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1.9.5 Space Technical Knowledge

Propellants

  1. Electric Propulsion Propellants (Noble Gases)

Primary propellants:

  • Xenon
  • Krypton

Why?

  • Used by almost all modern LEO constellations
  • Increasingly used in GEO satellites
  • Very high efficiency (high Isp)
  • Ideal for orbit raising + station keeping
  • Compatible with all-electric satellite platforms
  1. Storable Chemical Propellants (Hypergolic Family)

Primary combinations:

  • MMH + NTO
  • UDMH + NTO

Why still relevant:

  • Large installed GEO legacy fleet
  • High-thrust maneuvers
  • Reliable, flight-proven
  • Used in servicing vehicles and mission-critical burns

Core Factors Affecting Propellant Use

  1. Spacecraft Mass – Directly proportional to propellant required for a given ΔV.
  2. Orbit Altitude – Lower altitude → higher drag → higher propellant consumption.
  3. Mission Duration – Longer operational life → more accumulated station-keeping and drag compensation.
  4. Activity Profile – Nominal operations (sun alignment, orbital maintenance).
  5. Additional Maneuvers (DSO / Avoidance) – Each maneuver adds ΔV.
    Frequency per year directly increases total propellant use.

Formula to Calculate Propellant Use

Then the propellant mass is calculated using the Tsiolkovsky Rocket Equation.

m_prop = m₀ × (1 − exp(−ΔV / (Isp × g₀)))

Where:

  • m_prop = propellant mass (kg)
  • m₀ = initial total mass before burn (kg)
  • ΔV = total required delta-V (m/s)
  • Isp = specific impulse (seconds)
  • g₀ = 9.81 m/s²

 

Space Craft Weight

Uses the following approximations for calculations:

LEO Satellites

  • 400–700 kg → Good representative operational mass for modern commercial LEO spacecraft.

GEO Satellites

  • 2000–3000 kg → Reasonable mid-class GEO communications satellite mass (not the very large 6-ton class).

Sample Calculation for Propellant Use

LEO

  • LEO satellite mass: 600 kg
  • Mission duration: 5 years
  • Nominal operations only (drag makeup + station keeping)
  • Typical LEO ΔV budget (500–600 km altitude): ~50 m/s per year

10 Kgs

GEO

  • Mass at start of life: 3000 kg
  • Mission life: 15 years
  • Typical GEO station-keeping ΔV:
  • North–South: ~45 m/s per year
  • East–West: ~2 m/s per year
    → Total ≈ 50 m/s per year

Total ΔV over 15 years: 50 × 15 = 750 m/s

Propellant Type GEO satellites traditionally use hypergolic bipropellant: Isp ≈ 300 s

675 Kgs