Electric Space Tug Design: LEO to Lunar Flyby with Handover to Tether
Propellant Properties
| Propellant | ISP (s) | Exhaust Velocity (m/s) | Price ($/kg) |
|---|
| Xenon | 4500 | 44145 | 5000 |
| Krypton | 5620 | 55132 | 2500 |
| Argon | 8145 | 79902 | 10 |
Note: To meet the 1-year or less transit time requirement for the outbound leg, 6 Turion TIE-20 GEN2 thrusters are used for all propellants (total thrust: 330 mN, total power: 12,000 W).
Xenon Case
Masses
| Component | Mass (kg) |
|---|
| Thrusters (6x) | 138 |
| Solar Arrays | 60 |
| Structure | 20 |
| Tank | 55 |
| Propellant Outbound | 227 |
| Propellant Return | 47 |
| Total Propellant | 274 |
| Tank + Propellant | 328 |
| Dry Mass (bus + tank) | 273 |
| Whole Tug Mass (dry + propellant) | 546 |
Costs
| Component | Cost ($) |
|---|
| Thrusters | 900,000 |
| Solar Arrays | 1,200,000 |
| Structure | 20,000 |
| Tank | 27,354 |
| Propellant | 1,367,685 |
| Tank Full (tank + propellant) | 1,395,039 |
| Whole Tug (all above) | 3,515,039 |
Mission Times
Outbound: 351 days
Return: 73 days
Cost Analysis
| Case | Total Mass Launched (kg) | Other Costs ($) | Launch Costs ($) | Total Costs ($) | Cost per kg Payload ($/kg) |
|---|
| Disposable HighCost | 1546 | 3,515,039 | 1,546,000 | 5,061,039 | 5,061 |
| Disposable LowCost | 1546 | 3,515,039 | 309,200 | 3,824,239 | 3,824 |
| Reusable HighCost | 1328 | 1,395,039 | 1,328,000 | 2,723,039 | 2,723 |
| Reusable LowCost | 1328 | 1,395,039 | 265,600 | 1,660,639 | 1,661 |
Krypton Case
Masses
| Component | Mass (kg) |
|---|
| Thrusters (6x) | 138 |
| Solar Arrays | 60 |
| Structure | 20 |
| Tank | 42 |
| Propellant Outbound | 175 |
| Propellant Return | 35 |
| Total Propellant | 211 |
| Tank + Propellant | 253 |
| Dry Mass (bus + tank) | 260 |
| Whole Tug Mass (dry + propellant) | 471 |
Costs
| Component | Cost ($) |
|---|
| Thrusters | 900,000 |
| Solar Arrays | 1,200,000 |
| Structure | 20,000 |
| Tank | 21,056 |
| Propellant | 526,388 |
| Tank Full (tank + propellant) | 547,443 |
| Whole Tug (all above) | 2,667,443 |
Mission Times
Outbound: 339 days
Return: 68 days
Cost Analysis
| Case | Total Mass Launched (kg) | Other Costs ($) | Launch Costs ($) | Total Costs ($) | Cost per kg Payload ($/kg) |
|---|
| Disposable HighCost | 1471 | 2,667,443 | 1,471,000 | 4,138,443 | 4,138 |
| Disposable LowCost | 1471 | 2,667,443 | 294,200 | 2,961,643 | 2,962 |
| Reusable HighCost | 1253 | 547,443 | 1,253,000 | 1,800,443 | 1,800 |
| Reusable LowCost | 1253 | 547,443 | 250,600 | 798,043 | 798 |
Argon Case
Masses
| Component | Mass (kg) |
|---|
| Thrusters (6x) | 138 |
| Solar Arrays | 60 |
| Structure | 20 |
| Tank | 28 |
| Propellant Outbound | 116 |
| Propellant Return | 22 |
| Total Propellant | 139 |
| Tank + Propellant | 166 |
| Dry Mass (bus + tank) | 246 |
| Whole Tug Mass (dry + propellant) | 385 |
Costs
| Component | Cost ($) |
|---|
| Thrusters | 900,000 |
| Solar Arrays | 1,200,000 |
| Structure | 20,000 |
| Tank | 13,856 |
| Propellant | 1,386 |
| Tank Full (tank + propellant) | 15,241 |
| Whole Tug (all above) | 2,135,241 |
Mission Times
Outbound: 325 days
Return: 63 days
Cost Analysis
| Case | Total Mass Launched (kg) | Other Costs ($) | Launch Costs ($) | Total Costs ($) | Cost per kg Payload ($/kg) |
|---|
| Disposable HighCost | 1385 | 2,135,241 | 1,385,000 | 3,520,241 | 3,520 |
| Disposable LowCost | 1385 | 2,135,241 | 277,000 | 2,412,241 | 2,412 |
| Reusable HighCost | 1166 | 15,241 | 1,166,000 | 1,181,241 | 1,181 |
| Reusable LowCost | 1166 | 15,241 | 233,200 | 248,441 | 248 |
Time Value of Money Analysis
The lowest cost per kg payload from above is $248/kg (Argon, Reusable, LowCost launch).
Assuming a 10% annual interest rate for time value of money on the reusable tug capital cost ($2,120,000 for thrusters, solar, and structure), and assuming one mission per year, this adds an opportunity cost of $212,000 per mission, or $212/kg payload.
Adjusted best cost: $248 + $212 = $460/kg.
Note: This does not include time value for the payload itself, as its value was not specified. If the payload is valued at $10,000/kg, an additional $1,000/kg would be added (10% of $10,000).