Monday, January 29, 2007

INTERSTELLAR RAMJET

CONTENTS: 1. BACKGROUND: Outer Space has no air, but it is not a pure vacuum. There are a lot of particles (mostly Hydrogen atoms) in space, and they might help us travel to the stars.
2. INTERSTELLAR RAMJET: A vast electro-magnetic grid can "scoop" up these particles for proton-proton (p-p) fusion reactions to further enhance vessel's acceleration. Dr. Robert Bussard conceived the interstellar ramjet and published a paper in 1960.
3. CNO CATALYTIC:   Dr. Daniel Whitmire followed up with his own paper in 1975 and introduced some relevant concepts such as the Carbon-Nitrogen-Oxygen (CNO) catalytic fusion process, interstellar drag and ionization methods.
4.  RAMJET EVOLUTION:  During the lengthy cruise period between acceleration and deceleration powered by ship borne particle accelerators, we might learn to put that time to better use by learning to augment cruise speed via fusion of collected interstellar particles.  This learning curve would increase over time due to experience from many interstellar voyages.
BACKGROUND: Outer Space Particles

Outer space is not a perfect vacuum; instead, it is a tenuous plasma awash with charged particles, electromagnetic fields, and the occasional star. Outer space has very low density and pressure, and is the closest physical approximation of a perfect vacuum outside a high tech lab. However, no vacuum is truly perfect, not even in interstellar space, where there are still a few hydrogen atoms per cubic centimeter. Astrophysicists use number density (n) to describe these environments, in units of particles per cubic centimeter.
Bussard ramjet uses enormous electro-magnetic fields (hundreds of kilometers in diameter) as a ram scoop to collect and compress hydrogen from the interstellar medium. Vessel's high speed forces the reactive mass into a progressively constricted magnetic field, compressing it until thermonuclear fusion. The magnetic field then directs the energy as rocket exhaust opposite to the intended direction of travel, which accelerates the vessel.  Bussard’s original design envisaged a large cone shaped structure “scooping up” sufficient atomic hydrogen for constant g-force travel. However, typical regions of interstellar space might have a very low density of 1 Hydrogen atom per cubic centimeter. If so, the ramjet scoop must sweep 1.67×1024 cubic cm (1.67×109 cubic km) of space to collect one gram of hydrogen. If vessel's scoop had a "mouth" of 100 km radius, and it was moving at 60% light speed (.6c) between two stars; it would take 17 seconds for the vessel to scoop up one gram of Hydrogen (assume perfect efficiency).
Neighboring stars include Alpha Centauri to the south and Izar to the north
FUEL LIMITATION
The inherent logistics problem of a g-force interstellar flight is having enough onboard fuel for powered flight to/from a neighboring star.  Of course, limited onboard fuel implies strict planning to account for following factors:
a) Accelerate at g-force for a duration (tAcc) to achieve a reasonable cruise speed yet consume a practical portion of onboard fuel.  EXAMPLE:  In previous work, Thought Experiment (TE) postulates that after one year (365.25 days) of g-force propulsion, Earth observer would measure vessel's velocity of about 65% light speed (.65c) and distance of about .3 Light Years (LY).  TE further postulates that a capable vessel could achieve this with fuel equal to about 17% of the vessel's original Gross Weight (GW0).  Assume exhaust particle velocity of .99c.
b) Decelerate for a duration (tDec) which matches tAcc.  EXAMPLE:  G-force for 1 year, .3 LY and another 13% of GW0.  (NOTE: Takes less fuel to move less GW which already decreased 17% due to acceleration fuel consumption.)

c) Cruise for most of the flight at constant speed between the acceleration and deceleration phases of flight. NOTE: Without g-force propulsion, vessel simulates Earth gravity via centrifugal force by spinning vessel's habitat component about its longitudinal axis. EXAMPLE: For a trip from Sol to Alpha Centauri (distance = 4.3 LY), cruise distance is 4.3 LY - .3 LY - .3 LY = 3.7 LY. Earth observers measure a cruise duration of 3.7 LY ÷ .65c = 5.7 years.

It'd be great to shorten this lenghty cruise duration.
Interstellar ramjet might decrease the cruise duration with slight accleration.  Ramjet augments onboard fuel by collecting particles (mostly H protons) from the interstellar medium. The captured particles go to a nuclear fusion reactor to supply energy for a high-speed exhaust.

1) Bussard's concept:
Collect interstellar H atoms, implement p-p fusion process. The primary, practical model for a relativistic spacecraft is Bussard’s interstellar ramjet which collects particles from interstellar medium. To extract energy from these particles, Bussard proposed the Proton-Proton Interaction (PPI) cycle, the following sequence of reactions:
Just like the initial proton burning reaction for main sequence stars, this cycle converts four protons into a He nucleus with the release of 19.53 MeV of potentially usable energy.
PPI chain for fusing hydrogen could be much quicker; fortunately, there is a viable alternative.
2) Whitmire follows up:
Fortunately, Whitmire proposed a proton burning catalytic cycle. The best known catalytic cycle is the Carbon-Nitrogen-Oxygen (CNO) Bi-Cycle in sufficiently hot main sequence stars. The catalyst “fuel” may be carried on board the ship since it will not deplete; however, the ultimate source of energy is still the interstellar hydrogen.
The hot CNO catalytic Bi-Cycle consists of the following reaction chain:

The slowest link in CNO process is much faster than the fastest link in the PPI cycle.

The entire CNO cycle is 100 million times faster than the entire PPI chain.
Dr. Whitemire's schematic diagram
 of drag-free interstellar ramjet.
DRAG: Interstellar drag is momentum loss to the interstellar medium. Ship’s magnetic field is coupled with the ship; so, some protons will inevitably collide with the field (coupled to the ship) to impede ship’s acceleration (i.e., drag).
Neutral particles (neutrons as well as complete H atoms) will most likely pass unhindered through the mag field with no drag. However, "interstellar drag" might result from mag field's interaction with H ions.  Mag field's overall positive charge should repel all "ionized" H atoms without electrons(i.e., "protons") back toward center of field to eventually "funnel" all protons vessel's fusion reactor.  Numerous inevitable "bounces" might cause some drag.
Any such drag will detract from forward momentum in same manner as friction slows an automobile at a constant speed.
IONIZATION: Spray approaching hydrogen atoms with a laser beam to "ionize" them. Resulting protons will more readily react with a powerful magnetic field which extends far beyond the vessel's physical structure.
To ionize approaching interstellar Hydrogen atoms, shine lasers into the grid volume forward of ramjet. It takes only about 13 eV to ionize a single hydrogen atom; in return, the same atom provides about 1 MeV from the subsequent nuclear reaction. Hence, the ship should easily supply the required energy to power the lasers.
GRAND CHALLENGE:As much as possible, each laser packet of 13eV must hit each H atom once and only once. Otherwise, this laser ionization method presents two difficulties;
  1. The laser process must be incredibly efficient. For every laser packet which fails to impact an H atom, 13 eV of wasted photons travel out of the scoop volume into the universe.
  2. The laser process must be nonredundant. If an ion receives multiple shots of 13 eV, the extra energy will likely sweep it out of the ramjet’s scoop volume and not funneled into the ship's fusion reactor.
Consider Other Ramjet Challenges:
1. Power Requirements. The scoop's magnetic field requires considerable power as does the ionizing laser.
NOTE: Collecting high speed, interstellar particles might produce some energy for non-propulsion, internal uses; perhaps, a fusion reactor to support on-board life support as well as mag "scoop".
2. Particle Crowd Effect. Scoop’s magnetic field converges at the inlet funnel to cause a “crowd” effect; thus, leading charged particles start to “bunch up” and repel some of the following, like charged particles. (Perhaps a well designed sequence of periodic electron injections might counteract this “crowd” effect.)
3. Optimal Collection Speed. The interstellar ramjet concept works best with an minimal speed of .6c to collect sufficient interstellar mass per second for propulsion purposes. To boost the spacecraft to this critical speed, the spacecraft needs another propulsion system. (Fortunately, TE's notional g-force spaceship already has a conceptual propulsion system, particle accelerator, which is designed to take us to .6c in about a year. Spacecraft should be able to carry sufficient fuel for that duration; thereafter, onboard fuel can be augmented by the ship’s secondary system, the ramjet.)4. Deceleration. Prior to destination, the spacecraft must slowdown to an operational speed. This will likely necessitate turning the spacecraft 180 degrees so that propulsion particles exit in the same direction as travel. (Reconfigure net-like grid to collect particles in same direction as thrust. )

Consider Following Phases of Development:
As humanity does more interstellar flights, we'll get smarter in implementing the "ramjet" concept.
Perhaps following phases describe how this might happen.
All-sky map of the CMB,
created from 9 years of WMAP data.
PHASE 0: Constant Cruise With No Collected Particles. For initial voyages to neighboring stars, assume ramjet to be in the planning stage. This would be good time to collect data to validate particle densities throughout the flight.
Cosmic Microwave Background (CMB) compels one to conclude that interstellar space is not an absolute vacuum. If there were no particles in space, we could not precisely measure the CMB's variation which has been measured ubiquitously throughout the entire sky.
Thus, we assume the interstellar particles are there.
PHASE 1: Limited Collection With No Propulsion. Use a small magnetic grid to collect particles for proton-proton interaction (PPI) where Hydrogen nucleons fuse to form Helium nucleons.
 Such a fusion reactor might power on-board functions such as communication, life support, and of course the electromagnetic "collection" grid which funnels the particles to the vessel's fusion. This phase would also have to overcome "drag" due to incident protons impacting the grid. This phase would benefit from even the worst case scenario.
Worst Case Scenario: Assume one H atom per cubic cm (cc), a magnetic grid of one km radius and vessel's cruise speed of 60% light speed (.6 c) achieved after 350 days of g-force acceleration.
Simple calculations indicate a max collection less than .001 gms of Hydrogen per second, an infinitesimal amount. Far less than required to augment propulsion, but perhaps enough to augment on-board power.
PHASE 2: Slight acceleration above cruise speed. Use a larger magnetic grid to collect particles for Carbon-Nitrogen-Oxygen (CNO) catalytic process to greatly expedite fusion of Hydrogen nucleons to form Helium. (Experts claim that the CNO process could be more than 100 million times faster than the PPI process.) Such a fusion reactor could augment the vessel's cruise speed with some limited acceleration. Vessel would also have to provide ionization methods to greatly increase percentage of charged particles inside the collection area; recall that magnetic grid works best on charged particles. This phase would benefit most from the following, best case scenario.
Best Case Scenario: Assume ten H atoms per cubic cm (cc), a magnetic collection area of 100 km radius and a cruise speed of 86.6% light speed (.866 c) achieved after much more than a year of g-force acceleration. Simple calculations indicate a max collection of about 135 gms of Hydrogen per second, a reasonable amount. Even better, relativistic effects should double the particle mass for a collected mass of about 270 gms of H per sec.
PHASE 3: G-force throughout cruise via non-propulsive means.
CONCLUSION: Even the extreme "best case" falls far short of providing enough momentum to continue 1g travel during cruise phase. RECALL: Typical interstellar vessel is likely several 100 thousand metric tonnes of mass; they would need kilograms (kg) of exhaust particles for each second of 1-g propulsion. However, 270 grams of H particles per second might suffice to "augment" cruise speed by perhaps .1 g, a significant increase. During this augmented cruise, vessel occupants could still enjoy Earth like gravity via centrifugal force from spinning about longitudinal axis.
Improve Efficiency. As ramjet's cruise speed increases, the grid sweeps more interstellar volume to collect more particles. Also, as ionization method improves, more particles become ions to more readily fuse to produce more energy. Thus, grid size can decrease, and less power is needed to make/maintain; thus, more power used for propulsion and less power for grid.


RWikipedia Affiliate Buttonobert W. Bussard (August 11, 1928 – October 6, 2007) was an American physicist who worked primarily in nuclear fusion energy research. He received the Schreiber-Spence Achievement Award for STAIF-2004.[1] He was a fellow of the International Academy of Astronautics.
In 1956, Bussard designed the nuclear thermal rocket known as project Rover. Bussard and R.D. DeLauer wrote two important monographs on nuclear propulsion,
  • Nuclear Rocket Propulsion [2]
  • Fundamentals of Nuclear Flight.[3]Bussard ramjet
In 1960, Bussard conceived the Bussard ramjet, an interstellar space drive powered by hydrogen fusion using hydrogen collected with a magnetic field from the interstellar gas. Due to high-energy particles throughout space, much of the interstellar hydrogen exists in an ionized state (H II regions) that can be manipulated by magnetic or electric fields.
In the early 1970s, Dr. Bussard became Assistant Director under Director Robert Hirsch at the Controlled Thermonuclear Reaction Division of what was then known as the Atomic Energy Commission. Bussard and Hirsch founded the mainline fusion program for the United States: the Tokamak.
In 1984 with his wife, Dolly H. Gray, Bussard co-founded a company, Energy Matter Conversion Corporation (EMC²), to exploit a new method of inertial electrostatic confinement fusion.
Bussard’s Polywell is a new type of gridless IEC fusor. He built and tested 15 experimental devices from 1994 through 2006 when funding ran out.
During 2006 and 2007, Bussard sought the large-scale funding necessary to design and construct a full-scale Polywell fusion power plant. Unfortunately, the relevant line item from US Navy’s FY2006 budget was zero-funded.  In spite of denying him funds for further research, the Navy embargoed his Polywell work in lieu of funds previously paid.
June 23, 2006. Bussard bravely defied the U.S. Navy's embargo of his research publications by providing details of his breakthrough and the circumstances surrounding the end of his Navy funding in a letter to the James Randi Educational Foundation Internet Forum.
October 2-6, 2006. Bussard further defied the U.S. Navy's embargo by reviewing his historic work at the 57th International Astronautical Congress.
Throughout the rest of his life, Dr. Bussard continued to present his IEC fusion research at several venues. Bussard died from lung cancer on October 6, 2007 at age 79. His extremely capable team continues his work.
Daniel Whitmire, a retired astrophysics professor, believes that a "Planet X" causes extinction events on Earth. (See Source)
1. Whitmire recently published findings connecting the undiscovered Planet X to mass extinctions on Earth, (see Phys.org) in the Monthly Notices of the Royal Astronomical Society. Every 27 million years, Planet X passes through a distant Kuiper belt of comets, knocking comets into our solar system, and some comets then smash into the Earth.
2. Orbital Anomalies Indicate an Unknown, Large Planet.  Caltch researchers recently found orbital anomalies in the Kuiper Belt, which Whitmire proposes as the source of the mass extinction comet showers. The anomaly points to the presence of an undiscovered large planet that is 10 times the mass of the Earth and also 1,000 times more distant from the sun. The Astronomical Journal.
3. Is Brown's "Planet Nine" the Same as Whitmire’s Planet X?
Brown doesn’t think so.  “Whitmire has been speculating for decades about a very distant very massive planet with an orbital period of something like 27 million years,” Brown said to Discovery. “…It definitely has nothing to do with Planet Nine, which is much closer to the Sun and thus ‘only’ takes 15,000 years to orbit Sol.”
4. Whitmire Retired from Teaching Astrophysics & Now Teaches Math.
Whitmire retired from the University of Louisiana at Lafayette in 2012. In 2013, he began teaching math at the University of Arkansas.
At Arkansas, some students cosmetically complain that he isn’t familiar with current tech like Blackboard. However, others point out that he is indeed, a great professor, easy to talk to, and always willing to help his students.
5. Planet X: End-of-the-World Mythology
The idea of a planet causing worldwide destruction is also tied to mythology and doomsday predictions. A number of myths state a mysterious planet lurks out in the shadows of our solar system and hurtles asteroids to Earth to cause several past extinctions. One present day theory is about Nemesis,  a  not yet discovered, companion star to our sun, Sol. In 1984, AP reported on this theory proposed by scientists from the University of California in Berkeley and Princeton University. They hypothesized an undetected, dwarf star to periodically cause immense comet showers to extinguish up to 70 percent of life on Earth. (NOTE:  A small singularity; i.e., "black hole"; would be even harder to detect.)



VOLUME I: ASTEROIDAL
VOLUME II: INTERPLANETARY
VOLUME III: INTERSTELLAR



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