Chapter 8

8.1 The Need for Next-Generation Launch Technology

Today's chemical rockets are highly advanced, yet they still have fundamental limitations. Truly making access to space routine will require breakthrough technological innovation.

8.2 SSTO (Single-Stage-To-Orbit)

A launch vehicle that reaches orbit from the Earth's surface with a single stage. It is theoretically possible but technically extremely difficult.

8.2.1 Advantages of SSTO

• Simplicity: No stage separation → improved reliability
• Reusability: Recovery and reuse of the entire system
• Operational efficiency: Takeoff–landing–takeoff again, like an aircraft
• Cost savings: Lower manufacturing and operating costs (in theory)

8.2.2 Challenges of SSTO

The Rocket Equation Wall

According to the Tsiolkovsky equation, the delta-v required to reach LEO (~9,400 m/s) demands the following:

Δv = v_e × ln(m_0 / m_f)
9,400 = v_e × ln(mass ratio)

RP-1/LOX rocket (v_e ~ 3,500 m/s):
mass ratio = e^(9,400/3,500) = e^2.69 ≈ 14.7

That is, 93% of the liftoff weight must be propellant.
Payload + structure get only 7%.

In practice:
- Structural weight (tanks, engines, systems): 5-8%
- Payload: 1-2% (almost nothing)

Conclusion: With conventional chemical rockets, SSTO is nearly impossible, or even if possible, the payload is extremely small.

Solutions

• Extremely lightweight structures:
  • Composite materials
  • Pressure-stabilized tanks
  • Integrated design
• High-Isp propulsion:
  • LH2/LOX (Isp ~450s)
  • Air-breathing engines (within the atmosphere)
  • Nuclear propulsion
• Air Launch:
  • Launch from an aircraft → saves initial delta-v
  • Examples: Northrop Grumman Pegasus, Virgin Orbit LauncherOne (operated 2021-2023)

8.2.3 SSTO Attempts

VentureStar / X-33 (NASA, 1990s)

• Design:
  • Lifting body configuration
  • Linear aerospike engines
  • Composite cryogenic tanks
• Outcome: Cancelled in 2001
  • Immature composite tank technology
  • Excess weight problems
  • Cost overruns
• Lesson: SSTO was too ambitious a goal, with excessive technical risk

Skylon (Reaction Engines, UK)

• Design:
  • SABRE engine (Synergetic Air-Breathing Rocket Engine)
  • Within the atmosphere: air-breathing mode (up to Mach 5.5)
  • In space: rocket mode
• SABRE core technology:
  • Ultra-fast heat exchanger: cools air from 1,000°C → -150°C (in 0.01 seconds)
  • Cooling before compression → allows use of a turbine compressor
• Status: Development stopped when Reaction Engines entered administration in 2024
  • Heat exchanger ground tests successful
  • A complete engine and vehicle were never built

8.3 Air-Breathing Propulsion

Using oxygen from the air within the atmosphere removes the need to carry oxidizer, greatly improving the mass ratio.

8.3.1 Ramjet

• Principle: In supersonic flight, air is compressed by ram compression
• Operating speed: Mach 3-6
• Advantage: No moving parts (no turbine required)
• Disadvantage: Requires supersonic speed to operate → a booster is needed
• Use: Missiles (e.g., BrahMos)

8.3.2 Scramjet

• Principle: Supersonic Combustion
• Operating speed: Mach 5-15+
• Challenges:
  • Fuel-air mixing and combustion within supersonic flow
  • Residence time on the order of milliseconds
  • Requires materials for extreme temperatures
• Tests:
  • NASA X-43A: Mach 9.6 (world record, 2004)
  • X-51 Waverider: Mach 5.1 sustained flight (210 seconds)

8.3.3 SABRE Engine (Hybrid)

An innovative design combining air-breathing and rocket modes:

Theoretical advantage: much less oxidizer must be carried → SSTO becomes conceivable

8.4 Nuclear Propulsion

8.4.1 Nuclear Thermal Rocket (NTR)

• Principle:
  • A nuclear reactor heats the propellant (hydrogen)
  • The heated hydrogen is expelled through a nozzle
• Performance:
  • Isp: 800-1,000 seconds (twice that of chemical rockets)
  • Thrust: moderate to high
• Advantages:
  • High Isp → shorter interplanetary travel times
  • Mars: 6 months → 3 months
• Disadvantages:
  • Radiation hazard (in case of accident)
  • Political opposition
  • Heavy shielding required
  • Restrictions on ground testing
• History:
  • 1960s-70s: NERVA program (NASA)
    • Successful ground tests
    • Cancelled due to budget cuts
• Current:
  • DRACO (DARPA with NASA): aimed at an in-space demonstration around 2027
  • The program was discontinued in 2025

8.4.2 Nuclear Electric Propulsion (NEP)

• Principle:
  • A nuclear reactor generates electricity
  • The electricity drives ion thrusters
• Performance:
  • Isp: 5,000-10,000 seconds (extremely high)
  • Thrust: very low (millinewton level)
• Applications: Deep space exploration, cargo transport (when time is not critical)

8.5 Space Elevator

The ultimate dream of reaching space without rockets. It is theoretically possible from a technical standpoint, but its realization lies in the distant future.

8.5.1 Concept

• Structure:
  • A cable extending from the Earth's surface beyond geostationary orbit (GEO, 36,000km)
  • A heavy counterweight at GEO
  • Centrifugal force and gravity balance → the cable stays taut
• Operation:
  • A climber ascends along the cable
  • Electric motors or laser propulsion
  • Speed: ~200 km/h
  • Travel time: several days to several weeks

8.5.2 Physics

Cable Strength Requirements

The cable must support its own weight + the climber's weight.
Location of maximum stress: geostationary orbit (GEO)

Required material strength (tensile strength / density):
> 50 MPa/(kg/m³) = 50 MYuri

Strongest current materials:
- Steel: 0.2 MYuri (250 times too weak)
- Kevlar: 2.5 MYuri (20 times too weak)
- Carbon fiber: 4 MYuri (12 times too weak)
- Carbon nanotubes (CNT, theoretical): 50-100 MYuri (sufficient in theory)

Problem: Manufacturing defect-free CNT 36,000 km long is currently impossible

8.5.3 Technical Challenges

• Materials:
  • Mass production of perfect carbon nanotubes
  • Defect-free fabrication over extremely long lengths
• Construction:
  • Starting at geostationary orbit, extending upward and downward simultaneously
  • Takes years to decades
• Safety:
  • Micrometeoroid impacts
  • Space debris avoidance
  • Lightning, storms (lower section)
  • Catastrophe if the cable is severed (falls to Earth)
• Cost: Estimated at hundreds of billions to trillions of dollars

8.5.4 Alternative: Lunar Elevator

• Advantages:
  • Lunar gravity = 1/6 of Earth's → relaxed material requirements
  • Feasible with current materials (Zylon)
  • No atmosphere → no storms or lightning
• Location: from the lunar surface to the Earth–Moon L1 (near side) or L2 (far side) Lagrange point
• Application: Cargo transport between the lunar surface ↔ space station

8.6 Other Future Concepts

8.6.1 Orbital Ring

• Concept: A giant orbital ring encircling the Earth
  • An inner ring rotating at high speed (at or above orbital velocity)
  • A stationary outer structure
  • Connected by magnetic levitation
• Advantages:
  • Lower technical difficulty than a space elevator
  • Accessible from anywhere on Earth
• Disadvantage: Enormous construction cost and time

8.6.2 Railgun / Mass Driver

• Concept: Launches cargo at ultra-high speed along an electromagnetic track
  • Length: several km
  • Acceleration: hundreds to thousands of g
• Applications:
  • Launching cargo from the lunar/Martian surface (no atmosphere)
  • On Earth, atmospheric heating is a problem

8.6.3 Laser Propulsion

• Concept:
  • A ground-based laser heats propellant beneath the rocket (or a solar sail)
  • The rocket carries only fuel (no oxidizer or engine weight)
• Tests: Lightcraft (small scale)
• Challenges:
  • Requires extremely powerful lasers (megawatt class)
  • Atmospheric scattering
  • Maintaining a precise beam

8.7 Future Roadmap for Space Launch

The following roadmap is a speculative outlook, not a forecast; dates and cost figures indicate orders of magnitude only.

8.7.1 Short Term (2025-2035)

• Fully reusable rockets: Starship and New Glenn begin operations
• Launch cost: $100-500/kg LEO
• Launch frequency: Hundreds per year (SpaceX alone)
• Commercial space stations: Multiple private LEO stations
• Lunar bases: Artemis program, commercial landers

8.7.2 Medium Term (2035-2050)

• Crewed Mars missions: Starship or a successor system
• SSTO demonstration: Air-breathing or ultra-lightweight rockets
• Nuclear propulsion: Used for deep space exploration
• Launch cost: $10-50/kg
• In-space manufacturing: Orbital factories at full scale

8.7.3 Long Term (2050-2100)

• Space elevator: Construction begins (optimistic scenario)
• Orbital ring: Research and initial construction
• Asteroid mining: Full-scale commercialization
• Martian cities: Self-sustaining settlements
• Launch cost: On par with air travel

8.8 Conclusion: The Role of the WIA-SPACE-004 Standard

The WIA-SPACE-004 Launch Vehicle Standard encompasses both current and future launch technologies:

• Present: Establishing best practices for chemical rockets and reusable systems
• Near future: Monitoring air-breathing and SSTO-enabling propulsion (the spec lists these as emerging technologies in §10.1)
• Future: Tracking nuclear propulsion and long-term infrastructure concepts such as space elevators and mass drivers (§10)

Through this standard:

• Improved launch safety
• Enhanced international cooperation
• Democratized access to space
• The dawn of the space age for all humanity