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Description
Physical Specifications:

Dimensions: 15 x 45 m bottom, 135 m height

Composition: carbon-fiber reinforced silicon carbide aeroshell, boron nitride aerogel insulation, stainless steel tankage

Specific Impulse: 401 to 818 s (sea level), 492 to 919 s (vacuum)

Dry Mass: 600 tons

Propellant Mass: 1257 tons liquid hydrogen, 3143 tons liquid oxygen

Payload to LEO: 600 tons

Thrust: 21.5 to 94.5 MN (sea level), 24.5 MN to 120.9 MN (vacuum)

Thrust/Weight: 0.397 to 1.72 (wet, full payload), 3.65 to 16.0 (dry, no payload) (sea level)

Maximum Delta-V: 13.6 km/s

Powerplant: 50 MW thermionic generator

This is yet another iteration of my Single Stage to Orbit (SSTO) reusable nuclear shuttle designs, this one building upon the original Defiant. While the original was quite capable, further inspection had me questioning several design aspects. To summarize the major points, the shadow shield was vastly overbuilt (the original used pure tungsten to block gamma and neutron radiation, where a bilayer shield could handle these far more lightly), the landing system and structure were vastly underbuilt (not ideal when trying to build a robust vessel), and most critically, the engine piping layout was a disaster waiting to happen. To put the payload bay as low as possible for ease of access, the engines had to be placed in an array about it, leaving them so far apart from each other that they could only be fed from a single reactor via long pipes. These pipes would have to be able to safely handle 3000+ K degree hydrogen under megapascals of pressure - not impossible, but certainly daunting!

The workaround would lead to a ship far more similar to the Vehement on which the Defiant itself was based, having angled engines attached to a top-mounted reactor. Ideally, these engines should be angled as little as possible to minimize cosine losses, but that leaves a very narrow cone beneath to fit the rest of the ship in, which I further challenged by flattening the sides to give room for side-mounting payloads. Hence, where the Mark 1 was short and squat, the Mark 2 ends up tall and narrow (relatively speaking of course; its tanks are still much wider than even a Saturn V's). This change in configuration required significantly more structural mass than the Mark 1, which I further taxed by giving the Mark 2 more robustness features, significantly cutting into the payload capacity. However, it does enable a new and very useful capability. With the engines far from the ground, the plume would be largely dispersed well before reaching it, so the ship would not kick up much dust or significantly heat whatever lay below it, such that the Mark 2 could land on soft or loose ground without fear of melting or igniting it. In short, the Mark 2 can take off, land and be serviced just about anywhere large and flat enough, without a dedicated landing pad. That is something I certainly intend to take advantage of...

The central premise of the Mark 2 is the same as that of its predecessor. It uses a Liquid Oxygen Augmented Nuclear Thermal Rocket (LANTR), essentially a nuclear thermal rocket with a chemical afterburner, so it can throttle between specific impulse and thrust to optimize launch profile and minimize takeoff mass. Relative to a chemical launcher it can get by with much less propellant, and relative to a nuclear launcher it can get by with a much lighter engine and denser propellant mix that requires less bulky tankage, giving it plenty of mass to spare for structure and payload. Its wet mass is equivalent to SpaceX's Starship, yet in spite of having twice the dry mass, it can haul six times more payload, about the same as its own dry mass. Moreover, this is assuming very conservative nuclear specific impulse - this is nearly on the lower end of what's possible for such engines, a more advanced ship could take push this further - and a number of design decisions that add mass but make the ship much hardier.

Further detail of ship systems and functioning as well as references are available if desired. I must thank the Atomic Rockets website and ToughSF server for their invaluable contributions to the above, and hope it merits their seals of approval.

Description
Physical Specifications:

Dimensions: 15 x 45 m bottom, 135 m height

Composition: carbon-fiber reinforced silicon carbide aeroshell, boron nitride aerogel insulation, stainless steel tankage

Specific Impulse: 401 to 818 s (sea level), 492 to 919 s (vacuum)

Dry Mass: 600 tons

Propellant Mass: 1257 tons liquid hydrogen, 3143 tons liquid oxygen

Payload to LEO: 600 tons

Thrust: 21.5 to 94.5 MN (sea level), 24.5 MN to 120.9 MN (vacuum)

Thrust/Weight: 0.397 to 1.72 (wet, full payload), 3.65 to 16.0 (dry, no payload) (sea level)

Maximum Delta-V: 13.6 km/s

Powerplant: 50 MW thermionic generator

This is yet another iteration of my Single Stage to Orbit (SSTO) reusable nuclear shuttle designs, this one building upon the original Defiant. While the original was quite capable, further inspection had me questioning several design aspects. To summarize the major points, the shadow shield was vastly overbuilt (the original used pure tungsten to block gamma and neutron radiation, where a bilayer shield could handle these far more lightly), the landing system and structure were vastly underbuilt (not ideal when trying to build a robust vessel), and most critically, the engine piping layout was a disaster waiting to happen. To put the payload bay as low as possible for ease of access, the engines had to be placed in an array about it, leaving them so far apart from each other that they could only be fed from a single reactor via long pipes. These pipes would have to be able to safely handle 3000+ K degree hydrogen under megapascals of pressure - not impossible, but certainly daunting!

The workaround would lead to a ship far more similar to the Vehement on which the Defiant itself was based, having angled engines attached to a top-mounted reactor. Ideally, these engines should be angled as little as possible to minimize cosine losses, but that leaves a very narrow cone beneath to fit the rest of the ship in, which I further challenged by flattening the sides to give room for side-mounting payloads. Hence, where the Mark 1 was short and squat, the Mark 2 ends up tall and narrow (relatively speaking of course; its tanks are still much wider than even a Saturn V's). This change in configuration required significantly more structural mass than the Mark 1, which I further taxed by giving the Mark 2 more robustness features, significantly cutting into the payload capacity. However, it does enable a new and very useful capability. With the engines far from the ground, the plume would be largely dispersed well before reaching it, so the ship would not kick up much dust or significantly heat whatever lay below it, such that the Mark 2 could land on soft or loose ground without fear of melting or igniting it. In short, the Mark 2 can take off, land and be serviced just about anywhere large and flat enough, without a dedicated landing pad. That is something I certainly intend to take advantage of...

The central premise of the Mark 2 is the same as that of its predecessor. It uses a Liquid Oxygen Augmented Nuclear Thermal Rocket (LANTR), essentially a nuclear thermal rocket with a chemical afterburner, so it can throttle between specific impulse and thrust to optimize launch profile and minimize takeoff mass. Relative to a chemical launcher it can get by with much less propellant, and relative to a nuclear launcher it can get by with a much lighter engine and denser propellant mix that requires less bulky tankage, giving it plenty of mass to spare for structure and payload. Its wet mass is equivalent to SpaceX's Starship, yet in spite of having twice the dry mass, it can haul six times more payload, about the same as its own dry mass. Moreover, this is assuming very conservative nuclear specific impulse - this is nearly on the lower end of what's possible for such engines, a more advanced ship could take push this further - and a number of design decisions that add mass but make the ship much hardier.

Further detail of ship systems and functioning as well as references are available if desired. I must thank the Atomic Rockets website and ToughSF server for their invaluable contributions to the above, and hope it merits their seals of approval.