ESA's Sentinel-1A satellite has been struck by a space particle while orbiting at a height of 700 km (435 miles) above the Earth. The particle is estimated to have measured only a few millimeters across, yet the impact caused a dent in the solar panel of the spacecraft 40 cm (15.7 inches) in diameter. It is not yet known whether the debris was manmade or natural in origin.
The Sentinel-1A satellite is tasked with monitoring the health of Earth's oceans, highlighting changes in the use of land, and providing data for emergency response efforts in the wake of natural disasters, as part of the European Union's Copernicus Program.
At 17:07 GMT August 23, mission operators detected a minute drop-off in power output from the satellite's twin solar panels, which, combined with a slight alteration in the probe's orbital trajectory, indicated that the spacecraft may have been struck by a piece of orbital debris. To confirm the impact, the team decided to switch on the probe's side-facing cameras.
The cameras had been mounted on either side of the satellite in order to provide visual confirmation that Sentinel-1A's delicate solar arrays had successfully deployed in the hours following its launch. Having completed their initial task admirably following orbital insertion in April 2014, mission controllers had deactivated the cameras, with no intention of turning them back on again.
Following the events of the 23rd, the cameras were commanded into life once more, granting technicians a clear view of where the particle had struck the 10 m (32.8 ft) solar array, leaving the large dent in the process.
"Such hits, caused by particles of millimeter size, are not unexpected," comments Holger Krag, head of ESA's Space Debris Office in Darmstadt, Germany. "These very small objects are not trackable from the ground, because only objects greater than about 5 cm can usually be tracked and, thus, avoided by maneuvering the satellites."
Thankfully, Sentinel-1A has emerged from the ordeal intact, and able to continue its mission unhindered. However, space debris represents a very real problem for those hoping to operate in the increasingly crowded environment of low-Earth orbit (LEO), which is frequented by swarms of telecommunication, military and basically every other form of satellite.
Decades of orbital operations has led to over 500,000 pieces of manmade debris larger than a marble whizzing around in LEO. This number gets a lot higher the smaller the gauge of debris. No matter how small a piece of space trash is, when it's moving at over 17,500 mph (28,162 kmph) it is going to damage whatever it hits, with potentially catastrophic results.
These collisions do happen. In the past whole satellites have collided with one another, creating vast clouds of debris capable of crippling a spacecraft, or in a worst-case scenario, a manned outpost such as the International Space Station.
Space agencies across the globe are aware of this growing issue, and regulations have been put in place requiring satellites and launch vehicles to be designed with a the capacity to either de-orbit themselves, or to push themselves into a distant "graveyard" orbit.
There are also numerous concepts under development with the potential to de-orbit the multitude of debris and derelict satellites already present in LEO. Netting and harpooning space junk are two techniques that could be employed to de-clutter LEO, while using gas clouds and lasers to zap the orbital trash are also under consideration.
Hopefully, these new technologies will reduce mankind's inevitable footprint in orbit, and avoid a Kessler effect, whereby debris in LEO causes a cascade of collisions that would render the operation of satellites in certain orbits impossible.
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