Propulsion Δv & Deorbit Perigee Calculator
Compute Tsiolkovsky rocket Δv, Hohmann perigee-lowering requirements, and annual atmospheric drag make-up.
DETERMINISTIC PHYSICS & DATA METHODOLOGY
How This Calculator Works
Source modules: lib/physics/orbit.ts, lib/physics/decay.ts
Compares ideal Tsiolkovsky rocket Δv from onboard propellant mass and specific impulse against single-burn Hohmann perigee-lowering disposal Δv and annual atmospheric drag make-up Δv.
Governing Equations & Physical Model
Δv_avail = I_sp · g₀ · ln(m_wet / (m_wet − m_prop))Uses standard gravity g₀ = 9.80665 m/s².
Δv_deorbit = √(μ / r_a) − √(μ · (2 / r_a − 2 / (r_a + r_p)))Impulsive retrograde burn dropping circular radius r_a = R_E + h₀ to disposal perigee r_p = R_E + h_p.
Δv_yr = ½ · ρ(h₀) · v² · B · T_yearEvaluated for a 1P reference cross-section (37.5 cm², C_D = 2.2) under moderate Kennewell solar activity.
Inputs, Parameters & Units
| Parameter | Unit | Physical definition |
|---|---|---|
| m_wet, m_prop | g, g | Total wet spacecraft mass and usable propellant load. |
| I_sp | s | Thruster specific impulse (55–80 s cold gas; 200–300 s resistojet/monoprop; 500–1200 s electrospray/FEEP/VAT). |
| h₀, h_p | km, km | Initial circular orbit altitude and target disposal perigee altitude. |
Assumptions & Validity Limits
- Hohmann burn assumes an impulsive thrust arc; continuous low-thrust electric spirals require up to ~2× the impulsive Δv.
- No nozzle cosine, plume impingement, or propellant residual losses are subtracted.
Worked Default Reference Case
An 18 g propellant load at I_sp = 285 s delivers 208.8 m/s Δv, exceeding the 69.0 m/s impulsive burn to drop perigee to 280 km or ~18.9 years of 11.06 m/s/yr drag make-up at 525 km.
- Available Tsiolkovsky Δv
- 208.8 m/s
- Perigee-lowering Δv (to 280 km)
- 69.0 m/s
- Annual drag make-up (525 km)
- 11.06 m/s/yr
- Mass fraction m_prop / m_wet
- 7.2% (18 g / 250 g)