ESA’s ERS-2 satellite will reenter Earth’s atmosphere in February 2024. This page contains answers to some frequently asked questions about the satellite, its mission and its reentry. For more information see our ‘ERS-2 reentry – homepage’ and ‘ERS-2 reentry – live updates’ pages.

What is happening?

The European Space Agency’s (ESA) European Remote Sensing 2 (ERS-2) satellite will reenter Earth’s atmosphere and begin to burn up in mid-February 2024.

What is ERS-2?

ERS-2 launched on 21 April 1995. At the time, it was the most sophisticated Earth observation spacecraft ever developed and launched by Europe. Together with the almost-identical ERS-1, it collected a wealth of valuable data on Earth’s land surfaces, oceans and polar caps and was called upon to monitor natural disasters such as severe flooding or earthquakes in remote parts of the world.

When did the mission end?

In 2011, after 16 years of hugely successful operations, ESA took the decision to end ERS-2 operations and to deorbit the satellite.

ERS-2 underwent a series of 66 deorbiting manoeuvres in July and August 2011. These manoeuvres were planned and carried out by operators at ESA’s ESOC mission control centre in Darmstadt, Germany. The mission officially came to an end on 5 September 2011.

Why did you deorbit the satellite?

Deorbiting satellites at the end of their life and ensuring they reenter Earth’s atmosphere is a fundamental tool in keeping our busy space highways clear from defunct, lingering satellites, preventing collisions in orbit, and mitigating the creation of further space debris.

The ERS-2 deorbiting manoeuvres used up the satellite’s remaining fuel and lowered its average altitude from 785 km to about 573 km in order to greatly reduce the risk of collision with other satellites or space debris and to ensure the satellite’s orbit would decay fast enough for it to reenter Earth’s atmosphere within the next 15 years.

All instruments and electronic systems were then deactivated, and the satellite’s internal batteries discharged to reduce the risk of ERS-2 fragmenting into smaller pieces while passing through important regions during its orbital decay.

When & where will ERS-2 reenter the atmosphere?

ERS-2 will reenter Earth’s atmosphere and burn up in mid-February 2024 once its altitude has decayed to roughly 80 km. This is almost 13 years after the deorbiting manoeuvres and well within the targeted timeframe.

The satellite is under frequent observation, and we are tracking its orbital altitude as it decays. However, because the reentry is ‘natural’, it is impossible to predict exactly when and where the satellite will begin to burn up. The window during which reentry is possible will continue to shrink until the time of reentry.

What makes this reentry ‘natural’?

ERS-2 used up the last of its fuel in 2011 in order to minimise the risk of a catastrophic explosion that could have generated a large amount of space debris. Its batteries were depleted and its communication antenna and onboard electronics were switched off. There is no longer any way to actively control the motion of the satellite from the ground during its descent.

Why are the time and location of ‘natural’ reentries so difficult to predict?

The unpredictability of natural reentries is largely driven by our limited ability to forecast the density of the relevant layers of Earth’s atmosphere.

It is these layers that produce the drag that is responsible for the decay of the satellite’s orbit – the denser they are, the more drag they generate, and the faster the satellite’s orbit decays.

However, density forecasts depend on which atmospheric model you use and on unpredictable solar activity. Intense solar activity in 2023 had an influence on speeding up the predicted reentry of Aeolus, for example, which you can read more about here.

Other aspects that affect the speed of orbital decay, such as which direction the satellite is facing and so what surface area is exposed to the atmosphere, cannot be determined by simply monitoring the satellite’s trajectory alone.

More info on the challenges of predicting atmospheric reentries can be found here.

Where can I find updates on the reentry?

ESA’s Space Debris Office is frequently updating their prediction for where and when ERS-2 will reenter the atmosphere and begin to burn up. During the weeks prior to reentry, they will share this information and related graphical visualisations via daily updates on this blog.

We expect the blog to be updated with increasing frequency as we approach the day of reentry. A reentry map showing where and when ERS-2 reentered will be produced using data acquired during the reentry. This will be shared after the event.

Who is monitoring the ERS-2 reentry?

An international network of partners will track ERS-2 using their own sensors during its final orbits and reentry. This network includes the Inter-Agency Space Debris Coordination Committee (IADC), the Tracking and Imaging Radar (TIRA) of the Fraunhofer Institute for High Frequency Physics and Radar, the European Union Space Surveillance and Tracking (EU SST), and the United States Space Surveillance Network (US SSN).

What is the mass of ERS-2?

ERS-2 launched with a mass of 2516 kg. Now depleted of fuel, its current mass is estimated to be around 2294 kg. On average, an object of similar mass reenters Earth’s atmosphere every week or two.

Will any parts of the satellite survive the reentry and end up on Earth?

ERS-2 will break up into fragments around 80 km above Earth’s surface and the vast majority of these will burn up in the atmosphere. Some fragments could reach Earth’s surface, where they will most likely fall into the ocean. None of these fragments will contain any toxic or radioactive substances.

What is the risk of being hit by a piece of falling space debris?

The annual risk of an individual human being injured by space debris is under 1 in 100 billion.

That is:

  • ~1.5 million times lower than the risk of being killed in an accident at home
  • ~65,000 times lower than the risk of being struck by lightning
  • ~three times lower than the risk of being struck by a meteorite

Do reentries release dangerous chemicals into the atmosphere?

Understanding the direct and indirect impact of space industry activities on Earth’s climate is of utmost importance for the sustainable future utilisation of space for the betterment of humankind. ESA and other institutions are investigating the potential atmospheric pollution caused by the rapidly increasing volume of launch and reentry traffic.

ESA organised a dedicated event in January 2024 to address this topic. The Agency also carried out two studies on the atmospheric impact of spacecraft reentries in 2019. They concluded that the short-term impact on the atmosphere due to the burn up of a single spacecraft is modest, primarily because the particles created during a reentry are generally too large to react chemically with the atmosphere.

More details on the topic can be found here.

What action is ESA taking to minimise the creation of space debris?

The long-term sustainability of space is of crucial importance. Low-Earth orbits are a limited natural resource at particular risk of becoming unusable due to the presence of an overwhelming volume of space debris.

ESA is committed to ensuring the long-term sustainability of space activities through mitigating the creation of space debris wherever possible and ensuring the safest possible reentry of satellites at the end of their lives.

ESA is taking proactive steps to protect the space environment through the programmes, activities and initiatives including:

  • Space Debris Office – The SDO manages ESA’s activities related to measuring and modelling the space debris environment and mitigating the risk of in-orbit collisions and reentries. It coordinates such activities with national space agencies such as ASI, CNES and DLR and other external partners.
  • Clean Space initiative – ESA’s Clean Space initiative coordinates the development of new technologies for more sustainable space missions, including design for demise activities to reduce the risk on-ground caused by reentering objects.
  • Zero Debris approach – The Zero Debris approach is ESA’s new effort to significantly limit the production of debris in Earth and Lunar orbits by 2030 for all future ESA missions, programmes, and activities. It has so far involved updating the documents that govern how ESA designs, builds, operates, and disposes its missions and the co-development of the Zero Debris Charter (see below).
  • Zero Debris Charter – The Zero Debris Charter is a community-driven and community-building document and initiative for the global space community. Facilitated by ESA and created and written by 40 space actors, the Charter contains both high-level guiding principles and specific, jointly defined targets to achieve Zero Debris by 2030.
  • Protection of space assets Accelerator – The Accelerator supports high-level efforts towards the safeguarding of space assets from hazards such as space debris and space weather. This work often concerns collaboration with national, EU or other European initiatives, and the European space sector, such as the development of the Zero Debris Charter.