Russia reveals a formidable nuclear-powered space tug
After years of near silence, a prominent developer of Russian military spacecraft suddenly publicly floated the first pictures of a massive nuclear-powered space transport undergoing assembly at the company's facility in St. Petersburg. The KB Arsenal design bureau, which serves as the prime contractor in the project, is known for its Soviet-era nuclear-powered satellites, one of which infamously crashed in the Arctic region of Canada in 1977.
The TEM space tug deploys in orbit.
What is the nuclear-powered space tug?
A series of photos and computer-generated imagery, which surfaced on the Internet in 2020 and originated from KB Arsenal clearly revealed the latest version and the planned operation of a very large space tug propelled by electric engines and powered by a nuclear source.
The project officially known as the Transport and Energy Module, TEM, has been well known to the watchers of the Russian space program for more than a decade.
Tracing its roots to the dawn of the Space Age, the TEM concept is attempting to marry a nuclear reactor with an electric rocket engine. The electric propulsion systems heat up and accelerate ionized gas to create a thrust-generating jet and, therefore, are alternatively known as ion or plasma engines. When measured per unit of spent propellant mass, electric engines are more efficient than traditional liquid or solid-propellant rockets, but their thrust is relatively low at any given time and they require a great deal of electric power to operate. Because of this, until recently, the practical use of electric propulsion in space flight was mostly limited to orbit adjustment systems aboard satellites or to deep-space missions, in which spacecraft could take advantage of low thrust over very long periods of time.
To scale up the operation of power-hungry electric thrusters, engineers long considered replacing heavy and bulky solar panels with nuclear power sources which could provide plenty of electricity for years if not decades and would not be dependent on solar radiation in the remote and cold regions of the Solar System, as demonstrated by planetary missions such as Voyager, Cassini and many others.
However, the development of nuclear reactors for space still had to take place on Earth, where environmental and safety concerns slowed down the progress in this field.
Still, by the early 21st century, the Russian military apparently renewed interest in the great capacity of nuclear reactors to provide electricity not only for propulsion systems but also for other equipment aboard large spacecraft, such as powerful radar antennas for surveillance purposes.
With a large portfolio of nuclear technology and a hefty budget, the Russian Ministry of Defense apparently became the primary backer of the first post-Soviet attempt to build a nuclear power-generating system for space. Not surprisingly, the work on the reactor was largely classified, but in 2020, KB Arsenal released photos showing what appeared to be the assembly of the full-scale TEM vehicle or its prototype and an animation of its deployment in orbit.
The TEM space tug explained
The TEM space tug in folded position.
The heart of the TEM tug is a nuclear reactor, which generates heat. The heat is then converted into electrical power either through a mechanical turbine or via the so-called thermal emission method, which does not involve any moving parts. Though less effective than a turbine, the simpler, and more familiar to the Russian industry, thermo-emission conversion appeared to be in use aboard the TEM vehicle revealed in 2020.
The excessive heat energy inevitably generated in the process of reactor work is released into space with a system of radiators, which can also use a variety of different technologies to operate in weightlessness and beyond the atmosphere. The revealed TEM vehicle appeared to feature a trio of main and three auxiliary radiators. The latter smaller panels probably service the traditional needs of service systems aboard the spacecraft, while the larger deployable and stationary radiators were probably exclusively designed for removing the reactor's heat. The animation showed a very complex three-stage process of the main radiator deployment aboard the TEM module.
However, on the unveiled vehicle, the radiator panels appeared to be using heat-carrying cooling fluid pumped through the system by a turbine. It is a less progressive technology than the capillary heat pipe radiating system which was originally planned for the spacecraft and which Russia was known to be testing aboard the Mir space station at the turn of the 21st century.
To protect all the systems aboard the spacecraft from harmful radiation, the reactor is placed behind a cone-shaped shield which forms a protected conical "shadow" free of dangerous particles. To further increase the safe zone, the reactor is attached to what appeared to be a four-section telescopic boom made of a light-weight composite material. The boom deploys to its full length after the ship's separation from the launch vehicle in orbit.
According to the available publications, the nuclear reactor on the TEM vehicle would be activated only after the spacecraft reached a 600 or 800-kilometer orbit, which is far enough from the rarified atmosphere to prevent the natural decay and reentry of a stalled satellite. In the interim, all the service systems of the space tug and its payloads could still receive power from a pair of solar panels deployed on the sides of the propulsion module immediately upon entering orbit.
The photos released by KB Arsenal in 2020 showed key components of this very large vehicle, including the propulsion module, stationary and deployable radiators and the deployable boom which would carry the reactor. There were no photos of the reactor itself, however it was shown in the accompanying animation, which was dated 2020. It appeared that even without its payload, the Russian TEM would be a 20 or 30-ton vehicle, which could require either Angara-5M or Angara-5V heavy rockets to enter an initial orbit from the Vostochny spaceport. One depiction produced by GKNPTs Khrunichev around 2016 showed the Angara-5V rocket with a Briz upper stage carrying the TEM vehicle.
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The TEM space tug deploys its radiator system in orbit. Click to enlarge. Credit: KB Arsenal
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The TEM space tug in orbit. Click to enlarge. Credit: KB Arsenal
A close-up view of TEM's propulsion module in orbit. Click to enlarge. Credit: KB Arsenal
The propulsion module of the TEM space tug. Notable is what appeared to be small electric attitude control thrusters on the edges of the cube-shaped body of the spacecraft. Larger electric engines, which provide the main thrust, appear at the bottom of the vehicle. Click to enlarge. Credit: KB Arsenal
The main deployable truss of the TEM vehicle is probably made of carbon-based composite to provide minimum weight and maximum strength. Click to enlarge. Credit: KB Arsenal
The radiator system of the TEM space tug. Click to enlarge. Credit: KB Arsenal
Installation of the stationary radiators on the main truss of the TEM space tug. Click to enlarge. Credit: KB Arsenal