I had previously proposed all stages Hydrolox powered rocket. Similar to Starship's Falcon 9 or Starship that does not use a strapped booster and uses the same propellant combo in all stages. Today I would like to propose an alternative design in case realizing my initial idea required too much payload penalty. The idea is a hydrolox version of Falcon Heavy. The main hydrolox engine strapped from both sides with the same first stage as boosters to give takeoff boost to preserve the propellant on the main rocket. Classical hydrolox rockets use solid boosters to utilize their immense thrust during takeoff. For my design in order to replicate the idea I opted to have less engines on the main rocket likely four to reduce its dry mass and the rocket would not need that much thrust anyway after the assist of the side boosters. On the other hand, the side rockets would have more engines likely eight to generate enough thrust for takeoff.
By shifting the heavy atmospheric work onto two side boosters, we solve the biggest weakness of liquid hydrogen: its ultra-low density. Instead of forcing the center core to carry a giant cluster of sea-level engines and heavy wall reinforcement all the way to orbit, we let the side boosters do the heavy lifting early on, leaving the main rocket light, fuel-rich, and ready for deep space.
The Propulsion Core: Electric Pumps and Cutaway Aerospikes
To make an all-hydrolox heavy launcher work without solid boosters, we use two key technologies across all three cores:
Superconducting (MgB₂) Electric Pumps: Instead of traditional heavy turbopumps driven by hot gas, my rocket pumps are driven directly by electric motors powered by onboard fuel cells. This eliminates complex turbopump machinery and gives us complete, instant control over fuel flow.
Cutaway Perimeter Aerospikes: Instead of traditional bell nozzles that suffer from flow separation at sea level, we use perimeter aerospike segments. They automatically compensate for altitude changes from the launchpad all the way to vacuum, while keeping the engine bay geometry flat and flush with the rocket's outer body.
Supercritical GO₂ Cooling: The copper-alloy combustion chambers are regeneratively cooled using high-pressure gaseous oxygen rather than hydrogen, avoiding massive fluid pressure drops in the fuel loops.
How the Flight Trajectory Works
1. Liftoff (T+0 s): All 20 aerospike engines ignite (8 on each side booster, 4 on the center core). The boosters supply 80% of the liftoff thrust, giving us a clean TWR ≈ 1.4 - 1.5.
2. Deep Core Throttling: Right after clearing the tower, our electric pumps drop the center core's engines down to 20% power. The core acts as a lightweight structural spine while the side boosters push through the thick atmosphere.
3. Booster Staging (T+115 s): At Mach 5 and 58 km altitude, the side boosters cut off and separate. Because they stage early, they stay close to the launch site and need very little reserve fuel to fly back.
4. Main Core Acceleration: At separation, the center core's propellant tanks are still nearly 90% full. It ramps its 4 engines to 100% thrust in near-vacuum conditions, operating with an ultra-high wet-to-dry mass ratio (≈ 11.5 - 13.0) to push the payload to orbit.
Zero-Leg Reusability: Low-Profile Ground Catcher
Carrying landing legs to orbit is dead weight. Instead of putting legs on the rocket, we put the catching mechanism on the ground.
Direct Load Transfer: The landing pad uses a low-profile, diverging guide funnel with hydraulic shock absorbers. It catches the rocket directly by its lower primary thrust ring—the exact same structural ring that receives engine thrust during liftoff. The thin propellant tank walls take zero impact stress.
Nozzle Protection: Because aerospikes are flush and flat compared to flared bell nozzles, the bottom of the rocket drops cleanly into the pad catcher without hitting mechanical jaws or trapping exhaust back-blast.
Zero Hoverslam: Unlike Falcon 9, which cannot hover because its turbopumps cannot throttle low enough, my solid-state electric pumps can throttle down to 10% RPM. This lets the rocket gently hover at 5 meters altitude, adjust its position in milliseconds using differential throttling, and lower itself smoothly onto the pad catches.
The Moon, Mars, and Sea Landing Advantage
Using deep-throttled electric pumps and flush aerospikes doesn't just save mass on Earth—it solves three major operational problems in space:
1. Ship-Based Drone Catching (ASDS): When the center core comes down Mach 12-15 downrange onto an ocean platform, sea waves cause the deck to heave up and down. A "hoverslam" rocket will crush its legs if the deck rises to meet it. Our ability to hold a slow, gentle descent rate (0.3 m/s) lets the flight computer sync touchdown perfectly with the wave motion, catching the core on a low-profile deck ring without heavy landing towers.
2. Stopping Dust Blasts on the Moon and Mars: On off-world surfaces, high-thrust engine plumes blast craters into the dirt and launch hypervelocity regolith dust that destroys solar panels and habitats. By throttling the aerospikes down to low power, the exhaust spreads out horizontally instead of digging straight down. This stops dust clouds from kicking up during touchdown.
3. 100% ISRU Unified Fuel: Because every piece of this architecture—from the 8-engine boosters to the 4-engine core and off-world landers—runs purely on Hydrolox, the entire system connects directly to water-electrolysis fuel production on the Moon (polar ice) and Mars. No secondary kerosene or methane infrastructure is ever needed.
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