On-Orbit Results from the CanX-7 Drag Sail Deorbit Mission

As a proactive solution to the orbital debris problem, the Space Flight Laboratory (SFL) has developed a passive drag sail deorbit device to remove small satellites from low-Earth orbit (LEO). Upon end-of-mission, the drag sail can be deployed to decrease the ballistic coefficient of the host spacecraft. Without any further operator intervention, the drag sail will interact with Earth’s upper atmosphere to decrease the spacecraft’s orbital energy causing it to eventually deorbit. In order to demonstrate the drag sail technology on-orbit, it has been included as the primary payload on-board the CanX-7 mission, which was launched in September 2016. After successfully completing a seven-month aircraft tracking campaign using the CanX-7 ADS-B payload, the drag sails were deployed in May 2017. This paper provides a first look at the on-orbit results from the CanX-7 mission, focusing on the performance of SFL’s drag sail device

Application of the insulator coordination gap models and effect of line design to backflashover studies

Any insulation coordination study must accurately (or as accurately as possible) express the type and magnitude of all overvoltages on the power system. If these overvoltages are higher than the rating of the equipment, they will result in damage to that equipment. This paper presents the application of the insulator coordination gap models and the effect of line design to the line performance in terms of backflashover rate. The models which are ranging from as simple as voltage controlled switch to as detail as leader progression model will carefully be evaluated. Sensitivity analyses on the effect of line designs such as variation in footing resistance, height of tower/conductor, tower surge impedance and soil resistivity will also be carried out in determining the backflashover rate and the probability of transformer damage by comparing the maximum voltage recorded at the substation entrance with the basic lightning insulation level (BIL). Results will then be compared in finding which model makes the analysis more or less sensitive to any design parameter

Optimisation of high voltage electrical systems for aerospace applications

Increased electrical power demands are being experienced on the new generation of aircraft due to an increased reliance on electrical technology of systems such as air conditioning, de-icing systems and electrical flight control actuation. Distribution of power at higher AC and DC voltages is therefore now being seen in modern aircraft to avoid the penalties incurred due to high cable weights. Voltages have increased past the minimum of Paschen's law resulting in a risk that life limiting partial discharge (PD) damage can occur in the insulation systems. This thesis uses a theoretical analysis backed by PD experimental results to investigate the optimal operating voltage of a cabling system. In addition, it proposes a methodology for optimizing the operating voltage level based on an analysis of the power carrying capability of cabling within a fixed and a non-fixed volume system and the derivation of the cable weight as a function of voltage. Furthermore the power carrying capability of a certain round cable system is compared with an insulated flat conductor system as in a printed circuit board (PCB). An initial assessment has been carried out to determine whether more power can be delivered via insulated flat solid conductors as in a PCB, instead of using round cables. The reason why there is a need to investigate this aspect, is because using new PCB technology can offer several advantages over traditional cabling harnesses. The work done has shown that the optimal operating point (e.g. maximum power to weight ratio) for an aircraft power system, does not improve after certain voltage levels. A tradeoff between cable weight and power transfer is required and furthermore the use of DC systems can result in higher power transfers than conventional three phase/400Hz AC systems. The PCB maximum power transfer assessment has also shown that insulated flat conductor systems can offer higher power transfer efficiencies. In addition, experimental AC and DC PD tests on certain unscreened aerospace cables (laid out in different configurations), have shown that the theoretical analysis employed to determine cable safe operating voltages gives conservative results.EThOS - Electronic Theses Online ServiceEPSRCRolls-Royce plc.GBUnited Kingdo

Electrical tracking over solid insulating materials for aerospace applications

The concept of More Electric Aircraft, where is to utilize the electrical power to drive more or all aircraft subsystem instead of conventional combination of pneumatic, hydraulic, mechanical and electrical power, can be recalled to World War II. It has been proven to have more advantages for decades in terms of energy efficiency, environmental issues, logistics and operational maintenance. It can also enhance aircraft weight, volume and battle damage reconfigurability.Thanks to the new electronics technologies and the emergence of new materials, It becomes feasible for high power density electrical power components to drive the majority of aircraft subsystem. However, sustaining the transmission of hundreds of kilowatts of electrical power at low voltages is not feasible owing to the penalties incurred due to high cable weights and voltage drop may become critical. It is very easy to come up with the solution of the increase of voltage. However, higher voltage will introduce other problems such as the reliability of insulation coordination on the aircraft due to the increased probability of electrical discharge. For aircraft designers, it is very important to understand the rules of insulation coordination on the aircraft including determining clearance and creepage distances, and also have a clear investigation of the phenomena and mechanism of electrical discharges. Past research has identified a number of the concerns of operating electrical systems at higher voltages in an aerospace environment, especially for dimensioning of clearances. However, there is little study on dimensioning of creepage distances and relevantly flashover and electrical tracking on solid insulating material surfaces. This thesis firstly discusses the rules for determining clearances and creepage distances. The experimental validation work was done for breakdown in air gap and on the solid insulating material surfaces under dry condition so that some standard recommended values can be evaluated not only with theoretical values such Paschen's law. Suggestions of application of those standards were provided. Secondly, the complex electrical discharge under wet condition on solid insulating material surfaces was discussed. A mathematical model to predict this type of electrical failure -electrical tracking (the electrical discharges on solid insulation materials which will lead to physical damage in the materials) with the consideration of different environmental conditions including air pressure, ambient temperature, and pollution degrees was developed. A series of electrical tracking tests were carried out on organic materials to find out the mechanism of electrical tracking and validate the finding by the mathematic model. Finite element analysis simulations were also conducted to find out the background thermal transfer mechanism to support our explanation of those phenomena of electrical tracking. Different test techniques have ben developed for specific impact factors. Finally, the suggestions for utilization of the standards and feasible test techniques for electrical tracking under wet conditions were provided.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A study of the rapid rotator zeta Aql: differential surface rotation?

We report new, extremely precise photopolarimetry of the rapidly-rotating A0 main-sequence star ζ Aql, covering the wavelength range ∼400–900 nm, which reveals a rotationally-induced signal. We model the polarimetry, together with the flux distribution and line profiles, in the framework of Roche geometry with ω-model gravity darkening, to establish the stellar parameters. An additional constraint is provided by TESS photometry, which shows variability with a period, Pphot, of 11.1 h. Modelling based on solid-body surface rotation gives rotation periods, Prot, that are in only marginal agreement with this value. We compute new ESTER stellar-structure models to predict horizontal surface-velocity fields, which depart from solid-body rotation at only the ∼2 per cent level (consistent with a reasonably strong empirical upper limit on differential rotation derived from the line-profile analysis). These models bring the equatorial rotation period, Prot(e), into agreement with Pphot, without requiring any ‘fine tuning’ (for the Gaia parallax). We confirm that surface abundances are significantly subsolar ([M/H] ≃ −0.5). The star’s basic parameters are established with reasonably good precision: M = 2.53 ± 0.16 M☉, log (L/L☉) = 1.72± 0.02, Rp = 2.21 ± 0.02 R☉, Teff = 9693 ± 50 K, i = 85+−75◦, and ωe/ωc = 0.95 ± 0.02. Comparison with single-star solar-abundance stellar-evolution models incorporating rotational effects shows excellent agreement (but somewhat poorer agreement for models at [M/H] ≃ −0.4)