Space debris from more than 50 years of human space exploration is creating problems for current space missions. Launching million-dollar equipment into space now comes with the risk of space debris collisions. Costly damages can cause missions to be aborted.
In space, satellites are exposed to a plethora of natural risks. An increase in orbital space debris is further threatening satellite missions. The situation is grim, but space agencies and satellite operators are working on solutions to clean up Earth’s orbit.
Extreme temperatures, pressure variations and, unpredictable space weather – there is no doubt space is a dangerous environment for satellites. Humans have managed to make these already-harsh surroundings even more perilous. Since the beginnings of space endeavors in 1957, humanity has been leaving behind a trail of space debris littering Earth’s orbit with things like used rocket boosters, defunct satellites, and space exploration equipment. Even the smallest debris fragments have the potential to disrupt operations and severely damage satellites worth millions of dollars. In its white paper publication "Space Risks: A New Generation of Challenges", an Allianz Global Corporate & Specialty (AGCS) expert team on space risks explores the many challenges satellites face in the harsh space environment.
Satellites are exposed to risks before entering space to fulfill their missions. During the launch phase, they are subject to temperature and pressure variations. Then, once in orbit, satellites and their internal subsystems are exposed to significant temperature extremes. Exposure varies according to how different parts of the satellite are oriented with respect to the sun and how close they are to other components that generate large amounts of heat. To regulate temperatures inside a satellite, various inward and outward radiating techniques are employed, depending on the requirements of each subsystem. In addition, the satellite's external housing is partially insulated with special protective materials.
The Earth’s atmosphere also presents challenges to satellites, particularly those floating in LEOs, or Low Earth Orbits. The perpetual expansion and contraction of the atmosphere causes solar activity to vary significantly. Periods of greatest solar activity, known as solar maxima, force the atmosphere to expand and reach higher altitudes. As a result, satellites encounter varying degrees of residual air drag, creating a braking effect. Satellites must therefore perform station-keeping maneuvers to remain in their designated orbital coordinates.
Huge amounts of radiation
Solar flares pose another type of risk. Unpredictable and difficult to define, these coronal mass ejections release huge amounts of radiation, which disrupt radio transmissions. This affects satellites and, in extreme cases, can cause the loss of certain functions. Though better understood today and considered in the design of satellite missions, the erosion of a satellite's solar arrays remains a constant threat and can significantly shorten its life. A major solar flare could cause the total loss of control of one or more satellites.
To protect satellites, their solar arrays are progressively unfurled over the course of the transfer trajectory, and onboard electronic equipment is sized accordingly. "These risks are closely monitored, since they could be catastrophic and affect any number of satellites," says Thierry Colliot, Managing Director of SpaceCo and Head of Aviation Underwriting at AGCS France. "However, the probability of a major solar flare remains low." About 40 sat ellites are believed to have suffered critical or catastrophic anomalies as a result of solar storms.
Apart from solar flares, solar radiation is strongest in medium-Earth orbits, where it intersects the Van Allen radiation belt. This phenomenon also extends into LEOs and into one place in particular, known as the South Atlantic Anomaly. Here, satellites frequently encounter radiation-related incidences, though they are generally not serious.
Perhaps even more threatening than natural hazards is the risk of collision with space debris. Since mankind began launching objects into space, they have for the most part been left there, even after completing their missions. It is estimated that there are more than 16,000 debris objects that measure 10 cm or more in diameter.
“The space debris situation has become irreversible,” says Colliot. “The population of objects is now so high that it won’t decay on its own due to atmospheric drag. Instead, it’s actually increasing as objects collide and produce fragments, which in turn collide in a runaway chain reaction known as the Kessler syndrome.”
Faster than a bullet
Objects in space travel at very high velocities — approximately 10 km/s which is ten times faster than a bullet. Anything measuring more than 10 cm across can cause significant, even catastrophic, damage to operational satellites, as illustrated in 2009 by the collision between the now defunct satellite Kosmos 2251 and the operational satellite Iridium 33. Objects between 1 cm and 10 cm in diameter can be just as destructive and are, in some ways, a greater threat because of the sheer number of them. Estimates put the number of these smaller objects at 300,000. Also notable is the estimated number of objects measuring less than 1 cm. It is believed that about 35 million of these fragments exist, which can, upon colliding, perforate surfaces and cause erosion.
Once satellites have reached the ends of their lives, they are taken out of orbit. This entails relocating a satellite from its GEO, or Geostationary Orbit, to a new ‘graveyard’ orbit 300 km higher than its original coordinates. One drawback to this technique is that the deorbiting maneuver requires fuel, which cuts down on the satellite´s overall operational lifespan. Nonetheless, it repositions the satellite into an area that is less congested and thereby reduces the risk of a collision.
Deorbiting maneuvers are also performed with satellites in LEOs. The newest satellites residing in LEOs must be removed within 25 years after the missions end. Instead of raising LEO-stationed satellites to a higher, less congested orbit, such as with GEO-stationed satellites, these satellites are altogether eliminated through a destructive re-entry into the Earth’s atmosphere. The majority of a satellite’s structure burns up due to drag, which creates intense heat. The remaining fragments generally fall into uninhabited parts of the world, typically the South Pacific.
The concentration of space debris in different parts of near-Earth space are taken into account when missions are planned. Risks are assessed on the basis of observations and measurements, ground radar data and theoretical models produced by space agencies. In the case of minor collisions, damage may be limited by protecting satellite structures with special materials or impact absorption systems. Collision avoidance maneuvers may be performed to steer a satellite clear of high-risk objects, provided their trajectories are calculated accurately and in time.
Such evasion maneuvers are also routine practice on the International Space Station, which operates in a very low orbit where debris concentrations are highest. In 2010, and again in 2011, the astronauts were forced to evacuate on short notice, when an object came perilously close and was detected too late. If the space debris threat continues, such dangerous encounters could become more common.