KerbalX

Description

A powerful first stage powered by nine - yes, nine - Vectors. Similar to the Antilocapra I, but bigger and even more powerful. To reduce stress on the rocket as it builds up to max Q, only the six outer Vectors are active at launch, with the three attached to the central tri-adapter igniting at the first staging event. My rockets using the Antilocapra II generally use several powerful SRBs (Kickback or better), and I’ve found that using just six Vectors at liftoff, and air-starting the other three upon SRB jettison, greatly reduces the risk of Q becoming great enough to cause structural failure of the vehicle, and also significantly reduces first-stage propellant consumption, without reducing the first-stage thrust-to-weight ratio enough to seriously penalise the rocket early on; feel free to modify it to fire all nine Vectors at launch if you’re using it in a less-exuberantly-thrusty configuration with few to no SRBs, or for extremely heavy payloads that require every kN of thrust from all nine engines in order to get off the pad.

The three central Vectors have their engine gimbals factory-locked, as the six outer engines’ gimballing provides more than enough flight-control authority, and allowing the three central engines to gimbal as well would risk overcontrolling the vehicle and causing divergent attitude oscillations (especially in the late phase of the Antilocapra’s burn, when its TWR is highest due to propellant burnoff). Even with just the outer six Vectors gimballing, it’s still best to throttle down somewhat near the end of the burn to prevent overcontrol and oscillations.

This stage is meant to reenter and be recovered after use; the two sextuple banks of airbrakes (press Backspace, or manually click to activate the Abort action group, to toggle the airbrakes open/closed) are to ensure that it slows down enough that the parachutes can deploy (I found that otherwise, the nine heavy Vectors, totalling 36 tonnes - over three-fifths of the total dry mass of the stage! - gave the stage an excessively-high ballistic coefficient, causing it to plunge, dart-like, through Kerbin’s atmosphere and impact the surface without ever slowing down enough for even the drogue chutes to safely deploy), while the two drogue and eighteen main parachutes are for the actual landing. The asymmetric parachute arrangement is to help cause the stage to descend and touch down at an angle, so the upper end can then gently settle to the ground while still having the parachutes to slow it, rather than having the stage descend and touch down in a vertical orientation - momentarily slowing all the parachute attachments to a stop, and, thereby, triggering the release of all the parachutes - and then tip over, fall on its side, and (at least partly) explode.

For the very heavy upper stages and payloads I generally use the Antilocapra II with, it’s generally jettisoned onto a suborbital trajectory, with the remainder of the orbital insertion being performed by the upper stage. However, for use with lighter payloads which the Antilocapra II could potentially take all the way to orbit, the stage contains a preinstalled Even-More-Fuelled QBE Reentry Controller, with batteries and reaction wheels to point the stage retrograde, and some extra propellant tankage (locked out and inaccessible during powered flight, to preserve this propellant for deorbiting the stage; it must be manually reenabled once the stage has exhausted its primary propellant, been jettisoned, and its throttle taken to zero to prevent the reserve fuel and oxidiser from being inadvertently burned as soon as they are made available to the engines) to provide the Δv for deorbiting the stage. For missions where the stage never reaches orbit, the reserve propellant can be manually enabled and burned for some extra Δv; alternatively, it can be used to help slow the stage during reentry. (The deorbit/reentry controller can also help slow the stage by angling or tumbling it with its reaction wheels, although their control authority is limited, especially in the denser portions of Kerbin’s atmosphere.)

A stock subassembly called Antilocapra II. Built with 83 of the finest parts, its root part is Decoupler.3.

Built in KSP version 1.7.0.

Details

• Type: Subassembly
• Class: lifter
• Part Count: 83
• Pure Stock
• KSP: 1.7.0