Blogarchiv
Raumfahrt - How to better manage space traffic: Aeolus/Starlink encounter shows emails and late-night phone calls no longer cut it

22.11.2019

amos-slide-879x485

 

It was less a wake-up call than a reminder of the hazards of spaceflight that satellite operators are already acquainted with.

On Sept. 2, the European Space Agency announced it maneuvered its Aeolus satellite to avoid a close approach with a SpaceX Starlink satellite. The encounter attracted headlines in part because of reports — inaccurate, as they turned out — that SpaceX “refused” to move its satellite, forcing ESA to move Aeolus.

Others in the industry, though, shrugged it off. “We move our satellites on average once a week and don’t put out a press release to say who we maneuvered around,” remarked Matt Desch, chief executive of Iridium, which operates a 75-satellite constellation.

That encounter was nonetheless on the minds of the more than 900 attendees of the Advanced Maui Optical and Space Surveillance Technologies, or AMOS, conference in Hawaii a couple of weeks later. Over the course of three days, they agreed on a number of issues regarding space situational awareness (SSA) and space traffic management (STM), even if they don’t know how to resolve all those problems.

BETTER COORDINATION

One immediate challenge is how satellite operators discuss with each other potential collisions and maneuvers to avoid them. The current approach, a manual process involving emails and phone calls, doesn’t work well now and won’t scale as the number of objects, and close approaches, grows.

Both ESA and SpaceX, in the aftermath of the Aeolus/Starlink encounter, agree on that point. “It made us ask whether emails or late-night calls are the most efficient coordination mechanism, and would be advisable in a scenario with thousands more operational satellites,” said Francesca Letizia, an engineer in ESA’s Space Debris Office.

“We agree with ESA’s conclusions that it’s very difficult to be able to do this on an individual email basis,” said David Goldstein, director of special programs at SpaceX. “The personal relationships are super important, but we have to figure out some automated ways to do that.”

The future, they say, depends on automation. Letizia said ESA was planning a competition to give researchers access to historical data from its missions on conjunctions for analysis, hoping that machine learning techniques can better identify which close approaches warrant maneuvers.

SpaceX, meanwhile, is giving its Starlink satellites the ability to perform their own avoidance maneuvers, based on data about potential close approaches uploaded to them and the satellites’ knowledge of their own positions. Since May, Starlink satellites have made 21 such automated maneuvers.

But even if there’s better communication between operators, there’s still the question of who should move in the situation where both satellites are maneuverable. “Is it the satellite that got there first? Is it the satellite that has the most delta V available? Or, is it the satellite that can do the burn later?” Goldstein asked.

MORE DATA SHARING & TRANSPARENCY

Satellite operators have traditionally relied almost exclusively on tracking data from the U.S. Air Force. But as the government begins to transition those SSA services to the Department of Commerce, there’s also the opportunity to combine that catalog with data from other sources.

Kevin O’Connell, director of the Office of Space Commerce, said his office was working to implement Space Policy Directive 3, which directed that transition of SSA activities. That includes setting up what it calls an “open architecture data repository” that would combine Air Force data with that from other sources and be used to identify potential close approaches.

“It made us ask whether emails or late-night calls are the most efficient coordination mechanism, and would be advisable in a scenario with thousands more operational satellites,” said Francesca Letizia, an engineer in ESA’s Space Debris Office, referring to a Sept. 2 incident where ESA couldn’t raise SpaceX to coordinate a collision avoidance maneuver between Aeolus and a Starlink satellite. Credit: AMOS

One issue is how to validate the data placed into the repository. O’Connell suggested that will be handled by the “marketplace” as users determine which data is best. “It sort of sorts out in the market.”

The best source of satellite positions, though, comes from satellite operators themselves, if they’re willing to share. “I think increased transparency is key. Share your data,” said Walter Everetts, vice president of satellite operations and ground development at Iridium. “There is no such thing as keeping it close the vest because that doesn’t help anybody.”

“You cannot really hide in space,” said Agnieszka Lukaszczyk, senior director for European affairs at Planet. “We don’t need to know what your satellite is doing. We just need to know that it’s there.”

INCENTIVIZE GOOD BEHAVIOR

There’s ongoing work among U.S. government agencies to update orbital debris mitigation guidelines, including a discussion about whether the current 25-year deadline for deorbiting satellites at the end of their lives should be shortened. The problem, though, is that many operators don’t even bother to meet that deadline.

Letizia noted that, according to ESA’s latest Space Environment Report, only 15–25% of satellites in low Earth orbits high enough not to be “naturally compliant” — that is, not decay because of atmospheric drag within 25 years — are deliberately deorbited within that timeframe.

“These objects, if not disposed, can fuel the Kessler Syndrome,” she said, a scenario where collisions in LEO set off a chain reaction of other collisions, accelerating the growth of debris. “The current level of compliance is not sustainable.”

There may be ways to encourage operators to act responsibly in orbit, such as deorbiting satellites promptly or placing “beacons” on them to make them easier to track. Once such incentive, said Chris Kunstadter, global head of space for insurer AXA XL, would be insurance discounts. “We have the ability to give that ‘good driver’ discount,” he said. “We would like to see more people try to get that discount.”

Incentives alone may not be enough. Others at AMOS said that some kind of binding requirements and regulations will be needed, provided it’s done in a fair manner. “When we’re talking about requirements, they really need to be international,” said Planet’s Lukaszczyk. “We’re talking about a global space with all kinds of different players who can all cause a mess.”

DON’T FEAR THE MEGACONSTELLATIONS

This growing interest in space traffic management has been fueled by the plans for satellite megaconstellations, ranging from hundreds of satellites to a Starlink system of potentially more than 10,000. ESA, in its statement about the Aeolus maneuver, noted it was the first time one its satellites had to dodge a megaconstellation spacecraft — and probably not the last.

Constellations, though, may not be the biggest threat in LEO. Darren McKnight of Centauri said the bigger threat comes from hundreds of upper stages, primarily Russian, left in three “clusters” in low Earth orbit at altitudes between 775 and 975 kilometers. The stages are large, with masses of up to 8,000 kilograms, and can’t maneuver.

The threat is not theoretical. McKnight said that, in May, two of those stages passed within 87 meters of each other at a relative velocity of 14 kilometers a second, missing a collision by just seconds. Had they collided, he said, “it would have doubled the catalog population in one event.”

Dealing with that threat calls for new approaches to removing debris, he argued, offering ideas ranging from cubesat “nano-tugs” to space-based lasers to avoid collisions. “If we don’t do debris mitigation and remediation, we’re going to make it really hard for SSA and space traffic management,” he said.

By comparison, dealing with thousands of active satellites is much easier. “Constellations are not bad,” he said. “Clusters are worse.”

Quelle: SN

312 Views