Reinventing Space Flight

 

Ancient people saw auroras as messages from the gods, while modern science has linked them to electrified gas hurled by the sun. Now, a team of researchers is exploring plasma as a potential energy source for space travel. Dr. Ben Longmier and his team from the University of Michigan have designed a new type of rocket engine that promises faster and more efficient space travel. They are testing the rocket components by sending them aboard helium balloons to an altitude of 30 kilometers in the harsh environment above the North and South poles. The team aims to revolutionize space travel by tapping into the power of plasma, the fourth state of matter.

Traditional chemical rockets, which have hardly changed in over a hundred years, are not very efficient. The heavier the payload, the more fuel a rocket needs to lift it into space. However, more fuel means more weight and more fuel needed. This limits the distance a spacecraft can travel. Ben's rockets promise greater fuel efficiency and enough power to reach distant targets more quickly. The rockets use electricity to create a weak force in space, running on the same fuel that powers the cosmos - plasma.

Plasma is a unique state of matter that occurs in rare circumstances on Earth, such as in a flame, lightning, or an electrical transformer. It is made up of negatively charged electrons and positively charged ions, balancing each other out. The ionosphere, a natural plasma ceiling high above the Earth, reflects and absorbs radio waves. Engineers discovered that radio signals could be bounced off the ionosphere, leading to advancements in global communications during World War 2.

Ben and his team want to test their rocket components in the plasma-filled environment of the upper atmosphere. They plan to mount the components on a frame attached to a high-altitude balloon, equipped with sensors to measure various factors. The team is also using bacteria colonies and modified GoPro cameras to detect radiation and record infrared and ultraviolet light intensity. Their goal is to design spacecraft that can harness the explosive properties of plasma, which plays a significant role in the formation of structures like galaxies and black holes.

A complex and volatile substance it can be. In the core of our sun, high heat and crushing pressures cause hydrogen atoms to crash together. That sets off a nuclear reaction in which hydrogen atoms fuse into heavier ones like helium and carbon, generating heat. This heat slowly rises to the surface of the sun in vast plumes of plasma. You can see evidence of this process, called convection, in a pattern of ever-evolving blobs known as granules. They are like the tops of thunderstorms. Even as energy builds within, the sun's gravity and density can stifle its escape. What carries it out are magnetic fields. They twist and wrap around, channeling energy to the surface. The fields can power immense loops of hot gas, about 60,000 degrees Celsius, then rise up from the solar surface and fall back. The largest eruptions, called coronal mass ejections, can reach up to 6 million miles per hour as they hurtle out across the solar system. They can literally slam into Earth's own magnetic field. Because solar particles are charged, a portion follows the orientation of Earth's magnetic field lines. Finding an opening at the poles, these particles race down into the atmosphere. You know this is happening when you see the beautiful lights of the aurora borealis in the far north, or the aurora australis in the south. They appear when charged solar particles collide with oxygen molecules in the upper atmosphere, causing them to glow blue, red, and green depending on altitude. Flying 350 kilometers above the Earth, astronauts in the International Space Station watch in awe as the aurora shimmers, framed by the glow of stars and cities at night.

Back in Michigan, Ben and his team have set up a lab to harness this strange substance in a whole new generation of rocket engines. The lab recalls an earlier period of space exploration. It features a giant vacuum chamber, built in the 1960s in hopes of winning a contract to test Apollo moon rovers. The chamber has given this small university team the ability to accelerate their research into the physics of plasma and rocket engine design. They are actually part of a larger community of plasma rocket scientists within NASA and within private companies like Ad Astra of Houston, Texas. Because plasma does not occur naturally on Earth, the challenge is to create it, then harness it.

The teams inject a gas, commonly argon, into a chamber. They bombard it with radio waves, which strip electrons from the gas and turn it into a plasma. The soup of electrons and ions accelerates as it moves through a magnetic field generated by superconducting magnets. A second radio blast heats it up to a million degrees Celsius. That's enough to blast it out and propel a spacecraft.

The idea of using plasma to power rockets is not a new one. The Polish physicist Stanislav Ulam is said to have been inspired by atom bomb tests in the 1940s. He speculated that waves of plasma from small nuclear detonations could propel a spacecraft to extreme speeds. In the 1950s, that idea animated dreams of exploring the solar system in spacecraft like this 360-ton Mars-bound vehicle. The idea gained funding in the Orion project, with the idea of driving a spacecraft with nuclear pulses and landing on Mars in only a month. Concerns about radioactive exhaust helped doom the project.

Plasma rockets, energized by nuclear reactions, were revived in the Daedalus and NERVA projects of the 1960s, and again at the beginning of this century as part of a proposed journey to Jupiter's moon Europa. Rising costs killed that mission. Newer plasma rocket concepts have switched to solar energy to power their engines. Among the most ambitious, the Dawn mission was sent into orbit aboard a Delta 2 rocket in the year 2007. It then headed out on a ten-year mission to the asteroid belt. It uses only about 10 ounces of xenon gas fuel per day. With engines designed to fire for over 2000 days, over time it is expected to gain an additional 38,000 kilometers per hour. After a gravity assist from Mars, Dawn arrived at the asteroid Vesta in 2011. It spent a year mapping its surface and seeking clues to its interior structure. Now headed for Ceres, a dwarf planet located within the asteroid belt, Dawn will be the first probe ever to visit. Made up of rock and ice, Ceres may well have an internal ocean of water and ice. It takes us back to the formation of the solar system, when objects like this grew and developed into planets. Long-range missions like Dawn are just one of many uses for plasma rockets. So NASA launches spacecraft with ion engines and hall thrusters on board. Almost every new geostationary satellite that a company will invest in and put up in orbit will have some sort of electric propulsion device on board to do station keeping, to do little changes in attitude and maneuvers.