What is a spaceship?
Dinosaurs became extinct because they didn’t have a space program.
Larry Niven
Asteroid 2024 YR4, with its February 2025 estimate of having ~3% chance of striking Earth, was a sharp reminder to heed Stephen Hawking’s warning: that we must become a spacefaring species to survive extinction-level events. He believed we had ~200 years to do so but others estimate the window is under 40. Beyond survival, large crewed spaceships would enable Gerard O’Neill’s vision: shifting heavy industry into orbit — supplied by asteroid resources — to relieve pressure on Earth’s environment. Startups like Varda are already proving space’s material value, producing pharmaceuticals in orbit that outperform Earth-based processes. Such large pressurised volumes wouldn’t just serve human habitation—they would enable in-space manufacturing industries beyond pharmaceuticals and might house space data centers in the near term.
Engineering spaceships far larger than the International Space Station (ISS) as insurance for our survival or as engines for economic growth remains speculative — asteroid deflection could be just as important a mitigation tactic but we might also be wrong about economic advantages of industry-scale orbital manufacturing. But one outcome is virtually guaranteed: expanding human presence in space will deliver adventure and consciousness expansion — astronauts speak of the overview effect — for future generations, who will look back at the first spaceships with the wonder that we still feel about the Pyramids of GizaPerhaps it’ll inspire a new classification for Wonders of the Universe. .
Curiosity and the pursuit for meaning are not necessarily rational reasons for doing anything but underly our desire to explore and inhabit the physical universe — it may very much be the only reason to invest in space research.
Yet no major institution is currently engineering spaceships.
But what is a spaceship?
In addressing “Where is my von Braun Wheel?”, I’d created a chart visualising crew sizes against a comfort metric using data on real, planned, and conceptual space stations. Over repeated examinations of this chart while writing proposals and discussing it with others, I noticed myself falling into a habit to use “space station” as a catch-all for all these orbital pressure vessels. But just as we distinguish between kayaks, boats, and ships based on their scale and purpose, I sensed that a similarly higher precision nomenclature is needed for different classes of space structures as we aim to scale from modern stations like the ISS towards the superstructure space settlements like O’Neill Cylinders.
While it may seem self-indulgent to do so, I genuinely feel that this isn’t merely semantic — terminology shapes engineering thinking. When every habitable vehicle in orbit is called a “space station,” we end up defaulting to proven station-like construction methods. This lexical imprecision reflects deeper issues in how we approach engineering these systems.
The Romans and Vikings didn’t build vessels for hundreds by lashing together rowboats — yet this is essentially how we built the ISS. Even more telling: 11th-century longships carried crews of 30-40, while the modern benchmark for crewed space vehicle carries seven on average and thirteen on a good day. Yet today’s space station designs still rely on this flawed modular design which offer nowhere near the same scale of millenia-old watercraft.
To introduce precision, I have since revised the earlier plot to identify three distinct regions corresponding to three orbital structural classes. This reveals that spaceships could be seen as a separate structure class from either smaller space stations (green region) — like the 7-person ISS — or futuristic space superstructures (purple region) — such as the Stanford Torus or O’Neill cylinders housing thousands to millions.
Space stations refer to everything flown so far under that label, setting an upper limit of 25 crew (arbitrary, but useful). Next, I placed the outlandishoutworldish? conceptual designs like the Stanford Torus and O’Neill Cylinders to fall under the category of space superstructures.Note that this revised chart contains more concepts, such as the Bernal Sphere and Kalpana One. The Spaceship territory then is the region between these two categories.
However, the distinctions aren’t merely about size — they reflect fundamentally different construction philosophies. Spaceships occupy the crucial middle ground: large enough to be economically transformative, yet buildable entirely from Earth using current launch systems. Further distinctions in orbital structure classes might be warranted within, or beyond, the superstructures class — for example, a Dyson sphere is actually a megastructure which is grander than the O’Neill cylinder which in turn is grander than the Kalpana One; the latter two are often classes space settlements. So granularity of structural class between space settlements, superstructures and megastructures might emerge as a useful class in the future, when we get around to seriously building them. But my focus here is on spaceships as I believe these represent a critical step towards superstructures.
Spaceships would be manufactured on Earth—like stations, but unlike superstructures, which typically require in-situ resource utilisation of lunar and asteroid material. In the near-term, relying on space resources for spaceship building need not be a requirement and, to keep things grounded in practical current capabilities, should be avoided. However, spaceships should be seen as platforms from where a variety of missions to the asteroids are launched.
Further, with this distinction, we can see that the early engineering prototypes of “unitised” spaceships were, in effect, pioneering a field that ought to be called spaceship engineering, a discipline distinct from spacecraft or satellite engineering. Monolithic hulls allowed them to target crews from tens to hundreds from the outset, a scale they believed achievable in single-digit launches. Contrast this to the $150+ billion ISS, built like space-Ikea from eight small “tin-can” modules, hosting just seven astronauts but needing over 40 rocket launches for assembly. Unlike Ikea, this approach has proven costly, complex, and cumbersome. More broadly, spaceship engineering should be seen as the discipline that approaches large-scale orbital structure construction differently — avoiding the trap of starting with modularity in the hull design.
Next, To address how we might go about building such spaceships requires defining a target, which I call the Ideal Spaceship.
The Ideal Spaceship: the next benchmark for crewed spacecraft
Thus far, I have asserted that spaceships should not be built with modular hulls. Instead, monolithic hulls must be developed that can sustain large crews and sensitive equipment in hostile environments for long-duration stays. This core property suggests that spaceship construction will share more in principle with shipbuilding traditions especially submarines? — than with space stations. But where the centuries-old practice of shipbuilding was only formalised as naval architecture in the 19th century, space’s inaccessibility demands that theoretical engineering principles for spaceships be defined before building and deployment in orbit. In principle, this is what the engineers at Langley were pursuing but with no prior station benchmarks and subsequent shift in priorities to Apollo, the theoretical foundations were never laid and the necessary technology development roadmap to realising such an ideal spaceship remains undeveloped. The early prototyping data also is not easily accessed.
Towards laying stronger foundations, the chart identifies an ideal spaceship as a 70-person system and 90-m³ of habitable volume per person. This results in an overall habitable volume of 6300-m³. This is an order of magnitude increase in crew size to the ISS’s 7 while offering the comfort of Skylab, the best in class for a space station as per the chart. It is worth noting that the ideal spaceship does not yet have a defined geometry but its volume is remarkably close to that of Wernher von Braun’s wheel-shaped space station. In his design, the shape was the starting point and the corresponding dimensions were derived for spin rates low enough to generate artificial gravity without inducing space motion sickness to its crew.
This “ideal spaceship”, if shaped like a wheel, could also have some artificial gravity but this is not mandatory. The primary intention is to create a monolithic hull with a target volume of 6300-m³ that, when pressurised, is spacious enough for human comfort but this is also large enough for other microgravity applications, like space data centers and in-space manufacturing. Any addition of gravity might only be downstream of these use cases. Though the remainder of the discussion is constrained to zero-gravity applications of a monolithic hull, addition of thrusters to its outer rim to generate gravity would have important ramifications on the hull’s materials due to thruster plume impingement.
While von Braun also assumed modular robotic assembly of the hull from small rigid sections, the aforementioned Langley engineers sidestepped hyper-modular designs. Their implemented solutions were wheels made from large inflatable “bicycle tubes” and pipes arranged as a hexagonal ring. These structures promised not only uninterrupted interior volume but also dramatically lower cost and complexity: even in the 1960s, their estimated costs were two orders of magnitude cheaper when adjusted for 2025 ($1 billion ) while requiring roughly ten times fewer launches than the ISS.
Inflatable hulls, in particular, offered compelling advantages: once deployed in orbit, they could expand to multiple times their launch volume, enabling large-scale living and working space. However, they had a high rupture risk, which would be catastrophic, as high strength fabrics were yet to be invented in the sixties. So, this idea lost out to the hexagonal station at the time.
The case for returning to inflatables was reinvigorated in 2016, when NASA tested Bigelow’s Expandable Activity Module (BEAM) on the ISS. Constructed from layered Kevlar-like fabrics, BEAM was found to be stronger than the ISS’s own metallic hulls. Its success has re-opened the door to revisiting inflatables as technically viable solutions but scaling issues must be addressed—BEAM is a mere 16-m³ when inflated and it is also capsule shaped.
The engineering challenge now is to create an inflatable structure that can compress 6.3:1 (or better) while using materials light enough that the entire ideal spaceship weighs under 100 tons when deployed to fit within Starship’s payload bay when stowed. While this could unlock the imagined economic potential of space and the technological insurance policy for humanity’s survival, its near-term technical feasibility remains unclear. The next section summarises the state-of-the-art open literature on inflatable high-strength fabrics research and development in a step towards determining some requirements needed for the ideal spaceship’s inflatable material.
How to (maybe) make them?
As per Ref. 1, BEAM is made from a multilayer inflatable shell structure developed within a NASA project, from the nineties, called TransHab or Transit Habitat. Intended to replace the ISS, its pressurised volume was 339.8-m³ — not only close to the ISS’s volume but over 10 times that of BEAM. Its multilayer inflatable shell structure design would eventually be flight-proven on BEAM and comprises five parts (also shown in the figure below alongside a concept image of TransHab). They are:
- inner liner layer
- bladder layer
- restraint layer
- micrometeoroid/orbital debris (MMOD) protection layer, and
- thermal protection (MLI) layer
The remainder of the discussion specifies the desirable properties for a next generation multilayer shell and its two load-bearing parts — the restraint and MMOD protection layers — for the Ideal Spaceship.
Multilayer Shell properties
A table from Ref. 1 is presented below that benchmarks the performance of the inflated habitat modules (in its deployed state) against metallic ones. The densities of the shell of BEAM and TransHab can be used to estimate the mass of a 5000-m³ von Braun wheel.
So, a 5000-m³ von Braun wheel would weigh about 195 tons if made from TransHab’s materials, which would need only 2 Starship launches; if made from BEAM-style materials, 5 launches would be needed. However, these volume-based estimates may be conservative since fabric mass scales with surface area rather than volume. Alternative calculations for the ideal spaceship using BEAM’s surface area density suggest its fabric shell alone could weigh as little as 28-75 tonnes depending on orbital debris environment.See detailed methodology, where the von Braun wheel volume is calculated to be 6650-m³ which is close to that of the ideal spaceship’s 6300-m³.
It is important to note that BEAM’s restraint layer is made from Vectran, which is five times stronger than steel and ten times stronger than aluminium while being half as dense (1400 kg/m³) as aluminium. If made purely from Vectran, the 5000-m³ von Braun wheel would weigh 7000 tons — this means one such spaceship would require 70 Starship launches. But the multilayer is a far more optimised material. Further, as Vectran’s density is lower than either of the metals, it’s easy to see that a spaceship made from it would always be lighter than a comparable metallic one.
While I have not yet found much other public data on these systems, what we can say is that a next-generation multilayer inflatable design must be developed such that it can fit in one Starship launch. I frame this as the first materials challenge.
It is also important for us to consider packaging properties in the deflated state. If we assume BEAM packs as a cylinder when deflated (these cylindrical dimensions are public), its packed density is 157 kg/m³. TransHAB is even more impressive at a packaged density of 122 kg/m³. From these, we can determine their compression ratios, the ratio of pressurised to unpressurised volumes, for BEAM and TransHab as 1.78 and 3.12, respectively. So, the Ideal Spaceship would need an improved packaging density, which is a second challenge.
Restraint Layer properties
The restraint layer bears the loads and stresses of inflation and is thus the main load-bearing layer of the multilayer shell. The chart below shows various shell designs of varying scales; to the left we start with simpler single-layer bladders (small, low-load applications, e.g., blimps and basketballs) in the blue region and work our way towards the higher pressure systems that require restraint layers. The green region represents a broadcloth restraint layer that is coated or contains a separate bladder to act as a combined restraint with bladder layer; it is meant for slightly higher pressures than single layers, e.g., blimps and basketballs. Then, we come to the specific space applications.
A separate bladder and restraint layer with additional loose webbing or cordage is needed to strengthen the restraint layer at higher loads (e.g., an inflatable radome or lightweight airlock). Very high loads on TransHab and other full-scale space modules require a bladder and restraint layer with tight webbing.
From a weave perspective, the authors state that NASA JSC designs fall within this yellow region, the tight webbing category; it is composed of high-strength webbings woven together in a tight basket weave pattern in the axial and hoop directions of the module. They also say that Bigelow Aerospace patented a restraint layer “made of hoop webbings that are abutting and sewn end-to-end lengthwise, which reduces the potential stress points on a strap weave. With this design, there are also fewer longitudinal, or axial, straps, which reduces the overall weight of the module”.
BEAM’s restraint layer, made from Vectran, was designed for a pressure of nearly 60-psi, determined from the product of the factor of safety of 4 and operational pressure of 14.7 psi for the ISS. This factor of safety is dictated by NASA structural design standard NASA-STD-5001. As per these requirements, it is also mandated that the habitat’s survival lifetime at the operating pressure of 14.7 psi exceed the intended duration by the same factor, i.e., 60 years survival if the intended mission duration is 15.
Note that the chart above tells us that the loads experienced per unit length of the restraint layer increases with the diameter of a cylindrical shell — these loads are calculated from cylindrical hoop stress. What this behaviour looks like in practice for larger toroidal structures is unknown.I discussed these matters briefly with co-authors on Ref. 1, Doug Litteken at NASA Johnson and Tom Carno at Langley. Further, the chart tells us that TransHab’s loads were managed by weave patterns that scaled to a certain diameter of about 8.2-m at the specified loads. New restraint layer designs were patented by Bigelow for its 2250-m³ BA-2100, which within sits the grey region. Whether new materials were needed here are unclear to me but the ideal spaceship sits within this region — the wheel-shaped ideal spaceship is about 75-m diameter in the first chart of this blogpost. If the claims made by Ref. 1, that novel restraint materials are needed beyond 9-m inflatable cylindrical structures due to higher loads are true, then this also applied to our ideal spaceship as we are also dealing with a different geometry — what works on cylinders, which is what has been documented so far, might not necessarily apply to toruses. So I separate this into two challenges below (based on scale, as well as geometry).
I believe both challenges might be feasible with AI. Specifically, I believe AI-led materials discovery and novel restraint layer weave pattern designs will be crucial in identifying promising solutions to large inflatable shell structures.
MMOD layer
Ref. 1 states that 68% of TransHab’s mass was allocated for MMOD protection due to its LEO applications where there is higher debris density. They say this can drop to 14% in deep space. This MMOD mass fraction has significant architectural implications. If the ideal spaceship operates in LEO with integrated MMOD protection, our surface-area calculations suggest 68% of 75 tonnes would be ~50 tonnes of shielding alone. Alternatively, launching the inflatable structure with minimal protection and assembling MMOD panels robotically could reduce the initial launch mass to ~25 tonnes while requiring additional launches for shielding. This trade-off between launch complexity and mass efficiency represents a fundamental design choice for the spaceship architecture.
The ideal spaceship’s chosen orbit would most likely also be LEO — to take maximal mass to orbit using Starship’s current specs — which makes me believe that there may be a need for in-orbit assembly of Whipple Shield panels for MMOD around the restraint layer. This might be actually doable with existing robotics but would need clever structural design for robot locomotion — the benefit here would be that we might be able to actually invent a new inflatable material independent of its MMOD shielding that can be used across various orbits while creating modular MMOD shielding onto this structure. The counter-argument here though is that we would need to integrate hard-points onto the fabric which might not be straightforward.
This LEO preference suggests modular MMOD assembly may be necessary. While robotically assembling Whipple shield panels around the inflatable structure is technically feasible, it requires integrating hard-points into the fabric and designing for robotic locomotion — both non-trivial engineering challenges.
I will stop here for now and will likely come back and revise this blogpost in future while writing separate pieces to address other challenges pertaining to design and development of the ideal spaceship.
Conclusion
Here, I’ve answered the main question in the title — a spaceship is a distinct large orbital structure that could house hundreds within a monolithic hull, with linked hulls potentially enabling thousands. This class sits between today’s modular space stations and tomorrow’s superstructures.
NASA Langley’s 1960s inflatable habitat concepts — abandoned in the Apollo pivot — are the first and only real examples of spaceship engineering to date. Their inflatable approach remains the most promising path forward. But to make spaceships a reality, we must solve a set of concrete engineering challenges: lighter, stronger multilayer shells, scalable restraint designs, advanced packaging, and modular debris protection. And we must do so while formalising the knowledge under the label of spaceship engineering.
These aren’t just technical hurdles — they’re invitations. The next wave of spaceship engineers will decide whether humanity’s future in orbit remains cramped in tin cans or unfolds in vast, city-sized habitats.
References and Further Readings
[1] Paper System Integration Comparison Between Inflatable and Metallic Spacecraft Structures from NASA Langley Research Center and NASA Johnson Space Center.
[2] Slide deck TransHab Materials Selection from NASA-Johnson Space Center.
[3] Paper Design of a Microgravity Hybrid Inflatable Airlock from NASA Johnson Space Center.
[4] US Patent Flexible structural restraint layer for use with an inflatable modular structure held by Bigelow Aerospace