By 1981, confidence grew in remote sensing spacecraft development with launch of Bhaskara-1 and the PSLV project objectives were upgraded to have vehicle deliver 1000 kg payload in 900 km SSO. As technology transfer of Viking rocket engine firmed up, a new lighter configuration shifting away from relying on three large solid boosters was proposed by team led by A. P. J. Abdul Kalam and eventually selected. Funding was approved in July 1982 for finalized design employing a single large S125 solid core as first stage with six 9 tonne strap-ons (S9) derived from SLV-3 first stage, liquid fueled second stage (L33) and two solid upper stages S7 and S2. This configuration needed further improvement to meet the orbital injection accuracy requirements of IRS satellites and hence solid terminal stage (S2) was replaced with a pressure fed liquid fueled stage (L1.8 or LUS) powered by twin engines derived from roll control engines of first stage. Apart from increasing precision, liquid upper stage also absorbed any deviation in performance of solid third stage. Final configuration of PSLV-D1 to fly in 1993 was (6 × S9 + S125) + L37.5 + S7 + L2.