= Water from Ceres to Deimos =
== approximate calculations ==

|| Mars   || 1.52 AU || 24.0 km/s || 5.0 km/s ||
|| Ceres  || 2.77 AU || 17.9 km/s || 0.5 km/s ||
|| Deimos ||         || 1.35 km/s ||

Assume ice can be delivered to a catcher by impact. (WHAM!)  We are only concerned with launching the water to Deimos intercept.

G = V²R ≅ 17.9² × 2.77 AU-km²/s² ≅ 24.0² × 1.523 AU-km²/s² ≅ 880 AU-km²/s²

Ceres Hohmann aphelion = sqrt( 880 * 2 × 1.52 / (( 2.77 + 1.52 ) × 2.77 ) ) = 15 km/s

Ceres Launch ≅ sqrt(  ( 17.9 - 15 )² + 0.5² ) ≅ 2.95 km/s

Ceres Hohmann perhelion = sqrt( 880 * 2 × 2.77 / (( 2.77 + 1.52 ) × 1.52 ) ) = 27.3 km/s

Ceres to Deimos arrival velocity = sqrt( ( 27.3 - 24.0 )² + 2 × 1.35² ) ± 1.35 km/s ≅ 3.81 ± 1.35 km/s ( 2.46 to 5.16 km/s )

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Mars Launch ≅ sqrt(  5² - 1.35² ) ≅ 4.8 km/s ... 1.6 times larger than Ceres launch

Mars to Deimos apoapsis velocity ≅ 0.68 km/s  

Deimos arrival velocity = 0.67 km/s  ... 0.27 times smaller than the lowest Ceres arrival


Ice launched from Ceres needs only a 0.5 km/s direct boost; the rest of the delta V can be provided with electric thrust engines.  Those can also slow the delivery velocity at Deimos, if necessary.  That's a lot of repeated delta V's, though, and the electric thrust could be used with a Mars/Deimos synchronous cycler system.  

So ... it's complicated.