2409 new objects were launched into space in 2022, that’s more than ever before.
Last year though, also saw a record number of satellites reenter Earth’s atmosphere.
The rising number of reentries is not necessarily a bad thing. Disposing of satellites efficiently is one of the most important things for keeping low-Earth orbits safe.
However, most objects reenter in an uncontrolled manner: they are switched off at the end of their mission and left to fall and burn up in Earth’s atmosphere.
There is good news though. Advancing technology has seen a recent increase in “controlled reentries” for rocket bodies. A controlled reentry allows operators to remove their hardware from protected regions more quickly and with greater control over where, when and how it reenters – and even lands – at the cost of allocating some fuel to do so.
By the way, just because an older satellite wasn’t designed to be controlled during its descent doesn’t mean it’s impossible to do so. In July 2023, our teams guided the Aeolus satellite to burn up over uninhabited regions in the Atlantic and Antarctica, even though the satellite was designed in the late 1990s with no intention to control it in this way.
Our planet is surrounded by spacecraft helping us study our changing climate, save lives following disasters, deliver global communication and navigation services and help us answer important scientific questions.
But these satellites are at risk. Accidental collisions between objects in space can produce huge clouds of fast-moving debris that can spread and damage additional satellites with cascading effect.
In this animation, find out how teams at ESA’s European Space Operations Centre in Darmstadt, Germany, take action to keep satellites safe after receiving an alert warning of a possible collision between an active satellite and a piece of space debris.
When the alert is raised, ESA experts determine the risk of a collision and plan a collision avoidance manoeuvre that can be used to get the satellite out of harm’s way if necessary.
Additional observations of the piece of space debris help the team better understand its path and the risk of collision. If that risk remains too high (typically 1 in 10 000), the planned manoeuvre is carried out to temporarily change the orbit of the satellite until the threat has passed.
Each manoeuvre comes at a price. They take skill and time to plan, cost precious fuel – shortening the lifetime of the mission – and often require instruments to be temporarily shut off, preventing them from collecting important data.
While most alerts do not end up requiring evasive action, the number of alerts is rapidly increasing. Hundreds are already issued every week. Several companies have begun to launch large constellations into low-Earth orbit to provide global internet access. They have great benefits, but could be a source of huge disruption if we do not change our behaviour.
In just a few years, our current methods for avoiding collisions in space will no longer be enough. To safeguard humankind’s continued access to space for future generations, ESA is developing technologies for an automated collision avoidance system.
We are Europe’s gateway to space. Our mission is to shape the development of Europe’s space capability and ensure that investment in space continues to deliver benefits to the citizens of Europe and the world. Check out https://www.esa.int/ to get up to speed on everything space related.
Since arriving at Mars in October 2016, the ExoMars Trace Gas Orbiter has been aerobraking its way into a close orbit of the Red Planet by using the top of the atmosphere to create drag and slow down. It is almost in the right orbit to begin observations – only a few hundred kilometres to go! With aerobraking complete, additional manoeuvres will bring the craft into a near-circular two-hour orbit, about 400 km above the planet, by the end of April. The mission’s main goal is to take a detailed inventory of the atmosphere, sniffing out gases like methane, which may be an indicator of active geological or biological activity. The camera will help to identify surface features that may be related to gas emissions. The spacecraft will also look for water-ice hidden below the surface, which could influence the choice of landing sites for future exploration. It will also relay large volumes of science data from NASA’s rovers on the surface back to Earth and from the ESA–Roscosmos ExoMars rover, which is planned for launch in 2020.
Animation visualising Rosetta’s two-year journey around Comet 67P/Churyumov–Gerasimenko.
The animation begins on 31 July 2014, during Rosetta’s final approach to the comet after its ten-year journey through space. The spacecraft arrived at a distance of 100 km on 6 August whereupon it gradually approached the comet and entered initial mapping orbits that were needed to select a landing site for Philae. These observations also enabled the first comet science of the mission. The manoeuvres in the lead up to, during and after Philae’s deployment on 12 November are seen, before Rosetta settled into longer-term science orbits.
In February and March 2015 the spacecraft made several flybys. One of the closest flybys triggered a ‘safe mode’ event that forced it to retreat temporarily until it was safe to gradually draw closer again. The comet’s increased activity in the lead up to and after perihelion in August 2015 meant that Rosetta remained well beyond 100 km distances for several months.
In June 2015, contact was restored with Philae again – albeit temporary, with no permanent link able to be maintained, despite a series of dedicated trajectories flown by Rosetta for several weeks.
Following perihelion, Rosetta performed a dayside far excursion some 1500 km from the comet, before re-approaching to closer orbits again, enabled by the reduction in the comet’s activity. In March–April 2016 Rosetta went on another far excursion, this time on the night side, followed by a close flyby and orbits dedicated to a range of science observations.
The animation finishes at 9 August 2016, before the details of the end of mission orbits were known. A visualisation of the trajectories leading to the final descent to the surface of the comet on 30 September will be provided once available.
The trajectory shown in this animation is created from real data, but the comet rotation is not. An arrow indicates the direction to the Sun as the camera viewpoint changes during the animation.
What happens after Rosetta arrives at comet 67P/Churyumov–Gerasimenko? This animation describes the key dates for the next set of manoeuvres that will bring Rosetta even closer to the comet between August and October.
After arriving on 6 August, Rosetta will follow a set of two, three-legged triangular trajectories that require a small thruster burn at each apex. The legs are about 100 km long and it will take Rosetta between three and four days to complete each one.
The first triangle is conducted at a distance of about 100 km from the comet, the second at around 50 km. Then Rosetta will switch to a ‘global mapping phase’ at an altitude of about 30 km. During this period, it will make a ‘night excursion’, whereby the ground track of the spacecraft will be on the night-side of the comet (with the spacecraft still fully illuminated the Sun).
In October Rosetta will transfer to a close mapping phase to observe the comet from a distance of 10 km. The spacecraft will move even closer to dispatch lander Philae to the surface in November.
In this animation the comet is an artist’s impression and is not to scale with the spacecraft. The comet rotation is not representative (67P rotates once per 12.4 hours). Dates may be subject to change.
Rosetta is about to put on the brakes to ensure that it is on target for comet 67P/Churyumov-Gerasimenko.
This video explains the crucial orbit correction manoeuvres that are required to slow down Rosetta’s speed, relative to the comet, from 750 metres per second to just one metre per second between 21 May and 5 August. By then, nine thruster burns (including one test burn in early May) will have reduced the distance between them from one million kms to just under 200 kms.
We also see the first images of the comet from the spacecraft’s OSIRIS camera (Optical, Spectroscopic and Infrared Remote Imaging System), taken between 24 March and 4 May 2014. As the spacecraft gets closer to the comet, further images will improve the orbital corrections and provide more details about the comet’s shape, size and rotation.
MIRO, built by an international team for the European Space Agency, will start taking measurements from late May onwards and will measure gases released from the comet as it approaches the Sun.
