Sentinel (space telescope)
Sentinel is a space observatory currently being developed by Ball Aerospace for the private non-profit philanthropic B612 Foundation. The foundation is dedicated to the protection of Earth from asteroid strikes, and Sentinel is B612's first spacecraft to begin to tangibly address that mission. The space telescope is being designed to locate 90% of the asteroids greater than 140 metres (460 ft) in diameter that exist in near-Earth orbits. The telescope will orbit the sun in a Venus-like orbit (i.e. between Earth and the Sun) and have an operational time of 5 and a half years, and is being designed to "catalog 90% of the asteroids larger than 140 metres (460 ft) in Earth’s region of the Solar System. The craft will be placed in a Venus-following orbit, allowing it to view the night half of the sky every 20 days, and picking up objects that are currently often difficult, if not impossible, to see in advance from Earth."
The B612 project grew out of a one-day workshop on asteroid deflection organized by Piet Hut and Ed Lu at NASA Johnson Space Center, Houston, Texas, on October 20, 2001. Participants Rusty Schweickart, Clark Chapman, Piet Hut, and Ed Lu established the B612 Foundation on October 7, 2002. The Foundation's original plans were to have Sentinel launched by December 2016 and to begin data retrieval no later than 6 months after successful positioning. In April 2013, the plan had moved out to launching on a SpaceX Falcon 9 in 2018, following preliminary design review in 2014, and critical design review in 2015.
As of April 2013[update], B612 is attempting to raise approximately $450 million in total to fund the total development and launch cost of Sentinel, at a rate of some $30 to $40 million per year. That funding profile excludes the advertised 2018 launch date.
As opposed to similar projects to search for near-Earth asteroids or near-Earth objects (NEOs) such as NASA's Near-Earth Object Program, having the telescope located between Earth and the Sun means that the Sun will never inhibit Sentinel's ability to detect NEOs. This is because the Sun will always be behind the lens of the telescope, allowing for continuous observation and analysis.
Sentinel is anticipated to be capable of detecting 90% of the asteroids greater than 140 meters in diameter that exist in Earth's orbit, making them a potential source of existential risk to humanity. The B612 Foundation estimates that there are approximately half a million asteroids in Earth's neighbourhood which are equal to or greater than the one that struck Tunguska in 1908. It is planned to be launched atop the Falcon 9 rocket designed and manufactured by the private aerospace company SpaceX in 2016, and to be manoeuvred into position with the help of the gravity of Venus. Data gathered by the Sentinel Project will be provided through an existing network of scientific data-sharing that includes NASA and academic institutions such as the Minor Planet Center in Cambridge, Massachusetts.
The telescope measures 7.7 metres (25 ft) by 3.2 metres (10 ft), mass 1,500 kilograms (3,300 lb) and will orbit the Sun at a distance of 0.6 to 0.8 astronomical units (90,000,000 to 120,000,000 km; 56,000,000 to 74,000,000 mi), approximately in the same orbital distance as Venus. It will employ infrared astronomy methods to identify asteroids against the cold of outer space. The B612 Foundation is working in partnership with Ball Aerospace to construct Sentinel's 0.51 m (20 inches) aluminum mirror, which will capture the large field of view. "Sentinel will scan in the 7- to 15-micron wavelength using a 0.5-meter infrared telescope across a 5.5 by 2-deg. field of view. The IR array will consist of 16 detectors, and coverage will scan a 200-deg., full-angle field of regard."
Key features include:
- Most capable NEO detection system in operation
- 200 degree anti-sun Field of Regard, with a 2×5.5 degree Field of View at any point in time: scans 165 square degrees per hour looking for moving objects
- Precise pointing accuracy to sub-pixel resolution for imaging revisit, using the detector fine steering capability
- Designed for highly autonomous, reliable operation requiring only weekly ground contact
- Designed for 5.5 years of surveying operations. Actively cooled to 40K using a Ball Aerospace two-stage, closed-cycle Stirling-cycle cryocooler
- Ability to follow-up on objects of interest
- "Sentinel". Ball Current Programs. Ball Aerospace. 2013. Retrieved 2013-08-02.
- "The Foundation". B612 Foundation. Retrieved September 13, 2012.
- "The Sentinel Mission". B612 Foundation. Retrieved September 13, 2012.
- Norris, Guy (2013-04-09). "Ball Aerospace Ramps Up Sentinel Asteroid Search Mission". Aviation Week. Retrieved 2013-04-11.
- "Foundation History". B612 Foundation. Retrieved April 15, 2012.
- "Sentinel Factsheet" (PDF). B612 Foundation. Retrieved September 13, 2012.
- Wall, Mike (July 10, 2012). "Private Space Telescope Project Could Boost Asteroid Mining". Space.com. Retrieved September 14, 2012.