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Potential satellite collision shows need for active debris removal – SpaceNews

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WASHINGTON — Two decades-old defunct spacecraft are in danger of colliding Jan. 29, an event experts argue is more evidence of the need to clean up low Earth orbit.

LeoLabs, a California company that operates a network of ground-based radars that track objects in orbit, announced Jan. 27 that it had identified a potential conjunction, or close approach, between the Infrared Astronomical Satellite (IRAS) and the Gravity Gradient Stabilization Experiment (GGSE) 4 satellite in LEO. The company said there was an approximately 1-in-100 chance that the two satellites would collide at 6:39 p.m. Eastern Jan. 29 an altitude of about 900 kilometers, almost directly above the city of Pittsburgh.

LeoLabs, in an update Jan. 28, revised the probability of a collision downward, to about 1 in 1,000, estimating that the two spacecraft will pass between 13 and 87 meters of each other. Other sources have estimated similar probabilities of a collision between the two objects using other data, such as that from the catalog maintained by the U.S. Air Force.

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Neither IRAS, launched in 1983, nor GGSE-4, launched in 1967, are operational today and have the ability to maneuver. While close approaches between debris are not uncommon, the circumstances of this event make it unusual and, to some orbital debris experts, worrying.

“This is a little bit unusual,” said Dan Oltrogge, director of the Center for Space Standards and Innovation at Analytical Graphics, Inc., in a Jan. 28 interview. The two spacecraft are in “counterrotating” orbits, meaning a collision would effectively be head-on, at an estimated relative velocity of 14.9 kilometers per second. That would maximize the energy of any collision.

Moreover, IRAS is a large satellite, with a mass of more than 1,000 kilograms. GGSE-4 — also known as POPPY-5B, a signals intelligence satellite — is much smaller, at 85 kilograms. However, it has a boom 18 meters long that will be perpendicular to the direction of motion. “In this case, that tends to maximize the collision potential,” Oltrogge said.

It may not be clear for hours after closest approach if the two satellites avoided a collision, depending on what assets are available to track them. Even if they miss, though, he said the conjunction should serve as a reminder of the hazards that other large objects, both satellites and upper stages, pose in Earth orbit, and the need to remove them.

“Even if these don’t hit, there will be others that will,” he said. “I think this can serve as a wakeup call for us to look at not only avoiding collisions with active satellites, but also remediating, figuring out how to remove debris in orbit.”

A paper that Oltrogge and others presented at the International Astronautical Congress in October 2019 discussed the risks of such collisions. They modeled the collision of two upper stages in orbit at 981 kilometers, concluding it could create between 3,375 and 12,860 objects at least 5 to 10 centimeters in size, as well as more than 200,000 additional debris objects at least 1 centimeter across dubbed “lethal nontrackable” because they are large enough to damage or destroy a satellite but too small to be tracked.

Another co-author of that paper was Darren McKnight of Centauri, who made similar arguments in a presentation at the Advanced Maui Optical and Space Surveillance Technologies conference in September. He noted that, in May, two rocket bodies that are part of a “cluster” of such objects at an altitude of 850 kilometers passed within 87 meters of each other. “They’re big yellow school buses with no driver,” he said. “If they collide, it would have doubled the catalog population in one event.”

“I would hope that we could take this, and other conjunction events and close approaches, to try and get another look at active debris removal and other remediation techniques,” Oltrogge said of this potential conjunction. “But time will tell.”

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Using atomic clocks in space to solve dark matter mystery – Innovation News Network

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A team of international scientists is proposing to send atomic clocks into space to detect and understand enigmatic dark matter.

Dark matter is a mystery that has plagued researchers for decades. This unknown essence represents 85% of all matter in the Universe, and although its effects can be observed, it has not been directly detected. Experts from the University of Delaware, the University of California, and the University of Tokyo are collaborating to solve this longstanding mystery by sending atomic clocks into space.

The research, ‘Direct detection of ultralight dark matter bound to the Sun with space quantum sensors,’ which is published in Nature Astronomy, plans to send two atomic clocks into the inner reaches of the solar system to search for ultralight dark matter that has wavelike properties that may affect the operation of the clocks.

What are atomic clocks?

Atomic clocks tell time by measuring the rapid oscillations of atoms and are already utilised in space to enable the Global Positioning System (GPS). In the future, space clocks could help navigate spacecraft and provide links to Earth-based cocks.

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All clocks mark time by using some form of a repetitive process, such as a swinging pendulum. However, atomic clocks use laser technology to manipulate and measure the oscillations of atoms which are extremely fast. For example, a clock based on strontium atoms ticks 430 trillion times per second, and atomic clocks are exceedingly more precise than any mechanical devices.

Historically, atomic clocks can cover the size of a couple of tables, but recent advances in precision and portability mean that some atomic clocks can now fit into a van, with NASA’s Deep Space Atomic Clock being even smaller, at around the size of a toaster.

Nevertheless, different types of clocks, based on much higher frequencies, have been developed over the last 15 years, such as optical clocks that are orders of magnitude more precise and will not lose even a second of time over billions of years.

Marianna Safronova, a physicist at the University of Delaware, said: “We now have portable clocks, and it’s fun to think about how you would go about sending such high-precision clocks to space and establish what great things we can do.

“It is a beautiful synergy between a quantum expert and particle theorists, and we are working on new ideas at the intersection of these two fields.”

Unravelling the mysterious properties of dark matter

The proposed research would send space clocks closer to the Sun than Mercury – an area they believe there is more dark matter to detect. These include atomic, nuclear, and molecular clocks that are currently being developed and are otherwise known as quantum sensors.

Safronova explained: “This was inspired by the Parker Solar Probe, the ongoing NASA mission that sent a spacecraft closer to the Sun than any other spacecraft has gone before. It has nothing to do with quantum sensors or clocks, but it showed that you could send a satellite very close to the Sun, sensing new conditions and making discoveries. That is much closer to the Sun than what we are proposing here.”

The aim of the study is to investigate ultralight dark matter, which the researchers believe could make a huge halo-like region that is bound to the Sun. Ultralight dark matter could cause the energies of atoms to oscillate, which will change how the clock ticks, although this effect depends on the atoms the clock uses. The researchers then monitor the differences in the clocks to look for dark matter.

“It has very specific properties and is a very specific dark matter that is detectable by clocks. What is observable is the ratio of those two clock frequencies. That ratio should oscillate if such dark matter exists,” Safronova said.

She explained that nuclear clocks, which are based on nuclear energy levels rather than atomic energy levels, may be the best clock for this research. She is currently involved in a project to build a prototype funded by the European Research Council.

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Space Atomic Clocks Could Unravel the Nature of Dark Matter – AZoQuantum

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Analyzing an atomic clock onboard a spacecraft within the orbit of Mercury and very close to the Sun could be the trick to revealing the nature of dark matter according to a new research article published in the December 5th issue of the journal Nature Astronomy.

Artist’s impression of a space atomic clock used to uncover dark matter. Image Credit: Kavli IPMU.

Dark matter composes over 80% of the mass in the universe, but it has thus far dodged detection on Earth, regardless of decades of experimental endeavors. A core component of these hunts is a hypothesis regarding the local density of dark matter, which establishes the number of dark matter particles moving via the detector at all times and thus the experimental sensitivity.

In a few models, this density can be a lot higher than is typically supposed, and dark matter can become more intense in certain regions than in others.

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One vital group of experimental searches is those using nuclei or atoms because these have realized extraordinary sensitivity to signals of dark matter. This is conceivable, in part, because when dark matter particles have extremely small masses, they prompt oscillations in the very constants of nature.

These oscillations, for example the interaction strength of the electromagnetic force or in the mass of the electron, alter the transition energies of nuclei and atoms in foreseeable ways.

An international group of scientists, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Project Researcher Joshua Eby, University of California, Irvine, Postdoctoral Fellow Yu-Dai Tsai, and University of Delaware Professor Marianna S. Safronova, recognized the potential in these oscillating signals.

They stated that in a specific region of the Solar System, between the orbit of Mercury and the Sun, the dark matter’s density could be exceptionally large, which would mean extraordinary sensitivity to the oscillating signals.

These signals could be captured by atomic clocks, which work by meticulously measuring the frequency of photons discharged in transitions of various states in atoms. Ultralight dark matter in the region of the clock experiment could alter those frequencies as the oscillations of the dark matter marginally increase and decrease the photon energy.

The more dark matter there is around the experiment, the larger these oscillations are, so the local density of dark matter matters a lot when analyzing the signal.

Joshua Eby, Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe

While the accurate density of the dark matter near the Sun is not established, the scientists debate that even a comparatively low-sensitivity search could deliver crucial information.

The density of dark matter is just constrained in the Solar System by information concerning planet orbits. In the region between the Sun and Mercury, the planet closest to the Sun, there is nearly no constraint. Therefore, a measurement onboard a spacecraft could rapidly expose world-leading restrictions on dark matter in these models.

The technology to test their theory is already present. Eby says the NASA Parker Solar Probe, which has been functioning since 2018 with the help of shielding, has moved closer to the Sun than any manmade craft in history and is at present working within the orbit of Mercury, with plans to travel even closer to the Sun in a year.

Atomic clocks in space are already established for numerous reasons other than hunting for dark matter.

Long-distance space missions, including possible future missions to Mars, will require exceptional timekeeping as would be provided by atomic clocks in space. A possible future mission, with shielding and trajectory very similar to the Parker Solar Probe, but carrying an atomic clock apparatus, could be sufficient to carry out the search.

Joshua Eby, Project Researcher, Kavli Institute for the Physics and Mathematics of the Universe

More from AZoQuantum: Precise Atomic Clock Proves Einstein was Right on Time

Journal Reference

Tsai, Y-D., et al. (2022) Direct detection of ultralight dark matter bound to the Sun with space quantum sensors. Nature Astronomy. doi.org/10.1038/s41550-022-01833-6.

Source:  https://www.ipmu.jp/en

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After lunar flyby, NASA’s Orion spacecraft is set to splashdown on Sunday – Ars Technica

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Enlarge / Orion, the Moon, and a crescent Earth on Monday.
NASA

The Orion spacecraft swung by the Moon on Monday, flying to within 130 km of that world’s surface as it set course for a return to Earth this weekend.

In making this “powered flyby burn” to move away from the Moon, Orion’s service module performed its longest main engine firing to date, lasting 3 minutes and 27 seconds. After successful completion of the maneuver, NASA’s mission management team gave the “go” to send recovery teams out into the Pacific Ocean, where Orion is due to splashdown on Sunday, during the middle of the day.

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By getting into an orbit around the Moon, and back out of it again during its deep space mission, Orion has now completed four main propulsive burns. This completes a big test of the spacecraft and its propulsive service module, which was built by the European Space Agency. Although a boilerplate version of Orion made a flight in 2014, it did so without a service module.

As part of this Artemis I mission, NASA is now three weeks into a 25.5-day test flight of the Orion spacecraft. The goal is to validate the spacecraft’s capabilities ahead of a human flight of the vehicle in about two years’ time, the Artemis II mission.

Orion has met most of its main objectives to date, with only the entry, descent, and splashdown part of its mission ahead of it. The spacecraft’s heat shield must demonstrate its ability to survive reentry at a velocity of 39,400 kph. This big test will come Sunday during a fiery reentry into Earth’s atmosphere.

A minor power issue

So far, Orion’s test flight has gone remarkably well. Typically, with new spacecraft, there are issues with thrusters, navigation, or onboard avionics and more. However, Orion has had no major issues. The only real troubleshooting has involved a problem with power systems on the vehicle.

The issue has occurred with four “latching current limiters” that help route power to propulsion and heating systems on Orion. For some reason, automated controllers on Orion commanded the four current limiters to “open” when no such command was supposed to be sent. “We’re not exactly sure on the root cause of the problem, but teams are doing tests on the ground,” said Debbie Korth, the Orion Program deputy manager, during a briefing on Monday evening at Johnson Space Center in Houston.

Overall, the Orion spacecraft has performed like a champion.
Enlarge / Overall, the Orion spacecraft has performed like a champion.
NASA

This system is somewhat like a circuit breaker box in a home, and for some reason four of the breakers were opened when they were not supposed to be. This did not pose a threat to Orion, as there are backup power systems. Had a crew been on board it would have required a minor procedure to account for the problem.

In an interview after the news briefing, Korth said she did not think the glitch would have an impact on the service module that will be used for the Artemis II mission. This hardware is already built and being tested in the United States.

“I think it’s probably too early to say for sure, but ideally we will not want to perturb the Artemis II service module,” she said. “This may very well be something we can handle with software.”

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