This paper proves that deterministic relative attitude determination is possible for a formation of three vehicles. The results provide an assessment of the accuracy of the deterministic attitude solutions, given statistical properties of the assumed noisy measurements. Each vehicle is assumed to be equipped with sensors to provide line-of-sight, and possibly range, measurements between them. Three vehicles are chosen because this is the minimum number required to determine all attitudes given minimal measurement information. Three cases are studied. The first determines the absolute (inertial) attitude of a vehicle knowing the absolute positions of the other two. The second assumes parallel beams between each vehicle to determine relative attitudes, and the third assumes nonparallel beams for relative attitude determination, which requires range information to find deterministic solutions. Covariance analyses are provided to gain insight on the stochastic properties of the attitude errors and the observability for all three cases.1077 d T 1 c . Using the configuration of the LOS vector measurements between vehicles, this paper will prove that a deterministic solution for the relative attitude can be found. More detailed literature about deterministic attitude determination can be found in [3].Three cases will be shown in this paper: 1) In the inertial attitude case, the two deputies are treated as reference points and the inertial positions of each vehicle are assumed to be known. For this case, only LOS vectors from the chief to each deputy are required (not between the two deputies) and the determined attitude is with respect to an inertial frame.2) In the parallel-beam case, the beams between vehicles are assumed to be parallel, and so common vectors are given between vehicles but in different coordinates. For example, for a laser communication system, a feedback device can be employed to ensure that parallel beams are given in real time. As long as the communication system latencies are sufficiently known and the link distance divided by the speed of light is greater than the latencies, the communication system can simply be used as a repeater (or relay if the signal strength is sufficient). It will be shown that deterministic solutions for all relative attitudes with three vehicles are possible for the parallel-beam case.3) In the nonparallel-beam case, it is assumed that nonparallel beams are present. To achieve common vectors, additional knowl-

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Abstract-The purpose of this paper is to demonstrate that having two classifiers, a trichotomous classifier (true, false, or unknown) with workload-independent performance that turns over the data classified as unknown to a binary classifier (true or false) with workload-dependent performance, gives superior classification performance (lower probability of misclassification) compared to a single dichotomous classifier. We relate the classifier's performance to the inherent difficulty of the classification task at hand (classifiability), and compare the performance of different classifiers.

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