# Novel 3U Stand-Alone CubeSat Architecture for Autonomous Near Earth Asteroid Fly-By
## 4 Subsystems Analysis
### Payload  
Exploration of NEAs is linked to three main objectives: scientific research on the evolution of the solar system, planetary protection, and in-situ resources exploitation. The common point of these objectives is the poor information on the asteroid. By ground observations, it is not possible to retrieve accurate information on physical parameters (actual shape, dimension, rotational parameters), composition (surface and inner), mass, and even ephemeris. A small and low-cost CubeSat for NEAs exploration can be useful  
Figure 1: (433) Eros navigation evaluation: (**a**) days prior to fly-by the target becomes visible in the Field-of-View (FOV) of the star trackers as a function of phase angle and distance Sun-Near Earth Asteroid (NEA); (**b**) Achievable displacement from nominal condition in function of the \(\Delta V\) magnitude and the direction of an impulsive maneuver; (**c**) Navigation accuracy of the last 60 days of cruise, employing line-of-sight optical navigation, observing Mars and Jupiter. to enlarge the available dataset, performing basic observation during in-situ exploration. A Visible (VIS) range camera can be used to determine the actual shape, dimension, and rotational rate and axis. Moreover, it is needed for optical relative navigation, and merged relative and absolute navigation data can be used to improve asteroid ephemeris. Composition can be retrieved by means of InfraRed (IR) observation. Determining mass and/or density is however less straightforward, and some techniques and mission proposals identified solutions to the problem. One option would be to use a pair of CubeSats to fly-by the asteroid, and measuring their relative distance before, during, and after the encounter, information on the mass can be retrieved [26]. Sticking to the concept of only one CubeSat, the Yarkovsky effect can be exploited to estimate the mass of the asteroid [27]; to do that, rotational parameters, composition (thermal inertia), and temperature distribution are needed. However a large set of ground observation is needed. Based on these considerations, mass/density estimation can be assumed as a second level mission objective. Third level mission objectives can be connected to measuring magnetic field residuals. Off-the-shelf magnetometers (usually also already integrated in Attitude Determination and Control System (ADCS) for attitude determination purposes) are available with tiny mass, volume, and power consumption. Keeping in mind that they would not affect significantly the mass and volume budgets, they are not considered for this mission concept. To satisfy the mission objectives, based on previous considerations, a visible camera and IR spectrometer compose the minimum set of payload required for such missions (MR6 in Table 1). Usually the scientific payload is the most customized subsystem for a space mission, since it strongly depends on the objectives. Moreover, as of today, not many COTS payloads are available on the market, especially considering that they are designed for Earth observation. The 3U configuration further limits the range of applicable instrumentation. While only one off-the-shelf option for IR spectrometer is available (Thoth Technology Argus 2000 [28]), a larger range of visible cameras is available. However, just a few of them are compact and light enough to be included in a 3U CubeSat (as it will be shown in the Results section). Moreover, Ground Sampling Distance (GSD) needs to be considered. The GSD, measured in m/pixel and defined as the ground distance between two adjacent pixels of the captured image, quantifies the accuracy with which the asteroid shape can be described. As long as the GSD decreases, a larger number of pixels will be employed to describe the target.