50 Electric solar Sail powered nanocraft proposed for exploring 300 asteroids at total cost of $75 million

A mission concept, known as the Asteroid Touring Nanosat Fleet, would require 50 esail powered probes to return for a flyby of Earth after asteroid flybys, as the nano-spacecraft would only be able to carry a small antenna with a relatively short range for transmitting data. The nanosats would fly within 100 kilometers of their target asteroids, resolving the surfaces of the space rocks to 100 meters or better using 4-centimeter telescopes affixed to each probe. In addition to the small imaging telescopes, the probes would each carry a spectrometer to determine the chemical composition of the asteroids. The two instruments on each tiny craft could be pointed at the target asteroids using internal reaction wheels—a flywheel and electric motor combination developed for minute spacecraft movements.

A bold mission study led by the Finnish Meteorological Institute (FMI) suggests planetary scientists could harness the capabilities of nano-spacecraft to conduct an exploration survey of the asteroid belt on a scale never seen before. The study, presented today at the 2017 European Planetary Science Congress (EPSC) in Riga, Latvia, outlines a plan to send 50 nanoprobes propelled by electric solar wind sails (E-sails) to conduct flybys and science observations at more than 300 of the largest and most interesting asteroids in the belt. After a 3.2-year tour of the asteroid belt, the probes would return to Earth to download the mission data, comprised mainly of surface images and spectroscopy readings.

E-sails enable a solar system traveling probe to only weigh 10 kilograms.

The electric solar wind sail (E-sail) is a method for generating efficient low-thrust propulsion outside Earth’s magnetosphere. In its simplest form the E-sail is a single spinning ∼20km long tether biased at ∼10kV positive voltage by an onboard electron emit- ter and high-voltage source. Here we consider a fleet of ∼5kg spacecraft, propelled by the E-sail tether and making quasi-elliptic passes through the asteroid main belt. Each spacecraft also uses its tether to make a ∼1000km flyby of 6-7 asteroids. Data are stored in memory and downloaded at a final Earth flyby at the end of the mission using conventional non-directional radio subsystem. Using this mission architecture, the cost per imaged asteroid is only ∼200,000 euros which is a reduction by about 3 orders of magnitude with respect to the state of the art.

With 10 kV tether voltage, the tether generates 250nN/m thrust per unit length at 1 au in average solarwind. Hence, if a 5 kg spacecraft has a 20 km tether, characteristic acceleration of 1 mm/s2is obtained at 1 au. Orbital calculations show that this level of E-sail acceleration is enough to make the spacecraft fly through the asteroid main belt in a quasi-elliptic orbit taking ∼3.2years.

The E-sail uses full thrust after leaving Earth and before entering the main belt,and then enters reduced thrust science mode where the available E-sail propulsion is used for active manoeuvring to maximize the number of asteroids flown by at close range. The number of well-known (numbered)asteroids reached by the spacecraft is then typically 6-7. Data are stored in flash memory chips during the mission and downloaded at a final Earth flyby so that only∼3hours of deep-space network time is required to download the∼10GB of data. The surface resolution of the flyby images is 100 m pixel size or better (with 4 cm telescope at 1000 km distance the diffraction limit would be even ∼20m) and a separate NIR spectrometer can be used to identify surface minerals. The main science instrument is a 4 cm telescope which is used to image the asteroids at ∼1000 km flyby range. Between the asteroid encounters, the telescope is also used for autonomous optical navigation based on known nearby asteroids.

Larger proposed esail