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1.9 Appendix

    Naming Convention

    OPCON Stages Examples

    OPC-LAUNCH
    OPC-ORBIT_INSERT
    OPC-STANDBY
    OPC-RENDEZVOUS
    OPC-PROXIMITY_OPS
    OPC-DOCKING
    OPC-PROP_TRANSFER
    OPC-UNDOCKING
    OPC-RETURN
    OPC-DISPOSAL

    Requirements

    IOR-<LEVEL>-<CATEGORY>-NNN

    LEVEL

    • STKR = Stakeholder Requirement
    • MISR = Mission Requirement
    • SYSR = System Requirement
    • DERR = Derived Requirement
    • VERI = Verification Requirement
    • HSWR – High Level Software Requirement
    • LSWR – Low Level Software Requirement

    CATEGORY

    Discipline grouping

    • OPEC = Operational Coverage
    • FUNC = Functional Capability
    • PERF = Performance
    • SAFT = Safety
    • COMM = Communications
    • NAVI = Navigation
    • PROP = Propulsion
    • INTF = Interface
    • OPRS = Operations
    • REGU = Regulatory

    SUB-CATEGORY

    Is not part of the Requirements ID but SUB-CATEGORY is an optional attribute inside a requirement.

    NNN

    Three-digit number identified. Need not be sequential

    Examples

    IOR-MISR-OPEC-001: IOR-Mission Requirement-Operational Coverage-001

    IOR-MISR-FUNC-004: IOR-Mission Requirement-Functional Capability-004

    IOR-SYSR-PROP-012: IOR-System Requirement-Propulsion-012

    IOR-SYSR-COMM-003: IOR-System Requirement-Communications-003

    IOR-VERI-OPEC-001: IOR-Verification Requirement-Operational Coverage-001

    ARCADIA Model Naming Convention (Very Important)

    Model objects should be readable, not coded.

    Use: <Type> – <System> – <Function>

    Examples

    1. Operational Capability:LEO Servicing
    2. Operational Activity:Perform Rendezvous
    3. System Function:Transfer Propellant
    4. Logical Function:Regulate Propellant Flow
    5. Component:Service Vehicle
    6. Interface:SV-to-Depot Mechanical Interface
    7. Exchange:State Vector Data
    8. Component:Service Vehicle
    9. Component:Orbital Depot
    10. Component:Ground Segment

    Acronyms

    • ISAM – In-space Servicing, Manufacturing, and Assembly
    • DSO
    • IOR – In-Orbit Refueling
    • PRM – Northrop Grumman’s Passive Refueling Module
    • RAFTI – Orbit Fab’s Rapidly Attachable Fluid Transfer Interface
    • RPOD – Rendezvous, Proximity Operations, Docking
    • SERB – Space System Command’s System Engineering Review Board
    • SSM – sustained space maneuver

    Terms, Definitions and technologies

    1. Fuel Shuttle – Shuttle that services the spacecraft. Also called Service Vehicle
    2. Fuel Station – A space craft which stores the fuel or propellant, also called Fuel Depot
    3. Fuel Depot – Same as Fuel Station
    1. Service Vehicle – Same as Fuel Shuttle

    References

    1. RPOD NASA – https://www.nasa.gov/reference/jsc-rendezvous-prox-ops-docking-subsystems/
    2. RPOD – https://www.merl.com/publications/docs/TR2024-016.pdf

    IOR 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