A suborbital flight climbs above the altitude usually associated with the start of space, then falls back to Earth without reaching orbital speed. Technically this is well understood. Legally it is not: a single flight passes through airspace, governed by aviation law, and through what is commonly regarded as outer space, governed by space law. This article explains why the boundary matters, how international bodies approach it and how the United States already regulates people on board.
There is no agreed boundary between airspace and outer space
An altitude of 100 km, often called the Kármán line, is widely used as a reference. A 2017 submission to the UN Office for Outer Space Affairs by the Space Safety Law and Regulation Committee of the International Association for the Advancement of Space Safety describes it as the most prominent of many altitude proposals, roughly where the atmosphere becomes too thin for aircraft wings to generate sufficient lift.
It is not, however, a legally agreed limit. In a 2005 working paper, the International Civil Aviation Organization (ICAO) noted that the relevant international instruments give no indication of a vertical limit of airspace from which outer space would begin. The UN Committee on the Peaceful Uses of Outer Space (COPUOS) still has a working group on the definition and delimitation of outer space, which continues to collect the views of states.
Two ways of thinking: where you fly or what you do
The ICAO paper describes two competing approaches:
- Spatial approach: the law depends on location. Aviation law applies in airspace, space law above it. This requires a boundary, which does not exist in law.
- Functional approach: the law depends on the purpose and nature of the activity. For suborbital vehicles used for transport from one point on Earth to another, ICAO noted that air law could prevail, since airspace would be the main centre of their activities.
ICAO also pointed out that the Chicago Convention applies to international air navigation and that suitable technical standards would have to be developed if suborbital vehicles were treated as civil aircraft.
Not every state wants a boundary
Positions differ. At the 2025 session of the COPUOS Legal Subcommittee, the United States stated that there is no need to seek a legal definition or delimitation of outer space and that the current framework has presented no practical difficulties.
How the United States regulates people on board
The United States has created specific rules for commercial human spaceflight. Under 14 CFR 460.45, operators must inform each space flight participant in writing about known hazards and risks that could cause serious injury, death or disability, and that there are also unknown hazards. They must state that the US Government has not certified the vehicle as safe for carrying crew or space flight participants, disclose safety records, and obtain the participant's signed consent confirming that the participant understands the risk and that flying is voluntary.
And in Europe?
As early as 2008, ESA stated its intention to help set up legal frameworks for operation across Europe by involving civil aviation authorities and other relevant bodies in the debate. Academic work since then has discussed whether the EU and the European Union Aviation Safety Agency (EASA) should take on this role.
What it means for operators and customers
- A suborbital operator may need approvals under aviation rules, such as airspace use and coordination with air traffic, as well as under national space legislation.
- Which rules apply can depend on the country of launch and on whether the vehicle is treated as an aircraft, a spacecraft or something in between.
- For people on board, the protection they receive depends on national law, as the US example of informed consent shows.
For the technical side, see our article on suborbital vs orbital flight. For the international treaty framework, see our guide to the Outer Space Treaty.
Frequently asked questions
Is there a legal boundary between airspace and outer space?
No. ICAO noted that international instruments give no vertical limit of airspace, and the UN COPUOS still discusses the definition and delimitation of outer space. The 100 km Kármán line is a widely used reference, not an agreed legal boundary.
Does aviation law or space law apply to suborbital flights?
It is not settled internationally. Under a spatial approach the answer depends on altitude, under a functional approach on the purpose of the flight. In practice, national rules decide, and operators may need approvals under both.
How does the United States protect people on suborbital flights?
Under 14 CFR 460.45, operators must give space flight participants written information about the risks, state that the government has not certified the vehicle as safe, and obtain their signed informed consent.
Related reading
Sources
- ICAO: Concept of Sub-Orbital Flights (C-WP/12436), published by UNOOSA as A/AC.105/C.2/2010/CRP.9
- UNOOSA: Working Group on the Definition and Delimitation of Outer Space
- United States statement, COPUOS Legal Subcommittee 2025, agenda item 6(a)
- eCFR: 14 CFR 460.45, Operator informing space flight participant of risk
- IAASS Space Safety Law and Regulation Committee: Suborbital Flights and the Delimitation of Air Space vis-à-vis Outer Space (submission to UNOOSA, 2017)
- ESA: ESA and space tourism (2008)
- Leiden University: Regulation of Sub-orbital Space Tourism in Europe, A Role for EU/EASA?
Cover image: Layers of the Earth's atmosphere at sunset, photographed from the Space Shuttle on mission STS-52. Credit: NASA (sts052-15-007), public domain.