A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7.7E-7 of a circle. It is the angular diameter on object of 1 unit diameter at a distance of 360*60*60/2/π ≈ 206,265 units, such as (approximately) 1 cm at 2.1 km, or, directly from the definition, 1 astronomical units at 1 parsec .
Improving the performance of a magneto-plasma-dynamic arc thruster in the 600 to 2,100 seconds specific impulse range by locating its cathode in the exhaust beam downstream of the anode and main propellant injection point.
An MPD arc thruster as claimed in claim 1 and including at least one hollow tube extending through a wall of said hollow cylindrical anode for placing said chamber in communication with a supply of propellant.
Thermal arc jets, pulsed plasma thrusters, cesium contact ion thrusters and colloidal thrusters are not highly developed and are not as efficient as electron bombardment thrusters and resistojets.
A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree.
Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or (π/10800) radians.
Traditionally positions are given using degrees, minutes, and seconds of angles in two measurements: one for latitude, the angle north or south of the equator; and one for longitude, the angle east or west of the Prime Meridian.
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