Description

This document compares the star tracker options for FINCH. In order to achieve the desired image quality, high attitude knowledge accuracy is required.

Requirements

• Cost should be less than CAD 78k (ADCS budget - Cost of the TT module) (Lower is better)
• Higher accuracy is better
• A higher refresh rate is better
• Must fit in the satellite (As determined by mechanical)

Options

• The 3σ values for the ArcSec modules are estimated based on the 1σ numbers reported

** “The covariance of the fused estimate is based on the sqrt of the sums of the individual covariances (i.e. 2 sensors -> 1/sqrt(2) ~ 70% the uncertainty of a single sensor)”

Additional Simulation Information (May 2023)

According to simulations performed by ArcSec, the actual accuracy we can expect in space is significantly less than the numbers reported in brochures. Also, the CubeSpace star tracker slew rate requirement limits our imaging time to a maximum of 200 seconds, according to Tensor Tech’s simulation.

Evaluation

• The cost of the ST200 would put the cost of the complete ADCS module to around $110k, which is higher than the $100k budget. With a baffle it will likely cost even more.
• Because the error of the Twinkle and CubeSpace star trackers is 5-10px, choosing either of these components means attitude knowledge becomes the limiting factor for image quality, making it around 20 times worse than what optics provides. This guarantees failure of some scientific objectives
• Choosing the Sagitta star tracker may cause compromises to spatial resolution, but this is not the limiting factor for image quality even with Sagitta. It is the only option that has the potential of meeting all scientific objectives

Recommendation

ADCS recommends that we purchase the ArcSec Sagitta star tracker.

Result