Two types of space simulation ion gauges designed for measurement of vacuum level in aerospace environmental test chambers are discussed. These gauges indicate the incidence rate of background gas molecules impinging on the vehicle under test even though the gauges are remote from the vehicle surface and attached to the wall of the test chamber. The type 1 gauge incorporates a cryogenically-cooled condensing surface within the gauge to compensate for pumping effects of the cryogenically-cooled pumping panels in the simulator. With proper design, matching the chamber properties, the gauge reads directly the incident flux on the vehicle. The type 2 gauge measures the pattern of gas emission from the wall. From these data the gas incidence pattern on the vehicle can be calculated. The report describes the need for space simulation gauges, the operation of each type, and their advantages and limitations.