Rocket Engine Performance Improvement

To make manned Cylero contract and those up to Tydos, Urados in career mode possible, performance of existing rocket engine parts need to be improved towards cutting edge concept level.

There's nothing wrong to go beyond existing technology limit since we already have in game incredibly strong structure, super batteries with insane energy density, small jet engine with crazy TWR, highly simplified 'aerodynamic' lift and drag that enables electric-powered flight over M4.0 .

This also offers more fun in the game as players could actually interact with truly advanced technologies that opens new possibilities in space travel as they unlock high tier tech nodes.

Below are some of the rocket engine parts that needs improvement

1. Nuclear Thermal Rocket:
   The one in game is almost an early NERVA engine with TWR even worse than pressure-fed engine. Advanced concept design should reach TWR of 30 and chamber pressure up to 7 MPa to make it attractive as an end game tech.
   The NTR in game is also much bigger than a full flow staged engine at similar mass flow and same nozzle selection, it doesn't make sense.
   ---For comparison, water-based NTR(NERVA, 4MPa, 2400K) and Hydrolox Full flow staged engine(25MPa, 3600K) of same mass flow, as P = rho * R * T, propellant density in chamber would be ~ 0.24 :1 , inverse to get area ratio 4.17 : 1, linear size ratio around 2.04. However, in game it takes 118% size nuclear thermal to match the mass flow of 25% size Full flow staged (linear ratio 4.72 : 1)
   ---Also an NTR with radiator could have much less spool time than the one in game as it turns heat in to power at idle mode that gives recharging capability while allowing immediate shut down of propellant, keeping the core warm for immediate restart too.
   ( https://nucleus.iaea.org/sites/fusionportal/Atoms%20for%20Space/04_Emrich%20Promises%20and%20Challenges%20of%20Nuclear%20Propulsion%20for%20Space%20Travel.pdf )

2. Delta nozzle:
   200% length and 50% throat in game, while having almost 2x as much area ratio, has worse vacuum thrust and Isp compared to Alpha nozzle. It seems like either area ratio data is wrong or area ratio doesn't affect Isp correctly in game(bell nozzle in game can reach much high area ratio but no better Isp)

3. Aerospike nozzle:
   Another end-game tech node, has worse TWR than Alpha or Echo. Although aerospike TWR in historical research was not superior to conventional ones, new material (SiC, CMC, Carbon-Carbon) and regenerative cooling should give it enough advantage for operation in atmosphere, at least far better than Alpha nozzle that represents stainless steel SSME nozzle. Also the aerospike Isp in game at 10 km is worse than any conventional nozzle (50% throat, 200% length, vacuum optimized)

4. Ion thruster:
   Existing one in game already has concept level thrust and Isp, while the game missing a reliable power source to support it towards deep space as solar panel doesn't work when far from Juno, while RTG lacks the power and being too expensive to be used in career. To enable contracts (especially manned mission) to more distanced planets, tech node of fusion power generation / propulsion should be added.