(TSTO) launch vehicle, a series of technology demonstration missions have been conceived. For this purpose, the winged Reusable Launch Vehicle Technology Demonstrator (RLV-TD) has been configured. The RLV-TD acts as a flying testbed to evaluate various technologies such as hypersonic flight, autonomous landing, powered cruise flight, and hypersonic flight using air-breathing propulsion. First in the series of demonstration trials was the Hypersonic Flight Experiment (HEX). ISRO launched the prototype's test flight, RLV-TD, from the Sriharikota spaceport in February 2016. It weighs around and flew up to a height of . HEX was completed five months later. A scaled-up version of it could serve as fly-back booster stage for the winged TSTO concept. HEX will be followed by a landing experiment (LEX) and return flight experiment (REX). Spacecraft propulsion and power Electric thrusters India has been working on replacing conventional chemical propulsion with Hall-effect and plasma thrusters which would make spacecraft lighter. GSAT-4 was the first Indian spacecraft to carry electric thrusters, but it failed to reach orbit. GSAT-9 launched later in 2017, had xenon-based electric propulsion system for in-orbit functions of the spacecraft. GSAT-20 is expected to be the first fully electric satellite from India. Alpha source thermoelectric propulsion technology Radioisotope thermoelectric generator (RTG), also called alpha source thermoelectric technology by ISRO, is a type of atomic battery which uses nuclear decay heat from radioactive material to power the spacecraft. In January 2021, the U R Rao Satellite Centre issued an Expression of Interest (EoI) for design and development of a 100-watt RTG. RTGs ensure much longer spacecraft life and have less mass than solar panels on satellites. Development of RTGs will allow ISRO to undertake long-duration deep space missions to the outer planets. Extraterrestrial probes Lunar exploration Chandryaan-3 is India's planned second attempt to soft-land on the Moon after the failure of Chandrayaan-2. The mission will only include a lander-rover set and will communicate with the orbiter from the previous mission. The technology demonstrated in a successful Moon landing will be used in a joint Indo-Japanese Lunar Polar Exploration Mission for sampling and analysis of lunar soil. Mars exploration The next Mars mission, Mars Orbiter Mission 2 or Mangalyaan 2, has been proposed for launch in 2024. The newer spacecraft will be significantly heavier and better equipped than its predecessor; it will only have an orbiter. Venus exploration ISRO is considering an orbiter mission to Venus called Shukrayaan-1, that