Space missions lasting several decades - or even longer - will require a new generation of power supplies.
The power system is a vital component of the spacecraft. These systems must be extremely reliable and designed to withstand harsh environments.
Today's sophisticated devices require more and more power - what is the future of their power supplies?
An average modern smartphone can barely last a day on a single charge. And the Voyager probe, launched 38 years ago, is still transmitting signals to Earth after leaving the solar system.
Voyager computers are capable of 81 thousand operations per second - but the processor of a smartphone is seven thousand times faster.
When designing a telephone, of course, it is assumed that it will be regularly recharged and is unlikely to be several million kilometers from the nearest outlet.
It will not work to charge the spacecraft's battery, which, according to the plan, should be located a hundred million kilometers from the current source, it will not work - it needs to be able to either carry batteries of sufficient capacity on board to operate for decades, or generate electricity on its own.
It turns out to be quite difficult to solve such a design problem.
Promotional video:
Some on-board devices only need electricity from time to time, but others need to run continuously.
Receivers and transmitters must always be turned on, and in manned flight or on a manned space station, life support and lighting systems must also be turned on.
Dr. Rao Surampudi leads the Energy Technology Program at the Jet Propulsion Laboratory at the California Institute of Technology in the United States. For over 30 years he has been developing power systems for various NASA vehicles.
According to him, the energy system usually accounts for about 30% of the total mass of the spacecraft. It solves three main tasks:
- electricity generation
- storage of electricity
- electricity distribution
All of these parts of the system are vital to the operation of the apparatus. They must be lightweight, durable and have a high "energy density" - that is, generate a lot of energy with a fairly small volume.
In addition, they must be reliable, since sending a person into space to fix breakdowns is very impractical.
The system must not only generate enough energy for all needs, but also do so throughout the entire flight - and it could last for decades, and in the future, possibly for centuries.
“The design life should be long - if something breaks, there will be no one to repair,” says Surampudi. "The flight to Jupiter takes five to seven years, to Pluto more than 10 years, and it takes 20 to 30 years to leave the solar system."
The power systems of a spacecraft are in very specific conditions - they must remain operational in the absence of gravity, in a vacuum, under the influence of very intense radiation (which would disable most conventional electronic devices) and extreme temperatures.
“If you land on Venus, then 460 degrees will be overboard,” says the specialist. "And when landing on Jupiter, the temperature will be minus 150".
Spacecraft heading towards the center of the solar system have no shortage of energy collected by their photovoltaic panels.
These panels look little different from solar panels installed on the roofs of residential buildings, but at the same time they work with much higher efficiency.
It is very hot near the sun and the PV panels can overheat. To avoid this, the panels are turned away from the Sun.
In planetary orbit, photovoltaic panels are less efficient: they generate less energy, since from time to time they are fenced off from the Sun by the planet itself. In situations like this, a reliable energy storage system is needed.
Atomic solution
Such a system can be built on the basis of nickel-hydrogen batteries, which can withstand more than 50 thousand charging cycles and last more than 15 years.
Unlike conventional batteries, which do not work in space, these batteries are sealed and can function normally in a vacuum.
As we move away from the Sun, the level of solar radiation naturally decreases: for the Earth it is 1374 watts per square meter, for Jupiter - 50, and for Pluto - only one watt per square meter.
Therefore, if the spacecraft leaves the orbit of Jupiter, then atomic power systems are used on it.
The most common of these is the radioisotope thermoelectric generator (RTG) used on the Voyager and Cassini probes and on the Curiosity rover.
There are no moving parts in these power supplies. They generate energy by decaying radioactive isotopes such as plutonium. Their service life exceeds 30 years.
If it is impossible to use an RTG (for example, if a screen that is too massive for flight is needed to protect the crew from radiation), and photovoltaic panels are not suitable due to too great a distance from the Sun, then fuel cells can be used.
Hydrogen-oxygen fuel cells were used in the American space programs Gemini and Apollo. These cells cannot be recharged, but they release a lot of energy, and a byproduct of this process is water, which the crew can then drink.
NASA and the Jet Propulsion Laboratory are working to create more powerful, energy-intensive and compact systems with a high lifetime.
But new spacecraft need more and more energy: their onboard systems are constantly becoming complex and consume a lot of electricity.
This is especially true for ships that use an electric drive - for example, the ion propulsion device, first used on the Deep Space 1 probe in 1998 and has since become widespread.
Electric motors usually work by ejecting fuel electrically at high speed, but there are also those that accelerate the apparatus through electrodynamic interaction with the magnetic fields of planets.
Most of the earth's energy systems are not capable of operating in space. Therefore, any new scheme goes through a series of serious tests before being installed on a spacecraft.
NASA laboratories recreate the harsh conditions in which the new device will have to function: it is irradiated with radiation and subjected to extreme temperature changes.
Towards new frontiers
It is possible that improved Stirling radioisotope generators will be used in future flights. They work on a principle similar to the RTG, but much more efficient.
In addition, they can be made very small - although the design is further complicated.
New batteries are being built for NASA's planned flight to Europe, one of Jupiter's moons. They will be able to operate at temperatures ranging from -80 to -100 degrees.
And the new lithium-ion batteries that designers are currently working on will have twice the capacity than the current ones. With their help, astronauts can, for example, spend twice as long on the lunar surface before returning to the ship to recharge.
New solar panels are also being designed that could efficiently collect energy in low light and low temperatures - this will allow devices on photovoltaic panels to fly away from the Sun.
At some stage, NASA intends to establish a permanent base on Mars - and possibly on more distant planets.
The energy systems of such settlements should be much more powerful than those used in space today, and designed for much longer operation.
There is a lot of helium-3 on the moon - this isotope is rarely found on Earth and is the ideal fuel for thermonuclear power plants. However, it has not yet been possible to achieve sufficient stability of thermonuclear fusion in order to use this energy source in spacecraft.
In addition, the currently existing thermonuclear reactors occupy the area of an aircraft hangar, and in this form it is impossible to use them for space flights.
Is it possible to use conventional nuclear reactors - especially in vehicles with electric propulsion and in planned missions to the Moon and Mars?
In this case, the colony does not have to run a separate source of electricity - a ship's reactor can play its role.
For long-term flights, it is possible that atomic-electric propellers will be used.
“The Asteroid Deflection Mission requires large solar panels to have enough electrical power to maneuver around the asteroid,” Surampudi says. "We are currently considering a solar-electric propulsion option, but atomic-electric would be cheaper."
However, we are unlikely to see nuclear-powered spacecraft in the near future.
“This technology is not yet sufficiently developed. We must be absolutely sure of its safety before launching such a device into space,”explains the specialist.
Further rigorous testing is required to ensure that the reactor is capable of withstanding the rigors of space flight.
All of these promising power systems will allow spacecraft to last longer and fly long distances - but so far they are in the early stages of development.
When the tests are successfully completed, such systems will become a mandatory component of flights to Mars - and beyond.