ISRO SPADEX MISSION

On the 21st of December, 2024, the SPADEX mission was conducted by the Indian Space Research Organization (ISRO). The ISRO SPADEX mission is a cost-effective mission in space technology. In this mission, the in-space docking is demonstrated using two small spacecraft, which are launched by PSLV.

In-space docking technology is required for achieving India's space objectives, such as building and operating the Bharatiya Antariksh Station (BAS) and establishing a presence on the Moon. It is also required when multiple rocket launches are needed to accomplish the mission's common aims.

OBJECTIVES OF THE ISRO SPADEX MISSION

The main aim of the ISRO SPADEX mission is to make and demonstrate the technology required for docking, undocking, and rendezvous of two small spacecraft (SDX01, the Chaser, and SDX02, the target) in a low-Earth circular orbit.

The other objectives are:

Ø  Demonstration of the transfer of electric power within the docked spacecraft, which is required for future uses.

Ø  Payload operations after undocking.

Ø  Control of composite spacecraft.

ISRO SPADEX MISSION CONCEPT

The ISRO SPADEX mission comprises two small spacecraft (about 220 kg each), and they were launched by the PSLV-C60, independently, into a 470 km circular orbit, at an inclination of 55 degrees, with a local time cycle of 66 days. The precision of the PSLV vehicle will be used for providing a small relative velocity between the Target and Chaser spacecraft during separation from the launch vehicle. The incremental velocity will enable the Target spacecraft to produce a 10-20 km inter-satellite separation concerning Chaser within a day.

When the drift maneuver ends, the Target and the Chaser will be in the same orbit with the same velocity but separated by 20 km, called the Far Rendezvous. With the same technology of introducing and then compensating for a small relative velocity among the two spacecrafts, the Chaser will approach the Target with decreased inter-satellite distances of about 5km, 1.5 km, 500 m, 225m, 15m, and 3m, finally resulting in the docking of the two spacecrafts. After the docking is completed, the electrical power transfer among the two satellites will be shown before undocking and separation of the two satellites for beginning the operation of their respective payloads for the expected mission life, which is about two years.

NEW TECHNOLOGIES

The technologies developed for enabling the mission are as follows:

Ø  The technology of power transfer

Ø  Docking method

Ø  A suite of four Rendezvous and docking sensors

Ø  New autonomous rendezvous and docking technique

Ø  GNSS-based new relative orbit determination and propagation (RODP) processor for finding the relative position and relative velocity of the other spacecraft

Ø  Inter-satellite communication link (ISL) for autonomous communication among the spacecraft, equipped with inbuilt intelligence for knowing the states of the other spacecrafts

Ø  Simulation test beds for validation of both the hardware and software design, and their testing.

RENDEZVOUS AND DOCKING ALGORITHMS

ISRO SPADEX MISSION

The standard orbit maintenance and attitude control algorithms used in ISRO LEO spacecraft are used for up to inter-satellite distance of 5 km. The various algorithms used to decrease the ISD keep the satellites at fixed ISDs for evaluating the sensors and software, and finally docking, are the V-bar strategy using n-pulse, glideslope, and PV guidance algorithms. These algorithms are transformed into software for accomplishing rendezvous and docking.

POST-DOCKING ACTIVITIES

The spacecrafts will be separated and utilized for application missions after the docking and undocking events.

Ø  A miniature multi-spectral payload (MMX) is kept on the SDX02, made by the ISRO/SAC. This consists of 4 VNIR bands (B1/B2/B3/B4) at 450 nm to 860 nm. It also consists of a 25m IGFOV with a swath of 100 km from an altitude of 450 km. This imaging is essential for studies on natural resource monitoring and vegetation.

Ø  A radiation monitor payload (RadMon) is kept on the SDX02, which will evaluate radiation encountered in space. This can generate a radiation database for the measurements in the future total ionization dosimeter (TID) and single event upset (SEU) for studies in space science.

Ø     A high-resolution camera (HRC) with a 4.5 m IGFOV is kept on the SDX01. It has a swath of 9.2x9.2 km in the snapshot mode and 9.2x4.6 km in the video mode from an altitude of 450 km. This is a miniature version of the surveillance camera made by the ISRO/SAC.

SPACECRAFT DEVELOPMENT

The SPADEX spacecraft was made by the UR Rao Satellite Centre (URSC) along with the support of the other centres of ISRO, which are the LPSC, VSSC, LEOS, SAC, and IISU. This article provides you with insights about the ISRO SPADEX Mission. You can read this article to learn about the five amazing facts about Chandrayaan 3.