The assembly of 3D printed composites has a wide range of applications for ground preparation of space systems, in-orbit manufacturing, or even in-situ resource utilisation on planetary surfaces. The recent developments in composites additive manufacturing (AM) technologies include indoor experimentation on the International Space Station, and technological demonstrations will follow using satellite platforms on the Low Earth Orbits (LEOs) in the next few years. This review paper surveys AM technologies for varied off-Earth purposes where components or tools made of composite materials become necessary: mechanical, electrical, electrochemical and medical applications. Recommendations are also made on how to utilize AM technologies developed for ground applications, both commercial-off-the-shelf (COTS) and laboratory-based, to reduce development costs and promote sustainability. In the near term, 3D-printed structures currently prepared on Earth will be manufactured or/and assembled on low-Earth orbit (LEO); both on-Earth and off-Earth AM activities are expected to enhance the logistics and supply chain management of spare parts for space missions [ 1 , 2 , 3 , 4 ]. The long-term goal of establishing space habitats in on the Moon or Mars will require 3D printing of nearly all printable materials aforementioned to independently sustain astronauts’ lives through structural, electrical, and biomedical applications similar to those on Earth. 2. 3D-Printed Structures Mechanical components and structures are one of the space applications wherein AM can be applied almost immediately due to their high technology readiness level (TRL). Those 3D-printed components exhibit mechanical performance comparable to conventionally manufactured space structures; they can also be functionalised during the AM process to possess shielding capabilities against heat and radiation. After the ongoing technological demonstrations of AM onboard the ISS, the next envisioned step would be to utilise AM for servicing, assembling, and manufacturing in space. Later, polyetherimide/polycarbonate (PEI/PC) was considered to produce tools used by astronauts during spacewalks. Unlike earlier 3D printable materials whose usage was limited to the interior of the ISS, PEI/PC has chemically stable properties adequate for exterior applications as well [ 49 ]; spare parts of the ISS were printed with PEI/PC due to its superior properties in harsh space environments including low outgassing in vacuum and durability against atomic oxygen or ultraviolet ray, to name a few. Because PEKK requires extra post-treatment to enhance its thermomechanical properties, it is used for 3D printing parts on the ground; PEKK is used in Boeing’s CST Starliner, a space taxi for transporting crews and cargo to and from the ISS, and is also speculated to have been used for astronaut helmets manufactured by SpaceX [ 67 ]. On the other hand, PEEK is compatible with the AMF on the ISS and is being considered by industries for in-space or off-Earth manufacturing in the future. 3. 3D-Printed Electronics Printed electronics is a new research area for which electrically conductive or insulative thermoplastic filaments are needed. These advantages of multiple layers already exist in traditional PCBs, but 3D-printed PCBs might match or outsmart the traditionally manufactured counterparts in terms of electromagnetic compliance (EMC), power quality, and signal integrity by precisely controlling impedance of dielectric polymer ink [ 82 ]. Those extra layers can also be used for thermal management or other purposes, as briefly mentioned in the holistic approach. As for other ink materials, carbon black has higher electric resistivity than copper inks but can be used in harsh environments where metallic inks are prone to oxidation [ 83 ]. Polyetheretherketone (PEEK) filaments doped with carbon nanotubes (CNT) or/and graphite nanoplates were investigated in an ESA research initiative, where the conductive PEEK had conductivity of 10 S/m; a 100-fold increase from pure PEEK [ 84 ]. Conformal components for IT devices are immediate terrestrial applications of printed flexible PCBs [ 85 ]. An electronics printer will be launched to be used onboard the ISS, and radiofrequency components are being manufactured on the ground to be used on the ISS [ 86 , 87 ]. In a laboratory setting, PEKEKNK was synthesised by inserting a naphthyl group and was shown to have a higher rigidity and glass transition temperature then PEKEKK [ 120 ]. ESA and its industrial partners are developing a PEEK 3D printer operable in space and the prior ISS project (3D Printing in Zero G) demonstrated that microgravity did not generate significant engineering defects compared with the parts printed on the ground [ 113 , 121 ]. Whilst PAEKs’ medical usage is centred on surgical implants, medical/surgical instruments have been printed using less costly materials. Scalpel handles, sponge sticks, haemostats, forceps, and clamps are amongst the common handheld instruments used in various surgical procedures, which have been printed with acrylonitrile butadiene styrene (ABS) and evaluated by surgeons in practice [ 122 ]. As mentioned earlier, ABS has been used on the ISS for zero-gravity 3D printing to hundreds of spare parts. However, ABS printers should be operated in a sealed environment because of its ultrafine particle emission whose rates can be as large as 200 billion per minute [ 123 ]. Figure 5 South Atlantic Anomaly (SAA, red area) [ 34 ]. Credit: NASA. Figure 6 A broken 3D-printed part around the screw (top, onboard the ISS) and the same part during packaging for launch (bottom) [ 51 ]. Credit: NASA. Figure 7 The threaded insert ( left , avionics box) and radial cracks around it ( right , specimen) [ 51 ]. Credit: NASA. Figure 8 Gapped control sample that stayed together after the 3-point beam test, viewed from beneath ( left , rastered bottom/top) and sideways ( right , contoured sides) [