Mission Summary
The European Space Agency's (ESA) Proba-3 mission is an innovative dual-spacecraft project aimed at advancing high-precision formation flying techniques to enable detailed coronagraphic studies of the Sun. As part of ESA's PROBA series, which focuses on testing cutting-edge spacecraft technologies, Proba-3’s design will allow it to explore the solar corona in unprecedented detail.

Mission Design and Operations
Proba-3 consists of two independently controlled satellites—the Coronagraph Spacecraft (CSC) and the Occulter Spacecraft (OSC)—which will operate in a carefully coordinated orbit around Earth, extending to a maximum altitude of 60,500 km. When spaced approximately 150 meters apart, the OSC will cast a shadow over the CSC’s telescope, allowing it to image the solar corona by blocking the Sun’s intense light. This precise alignment will be maintained through autonomous formation control, with the CSC held in position within the shadow cast by the OSC, enabling uninterrupted observations of solar events, like coronal mass ejections (CMEs).

Both spacecraft are equipped with advanced metrology systems that include laser and visual sensors to maintain accurate positioning. During each orbit, they will separate at perigee to safely avoid collision, then reunite at apogee, where gravitational influences are minimized. Proba-3 is expected to provide vital data on CMEs and total solar irradiance, contributing insights into solar processes that may impact Earth’s climate.

Design and Scientific Instruments
- Coronagraph Spacecraft (CSC): Weighing 300 kg, the CSC is designed with a mono-propellant propulsion system that enables it to maintain tight formation with the OSC. It houses the ASPIICS coronagraph, which will capture images of the Sun’s corona in visible and ultraviolet light.
- Occulter Spacecraft (OSC): The OSC, weighing 250 kg, is equipped with a 1.4-meter occulter disk that blocks direct sunlight. It uses a cold-gas propulsion system for precise control, ensuring the corona remains observable through the CSC’s coronagraph.

The primary scientific instrument, ASPIICS, is designed as a classical Lyot coronagraph, with an external occulter mounted on the OSC. A secondary instrument, the Davos Absolute Radiometer (DARA), on the OSC will measure total solar irradiance, aiding in the study of solar energy output fluctuations.

The PSLV-XL is a powerful variant of India's Polar Satellite Launch Vehicle (PSLV), developed by the Indian Space Research Organisation (ISRO). The “XL” stands for “Extended Length,” referring to its larger solid strap-on boosters, which give it more thrust than the standard PSLV version. It is ISRO’s most frequently used configuration when missions require heavier payloads or higher orbits, such as sun-synchronous orbits (SSO) or geosynchronous transfer orbits (GTO).

Specs
Height: 44.5 meters

Diameter: 2.8 m (9 ft 2 in)

Mass:

PSLV-G: 295,000 kg (650,000 lb)
PSLV-CA: 230,000 kg (510,000 lb)
PSLV-XL: 320,000 kg (710,000 lb)

Stages: 4

The PSLV-XL features a four-stage design with alternate solid and liquid propulsion systems. The first stage is powered by a large solid rocket motor (S139), supported by six extended strap-on boosters (PSOM-XL), each loaded with 12 tonnes of solid propellant. The second stage uses a liquid Vikas engine fueled by UH25 and nitrogen tetroxide. The third stage is again solid-fueled, while the fourth and final stage consists of two liquid-fueled engines using MMH and MON-3, allowing fine orbital adjustments.

This configuration has earned a reputation for high reliability and flexibility, having launched a wide variety of payloads including remote sensing satellites, navigation spacecraft, and interplanetary probes. It’s particularly known for notable missions such as Chandrayaan-1, India’s first lunar orbiter, and the Mars Orbiter Mission (Mangalyaan). The PSLV-XL also made headlines for launching 104 satellites in a single mission (PSLV-C37), a world record at the time.

Satish Dhawan Space Centre or Sriharikota Range is a rocket launch center operated by the Indian Space Research Organisation. It is located in Sriharikota in Andhra Pradesh.

Chosen for its remote location, the center became operational in 1971 and hosted its first launch that year for a suborbital mission.

The first orbital launch took place on August 10, 1979.

The spaceport received its current name in 2005 when it was named in honor of Satish Dhawan, the former head of the Indian Space Research Organisation.

The facility has two launch pads and will be the base of India's upcoming human spaceflight program.

Image: ISRO