The story so far: The Indian Space Research Organisation (ISRO) on July 3 successfully conducted the ground test of the Sub-Orbital Launch Vehicle for Experiments (SOLVE) solid motor at the Static Test Facility, Satish Dhawan Space Centre, Sriharikota. This test is another important event in the preparation for India’s human spaceflight mission, Gaganyaan.
What is SOLVE?
ISRO is developing a solid motor based SOLVE as a test platform to carry out Integrated Parachute Tests for validation of deceleration system of Gaganyaan’s Crew Module under various test conditions. The solid stage of SOLVE is derived from ISRO’s workhorse rocket the Polar Satellite Lunch Vehicle (PSLV) Strap-on Motor.
Generally the PSLV uses six, four and two solid rocket strap-on motors to augment the thrust provided by the first stage in different variants of the PSLV like XL, QL and DL respectively. However for SOLVE the space agency had made a few modifications to meet the Gaganyaan test requirements which includes development of slow burn rate propellant and straight nozzle with secondary injection thrust vector control. Besides, this is a sub-orbital launch vehicle and unlike the traditional PSLV which can launch satellites in Low Earth Orbits, Geosynchronous and Geostationary orbits.
What will SOLVE test?
Using SOLVE as a test platform ISRO in the future will carry out numerous tests for the Gaganyaan mission where in various conditions would be simulated to resemble the actual mission. As part of the test missions ISRO is looking to certify many vital systems like deceleration system, crew escape system, crew module propulsion systems. During these test missions, the Crew Module will be carried to an altitude of 10 – 17 km and separated from the vehicle. A series of 10 parachutes will be deployed to reduce the velocity of the Crew Module before splashdown in the sea. The Crew Module is where the astronauts would be in a pressurized earthlike atmospheric condition during the Gaganyaan mission.
Why are these tests important for Gaganyaan?
The Gaganyaan is envisaged to launch a crew of three members to low earth orbit and bring them back safely to earth by landing in Indian sea waters. The mission has three important phases which are the ascent phase, orbital phase and descent phase.
In the ascent phase the human rated launch vehicle will carry the Orbital Module that will be Orbiting Earth comprising Crew Module and Service Module to a low earth orbit. This will be followed by the orbital phase wherein the Orbital Module is injected into an elliptical orbit by the launch vehicle. The final phase is the descent phase which activates when the de-boost maneuvers are initiated to steer the module towards the designated touchdown location. During this phase a series of activities are carried out following which the three day mission will finally culminate with a low-velocity splash down at a designated location in sea waters.
While all phases are crucial in particular the ascent and descent are very important and involve a lot of risk. Slightest errors or deviation could risk the astronauts lives which is why various tests are carried out to ensure that they are fool proof and the parachute deployment takes place as planned.
ISRO said that the development of the SOLVE vehicle provides flexibility in conducting Gaganyaan Test Missions simulating various conditions in the actual mission. These tests further validate the parachute-based deceleration system of the Crew Module for Gaganyaan mission in actual mission scenarios.
What are Gaganyaan’s deceleration systems?
The Gaganyaan mission employs a parachute-based deceleration system during the descent phase to reduce the touchdown velocity of Crew Module to an acceptable limit for ensuring its safe landing in the sea waters. The deceleration system of Gaganyaan Crew Module comprises a total of 10 parachutes of four types. According to the space agency the descent sequence begins with two apex cover separation parachutes that remove the protective cover of the parachute compartment, followed by two drogue parachutes that stabilize and decelerate the module. Upon release of the drogues, three pilot parachutes are deployed to extract three main parachutes, which further slow down the Crew Module to ensure a safe touchdown.
What are the other tests?
Apart from the SOLVE, ISRO has also carried out two Integrated Air Drop Tests (IADT), one last year and another one this year. These tests are part of system level qualification of parachute-based deceleration system, in which a dummy Crew Module, encompassing the deceleration system is dropped using a helicopter. In these tests a simulated Crew Module was lifted by an Indian Air Force Chinook helicopter to an altitude of about 3 km and released over a designated drop zone in the sea, near the Sriharikota coast. However unlike IADT where the Crew Module is dropped off from an altitude of about 3 km, during the SOLVE test missions, the Crew Module will be carried to an altitude of 10-17 km and then dropped off from the vehicle.
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