Quadrupole

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Quadrupole

A quadrupole or quadrapole is one of a sequence of configurations of things like electric charge or current, or gravitational mass that can exist in ideal form, but it is usually just part of a multipole expansion of a more complex structure reflecting various orders of complexity.

Mathematical definition

The quadrupole moment tensor Q is a rank-two tensor—3×3 matrix. There are several definitions, but it is normally stated in the traceless form (i.e. ${\displaystyle Q_{xx}+Q_{yy}+Q_{zz}=0}$). The quadrupole moment tensor has thus 9 components, but because of transposition symmetry and zero-trace property, in this form only 5 of these are independent.

For a discrete system of point charges or masses in the case of a gravitational quadrupole, each with charge ${\displaystyle q_{l}}$, or mass ${\displaystyle m_{l}}$, and position ${\displaystyle {\vec {r_{l}}}=\left(r_{xl},r_{yl},r_{zl}\right)}$ relative to the coordinate system origin, the components of the Q matrix are defined by:

${\displaystyle Q_{ij}=\sum _{l}q_{l}\left(3r_{il}r_{jl}-\left\|{\vec {r_{l}}}\right\|^{2}\delta _{ij}\right)}$.

The indices ${\displaystyle i,j}$ run over the Cartesian coordinates ${\displaystyle x,y,z}$ and ${\displaystyle \delta _{ij}}$ is the Kronecker delta. This means that ${\displaystyle x,y,z}$ must be equal, up to sign, to distances from the point to ${\displaystyle n}$ mutually perpendicular hyperplanes for the Kronecker delta to equal 1.

In the non-traceless form, the quadrupole moment is sometimes stated as:

${\displaystyle Q_{ij}=\sum _{l}q_{l}r_{il}r_{jl}}$

with this form seeing some usage in the literature regarding the fast multipole method. Conversion between these two forms can be easily achieved using a detracing operator.

For a continuous system with charge density, or mass density, ${\displaystyle \rho (x,y,z)}$, the components of Q are defined by integral over the Cartesian space r:

${\displaystyle Q_{ij}=\int \,\rho (\mathbf {r} )\left(3r_{i}r_{j}-\left\|{\vec {r}}\right\|^{2}\delta _{ij}\right)\,d^{3}\mathbf {r} }$

As with any multipole moment, if a lower-order moment, monopole or dipole in this case, is non-zero, then the value of the quadrupole moment depends on the choice of the coordinate origin. For example, a dipole of two opposite-sign, same-strength point charges, which has no monopole moment, can have a nonzero quadrupole moment if the origin is shifted away from the center of the configuration exactly between the two charges; or the quadrupole moment can be reduced to zero with the origin at the center. In contrast, if the monopole and dipole moments vanish, but the quadrupole moment does not, e.g. four same-strength charges, arranged in a square, with alternating signs, then the quadrupole moment is coordinate independent.

If each charge is the source of a "${\displaystyle 1/r}$ potential" field, like the electric or gravitational field, the contribution to the field's potential from the quadrupole moment is:

${\displaystyle V_{\text{q}}(\mathbf {R} )={\frac {k}{|\mathbf {R} |^{3}}}\sum _{i,j}{\frac {1}{2}}Q_{ij}\,{\hat {R}}_{i}{\hat {R}}_{j}\ ,}$

where R is a vector with origin in the system of charges and R̂ is the unit vector in the direction of R. Here, ${\displaystyle k}$ is a constant that depends on the type of field, and the units being used. The factors ${\displaystyle {\hat {R}}_{i},{\hat {R}}_{j}}$ are components of the unit vector from the point of interest to the location of the quadrupole moment.

Electric quadrupole

Contour plot of the equipotential surfaces of an electric quadrupole field

The simplest example of an electric quadrupole consists of alternating positive and negative charges, arranged on the corners of a square. The monopole moment (just the total charge) of this arrangement is zero. Similarly, the dipole moment is zero, regardless of the coordinate origin that has been chosen. But the quadrupole moment of the arrangement in the diagram cannot be reduced to zero, regardless of where we place the coordinate origin. The electric potential of an electric charge quadrupole is given by

${\displaystyle V_{\text{q}}(\mathbf {R} )={\frac {1}{4\pi \epsilon _{0}}}{\frac {1}{|\mathbf {R} |^{3}}}\sum _{i,j}{\frac {1}{2}}Q_{ij}\,{\hat {R}}_{i}{\hat {R}}_{j}\ ,}$

where ${\displaystyle \epsilon _{0}}$ is the electric permittivity, and ${\displaystyle Q_{ij}}$ follows the definition above.

Generalization: higher multipoles

An extreme generalization ("point octopole") would be: Eight alternating point charges at the eight corners of a parallelepiped, e.g. of a cube with edge length a. The "octopole moment" of this arrangement would correspond, in the "octopole limit" ${\displaystyle \lim _{a\to 0;\,a^{3}\cdot Q\to {\text{const.}}}}$, to a nonzero diagonal tensor of order three. Still higher multipoles, e.g. of order 2^l, would be obtained by dipolar (quadrupolar, octopolar, ...) arrangements of point dipoles (quadrupoles, octopoles, ...), not point monopoles, of lower order, e.g. 2^l−1.

Magnetic quadrupole

Coils producing a quadrupole field

Schematic quadrupole magnet ("four-pole")

All known magnetic sources give dipole fields. However, it is possible to make a magnetic quadrupole by placing four identical bar magnets perpendicular to each other such that the north pole of one is next to the south of the other. Such a configuration cancels the dipole moment and gives a quadrupole moment, and its field will decrease at large distances faster than that of a dipole.

An example of a magnetic quadrupole, involving permanent magnets, is depicted on the right. 

Electromagnets of similar conceptual design (called quadrupole magnets) are commonly used to focus beams of charged particles in particle accelerators and beam transport lines, a method known as strong focusing. There are four steel pole tips, two opposing magnetic north poles and two opposing magnetic south poles. The steel is magnetized by a large electric current that flows in the coils of tubing wrapped around the poles. Also, the quadrupole-dipole intersect can be found by multiplying the spin of the unpaired nucleon by its parent atom.

A changing magnetic quadrupole moment produces electromagnetic radiation.

Gravitational quadrupole

The mass quadrupole is analogous to the electric charge quadrupole, where the charge density is simply replaced by the mass density and a negative sign is added because the masses are always positive and the force is attractive. The gravitational potential is then expressed as:

${\displaystyle V_{\text{q}}(\mathbf {R} )=-{\frac {G}{2|\mathbf {R} |^{3}}}\sum _{i,j}Q_{ij}\,{\hat {R}}_{i}{\hat {R}}_{j}\ .}$

For example, because the Earth is rotating, it is oblate (flattened at the poles). This gives it a nonzero quadrupole moment. While the contribution to the Earth's gravitational field from this quadrupole is extremely important for artificial satellites close to Earth, it is less important for the Moon because the ${\displaystyle {\frac {1}{|\mathbf {R} |^{3}}}}$ term falls quickly.

The mass quadrupole moment is also important in general relativity because, if it changes in time, it can produce gravitational radiation, similar to the electromagnetic radiation produced by oscillating electric or magnetic dipoles and higher multipoles. However, only quadrupole and higher moments can radiate gravitationally. The mass monopole represents the total mass-energy in a system, which is conserved—thus it gives off no radiation. Similarly, the mass dipole corresponds to the center of mass of a system and its first derivative represents momentum which is also a conserved quantity so the mass dipole also emits no radiation. The mass quadrupole, however, can change in time, and is the lowest-order contribution to gravitational radiation.

The simplest and most important example of a radiating system is a pair of mass points with equal masses orbiting each other on a circular orbit, an approximation to e.g. special case of binary black holes. Since the dipole moment is constant, we can for convenience place the coordinate origin right between the two points. Then the dipole moment will be zero, and if we also scale the coordinates so that the points are at unit distance from the center, in opposite direction, the system's quadrupole moment will then simply be

${\displaystyle Q_{ij}=M\left(3x_{i}x_{j}-|\mathbf {x} |^{2}\delta _{ij}\right)}$

where M is the mass of each point, and ${\displaystyle x_{i}}$ are components of the (unit) position vector of one of the points. As they orbit, this x-vector will rotate, which means that it will have a nonzero first, and also the second time derivative (this is of course true regardless the choice of the coordinate system). Therefore the system will radiate gravitational waves. Energy lost in this way was first inferred in the changing period of the Hulse–Taylor binary, a pulsar in orbit with another neutron star of similar mass.

Just as electric charge and current multipoles contribute to the electromagnetic field, mass and mass-current multipoles contribute to the gravitational field in general relativity, causing the so-called gravitomagnetic effects. Changing mass-current multipoles can also give off gravitational radiation. However, contributions from the current multipoles will typically be much smaller than that of the mass quadrupole.

Virtual private network

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Virtual_private_network

The term virtual private network (abbreviated VPN) describes any technology that can encapsulate and transmit network data, typically Internet Protocol data, over another network. Such a system enables users to access network resources that may otherwise be inaccessible from the public internet. VPNs are frequently used in the information technology sector to provide access to resources for users that are not physically connected to an organization's network, such as telecommuting workers. VPNs are so named because they may be used to provide virtual (as opposed to physical) access to a private network.

Colloquially, the term VPN may be used to refer, albeit improperly, to a proxy service that uses VPN technology (such as OpenVPN) as opposed to higher-level proxy server protocols (such as SOCKS) as it does not require configuration of individual applications to tunnel their traffic through the proxy server, instead employing routing to redirect traffic.

Configurations

VPN classification tree based on the topology first, then on the technology used.

 

VPN connectivity overview, showing intranet site-to-site and remote-work configurations used together

Broadly speaking, VPN configurations fall into two categories:

Remote access

Analagous to simply plugging one's computer into a network, this configuration enables an individual to access an intranet as if they were physically connected to it. Such a configuration may be employed when a remote worker needs access to private resources, or to enable a mobile worker (such as a cable technician) to access important tools without exposing them to the public internet.

Site-to-site

Instead of connecting a single endpoint to a larger network, site-to-site connections connect two routers. These routers then route traffic bound for other sites over the VPN, effectively creating one seamless local area network that spans multiple physical locations. This configuration is of particular use for businesses, as this allows for distinct offices, data centers, and cloud computing platforms to seamlessly interconnect.

Typically, individuals interact with remote access VPNs, whereas businesses tend to make use of site-to-site connections for business-to-business, cloud computing, and branch office scenarios. Despite this, the two technologies are not mutually exclusive and, in a significantly complex business network, may be combined to enable remote access to resources located at any given site, such as an ordering system that resides in a datacenter.

Intranet versus extranet site-to-site VPNs

In the context of site-to-site configurations, the terms intranet and extranet are used to describe two different use cases. An intranet site-to-site VPN describes a configuration where the sites connected by the VPN belong to the same organization, whereas an extranet site-to-site VPN joins sites belonging to many organizations.

Security mechanisms

VPNs cannot make online connections completely anonymous, but they can usually increase privacy and security. To prevent disclosure of private information, VPNs typically allow only authenticated remote access using tunneling protocols and encryption techniques.

The VPN security model provides:

• confidentiality such that even if the network traffic is sniffed at the packet level (see network sniffer and deep packet inspection), an attacker would see only encrypted data
• sender authentication to prevent unauthorized users from accessing the VPN
• message integrity to detect any instances of tampering with transmitted messages.

The life cycle phases of an IPSec Tunnel in a virtual private network.

Secure VPN protocols include the following:

• Internet Protocol Security (IPsec) was initially developed by the Internet Engineering Task Force (IETF) for IPv6, which was required in all standards-compliant implementations of IPv6 before RFC 6434 made it only a recommendation.^[2] This standards-based security protocol is also widely used with IPv4 and the Layer 2 Tunneling Protocol. Its design meets most security goals: availability, integrity, and confidentiality. IPsec uses encryption, encapsulating an IP packet inside an IPsec packet. De-encapsulation happens at the end of the tunnel, where the original IP packet is decrypted and forwarded to its intended destination.
• Transport Layer Security (SSL/TLS) can tunnel an entire network's traffic (as it does in the OpenVPN project and SoftEther VPN project^[3]) or secure an individual connection. A number of vendors provide remote-access VPN capabilities through SSL. An SSL VPN can connect from locations where IPsec runs into trouble with Network Address Translation and firewall rules.
• Datagram Transport Layer Security (DTLS) – used in Cisco AnyConnect VPN and in OpenConnect VPN to solve the issues SSL/TLS has with tunneling over TCP (tunneling TCP over TCP can lead to big delays and connection aborts).
• Microsoft Point-to-Point Encryption (MPPE) works with the Point-to-Point Tunneling Protocol and in several compatible implementations on other platforms.
• Microsoft Secure Socket Tunneling Protocol (SSTP) tunnels Point-to-Point Protocol (PPP) or Layer 2 Tunneling Protocol traffic through an SSL/TLS channel (SSTP was introduced in Windows Server 2008 and in Windows Vista Service Pack 1).
• Multi Path Virtual Private Network (MPVPN). Ragula Systems Development Company owns the registered trademark "MPVPN".
• Secure Shell (SSH) VPN – OpenSSH offers VPN tunneling (distinct from port forwarding) to secure remote connections to a network or to inter-network links. OpenSSH server provides a limited number of concurrent tunnels. The VPN feature itself does not support personal authentication.
• WireGuard is a protocol. In 2020, WireGuard support was added to both the Linux and Android kernels, opening it up to adoption by VPN providers. By default, WireGuard utilizes Curve25519 for key exchange and ChaCha20 for encryption, but also includes the ability to pre-share a symmetric key between the client and server.

Authentication

Tunnel endpoints must be authenticated before secure VPN tunnels can be established. User-created remote-access VPNs may use passwords, biometrics, two-factor authentication or other cryptographic methods. Network-to-network tunnels often use passwords or digital certificates. They permanently store the key to allow the tunnel to establish automatically, without intervention from the administrator.

Routing

Tunneling protocols can operate in a point-to-point network topology that would theoretically not be considered a VPN because a VPN by definition is expected to support arbitrary and changing sets of network nodes. But since most router implementations support a software-defined tunnel interface, customer-provisioned VPNs often are simply defined tunnels running conventional routing protocols.

Provider-provisioned VPN building-blocks

Site-to-Site VPN terminology.

Depending on whether a provider-provisioned VPN (PPVPN) operates in layer 2 or layer 3, the building blocks described below may be L2 only, L3 only, or a combination of both. Multi-protocol label switching (MPLS) functionality blurs the L2-L3 identity.

RFC 4026 generalized the following terms to cover L2 MPLS VPNs and L3 (BGP) VPNs, but they were introduced in RFC 2547.

Customer (C) devices

A device that is within a customer's network and not directly connected to the service provider's network. C devices are not aware of the VPN.

Customer Edge device (CE)

A device at the edge of the customer's network which provides access to the PPVPN. Sometimes it is just a demarcation point between provider and customer responsibility. Other providers allow customers to configure it.

Provider edge device (PE)

A device, or set of devices, at the edge of the provider network which connects to customer networks through CE devices and presents the provider's view of the customer site. PEs are aware of the VPNs that connect through them, and maintain VPN state.

Provider device (P)

A device that operates inside the provider's core network and does not directly interface to any customer endpoint. It might, for example, provide routing for many provider-operated tunnels that belong to different customers' PPVPNs. While the P device is a key part of implementing PPVPNs, it is not itself VPN-aware and does not maintain VPN state. Its principal role is allowing the service provider to scale its PPVPN offerings, for example, by acting as an aggregation point for multiple PEs. P-to-P connections, in such a role, often are high-capacity optical links between major locations of providers.

User-visible PPVPN services

OSI Layer 2 services

Virtual LAN

Virtual LAN (VLAN) is a Layer 2 technique that allows for the coexistence of multiple local area network (LAN) broadcast domains interconnected via trunks using the IEEE 802.1Q trunking protocol. Other trunking protocols have been used but have become obsolete, including Inter-Switch Link (ISL), IEEE 802.10 (originally a security protocol but a subset was introduced for trunking), and ATM LAN Emulation (LANE).

Virtual private LAN service (VPLS)

Developed by Institute of Electrical and Electronics Engineers, Virtual LANs (VLANs) allow multiple tagged LANs to share common trunking. VLANs frequently comprise only customer-owned facilities. Whereas VPLS as described in the above section (OSI Layer 1 services) supports emulation of both point-to-point and point-to-multipoint topologies, the method discussed here extends Layer 2 technologies such as 802.1d and 802.1q LAN trunking to run over transports such as Metro Ethernet.

As used in this context, a VPLS is a Layer 2 PPVPN, emulating the full functionality of a traditional LAN. From a user standpoint, a VPLS makes it possible to interconnect several LAN segments over a packet-switched, or optical, provider core, a core transparent to the user, making the remote LAN segments behave as one single LAN.

In a VPLS, the provider network emulates a learning bridge, which optionally may include VLAN service.

Pseudo wire (PW)

PW is similar to VPLS, but it can provide different L2 protocols at both ends. Typically, its interface is a WAN protocol such as Asynchronous Transfer Mode or Frame Relay. In contrast, when aiming to provide the appearance of a LAN contiguous between two or more locations, the Virtual Private LAN service or IPLS would be appropriate.

Ethernet over IP tunneling

EtherIP (RFC 3378) is an Ethernet over IP tunneling protocol specification. EtherIP has only packet encapsulation mechanism. It has no confidentiality nor message integrity protection. EtherIP was introduced in the FreeBSD network stack and the SoftEther VPN server program.

IP-only LAN-like service (IPLS)

A subset of VPLS, the CE devices must have Layer 3 capabilities; the IPLS presents packets rather than frames. It may support IPv4 or IPv6.

OSI Layer 3 PPVPN architectures

This section discusses the main architectures for PPVPNs, one where the PE disambiguates duplicate addresses in a single routing instance, and the other, virtual router, in which the PE contains a virtual router instance per VPN. The former approach, and its variants, have gained the most attention.

One of the challenges of PPVPNs involves different customers using the same address space, especially the IPv4 private address space. The provider must be able to disambiguate overlapping addresses in the multiple customers' PPVPNs.

BGP/MPLS PPVPN

In the method defined by RFC 2547, BGP extensions advertise routes in the IPv4 VPN address family, which are of the form of 12-byte strings, beginning with an 8-byte route distinguisher (RD) and ending with a 4-byte IPv4 address. RDs disambiguate otherwise duplicate addresses in the same PE.

PEs understand the topology of each VPN, which are interconnected with MPLS tunnels either directly or via P routers. In MPLS terminology, the P routers are Label Switch Routers without awareness of VPNs.

Virtual router PPVPN

The virtual router architecture, as opposed to BGP/MPLS techniques, requires no modification to existing routing protocols such as BGP. By the provisioning of logically independent routing domains, the customer operating a VPN is completely responsible for the address space. In the various MPLS tunnels, the different PPVPNs are disambiguated by their label but do not need routing distinguishers.

Unencrypted tunnels

Some virtual networks use tunneling protocols without encryption for protecting the privacy of data. While VPNs often do provide security, an unencrypted overlay network does not neatly fit within the secure or trusted categorization. For example, a tunnel set up between two hosts with Generic Routing Encapsulation (GRE) is a virtual private network but is neither secure nor trusted.

Native plaintext tunneling protocols include Layer 2 Tunneling Protocol (L2TP) when it is set up without IPsec and Point-to-Point Tunneling Protocol (PPTP) or Microsoft Point-to-Point Encryption (MPPE).

Trusted delivery networks

Trusted VPNs do not use cryptographic tunneling; instead they rely on the security of a single provider's network to protect the traffic.

• Multi-Protocol Label Switching (MPLS) often overlays VPNs, often with quality-of-service control over a trusted delivery network.
• L2TP which is a standards-based replacement, and a compromise taking the good features from each, for two proprietary VPN protocols: Cisco's Layer 2 Forwarding (L2F) (obsolete as of 2009) and Microsoft's Point-to-Point Tunneling Protocol (PPTP).

From the security standpoint, VPNs either trust the underlying delivery network or must enforce security with mechanisms in the VPN itself. Unless the trusted delivery network runs among physically secure sites only, both trusted and secure models need an authentication mechanism for users to gain access to the VPN.

VPNs in mobile environments

Mobile virtual private networks are used in settings where an endpoint of the VPN is not fixed to a single IP address, but instead roams across various networks such as data networks from cellular carriers or between multiple Wi-Fi access points without dropping the secure VPN session or losing application sessions. Mobile VPNs are widely used in public safety where they give law-enforcement officers access to applications such as computer-assisted dispatch and criminal databases, and in other organizations with similar requirements such as Field service management and healthcare.

Networking limitations

A limitation of traditional VPNs is that they are point-to-point connections and do not tend to support broadcast domains; therefore, communication, software, and networking, which are based on layer 2 and broadcast packets, such as NetBIOS used in Windows networking, may not be fully supported as on a local area network. Variants on VPN such as Virtual Private LAN Service (VPLS) and layer 2 tunneling protocols are designed to overcome this limitation.

VPN services

A wide variety of entities provide "VPNs" for several purposes. But depending on the provider and the application, they do not always create a true private network. Instead, many providers simply provide an Internet proxy that utilizes VPN technologies such as OpenVPN or WireGuard. The term VPN service is sometimes used to refer to these proxies when offered as a commercial service. These services are often used by users wishing to disguise or obfuscate their physical location or IP address, typically as a means to evade Internet censorship or geo-blocking.

Providers often market VPN services as privacy-enhancing, citing security features, such as encryption, from the underlying VPN technology. However, users must consider that when the transmitted content is not encrypted before entering the proxy, that content is visible at the receiving endpoint (usually the VPN service provider's site) regardless of whether the VPN tunnel itself is encrypted for the inter-node transport. The only secure VPN is where the participants have oversight at both ends of the entire data path or when the content is encrypted before it enters the tunnel.

On the client side, configurations intended to use VPN services as proxies are not conventional VPN configurations. However, they do typically utilize the operating system's VPN interfaces to capture the user's data to send to the proxy. This includes virtual network adapters on computer OSes and specialized "VPN" interfaces on mobile operating systems. A less common alternative is to provide a SOCKS proxy interface.

Legality

In March 2018, the use of unapproved VPN services was banned in China as they can be used by citizens to circumvent the Great Firewall.  There have been jail terms and fines imposed on people operating unauthorized VPN services. Individuals have also been fined for accessing websites using a VPN service.

Space law

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Space_law 

  

Hubble Deep Field (full mosaic) released by NASA on January 15, 1996.

Space law is the body of law governing space-related activities, encompassing both international and domestic agreements, rules, and principles. Parameters of space law include space exploration, liability for damage, weapons use, rescue efforts, environmental preservation, information sharing, new technologies, and ethics. Other fields of law, such as administrative law, intellectual property law, arms control law, insurance law, environmental law, criminal law, and commercial law, are also integrated within space law.

The origins of space law date back to 1919, with international law recognizing each country's sovereignty over the airspace directly above their territory, later reinforced at the Chicago Convention in 1944. The onset of domestic space programs during the Cold War propelled the official creation of international space policy (i.e. the International Geophysical Year) initiated by the International Council of Scientific Unions. The Soviet Union's 1957 launch of the world's first artificial satellite, Sputnik 1, directly spurred the United States Congress to pass the Space Act, thus creating the National Aeronautics and Space Administration (NASA). Because space exploration required crossing transnational boundaries, it was during this era where space law became a field independent from traditional aerospace law.

Since the Cold War, the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (the "Outer Space Treaty") and the International Telecommunications Union have served as the constitutional legal framework and set of principles and procedures constituting space law. Further, the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), along with its Legal and Scientific and Technical Subcommittees, are responsible for debating issues of international space law and policy. The United Nations Office for Outer Space Affairs (UNOOSA) serves as the secretariat of the Committee and is promoting Access to Space for All through a wide range of conferences and capacity-building programs. Challenges that space law will continue to face in the future are fourfold—spanning across dimensions of domestic compliance, international cooperation, ethics, and the advent of scientific innovations. Furthermore, specific guidelines on the definition of airspace have yet to be universally determined.

Early developments

One of the earliest works on space law was Czech jurist Vladimír Mandl's Das Weltraum-Recht: Ein Problem der Raumfahrt (Space Law: A Problem of Space Travel), written in German and published in 1932.

At Caltech in 1942 Theodore von Kármán and other rocket scientists banded together to form Aerojet rocket company with the help of lawyer Andrew G. Haley. To toast the new corporation, Kármán said, "Now, Andy, we will make the rockets—you must make the corporation and obtain the money. Later on, you will have to see that we behave well in outer space. ... After all, we are the scientists but you are the lawyer, and you must tell us how to behave ourselves according to law and to safeguard our innocence." Indeed, twenty years later Haley published the fundamental textbook, Space Law and Government.

Beginning in 1957 with the Space Race, nations began discussing systems to ensure the peaceful use of outer space. Bilateral discussions between the United States and USSR in 1958 resulted in the presentation of issues to the UN for debate. In 1959, the UN created the Committee on the Peaceful Uses of Outer Space (COPUOS). COPUOS in turn created two subcommittees, the Scientific and Technical Subcommittee and the Legal Subcommittee. The COPUOS Legal Subcommittee has been a primary forum for discussion and negotiation of international agreements relating to outer space.

In 1960 the International Astronautical Congress met in Stockholm and heard several submissions including a survey of legal opinion on extraterrestrial jurisdiction by Andrew G. Haley.

General Assembly Resolutions 1721 (XVI) and 1802 (XVII), both titled "International Cooperation in the Peaceful Uses of Outer Space", and Resolution 1962 (XVIII), or a "Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space" were passed unanimously. These basic principles formed the foundation of the 1963 Outer Space Treaty.

International treaties

Five international treaties have been negotiated and drafted in the COPUOS:

• The 1967 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (the "Outer Space Treaty").
• The 1968 Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space (the "Rescue Agreement").
• The 1972 Convention on International Liability for Damage Caused by Space Objects (the "Liability Convention").
• The 1975 Convention on Registration of Objects Launched into Outer Space (the "Registration Convention").
• The 1979 Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (the "Moon Treaty").

The Outer Space Treaty is the most widely adopted treaty, with 110 parties. The Rescue Agreement, the Liability Convention and the Registration Convention all elaborate on provisions of the Outer Space Treaty. The Moon Treaty has only 18 parties however, and many consider it to be a failed treaty due to its limited acceptance.

In addition, the 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space, and Under Water ("Partial Test Ban Treaty") banned the testing of nuclear weapons in outer space.

1998 ISS agreement

In addition to the international treaties that have been negotiated at the United Nations, the nations participating in the International Space Station have entered into the 1998 Agreement among the governments of Canada, Member States of the European Space Agency, Japan, Russian Federation, and the United States concerning cooperation on the Civil International Space Station. This agreement provides, among other things, that NASA is the lead agency in coordinating the member states' contributions to and activities on the space station, and that each nation has jurisdiction over its own module(s). The agreement also provides for protection of intellectual property and procedures for criminal prosecution. This agreement may very well serve as a model for future agreements regarding international cooperation in facilities on the Moon and Mars, where the first off-world colonies and scientific/industrial bases are likely to be established.

International principles and declarations

The five treaties and agreements of international space law cover "non-appropriation of outer space by any one country, arms control, the freedom of exploration, liability for damage caused by space objects, the safety and rescue of spacecraft and astronauts, the prevention of harmful interference with space activities and the environment, the notification and registration of space activities, scientific investigation and the exploitation of natural resources in outer space and the settlement of disputes".

The United Nations General Assembly adopted five declarations and legal principles which encourage exercising the international laws, as well as unified communication between countries. The five declarations and principles are:

• The Declaration of Legal Principles Governing the Activities of States in the Exploration and Uses of Outer Space (1963)
• All space exploration will be done with good intentions and is equally open to all States that comply with international law. No one nation may claim ownership of outer space or any celestial body. Activities carried out in space must abide by the international law and the nations undergoing these said activities must accept responsibility for the governmental or non-governmental agency involved. Objects launched into space are subject to their nation of belonging, including people. Objects, parts, and components discovered outside the jurisdiction of a nation will be returned upon identification. If a nation launches an object into space, they are responsible for any damages that occur internationally.
  • Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (1979)
    

• Apollo 15 Moon landing. Jul 26, 1971 – Aug 7, 1971
  The agreement exists to promote the exploration of outer space but to keep the moon and other celestial bodies in pristine conditions for the common heritage of mankind, meaning that no nation may claim sovereignty over any part of space. All countries should have equal rights to conduct research on the moon or other celestial bodies. Weapons of mass destruction of any kind including nuclear and bases built for military purposes are specifically banned by the treaty. The United Nations resolution also states that all State Parties may conduct their enterprises below the surface of the moon or any celestial body so long as efforts are made to protect it from contamination. All activities in space are required to be attached to a nation and any damages to other nations equipment or facilities caused by another party must be repaid in full to that nation. Any discovery of a dangerous hazard such as an area that is radioactive must notify the United Nations Secretary General and the greater international scientific community immediately.

All missions in space lasting longer than 60 days must notify the UN Secretary General and the greater scientific community every 30 days of progress. Any samples that are collected from space must be made available at earliest convenience to the scientific community. The agreement does not include meteorites that fall to earth by natural means. Currently not a single nation that conducts its own missions in space has ratified the agreement. This likely signifies that the 'Moon Treaty is likely a failed treaty because none of the nations that actually go into space signed or ratified the agreement.

• The Principles Governing the Use by States of Artificial Earth Satellites for International Direct Television Broadcasting (1982)

Activities of this nature must be transpired in accordance with the sovereign rights of States. Said activities should "promote the free dissemination and mutual exchange of information and knowledge in cultural and scientific fields, assist in educational, social and economic development, particularly in the developing countries, enhance the qualities of life of all peoples and provide recreation with due respect to the political and cultural integrity of States". All States have equal rights to pursue these activities and must maintain responsibility for anything carried out under their boundaries of authority. States planning activities need to contact the Secretary-General of the United Nations with details of the undergoing activities.

• The Principles Relating to Remote Sensing of the Earth from Outer Space (1986)

Fifteen principles are stated under this category. The basic understanding comes from these descriptions given by the United Nations Office for Outer Space Affairs:

(a) The term "remote sensing" means the sensing of the Earth's surface from space by making use of the properties of electromagnetic waves emitted, reflected or :diffracted by the sensed objects, for the purpose of improving natural resources management, land use and the protection of the environment;

(b) The term "primary data" means those raw data that are acquired by remote sensors borne by a space object and that are transmitted or delivered to the ground :from space by telemetry in the form of electromagnetic signals, by photographic film, magnetic tape or any other means;

(c) The term "processed data" means the products resulting from the processing of the primary data, needed to make such data usable;

(d) The term "analysed information" means the information resulting from the interpretation of processed data, inputs of data and knowledge from other sources;

(e) The term "remote sensing activities" means the operation of remote sensing space systems, primary data collection and storage stations, and activities in :processing, interpreting and disseminating the processed data.

• The Principles Relevant to the Use of Nuclear Power Sources in Outer Space (1992)

"States launching space objects with nuclear power sources on board shall endeavour to protect individuals, populations and the biosphere against radiological hazards. The design and use of space objects with nuclear power sources on board shall ensure, with a high degree of confidence, that the hazards, in foreseeable operational or accidental circumstances, are kept below acceptable levels. ..."

• The Declaration on International Cooperation in the Exploration and Use of Outer Space for the Benefit and in the Interest of All States, Taking into Particular Account the Needs of Developing Countries (1996)

"States are free to determine all aspects of their participation in international cooperation in the exploration and use of outer space on an equitable and mutually acceptable basis. All States, particularly those with relevant space capabilities and with programmes for the exploration and use of outer space, should contribute to promoting and fostering international cooperation on an equitable and mutually acceptable basis. In this context, particular attention should be given to the benefit for and the interests of developing countries and countries with incipient space programmes stemming from such international cooperation conducted with countries with more advanced space capabilities. International cooperation should be conducted in the modes that are considered most effective and appropriate by the countries concerned, including, inter alia, governmental and non-governmental; commercial and non-commercial; global, multilateral, regional or bilateral; and international cooperation among countries in all levels of development."

Consensus

The United Nations Committee on the Peaceful Uses of Outer Space and its Scientific and Technical and Legal Subcommittees operate on the basis of consensus, i.e. all delegations from member States must agree on any matter, be it treaty language before it can be included in the final version of a treaty or new items on Committee/Subcommittee's agendas. One reason that the U.N. space treaties lack definitions and are unclear in other respects, is that it is easier to achieve consensus when language and terms are vague. In recent years, the Legal Subcommittee has been unable to achieve consensus on discussion of a new comprehensive space agreement (the idea of which, though, was proposed just by a few member States). It is also unlikely that the Subcommittee will be able to agree to amend the Outer Space Treaty in the foreseeable future. Many space faring nations seem to believe that discussing a new space agreement or amendment of the Outer Space Treaty would be futile and time-consuming, because entrenched differences regarding resource appropriation, property rights and other issues relating to commercial activity make consensus unlikely.

National law

Space law also encompasses national laws, and many countries have passed national space legislation in recent years. The Outer Space Treaty gives responsibility for regulating space activities, including both government and private sector, to the individual countries where the activity is taking place. If a national of, or an organization incorporated in one country launches a spacecraft in a different country, interpretations differ as to whether the home country or the launching country has jurisdiction.

The Outer Space Treaty also incorporates the UN Charter by reference, and requires parties to ensure that activities are conducted in accordance with other forms of international law such as customary international law (the custom and practice of states).

The advent of commercial activities like space mining, space tourism, private exploration, and the development of many commercial spaceports, is leading many countries to consider how to regulate private space activities. The challenge is to regulate these activities in a manner that does not hinder or preclude investment, while still ensuring that commercial activities comply with international law. The developing nations are concerned that the spacefaring nations will monopolize space resources. Royalties paid to developing countries is one reason the United States has not ratified the United Nations Convention on the Law of the Sea, and why some oppose applying the same principles to outer space.

Several nations have enacted or recently updated their national space law, for example, Luxembourg in 2017, the United States in 2015, and Japan in 2008. Due to the expansion of the domain of space research and allied activities in India, the Draft Space Activities Bill was introduced in the year 2017.

Defining "space"

Many questions arise from the difficulty of defining the term "space". Scholars not only debate its geographical definition (i.e. upper and lower limits), but also whether or not it also encompasses various objects within it (i.e. celestial objects, human beings, man-made devices). Lower limits are generally estimated to be about 50 kilometers. More difficulties arise trying to define the upper bounds of "space", as it would require more inquiry into the nature of the universe and the role of Earth as a planet.

Geostationary orbit allocation

Source: Own work, Earth bitmap is File:North_pole_february_ice-pack_1978-2002.png by Geo Swan. Creative Commons Attribution-Share Alike 3.0 Unported license. (No changes made.)

Allocative Limitations

Objects in geostationary orbits remain stationary over a point on the earth due to gravity. There are numerous advantages in being able to use these orbits, mostly due to the unique ability to send radio frequencies to and from satellites to collect data and send signals to various locations. The United Nations Committee on Peaceful Uses of Outer Space has approved seven nonmilitary uses for these orbits: communications, meteorology, earth resources and environment, navigation and aircraft control, testing of new systems, astronomy, and data relay. The requirement to space these satellites apart means that there is a limited number of orbital "slots" available, thus only a limited number of satellites can be placed in geostationary orbit. This has led to conflict between different countries wishing access to the same orbital slots (countries at the same longitude but differing latitudes). These disputes are addressed through the ITU allocation mechanism.

Countries located at the Earth's equator have also asserted their legal claim to control the use of space above their territory, notably in 1976, when many countries located at the Earth's equator created the Bogota Declaration, in which they asserted their legal claim to control the use of space above their territory.

Political Controversy

Future developments using geostationary orbits may include an expansion of services in telecommunication, broadcasting, and meteorology. As a result, uses for geostationary orbits may stir political controversy. For example, broadcasting and telecommunication services of satellites orbiting above Earth from certain nations may accidentally "spill over" into other nations' territory. This may prompt conflict with nations that wish to restrict access to information and communication. Current and future political and legal concerns allocation may pose may be addressed by international legislatures, such as the United Nations Committee on the Peaceful Uses of Outer Space and the International Telecommunication Union.

Environmental Protection

More recent discussions focus on the need for the international community to draft and institute a code of space ethics to prevent the destruction of the space environment. Furthermore, the advancement of life in space pertain to questions related to the ethics of biocentrism and anthropocentrism, or in other words, determining how much value we place in all living things versus human beings specifically. Currently, researchers in the bioengineering field are working towards contamination control measures integrated into spacecraft to protect both space and earth's biosphere.

Ethics

In space law, ethics extend to topics regarding space exploration, space tourism, space ownership, the militarization of space, environmental protection, and distinguishing the boundaries of space itself.

Human representation and participation

Participation and representation of all humanity in space is an issue of international space law ever since the first phase of space exploration. Even though rights of non-spacefaring countries have been secured by declaring the exploration and use of outer space as the "province of all mankind", understanding spaceflight as its resource, sharing of space for all humanity is still criticized as imperialist and lacking. It has been argued that the present politico-legal regimes and their philosophic grounding advantage imperialist development of space.

Space colonization has been discussed as particular continuation of imperialism and colonialism. Questioning colonial decisionmaking and reasons for colonial labour and land exploitation with postcolonial critique. Seeing the need for inclusive and democratic participation and implementation of any space exploration, infrastructure or habitation.

Early on in the development of international space law outer space was framed as res communis and explicitly not as terra nullius in the Magna Carta of Space presented by William A. Hyman in 1966 and subsequently influencing the work of the United Nations Committee on the Peaceful Uses of Outer Space.

Commercial Use

Early discussions regarding space ethics revolved around whether or not the space frontier should be available for use, gaining prominence at the time of the Soviet Union and United States' Space Race. In 1967, the "Outer Space Treaty" dictated that all nations in compliance with international regulation are permitted to exploit space. As a result, the commercial use of space is open to exploitation by public and private entities, especially in relation to mining and space tourism. This principle has been the subject of controversy, particularly by those in favor of environmental protection, sustainability, and conservation.

Exploitation

American Society of International Law Space Interest Group 2014 Board meeting

While this field of the law is still in its infancy, it is in an era of rapid change and development. Arguably, the resources of space are infinite. If commercial space transportation becomes widely available, with substantially lower launch costs, then all countries will be able to directly reap the benefits of space resources. In that situation, it seems likely that consensus will be much easier to achieve with respect to commercial development and human settlement of outer space. High costs are not the only factor preventing the economic exploitation of space: it is argued that space should be considered as a pristine environment worthy of protection and conservation, and that the legal regime for space should further protect it from being used as a resource for Earth's needs. Debate is also focused on whether space should continue to be legally defined as part of the "Common heritage of mankind", and therefore unavailable for national claims, or whether its legal definition should be changed to allow private property in space.

As of 2013, NASA's plans to capture an asteroid by 2021 has raised questions about how space law would be applied in practice.

In 2016, the nation of Luxembourg has set out a formal legal framework which ensures that private companies engaged in mining resources in space have rights to those resources.

Contact regime

There have been some proposals as with the Magna Carta of Space presented by William A. Hyman in 1966 or through the concept of metalaw to introduce legal basics in case of detection of or contact with indigenous extraterrestrial intelligence.

Future developments

Future coordination and cooperation

International coordination and cooperation is facilitated by the growing inter-agency International Space Exploration Coordination Group and planned for the Lunar Gateway space station, emulating the cooperation for the ISS.

Legal Profession

Michael Dodge, of Long Beach, Mississippi, was the first law school graduate to receive a space law certificate in the United States. Dodge graduated from the National Center for Remote Sensing, Air and Space Law at the University of Mississippi School of Law in 2008. He is now an assistant professor in the Department of Space Studies at the University of North Dakota.

There is a growing emphasis on space law in academia. Since 1951, the McGill Faculty of Law in Montreal, Canada hosts the Institute of Air and Space Law, and offers an LL.M. in Air and Space law. The University of Mississippi School of Law publishes the world's only law journal devoted to space law, the Journal of Space Law. The University of Mississippi School of Law is also the only ABA accredited law school in the world to offer a JD Concentration in Air and Space Law. Over the last decade, other universities have begun to offer specialized courses and programs in the USA, UK, France, the Netherlands, and Australia.

In September 2012, the Space Law Society (SLS) at the University of Maryland Francis King Carey School of Law was established. A legal resources team united in Maryland, a "Space Science State", with Jorge Rodriguez, Lee Sampson, Patrick Gardiner, Lyra Correa and Juliana Neelbauer as SLS founding members. In 2014, students at American University Washington College of Law founded the school's Space Law Society, with the help of Pamela L. Meredith, space lawyer and adjunct professor of Satellite Communications and Space Law.

Efforts to codify the legal regime are mostly represented in the Manual on International Law Applicable to Military Uses of Outer Space (MILAMOS) and the Woomera Manual. Like the San Remo and Tallinn Manuals, the goal is to clarify the law as it relates to outer space.

In 2018, two space lawyers - Christopher Hearsey and Nathan Johnson - founded the Space Court Foundation, a 501(c)(3) educational nonprofit corporation that promotes and supports space law and policy education and the rule of law. The Space Court Foundation produces educational materials and scholarship through the administration of two major projects: Stellar Decisis and the Space Court Law Library. The Foundation engages in partnerships and collaborations that help grow greater awareness of space law and how disputes in space may be resolved as humans venture farther from Earth in the not too distant future. 

International efforts to inform progressive development of International Space Law

The McGill Institute of Air and Space Law is leading multiple international collaborative projects to contribute towards clarifying international space law and promote rules-based global order. One such project announced in 2017, being lead by Prof. Ram S. Jakhu, is the McGill Manual on International Law Applicable to Military Uses of Outer Space (MILAMOS Project) which aims to clarify existing rules of international law as they apply to military uses of outer space. The MILAMOS Project aims to contribute to "a future where all space activities are conducted in accordance with the international rules-based global order, without disrupting, and preferably contributing to, the sustainable use of outer space for the benefit of present and future generations of all humanity." Another international collaborative project announced in 2020, being led by Prof. Ram S. Jakhu, Bayar Goswami and Kuan-Wei (David) Chen, is the McGill Encyclopedia of International Space Law (at SpaceLawPedia.com) which aims to "fulfill the need for an objectively curated online resource on key subject-matters of international space law. With the input of a team of global practitioners and academics in the field of international space law and general international law, the SpaceLawPedia aims to be the definitive source of peer-reviewed reference material for anyone practising, conducting research on or teaching international space law."