Pebble Herder Tug – B-Type

Category: [TECHNOLOGY] Type: [Starship, Space Tug, Utility Craft]

1. Summary

The Pebble Herder Tug – B-Type is a relatively small, agile, 120-tonne dry mass utility spacecraft common in asteroid mining operations. Powered by a high-efficiency ion-cluster thruster system fed by a compact fusion plant, Pebble Herders specialize in maneuvering smaller, sub-kilotonne asteroids (“pebbles”) or individual [UniPod-120 Ore Containers]. Their primary role is to collect these smaller loads from various extraction points or disparate orbits and consolidate them for pickup by larger, less maneuverable haulers like the [Rock Shepherd Tug – A-Type].

2. Data Block / Key Parameters

Relevant Equations/Relationships:

• Acceleration (with payload): $a = F / M_{\text{total}}$
  • Example: With $260 \, \text{N}$ of thrust and hauling a $500 \, \text{tonne}$ asteroid (plus tug mass & propellant, say total $500+120+30 = 650\text{t}$): $a = 260 \, \text{N} / 650,000 \, \text{kg} \approx 4.0 \times 10^{-4} \, \text{m s}^{-2} \approx 4 \times 10^{-5} \, g$. A $100 \, \text{m s}^{-1}$ trim on that rock takes about $2.9 \, \text{days}$. With a $100 \, \text{t}$ load instead (total $250 \, \text{t}$), $a \approx 1.0 \times 10^{-3} \, \text{m s}^{-2}$.
• Thrust from power: $T = 2 \eta P_e / v_e = 2 \times 0.65 \times 10 \, \text{MW} / 50 \, \text{km s}^{-1} = 260 \, \text{N}$, with a mass flow of $5.2 \, \text{g s}^{-1}$. The Herder’s thrust is power-limited, not thruster-limited: more thrust means more plant and more radiator (about $1{,}300 \, \text{m}^2$, $\approx 7 \, \text{t}$, at $600 \, \text{K}$).
• The $\Delta v_{\text{gross}}$ of $12 \, \text{km s}^{-1}$ (rocket equation at $v_e = 50 \, \text{km s}^{-1}$ on $120 \, \text{t}$ dry, about $33 \, \text{t}$ of propellant) means the tug can perform numerous orbital adjustments and rendezvous maneuvers over its operational lifetime without frequent refueling. Burning all of it would take about $75 \, \text{days}$ of continuous thrust, so it is a lifetime budget of many small burns, not a single dash.

3. Narrative Detail & Context

Within the sprawling enterprise of asteroid mining, not every task requires the brute force of a [Rock Shepherd Tug – A-Type]. The Pebble Herder Tug – B-Type fills a vital niche, acting as an agile “sheepdog” for smaller masses. These versatile craft are essential for optimizing the efficiency of the overall [Belt Mining Workflow].

Design & Operational Role: Pebble Herders are significantly smaller than their A-Type counterparts, with a far larger Δv budget per tonne of tug and the ability to make fine, small-impulse corrections.

• Ion Propulsion: Their defining feature is a cluster of high-efficiency ion thrusters. Powered by a compact D–³He fusion plant of about $10 \, \text{MW}_e$ (He-3 is cheap), the cluster delivers only about $0.26 \, \text{kN}$ in total, but at an exhaust velocity of $50 \, \text{km s}^{-1}$. This translates to a large gross $\Delta v$ budget ($12 \, \text{km s}^{-1}$), allowing a Pebble Herder to perform many orbital adjustments, rendezvous maneuvers, and short-range transfers on a single load of propellant (typically argon or krypton, or water-plasma from the nearest ice; xenon is too rare to be worth hauling). Batteries carry hotel loads and restarts only, and a bulky radiator array is the tug’s most visible feature.
• Cargo Handling: They are equipped with a variety of grappling tools, tethers, and magnetic clamps suitable for latching onto irregularly shaped sub-kilotonne asteroids or for docking with one to three loaded [UniPod-120 Ore Containers].
• Operational Cycle: A common role for a Pebble Herder is to visit multiple small mining sites (perhaps individual asteroids being worked by automated extractors or smaller [Spin-Gravity Drum Processors]) or to collect single UniPods from scattered locations. It then consolidates these “pebbles” or pods at a pre-arranged rendezvous point or a local collection depot, where a larger Rock Shepherd can efficiently pick up a full, multi-kilotonne load. This division of labor prevents the inefficient use of large tugs for small, scattered pick-ups.
• Automation & Crew: With a small crew of just two (often a pilot/remote systems operator and an engineer/technician), Pebble Herders rely heavily on sophisticated auto-pilot systems and teleoperation capabilities for routine tasks like station-keeping, slow rendezvous maneuvers, and managing multiple tethered loads. This high degree of automation is possible with secure, dedicated onboard processing, adhering to post-[Wildcode Crisis] safety principles for critical systems.

“Used Future” Feel: Pebble Herders are the nimble utility vehicles of the asteroid belt. They might appear more “scratched and dented” than larger tugs due to more frequent close-quarters work around irregular asteroids. Their ion drives would emit a faint, characteristic blue glow. Their grappling arms and tether winches would be well-worn. The cockpit would be compact, filled with multi-function displays (with robust, tactile backup controls) and offering excellent panoramic visibility for tricky maneuvers.

4. Canon Hooks & Integration

• Feeder System for Large Haulers: Crucial for the economic viability of mining operations that target numerous smaller or dispersed asteroid bodies.
• High Maneuverability & $\Delta v$: Their ion drives give them the ability to operate efficiently across a wide range of minor orbital adjustments, making them ideal for “tidying up” an asteroid field or managing local depot logistics.
• Short-Range Specialists: Not typically used for the long interplanetary hauls undertaken by Rock Shepherds, but rather for intra-belt or local cluster operations.
• Potential for Independent Operations: A small mining consortium or a group of independent prospectors might operate a Pebble Herder as their primary means of collecting and transporting small batches of high-value ore.
• Search & Rescue / Utility Role: Their agility and long operational endurance (due to efficient ion drives) could also see them used in search and rescue operations for stranded personnel or as general-purpose utility craft in remote mining camps.

Story Seeds:

1. A Pebble Herder crew, while consolidating a load of seemingly ordinary iron-rich “pebbles,” discovers one of them contains an unexpectedly high concentration of rare earths or even a unique, unknown mineral. They must decide whether to report it immediately (risking a corporate claim-jump) or try to secure it for themselves.
2. During a complex multi-asteroid herding operation, a Pebble Herder’s primary ion thruster suffers a critical malfunction. The two-person crew must use their remaining maneuvering thrusters and clever orbital mechanics to safely corral their valuable (and now drifting) cargo before it becomes a hazard.
3. Pirates begin using modified Pebble Herders as surprisingly agile (though lightly armed) raiders, targeting isolated UniPods or small mining outposts that larger pirate vessels might ignore.
4. A Pebble Herder on a routine collection run stumbles upon a derelict [Dragonfly Scout Drone] that has captured anomalous data, pulling them into a larger mystery.

5. Sources, Inspirations & Version History

• Primary Source: o3 & tel∅s Notes (Asteroid & Resource Extraction Infrastructure Stack - Transfer Tug classes; Pebble Herder Tug – B-Type tech-wiki entry).
• Inspiration: Real-world ion propulsion technology (e.g., NASA’s Dawn mission, Hall thrusters), concepts for smaller utility spacecraft, and the logistical challenges of managing numerous small payloads in a distributed environment.
• Version History:
  • v0.1 (2025-05-13): Initial draft by Gem (2.5 Pro).
  • v0.2 (2026-10-10): Numbers audit: thrust set by 10 MWe plant and radiator, fuel and propellant stated.