SPACE: New propulsion technologies
Sun, 15 Aug 1999 09:48:14 EDT

In increasing order of "mad-scientist factor", here's three interesting pieces about promising new propulsion technologies (apologies if these have appeared here before; I've been weeding pretty ruthlessly in my in-box and may have missed a previous post of these items):

Sacramento - August 10, 1999 - NASA's Marshall Space Flight Center (MSFC) has awarded GenCorp Aerojet a multimillion dollar extension for continued development of the Strutjet Rocket-Based Combined Cycle (RBCC) engine through 2001.
This revolutionary propulsion system combines air-breathing and rocket engine technologies in a single engine for use on future reusable, single-stage-to-orbit launch vehicles. This type of engine allows the vehicle to take off horizontally, like an airplane, for greater safety and reliability and a dramatic reduction in cost of access to space. The Strutjet RBCC is a candidate as the primary propulsion for a third-generation space shuttle engine.

"Aerojet is proud to be working closely with MSFC as it moves forward on
reusable launch vehicle technology. We believe our technology will provide the capability for early demonstration of a vehicle powered by an RBCC engine," said Bob Harris, vice president, Strategic and Space Propulsion.

Since 1996, Aerojet has successfully progressed in building the Strutjet RBCC, which is part of MSFC's Advanced Reusable Technologies Project. This contract extension will refine the Strutjet RBCC into a highly integrated engine/vehicle concept, and a new emphasis will be placed on the development of flight-type cooled components, including the use of advanced materials and fabrication processes. These flight-type components will be exposed to engine thermal environments in a Component Development Rig at Aerojet's Sacramento site.

The Strutjet RBCC is an advanced, hydrogen-fueled engine that combines the best elements of air-breathing and rocket propulsion. It operates initially as an air-augmented rocket as it accelerates to low supersonic speeds, transitions to ramjet operation by turning off the rockets, then converts to a scramjet as flight speed increases. The rockets are turned back on as atmospheric oxygen diminishes, then the engine transitions to a high-expansion rocket for final ascent.

During the initial program phase, the Strutjet RBCC demonstrated superior performance and a robust operating capability in wind tunnel tests over the entire flight operating range. Also, Aerojet's patented cascade fuel injector efficiency and rocket durability and flexibility have been proven in the large number of tests conducted.

Aerojet, a leading proponent of RBCC propulsion, has demonstrated excellent performance using both hydrogen and hydrocarbon fuels, providing evidence of the flexibility of this engine. Aided by Aerojet technology advances on this program, NASA placed recent emphasis on continuing the advancement of this promising concept through flight.

Aerojet, a leader in propulsion, electronics and weapon systems, and fine chemicals, is a segment of GenCorp, a technology-driven company with strong positions in polymer products, automotive, and aerospace and defense industries.

Washington - August 12, 1999 - Researchers at NASA'ss Glenn Research Center have made for the first time tiny particles of frozen hydrogen suspended in liquid helium, a first step towards new rocket fuels that could revolutionize rocket propulsion technology.
In the experiments, small amounts of liquid hydrogen were poured onto the surface of liquid helium. The liquid hydrogen was at a temperature of 14 kelvins (minus 435 degrees F), just above freezing point; and the liquid helium was held at 4 kelvins (minus 452 degrees F), or just above absolute zero.

As the liquid hydrogen fell toward the surface of the helium, small, solid hydrogen particles formed and then floated on the surface of the helium.

The suspension will be used to make futuristic atomic fuels that take advantage of the chemical recombination of atoms into molecules.

"Atomic fuels will make possible rockets with liftoff weights one-fifth that
of today's or with payloads three to four times more massive," said Bryan Palaszewski, Glenn principal investigator for the experiment.

Using atomic fuels could reduce or eliminate on-orbit assembly of large space vehicles, thereby eliminating multiple launches and years of assembly time and making flights to all parts of the solar system less expensive and more practicable.

In atomic fuels, atoms of very active elements would be stored in a medium that prevents their recombination. Solid molecular hydrogen is a promising medium for storing and keeping atoms separate because it becomes solid at temperatures just a few degrees above absolute zero, where atomic activity due to heat is at a minimum.

Helium, in turn, is the ideal medium for creating and holding the solid hydrogen particles because it remains liquid below the freezing point of hydrogen. In the rocket's reaction chamber, or engine, the fuel would warm, and the atoms would be freed.

In less than an instant, they would recombine into molecules, and temperatures would go from 4 to 2000 kelvins (minus 452 to 3140 degrees F). Both hydrogen and helium would instantly vaporize and shoot out of the engine at tremendous speed, propelling the rocket forward.

Details about the behavior and characteristics of the particles are described in a paper presented at the U.S. Air Force High Energy Density Materials Meeting in Cocoa Beach, FL, in June of this year.

The advanced fuels experiments are part of Glenn's continuing efforts to advance the state of the art of propulsion technology. The experiments were conducted under the auspices of the NASA Advanced Space Transportation Program (ASTP), led by NASA Marshall Space Flight Center, Hunstville, AL. Current research is underway with an extensive team that includes researchers from Glenn, Marshall, the U.S. Air Force, the Department of Energy, universities and industry.

Fusion fuels dreams of space travel

Concepts could yield new propulsion techniques in a few years Terry Kammash, an astrophysicist and engineer at the University of Michigan, is developing a concept for a gas-dynamic mirror fusion propulsion engine.

By Anne Rueter

ANN ARBOR, Mich., Aug. 11-To Terry Kammash, going to the stars is not sci-fi stuff. In the new millennium, the nuclear engineer envisions missions to Alpha Centauri, closest star to our solar system. In just the next 20 to 25 years, he predicts spacecraft will reach one milepost on the route, the Oort Cloud, a debris-filled comet belt 932 billion miles away. And heís betting the missions will use fusion, the basic energy source of stars themselves.

NEVER MIND that efficient fusion reactors to power industry and light our homes have so far eluded scientists and engineers. Kammash has designed two propulsion engines that take one of fusionís serious flaws and turn it into an asset for space travel. And as scientists search for ways to explore the vast distances in space, Kammashís most developed design looks like a front-runner.

The physics is well understood, the technology is available, said Kammash, a University of Michigan professor emeritus. Itís just a question of putting it together.

Thatís what NASA scientists have been doing at the Marshall Space Flight Center in Huntsville, Ala., where several alternatives to chemical rockets are being explored. Kammashís concept is the furthest along, said Bill Emrich, a senior engineer at the center. Heís getting a working model ready to test the design the first such test of fusion propulsion for use in space.

I think itís a reasonably promising (concept), although there are others that look promising too, Emrich said. Itís hard to say at this point which one is going to be the winner.

Kammashís gas-dynamic mirror engine holds promise for faster travel to planets such as Mars and Pluto. Emrich and other NASA scientists have electromagnets in place in a 2-meter-long model of the engine. In the next few months, they hope to start injecting plasma, the superheated fuel that the magnets are designed to confine long enough to produce nuclear fusion reactions. The scientists hope to achieve fusion during the next year or two.

Meanwhile, Kammash is pushing forward with his second engine design, one with the thrust needed for more distant interstellar missions. He got a boost recently when this design was among a handful of propulsion ideas to receive funding from NASAís newly formed Institute for Advanced Concepts.

Both engines, Kammash said, aim to cut to a realistic level the time and cost of missions to planets in our solar system and beyond. And time is of the essence. Using conventional chemical rockets, missions to Mars are long enough to be daunting for humans: At seven to nine months each way, a trip might last two years. At a typical shuttle speed of 17,600 mph, it would take 168,000 years or more for a robotic mission to reach Alpha Centauri.

Kammash estimates his gas-dynamic mirror fusion propulsion engine would take three to four months to travel to Mars and back. He thinks his newer design, fast enough for interstellar missions, could reach Alpha Centauri, 259 trillion miles away, in as little as 213 years. This new engine might take a mere 29 years to make a one-way trip to the Oort Cloud.

Now it costs $10,000 to put a kilogram in space, Kammash said. He and other space scientists take seriously NASAís challenge to cut this figure to $2,000 or less. Alternative propulsion methods are key because conventional fuels for long missions are extremely bulky and costly. It takes huge amounts of fuel to lift a spacecraft into space if it must carry fuel to travel to distant planets or stars.

Fusion energy, produced when the light nuclei of certain atoms fuse together under intense heat, is not the only energy source being eyed for long-distance space missions. Energy from fission, the splitting
of heavy atoms, is still a contender. Fission rockets, though they evoke safety concerns, havenít been abandoned and could power missions to the relatively near moon and Mars. For more distant ones, scientists believe fusion has greater potential.

The idea of a robotic mission to explore the environs of Alpha Centauri draws many skeptics, but also many restless minds eager to try. If man does not explore he becomes stagnant, civilization becomes stagnant, Kammash said.

Streams of leaking energy are one reason fusion hasnít lived up to hopes as an energy source on Earth. Some fusion reactors have had trouble producing more energy than they lose because hot plasma, the systemís fuel, is hard to contain. Kammash worked on designs for such fusion reactors for decades. Fusion enthusiasm ran high in the late 1970s and early í80s; now Congress continues to reduce funds for fusion research.

In the early 1990s, Kammash came to see possibilities in fusionís problems. You want to eject hot plasma because thatís propulsion, Kammash said. Fusion is inherently leaky, so letís take advantage of it.

The gas-dynamic mirror engine relies on powerful magnets to create electromagnetic fields that will confine plasma particles long enough for sufficient fusion reactions to occur. Mirror refers to the magnetic fields at each end that bounce particles back and forth. The engine retains some of the plasma to keep the fusion reaction going, and lets a fraction of it escape through a nozzle to produce thrust.

The second engine, called MICF (Magnetically Insulated Inertial Confinement Fusion), uses a different method to achieve fusion. A laser beam zaps BB-sized pellets of fuel, creating a hot plasma contained by a metallic shell. The plasma should be contained long enough to lead to large energy gains, Kammash writes in Ad Astra, a magazine read by astronauts and other space enthusiasts.

His idea is a concept that brings together antimatter and fusion propulsion, said Robert Cassanova, director of the Institute for Advanced Concepts. We found that intriguing.

Instead of a laser, Kammash ultimately wants to use antimatter, an experimental technique, to zap the fuel pellets. Giant particle accelerators produce fleeting forms of antimatter. Scientists are trying to find ways to trap one form, antiprotons, and use the energy they produce. Using a stream of antiprotons instead of a bulky laser apparatus would make Kammashís design very attractive in space.