Compare the four development flights

The four developmental flights span 1987 to 1994. D1 on March 24, 1987 and D2 on July 13, 1988 did not achieve their orbital-launch objectives. The D1 investigation remains useful, but it should not be copied onto D2 as an explanation without evidence specific to that flight.

A development flight can test several functions, yet the mission result depends on the required combination. Separately recording useful observations and the unmet overall objective allows engineers and historians to learn from an unsuccessful attempt without relabeling it as a successful launch.

ASLV-D3 launched SROSS-C on May 20, 1992. ISRO describes the flight as successful and reports an orbit of roughly 255 by 430 kilometres. These two heights describe an elliptical orbit, with different low and high points; they are not the 400-kilometre circular reference used in the vehicle overview.

D4 delivered SROSS-C2 on May 4, 1994. That date is supported by ISRO’s ASLV overview, U R Rao Satellite Centre and NASA’s contemporary launch bulletin. Some ISRO summary entries instead print May 5. This course uses the corroborated May 4 date and preserves that source disagreement in its research record.

Four ASLV flights, with their outcomes kept distinct

The reference capability of a vehicle is a useful design description, but the actual mission has a particular payload, trajectory and acceptance criteria. A general reference orbit alone is not enough to reclassify a flight that the mission record calls successful. Equally, a success label should not replace the measured trajectory when explaining what happened.

Consider an original example. A launcher brochure illustrates a 400-kilometre circle, while a test plan specifies an elliptical delivery for an experiment. The test should be assessed against its approved plan and measured state. Neither matching a brochure picture nor completing one revolution is a universal definition of meeting every requirement.