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  • This episode of Real Engineering is brought to you by CuriosityStream, watch over 2,400

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  • On March 27th 2019, Indian Prime Minister Narendra Modi announced to the world that

  • India had conducted its first successful anti-satellite test.

  • Launching a three-stage missile from Abdul Kalam island on the north-eastern coast of

  • India, with a trajectory taking it over the Bay of Bengal.

  • A trajectory that would eventually lead to it intercepting India's military satellite,

  • Microsat-R, 283 kilometres overhead.

  • The seven hundred and forty-kilogram satellite met its end when the kinetic kill vehicle

  • ploughed through it.

  • Shattering it into hundreds of pieces which proceeded to spread in earth's orbit.

  • The test was universally condemned.

  • A completely unnecessary political posturing move that added significantly to Earth's

  • growing space debris problem.

  • This isn't some far off distant problem that we need to worry about, and the probability

  • of collisions occurring is not only continually rising, but there have already been several

  • collision events that have damaged the international space station and other high-value satellites.

  • We can't blame the current state of affairs entirely on anti-satellite tests like this.

  • Every single time we launch into space we generate some sort of unwanted waste.

  • Solid-fuel rockets deposit aluminium-oxide particles.

  • Explosive bolts fragment into pieces.

  • Even chips of paint can cause issues.

  • In 1983 the Challenger space shuttle was struck by a 0.2 mm chip of paint that managed to

  • gouge this pit out of one of its windows.

  • In fact, in the first 67 Space Shuttle launches 177 impacts were found in the windows.

  • 45 of which were large enough to warrant a replacement window.

  • Post-mission analysis determined all of these impacts we caused by space debris, with 44%

  • being caused by aluminium alloys, 37% by paint chips, 12% by steel, 5% by copper and 2% by

  • titanium.

  • [11]

  • At fifty thousand dollars a pop, this did not come cheap.

  • Based on these numbers, the Space Shuttle had 67% chance of impact causing significant

  • damage to the windows during their 10 day missions, and these probabilities have only

  • risen over time.

  • In 2007 the likelihood of a collision between any satellite in low earth orbit and a piece

  • of debris over 1 centimeter in size was 17-20% in a single year.

  • [2] That statistic increased to 25-33% later that year when China tested their own anti-satellite

  • missile.

  • By 2010 the chance of a 1-centimetre piece of debris striking a satellite had increased

  • to 50% a year, after two full-sized satellites Iridium 33, a US communications satellite,

  • and Kosmos 2251, a retired Russian communications satellite, collided at 42,000 kilometres per

  • hour.

  • Obliterating both satellites and producing over 1000 fragments over 10 centimetres in

  • size, and many more too small to be tracked.

  • So the chances of collision are not small by any measure, they are common and it's

  • only a matter of time before another serious incident like this 2009 collision occurs again,

  • so it is prudent that we design satellites to be capable of not only withstanding small

  • impacts but be capable of dodging larger ones.

  • The ISS, for example, is designed to withstand objects up to 1 centimetre in size [3], and

  • can dodge larger trackable objects 10 centimetres wide.

  • The biggest danger to the occupants of the ISS are objects in between these sizes.

  • That are untrackable but large enough to cause serious damage to the international space

  • station.

  • [3]

  • When the ISS was being planned, NASA laid out a basic risk management policy.

  • That the probability of any critical component of the ISS being penetrated by space debris

  • would be less than 19% over 10 years.

  • [4][5] A critical component is characterized by anything that could potentially lead to

  • a loss of life if it is damaged, and designers are careful to correctly categorise each component

  • on the ISS to ensure this is the case, which often involves performing hypervelocity impact

  • test here on earth.

  • This resulted in things like batteries and ammonia accumulators being categorized as

  • non-critical when they didn't explode during tests, and so received less shielding that

  • other critical components.

  • Space debris is just a fact of everyday life on the ISS that astronauts need to be aware

  • of.

  • To get a better sense of what it's like living with this.

  • I spoke with former ISS commander Chris Hadfield on the phone.

  • When you are onboard a spaceship you have a constant undercurrent awareness of the ever

  • prevalent risk of something hitting your spaceship and causing a leak.

  • Sort of like when you are driving a car, you always know at some point you could have some

  • kind of accident.

  • Yo u know, It's not heavy on your mind.

  • You know it happens.

  • You know the odds are that eventually it will happen for sure, and you just have to find

  • a way to live with it.

  • And so the way we live with it is to understand the risk as accurately as we can.

  • We know the statistics.

  • We know the relatively risk of man made debris versus naturally occurring debris, and we

  • know how the space station is designed to resist it with the multilayer shielding, and

  • then we also have procedures.

  • So let's talk about that shielding first.

  • Shielding the ISS with heavy plates, as tanks do here on earth, is not an option.

  • This is the damage a 13-millimetre spherical bullet will do to a 18-centimetre aluminium

  • plate when travelling at 7 kilometres per second.

  • It prevented penetration and only just managed to prevent a large chunk of spall to break

  • off from the interior surface.

  • [6]

  • At 13 centimetres a 1 metre squared aluminium plate like this would weigh about 338 kilograms.

  • When the ISS started construction in 1998 the per kilo cost to launch to the International

  • Space Stations orbit using the Space Shuttle was about 93,400 dollars.

  • [7] Placing a 1 metre squared shield like this at a cost of 31.5 million dollars.

  • This is an extremely inefficient use of material, and the ISS uses something much more elegant

  • called a Whipple shield.

  • The Whipple shield uses the debris' own velocity to stop it.

  • At 4 kilometres per second and higher, the energies involved are so immense that the

  • projectile itself breaks apart and vaporises on impact.

  • [8] Whipple shields take advantage of this by creating a shield that is composed of several

  • thin sheets of armour separated by space.

  • So when a meteoroid or debris does strike it, it first breaks up into thousands of smaller

  • superheated fragments.

  • Thereby spreading the energy of the impact over a larger area for the following shield

  • layer.

  • The European Space Agency conducted tests of their kevlar Whipple shields which protect

  • their ATV vehicle.

  • They did this by shooting a 7.5 mm diameter aluminium bullet at 7 kilometres per second,

  • which tore straight through the kevlar shield, but left only a scorch mark on the 3-millimetre

  • aluminium wall behind it.

  • [9]

  • These kind of impacts occur fairly frequently and as Chris Hadfield told me during the call:

  • If you just sit quietly by the wall of the space station and wait a while, you can hear

  • things hit your ship.

  • And that's kind of an interesting thing.

  • It doesn't happen too often and sometimes all you are hearing is the vehicle cooling

  • and heating in the sun, so you are hearing the natural popping of metal expanding or

  • contracting, but occasionally you hear just like the sound of a small bullet or high speed

  • stone banging into the thin aluminum hull of your ship

  • So astronauts are occasionally reminded of the space debris problem, and have to be careful

  • not to cut their suits while on space walks on sharp impact edges.

  • While this is a highly effective form of shielding that minimises the weight of shielding needed,

  • it is only effective for smaller debris.

  • Larger particles would tear right through this shield, and for those circumstances,

  • the ISS and other satellites literally have to dodge the incoming shrapnel.

  • Ground-based radar like the Haystack Radar are the main source of spatial data we have

  • on space debris.

  • It is an X-band radar system that simple stares at selected points in space and waits for

  • debris to pass through its radar beam.

  • [12] This gives us size, speed and direction information, which is fed into a database

  • that allows NASA and other space agencies around the world to predict potential collisions.

  • When a collision is predicted maneuvres can be planned to allow the international space

  • station to dodge it, but these maneuvres come with a cost, and mission control needs to

  • assess if the risk is worth that cost.

  • They start by drawing an imaginary box around the international space station.

  • 50 kilometres squared and point seven five kilometres deep.

  • This acts as an exclusion zone and any tracked debris that passes through it will send an

  • alert to mission control.

  • From there careful risk analysis begins.

  • If there is a one in ten thousand to one in one hundred thousand chance of collision the

  • ISS receives a yellow warning.

  • [14]Which means flight controllers must perform avoidance maneuvres if they do not interfere

  • with mission objectives.

  • This can be as simple as interfering with microgravity experiments to forcing the Soyuz

  • to miss a launch window.

  • If there is a greater than one in ten thousand risk [14], then a red warning is received

  • and the international space station must take action.

  • Control momentum gyros can be used to alter the stations orientation, while thrusters

  • on the Zvezda module or on docked vehicles can be used to provide the necessary acceleration.

  • Boosting to a higher orbit requires expensive propellant, but the ISS already needs to perform

  • reboosts every few months to maintain its orbit, so these dodging maneuvers will just

  • alter the scheduling of these already needed boost burns.

  • These exclusion zones exist for all satellites in NASA's database and on March 29th 2012,

  • Julie McEnery (hup the Irish) the project scientist for the Fermi Gamma-Ray Space Telescope

  • received an automated email alert.

  • Informing her of a predicted incursion between Fermi and Cosmos 1805, a retired Russian spy

  • satellite, where the two would pass within 700 feet of each other.

  • The decision on what to do with this information was left to her, and the lessons learned from

  • the previous satellite collision were not lost on her.

  • In order to ensure they did not collide Fermi would need to rotate away from its view of

  • the sky to point its thrusters in the direction of travel.

  • It then performed a 1-second burn that would separate the two satellites crossing temporally.[15]

  • These thrusters had not been tested before, as they were designed to take the satellite

  • out of orbit at the end of its life, and so there was significant anxiety within the team

  • that they could malfunction and end Fermi's mission prematurely.

  • Thankfully that did not happen, and Fermi continues to give us valuable information

  • about the Universe to this day.

  • These issues are only going to grow as human activities in space grows, and it's time

  • we began thinking more seriously about how we manage our cosmic neighbourhood.

  • Mainstream media tends to incredibly alarmist about this issue.

  • β€œSo all of that is debris that you are looking at there, so your concern for debris is well

  • placed.

  • We maybe putting so much debris is space that we will close ourselves off from space travel

  • because of the dangers it would take to get through our own garbage heap.

  • Space debris, obviously does not look like this, the vast majority of it is too small

  • to see.

  • Occasionally we have massive debris, like the upper stage of Apollo 12s Saturn V rocket,

  • which is still in orbit and expected to return to earth in the next couple of decades, but

  • this material is easy to dodge.

  • After all, space is a big place.

  • We are not going to be trapped on the planet, we are not going to lose all technology related

  • to satellites.

  • Even now, just a few weeks after India's anti-satellite test, a decent amount of the

  • debris will have drifted back to earth.

  • We can take Operation Burnt Frost, the US's own anti-satellite test in 2008, as proof

  • of this.

  • There were multiple similarities between this and India's own test, with similar orbits

  • and altitudes.

  • Data from the Combined Space Operations Centre shows that the majority of the debris from

  • this test had fallen back to earth within 2 months, while other pieces that managed

  • to be ejected into higher orbits eventually return to earth about 2 years later [1]

  • This was just the larger trackable debris.

  • Smaller debris decays faster as it has a larger area to mass ratio, making them more sensitive

  • to atmospheric drag.

  • Even in orbit, molecules do exist that collide with satellites and debris, causing them to

  • lose slow down and lose altitude.

  • This isn't a reason to ignore the problem.

  • If the problem continues to grow as our space activities grow, the potential loss in money

  • from damaging collisions and the potential chain reaction this could cause in a busy

  • earth orbit is going to motivate efforts to fix the problem.

  • It's not just the cost of the satellite that will motivate efforts.

  • Entire economies have been built upon the services they provide.

  • International treaties dictating space operations need to be updated to mitigate the issue,

  • ensuring any satellite placed in Earth orbit will be required to be capable of bringing

  • itself out of orbit and be capable of dodging debris when needed.

  • As we saw earlier with Fermi this is a feature of some satellites, but not all.

  • Some satellites simply become giant bullets when they retire.

  • This cannot be allowed to continue.

  • This alone will not be enough to ensure space debris is kept to a reasonable level, and

  • active clearance may be needed if trends continue.

  • Launching more objects into orbit to solve the problem seems to me to be a very expensive

  • and ineffective way to deal with the problem.

  • Someone will have to fund it, which will be difficult as most companies want to add things

  • to space not remove them.

  • Not only that, but it will also add to the space debris problem with the natural bi-products

  • of launches, while only being capable of taking down large objects.

  • A more promising technology will involve using high power lasers that will be powerful enough

  • to ablate material from the object, which will provide thrust to slow its orbit and

  • thus increase its rate of decay.

  • There are issues with a technology like this, as it could be used as an anti-satellite weapon

  • which would not sit well with other space faring nations.

  • To overcome that it would need to be a joint venture between all space faring nations.

  • [17] Just as the ISS became an international effort to unite mankind, cleaning up our cosmic

  • neighbourhood can also become a uniting problem.

  • International cooperation and rivalries have long been the driving force for advancement

  • in the field of aerospace.

  • World War 1 and 2 advanced aviation at a unprecedented rate, and it's conclusion led to an international

  • race to the moon.

  • If you want to learn more about this troubled birth of aerospace.

  • I highly recommend watching this documentary titled β€œPioneers in Aviation” on curiositystream.

  • It will take you from the early years of the Wright Brothers to the foundation of the Boeing

  • and Douglas Aircraft Companies through the difficult years of the great depression and

  • the rapid advancement during the world wars, culminating in the space race.

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