Visiting NASA: exploring the first probe designed to protect Earth from dangerous asteroids. Its launch is scheduled for next year.
The best we can hope for to defend against killer asteroids is a white cube the size of a washing machine, half-disassembled in a clean room.in Maryland. Last week, I arrived at the Johns Hopkins Applied Physics Laboratory, a sprawling research center where most researchers are working on government projects they cannot talk about. Then the spacecraft was missing two side panels, its ion engine was being cleaned, and the main chamber lay in a refrigerator in the hallway. A normally sterile storage room would be teeming with technicians in clean white protective suits bustling over the ship - however, on that day, most of them were on the other side of the glass. They were trying to get the unfinished cube to communicate with a massive parabolic antenna across the country.
Next summer, this same antenna, located in California, will be the main link with the spacecraft, which will rapidly move on to the first suicide mission of its kind. The goal of the DART experiment ( Double Asteroid Redirection Test, double asteroid redirection tests) - collide a cube with a small asteroid orbiting a larger asteroid located 11 million km away. from the earth. So far, no one knows exactly what will happen after the collision of the probe with the target. We know for sure that nothing will remain of the ship. At the same time, he should be able to change the orbit of the asteroid strongly enough to be noticed from Earth, and thereby demonstrate that such a blow can deflect a potential threat approaching us. Well, everything else is from the category of reasonable assumptions. That is why NASA wants to hit the asteroid with a robot.
According to the calculations of astronomers, in our solar system hides about 16,000 asteroids with diameters from 140 to 1000 m. The objectives of DART will dimorph and Didimaround which he revolves. The first is at the bottom of this range, and the second is at the top. If any of them collided with the Earth, it would lead to regional catastrophic destruction, the analog of which has not been in the entire history of the planet. More than a thousand asteroids with a diameter larger than Didyme and Dimorph combined have already been discovered, and if any of them collide with the Earth, this could lead to mass extinction and the fall of civilization. The chances of this are extremely small, but given the severity of the consequences, NASA and other space agencies want to be prepared for this just in case.
On the plus side, scientists believe it is possible to deflect a killer asteroid if it is discovered early enough. There are no guarantees for this - asteroids creep up to Earth with an unpleasant regularity - however, over the years, enough proposals have been made on the topic of approaches to solving this problem. The most practical ideas suggest an asteroid explosion or collision. But for them to be effective, scientists need to better understand the asteroid's reaction. So they built DART, a deep space probe that would self-destruct to prove that ideas work.
“Everyone knows you can crash into an asteroid,” says Justin Atchison, the DART mission designer at Johns Hopkins University's Applied Physics Laboratory. “However, there is a big difference between saying that it is possible and actually doing it. You learn quite a lot in the process. "
Andy Rivkin, one of the two leading researchers on the DART mission, is surprisingly indifferent to the task of creating a spacecraft that can save the planet. “I'm not intimidated by an asteroid impact at all,” he says. - We have a good idea of the chances for this, and in the near future we do not have such problems. The task is connected with work for the distant future, in which people may need such a tool - and we are creating it for them. "
In a typical NASA mission, a man in Rivkin's position would be in charge of managing a flock of scientists willing to use the spacecraft for their research. However, DART's primary mission is not scientific. This is a demonstration that should demonstrate the ability to deflect an asteroid while testing some new technology.
In general, spacecraft developers try to minimize risks, which is why they usually use equipment that has already shown itself in space, and try not to test new technologies. Because there are strict weight limits on these vehicles, engineers cannot simply add extra components to the ship to test them along the way. In this regard, the DART project looks even more unusual, since many of its critical technologies will go into space for the first time. And since the main purpose of DART is to crash, not collect scientific data, engineers have more freedom to maneuver in terms of the weight of the apparatus - so it can carry some technology just to test it in operation.
“When I joined the project, I immediately noticed that we were collecting a whole garland of new technologies, and said: No, we can’t handle this,” says Elena Adams, DART lead engineer, who joined the team after working on missions such as the Parker solar probe and the Juno spacecraft . "However, a new technology can only prove its worth by going on a mission and showing itself at work."
The DART launch window will open next July, before the asteroid's closest approach to Earth - just 11 million km. The SpaceX Falcon 9 rocket will accelerate the probe, sending it on the right course, and for about a year it will rush through the solar system at a speed of 104,000 km / h. Although specialists from the control center will be able to intervene in the DART flight until there is only a few minutes left before the collision, the ship is designed so that its mission can be completed with minimal human intervention.
Separated from the Falcon 9 rocket, DART will deploy its solar panels. The panels are fixed on an elastic material that will stretch between a pair of beams on either side of the ship. Compared to conventional solar panels, such systems will weigh 5 times less. “Solar arrays will allow us to send many missions to the outer planets,” says Adams. "Every kilogram saved in space is a big deal."
The mechanism for deploying solar panels was tested on the ISS in 2017, but for the first time it will be used with real solar cells. Having prepared the power source, the ship will begin to supply electricity from the panels to the ion engine.also on board. Ionic engines electrically knock electrons out of the fuel, ionizing it. The positively charged gas is repelled by the electric field and ions are emitted from the engine, propelling it forward.
Ion engines do not provide high thrust, but they are much more efficient than rocket engines that burn fuel. DART will use 12 small, conventional, chemical-fueled engines for course correction and reorientation, but in parallel will test a commercial version of NASA's new xenon engine: NASA's Evolutionary Xenon Thruster, or NEXT-C... This engine has been in development for almost twenty years, but has yet to be tested in space. Its operating power is three times that of other engines used by NASA in deep space missions, and it is about 10 times more efficient than conventional chemical-fueled engines.
According to Atchison, the real potential of the NEXT-C engine has to do with its ability to vary widely in thrust — most ion engines are limited to a narrow range. So instead of carrying many engines for different stages of a mission, a spaceship can get by with one. He will simply shift his only engine to the upper gear, approaching the Sun, where there are plenty of photons to convert into electricity, and then, moving away from the star, he will go down.
The NEXT-C will be used for short term testing and is a backup to the main propulsion system. It is important to prove that the system works in space after such long tests in the laboratory. During the flight of the probe, the ion drive will only be used for correcting the DART course or for small demonstrations that slightly change the probe's trajectory, and then return it back. “After the demonstration, it will be possible to use it on many different missions,” says Atchison. "This is a very cool technology."
The solar panels will also power the DART radio antenna, which will also be tested for the first time in space. Because it is a flat circular antenna, it will be easier to launch into space than the large parabolic dishes usually required for a spacecraft to call home. All data sent to ground will be handled by a field programmable gate array, or FPGA . Unlike general purpose computers, these chips are specially designed to perform specific tasks efficiently. This is important for DART - he will need to conduct a lot of accurate calculations to hit the target.
At the final stage of the approach, it will transmit images from the camera to Earth, up to the moment a few seconds before the collision. At the same time, another computer will need to process these images and feed them to the ship's special autonomous navigation system, Smart Nav. The DART algorithmic pilot is based in part on systems designed to target missiles on Earth. But it was modified to direct the spacecraft towards the center of the asteroid. “Smart Nav is our distinctive key technology for impacting an asteroid,” says Adams.
For most of the DART journey, it will, in effect, fly blind. Although he will be provided with star-tracking equipment by which he can determine his location in the solar system by the location of stars from our galaxy, he will only see his target when there is only a month before the collision. And even then he will not be able to see Dimorph - only Didyme, the larger master of the system, will be distinguishable as a single pixel. Dimorph will become visible only an hour before the collision.
“Draco will constantly feed us images, every second,” Adams says, referring to the ship's onboard camera. - It will be a very boring one pixel video. Surprisingly, in order to see this pixel, we will need to enlarge the image, but by that time the navigation system will already begin to direct the ship towards it and lock onto it. "
At this point, it will be too late to make changes to the trajectory from the control center from the ground. The success of the mission will depend on the ability of the Smart Nav algorithms to keep the tiny asteroid in the center of the field of view and direct the ship to the target. The DART team spent many hours simulating the approach of a ship and an asteroid, training the algorithm to recognize and focus on an asteroid when it is still barely visible. It's an excruciatingly boring pastime, but absolutely essential to mission success. If the probe does not know how to recognize its target, it can confuse it with a speck of dust on the lens or target the main asteroid, and not its satellite.
Building a camera capable of meeting the rigorous demands of an asteroid-driven mission is a daunting task. Draco is primarily a navigation tool, which means her photographs must be extremely accurate. The problem is that optical devices are extremely sensitive to temperature changes. “As it cools, things start to shift,” says Zach Fletcher, systems engineer for Draco. Even a small change to Draco's optical system - moving the main and secondary cameras one micrometer relative to each other - can defocus the image and blind the DART. Therefore, a special glass is used in the optics of the camera, which does not experience distortion when the temperature changes. “It's completely different,” says Fletcher. "Such glass would not be used on Earth."
After Draco is fully assembled, Fletcher and his team will be adjusting the camera for several weeks in preparation for launch. They will use interferometers - laser systems of extreme precision - to measure the microscopic distortion in Draco's optics while it sits in a chamber simulating the freezing temperature of outer space. The camera will need to be fine-tuned to be able to recognize the dim Didyma system from millions of kilometers away. At the same time, it must be able to transmit clear images of space stones back to Earth. “We want to try to get as much data as possible so we can see the sub-bright parts of the asteroid,” says Fletcher. The camera must be able to work in a large dynamic range, which is a difficult task also because no one on the DART team knows for sure.what the spaceship might encounter upon arrival.
One of the most unique features of a mission has to do with how little the architects actually know about the mission. Didyme was discovered in 1996, and astronomers then suspected that it might have a satellite, but only confirmed its existence in 2003. Didim's diameter is about 800 m, which is much larger than Dimorph - its diameter is only about 150 m.Dimorph is too dim to be seen directly with telescopes from Earth, like the main asteroid most of the time. When Didyme gets close enough to resume sightings next year, it will be 100,000 times less bright than the faintest star visible to the naked eye at night.
What little we know about Didyme and Dimorf comes from observations from ground-based optical and radio telescopes. Astronomers have guessed that Didim has a satellite only because its brightness falls at regular intervals, which indicates the presence of an object in its orbit. “Most of the information about the Didyma system came from observations in 2003,” says Christina Thomas, an astronomer at the University of North Arizona and leader of the DART Observations Working Group. "The observation window for the Didyma system opens every two years, and when the idea for DART came up, we started monitoring it regularly."
The history of DART begins with the project " Don Quixote"- a spacecraft colliding with asteroids, proposed by the European Space Agency in the early 2000s. The idea was to send two ships at the same time, and while one collides with an asteroid, the other should observe it. Then it was supposed to study the change in the trajectory of the asteroid around After the impact of the sun, ESA eventually decided that the mission would be too expensive and abandoned it.A few years later, the National Academies of Science, Engineering and Medicine, which prioritized various scientific disciplines, issued a report strongly recommending that an asteroid impact mission be implemented. was in reducing its value.
A fresh idea for a low-cost mission came to Andy Chen, now the chief scientific adviser of the Applied Physics Laboratory and one of the principal investigators of the DART mission, when he was busy with work affairs one morning shortly after the publication of the report. “I suddenly thought that we should do the project on a double asteroid, because then we would not need a second spacecraft to observe the deflection,” says Cheng. "We can do it from Earth, from ground-based telescopes."
It remained to find the goal. There are not so many binary asteroids in space, and only a small part of them pass close enough to the Earth to be visible through ground-based telescopes at the time of a collision with a spacecraft. Even fewer are small enough for a ship to noticeably change their orbit. By the time Cheng and his team had thinned out the list of possible targets, they had only two options left, one of which was Didyme. “This option was in the lead with a big advantage,” says Cheng. So he and a small group of colleagues put together a proposal and promoted the idea to NASA in 2011. The agency did not think long. By 2012, DART was officially on the budget.
Choosing Didyme as a target, astronomers began to monitor this system as it approached Earth every two years. “We realized that we needed to study as closely as possible the behavior of the system before the collision, before we permanently change its parameters,” says Rivkin. The first observation of Didim since 2003 began in 2015, and has been carried out every two years since then.
Based on previous observations, astronomers know that Dimorf orbits Didim about once every 12 hours, and has a diameter of about 150 m. Everything else remains a mystery. Before Didyme became the target of DART, there was no point in watching him - at least for the foreseeable future, he does not pose a threat to Earth. “We have no idea what Dimorph looks like,” says Adams. "We only saw Didyma."
How to plan an asteroid collision mission if you don't even know what it looks like? With simulations - lots and lots of simulations. The most important unknown parameters that the DART team must model before launch is the Dimorph shape and composition, as these factors play a large role in determining the impact of the collision on the trajectory. For example, an asteroid in the shape of a dog bone will behave differently from a spherical asteroid, and it will be more difficult for a ship to find its center and get into it. According to various evidence, many asteroids are not solid bodies, but simply heaps of debris held together by gravity. The size and distribution of these debris will determine how the DART impact will affect them, as cobblestones near the impact site will fly into space. Pushing off the asteroidthey will alter its trajectory even more.
Modeling the various possible shapes will allow DART to autonomously decide where to target. By simulating the contributions of different shapes and compositions of the asteroid, scientists can compare the simulation results with real-life collision data. The DART team worked with the planetary defense team at Livermore National Laboratory, simulating various collision scenarios on the lab's two supercomputers. Such scenarios are nothing new in the laboratory - they simulate the results of an asteroid explosion using nuclear warheads. By studying how debris travels from an asteroid, they can better understand what it is made of and how its composition affects trajectory changes. If we ever need to launch a real mission to protect the planet, it will be critical to accurately predict the asteroid's reaction to impact.
The collision data will be collected by the only device of all, not designed to direct the ship to a target or transmit data to Earth. It is an Italian microsatellite called LICIACube, which will be pushed out just minutes before the DART impact with the asteroid. Shortly thereafter, LICIACube will fly past the asteroid and take pictures of the aftermath. These images will help scientists confirm their models. The microsatellite will be located quite far from the asteroid, so its images will not be very clear. However, it will be better than nothing - namely, with nothing NASA could be left with when ESA abandoned the mission in 2016.
Although DART was originally intended to be a separate NASA project, Cheng and the mission designers soon partnered with ESA to conduct a joint Asteroid Impact and Deflection Assessment mission . It was planned that the Europeans will make an AIM probe, which will launch in front of DART, and will survey the asteroid several months before the arrival of the main ship. And when the DART hits the surface, AIM will watch what happens.
Despite the active support of the AIM mission from the ESA members, everything fell apart in 2016 when they did not allocate a budget for this program by voting. “There is a long list of missions that started out as partnerships between NASA and ESA, and then fell apart because one of the parties could not fulfill their responsibilities for various reasons,” says Cheng. "We proposed to make these missions independent, so that any of them should be continued even after the refusal of the other partner." This approach proved to be prudent.
Until 2018, it seemed that DART would do everything on its own. Then the Italian space agency made an offer to NASA to take with it one of the microsatellites it had built. NASA executives liked the idea and added LICIACube to the mission. Soon after, ESA came out with the successor to AIM, the Hera apparatus. The idea was to send a small spacecraft with two microsatellites into orbit around the Didyma system to observe the aftermath of the DART mission. While the new ESA probe won't be in time for the main event as it won't be ready to launch until 2024, when it does arrive, it will be able to measure the crater left by DART and take detailed measurements of Dimorph to understand how the impact affected it.
Meanwhile, a network of telescopes will monitor the Didyma system from Earth. They will begin observing many months before the DART reaches its target, and their observations will be critical in determining the location of the asteroid's satellite. The team absolutely does not need Dimorph to be on the other side of Didim when a ship flies up to him - then the latter will simply collide with the wrong asteroid. By the time DART gets close enough to independently determine the parameters of the satellite's orbit, it will be too late to put on the brakes. Rivkin says that the final pre-launch observational campaign, which will begin in the spring, will be enough to determine the parameters of the orbit with the necessary accuracy, and to ensure that Dimorph is in the right place at the right time.
Thomas says there is even a chance that ground-based telescopes will be able to see the collision itself. “If we get the chance, it will most likely look like a flash of light,” she says. - It will be great".
But even if telescopes do not detect the collision flare, they will still have an important role in observing the aftermath. After all, the whole point of the operation is to determine how a spacecraft can change the trajectory of an asteroid when it collides with it. The DART collision will add only about 10 minutes to the 12-hour orbit around Didim. However, this will be enough for Thomas and the team of astronomers to be able to see the difference by observing the change in brightness of the asteroid around which Dimorph orbits. This data, like the images from the LICIACube, will help scientists refine models of the asteroid collision until Hera collects additional data. It is important for the team to maximize the amount of data collected immediately after the collision, since the Didyma system will be further from Earth for the next 40 years than it is now.
The DART mission is led by NASA, but protecting the planet is by nature a global challenge. In 2016, NASA set up a Planetary Defense Coordination Service headquartered in Washington, DC, to work collaboratively with related programs from the world's space agencies. So far, most of the work to protect the planet has been coordinating a worldwide surveillance campaign for potentially dangerous asteroids and plotting their trajectories. “People keep looking for asteroids because the sooner you find something, the more time you'll have to do something about it,” says Rivkin.
After we barely missed an asteroid capable of wiping out civilization in the late 1980s, the U.S. Congress puzzled NASA with calculations of how seriously asteroids threaten life on Earth. An eerie picture was drawn in the agency's official report, and a proposal was made to allocate a budget to solve this problem - starting with a meticulous search for all potentially dangerous asteroids in the solar system. "Although the likelihood of the Earth meeting with a large asteroid or comet within a year is extremely small," the report noted, "the consequences of such a collision look so catastrophic that it seems reasonable to assess the nature of the threat and prepare to repel it."
Two years later, the US Congress directed NASA to find 90% of the asteroids in the solar system over 1 km in diameter. Asteroids like these will almost certainly cause a mass extinction after colliding with us. In 1998, the agency officially began searching, and by 2010 it had completed its task. However, asteroids less than 1 km in diameter can also cause severe local destruction. Therefore, in 2005, the US Congress expanded the powers of NASA and set the task to find by the end of 2020 90% of asteroids with a diameter of more than 140 m (this is comparable to the height of the Leningradskaya Hotel on Komsomolskaya Square in Moscow).
But even if the agency fulfills this task, hundreds of unnoticed asteroids could enter the remaining 10%. Also, finding a deadly space rock in the solar system is half the battle. Although NASA has found almost all of them, it can take years to calculate their orbits. Therefore, not only are there many large asteroids that we have not noticed - even the asteroids that we have noticed can pose a threat to us, until we predict their trajectories with sufficient accuracy.
In the event of an actual asteroid alert, a critical factor in determining the success of a mission to save the world like DART will be how early we detect the asteroid. This is important for several reasons. First, it takes a long time to get the spacecraft ready for launch. The transition from concept to nearly completed ship took DART almost ten years. Adams says that this process can be accelerated if an asteroid really headed in our direction, capable of wiping a country off the face of the planet. “If you're trying to protect Earth, you won't be sending so many new technologies flying,” she says. “We’ve learned so much already that I think we’ll do it faster next time.”
Another factor has to do with how real the ship can change the orbit of the asteroid. Dimorph is not that big compared to other asteroids, but DART is not the largest ship either. Even colliding with an asteroid at a speed of 6 km / s, it will barely move it - its orbit will change by no more than a millimeter per second. “Depending on what kind of temporary head start you have, this may be quite enough, or very little,” says Rivkin. Time is of the essence in planetary defense.
The lab team still has a lot to do before the ship is ready for launch next summer. Once the team confirms that DART can send and receive data over NASA's deep space communications network, it will need to carefully work out the launch procedure using computer simulations. Things like discharging batteries before launch and tracking the deployment of solar panels will be practiced.
The goal is to obtain the basic parameters of the spacecraft before being tested for interaction with the environment. Engineers call this process shake and bake; it is also a brand of bread crumbs / approx. transl.]. The DARTs will be shaken on a large vibration platform up to 3,000 times per second to simulate launch loads, and periodically exposed to high temperatures in a chamber simulating the effects of space vacuum. When the DART passes all the tests, the team will do another run of the entire equipment to make sure it is working properly. If all goes well, the ship will be sent to Vandenberg Air Force Base in California in May for final checks before SpaceX technicians load it into a rocket for launch.
Spaceship engineers are often attached to their brainchildren; after all, they often work on the same project for years, and some will study the data that the ship will transmit to Earth for several more years. But all of the DART team members I spoke with are enthusiastic about the idea of destroying their fearless robot. “A part of me always rejoices when I manage to smash or blow something up,” says Cheng. Fletcher agrees: “I have nightmares in which a ship hits an asteroid and nothing happens to it. It would be a failure. I can't wait to be destroyed. "
Notably, the team was able to maintain a pre-launch schedule during the pandemic, but Adams says they quickly found ways to work around the new restrictions. The people who needed to assemble the ship in the workshop worked in shifts in small groups, while the rest worked together on simulations remotely. This winter and spring, the situation will get more complicated - the entire team will need to be present in person for simulations. They have already begun planning future work based on social distancing protocols.
The risk of an asteroid collision, like the risk of a pandemic, seems unlikely and abstract - until it happens. The main thing here is to know how to react quickly and decisively to this even in the face of adverse circumstances. This is what the DART mission is about. “We're not going to be stopped by the coronavirus or anything else,” Adams says. "We have one goal and we will achieve it."