P3_5 Fire at Will!

We consider the force produced by Zarya's "Graviton Surge" in the video game Overwatch. Themass required to produce a gravitational field of the necessary strength is found and the conse-quences of utilising such a mass considered. It is shown that the surge must have a mass of 9.4x10^12 kg, but limitations from special relativity make the existence of such a weapon impossible

P3_1 Black Hole formation within Starkiller Base

In the film "Star Wars: The Force Awakens", Starkiller Base pulls an entire star into its fuel chamber to power a laser weapon system. By estimating the dimensions of the fuel chamber, we find that the maximum mass a fuelling star can have before it collapses into a black hole is approximately 7.5 M☉, however, the additional gravitational force produced would make the planet uninhabitable

P3_2 Thick Skin

We determine the thickness of human skin that would be required to be bulletproof. The kineticenergy of bullets with various calibres are determined and the tensile strength of skin used to find the stopping distance of a bullet inside skin. We find that skin with a thickness of 5-40 cm is required to be bulletproof, dependent on the calibre of the bullet. The limitations of possessing such skin are considered to determine the feasibility of a bulletproof human

P3_7 Why Does Venus Spin Backwards?

Venus has a very slow, retrograde rotation compared to the 24 hour prograde rotations ofEarth and Mars. We find that for an impacting asteroid to have changed Venus' rotation froman Earth-like period and direction to its current state, a minimum asteroid mass of 2x10^29kgwould be required, and that such a collision would destroy Venus. This makes it unlikely thatsuch a collision is responsible for the odd Venusian rotation

P3_4 Honey, I Shrunk the Tank!

In the 2015 film "Ant-Man", a Russian T-34 tank is shrunk down to the size of a keychain,during which its mass remains constant. By estimating the change in inter-atomic spacing, andthe resulting increase in Coulomb repulsion between atomic nuclei, the energy required for thiscompression is found to be approximately 7.08x10^15 J. This an extremely large amount of energy, making the possibility of such a situation infeasible

P3_8 Life with Bulletproof Skin

We consider some of the consequences of possessing skin thick enough to be bulletproof as determined in "P3 2 Thick Skin" [1]. We find that the extra skin would weigh 103 kg however even if this weight could be carried the temperature increase in the body would result in death in as little as 5 hours if not counteracted

Eddy-covariance data with low signal-to-noise ratio:time-lag determination, uncertainties and limit of detection

All eddy-covariance flux measurements are associated with random uncertainties which are a combination of sampling error due to natural variability in turbulence and sensor noise. The former is the principal error for systems where the signal-to-noise ratio of the analyser is high, as is usually the case when measuring fluxes of heat, CO2 or H2O. Where signal is limited, which is often the case for measurements of other trace gases and aerosols, instrument uncertainties dominate. Here, we are applying a consistent approach based on auto- and cross-covariance functions to quantify the total random flux error and the random error due to instrument noise separately. As with previous approaches, the random error quantification assumes that the time lag between wind and concentration measurement is known. However, if combined with commonly used automated methods that identify the individual time lag by looking for the maximum in the cross-covariance function of the two entities, analyser noise additionally leads to a systematic bias in the fluxes. Combining data sets from several analysers and using simulations, we show that the method of time-lag determination becomes increasingly important as the magnitude of the instrument error approaches that of the sampling error. The flux bias can be particularly significant for disjunct data, whereas using a prescribed time lag eliminates these effects (provided the time lag does not fluctuate unduly over time). We also demonstrate that when sampling at higher elevations, where low frequency turbulence dominates and covariance peaks are broader, both the probability and magnitude of bias are magnified. We show that the statistical significance of noisy flux data can be increased (limit of detection can be decreased) by appropriate averaging of individual fluxes, but only if systematic biases are avoided by using a prescribed time lag. Finally, we make recommendations for the analysis and reporting of data with low signal-to-noise and their associated errors

Characterization and calibration of the James Webb space telescope mirror actuators fine stage motion

The James Webb Space Telescope’s (Webb’s) deployable primary and secondary mirrors are actively controlled to achieve and maintain precise optical alignment on-orbit. Each of the 18 primary mirror segment assemblies (PMSAs) and the secondary mirror assembly (SMA) are controlled in six degrees of freedom by using six linear actuators in a hexapod arrangement. In addition, each PMSA contains a seventh actuator that adjusts radius of curvature (RoC). The actuators are of a novel stepper motor-based cryogenic two-stage design that is capable of sub-10 nm motion accuracy over a 20 mm range. The nm-level motion of the 132 actuators were carefully tested and characterized before integration into the mirror assemblies. Using these test results as an initial condition, knowledge of each actuator’s length (and therefore mirror position) has relied on software bookkeeping and configuration control to keep an accurate motor step count from which actuator position can be calculated. These operations have been carefully performed through years of Webb test operations using both ground support actuator control software as well as the flight Mirror Control Software (MCS). While the actuator’s coarse stage length is cross-checked using a linear variable differential transformer (LVDT), no on-board cross-check exists for the nm-level length changes of the actuators’ fine stage. To ensure that the software bookkeeping of motor step count is still accurate after years of testing and to test that the actuator position knowledge was properly handed off from the ground software to the flight MCS, a series of optical tests were devised and performed through the Center of Curvature (CoC) ambient optical test campaigns at the Goddard Space Flight Center (GSFC) and during the thermal-vacuum tests of the entire optical payload that were conducted in Chamber A at Johnson Space Center (JSC). In each test, the actuator Fine Step Count (FSC) value is compared to an external measurement provided by an optical metrology tool with the goal of either confirming the MCS database value, or providing a recommendation for an updated calibration if the measured FSC differs significantly from the MCS-based expectation. During ambient testing of the PMSA hexapods, the nm-level actuator length changes were measured with a custom laser deflectometer by measuring tilts of the PMSA. The PMSA RoC fine stage characterization was performed at JSC using multi-wave interferometric measurements with the CoC Optical Assembly (COCOA). Finally, the SMA hexapod fine stage characterization test was performed at JSC using the NIRCam instrument in the “pass-and-a-half” test configuration using a test source from the Aft-Optics System Source Plate Assembly (ASPA). In this paper, each of these three tests, subsequent data analyses, and uncertainty estimations will be presented. Additionally, a summary of the ensemble state of Webb’s actuator fine stages is provided, along with a comparison to a Wavefront Sensing and Control (WFSC)-based requirement for FSC errors as they relate to the optical alignment convergence of the telescope on-orbit