There are more than 30,000 debris objects in the sky that are regularly tracked. This only accounts for the larger objects and doesn't include the millions of tiny bits of "space junk" There are an estimated 36,500 objects greater than 10 cm in diameter, 1 million space debris objects, and 130 million space debris objects.
These objects pose a regular threat to the International Space Station and will only get worse as satellites are deployed to the lower atmosphere. A team of Canadian engineers created an Implosion-Driven Launcher that could accelerate magnesium projectiles up to 10 kilometers a second. This gun will make you think of the damage micro- objects could cause.
The team was made up of mechanical and chemical engineers from two Canadian universities. The study that describes their findings is currently being reviewed for publication in a journal. The IDL is 8mm in diameter and uses shock-compressed helium gas to launch magnesium projectiles. Micro-objects ranging from 1 millimeter to 1 cm in diameter are sped up by Earth.
The shielding on the International Space Station is strong enough to protect against small objects. Tracking larger objects in space allows for a degree of advanced warning so they can be avoided by the International Space Station. The objects from 1 to 10 cm are particularly dangerous because they can't be tracked and generate more impact energy than current shielding can handle.
“There are likely tens of thousands of objects in this size range in Low Earth Orbit. When these impacts occur, the events are so extreme [and the] properties of materials are not well understood under these conditions. Thus, while computer simulations of hypervelocity impacts are performed, there is considerable uncertainty in how well they can be trusted (the “garbage in, garbage out” problem). So, experimental testing is necessary, particularly at velocities of 10 km/s and faster.”
The nature of the debris makes them very dangerous. Earth's rotation causes objects to be sped up to 8 km/s.
He said that the most likely collision would be at 11 km/s. The most probable impact would be a side-on collision at 11 km/s. Studies done by the U.S. National Academy of Science have identified the requirement for testing orbital debris shielding as important.
Hypervelocity impacts and shielding have been limited to launchers that can achieve about 8 km/s in the lab. It has been difficult to test objects at higher speeds because of the extreme temperatures and pressures created by the propellant gas launchers. They can only fire projectiles that are less than a gram in mass. Light gas guns are what these are called.
“As high-pressure gas pushes a projectile down the launch tube, the gas expands and cools and eventually cannot push the projectile any faster: The projectile has outrun the gas. For this reason, scientific gas guns for testing at the greatest speeds use either hydrogen or helium as a propellant. Being a light gas, they have a high speed of sound and are able to keep up with the projectile, but even then, there is a limit.
“To get the greatest possible pressure, laboratory light gas guns fire a larger piston (using gun powder or another high-pressure gas) down a cylinder filled with hydrogen or helium, compressing the light gas to very high temperatures and pressures. This high-pressure light gas then acts to push the smaller projectile. Hence, a two-stage light gas gun [see video above].”
In order to achieve speeds over 10 km/s with projectiles larger than 2.5 cm, they needed a launcher that could do it. They used high explosives to squeeze the propellant gas out of it's container. The first stage of the pump tube is replaced by an explosion-driven tube. All the metal is recycled after each test, and the launchers are single use only.
Further technical details were provided by Higgens to Universe Today.
“A layer of explosive surrounds a tube filled with helium. When the explosive is detonated, a detonation wave sweeps down the tube and squeezes and compresses the helium, similar to how you would squeeze a nearly empty tube of toothpaste. The pressures and temperature in the helium can get to greater than fifty thousand atmospheres and 30,000 C, which is then able to push the projectile to speeds of 10 km/s. The explosives can even extend onto the launch tube, to help contain the pressure and continue to squeeze the propellant. Remarkably, the projectile can withstand these pressure and accelerations—approaching one million times Earth’s gravity—and emerge from the end of the launch tube intact.”
The growing human presence in space, the commercialization of LEO, and the growing problem of orbital debris make these studies important. There is a phenomenon called the Kessler Syndrome, where the amount of debris in the sky causes a cascade of events. The situation is projected to get worse even if we stop launching satellites today. At the moment, broadband internet satellite providers like Starlink and OneWeb want to grow their businesses in the future.
Space debris collision costs are a growing concern. The first report by the Organization for Economic Co-operation and Development was titled " Space Sustainability." The main risks and costs lie in the future if the generation of debris spins out of control.
There will be a space-faring civilization that needs to adapt to the problem of orbital debris. Since collision will happen, how to best protect and minimize the generation of new debris in such crashes. Addressing these issues will involve testing in the lab and this is where the implosion-driven launcher can help.
The implosion driven launcher Higgens and his colleagues built is currently being used to test samples of different materials. Since it was installed in 2001, the robotic arm has been an important part of the station. It plays a vital role in the operations of the International Space Station. The Canadarm2 was hit by a tiny piece of space debris last year, but it still worked.
ArXiv is further reading.
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