India’s first space-based solar observatory, the Aditya L-1 satellite, is nearing a significant milestone. ISRO (Indian Space Research Organisation) has announced that the satellite is expected to reach its operational orbit at 4 pm on January 6.
During its 126-day journey, which started on September 2 last year, Aditya L-1 has travelled roughly 3.7 million kilometres. This journey involved a complex route to its designated operational area in space from where it will carry out its mission for the next 5.2 years.
From its position at the Lagrange Point-1 (L-1), the Aditya L-1 satellite will conduct studies to understand the Sun better. This unique location allows for an uninterrupted view of the Sun, aiding in studying space weather. The satellite will serve as a tool to forecast—and warn about—solar storms, providing crucial information about our solar system’s central star, the Sun.
Lagrange Point-1 (L-1) is a position in space where the gravity of two large bodies—such as the Sun and Earth—balances the centrifugal force of a smaller object, such as a spacecraft. At L-1, the smaller object can maintain a stable orbit with the two large bodies. Aditya’s orbit, shaped like a halo, is around 1.5 million kilometres from Earth. It is closer to the Sun than Earth but still quite distant, as the Sun is about 150 million kilometres away from Earth.
Other spacecraft—such as NASA’s WIND, ACE and DSCOVR, and the combined ESA/NASA mission, SOHO—are positioned near L-1, just as Aditya L-1 intends.
SOHO versus Aditya L1 Overview
SOHO and Aditya L-1 are spacecraft that observe the Sun from L-1 between Earth and the Sun. But they have some differences in their objectives, instruments and launch dates. Here are some of the main differences.
1. International and Indian Ventures
SOHO (Solar and Heliospheric Observatory) is a collaborative effort between the European Space Agency (ESA) and NASA (National Aeronautics and Space Administration), whereas ISRO operates the Aditya L-1 mission from India.
SOHO was built by companies from 14 European countries, led by Matra-Marconi (now Astrium). The spacecraft’s service module—which includes solar panels, thrusters, control systems and communication technology—was made in Toulouse, France. The part carrying scientific instruments was put together in Portsmouth, UK, and then joined with the service module in Toulouse. NASA is responsible for launching SOHO and tracking, data reception, and command transmission.
2. Space Missions for Studying the Sun
Since its December 1995 launch, SOHO has conducted research on the Sun for more than two solar cycles. A solar cycle lasts for about eleven years. Aditya L-1 was launched in September 2023 and is anticipated to enter orbit after roughly 125 days on January 6.
3. Instrumentation for Sun Observation
SOHO has 12 instruments on board that monitor the Sun’s interior, atmosphere and solar wind. Aditya L-1 has seven instruments that focus on the Sun’s chromosphere, corona and space weather.
4. Comets and Solar Eruptions Study
SOHO has discovered thousands of comets that orbit the Sun. Aditya L-1 will investigate the origin and dynamics of solar eruptions and their impact on Earth.
5. Comparing Missions for Solar Study
The Aditya L-1 mission is set to take about 5.2 years. On the other hand, the SOHO mission, launched in December 1995—and initially intended to operate until 1998—has remarkably exceeded its expected lifespan. It continues functioning, making it one of the longest-running solar observation missions. This longevity has established SOHO as a significant contributor to solar studies.
6. SOHO & Aditya L-1: Orbital Journeys
At its launch, the SOHO spacecraft weighed 1,850 kg, including its service and payload modules essential for power, communication and scientific experiments. The Aditya L-1 spacecraft has a total weight of 1,475 kg, of which 244 kg is the mass of its scientific payloads.
SOHO was launched into a halo orbit around the first Lagrange Point. It took SOHO about three and a half months to reach L-1 after its launch. In comparison, the Aditya L-1 mission is also targeted to reach a halo orbit around L-1, and it is expected to take approximately four months from its launch to reach this point. This duration is slightly longer than that of SOHO.
7. Size Comparison: SOHO versus Aditya L-1
Aditya L-1 is considerably smaller compared to SOHO. SOHO measures 4.3 metres along its sun-pointing axis and has a solar panel span of 9.5 metres. Aditya L-1, on the other hand, has a length of only 0.89 metres along its sun-pointing axis, roughly 20.7% of SOHO’s length. While the exact span of Aditya L-1’s solar panels is not specified, if they are proportionate to its body size, they would be about 1.78 metres wide, approximately 18.7% of SOHO’s solar panel span.
