NASA's new spacecraft will fly with light

In 1418, European sailboats left theirports to explore the Atlantic Ocean, and the era of great geographical discoveries began. In 2018, a small space probe will deploy the sail and begin the journey to a distant asteroid. This will be the first NASA spacecraft to move beyond the orbit of the Earth solely through sunlight. Such technology could open the way for low-cost exploration of the solar system and ultimately interstellar space.

Near-Earth Asteroid Scout probe worth 16million dollars is among the 13 valuable goods announced by NASA the other day. All of them will go together with the launch of the Space Launch System, a large rocket designed to replace space shuttles that will once take the Orion spacecraft to Mars.

It will take 2.5 years for NEA Scout to reachdestination, a small asteroid 1991 VG. But it will not be a relaxed cruise. Continuous traction will be provided by sunlight striking a solar sail, and it will accelerate the probe to a speed of 103,000 km / h relative to the Sun.

After a certain time, a spacecraft equipped with a solar sail can accelerate more than a spacecraft of similar sizes with a conventional chemical rocket.

“The sail wins the race in terms of ultimatespeed like a turtle goes around a hare, ”says Les Johnson, technical advisor for advanced NASA concepts at the Space Center. Marshall. A chemical rocket provides huge initial thrust, but ultimately burns its fuel. “Since the sail does not use any fuel, we can maintain traction while the sun is shining.”

Content

• 1 Lightweight material
• 2 Light movement
• 3 Positive energy
• 4 Next stop: Alpha Centauri

Lightweight material

Solar sails made of ultra-thin materialwith high reflectivity. When the sun’s photon hits the mirror surface, it bounces off the sail and transmits its momentum to the spacecraft - just like a billiard ball transmits its momentum when it collides with another ball on the table.

The idea of ​​a solar sail has existed since 1924,when the legend of Soviet rocket science Konstantin Tsiolkovsky and Fridrik Zander conceived a spacecraft "using huge mirrors from very thin sheets" and "the pressure of sunlight to achieve space speeds." Forty years later, science fiction writer Arthur Clark popularized this idea in his novel, The Wind of the Sun.

NASA began investing in solar technologysails in the late 90s. In 2010, the agency successfully launched a small sailing satellite into Earth’s orbit, where it remained for 240 days until it entered the atmosphere and burned out.

In the same year, the Japan Space Agencydemonstrated the possibility of using solar sails for interplanetary travel. The test apparatus was attached to the board of the Venusian probe "Akatsuki". A solar-powered device called IKAROS was discovered in space by a probe when it was 7 million kilometers from Earth. Six months later, IKAROS successfully flew past Venus.

Solar sails became possible thanks to the revolution in the field of electronics.

The thing is that the solar sail projectis a kind of hostage to Newton’s second law of motion: force is equal to mass times acceleration. The power of sunlight is constant, so to achieve high acceleration you will need low mass.

“25-30 years ago, electronics was notso easy, says Johnson. - It was impossible to imagine the construction of a sufficiently small spacecraft that would not need a huge sail. With the advent of smartphones and the miniaturization of components, now we can make a really light and small spacecraft, which means it will need a sail of a reasonable size. "

Johnson cites CubeSat as an example - miniaturedice satellites built from "ready-to-use" technologies. The NEA Scout will be a CubeSat the size of a shoe box that a 86-square-foot solar sail will push. m

Despite its modest size, the probe is packedenough tools to conduct extensive research on the 1991 VG asteroid, photographing and measuring the chemical composition, size and movement of the object.

NASA sees in such intelligence an important first step towardsfuture manned missions to asteroids. If an astronaut is about to explore the surface of a cosmic rock, NASA wants to be sure that it is spinning in a slow and predictable way, and not spinning around in different directions. Similarly, the space agency wants to know in advance whether the asteroid is solid or represented by a pile of stones held by gravity.

Light movement

During its mission, NEA Scout will implement bothat least one slow approach at close range - its speed will drop to 10 meters per second, and the device will pass half a kilometer from the surface of the asteroid. This indicates another advantage of solar sails: they are very maneuverable, sometimes even superior to traditional methods of movement.

The key to sail control - be it the Atlanticocean or space - lies in the creation of asymmetric thrust. There are many different ways to create it using the celestial equivalents of masts and rigging. IKAROS has an electro-optical coating that darkens when voltage is applied, absorbing light rather than reflecting it. It is thus possible to “tune” part of the sail so that it receives half the sun than the other, and deploy the apparatus.

NEA Scout will take a different approach using a sliding mechanism that moves the CubeSat forward and backward relative to the frames on which the sail is deployed.

“If you imagine a can of cola, which willwith our machine, and place a sheet of paper flat on top, it will be a sail, ”says Johnson. - Then imagine that you are just physically moving the sheet left and right. That's how it will be. ” Tilt the sail also allows you to adjust the speed.

The flexibility of a spacecraft with a solar sail - combined with constant thrust, thanks to an inexhaustible supply of fuel - opens the way to several interesting possibilities.

Say you want to send a probe above a planeecliptic solar system to explore the north pole of the sun. To dramatically change direction and speed — without using precious fuel — engineers usually rely on gravity. “Now we have to send the spacecraft to Jupiter for a gravitational maneuver to get it out of the ecliptic plane and get a larger orbit around the Sun,” Johnson says. “With a sail, it will be quite simple to direct it up.”

Another potential application is already closer tohome, this is a "sitting on the pole" satellite. Now, if you want to fix a satellite in a certain position relative to a place on Earth - and this would be very useful for communication technologies - you can only send it to a geostationary orbit, strictly above the equator, to an altitude of 35,786 kilometers above the Earth.

But with a sail "you can be above the Northor the Earth’s South Pole and spin around the Sun at the same speed as the Earth rotates around the Sun, ”says Johnson. - To overcome the Earth's gravity, it is enough to direct the sail so that it pushes you up all the time. Thus, you hover motionless over the North or South Pole. ”

Positive energy

Photons - which we see as sunlight - are notthe only fuel for the spacecraft produced by the sun. NASA scientists recently received additional funds to research the advanced concept of ultra-fast sail, propelled by charged particles in the solar wind.

It is called an electric sail, e-sail. This idea was first proposed by Pekka Janhunen, a researcher at the Finnish Meteorological Institute. He presented an apparatus surrounded by 20 thinnest wires each 20 kilometers long.

These wires generate a positively chargedan electric field stretching tens of meters into space. The protons of the solar wind traveling at speeds above 750 kilometers per second are repelled by this electric field, in response to expelling the spacecraft. Negatively charged particles of the solar wind are quenched by a kind of "electron gun", so that the electric sail maintains a positively charged electric field.

The electric sail will have a lot of fuel. If the sunlight pushing the solar sail weakens significantly when the spacecraft reaches the asteroid belt, the solar wind still blows violently. Over time, the electric sail can be accelerated to 100-150 km / s.

This means that space probes can reachJupiter in just two years or Pluto in five. An electric sail can provide completely new opportunities for space exploration, allow us to carry out an express journey outside the solar system, into interstellar space.

Voyager 1 took 35 years to reach the borders of the solar system. A solar sail would carry out such a tour in 20 years, and an electric sail in 10.

“I must admit, two and a half years ago,when my boss came to me and said, “we want you to look at this,” I frankly neighed, ”says Bruce Wigmann, NASA's systems engineer. - Then we looked and said, they say, very interesting. They have gone from unbelievers to believers. ”

In fact, Wigmann believes that the prototypecan be launched in just five years. But you have to solve a couple of important issues. Although an electric sail does not need fuel, it needs a powerful source of energy for an electron gun that beats electrons. How much energy? Depends on the number of electrons that the electric sail collects. NASA experts are studying this issue using a charged wire in a plasma chamber simulating the solar wind.

Another problem is preventingbends of thin long wires as they are exposed to the solar wind. Solution: rotate the device at a speed that will provide enough centrifugal force so that the wires remain stretched.

Next stop: Alpha Centauri

Outside of NASA, Forest Johnson has another job: he writes science fiction. In fact, he is grateful to the 1974 novel “The Bitch in the Eye of God” for arousing interest in solar sails.

No wonder he dreams of a distant future. He wants the solar sail to go to another solar system.

“We could build a big laser,” sayshe. - As the sail moves away from the Sun and the sunlight becomes less and less, you can highlight it with laser light, continuing to move. The laser will remain in the orbit of the sun, continuing to accelerate the sail faster and faster until it leaves the solar system. ”

Of course, technical difficulties remain,which will have to be decided. First, the sail should be the size of Texas. And the orbital laser will have to generate energy, the volume of which can be compared with that which the whole world is producing today. It sounds, of course, so-so, but a lot can be done in a hundred years.

The first spacecraft created by humans andsent to another system, can arrive there as its oceanic ancestors during the era of the Great geographical discoveries: under deployed sails, sailing through the stars.