Launch vehicle Falcon 9 a few days ago brought into orbit thespace truck Dragon, on board which is an experimental space scavenger, the device RemoveDebris. It will make it possible to test in practice the technology of harvesting used space vehicles and their fragments with the help of a harpoon and a network. How much is the near-Earth space littered? Will there be enough space for new companions? We decided to investigate this issue with the help of a research associate of the Institute of Applied Mathematics named after MV Lomonosov. Keldysh Mikhail Zahvatkin.
Such devices as RemoveDebris will have something to do. According to the NASA space debris program, the number of garbage objects larger than 10 centimeters is approaching 20,000, and their total mass is to 8,000 tons, with most of them being fragments of space vehicles.
According to the calculations of the European Space Agency, the number of objects larger than one centimeter is 750 thousand, and smaller fragments can be thousands of times larger. A huge number of small fragments of micron size generates the work of engines, among them there are a lot of small particles of paint, and this man-made dust is already causing real damage today, leaving holes and microcraters in the shells and solar batteries of space vehicles.
Where does the garbage come from?
At the same time, the debris reserves in the orbit are constantly replenished: every year around the world, hundreds of new spacecraft appear, not only satellites, but also third stages of rockets, upper stages.
Sooner or later, intense orbital settlement would lead to “communal problems”, and in 1978 NASA employees Donald Kessler and Burton Kur-Palais came to the conclusion that in the near future collisions between failed satellites would begin to occur so often that the amount of debris will grow exponentially (even if at that point the space launches stop altogether) and eventually a ring of debris of spacecraft, similar to the ring of Saturn, will form around the Earth. They predicted that the first collision of spacecraft would occur before the year 2000. In reality, the collision of satellites “Kosmos-2251” and Iridium 33 was February 19, 2009, and their “meeting” has spawnedimmediately 1150 so large fragments that they could be noticed by the radars of the space control system.Although Kessler’s syndrome is an uncontrolled chain reaction of the destruction of vehicles in orbit and the transformation of near-Earth space into a forbidden zone, we can still see only in films such as “Gravitation” or “Valley-I”, space debris is already becoming a tangible hindrance. Suffice it to recall that the International Space Station (ISS) regularly has to adjust the orbit in order to avoid collisions, and even more often the cosmonauts have to drop all the cases and get into the Soyuz spacecraft in order to wait for the dangerous approach of the station with a fragment of space debris. Details delivered to Earth with the ISS often carry microdamages – traces of small debris strikes.
Some self-purification of near-Earth space still occurs, explains N + 1researcher at the Institute of Applied Mathematics named after MV Lomonosov. Keldysh Mikhail Zahvatkin. According to him, within the 11-year cycle of solar activity about 250-300 garbage objects per year have to be excluded from the catalogs – they simply enter the atmosphere and burn. But the rate of this cleansing varies greatly depending on the phase of the solar activity cycle (in the periods of the active Sun, the Earth’s atmosphere “swells” and begins to slow down the objects more) and from the altitude of the orbit.”Although the influence of the atmosphere is felt at altitudes of up to 1500 kilometers, the atmospheric brake actually works effectively only in low-Earth orbit, that is, in orbits of a height of 500-600 kilometers. In this zone, satellites without a constant orbit rise with the help of engines can last a couple of decades maximum, then they enter the atmosphere and will burn. But already at altitudes of 700-1000 kilometers spacecraft can be 50-100 years, that is, in the scale of human life – almost forever. Moreover, these orbits are the most popular, there are a lot of sun-synchronous satellites, because they do not need to spend a lot of fuel to support this orbit. These heights are launched by many vehicles, because they can survive there long enough, “the scientist says.
The floor from 700 to 1000 kilometers is the most popular and populated most quickly, but even at these heights the realization of the catastrophic scenario described by Kessler is a matter of the distant future.”13 thousand satellites rotate in low orbits, for 200 years in the worst case scenario their number will increase to 100 thousand, which means that the probability of collisions will grow approximately 100 times. Today, the probability of a catastrophic collision is about once every five years, with an increase in the probability of collisions, we get about 20 incidents per year for a population of 100,000 units. This is not so high a risk to make the launching of satellites into this zone commercially meaningless, “explains Zakhvatkin.
However, the scientist believes, one should not exacerbate the problem, leaving it to future generations, therefore, measures to combat pollution of near-Earth space should be worked out now.
Purely there where do not litter
To begin with, it would be nice to make sure that space debris does not get bigger, but for this it is necessary that space vehicles do not explode. The main source of small fragments in orbit today are not collisions of satellites with each other (as long as we know only one such event – the collision of “Iridium” with the “Cosmos”, mentioned above), and the so-called “fragmentation events”, the destruction of various internal reasons.
According to NASA’s calculations , as of August 2007, 194 cases of explosive destruction of satellites, upper stages of rockets and upper stages, and 51 other anomalous events-the separation of any fragments (solar panels, pieces of thermal insulation, structural parts) from the remaining whole apparatus . At the same time, explosions of vehicles in orbit are the source of about 47 percent of the total number of space debris objects.
Space vehicles explode mainly due to overheating of fuel residues in tanks – for this reason explosive destruction occurs in more than 45 percent of cases. One such incident, widely reported in the press, occurred on October 19, 2012, when the Breeze-M upper stage exploded in orbit , forming a cloud of more than 100 debris. Quite recently, a month and a half ago, an additional fuel tank of the Fregat upper stage exploded , which was used to launch the “Angosat-1” satellite, after which 25 more debris appeared in the catalog of space objects.
“It’s quite simple to solve this problem: it is necessary to ensure the passivation of the spent vehicles, that is, to install valves in the tanks that would bleed off the fuels, or to ensure the operation of the engines before it is completely exhausted, while reducing the orbit of the apparatus,” says Mikhail Zakhvatkin.
However, he notes, while maintaining the current frequency of launching new spacecraft into low orbits and taking significant steps to remove spent satellites and passivation, the total number of objects larger than 10 centimeters will still increase by 30 per cent over the next 200 years. “At the same time, the main role in the growth of this number will be played by collisions of satellites in the most overpopulated area of altitudes of 700-1000 kilometers, the largest of which will occur every 5 to 9 years,” the scientist explains.
How to remove
The rules that prevent the increase of the debris load in orbit have long been developed – there are UN recommendations , the corresponding standard is approved by ISO. However, so far there is no legally binding international treaty in this field, and each country follows its own rules, sometimes acting at the expense of common interests. Thus, in 2007, China shot down its own meteorological satellite, resulting in orbit more than 2,000 new fragments of space debris.
General recommendations, in general, are quite simple: you should take the device out to where it will not interfere with the new satellites, and if possible, direct it to low orbits to burn it in the atmosphere. So far, this rule as a whole is being carried out only with regard to devices located in a geostationary orbit with a height of 36 thousand kilometers. The location on the geostationary is a scarce resource, therefore the geostationary satellites that have served their end are put on the “burial orbit” for 100-200 kilometers higher, Zakhvatkin explains. However, in other orbits this rule is not always fulfilled.
On the one hand, it is commercially unprofitable to carry a fuel onboard of the satellite, intended only to bring the device from orbit at the end of its life. On the other hand, many satellites, especially CubeSat standard cameras, do not have their own engines at all. Engineers offer a variety of options for additional devices that can speed up the descent of the vehicle from orbit. This, for example, inflatable cylinders, which increase the area of the apparatus and, accordingly, air resistance, cable systems that brake the device due to the influence of electromagnetic fields. But so far none of these devices have become a standard.Specialized space debris cleaners, despite the high cost of such projects, can be useful in preventing cases of fragmentation of large spacecraft. “A large satellite is potentially thousands of small fragments that can arise from collision with another device or spontaneous destruction. A specialized “cleaner” can clean up these large objects, potentially sposbnye fragmented, and then they will not be in these orbits endlessly. If we remove about 4-5 objects a year from high orbits, this can level out the potential growth in the number of small fragments in the long term, “says Zakhvatkin.
Many fears are caused by Ilona Mask’s plans to put into orbit about 12,000 Starlink satellite systems, which should provide global access to the Internet. However, Mikhail Zakhvatkin believes that seriously this situation with space debris this project will not worsen.
“For groupings of the Starlink and Oneweb systems, it is planned to use orbits with a height of more than 1.1 thousand kilometers. Now the concentration of potentially dangerous fragments in this area is an order of magnitude lower than the values at altitudes of 800-900 kilometers. Therefore, the addition of such a large number of devices will not make the situation in these orbits critical, “- says the scientist.