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by Aleksandar Grgic, Director, Space Solutions at Weibel Scientific
edited by Curtis Hand

Space objects usually disintegrate when entering Earth’s atmosphere, but the immensity of some objects cause great concern. This was the case when all eyes were on a 21-tonne, 30-metre section of a rocket hurtling towards Earth in the days leading up to 9 May 2021.

Observers were faced with two significant challenges: 1) uncertainty about whether the massive rocket would adequately break and burn-up completely on re-entry into the atmosphere; and, 2) the difficulty in accurately predicting where any enduring debris might land.

Agencies around the world followed the path of the object carefully in the days preceding re-entry. The large space object, labelled CZ-5B R/B (2021-035B), was the booster stage of the rocket launched on April 29 this year carrying the first section of China’s space station, Tiānhé (-xié) – or, “Heavenly Harmony” (天和). It was one of the largest quantities of space debris to approach Earth in recent years.

For the safety of people, infrastructure and land, it was crucial that the rocket section, orbiting Earth at about 29,000 kilometres per hour, was tracked and that its behaviour on re-entry was closely monitored and accurately analysed. The final hours before re-entry were crucial. Before then, the best possible prediction for any remaining parts was a wide section of Earth running from southern regions of Spain, Portugal and Italy down to Australia – between 41 degrees north and 41 degrees south.

Accurate tracking data ensures safety on the ground
From a location in Italy, a Weibel Multi-Frequency Doppler Radar tracked the remains of Tianhe, providing valuable data to enable the best possible estimation for the expected re-entry location and time.

Weibel’s long-range tracking radar enabled the Doppler variation of the spinning Chinese rocket booster section to be captured as it passed over Europe. This radar also provided accurate Time Space Position Information – or, TSPI – trajectory readings and accurate data for analysing the object’s tumbling rate, which helped more precisely predict its entry time and position. This was particularly important as the debris made its final approach.

Building global Space Situational Awareness capability
About 150 tonnes of space debris re-enter into the atmosphere each year, with most falling into the Pacific Ocean. Despite a very low incident rate, there is growing concern about the potential of large objects to cause damage on Earth. In one example, various press accounts reported on building damage by falling space junk on the Ivory Coast in 2020.

Photo caption: Any surviving parts of CZ-5B R/B space debris were expected to land anywhere from 41 degrees north to 41 degrees south. (Source: EU SST)

The ability to detect, track and monitor space debris, analyse data and build an accurate picture is crucial to Space Situational Awareness – or, SSA – a cornerstone of the EU’s major focus on building space capabilities.

Photo caption: Doppler variations with a period of 4.5 seconds detected during the pass, which help inferred the rotation of the object (Source: EU SST)

About Weibel Scientific
Supplying long-range tracking radar systems to various space agencies around the world, Weibel plays an important part in building this capability globally. Weibel’s radars are well-suited for space surveillance and tracking – or, SST – systems.

Photo caption: 45dB, MFTR-2100 long range tracking radar in operation at a Weibel customers’ site (Source: Weibel Scientific)

Their customers include NASA and Japan Aerospace Exploration Agency among a host of other defence, research, scientific, security and scientific establishments worldwide. Weibel’s tracking radar family enables accurate tracking and surveillance of all types of space objects approaching Earth, including satellites, re-entry vehicles, missiles, debris and unmanned space vehicles.