Difference between revisions of "Duna"

Revision as of 23:36, 1 October 2012

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Duna is the fourth planet of the Kerbol star system. It is the Mars analog for Kerbal Space Program and is mostly red with polar icecaps. It has one natural satellite, the moon Ike. Due to Ike's size and proximity, Ike and Duna are tidally locked to each other.

Topography

A 3200 by 1600 topographic map of Duna made with the ISA MapSat plugin

Duna is a iron-rich planet which has greatly varying land altitude, the consequence of which is very difficult judgment of a safe landing position. Its mountainous ranges are a peril to landing craft, especially considering the thin atmosphere, where very little aerobraking can be done safely. It is important to slow one's ship down before coming into the atmosphere, to ensure a safe descent. Its two poles are very expansive and are the result of a thin atmosphere.

Atmosphere

Duna's atmosphere begins at approximately 41,450 m and is only 20% as dense as Kerbin's.^[1] Taking Duna's reduced gravity into account, terminal velocity at a given altitude on Duna is 22.5% faster than at the same altitude on Kerbin.^[2]

Parachutes work at lower efficiency than on Kerbin, making powered descent necessary when landing from orbit (unless your craft is a glider or just a pod with a parachute).

Orbital Statistics

The geosynchronous orbit of Duna is at an altitude of 2862.702 km above Duna. The speed of the satellite is 307.75 m/s and it has an orbital periode resonating with 1 Duna day (18.05 hours or 64980 seconds.) For a semisynchronous orbit of ½ Duna day (9.025 hours or 32490 seconds) an orbit of 1648.977 km above Duna is needed with a velocity of 387.74 m/s.

Gallery

• 

  ISA satellite in orbit over Duna being used to map the planet surface.

• 

  Duna's surface at Dawn.

• Duna projection.png

  A false color Mercator projection of Duna's surface using MapSat.

Changes

0.17

• Initial Release

Notes

1. ↑ A nuclear engine has a specific impulse of 220 at 1 atm, 800 in vacuum, and 684.2 at Duna altitude 5 m. This means the Duna atmospheric pressure at 5 m is roughly 1 - (684.2 - 220) / (800 - 220) = 0.1997 atm.
2. ↑ Terminal velocity is the speed at which the force of gravity equals the force of drag: ${\displaystyle m\ a=0.5\ p\ v^{2}A\ D}$, where m is the ship's mass, a is the gravitational acceleration of the planet, p is the atmospheric pressure, v is the ship's velocity, A is the ship's reference area, and D is the ship's coefficient of drag. The only things that differ between Kerbin and Duna are a, p and v, indicated as ${\displaystyle a_{k}}$, etc. for Kerbin's values and ${\displaystyle a_{d}}$, etc. for Duna's.

   ${\displaystyle m\ a_{d}=0.5\ p_{d}\ {v_{d}}^{2}A\ D}$

   ${\displaystyle m\ a_{k}=0.5\ p_{k}\ {v_{k}}^{2}A\ D}$

   Dividing one equation by the other, a lot of things cancel out:

   ${\displaystyle {\frac {a_{d}}{a_{k}}}={\frac {p_{d}}{p_{k}}}\cdot {\frac {{v_{d}}^{2}}{{v_{k}}^{2}}}}$

   Duna's gravity is 0.3 g, so ${\displaystyle a_{d}/a_{k}}$ is 0.3. Duna's atmosphere is 20% as thick as Kerbin's, so ${\displaystyle p_{d}/p_{k}}$ is 0.2. This means:

   ${\displaystyle 0.3=0.2\cdot {\frac {{v_{d}}^{2}}{{v_{k}}^{2}}}\,\,\,\,\,\,\,\,\,\,{v_{d}}^{2}=1.5\ {v_{k}}^{2}\,\,\,\,\,\,\,\,\,\,v_{d}=sqrt(1.5)\ v_{k}=1.225\ v_{k}}$

v t e Kerbol System Kerbol Moho Eve Kerbin Duna Dres Jool Eeloo (The Sun)   Gilly Mun Minmus Ike   Laythe Vall Tylo Bop Pol