Radio Verulam Science Feature 26-03-2018
Space junk clean up
Every time we launch a rocket into space, it is likely to leave a piece of itself, that cannot be reused, orbiting the Earth. This litter cloud has been considered a problem since the 1970s but now we are really thinking about how to clean this mess up.
There are 20,000 pieces of space junk that are bigger than 10 cm, which are being tracked by NASA, ESA and other organisations. These pieces are monitored so that if there is any chance of collision between them and any operational satellite including the International Space Station (ISS), then orbit correction commands can be sent to the operational craft for it make an avoidance manoeuvre.
There are many, many more pieces that are smaller than 10 cm, an estimate of around 500,000 pieces between 1 cm and 10 cm orbit the Earth. These are the most dangerous pieces of junk because they are difficult if not impossible to track, but if they collide with an operational satellite they could cause catastrophic damage.
Beyond that there is an estimate of around 100 million pieces that are less than a 1 cm in size. And while these also pose a risk to spacecraft, they are less likely to cause catastrophic failure.
There are around 2000 satellites in various orbits including Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO). LEO includes Earth monitoring craft and the ISS, GEO includes television and other communication craft.
Donald Kessler, a scientist at NASA, proposed in 1978 the scenario (called the Kessler effect) where the density of objects in LEO is high enough that collisions between objects could cause a cascade where each collision generates space debris that increases the likelihood of further collisions. It has been calculated today that even if no further satellites were launched, the amount of junk up there at the moment, any collisions would create more pieces greater than 10 cm than atmospheric drag would remove.
Though the atmosphere is almost non-existent at the height of a LEO orbit, there is still enough of it to cause an atmospheric drag. All LEO satellites, including the ISS, have to use a bit of thrust every now and then to stop them from eventually falling into the Earth’s atmosphere and burning up.
This atmospheric drag process can be used to remove old satellites or pieces of rocket from orbit and this is often done to safely dispose of parts of rocket. However, what happens if you can’t control the re-entry?
There is an International Guideline set out, which says that satellites must be deorbited or sent to a graveyard orbit within 25 years after the end of the life of the craft. However, depending on the kind of mission it can be hard and difficult to ensure this. Hence, one fifth of cubesats launched between 2003 and 2014 didn’t meet this and a total of 35 % of satellites launched in 2015 also do not comply. It is a guideline and it cannot be enforced.
Even if your craft has this deorbiting built in, you still may not be able to control it. For example, ESA lost contact with the satellite Envisat in 2012, mid-operations. It is the size of a double decker bus and no-one has any control of it. In 150 years it will fall back into the atmosphere, but before then? It could crash into any number of other craft or another piece of space junk could crash into it, causing catastrophic damage and disintegrating into innumerable pieces of various sizes, which in turn could cause damage to other craft in the future.
Another example is Tiangong-1, a 10 x 4 metre Chinese space station that was visited by Chinese astronauts as a precursor for follow up manned missions on other future space stations. Its service life ended in 2016 and later it was discovered that control had been lost and it was in a decaying orbit. It is expected to re-enter the atmosphere sometime between the 30th March and 2nd April between latitudes of 43 ° N and 43 ° S at an unknown longitude.
Envisat or any one of the other millions of pieces of space junk could cause a domino effect or a Kessler Cascade, which could lead to the awful fact that the near-Earth space environment would be impenetrable by new launches as they would be immediately destroyed by all the resulting pieces of space junk in orbit. This would mean that new communications satellites and manned missions would be impossible, trapping us on the planet and reducing satellite communications greatly, if not to zero.
What can we do!? A team from Airbus, in Stevenage, UK are working on a harpoon attached to a chase spacecraft that will grab Envisat and then perform manoeuvres that will bring the space junk under control, so it can be destroyed safely. Other ideas include shooting high powered lasers at pieces of space junk, which alters their orbit enough so that they would burn up in the atmosphere sooner than they would otherwise have; or perhaps giant space nets to round up the larger pieces would work. Unfortunately, part of the difficulty is that everything in orbit is travelling at great speeds, at least 18,000 mph, so intercepting these objects requires careful planning. Reducing the number of launches and/or enforcing rules about having to deorbit old satellites would certainly help, but so far, neither of these options look likely to be put in place any time soon.
Scientist of the Month #SotM
Director of the Bloomington Drosophila Stock Center at Indiana University and co-founder of FlyBase, a catalogue of Drosophila genetics.
Drosophila are small flies (the vinegar fly – it feeds on yeast, but often thought of as a fruit fly) that are extensively studied because they have some similarities to us, for example, the gene that regulates the patterning of the body plan and organ development is the same as the gene in humans. However, an example of how they are quite different is that they only contain four chromosomes, whereas humans have 23.
Kathy was born in Japan in 1954 and spent the later part of her childhood in Texas. She earned her bachelor’s and doctoral degrees from the University of Texas at Austin, the latter in genetics.
In 1979, she worked at Indiana University as a postdoc and studying transposable elements in Drosophila. (Transposable elements are DNA sequences that are able to move in the genome and can be responsible for mutations.)
Kathy was central to two of the most important research resources for Drosophila genetics and “[i]t is easy to say that without Kathy, the fly community would not be what it is today.”
What makes transposable elements move in the Drosophila genome? https://www.nature.com/articles/hdy201189
Night Sky this Month
31 March – (second) Blue Moon, Full Moon (2 March was also a Full Moon)
22/23 April Peak of the Lyrids meteor shower. Runs 16 to 25 April, up to 20 meteors per hour. Results from debris trail left by comet C1861 G1 Thatcher. Moon sets just after midnight leaving dark skies for the meteor shower.
29 April Mercury at greatest western elongation. Mercury is visible with the naked eye before sunrise.
Good opportunities to see the ISS over the next week: https://spotthestation.nasa.gov/
Direct link to St Albans sightings:
Mon Mar 26, 9:11 PM
10° above SW
36° above S