“No good. I can't install all six coils in forty minutes.” The defibrillator's beep interrupted them. Might as well give the poor bastard one last chance. David set the paddles in place and squeezed the buttons down.
“Time's up.” He dropped the paddles without waiting to see the results, and hurled himself out of the cabin, towards the first access panel, with Porter on his heels. He handed her three coils and helped her into the tunnel. As she pulled her legs in and grabbed a voltmeter, the monotonous buzz of the alarm stopped, replaced by the irregular beep of a heartbeat.
* * * *
Mars loomed large, a great, rusty disk filling the viewscreen from edge to edge. David muttered a silent prayer and pulled the magbeam harness release handle. The McAuliffe shook with a series of sharp cracks as the explosive bolts fired. Six red lights flickered, went blank, then turned to green. Weight vanished as the ship's drive floated free, and the view tilted as the McAuliffe oriented herself to meet the Martian atmosphere.
David turned to Porter, strapped into the cockpit next to him. “It worked. The harness is loose. The referee just raised our glove."
The viewscreen washed white, and a rumble of thunder drowned out Porter's reply as the aerobraking began. David closed his eyes while the ship shook and bucked around him, and the heat and the roaring propelled him back through the years, to a time when he'd stood in front of a crowd, tired and bloody but unbeaten, in a boxing ring under the desert sun.
* * * *
A combination of fatigue and Martian gravity anchored David and Porter in their seats while they watched a tank-like vehicle roll across the rocky surface to meet them. The wind whistled softly over the McAuliffe, like a new father soothing a restless infant. A cloud of red dust roiled up from the vehicle's treads and spun away to the south, whirling off toward the star-crowned horizon of an alien world.
David turned his gaze to Porter. “Welcome to Mars, Vicky."
* * * *
David fastened his seatbelt and gazed out at the disk of blue and white visible through the shuttle window. In a few short hours, he and Porter would be landing at Dulles spaceport to face more cheering crowds. In the evening, they were due at a presidential dinner. It seemed like the whole world had listened to his emergency broadcast, prayed for the fate of the colonists, watched through the Martian cameras while they landed.
But however much the public and media trumpeted his supposed heroism, six months after the fact, saving the Martian colonists seemed a hollow victory. David couldn't shake the feeling that Ellen should have been there with him. On arriving at HEO the day before, he'd found Gin waiting—waiting to deliver his decommissioning papers. He'd passed the mandatory retirement age for active space duty during the flight home from Mars, and was sentenced to a life's imprisonment on the surface of the Earth, with no right of appeal. He'd boarded the shuttle headed for LEO after only a few minutes’ good-bye. She'd leave for Mars soon, to take up her new post as Colony Coordinator. She'd be fine, he was sure. They'd probably exchange messages at first, then she'd become too submerged in the work to remember him, casting aside her old life in the Space Transit System for a new one in the colony.
Beaume had survived. STS was set to settle quietly to prevent any claim of malfeasance, even though the inquest suggested Beaume's own careless attempt at a battery check had caused the accident. He'd soon be sitting pretty in some tropical paradise on Earth, surrounded by beautiful women who only wanted his money and not the cripple in the wheelchair. David didn't envy him.
“You're drinking in that view like it's a desert oasis."
David turned his attention to Porter, still fumbling with the straps of her harness. She'd never mastered weightlessness despite all the long hours traveling to Mars and back. He reached over to help her.
“Thanks.” She flashed him a smile and glanced out of the porthole. “These presidential receptions are only one-night stands. You'll be back up here before you know it."
The mournful look on his face must have revealed the truth.
“You're not coming back, are you?” she said. “Oh, David, I'm sorry. I know how much you love it out here. What will you do?"
“I don't know. I'd like to make sure that Christa McAuliffe, Ellen Francis, and the two colonists who died on Mars aren't forgotten when some new president decides to pull the plug on the space program. Perhaps I'll do the rounds of the talk shows, let Hollywood make their vid of my life story, and advocate like hell for more space investment while people still remember who I am."
“Hm. Fame's a fleeting thing, and fans can prove fickle in the long run."
David looked again out the window. “The ‘26 elections are coming up. I could file for the Senate seat left vacant after Senator Ferrera's heart attack. A senator could be a powerful friend to the space program. I've never really seen myself as the Washington type, but maybe I should strike while the iron's hot."
Porter lifted an eyebrow. “And your kids at the gym? Your grandchild? Will you still find time for them?"
“Wyoming's a short hop from Washington by scramjet. Besides, how much more good could I do from Congress? Keeping space open as a possibility for those kids is just as important as what I do at the gym. What will you do when you get back?"
Porter gave him a crafty look. “I've been offered a promotion from Assistant Director of my division to Associate Director of Technology."
“Sounds impressive."
“One step below the top; without even a spell as Deputy Associate Director first. And the director's already made it clear he won't stay for a second term when the president carries the ‘28 elections. I'll be nicely positioned to move into the open slot."
“So the headlines helped a little, did they?"
She blushed.
“The president is bound to ask your opinion of the space program at the dinner tonight,” David said. “What will you tell her?"
“Well, I didn't find anything significantly wrong with STS, however much I wanted to. There's no indication of malfeasance, fraud, or inefficiency. The only problems are down to underfunding. It'll be up to her to decide what to do with my report. What will you advise her to do?"
David narrowed his eyes. She was getting at something. “I'll tell her to back the Mars colony one hundred percent."
Porter nodded. “And what will you offer her in return? It would be political suicide for her to resist expanding the Mars colony transport system right now, but with all the attention you'll be focusing on disaster contingencies, and her ‘24 campaign promises about building arcologies, she'll need something to demonstrate her commitment to people stuck here on Earth. She also has to balance the budget. You'll need to offer her something of equal value."
He shook his head in confusion. “Give me an example."
“Tell her to pull out of the US/EU Jovian expedition and use its budget to build arcologies on Earth."
“The Jovian expedition is the next step toward colonies at places beyond Mars. I can't recommend it be cancelled!"
Porter snorted. “Amateurs. Always thinking they can have it all. If you want to survive more than five minutes in Washington, learn that life is about compromise."
David opened his mouth, closed it, then nodded ruefully. “All right, I'll do it. I'll recommend postponing the new Jovian expedition in favor of expanding the Mars colony."
Did he detect disappointment? Porter's face settled into the old, frosty look he hadn't seen since their landing on Mars. David gazed out the window for a few moments. “We can launch the Jovian expedition much more economically from an independent Martian colony, anyway."
Beside him, Porter shook with peals of laughter.
* * * *
Jodie looked out the shuttle window at the receding Earth, thankful that her husband and son were waiting safely on Mars to begin their trip to the new colony on Ganymede. Below, a cancerous black cloud obscured half of Montana and most of Wyoming, blanketed South Dakota and Nebraska, then crossed the Mississi
ppi, creeping relentlessly eastward. The eruption of the Yellowstone supervolcano was only eleven hours old, but already death tolls were rising. The vulcanologists didn't know when it would stop, or how much of the world would be left.
She glanced down at the pamphlet in her hand, read her grandfather's name on the cover: David William Longrie. She'd attended his funeral service with her mother only the day before. So many years spent as a champion of the space colonization effort, warning against an event exactly like the one occurring now. At least he hadn't perished in it the way his own father had died in the ‘21 eruption. How ironic the eruption should start on the day of his memorial service.
Jodie's gaze returned to the window. She hoped her mother would be safe in the arcology under Mexico. The evacuation of the selected few was underway, starting the week before when the first rumblings sounded deep beneath the earth. That nice doctor who'd given her mother the arcology lottery ticket five years ago had attended the service as well. Jodie couldn't remember her name. Although elderly, she'd been ramrod straight, a quiet pillar of strength among the mourners, paying her respects to a great man.
Copyright © 2006 James Grayson and Kathy Ferguson
[Back to Table of Contents]
* * *
Science Fact: Solar System Commuter Trains: Magbeam Plasma Propulsion
by James Grayson & Kathy Ferguson
In the age of the Internet, when communication moves faster, when cramjet technology makes it possible to be anywhere on the planet in a matter of hours, we still don't have the ability to investigate our nearest planetary neighbors in anything less than years, and then only when the planets are in optimum alignment. With the success of SpaceShipOne, the first reusable manned spacecraft to reach orbital altitudes twice in a two-week period, we stand on the cusp of a new age, where getting people and supplies into orbit may become as commonplace as flying from New York to California.
Once we reach orbit, how do we travel around our own neighborhood and beyond in a safe, fast, and cost-effective manner? Because of the risk and immense up-front cost of even a single manned space mission, off-world colonies and interstellar travel have long been regarded as pipe-dreams by the astronautical establishment. But, at the annual meeting of the NASA Institute for Advanced Concepts (NIAC) in March 2005, Professor Robert Winglee, of the Earth and Space Sciences Department at the University of Washington, proposed a new kind of ion propulsion system that may make fast solar system travel and interstellar exploration a reality, a system that could allow astronauts to make a round trip to Mars in less than a hundred days [1]. He calls it MagBeam.
Ion Propulsion Systems
When a gas—usually argon or xenon—is sufficiently energized, electrons are stripped away from their nuclei, and the gas becomes charged (or ionized). Because of its charge, this cloud of ionized particles (or plasma) can be accelerated to very high speeds (tens of kilometers per second) by exerting a force on them with an electric or magnetic field. If these fast-moving ions are directed out of a spacecraft, they impart a force to the spacecraft according to Newton's Third Law. This approach does not produce very high levels of thrust, but it does have much lower fuel consumption than traditional chemical rockets, allowing ion drive spacecraft to continue accelerating for much longer periods of time. Thanks to the very high speed at which the ions are ejected, ion thrust is ultimately capable of propelling a spacecraft much faster than chemical propellant drives.
Using a stream of ions to propel a spacecraft is not a new concept. It was used in the Russian Zond-2/1 satellite in 1964, and the USAF/TRW Vela/2 craft in 1965[2]. Satellites presently in orbit around Earth use ion propulsion to keep themselves in position and prevent their orbits from decaying over time. On a larger scale, the Deep Space-1 (DS-1) vessel, launched in 1998, used an ion drive for its flyby of the asteroid Braille and Comet Borrelly, while the Dawn mission will carry three separate ion drives for its flyby of Vesta and Ceres when it sets off in May 2006 for the asteroid belt beyond Mars [3,4].
Helicon Plasma Propulsion vs.
Electrode Ion Drives
All of the systems on these spacecraft use what are known as electrode ion drives. The typical design is called a gridded ion drive [2]. These use an electron source to energize the fuel gas, splitting it into negatively charged electrons and positively charged ions. A metal grid, held at high voltage, attracts the positively charged ions, which pass through the grid and out of a nozzle at high speed, creating thrust for the craft. Meanwhile, the electrons are gathered and reintroduced into the exhaust to neutralize it and prevent charge building up on the spacecraft. The voltage of the grids can be adjusted to vary the thrust, varying the velocity imparted to the ions.
The problem with this approach is that to get the high levels of thrust needed to move larger payloads, the power requirements and grid sizes become so large that they're no longer practical [5]. And, as the level of thrust is increased, the grid electrodes begin to erode, limiting the useful lifetime of the system.
By contrast, the MagBeam system proposed by Professor Winglee uses a helicon plasma source to create thrust, rather than a gridded ion drive. A helicon consists of a quartz tube with a radio antenna wrapped around it [6], into which gas is injected (again, usually argon or xenon, although almost any gas can be used). Radio frequency (rf) electric currents are passed through the antenna, and the rapid variation of the electric field ionizes the gas. The ionized gas is then accelerated by electric or magnetic fields to produce thrust.
The helicon technology has several advantages over gridded ion drives. First, it produces more efficient ionization than a gridded system, resulting in a much denser plasma, which can produce much more thrust. Second, while a gridded electrode system has to grow in size in order to produce more thrust, a helicon system can simply use more power to produce more ionization. For example, a gridded ionization system with a 40-kW power source would need to be 5 to 10 times larger than a helicon system using the same power source [7]. This compactness is of great benefit in space missions, where every kilogram of mass has to be paid for in extra fuel consumption. Finally, because the ionized gas never comes into contact with the antenna producing it—the system has no electrodes—the helicon system does not experience the erosion that limits the lifetime of electrode ion drives, and has an essentially infinite lifetime.
Helicons, with their potential for increased thrust and decreased wear, have obvious advantages over electrode ion drive systems. However, another property of the helicon technology is even more important for the MagBeam system. Most ion drives produce quite broad plumes of exhaust, but if the exhaust doesn't hit the spacecraft superstructure, no one really cares about the dispersion. In MagBeam, however, the helicons produce a much tighter beam of ions, because the magnetic field that accelerates them is “frozen” into the plasma and carried along with it, creating an elongated magnetic field continuing out into space. (See Figure 1.) When a focusing magnet is used, the result is a tight beam with very little divergence, much like a laser. Even in a conventional system, this is a significant advantage; it can yield an improvement in efficiency of about 50% over normal ion drives [1].
* * * *
* * * *
Figure 1 (image used courtesy of Robert M. Winglee):
Magnetic field distortion with MagBeam propagation.
* * * *
In MagBeam, though, the dense, focused beam is crucial to how the system works. That's because, in MagBeam, the helicon doesn't push itself through space, but sends its ion beam through space to push other spacecraft. So, how does this translate into more efficient space travel?
How the MagBeam System Works
In the January/February 2004 issue of Analog, Gary Lai reported on efforts by Professor Winglee's team to produce a craft (dubbed the “M2P2” for Mini-Magnetospheric Plasma Propulsion) that used a giant magnetic ion bubble to extract thrust from the solar wind—the stream of fast-moving ionized particles that flows outward from the Sun [8].
This concept, while interesting, proved impossible to demonstrate adequately on the ground because of the scale of the testing facilities required [7]. Technologies that cannot first be proved on the ground cannot be included in space test missions. However, the limited, on-ground testing stage of that project sparked an idea for a new and different propulsion system, with potentially revolutionary capabilities: MagBeam.
* * * *
* * * *
Figure 2 (image used courtesy of Robert M. Winglee):
Schematic layout of MagBeam system.
* * * *
While the University of Washington group was testing the M2P2 prototype in the laboratory, they conceived the idea of using a plasma thruster to imitate the solar wind. The solar wind is itself a plasma, although very much less dense than that produced by any kind of ion drive, so using a plasma source to simulate it was a natural decision. This experiment inspired the idea of using a plasma source to beam energy across space to an unpowered spacecraft and became the basis of the MagBeam system. It works like this:
Professor Winglee proposes the use of orbiting platforms carrying high-power helicons, each able to focus a very dense ion beam with a power of about 300 megawatts onto a transport spacecraft from a distance. These transport craft carry a small store of a gaseous propellant, such as argon or xenon, and a set of electromagnets, in addition to a small power source and a payload. The propellant is ejected into space, where it is heated and ionized by the incoming plasma beam. This ionized gas is then repelled by the electromagnets, imparting thrust to the craft in reaction. (See Figure 2 for a schematic of the system.) A good analogy is driving a floating bottle along by splashing stones in the water just behind it. The platform carrying the helicon remains in orbit, pushing the spacecraft away at high speed, while a similar platform at the destination uses its plasma beam to slow the vessel down again when it arrives.
Unlike the earlier M2P2 project, where the force of the solar wind against the ion bubble was always directed away from the Sun, a MagBeam system can impart thrust in any direction simply by having the target craft eject the propellant gas in a different direction (or, in the analogy used before, splashing the stones on the other side of the bottle). A large bubble or sail area to intercept the plasma beam is not required. The payload spacecraft doesn't have to carry a massive power source or large store of propellant, because all of this equipment is on the orbiting platform instead. The energy for propulsion is beamed to the vessel through space, rather than being carried with it, making it far lighter than any existing craft can be.
Analog SFF, June 2006 Page 7