|Beam Me to Mars||
"Are we there yet?" Everyone has faced this exasperating question from impatient companions on a long road trip. Imagine if the trip lasted six months. One way. |
It takes conventional rockets about six months just to get to Mars. Total roundtrip times can be as long as three years, because an extended stay on the Red Planet is required while the Earth and Mars progress in their orbits enough to be closely aligned again for the return trip.
However, future astronauts may race to Mars up to six times faster by riding a beam of electrified and magnetized gas (plasma). A roundtrip Mars mission could be completed in about 90 days using the Magnetized Beam Plasma Propulsion (Magbeam) system proposed by Dr. Robert Winglee of the University of Washington.
How it works and where it came from
The proposed Magbeam system will use space stations to generate the plasma and beam it to a spacecraft. The spacecraft generates its own magnetic field, which deflects the plasma beam. Like wind pushing on an umbrella, the deflection of the plasma beam generates a force that propels the spacecraft. Another space station orbiting the destination generates a beam to slow down the spacecraft upon its arrival, and to launch it on the return journey.
Image above: Artist's concept of a space station in low Earth orbit fitted with the Magbeam system. The Magbeam unit extends from the bottom module of the station, and the blue line represents the plasma beam. The plasma beam links magnetically to the target spacecraft on the bottom right, launching it on its journey. Image credit: U. of Washington/Robert Winglee. Click here for a 3.6 meg print-resolution image (tif format)
Research into this radical design is being funded by the NASA Institute for Advanced Concepts (NIAC). NIAC was created in 1998 to solicit revolutionary concepts that could greatly advance NASA's missions from people and organizations outside NASA. The proposals push the limits of known science and technology, and thus are not expected to be realized for at least decade or more. NIAC's intention is to discover ideas which may result in beneficial changes to NASA's long-range plans. The Universities Space Research Association operates NIAC for NASA.
Why it works
Conventional engines that generate plasma for propulsion, like ion engines, can eventually reach high speeds because they are extremely efficient. However, they produce very low levels of thrust, so it takes a long time for spacecraft to reach high speeds using ion engines. This makes them impractical for human space flight. However, the Magbeam system gets around this problem by separating the engines from the spacecraft.
"Keeping the heavy power and plasma generation system separate from the spacecraft is our key breakthrough," said Winglee. "In the same way that you can push a chair faster than a piano, the spacecraft then has much less mass, but the same force is pushing on it, giving it relatively high acceleration."
Also contributing to the high acceleration of the Magbeam system is the high density of its plasma; the higher the plasma density, the greater the thrust. Magbeam uses intense radio waves to strip electrons from the atoms of its propellant, creating a plasma that is 100 times denser than what is generated by typical ion engines.
Magbeam to Mars
A typical Mars mission would begin as Earth and Mars are approaching the point of closest alignment as they progress in their orbits, with the Earth slightly behind Mars. A conventional rocket first launches the target spacecraft into orbit around Earth. The Magbeam station, called the High Power Platform (HPP), would fire a plasma beam at the target spacecraft for about four hours, giving it a boost of about 20 kilometers per second (12.4 miles/sec.) toward Mars. The spacecraft coasts to Mars in about 50 days, after which another HPP in orbit around Mars fires a plasma beam at the spacecraft to slow it down.
The spacecraft goes into orbit around Mars and the astronauts descend to explore the surface. After 11 days, they launch to Mars orbit, where the Martian HPP fires its plasma beam again to accelerate the spacecraft toward Earth. After about 35 days coasting toward Earth, the HPP in orbit around Earth fires its plasma beam at the spacecraft to capture it in Earth orbit.
Differences between departure and return travel times are due to the two planets progressing in their orbits. In this case, the return distance is shorter. During the coasting periods, the HPPs can recharge their batteries, if a solar-powered system is used (this would not be necessary if a nuclear-powered system is used).
The HPPs will fire their plasma beams during this period as well, but not at the target spacecraft. Instead, they will use them as an ion rocket engine to regain their original orbits. This is because firing the beam at the target spacecraft also exerts a force on the HPP stations, altering their orbits.
The technical challenges
To make this system a reality, the primary challenge that must be overcome is keeping the plasma beam focused over long distances. Other naturally-occurring plasmas in space act to disperse the beam. For example, the Sun continually emits plasma as the solar wind, and occasionally blasts billion-ton clouds of plasma into space when magnetic energy in the solar atmosphere is violently released.
"By the time the HPP station has finished accelerating the target spacecraft, the two will be separated by several tens of thousands of kilometers (miles)," said Winglee. "We don't think this will be a problem, because nature creates plasma beams over similar distances. Also, the beam in our system links to the magnetic field around the target spacecraft, closing a circuit for an electric current that makes the beam self-focusing. Finally, our plasma beam is billions of times denser than natural space plasmas."
Image above: Artist's concept of magnetic nozzles for the Magbeam system. The magnetic nozzles (series of blue and orange rings) help to focus the plasma beam over long distances. Image credit: U. of Washington/Robert Winglee Click here for a 2.7 meg print-resolution image (tif format)
If the challenges can be overcome, the Magbeam system will offer several benefits: First, a fast trip to Mars will reduce the space radiation hazard to astronauts. High-speed particles from the Sun and interstellar space continually bombard any spacecraft traveling between planets. However, this space radiation can be deflected by planetary magnetic fields or absorbed by a planet's atmosphere. Getting astronauts quickly from one planet to another will reduce their exposure to space radiation. The high-speed makes Magbeam useful for missions beyond Mars as well, "We think this would be a good system for delivering payloads to Jupiter and beyond," said Winglee.
Image above: Artist's concept of a Magbeam station at Jupiter. The plasma beam, represented by the blue line, links to the magnetic field generated by the target spacecraft (top right). Image credit: U. of Washington/Robert Winglee. Click here for a 365 k print-resolution image (jpg format)
Also, the HPP stations can be used over and over again. The heavy, expensive power and plasma generation system does not have to be rebuilt and launched for every mission. This will greatly lower the costs for the Mars exploration program.
The Magbeam system will also save costs by reducing the mass required for a Mars mission. To boost a 10,000 kilogram spacecraft to Mars at 20 km/sec with Magbeam consumes about 7,000 kg of propellant. A chemical rocket would require 18,000,000 kg of propellant. With current launch costs around $10,000 per kilogram, the savings with the more efficient Magbeam system are significant. (One kilogram is about 2.2 pounds.)
Additional mass savings are possible if a second HPP is placed in low Earth orbit (LEO). The LEO HPP can boost the spacecraft from suborbital speeds to orbit, then it can launch the spacecraft to a high orbit where it can be targeted by the other HPP for the boost to Mars.
"Once the technical challenges are overcome, the Magbeam system will offer faster travel, improved safety, and lower costs for planetary exploration missions," said Winglee.
More about Magbeam (PDF document)
The Vision for Space Exploration
NASA Goddard Space Flight Center