Fuel from space debris

 In the sci-fi thriller "Gravity" (2013), an American astronaut finds himself in outer space after the destruction of the ship due to the fact that Russia explodes a spy satellite with a rocket and creates a rapidly expanding cloud of space debris. Ironically, this scenario has recently been repeated in reality, when Russia shot down an old Soviet satellite, as part of tests of an anti-satellite missile. The probability that debris from space debris can penetrate a spacesuit during a spacewalk is usually 1 in 2700, but Russian tests have increased this risk by 7%.

Space debris is a danger to active satellites and spacecraft. Presumably, Earth's orbit will become impassable when the risk of collision is too high. Today, when most of the space debris is cataloged, there is no particular problem with this so far. All the world's space powers scan outer space for the presence of debris, of which there is a lot in low orbits: idle satellites, upper stages and spacecraft debris. It is very difficult to solve the problem of space debris quickly because of financial and political problems. Old satellites that have served their time should either be introduced into the Earth's atmosphere for disposal at the "spaceship cemetery" in the Pacific Ocean, or put into a "burial orbit" if the device is far from Earth.

Scientists have asked the question: why not develop a spacecraft that will dispose of space debris directly in space? And there is a prototype of such a device. The idea of creating a spacecraft for the disposal of space debris is based on the processing of space debris into fuel.

Not to litter will not work

Space debris is non-functioning artificial objects in near-Earth orbit that no longer perform a useful function. These include non-functional spacecraft and launch vehicle stages, as well as ih debris, color spots, solidified liquids ejected from the spacecraft, and unburned particles around solid-fuel rocket engines. NASA has announced 20,000 artificial objects in orbit above the Earth, including 2,218 active satellites. As of January 2019, there were 128,000,000 pieces of debris smaller than 1 cm in orbit, about 900,000 pieces between 1 and 10 cm in size, and about 34,000 pieces larger than 10 cm. Meteoroids in Earth orbit should also be added to artificial debris, which can be grouped with artificial debris and increase the risk of collision. This poses a danger to spacecraft: even the smallest objects cause damage, especially to solar panels, telescope optics and star trackers, which cannot be easily protected by a ballistic shield.

Over the years, the Earth's orbit has become more and more littered. According to the European Space Agency (ESA), humanity has launched 12,170 satellites since the beginning of the space age in 1957, and 7,630 around them remain in orbit today, but only about 4,700 are still operational. This means that almost 3,000 non-functional spacecraft are flying around the Earth at great speed along with other large and dangerous debris. For example, the orbital speed at an altitude of 400 kilometers (the altitude at which the ISS operates) is 27,500 km/h. At such speeds, even tiny fragments of debris can cause serious damage to the spacecraft. According to ESA estimates, there are at least 36,500 debris larger than 10 cm wide, 1 million objects from 1 to 10 cm across and more than 300 million objects from 1 mm to 1 cm in size in the near-Earth orbit.

The "cascade effect" (Kessler syndrome), which in the long term may arise from the collision of objects and particles of space debris, can be considered to be already making itself felt, although the cataclysm of the scale of "Gravity" is still far away. Evidence of this may be the collision of two satellites with each other. The most famous such incident occurred in February 2009, when the non-functioning Russian satellite Kosmos-2251 crashed into the operational communications ship Iridium-33, forming over 2,000 fragments.

Under the existing conditions of clogging of low Earth orbits, when measures to reduce man-made space clogging remain only theoretical, the cascade effect can lead to a catastrophic increase in the amount of space debris in low orbit, and as a consequence, to the practical impossibility of further space exploration.

General cleaning

As the problem escalates, organizations around the world are trying to find solutions - from magnets to "space claws" and harpoons. There are different ways to counteract space debris: crushing of large space debris, removal of debris from orbit or removal of a spacecraft from the orbit of debris, knocking down debris with a laser or processing it into fuel. It is not possible to use only one counteraction method for all types of garbage. For example, it is impossible to catch small space debris with a net, and it is useless to stop large space debris with gas.

Basically , there are two directions for combating space debris:

crushing of space debris directly in orbit;

deceleration and removal of large space debris from low orbits for subsequent combustion in the atmosphere or removal of space debris from geostationary orbit to a burial orbit.

Moreover, both methods have disadvantages associated with the formation of fragments of a smaller fraction, the fall of unburned debris to the Ground and the clogging of higher orbits.

The easiest way to clean up outer space is to suspend space activities for a decade until the Earth's gravity does its job, but then humanity will stop developing. If nothing is done, then at the current rate of growth of space activity, soon we will simply not be able to launch spacecraft due to debris in orbit and will also stop developing.

The American company Cislunar Industries is developing a space "foundry" for melting debris into homogeneous metal rods. And the propulsion system from Neumann Space can use these metal rods as fuel — their system ionizes metal, which then creates thrust to move in orbit. It's like making a gas station in space. The SCM processes garbage into fuel, which allows the spacecraft to gradually ascend to higher orbits, up to the burial orbit (over 40 thousand km), clearing outer space.

Most space propulsion systems use gas as fuel. Even in liquid form, fuel takes up a lot of space and is not suitable for space travel. And if there is a problem, as happened with the mission of the Challenger spacecraft, the results can be disastrous. It is better if the propulsion system will run on solid fuel, which is much safer than explosive liquid or gas.

Electricity is applied to metals such as titanium or magnesium, or to any solid conductive fuel rod, to produce plasma and burn the charged gas through the rear of the engine, creating thrust.

Simplified scheme of the Neumann engine

Paddy Neuman himself

The author of the project, Dr. Paddy Neuman, as a student, participated in a project on plasma diagnostics, which consisted in diagnosing how hot it is, how dense it is, how fast it moves, etc. Analyzing his results, he was able to determine the average effective plasma velocity, which was 23 km/s. He said that you can make a rocket out of it.

One of the efficiency metrics that engineers like to talk about in this field is called specific impulse. The specific impulse is, in fact, the amount of push that can be obtained from a given fuel weight. Thus, a higher specific impulse means that the fuel is used more efficiently. This is just one element that should be taken into account when developing a space engine. In addition, since it is very expensive to put something into orbit, it is very convenient to have fuel that allows you to do this with a smaller mass or volume. The specific impulse is measured in seconds. When Dr. Neuman began testing his engine, the existing ion engines produced 3,500 seconds of specific impulse. NASA's HiPEP experimental system can work a little better, 10,000 seconds. After testing several different fuels, Dr. Neuman published his results: magnesium as fuel and had a specific impulse of 11,000 seconds. So, three times better than what is used today.

Although the Neumann engine will not be able to compete with chemical-fueled internal combustion engines to take the ship into space, it can be installed on smaller ships or satellites to keep them in orbit. The Moon and the Sun will always pull the satellites a little behind them, so a small engine will be needed to keep them in the correct orbit.

Last year, Neumann Space received $2 million in seed funding from government grants. They say they plan to test the Neumann engine in space in the near future.

Now a kind of ecosystem is emerging in near-Earth outer space. In this ecosystem, as in any other, there are "creatures" that "live", "feed", perform their functions and, "dying", give food to other creatures. And the creatures that "feed on carrion" can and should become space debris collectors in the broadest sense of the word.