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 revealed the apparent 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 or anti-satellite lasers capable of blinding sensors aboard enemy spacecraft.
With a large portfolio of nuclear technology and a hefty budget, the Russian Ministry of Defense seemingly 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.
In its corporate brochure, KB Arsenal reported that between 2016 and 2018, the company had conducted several early studies, NIRs, and preliminary designs, OKRs, looking into a megawatt-class nuclear-powered spacecraft. The program included the development and testing of the Design and Technical Mockups, KTMs, of the TEM module and its components, such as the Truss Carrier Section, ONF, the Support Systems Block, BOS, the Propulsion Unit Module, MDU, and the Power Unit, EB. These mockup elements have undergone functional tests, according to KB Arsenal. The company also published new photos of the spacecraft elements during assembly and testing.
In 2018 and 2019, Arsenal conducted the Yadro (Core) study, which looked at military and civilian applications of the megawatt-class power module, including its implied use as an anti-satellite weapon. The potential tasks under consideration, as defined by Arsenal, included "remote-sensing of the Earth's surface and of the airspace, electromagnetic impact on the radio-electronic command and control assets, reconnaissance, communications, navigation, inter-orbital transport and cargo delivery to near-lunar orbits." The proposals also included using the module for powering data-relay spacecraft in the Martian L1 Lagrange point to provide communications between a base on the surface of Mars, Mars orbiters and the Earth. The delivery of power-producing nuclear systems to the Martian surface base was also mulled.
A full-scale mockup of the Truss Carrier Section, ONF, during functional tests at KB Arsenal.
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, but likely showing a full-scale mockup assembled as early as 2018, 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.
During Moscow Air and Space Show, MAKS, opening on July 20, 2021, at Zhukovsky airfield near Moscow, Roskosmos displayed a scaled model of the nuclear-electric space tug for the Zevs (Zeus) complex. The exhibit appeared to be included the initial experimental version of the vehicle equipped with ion engines and another scaled-up variant sporting the so-called rotor magnetic plasma engines.
The TEM vehicles were displayed alongside historic reactor-carrying US-A spacecraft which were developed during the Soviet period for guiding cruise missiles to their targets and appeared to be shown to the same scale with Zevs models, giving a general idea about the ambition of the current effort.
It is known that the operational version of the Zevs space tug was sized for launch on the Angara-5V rocket capable of delivering up to 38 tons of payload to the low Earth's orbit.
During a military trade show in Russia in August 2021, KB Arsenal circulated a leaflet with logos of the company and its parent Roskosmos State Corporation and featuring more renderings of what was identified as the Zevs Orbital Complex. The accompanying text said that the vehicle was being developed for launch into a 1,000-kilometer (circular?) orbit on an Angara-A5 rocket from Vostochny spaceport. The space tug's mission was described as delivering scientific equipment toward the Moon and the planets of the Solar System.
Photo released in May 2022 apparently showing a turbine test vacuum facility at Keldysh center.
In May 2022, Head of Roskosmos Dmitry Rogozin admitted that the Zevs program had lacked funding, apparently reflecting new realities after Russia's escalation of the war against Ukraine on February 24. At the same time, Rogozin published photos of a thermal and vacuum chamber at the GNTs Keldysh Center in Moscow built for testing operation of high-speed turbines converting heat energy into electric power. It is a critical mechanism for the nuclear electric space tug, because it converts heat energy generated by the nuclear reactor into electricity required in huge quantities for the operation of high-thrust plasma engines.
The experimental stand at Keldysh operated in conjunction with a heat-generating unit with an output of 2 Megawatts, which simulates thermal loads produced by the reactor. According to Rogozin, during the successful tests of the experimental unit on May 13, the temperature of the driving substance at the turbine's entrance had reached 1,200 Kelvins and the turbine's speed had reached 34,000 rotations per minute. The subsequent tests aim to spin the turbine up to a target speed of 60,000 rotations per minute or 1,000 rotations per second, Rogozin said.
According to the Keldysh center, its multi-functional stand could accommodate experimental gas turbines and their components with a power of up to 250 Kilowatts. The center also had a cryogenic and vacuum test facility for test firing of Hall and ion engines with a power of up to 35 Kilowatts.
Rogozin also described a joint Russo-Belorussian effort to develop turbine blades which could operate at temperatures of 1,500 Kelvins and higher. Specialists reportedly tried several candidate materials from metal alloys to ceramics and composite materials. The development of new blades with higher heat resistance could allow higher temperature in the turbine, which, in turn would make it possible to reduce the size and weight of a radiator system for rejecting excessive heat into space aboard the space tug.
In the aftermath of the visit by Roskosmos head Yuri Borisov to GNTs Keldysh in Moscow on Dec. 1, 2022, the State Corporation released a photo clearly showing the turbine section of the Zevs space tug on a movable tray of the vacuum facility indicating still ongoing tests. According to the known configuration of the vehicle, its power-producing nuclear reactor would be located next to the visible truss structure, but the official photo was probably intentionally framed to avoid revealing whether the prototype of the power source was a part of the test.
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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 service 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
The mockup of the Truss Carrier Section, ONF. Credit: KB Arsenal
The mockup of the Propulsion Unit Module, MDU. Credit: KB Arsenal
The mockup of the Service Systems Block, BOS. Credit: KB Arsenal
A mockup of the Zevs complex presented at the MAKS air show in July 2021. Click to enlarge. Credit: Michael Jerdev
A reactor section of the Zevs vehicle. Click to enlarge. Credit: Michael Jerdev
The propulsion and payload section of the Zevs vehicle. Click to enlarge. Credit: Michael Jerdev
A close-up view of the radiator section of the Zevs vehicle. Click to enlarge. Credit: Michael Jerdev
Click to enlarge. Credit: KB Arsenal via Michael Jerdev
Renderings of the Zevs space tug released in August 2021. Click to enlarge. Credit: KB Arsenal via Michael Jerdev
Photo released in May 2022 apparently showing an electric propulsion test stand at Keldysh center in Moscow.
Head of Roskosmos Borisov visits Keldysh on Dec. 1, 2022. Click to enlarge. Credit: Roskosmos