Sir - In the generally excellent coverage of the European Space Agency's launcher, the Ariane 5 (Flight International, 14-20 June, P61), Julian Moxon quite correctly makes the point that, because the vehicle was designed to higher, man-rated, reliability than were previous Ariane launchers, pressure on the insurance industry will be eased.

Critics of the man-rated specification for the Ariane 5, especially those who crowed when the Hermes space plane was cancelled, should bear in mind that, the Ariane 5 programme will save money for its operators (and customers), by not incurring so frequently, the cost of restoring the vehicle to flight status after the several failures, which would otherwise take place.

Confusion reigns, however, regarding your declarations of nominal sea-level thrust for each Ariane 5 solid-rocket booster (SRB).

On P63, the main feature declares each SRB to have a thrust of 5,774kN and converts that to 299,150lb of thrust. In fact, that conversion should read 1,299,150lb.

The box on P67 claims each SRB to have a nominal sea-level thrust of 6,367kN, converted to 1,440,000lb, which should be 1,432,600lb). The actual Ariane 5-rated SRB thrust at sea level is a nominal 5,337kN, with flight motors capable of 5,870kN.

Each of NASA's Space Shuttle SRBs delivers 14,000kN, which means that the French Ariane 5 boosters deliver little more than one-third of the thrust of each Shuttle booster, and not the "slightly more than half" which is claimed on P67.


Cambridge, UK


Source: Flight International