UN resolutions outlawed mercury being used as a propellant in the manoeuvring of satellites. This was before the thrusters were ever placed into orbit. The ban was in response to interest in mercury-thruster techniques, which could have resulted in the toxic heavy metal falling back to Earth’s upper atmosphere, posing serious environmental and health threats.
Because they have high atomic masses, ion drives that propel small satellites typically use xenon or krypton. They are scarce so alternatives are needed to meet demand for the tens to thousands of minisatellites that will be launched in the next decade. SpaceX and Amazon are also expected to populate low Earth orbit with megaconstellations of satellites for broadband communications.
Mercury’s appeal lies in its low cost and ability to be stored and ionized easily to produce excellent thrust. In 1964, Nasa used mercury in an experiment to demonstrate ion thrusters in space. Mercury’s toxicity meant that industry and Nasa had mostly rejected it as a propellant by the 1970s. Mercury bioaccumulates in food chains and can cause vision loss, developmental disorders and IQ cuts.
However, in 2018, Kevin Bell from the Public Employees for Environmental Responsibility was contacted and informed by a whistleblower from within the space industry. An insider informed Bell that Apollo Fusion, a California-based company, had developed a new mercury-based thruster. He was now promoting it to satellite manufacturers.
Bell says that the whistleblower had already contacted at most two other environmental organizations before us, but they had not responded to them or taken them seriously. Bell also said that he had contacted at minimum one state regulatory agency. They were probably just looking for information in the environmental phone directory and I was the one who believed them.
Bell quickly learned that space law regulations were lacking in regards to sending items into orbit on satellites, unless they involved weapons. Peer raised this issue with the US Federal Communications Commission. The FCC has the regulatory authority to approve or deny any proposed communication satellite networks. The FCC has denied that networks of thousands satellites could cause any environmental damage.
In the meantime, the UN’s 2013 treaty on mercury reductions and elimination of all mercury uses, had ignored the space industry when it was written.
Propellant prevention
Bell’s efforts helped generate some publicity about the Apollo Fusions mercury thrusters issue and brought it to attention by the research community, which included some who shared the environmental concerns. A team of US and Italian researchers performed simulations and modeling.1To estimate how much mercury could return to Earth if used for satellite propellant.
The results showed that 2000 mercury-powered satellites could potentially emit 20 tonnes per year, most of which would return back to Earth. This is approximately half of all North American emissions, and 1% of global annual emissions. Bell says that while 1% may not sound like much, any source of mercury is worth stopping in order to prevent mercury from accumulating.
Environmental scientist says that the use of mercury in satellite propellants could introduce new mercury sources into the upper atmosphere. Elsie SunderlandHarvard University, who was involved in the simulation study. Mercury is distributed in the atmosphere and eventually deposits to ocean surface. This mercury can accumulate in fish that are sold on the commercial market.
Peer joined forces with the Zero Mercury Working GroupThe issue was brought to the attention of world leaders by a global coalition of more than 110 health and environmental organizations from more 55 countries. At a meeting held in March, the UN treaty of mercury was amended to include a provision that will see the end of the use mercury as a satellite propellant by 2025.
Bell states that it is very rare for an environmental protection to be put in place before the thing it protects has already caused irreparable damage. I am proud of the work we did on this case and hope it serves as a model to other governments. They have a responsibility to ensure that space exploration is done responsibly and without further damage to the Earth.
Trevor Lafleur is the principal engineer at French company, French Space. The industry has experienced unprecedented growth in the past ten years and this trend is expected to continue. ThrustMeSpacecraft pioneers iodine thrusters were demonstrated by the University of California, Berkeley last year. To ensure safe and sustainable growth, regulations, especially those relating to hazardous materials, are essential.
