Envisat
Envisat was the largest Earth-observation satellite Europe ever built. In April 2012 it stopped answering, and it has been drifting uncontrolled ever since — eight tonnes of it, in one of the busiest orbits there is.
What makes Envisat different
It stopped answering with no warning
On 8 April 2012, ten years and one month after launch, contact was lost. No cause was ever confirmed. Recovery attempts ran for two months before ESA formally declared the mission over.
Nothing can steer it now
A working satellite moves aside when a close approach is predicted. Envisat cannot. Anything on a collision course with it has to do the avoiding, and it cannot be commanded, slowed or deorbited.
It sits in a very crowded lane
Its sun-synchronous orbit near 770 km is among the most-used altitudes in space, shared with Earth-observation satellites and thousands of other objects. That is exactly where a large derelict matters most.
It will be there for about 150 years
Too high for drag to remove it on any useful timescale. It has become the standard example in debris-removal studies precisely because it is large, uncontrolled and long-lived.
Envisat carried ten instruments and, at roughly eight tonnes, was the heaviest civilian Earth-observation satellite ever flown when it launched in 2002. It worked for a decade, doubling its planned life, and then went quiet. What makes it significant now is not what it did but what it is: a large uncontrolled object at an altitude that will not clear itself, in an orbit crowded with active satellites. A collision involving that much mass would produce a debris cloud lasting far longer than the satellite itself, which is why it appears repeatedly in studies of whether anything could be sent up to capture and deorbit a derelict. Nothing has been, yet. It is still going round, still tracked, and the position above is current.
Frequently asked questions
What happened to Envisat?
Contact was lost abruptly on 8 April 2012 and never re-established. The cause was never determined; ESA declared the mission ended two months later.
Why is Envisat considered a problem?
It is large, massive and uncontrollable, in a heavily used orbit. It cannot manoeuvre away from anything, and a collision would produce long-lived debris.
Will Envisat fall down?
Eventually. Estimates put natural re-entry around 150 years away, because atmospheric drag is very weak at its altitude.
Could it be removed?
It is one of the main candidates studied for active debris removal, but no mission has flown to capture it. Grappling an uncontrolled tumbling object is the hard part.