OrbitalHub

Wikipedia dixit:

“The Larsen Ice Shelf is a long, fringing ice shelf in the northwest part of the Weddell Sea, extending along the east coast of the Antarctic Peninsula from Cape Longing to the area just southward of Hearst Island. It is named for Captain Carl Anton Larsen, the master of the Norwegian whaling vessel Jason, who sailed along the ice front as far as 68°10′ South during December 1893. In finer detail, the Larsen Ice Shelf is a series of shelves that occupy (or occupied) distinct embayments along the coast. From north to south, the segments are called Larsen A (the smallest), Larsen B, and Larsen C (the largest) by researchers who work in the area. Further south, Larsen D and the much smaller Larsen E, F and G are also named. The breakup of the ice shelf since the mid 1990s has been widely reported, with the collapse of Larsen B in 2002 being particularly dramatic.

Larsen C is the fourth largest ice shelf in Antarctica, with an area of about 50,000 km2 (19,000 sq mi). In 2004, a report concluded that although the remaining Larsen C region appeared to be relatively stable, continued warming could lead to its breakup within the next decade. News reports in summer of 2016 suggested that this process has begun. On 10 November 2016 scientists photographed the growing rift running along the Larsen C ice shelf, showing it running about 110 kilometres (68 mi) long with a width of more than 91 m (299 ft), and a depth of 500 m (1,600 ft). By December 2016, the rift had extended another 21 km (13 mi) to the point where only 20 km (12 mi) of unbroken ice remained and calving was considered to be a certainty in 2017. This will cause the collapse of between nine and twelve percent of the ice shelf, 6,000 km2 (2,300 sq mi), an area greater than the size of the US state of Delaware. After calving, the broken fragment will be 350 m (1,150 ft) thick and have an area of about 5,000 km2 (1,900 sq mi). If it calves without breaking into small fragments, it will be among the largest icebergs ever recorded.

On 1 May 2017 members of the Antarctic research group Project MIDAS, a British Antarctic research project observing the ever-growing crack, reported that satellite images showed a new crack, around 9 miles long (15 kilometers), branching off the main crack approximately six miles behind the previous tip, heading toward the ice front. Scientists with Swansea University in the UK say the crack lengthened 11 miles from 25 May to 31 May, and that less than 8 miles of ice is all that prevents the birth of an enormous iceberg.

Since the ice shelf is already floating, its departure from Antartica would not affect global sea levels. But a number of glaciers discharge onto it from the lands behind the ice shelf, and therefore might flow faster if it breaks away from the continent. If all the ice that the Larsen C shelf currently holds back were to enter the sea, it is estimated that global waters would rise by 10 cm (4 in).”

Video credit: ESA

ESA dixit:

“Space debris – a journey to Earth takes the audience on a journey from the outer solar system back to our home planet. The objects encountered along the way are man made. Originally designed to explore the universe, these are now a challenge for modern space flight. An estimated number of 700,000 objects larger than 1 cm and 170 million objects larger than 1 mm are expected to reside in Earth orbits.

The video gives a closer look at the different regions used for space flight and explains how mitigation and removal measures could preserve future usage of these orbits.”

Video credit: ESA/ID&Sense/ONiRiXEL, CC BY-SA 3.0 IGO

Credits: Ronald C. Wittmann

There are numerous examples of successful implementation of mitigation measures, but also some not so successful, and even failures. There are two cases that I will mention, one from each camp.

Cosmos 954 was a Soviet Radar Ocean Reconnaissance Satellite (RORSAT) powered by an onboard nuclear reactor. At the time, the Russian designers were not able to find an alternative for the power system due to the power requirements of the payload carried by the spacecraft, which was a powerful radar. A post-mission mitigation method that involved parking the nuclear reactor on a higher orbit (with an estimated lifetime of hundreds of years) was adopted.

It seems that not enough effort was put into designing a reliable solution for the post-mission disposal method of the nuclear reactor. Besides the inherent low reliability associated with hardware in developmental phases, the quality assurance practices at that time were most likely affected by the conditions of the Cold War. In both camps, the concerns regarding the environment were ignored in favor of the military and political goals.

In 1978, COSMOS 954 failed to separate its nuclear reactor core and boost it into the post-mission parking orbit as planned. The reactor remained onboard the satellite and eventually re-entered into the Earth atmosphere and crashed near the Great Slave Lake in Canada’s Northwest Territories. The radioactive fuel was spread over a 124,000 km2 area. The recovery teams retrieved 12 large pieces of the reactor, which comprised only 1% of the reactor fuel. All of these pieces displayed lethal levels of radioactivity.

To highlight how dangerous and how serious the use of nuclear power sources for space mission is, consider these figures: at present, there are 32 defunct nuclear reactors in orbit around the Earth. There are also 13 reactor fuel cores and at least 8 radio-thermal generators (RTGs). The total mass of RTG nuclear fuel in orbit is in the order of 150 kg. The total mass of Uranium-235 reactor fuel in orbit is in the order of 1,000 kg.

RADARSAT-1 is an Earth observation satellite developed in Canada. Equipped with a powerful synthetic aperture radar (SAR) instrument, RADARSAT-1 monitors environmental changes and the planet’s natural resources. Well beyond the planned five-year lifetime, the satellite continues to provide images of the Earth for both scientific and commercial applications.

Following the guidelines of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) document entitled Guidelines for Space Debris Mitigation, and implementing mitigation measures required for the space hardware manufacturers in Canada, the Canadian Space Agency has prepared post-mission disposal plans for its remote sensing satellite RADARSAT-1. As a prerequisite to the end of mission procedures, the energy stored in the propellant tanks, the wheels, and the batteries of the satellite will be removed, as suggested in the COPUOS guidelines. Also, the remaining fuel will be used to lower the orbit in addition to orienting the satellite so that drag is maximized. These measures will aim to reduce the orbit life span of the satellite to the lowest possible.

Simulations performed using NASA’s long-term debris environment evolutionary model (LEO-to-GEO Environment Debris model or LEGEND) or ESA’s debris environment long-term analysis tool (DELTA) have shown that even if new launches are not conducted, the existing population of orbital debris will continue to increase. This increase in number is caused by collisions between the objects already orbiting the Earth at the present time. Following the Iridium/Cosmos collision in 2009, the U.S. Air Force has issued hundreds of notifications to Russia and China regarding potential crashes between their satellites and other objects in orbit.

Even if we are contemplating grim future developments like the one mentioned above, international initiatives do not seem to gain enough momentum. NASA (National Aeronautics and Space Administration) and DARPA (Defense Advanced Research Projects Agency) were the sponsors of the first International Conference on Orbital Debris Removal, which was held in Chantilly, Virginia, December 8-10, 2009. The conclusions of the conference included the observation that:

“No evident consensus or conclusions were reached at the conference. Removing existing, non-cooperative objects from Earth orbit is an extremely difficult and likely expensive task. Although some of the techniques for removal discussed at the Conference have the potential of being developed into technically feasible systems, each concept seems to currently suffer from either a lack of development and testing or economic viability.”

Credits: Orbital Sciences Corporation

We can identify two categories of risks associated with mitigation methods: operational risks and risks associated with re-entry.

Operational risks are linked to three major factors. The first is the limited amount of information that satellite operators are willing to share, in some cases for national security reasons. Obviously, a balance must be found between the need for operators to protect sensitive information and the need to share information in order to ensure the safety of space missions.

The second is that satellites can trespass into the operating space of other satellites. This can happen during launch, when relocating to a new orbit, or during the decommissioning phase. Information related to these operations must be shared among satellite operators. If not, collisions are very likely to occur.

Finally, decreased reliability due to implementation of mitigation measures can cause partial or complete loss of control of satellites, which drift from designated orbits. Events like these must be announced as they can lead to collisions as well.

Risks associated with re-entry are due to the fact that in most cases the re-entry happens at random, with no control over the parameters of the impact. For large objects, it is expected that 20% to 40% of the mass survives the ablation and reaches the ground. Even if there is a residual risk to the ground population, to air traffic, and to maritime traffic, re-entry, as a post-mission disposal method, is a viable option in order to preserve a safe level for space operations.

The most important economic implication caused by the adoption of space debris mitigation methods is the increased costs of spacecraft and launch vehicles as well as their operations. In general, modifying the designs of spacecraft and launch vehicles adds to the development costs. However, including mitigation measures early in the design and striving to achieve simpler designs, may lead to simpler and more cost-effective solutions. Launch performance and mass penalty must also be taken into account. Mission profiles that require upper stages of launch vehicles to have a short orbital lifetime will affect launch performances. In the same way, additional mass added to meet mitigation objectives will lower the payload capacity. Mission lifetime can also be affected by post-mission disposal methods. Many satellite operators have accepted the time penalty because it allows them to preserve their orbital regimes.

Reliability is also of great concern, as embedding debris mitigation measures into the spacecraft can affect the overall reliability of the system.

An important observation to make is that as long as mitigation methods are not imposed to hardware manufacturers, the early adopters will have a slight disadvantage. Slogans like ‘True, more expensive, but we are green!’ might not do the trick in this case.

Credits: NASA

The International Organization for Standardization (ISO) has implemented the UN Space Debris Mitigation guidelines in a number of standards.

The standards prescribe requirements that are derived from already existing international guidelines, but they capture industry best practices and contain specific actions to be taken by hardware manufactures to achieve compliance.

The highest level debris mitigation requirements are contained in a Space Debris Mitigation standard. This standard defines the main space debris mitigation requirements applicable over the life cycle of a space system and provides links to lower-level implementation standards. It is also important to be able to assess, reduce, and control the potential risks that space vehicles that re-enter Earth’s atmosphere pose to people and the environment. The Re-entry Risk Management standard provides a framework that is useful in this regard.

The seven guidelines endorsed by the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), also known as the Space Debris Mitigation Guidelines of COPUOS, are:

“limit debris released during normal operations;

minimize the potential for break-ups during operational phases;

limit the probability of accidental collision in orbit;

avoid intentional destruction and other harmful activities;

minimize potential for post-mission break-ups resulting from stored energy;

limit the long-term presence of spacecraft and launch vehicle orbital stages in LEO after the end of their mission;

limit the long-term interference of spacecraft and launch vehicle orbital stages with GEO region after the end of their mission;”

The good news is that as of the end of 2010, most of the space faring nations have implemented regulations on space debris mitigation at the national level.

Credits: CSA

Canada is actively involved in space debris mitigation research and development activities. At the international level, Canada hosted the International Conference on Protection of Materials and Structures from the Space Environment (ICPMSE) in May 2008, and contributed to the 37th Committee on Space Research (COSPAR) Scientific Assembly in July 2008.

At the national level, the space debris research and development activities are coordinated by the Canadian Space Agency (CSA), which formed the Orbital Debris Working Group (ODWG). The group was formed in order to address a number of objectives:

“to increase the Scientific and Technical (S&T) knowledge and awareness of orbital debris in the space community;

to identify and encourage targeted Research and Development (R&D) in orbital debris and mitigation measures;

to identify and encourage development of orbital debris detection and collision avoidance techniques and technologies;

to promote Scientific and Technical (S&T) collaboration across Canada and with our international partners;

to identify Scientific and Technical (S&T) opportunities in relation to future potential missions which can directly benefit from the results of targeted Research and Development (R&D) and novel operational techniques, and develop and coordinate technical solution in Canada and with international partners; and

to establish and maintain technical liaison with our international partners in order to foster a sustainable space environment.”

The Canadian space debris mitigation research and development activities are focused on three main areas: hypervelocity impact facilities, debris mitigation and self healing materials, and spacecraft demise technologies. Hypervelocity impact facilities are facilities that are capable of accelerating projectiles to velocities of more than 10 km/s. Canada is developing an implosion-driven hypervelocity launcher facility. Such a facility could accelerate projectiles having a mass of 10 g to speeds of 10 km/s, facilitating meaningful impact studies. Self healing materials have the capability to initiate a self healing process after an impact, being an in-situ mitigation of space debris damage on board spacecraft. The Canadian Space Agency has supported the efforts to develop and test a self healing concept demonstrator. The spacecraft demise technologies ensure intentional and integral disintegration during re-entry, so that no debris reaches Earth. In this direction, studies that investigate various technologies that could be used to de-orbit micro- and nanosatellites have been conducted.

In Canada, the space operators and manufacturers are adopting the space debris mitigation measures on a voluntary basis. The Inter-Agency Space Debris (IADC) guidelines are used for monitoring activities to prevent on-orbit collisions and conduct post-mission disposal. There are also strict requirements integrated in its policies and regulations that address the post-mission disposal of satellites. For example, as required by the Canadian Remote Sensing Space System Act, space system manufacturers have to provide information regarding the method of disposal for the satellite, the estimated duration of the satellite disposal operation, the probability of loss of human life, the amount of debris expected to reach the surface of the Earth upon re-entry, an estimate of the orbital debris expected to be released by the satellite during normal operations by explosion, etc. There are also interesting recommendations made for the operation and post-mission disposal of satellites in Geostationary Orbits. The Environmental Protection of the Geostationary Satellite Orbit recommends “that as little debris as possible should be released into the geostationary orbit during the placement of a satellite in orbit”, and also that “a geostationary satellite at the end of its life should be transferred, before complete exhaustion of its propellant, to a super synchronous graveyard orbit”, where the recommended minimum re-orbiting altitude is given as 300 km.