NEO Surveyor

NEO Surveyor, formerly called Near-Earth Object Camera (NEOCam), then NEO Surveillance Mission, is a planned space-based infrared telescope designed to survey the Solar System for potentially hazardous asteroids.

The NEO Surveyor spacecraft will survey from the Sun–Earth L1 (inner) Lagrange point, allowing it to see objects inside Earth's orbit, and its mid-infrared detectors sensitive to thermal emission will detect asteroids independently of their illumination by the Sun. The NEO Surveyor mission will be a successor to the NEOWISE mission, and the two missions have the same principal investigator, Amy Mainzer at the University of Arizona.

Since first proposed in 2006, the concept repeatedly competed unsuccessfully for NASA funding against science missions unrelated to planetary defense, despite an unfunded 2005 US Congressional directive to NASA. In 2019, the Planetary Defense Coordination Office decided to fund this mission outside NASA's science budget due to its national security implications. On 11 June 2021, NASA authorized the NEO Surveyor mission to proceed to the preliminary design phase. The Jet Propulsion Laboratory will lead development of the mission.

As of December 2022, NEO Surveyor is expected to be launched no later than June 2028. As of October 2023 the launch is planned for September 2027.

History
In 2005, the U.S. Congress mandated NASA to achieve by the year 2020 specific levels of search completeness for discovering, cataloging, and characterizing dangerous asteroids larger than 140 m (Act of 2005, H.R. 1022; 109th), but it never appropriated specific funds for this effort. NASA did not prioritize this mandate, and directed the NEOCam project to compete against science missions for general funds unrelated to planetary defense and disaster mitigation planning.

Proposals for NEOCam were submitted to NASA's Discovery Program in 2006, 2010, 2015, 2016 and 2017, but each time were not selected for launch. The mission concept nonetheless received technology development funding in 2010 to design and test new infrared detectors optimized for asteroid and comet detection and sizing. The project received additional funding for further technological development in September 2015 (US$3 million), and in January 2017.

Following calls to fully fund the mission outside NASA's Planetary Science Division or directly from Congress itself, NASA's associate administrator for science announced on 23 September 2019 that instead of competing for funding, NEOCam will be implemented under the name NEO Surveillance Mission with budget from NASA's Planetary Defense Coordination Office, within the Planetary Science Division. The near-miss of asteroid 2019 OK, which slipped past extant detection methods in July 2019, has been suggested to have helped prompt this decision.

For funding and management purposes, the NEO Surveillance Mission is officially a new project, but it is the same space telescope, the same team, and the mission's goals remain unchanged.

Objectives
The main objective of the mission is to discover most of the potentially hazardous asteroids larger than 140 m over the course of its mission and characterize their orbits. Its field of view and its sensitivity will be wide and deep enough to allow the mission to discover about 200,000 to 300,000 of new NEOs with sizes as small as 10 m in diameter. Secondary science goals include detection and characterization of approximately one million asteroids in the asteroid belt and thousands of comets, as well as identification of potential NEO targets for human and robotic exploration.

The Jet Propulsion Laboratory (JPL) will lead development of the mission. The total cost of the mission is estimated to be between US$500 million and US$600 million.

On the NEO Surveyor website the following mission requirements are stated:


 * Find ⅔ of Asteroids Larger than 140 Meters in Diameter
 * Assess the Overall Threat Posed by Potential Earth Impactors
 * Assess the Impact Threat Posed by Comets
 * Determine Orbits and Physical Characteristics of Specific Discovered Objects

Spacecraft
The NEO Surveyor spacecraft will have a total mass of no more than 1300 kg, allowing it to launch on a vehicle like a Falcon 9 Block 5 to the Sun–Earth L1 Lagrange point. The mission should reach the 90% congressional goal within 10 years, with an anticipated mission lifetime of 12 years.

Telescope and camera
Asteroids are dark, with albedos of at most 30% and as low as 5%. An optical telescope looks for the light they reflect and can therefore only see them when looking away from the Sun at the sunlit side of the asteroids, and not when looking towards the Sun at the unlit backside of the object. In addition, opposition surge makes asteroids even brighter when the Earth is close to the axis of sunlight. The combined effect is equivalent to the comparison of a Full moon at night to a New Moon in daytime, and the light of the Sun-lit asteroids has been called "full asteroid" similar to a "full moon". A telescope operating at thermal infrared wavelengths instead detects their surfaces that have been warmed by the Sun and is almost equally sensitive to their lit and unlit sides, but needs to operate in space to achieve good sensitivity over a wide field of view.

The NEO Surveillance Mission will employ a 50 cm infrared telescope operating wide-field cameras at two thermal infrared wavelength channels for a total wavelength range between 4 μm and 10 μm. The camera will have two channels: NC1 has a wavelength range of 4-5.2 μm and NC2 spans 6-10 μm. NC1 is intended to detect background stars for astrometric registration and calibration, as well as the measurement of effective temperatures. NC2 is optimized to maximize sensitivity to typical NEO thermal emission at 200-300 K. Its field of view is 11.56 square degrees. It will use a modified version of the Astronomical Wide Area Infrared Imager (HAWAII) mercury–cadmium–telluride detector developed by Teledyne Imaging Sensors. The mission prototype detector was successfully tested in April 2013. The detector array is 2,048 × 2,048 pixels and will produce 82 gigabits of data per day. For good infrared performance without the use of cryogenic fluid refrigeration, the detector will be passively cooled to 30 K using techniques proven by the Spitzer Space Telescope. Unlike its predecessor NEOWISE, it will therefore not suffer from a performance degradation due to running out of coolant (its mission duration will however still be limited, as the orbital station keeping needed to maintain its position at SEL1 uses propellant).

Operations
The NEO Surveyor spacecraft will operate in a halo orbit around the Sun–Earth L1, and employ a sunshade. This orbit will allow fast data downlink speeds to Earth, allowing full-frame images to be downloaded from the telescope.

One advantage over NEOWISE is the wide field of regard. NEO Surveyor will be able to point anywhere from 45-120° in longitudinal distance from the sun and stopping at ±40° ecliptic latitude. The survey will be optimized to detect potentially hazardous objects and be performed continuously during the baseline mission (5 years). The survey will be halted each day for 2.25 hours to downlink the data. It will also be halted for calibration, station-keeping and momentum management maneuvers. NEO Surveyor will also be able to conduct targeted follow-up (TFO) to obtain more information for an object of special interest.

It is planned that moving object tracklets are delivered to the Minor Planet Center 2 to 3 times a day, on average 72 hours after their discovery. Additionally deep co-added images are published every 12 months. These deep co-added images most likely will be used by astronomers to study stars and brown dwarfs. It was also proposed that NEO Surveyor will include a transient alerting infrastructure, but none are planned to this date (October 2023).

In the first 30 days after the launch the in-orbit checkouts will be performed. After arriving at L1 NEO Surveyor team will conduct a 6-month survey verification. In the nominal survey the telescope is expected to detect ⅔ of asteroids with a diameter larger than 140 meters in the first 5 years. The nominal mission will last for at least 12 years. After the survey end, the telescope will be decommissioned and put into a heliocentric orbit.