Today, most rockets are fueled by hydrazine, a toxic and hazardous chemical comprised of nitrogen and hydrogen. Those who work with it must be kitted up in protective clothing. Even so, around 12,000t of hydrazine is released into the atmosphere every year by the aerospace industry
Now, researchers are in the process of developing a greener, safer rocket fuel based on metal organic frameworks (MOFs), a porous solid material made up of clusters of metal ions joined by an organic linker molecule. Hundreds of millions of connections join in a modular structure.
Robin Rogers, formerly at McGill University, US, has worked with the US Air Force on hypergolic liquids that will burn when placed in contact with oxidisers, to try get rid of hydrazine. He teamed up with Tomislav Friščić at McGill who has developed ways to react chemicals ‘mechanochemically’ – without the use of toxic solvents.
The pair were interested in a common class of MOFs called zeolitic imidazole frameworks, or ZIFs, which show high thermal stability and are usually not thought of as energetic materials.
They discussed the potential of using ZIFs with the imidazolate linkers containing trigger groups. These trigger groups allowed them to take advantage of the usually not accessible energetic content of these MOFs.
The resulting ZIF is safe and does not explode, and it does not ignite unless placed in contact with certain oxidising materials, such as nitric acid, in this case.
Authorities continue to use hydrazine because it could cost millions of dollars to requalify new rocket fuels, says Rogers. MOF fuel would not work in current rocket engines, so he and Friščić would like to get funding or collaborate with another company to build a small prototype engine that can use it.
Spaceflight is a high-risk business. Spacecraft break down all the time and when that happens funding and careers evaporate. Back in the late 1960s, NASA decided to double the odds of success and send two spacecraft on one mission. Voyagers 1 and 2, for example, were the spacecraft that returned the first detailed pictures of the outer planets of our solar system and introduced us to the neighbourhood. Launched in 1977, both are still flying.
Any spacecraft must have three components: a payload, an engine and a fuel supply – by far the heaviest component. But what if we could do away with the onboard fuel supply and replace it with an external fuel supply? Say light itself?
Can you push a spacecraft with light? Video: Physics Girl
The idea of solar sail technology has been floating around for decades. Indeed, the notion of a solar pressure can be traced back to 1610 in a letter that Johannes Kepler wrote to Galileo.
But it was only in the 20th century that solar sails began to be considered as an achievable engineering reality. Broadly, solar sails fall into two categories: those using light from natural sources – the sun and ambient starlight in space; and those using coherent light from lasers.
A huge challenge faced in the pursuit of a mission to Mars is space radiation, which is known to cause several damaging diseases – from Alzheimer’s disease to cancer.
And soon, these problems will not just be exclusive to astronauts. Speculation over whether space tourism is viable is becoming a reality, with Virgin Galactic and SpaceX flights already planned for the near future. The former reportedly sold tickets for US$250,000.
But could questions over the health risks posed hinder these plans?
What is space radiation?
In space, particle radiation includes all the elements on the periodic table, each travelling at the speed of light, leading to a high impact and violent collisions with the nuclei of human tissues.
The type of radiation you would endure in space is also is different to that you would experience terrestrially. On Earth, radiation from the sun and space is absorbed by the atmosphere, but there is no similar protection for astronauts in orbit. In fact, the most common form of radiation here is electrochemical – think of the X-rays used in hospitals.
The sun is just one source of radiation astronauts face in space. Image: Pixabay
On the space station – situated within the Earth’s magnetic field – astronauts experience ten times the radiation that naturally occurs on Earth. The station’s position in the protective atmosphere means that astronauts are in far less danger compared with those travelling to the Moon, or even Mars.
Currently, NASA’s Human Research Program is looking at the consequences of an astronaut’s exposure to space radiation, as data on the effects is limited by the few subjects over a short timeline of travel.
Radiation poses one of the biggest problems for space exploration. Video: NASA
However, lining the spacecraft with heavy materials to reduce the amount of radiation reaching the body isn’t as easy as a solution as it is seems.
‘NASA doesn’t want to use heavy materials like lead for shielding spacecraft because the incoming space radiation will suffer many nuclear collisions with the shielding, leading to the production of additional secondary radiation,’ says Tony Slaba, a research physicist at NASA. ‘The combination of the incoming space radiation and secondary radiation can make the exposure worse for astronauts.’
As heavy materials cannot hamper the effects of radiation, researchers have turned to a more light-weight solution: plastics. One element – hydrogen – is well recognised for its ability to block radiation, and is present in polyethylene, the most common type of plastic.
A thick dust cloud called the Dark Rift blocks the view of the Milky Way. Image: NASA
Engineers have developed plastic-filled tiles, that can be made using astronauts rubbish, to create an extra layer of radiation protection. Water, which is already an essential for space flight, can be stored alongside these tiles to create a ‘radiation storm shelter’ in the spacecraft.
But research is still required. Plastic is not a strong material and cannot be used as a building component of spacecrafts.