Uncertain Propulsion Breakthroughs?

by | Dec 30, 2016 | Exotic Physics | 110 comments

Now that the EmDrive has made its way into the peer-reviewed literature, it falls in range of Tau Zero’s network of scientist reviewers. Marc Millis, former head of NASA’s Breakthrough Propulsion Physics project and founding architect of the Tau Zero Foundation, has spent the last two months reviewing the relevant papers. Although he is the primary author of what follows, he has enlisted the help of scientists with expertise in experimental issues, all of whom also contributed to BPP, and all of whom remain active in experimental work. The revisions and insertions of George Hathaway (Hathaway Consulting), Martin Tajmar (Dresden University), Eric Davis (EarthTech) and Jordan Maclay (Quantum Fields, LLC) have been discussed through frequent email exchanges as the final text began to emerge. Next week I’ll also be presenting a supplemental report from George Hathaway. So is EmDrive new physics or the result of experimental error? The answer turns out to be surprisingly complex.

by Marc Millis, George Hathaway, Martin Tajmar, Eric Davis, & Jordan Maclay

It’s time to weigh in about the controversial EmDrive. I say, controversial, because of its profound implications if genuine, plus the lack of enough information with which to determine if it is genuine. A peer-reviewed article about experimental tests of an EmDrive was just published in the AIAA Journal of Propulsion and Power by Harold (Sonny) White and colleagues: White, H., March, P., Lawrence, J., Vera, J., Sylvester, A., Brady, D., & Bailey, P. (2016), “Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum,” Journal of Propulsion and Power, (print version pending, online version here.

That new article, plus related peer-reviewed articles, were reviewed by colleagues in our Tau Zero network, including two who operate similar low-thrust propulsion tests stands. From our reviews and discussions, I have reached the following professional opinions – summarized in the list below and then detailed in the body of this article. I regret that I can only offer opinions instead of definitive conclusions. That ambiguity is a significant part of this story that also merits discussion.

Overview

Technical

(1) The experimental methods and resulting data indicate a possible new force-producing effect, but not yet satisfying the threshold of “extraordinary evidence for extraordinary claims” – especially since this is a measurement of small effects.

(2) The propulsion physics explanations offered, which already assume that the measured force is real, are not sound.

(3) Experiments have been conducted on other anomalous forces, whose fidelity and implications merit comparable scrutiny, specifically Jim Woodward’s “Mach Effect Thruster.”

Implications

(1) If either the EmDrive or Mach Effect Thrusters are indeed genuine, then new physics is being discovered – the ramifications of which cannot be assessed until after those effects are sufficiently modeled. Even if it turns out that the effects are of minor utility, having new experimental approaches to explore unfinished physics would be valuable.

(2) Even if genuine, it is premature to assess the potential utility of these devices. Existing data only addresses some of the characteristics necessary to compare with other technologies. At this point, it is best to withhold judgment, either pro or con.

Pitfalls to Avoid

(1) The earlier repeated tactic, to attempt fast and cheap experimental tests, has turned out to be neither fast nor cheap. It’s been at least 14 years since the EmDrive first emerged (2002) and despite numerous tests, we still lack a definitive conclusion.

(2) In much the same way that thermal and chamber effects are obscuring the force measurements, our ability to reach accurate conclusions is impeded by our natural human behavior of jumping to conclusions, confirmation biases, sensationalism, and pedantic reflexes. This is part of the reality that also needs understanding so that we can separate those influences from the underlying physics.

Recommendations

(1) Continue scrutinizing the existing experimental investigations on both the EmDrive and Mach Effect Thrusters.

(2) To break the cycle of endlessly not doing the right things to get a definitive answer, begin a more in-depth experimental program using qualified and impartial labs, plus qualified and impartial analysts. The Tau Zero Foundation stands ready to make arrangements with suitable labs and analysts to produce reliable findings, pro or con.

(3) If it turns out that the effects are genuine, then continue with separate (a) engineering and (b) physics research, where the engineers focus on creating viable devices and the physicists focus on deciphering nature. In both cases:

  • Characterize the parameters that affect the effects.
  • Deduce mathematical models.
  • Apply those models to (a) assess scalability to practical levels, and (b) understand the new phenomena and its relation to other fundamental physics.
  • On all of the above, conduct and publish the research with a focus on the reliability of the findings rather than on their implications.

Details

Pitfall 1 – The Fog of Want

Our decisions about this physics are influenced by behaviors that have nothing to do with physics. To ignore this human element would be a disservice to our readers. To get to the real story, we need to reveal that human element so that we can separate it from the rest of the data, like any good experiment. I’m starting off with this issue so that you are alert to its influences before you read the rest of this article.

As much as I strive to be impartial, I know I have an in-going negative bias on the EmDrive history. To create a review that reflects reality, rather than echoing my biases, I had to acknowledge and put aside my biases. Similarly, if you wish to extract the most from this article, you might want to check your perspectives. Ask yourself these three questions: (1) Do you already have an opinion about this effect and are now reading this article to see if we’ll confirm your expectation? (2) Do you want to know our conclusions without any regard to how we reached those conclusions? (3) Are you only interested in this EmDrive assessment, without regard to other comparable approaches?

If you answered “yes” to any of those questions, then you, like me, have natural human cognitive dysfunctions. To get past those reflexes, start by at least noticing that they exist. Then, take the time to notice both the pros and cons of the article, not just the parts you want to be true. Deciphering reality takes time instead of just listening to reflexive beliefs. It requires that one’s mind be open to the possibility you might be right and equally open to the possibility you might be wrong.

EmDrive History

This history is a recurring theme of incredible claims with non-credible evidence for those claims. In all cases, the effect is assumed to be real before the tests – which reflects a blinding bias. This dates back to at least 2002 when Roger Shawyer claimed to invent a device that “provides direct conversion from electrical energy to thrust, without expelling propellant.” I was still at NASA and vaguely remember reviewing it then. Regardless of the claims, the fidelity of the methods were below average. Over the years I heard about several other tests, but never saw any data. Eventually there was a press story about tests in China, along with this photo. It turns out that this photo is not a Chinese rig, but one of Shawyer’s:

fig01

Shawyer’s device and supporting equipment are on a rotating frame, where that rotation is used to determine if the device is thrusting. Note, however, the radiator and coolant lines. Any variation in the coolant flow would induce a torque that would obscure any real force measurements. Knowing the claimed thrusting effect is small and having enough experience to guess the likely variations in coolant flow, I considered this test set-up flawed.

Regarding the Chinese tests, I did not previously know they are described in peer-reviewed articles. Since many of us did not know either, I’m listing them here along with cursory impressions:

Juan, Y., et al, (2012). Net thrust measurement of propellantless microwave thrusters. Acta Physica Sinica, Chinese Physical Society.

Due to all of the impressions below, I do not have any confidence in their data:

  • Assumes first that the EmDrive is genuine.
  • Verbally describes theory, but without predicting experimental findings.
  • The experiment is not described in enough detail to assess its fidelity, but is similar to the one in the photo. Regardless, there is absolutely no discussion of possible influences on the rotation from tilting, power lead forces, vibration effects, thermal effects, or others.
  • The behavior of the thrust stand was not characterized before installing the EmDrive. Testing the two together without first having characterized the thrust stand separately prevents separating their distinct characteristics from the data.
  • The data plots lack error bands.

Juan, Y., et al (2013). Prediction and experimental measurement of the electromagnetic thrust generated by a microwave thruster system. Chinese Physics B, 22(5), 050301.

Due to all of the impressions below, I do not have any confidence in their data:

  • The description of the experiment is improved from the 2012 paper and appears to be the same configuration. This time possible effects from tilting and the power lead forces are mentioned, but they still do not address vibration, thermal, coolant loop, or other effects.
  • Again, they fail to characterize the thrust stand separately from the EmDrive.
  • Unlike the 2012 paper, they attempt to make numerical predictions. Details are provided for their physics derivations (which I did not scrutinize). That theory is then applied to make predictions for their specific hardware, but only verbally described it, rather than showing an explicit derivation. They show plots of the predicted force versus power, but only up to 200W, where the experimental runs span about 100W to 2400W.
  • The experimental results do not match their linear predictions for the ratio of force-to-power. These differences are then evasively dismissed.

Juan, Y., et al. (2016), “Thrust Measurement of an Independent Microwave Thruster Propulsion Device with Three-Wire Torsion Pendulum Thrust Measurement System,” Journal of Propulsion Technology, vol. 37, no. 2, pp 362-371.

The text is in Chinese, which I did not translate, but the figures and plots are captioned in English. Therefore I comment only on those diagrams. Again, what is shown is not enough to support claims of anomalous forces:

  • From figures 2, 3, 6, 7, 16, and 19, it appears the prior apparatus is now hung from torsion wires instead of a rotating support from below. This time the coolant loop is explicitly shown, but in a conceptual drawing instead of showing specifics. Again, the influence of the coolant loop is ignored.
  • The only “measurement results” plot is “force versus serial number” – which conveys no meaningful information (without being able to read associated text).
  • I learned later from Martin Tajmar, that the observed thrust drops by more than an order of magnitude when the device is powered by batteries instead of the external cables (cables whose currents can induce forces).

I chose not to cite and comment on the many non-peer-reviewed articles on Shawyer’s website and related AIAA conference papers.

Shawyer eventually published a peer-reviewed article, specifically: Shawyer, R. (2015), “Second generation EmDrive propulsion applied to SSTO launcher and interstellar probe,” Acta Astronautica, vol. 116, pp 166-174. Shawyer states: “Theoretical and experimental work in the UK, China and the US has confirmed the basic principles of producing thrust from an asymmetric resonant microwave cavity.” That assertion has not held up to scrutiny. Therefore, all related assertions are equally unfounded. Instead of offering substantive evidence, this article instead predicts the performance for three variations of EmDrives that now claim to use superconductivity. From these, he presents conceptual diagrams for their respective spacecraft. He also mentions the “Cannae Drive,” by Guido Fetta, as another embodiment of his device.

Latest EmDrive Paper

The latest paper, in the AIAA Journal of Propulsion and Power, is an improvement in fidelity on the prior tests and may be indicative of a new propulsive effect. However, the methods and data are still not crossing the threshold of “extraordinary evidence for extraordinary claims” – especially since this is a measurement of small effects. With the improved fidelity of the reporting and the data traces themselves, I have to question my earlier bias that the prior data was entirely due to experimental artifacts and proponent biases.

The assessment offered below is a summary of discussions with the coauthors of this report plus a few other colleagues. Both Martin Tajmar and George Hathaway operate similar low-thrust propulsion test stands and thus are familiar with such details. George Hathaway’s more focused analysis will be posted in a future Centauri Dreams article.

The major problems with the paper are (1) lack of impartiality, (2) the test hardware is not sufficiently characterized to separate spurious effects from the test article’s effects, (3) the data analysis is marred by the use of subjective techniques, and (4) the data can be interpreted in more than one way – where one’s bias will affect one’s conclusions.

The first shortcoming of the paper is that it is biased. It assumes that the propulsion effect is genuine and then goes on to invent an explanation for that unverified effect. This bias skews how they collect and analyze the data. To be more useful, the paper should have reported impartially on its experimental and analytical methods to isolate a potential new force-producing effect from other contaminating influences.

The next shortcoming is insufficient testing for how spurious causes can affect the thrust stand. While this new paper is a significant improvement over the previous publications, it falls short of providing the needed information to reach a definitive conclusion. They use techniques comparable to engineering tests of conventional low-thrust electric propulsion. While such engineering techniques might be passable for checking electric propulsion design changes, it is not sufficient to demonstrate that a new physics effect exists. The specific shortcomings include:

  • Thrust stand tilting: The thrust stand has a vertical axis, where even slight changes of that alignment will affect how the thrust stand behaves. There are three parts to this, none of which are quantified: the fidelity of the thrust stand flexures and pivots, the alignment fidelity of that structure to the vacuum chamber, and the sustained levelness of the “optical bench” upon which the vacuum chamber is mounted.
  • Thrust stand characterization: The thrust stand does not return to its original position after tests, even for most calibration events. Additionally, the thrust stand is over-damped, meaning that it is slow to respond to changes, including the calibration events. Those characteristics (time for the thrust stand to respond to a known force and the difference between its before/after positions) are important to understand so that those artifacts can be separated from the data. These facets are largely ignored in the paper. The report does mention that the location of the masses on the thrust stand affects its response rate (“split configuration” versus “non-split”), but this difference is not quantified. The thrust stand uses magnetic dampers. Similar dampers used on one of Martin Tajmar’s thrust stands were found to cause spurious effects (subsequently replaced with oil dampers). Given the irregular behavior, it is fair to suspect that other causes are interfering with the motion of the thrust stand. The flexural bearings might be operated beyond their load capacity or might be affected by temperature.
  • Forces from power cables: To reduce the influence of electromagnetic forces from the power leads, Galinstan liquid metal screw and socket connections are used. While encouraging, it is not specified if these connections (several needed) are all coaxially aligned with the stand’s rotation axis (as required to minimize spurious forces). Also, there are no tests with power into a dummy load to characterize these possible influences.
  • Chamber wall interactions: Though mentioned as a possible source of error, the electromagnetic forces between the test device and the vacuum chamber walls are dismissed without quantitative estimates or tests. One way that this could have been explored is by using more variations in the position and orientation of the test device relative to the chamber. For example, in the “null thrust” configuration, only one of four possibilities is used (the device pointed toward the pivot axis). If also pointed up, down, and away from the pivot, more information would have been collected to help assess such effects.
  • Thermal effects: The paper acknowledges the possible contributions from thermal effects, but does not quantify that contribution. For example, there are no measurements of temperature over time compared to the thrust stand’s deflection. Such measurements should have been made during operation of the device and when running power through a dummy load. Absent that data, the paper resorts to subjectively determining which parts of the data are thermal effects. For example, without any validation, the paper assumes that the displacement measured during the “null thrust” configuration is entirely a thermal effect. It does not consider chamber wall interactions or any other possible sources. The paper does speculate that temperature changes might shift the center of gravity of the test article in a way that affects the thrust stand, but no diagrams are offered showing how a slight change in one of those dimensions would affect the thrust stand.

The third and most egregious shortcoming in the report is that they apply a vaguely described “conceptual simulation” (which is never mathematically detailed) as their primary tool to deduce which part of the data is attributable to their device and which is due to thermal effects. They assume a priori the shapes of both the “impulsive thrust” (their device) and thermal effects and how those signals will superimpose. There is no consideration of chamber wall effects, power lead forces, tilting, etc. As a reflection of how poorly defined this assumed superposition, the ‘magnitude’ and ‘time’ axes on the chart showing this relation (Fig. 5) are labeled as “arbitrary units.” Another problem is that their assumed impulsive thrust curve does not match the shape of most of the data that they attribute to impulsive thrust. Instead of the predicted smooth curve, the data shows deviations about halfway through the thrusting time. They then apply this subjective and arbitrary tool to reach their conclusions. Because they are biased that the effect is genuine and because their methods overlook critical measurements, I cannot trust the authors’ interpretations of their results.

Absent an adequate accounting for the magnitude and characteristics of secondary causes and how to remove those possible influences from the data, the fourth major problem with the report is that its data can then be interpreted more than one way.

Rather than evoking subjective techniques here, the comments that follow are based only on examining their data plots as a whole. To illustrate how this data can then be interpreted in more than one way, both dismissive and supportive interpretations are offered. In particular, we compare the traces from the “forward,” “null,” and “reverse” thrust configurations and then the force versus power compilation of the runs.

The data for the 80W operation of the device in the “forward,” “null,” and “reverse” thrust configurations is presented in Figures, 9c, 18, and 10c, respectively. Recall from the above discussions that this data includes all the uncharacterized spurious causes (thermal, chamber wall interactions, power lead forces, tilting of the thrust stand, and seismic effects), plus any real force from the test device. The values shown in the table below were read from enlarged versions of the figures.

emdrive_table

Table of Noteworthy Data Comparisons Between Forward, Null, and Reverse Thrust Orientations

For a genuine thrusting effect, one would expect the results to show near-matching magnitudes for forward and reverse thrust and a zero magnitude for the null-thrust orientation. If one looks only at the “Total deflection,” all the magnitudes are roughly the same, including the null-thrust. Pessimistically, one could then infer that the spurious effects are great enough to be easily misinterpreted as a genuine thrust.

emdrive_figure

Conversely, if one considers how quickly the deflections occur, then the attention would be on the “Rate of deflection.” In that case, the thrusting configurations are roughly twice as large as the null-thrust configuration. From only that, one might infer that a new force-producing effect is larger than spurious causes.

To infer conclusions based on the deflection rates, one must also examine the rate of deflection for the calibration events, which should be the same in all configurations. The calibration deflection rate appears roughly the same in the forward and reverse thrust configuration, but more than 2.5 times larger in the null thrust configuration. That there is a difference compounds the difficulty of reaching conclusions. There are also significant inconsistencies with how the thrust stand rebounds once the power is turned off between the thrusting and null-thrust configurations, again compounding the difficulty of reaching conclusions.

Because a possible positive interpretation exists within those different perspectives, I cannot rule out the possibility that the data reflects a new force-producing effect. But as stated earlier, given all the uncharacterized secondary effects and the questionable subjective techniques used in the report, this is not sufficient evidence. Given the prominent role played by the rate of deflections, the dynamic behavior of the thrust stand must be more thouroughly understood before reaching firm conclusions.

Next, let’s examine the compilation of runs, namely Fig. 19. Based on a linear fit through the origin with the data, they conclude a thrust-to-power ratio of 1.2 ± 0.1 mN/kW (=µN/W). While this is true, the data can be interpreted more than one way. Note that the averages for 60 and 80 watts operations are the same, so a linear fit is not strictly defensible. One could just as easily infer that increasing power yields decreasing thrust, a constant 50 µNewton force, or an exponential curve that flattens out to a constant (saturated) thrust of about 100 uN. Note too that the null-thrust data (which could be interpreted to be as high as 211 µN) is not shown on this chart.

white_fig19

Recall too that they did not quantify the potential spurious effects, so their presumed error band of only ±6 µN does not stand up to scrutiny. Note, for example, the span in the 40W data is about ± 17µN, the 60W about ± 50µN, and the 80W about ± 32µN. What is not clear is if these 40, 60, and 80 Watt runs represent different operating parameters (Q-factor?), or if instead, these are the natural variations with fixed settings.

The pessimistic interpretation is that the deviations in the data represent variations for the same operating conditions, in which case the data are too varied from which to conclude any correlations. Conversely, the optimistic interpretation is to assume the variations are due to changes in operating parameters, but then that additional information should be made available and be an explicit part of the analysis.

In summary, this most recent report is a significant improvement, but has many shortcomings. Questionable subjective techniques are used to infer the “thrust” from the data. Other likely influences are not quantified. But also, despite those inadequacies, the possibility of a new force-producing effect cannot be irrefutably ruled out. This is intriguing, but still falling short of defensible evidence.

EmDrive and Other Space Drive Theories

First, I cannot stress enough that there is no new EmDrive “effect” yet about which to theorize. The physical evidence on the EmDrive is neither defensible nor does it include enough operating parameters to characterize a new effect. The data is not even reliable enough to deduce the force-per-power relationship, let alone any other important correlations. What about the effects of changing the dimensions or geometry, changing the materials, or changing the microwave frequencies or modulation? And then there is the unanswered question, what are the propulsion forces pushing on?

Assuming for the moment that the EmDrive is a new force-producing effect, we know at least two things (1) it is not a photon rocket, because the claimed forces are 360 times greater than the photon rocket effect, and (2) a force, without an “equal and opposite force,” goes beyond Newton’s laws. Note that I did not evoke the more familiar “violating conservation of momentum” point. That is because these experiments are still trying to figure out if there is a force. We won’t get to conservation of momentum until after those forces are applied to accelerate an object. If that happens, then we must ask what reaction mass is being accelerated in the opposite direction. If the effects are indeed genuine, then new physics is being discovered or old physics is being applied in a new, unfamiliar context.

For those claiming to have a theory to predict a new propulsion effect, it is necessary that those theories make testable numeric predictions. The predictions in Juan’s 2013 paper did not match its results. The analytical discussions in White’s 2016 experimental paper do not make theoretical predictions. The same is true with his 2015 theoretical paper: White (2015), “A discussion on characteristics of the quantum vacuum,” Physics Essays, vol. 28, no. 4, 496-502.

Short of having a self-consistent theory, any speculations should at least accurately echo the physics they cite. The explanations in the White’s 2016 experimental paper, White’s 2015 theory paper, and even White’s 2013 report on the self-named “White-Juday Warp Field Interferometer” (White (2013), “Warp Field Mechanics 101,” Journal of the British Interplanetary Society, vol. 66, pp. 242-247), did not pass this threshold. I’ll leave to other authors to elaborate on the 2015 and 2016 papers, while a review of the 2013 warp drive claims is available here. It is Lee & Cleaver (2014), “The Inability of the White-Juday Warp Field Interferometer to Spectrally Resolve Spacetime Distortions,” [physics.gen-ph].

In contrast, it is also important to avoid pedantic reflexes – summarily dismissing anything that does not fit what we already know, or assuming all of our existing theories are completely correct. For example, the observations that lead to the Dark Matter and Dark Energy hypotheses do not match existing theories, but that evidence has been reliably documented. Using that data, many different theories are being hypothesized and tested. The distinction here is that both the proponents and challengers make sure they are accurately representing what is, and is not yet, known.

If a propulsion physics breakthrough is to be found, it will likely be discovered by examining relevant open questions in physics. A relevant theoretical question to non-rocket propulsion concepts (including the EmDrive) is ensuring conservation of momentum. One way to approach this is to look for phenomena is space that might serve as a reaction mass in lieu of propellant, perhaps like the quantum vacuum. Another approach is to dig deeper into the nature of inertial frames. Inertial frames are the reference frames upon which the laws of motion and the conservation laws are defined, yet it is still unknown what causes inertial frames to exist or if they have any deeper properties that might prove useful.

Woodward Tests and Theory

In addition to the overtly touted EmDrive, there are about two-dozen other space drive concepts of varying degree of substance. One of them started out as a theoretical investigation into the physics of inertial frames which then advanced to make testable numeric predictions. Specifically I’m referring to what is now called the “Mach Effect Thruster” concept of James F. Woodward, which dates back at least to this article:

Woodward, James F. (1990), “A new experimental approach to Mach’s principle and relativistic gravitation,” Foundations of Physics Letters, vol. 3, no. 5, pp. 497-506.

A more in-depth and recent publication on these concepts is available as:

Woodward, James F. (2013) Making Starships and Stargates: The Science of Interstellar Transport and Absurdly Benign Wormholes. Springer Praxis Books.

Experiments have been modestly underway for years, including three recent independent replication attempts by George Hathaway in Toronto Canada, Martin Tajmar in Dresden Germany, and Nembo Buldrini in Wiener Neustadt, Austria. A workshop was held to review these findings in September 20-23, 2016, in Estes Park, Colorado. I understand from an email conversation with Jim Woodward that these reports and workshop proceedings are now undergoing peer review for likely publication early in 2017.

The main point here, by citing just this one other example, is that there are other approaches beyond the highly publicized EmDrive claims. It would be a disservice to our readers to let a media fixation with one theme blind us to alternatives.

Implications

If either the EmDrive or Mach Effect Thruster is indeed genuine, then new physics is being discovered or old physics is being applied in a new, unfamiliar context. Either would be profound. Today it is premature to assert than any of these effects are genuine, or conversely, to flatly rule out that such propulsion ambitions are impossible. When the discussions are constrained to exclude pedantic disdain and wishful interpretations, and limited to people who have either the education or experience in related fields, one encounters multiple, even divergent, perspectives.

Next, even if new physics-to-engineering is emerging, it is premature to assess its utility. The number of factors that go into deciding if a technology has an advantage over another are way beyond what data is yet available. Recall that the performance of the first aircraft, jet engine, transistor, etc, were all tiny examples of what those breakthroughs evolved to become. Reciprocally, we tend to forget about all the failed claims who have faded into obscurity. We just do not know enough today, pro or con, to judge.

I realize the urge within human behavior for fast, definitive answers that we can act on. This lingering uncertainty is aggravating, even more so when peppered with distracting hype or dismissive disdain. To get to the underlying reality, we must continue with a focus on the fidelity of the methods to produce reliable results, rather than jumping to conclusions on the implications.

What to Do About It

If you want definitive answers, then we must improve the reliability of the methods and data, and remain patiently open for the results to be as they are, good news or bad news. I alluded earlier to the broken tactic of trying to get answers with fast and cheap experiments. How many inadequate experiments and over how many years does it take before we change our tactics? I’ve had this debate more than once with potential funding sources and I hope they are reading now to see… “I told ya so!” Sorry, I could not resist that human urge to emotionally amplify a well-reasoned point. To break the cycle of endlessly not doing the right things to get a definitive answer, we must begin a more in-depth experimental program using qualified and impartial labs, plus qualified and impartial analysts. Granted, those types of service providers are not easy to find, where impartiality is the hardest to come by. Also, it might take three years to get a reliable answer, which is at least better than 14 years. And the trustworthy experiments will not be cheap, but quite likely far less than the aggregate spent on the repeated ‘cheap’ experiments. If any of those prior funding sources (or new) are reading this and finally want trustworthy answers, contact us. Tau Zero stands ready to make arrangements with suitable labs and analysts to conduct such a program.

And what if we do discover a breakthrough? In that case, we recommend distinguishing two themes of research, one from an engineering point of view to nudge the effect into a useful embodiment, and another from an academic point of view, to fully decipher and compare the new effects to physics in general. In both those cases we need to:

1. Characterize the parameters that affect the effects. Instead of just testing one design, vary the parameters of the device and the test conditions to get enough information to work with.

2. Deduce mathematical models from that more complete set of information.

3. Apply those models to (a) assess scalability to practical levels, and (b) explore the new phenomena and its relation to other fundamental physics.

4. On all of the above, conduct and publish the research with a focus on the reliability of the findings rather than on their implications.

For those of you who are neither researchers nor funding sources, what should you do? First, before reposting an article, take the time to see if it offers new and substantive information. If it turns out to be hollow click-bait, then do not share it. If it has both new information with meaningful details, then share it. Next, as your read various articles, notice which sources provide the kind of information that helps you understand the situation. Spend more time with those sources and avoid sources who do not.

Regarding questionable press stories, I’m not sure yet what to make of this: “The China Academy of Space Technology (CAST), a subsidiary of the Chinese Aerospace Science and Technology Corporation (CASC) and the manufacturer of the Dong Fang Hong satellites, has held a press conference in Beijing explaining the importance of the EmDrive research and summarizing what China is doing to move the technology forward.” Some stories claim there is a prototype device in orbit. If true, I would expect to see at least one photo of the device being tested in space. But we’ll see…

When faced with uncertain situations and where the data is unreliable, the technique I use to minimize my biases is to simultaneously entertain conflicting hypotheses, both the pro and con. Then, as new reliable information is revealed, I see which of those hypotheses are consistent with that new data. Eventually, after enough reliable data has accrued, the reality becomes easier to see.

Note

The cited devices have gone by multiple names (e.g. EmDrive, EM Space Drive; Mach Effect Thruster, Mach-Lorentz Thruster), and the versions used in this article are the ones with the greatest number of Google search hits.

tzf_img_post

New Horizons: Going Deep in the Kuiper Belt

by | Dec 29, 2016 | Outer Solar System | 11 comments

We’ve retrieved all the data from New Horizons’ flyby of Pluto/Charon in 2015, the last of it being acquired on October 25 of this year. But data analysis is a long and fascinating process, with papers emerging in the journals and new discoveries peppering their pages. The New Horizons science team submitted almost 50 scientific papers in 2016, and we can expect that stream of publication to continue in high gear as we move deeper into the Kuiper Belt.

For New Horizons is very much an ongoing enterprise, as Alan Stern’s latest PI’s Perspective makes clear. We have an encounter with a small Kuiper Belt object (KBO) called 2014 MU69 to think about, and the symmetry that Stern points to in his essay is striking. Two years ago New Horizons had just emerged from cruise hibernation as preparations for the Pluto/Charon encounter began. And exactly two years from now, we’ll be again following the incoming datastream as the last of the New Horizons targets comes into breathtaking proximity.

2016-12-year-of-kbo-artwork-1

But 2014 MU69 isn’t the only KBO in the cards. Stern describes what’s next:

The year ahead will begin with observations of a half-dozen KBOs by our LORRI [LOng Range Reconnaissance Imager] telescope/imager in January. Those observations, like the ones we made in 2016 of another half-dozen KBOs, are designed to better understand the orbits, surface properties, shapes, satellite systems and frequency of rings around these objects. These observations can’t be done from any ground-based telescope, the Hubble Space Telescope, or any other spacecraft – because all of those other resources are either too far away or viewing from the wrong angles to accomplish this science. So this work is something that only New Horizons can accomplish.

Ponder that 2014 MU69 is almost 6.5 billion kilometers out and you have to wonder when we’ll next get a spacecraft this deep into the system. The answer has as much to do with funding as our technologies, since a wide variety of outer system probes have been under discussion in the last forty years. Each new deep space mission that actually flies fuels public interest, but the phenomenon is all too brief, and although space exploration seems to be flourishing in the movies these days, it’s hard to see a New Horizons sequel any time soon.

Even so, I’m optimistic in the longer term because the process in view in a mission of this complexity works its own kind of magic. Yesterday I wrote about Vera Rubin’s ability to communicate not just her love of the stars to young scientists she worked with but her values of tenacity, curiosity and exploration. In the same way, a mission executed with the precision of New Horizons has to set an example for budding scientists everywhere, a young population out of which will surely grow at least a few future principal investigators like Alan Stern.

New Horizons is a long way from home, and January will be used to take advantage of its position through measurements of hydrogen gas in the heliosphere (using the Alice ultraviolet spectrometer) and charged particles and dust (through the SWAP, PEPSSI and SDC instruments). What’s different today about space missions is that a student with a PC can drill deep into all this, following tweets from researchers, exploring ideas on blogs and reading direct communications from the mission team. The Apollo days were fantastic, but we could never get as close to a mission as we can get to a New Horizons, or a Dawn or a Rosetta.

There are going to be things to track in early 2017 as New Horizons makes yet another course correction, but the spacecraft will then enter hibernation until September, when a new round of KBO observations begins. As Stern points out, flyby operations for 2014 MU69 are set to commence in July of 2018, meaning that while the vehicle hibernates, the mission teams will be writing and testing the command sequences for the January 1, 2019 flyby.

So the absorbing process of a deep space mission continues to play out in space and on Earth. The first observations ever made of a Kuiper Belt Object from within the Kuiper Belt itself are now out in the form of a paper in Astrophysical Journal Letters. The object is 1994 JR1, studied through the LORRI instrument after the Pluto/Charon flyby from a distance of 1.85 AU and then about six months later from a distance of 0.71 AU. The earlier observations were supplemented with simultaneous Hubble studies of the same object. We learn quite a lot from these early observations. From the paper’s summary:

(15810) 1994 JR1 has a V-R of 0.76, making it a very red KBO [V-R refers to spectral slope, a measure of reflectance vs wavelength]. Unique New Horizons observations showed that JR1 has a high surface roughness of 37±5°, indicating that it is potentially very cratered. They also showed that the rotational period of JR1 is 5.47±0.33 hours, faster than most similar-sized KBOs, and enabled a reduction of radial uncertainty of JR1’s position from 105 to 103 km.

Moreover, New Horizons has revealed this KBOs interactions with the objects around it:

Neptune perturbations bring Pluto and JR1 close together every 2.4 million years, when Pluto can perturb JR1’s orbit. Future ground-based photometry of JR1 would be useful to better constrain the period and opposition surge, and to allow preliminary estimates of JR1’s shape and pole. These proof of concept distant KBO observations demonstrate that the New Horizons extended mission will indeed be capable of observing dozens of distant KBOs during its flight through the Kuiper Belt.

Ongoing science like this from the outer Solar System will snare the attention of people making their initial way into astronomy and astronautics. Who knows what careers will be shaped by these studies, and what new targets that next generation will explore?

The paper is Porter et al., “The First High-Phase Observations of a KBO: New Horizons Imaging of (15810) 1994 JR1 from the Kuiper Belt,” Astrophysical Journal Letters Vol. 828, No. 2 (2016). Preprint available.

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Vera Rubin (1928-2016)

by | Dec 28, 2016 | Deep Sky Astronomy & Telescopes | 11 comments

When Vera Rubin went to Cornell University to earn a master’s degree, she quickly found herself immersed in galaxy dynamics, lured to the topic by Martha Stahr Carpenter. The interest, though, was a natural one; it drew on Rubin’s childhood fascination with the motion of stars across the sky. You could say that motion captivated her from her earliest days. At Cornell, she studied physics from such luminaries as Richard Feynman, Philip Morrison and Hans Bethe. She would complete the degree in 1951 and head on to Georgetown.

Rubin, who died on Christmas day, was possessed of a curiosity that made her ask questions others hadn’t thought of. In Bright Galaxies, Dark Matters (1997), a collection of her papers, the astronomer recalls writing to Milton Humason in 1949, asking him about the redshifts he and his colleagues were compiling. Rubin had heard that many had yet to be published, and she would use those she had to look for systematic motion among the galaxies, motion that would show up if you removed the Hubble expansion from the data.

“I found that many of these galaxies defined a great circle on the sky, or roughly a circle, and that there were large regions of positive and negative values of residual velocity,” Rubin told editor Sally Stephens in a 1992 interview. “What in fact I really found was the supergalactic plane, although I entitled the paper ‘Rotation of the Universe.’”

Rubin tended to dismiss this early work in later life (“I presume none of this work would hold up today”), and her paper was rejected by the Astrophysical Journal as well as the Astronomical Journal, though later presented at a 1950 AAS meeting. Even so, the questions she raised were hugely significant, and at the time under study by Kurt Gödel at Princeton, the school that turned down her graduate application because of her gender. What Rubin was homing in on was the presence of large-scale galactic motion.

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Today, we talk about the Rubin-Ford effect, the observation that describes the motion of our galaxy relative to a sample of galaxies at varying distances and compares this to its motion relative to the cosmic microwave background (the Ford here is Kent Ford, an astronomer whose spectrometer became critical for Rubin’s studies of stellar motion in spiral galaxies). Early work that had been flawed by insufficient data would eventually grow into this result.

I always tend to link Rubin and Fritz Zwicky in my thinking. Way back in 1933, the Swiss astronomer who taught most of his career at Caltech was noting discrepancies between the apparent mass of galaxies in the Coma cluster and the amount of light they produced, leading him to coin the phrase ‘dunkle Materie’ (dark matter) to explain the effect. Both Zwicky and Rubin had an uncanny knack for seeing places where the universe was posing questions. For Rubin, it would become the motion of spiral galaxies that defined her career.

The problem leaped out at astronomers once Rubin put her finger on it. You would expect galaxies to spin in fairly conventional ways, with stars nearer the center moving faster than those on the outskirts, just as in our own Solar System, the inner planets orbit the Sun much faster than the outer worlds. But by 1974 Rubin was able to show that the outer stars in spiral galaxies move much faster than could be explained by the mass of the visible matter in the galaxies. Dark matter again reared its head, and became the subject of intense investigation.

We still haven’t observed dark matter directly, though the current calculation is that about 27 percent of the universe is made up of the stuff, with only 5 percent being the normal matter we had until recently assumed was all there was. By 1998, we had learned, too, of dark energy and the continuing expansion of the universe, yet another mystery demanding an explanation. The dark energy work would produce a Nobel Prize; dark matter has yet to do so. Rubin’s exclusion from the Nobel occupies much of the media commentary on her death. I think Phil Plait’s discussion is on the money.

Rubin would put her painstaking methods to work on over 200 galaxies in her career. Finishing her PhD in 1954 (her thesis advisor at Georgetown was George Gamow, a science popularizer and early advocate of Big Bang theory), Rubin taught at Georgetown for eleven years before joining the Carnegie Institution for Science in 1965, where she began her collaboration with Ford. She would become the second female astronomer elected to the National Academy of Sciences and would receive the National Medal of Science in 1993.

Rubin’s loss resonates through the world of astronomy and is keenly felt by the many she influenced, especially women who were inspired by her example to tackle a career in the physical sciences. We can measure careers by papers published and ideas propagated, but it’s all too easy to miss the more intangible factors like lives touched and careers launched. On all these scores Vera Rubin deserves the thanks of the field she did so much to shape.

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Orbital Determination for Proxima Centauri

by | Dec 27, 2016 | Exoplanetary Science | 20 comments

Let’s talk this morning about the relationship of Proxima Centauri to nearby Centauri A and B, because it’s an important issue in our investigations of Proxima b, not to mention the evolution of the entire system. Have a look at the image below, which shows Proxima Centauri’s orbit as determined by Pierre Kervella (CNRS/Universidad de Chile), Frédéric Thévenin (Observatoire de la Côte d’Azur) and Christophe Lovis (Observatoire astronomique de l’Universite? de Gene?ve). The three astronomers have demonstrated that all three stars — Proxima Centauri as well as Centauri A and B — form a single, gravitationally bound system.

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Image: Proxima Centauri’s orbit (shown in yellow) around the Centauri A and B binary. Credit: Kervella, Thévenin and Lovis.

A couple of things to point out here, the first being the overall image. You’ll see Alpha Centauri clearly labeled within the yellow ellipse of Proxima’s orbit. Off to the right of the ellipse, you’ll see Beta Centauri. I often see the image of these two stars identified as Centauri A and B, but Kervella et al have it right. The single bright ‘star’ within the ellipse is the combined light of Centauri A and B. Beta Centauri, at the right, is an entirely different star, itself a triple system in the constellation Centaurus, at a distance of about 400 light years.

Now as to that orbit — 550,000 years for a single revolution — things get interesting. One reason it has been important to firm up Proxima’s orbit is that while a bound star would have affected the development of the entire system, the question has until now been unresolved. Was Proxima Centauri actually bound to Centauri A and B, or could it simply be passing by, associated with A and B only by happenstance? Back in 1993 Robert Matthews and Gerard Gilmore found this to be a borderline case, calling for further kinematic data to clarify the issue.

When Jeremy Wertheimer and Gregory Laughlin (UC-Santa Cruz) attacked the problem in 2006, they found it ‘quite likely’ that Proxima Centauri was bound to the A/B pair. If this were the case, it would mean that the trio probably formed together out of the same nearby material, with the result that we could expect them to have the same age and metallicity. Laughlin and Wertheimer assumed that future, yet more accurate kinematic measurements would make it clear ‘that Proxima Cen is currently near the apastron of an eccentric orbit…’

And now we have Kervella and team, who have used the HARPS instrument (High Accuracy Radial Velocity Planet Searcher) on ESO’s 3.6m instrument at La Silla to make the call. Using radial velocity and astrometry, the researchers have surmounted the main problem with determining Proxima’s bound state. The lack of high-precision radial velocity measurements has been the result of Proxima’s relative faintness, but drilling down into HARPS data has produced a new radial velocity of ?21.700 ± 0.027 km s?1, which tracks nicely with the prediction of Wertheimer and Laughlin, and is low enough to indicate a bound state.

As we consider that interesting planet around Proxima Centauri, we now can ponder that its star is the same age as Centauri A and B, and that its age is a comparable 6 billion years, making the planet about a billion years older than our Earth. Exactly how the planet formed becomes an interesting issue as well, because we have interactions between three stars to think about. From the paper:

The orbital motion of Proxima could have played a significant role in the formation and evolution of its planet. Barnes et al. (2016) proposed that a passage of Proxima close to ? Cen may have destabilized the original orbit(s) of Proxima’s planet(s), resulting in the current position of Proxima b. Conversely, it may also have influenced circumbinary planet formation around ? Cen (Worth & Sigurdsson 2016). Alternatively, Proxima b may also have formed as a distant circumbinary planet of ? Cen, and was subsequently captured by Proxima. In these scenarios, it could be an ocean planet resulting from the meltdown of an icy body (Brugger et al. 2016). Proxima b may therefore not have been located in the habitable zone (Ribas et al. 2016) for as long as the age of the ? Cen system (5 to 7 Ga; Miglio & Montalbán 2005; Eggenberger et al. 2004; Kervella et al. 2003; Thévenin et al. 2002).

So there we are. Plenty of alternatives to ponder as we look into the origins of the nearest known planet to our Solar System. Just how the researchers tuned up the radial velocity data to avoid the problem of convective blueshift — where the star’s unstable surface can shift the observed wavelength of spectral lines – and gravitational redshift, which can likewise be misleading, is covered in the paper’s appendix. The selection of four strong very high signal-to-noise emission lines made the difference in this exquisitely tight measurement.

The paper is Kervella, Thévenin & Lovis, “Proxima’s orbit around ? Centauri,” accepted at Astronomy & Astrophysics (preprint).

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Seasonal Break

by | Dec 22, 2016 | Administrative | 30 comments

The other day on the hugely enjoyable Galactic Journey site, I ran into an interesting historical tidbit. Here, from the 1753 Cyclopædia: or, An Universal Dictionary of Arts and Sciences by Ephraim Chambers is a definition of the word ‘interstellar.’

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And with a modernized presentation:

“Interstellar, is a word used by some authors to express those parts of the universe that are without and beyond our Solar system; in which are supposed to several other systems of planets moving around the fixed stars as the centers of their respective motions: and if it be true, as it is not improbable, that each fixed star is thus a sun to some habitable orbs, that move round it, the interstellar world will be infinitely the greater part of the universe.”

Another early instance of planetary systems around other stars in wide circulation at an early date. Chambers was working for John Senex, a London-based globe-maker, when he conceived the plan for his Cyclopædia, a project to which he soon devoted his entire attention. The first edition appeared by subscription in 1728 in a two volume, 2466 page folio, but the work, one of the first general encyclopedias to be published in English, would see numerous further editions, including one in Ireland as well as an Italian translation.

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Those of you who are not yet familiar with Galactic Journey will want to remedy the lack, especially if you enjoy science fiction as much as most Centauri Dreams readers do. The site is something of a time machine, written from the perspective of science fiction magazines and events of over 50 years ago, and what’s delightful to me is that I often find issues of Analog or Fantastic discussed that I bought off the newsstand when they appeared. And because I love magazine fiction, every one of those issues is still here on my shelves, approximately ten feet from where I’m now writing.

We’re pushing into holiday travel time, so I’m going to close up shop until next week. Let me wish all of you a happy season and thank you for the comments and suggestions with which you’ve always enlivened the site. We have much to talk about in coming days, but for now, safe journey to all of you on the road.

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