Development of throttleable solid-rocket motors
Liquid-fuelled rockets motors are heavy and complex, but they have the advantage that they can be throttled in real-time. Solid rockets, on the other hand, are of a simpler construction but their thrust profile is ‘baked-in’ at the time of their manufacture.
This project seeks to combine the advantages of the two engine types by producing a throttleable solid rocket motor. The University of Glasgow, in collaboration with Dnipro National University in Ukraine, has achieved a test-firing of a solid-fuelled rocket motor which has demonstrated several throttle cycles, but there are some outstanding difficulties. In particular, the force required to push the solid-fuel rod into the combustion chamber is significant because it must overcome the pressure in the combustion chamber itself. The objective is to build a resonant chamber in the style of a pulse-jet, such that the fuel can be added during periods of relatively low local pressure.
The project will require modelling of combustion-chamber gas dynamics, using ground-truth from previous experiments in Ukraine. The intention is that, when these results are satisfactory, the model will be used to drive the design of a new combustion chamber that would be manufactured and test-fired in Ukraine.
In addition to tuning a resonant combustor to operate, for the first time, on the basis of vaporised solid propellant, effort will be expended to maximise heat transfer into the propellant itself. This effect is important because heat transfer from gases to solid impingement plates is affected by flow pulsations, and there may well be a design driver that seeks to balance the effects of pulse frequency (essentially a function of chamber size) and heating efficiency (a function of Reynolds and Strouhal numbers). This process must be optimised, because it is the heat of the combustion chamber, transmitted back into the propellant rod, which vaporises the fuel and allows the safe operation of the engine concept.
The student, in this project, will work in a team dedicated to the exploration of space and hazardous environments, but will also be expected to develop strong links with our Ukrainian partners.
Design and optimisation of orbits in proximity of asteroids using solar sails
Close-up observations of asteroids (particularly near-Earth asteroids, or NEAs) are important both for scientific reasons (many characteristics are largely unknown today, and asteroids are very different one another), for planetary protection and for future exploitation of their resources (metals, water). A possible way to visit multiple asteroids is with a solar sail spacecraft. A solar sail is a large, reflective and lightweight membrane that is deployed from a spacecraft and provides a thrust by reflecting the photons from the sun. This is appealing because it generates a small, but continuous, acceleration over time without propellant expenditure, enabling high-Δv missions.
Research in this group has shown the potential of solar sails to enable missions that can visit up to five near-Earth asteroids within ten years. In addition, trajectories were found for a variety of combinations of NEAs, as well as launch dates, demonstrating the flexibility offered by this type of propulsion. While the interplanetary journey is possible, a further research challenge is how to orbit around (or in proximity of) the asteroids: this PhD will investigate the dynamics and trajectories in proximity of the asteroids, together with the transfer to/from the interplanetary legs.
Asteroid orbits are challenging for several reasons: asteroids are highly irregular bodies, and their shape and density are not known in advance; in addition, most are tumbling, generating an irregular and time-varying gravity field. An additional challenge comes from the use of the solar sail, whose acceleration can only be controlled, through attitude manoeuvres, within certain limits and constraints.
Multi- and irregular body dynamics will be used. It is likely that an initial approach will be based on the energy levels and zero-velocity curves, to ensure bounded trajectories near the asteroid. Further research will involve numerical optimisation to target specific trajectories that maximise scientific return, reliability, and/or other merit figures. The ultimate goal is to design and optimise complete trajectories that inject into asteroid orbit starting from the interplanetary phase, orbit around the asteroid for a desired amount of time, and eventually depart into the next interplanetary transfer.
The PhD will involve both analytical and computer-based (numerical) research, preferably in the MATLAB and/or Mathematica environments. The ideal PhD candidate will have a degree in aerospace engineering or applied mathematics, and an excellent track record, preferably including evidence of outstanding research, such as previous awards and/or publications.
Nanosatellites beyond Earth orbit: CubeSats for deep space
A CubeSat is a nanosatellite of 10x10x10 cm of size and up to 1 kg of mass. Its frame and components are highly standardised, allowing a high degree of modularity and use of off-the-shelf parts. In addition, due to its small size and mass, it can be launched economically as secondary payloads by means of launchers carrying other conventional spacecraft. Because of these advantages, CubeSat platforms have been widely used for educational purposes, to test new technologies in space inexpensively, and lately also for science.
However, the platform also has significant limits with respect to conventional spacecraft, in terms of thrusting capabilities, attitude control, electrical and computational power available, telecommunication data rate, and radiation shielding. Most importantly, there is a strict limit for the maximum total mass. For these and other reasons, so far most CubeSat missions have flown in low Earth orbit (below 1000 km), and naturally deorbited and burned into the atmosphere at end of life.
This PhD will investigate the trajectory and propulsion system design for future interplanetary CubeSat-like nanosatellites, for high Earth orbits, deep space (e.g. Lagrangian points), Moon missions, near-Earth asteroids and beyond. Starting from an analysis of the limitations of current nanosatellite technology, this study is an exciting opportunity to explore new very-low-Delta-V trajectories and key propulsion technologies which will enable this platform to overcome the limitations mentioned before, and to fly to distant targets. For example, the limited thrusting capabilities of CubeSats require the use of advanced, highly-efficient engines (e.g. pulsed plasma thrusters), but reflective deployables (solar or wind sails) could also be used for photonic propulsion; the two systems could also be combined to maximise the benefit of both. Together with the system design, the study will identify potential mission scenarios that will benefit most from the deep-space nanosatellites, either in terms of cost reduction or increased return. The potential of using nanosatellites beyond low Earth orbit in the near future is huge. First and most importantly, it will enable low-cost deep space exploration. In addition, the modularity of the platform opens the way for mass production of similar spacecraft at relatively low cost, thus envisaging the use of multiple spacecraft in swarms or formations to achieve a common mission goal. Examples are real-time global remote imaging of the Earth or simultaneous local sensing of the space environment at different locations.
In addition, the candidate will take the lead of the development of a CubeSat engineering kit, which can be used for proof-of-concept implementation and testing of the solutions being investigated. In addition, this will open collaborations with the Physics & Astronomy (payloads, interaction with the space environment), Computing Science (on-board computer) and Electronics & Electrical Engineering (power system, electronics).
The ideal PhD candidate will have enthusiasm, a degree in aerospace engineering or applied mathematics, and an excellent track record, preferably including evidence of outstanding research, such as previous awards and/or publications.
Coupled trajectory and economic analysis of near Earth asteroid resources
Near Earth Asteroids (NEA) represent an important resource for future commercial and scientific space ventures through the in situ provision of water and other material resources. This has been recognised by growing space agency and venture capital interest in such resources.
Our prior work has focused on minimising capture energy requirements to lower costs. However, aside from minimising capture energy, trajectory design which maximises economic return on investment will be investigated as a key consideration for future commercial ventures. Here the total time taken for NEA resources to be returned to near Earth space is also key, since interest will accumulate on debt financing. Trajectory design will therefore be a function of capture energy requirements and roundtrip mission duration, leading to rich new families of trajectories which have been little explored.
This integration of trajectory optimisation and economic modelling is an exciting research challenge. Open questions to be addressed include the optimum selection of propulsion technology. For example high specific impulse, low thrust propulsion (including solar sails) will minimise propellant mass requirements, while low specific impulse propulsion may lead to shorter round-trip transfer times. This will lead to a tight coupling between engineering requirements and economic Net Present Value (NPV) which will be explored.
In particular, solar sailing offers an efficient means of returning NEA resources by leveraging light pressure rather than using propellant. A key research challenge will be to understand the optimum solar sail payload mass fraction to maximise the long-term rate of return of resources; a large mass per unit area will deliver a significant payload but with a long total trip time. Moreover, a number of large solar sails may be considered cycling between near Earth space and a set of suitable target objects for resource extraction.
Candidates should have a strong interest in mathematical modelling. Prior experience of orbital dynamics and MATLAB would be welcome.
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