Electric Space Tug Analysis

Mission Parameters

Payload: 1,000 kg
Mission: LEO to TLI (Trans-Lunar Injection), payload handoff near Moon, return to LEO
Transit Time: ≤ 1 year each way
Thruster: Turion TIE-20 GEN2 (55 mN, 4500s ISP, 2000W, 23 kg, $150,000)
Delta-V Required: ~3,200 m/s LEO to TLI, ~900 m/s TLI to LEO

Propellant Properties

Propellant	Estimated ISP (s)	Exhaust Velocity (m/s)	Price ($/kg)
Xenon	4,500	44,145	$3,000
Krypton	3,600	35,316	$300
Argon	3,000	29,430	$3

Note: ISP values are scaled from the Xenon baseline (4500s) based on atomic mass ratios. Exhaust velocity = ISP × 9.81 m/s²

Mission Delta-V Analysis

Rocket Equation: Δv = Ve × ln(m_initial / m_final)
Mass Ratio = exp(Δv / Ve)

Outbound: LEO to TLI (Δv = 3,200 m/s)

Propellant	Mass Ratio	Propellant Mass (kg)
Xenon	1.0748	261
Krypton	1.0944	337
Argon	1.1147	423

Return: TLI to LEO (Δv = 900 m/s)

Propellant	Mass Ratio	Propellant Mass (kg)
Xenon	1.0207	17
Krypton	1.0259	21
Argon	1.0312	26

Space Tug Component Masses

Component	Xenon (kg)	Krypton (kg)	Argon (kg)	Unit Cost
Thrusters (4 units)	92	92	92	$600,000
Solar Arrays (8 kW)	80	80	80	$400,000
Power System & Structure	150	150	150	$300,000
Propellant Tank (disposable)	35	45	56	$50,000
Propellant (outbound + return)	278	358	449	Varies
Payload	1,000	1,000	1,000	-
Total Initial Mass (LEO)	1,635	1,725	1,827	-
Dry Tug Mass (reusable)	322	322	322	-
Tank + Propellant Mass	313	403	505	-

Assumptions: Tank mass = 12.5% of propellant mass; 4 thrusters for redundancy and faster transit; 8 kW solar arrays at 100 W/kg; structural mass estimated at 150 kg

Cost Analysis: Disposable Space Tug

Xenon Propellant

Cost Category	High Launch Cost ($1000/kg)	Low Launch Cost ($200/kg)
Tug Hardware	$1,300,000	$1,300,000
Propellant (278 kg @ $3000/kg)	$834,000	$834,000
Tank	$50,000	$50,000
Launch Cost (1,635 kg)	$1,635,000	$327,000
Total Cost	$3,819,000	$2,511,000
Cost per kg Payload	$3,819	$2,511

Krypton Propellant

Cost Category	High Launch Cost ($1000/kg)	Low Launch Cost ($200/kg)
Tug Hardware	$1,300,000	$1,300,000
Propellant (358 kg @ $300/kg)	$107,400	$107,400
Tank	$50,000	$50,000
Launch Cost (1,725 kg)	$1,725,000	$345,000
Total Cost	$3,182,400	$1,802,400
Cost per kg Payload	$3,182	$1,802

Argon Propellant

Cost Category	High Launch Cost ($1000/kg)	Low Launch Cost ($200/kg)
Tug Hardware	$1,300,000	$1,300,000
Propellant (449 kg @ $3/kg)	$1,347	$1,347
Tank	$50,000	$50,000
Launch Cost (1,827 kg)	$1,827,000	$365,400
Total Cost	$3,178,347	$1,716,747
Cost per kg Payload	$3,178	$1,717

Cost Analysis: Reusable Space Tug

Assumption: Tug already in orbit, only refueling (tank + propellant) and payload launch costs per mission

Xenon Propellant

Cost Category	High Launch Cost ($1000/kg)	Low Launch Cost ($200/kg)
Tank + Propellant (313 kg)	$884,000	$884,000
Launch: Tank + Propellant	$313,000	$62,600
Launch: Payload (1,000 kg)	$1,000,000	$200,000
Total Cost per Mission	$2,197,000	$1,146,600
Cost per kg Payload	$2,197	$1,147

Krypton Propellant

Cost Category	High Launch Cost ($1000/kg)	Low Launch Cost ($200/kg)
Tank + Propellant (403 kg)	$157,400	$157,400
Launch: Tank + Propellant	$403,000	$80,600
Launch: Payload (1,000 kg)	$1,000,000	$200,000
Total Cost per Mission	$1,560,400	$438,000
Cost per kg Payload	$1,560	$438

Argon Propellant

Cost Category	High Launch Cost ($1000/kg)	Low Launch Cost ($200/kg)
Tank + Propellant (505 kg)	$51,347	$51,347
Launch: Tank + Propellant	$505,000	$101,000
Launch: Payload (1,000 kg)	$1,000,000	$200,000
Total Cost per Mission	$1,556,347	$352,347
Cost per kg Payload	$1,556	$352

Summary Comparison

Scenario	Xenon ($/kg)	Krypton ($/kg)	Argon ($/kg)
Disposable Tug - High Launch Cost	$3,819	$3,182	$3,178
Disposable Tug - Low Launch Cost	$2,511	$1,802	$1,717
Reusable Tug - High Launch Cost	$2,197	$1,560	$1,556
Reusable Tug - Low Launch Cost	$1,147	$438	$352

Key Findings

Best Option: Reusable tug with Argon propellant at low launch costs = $352/kg
Propellant Choice: Argon offers the lowest cost despite lower ISP due to its dramatically lower price ($3/kg vs $3,000/kg for Xenon)
Reusability Impact: Reusable tug reduces costs by 40-80% compared to disposable, depending on scenario
Launch Cost Sensitivity: Low launch costs ($200/kg) reduce total mission costs by 50-70% compared to high costs ($1,000/kg)
Transit Time: With 4 thrusters (220 mN total), estimated spiral-out time from LEO is approximately 180-240 days, well within the 1-year requirement

Technical Notes

Delta-V estimates: LEO to TLI requires approximately 3,200 m/s for a low-thrust spiral trajectory; return from lunar vicinity to LEO requires approximately 900 m/s
Four thrusters provide redundancy and reduce transit time compared to a single thruster
Solar arrays sized at 8 kW (4 × 2 kW) with 100 W/kg specific power
Tank mass estimated at 12.5% of propellant mass for composite pressure vessels
ISP values for Krypton and Argon scaled by square root of atomic mass ratio from Xenon baseline

Electric Space Tug Analysis: LEO to Lunar Transfer

Mission Parameters

Propellant Properties

Mission Delta-V Analysis

Outbound: LEO to TLI (Δv = 3,200 m/s)

Return: TLI to LEO (Δv = 900 m/s)

Space Tug Component Masses

Cost Analysis: Disposable Space Tug

Xenon Propellant

Krypton Propellant

Argon Propellant

Cost Analysis: Reusable Space Tug

Xenon Propellant

Krypton Propellant

Argon Propellant

Summary Comparison

Key Findings

Technical Notes