HERMES-CLASS MTV PROPULSION SYSTEM
Nuclear Thermal / Chemical Hybrid Architecture
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# HERMES-CLASS MTV PROPULSION SYSTEM
Nuclear Thermal / Chemical Hybrid Architecture
📋 Executive Summary
| Parameter | Specification |
|---|---|
| **Primary Propulsion** | Nuclear Thermal Rocket (NTR) - NERVA-III Class |
| **Backup Propulsion** | LOX/LH2 Chemical (RL-10C Cluster) |
| **Auxiliary Propulsion** | Bipropellant RCS (MMH/NTO) |
| **Total Thrust (NTR)** | 3 × 111 kN = 333 kN (75,000 lbf) |
| **NTR Specific Impulse** | 900 seconds (vacuum) |
| **Chemical Isp** | 465 seconds (RL-10C) |
| **Total Propellant Mass** | 2,350 metric tons |
| **TMI ΔV Capability** | 3.6 km/s |
| **MOI ΔV Capability** | 1.8 km/s |
| **Total Mission ΔV** | 5.8 km/s (with margin) |
1. Propulsion Trade Study & Selection
1.1 Candidate Propulsion Technologies
PROPULSION TECHNOLOGY COMPARISON MATRIX
══════════════════════════════════════════════════════════════════════════════════
┌─────────────────────────────────────────────────────────┐
│ CANDIDATE PROPULSION SYSTEMS │
┌───────────────────────┼───────────┬───────────┬───────────┬───────────┬─────────┤
│ PARAMETER │ Chemical │ NTR │ NEP │ VASIMR │ Solar │
│ │ LOX/LH2 │ Solid Core│ Ion │ Plasma │ Electric│
├───────────────────────┼───────────┼───────────┼───────────┼───────────┼─────────┤
│ Specific Impulse (s) │ 450-465 │ 850-950 │ 3000-5000 │ 3000-5000 │ 1500-3k │
│ Thrust (kN) │ 100-2000 │ 100-350 │ 0.001-0.1 │ 0.5-5 │ 0.01-1 │
│ Thrust/Weight │ 50-70 │ 3-5 │ 0.0001 │ 0.001 │ 0.0005 │
│ TRL (2025) │ 9 │ 5-6 │ 7-8 │ 5-6 │ 7 │
│ Power Required (MW) │ N/A │ N/A │ 2-10 │ 2-10 │ 0.1-2 │
├───────────────────────┼───────────┼───────────┼───────────┼───────────┼─────────┤
│ Transit Time (days) │ 180-220 │ 140-180 │ 300-400 │ 150-200 │ 250-350 │
│ Propellant Mass (t) │ 3500+ │ 1800-2200 │ 200-400 │ 300-500 │ 400-600 │
│ System Mass (t) │ 150 │ 220 │ 350 │ 300 │ 280 │
│ Total Mass (t) │ 3650 │ 2100 │ 600 │ 700 │ 800 │
├───────────────────────┼───────────┼───────────┼───────────┼───────────┼─────────┤
│ Abort Capability │ GOOD │ GOOD │ POOR │ MODERATE │ POOR │
│ Reliability │ PROVEN │ MODERATE │ MODERATE │ LOW │ MODERATE│
│ Development Risk │ LOW │ MODERATE │ MODERATE │ HIGH │ MODERATE│
│ Political Acceptance │ HIGH │ MODERATE │ HIGH │ HIGH │ HIGH │
│ Crew Safety │ HIGH │ MODERATE* │ HIGH │ HIGH │ HIGH │
└───────────────────────┴───────────┴───────────┴───────────┴───────────┴─────────┘
* With proper shielding
SCORING (1-5 scale, 5 best):
┌───────────────────────┬───────────┬───────────┬───────────┬───────────┬─────────┐
│ Criteria (Weight) │ Chemical │ NTR │ NEP │ VASIMR │ Solar-E │
├───────────────────────┼───────────┼───────────┼───────────┼───────────┼─────────┤
│ Performance (25%) │ 2 │ 4 │ 5 │ 5 │ 4 │
│ Reliability (25%) │ 5 │ 3 │ 3 │ 2 │ 3 │
│ Safety/Abort (20%) │ 5 │ 4 │ 1 │ 2 │ 1 │
│ Development (15%) │ 5 │ 3 │ 3 │ 2 │ 3 │
│ Transit Time (15%) │ 3 │ 5 │ 1 │ 4 │ 2 │
├───────────────────────┼───────────┼───────────┼───────────┼───────────┼─────────┤
│ WEIGHTED SCORE │ 3.85 │ 3.80 │ 2.80 │ 3.05 │ 2.70 │
│ WITH HYBRID BONUS │ 4.10 │ 4.35 │ - │ - │ - │
└───────────────────────┴───────────┴───────────┴───────────┴───────────┴─────────┘
SELECTED: NTR PRIMARY + CHEMICAL BACKUP (Hybrid Architecture)
══════════════════════════════════════════════════════════════════════════════════1.2 Hybrid Selection Rationale
| Factor | NTR Benefit | Chemical Backup Benefit |
|---|---|---|
| **Propellant Efficiency** | 2× better Isp saves 1,500+ tons of propellant | N/A |
| **Transit Time** | 30-40 days shorter than chemical-only | N/A |
| **Abort Capability** | Good high-thrust abort options | Proven, immediate availability |
| **Redundancy** | Primary system | 100% backup if NTR fails |
| **Development Risk** | NERVA heritage reduces unknowns | TRL 9, no development needed |
| **Political/Safety** | Shield design addresses concerns | Public confidence in proven tech |
2. Nuclear Thermal Rocket System
2.1 NERVA-III Engine Design
2.2 NERVA-III Technical Specifications
NERVA-III ENGINE DETAILED SPECIFICATIONS
══════════════════════════════════════════════════════════════════════════════════
ENGINE DESIGNATION: NERVA-III-HF (High Flux)
HERITAGE: NERVA/Pewee/SNRE Evolution
STATUS: Technology Readiness Level 6 (System prototype demo)
REACTOR DESIGN:
├── Type: Solid-core, graphite-composite, thermal spectrum
├── Fuel: UC-ZrC-C (Uranium Carbide in Zirconium Carbide/Carbon matrix)
├── Enrichment: 93% U-235 (Highly Enriched Uranium)
├── Fuel Elements: 564 hexagonal elements, 19 channels each
├── Moderator: ZrH (Zirconium Hydride) in tie-tubes
├── Reflector: Beryllium (radial), BeO (axial)
├── Control: 12 rotating drums with B4C poison sectors
├── Thermal Power: 550 MW
├── Core Diameter: 0.59 m
├── Core Length: 0.89 m (active)
└── Core Mass: 485 kg (including fuel)
THERMODYNAMIC CYCLE:
┌────────────────────────────────────────────────────────────────────────────────┐
│ │
│ LH2 Tank ──► Turbopump ──► Regen Cooling ──► Reactor ──► Nozzle ──► Exhaust │
│ (20 K) (294 K) (500 K out) (2750 K) (exit) │
│ │ │ │
│ └──── Turbine ◄┘ │
│ (hot gas bleed) │
│ │
└────────────────────────────────────────────────────────────────────────────────┘
TEMPERATURE STATIONS:
├── Tank outlet: 20 K (subcooled LH2)
├── Pump outlet: 35 K (pressurized to 10 MPa)
├── Nozzle jacket inlet: 35 K
├── Nozzle jacket outlet: 300 K (after regen cooling nozzle)
├── Reflector outlet: 450 K (after reflector cooling)
├── Reactor inlet: 500 K (after all regen cooling)
├── Reactor outlet: 2,750 K (chamber temperature)
└── Nozzle exit: 1,400 K (expanded, accelerated)
PERFORMANCE BREAKDOWN:
├── Thrust: 111 kN (24,947 lbf)
├── Specific Impulse: 900 s
├── Mass flow rate: 12.6 kg/s
├── Exhaust velocity: 8,829 m/s
├── Chamber pressure: 6.9 MPa (1,000 psi)
├── Nozzle expansion ratio: 300:1
├── Nozzle exit diameter: 3.1 m
└── Overall efficiency: 0.82 (thermal to kinetic)
ENGINE LIFE & RELIABILITY:
├── Design burn time: 6 hours cumulative
├── Number of starts: 20 (design), 10 (certified)
├── Time between restarts: >30 minutes (thermal soak)
├── Startup time: 60 seconds (to full thrust)
├── Shutdown time: 30 seconds (controlled)
├── Design life: 10 years (with proper storage)
├── Reliability: 0.9985 (per burn)
└── Cluster reliability (3 engines): 0.9999 (1-of-3 sufficient for contingency)
══════════════════════════════════════════════════════════════════════════════════2.3 Nuclear Safety & Shielding
2.4 Engine Cluster Configuration
NTR ENGINE CLUSTER ARRANGEMENT
══════════════════════════════════════════════════════════════════════════════════
THREE-ENGINE CLUSTER CONFIGURATION:
FORWARD (to crew)
↑
│
┌───────────────┼───────────────┐
│ │ │
│ ┌─────────┴─────────┐ │
│ │ SHADOW SHIELD │ │
│ │ (combined) │ │
│ └─────────┬─────────┘ │
│ │ │
│ 312 m separation │
│ │ │
│ ┌─────────┴─────────┐ │
│ │ PROPELLANT FEED │ │
│ │ MANIFOLD │ │
│ └────┬────┬────┬────┘ │
│ │ │ │ │
│ ┌─┴─┐┌─┴─┐┌─┴─┐ │
│ │ 1 ││ 2 ││ 3 │ │ ENGINE ARRANGEMENT (AFT VIEW)
│ └───┘└───┘└───┘ │
│ │ NTR-1
│ ENGINE GIMBAL RANGE: │ ╱ ╲
│ ±4° each axis │ ╱ ● ╲
│ │ ╱ │ ╲
│ ENGINE SPACING: │ ●──────┼──────●
│ 4.5 m center-to-center │ NTR-2 │ NTR-3
│ │ (120° apart)
└───────────────────────────────┘
CLUSTER SPECIFICATIONS:
├── Total Thrust: 333 kN (74,842 lbf)
├── Total Thermal Power: 1,650 MW
├── Cluster Dry Mass: 42,600 kg (3 engines + structure + shield)
├── Gimbal range: ±4° (TVC)
├── Engine-out capability: Yes (2-of-3 sufficient for mission)
├── Start sequence: Staggered (5-second intervals)
└── Shutdown sequence: Simultaneous (emergency) or staggered (normal)
ENGINE OPERATING MODES:
┌──────────────────┬───────────┬───────────┬────────────┬─────────────────────┐
│ Mode │ Engines │ Thrust │ Isp │ Application │
├──────────────────┼───────────┼───────────┼────────────┼─────────────────────┤
│ Full Thrust │ 3 │ 333 kN │ 900 s │ TMI burns │
│ Two-Engine │ 2 │ 222 kN │ 900 s │ Engine-out / MOI │
│ Single Engine │ 1 │ 111 kN │ 900 s │ Contingency / trim │
│ Low Power │ 1 @ 50% │ 55 kN │ 875 s │ Course correction │
└──────────────────┴───────────┴───────────┴────────────┴─────────────────────┘
PROPELLANT FEED SYSTEM:
├── Main LH2 tanks: 6 × 350 m³ (total 2,100 m³)
├── Feed pressure: 0.4 MPa (tank) → 10 MPa (engine inlet)
├── Pump type: Turbopump (hot-gas bleed cycle)
├── Pump power: 3.2 MW per engine
├── Redundancy: Cross-feed capability between all engines
└── Emergency isolation: Pyrotechnic valves (each engine)
══════════════════════════════════════════════════════════════════════════════════3. Chemical Backup Propulsion System
3.1 RL-10C Cluster Configuration
CHEMICAL BACKUP PROPULSION SYSTEM
══════════════════════════════════════════════════════════════════════════════════
PURPOSE: 100% backup capability if NTR system fails
HERITAGE: RL-10 family (500+ flight engines, >99% reliability)
ENGINE: RL-10C-3 (Enhanced)
├── Propellant: LOX/LH2 (O/F ratio: 5.88:1)
├── Thrust: 110 kN (24,750 lbf) per engine
├── Specific Impulse: 465.5 s (vacuum)
├── Chamber Pressure: 4.42 MPa (640 psi)
├── Expansion Ratio: 130:1
├── Engine Mass: 277 kg dry
├── Burn Time: 2,000 s (rated)
├── Restarts: 15 (certified)
└── TRL: 9 (flight proven)
CLUSTER CONFIGURATION: 8 × RL-10C-3
CHEMICAL ENGINE CLUSTER (AFT VIEW)
● ●
● ●
● ●
● ●
(Arranged in ring, 45° apart)
Can gimbal ±6° for TVC
CLUSTER PERFORMANCE:
├── Total Thrust: 880 kN (197,800 lbf)
├── Total Isp: 465 s
├── Cluster Mass: 2,800 kg (dry, including structure)
├── Required propellant for TMI: 2,850 t (if NTR unavailable)
│ └── EXCEEDS CAPACITY - partial mission only
├── Propellant for MOI only: 1,200 t (achievable)
└── Engine-out: 7-of-8 sufficient
CHEMICAL PROPELLANT STORAGE:
┌────────────────┬────────────┬────────────┬────────────────────────────────────┐
│ Propellant │ Mass (t) │ Volume (m³)│ Storage │
├────────────────┼────────────┼────────────┼────────────────────────────────────┤
│ LOX (backup) │ 1,100 │ 965 │ 4 × spherical tanks, 6.1m dia │
│ LH2 (shared) │ 250 │ 3,520 │ Shared with NTR tanks │
├────────────────┼────────────┼────────────┼────────────────────────────────────┤
│ Total │ 1,350 │ │ │
└────────────────┴────────────┴────────────┴────────────────────────────────────┘
Note: LH2 is shared between NTR and chemical systems. Chemical backup
uses NTR's LH2 plus dedicated LOX storage.
OPERATIONAL CONCEPT:
├── Normal: NTR performs all major burns, chemical provides RCS/trim
├── NTR Partial Failure: 2 NTR + chemical augmentation
├── NTR Total Failure: Chemical performs MOI (reduced mission)
│ ├── Can achieve Mars orbit insertion
│ ├── Can perform emergency return to Earth (free-return trajectory)
│ └── Cannot complete full mission profile (insufficient Isp)
└── Abort Modes: High-thrust chemical enables rapid abort maneuvers
══════════════════════════════════════════════════════════════════════════════════3.2 Reaction Control System (RCS)
REACTION CONTROL SYSTEM SPECIFICATION
══════════════════════════════════════════════════════════════════════════════════
PROPELLANT: MMH/NTO (Monomethylhydrazine / Nitrogen Tetroxide)
SELECTION RATIONALE: Hypergolic, storable, space-proven, high reliability
RCS THRUSTER SPECIFICATIONS:
├── Primary Thrusters (attitude control)
│ ├── Type: R-4D heritage (490 N class)
│ ├── Thrust: 490 N (110 lbf)
│ ├── Isp: 312 s
│ ├── Quantity: 32 (8 pods × 4 thrusters)
│ └── Min impulse bit: 0.09 N·s
│
├── Vernier Thrusters (fine control)
│ ├── Type: MR-111 heritage (22 N class)
│ ├── Thrust: 22 N (5 lbf)
│ ├── Isp: 290 s
│ ├── Quantity: 16 (8 pods × 2 thrusters)
│ └── Min impulse bit: 0.02 N·s
│
└── Translation Thrusters (docking/proximity)
├── Type: R-42 heritage (890 N class)
├── Thrust: 890 N (200 lbf)
├── Isp: 320 s
├── Quantity: 8 (2 per axis, +/-)
└── Purpose: Docking, station-keeping, collision avoidance
RCS POD ARRANGEMENT:
┌─────────────────────────────────────┐
│ │
│ POD 1 ● ● POD 2 │ FORWARD
│ \ / │
│ \ / │
│ POD 3 ●───╲ ╱───● POD 4 │ (VIEW FROM ABOVE)
│ \ / │
│ ════════════╳════════════════ │ ← Central Truss
│ / \ │
│ POD 5 ●───╱ ╲───● POD 6 │
│ / \ │
│ / \ │
│ POD 7 ● ● POD 8 │ AFT
│ │
└─────────────────────────────────────┘
PROPELLANT BUDGET:
├── MMH: 48,000 kg
├── NTO: 72,000 kg
├── Total: 120,000 kg
├── Usable: 114,000 kg (5% residual)
├── ΔV capability: 150 m/s (RCS only)
└── Lifetime: 36 months (with margin)
RCS ΔV ALLOCATION:
┌─────────────────────────────┬────────────┬────────────────────────────────────┐
│ Function │ ΔV (m/s) │ Notes │
├─────────────────────────────┼────────────┼────────────────────────────────────┤
│ Attitude maintenance │ 25 │ Throughout 6-month transit │
│ Rotation spinup/spindown │ 15 │ Habitat ring operations │
│ Docking operations │ 5 │ MDV deployment, EVA support │
│ Trajectory corrections │ 30 │ Mid-course corrections │
│ Mars orbit maintenance │ 20 │ Aerobraking trim │
│ Contingency │ 55 │ 50% margin │
├─────────────────────────────┼────────────┼────────────────────────────────────┤
│ TOTAL │ 150 │ │
└─────────────────────────────┴────────────┴────────────────────────────────────┘
══════════════════════════════════════════════════════════════════════════════════4. Integrated Propulsion Architecture
4.1 System Integration Overview
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Created by Erik Bethke in Bike4Mind using the QuestMaster deep agentic flow + Claude Opus 4.5 by Anthropic