When you imagine Earth from space, the picture above most likely resembles what you think of. We see this Earth in picture books and on TV. And that makes sense — this is Earth. Or, at least the Earth we’ve been taught about. But, in reality, this is what Earth used to look like.
In fact, today it looks something more like the animation below. As time passed, our need for telecommunications and weather satellites grew and launches occurred with increasing frequency. Currently, our planet is enveloped by millions of pieces of space debris and with time this number will only grow.
This growth is due to something called the Kessler Syndrome which states that the more objects that are launched into space, the more collisions will occur. This will in turn create more collisions. It’s a never ending cycle of debris breaking into smaller and smaller pieces, with the numbers accelerating exponentially. In fact, SpaceX and Blue Origin are planning to launch more satellite constellations making the danger these collisions present even more relevant.
According to the European Space Agency (ESA), “Among the more than 8,700 objects larger than 10 cm in Earth orbits, only about 6% are operational satellites and the remainder is space debris.” Currently, NASA tracks about 500,000 pieces of space debris orbiting our planet, but the ESA estimates the number is over 1.7 million. Thus, the vast majority of debris orbiting Earth is under 10 cm. As more collisions occur, the debris will keep breaking apart and become even harder to detect and this can all be attributed to the Kessler Syndrome.
Currently, we can track space debris in the range of 10 cm and up, but between 1mm and 10cm, it’s virtually impossible to detect pieces of debris and prevent collisions.
And this is a huge issue.
In April of 2016, an object moving at 8 km/s collided with the glass cupola module on the ISS, resulting in a crack within heavily reinforced windows. This object was predicted to be a paint chip from a previous collision and its size estimated to be within the mm range.
Not only did the paint chip put all the lives on the ISS at risk, but also the groundbreaking research being conducted on the ISS. It’s no doubt that if this piece of debris were larger, we would have been able to detect it and prevent the collision, but because it was within a certain size range, it was completely undetectable.
These incredibly small pieces of debris move at high velocities. How fast, you ask? About 27,724 km/h, 20 times faster than a bullet at LEO. What makes it worse is that satellites are launched in all directions, making anything and everything more prone to collisions.
With the amount of small space debris in LEO rising exponentially, this problem will only grow with time. It could potentially put a stop to launching anything into orbit, limiting the research of the universe, and could also limit the research we gain from studying Earth from space.
Satellites give us GPS, weather forecasts, radio and TV, and so much more, so a world without them would be very different. Unfortunately, that’s exactly where we’re heading.
According to the ESA, “An object up to 1 cm in size could disable an instrument or a critical flight system on a satellite. Anything above 1 cm could penetrate the shields of the Station’s crew modules.”
All that being said, my team and I set out to solve this pending issue and detect the undetectable.
After thorough investigation and countless research papers, we determined that we could leverage LiDAR technology (the acronym for light detection and ranging) as a possible solution for keeping track of small space debris in LEO, ranging from 1 mm — 10 cm.
LiDAR is familiar to most for its ability to create an accurate image of a car’s surroundings, allowing for autonomous vehicles to become a reality.
We propose something to the similar effect, that would also incorporate the Doppler shift of space debris. Our LiDAR system would rapidly fire out narrow beams of infrared light from a laser that backscatters off any object in range. These wavelengths are super focused and precise, something that ground-based RADAR systems for space debris can’t achieve. We would use a narrow enough beam to find the 1 mm -10 cm range space debris. Using the equation below we will be able to determine the exact diameter of the beam.
When the light is backscattered off a given piece of debris, we can easily calculate the position of the debris from the time delay and the velocity of the debris from the Doppler shift.
Velocity of small space debris
All moving objects experience a Doppler shift. The signals from moving objects, such as our space debris, have a Doppler shift proportional to their speed. We can measure the Doppler frequency shift of the backscattered radiation which is how we plan to calculate velocity of the debris.
Position of small space debris
Our Doppler LiDAR releases pulses of light in succession while scanning the backscattered light from debris. This means that from the time delay between each outgoing transmitted pulse and the backscattered signal, the distance to the debris can be measured.
Our LiDAR system would calculate the distance of a piece of space debris by multiplying the speed of light and the time taken by the light to reach the detector again after backscattering. This product would then be divided by 2.
The distance of the object = (speed of light x time of flight)/2
Current ground-based LiDAR systems that measure aerosols in the wind have a range up to 30 km. We plan to scale this up in space and have higher sensitivity detectors without the limitation of the atmosphere.
Profile of our Detection System
Ultimately, all of this proves that a LiDAR system is a good candidate for detecting small space debris because of its precision. If we mount a LiDAR system onto a microsatellite, we could have a functioning, accurate prototype to solve our problem. Microsats are more cost-efficient and have faster production rates than conventional satellites. Also, since we are trying to steer away from further cluttering space, using a microsatellite would align more with our mission instead of larger-sized satellites.
We propose launching multiple microsatellites, both orbiting around the poles and orbiting around the equator. The number of microsats we need will be determined by the range of each LiDAR system. This all depends on the diameter of the beam, and we can find this out by using the same equation mentioned above. With these microsatellites, we will ensure that we have a greater coverage, thus allowing us to track as much small space debris as possible.
The data collected by our LiDAR systems on the microsats could then be sent to different space agencies. By knowing the positions and trajectories of small space debris, it would allow them to calculate the best launch window to encounter the least amount of small debris and have the least probability of malfunction. Given that we now have a way to track smaller scale debris, we could use our data to move forward with the elimination of space debris, no matter the size.
A Doppler LiDAR system could lead us into the next steps of clearing space debris. We would have safer missions and less chance of malfunctions and danger to astronauts, all while eliminating barriers to conduct new research and creating more space in space.
This piece was co written by Kai Kim-Suzuki, Kareena Shah, Urzsula Solarz, and Simone Lilavois