September 29, 2012

Sloppy warp fields should be much easier to engineer

Warp Field Mechanics 101 (33 pages)

Almost all of the information in this post is from the Harold White paper "Warp Field Mechanics 101" and a presentation he made on September, 2011 at the 100 Year Starship Symposium which were all posted at the NASA server. The video is an interview of Eric Davis on "Attack of the Show" from G4 TV. The original Alcubierre space warp theories required massive amounts of energy and exotic matter. If Harold White is correct with his ideas for a higher dimension manifold and thicker shell, then the amount of energies needed will come down to a feasible level. Experiments at NASA over the next few months with a moderate sized laser could show that a detectable space warp is formed with 1 ten millionth the level of warping than would be needed for actual propulsion.

Hard "Sonny" White's bio is at the Icarus Interstellar project website

Dr. White holds a Ph.D. in Physics from Rice University, a Master’s of Science in Mechanical Engineering from Wichita State University, and a Bachelors of Science in Mechanical Engineering from University of South Alabama. Dr. White has accumulated over 15 years of experience working in the aerospace industry with Boeing, Lockheed Martin, and NASA. He currently serves as the Advanced Propulsion Theme Lead for the NASA Engineering Directorate and is the JSC representative to the Nuclear Systems Working Group. In his role, Dr. White is serving to help the Agency incorporate high TRL advanced power and propulsion technologies into near and mid-term human exploration architectures. He is also pursuing theoretical and laboratory research on developing lower TRL advanced propulsion and power technologies in the advanced propulsion physics laboratory known as Eagleworks that is located at the Johnson Space Center.

The idea of a warp drive in higher dimensional space-time (manifold) will then be briefly considered by comparing the null-like geodesics of the Alcubierre metric to the Chung-Freese metric to illustrate the mathematical role of hyperspace coordinates. The net effect of using a warp drive “technology” coupled with conventional propulsion systems on an exploration mission will be discussed using the nomenclature of early mission planning. Finally, an overview of the warp field interferometer test bed being implemented in the Advanced Propulsion Physics Laboratory: Eagleworks at the Johnson Space Center will be detailed.

The advantage of allowing a thicker warp bubble wall is that the integration of the total energy density for the right-most field is orders of magnitude less that the left-most field. The drawback is that the volume of the flat space-time in the center of the bubble is reduced. Still, a minimal reduction in flat space-time volume appears to yield a drastic reduction in total energy requirement that would likely outweigh reduced real-estate. Sloppy warp fields would appear to be “easier” to engineer than precise warp fields. Some additional appealing characteristics of the metric is that the proper acceleration α is zero, meaning there is no acceleration felt in the flat space-time volume inside the warp bubble when the field is turned on, and the coordinate time t in the flat space-time volume is the same as proper time τ, meaning the clocks on board the spacecraft proper beat at the same rate as clocks on earth.

Eric Davis explains on Attack of the Show
Eric Davis in another talk on Hyperspace Dr. Eric Davis outlines Dr. Giorgio Fontana's "Hyperspace for Space Travel". Fontana postulates that a localized strong gravitational field may allow travel to different local universes or Faster Than Light (FTL) travel within the same local universe, thus potentially allowing the collision or focusing of gravitational waves to produce effects comparable to those of short-lived black holes to facilitate Faster-Than-Light (FTL) space propulsion. Fontana is a professor at the University of Trento in italy, and Davis is a theoretical physicist working at EarthTech International.
The concept of operations as described by Alcubierre is that the spacecraft would depart the point of origin (e.g. earth) using some conventional propulsion system and travel a distance d, then bring the craft to a stop relative to the departure point. The field would be turned on and the craft would zip off to its stellar destination, never locally breaking the speed of light, but covering the distance in an arbitrarily short time period of time just the same. The field would be turned off a similar standoff distance from the destination, and the craft would finish the journey conventionally. This approach would allow a journey to say Alpha Centauri as measured by an earth bound observer (and spacecraft clocks) measured in weeks or months, rather than decades or centuries.
Using this new information, a modified concept of operations is proposed that may resolve the asymmetry/symmetry paradox. In this modified concept of operations, the spacecraft departs earth and establishes an initial subluminal velocity vi, then initiates the field. When active, the field’s boost acts on the initial velocity as a scalar multiplier resulting in a much higher apparent speed, = γ vi as measured by either an earth bound observer or an observer in the bubble. Within the shell thickness of the warp bubble region, the spacecraft never locally breaks the speed of light and the net effect as seen by earth/ship observers is analogous to watching a film in fast forward. Consider the following to help illustrate the point – assume the spacecraft heads out towards Alpha Centauri and has a conventional propulsion system capable of reaching 0.1c. The spacecraft initiates a boost field with a value of 100 which acts on the initial velocity resulting in an apparent speed of 10c. The spacecraft will make it to Alpha Centauri in 0.43 years as measured by an earth observer and an observer in the flat space-time volume encapsulated by the warp bubble. While this line of reason seems to resolve the paradox, it also suggests that the York Time may not be the driving phenomenon, rather a secondary result. In this physical explanation of the mathematics, the York Time might be thought of as perhaps a Doppler strain on space as this spherical region is propelled through space. A pedestrian analog to use to help envision this concept would be to consider the hydrodynamic pressure gradients that form around a spherical body moving through a fluid – the front hemisphere has a high pressure region while the rear hemisphere has a low pressure region. Analogously, the warp bubble travelling through space-time causes space to pile up (contract) in front of the bubble, and stretch out (expand) behind the bubble. Figure 3 depicts the boost field for the metric, and shows that the toroidal ring of energy density creates spherical boost potentials surrounding a flat space-time volume. Also note pseudo-horizon at v2f(rs)2=1 where photons transition from null-like to space-like and back to null like upon exiting. This is not seen unless the field mesh is set fine enough. The coarse mesh on the right did not detect the horizon.
Mission Planning with a Warp-enabled System - faster sublight in the solar system
To this point, the discussion has been centered on the interstellar capability of the models, but in the interest of addressing the crawl-walk-run paradigm that is a staple of the engineering and scientific disciplines, a more “domestic” application within the earth’s gravitational well will be considered. As a preamble, recall that the driving phenomenon for the Alcubierre metric was speculated to be the boost acting on an initial velocity. Can this speculation be shown to be consistent when using the tools of early reference mission planning while considering a warp-enabled system? Note that the energy density for the metric is negative, so the process of turning on a theoretical system with the ability to generate a negative energy density, or a negative pressure as was shown in, will add an effective negative mass to the spacecraft’s overall mass budget. In the regime of reference mission development using lowthrust electric propulsion systems for in-space propulsion, planners will cast part of the trade space into a domain that compares a spacecraft’s specific mass α to transit time. While electric propulsion has excellent “fuel economy” due to high specific impulses that are measured in thousands of seconds, it requires electric power measured in 100’s of kW to keep trip times manageable for human exploration class payloads. Figure 4 shows a notional plot for a human exploration solar electric propulsion tug sized to move payloads up and down the earth’s well – to L1 in this case. If time were of no consequence, then much of this discussion would be moot, but as experience shows, time is a constraint that is traded with other mission constraints like delivered payload, power requirements, launch and assembly manifest, crew cycling frequency, mission objectives, heliocentric transfer dates, and more. The specific mass of an element for an exploration architecture or reference mission can be determined by dividing the spacecraft’s beginning of life wet mass by the power level. Specific mass can also be calculated at the subsystem level if competing technologies are being compared for a particular function, but for this exercise, the integrated vehicle specific mass will be used. The transit time for a mission trajectory can then be calculated and plotted on a graph that compares specific mass to transit time. This can be done for a few discrete vehicle configurations, and the curve that fits these points will allow mission planners to extrapolate between the points when adding and subtracting mass, either in the form of payload or subsystem, for a particular power level. Figure 4 shows a simple plot of this approach for two specific impulse/efficiency values representing notional engine choices. It is apparent from the graph that lower specific impulse yields reduced trip times, but this also reduces delivered payload. However, if negative mass is added to the spacecraft’s mass budget, then the effective specific mass and transit time are reduced without necessarily reducing payload. A question to pose is what effect does this have mathematically? If energy is to be conserved, then ½ mv2 would need to yield a higher effective velocity to compensate for apparent reduction in mass. Assuming a point design solution of 5000kg BOL mass coupled to a 100kW Hall thruster system (lower curve), the expected transit time is ~70 days for a specific mass of 50 kg/kW without the aid of a warp drive. If a very modest warp drive system is installed that can generate a negative energy density that integrates to ~2000kg of negative mass when active, the specific mass is dropped from 50 to 30 which yields a reduced transit time of ~40 days. As the amount of negative mass approaches 5000 kg, the specific mass of the spacecraft approaches zero, and the transit time becomes exceedingly small, approaching zero in the limit. In this simplified context, the idea of a warp drive may have some fruitful domestic applications “subliminally,” allowing it to be matured before it is engaged as a true interstellar drive system.
There will be test to try to generate a detectable warping of space.
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