A Canadian Space Telescope

The Cosmological Advanced Survey Telescope for Optical and uv Research (CASTOR) is a proposed Canadian Space Agency (CSA) mission that would image the skies at ultraviolet (UV) and blue-optical wavelengths. Operating close to its diffraction limit (the best possible angular resolution achievable by a mirror of a given size), the 1m CASTOR telescope would have a spatial resolution similar to the Hubble Space Telescope (HST), but would cover a field of view about one hundred times larger.

The origin of CASTOR mission concept can be traced back to 2010. That year, the Canadian astronomical community released its "Long Range Plan" for the period 2010 to 2020. The report, entitled Unveiling the Cosmos: A Vision for Canadian Astronomy, outlined the broad goals and directions of astronomy research in Canada. Aiming to identify research priorities and focus economic resources in a way that maximizes scientific impact, the 2010 LRP report noted that "... Canadian space astronomy technology has reached the point that [Canada] could [now] lead a large space astronomy mission."


The report concluded that the highest priority in Canadian space astronomy was "...significant involvement in the next generation of dark energy missions — ESA‘s Euclid, or the NASA’s WFIRST mission, or a Canadian-led mission, the Canadian Space Telescope (CST)."

CASTOR is the outcome of that bold vision. Since 2011, a team of Canadian scientists and engineers — drawn from industry, academia and government — has worked to develop a mission concept that is uniquely powerful and scientifically versatile.


In December 2020, the Canadian astronomical community released its decadal plan for the next decade — the 2020 Long Range Plan for Canadian Astronomy — and CASTOR was selected as Canada's highest priority for space astronomy in the 2020s. In their report, the 2020 LRP panel stated:

We recommend that the Cosmological Advanced Survey Telescope for Optical and ultraviolet Research (CASTOR) be approved for development toward launch. The CASTOR mission is a mature concept that has a world-leading and transformational science case, strong and long-standing community support, substantial interest and involvement from Canadian industry, and enthusiastic international partners who are looking to Canadian leadership to develop and fly a wide-field optical-ultraviolet space telescope. CASTOR will also provide a superb complement to JWST and other forthcoming optical and infrared facilities. A top priority in LRP2010 and MTR2015, CASTOR continues to be an outstanding prospect for Canada's first marquee space astronomy mission.


After a decade of scientific and technological development, and now with an unambiguous endorsement by the Canadian astronomical community, CASTOR is  poised a to have transformational impact on international astrophysics in the 2020s.

The 2010 Long Range Plan for Canadian Astronomy.

Using celestial themes, the CASTOR logo pays homage to Castor Canadensis — the North American Beaver — Canada’s national animal and an official “symbol of the sovereignty of Canada” (National Symbol of Canada Act R.S.C., 1985, c. N-17).

CASTOR in the International Landscape

Later in this decade, a suite of powerful new telescopes on the ground and in space will begin to monitor the sky at optical and infrared wavelengths.


On the ground, the USA's Rubin Observatory (formerly LSST), a partnership between NSF and the DoE, will repeatedly survey the southern skies at optical wavelengths. In space, ESA's Euclid mission and NASA's Roman Space Telescope (formerly WFIRST) mission will image the sky at red-optical and infrared wavelengths. These facilities have been designed to address some of the key outstanding questions in astronomy, including the nature of Dark Energy — a mysterious component of the universe that leads to an acceleration in the rate of cosmic expansion. But the legacy value of these telescopes is so immense that no field in astronomy will remain untouched.


A critical, but missing, capability among these next generation telescopes is high-resolution imaging at short wavelengths: i.e., in the UV and blue-optical regions. At present, the legendary Hubble Space Telescope (HST) offers such a capability, but only over a tiny field. And, HST, which was launched in 1990, relies on a number of critical systems, such as batteries and gyroscopes, that have limited lifetimes.  Astronomers worldwide have come to rely on Hubble but, by the time the next generation of ground- and space-based telescopes are in routine operation, high-resolution imaging at UV/blue-optical wavelengths will likely be a missing capability among the international portfolio of astronomical facilities. With a mapping speed a hundred times greater than Hubble, CASTOR would fill that void.

Unlike the upcoming James Webb Space Telescope (JWST), Euclid and the Roman space telescopes, all of which will focus on red-optical and infrared wavelengths, CASTOR is unique in targeting the ultraviolet and blue-optical region. Because the Earth’s atmosphere is opaque at ultraviolet wavelengths, this critical region is unobservable from the ground, yet provides critical information on the hottest, youngest and most energetic sources in the Universe.

A New Canadian Icon in Space

As one of the world's first space-faring nations, Canada has a proud history in space.


The Alouette 1 satellite, which carried out pioneering studies the Earth's upper atmosphere, was built by Canada and launched by NASA in 1962. It was the first satellite designed and constructed by a country other than the United States or the Soviet Union, and operated successfully for ten years.

The Shuttle Remote Manipulator System (SRMS, or Canadarm), a series of robotic arms that were used on NASA's Space Shuttles to capture and deploy payloads, flew on 90 Shuttle missions between 1981 and 2011.


In late 2021, NASA will launch the James Webb Space Telescope (JWST), an ambitious 6.5m space telescope that will provide unparalleled views of the Universe at infrared wavelengths. JWST, a collaboration between NASA, ESA and the CSA, includes key Canadian hardware contributions — namely its guidance system and an infrared imaging spectrograph (FGS/NIRISS).

As the world's preeminent UV/blue-optical imaging telescope, CASTOR would build on this legacy. It would offer the same high-resolution imaging capabilities of HST — a capability that has captured the imagination of the public for more than a quarter century — but over much larger fields than is possible with HST. It would be a unique tool for communicating the importance of science, technology, engineering and mathematics (STEM) to the public and a worthy heir to Alouette 1 and Canadarm as icons of Canada's presence in space.

Artist's conception of the Alouette I satellite, launched in 1962.

The Shuttle Remote Manipulator System (SRMS), or Canadarm, mounted on the port side of the cargo bay during Shuttle mission STS-72.