Why do a review of NASA papers on trusses?
Well, because trusses are cool, for a variety of reasons. In buildings, they became one of the trademarks of the late modernist architecture period, representing “cool” and making the prior brutalist or streamlined or art deco or merely modern buildings look dated. In space, they represented a turning point of dreams where the Space Station Freedom then ISS had a truss structure in contrast to prior stations that were mostly made of docked cylinders. In science fiction, starting in the 1980s, trusses became something fun and vaguely futuristic one could throw into the background. Mind you, this was quite convenient because all they needed to do was grab a regular old lighting truss because by that time, those were a good standard way to build up a lighting rig.
When it comes to NASA, there was this focused effort starting in the mid-1970s to come up with even more ambitious problems for NASA to solve to justify ever increasing budgets. Ergo, the construction of very large things in space became a focus of research. Space Station Freedom was actually just one tiny piece of these grandiose ideas. There were research papers on giant antennas, solar power satellites, space hangars, and giant telescopes, all of which were bigger than even the Saturn V rocket could handle.
Trusses work pretty well on Earth. They work incredibly well in space, especially when you want something relatively large that fits in a smaller container.
Consider the recent JWST mission that featured an absurdly protracted and grossly overbudget development cycle as well as a nail-biting two week unfolding process but eventually delivered a 6.5m segmented mirror as well as a giant sunshield inside of a 5.4m fairing. This, as well as the ISS, draws on a lot of the ideas discussed in the NASA truss papers, but there is a huge body of other research. NASA has been talking about telescopes that were not only larger than the Hubble’s 2.4m mirror but also larger than the JWST’s 6.5m mirror for a long time.
The JWST was designed very carefully to unfurl itself by a careful sequencing of actuators. The ISS ended up being assembled out of relatively large pre-integrated truss sections.
On the other hand, the research in these papers largely assumes that astronauts in spacesuits and/or robotic arms would join, deploy, and connect various truss structures from compact elements, where the size of these truss structures could be limited only by upward cargo mass limitations. One of the explicit goals of the Space Station Freedom was to provide a construction shack for these projects. The current purpose of the ISS as a primarily research-oriented station came much later.
So why has most of this research never been applied to an actual mission?
Well, the Space Station Freedom initial flights had astronauts constructing a truss and installing modules inside of it, so it wasn’t actually a funcioning orbital object until they had completed all of the spacewalks for those initial missions. One imagines the consequences of an early Space Station Freedom assembly mission where they ran out the EVA clock with critical systems not yet properly installed.
Thus, NASA became progressively more cautious and started looking for alternative options relatively early in the design process. The ISS shipped with a very prosaic and simple pre-integrated truss structure, using neither the research on assembling a truss from segments nor trusses that fold up.
However, this feels like it ought to be useful.
There’s a whole bunch of space mission designs from the entire span of space explorations that made it into the popular-science kids books that I read when I was a kid. You can find the roots of most of them in the NTRS databases, frequently using the exact same renderings from the kids books. On the other hand, there’s a lot of surprises I’ve found while hunting through references and search queries and papers.
There’s clearly a bunch of wild fever-dreams that would not have panned out, largely because computers went through so many orders of magnitude improvements. However, there also seems like there’s stuff that maybe should have been explored. It’s just been stuck in the same technology readiness level for a long time without anybody being able to sell a use case so awesome to justify actually trying it out.
From 1976-1988 - The heady days of large spacecraft of all sorts deployed via multiple space shuttle flights through the EASE/ACCESS mission
The Space Transportation System was never actually meant to be just the space shuttle. It was a system of interconnected space and ground assets where the space shuttle part of it was delivered first. Later pieces of the system would deliver payloads to the intended higher orbits and enable the American dominance of space.
The key ideas here was that you could visit a satellite and repair it, or you could launch a satellite in pieces and assemble it in orbit. Or, even better, assemble a large payload from multiple launches.
As I said above, only one of these large payloads was the space station. Picture a whole fleet of large missions, like a giant microwave survey satellite, a solar power station, a giant telescope, or a single giant geosynchronous satellite with a massive dish reflectors and many feedhorns that could provide phone service to the entire continental US.
Thus, NASA had convened out of the Langley Research Center the Large Space Systems Technology Program.
Not included here is the parallel mutation of the space station program from a relatively compact set of cylindrical modules docked together to the “power tower” or “dual-keel” elaborate truss structures. By 1984 when the space station was announced, it was a very large structure in space built around a truss structure based on this research.
Most of these papers were written based on assumptions that were largely unchecked by reality. Nobody had tried to assemble these trusses in space and the shuttle was still getting the kinks worked out of it. For example, the shuttle was supposed to have a 12 day turnaround between missions.
The EASE/ACCESS mission was the first chance to know, in an unsimulated spacewalk environment, what it would look like to assemble any of these. It flew on STS-61B at the end of 1985 shortly before the Challenger Disaster.
The way the papers represent things, the EASE/ACCESS mission was only somewhat intended to actually test what might be used on the ISS but also to calibrate the wealth of experimentation done on assembling large truss structures on the ground in a neutral bouyancy pool with what it was like for actual astronauts.
A Nestable Tapered Column Concept for Large Space Structures
One of the earliest treatments of this subject, featuring the nestable tapered column that appears frequently in later papers. The idea here is that the cone-shaped columns would be snapped together to form a beam and then connected to nodes and the whole thing would pack very efficently in the space shuttle’s cargo bay.
Structural stiffness, strength and dynamic characteristics of large tetrahedral space truss structures
Describes the math for large tetrahedral space truss structures.
Structural efficiency of long lightly loaded truss and isogrid columns for space applications
Provides equations for the structural efficiency of these shapes:
- Tubular column
- Three longeron truss column constructed from tubular members
- Three longeron truss column constructed from solid members
- Tubular column constructed from open isogrid walls
Preliminary design of large reflectors with flat facets
Geometry and RF design notes for constructing a curved surface antenna that is 1150m in radius using flat panels instead of curved panels for the Microwave Radiometer Satellite.
History note: That which the Microwave Radiometer Satellite was supposed to do ended up being done using Synthetic Aperture Radar.
Structural concepts for large spacecraft
(part of Large Space Systems Technology, 1979)
Some notes on large spacecraft design, oriented towards showing the maximum size of a stable zero-g structure that can be accommodated by an 18m long space shuttle cargo bay.
Erectable concepts for large space system technology
(part of Large Space Systems Technology, 1980, Volume 1)
Talks through some concepts for deployable/erectable truss structures:
- Design 36 Automated Coupler Clevis Joint - It starts with a standard clevis pin joint and modifies the geometry such that you can insert from specific directions (either side or the end) and it will tend to lock in place.
- Design 27 Side Latching Detent Joint - A side-insert joint that will lock in place
- Design 22B Module-to-Module Auto-Lock coupler
- Deployable module built from telescoping diagonals, single clevis joints, and double swivel clevis joints
As best I can tell, all of those joints slowly disappear from the papers over time.
EVA manipulation and assembly of space structure columns
There were three joint setups: Graphite/Epoxy columns with snap joints, Graphite/Epoxy columns with ball/socket joints, and Aluminum alloy columns equipped with ball/socket joints and the simulations covered having MMU and/or RMS available.
Recent advances in structural technology for large deployable and erectable spacecraft
Repeats some of the content from other papers around the same era
Deployable and erectable concepts for large spacecraft
Repeats some of the content from other papers around the same era, includes equations for structural designs.
Development of assembly and joint concepts for erectable space structures
The core idea here is the space assembly of a space platform that can have solar arrays, reflectors, astronaut habitats, and other supporting equipment attached to it from pieces that were transported to orbit via the space shuttle. This was during the time period where people were thinking not just of a truss-based space station but also large communication satellites, multi-kilowatt solar power modules, and space manufacturing facilities.
The beam was a pre-existing Langely Research Center graphite-epoxy nestable half-columns — the baseline was a 10m round hollow half-column that tapered from 25cm to 5cm in diameter where you could stack the half-columns atop each other for storage in the shuttle bay. The 10m columns were found to be more optimal than any shorter structure.
The truss used is a tetrahedral truss made from equal-length columns but the joints only have six planar connectors and three axial connectors, where a fully space-filling structure would require three additional axial connectors.
There were two connector mechanisms, the snap-lock mechanism and the finger-type mechanism, both of which were designed primarily to be actuated in orbit by a robot arm with the help of a gimbaled parallelogram assembler, as opposed to astronauts in spacesuits.
History note: This was written at an interesting time for the space shuttle. The shuttle was assumed to have a 12 day turnaround time and this was during the time period where there was still the idea that the shuttle would have an OMS kit to reach higher orbits. At the same time, the ambitions were to create a 1km2 structure in 141 days with 10 shuttle flights.
(There’s not an apples-to-apples comparison against reality here: the ISS integrated truss is 94 m × 5 m (more or less) and is thus around 470m2 and took about 10 flights to get up, however, those 10 flights also included the solar arrays and attached systems)
Space deployable truss structure design
(Part of The 15th Aerospace Mechanisms Symposium)
Designs for a deployable box truss
On the design of large space deployable modular antenna reflectors
(Part of The 15th Aerospace Mechanisms Symposium)
Designs for a modular antenna out of hexagon truss pieces
EVA assembly of large space structure elements
A follow-on to EVA manipulation and assembly of space structure columns where a new quick-connect joint system was used instead and the MMU was not tested.
The potential of nonperiodic truss structures for space applications
(Part of Large space systems technology, 1981)
Introduces dipenta-dodecahedron (or DPD-Hedron) and pentatriangular-octahedron (PTO-hedron) structures
Sequential deployment of truss structures
(Part of Large space systems technology, 1981)
Describes how to create the same tetrahedral truss as some of the prior experiments and papers but to deliver it as something which can unfold.
General description of nestable column structural and assembly technology
Mostly a re-hash of earlier work
A mobile work station concept for mechanically aided astronaut assembly of large space trusses
Another study on earth about the speed of assembly for the quick-connect joint system and a work platform
Status of deployable geo-truss development
(Part of Large Space Antenna Systems Technology, part 1)
The geo-truss is built around the tetrahedron structure with a leaf-spring to unfold each bay.
Box truss development and applications
(Part of Large Space Antenna Systems Technology, part 1)
Describes further developments along the subjects of the prior paper on box trusses, Space deployable truss structure design
Hinge specification for a square-faceted tetrahedral truss
Describes the math for how to construct a folding tetrahedral truss using only hinges
A manned-machine space station construction concept
Describes some of the space station configurations and a machine that could be used to construct them.
Definition of technology development missions for early space stations. Large space structures, phase 2, midterm review
A midterm review of some large space structure truss projects showing some interesting truss structures as well as a summary of much of the earlier papers as part of these concrete projects.
Structural performance of orthogonal tetrahedral truss Space-Station configurations
Describes some of the truss structures being considered for the space station and some of the basic design layouts
Space Station truss structures and construction considerations
Various truss structures being considered for the space station including some new variations on the themes.
Swing-arm beam erector (SABER) concept for single astronaut assembly of space structure
Features a variation on the node structure and a different work platform design.
Box truss development and its application
(Part of Large Space Antenna Systems Technology, 1984)
A follow on to Box truss development and applications, adds some more joint complexity and “pillow” shaping.
Definition of technology development missions for early space stations: Large space structures
A midterm review of some large space structure truss projects showing some interesting truss structures as well as a summary of much of the earlier papers as part of these concrete projects.
Deployable/erectable trade study for space station truss structures
A review of different truss structures being considered including some folding and nodal mechanisms
Evaluation of Pactruss design characteristics critical to space station primary structure
Structural equations for the Pactruss deployable box-truss
Structural concepts for large solar concentrators
Large trusses for reflectors, includes the a non-box-truss version of the pactruss system and algoritms for designing a solar concentrator using the pactruss
Design, construction, and utilization of a space station assembled from 5-meter erectable struts
Design work for the then-baseline of 5-meter erectable struts for the space station, using a truncated cube node and a joint structure as in previous papers, includes a new set of truss experiments and some thoughts on equipment mounting.
Experimental assembly of structures in EVA Hardware morphology and development issues
This mostly talked about the EASE part of the EASE/ACCESS flight and primarily focused on the hardware flown. There were many structures shown but the only one that flew was the single tetrahedron.
History note: From the NASA EVA chronology, the EASE part of the mission was described as “probably not the preferred way of building a space station”.
Marshall Space Flight Center’s role in EASE/ACCESS mission management
A description of some of the EASE/ACCESS hardware.
Results of the ACCESS experiment
Some actual results, for the ACCESS side of things. The ACCESS experiment constructed a trusswork beam using a workstation that enabled them to stay anchored in the cargo bay. This required a lot of hand usage. They then did a number of tasks on the truss using the robot arm.
The effort was also compared against the time in the pool.
EASE (Experimental Assembly of Structures in EVA) overview of selected results
Some actual results, for the EASE side of things. In the objective section they note that the goal of the EASE experiments was not a structural experiment but was primarily used as a measurable activity comparison for space construction to calibrate against using the neutral bouyancy pools. As above, this experiment had the astronauts climbing around on the truss and manually torquing things, which was hard.
Overview of crew member energy expenditure during Shuttle Flight 61-8 EASE ACCESS task performance
An overview of how much physical effort was required. This does alude to the difficulties of the EASE task.
From 1988…
(not complete yet)