Difference between revisions of "Ike"
Gondor2222 (talk | contribs) (Added approximate Duna longitudes, latitudes for which Ike passes directly overhead, changed descriptions of the stationary appearance to account for libration.) |
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Stationary orbit around Ike is not possible — it would require an altitude of | Stationary orbit around Ike is not possible — it would require an altitude of | ||
| − | {{OrbitAltitude | period_s=64980 | mass_kg=2.78219487161284e20 | radius_km=130 }}, outside of Ike's sphere of influence. However, since Ike and Duna are tidally locked to each other, a spacecraft in stationary orbit around Duna will see Ike in a near stable, non-rotating position, as if it were in a stationary Ike orbit. | + | {{OrbitAltitude | period_s=64980 | mass_kg=2.78219487161284e20 | radius_km=130 }}, outside of Ike's sphere of influence. However, since Ike and Duna are tidally locked to each other, a spacecraft in stationary orbit around Duna will see Ike in a near stable, non-rotating position, as if it were in a stationary Ike orbit. It is not perfectly stationary as Ike has both a non-zero orbital eccentricity and a very small orbital inclination. |
== Geostationary Properties and Libration == | == Geostationary Properties and Libration == | ||
Revision as of 10:23, 19 May 2013
Ike is a moon and the only natural satellite of Duna. Ike has steep, rocky slopes and no atmosphere. Ike and Duna are tidally locked due to their proximity and Ike's size. This means that Ike's orbit around Duna is geosynchronous, and that Ike is only visible from slightly more than half of Duna, and vice versa. (It would be exactly half but Ike's slightly eccentric orbit creates regions for which Ike can be seen to set and rise. See Libration, below)
An encounter with Ike is quite likely when approaching Duna, provided the player's trajectory is near the plane of Ike's orbit. This is because Ike's sphere of influence is very high relative to the semi-major axis of its orbit — in fact, no other moon in the game has a larger SOI-to-semi-major-axis ratio.
Stationary orbit around Ike is not possible — it would require an altitude of 0.00 m, outside of Ike's sphere of influence. However, since Ike and Duna are tidally locked to each other, a spacecraft in stationary orbit around Duna will see Ike in a near stable, non-rotating position, as if it were in a stationary Ike orbit. It is not perfectly stationary as Ike has both a non-zero orbital eccentricity and a very small orbital inclination.
Contents
Geostationary Properties and Libration
Ike's orbit keeps it directly above a short range of Duna longitudes. The average Duna longitude where Ike tends to stay directly above in the sky (at the Zenith) is 3 degrees east, but the exact longitude oscillates between about 0 degrees and 6 degrees east due to the eccentricity of Ike's orbit. This eccentricity also makes Ike appear to grow slightly larger and smaller to an observer on the surface of Duna. The latitude for which Ike is in the Zenith also oscillates between 0.2 degrees south and 0.2 degrees north due to Ike's orbital inclination, making Ike appear to rotate upwards and downwards as viewed from the surface, but due to the extremely small orbital inclination, this effect is nearly imperceptible. These phenomena together are known as libration. Due to the oscillation in Ike's position above the horizon, areas from 90°W to 84°W and 90°E to 96°E on Duna can observe Ike rise and set at least partially across the horizon, as can any areas north of 89.8°N or south of 89.8°S
Traveling from a 50 km Duna orbit to a 10 km Ike orbit requires approximately 435 m/s of delta-V.
Topography
Ike is extremely rocky, with craters that span for many kilometers. Its tallest points are 12.75 km above its lowest, giving it an elevation range over 3 times that of the Mun despite the fact that the Mun has a 54% wider radius and 137% more surface area. The increased elevation and smaller size result in many steep slopes and make landing quite difficult. The bottoms of craters are among the flatter, safer landing locations.
Reference Frames
Gallery
A gravitational assist from Ike can help reduce descent velocity down to Duna's surface.
Ike eclipsing Duna
Ike as seen in the Tracking Station
Topographical map of Ike
Polar topographical map
A topographic height map of Ike made with the ISA MapSat plugin
Changes
- Initial Release
