Sentinel-1A Satellite Takes A Direct Hit From Millimetre Size Particle

Sentinel-1 satellite, the first satellite to be launched as part of the ESA/EC's Copernicus program. Credit: ESA/ATG medialab

One of the worst things that can happen during an orbital mission is an impact. Near-Earth orbit is literally filled with debris and particulate matter that moves at very high speeds. At worst, a collision with even the smallest object can have catastrophic consequences. At best, it can delay a mission as technicians on the ground try to determine the damage and correct for it.

This was the case when, on August 23rd, the European Space Agency’s Sentinel-1A satellite was hit by a particle while it orbited the Earth. And after several days of reviewing the data from on-board cameras, ground controllers have determined what the culprit was, identified the affected area, and concluded that it has not interrupted the satellite’s operations.

The Sentinel-1A mission was the first satellite to be launched as part of the ESA’s Copernicus program – which is the worlds largest single earth observation program to date. Since it was deployed in 2014, Sentinel-1A has been monitoring Earth using its C-band Synthetic Aperture Radar, which allows for crystal clear images regardless of weather or light conditions.

In addition to tracking oil spills and mapping sea ice, the satellite has also been monitoring the movement of land surfaces. Recently, it provided invaluable insight into the earthquake in Italy that claimed at least 290 lives and caused widespread damage. These images were used by emergency aid organizations to assist in evacuations, and scientists have begun to analyze them for indications of how the quake occurred.

The first indication that something was wrong came on Tuesday, August 23rd, at 17:07 GMT (10:07 PDT, 13:07 EDT), when controllers noted a small power reduction. At the time, the satellite was at an altitude of 700 km, and slight changes in it’s orientation and orbit were also noticed.

After conducting a preliminary investigation, the operations team at the ESA’s control center hypothesized that the satellite’s solar wing had suffered from an impact with a tiny object. After reviewing footage from the on-board cameras, they spotted a 40 cm hole in one of the solar panels, which was consistent with the impact of a fragment measuring less than 5 mm in size.

However, the power loss was not sufficient to interrupt operations, and the ESA was quick to allay fears that this would result in any interruptions of the Sentinel-1A‘s mission. They also indicated that the object’s small size prevented them from advanced warning.

As Holger Krag – Head of the Space Debris Office at ESA’s establishment in Darmstadt, Germany – said in an agency press release:

“Such hits, caused by particles of millimeter size, are not unexpected. 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. In this case, assuming the change in attitude and the orbit of the satellite at impact, the typical speed of such a fragment, plus additional parameters, our first estimates indicate that the size of the particle was of a few millimeters.

While it is not clear if the object came from a spent rocket or dead satellite, or was merely a tiny clump of rock, Krag indicated that they are determined to find out. “Analysis continues to obtain indications on whether the origin of the object was natural or man-made,” he said. “The pictures of the affected area show a diameter of roughly 40 cm created on the solar array structure, confirming an impact from the back side, as suggested by the satellite’s attitude rate readings.”

In the meantime, the ESA expects that Sentinel-1A will be back online shortly and doing the job for which it was intended. Beyond monitoring land movements, land use, and oil spills, Sentinel-1A also provides up-to-date information in order to help relief workers around the world respond to natural disasters and humanitarian crises.

The Sentinel-1 satellites, part of the European Union’s Copernicus Program, are operated by ESA on behalf of the European Commission.

Further Reading: Sentinel-1

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ESA Regrets Not Buying Windshield Insurance

The chip in the ISS' Cupola window, photographed by astronaut Tim Peake. Credit: ESA/NASA/Tim Peake

It is known as the Cupola, an observation and work area that was installed aboard the International Space Station in 2010. In addition to giving the crew ample visibility to support the control of the Station’s robotic arms, it is also the best seat in the house when it comes to viewing Earth, celestial objects and visiting vehicles. Little wonder then why sp many breathtaking pictures have been taken from inside it over the years.

So you can imagine how frustrating it must be for the crew when a tiny artificial object (aka. space debris) collides with the Cupola’s windows and causes it to chip. And thanks to astronaut Tim Peake and a recent photo he chose to share with the world, people here on Earth are able to see just how this looks from the receiving end for the first time.

The picture was snapped last month, and shows a chip in the Cupola window that measures 7 mm in diameter. The crew speculate that it was most likely caused by the impact of a tiny piece of space debris, possibly a paint flake or small metal fragment. Though it would have been no bigger than a few thousandths of a millimeter across, the orbital velocity of debris and the ISS meant that when they struck, the impact was hard enough to leave a mark!

According to Peake, the picture was motivated in part by a question which – as an astronaut – he is routinely asked. “I am often asked if the International Space Station is hit by space debris,” he said. “Yes – this is the chip in one of our Cupola windows, glad it is quadruple glazed!”

In other words, there was no threat of decompression from this chip in the window. Still, I’m betting that it’s times like these that the ISS wishes there was such a thing as orbital window insurance! And while the chip shown in the pictures was minor in nature, larger debris can pose a serious threat to orbiting labs and spaceships.

An object up to 1 cm in size – which by definition falls into the category of a meteoroid – could disable an instrument or a critical flight system aboard the ISS or anything else in orbit of Earth. Something larger than 1 cm could penetrate the shields on the Station’s crew modules, leading to dangerous decompression. And anything larger than 10 cm, could literally destroy the ISS.

And given it position in Low Earth Orbit (LEO), the threat of space debris, which comes in all forms – spent rocket stages, satellites that are no longer in use, paint flakes, metal fragments, and natural meteoroids and micrometeoroids – are a significant threat. In fact, it was estimated in 2013 that more than 500,000 pieces of debris – which travel at speeds up to 28,164 km/h (17,500 mph) – were being tracked as they orbited the Earth.

However, NASA, the ESA, Roscosmos and other space agencies routinely monitor Earth’s orbit to determine if there’s any potential for collisions between the ISS and large pieces of space junk. The station itself is also protected by layers of shielding designed to withstand collisions with smaller ones, so there is little chance the station and its crews are ever threatened.

The larger objects in LEO are less of a threat because their orbits can be predicted, and these are tracked remotely from the ground. This allows the crews to conduct Debris Avoidance Maneuvers (DAMs), which uses thrusters on the Russian Orbital Segment to alter the station’s orbital altitude. The ISS performed eight DAMs between Oct 1999 and March 2009, and another two between late March and mid-July of 2009.

In the event where a potential threat was identified too late to conduct a DAM, the crews close all the hatches aboard the station and retreat into their Soyuz spacecraft (or whichever module is currently docked) so they may evacuate if a serious collision occurs. Such partial evacuations have been conducted four times in the station’s history, between March 2009 and June 2015.

As for objects that are too small to track, the station relies on shielding, which is divided between the Russian Orbital Segment (ROS) and the US Orbital Segment (USOS). The USOS is protected by a thin aluminum sheet space from the hull. This shield causes objects to shatter into a cloud before hitting the hull, thereby spreading the energy of the impact.

The ROS, meanwhile, is protected by a carbon plastic honeycomb screen, an aluminum honeycomb and a glass cloth cover, all of which are separated from the hull by a screen-vacuum thermal insulation covering. The ROS’ shielding is about 50% less likely to be punctured, which is why the crew move to the ROS whenever the station is under threat. The ISS also relies on ballistic panels (aka. “micrometeorite shielding) to protect pressurized sections and critical systems.

And of course, the ESA chose to take this occasion to remind everyone that with this and other impacts, they are on top of things. As Holger Krag, Head of ESA’s Space Debris Office said in a recent statement:

“[The] ESA is at the forefront of developing and implementing debris-mitigation guidelines, because the best way to avoid problems from orbital debris is not to cause them in the first place. These guidelines are applied to all new missions flown by ESA, and include dumping fuel tanks and discharging batteries at the end of a mission, to avoid explosions, and ensuring that satellites reenter the atmosphere and safely burn up within 25 years of the end of their working lives.”

The Cupola is also where ESA’s Nightpod camera aid is installed to help astronauts take sharper pictures at night. Over the years, this has allowed for some of the most breathtaking photos of Earth from orbit to be snapped. You can check some of them out at the Space in Images section of the ESA’s website. And in the meantime, it not be too soon to start contemplating insurance for orbital habitats!

Further Reading: ESA- Space in Images

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Could Lizard Hands Help Us Clean Up Space Junk?

We’ve written extensively about the orbital debris problem here on Universe Today. In a nutshell, just about every time we launch something from Earth there are bits and pieces that are left behind. Screws. Paint flecks. Sometimes bigger pieces from rocket stages, or at worst, dysfunctional satellites. Added to the list of lasers, magnets, robot […]