PRE-PHASE A · CONCEPT · Doc rev 0.2 · Updated tug.flight
TUG Reusable cislunar transit stage
00 Concept brief

Cargo to cislunar
on a reusable Tug.

A rail launch lofts a ballistic pod to apogee. A reusable Tug — already circling in a phasing orbit — performs apogee rendezvous, captures the pod, and burns trans-lunar injection. The Tug returns. The pod continues to the Moon.

8–10km/s
Tug ΔV / lifetime
~150km
Pod apogee target
≥10×
Tug reuse cycles
0kg
Pod propellant to TLI
See the orbit Run the ΔV calc →
01Mission overview

Decouple lift from transit. Reuse the expensive part.

The cargo chain is three vehicles, one mission. A magnetic rail does what magnetic rails are good at — accelerating dumb mass cheaply. A ballistic pod does what dumb cargo can — coast. The Tug does what only an active spacecraft can — match orbits, capture, and burn for somewhere else.

Nothing on the pod has to survive a return trip. Nothing on the rail has to fly. The Tug is the only piece that must be precise, recoverable, and reusable — so make it the only piece you build well.

↻

Reusable where it matters

The Tug catches, transfers, and returns. ≥10 cycles per airframe.

∅

Zero pod propellant

Pods are inert mass with a beacon. All ΔV lives on the Tug.

↗

Cadence over capacity

One catch per pod. Throughput scales with rail launches, not Tugs.

02Concept of operations

Eight steps from rail to lunar handoff.

A nominal mission, summarized at flight-card resolution.

  1. T+0 T-00

    Rail launch

    BGKPJR rail accelerates 5,000 kg pod to ~6.4 km/s, 34.93°N.

  2. T+02m T-01

    Coast to apogee

    Ballistic arc; pod cold-gas detumbles, broadcasts beacon.

  3. T+04m T-02

    Apogee rendezvous

    Tug already in phasing orbit; closes to within 200 m.

  4. T+05m T-03

    Capture

    Compliant net intercepts at < 0.8 m/s; clamp to cradle.

  5. T+02h T-04

    TLI burn

    Single-burn ~3.15 km/s departure to lunar transfer.

  6. T+72h T-05

    Lunar SOI

    Cross lunar SOI; pod release with retro pulse.

  7. T+04d T-06

    Tug return

    Lunar gravity-assist or direct return burn back to phasing orbit.

  8. T+07d T-07

    Re-arm

    Catch-up burns + plane clean for next pod window.

03Orbit + transit

The geometry, in motion.

Phasing orbit (green), trans-lunar ellipse (amber), lunar orbit (grey). Scrub the timeline. All distances are real ratios; bodies are sized for legibility.

04Live ΔV calculator

Tune the mission. Watch propellant move.

Tsiolkovsky over a stacked phase budget. TLI ΔV recomputes from your apogee input; propellant carries forward through every prior burn.

Total ΔV 13.91 km/s
Propellant 463,884 kg
GTOW 473,084 kg
Mass fraction 98.1%
PhaseΔV (km/s)Share
Phasing trim0.10 0.7%
Apogee rendezvous0.05 0.4%
Catch + circularize6.13 44.1%
TLI burn3.15 22.6%
Mid-course corr.0.05 0.4%
Pod release0.02 0.1%
Return to LEO2.20 15.8%
Plane / phase clean0.40 2.9%
Margin 15%1.81 13.0%
vs canonical mission preset: 0.00 km/s
05Mass + power budget

Every kilogram, every watt, in one view.

Toggle metric. Bars are sorted by share so the dominant cost line surfaces first.

2,695 kg 9 subsystems
  • Primary structure & MMOD shielding 820 kg
  • Main propulsion (LOX/CH₄ bipropellant) 540 kg
  • Cryogenic tanks + insulation 380 kg
  • Capture mechanism (compliant net + clamps) 310 kg
  • EPS (solar + Li-ion) 230 kg
  • GNC (avionics + sensors) 140 kg
  • Thermal control (active + passive) 110 kg
  • Reaction control (16× RCS thrusters) 90 kg
  • Communications (S+Ka) 75 kg

Sorted by mass. Mass excludes propellant (LOX + CH₄ ≈ 9,000 kg @ baseline ΔV). Power is peak draw across nominal modes; cruise consumes ≈ 60% of peak.
06Vehicle dossier

Subsystems with TRL, mass, power, and notes.

Click any panel to expand technical detail and watch-items.

Primary structure & MMOD shielding 820 kg 0 W TRL 8

Aluminum-lithium honeycomb truss with deployable Whipple shielding around prop tanks and capture mechanism.

  • 3 hard-points for pod cradle
  • Rad-9 micrometeoroid spec
  • 5 yr LEO lifetime margin
Main propulsion (LOX/CH₄ bipropellant) 540 kg 220 W TRL 6

Single throttleable cryogenic main engine, 25 kN class, vacuum Isp 360 s.

  • Pump-fed, 60 % throttle range
  • Restartable up to 50 cycles
  • Cryo settling via aux RCS
Reaction control (16× RCS thrusters) 90 kg 60 W TRL 9

Hypergolic MMH/NTO 22 N pods for fine attitude + sub-m/s closing burns at capture.

  • Cross-string redundancy
  • Min impulse bit < 5 mN·s
  • Common feed lines, two banks
Cryogenic tanks + insulation 380 kg 50 W TRL 7

Composite-overwrap cryo tanks with multilayer insulation and ZBO subcooler. Boil-off held < 0.1 %/day.

  • LOX 7,200 kg
  • CH₄ 1,800 kg
  • ZBO active cryo cooler 50 W
Capture mechanism (compliant net + clamps) 310 kg 80 W TRL 3

Articulated truss-deployed compliant net with motorized clamp transfer to hard-point cradle.

  • ±0.4 m positional tolerance
  • 0.8 m/s max closing at contact
  • TRL gating risk — see risks register
GNC (avionics + sensors) 140 kg 220 W TRL 8

Triple-redundant flight computers, dual star trackers, IMU stack, lidar + RGB stereo for terminal capture.

  • Sub-arcsec attitude knowledge
  • Onboard relative-orbit Kalman filter
  • TRL gated by lidar at capture range
Communications (S+Ka) 75 kg 140 W TRL 9

S-band omnis for safe-mode plus Ka-band steerable for high-rate telemetry on TLI.

  • TT&C link budget closes at lunar SOI
  • Cross-link to Manna pods during catch
EPS (solar + Li-ion) 230 kg 0 W TRL 9

Two deployable solar wings (5.6 m²), 28 V bus, 1.2 kWh Li-ion buffer for eclipse + peak-burn comms.

  • End-of-life array power 1.7 kW
  • Sun-pointed during cruise
Thermal control (active + passive) 110 kg 90 W TRL 9

Loop-heat-pipe radiators for avionics; MLI plus VCHPs for cryo tank zone; survival heaters on hypergols.

  • −40 °C → +60 °C control
  • Single-string survival heaters always live
Dry mass2,695 kg
Peak power860 W
Subsystems9
07Risks register

Likelihood × Consequence, with mitigations.

Click a risk pill to see its mitigation. Pills cluster in the top-right when capture or thermal threats compound.

L = 1
L = 2
L = 3
L = 4
L = 5
C = 5
C = 4
C = 3
C = 2
C = 1
Likelihood → ↑ Consequence
08Field comparison

Where the Tug sits beside operational and concept tugs.

Vehicle Status Payload (kg) Reuses Primary route Capture / dock Notes
MEV-1 (Northrop) operational — 5 GEO life-extension LAE / docking probe Operational since 2020. Docks to satellites for station-keeping; not a cargo carrier.
Mission Extension Pod (MEP) in-dev — 1+ GEO Bolt-on jet pack Smaller, single-host MEP successor.
ACES / Centaur V (cislunar tug) concept 20,000–40,000 3–5 LEO ↔ Lunar Standard docking Crew + cargo upper stage with refuelable LH₂/LOX.
Starship as tug in-dev 100,000+ 100 LEO ↔ Anywhere Pez deploy / TBD Brute force — orbital refueling required for cislunar duty.
TUG (this concept) this 5,000 10 Apogee → Lunar Compliant net + clamp Catches rail-launched ballistic pods at apogee; no propellant on the pod.