Fusion Powered "Bubble Craft"

SpaceScience.com; Oct. 4, 2000; NASA Science News: "Hitching a Ride on a Magnetic Bubble"

Exciting researched, at Marshall Space Flight Center, is proving the feasibility of spacecraft that use the Sun to speed them to the edges of our solar system.  All that's needed is an artificial magnetosphere around the craft so it can be pushed by the ever-present, fusion-driven solar wind.  (Planets with molten metal cores -- like Earth -- have magnetic fields that extend into space and interact with the solar wind to form natural magnetospheres.) 

According to physicist Dennis Gallagher, the principal investigator for the project, a 15-km-wide magnetosphere "bubble" in space would experience a constant, accelerating force of several pounds due to the solar wind.  Over a 3-month period this would shift a 200-kg craft from zero to a blistering 180,000-mph.  In fact, the constant acceleration would allow it to overtake the Voyager spacecrafts and beat them in reaching interstellar space!  This is not just a theory: a solenoid device to generate such a magnetosphere has just finished testing in a vacuum chamber at Marshall.  Consisting of a 1-foot diameter coil, of 16-gauge enameled wire, carrying 5 to 30 amp of current, it generates a magnetic field only three times greater than a refrigerator magnet.  To expand this field into a magnetosphere of great size, a plasma of ions is injected into it.  In space this device would require 1-kW of power and about 1-kg of helium per-day as a plasma source.  Perhaps most exciting, to those of us that yearn for such propulsion breakthroughs, is that all the components are "off-the-shelf," and no new technology had to be invented.

This importance of the plasma injection technique is recognized in the project's name: "Mini-Magnetospheric Plasma Propulsion" or M2P2.  Earth's magnetosphere is naturally expanded by the presence of plasma and Jupiter's is greatly so.  Jupiter's big dose of plasma is due to volcanic activity on its big moon Io blasting plasma into the giant planet's magnetic field.  If it were visible, the plasma bloated magnetosphere of Jupiter would appear from Earth to extend a full-Moon width on either side of the planet.

What about the decrease in solar wind density felt by a craft leaving the inner solar system?  That's not a problem.  The decrease in solar wind force on the magnetic bubble would allow it to expand.   Fortuitously, "the bubble increases by the same factor that the solar wind pressure declines. The two effects completely cancel, " says Gallagher.  So the thrust of the M2P2 stays constant throughout the solar system.

Another plus for a M2P2 "bubble craft" is that the mini-magnetosphere would, just as Earth's  magnetosphere does, shield it from cosmic rays and solar flares.  This is a very useful bonus for a future human-occupied "bubble ship" making passage outside the Earth's magnetosphere.

Puzzling Gifts from Mars

Space.com; Aug 30, 2000; Solar System News: "New Clues About Martian Meteorites Baffle Scientists"

Mysteries concerning the ages of Martian meteorites found on Earth will only be solved by going to Mars and bringing back fresh samples from known locations. This assessment was made at the recent Meteoritical Society meeting in Chicago, where findings from several Mars rocks were announced. Rocks from Mars are dislodged and make their way to Earth as a result of asteroid impacts on that planet. Due to low gravity, the ejected material achieves escape velocity and occasionally enters our atmosphere -- to flash across the sky and come to rest on our planet.

Seven Martian meteorites, composed of crystallized magma from near that planet's surface, have been found to have solidified only 180 million years old.  These seven meteorites are out of a population of 15 with known ages.  What's puzzling is that the remaining meteorites have ages in the billions of years.  Age was determined by measuring certain radioactive isotopes within the rock.

The composition and age of the young meteorites indicate that volcanoes on Mars had been active in the recent geologic past. Mars Global Surveyor, orbiting and imaging Mars since 1997, has returned images that indicate young volcanic deposits on the surface. Based on accepted understanding of cratering on Mars (new surfaces have fewer craters), at most 15% of the surface is within the ages of the young meteorites. But, the majority of Mars' surface is billions of years old: so, why so few Martian meteorites that reflect that?

A simple explanation that all the young samples left Mars together, from an area of recent volcanism, as a result of asteroid impact. This theory is dispelled by cosmic-ray-exposures studies on the samples that indicate how long they traveled in space to reach Earth. Results indicate the young samples left Mars by four different impacts. In total, all studied Martian meteorites come from nine ejection events. Scientists can't explain why half the ejection events took place on 15% of the surface.

As a result, there is speculation that Mars was volcanically active much longer than previously accepted. Ingrained theories hold that geologic activity on Mars ended billions of years ago. This problem also cast doubts on the accepted rate that meteor craters appear on Mars. Scientists hope an automated mission to retrieve material from known locations on Mars will help them make sense of these Martian meteor mysteries.

Cosmiverse.com; Sept 26, 2000; Space News: "X-33 on Chopping Block"

Venturstar is a NASA funded project to create a true "space plane."  Using advanced composite technologies and novel "aerospike" engines, the craft ascends into space in one piece -- no stages are dropped.  On return the lifting-body design lands on a runway -- just like a plane.  This project promised cheaper access to space: 1-lb of payload would cost only $1,000 to boost into orbit on Venturstar versus $10,000 today for a Space Shuttle flight.  Space tourism and manufacturing could become practical at those rates.  Flights were to begin in the first decade of the new century, for this 21st century spacecraft.

But first, a sub-scale technology demonstrator, known as the X-33, would be built and flown into sub-orbit in the late 1990's by Lockheed Martin.  In 1998 it would cover 450-miles in a dramatic 15-minute self-powered flight, from Edwards Air Force Base to the edge of space, to end on a conventional runway in Utah.  

There is one problem in this "next-step" in the conquest of space: the X-33 test flight was scheduled 18-months ago, and the ship is still only half-built.  Where did four years and $1-billion go?

Setbacks have plagued construction of the X-33, which has been criticized as being a high-risk, "Buck Rogers" design.  Aerospike engines, that thrust efficiently by allowing exhaust exit pressure to vary with atmospheric pressure, have never been used on a launch vehicle.  Boeing, the contractor for the engines, was late with delivery and $36-million over budget.  But the biggest problems are centered around the fuel tanks.  They are characterized as "oddly shaped," of a new composite material design, and required to hold freezing liquid hydrogen under pressure.  In late 1998 bubbles and cracks in one of the two tanks led to $5-million in cost overruns to replace it.  Also, the original design was modified -- with an increased weight penalty.

NASA-allocated money for the project has all been spent, and Lockheed Martin has gone over-budget on the X-33.  Critics say the current fuel tanks, or an alternative pair made out of aluminum, may be fine for a test flight but not for scaling up for the actual Venturestar vehicle.  It is expected that NASA will announce after the elections this November whether to continue the project or drop it and perhaps pursue a more "down-to-earth" strategy for a Space Shuttle replacement. 

Worth Reviewing in Another 55-Years!

Wireless World, Oct. 1945, Article: "Extra-Terrestrial Relays"

This month is the 55th publication anniversary, in the October 1945 issue of "Wireless World," of Arthur C. Clarke's prophecy on global telecommunications. The oft-cited, four-page article, entitled "Extra-Terrestrial Relays," has earned Sir Clarke the distinction of being the "father" of the communications satellite concept. While an important milestone in popularizing the notion of a global communications network, it is also well worth reading for insight into the thinking of a modern visionary. But relatively few interested people born in the space age have read it or can find a crumbling copy in the library to read. A search of the Internet will turn up scanned copies barely good enough to make out. So, here are some highlights and notes concerning the seminal paper of the nascent space age. You will find a few surprises, predictions that came true, and some that didn't.

In the opening paragraph Clarke states the necessity for global communications in a world-spanning society: "A true broadcast service, giving constant field strength at all times over the whole globe would be invaluable, not to say indispensable, in a world society." Clarke grasped the looming importance of television in world society at a time when television was regarded as an expensive "toy." Therefore his main thrust -- for an alternative to ground-based, long-distance radio transmission across contents and oceans -- is on the unsuitability of such systems for television. Being farsighted, he knew his concept, though feasible, was ahead of current technology. This led him to caution early in the piece that: "Many may consider the solution proposed in this discussion too farfetched to be taken very seriously," but he continued that everything envisioned was a "logical extension" of recent developments.

To educate the reader on the concept of space flight, he briefly discusses the required velocity to reach low orbit.  He then charts orbits of various distances from Earth with their velocities and orbital periods. He uses the term "artificial satellite" -- calling such a device in orbit a "second moon." Next he introduces the important concept of a satellite, in an equatorial orbit, who's period matches the rotation of the Earth. The benefit of this is that the satellite is stationary over one spot and does not needed to be tracked across the sky: this is known as a "geostationary" orbit -- though Clarke does not use that term. With the potential of transmitting to a whole hemisphere at once, only three satellites would be needed to cover the world. According to Clarke, the technology to reach these orbits is an extension of the missile technology developed by the Germans during the just concluded World War. He discusses newly released information on German rocket technologies and their (now derailed) plans to exploit space. The German plans for a medium-orbit space station assumed a long 50 to 100-years development timeline. Clarke doesn't comment on that timeline but suggests "radio controlled" rockets will enter orbit in a few years, to be followed by manned rockets.

What is, at first, surprising to the modern reader is that the geostationary "relays" he is discussing are manned space stations -- not the automated, solid-state communications satellites we've been lofting since the 60's. But stations made sense in the "vacuum tube" era he was writing in, due to maintenance requirements of the communications technology. Construction would take place in space, and "regular rocket service" would bring supplies and rotate the crew. Clarke notes that such a station would additionally serve to "contribute enormously to our knowledge of astronomy, physics and meteorology."

Let us compare prophecy with history: only the MIR space station, which was crewed for many years before its current semi-retirement, met the criteria of being permanently manned, and its orbit is far lower than the required geostationary. The International Space Station, under construction, is in a similar low orbit. Our permanent entry into space seems to be following the German timeline Clarke mentioned.

Next Clarke discusses radio frequency issues and states research needs to be done on the affect of sending signals straight thought the atmosphere.  He suggests using captured German V2 rockets or bouncing signals off the Moon to accomplish this. Clarke also notes the possibility of using "optical beams" to communicate between the space stations. This is, of course, written before the development of the laser. Power requirements for signal transmission and the use of solar energy for the station are mentioned. The solar energy Clarke discusses is not with solar panels but with mirrors to concentrate light and generate heat for a steam "solar engine." Only at the end of the discussion does he correctly note that the photoelectric effect might one day provide energy directly.

The space and ground stations Clarke envisioned employ "parabolic antennas" to send and receive signals. In recognition of their wide use in this application today, we now refer to these antennas as "satellite dishes". Interestingly, Clarke estimated that the ground-receiving antenna would be just a foot across -- coincidently similar to the dish size of modern home-satellite television-systems. But, after all, the whole concept under discussion is "direct TV" to obviate the need to build repeaters and transmitters all over the world.

In an appendix, entitled "Rocket Design," Clarke envisioned that rockets would be launched from "very high country" to lessen air resistance. While he missed on that one, he also concluded correctly that "step rockets" -- rockets that use stages -- would be required to reach orbit. Further, in an epilogue titled "Atomic Power," Clarke predicts that within 20-years atomic-powered rockets would "reach even the remoter planets." This serves as a reminder that visionaries are celebrated for "hitting the nail on the head" and not for missed strikes. Clarke had enough hits 55-years ago that, in April 2000, the European Telecommunications Satellite Organization (EUTELSAT) named a newly launched geostationary communications satellite in his honor.