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A solar-powered rocket might be our ticket to interstellar space



Haitong Yu | Getty Images

If Jason Benkoski is right, the path to interstellar space begins in a shipping container tucked behind a laboratory high bay in Maryland. The set up looks like something out of a low-budget sci-fi film: One wall of the container is lined with thousands of LEDs, an inscrutable metal trellis runs down the center, and a thick black curtain partially obscures the apparatus. This is the Johns Hopkins University Applied Physics Laboratory solar simulator, a tool that can shine with the intensity of 20 suns. On Thursday afternoon, Benkoski mounted a small black and white tile onto the trellis and pulled a dark curtain around the set-up before stepping out of the shipping container. Then he hit the light switch.

Once the solar simulator was blistering hot, Benkoski started pumping liquid helium through a small embedded tube that snaked across the slab. The helium absorbed heat from the LEDs as it wound through the channel and expanded until it was finally released through a small nozzle. It might not sound like much, but Benkoski and his team just demonstrated solar thermal propulsion, a previously theoretical type of rocket engine that is powered by the sun’s heat. They think it could be the key to interstellar exploration.

“It’s really easy for someone to dismiss the idea and say, ‘On the back of an envelope, it looks great, but if you actually build it, you’re never going to get those theoretical numbers,’” says Benkoski, a materials scientist at the Applied Physics Laboratory and the leader of the team working on a solar thermal propulsion system. “What this is showing is that solar thermal propulsion is not just a fantasy. It could actually work.”

Only two spacecraft, Voyager 1 and Voyager 2, have left our solar system. But that was a scientific bonus after they completed their main mission to explore Jupiter and Saturn. Neither spacecraft was equipped with the right instruments to study the boundary between our star’s planetary fiefdom and the rest of the universe. Plus, the Voyager twins are slow. Plodding along at 30,000 miles per hour, it took them nearly a half century to escape the sun’s influence.

But the data they have sent back from the edge is tantalizing. It showed that much of what physicists had predicted about the environment at the edge of the solar system was wrong. Unsurprisingly, a large group of astrophysicists, cosmologists, and planetary scientists are clamoring for a dedicated interstellar probe to explore this new frontier.

In 2019, NASA tapped the Applied Physics Laboratory to study concepts for a dedicated interstellar mission. At the end of next year, the team will submit its research to the National Academies of Sciences, Engineering, and Medicine’s Heliophysics decadal survey, which determines sun-related science priorities for the next 10 years. APL researchers working on the Interstellar Probe program are studying all aspects of the mission, from cost estimates to instrumentation. But simply figuring out how to get to interstellar space in any reasonable amount of time is by far the biggest and most important piece of the puzzle.

The edge of the solar system—called the heliopause—is extremely far away. By the time a spacecraft reaches Pluto, it’s only a third of the way to interstellar space. And the APL team is studying a probe that would go three times farther than the edge of the solar system, a journey of 50 billion miles, in about half the time it took the Voyager spacecraft just to reach the edge. To pull off that type of mission, they’ll need a probe unlike anything that’s ever been built. “We want to make a spacecraft that will go faster, further, and get closer to the sun than anything has ever done before,” says Benkoski. “It’s like the hardest thing you could possibly do.”

In mid-November, the Interstellar Probe researchers met online for a weeklong conference to share updates as the study enters its final year. At the conference, teams from APL and NASA shared the results of their work on solar thermal propulsion, which they believe is the fastest way to get a probe into interstellar space. The idea is to power a rocket engine with heat from the sun, rather than combustion. According to Benkoski’s calculations, this engine would be around three times more efficient than the best conventional chemical engines available today. “From a physics standpoint, it’s hard for me to imagine anything that’s going to beat solar thermal propulsion in terms of efficiency,” says Benkoski. “But can you keep it from exploding?”

Unlike a conventional engine mounted on the aft end of a rocket, the solar thermal engine that the researchers are studying would be integrated with the spacecraft’s shield. The rigid flat shell is made from a black carbon foam with one side coated in a white reflective material. Externally it would look very similar to the heat shield on the Parker Solar Probe. The critical difference is the tortuous pipeline hidden just beneath the surface. If the interstellar probe makes a close pass by the sun and pushes hydrogen into its shield’s vasculature, the hydrogen will expand and explode from a nozzle at the end of the pipe. The heat shield will generate thrust.

It’s simple in theory, but incredibly hard in practice. A solar thermal rocket is only effective if it can pull off an Oberth maneuver, an orbital mechanics hack that turns the sun into a giant slingshot. The sun’s gravity acts like a force multiplier that dramatically increases the craft’s speed if a spacecraft fires its engines as it loops around the star. The closer a spacecraft gets to the sun during an Oberth maneuver, the faster it will go. In APL’s mission design, the interstellar probe would pass just a million miles from its roiling surface.

To put this in perspective, by the time NASA’s Parker Solar Probe makes its closest approach in 2025, it will be within 4 million miles of the sun’s surface and booking it at nearly 430,000 miles per hour. That’s about twice the speed the interstellar probe aims to hit and the Parker Solar Probe built up speed with gravity assists from the sun and Venus over the course of seven years. The Interstellar Probe will have to accelerate from around 30,000 miles per hour to around 200,000 miles per hour in a single shot around the sun, which means getting close to the star. Really close.

Cozying up to a sun-sized thermonuclear explosion creates all sorts of materials challenges, says Dean Cheikh, a materials technologist at NASA’s Jet Propulsion Laboratory who presented a case study on the solar thermal rocket during the recent conference. For the APL mission, the probe would spend around two-and-a-half hours in temperatures around 4,500 degrees Fahrenheit as it completed its Oberth maneuver. That’s more than hot enough to melt through the Parker Solar Probe’s heat shield, so Cheikh’s team at NASA found new materials that could be coated on the outside to reflect away thermal energy. Combined with the cooling effect of hydrogen flowing through channels in the heat shield, these coatings would keep the interstellar probe cool while it blitzed by the sun. “You want to maximize the amount of energy that you’re kicking back,” says Cheikh. “Even small differences in material reflectivity start to heat up your spacecraft significantly.”

A still greater problem is how to handle the hot hydrogen flowing through the channels. At extremely high temperatures, the hydrogen would eat right through the carbon-based core of the heat shield, which means the inside of the channels will have to be coated in a stronger material. The team identified a few materials that could do the job, but there’s just not a lot of data on their performance, especially extreme temperatures. “There’s not a lot of materials that can fill these demands,” says Cheikh. “In some ways that’s good, because we only have to look at these materials. But it’s also bad because we don’t have a lot of options.”

The big takeaway from his research, says Cheikh, is there’s a lot of testing that needs to be done on heat shield materials before a solar thermal rocket is sent around the sun. But it’s not a dealbreaker. In fact, incredible advances in materials science make the idea finally seem feasible more than 60 years after it was first conceived by engineers in the US Air Force. “I thought I came up with this great idea independently, but people were talking about it in 1956,” says Benkoski. “Additive manufacturing is a key component of this, and we couldn’t do that 20 years ago. Now I can 3D-print metal in the lab.”

Even if Benkoski wasn’t the first to float the idea of a solar thermal propulsion, he believes he’s the first to demonstrate a prototype engine. During his experiments with the channeled tile in the shipping container, Benkoski and his team showed that it was possible to generate thrust using sunlight to heat a gas as it passed through embedded ducts in a heat shield. These experiments had several limitations. They didn’t use the same materials or propellant that would be used on an actual mission, and the tests occurred at temperatures well below what an interstellar probe would experience. But the important thing, says Benkoski, is that the data from the low temperature experiments matched the models that predict how an interstellar probe would perform on its actual mission once adjustments are made for the different materials. “We did it on a system that would never actually fly. And now the second step is we start to substitute each of these components with the stuff that you would put on a real spacecraft for an Oberth maneuver,” Benkoski says.

The concept has a long way to go before it’s ready to be used on a mission—and with only a year left in the Interstellar Probe study, there’s not enough time to launch a small satellite to do experiments in low Earth orbit. But by the time Benkoski and his colleagues at APL submit their report next year, they will have generated a wealth of data that lays the foundation for in-space tests. There’s no guarantee that the National Academies will select the interstellar probe concept as a top priority for the coming decade. But whenever we are ready to leave the sun behind, there’s a good chance we’ll have to use it for a boost on our way out the door.

This story originally appeared on

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The 2020 Atlantic hurricane season is finally over. What should we make of it?



Enlarge / All of 2020’s tropical storms and hurricanes in a single image.


Monday was the last “official” day of the Atlantic hurricane season, drawing down the curtain on what has been a frenetic year for storms forming in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea.

The top-line numbers are staggering: there were a total of 30 tropical storms and hurricanes, surpassing the previous record of 28 set in the year 2005. For only the second time, forecasters at the National Hurricane Center in Miami ran out of names and had to resort to using the Greek alphabet.

Of all those storms, 12 made landfall in the United States, obliterating the previous record of nine landfalling tropical storms or hurricanes set in 1916. The state of Louisiana alone experienced five landfalls. At least part of the state fell under coastal watches or warnings for tropical activity for a total of 474 hours this summer and fall. And Laura became the strongest hurricane to make landfall in the Pelican State since 1856.

Not all records broken

By some measures, however, this season was not all that extraordinary. Perhaps the best measurement of a season’s overall activity is not the number of named storms but rather its “accumulated cyclone energy,” or ACE, which sums up the intensity and duration of storms. So a weak, short-lived tropical storm counts for almost nothing, whereas a major, long-lived hurricane will quickly rack up dozens of points.

The ACE value for the 2020 Atlantic season to date is 179.8—and another weak tropical or subtropical storm could still form. This is notably higher than the climatological norm for ACE values (about 104), but it would not quite make the top 10 busiest Atlantic seasons on record, which is paced by the 1933 and 2005 seasons.

In terms of estimated damages, this season has been far from a record-breaker as well. So far, damages across the Atlantic basin are estimated at $37 billion. This is substantially less than the devastating 2017 season that included hurricanes Harvey and Irma and totaled more than $300 billion. It is also less than 2005, which featured Katrina, Rita, Wilma, and other storms topping $200 billion. One factor in 2020 was that most of the biggest storms missed heavily populated areas.

Also, the hyperactive Atlantic basin stands out amidst the other basins where tropical activity typically occurs, including the northeastern and northwestern Pacific Ocean, which were much quieter than normal this year. Overall, in 2020, the Northern Hemisphere is seeing an ACE value about 20 percent below normal levels for a calendar year.

Legacy of 2020

Perhaps the biggest legacy of this Atlantic hurricane season is the disturbing trend of tropical storms rapidly developing into strong hurricanes. This “rapid intensification” occurs when a storm’s maximum sustained winds increase by 35mph or more within the period of 24 hours, and it was observed in 10 storms this year.

Moreover, three late season storms—Delta, Eta, and Iota—increased their speeds by 100mph or more in 36 hours or less. Iota, which slammed into Nicaragua on November 17, was the latest Category 5 hurricane on record in the Atlantic.

Some recent studies, including a paper published by Nature Communications in 2019, have found that climate change has goosed intensification. The study observed, for the strongest storms, that rate of intensification over a 24-hour period increased by about 3 to 4 mph per decade from 1982 through 2009. Storms that strengthen more quickly, especially near landfall, leave coastal residents and emergency planners with less time and information to make vital preparations and calls for evacuation.

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Arecibo radio telescope’s massive instrument platform has collapsed



The immense instrument platform and the large collection of cables that supported it, all of which are now gone.

On Monday night, the enormous instrument platform that hung over the Arecibo radio telescope’s big dish collapsed due to the failure of the remaining cables supporting it. The risk of this sort of failure was the key motivation behind the National Science Foundation’s recent decision to shut down the observatory, as the potential for collapse made any attempt to repair the battered scope too dangerous for the people who would do the repairs.

Right now, details are sparse. The NSF has confirmed the collapse and says it will provide more information once it’s confirmed. A Twitter account from a user from Puerto Rico shared an image that shows the support towers that used to hold the cables that suspended the instrument platform over the dish, now with nothing but empty space between them.

The immense weight of the platform undoubtedly caused significant damage to the disk below. The huge metal cables that had supported it would likely have spread the damage well beyond where the platform landed. It’s safe to say that there is very little left of the instrument that’s in any shape to repair.

It’s precisely this sort of catastrophic event that motivated the NSF to shut down the instrument, a decision made less than two weeks ago. The separate failures of two cables earlier in the year suggested that the support system was in a fragile state, and the risks of another cable snapping in the vicinity of any human inspectors made even evaluating the strength of the remaining cables unacceptably risky. It’s difficult to describe the danger posed by the sudden release of tension in a metal cable that’s well over a hundred meters long and several centimeters thick.

With inspection considered too risky, repair and refurbishment were completely out of the question. The NSF took a lot of criticism from fans of the telescope in response to its decision, but the collapse both justifies the original decision and obviates the possibility of any alternatives, as more recent images indicate that portions of the support towers came down as well.

The resistance the NSF faced was understandable. The instrument played an important role in scientific history and was still being used when funding was available, as it provided some capabilities that were difficult to replicate elsewhere. It also played a role as the most important scientific facility in Puerto Rico, drawing scientists from elsewhere who engaged with the local research community and helped inspire students on the island to go into science. And beyond all that, it was iconic—until recently, there was nothing else like it, which made it a feature in popular culture and extended its draw well beyond the island where it was located.

Lots of its fans were sad to contemplate its end and held out hope that some other future could be possible for it. With yesterday’s collapse, the focus will have to shift to whether there’s a way to use its site for something that appropriately honors its legacy.

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Russian spaceport officials are being sacked left and right



Vladimir Putin, center, and Dmitry Rogozin, far right, tour Russia’s new Vostochny Cosmodrome in October 2015.


The controversial leader of Russia’s space enterprises, Dmitry Rogozin, has continued a spree of firings that have seen many of the nation’s top spaceport officials fired, arrested, or both.

Most recently, on November 27, Russian media reported that Rogozin fired the leader of the Center for Exploitation of Ground-Based Space Infrastructure, which administers all of Russia’s spaceports. Andrei Okhlopkov, the leader of this Roscosmos subsidiary, had previously faced a reprimand from Rogozin for “repeated shortcomings in his work.” The spaceport organization has more than 12,000 employees.

Earlier this month, Rogozin also fired Vladimir Zhuk, chief engineer of the center that administers Russian spaceports. According to Russian media reports, Zhuk was then arrested for abusing his authority in signing off on water supply contracts.

Both of these officials were working to bring Russia’s newest spaceport, Vostochny, in the far eastern region of the country, up to its full capacity. In an article titled “At Vostochny A Day Never Goes By Without Someone Going to Jail,” The Kommersant newspaper reported that Zhuk knew that water supply networks for the Vostochny spaceport were not completed when he authorized their payment. (This article was translated for Ars by Rob Mitchell).

Construction project drags on

Several other key officials connected with the Vostochny Cosmodrome—under development since 2011 and intended to reduce Russia’s reliance on the Baikonur Cosmodrome in Kazakhstan—have also been recently let go. These include Vostochny head Evgeny Rogoz (fired and under house arrest), Vostochny Director Roman Bobkov (fired and arrested), and Defense Ministry Inspector General Dmitriy Fomintsev (arrested).

Construction of the spaceport has been riven with corruption, often through embezzlement, and overall cost estimates of the facility have increased to more than $7.5 billion. Of the planned seven launch pads, just one is operational. A Soyuz-2 rocket first launched from this “Site 1S” in April 2016. A second pad, “Site 1A,” may see the launch of an Angara rocket next year.

Russian President Vladimir Putin has been critical of delays at Vostochny, most recently in 2019, citing concerns about corruption. It is not clear whether the latest round of firings is related to a recent meeting Putin had with Rogozin to go over the country’s space affairs. It seems that by firing and arresting his subordinates, Rogozin has so far been able to shirk the blame for the Vostochny troubles onto other officials.

Nevertheless, his time may be coming. Rogozin is no stranger to corruption concerns, and Roscosmos is facing serious financial challenges. Not only is Russia no longer receiving large payments from NASA for Soyuz seats to carry its astronauts to the International Space Station, but funding from United Launch Alliance for the RD-180 rocket engine will also be ending within a few years. And there are serious questions about whether Russia’s next-generation Angara rocket will be able to compete with SpaceX’s Falcon 9 rocket for commercial launches.

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