A Japanese startup called Astroscale has unveiled plans to develop a ground-based laser system to tackle the growing threat posed by space debris. The system aims to vaporize debris in low Earth orbit using high-powered laser beams fired from the ground.
The Threat of Space Junk
Over decades of space activity, the area around Earth has become increasingly cluttered with defunct satellites, spent rocket stages and fragments produced by explosions and collisions. There are estimated to be over 128 million pieces of debris smaller than 1 cm, 900,000 pieces between 1 and 10 cm, and 34,000 larger chunks of junk orbiting the planet.
While the Earth’s atmosphere causes debris under 600 km to eventually burn up, higher altitudes are more stable. Objects here can remain in orbit for decades or centuries before decaying. This long-lived space junk poses a collision threat to the International Space Station and operational satellites providing vital services. Even collisions between small pieces generates more fragments, further worsening the problem in a runaway effect known as Kessler Syndrome.
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“Space debris is becoming a huge challenge especially with large constellations going up, even for spacecraft in low Earth orbit below 600 kilometers.” – Nobu Okada, Astroscale
There have already been collisions between satellites and debris. In 1996, a French satellite was hit and damaged by debris from an Ariane rocket stage. In 2009, a dead Russian satellite collided with a functioning US Iridium satellite at 42,000 km/hr, destroying both and generating 2,000 trackable fragments. Events like these highlight the urgent need for debris remediation measures.
Ground-Based Laser Solution
Astroscale’s solution involves using a high-powered laser directed from a ground station to alter the orbits of space debris and cause it to burn up in the atmosphere. The exact details of the system are unclear but it is thought to use a specialized fusion-enabled laser able to deliver sufficient power to vaporize uncooperative debris targets.
Speaking to Nikkei Asia, Astroscale CEO Nobu Okada explained “Space debris is becoming a huge challenge especially with large constellations going up, even for spacecraft in low Earth orbit below 600 km.” By developing a ground-based system, Astroscale aims to provide a solution that is lower-cost than launching satellites equipped with lasers.
How Lasers Can Remove Space Junk
Laser orbital debris removal relies on imparting momentum to change the orbit of debris using photon pressure from a laser beam. Done precisely, this can shift the perigee low enough that atmospheric drag pulls the object in to burn up. Key factors for an effective system include:
- Precision tracking: The narrow laser beam must stay precisely targeted on debris objects travelling at 7.5 km/s to impart enough photon momentum for orbital changes.
- Sufficient power: Enough laser energy must be delivered to alter orbits of uncooperative targets before the beam divergence becomes too great.
- High beam quality: Laser light must have high coherence and low divergence to maximize photon pressure downrange.
- Target accessibility: The system is limited by what objects in orbit can be targeted from any ground site. Equatorial sites can access more inclination angles.
While Astroscale are bullish on the prospects of ground-based laser solutions, experts have raised questions about the viability and safety of such proposals:
- The power levels proposed are extremely high and could pose risks to aircraft and satellites passing through the beam. Meeting safety regulations for visible and invisible beams traversing airspaces is complex.
- Most space debris is only visible sunlight conditions which limits accessible targets for any ground-based scheme. Power requirements to vaporize uncooperative debris in seconds are extreme compared to other gradual orbital-decay approaches.
- Fundamental physics limits the amount of photon momentum (radiation pressure) imparted before lasers diffuse too much to remain on target beyond a few hundred meters. This restricts feasible engagement ranges.
Astroscale are working towards demonstrating orbital debris laser removal from 2024 but technical challenges may delay this schedule. With growing collision risks, research efforts continue on various other debris remediation concepts like drag sails, robotic grappling, electrodynamic tethers and active debris nets. Most experts agree an integrated approach combining multiple solutions is required to confront the worsening space junk problem in the long term.
Outlook for Orbital Environment Remediation
Addressing the space debris challenge is rising up national agendas, regulatory roadmaps and corporate strategies. The problem can still be managed if action is taken swiftly to curb debris generation and remove existing junk. The UN Inter-Agency Space Debris Coordination Committee has set guidelines including passivation, de-orbiting rules and post-mission disposal.
Commercial operators are exploring services for satellite refueling, repair, retrieval and deorbiting to extend asset lifetimes responsibly. Governments support technology demonstrations of debris remediation mechanisms like nets, tugs, dragsails and lasers. As costs fall however, huge growth in constellations risks outpacing debris mitigation capacities. “2021 has seen another record in the number of satellites put into Earth orbit — and with that the risk of debris pollution increases” sums up Holger Krag, Head of ESA’s Space Safety Program Office.
With collisions between objects probable to continue, the calls for action to preserve safe space operations will only get louder. If ambitious technical solutions like laser-vaporization of debris can be proven effective, they may form part of the answer. For now however, the jury is still out on whether ground-based lasers will be up to the task of clearing away space junk.
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