1. The short version / what to know first / where this fits in the series

• A satellite is a "bus" plus a "payload". The bus is the base that keeps the satellite alive and moving (structure, power, communications, pointing control, thermal, propulsion, data handling); the payload is the mission equipment (cameras, relays and so on). This article's subject is the "structure" inside the bus and the materials behind it Sourced[Ref. 2]
• Small satellites are defined by mass classes and a standard box. NASA's report divides small satellites by mass (nano 1 to 10 kg, micro 10 to 100 kg, mini 100 to 180 kg and so on). A CubeSat is a standard box built on a 10 cm cube, 1U; the specification sets a maximum of 2 kg for 1U, aluminum alloy as the default frame material, and a TML of 1.0 % or less and CVCM of 0.1 % or less for materials Sourced[Ref. 1, 4]
• Frame materials are chosen by four things: loads, heat, radiation and gas. These are launch vibration, heat paths in vacuum, shielding for the electronics, and outgassing. For example, for a CubeSat with a 0.2 cm aluminum structure in low orbit, a reported estimate of the yearly radiation dose approaches the dose that commercial parts are said to tolerate (2 to 10 krad) Sourced[Ref. 3]

2. What a satellite is made of: bus and payload

Think of a satellite as a vehicle. A bus carries passengers to their destination and takes care of driving, electricity and air conditioning. The passengers correspond to the observation or communication equipment the satellite carries, the payload. In a satellite, the part that plays the role of the vehicle body is called the bus. Where the analogy breaks down: a bus passenger just sits, but a satellite payload demands a great deal of power, heat control and pointing, and ends up dictating the bus design.

NASA's report on small-spacecraft technology organizes the technologies that make up a bus into chapters on power, propulsion, guidance, navigation and control (pointing control), structures, materials and mechanisms, thermal control, avionics (on-board electronics and data handling) and communications Sourced[Ref. 2].

View original SVG, values and sources

Original SVG reference: Concept diagram (vector drawing). A satellite split into the bus (seven subsystems) and the payload. The subsystem division follows the chapters of NASA's report, and the material examples are illustrative. That the payload's size and power set the bus design is our own commentary.

3. Classes of orbit and size: altitude and mass

Orbits: altitude changes the time per lap and the environment

According to ESA, low Earth orbit (LEO) extends to about 2,000 km, an upper limit set by the harsh environment of the Van Allen belts above it (regions of strong radiation). Satellites normally do not fly below 180 km because of the atmosphere. A LEO satellite moves at about 7.8 km per second relative to the Earth and completes a lap in about 90 minutes; the ISS circles the Earth about 16 times a day Sourced[Ref. 5].

Geostationary orbit (GEO) is above the equator at 35,786 km, where one lap takes 23 hours 56 minutes 4 seconds (a sidereal day), so the satellite appears to stand still from the ground. Its speed is about 3 km per second. Medium Earth orbit (MEO) covers the wide range from above the Van Allen belts in LEO up to GEO. Sun-synchronous orbit (SSO) is a kind of polar orbit that passes over the same place at the same local time each day; its altitude is usually 600 to 800 km Sourced[Ref. 5].

Mass: small satellites are classed by weight

NASA's report takes 180 kg as the guide to the upper mass limit of a small satellite (it became a convenient benchmark because one slot of the ESPA ring, an adapter for secondary payloads, had a 180 kg allocation). The classes are: minisatellite 100 to 180 kg, microsatellite 10 to 100 kg, nanosatellite 1 to 10 kg, picosatellite 0.1 to 1 kg and femtosatellite 0.01 to 0.09 kg. The preface of the same report, however, describes the "mini-class" constellations that have grown since 2023 as 201 to 600 kg and a newer generation of small-satellite fleets as 600 to 1,200 kg Sourced[Ref. 1, 2]. In other words, the names and boundaries differ by source and by period.

4. CubeSats: the idea of a standard box

CubeSats are a family of small satellites with a standard size and shape, built on a 10 cm cube called one "U". The CubeSat Project started in 1999 as a collaboration between Prof. Puig-Suari at California Polytechnic State University, San Luis Obispo (Cal Poly), and Prof. Twiggs at Stanford University, with the aim of cutting cost and development time, widening access to space and sustaining frequent launches. The CubeSat Design Specification (CDS) sets the design requirements for 1U to 12U and the interface to the dispenser (deployer) Sourced[Ref. 4].

What does a standard box buy? Because dispensers are standardized too, the launch side can load a satellite without worrying about its contents, and the cost of launch procedures drops. We pick out the main CDS requirements (Rev. 14.1) with a materials engineer's eye Sourced[Ref. 4].

• Mass: 1U up to 2.00 kg, 2U 4.00 kg, 3U 6.00 kg, 6U 12.00 kg, 12U 24.00 kg (the table's "typical maximum"; it changes with the dispenser's capability).
• Materials: the structure should be an aluminum alloy; 7075, 6061, 6082, 5005 and 5052 are typically used. External aluminum surfaces that touch the dispenser rails must be hard-anodized to prevent cold welding.
• Outgassing: materials must have a TML of 1.0 % or less and a CVCM of 0.1 % or less, and the specification points to NASA's list of approved low-outgassing materials.
• Testing: random vibration to levels set by the launch provider; thermal-vacuum bakeout to drive out outgassing; shock testing is typically not required.

The CubeSat mass limits have changed with each revision. The CDS revision history records an acceptance-checklist mass limit for 1U being revised to "1.33 kg", whereas the Rev. 14.1 table says 2.00 kg Sourced[Ref. 4]. Always check the edition of the specification.

5. The first great test, launch: loads and vibration

Almost the first ordeal a satellite frame meets is launch. Rocket engines and airflow shake the satellite hard. The frame must carry these loads without breaking and must not pass too much of them on to the parts inside.

View original SVG, values and sources

Original SVG reference: Concept diagram (vector drawing). How launch vibration travels from the rocket to the dispenser and the satellite frame, with a summary of the rules in the specification and the report. A concept diagram for a rail-type CubeSat dispenser, not the structure of any specific dispenser.

NASA's report says that NASA's CubeSat call (CSLI) requires a satellite to withstand the vibration environment of GEVS (the General Environmental Verification Standard), about 10 G rms for 2 minutes. The vibration conditions of an actual launch are given by the launch provider. With rail-type dispensers there is a thin gap between the satellite frame and the dispenser rails, and the report also says that rattling (chatter) in that gap raises the loads in testing and launch Sourced[Ref. 3]. GEVS is a standard for environmental testing for NASA Goddard flight projects; Version B (2021) is active, but NASA's page shows it is neither a NASA mandatory standard nor a NASA endorsed standard Sourced[Ref. 6].

An example of design conditions: a 2U CubeSat in one paper

Rinaldi and colleagues give the design conditions for a 2U CubeSat structure to be launched on Soyuz. Based on the launch vehicle user's manual, they set lower limits on the first five natural frequencies of 50, 51, 70, 90 and 110 Hz, and multiplied quasi-static loads by a model-uncertainty factor of 1.1 and a design-and-environment factor of 1.25 (1.375 in all). The resulting loads were ±4.675 g laterally and -7.9 g/+4.95 g longitudinally, with an equivalent stress limit below 45.45 MPa Sourced[Ref. 14]. These are the conditions of one design in one paper and do not apply to other launchers or satellites. They do show, though, that in frame design keeping the natural frequencies away from the rocket's vibration frequencies matters about as much as the size of the load (commentary).

6. Frame materials: aluminum, sandwich panels, composites, 3D printing

NASA's report describes choosing the frame material of a small satellite as a problem of satisfying both physical properties (density, thermal expansion, radiation resistance) and mechanical properties (modulus, strength, toughness). A typical satellite structure mixes metals and non-metals: metals are homogeneous and isotropic, while composites are inhomogeneous and anisotropic but can have properties tailored to load paths. The operating environment governs the choice, with adequate margin for launch and operating loads, and thermal balance and thermal-stress management, as well as the payload's sensitivity (to outgassing and thermal displacement), must be considered too Sourced[Ref. 3].

Primary and secondary structures

NASA's report divides a satellite's structure into primary and secondary structures. If the primary structure (frame, chassis) fails, the mission usually fails. Secondary structures (solar panels, thermal blankets, subsystems) attach to the primary structure, are self-supporting and carry few critical loads. In somewhat larger small satellites such as the ESPA class, assemblies machined from aluminum alloy remain the mainstream for primary structure. CubeSat frames are mostly machined from 6061 or 7075 aluminum alloy Sourced[Ref. 3].

Sandwich panels: a thin skin around a thick core

Why can a panel be light and yet hard to bend? Because bending strength depends on how far the material sits from the middle. It is like a ruler, which bends less when stood on edge than when laid flat. A sandwich panel bonds thin skins to both faces of a light core (honeycomb, in the shape of a beehive), moving the skins away from the center. NASA's report also lists aluminum honeycomb sandwich panels among the well-proven lightweighting methods Sourced[Ref. 3].

Composites and 3D printing

As for composites, the DiskSat that the Aerospace Corporation is developing (a disk 1 m in diameter and 2.5 cm thick) has a graphite (carbon-fiber) epoxy sandwich structure with a structural mass below 3 kg/m². NASA's report says its first launch took place in December 2025, the dispenser worked as designed, communications with the ground succeeded, and it is now in checkout and initialization Sourced[Ref. 3]. The in-orbit record of carbon-fiber PEEK composites is covered in our explainer on super engineering plastics for space, which treats the thermal-expansion measurement on Ten-Koh [Ref. 15].

3D printing was once used only for secondary structures, but NASA's report says it is beginning to be used for primary structures in CubeSat and even smaller PocketQube-class spacecraft. KickSat-2 (a device that released chip-sized satellites) flew with a structure made entirely of ABS plastic, because the single-use design, short mission, and intricate frame made a conventionally machined deployer prohibitive in mass and cost Sourced[Ref. 3]. Additive manufacturing is covered in detail in our explainer on additive manufacturing for space.

7. The frame is also a radiation shield

The thickness of the frame has another job: it is a shield that protects electronic parts from radiation. NASA's report calls shielding a cost-effective way to cut the risk of failure of electronics from total ionizing dose (TID) and internal charging, and says that historically the cost of adding shielding has averaged below 10 % of a spacecraft's total cost. The simplest method is shielding by the mass already there, such as the outer skin and chassis (inherent mass shielding) Sourced[Ref. 3].

Shields-1 was an experiment in low orbit that measured the effect of shielding made of aluminum and of "high-Z" (high atomic number) laminates. As the figure shows, the model value for 0.198 cm of aluminum (areal density 0.535 g/cm²) is 1,383 rad(Si) per year, whereas at 1.26 g/cm² (0.465 cm thick) the measurement is 90.9 rad(Si) per year Sourced[Ref. 3]. Raising the areal density by about 2.4 times (1.26 ÷ 0.535) lowers the dose to about 1/15 (1,383 ÷ 90.9 ≈ 15) Our calculation. Beyond about 1.3 g/cm², the values tend to level off near 75 to 90 rad per year. Inference: the reason for the leveling off (secondary particles, more energetic particles, the measurement floor and so on) cannot be told from the report's table alone. A 3.02 g/cm² high-Z electronics box (vault) gave 75.6 rad(Si) per year, which NASA's report states as a reduction of more than 18 times against modeled 0.20 cm aluminum.

8. Outgassing of structural materials and their pre-treatment

Frame materials are also judged by the gas they release in vacuum. The CubeSat specification sets a TML of 1.0 % or less and a CVCM of 0.1 % or less for materials. The NASA Goddard outgassing database holds many records on structural materials; we list a few Sourced[Ref. 17, 4].

All Sourced (NASA Goddard Outgassing Database [Ref. 17], checked 17 October 2026). RML is Our calculation as TML minus WVR. The "treatment column" is the entry in the database's Time and Temp columns, which we read as cure or treatment conditions (the sort fields are named CureTime and CureTemp). Sample shape and laboratory differ between records, so we do not rank them.

Three things can be read from this. First, a carbon-fiber/cyanate-ester laminate has a TML of 0.07 %, a record of very little gas. Second, an aluminum honeycomb panel has a TML of 2.9 % because of its adhesive, and an RML of 1.75 % even without water, over both the CDS criterion (TML 1.0 % or less) and the ECSS RML criterion (below 1.0 %). Third, the same kind of epoxy adhesive gives a TML of 1.73 % and 0.88 % in two records with different treatment conditions. Inference: compared with a long room-temperature cure, a treatment of 24 hours at 125 °C may have reduced the gas released. This is why the specification makes thermal-vacuum bakeout mandatory [Ref. 4].

9. Limits, and what could not be confirmed

• Structures of large satellites: this article centers on NASA's report on small satellites and the CubeSat specification. We do not cover primary sources on the structures of large geostationary satellites or probes (central cylinders, propellant-tank supports and so on)
• The mass fraction of the structure: we could not confirm a primary-source figure for the share of a satellite's mass taken by the structure
• Official mass classes in Japan: we could not confirm official JAXA or Japanese materials on the mass classes of microsatellites (Ten-Koh is covered in our explainer on super engineering plastics for space)
• Radiation numbers: the Shields-1 values are a measurement and a model for one orbit (500 km, 85 degrees inclination). We do not cover doses in geostationary or other orbits
• The sandwich-panel calculation: illustrative values from a simple beam formula and assumptions we set, not values of a real panel
• The text of standards: we did not confirm the requirements in the text of ISO 17770 (paywalled) or of the ECSS standards. For the CDS we checked the relevant passages of the publicly available PDF
• ASTM: we did not open ASTM's site. The names of test methods are only those written in NASA's materials

10. How to read the yardsticks and standards

Satellite structures and small satellites are judged less by "a performance number" than by "whether it was checked by a prescribed procedure". The yardsticks are: (1) size and mass (for a CubeSat, the dimensions and maximum mass per U); (2) how loads are carried (natural frequency, quasi-static loads, random-vibration testing); (3) behavior in thermal vacuum (bakeout, outgassing); (4) readiness for radiation (dose calculation and shielding); and (5) whether it stays in orbit (debris mitigation). What these measure are conditions reproduced by ground tests; they do not directly guarantee lifetime or success in orbit.

The arrangement of this table is Our calculation (our own reordering). Standard numbers, titles and status were checked on the official pages of ECSS, ISO and NASA (checked 17 October 2026). ISO texts are paywalled, so we limited ourselves to titles and scope. We did not open ASTM's site.

Cautions in reading (for materials engineers)

• Ground tests and flight results are different things: a vibration test imitates the shaking of launch but is not the actual launch load. Radiation doses carry a model uncertainty of a factor of two or more
• A specification is not always an "international standard": the CubeSat Design Specification is Cal Poly's specification and is separate from ISO 17770. Check which one is the basis
• Check whether a standard is a recommendation or a requirement: GEVS is not a NASA mandatory standard, and an ECSS standard becomes a requirement when a contract applies it. A "shall" in the CDS is a requirement within that specification
• Qualification and acceptance are different: the CDS distinguishes qualification or protoflight testing from acceptance and workmanship testing. Confirming a design and confirming each unit are different matters

11. Glossary

12. References

1. NASA (Small Spacecraft Systems Virtual Institute) "State-of-the-Art of Small Spacecraft Technology", Chapter 1 Introduction (classes by mass; 2026 edition; checked 17 October 2026) — nasa.gov/smallsat-institute/sst-soa/introduction/
2. NASA (Small Spacecraft Systems Virtual Institute) "State-of-the-Art of Small Spacecraft Technology" (preface and chapter list; 2026 edition; checked 17 October 2026) — nasa.gov/smallsat-institute/sst-soa/
3. NASA (Small Spacecraft Systems Virtual Institute) "State-of-the-Art of Small Spacecraft Technology", Chapter 6 Structures, Materials, and Mechanisms (2026 edition; checked 17 October 2026) — nasa.gov/smallsat-institute/sst-soa/structures-materials-and-mechanisms/
4. The CubeSat Program, Cal Poly SLO "CubeSat Design Specification Rev. 14.1" (February 2022); requirements on size, mass, materials and testing — cubesat.org/s/CDS-REV14_1-2022-02-09.pdf
5. ESA "Types of orbits" (altitude and period of LEO, SSO, MEO and GEO; checked 17 October 2026) — esa.int/Enabling_Support/Space_Transportation/Types_of_orbits
6. NASA Goddard GSFC-STD-7000 "General Environmental Verification Standard (GEVS) for GSFC Flight Programs and Projects" (Version B, 28 April 2021; checked on the NASA Standards page) — standards.nasa.gov/standard/GSFC/GSFC-STD-7000
7. ISO ISO 17770:2017 "Space systems — Cube satellites (CubeSats)" (edition 1, June 2017; under revision; checked on the ISO page) — iso.org/standard/60496.html
8. ECSS ECSS-E-ST-32C Rev.1 "Structural general requirements" (15 November 2008) — ecss.nl/standard/ecss-e-st-32c-rev-1-structural-general-requirements/
9. ECSS ECSS-E-ST-10-03C Rev.1 "Testing" (31 May 2022) — ecss.nl/standard/ecss-e-st-10-03c-rev-1-testing-31-may-2022/
10. ECSS ECSS-E-ST-10-02C Rev.1 "Verification" (1 February 2018) — ecss.nl/standard/ecss-e-st-10-02c-rev-1-verification-1-february-2018/
11. ECSS ECSS-E-ST-10-04C Rev.1 "Space environment" (15 June 2020) — ecss.nl/standard/ecss-e-st-10-04c-rev-1-space-environment-15-june-2020/
12. ECSS ECSS-E-ST-10-12C "Methods for the calculation of radiation received and its effects, and a policy for design margins" (15 November 2008) — ecss.nl/standard/ecss-e-st-10-12c-methods-for-the-calculation-of-radiation-received-and-its-effects-and-a-policy-for-design-margins/
13. ECSS ECSS-U-AS-10C Rev.2 "Adoption Notice of ISO 24113: Space systems - Space debris mitigation requirements" (9 February 2024) — ecss.nl/standard/ecss-u-as-10c-rev-2-adoption-notice-of-iso-24113-space-systems-space-debris-mitigation-requirements-9-february-2024/
14. Rinaldi M. et al. (University of Rome Tor Vergata, Thales Alenia Space Italia, ESA/ESTEC) "Additive Manufacturing of Polyether Ether Ketone (PEEK) for Space Applications: A Nanosat Polymeric Structure", Polymers 13(1), 11 (2021), DOI 10.3390/polym13010011 (open access) — doi.org/10.3390/polym13010011
15. Abdullah F., Okuyama K., Fajardo I., Urakami N. (Kyushu Institute of Technology) "In Situ Measurement of Carbon Fibre/Polyether Ether Ketone Thermal Expansion in Low Earth Orbit", Aerospace 7(4), 35 (2020), DOI 10.3390/aerospace7040035 — doi.org/10.3390/aerospace7040035
16. ECSS ECSS-Q-ST-70-02C "Thermal vacuum outgassing test for the screening of space materials" (15 November 2008; checked on the ECSS page and PDF) — ecss.nl/standard/ecss-q-st-70-02c-thermal-vacuum-outgassing-test-for-the-screening-of-space-materials/
17. NASA Goddard Outgassing Database (searchable test results; checked 17 October 2026) — outgassing.nasa.gov/
18. NASA NASA-STD-6016 "Standard Materials and Processes Requirements for Spacecraft" (Version C with Change 1; dated 30 September 2021, changed 15 November 2023; checked on the NASA Standards page) — standards.nasa.gov/standard/NASA/NASA-STD-6016

13. Claim-to-source audit

Last updated: 17 October 2026 / Sources are limited to primary materials (NASA's report on small-spacecraft technology, the CubeSat Design Specification, ESA's explanation, the NASA Goddard database, the official pages of ECSS, ISO and NASA, and peer-reviewed papers). Class names, dimensions and masses differ with source and edition. Calculated values are illustrative values made for this article and are not values of a real satellite or panel. We could not confirm the structures of large satellites, the mass share of the structure, official Japanese mass classes, or the requirements in the standards' texts, so we do not state them.