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tokens: in Table 2 . For an easy display, only the deviations of the parameters ( a , e , i , ω , Ω, and w ) from the true values (6922.8781 km, 0.00181017, 429715, 2070229, 1169049, and 225215) are listed. Table 2 The Orbit Parameter Spaces Note. “Δ a ,” “Δ e ,” “Δ i ,” “Δ ω ,” “ΔΩ,” and “Δ w ” are the deviations for the semimajor axis, eccentricity, inclination angle, RAAN, argument of perigee, and mean anomaly, respectively. First, the orbit determination method is demonstrated with LE. At each grid point of the parameter space, the “predicted” profile is folded and its significance is obtained. As shown in Figure 3 , the significance of the profile varies significantly with the deviation of the orbital parameters and has a maximum around the true value (zero deviation). Then, the maxima obtained by fitting a Gaussian function curve give the optimal values for the six orbital parameters separately, i.e., each time one parameter is free with the other five fixed, and the results are shown in Table 3 . The process obtaining the best parameters is very similar to that used by Sheikh et al. ( 2007 ) to get the TOAs from the observed pulse profiles (Sheikh 2005 ). Therefore, the uncertainties of these parameter values can be obtained in a similar way as follows:where W is the FWHM, and S/N is the signal-to-noise ratio obtained by the bootstrap method (Diaconis Efron 1983 ). As mentioned by Sheikh (Sheikh 2005 ), the S/N is limited to a maximum of 1000 by Figure 3. Orbit determine result with Insight/LE: χ 2 of the orbit elements of calculations (blue squares) and fitted results (red lines). “Δ a ,” “Δ e ,” “Δ i ,” “Δ ω ,” “ΔΩ,” and “Δ w ” are the deviations for the semimajor axis, eccentricity, inclination angle, RAAN, argument of perigee, and mean anomaly, respectively. Table 3 Best Estimated Value of the Elements and Errors (3 σ ) Then, similar demonstrations are also done for HE and ME, as shown in Table 3 . It shows that the errors for HE are less than those for ME and LE, because it has collected more pulsed photons. By combining all the data from HE, ME, and LE, the errors become smaller. By transferring the orbit elements to the cartesian parameters, we obtain the 3 σ errors of the current position and velocity, which are 3.15 km, 6.61 km, and 4.46 km for x, y, and z ; and 0.0073 km s −1 , 0.0033 km s −1 , and 0.0042 km s −1 for v x , v y , and v z , respectively. In short, the position and velocity are pinpointed within 10 km (3 σ ) and 10 m s −1 (3 σ ). 5. Discussions Conventionally, a minimum of three pulsars are required to get the absolute navigation. Considering the clock time-offset on the spacecraft, another pulsar is needed. Thus, at least four pulsars should be observed simultaneously, which would require at least four detectors, increasing the technical complexity and the cost of the mass, energy, and money. An alternate choice is to observe different pulsars sequentially using a single detector, which would increase the risk of the