Magnetic propulsion system offers new possibilities for space exploration

New electromagnetic propulsion technology being tested by the University of Maryland’s Space Power and Propulsion Laboratory (SPPL) on the International Space Station could revolutionize the capabilities of satellites and future spacecraft by reducing reliance on propellants and extending the lifecycle of satellites through the use of a renewable power source.

Because a finite propellant payload is often the limiting factor on the number of times a satellite can be moved or repositioned in space, a new propulsion method that uses a renewable, onboard electromagnetic power source and does not rely on propellants could exponentially extend a satellite’s useful life span and provide greater scientific return on investment.

Associate Professor of Aerospace Engineering Ray Sedwick and his research team have been developing technology that could enable electromagnetic formation flight (EMFF), which uses locally generated electromagnetic forces to position satellites or spacecraft without relying on propellants. Their research project is titled Resonant Inductive Near-field Generation System, or RINGS.

RINGS was sent to the International Space Station on August 3 as part of a payload launched on Japan’s HTV-4 Cargo Ship from the Tanegashima Space Center. The project is scheduled for four test sessions on the research station. Astronauts will unpack the equipment, integrate it into the test environment and run diagnostics. From there, RINGS will undergo three science research sessions where data will be collected and transmitted back to the ground for analysis.

RINGS is composed of two units, each of which contains a specially fabricated coil of aluminum wire that supports an oscillating current of up to 18 amps and is housed within a protective polycarbonate shell. Microcontrollers ensure that the currents oscillate either in-phase or out-of-phase to produce attracting, repelling and even shearing forces. While aluminum wire was chosen for its low density in this research prototype, eventual systems would employ superconducting wires to significantly increase range and performance.

In the spring of 2013, RINGS was tested for the first time in a microgravity environment on NASA’s reduced gravity aircraft. UMD graduate students Allison Porter and Dustin Alinger were on hand to oversee the testing. RINGS achieved the first and only successful demonstration of EMFF in full six degrees of freedom to date.

“While reduced gravity flights can only provide short, 15-20 second tests at a time, the cumulative test time over the four-day campaign provided extremely valuable data that will allow us to really get the most from the test sessions that we’ll have on the International Space Station,” said Sedwick.

In addition to EMFF, the RINGS project is also being used to test a second technology demonstrating wireless power transfer (WPT). WPT may offer a means to wirelessly transfer power between spacecraft and in turn power a fleet of smaller vessels or satellites. Having the power to support multiple satellites, and using EMFF as a propellant-less means to reposition those same satellites, provides the flexibility to perform formation control maneuvers such as on-orbit assembly or creating synthetic aperture arrays. A synthetic aperture array uses a network of smaller antennas to function collectively as one large antenna. Larger antennas are capable of producing higher resolution images and better quality data.

The RINGS project has been a collaborative effort between UMD SPPL and partners from the Massachusetts Institute of Technology (MIT) and Aurora Flight Sciences (AFS). MIT’s SPHERES (Synchronized Position Hold Engage Re-orient Experimental Satellites) program provided SPPL an existing test bed of miniature satellites and control algorithms that will be used to integrate and test the RINGS technology. AFS has provided hardware development and support for the integration of RINGS onto the SPHERES platform.

Where comets go to die

A team of astronomers from the University of Anitoquia, Medellin, Colombia, have discovered a graveyard of comets. The researchers, led by Anitoquia astronomer Prof. Ignacio Ferrin, describe how some of these objects, inactive for millions of years, have returned to life leading them to name the group the ‘Lazarus comets’. The team publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society. Comets are amongst the smallest objects in the Solar System, typically a few km across and composed of a mixture of rock and ices. If they come close to the Sun, then some of the ices turn to gas, before being swept back by the light of the Sun and the solar wind to form a characteristic tail of gas and dust. Most observed comets have highly elliptical orbits, meaning that they only rarely approach the Sun.

Some of these so-called long period comets take thousands of years to complete each orbit around our nearest star. There is also a population of about 500 short period comets, created when long period comets pass near Jupiter and are deflected in orbits that last anything between 3 and 200 years. Although uncommon events, comets also collide with the Earth from time to time and may have helped bring water to our planet. The new work looked at a third and distinct region of the Solar System, the main belt of asteroids between the orbits of Mars and Jupiter. This volume of space contains more than 1 million objects ranging in size from 1 m to 800 km. The traditional explanation for asteroids is that they are the building blocks of a planet that never formed, as the movement of the pieces was disrupted by the strong gravitational field of Jupiter. In the last decade 12 active comets have been discovered in the asteroid main belt region. This was something of a surprise and the Medellin team set out to investigate their origin. The team, made up of Prof. Ferrin and his colleagues Profs. Jorge Zuluaga and Pablo Cuartas, now think they have an explanation. “We found a graveyard of comets”, exclaims Professor Ferrín. He adds: “Imagine all these asteroids going around the Sun for aeons, with no hint of activity. We have found that some of these are not dead rocks after all, but are dormant comets that may yet come back to life if the energy that they receive from the Sun increases by a few per cent.” Surprisingly, this can happy fairly easily, as the orbits of many objects in the asteroid belt are nudged by the gravity of Jupiter. The shape of their orbits can then change, leading to a decrease in the minimum distance between the object and the Sun (perihelion) and a slight increase in average temperature. According to this interpretation, millions of years ago the main belt was populated by thousands of active comets. This population aged and the activity subsided. What we see today is the residual activity of that glorious past. Twelve of those rocks are true comets that were rejuvenated after their minimum distance from the Sun was reduced a little. The little extra energy they received from the Sun was then sufficient to revive them from the graveyard. Prof. Ferrin describes the 12 active comets. “These objects are the ‘Lazarus comets’, returning to life after being dormant for thousands or even millions of years. Potentially any one of the many thousands of their quiet neighbours could do the same thing.”