The Sackträger is a rotating orbital elevator system introduced in ∀ Gundam, designed for transporting payloads between Earth and space.
Overview[]
The Sackträger is a specialized type of tether satellite, designed as a rotating tether system with its center of mass positioned in geostationary orbit. Often called a rotating orbital elevator or a rotovator, its purpose is to transport large payloads to and from orbit or even deeper into space without using rocket fuel.[1]
The Sackträger's rotation axis orbits 4,330 km above the Earth's surface. It completes one rotation approximately every two hours, with the barrel tip moving at about 3.7 km/s. Its orbital motion completes one revolution roughly every three hours, and at the release altitude, the velocity reaches about 8.7 km/s. The combined velocity at the time of payload release is approximately 12.4 km/s. The structure’s arm length, or rotational radius, is 4,250 km. At the recovery altitude, around 80 km above Earth, the motion of the barrel, when accounting for Earth's rotation as well as the Sackträger’s rotation and orbit, appears to move westward, opposite to the direction of Earth's spin. The time from capture to release, corresponding to half a rotation, is about one hour.[1]
By spinning, the Sackträger can transfer angular momentum to outbound spacecraft, effectively “throwing” them into space, or absorb momentum from incoming vehicles to slow and capture them. This mechanism is analogous to spinning a rope with weights attached at both ends, when released at the right moment, the object is flung outward by centrifugal force. The Sackträger operates on the same principle, transferring part of its rotational energy to launch payloads into space.[1]
If mass is only sent outward without capturing anything in return, the structure will eventually lose its rotation and become non-functional. Therefore, the system must capture inbound objects descending from space and absorb their momentum to maintain a net angular momentum balance. However, due to the immense mass of the Sackträger, it can launch several standard spacecraft consecutively without immediately compromising functionality. The system remains stable in the short term, but long-term imbalance would gradually degrade its performance.[1]
Structure & Operation[]
The Sackträger's central hub station sits at the midpoint of its orbit. From this massive structure, two tether cables stretch in opposite directions, each ending in a scoop (recovery) barrel designed to capture and dock with payloads. The hub station, literally the heart of the system, is an enormous space station that houses control rooms, living quarters, various payloads, ships, and even factory zones for repair and maintenance. The tether cables are composed of bundled artificial muscle fibers, products of nanotechnology and biotechnology. These fibers combine strength and flexibility, enabling near-perpetual function.[2]
The cables converge toward the ends and are hollow in structure, allowing them to transport captured spacecraft from the scoop barrels back to the hub station. The muscle fibers are re highly resistant to micrometeoroid collisions and impacts from off-course spacecraft and are capable of self-repair. Furthermore, the tethers can expand and contract, enabling the system to dampen irregular vibrations and correct imbalances caused by asymmetric payload distribution. The artificial muscle fiber layer connects the scoop barrel on one end, through the hub station, to the scoop barrel on the opposite end seamlessly. Each scoop barrel is a massive hollow cylinder outfitted with internal arms and securing mechanisms for incoming spacecraft. The outer rims of the barrels are lined with flexible body flaps, which provide aerodynamic control during atmospheric entry and exit.[2]
The Sackträger offers numerous advantages when operated on Earth. Compared to conventional rockets, it requires significantly fuel for both launch and descent, offering a lower operational cost, even if not as economical as a fixed orbital elevator. Its environmental impact is minimal; as space travel became more frequent, the growing concerns of rocket exhaust pollution and global warming highlighted the need for cleaner alternatives, and Sackträger presents itself as a sustainable solution. It also provides a gentler experience for passengers and cargo, rarely exceeding 3G during acceleration and deceleration, significantly reducing physical stress. In terms of infrastructure, the Sackträger is semi-permanent and requires little maintenance. With boundary-layer control via deployed fields, self-repairing nanomachines, and orbital correction using electromagnetic interaction with Earth's magnetic field, it operates with near-maintenance-free longevity.[2]
Its orbital path, located roughly 4,400 km above Earth, is much lower than the 36,000 km geostationary orbit required by fixed elevators. This substantially reduces material requirements and construction complexity, making it easier and more efficient to build. Moreover, it allows for multiple rendezvous points on Earth. Completing one orbit every three hours, the system supports docking with scoop barrels at three equatorial locations at one-hour intervals, something a fixed elevator would need three separate towers to replicate, an impractical feat over oceans or rugged terrain. In contrast, Sackträger is unburdened by such geographical constraints.[2]
The operation of the Sackträger posed significant engineering challenges and necessitated a series of technological breakthroughs. One of the most critical threats to long-term system operation is orbital decay due to decreased orbital speed over time. Over extended periods, various factors are expected to cause the Sackträger's orbit to gradually descend. Additionally, the scoop barrels located at both ends of the cable pass through Earth’s atmosphere once every two hours. Although the Sackträger aligns its rotation and revolution speeds to reduce horizontal movement within the atmosphere to near-zero, some components, particularly the scoop barrels, still collide with atmospheric molecules at speeds exceeding 10,000 km/h, despite the thin air. This, too, presents a non-negligible factor for long-term use.[3]
To address these issues, the designers of the Sackträger incorporated a number of technological breakthroughs. One such advancement is the application of fields derived from Minovsky physics. The Sackträger is continuously protected by a finely tuned low-level field, which helps to prevent friction with the atmosphere and collisions with micro-meteoroids. Around the scoop barrels, the field becomes more active, working in tandem with body flaps to actively control the Sackträger’s motion. This system also facilitates the capture and stabilization of incoming payload craft attempting to dock with the scoop barrels.[3]
To prevent orbital decay, the Sackträger uses electromagnetic interactions between Earth’s magnetic field and the materials in its rotating components. This mechanism allows the structure to maintains its position continuously along the designated orbit. In cases of mechanical failure or material degradation, the nanomachines built into the Sackträger autonomously repair damaged components. These nanomachines require periodic resupply of raw materials, a task managed by the payload craft servicing the system. However, resource depletion is minimal. Initial estimates suggest that, even without resupply, the Sackträger could sustain autonomous operations and self-repair for over 5,000 years using its internal stockpile.[3]
History[]
The origins of the Sackträger system can be traced all the way back to the 1960s of the Gregorian calendar. The first to bring this concept to public attention was Russia’s Yuri Artsutanov. Later, American thinkers such as Hans Moravec and Robert L. Sheffield refined the idea and explored its technical feasibility.[3] However, as humanity’s activities expanded into space and the mass production of reliable, low-cost rockets became feasible, this once-fascinating transit system fell into obscurity. Behind this shift was a complex web of factors: the ascension of traditional space companies into powerful industrial foundations through rocket manufacturing; conflicts with emerging space enterprises focusing on megastructures like orbital elevators; and the military's prioritization of mobility and durability over cost-efficiency. These dynamics collectively influenced the decline of the concept. Unfortunately, due to the loss of many historical records, the full extent of these influences can no longer be definitively verified. The Sackträger system would not return to the stage of history until the end of the war-torn Universal Century era.[3]
As the repeated great wars of space in the late Universal Century began to wane, Earth’s natural resources had been nearly exhausted through endless wars of attrition. Despite this depletion, Earth remained the political and cultural center of the human sphere, and rebuilding its civilization became an urgent priority. To achieve this, vast quantities of mineral resources were needed, and the only viable source was beyond Earth. Records indicate that during this period, countless resource-rich asteroids were relocated to near-Earth orbit. Fixed orbital elevators, considered the predecessors to the Sackträger, were constructed to transport these space-based resources back to Earth. At the same time, these megastructures also served as monuments, symbolizing the end of humanity’s long history of warfare and the dawn of a new era of peace. For several centuries following the construction of the orbital elevators, the human sphere enjoyed a sustained period of peace. Multiple orbital elevators were established on Earth during this time. One of their ground-based anchor points appears to have been a place known as "Maniupich". Evidence confirms the existence of an operational mass driver in Maniupich, which is believed to have functioned as a facility for distributing the materials brought down by the elevators to other regions.[4]
Centuries later, however, another large-scale space war erupted. Although the details remain obscure, the intensity of the conflict led to the destruction and collapse of the entire orbital elevator network. Debris from the collapsed structures rained down from orbit and caused catastrophic damage across the Earth. This devastation is echoed in folklore suggesting that parts of the collapsed elevators eventually became the Sackträger, though this is historically inaccurate. One such legend is the “Bough of Ades,” still told in Maniupich. In reality, there is no direct continuity between the ruined orbital elevators and the Sackträger. The two were constructed independently in entirely separate eras. Nonetheless, the overwhelming scale of the elevator catastrophe caused historical records to lose accuracy. As memory was compressed and unconscious historical revisionism crept in, the two megastructures became fused in collective memory.[4]
Incidentally, in Maniupich, there exists a mask that only the king is permitted to wear. This mask closely resembles a helmet from an earlier era of space suits, leading researchers to believe that other culturally and historically significant traditions may have remain preserved in this region. In any case, the fixed orbital elevators were never rebuilt after their collapse. In their place, a new structure was created, one not fixed to the ground: the rotating orbital elevator, Sackträger. The term is derived from an old regional dialect of Europe (modern-day Gaul), namely German, where it means “bagworm”. The name is thought to have originated because, from the surface of Earth, the Sackträger’s movement as it entered and exited the atmosphere resembled a bagworm dangling and moving up and down from the sky. The reason why a German word came to be used remains unknown, as no surviving records provide an answer.[4]
In the year C.C. 2345, the Sackträger remained operational in Earth's orbit, and was one of the few available means of reaching the Moon.[3] Amidst escalating political tensions and internal coups within the Moonrace, Dianna Soreil was covertly taken back to the Moon aboard the Gendarme. The ship launched from Earth using the mass driver at Maniupich to the Sackträger, At the same time, the Willgem, carrying Kihel Heim (posing as Dianna), also launched to the Sackträger, assisted by Loran Cehack in the ∀ Gundam and Harry Ord in the Gold SUMO. Following a standoff aboard the Sackträger and subsequent de-escalation, both the Gendarme and the Willgem departed the orbital elevator and headed for the Moon.
Gallery[]
Animation[]
∀ Gundam[]
References[]
| Correct Century | |
|---|---|
| Anime | ∀ Gundam | Comprehensive Episode Listing |
| Films | ∀ Gundam I: Earth Light | ∀ Gundam II: Moonlight Butterfly |
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| Books | ∀ Gundam (Manga) | ∀ Gundam (Manga 2) | ∀ Gundam: Wind of the Moon | ∀ Gundam: Episodes | ∀ Gundam (Novel) | ∀ Gundam (Novel 2) |
| Timelines | Ad Stella | Advanced Generation | After Colony | After War | Anno Domini | Build Fighters | Correct Century | Cosmic Era | Future Century | Mars Century | Post Disaster | Regild Century | SD Gundam | Universal Century |