Planned solar sail spacecraft
The Near-Earth Asteroid Scout (NEA Scout) is a planned mission by NASA to develop a controllable low-cost CubeSat solar sail spacecraft capable of encountering near-Earth asteroids (NEA).[4][5] The NEA Scout will be one of 10 CubeSats to be carried with the Artemis 1 mission into a heliocentric orbit in cis-lunar space on the maiden flight of the Space Launch System (SLS) planned to launch in 2022.[6] The current target for the mission is asteroid 2020 GE,[7] but this may change based on launch date or other factors.[8] After deployment in cislunar space, NEA Scout will perform a series of lunar flybys to achieve optimum departure trajectory before beginning its two-year-long cruise.
NASA's Marshall Space Flight Center (MSFC) and Jet Propulsion Laboratory (JPL) are jointly developing this mission with support from NASA's Goddard Space Flight Center (GSFC), Lyndon B. Johnson Space Center (JSC), Langley Research Center (LRC), and NASA Headquarters.[4] The principal investigator (science) is Julie Castillo-Rogez from NASA's JPL. The principal investigator (solar sail) is Les Johnson from NASA MSFC.
Overview
The mission is funded by NASA's Human Exploration and Operations Mission Directorate. Near-Earth asteroids (NEAs) are of interest to science, and as NASA continues to refine its plans to possibly explore these small objects with human explorers, initial reconnaissance with inexpensive robotic precursors is necessary to minimize risks, and inform the required instruments for future reconnaissance missions. The characterization of NEAs that are larger than 20 m (66 ft) in diameter is also of great relevance to plan mitigation strategies for planetary defense.[5]
The NEA Scout spacecraft will be one of thirteen CubeSats carried as secondary payload on the maiden flight of the Space Launch System (SLS), a mission called Artemis 1.[9] To measure the physical properties of a near-Earth object, the spacecraft will be performing a slow (10–20 m/s)[10] close (<1 mi) flyby.
Goal
The NASA Near Earth Asteroid (NEA) Scout mission will demonstrate the capability of an extremely small spacecraft, propelled by a solar sail, to perform reconnaissance of an asteroid at low cost. The goal is to develop a capability that would close knowledge gaps at a near-Earth asteroid in the 1–100 m range.[5][11][10] NEAs in the 1–100 m range are poorly characterized due to the challenges that come with detecting, observing, and tracking these for extended periods of time. It has been thought that objects in the 1–100 m size range are fragments of bigger objects. However, it has also been suggested that these objects could actually be rubble-piles.[5]
The mission researchers argue that "characterization of NEAs that are larger than 20 m in diameter is also of great relevance to inform mitigation strategies for planetary defense".
Target
The planned target, subject to change, is near-Earth asteroid 2020 GE.[7] The asteroid will make a close approach to Earth in September 2023 of around 5.7 million kilometres, which is when NEA Scout is scheduled to make its flyby.[7] The spacecraft will approach the asteroid at less than a mile distant, and make the slowest flyby of any asteroid by any spacecraft at less than 30 m/s. A 14 megapixel camera, the missions sole instrument, will image the object at very high resolutions of up to 10 cm/pixel.
2020 GE is no more that 18 meters across, and will be the smallest object yet explored by spacecraft.[7]
Payload
Observations will be achieved using a CubeSat performing a close (~10 km) flyby, equipped with a high resolution science-grade monochromatic camera to measure the physical properties of a near-Earth object. The camera is a custom JPL design.[12] The electronics are based on the context camera design for the Orbiting Carbon Observatory 3 (OCO3) instrument[13] with a custom firmware, a ruggedized commercial lens and a fully re-designed enclosure.[12] The measurements to be addressed include target's accurate positioning (position and prediction), rotation rate and pole position, mass, density, mapping of particles and debris field in target vicinity, albedo and asteroid spectral type, surface morphologies and properties, and regolith properties.[5] The mission will use NASA's Deep Space Network as the primary component for communications and tracking.[5]
Design
The spacecraft architecture, first presented in 2014, is based on a 6-unit CubeSat with a stowed envelope slightly larger than 10 × 20 × 30 cm, a mass of 14 kg (31 lb),[2] cold gas thruster system,[14] and primarily based on the use of commercial off-the-shelf parts.[5] While it is possible for a 6U CubeSat to reach an NEA with conventional chemical propulsion, both the number of targets and the launch window would be tightly constrained. By utilizing solar sail propulsion, intercepting a large number of targets in any launch window is made possible.[2] The mission duration is estimated at 2.5 years.[1]
After deployment in cislunar space, NEA Scout will deploy its solar panels and antenna. Following a lunar flyby, the solar sail will deploy and spacecraft checkout will begin. NEA Scout will then perform a series of lunar flybys to achieve optimum departure trajectory before beginning its 2.0 – 2.5 year-long cruise to the asteroid 1991 VG.[10]
- Sail
Four 6.8 m booms will deploy the single 85 m2 aluminized polyimide solar sail, which is 2.5 μm thick. The sail deployment mechanism is a modification of those of NanoSail and The Planetary Society's LightSail 2 spacecraft.[2][10] The deployment time for the full sail is approximately 30 minutes.
- Avionics
The avionics module accommodates the printed circuit boards for telecommunications, power distribution unit, command and data handling system, Sun sensors, and a miniaturized star tracker. This module also includes reaction wheels, lithium batteries, and a camera.[5] The solar sail spacecraft attitude control system consists of three actuating subsystems: a reaction wheel control system, a reaction control system, and an adjustable mass translator system.[15]
- Propulsion
The cold gas propulsion system is situated below the solar sail and provides detumbling, initial impulsive maneuvers (required for lunar-assisted escape trajectories), and momentum management.[14]
- Communications
The spacecraft will use the Iris transponder for communications in the X-band.[5]
- Power
Photovoltaic solar panels, with rechargeable batteries.
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