LightSail-2: Miracle of Solar radiation propulsion!!!

Well, once in a while, some amazing humans come forward with their amazing inventions which have the potential to improve human technology drastically. LightSail is such a technology!!!

LightSail is a crowdfunded project of the Planetary Society, a non-profit organization. This project was started to test the solar sailing technology. This technology primarily focused on CubeSats. They decided to make this technology for CubeSats because they have revolutionized the space industry mainly because of tech miniaturization and at the same time carry good payloads.

The concept of solar sailing was first imagined by Johannes Kepler over 400 years ago. It was later embraced by famous scientists like Carl Sagan, Bruce Murray and Louis Friedman.

Johannes Kepler

LightSail project consists of two spacecraft namely LightSail-1 and LightSail-2. This article will be more focussed on LightSail-2 as it’s the most recent and most influential spacecraft of LightSail project.

But before understanding LightSail-2, firstly, we have to know the basics of LightSail-1 spacecraft and its mission.

LightSail-1 (formerly LightSail-A) was more like a technological and engineering sample spacecraft. It didn’t perform solar sailing. It was launched by Atlas V rocket on 20^th May 2015. During its mission, the mission-control lost the communications with the spacecraft for two times. Later the communications were re-established and on 10^th June 2015 the mission was declared a success. It re-entered the atmosphere on 14^th June 2015.

LightSail-1's successful deployment

After the success of LightSail-1, Planetary Society’s next target was LightSail-2 and this time they intended to perform actual solar sailing. After learning from all the mistakes, they did in their first mission, they were ready to launch it. So, it was launched on 25^th June 2019 by SpaceX’s Falcon Heavy. LightSail-2 was enclosed within a Georgia Tech student-built spacecraft named as Prox-1. Prox-1 detached from the Falcon heavy into a circular, 720 km high orbit and successfully deployed LightSail-2. This orbit is much higher than that of LightSail-1. After deployment, it opened its hinged solar arrays on 23^rd July 2019.

SpaceX's Falcon Heavy carrying LightSail-2 (source: NASA)

Once the sail was deployed, the spacecraft was ready to perform its real task, i.e. solar sailing. The mission objective was to raise its orbit and for that, the spacecraft had to swing its solar sails into and away from the sun.

As it’s a solar sail, the craft’s propulsion relies on solar radiation and not the charged particles of the solar wind. Since it is using solar radiation for propulsion, the photons of the light coming from the sun exert radiation pressure on the sail and thus producing acceleration. Acceleration is relative to sail’s area to its mass. It means that the larger the area and lower the mass, the acceleration will be better provided that the spacecraft is getting the same amount of solar radiation.

Radiation pressure is the mechanical pressure exerted by the exchange of momentum between an object (here, sail) and electromagnetic field.

Orbit raising procedure of LightSail-2 (source: The Planetary Society. Josh Spradling)

The LightSail-2 sail control algorithm is designed in such a way that the spacecraft can orient itself and its sail’s edge towards the direction of Sun when moving towards the Sun and can orient sail’s face towards Sun when moving away from the Sun. To orient itself, it uses an internal reaction wheel. As we know, every action has an equal and opposite reaction, so whenever the wheel rotates, due to the opposite force the spacecraft also orient itself to fix its orientation accordingly. This strategy was used to increase orbit apogee and they did it successfully and they announced it on 31^st July, 2019. But, as the orbit perigee decays, it will no longer possible to raise the orbit apogee by using solar sailing.

LightSail-2's Succesful deployment

The project team initially planned to re-enter Earth’s atmosphere after approximately one year but thankfully an extended mission was approved on 25^th Jun, 2020. According to their estimations, LightSail-2’s orbit decay is around 20-34 meters per day and depends upon the level of active sail control and with this estimation, it is expected that this craft will be in the orbit until the first or second half of 2021. Its extended mission objectives may include the characterization of the orbit decay rates and parallelly imaging operation will continue during the deorbit phase.

Total Cost of LightSail project (both LightSail-1 and LightSail-2) is about US $ 7 million and it was paid approximately by 40,000 individuals. It is including US $ 1.24 million raised from a Kickstarter program.

After, the success of LightSail-2, Planetary Society stated that they currently have no plans for LightSail-3.

LightSail-2 Specifications:

Dimensions when sails stowed: 10 x 10 x 30 cm

Mass: 5 Kg

Sail Thickness: 4.5 micro metre

Sail material: Mylar, a reflective polyester film

Sail Width: 5.6 m

Sail Boom length: 4 m

Total Sail Area: 32 m^2 or 340 sq ft

Bus (general model of spacecraft): 3U CubeSat

Sail Layout: 4 triangular sails forming a square connected with cobalt steel booms and booms unwind like tape measures

LightSail has created new possibilities in the field of solar propulsion. This type of innovations can be used later to develop more complex satellites which will eventually help us to conquer new heights in space exploration.

In my future posts, I will continue to write about various space exploration articles which will include the contribution of great space agencies like ISRO, NASA, ESA, JAXA etc. along with articles related to Quantum physics, astrophysics and astronomy. If you like my articles then please consider subscribing our newsletter and follow this blog to get the latest updates directly to you (buttons are available in the right sidebar).

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                                                                 -Ratnadeep Das Choudhury

                                                  Founder and writer of The Dynamic Frequency