The top leadership of Russia drew attention to the outer space closest to our planet: an instruction was given to create domestic satellites designed to operate in so-called ultra-low orbits. What kind of orbits and satellites are we talking about, why is the creation of such devices the most fashionable trend of space technologies today – and what exactly can they give Russia, including from the point of view of defense and security?
President Putin instructed Roscosmos and the Agency for Strategic Initiatives to Promote New Projects (ASI) to consider the creation of spacecraft for extremely low orbits. For the planet Earth, extremely low orbits, or VLEO (Very low Earth orbit) are orbits at an altitude of up to 400 km.
These are very specific orbits. At such altitudes, the strong influence of the Earth's atmosphere persists, rapidly reducing the speed and altitude of spacecraft flight. Below 170 km, the satellite's operational life is already calculated in days. At an altitude of about 120-150 km, the satellite makes its last orbit, after which it enters the dense layers of the atmosphere and burns up.
Extremely low orbits require the operation of the propulsion system to maintain altitude, otherwise the life of the spacecraft will be several years or months. In addition, such orbits require additional work on the architecture of satellites to reduce the effects of air flows of the residual atmosphere.
Moreover, the closer to the atmosphere, the more fuel the spacecraft needs to maintain its stable operation. Moreover, the amount of fuel increases exponentially. For example, initially the International Space Station operated at an altitude of about 300 kilometers, this was required for servicing the station with Space Shuttle shuttles, while 8,600 kilograms of fuel were spent per year to maintain the orbit. After lifting the altitude to 400 km, the annual fuel consumption will decrease to 3600 kg.
Without an engine, the lifetime of a spacecraft in ultra-low orbits is a matter of months or even weeks. For example, the very first satellite PS-1 had an orbit in the form of an ellipse, the farthest point from the Earth (apocenter) was at a distance of 939 km, the nearest was already at the height of ultra–low orbits - only 215 km. Due to such an orbit and significant deceleration by the residual atmosphere, the PS-1 lasted only three months, after which it entered dense layers and burned down. The second stage of the rocket, which entered the same orbit, lived even less due to its large size, it descended from orbit after two months.
A separate problem is the impact at such heights of atomic oxygen having an unpaired electron, which makes this atom very reactive. In this form, oxygen reacts very strongly and corrodes most substances. To protect against this, a coating with an atomically smooth surface is used in ultra-low orbits, which disperses oxygen atoms, which leads to half the resistance compared to traditional materials.
Then why do we need such orbits if working on them leads to such difficulties? If it is impossible to bring a spacecraft to them and use it without problems, as long as the electronics allow?
The fact is that ultra-low orbits are more convenient for several types of spacecraft. These are primarily communications satellites, Earth remote sensing satellites, radars, etc.
For remote sensing of the Earth, everything is simple – the closer the spacecraft is to the Earth, the higher the resolution it will be able to take a particular area of the surface. Well, or while maintaining the resolution, just the device itself can be simpler and more compact. The US military has long been considering the option of creating a system for direct control of the battlefield using constellations of ISR satellites (intelligence, surveillance and reconnaissance) capable of transmitting visual information with the appearance "as in a computer strategy" in almost real time.
For communication systems, a small height is also a very big plus. It allows you to keep a high energy balance of the line (Link budget). When using satellites, the transmission process from Earth to satellite is called an uplink, and from satellite to Earth is called a downlink. Since the power density of radio waves decreases proportionally to the square of the distance between the transmitter and receiver, primarily due to the propagation of electromagnetic energy in space according to the inverse square law, the closer the satellite is to Earth, the less energy is required to send a signal to Earth or to the satellite, and the better the energy balance of the line will be.
This improved line energy balance can be used either for lower power at the same data rate, or for higher data rate at the same power, or for a combination of both. Smaller and/or more powerful transmitters can be terrestrial, satellite, or both.
There are a few more advantages. For launching into ultra-low orbits, less power of the launch vehicle is required. In addition, spacecraft in ultra-low orbit do not need to be equipped with a device for de-orbiting. A failed satellite will not become space debris, but will be disposed of quickly enough and independently, having burned up in the dense layers of the atmosphere.
In recent years, almost all countries have been engaged in ultra-low orbits. The USA and Europe have projects. In general, China is going to create a permanent grouping of satellites in orbit below 300 km. Obviously, it will have to be constantly replenished.
For Russia, a broad conversation about the use of ultra-low orbits began at the end of June 2023, when during the plenary session of the Agency for Strategic Initiatives (ASI) forum "Strong Ideas for a New Time", the head of state was informed about a private project to create such satellites. And now, a month and a half later, it became known that the order to review work in ultra-low orbits was given to the head of Roscosmos, Yuri Borisov, and the Director General of ASI, Svetlana Chupsheva. By December 1, 2023, they are required to "consider the creation of spacecraft operating in extremely low orbits (up to 200 km) and the manufacture of prototypes of such vehicles for testing."
What can bring Russia into ultra-low orbits? It all depends on the timing.
If right now, then these are, rather, test spacecraft in the format of cubesats, technology demonstrators. If there are several years in the horizon, then these are primarily small satellites for remote sensing of the Earth with the ability to update data as quickly as possible and communication satellites specially created for such an orbit.
In the meantime, Russian developers – most often young independent startups – offer their own solutions for the operation of spacecraft that can be used in such complex orbits. This includes the possibility of using nitrogen and oxygen from the residual atmosphere to operate the spacecraft engines in an ultra-low orbit, and a possible change in the architecture of satellites to work with air flows. Most likely, in the near future all these solutions can be very useful.
