is Hefei Bitland.

The Chinese government says that Xinjiang Aid is voluntary. But rights advocates say that the program is a barbaric way of lowering labor costs while stamping out the Uyghur culture and language. “Why would they transfer the workers across the country?” said Peter Irwin, a senior program officer at the Uyghur Human Rights Project in Washington, D.C. “Part of it is cheap labor. Secondly it serves the purpose of assimilating people.”

In 2018, party cadres reportedly transferred 1,554 workers from rural Awat County in Xinjiang to Hefei Bitland’s facility, along with two factories owned by other manufacturers. Although it is not clear whether Hefei Bitland is currently employing Uyghurs, the labor arrangements are typically ongoing, with workers cycled out every six to 12 months and replaced with new transplants. According to ASPI, the Australian think tank, both local officials in Xinjiang and factories in eastern China get kickbacks for arranging placements.

Uyghur laborers are often paid, but they are believed to receive less than their Han Chinese counterparts. After finishing their shifts, the workers are often forced to study Mandarin. They are closely watched by minders and in some cases may be required to download an app on their phone that rights advocates believe is used for surveillance.

“Once they get to the factories, they generally have very strict restrictions on their movements,” said Nathan Ruser, a researcher with ASPI’s International Cyber Policy Centre. “Sometimes they’re allowed permission to leave, but generally not — and never without permission.” Satellite photos of the Hefei Bitland campus reveal a structure that appears to be a guard station was constructed next to worker dormitories in the second half of 2018. Bitland, Hefei Bitland’s parent company, did not respond to a request for comment.


A satellite image of Hefei Bitland’s campus shows an apparent guard station, adjacent to worker dormitories, that was constructed in late 2018.


Image: Google Map

SUPPLY CHAIN disclosure plays a critical role in holding companies accountable for human rights abuses. In recent years, global pressure over unsafe working conditions in Bangladesh’s garment factories has forced major brands to provide meaningful information about how their products are manufactured.

“Robust and publicly available trade data is key to enabling oversight for supply chains, ensuring that companies purchasing goods produced through forced labor, as well as the manufacturers, can be held to account,” said William George, an analyst with Import Genius. “Without transparency in global trade, manufacturers who violate human rights can operate with near anonymity.”

Laptops are hardly the only product to come under scrutiny since the start of the pandemic. The New York Times recently reported that some face masks and other protective equipment sold in the United States are manufactured using forced Uyghur labor. In June, brands including Gap, H&M, Victoria’s Secret, and Zara came under pressure to clean up their supply chains from a campaign called End Uyghur Forced Labor, which highlights abuses in apparel production. BIS issued the Entity List designations the following month. A bill introduced in Congress in March would ban certain imports from Xinjiang and require more disclosures from companies that work in the region.

But many companies have been slow to purge their supply chains of forced labor. If Lenovo doesn’t commit to forgoing sales of computers made by Hefei Bitland, said Nova, “then it is likely that some institutional and individual consumers will end up buying notebook computers, in the weeks ahead, made by a supplier that has been identified as a major human rights violator.”

Rights advocates called on governments in the United States and Europe to better enforce prohibitions on forced labor. “It’s up to governments to ensure that these kinds of products aren’t landing in the laps of schoolchildren,” Irwin said.


Mara Hvistendahlmara.hvistendahl@​

Lee Fanglee.fang@​

With Ultralight Lithium-Sulfur Batteries, Electric Airplanes Could Finally Take Off

With Ultralight Lithium-Sulfur Batteries, Electric Airplanes Could Finally Take Off

Oxis Energy’s design promises outstanding energy density, manufacturability, and safety

By Mark Crittenden
A jet airliner with batteries for engines.
Photo-illustration: Edmon de Haro

Electric aircraft are all the rage, with prototypes in development in every size from delivery drones to passenger aircraft. But the technology has yet to take off, and for one reason: lack of a suitable battery.

For a large passenger aircraft to take off, cruise, and land hundreds of kilometers away would take batteries that weigh thousands of kilograms—far too heavy for the plane to be able to get into the air in the first place. Even for relatively small aircraft, such as two-seat trainers, the sheer weight of batteries limits the plane’s payload, curtails its range, and thus constrains where the aircraft can fly. Reducing battery weight would be an advantage not only for aviation, but for other electric vehicles, such as cars, trucks, buses, and boats, all of whose performance is also directly tied to the energy-to-weight ratio of their batteries.

For such applications, today’s battery of choice is lithium ion. It reached maturity years ago, with each new incremental improvement smaller than the last. We need a new chemistry.

Since 2004 my company, Oxis Energy, in Oxfordshire, England, has been working on one of the leading contenders—lithium sulfur. Our battery technology is extremely lightweight: Our most recent models are achieving more than twice the energy density typical of lithium-ion batteries. Lithium sulfur is also capable of providing the required levels of power and durability needed for aviation, and, most important, it is safe enough. After all, a plane can’t handle a sudden fire or some other calamity by simply pulling to the side of the road.

The new technology has been a long time coming, but the wait is now over. The first set of flight trials have already been completed.

Fundamentally, a lithium-sulfur cell is composed of four components:

  • The positive electrode, known as the cathode, absorbs electrons during discharge. It is connected to an aluminum-foil current collector coated with a mixture of carbon and sulfur. Sulfur is the active material that takes part in the electrochemical reactions. But it is an electrical insulator, so carbon, a conductor, delivers electrons to where they are needed. There is also a small amount of binder added to ensure the carbon and sulfur hold together in the cathode.
  • The negative electrode, or anode, releases electrons during discharge. It is connected to pure lithium foil. The lithium, too, acts as a current collector, but it is also an active material, taking part in the electrochemical reaction.
  • A porous separator prevents the two electrodes from touching and causing a short circuit. The separator is bathed in an electrolyte containing lithium salts.
  • An electrolyte facilitates the electrochemical reaction by allowing the movement of ions between the two electrodes.

These components are connected and packaged in foil as a pouch cell. The cells are in turn connected together—both in series and in parallel—and packaged in a 20 ampere-hour, 2.15-volt battery pack. For a large vehicle such as an airplane, scores of packs are connected to create a battery capable of providing tens or hundreds of amp-hours at several hundred volts.

Lithium-sulfur batteries are unusual because they go through multiple stages as they discharge, each time forming a different, distinct molecular species of lithium and sulfur. When a cell discharges, lithium ions in the electrolyte migrate to the cathode, where they combine with sulfur and electrons to form a polysulfide, Li2S8. At the anode, meanwhile, lithium molecules give up electrons to form positively charged lithium ions; these freed electrons then move through the external circuit—the load—which takes them back to the cathode. In the electrolyte, the newly produced Li2S8 immediately reacts with more lithium ions and more electrons to form a new polysulfide, Li2S6. The process continues, stepping through further polysulfides, Li2S4 and Li2S2, to eventually become Li2S. At each step more energy is given up and passed to the load until at last the cell is depleted of energy.

Recharging reverses the sequence: An applied current forces electrons to flow in the opposite direction, causing the sulfur electrode, or cathode, to give up electrons, converting Li2S to Li2S2. The polysulfide continues to add sulfur atoms step-by-step until Li2S8 is created in the cathode. And each time electrons are given up, lithium ions are produced that then diffuse through the electrolyte, combining with electrons at the lithium electrode to form lithium metal. When all the Li2S has been converted to Li2S8, the cell is fully charged.

This description is simplified. In reality, the reactions are more complex and numerous, taking place also in the electrolyte and at the anode. In fact, over many charge and discharge cycles, it is these side reactions that cause degradation in a lithium-sulfur cell. Minimizing these, through the selection of the appropriate materials and cell configuration, is the fundamental, underlying challenge that must be met to produce an efficient cell with a long lifetime.


One great challenge for both lithium-ion and lithium-sulfur technologies has been the tendency for repeated charging and discharging cycles to degrade the anode. In the case of lithium ion, ions arriving at that electrode normally fit themselves into interstices in the metal, a process called intercalation. But sometimes ions plate the surface, forming a nucleus on which further plating can accumulate. Over many cycles a filament, or dendrite, may grow until it reaches the opposing electrode and short-circuits the cell, causing a surge of energy, in the form of heat that irreparably damages the cell. If one cell breaks down like this, it can trigger a neighboring cell to do the same, beginning a domino effect known as a thermal runaway reaction—in common parlance, a fire.

With lithium-sulfur cells, degradation of the lithium-metal anode is also a problem. However, this occurs via a very different mechanism, one that does not involve the formation of dendrites. In lithium-sulfur cells, uneven current densities on the anode surface cause lithium to be plated and stripped unevenly as the battery is charged and discharged. Over time, this uneven plating and stripping causes mosslike deposits on the anode that react with the sulfide and polysulfides in the electrolyte. These mosslike deposits become electrically disconnected from the bulk anode, leaving less of the anode surface available for chemical reaction. Eventually, as this degradation progresses, the anode fails to operate, preventing the cell from accepting charge.

Developing solutions to this degradation problem is crucial to producing a cell that can perform at a high level over many charge-discharge cycles. A promising strategy we’ve been pursuing at Oxis involves coating the lithium-metal anode with thin layers of ceramic materials to prevent degradation. Such ceramic materials need to have high ionic conductivity and be electrically insulating, as well as mechanically and chemically robust. The ceramic layers allow lithium ions to pass through unimpeded and be incorporated into the bulk lithium metal beneath.

We are doing this work on the protection layer for the anode in partnership with Pulsedeon and Leitat, and we’re optimistic that it will dramatically increase the number of times a cell can be discharged and charged. And it’s not our only partnership. We’re also working with Arkema to improve the cathode in order to increase the power and energy density of the battery.

Indeed, the key advantage of lithium-ion batteries over their predecessors—and of lithium sulfur over lithium ion—is the great amount of energy the cells can pack into a small amount of mass. The lead-acid starter battery that cranks the internal combustion engine in a car can store about 50 watt-hours per kilogram. Typical lithium-ion designs can hold from 100 to 265 Wh/kg, depending on the other performance characteristics for which it has been optimized, such as peak power or long life. Oxis recently developed a prototype lithium-sulfur pouch cell that proved capable of 470 Wh/kg, and we expect to reach 500 Wh/kg within a year. And because the technology is still new and has room for improvement, it’s not unreasonable to anticipate 600 Wh/kg by 2025.

When cell manufacturers quote energy-density figures, they usually specify the energy that’s available when the cell is being discharged at constant, low power rates. In some applications such low rates are fine, but for the many envisioned electric aircraft that will take off vertically, the energy must be delivered at higher power rates. Such a high-power feature must be traded off for lower total energy-storage capacity.

Photo of an airplane.Photo of a man standing over a machine.
Photos: Bye Aerospace; Oxis Energy
All Amped Up: Bye Aerospace’s eFlyer 2 [top] is designed to train pilots. Bye is working with Oxis Energy on a lithium-sulfur battery that promises to increase the plane’s range. Here a reel of positive electrode, made of sulfur, is being coated onto a current collector [bottom].      

Furthermore, the level of energy density achievable in a single cell might be considerably greater than what’s possible in a battery consisting of many such cells. The energy density doesn’t translate directly from the cell to the battery because cells require packaging—the case, the battery management system, and the connections, and perhaps cooling systems. The weight must be kept in check, and for this reason our company is using advanced composite materials to develop light, strong, flameproof enclosures.


If the packaging is done right, the energy density of the battery can be held to 80 percent of that of the cells: A cell rated at 450 Wh/kg can be packaged at more than 360 Wh/kg in the final battery. We expect to do better by integrating the battery into the aircraft, for instance, by making the wing space do double duty as the battery housing. We expect that doing so will get the figure up to 90 percent.

To optimize battery performance without compromising safety we rely, first and foremost, on a battery management system (BMS), which is a combination of software and hardware that controls and protects the battery. It also includes algorithms for measuring the energy remaining in a battery and others for minimizing the energy wasted during charging.

Like lithium-ion cells, lithium-sulfur cells vary slightly from one another. These differences, as well as differences in the cells’ position in the battery pack, may cause some cells to consistently run hotter than others. Over time, those high temperatures slowly degrade performance, so it is important to minimize the power differences from cell to cell. This is usually achieved using a simple balancing solution, in which several resistors are connected in parallel with a cell, all controlled by software in the BMS.

Even when charging and discharging rates are kept within safe limits, any battery may still generate excessive heat. So, typically, a dedicated thermal-management system is necessary. An electric car can use liquid cooling, but in aviation, air cooling is much preferred because it adds less weight. Of course, the battery can be placed at a point where air is naturally moving across the surface of the airplane—perhaps the wing. If necessary, air can be shunted to the battery through ducts. At Oxis, we’re using computational modeling to optimize such cooling. For instance, when we introduced this technique in a project for a small fixed-wing aircraft, it allowed us to design an effective thermal-management system, without which the battery would reach its temperature limits before it was fully discharged.

As noted above, a battery pack is typically arranged with the cells both in parallel and in series. However, there’s more to the arrangement of cells. Of course, the battery is a mission-critical component of an e-plane, so you’ll want redundancy, for enhanced safety. You could, for instance, design the battery in two equal parts, so that if one half fails it can be disconnected, leaving the aircraft with at least enough energy to manage a controlled descent and landing.

Another software component within the BMS is the state-of-charge algorithm. Imagine having to drive a car whose fuel gauge had a measurement error equivalent to 25 percent of the tank’s capacity. You’d never let the indicator drop to 25 percent, just to make sure that the car wouldn’t sputter to a halt. Your practical range would be only three-quarters of the car’s actual range. To avoid such waste, Oxis has put a great emphasis on the development of state-of-charge algorithms.

In a lithium-ion battery you can estimate the charge by simply measuring the voltage, which falls as the energy level does. But it’s not so simple for a lithium-sulfur battery. Recall that in the lithium-sulfur battery, different polysulfides figure in the electrochemical process at different times during charge and discharge. The upshot is that voltage is not a good proxy for the state of charge and, to make things even more complicated, the voltage curve is asymmetrical for charge and for discharge. So the algorithms needed to keep track of the state of charge are much more sophisticated. We developed ours with Cranfield University, in England, using statistical techniques, among them the Kalman filter, as well as neural networks. We can estimate state of charge to an accuracy of a few percent, and we are working to do better still.

All these design choices involve trade-offs, which are different for different airplanes. We vary how we manage these trade-offs in order to tailor our battery designs for three distinct types of aircraft.

  • High-altitude pseudo satellites (HAPS) are aircraft that fly at around 15,000 to 20,000 meters. The hope is to be able to fly for months at a time; the current record is 26 days, set in 2018 by the Airbus Zephyr S. By day, these aircraft use solar panels to power the motors and charge the batteries; by night, they fly on battery power. Because the 24-hour charge-and-discharge period demands only a little power, you can design a light battery and thus allow for a large payload. The lightness also makes it easier for such an aircraft to fly far from the equator, where the night lasts longer.
  • Electric vertical take-off and landing (eVTOL) aircraft are being developed as flying taxis. Lilium, in Germany, and Uber Elevate, among others, already have such projects under way. Again, weight is critical, but here the batteries need not only be light but must also be powerful. Oxis has therefore developed two versions of its cell chemistry. The high-energy version is optimized in many aspects of the cell design to minimize weight, but it is limited to relatively low power; it is best suited to HAPS applications. The high-power version weighs more, although still significantly less than a lithium-ion battery of comparable performance; it is well suited for such applications as eVTOL.
  • Light fixed-wing aircraft: The increasing demand for pilots is coming up against the high cost of training them; an all-electric trainer aircraft would dramatically reduce the operation costs. A key factor is longer flight duration, which is enabled by the lighter battery. Bye Aerospace, in Colorado, is one company leading the way in such aircraft. Furthermore, other companies—such as EasyJet, partnered with Wright Electric—are planning all-electric commercial passenger jets for short-haul, 2-hour flights.


Three factors will determine whether lithium-sulfur batteries ultimately succeed or fail. First is the successful integration of the batteries into multiple aircraft types, to prove the principle. Second is the continued refinement of the cell chemistry. Third is the continued reduction in the unit cost. A plus here is that sulfur is about as cheap as materials get, so there’s reason to hope that with volume manufacturing, the unit cost will fall below that of the lithium-ion design, as would be required for commercial success.

Oxis has already produced tens of thousands of cells, and it is currently scaling up two new projects. Right now, it is establishing a manufacturing plant for the production of both the electrolyte and the cathode active material in Port Talbot, Wales. Later, the actual mass production of lithium-sulfur cells will begin on a site that belongs to Mercedes-Benz Brazil, in Minas Gerais, Brazil.

This state-of-the-art plant should be commissioned and operating by 2023. If the economies of scale prove out, and if the demand for electric aircraft rises as we expect, then lithium-sulfur batteries could begin to supplant lithium-ion batteries in this field. And what works in the air ought to work on the ground, as well.

This article appears in the August 2020 print issue as “Ultralight Batteries for Electric Airplanes.”

About the Author

Mark Crittenden is head of battery development and integration at Oxis Energy, in Oxfordshire, U.K.


Wigner’s Quantum paradox points to shaky foundations of reality

Not just “philosophical mumbo-jumbo”: An experiment shows how facts may depend on the observer.



Quantum paradox points to shaky foundations of reality

Nearly 60 years ago, the Nobel Prize–winning physicist Eugene Wigner captured one of the many oddities of quantum mechanics in a thought experiment. He imagined a friend of his, sealed in a lab, measuring a particle such as an atom while Wigner stood outside. Quantum mechanics famously allows particles to occupy many locations at once—a so-called superposition—but the friend’s observation “collapses” the particle to just one spot. Yet for Wigner, the superposition remains: The collapse occurs only when he makes a measurement sometime later. Worse, Wigner also sees the friend in a superposition. Their experiences directly conflict.

Now, researchers in Australia and Taiwan offer perhaps the sharpest demonstration that Wigner’s paradox is real. In a study published this week in Nature Physics, they transform the thought experiment into a mathematical theorem that confirms the irreconcilable contradiction at the heart of the scenario. The team also tests the theorem with an experiment, using photons as proxies for the humans. Whereas Wigner believed resolving the paradox requires quantum mechanics to break down for large systems such as human observers, some of the new study’s authors believe something just as fundamental is on thin ice: objectivity. It could mean there is no such thing as an absolute fact, one that is as true for me as it is for you.

 “It’s a bit disconcerting,” says co-author Nora Tischler of Griffith University. “A measurement outcome is what science is based on. If somehow that’s not absolute, it’s hard to imagine.”


For physicists who have dismissed thought experiments like Wigner’s as interpretive navel gazing, the study shows the contradictions can emerge in actual experiments, says Dustin Lazarovici, a physicist and philosopher at the University of Lausanne who was not part of the team. “The paper goes to great lengths to speak the language of those who have tried to merely discuss foundational issues away and may thus compel at least some to face up to them,” he says.

Wigner’s thought experiment has seen renewed attention in recent years. In 2015, Časlav Brukner of the University of Vienna tested the most intuitive way around the paradox: that the friend inside the lab has, in fact, seen the particle in one place or another, and Wigner just doesn’t know what it is yet. In the jargon of quantum theory, the friend’s result is a hidden variable.

Brukner ruled out that conclusion in a thought experiment of his own, using a trick—based on quantum entanglement—to bring the hidden variable out into the open. He imagined setting up two friend-Wigner pairs and giving each a particle, entangled with its partner in such a way that their attributes, upon measurement, are correlated. Each friend measures the particle, each Wigner measures the friend measuring the particle, and the two Wigners compare notes. The process repeats. If the friends saw definite results—as you might suspect—the Wigners’ own findings would show only weak correlations. But instead, they find a pattern of strong correlations. “You run into contradictions,” Brukner says. His experiment and a similar one in 2016 by Daniela Frauchiger and Renato Renner of ETH Zürich led to an outpouring of papers and heated discussion at conferences.

But in 2018, Richard Healey, a philosopher of physics at the University of Arizona, pointed out a loophole in Brukner’s thought experiment, which Tischler and her colleagues have now closed. In their new scenario they make four assumptions. One is that the results the friends obtain are real: They can be combined with other measurements to form a shared corpus of knowledge. They also assume quantum mechanics is universal, and as valid for observers as for particles; that the choices the observers make are free of peculiar biases induced by a godlike superdeterminism; and that physics is local, free of all but the most limited form of “spooky action” at a distance.

Yet their analysis shows the contradictions of Wigner’s paradox persist. The team’s tabletop experiment, in which they created entangled photons, also backs up the paradox. Optical elements steered each photon onto a path that depended on its polarization: the equivalent of the friends’ observations. The photon then entered a second set of elements and detectors that played the role of the Wigners. The team found, again, an irreconcilable mismatch between the friends and the Wigners. What is more, they varied exactly how entangled the particles were and showed that the mismatch occurs for different conditions than in Brukner’s scenario. “That shows that we really have something new here,” Tischler says.

It also indicates that one of the four assumptions has to give. Few physicists believe superdeterminism could be to blame. Some see locality as the weak point, but its failure would be stark: One observer’s actions would affect another’s results even across great distances—a stronger kind of nonlocality than the type quantum theorists often consider. So some are questioning the tenet that observers can pool their measurements empirically. “It could be that there are facts for one observer, and facts for another; they need not mesh,” says study co-author and Griffith physicist Howard Wiseman. It is a radical relativism, still jarring to many. “From a classical perspective, what everyone sees is considered objective, independent of what anyone else sees,” says Olimpia Lombardi, a philosopher of physics at the University of Buenos Aires.

And then there is Wigner’s conclusion that quantum mechanics itself breaks down. Of the assumptions, it is the most directly testable, by experiments that are probing quantum mechanics on ever larger scales. But the one position that doesn’t survive the analysis is to have no position, says another co-author at Griffith, Eric Cavalcanti. “Most physicists, they think: ‘That’s just philosophical mumbo-jumbo,’” he says. “They will have a hard time.”

*Clarification, 18 August, 10:10 a.m.: Howard Wiseman’s comments about objectivity have been clarified.

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George Musser

George Musser is a journalist based in New Jersey and author of Spooky Action at Distance.