PEGAS v1.3 "Olympus"

The final major version of PEGAS: now it has all you might possibly use.

Features:

• GUI overhaul: better reporting of the vehicle and guidance status,
  including an event-by-event flight plan display (#37), which is possible because...
• UPFG is now aware of jettison and shutdown events before they happen (via a mechanism called virtual stages)
• new passive guidance mode, pitchProgram, allows fine-tuning the ascent with a pitch-altitude schedule - by Aram1d
• new event type: shutdown, allows shutting down specific engines (by part tags), also during active guidance
• new event type: action, allows execution of standard action groups
• new ullage type: hot, allows hot-staging by reversing the jettison-ignition order
• new staging option: postStageEvent, allows jettison after ignition (e.g. an interstage ring, Saturn-style)
• addons: you can now create custom extensions to PEGAS
  an addon sharing repository has also been started

Tweaks:

• unscheduled loss of thrust will now be detected and handled by aborting the mission
• known errors in vehicle/controls configuration will now crash the system prior to launch
• improved error checking for vehicle staging configuration
• "jettison but no ignition" configuration on a first stage is now banned - instead, use either the postStageEvent option in staging or the jettison event in sequence
• settings are now grouped together in a lexicon instead of being a bunch of scatterred globals
• default settings have been changed to relax the overly strict convergence criterion and increase the initial convergence time

Fixes:

• PEGAS will now maintain min-AoA control while initially converging UPFG
• UFPG will not longer steal control the instant it converges, but actually wait until the moment defined by user in controls["upfgActivation"]
• throttle control in active guidance phase now correctly (i.e. instantly) switches between constant-acceleration and default modes
• countdown clock is now accurate
• documentation upgrades

Under the hood:

• unified events system (pegas_events): no more "user", "staging", and "system" events (#43)
• refactored the passive guidance loop, moving the atmospheric guidance part to a new module, pegas_atmo
• initializeVehicle renamed to initializeVehicleForUPFG and refactored
  (recalculateVehicleMass, accLimitViolationTime, and createAccelerationLimitedStage have been merged into it)
• for legibility, stagingInProgress is now used consistently and several new technical flags are introduced (see e8c051b)
• version number is no longer stored in the UI code ;)

PEGAS v1.2

Features:

• new, faster CSE implementation by pand5461
• delegate events - call any function at any time via sequence
• settings file - no more need to modify pegas.ks

Bugfixes:

• minor (but potentially breaking) typo in pegas_comm.ks (@Patrykz94)
• cleaner pre-check routine with better feedback

PEGAS v1.1

Multiple fixes for bugs identified after the initial release and new features requested since.

Features:

• inter-CPU communication system by Patrykz94,
• roll control via user events,
• better throttle control via user events,
• new user event type (jettison) to account for the amount of jettisoned mass,
• stages can explicitly shut down engines (useful for Falcon 9 style missions),
• LAN and inclination as optional parameters,
• launch direction (northerly and southerly, as well as "nearest opportunity"),
• automatic seizing control from the kOS CPU part.

Bug fixes:

• throttling obeys the way Realism Overhaul works,
• sustainer-type stages are now handled properly,
• minor code clean-ups, GUI and documentation fixes.

UPFG Unleashed

After almost 1.5 years, PEGAS returns in a much upgraded form.
Having implemented UPFG - the Unified Powered Flight Guidance from the Space Shuttle GN&C computer - it is capable of things previously out of reach:

• targeting orbital planes, given by inclination & LAN or selecting a target from the in-game map,
• targeting any elliptic orbit, given by apoapsis and periapsis,
• simple atmospheric ascent by just 2 parameters: vertical ascent time and pitch-over angle,
• powerful and fuel-efficient orbital guidance with UPFG,
• handling of multiple stages and special jettison events.

So far I have managed to test it on Atlas V 532 (both with very light payloads, and pushing its capabilities) and Saturn V (with payload mass equivalent to a lunar landing mission).
Those missions went almost flawlessly, but I cannot guarantee that any vehicle will go equally smooth.
Feel free to submit any issues you might have, and I will do my best to correct them.