Tag Archives: European Space Agency (ESA)

Nuclear Waste Helps Reach Dark Places of Universe

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European scientists are developing a breed of battery for space missions that is powered by nuclear waste. The European Space Agency (ESA) hopes that the technology will, by the end of the decade…Ministers at ESA’s ministerial council meeting in Paris on 22 and 23 November, 2022 agreed to fund a €29-million (US$30-million) program called European Devices Using Radioisotope Energy (ENDURE). This aims to develop long-lasting heat and electricity units powered by the radioactive element americium-241, in time for a series of ESA Moon missions in the early 2030s.

Americium, a by-product of plutonium decay, has never been used as a fuel. For missions in which solar power would not suffice — either because of shade or because of distance from the Sun — ESA has relied on US or Russian partners, which have used plutonium-238 batteries to power missions since the space race. 

The lack of a power source has long restricted the solo missions that European scientists propose, and limited others. The agency felt its lack of radioisotope power keenly in 2014, when its comet-landing Philae probe was operational for less than three days because it ended up in a shaded spot where its solar panels were useless. “For years, European scientists have been saying that if you want to go far, or to dark and cold places, there is no other way,” says Coustenis.

Americium’s big advantage over plutonium is that it is cheaper and more abundant, repurposing waste that would otherwise be useless…Americium has a longer half-life than plutonium-238, which means it lasts longer but packs less power per gram. But because americium is more readily available, producing one watt of power costs about one-fifth as much as it does using plutonium…

Excerpts from Elizabeth Gibney, How Nuclear Waste Will Help Spacecraft Explore the Moon and Beyond, Nature, Dec. 6, 2022

Cleaning Up Space Junk

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A four-armed robotic junk collector will be launched into space by the European Space Agency in what it says will be the first mission to remove an item of debris from orbit. About 3,500 defunct satellites and an estimated 750,000 smaller fragments are orbiting the Earth at an average speed of 20,000km/h.  Unless a clear-up operation is mounted, the chances of collisions will escalate as thousands more satellites are put into orbit.

The ClearSpace-1 mission, scheduled for launch in 2025, will cost €120m and will grab a single piece of junk. But the agency hopes the mission will pave the way for a wide-reaching clear-up operation, with Esa’s director general calling for new rules that would compel those who launch satellites to take responsibility for removing them from orbit once they are retired from use.  “Imagine how dangerous sailing the high seas would be if all the ships ever lost in history were still drifting on top of the water,” said Jan Wörner, Esa’s director general. “That is the current situation in orbit, and it cannot be allowed to continue.”

The target for ClearSpace-1 is a piece of junk called Vespa, which was left in an orbit around 800km above the Earth by ESA’s Vega launcher in 2013. Vespa weighs 100kg – around the size of a small satellite – and was selected because it has a simple shape and sturdy construction, which make it unlikely to fragment when it is grabbed. The “chaser” ClearSpace space probe will be launched into the target orbit where it will track down Vespa, grab it using a quartet of robotic arms and drag it out of orbit, with Vespa and the chaser both burning up in the atmosphere on the way down to Earth. A future ambition is to create a clear-up robot that could eject junk into the atmosphere, before continuing to capture and de-orbit other pieces of junk.

European Space Agency to launch space debris collector in 2025, Guardian, Dec. 9, 2019

The Traffic Congested Space: Collision Avoidance

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On September 3, 2019, it was the first time that European Space Agence (ESA) performed a ‘collision avoidance manoeuvre’ to protect one of its spacecraft from colliding with a satellite in a large constellation,  a SpaceX satellite in the Starlink constellation.  Constellations are fleets of hundreds up to thousands of spacecraft working together in orbit. They are expected to become a defining part of Earth’s space environment in the next few years.  As the number of satellites in space dramatically increases, close approaches between two operated spacecraft will occur more frequently. Compared with such ‘conjunctions’ with space debris – non-functional objects including dead satellites and fragments from past collisions – these require coordination efforts, to avoid conflicting actions. 

Today, the avoidance process between two operational satellites is largely manual and ad hoc – and will no longer be practical as the number of alerts rises with the increase in spaceflight.
 “This example shows that in the absence of traffic rules and communication protocols, collision avoidance depends entirely on the pragmatism of the operators involved,” explains Holger Krag, Head of Space Safety at ESA.   “Today, this negotiation is done through exchanging emails – an archaic process that is no longer viable as increasing numbers of satellites in space mean more space traffic.”

ESA is proposing an automated risk estimation and mitigation initiative as part of its space safety activities. This will provide and demonstrate the types of technology needed to automate the collision avoidance process, allowing machine generated, coordinated and conflict-free manoeuvre decisions to speed up the entire process – something desperately needed to protect vital space infrastructure in the years to come.

Data is constantly being issued by the 18th Space Control Squadron of the US Air Force, who monitor objects orbiting in Earth’s skies, providing information to operators about any potential close approach.  With this data, ESA and others are able to calculate the probability of collision between their spacecraft and all other artificial objects in orbit. 

In August 2019, the US data suggested a potential ‘conjunction’ [collision] at 11:02 UTC on Monday, 2 September, between ESA’s Aeolus satellite and Starlink44 – one of the first 60 satellites recently launched in SpaceX’s mega constellation, planned to be a 12 000 strong fleet by mid-2020.  As days passed, the probability of collision continued to increase, and by Wednesday 28 August the team decided to reach out to Starlink to discuss their options. Within a day, the Starlink team informed ESA that they had no plan to take action at this point.**  ESA’s threshold for conducting an avoidance manoeuvre is a collision probability of more than 1 in 10 000, which was reached for the first time on August 29, 2019 evening.  An avoidance manoeuvre was prepared which would increase Aeolus’ altitude by 350 m, ensuring it would comfortably pass over the other satellite, and the team continued to monitor the situation.

On September 2, 2019, the commands triggered a series of thruster burns at 10:14, 10:17 and 10:18 UTC, half an orbit before the potential collision.  About half an hour after the conjunction was predicted, Aeolus contacted home as expected. This was the first reassurance that the manoeuvre was correctly executed and the satellite was OK.

Since the first satellite launch in 1957, more than 5500 launches have lifted over 9000 satellites into space. Of these, only about 2000 are currently functioning, which explains why 90% of ESA’s avoidance manoeuvres are the result of derelict and uncontrollable ‘space debris’.    In the years to come, constellations of thousands of satellites are set to change the space environment, vastly increasing the number of active, operational spacecraft in orbit.  This new technology brings enormous benefits to people on Earth, including global internet access and precise location services, but constellations also bring with them challenges in creating a safe and sustainable space environment.

This example does show the urgent need for proper space traffic management, with clear communication protocols and more automation,” explains Holger.  “This is how air traffic control has worked for many decades, and now space operators need to get together to define automated manoeuvre coordination.”  As the number of satellites in orbit rapidly increases, today’s ‘manual’ collision avoidance process will become impossible, and automated systems are becoming necessary to protect our space infrastructure.

**On August28th, 2019, SpaceX informed ESA via email that the company did not intend to move the Starlink probe.   At that time, the probability of collision was about 1 in 50,000, according to SpaceX, which is too low to require any preventive action.  The ESA contacted SpaceX daily about its evolving calculations, but the agency did not receive any additional replies after the original email response. SpaceX acknowledges that it failed to communicate due to a bug in its communication system and missed the emails about a higher probability of collision.

Excerpts from ESA Spacecraft Dodges Satellite Constellation, ESA, Sept. 3, 2019 &

A bug in SpaceX’s communication system kept the company in the dark about potential satellite collision, The Verge, Sept. 4, 2019