ISO 20991:2025

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

• Status: Published
• Publication Date: 06-Oct-2025
• ICS: 49.020 - Aircraft and space vehicles in general
• Technical Committee: ISO/TC 20/SC 14 - Space systems and operations
• Drafting Committee: ISO/TC 20/SC 14/WG 1 - Design engineering and production
• Current Stage: 6060 - International Standard published
• Start Date: 07-Oct-2025
• Due Date: 11-Dec-2025
• Completion Date: 07-Oct-2025

Relations

• Revises: ISO/TS 20991:2018 - Space systems - Requirements for small spacecraft
• Effective Date: 15-Jun-2024

Overview

ISO 20991:2025 is a key international standard published by the International Organization for Standardization (ISO) that establishes minimum requirements for small spacecraft. Covering categories such as mini-, micro-, nano-, pico-, femto-, and CubeSat spacecraft, this standard serves as a comprehensive guideline for developers, dispenser providers, and launch operators involved in the small spacecraft sector.

The standard addresses essential aspects throughout the spacecraft life-cycle, with a focus on design, launch, deployment, operation, and disposal phases. It aims to ensure safety, harmlessness to other payloads and launch vehicles, and space debris mitigation. ISO 20991:2025 is particularly relevant in a context where the proliferation of small spacecraft has grown rapidly since 2013, driven by universities, startups, and innovative space ventures emphasizing cost-effective and rapid development cycles.

Key Topics

• Launch Interface
  Agreements on interface control documents (ICDs) between small spacecraft developers and launch operators are mandatory. If launched as auxiliary payloads, ICDs must align with ISO 26869 to ensure compatibility and safety during integration and launch.

• Safety Requirements
  All small spacecraft must comply with the safety provisions in ISO 14620-1, addressing hazards related to launch site operations, such as pressure effects, pyrotechnics, electromagnetic compatibility (EMC), contamination, and chemical risks.

• Harmlessness to Payloads and Launch Vehicle
  Critical requirements include:

  • Demonstrated reliable separation and jettison capabilities to prevent collisions with the main or adjacent payloads.
  • Controlled outgassing that does not affect the launch vehicle or other payloads, with reference to CubeSat-specific outgassing criteria in ISO 17770:2017.
  • Provision of dummy specimens for mass centering and inertia (MCI) balancing when necessary.
  • Managed power states, radio transmissions, and deployment mechanisms during launch to avoid interference or hazards.

• Debris Mitigation
  Small spacecraft must adhere to ISO 24113 on space debris mitigation, ensuring sustainable space operations by minimizing post-mission debris risks.

• Radio Frequency Use and Compatibility
  The standard enforces stringent controls on radio frequency emissions to prevent harmful interference with other space and terrestrial stations. Coordination with the International Telecommunication Union (ITU) and adherence to domestic regulations are required for frequency assignments.

• United Nations Registration
  Post-launch, every small spacecraft needs to be registered with the United Nations in line with the UN General Assembly resolution 62/101. This includes notifying relevant bodies of significant status changes, such as the spacecraft becoming non-functional.

• Verification and Testing
  Verification processes emphasize design and manufacturing validation with minimal testing costs, as outlined in ISO 19683. The standard supports rapid delivery while ensuring reliability, focusing on managing post-launch infant mortality risks.

Applications

ISO 20991:2025 offers practical value for various stakeholders involved in the development, launch, and operation of small spacecraft:

• Small Spacecraft Developers utilize the standard to align their designs and manufacturing processes with internationally recognized minimum requirements, ensuring safety and launch compatibility.

• Dispenser Providers apply the requirements to manage interface specifications and operational procedures that support safe storage, deployment, and release of small spacecraft.

• Launch Operators rely on the standard to establish clear contractual interface control documents and enforce safety and radio frequency compatibility measures across multiple payloads sharing a launch vehicle.

• Educational and Research Institutions working on CubeSat and other small spacecraft projects follow ISO 20991:2025 to maintain compliance with safety, debris mitigation, and operational standards necessary for successful mission integration.

This standard effectively supports a fast-growing market segment by providing a structured framework for risk management, operational safety, and regulatory compliance tailored to the unique challenges of small spacecraft missions.

Related Standards

ISO 20991:2025 references important complementary ISO documents that augment the requirements for small spacecraft:

• ISO 26869 – Space systems: Small-auxiliary-spacecraft-to-launch-vehicle interface control document
• ISO 17770 – Space systems: Cube satellites (CubeSats) specification and requirements
• ISO 19683 – Design qualification and acceptance tests for small spacecraft and units
• ISO 24113 – Space debris mitigation requirements for space systems
• ISO 14620-1 – Safety requirements for space systems – System safety part

These related standards provide detailed guidance on specific aspects of small spacecraft development, interface management, testing, safety, and debris mitigation, creating a cohesive framework facilitating responsible and effective small spacecraft missions globally.

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ISO 20991:2025 stands as a vital resource for ensuring the safe, reliable, and sustainable deployment of small spacecraft, reflecting the evolving needs of the space industry and international regulatory environment.

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
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
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,
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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).
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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)
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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 spa
...