AbstractThe present work provides a detailed analysis of already published reports on the observation of an anomalous force in a vacuum associated with vacuum sparks in asymmetric capacitors charged with “constant” high voltages. Known experimental details of these experiments are put forward and propulsion performance is compared with the only known propulsion system known to exist in a vacuum associated with sparks: the vacuum arc thruster (VAT). VAT's are known for decades and work on principles of momentum conservation. They vaporize particles from the electrodes themselves through a high spark current in one direction in order to develop a thrust in the opposite direction. However, the known performance trend for these thrusters does not account for the vacuum spark force values published by NASA. Furthermore, they have not observed the electrode erosion usually associated with VAT operation, even after extended testing. Therefore it is possible that a new propulsion mechanism might be at work, but that should be verified and confirmed experimentally in the future in order to resolve the question.