The scientists grapple with the question "What developments in energy technology are needed to send human and robotic explorers around the solar system?"
NASA website. Translation - Nahum Sherashevsky
Beyond all the planets in our solar system, in the cold, dark and empty region of space, Voyager 1 continues its 25-year journey of discovery. It heads towards the heliopause, that boundary where the influence of the sun ends and the dark depths of interstellar space begin. From where Voyager is, the Sun is only the brightest star in the sky - seven thousand times dimmer than we see it from Earth.
Voyager has no solar collectors; They would be of no use so far from the sun. The spacecraft maintains contact using its own power source, an early type of radioisotope thermoelectric generator (RTG), which converts the heat generated by the natural decay of its radioactive fuel into electricity. Its generator will provide Voyager with electricity until at least 2020.
Spacecraft moving far beyond Mars need more energy than solar cells can provide. Another example is the spaceship Ulysses. It was launched in October 1990 from the Space Shuttle with its mission to study the poles of the Sun. To get above the Sun, Ulysses had to fly around Jupiter and shoot like a slingshot out of the plane of the planets. Near Jupiter, the sun's rays are 25 times weaker than near Earth. Solar collectors large enough to absorb this weak energy would weigh about 550 kg, doubling the weight of the spacecraft and making it too heavy for the shuttle's booster rockets. In their place, Ulysses was equipped with a radioisotope thermoelectric generator weighing only 56 kg. It easily supplies power to all spacecraft systems, including navigation, communications and scientific instruments.
A spacecraft like Ulysses needs a power of about two hundred watts to operate the systems inside. For comparison, the systems on the space shuttle consume 5 to 10 kilowatts (kW), 50 times the power. The International Space Station consumes 10 times, or around 100 kW for the systems inside.
Above: 375 km above the Earth's surface, solar arrays provide energy to the International Space Station.
The International Space Station never leaves Earth's orbit, which reduces the energy it needs. However, in manned missions outside the neighborhood of the Earth, not only energy will be required for the systems in the spacecraft, but also for the propulsion and the systems to support the humans when they reach the destination to which they fly. "To carry out ambitious manned missions around the solar system, perhaps returning to the moon, perhaps continuing to Mars, would require hundreds to thousands of kilowatts on the surface of the planet and hundreds to thousands of kilowatts for transportation systems," says John Mankins, chief technologist of the systems program advanced at NASA headquarters. You can't just plug into the nearest power outlet, he added. You must bring your own power source. Ideally, you'll want to find something that can provide power for both propulsion and operational activity.
Chemical rockets propel the space shuttle away from Earth.
Since Robert Goddard's first rocket launch test in 1916, space missions have used chemicals to achieve the acceleration needed to escape Earth's gravity. The 5 to 10 minutes of the rocket burning sends the spacecraft towards its destination; It then coasts the rest of the way, unless it uses the gravity of other planets for extra acceleration. Voyager took years to reach Saturn and then the spacecraft managed to be only days in Saturn's system and only hours near the planet itself.
Mission planners want to be more successful in the future.
From the perspective of the Office of Space Exploration at the Johnson Space Center, Jeff George sees "an evolving family of interrelated power and propulsion technologies" for the next wave of manned space exploration. The first possible candidate is the electric drive (EP). In space, you don't need as much thrust as you need to escape Earth's gravity, George explains, but it's necessary to generate thrust using very little fuel because of weight limitations. Electric propulsion could provide fuel-efficient thrust after initial chemical acceleration into space.
Specific stroke—that is, the pounds of thrust produced per pound of propellant per second of use—is a measure of how efficiently a system uses fuel to produce thrust. higher is better. The space shuttle, which stays close to Earth, has chemical propulsion with a specific thrust of 450 seconds or 450 pounds of thrust per pound of propellant per second. The specific stroke of the electric drive is ten times that of the chemical drive and potentially it can reach up to 10,000 seconds.
Electric propulsion was first tested in 1998 in Deep Space 1 - a spacecraft where many new technologies were tested before it flew by Comet Borelli in 2001. Deep Space 1 needed 2.5 kilowatts to power both its electric ion drive (pictured left) and other systems inside. The energy came from an innovative array consisting of advanced solar cells and a lens to concentrate the sunlight on the collectors. Together they achieved a 23% efficiency in converting sunlight into electricity compared to the 14% efficiency of the International Space Station's solar arrays.
Above: The blue ejector of the Deep Space Ion Propulsion Engine 1. Electricity collected from the spacecraft's solar arrays is used to ionize atoms of a filter. As these ions are pushed through the back hatch by a strong electric field, the spacecraft slowly gains speed.
Building on the success of Deep Space 1, a new mission called "Dawn" will leave Earth in 2006. Powered by an ion engine with a specific thrust of 3000 seconds, Dawn will fly to Vesta and Ceres, two of the largest asteroids in the Solar System. Although Vesta and Ceres are further from the Sun than Mars, the spacecraft will be able to draw all the energy it needs from 7.5 kilowatt solar arrays.
Manned missions require more energy. "The next step for a [manned] Mars mission," says Jeff George, "is to go up to 5-10 megawatts of nuclear power and then size the electric thrusters to megawatts per engine." The transition from kilowatts to megawatts is not a simple problem. NASA is now working on a next-generation 5-10 kilowatt ion propulsion system. George envisions small, 100-200 kilowatt electric-nuclear vehicles exploring the distant planets as an experimental version of the megawatt scale that would be used for manned space exploration.
Above: Fission, the same process of splitting the atom that powers modern nuclear power plants, is one way to create high levels of energy to power spacecraft.
To operate a megawatt electric drive system, a source that is both high energy and high power is needed. As John Cole, director of the Revolutionary Propulsion Research Project Office, explains, "Energy is the most important factor, but the power (the energy released per unit of time) determines the acceleration." So which source provides enough power? "The atom has a lot of energy - and potentially a lot of power as well," notes Cole. "Solar collectors provide power that is not enough to accelerate the entire vehicle to levels that allow short journey times."
Sources of radioisotope energy (like the radioisotope thermoelectric generators on Voyager) produce a lot of energy for a long time, but not a lot of power, only tens to hundreds of watts. To get kilowatts to megawatts of power, you have to turn to nuclear fission, says Liz Johnson, of NASA's Advanced Space Transportation Program.
Above: The radioactive decay, in this image, is the source of energy for the radioisotopic thermoelectric generators. It is not as powerful as nuclear fission.
Fission, in which a neutron splits an atom into two radioactive isotopes, is the process used in nuclear power plants on Earth to generate electricity. "Bringing a fission reactor to a spacecraft would be like bringing your own [mini] power plant," says Johnson. A fission reactor has the ability to fuel high-performance electric propulsion beyond the inner solar system. It has a longer duration and is highly capable of performing sophisticated scientific research, high-speed data communication, and complicated spacecraft operations.
That's a pretty good resume for the split, but it still doesn't pass the John Cole test. Cole set himself the requirement to bring humans to the distant planets within a year and back within a year. Nuclear fission has enough energy, but not enough power to provide the necessary acceleration. NASA is planning a 300 kilowatt flight configuration system using nuclear fission. But in order to pass the test of a sound, "a very high specific power is needed, the power per unit mass of a vehicle that is three orders of magnitude better than what is currently planned for nuclear fission." For this, you need to step up to nuclear fusion - the same process that supplies energy to the sun and the stars.
Above: Go outside at night and look at the stars. Every star you see is a melting pot. The scientists want to harness this power to propel spaceships and supply energy to distant colonies. ]More[.
Fusion, which releases energy by uniting atoms instead of splitting them, could in principle provide gigawatts of clean energy. However, fusion propulsion systems as we understand them today would be very large and would require a vehicle the size of the space station or Telstar Galactica, weighing hundreds of tons - although the size may decrease with research.
Fusion engines will be very efficient fuel burners with a specific stroke of 100,000 seconds. "Although we won't be able to do it in ten years, if we could launch a fusion propulsion system 10 years from now, we could send a vehicle to catch Voyager and bring it back," Cole says. That kind of power and speed shortens the time astronauts are exposed to harmful cosmic radiation and the bone loss that results from prolonged weightlessness.
There might be something that's even better than fusion: to prevent an impulse driven by a matter-antimatter ionization would be a 2,000,000-second specific attack, according to Cole.
It sounds like science fiction, but researchers are already learning to create and store small amounts of antimatter in real labs. A portable electromagnetic antimatter trap at Penn University, for example, can hold 10 billion antiprotons. If we learn how to use such antimatter safely, we can inject some into a thin stream of hydrogen gas to create thrust. Alternatively, you can inject some antimatter into a fusion crucible to lower the temperature needed to start a fusion reaction.
Above: This "confinement trap" developed at Penn University stores antiprotons [more].
"Propulsion is not the only reason to move to the atom," notes Colleen Hartman, Director of Solar System Research at NASA Headquarters. "This also benefits the systems in the spacecraft. The excess energy is like having the Las Vegas strip instead of a single light bulb. You get more communication and flexibility in the task."
The Smart Mars Ground Vehicle and Mobile Laboratory, slated for launch as early as 2009, was originally driven as a solar-powered mission. But now the researchers are considering an upgrade from solar to nuclear energy: "Putting nuclear energy in the spacecraft will extend the mission from 3-6 months [with solar energy] to 5 years [with radioisotope energy]," says Ed Wheeler, head of the space science project at Nass headquarters. A. "It will allow the vehicle to drive to the site instead of having to land there. The bandwidth for data communication is much increased, and the vehicle can operate 24 hours a day. Everything increases by a factor of 10 when a radioisotopic thermoelectric generator is added to the mission.
The upgrade from the Mars rover to a manned mission on Mars requires more power – about 30 kilowatts to heat and cool a human living environment, operate computers and lighting, create oxygen, recycle water and recharge the ground vehicle, says Jeff George. For a long mission, "we don't have the energy to run back home [in an emergency]," adds Gary Martin, associate administrator for advanced systems at NASA's Space Agency. "You build things that have to be extremely reliable, have the ability to repair themselves, and feel independent when they are damaged." It will be necessary to manufacture or repair broken parts on the spot: it is impossible to bring spare parts. Power-intensive processes such as manufacturing parts or creating the driving force to leave Mars would be another 60 kilowatts, according to George.
Above: It's not the Las Vegas Strip, but the first colony on Mars will still need a lot of electricity. Image source: Frassanito & Associates, Inc..
Ultimately, one energy source does not fit all needs. Looking at the whole picture, John Mankins says “We need very high efficiency, high power electric propulsion for interstellar flight; We need reliable high-energy chemical propulsion systems that are within the range of possibilities for landing on the surface of the stars and taking off from them; And we need the ability to store chemical or solar energy to live and work on the surface of the stars. Robots will be able to use radioisotopic energy; And we must also consider energy from a hookah and wireless screening."
The selection is many, but one thing is clear: wherever we fly in space and whatever we do there, we will need more energy.
Translated by Nahum Sherashevsky, professional translation and technical translation, NIS 45 per 250 words (in the Hebrew version). Dew. 02-6435139
To Nahum Sherashevski's website
to send e-mail
