ISRO, which has been making quiet progress on the reusable launch vehicle-technology demonstrator (RLV-TD) is looking to carry out a key landing Experiment — RLV-LEX — in the next few months that will push it closer to an orbital re-entry experiment (ORE). The planned landing experiment will be carried out in Challakere in Chitradurga district, some 220km from Bengaluru.
Isro chairman S Somanath, while confirming that the agency has planned the RLV-LEX this year, said: “…We will be demonstrating one of the critical technologies — the approach and autonomous landing on a runway. This will happen in Challakere. We are preparing for the test and systems are being readied. We will soon make an announcement.”
In the LEX, the vehicle will be carried using a helicopter to an altitude of about 3km to 5 km and released at a distance of approximately 4km to 5km ahead of the runway with a horizontal velocity. As per Isro, after the release, the RLV glides, navigates towards the runway and carries out a conventional autonomous landing with a landing gear.
S Unnikrishnan Nair, director, Vikram Sarabhai Space Centre (VSSC), said: “We are planning for the test in the next three to four months, the hardware is nearly ready. The RLV will be released from the helicopter under controlled conditions. It will have various control systems, including its own navigation and guidance control systems and aerodynamics sensors etc. This experiment will simulate the last 800m to 1km of the actual orbital mission.”
Pointing out how landing is among the most complex activities in any mission, Nair said the RLV-LEX would take the technology demonstration one step closer to the planned ORE.
“Once we successfully complete this mission and we have validated the software, landing gear and get data on how the aerodynamics sensors worked to manoeuvre the aircraft and bring it back to the intended spot on the runway and other critical technologies, we will be ready for the orbital re-entry experiment. For this the RLV will be scaled up,” Nair said.
As per Isro, in ORE, a wing body called Orbital Re-entry vehicle (ORV) will be taken to an orbit by an ascent vehicle derived from the existing GSLV and PSLV stages and stay in orbit for a stipulated period, re-enter and land in a runway autonomously with a landing gear.
“Before the RLV-LEX we’d done the RLV-TD HEX-01 (hypersonic experiment) mission in which we successfully validated autonomous navigation, guidance & control, reusable thermal protection system and re-entry mission management. Once LEX is done, we’ll need to integrate both for the ORE,” Nair said.
Carried out on May 23, 2016, the RLV-TD HEX was a 770-second suborbital flight and designed to land on sea. The experimental mission saw the HS9 solid rocket booster carrying RLV-TD to a height of about 65km from where the vehicle began its descent followed by atmospheric re-entry at around Mach 5 (five times the speed of sound).
Isro, which has been working on this technology for more than a decade, decided to develop it primarily to address the cost and time issues. “The cost of access to space is the major deterrent in space exploration and space utilisation. A reusable launch vehicle is the unanimous solution to achieve low cost, reliable and on-demand space access,” Isro has said.
However, mastering this technology will provide multiple other benefits, including in development of different types of launch vehicles, space transportation and so on. While the ORE will be a major milestone, the RLV-TD is only a technology demonstrator and the development of an actual re-usable launch vehicle will take more time.