Astra on International Space Station
by Greg N. Holt , Brandon Wood12 November 20252 min read
A manual, crew-operated method for backup and emergency navigation on lunar flights has been proposed since the early planning of such missions. Theoretical approaches to manual space navigation were presented in the 1960s by authors such as Nordtvedt and Havill, and recently by Zanetti. One of the primary differences in this study versus previous manual navigation efforts is its focus solely as an emergency backup, where the proposed method gives the crew an opportunity to effect their own rescue.
The flight instrument was a Celestaire Astra III Professional hybrid brass/aluminum sextant, serial number 1183118. It was outfitted with a 7x35, 6.5◦field-of-view prism telescope for sighting.
The manufacturers calibration certificate is dated Feb 11, 2015 and indicates performance within 0.1 arc min in the regions as indicated in Table 1. This model was chosen based on results from the 2015 study for its accuracy (achieved by the superior machining tolerances of the brass arc vs. aluminum) combined with the lower mass and slightly more compact construction of the aluminum
frame than a solid brass instrument. A spare telescope, horizon mirror, and index mirror were flown for the experiment as well as a microfiber cleaning cloth, adjustment wrench, and screwdriver. A
lanyard was included but was not used by the crew, as they indicated it was not needed in microgravity and having hook-and-loop fastener tape on the handle was more useful for temporarily securing the sextant to a wall if needed.
The model of sextant instrument used is shown in Figure 2. Flight certification required evaluating and documenting all the components for acceptable characteristics of flammability, outgassing, fracture, etc. The main safety concern for use on ISS was breakage of the glass or mirror components during vibration loads, so it was placed in two plastic bags and stowed in protective foam for launch as shown in Figure 3. The crew reported the instrument had no damage upon first unpackand inspection on-orbit.
The manufacturers calibration certificate is dated Feb 11, 2015 and indicates performance within 0.1 arc min in the regions as indicated in Table 1. This model was chosen based on results from the 2015 study for its accuracy (achieved by the superior machining tolerances of the brass arc vs. aluminum) combined with the lower mass and slightly more compact construction of the aluminum
frame than a solid brass instrument. A spare telescope, horizon mirror, and index mirror were flown for the experiment as well as a microfiber cleaning cloth, adjustment wrench, and screwdriver. A
lanyard was included but was not used by the crew, as they indicated it was not needed in microgravity and having hook-and-loop fastener tape on the handle was more useful for temporarily securing the sextant to a wall if needed.
The model of sextant instrument used is shown in Figure 2. Flight certification required evaluating and documenting all the components for acceptable characteristics of flammability, outgassing, fracture, etc. The main safety concern for use on ISS was breakage of the glass or mirror components during vibration loads, so it was placed in two plastic bags and stowed in protective foam for launch as shown in Figure 3. The crew reported the instrument had no damage upon first unpackand inspection on-orbit.