For the P1B, the first set of P39 boosters would be ignited at lift-off and then jettisoned, while the second set, depending on the configuration, could be ignited in flight and not jettisoned.
Bonnal says CNES is preparing wind-tunnel tests to adjust the margin policy, and pressure oscillation has been assessed for different flight phases.
Similar to the P1B, the all-liquid H2C would use up to six strap-on boosters to carry as much as 8,400 kg to GTO. Twin main engines, capable of 150 tons of vacuum thrust derived from the Ariane 5's Snecma-built Vulcain 2, would comprise the H165 first stage, which would be topped by a 31-ton cryogenic upper stage, he says.
A third design, the P7C, would use a single solid-rocket stage based on the P135 engine as a building block to be arranged in linear and “faggot” configurations. Like the P1B, the P7C would use a 3.7-meter-dia. monolithic casing. But, unlike the P1B, each of the P7C stages would feature TVC, a factor that could increase costs.
“You could have a configuration with three P135s making a real first stage, ignited all together on the ground and separated all together, so there is no need to have separations between the stages,” Bonnal says.
The P7C has the advantage of smaller stages, with the P135 falling in the range of what Europe's mostly Italian-built Vega launcher demonstrated this year with its P80 first-stage engine, Bonnal says.
Indeed, Italy is eager for ESA to approve early work on such an Ariane 6 design, which could facilitate new development of a more powerful Vega engine that could lower production costs and greatly improve its competitiveness in the commercial smallsat market.
“For Vega, we want a P120 at a minimum,” says Enrico Saggese, head of Italian space agency ASI.
Saggese says moving to the more robust P135 could be a greater challenge, requiring a larger diameter for the stage, a new payload adapter and changes to existing tooling and production processes.
“But if we have a P135 for the Ariane 6, this could be worked,” he said on the IAC sidelines. “We are pushing for a design decision in Caserta,” a Naples suburb where the November ministerial will take place. c