Solid stages and a restartable upper stage

Vega-C combines three solid-propellant stages with the liquid-propellant AVUM+ upper stage. The lower stages are P120C, Zefiro-40 and Zefiro-9. The first two differ from the original Vega’s P80 and Zefiro-23, while Zefiro-9 continues across the two designs. The fairing protects the payload during the atmospheric part of ascent.

Think of staging as an original bookkeeping exercise. A fictional vehicle has 12 mass units after a lower stage finishes burning, including 3 units of now-unneeded lower-stage hardware. Separation leaves 9 units for the remaining vehicle to accelerate. This is not a Vega mass specification or a full performance calculation; it isolates the effect of discarding hardware.

AVUM+ can reignite its engine, supporting separated maneuvers and orbital positioning. A mission may coast between burns rather than fire continuously from launch to final delivery. Restart capability is a design feature, while a successful restart on a particular flight is an observed result. Those two claims need different evidence.

In a teaching sequence, the upper stage first reaches an initial orbit, later adjusts the delivery orbit and finally performs its planned disposal maneuver. The order matters: a maneuver that occurs before a passenger separates changes that passenger’s delivery conditions. A flight plan must connect engine commands, attitude, payload releases and the remaining propellant.

Budget the complete maneuver sequence

A restartable upper stage does not make every destination available on one launch. Orbit changes and disposal consume resources, and payloads must remain within the vehicle’s compatible mission envelope. Having enough mass capacity does not by itself prove that two spacecraft with very different orbital needs can travel together.

For an original planning exercise, allocate ten fictional maneuver units: six for delivery, two for payload-orbit adjustment and two for disposal. Adding a three-unit change creates a deficit unless another requirement or allocation changes. The figures are invented; the point is to retain the complete mission budget instead of treating disposal as free.