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How CubeSats are deorbited

CubeSats, like all satellites, have a finite life expectancy. They cannot stay in orbit forever, and growing concerns over space debris mean that expended satellites must be dealt with so as not to add more clutter to Earth’s useful orbits.

With more and more entities looking to launch satellites, the importance of controlling spacecrafts’ lifespans can’t be overlooked.

CubeSat lifespan and why they need to be deorbited

A CubeSat’s lifespan can be interpreted in different ways.

It could be the operational life of the satellite before its power supplies cease and it becomes little more than piece of space debris, or it could be more concerned with the time that the CubeSat spends in orbit before being manoeuvred out or destroyed in the atmosphere.

Some CubeSats have operated for almost a decade. To some degree a lifespan can be incorporated into the design stage, such as by deliberately using components that won’t grant the CubeSat a lifespan of multiple years.

Though there are no current international laws on the lifespan of satellites, it has been recommended by the Inter-Agency Space Debris Coordination Committee (IADC) that satellites spend no longer than 25 years in orbit before being either moved into a graveyard orbit — where decommissioned satellites are moved away from operational orbit zones so as not to present collision hazards — or deorbited entirely.

The White House has only recently called this 25-year length into question, and its National Orbital Debris Implementation Plan questions whether this should be shortened. However, there remains no definite law in place.

Though CubeSats arguably don’t present the most dangerous or potentially damaging form of space debris when compared with things like rocket bodies, their lower cost and easier launch processes means that their lack of size could be balanced out by a greater quantity in space, making them as considerable an issue as larger single pieces of debris in future.

Once they’ve reached the end of their operational lives, CubeSats share many of the same reasons as conventional satellites for being deorbited. Every satellite put into orbit is another piece of solid, fast-travelling mass surrounding the Earth. Leaving these satellites where they are once they’ve served their purposes is akin to littering space, and there are risks and consequences to this.

Satellites that are no longer operational cannot be issued Command & Control (C2) orders. Whereas a functional satellite can be given orders to perform orbital correction, a ‘dead’ satellite cannot do the same, meaning they present collision hazards. Given that satellites travel around Earth at many thousands of miles per hour, even small bodies can cause serious damage if they collide. They might even stick together, presenting bigger problems.

As the number of CubeSats in orbit is expected to continue to grow exponentially, there may also be the need to make room for new satellites so that they might carry out their own missions. Though competition in space is of high interest to developed nations, it remains the property of no one, and so no nation holds a greater claim to having satellites in orbit than any other, despite the potential viewpoints of defence and military entities.

Methods of deorbiting

Ways to deorbit satellites range from surprisingly simple objects attached to the CubeSats themselves, to costly missions aiming to reap huge amounts of space debris and bring it back down to Earth. Broadly speaking, these can be split between passive and active deorbiting systems.

Passive deorbiting methods

These are methods that typically require no outside intervention to work in deorbiting the satellite (outside of potential C2 controls issued from the ground). They can be built into the satellite itself or attached before launch, activating once the satellite’s mission is done and deorbiting can begin.

Space tethers

Space tethers are cables that hang from the bottom of spacecraft. They’ve typically served as ways to stabilise satellites or enable attitude control, but an adaptation of the idea is now being tested as a method of deorbiting satellites without the need for propellants.

One such project aims to test the ‘electrodynamic space tether’, an aluminium tape measuring roughly 2km long. The tether creates drag by interacting with the planet’s geomagnetic field, gradually reducing the satellites altitude until it re-enters the atmosphere and ablates.

Drag sails

Similar to the drogue parachutes that help to slow down drag racing cars or landing jet engines, drag sails are designed to reduce a satellite’s speed of motion and ultimately drop its altitude much faster than it would otherwise occur.

Drag sails are deployed perpendicular to the spacecraft’s direction of travel, utilising atmospheric drag to cause the slowdown. In one test of a drag sail, a nanosatellite originally thought to take 50 years to fall to Earth instead took less than one.

Active deorbiting methods

These methods involve spacecraft retrieving other spacecraft, often physically apprehending them and forcibly bringing them down to deorbit. Active methods are more costly and complex to perform, but they can be retroactively applied to spacecraft that lack their own methods of passively deorbiting.

RemoveDEBRIS

Developed by a consortium of partners including Airbus and the Surrey Space Centre, RemoveDEBRIS has tested several methods of active deorbiting on CubeSats in orbit. These have included a net that wraps around the satellite and accelerates deorbiting, and a harpoon that is fired into the satellite and tethers it to the ‘mothership’.

ClearSpace

Swiss company ClearSpace has proposed a mission, ClearSpaceOne, that will see a chaser spacecraft pursue a tumbling piece of space debris. Once caught up, the spacecraft will use robotic arms to grab the debris, pulling it down into the atmosphere to be disintegrated. This mission is set to take place in 2025.

Momentus

Momentus is a company operating space transportation systems that are capable of both propelling other spacecraft and deorbiting them. The company aims to offer “in-space infrastructure”, being able to carry satellites between orbits and even stay with payloads if requested.

With so many options and more competing for innovative solutions, CubeSat deorbit may soon be a problem of the past.

To learn more about CubeSats and how COTS software can help your mission make the most of its time in orbit, contact Bright Ascension today.