Defence: the European strategy against spatial collisions

You are the pres­id­ent of the European pro­gram EU SST. What does it con­sist of? 

Pas­cal Fauch­er. EU SST stands for European Uni­on Space Sur­veil­lance and Track­ing. It is a civil pro­gram man­aged by a con­sor­ti­um of sev­en Mem­ber States (France, Ger­many, Italy, Spain, Poland, Por­tugal and Romania). The fact that the European Com­mis­sion asks coun­tries to organ­ise them­selves to man­age and offer a sort of “pub­lic ser­vice” to all European users is quite unique. With Europe’s new mul­tian­nu­al fin­an­cial frame­work and the new Space Reg­u­la­tions, ini­ti­ated in May 2021, the pro­gram will also be renewed. New part­ner­ships are under dis­cus­sion with 19 oth­er Mem­ber States.

The SST was cre­ated to face the increas­ing risk of col­li­sions between space objects. These risks increas­ingly threaten eco­nom­ies and European cit­izens. Indeed, we depend more and more on nav­ig­a­tion, com­mu­nic­a­tion and obser­va­tion apps relayed via satel­lites, which can be ser­i­ously dam­aged by a col­li­sion. Just one of these col­li­sions can gen­er­ate thou­sands of new debris. The role of the con­sor­ti­um is to provide ser­vices linked to secur­ity, safety and long-term sus­tain­ab­il­ity of space oper­a­tions. In oth­er words, we pro­tect our infra­struc­tures in orbit against haz­ards and inten­tion­al threats.

What are your object­ives, and what means do you have to carry them out? 

We offer sev­er­al ser­vices: eval­u­ation of col­li­sion risks in orbit and fol­low­ing return of risky space debris into the Earth’s atmo­sphere, as well as the detec­tion and the ana­lys­is of frag­ment­a­tion in orbit. To that end, we have a net­work of around fifty sensors on the ground, radars and tele­scopes of mil­it­ary, sci­entif­ic or com­mer­cial ori­gin to track objects in space, but also data pro­cessing means. The Centre for Oper­a­tion­al Orbi­to­graphy (COO) of the CNES in Toulouse col­lects data and con­stantly mon­it­ors the orbits of European satellites.

For the past two years, the Mem­ber States have been build­ing a com­mon data­base whose pur­pose is to share thou­sands of meas­ures about objects in space on a daily basis.

The fusion of these data allow us to cata­logue orbit­al objects. Until now, Europe used a lot of mil­it­ary data provided by the Amer­ic­an defence agency, which are a bench­mark in that regard. Admit­tedly, they have inves­ted heav­ily in this field and for a long time: more than half of the act­ive satel­lites – civil, mil­it­ary or com­mer­cial – are Amer­ic­an. One of the object­ives of the SST is to raise the cap­ab­il­ity level and to build a stra­tegic autonomy of Europe in this field, to pro­tect European infra­struc­tures, primar­ily the flag­ship pro­jects Galileo and Coper­ni­cus and also to offer reli­able ser­vices to its partners.

And it is begin­ning to take shape. For example, at the end of Feb­ru­ary 2021, a col­li­sion risk was detec­ted between a Galileo satel­lite orbit­ing at 20 000 km and a launch­er stage, a space debris. Thir­teen sensors of the SST net­work were activ­ated and con­firmed a very strong col­li­sion prob­ab­il­ity. The oper­at­or decided on 6^th March to man­oeuvre the satel­lite in order to pro­tect it.

How, and by whom, is the decision taken in such cases? 

SST offers a ser­vice of inform­a­tion: we show oper­at­ors what is the risk, and where it is found. We cal­cu­late the “Time of Closest Approach” and give it to them, it is the moment in which two objects are the closest to one anoth­er. We also detect the

“miss dis­tance” and “radi­al sep­ar­a­tion”, inform­a­tion regard­ing the dis­tance between the two objects and the prob­ab­il­ity of col­li­sion, “scaled prob­ab­il­ity of col­li­sion”. Thus informed, they can decide to launch an avoid­ance man­oeuvre or not; if the meas­ure is above the threshold fixed by the oper­at­or. A satel­lite is expens­ive, cost­ing sev­er­al €100M, so any respons­ible oper­at­or would prefer to avoid a col­li­sion than risk los­ing a satel­lite. Fur­ther­more, it is often pos­sible to syn­chron­ise the pro­tec­tion man­oeuvre of the satel­lite with the sta­tion keep­ing man­oeuvre, which is per­formed once a month on average. 

There is always a great deal of uncer­tainty. We provide approx­im­a­tions to loc­ate objects, but these are sub­ject to vari­ous fric­tions which means that orbits are nev­er per­fectly accur­ate. That being said, the more we have inform­a­tion, the more we can determ­ine pre­cisely the orbit of a space object. Today, we have 17 mil­lion meas­ure­ments for 9,500 orbit­al objects.

How fre­quently are these risks detected?

In 2020, for the fleet of 148 satel­lites we mon­itored at the time – we now mon­it­or 213 satel­lites – we detec­ted 377 “high interest events”, namely high secur­ity risk events, which led to 31 avoid­ance man­oeuvres. The risks, and there­fore the man­oeuvres, are very rare in high- or medi­um-Earth orbits. They are far more fre­quent in low orbit, where the vast major­ity of space objects and debris are found, most being due to two major events cre­ated thou­sands of debris in this already con­ges­ted orbit. Half of col­li­sion risks in low orbit are due to debris from the explo­sion of an obsol­ete Chinese weath­er satel­lite, vol­un­tar­ily des­troyed in 2007 by China with an anti-satel­lite mis­sile. The second cata­stroph­ic event is a col­li­sion in 2009 between the deac­tiv­ated Rus­si­an satel­lite Kos­mos and the act­ive Amer­ic­an com­mu­nic­a­tions satel­lite Iridium. 

Our mis­sion is to ensure the pro­tec­tion of all act­ive satel­lites. How­ever, the risk some­times involves inert debris, and we are then power­less. It happened recently. On April 7, we detec­ted a risk in low orbit at 780 km of alti­tude, between two inert satel­lites, one Rus­si­an and the oth­er Amer­ic­an. The col­li­sion prob­ab­il­ity was very high. Finally, on April 9, the two objects brushed against each oth­er, only sev­er­al metres apart, but did not col­lide. But they could have exploded and cre­ated a myri­ad of new debris!