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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| EmDrive | 4/5 | https://en.wikipedia.org/wiki/EmDrive | reference | science, encyclopedia | 2026-05-05T09:19:20.530876+00:00 | kb-cron |
=== Dresden University of Technology === In July 2015, an aerospace research group at the Dresden University of Technology (TUD) under Martin Tajmar reported results for an evaluation of an RF resonant tapered cavity similar to the EmDrive. Testing was performed first on a knife-edge beam balance able to detect force at the micronewton level, atop an antivibration granite table at ambient air pressure; then on a torsion pendulum with a force resolution of 0.1 mN, inside a vacuum chamber at ambient air pressure and in a hard vacuum at 400 μPa (4×10−6 mbar). They used a conventional ISM band 2.45 GHz 700 W oven magnetron, and a small cavity with a low Q factor (20 in vacuum tests). They observed small positive thrusts in the positive direction and negative thrusts in the negative direction, of about 20 μN in a hard vacuum. However, when they rotated the cavity upwards as a "null" configuration, they observed an anomalous thrust of hundreds of micronewtons, much larger than the expected result of zero thrust. This indicated a strong source of noise which they could not identify. This led them to conclude that they could not confirm or refute claims about the device. In 2018, they published results from an improved test rig, which showed that their measured thrust had been a result of experimental error from insufficiently shielded components interacting with the Earth's magnetic field. In new experiments, they measured thrust values consistent with previous experiments and again measured thrust perpendicular to the expected direction when the thruster was rotated by 90°. Moreover, they did not measure a reduction in thrust when an attenuator was used to reduce the power that actually entered the resonant cavity by a factor of 10,000, which they said "clearly indicates that the "thrust" is not coming from the EMDrive but from some electromagnetic interaction." They concluded that "magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper μN thrust measurements for these type of devices," and they planned on conducting future tests at higher power and at different frequencies, and with improved shielding and cavity geometry. In 2021, they revisited these experiments again and ran more precise tests. They reported with high confidence that the forces previously measured could be completely explained by experimental error, and that there was no evidence for any measurable thrust once these errors were taken into account. They were able to run the experiment and show no thrust in any direction, and to reintroduce the previous sources of experimental error to replicate the earlier results. They also replicated White's setup, showing that thermal effects could replicate the apparent thrust his team had observed, and that this thrust went away when measured with a more precise suspension. They went on to publish two further papers, showing similar negative results for the laser-based LemDrive variant and Woodward's Mach-Effect thruster.
=== Abandoned plans for tests in space === Since 2016, a few groups have raise funds for planned tests of EM drives or similar devices in space. As of 2025, there is no independent confirmation that any such device has gone to space, as none of the groups have published updates or technical details about the tests. In August 2016, Cannae announced plans to launch a thruster on a cubesat which they would run for 6 months to observe how it functions in space. As of 2025, no launch details had been announced. In December 2016, Yue Chen told a reporter at China's Science and Technology Daily that his team would test an EmDrive in orbit. Chen claimed their prototype's thrust was at the "micronewton to millinewton level", which would have to be scaled up to at least 100–1000 millinewtons for a chance of conclusive experimental results. After 2017, no further updates were announced. In 2023, a new company, IVO Limited, claimed to be developing a similar drive, which they would test in space later that year on a cubesat, but in the end did not do so.
== Experimental errors == The strongest early result, from Yang's group in China, was later reported to be caused by an experimental error. Tajmar published an explanation of how all reports of apparent thrust could have been caused entirely by failing to account for all sources of error or noise. Experimental errors in the testing of the prototypes generally fall into four categories
Measurement error and noise. Most theoretical scientists who have looked at the EmDrive believe this to be the likely case. Thermal effects. Electromagnetic effects, including interaction with ambient magnetic fields and Lorentz forces from power leads. Other potential sources of error include confirmation bias and publication bias (discarding negative results).
=== Measurement errors ===
The simplest and most likely explanation is that any thrust detected is due to experimental error or noise. In all of the experiments set up, a very large amount of energy goes into generating a tiny amount of thrust. When attempting to measure a small signal superimposed on a large signal, the noise from the large signal can obscure the small signal and give incorrect results.
=== Shift in center of gravity due to thermal effects ===