Martian sand and dust storms and effects on spacecraft coatings.

Abstract

ENGINEERING NOTES 473 through initiation of re-entry; and T±, initiation of re-entry through completion of recovery.Let each Ti have associated with it an S i} the event that no serious injury occurs during Tt. The probability associated with each Si is P{Si}. In order to complete a safe mission, it is necessary that all four Si events be completed safely. Each ith event can be completed safely if 1) the nominal activities scheduled for the ith interval are completed, event Sn, or 2) abort is initiated during the ith interval and is completed safely, event >S i2 . That is, P{Si} = P{SnUSi 2 } . Since events Sn and & 2 are mutually exclusive, P{S t ] = P{S.i}+P{S*}.The ability to initiate event Szi is conditional upon completion of event /Sn. The probability that event Si occurs, given that S 3 -occurs, is written P'{&|Sy} and may be calculated 2 from P{S t \S j ] = P{S<nSj}/P{Sf}. P{S} may therefore be written 3 as P{S} =The event that serious injury occurs during the interval, T is denoted as F, and the probability associated with this event occurring is P{F} , where P{S\ ' + P{F\ = 1. As in the case of S, F may be subdivided into events Fi-F 4 , one for each Ti. The expression f or P { F } is P[F\ = P{F U } + P{F 12 }since Fn and F t -2 are not mutually exclusive and P{Fi} = P{Fa{ + P{Fv} -P{Fa/2F*} The relationship between P{S\ and P{F} holds for each phase of the mission. For i = 1, P{Sn} + P{Su} + P{Fn} + P{F 12 j = 1 For i = 4,

Saltation and Martian sandstorms

“…Zingg [1953] and Chepil [1945, 1958] also obtained detaiied and useful wind tunnel measurements. Experiments simulating the low densities near the Martian surface have been carried out by several investigators [Hertzler et al, 1967;Dyhouse, 1968;Adlon et al, 1969]. However, a serious problem associated with the latter studies is the inability of accurately simulating the Martian atmospheric boundary layer flow.…”

“…Unfortunately, quantitative data on vertical distributions within a saltation layer (0 < z </i8) are completely lacking, and only a limited number of data are available on the variation of mass flux for z >/i8. Within the saltation layer the mass flux distribution should be fairly uniform, while above the layer the flux has been found to fall off approximately exponentially [Bagnold, 194 l;Sharp, 1964;Dyhouse, 1968]. According to Bagnold, about one half of the total transported sand mass (i.e., }q) is contained within the saltation layer 0 < z < t•s.…”