ISO 20991:2025
(Main)Space systems — Requirements for small spacecraft
Space systems — Requirements for small spacecraft
This document describes minimum requirements for small spacecraft. This document covers different categories of small spacecraft – so-called mini-, micro-, nano-, pico- and femto-, as well as CubeSat, spacecraft. Therefore, for the sake of convenience, the term “small spacecraft” is used throughout this document as a generic term. This document can be applied by small spacecraft developers, as well as dispenser providers and launch operators.
Systèmes spatiaux — Exigences relatives aux petits engins spatiaux
Le présent document décrit les exigences minimales relatives aux petits engins spatiaux. Les petits engins spatiaux peuvent employer une philosophie non traditionnelle de développement et de management d'engins spatiaux. Ces projets d'engins spatiaux sont généralement limités en termes de budget ou de masse, ce qui rend un seul lancement (exclusif) inabordable. Le domaine d'application du présent document englobe différentes catégories de petits engins spatiaux — dits mini-, micro-, nano-. pico- et femto-, ainsi que des engins spatiaux CubeSat (satellites cubiques). Par conséquent, pour des raisons de commodité, le terme «petit engin spatial» est utilisé dans le présent document comme terme générique. Indépendamment de la philosophie de développement, il existe des exigences minimales auxquelles chaque engin spatial se conforme. Le présent document énonce explicitement ces exigences et fait également référence aux normes applicables existantes. En ce sens, le présent document sert de document de référence pour couvrir les exigences minimales pour les différentes étapes du cycle de vie des systèmes des petits engins spatiaux en mettant l'accent sur les phases de conception, de lancement, de déploiement, d'exploitation et de retrait de service. De cette façon, (1) la sécurité, (2) l'innocuité pour les co-passagers et le lanceur ainsi que (3) la mitigation des débris, sont tous assurés. Le présent document s'adresse aux petits développeurs d'engins spatiaux, ainsi qu'aux fournisseurs de distributeurs et/ou d'opérateurs du lancement.
General Information
Standards Content (Sample)
International
Standard
ISO 20991
First edition
Space systems — Requirements for
2025-10
small spacecraft
Systèmes spatiaux — Exigences relatives aux petits engins
spatiaux
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Requirements . 2
5.1 Launch interface . .2
5.2 Safety.2
5.3 Main payload, adjacent payload(s), and launch vehicle harmlessness .2
5.3.1 Separation .2
5.3.2 Outgassing.3
5.3.3 Dummy specimen .3
5.3.4 Power state, radio transmission and deployable mechanism . .3
5.3.5 Radio frequency compatibility .3
5.4 Debris mitigation .3
5.5 Use of radio frequencies .3
5.6 UN registration .3
5.7 Verification for design and manufacturing .4
5.8 CubeSat .4
5.9 Release from ISS .4
5.10 Collision avoidance .4
5.11 Management . . .4
6 Verification . 4
Bibliography . 6
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, Space systems and operations.
This first edition cancels and replaces ISO/TS 20991:2018, which has been technically revised.
The main changes are as follows:
— reorganized Introduction and Scope to clarify the target;
— changed the wordings referring to contractual requirement, or legal or statutory requirements in 5.1,
5.3.3 and 5.5;
— changed the wordings to focus on the specification process of the applicable minimum requirements in
the project, in 5.1, 5.2, 5.3.2, 5.3.3, 5.3.4 and 5.3.5;
— added 5.10 and 5.11;
— removed the wording of “In the event of any conflict regarding requirements between ISO 17770 and this
document, the requirements in this document supersedes.” from 5.8;
— added ISO 17981 as a normative reference.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Since 2013, the number of small spacecraft built and launched has shown explosive growth. These small
spacecraft are often built by universities, or by newcomers to the space sector, employing untraditional
development and management philosophy that manages risks in cost and time effective manner to achieve
low-cost and fast-delivery. Because of the risk taking approach, small spacecraft often fails in orbit. But
the replacement spacecraft is quickly built and launched reflecting the lessons obtained in the previous
spacecraft. As the launch cost depends on either the spacecraft size or mass, or both, the spacecraft size
becomes “small”.
These spacecraft projects are usually budget-limited or mass-limited, which makes a single (exclusive)
launch unaffordable. Therefore, small spacecraft is very often launched either with a main payload or in a
grapple, which implies specific requirements.
Besides requirements regarding mission success or other goals, which are beyond the scope of this document,
there are minimum requirements that apply to every small spacecraft regardless of its size, mission, value,
capability or any other nature. The purpose of this document is to clearly state those minimum requirements.
In that sense, this document serves as the top document to cover the minimum requirements for various
stages of small spacecraft system life-cycle – with emphasis on design, launch, deployment, operation, and
disposal phases. In this way, the following aspects are ensured:
a) safety;
b) harmlessness to co-passengers and launch vehicle;
c) debris mitigation.
This document provides references to existing standards and documents that elaborate on those
requirements, especially for the benefit of those who are entering the space sector through small spacecraft
development and utilization.
v
International Standard ISO 20991:2025(en)
Space systems — Requirements for small spacecraft
1 Scope
This document describes minimum requirements for small spacecraft.
This document covers different categories of small spacecraft – so-called mini-, micro-, nano-, pico- and
femto-, as well as CubeSat, spacecraft. Therefore, for the sake of convenience, the term “small spacecraft” is
used throughout this document as a generic term.
This document can be applied by small spacecraft developers, as well as dispenser providers and launch
operators.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 26869, Space systems — Small-auxiliary-spacecraft (SASC)-to- launch- vehicle interface control document
ISO 17770, Space systems — Cube satellites (CubeSats)
ISO 19683, Space systems — Design qualification and acceptance tests of small spacecraft and units
ISO 24113, Space systems — Space debris mitigation requirements
ISO 14620-1, Space systems — Safety requirements — Part 1: System safety
ISO 17981, Space systems — Cube satellite (CubeSat) interface
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
CubeSat
picosatellite measuring 100 mm cubic and weighting 1,33 kg or less
[SOURCE: ISO 17770:2017, 3.1, modified — Note 1 to entry has been removed.]
3.2
deployer
box that encloses CubeSats (3.1) within a confined volume with a lid at one side that closes the ejection port
during the launch phase
EXAMPLE POD (picosatellite orbital deployer).
[SOURCE: ISO 17770:2017, 3.2, modified — "box that" has been added; note 1 to entry has been removed;
EXAMPLE has been added.]
3.3
launch operator
private or institutional entity in charge of launching spacecraft
Note 1 to entry: This entity is in charge of the corresponding interface control document (ICD) with the launch
provider, and operates or delegates the launch in accordance with the contract.
4 Abbreviated terms
COTS commercial-off-the-shelf
ICD interface control document
ISS International Space Station
UN United Nations
EMC electromagnetic compatibility
MCI mass centering and inertia
5 Requirements
5.1 Launch interface
A launcher ICD shall be agreed between small spacecraft and the launch operator. Once agreed, small
spacecraft shall comply with the ICD. If small spacecraft is launched as an auxiliary payload, i.e. piggy-back
payload, the ICD shall be written and formatted in accordance with ISO 26869.
5.2 Safety
Every small spacecraft, regardless of its size, mission, value, capability or any other nature, shall conform to
safety requirements in ISO 14620-1.
The project shall agree with the
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