Use of solid propellant criticised as investigation begins into what caused VLS-1 rocket to explode during routine checks

The third prototype of Brazil's satellite launch vehicle, VLS-1 V3, exploded on 23 August, three days before its scheduled launch from the Alcântara launch centre on the Atlantic coast 2,300km (1,430 miles) north of Rio de Janeiro.

Housed inside a moveable assembly and launch tower, the VLS was undergoing pre-launch testing when one of the four solid-propellant boosters ignited and toppled the 19.4m (63.5ft)-tall rocket. The subsequent explosion within the assembly/launch tower killed 21 people, further setting back Brazil's fledgling space programme.

According to Maj Brig Tiago da Silva Ribeiro, commanding officer of the Alcântara launch centre, three teams were performing routine inspections at the time of the accident. None of the assigned tasks involved any noteworthy risk. "That makes it even more difficult to understand this unusual accident," he says. Remote cameras confirmed preliminary indications that the explosion's source was centred beneath the rocket - reinforcing the theory of spontaneous ignition of the S-43 engine on the "A" booster.

V3 was carrying the locally developed Satec-1 and Unosat satellites, which were designed to enter orbit attached. Satec was a microsatellite developed by national space research institute INPE, while Unosat was a nanosatellite built by Brazil's Unopar university.

An accident investigation committee established by the Brazilian ministry of defence is believed to be focusing on the ignition system of the 68,000lb-thrust (300kN) S-43 engine, its solid fuel and human-related factors. Ignition could have been caused by an electrical discharge, an electromagnetic pulse or a piece of metal in the fuel, says Mauro Tolinky, vice-director of the Brazilian IAE institute of aeronautics and space. Brazilian space agency AEB has been criticised for insisting on using solid propellants for the VLS-1.

The two previous launches of the VLS-1, in 1997 and 1999, both ended in failure when the boosters were destroyed by the range safety officer. Despite the latest accident, AEB president Luiz Bevilacqua says Brazil's space plans remain unchanged. Hours before the accident, the AEB and two Ukrainian enterprises established guidelines for an agreement expected to be signed next month by Brazil and Ukraine.

The deal calls for a $50 million investment in development of the Alcântara launch centre, equally divided between the two countries. The Ukrainian government has signalled its intent to invest a further $40 million in its Tsyklon-4 launch vehicle, which is scheduled for launch from Alcântara in 2006.

Brazil's government has vowed to continue its space programme, conceding the budget is probably insufficient. Alcântara has attracted international interest from potential commercial launch operators because its equatorial location offers lower-cost launches to geostationary as well as low-inclination orbits. Israel has expressed interest in using Alcântara for Shavit launches (Flight International, 26 August-1 September).

The Alcântara accident is not the worst of its kind. In October 1960 a Soviet R-16 ballistic missile exploded on the pad at Baikonur, killing 91 people, and 50 died when a Vostok booster exploded at Plesetsk in March 1980. In August 1965, 53 civilian workers died of suffocation in a US Titan II missile silo after an electrical fire caused a minor explosion.

Source: Flight International