Most spacecraft propulsion concepts can be classified into two categories: chemical and electric. Chemical propulsion relies on chemical reactions and can produce high thrust, but requires a large amount of fuel. Electric propulsion uses electromagnetic fields to accelerate ionized gases and is very fuel-efficient, but produces small amounts of thrust …

Consumer electronics constitute a rapidly increasing source of waste. Cell phones, tablets and the like are typically made of non-renewable, non-biodegradable, partly environmentally toxic materials. A report from United Nations University (UNU) found that the world produced 41.8 million metric tons of e-waste in 2014 – an amount that would fill …