Presentation: May 2019

This month's AE presenter: James Aubuchon
Date of presentation: May 2019 (exact date uncertain)
Subject: How to Build a Space System II, the Space Environment Proper
Description: Space is by its nature a difficult environment in which to place and operate any kind of system.  The space environment is characterized by high vacuum, temperature extremes, thermal cycling, and low gravity.

Though a small speck can damage a satellite, over 500,000 pieces of orbital debris larger than 10 cm are currently tracked by NASA.  There are over 40 known meteor showers that pass through Earth’s upper atmosphere.  There are also cosmic rays, micrometeoroids, and other particulates.  The chemical environment includes very reactive atomic oxygen and the Van Allen radiation belts.  There is an induced environment as the result of venting and outgassing from the space system itself which can interact with the space system.

Space weather variations, due mainly to the Sun, make the environment more challenging.  While visible light is approximately constant, X-ray and ultraviolet light are highly variable in time and space.

Solar wind, solar flares, coronal mass ejections, solar energetic particles, x-ray flares, solar radio bursts, & solar proton events are unpredictable and are sometimes huge to monumental.  These can react directly with the space system or with the Earth’s magnetosphere to cause geomagnetic storms.  They can energize the ionosphere and the Van Allen radiation belts.

Direct effects on the space system may include radiation damage which can cause single event upset, latchup, loss of orientation, execution of phantom commands, and degradation of solar panels.  They may result in spacecraft charging with subsequent spark discharge and possible damage.  Effects on the atmosphere may result in scintillation of satellite to ground communication.

These are some of the factors which make space a difficult environment.  Taken individually, any one might prove hazardous to endurance, navigation, or general operation of a space system.  Taken collectively, they make operating any such system in space a massive and yet delicate undertaking.

Presentation: March 2019

This month's AE presenter: James Aubuchon
Date of presentation: 25-Mar-2019
Subject: How to Build a Space System I, Dealing with the Earth’s Atmosphere
Description: A space system must ascend (and possibly descend) through the atmosphere.  We must communicate with that system through the atmosphere.  Some very small portion of the atmosphere remains even at the altitude of man-made satellites.  The atmosphere has layers determined not by arbitrary boundaries, but by physical characteristics.  Still, there is more than one layering system.


The best known (Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere) is determined by temperature gradient (not temperature).  For example, temperature decreases with altitude in the troposphere and increases with altitude in the stratosphere.


The atmosphere is also layered by chemical composition.  The atmosphere can be divided into the lower homosphere in which the atmosphere is well stirred and the higher heterosphere where chemical layering is more pronounced.  There is also an ozone layer, and an ionosphere (which, itself, has layers).


There is a lower acoustic zone and a higher anacoustic zone in which sound will not propagate.  These classifications schemes overlap one another.


The physical characteristics of the various layers were discussed.  The exosphere blends smoothly into outer space where the gravity of the Earth is no longer strong enough to prevent the solar radiation from removing particles from the Earth’s atmosphere.