Tacking sails to a satellite
Satellites ending their working lifetimes could sprout sails in future to ensure they are dragged down into Earth’s atmosphere, keeping crucial low orbits free of space debris. ESA’s Clean Space initiative is looking to test how this promising concept might work in practice.
In 2008 ESA pledged to remove satellites from key orbits within 25 years after their missions have ended.
The most straightforward method of satellite disposal would be to reserve sufficient propellant to steer the satellite downwards – but this might seriously drive up the satellite mass while cutting the overall mission lifetime.
What are sometimes called ‘terminator’ or drag sails, deployed to increase the drag on low-orbiting satellites at the top of the atmosphere, are a low-cost, low-mass alternative.
ESA has researched various aspects of sail technology, including deployable booms and suitable ultra-light sail membranes.
Now ESA’s Clean Space initiative has issued a pair of research contracts: one to design a complete sail subsystem and another to select an optimal sail material, going on to produce testable ‘breadboard’ prototypes and devise plans for follow-on development.
The aim for the ‘Architectural Design and Testing of a De-orbiting subsystem’ tender is to consider the trade-offs of the various available technologies and design an overall subsystem that could easily be accommodated on a variety of satellites.
This subsystem is intended to be modular and scalable – its scale, and the area of its sail, could be varied based on the size and altitude of its satellite host: the higher the satellite, the greater the need to augment its atmospheric drag.
For the purpose of the study, the intention is to design a unit to serve a satellite compact enough to be launched by ESA’s Vega rocket, able to transport satellites of 150 kg or less into low-Earth orbit.
The challenge is to come up with a unit that can endure years of storage before it is finally put to use, before finally deploying flawlessly, with sails solidly attached to the booms to provide all the necessary strength and stiffness.
Potentially relevant technologies include deployable booms based on carbon-fibre reinforced polymer, developed by Germany’s DLR space agency, and inflatable booms incorporating a new resin material and LED-based curing developed by ESA together with Airbus Space and Defence. Ground-based deployment of 20 x 20 m sails have been tested on the ground, while a 5 x 5 m gossamer sail engineering model has also been demonstrated.
Once the breadboard is complete it will undergo rigorous thermal vacuum testing to ensure it can withstand the space environment over many years.
Clean Space’s second ‘Deployable Membrane’ tender involves a review of all available membrane materials to select an optimal candidate for a drag sail.
This material would need to be compatible with parachute-style packaging, withstand years of ageing, be reliably unfurled, and – once deployed in open space – endure years of meteoroid and space debris damage, ultraviolet and particle radiation, thermal extremes and outgassing.
A prototype breadboard and test rig would then be produced for practical testing, with plans drawn up for future development.
For more information, check these two new invitation to tender packages, accessible via ESA’s Electronic Mailing Invitation to Tender System (EMITS).