ISRO To Sign Off 2024 With SpaDex

India is marching towards becoming the fourth country in the world to have space docking technology.

The Indian space agency plans to sign off 2024 with the docking of two satellites in space -- the SpaDex mission -- to become the fourth nation in the world to have such a technology.

On December 30, the Indian Space Research Organisation (ISRO) will be orbiting the two satellites with its workhorse rocket Polar Satellite Launch Vehicle (PSLV-C60).

This time ISRO will be using its Core Alone variant of PSLV.

According to ISRO, the technology demonstrator mission is essential for India's ambitious space programmes like setting up its own space station -- the Bharatiya Antariksh Station (BAS), mission to the moon, bringing back samples from the moon and others.

In-space docking technology is essential when multiple rocket launches are required to achieve common mission objectives and also for sending people and cargo to space stations.

Through this mission, India is marching towards becoming the fourth country in the world to have space docking technology.

Aerospace and defence player Ananth Technologies Private Ltd had integrated two satellites for ISRO.

ISRO said the SpaDeX mission consists of two small spacecraft (about 220 kg each -- one called Target/SDX01 and the other Chaser/SDX02) to be orbited independently and simultaneously, into a 470 km circular orbit at 55° inclination, with a local time cycle of about 66 days.

The demonstrated precision of the PSLV vehicle will be utilised to give a small relative velocity between the Target and Chaser spacecraft at the time of separation from the launch vehicle.

This incremental velocity will allow the Target spacecraft to build a 10 to 20 km inter-satellite separation with respect to the Chaser within a day.

At this point, the relative velocity between the Target will be compensated using the propulsion system of the Target spacecraft.

At the end of this drift arrest maneuver, the Target and Chaser will be in the same orbit with identical velocity but separated by about 20 km, known as Far Rendezvous, ISRO said.

'With a similar strategy of introducing and then compensating for a small relative velocity between the two spacecraft, the Chaser will approach the Target with progressively reduced inter-satellite distances of 5 km, 1.5 km, 500 m, 225 m, 15 m, and 3 m, ultimately leading to the docking of the two spacecraft,' ISRO added.

After successful docking and rigidisation, electrical power transfer between the two satellites will be demonstrated before undocking and separation of the two satellites to start the operation of their respective payloads for the expected mission life of up to two years.

The Indian space agency said the mission is for demonstration of the transfer of electric power between the docked spacecraft, which is essential for future applications such as in-space robotics, composite spacecraft control, and payload operations after undocking.

Like all ISRO satellites in low-Earth orbit, both the SpaDeX spacecraft carry a differential GNSS-based Satellite Positioning System (SPS), which provides PNT (Position, Navigation, and Timing) solutions for the satellites.

In SpaDeX, a novel RODP processor is included in the SPS receiver, which allows accurate determination of the relative position and velocity of the Chaser and the Target.

By subtracting the carrier phase measurements from the same GNSS satellites in both Chaser and Target SPS receivers, highly accurate relative states of the two satellites are determined.

The VHF/UHF transceivers in both satellites aid this process by transferring the GNSS satellite measurements from one satellite to the other.

Hardware and software test beds, including closed-loop verifications, were carried out to characterise the RODP performance.

After the docking and undocking events, the spacecraft will be separated and used for application missions.

A High-Resolution Camera (HRC) with a 4.5 m IGFOV and a swath of 9.2 x 9.2 km (snapshot mode) and 9.2 x 4.6 km (video mode) from a 450 km altitude is mounted on the SDX01.

This is a miniature version of the surveillance camera developed by Space Applications Centre (SAC), ISRO.

A Miniature Multi-Spectral Payload (MMX) is mounted in SDX02, developed by SAC/ISRO.

This has four VNIR bands (B1/B2/B3/B4) at 450 nm to 860 nm and a 25 m IGFOV with a swath of 100 km from a 450 km altitude. The imaging is useful for natural resource monitoring and vegetation studies.

A Radiation Monitor (RadMon) payload is mounted in SDX02, which will measure radiation dose encountered in space.

This will help in generation of a radiation database for future Total Ionization Dosimeter (TID) and Single Event Upset (SEU) measurements for space science studies, with applications in human spaceflight.

Venkatachari Jagannathan can be reached at venkatacharijagannathan@gmail.com

Feature Presentation: Rajesh Alva/Rediff.com