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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.”

 

 

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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.

 

 

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Credits: CSA

 

RADARSAT-1 is the first commercial Earth observation satellite developed in Canada, and it is equipped with a powerful synthetic aperture radar (SAR) instrument.

 

Launched on November 4, 1995, from Vandenberg Air Force Base in California, the satellite is well beyond the planned five-year lifetime, and continues to provide images of the Earth for both scientific and commercial applications.

 

 

Canada is involved in space debris mitigation research and development activities. In Canada, these activities are coordinated by the Canadian Space Agency, which formed a group, the Orbital Debris Working Group, in order to address a number of objectives such as to increase the knowledge and awareness of orbital debris in the space community, to encourage research in orbital debris and mitigation measures, and to support development of orbital debris detection and collision avoidance techniques and technologies.

 

In Canada, the space operators and manufacturers are adopting space debris mitigation measures on a voluntary basis. Existing guidelines are used for monitoring activities to prevent on-orbit collisions and conduct post-mission disposal procedures. Space system manufacturers have to provide, among other things, information regarding the method of disposal for the satellite and the estimated duration of the satellite disposal operation.

 

Credits: NASA/GSFC Scientific Visualization Studio

 

The Canadian Space Agency has prepared post-mission disposal plans for its remote sensing satellite RADARSAT-1, plans that comply with the guidelines of the United Nations document entitled Guidelines for Space Debris Mitigation and with the measures required for the space hardware manufacturers in Canada.

 

The remaining fuel will be used to lower the orbit and orient the satellite so that drag is maximized.

 

 

Also, the energy stored in the propellant tanks, the reaction wheels, and the batteries of the satellite will be removed. In this way, the on-orbit retirement period of the satellite is reduced to the lowest possible.

 

You can find more information about RADARSAT-1 on the Canadian Space Agency’s web site.

 

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01-17-10

Sentinel

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Credits: ESA – P.Carril

 

The European Union’s Global Monitoring for Environment and Security (GMES) initiative was born as the result of a growing need for accurate and accessible information about the environment, the effects of climate change, and civil security. GMES uses as its main information feed the data collected by satellites developed by ESA. Data is also collected by instruments carried by aircraft, floating in the ocean, or located on the ground.

 

 

GMES provides services that can be grouped into five main categories: land management, marine environment, atmosphere, aid emergency response, and security.

 

There are five Sentinel missions designed as components of the GMES initiative. These missions will complement the national initiatives of the EU members involved. The missions will collect data for land and ocean monitoring, and atmospheric composition monitoring, making use of all-weather radar and optical imaging. Each of the Sentinel missions is based on a constellation of two satellites.

 

Sentinel-1 is an all-weather radar-imaging mission. The satellites will have polar orbits and collect data for the GMES land and ocean services. The first satellite is scheduled for launch in 2012. Sentinel-1 will ensure the continuity of Synthetic Aperture Radar (SAR) applications, taking over from systems carried by ERS-1, ERS-2, Envisat, and Radarsat. Sentinel-1 satellites will be carried to orbit by Soyuz launch vehicles lifting off from Kourou.

 

Sentinel-2 will provide high-resolution multi-spectral imagery of vegetation, soil, and water, and will cover inland waterways and coastal areas. Sentinel-2 is designed for the data continuity of missions like Landsat or SPOT (Satellite Pour l’Observation de la Terre). Each satellite will carry a Multi-Spectral Imager (MSI) that can ‘see’ in thirteen spectral bands spanning from the visible and near infrared (VNIR) to the shortwave infrared (SWIR). The first Sentinel-2 is planned to launch in 2013. Vega will provide launch services for Sentinel-2 missions.

 

Credits: ESA – P.Carril

 

Sentinel-3 will determine parameters such as sea-surface topography and sea and land surface temperature. It will also determine ocean and land colour with high accuracy. The first Sentinel-3 satellite is expected to reach orbit in 2013. The spacecraft bus has a three-meter accuracy real-time orbit determination capability based on GPS and Kalman filtering.

 

 

Sentinel-4 is devoted to atmospheric monitoring and it will consist of payloads carried by Meteosat Third Generation (MTG) satellites that are planned to launch in 2017 and 2024. Sentinel-5 will be used for atmospheric monitoring as well. The payload will be carried by a post-EUMETSAT Polar System (EPS) spacecraft, planned to launch in 2020. A Sentinel-5 precursor will ensure that no data gap will exist between the Envisat missions and Sentinel-5.

 

You can find out more about the GMES initiative and the Sentinel missions on a dedicated page on ESA’s website.

 

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