Frontiers of Propulsion Science - Progress in Astronautics and Aeronautics, Volume 227

792 Pages·2009·10.8 MB·English

by  Millis

Frontiers of Propulsion Science
Edited by
Marc G. Millis
NASAGlenn Research Center
Cleveland, Ohio
Eric W.Davis
Institutefor AdvancedStudies atAustin
Austin, Texas
Volume227
PROGRESSIN
ASTRONAUTICSANDAERONAUTICS
Frank K.Lu, Editor-in-Chief
UniversityofTexasat Arlington
Arlington,Texas
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Preface
“Fortune favorsthe bold.”
—Book XofThe Aeneidby Virgil (19B.C.E.)
I. Purpose
THISbookisthefirst-ever compilationofemergingscience relevanttosuch
notions as space drives, warp drives, gravity control, and faster-than-light
travel—the kind of breakthroughs that would revolutionize spaceflight and
enable human voyages to other star systems. Although these concepts might
soundlikesciencefiction,theyareappearinginincreasingnumbersinreputable
scientific journals. The intent of this book is to provide managers, scientists,
engineers, and graduate students with enough starting material to comprehend
the status of this research and decide for themselves if and how to pursue this
topic inmore depth.
Aswithanyyoungtopic,itcanbedifficulttocomprehendthepotentialbenefits,
theprosandconsofthecompetingapproaches,andthendecidewhatactionsare
warranted.Tothatend,theeditorshaveendeavoredtocollectimpartialoverviews
ofthebest-knownandmostrelevantapproaches.Inmanycases,dead-endlessons
areincludedtocounterrecurringclaimsandofferexamplesforhowtoassesssuch
claims. In addition, the methods for dealing with such pioneering topics are
included, both from the historical perspective and more specifically from the
lessons learned from NASA’s Breakthrough Propulsion Physics Project. It is
hopedthatthisvolumewillgivefutureresearchersthefoundationstoeventually
discoverthebreakthroughsthatwillallowhumanitytothrivebeyondEarth.
Thisresearchfallswithintherealmofscienceinsteadoftechnology,withthe
distinctionthatscienceisaboutuncoveringthelawsofnaturewhiletechnologyis
aboutapplyingthatsciencetobuildusefuldevices.Becauseexistingtechnology
is inadequate for traversing astronomical distances between neighboring stars
(evenifadvancedtothelimitofitsunderlyingphysics),theonlywaytocircum-
venttheselimitsistodiscovernewpropulsionscience.Inadditiontotheirutility
for spaceflight, the discovery of any new force-production or energy-exchange
principles would lead to a whole new class of technologies. The implications
ofsuccessare profound.
Objectively, the desired breakthroughs might turn out to be impossible, but
progress is not made by conceding defeat. Breakthroughs have a habit of
takingpessimistsbysurprise,butcanequallyremainelusive.Althoughnobreak-
throughs appear imminent, enough progress has been made to provide the
groundworkfordeeperstudies,bothwiththescienceitselfandwiththeprogram-
maticmethodsfortacklingsuchprovocativegoals.Ifthehistoryofscientificand
technologicalrevolutionsisanyindication,thistopiccouldonedayeclipsefam-
iliar aerospace technology and enable humanity to travel to habitable planets
around neighboring stars. For now, however, the work is predominantly at
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xviii
stages1and2ofthescientificmethod;thatis,definingtheproblemandcollect-
ing data, with a fewapproaches already testing hypotheses.
Regardless of whether the breakthroughs are found, this inquiry provides an
additional perspective from which to seek answers to the lingering unknowns
of our universe. While general science continues to assess cosmological data
for its implication to the birth and fate of the universe, a spaceflight focus will
cast these observations in different contexts, offering insights that might other-
wise be overlooked from the curiosity-driven inquiries alone. Therefore, even
iftherearenospaceflightbreakthroughstobefound,addingtheinquiryofspace-
flightexpandsourabilitytobetterunderstandtheuniverse.Thelessonslearnedin
the attempt will advancescience ingeneral.
The editors of this volume optimistically look forward to a time when this
first-evertechnicalbookonspacedrivesandfaster-than-lighttravelbecomesout-
dated.Itwillbeinterestingtolookbackdecadesfromnowtoseewhatfuturedis-
coveriestranspiredandthencomparethemwiththedirectionsexaminedinthese
chapters.Regardlessofthebook’sinevitableobsolescence,theeditorshopethat
themethodsofcontinueddiscoveryimplicitinthisbookwillhavelastingimpact.
II. Chapter byChapter
An introduction to each chapter follows, so that the context of each can be
better understood. Consider each chapter to be a primer to its topic rather than
a definitive last word. There is much that could change with further research,
and in some cases different interim conclusions are found in different chapters.
Such divergent conclusions are a reflection of the embryonic state of this
research, where many unresolved issues still exist. In many cases, chapters
presentideasthatarefoundtonotwork.FromexperiencewiththeNASABreak-
through Propulsion Physics Project, it was found that dead-end approaches are
repeatedlyresearchedbecausethenullresultswereneverdistributed.Otherchap-
ters describe work that is currently under investigation where more definitive
resultsareimminent.Andlastly,muchresearchonthistopichasnotevenbegun.
Toconveytherelativematurityofpropulsionstudies,ahistoricalperspective
isofferedinChapter1.Althoughthenotionsforbreakthroughspaceflighthave
been around for quite some time, the actual scientific publications started to
accumulate around 1995, with a few examples predating this by many years.
From 1996 through 2002, NASA funded work on these subjects through the
Breakthrough Propulsion Physics Project. During that same period, several
other organizations sponsored work of their own, including British Aerospace
Systems. Most of this research now continues under the discretionary time and
resources ofindividual researchers scattered across the globe.
It would not be appropriate to have a book about seeking new propulsion
science without first articulating the edge of interstellar flight technology, both
the foreseeable embodiments and their upper theoretical limits. Chapter 2 pro-
vides a thorough overview of the edge of interstellar technology, along with
details about optimum trajectory and mission planning. Comparisons between
the required mission energies and available terrestrial energy are provided to
convey the scale of the challenge. Methods to minimize trip time and vehicle
system mass are offered, including assessments of the impact of acceleration
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andmaximumcruisevelocity.Anumberoftechnologicaloptionsaredescribed,
including their performance predictions, spanning the technology of light sails
through antimatter-annihilation rockets.
Presently, the scientific foundations from which to engineer space drives—
propulsionthatusesonlytheinteractionsbetweenthespacecraftanditssurround-
ingspace—donotexist.Tohelpinitiatethesystematicsearchandassessmentof
possibilities,Chapter3transformsthemajorobjectionstothenotionofaspace
driveintoaproblemstatementtoguidefutureresearch.Themajorobjectionsare
the scarcity of indigenous reaction mass (for momentum conservation), and the
lack of known methods to impart net forces against such matter. By examining
these issues and the various forms of matter in the universe, and by examining
10 hypothetical space drives, a problem statement is derived. From simple
energy analyses, estimates for potential benefits and various analytical
approaches are identified. It is found that the very definitions of spacetime and
inertialframeswarrantdeeperresearch.Whenviewedinthecontextofspacepro-
pulsion rather than general science, these questions present different research
paths that stillhave notbeen explored.
Whenitcomestomovingspacecraftwithoutusingrocketsorlightsails,one
of the most commonly raised approaches is that of manipulating gravity.
Chapter 4 examines several ways of approaching this challenge, from simple
Newtonian concepts, General Relativity Theory, semi-classical Quantum
Gravity Theory, Quantum Field Theory, and others. Although it is possible, in
principle, to create or modify acceleration fields, the present theoretical
approaches require large (kilometer scale) and massive (solar-system scale)
devices operating at extremely high energy levels (relativistic). The chapter
also addresses the cosmological antigravity interpretations of dark energy, to
find that this does not lead to obvious propulsion opportunities. The details of
a wide variety of specific approaches are discussed, and key issues and unex-
plored researchpathsare identified.
Whereas Chapter 4 dealt with theoretical approaches, Chapter 5 examines
recentexperimentalapproachestocreategravitational-likeeffectsusingsupercon-
ductors.Anintroductiontothetheoreticalbasisfortherelationshipbetweengravity
andsuperconductorsfromGeneralRelativityispresented,followedbydescriptions
ofavarietyofexperimentalcomplicationsthatoccurwhenexploringsuchnotions.
Thesecomplicationsareincludedtobetterconveythedifficultyofaccuratelydedu-
cinghownatureworksvialow-temperatureexperiments.Andfinally,anoverviewis
provided of earlier and ongoing attempts to experimentally observe gravitational
effects with superconducting and low-temperature devices. Some experiments
haveturnedouttobedead-ends,whileothersarestillunderevaluation.
Asmuchasitisimportanttoidentifythepromisingareasoffutureresearch,it
isalsoimportanttoclearlystatewhysomeapproacheswillnotwork,especially
whensuchapproachesarerepeatedlysuggested.Thisisthecasewithmechanical
devices that purport to create net forces or antigravity-like effects. Chapter 6
gives examples of very common devices, discusses why they might appear to
be breakthroughs, and explains why they are not. It also offers suggestions for
tests to provide convincing evidence of their operation, including methods that
are written at a level suitable for the independent researchers who frequently
propose similar devices. It is hoped that, by providing this information, other
xx
researchers who are asked to review such submissions can more quickly and
effectivelyrespond.
Chapter7presentsthefindingsoftheYamishitaelectrogravitationalpatent,
which is another null result that warrants reporting. The patent claim involves
coupling electrical charge with a rotating mass to produce a gravitational-like
force (which was not observed in these independent tests). The chapter also
shows how to inexpensively test such claims in a manner that helps educate
studentsonthemethodsofscientificinquiry.Theseexperimentswereconducted
as student projects at the U.S. Air Force Academy, in Colorado Springs,
Colorado.
AverycommondevicepromotedovertheInternetisthe“Lifter,”whichhas
numerousvariants(Biefeld–Brown,AsymmetricalCapacitorThrusters,electro-
gravitics,etc.),someofwhichhaveexistedformorethan80years.Thisdevice
involves high-voltage capacitors that create thrust by interacting with the sur-
rounding air. Perhaps because of the ease of their construction and the scarcity
of rigorous publications on this phenomenon, many jump to the conclusion
thattheeffectisevidenceof“antigravity.”Chapter8reportsoncarefulmeasure-
ments of various capacitor configurations, itemizing the resulting correlations.
The final conclusion is that the observed effects are consistent with corona
wind, which can alsobe referred toas iondrift.
In addition to the comprehensive in-air tests of the previous chapter,
Chapter 9 reports on tests in nitrogen and argon at atmospheric pressure and
at various partial vacuums. Several other device geometries are examined also
asarethoroughvariationsofpolarityandgroundconnections.Thecombination
ofgroundingoptions,geometry,andpolarityarefoundtoaffectthrust.Because
the thrust is found to be inversely proportional to the pressure, these findings
support the coronal wind conclusion of Chapter 8. More specifically, this
chapter concludes that the thrust is from the charged ions leaking across the
capacitor that undergo multiple collisions with air, transferring momentum to
neutral airmolecules in the process.
Whereas the momentum of a photon in vacuum is well understood, the
momentum of a photon passing through dielectric media has generated signifi-
cant debate, beginning with the Abraham–Minkowski controversy of 1908. In
particular, the Abraham formulation of the electromagnetic stress tensor in a
dielectricmediumpredictsaphotonmomentumthatdiffersfromtheMinkowski
formulation,andexperimentaltestshavenotyetbeenabletoresolvewhichper-
spective is correct. This controversy has entered the realm of breakthrough
spaceflight,withmorethanonedeviceproposedtocreatenetthrustviamechan-
ismsembodiedbythisambiguity(Corum,Brito).Chapter10reviewstheunder-
lying physics of photon momentum in dielectric media and the potential
propulsion implications. The most critical make-or-break issues are identified,
as are the conceptual and operational difficulties associated with known exper-
iments.Inshort,itisfoundthatboththeAbrahamandMinkowskiformulations
matchexperiments,withthecaveatthattheassumptionsandconventionsofeach
formulation must be applied consistently when analyzing the entire system.
Because some of these details are subtle, it is easy to reach misleading con-
clusions if one errantly uses portions of each formulation to analyze a given
problem.
xxi
James F. Woodward, a science professor at California State University, has
been experimenting with a technique to induce net thrust using a particular
interpretationofMach’sprinciple—aprinciplethatdealswiththeverydefinition
of an inertial frame. Chapter 11 reports independent tests of this propulsion
concept, comparing it with previous experimental claims. Two devices that
weredevelopedandtestedbyWoodwardwereindependentlytestedusingasen-
sitive thrust balance developed for field-emission electric thrusters. The results
do not seem to be in full agreement with the findings claimed by Woodward
andcollaborators.Nevertheless,theimportanceofsuchadiscoveryissufficient
torecommendcontinuingexperimentationtoreachacompleteunderstandingof
the phenomenon. Even if this effect is found not to occur, the issues raised by
Woodward’s approach offer several provocative questions for deeper
investigation.
Quantumelectrodynamicstheory,whosepredictedeffectshavebeenverified
to1partin10billion,predictsthatthelowestenergystateoftheelectromagnetic
field still contains energy that can produce forces between nearby surfaces.
These Casimir forces have been measured and found to agree with predictions.
Chapter 12 examines whether this quantum vacuum might be exploited to
propel a spacecraft. Restrictions resulting from the conservation of energy and
momentumarediscussed.Apropulsionsystembasedonanuncharged,conduct-
ing, mirror that vibrates asymmetrically in the vacuum produces real photons
that create thrust. Even though the thrust is even less than a photon rocket,
this action demonstrates that the vacuum can be used for propulsion. Techno-
logicalimprovements,someofwhichareproposed,mayincreasetheaccelerat-
ing force. Many questions remain about the supporting theory, and further
experiments are needed to probe questions about the quantum vacuum that are
far beyond current theory.
Controversial theories exist in the peer-reviewed literature that assert that
inertia is a side effect of accelerated motion through quantum vacuum fluctu-
ations. Chapter 13 examines the constructs of one of these theories to identify
the critical make-or-break issues and opportunities for discriminating tests.
Although the specific approach examined in this chapter has several shortcom-
ings, the more general notion of the connection between inertia and quantum
fields remainsopen for deeperinvestigations.
Toopenthenextsectiononfaster-than-lighttravel,itisappropriatetohavea
chapteronSpecialRelativity,thetheoreticaltoolfordescribingtheconsequences
ofhyper-fastmotionthroughspacetime.Experimentalobservationsthatsupport
special relativity are described in Chapter 14. The chapter outlines the basic
groundwork of special relativity and then proceeds to show the paradoxes
created if faster-than-light travel were allowed within spacetime. Paradoxes are
presented and shown to be primarily concerned with our concept of time.
Dependingonhowtimeisdefined,itmaybepossibletoresolveallofthesepara-
doxes.Theothercaveattofaster-than-lighttravelistheissueofspacetimeitself.
Althoughfaster-than-lightmotionisclearlyaproblemwithinspacetime,thesitu-
ationisdifferentwhentoyingwithmanipulatingspacetime.Thosemanipulations
are the subject ofthe next chapter.
Whereas Special Relativity forbids faster-than-light travel within spacetime
(or at least sets interesting constraints upon motion), the situation is different
xxii
in General Relativity where spacetime itself can be manipulated. Chapter 15
examines the variety of theoretically postulated faster-than-light schemes
(warp drives and wormholes in particular) to identify the energy requirements
and make-or-break issues. Many of the related issues are provocative topics in
their own right in science, and when viewed from the point of view of hyper-
fast travel, present interesting approaches toward their resolution. It is shown
that many of the energy restrictions commonly imposed are conventions rather
than physical absolutes. The possibility of testing some elements of theory is
raised,inparticulartheuseofextremeelectricandmagneticfieldstrengthsposs-
ible with ultrahigh-intensity lasers.
General Relativity is not the only branch of science with curious issues of
faster-than-light phenomenon. Quantum Theory has its own set of provocative
topics that are commonly, and sometimes errantly, associated with faster-than-
lighttravel.Chapter16reviewssuchquantum“nonlocality”effectsandarticu-
latesnumerousexperimentsandtheirinterpretations.Oneoftheprimecomplex-
ities is having exacting definitions of what is meant by “entanglement” and
“nonlocality” and how these compare to the light-speed constraints of Special
Relativity. These complexities are explained in the chapter, and it is shown
that, in many situations, there are no conflicts. The chapter also shows that the
assumptions that lead to the “no-signal theorems” warrant close inspection
when assessing their applicability to some contemporary experiments. Under
certain circumstances, situations leading to retrocausal paradoxes can be con-
ceived where the effect precedes the cause. These situations are described, but
no resolutions exist at thispoint.
Toopenthenextsectionaboutenergyimplications,Chapter17reviewsthe
past and projected technology that is based on accrued science. Numerous
devices are reviewed, including multiple power sources and conversion
methods and estimates oftheir upper performance limits.
The phenomenon of quantum fluctuations and its high-energy density—as
calculated from some estimates—has led some to ponder if the quantum
vacuum can be tapped as an energy source. Chapter 18 examines a span of
both theoretical and experimental approaches. It concludes that energy con-
versions between vacuum fluctuations and tangible effects are possible in prin-
ciple (albeit small), but that continuous energy extraction appears problematic
on the basis of the current understanding of quantum electrodynamics theory.
Specific experimental approaches are described for investigating these issues
directly.
Sonoluminescence,whichislightgeneratedfromacousticcavitationinfluids,
has been associated with claims of energy production. To provide grounding in
thistopic,Chapter19coversrecentexperimentalmethodsandfindings.Instru-
mentation techniques that measure optical, radiation, and thermal properties of
the phenomenon of sonoluminescence are described. Initial efforts are directed
to the generation and the imaging of sonoluminescence in water and solvents.
Evidenceofhigh-energygenerationinthemodificationofthinfilmsfromsono-
luminescence is seen in heavy water but not seen in light water. The attainable
energyoutputwasfoundtobelessthantheenergyinputfortheexperimentsdis-
cussed. Improvements for realizing fusion processes and energy harvesting are
xxiii
suggested. This phenomenon also serves as an empirical path to further under-
stand the interactionof sound,light,andfluidphysics.
In much the same way that it is important to publish the space drive
approachesthatproducednullfindings,Chapter20presentsexperimentalfind-
ingsofavarietyofenergyconversiondevicespurportedtoproducemoreenergy
thantheyconsume.Althoughsuchconceptscanbesummarilydismissedforvio-
latingthermodynamiclaws, theprospectthattheremightbegenuineunobvious
energy sources has led many to suggest such devices. This chapter details the
experimental methods and experiences derived from testing such claims to
help other researchers become alert to the complexities and possible pitfalls of
related experiments.
To address challenges of breakthrough spaceflight within the sciences of
General Relativity and Quantum Field Theory, computer computational tools
are required. Calculations in these disciplines are extensive and involve
complex notational conventions. The time to do these calculations manually is
prohibitive, as is the risk of inducing transcription errors. Chapter 21 reviews
the main tensor calculus capabilities of the three most advanced and commer-
ciallyavailable“symbolicmanipulator”tools.Italsoexaminesdifferentconven-
tionsintensorcalculusandsuggestsconventionsthatwouldbeusefulforspace
propulsionresearch.
Based on lessons from history and the NASA Breakthrough Propulsion
PhysicsProject,suggestionsareofferedinChapter22forhowtocomparatively
assessthevarietyofapproachestowardrevolutionaryspaceflight.Perspectivesof
prior scientific revolutions are examined in the context of seeking spaceflight
revolutions. The intent is to identify techniques to improve the management of
such visionary research. Methods tested in the course of the Breakthrough Pro-
pulsion Physics Project are provided, including details from its one formal
cycle of research solicitations. Key recommendations are to rigorously contrast
existing foundations of science with the visionary goals of breakthrough space-
flight, and to dissect the grand challenges into more approachable, short-term
researchobjectives.
III. Snapshot ofthe Book
Followingthe principlesofa“traceability map,”asdiscussed inChapter 22,
Fig. 1 shows a relational depiction of the contents of this book. In the far left
column of this map, the relevant disciplines of science are listed. In the far
right column, the visionary goals are listed and broken down into categories of
differentapproaches.Fromthere,thesecategoriesbranchoutintonumerouscon-
cepts anddevices.Inthecolumnsbetween thefoundations ofscienceandthese
concepts and devices, there are various unknowns, critical issues, and curious
effects.
Because of printing limitations, the connecting lines between these various
facets cannot be shown, but many of the connections can be inferred by noting
the numbers in the parallelograms attached to the blocks. These numbers refer
tothechaptersinwhichthespecificitemsarediscussed.Fromthisrepresentation
itisobviousthatagivenconceptisconnectedtomanyissuesandthatthereare
xxiv
Fig.1 Relationaldepictionofthisbook’scontents.
issuesthatpertaintomanyconcepts.Inanexpandedversionofthismapitwould
bepossibletoseehowalloftheitemsareinterconnected.Theitemshavingmore
connectionswouldbethosethataremorerelevanttootherfacets.Anotherdetail
of the figure is that the shaded blocks refer to null tests or to concepts that are
shown analytically not to be viable. All of the rest of the subjects are open for
further study.