For the past three years, a small spacecraft the size of a loaf of bread with giant wings has sailed on sunbeams in low Earth orbit. LightSail 2 has far exceeded its life expectancy and has proven that solar sails can indeed be used to pilot spacecraft. But its journey around our planet sadly comes to an end as Earth’s atmosphere drags the spacecraft down where it will eventually burn up in atmospheric flames.
The Planetary Society’s LightSail 2 was launched in June 2019 and unfolded its 32 square meter solar sail a month later. Just two weeks after spreading its wings, LightSail 2 reached 2 miles (3.2 kilometers) altitude, making this experiment a success. But in recent months, LightSail 2 is increasingly losing altitude. It now sails at an average elevation of about 390 miles (627 km), down from about 446 miles (718 km) at the start of the mission, according to the Planetary Association.
The scientists behind the mission expect LightSail 2 to re-enter Earth’s atmosphere in a few months, but they don’t have an exact date. During reentry, the spacecraft will move so fast that it will create an energetic pressure wave ahead of it, heating the air around it and burning LightSail in a fiery shroud.
Shade sails run on photons from the sun, causing small bursts of momentum that propel the spacecraft; as the photons hit LightSail’s wings, the spacecraft is pushed further away from the sun. If a spacecraft can exceed the resistance of the Earth’s atmosphere, it can potentially reach very high altitudes.
During its mission, LightSail has had 2 (literally) highs and lows. The orbiter sometimes lost a few meters of altitude per day and sometimes gained a few meters. But after sailing around Earth for three years, the experimental device began to experience a steep drop in altitude due to several factors.
As the spacecraft got lower, the atmospheric density increased very quickly, resulting in atmospheric drag. LightSail collided with atmospheric particles as it traveled at speeds of up to 32,187 miles per hour (32,000 kph), causing the spacecraft to slow down. “Our case is more extreme than most spacecraft because the area of our sail is very large compared to the mass of the spacecraft,” the Planetary Society wrote in a statement. pronunciation† “Imagine throwing a rock compared to throwing a piece of paper. Atmospheric resistance will stop the paper much faster than the rock.”
Ironically, the sun also worked against LightSail 2. When the sun is more active, it heats the Earth’s upper atmosphere, causing it to expand to higher altitudes. At the start of the mission, the sun went through a period of static as part of its 11-year cycle, but our host star has recently ramped up activity for its solar maximum period. This has resulted in the atmosphere being denser at higher altitudes, even reaching the spacecraft, dragging LightSail 2 down.
The third factor leading to LightSail’s demise is more human than cosmic. The mission experienced communication failures due to faulty equipment at the ground station. During times of loss of communication, the team was unable to send data to the spacecraft, causing the sailing to suffer, albeit slightly.
Although LightSail 2 will soon meet its fiery death, the spacecraft’s legacy will live on. The orbiter has inspired several other missions, including: NASA’s NEA Scout mission to a near-Earth asteroid (scheduled for launch in August), NASA’s Advanced Composite Solar Sail System to test sail boom equipment in orbit (scheduled for launch sometime in mid-2022), and NASA’s Solar Cruiser (planned for a 2025 launch). It seems that the era of the solar sail is fast approaching.
More: LightSail 2 propelled by sunlight increases its orbit by 3,200.40m in just two weeks
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