This artist's rendering of orbital debris around Earth shows only the largest fragments that can be tracked. If one of them collides with a spacecraft, it could cause serious damage or failure. Credit: NASA
There's no doubt that we've begun polluting the space around Earth. While governments around the world have been involved in cataloging and tracking the biggest orbital hazards, astronomers have recently pointed out that the biggest threat to future missions comes from the tiniest bits of debris — fragments that are currently untracked.
In a Article published on August 27 on the arXiv preprint serverTwo MIT astronomers have found that future space missions need to have much better plans for disposing of satellites and rockets to create a safer space environment.
Dodging bullets
There are currently tens of thousands of known pieces of space junk orbiting Earth. While there are some larger fragments, such as entire dead satellites, most of this junk consists of smaller bits of debris, including fragments of disintegrated rockets, screws and other pieces that have fallen off from larger missions, and even tools that astronauts accidentally dropped.
Space junk must be taken into account by planners for successful space missions to Earth orbit. Each piece of debris travels at tens of thousands of miles per hour. At such speeds, even the smallest piece can cause serious and catastrophic damage to a mission. For example, the International Space Station performs an average of one evasive maneuver each year to avoid space junk.
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Today, public and private space agencies rely on a network of databases provided by government monitoring groups, such as the U.S. Space Force. These groups use a combination of telescopes and radars to continuously monitor Earth's orbit, providing real-time estimates of where known space debris is located.
But the problem of space junk is getting worse, especially with the increase in mega communications constellations It's made up of tens of thousands of satellites. And worse, as the MIT astronomers stated in their preprint, our current technology only allows us to detect and track space junk up to a certain size limit, meaning we don't yet have an accurate assessment of the risk that future missions may face.
Currently, we can only track space junk larger than 10 centimeters in size, though the vast majority of debris in Earth orbit is smaller. Most of that small debris is considered “nonlethal,” since it lacks the kinetic energy needed to severely damage a vital component of a spacecraft. But we’ve seen the damage it can inflict, for example, when NASA replaced the solar panels on the Hubble Space Telescope in 1993 and 2002.
And we also know that smaller debris can be extremely dangerous if it has the right combination of kinetic energy and trajectory. If such a fragment hits the wrong component of the spacecraft at the wrong time, it could become “lethal” and result in the loss of the spacecraft.
A growing and unmonitored problem
We have not yet been able to develop an adequate risk assessment of the lethal but untrackable population of space debris because we do not have accurate estimates of their population and simulating their hypothetical orbits is incredibly expensive.
Instead, the MIT researchers used probabilistic models and created a series of scenarios that could play out over the next few decades about what the space junk population might be and how often different types might lead to catastrophic disasters. Their simulations included various scenarios about how many satellites are expected to be launched in the next few decades, how much additional space junk each launch would create, and what the odds of benign or mission-ending collisions might be.
They found that over the next two centuries, we can expect thousands of collisions caused by objects too small to track. Most of those collisions will be benign, but hundreds still have the potential to cause disaster.
Researchers have found that there is no way to completely eliminate the threat of this “invisible” space junk. We can only reduce the problem by enforcing rigorous standards for disposing of dead satellites at the end of their missions. Historically, most satellites have remained in orbit after their lifespan. With no remaining fuel, we have no way to change their orbit, making them at high risk for future collisions leading to an explosion in the population of smaller, untraceable debris.
Including aggressive plans to deorbit satellites at the end of their useful life and let them burn up safely in the atmosphere can dramatically reduce the risk of catastrophic collisions with debris in the future. At certain altitudes, the collision risk is reduced to one-third of its predicted value without aggressive disposal, and the total number of collisions is cut in half.
The only way to make the space around Earth safe for future missions is to continue our monitoring and tracking programs. And for the smallest fragments of space debris, we need regulations that ensure mission designers include adequate end-of-life plans for their satellites.
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