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Yet another SRB-boosted Acapello, this time with the powerful Clydesdale booster. The Clydesdale’s very high thrust and long burn time make it a bit tricky to make full use of the Clydesdale’s Δv: too steep, and much of the burn is wasted lofting the vehicle rather than getting it up to orbital speed; too shallow, and the vehicle suffers high losses from aerodynamic drag and experiences severe shock compression heating, potentially causing parts to burn off during ascent.
The optimal trajectory appears to be to lift off, gravity-turn fairly aggressively (start turning at ~50 m/s, reach +70° by 100 m/s, hold this pitch attitude until the velocity vector drops through +70°, then let the nose follow the velocity vector) but not too much so (to keep the vehicle’s flightpath angle from becoming overly shallow and sending the vehicle through the dense lower atmosphere at high speed), and then, once above 15 km altitude or so, pitching down to point the vehicle’s nose - and, thereby, its thrust vector - below its velocity vector (to minimise lofting and keep the vehicle from gaining too much altitude at the expense of horizontal speed).
A couple things to note:
- With SAS engaged in Prograde Hold mode during first-stage ascent, the nose tends to lag noticeably behind the velocity vector; some degree of manual steering input is typically necessary in order to keep the nose aligned with the velocity vector.
- Preventing excessive lofting late in first-stage ascent can easily require very large negative angles of attack to be held, often as great as -30°. This angle must be held through first-stage burnout, and the vehicle then has to rapidly pitch up to realign its nose with the surface-relative velocity vector (in order to minimise aerodynamic drag losses during coast-phase flight); the CSM’s RCS thrusters should be used to assist with this manoeuvre (they can be turned off for the remainder of the coast phase).
Built with 59 of the finest parts, its root part is LiquidEngineLV-T91.
Built in the VAB in KSP version 1.9.0.
- Type: VAB
- Class: ship
- Part Count: 59
- Pure Stock
- KSP: 1.9.0