Work Package 2: Delivery Methods - Putting Particles up into the Stratosphere
This section of the SPICE project hopes to discover how we might be able to deliver the particles chosen by the scientists in Work Package 1 into the stratosphere. There have been many delivery methods suggested such as using aeroplanes or balloons, releasing them from very tall towers or using a pipe supported by a balloon. Choosing the right delivery method to put the particle up in the Stratosphere means choosing a method that is: not too expensive, gets the particles to the right place, correctly distributes them and can be easily controlled in case of unforeseen events.
It is believed that a pipe attached to a very large balloon and a pump will be the best option (a tethered balloon delivery system). But no-one has ever built a balloon that large or to go to that altitude before, so the scientists also need to investigate the materials they need to construct the balloon and the pipe. Moreover they need to pick the perfect pump to go with their record-breaking balloon and pipe design. This will all require rigorous laboratory testing. The design produced by Work Package 2 will not now be tested outside at a very small scale (a testbed situation) spraying only water. The decision to call-off the test-bed was made by the project management team because external delays to the project had reduced the time available for performing adequate stakeholder engagement prior to any test-bed activities. As such it was felt inappropriate to continue with a test-bed without such stakeholder engagement.
To investigate howbest to deliver reflective particles into the Stratosphere using existing or new technologies. After a detailed comparison and expert discussion the method considered most feasible and cost-effective was “Tethered Balloons”. These would behelium or hydrogen filled balloons attached to a pump at ground level by a 25km long pipe.
No-one has ever built a balloon as large as would be needed or pumped materials to this altitude. The pump would need to generate high pressures and the balloon and pipe would need to remain steady in high winds. This requires rigorous laboratory testing and computer modelling. Research is also being conducted into the materials required to construct the pipe.
The Engineering Dynamics- Tests, Studies and Modelling
- Observations of the movement of ordinary tethered kites/balloons (to validate models)
- Computer modelling of tethered balloon dynamics (under various wind conditions)
- Desktop study on a high pressure fluid delivery system (suitable for a 25km pipe)
- Identification and assessment of possible transport media and dispersion mechanisms
- Small-scale laboratory tests of high pressure pumping systems
- A study of issues relating to deployment and recovery of balloon and pipe
The delivery method design suggested by Work Package 2 will not be tested outside (even at a very small scale). The project team decided it was inappropriate to carry out a test due to the lack of appropriate governance structures for climate engineering and intellectual property issues.
The Engineering Materials Challenges
The pipe will be constructed from a braided or filament wound fibre composite and will be subject to:
- High Tensile Pressure
- High Bursting Pressure
- Very Low Temperatures
- Extreme Weather Events
- Strong and Fluctuating Winds
Fibres being considered for the pipe:
- Aramids (e.g. Kevlar/Twaron/Technora)
- PBO (Polybenzoxazole Fiber)
Knowledge exists about the performance of aramids at high stresses, temperatures and pressures. But PBO is so novel that we must conduct the necessary tests ourselves using established techniques.
The engineers from Work Package 2 are working together with Dr Jack Stilgoe, an expert in public engagement, to discuss geoengineering with stakeholders and the general public.
Tethered balloon delivery method was chosen based on:
- Ability to correctly distribute the particles
- Latitude from which it could be deployed
- Controllability (for switch-off or unforeseen events)