How to Calculate Space Tug Delta-v Budget
Space tugs reposition satellites, deliver payloads, and clear debris by executing sequences of orbital manoeuvres. Each mission demands a delta-v budget that aggregates transfer burns, rendezvous operations, and contingency reserves. This walkthrough provides a deterministic method for computing total delta-v, propellant mass, and launch mass using the Tsiolkovsky rocket equation. Pair it with collision avoidance planning from the conjunction delta-v guide and communications planning in the downlink margin walkthrough to ensure mission readiness across subsystems.
You will define manoeuvre segments, translate them into total delta-v, apply contingency margins, and compute propellant mass given propulsion specific impulse. The embedded calculator mirrors these equations, outputting formatted results for mission design reviews and customer proposals.
Mission context and assumptions
Space tug missions often include multiple burns: orbit raising, plane changes, rendezvous approach, docking, and disposal manoeuvres. Each burn consumes propellant based on the required delta-v and the propulsion system’s specific impulse (Isp). The rocket equation links delta-v to the ratio between initial and final mass. For planning, we treat the “final mass” as the mass remaining after all manoeuvres (tug dry mass plus retained hardware).
The method assumes impulsive burns and constant Isp. Low-thrust electric missions require trajectory optimisation to estimate equivalent delta-v; you can still use this workflow by substituting the effective delta-v output from those tools.
Variables and units
Define the following inputs:
- Mf – Final mass after burns (kg), including tug dry mass and any payload retained.
- Δvtransfer – Delta-v for transfer manoeuvres (m/s).
- Δvrendezvous – Delta-v for rendezvous, docking, and station-keeping (m/s).
- Isp – Specific impulse of the propulsion system (s).
- c – Contingency margin (%) applied to the total delta-v (optional).
Additional inputs such as gravity constant g0 = 9.80665 m/s² are constants. Gather delta-v segments from mission analysis tools or orbital mechanics calculations. Contingency margins usually range from 5% to 15% depending on navigation accuracy and mission risk appetite.
Equations for delta-v and propellant mass
Combine the inputs using the following formulas:
Δvtotal = (Δvtransfer + Δvrendezvous) × (1 + c ÷ 100)
Mass ratio = exp(Δvtotal ÷ (Isp × g0))
Mprop = Mf × (Mass ratio − 1)
M0 = Mf + Mprop
Mprop is the propellant mass required, while M0 is the initial launch mass before manoeuvres. Ensure units remain consistent: delta-v in m/s, Isp in seconds, mass in kilograms. Contingency defaults to zero when not provided.
Step-by-step workflow
Step 1: Break down mission phases
Identify each manoeuvre: departure, transfer, rendezvous, and disposal. Assign delta-v requirements using analytical formulas or high-fidelity simulations. Document assumptions such as plane change angles or phasing orbits.
Step 2: Determine final mass
Sum the tug structure, remaining payload (if any), docking hardware, and propellant residuals required for safe disposal. This final mass anchors the rocket equation.
Step 3: Select propulsion parameters
Choose Isp based on propulsion type—chemical biprop, green monopropellant, or electric thrusters. Ensure the value reflects operating conditions (throttle level, mixture ratio). If multiple propulsion systems are used, calculate segments separately and sum propellant masses.
Step 4: Apply contingency margins
Add margin for navigation errors, plume impingement avoidance, or unplanned debris avoidance. Mission assurance teams often specify minimum margins; coordinate with them to set c.
Step 5: Compute propellant and launch mass
Use the equations to calculate Δvtotal, mass ratio, propellant mass, and initial mass. Validate results against heritage missions or simulation outputs. Update calculations as mission design evolves.
Validation and scenario analysis
Validate the delta-v budget using high-fidelity trajectory tools or Monte Carlo analysis. Compare computed propellant mass with propellant tank capacity and structural limits. Run sensitivity scenarios: increase Δvtransfer by 5% or reduce Isp by 10 s to understand margins.
Integrate the delta-v budget with logistics planning—launch vehicle selection, rideshare constraints, and downlink capacity. Reference communications planning in the downlink margin guide to ensure the tug can transmit telemetry during burns and docking.
Limitations and extensions
The impulsive-burn assumption breaks down for electric propulsion or long-duration thrust arcs. For those missions, derive equivalent delta-v from trajectory optimisation and ensure mass budgets include power system impacts. Multi-tug operations may require staging; adapt the rocket equation to model each stage separately.
Future enhancements include integrating thermal budgets, thruster duty-cycle constraints, and servicing payload release mass changes. Keep documentation under configuration control so regulators and insurers can audit mission readiness.
Embed: Space tug delta-v budget calculator
Provide final mass, delta-v segments, propulsion specific impulse, and optional contingency margin. The embedded calculator outputs total delta-v, propellant mass, and initial launch mass.