How and why did the two satellites collide last week?

The simulation conducted before last Tuesday predicted that the Iridium satellite and the Russian Cosmos satellite would approach each other a distance of about 500 meters, in reality they collided and experts say that this is due to inaccuracy in the satellites' position due to the effects of the moon's gravity and solar radiation

the collision that occurred On February 10, 2009, the collision between an active American Iridium series communications satellite and the inactive Russian Cosmos 2251 satellite in low Earth orbit raised public awareness of the growing problem of space debris. But how and why did the collision occur?

With NORAD, the US Air Force Space Scanning Network, NASA's Space Debris Program, and other entities tracking the space debris, did anyone know the collision was going to happen? Those who analyze the data and track the satellites say that predicting collisions is a complicated matter due to the frequent changes in satellite orbits that occur due to solar radiation and the gravitational effects of the moon and Earth. Therefore, the trajectory analysis is only good according to the nature of the data, which may be inaccurate.

"The main problem is the quality of the data that represents the location of the satellites," says Bob Hall, the technical director of Analytical Graphics (AGI), the company that published the video and images of the collision, in an interview with Universe Today. "Given the uncertainties as to the accuracy of the orbital data, I don't believe anyone predicted the event or even expected it."

AGI's tool automatically runs SOCRATES (Satellite Orbital Conjunction Reports Assessing Threatening Encounters in Space) software daily, based on the precise satellite catalog provided to the company by NORAD to track approaches. "These analyzes are performed automatically every day and the predictions of the day of the event can be checked. "Since the data is carried out with the help of the two-line element (TLE) public catalog, which updates the position of the satellites, the analysis can be good according to the accuracy of the data. Therefore when it shows an approach on any given day (and last Tuesday, the Iridium event was not even in the top ten of predicted approaches) it should be taken into account with some uncertainty.”

Hall said the closest approach observed to the Iridium satellite and the Cosmos satellite on February 10 was 584 meters. "Again, as close as it sounds and it is close, there were at least 10 predicted approaches at shorter miss distances that day." Hall said. The approach took place on Tuesday, at an altitude of 790 kilometers above northern Siberia in the tight polar orbit used by satellites that monitor weather, are used for communication relays and carry out scientific research.

The International Space Station, as well as most satellites, can be maneuvered out of the dangerous area to avoid possible collisions, but inactive satellites, such as the Russian Cosmos 2251 satellite, do not have this ability (either due to loss of communication or because the fuel used for these maneuvers has run out).

Despite uncertainties in tracking the satellites in orbit, one group, the Global Security Fund, demanded the establishment of a civilian space traffic control system. "Unfortunately, it appears that there was a prediction as to the possibility of this collision in advance," said Brian Weeden, a technical advisor to the foundation. "However, according to the data, an approach between two satellites somewhere in orbit around the Earth occurs at least once a week, and until the current event did not end in an actual collision."

Wieden agrees that in any case it is not possible to provide an exact answer as to whether two objects will actually collide, only probabilities and potential risks." The Global Space Security Fund wishes to promote the establishment of a body in Teli dependent on the governments that will carry out the monitoring.

"This collision dramatically illustrates the importance of the Civilian Space Institute to increase awareness of emergency situations in space situational awareness (SSA), as quickly as possible," said Dr. Ray Williamson, CEO of the Global Security Fund. Williamson says that a civilian SSA system could be used to warn Iridum operators of the danger of a collision and allow them to take preventive actions. "In the absence of reliable ways to clear debris from orbit, it will be especially important to track all active satellites to avoid preventable collisions," he added.

Before this collision, there was a collision in 1996 when a French intelligence satellite named Cerise was badly damaged by debris blown from the rocket that launched it. The US tracks micrometeorite fragments up to 10 centimeters in diameter, but objects as small as paint chips that fall from satellites can pose a threat if they hit a satellite at the tremendous speeds of orbit.

For the news in Universe Today

Sources: Email exchange with Bob Hall of AGI, Secure World Foundation press release, Reuters

Source: Correspondence (by Universe Today) with Bob Hall of AGI and Global Space Security Foundation press release