Launch Vehicles

Abstract

The evolution of launch vehicles from the 1940s has seen transformative advancements, beginning with military rocket technology during World War II and progressing to modern reusable rockets. Early developments like Germany’s V-2 rocket laid the groundwork for space exploration, while the Cold War space race between the USA and USSR spurred innovation. The post-1990s era saw a transition to commercialization, with private companies like SpaceX revolutionizing costs and reusability. Each era emphasized improving reliability, payload capacity, and accessibility.

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Historical overview

1. 1940s: Pioneering Rocket Technology:
   • Germany’s V-2 Rocket: The world’s first long-range guided ballistic missile (1944), foundational for modern rocketry.
   • Post-war, the US and USSR acquired German rocket technology, leading to the Redstone (US) and R-7 Semyorka (USSR) programs.
2. 1950s: Dawn of the Space Age:
   • The USSR launched Sputnik 1 (1957), the first artificial satellite, using the R-7 rocket.
   • The USA responded with Explorer 1 (1958) using the Juno I rocket.
   • Both nations focused on modifying military rockets for space exploration.
3. 1960s: The Apollo Era and Heavy-Lift Rockets:
   • Development of Saturn V (USA): Capable of delivering payloads to the Moon, it remains the most powerful rocket ever built.
   • USSR’s N1 rocket attempted to rival Saturn V but failed to achieve operational status.
   • Advances in multi-stage rocketry allowed heavier payloads and missions beyond Earth’s orbit.
4. 1970s: Space Stations and Reusability Concepts:
   • The USSR’s Proton rocket launched the Salyut space stations, solidifying its role as a heavy-lift vehicle.
   • Early concepts for reusability emerged, leading to the development of the Space Shuttle (USA).
5. 1980s: Emergence of Modular and International Launch Systems:
   • Europe introduced the Ariane series, focusing on commercial satellite deployment.
   • China’s Long March rockets entered the global market.
   • The Space Shuttle became the first reusable spacecraft but faced challenges like the Challenger disaster (1986).
6. 1990s: Commercialization and International Cooperation:
   • The fall of the USSR enabled Russian rockets like Soyuz and Proton to enter the global market.
   • The Commercial Space Launch Act (1984) in the US encouraged private-sector involvement.
   • Delta II and Atlas II/III became workhorses for satellite launches.
7. 2000s: Reusability and Private Innovation:
   • SpaceX emerged with the Falcon 1 (2008), followed by the reusable Falcon 9.
   • Focus shifted to cost reduction and increasing launch cadence.
   • Smaller rockets, such as Rocket Lab’s Electron, targeted the nanosatellite market.
8. 2010s-Present: Reusability and Heavy-Lift Advances:
   • SpaceX’s Falcon Heavy and Starship redefined payload capacities.
   • Blue Origin’s New Shepard and New Glenn expanded reusability efforts.
   • International competition intensified with India’s PSLV, Japan’s H-IIA, and China’s Long March series achieving global prominence.

Current Launch Vehicle Landscape

• Major Western launch systems: Delta IV, Atlas V, Falcon 9, Vulcan Centaur, and Ariane 6.
• Advances in reusable rockets led by SpaceX (Falcon 9 and Falcon Heavy).
• Focus on cost reduction, higher efficiency, and modular designs to meet diverse mission profiles.

Key Launch Vehicle Design and Performance Factors

• Propulsion technologies: Liquid-fueled systems (e.g., hydrolox) offer high efficiency but require cryogenic handling, while hypergolic propellants provide simplicity and storability but are crazy toxic!
• Engine cycles (e.g., dual-combustion chamber RD-180 vs. methane-based BE-4).
• Modularity and scalability for payload adaptability like the Ariane 6.

Launch vehicle selection

Orbit accuracy:

• Accuracy is hard to quantify but there are some principles:
  • Solid upper stages are less precise than liquid ones
  • Long burning upper stages are less precise than short burning ones
  • smaller engines are more precise than large ones.

Different launchers (and launchpads) are specialised for different orbits. In the following image it is visible that Ariane 6 is better for a GTO while the falcon 9 is better for the ISS.

Different mission types have different requirements for launchers.

Science Missions with a unique instrument are willing to accept schedule risks and a higher price but do not accept technical risks. A constellation satellite does accept technical risk and schedule risk but does not accept higher costs.

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Excursion Launch Phases

Phase	Key Events	Approx. Altitude
Liftoff	Ignition, tower clearance	0–1 km
Max Q	Max aerodynamic pressure	~10–15 km
Stage Separation	Spent stage jettisoned	~40–100 km
Upper Atmosphere	Fairing jettison, near-vacuum flight	~100–200 km
Orbital Insertion	Achieving orbital velocity	~200 km or higher
Payload Deployment	Release of satellite or spacecraft	Target orbit altitude

Vibrations and Structural Considerations

• Vibrational loads (sinusoidal and random) and acoustic stresses during ascent.
  • Sinusoidal Vibrations:
    • Narrow-band vibrations caused by engine resonances and structural dynamics.
    • Persistent during the entire burn phase of a rocket stage.
  • Random Vibrations:
    • Broad-spectrum excitations caused by turbulent airflows, engine combustion, and rocket dynamics.
    • Prominent during key phases like liftoff.
• Importance of dynamic coupling and resonance management between spacecraft and launch vehicle.
  • Dynamic Interaction
    • Spacecraft and launch vehicle form a single dynamic system, where resonances must be avoided.
    • Resonance occurs when natural frequencies of spacecraft components align with launch vehicle-induced frequencies.
  • Avoiding Resonances
    • Design spacecraft such that its fundamental frequencies are higher than those of the launch vehicle.
  • Coupled Load Analysis
    • Conduct simulations to identify critical resonances and ensure decoupling.
• The Spacecraft further needs to be able to persist the enormous acoustic loads.
  • Sources:
    • Engine noise and aerodynamic effects create high acoustic pressures during liftoff and max-Q.
  • Mitigation Strategies:
    • Acoustic blankets in payload fairings (e.g., Falcon 9: 4–6 dB reduction).
• Load factor limits imposed by axial and lateral stresses (90° off the flight direction) and techniques for shock mitigation.
• Rules of thumb:
  • Larger launch vehicles have smaller sinusoidal vibrations than smaller ones
  • Smaller launch vehicles have smaller acoustic loads than larger ones
• During a Launch there are different shocks on the spacecraft (sorted from high shocks to low):
  • Spacecraft separation
  • Fairing deployment
  • Stage separation
  • Booster separation
  • Release of LV hold-down at liftoff

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Key Facts to Memorize

• V-2 Rocket (1944): First long-range ballistic missile; foundational for space technology.
• Sputnik 1 (1957): First artificial satellite, marking the start of the Space Age.
• Saturn V (1967-1973): Most powerful rocket, instrumental in the Apollo Moon landings.
• Space Shuttle (1981-2011): First partially reusable spacecraft, despite high costs and risks.
• Falcon 9 (2010): Revolutionized the industry with reusability and lower costs.
• Proton and Soyuz: Workhorses of the Russian space program, critical for both national and commercial missions.

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Important Formulas and Metrics

1. Rocket Equation (Tsiolkovsky):
   • $\Delta v=v_e\ln \left(\frac{m_0}{m_f}\right)$
   • Describes the relationship between a rocket’s change in velocity (Δv), exhaust velocity (ve​), and the initial (m0​) and final (mf​) masses.
2. Payload Fraction:
   • $PayloadFraction=\frac{\text{Payload Mass}}{\text{Total Launch Mass}}$
   • Key metric to evaluate efficiency.
3. Cost-per-Kilogram to Orbit:
   • $CostEfficiency=\frac{\text{Total Launch Cost}}{\text{Payload Mass}}$
   • A critical measure reduced significantly by reusable rockets.
4. Launch Success Rates:
   • $Reliability=\frac{\text{Successful Launches}}{\text{Total Launches}}\times 100\%$
   • Modern rockets aim for >95% reliability.