For the SMILE proposal we assumed a highly inclined Molniya-type orbit with baseline parameters as given in the table below. However, subsequent studies have led to the current baseline orbit (for launch on Vega-C in late 2024) with inclination of 73 degrees, argument of perigee 287.5 degrees, and period of ~50 hours.
|Apogee (Earth radii):||20|
|Perigee (Earth radii):||2|
|Right Ascension of the ascending node (degrees):||270|
|True anomaly (degrees):||0|
The SXI and UVI instruments will be pointed in different directions. The SXI will be oriented so that it observes the subsolar magnetosheath while the UVI will be pointed to the northern hemisphere auroral oval.
Observing simulations to investigate optimal pointings and to calculate observing efficiencies have been undertaken by members of the SMILE consortium. The table below points to a set of movies showing the SMILE orbit configurations at various times of the year for the Molniya-type orbit used in the proposal.
|Time of interest||Link to movie|
|June 2020||Link to movie|
|September 2020||Link to movie|
|December 2020||Link to movie|
|March 2021||Link to movie|
Each panel, for each of the movies listed above, is described as follows:
(i) Orbit windows (top-left): Single example orbit (black curve), extracted from the full SMILE orbit set, in three planes [L to R] GSE-X-Y, GSE-X-Z and GSE-Y-Z (units are in Earth radii, RE). The Earth is at [0,0,0] and the (Earth-sized) North cusp (dark red circle), South cusp (pink circle) and magnetopause nose (orange circle) are shown, together with a sketch of the magnetopause (orange curve). The cross indicates the aim-point. The Sun lies at large +ve X [Y=0, Z=0]. The green box shows the spacecraft position which moves along the orbit, synchronized with the other windows.
(ii) Angle window (bottom-left): Curves depict angles (y-axis, degrees) away from the SMILE SXI aim-point of the Sun (orange), Earth (blue), nose (red) and North cusp (dark red) for the orbit. The dashed orange horizontal line shows the Sun avoidance angle (here 28.5°). Horizontal bars at top and bottom show good observability times (object is in the SXI FOV) for nose (N, red), North cusp (C, dark red) & South cusp (K, pink). Bar A shows when the Earth is in the UVI FOV, bar B when the Earth is fully outside the SXI baffle, and bar S when the Sun is outside of the Sun avoidance angle. These observability fractions are given numerically in the window centre. Angular diametres (degrees) of Earth, Nose, North and South cusp are also given (left).
(iii) FOV window (right): Field-Of-View (FOV) of what is visible from the spacecraft position. The projection can be very wide and is 'North-up' with the x-axis parallel to the ecliptic. Features include: the aim-point (cross at [0,0]), the Earth, the magnetopause nose (dashed dark orange circle) and the North and South Cusps (dark red and pink spheres) (nose and cusps are all Earth-sized), the magnetopause (green/blue Shue-model [alpha=0.6]), the Sun (yellow square, radius=0.25 deg) and the Sun angle constraint (yellow circle). The SXI FOV is shown by the large dark rectangular box (here 28x25 deg) angled to minimize Sun/Earth effects, with the SXI baffled area shown dashed orange. The UVI FOV is shown by the smaller (10x10 deg) dashed orange box. Various data regarding positions, angles, times etc. are also shown in the window.