The large number of man-made uncontrolled objects orbiting the Earth is becoming a serious threat to space activities. Existing models of this orbital debris population are inadequate, particularly in the debris size range between sub-millimeter and tens of centimeters. This is due to the limitations of current detection techniques, which use ground based sensors and long-duration recoverable spacecraft. Debris larger than 10-20 cm are few in number and can generally be avoided by maneuver. However, debris in the 0.1 mm - 10 cm size range are so numerous yet so damaging that must be dealt with by external or internal shielding, redundancy, and related spacecraft techniques, all of which are expensive. This is particularly true for large constellations of spacecraft as well of large area long-lived spacecraft. This paper addresses detection of debris objects using space sensors, which result in the range being short enough that even very small particles are detectable. A number of innovative concepts for detecting such orbital debris objects are described, and their performance is calculated. These techniques include the use of passive optical sensors, active lidar sensors, bistatic radar sensors where both transmitters and receiver are in space, and bistatic radar sensors in which the receiver is in space and the transmitter is that of a communication satellite earth station. In addition, a multistatic radar using the same ground station, but a ground receiver, is analyzed. It is shown that some of these techniques can reliably detect millimeter and even sub-millimeter debris objects. It is also shown that some of these techniques can detect a reasonable percentage of the population of debris objects in one, or at most a few years of operation. Thus some of these sensor concepts appear to represent a practical and probably inexpensive solution to the generation of reliable models of the population of small orbital debris. The implementation of some of these systems is described, including one with multiple sensing spacecraft to reduce the time required to produce a statistically significant population model.