Economical remote sensing from a low altitude with continuous drag compensation

High-resolution imagery from remote sensing spacecraft could find a mass market in applications such as town planning, mapping and agriculture. However, such an expansion of demand is inhibited by the relatively high prices involved, which are mainly driven by the cost of the large and complex spacecraft required and of the associated launch vehicles. It is shown in this paper that it might be feasible to reduce these costs substantially by employing a spacecraft which is much smaller and lighter than conventional remote sensing satellites. Its cost is therefore much less and it also requires a relatively inexpensive launch. This is made possible by reducing the altitude of the mission very considerably, to around 300 km or below from the usual 600-800 km. A significant aerodynamic drag force will then be experienced by the satellite, but this can be balanced by a suitable propulsion system. For this, the use of gridded ion thrusters operating at very high exhaust velocity is suggested, thereby enabling the propellant required to be well below that needed if the chemical propulsion alternative was adopted. The optimisation of such a low-cost mission is also discussed.