Sigma 7, Six Times Round
Sixty-four years ago today, at 12:15:12 UTC on 3 October 1962, Wally Schirra lifted off from Cape Canaveral for six orbits. This map rebuilds his path from a single line of NASA's flight report and plays it against his own radio transcript.
How the path is made
NASA's 1968 flight report (TN D-4807, Table XXIII) gives the actual state at orbital insertion. At 5 min 18.9 s after liftoff, the capsule was at 30.5885°N 71.9946°W, 86.98 nautical miles up, moving at 25,751 ft/s on a heading of 77.82°. Everything on the map is that one state run forward: a Kepler ellipse, plus the slow drift that Earth's bulge adds to the orbit (the J2 term), under a rotating Earth. There is no air drag and no tracking data after insertion.
The checks
| Check | Report | This model |
|---|---|---|
| Period | 88 min 55 s | |
| Inclination | 32.55° | |
| Apogee | 152.8 n. mi. | |
| Splashdown 32°06′N 174°28′W, after nine hours | reported by the recovery ship | |
| Stations in line of sight during their transcript sections | 38 sections at fixed stations |
The splashdown check is the strong one. After six orbits from a single starting point, the computed track passes the place where USS Kearsarge recovered him within a few kilometres. The orbit would have crossed that point at 9 h 04 min. The capsule got there at 9 h 13 min, because the retrorockets (sequence set for 8 h 51 min 33 s) slowed it and the parachute did the rest.
The six transcript sections that the model puts out of sight all have reasons printed in the transcript itself:
- Hawaii on pass 1, Canary on pass 3 and Kano on pass 3 were on HF radio, which bounces off the ionosphere ("Transmitting on HF… I read you very weak").
- The Cape on passes 5 and 6 came through relay aircraft ("Auto One relay", "Got you through Grand Turk relay now").
- Muchea on pass 4 sits at −0.5°, on the horizon. Its Cap Com said "I did not read you very well".
I first guessed that HF would mark every out-of-sight section. It doesn't: 18 of the 32 in-sight sections mention HF too.
Every station section
What stands on what
| Item | Source |
|---|---|
| Insertion state, period, inclination, apogee, landing point, retrosequence time | Boynton (ed.), First U.S. Manned Six-Pass Orbital Mission, NASA TN D-4807 (1968), Table XXIII and text; NTRS 19680025550 |
| Transcript, section headings, speaker codes | Results of the Third United States Manned Orbital Space Flight, NASA SP-12 (1962), appendix "Air-ground communications", from the onboard tape; NTRS 19630002114. Text is OCR of the scan, mistakes kept. Times are capsule elapsed time. |
| Launch 12:15:12 UTC, landing 21:28:22 UTC | Wikipedia, Mercury-Atlas 8, citing TN D-4807 |
| Which stations existed | Wikipedia, Manned Space Flight Network |
| Station positions | Wikipedia coordinates of the town or island (Cape Canaveral SFS, Bermuda, Gran Canaria, Kano, Zanzibar City, Muchea, Woomera, Canton Island, Kauaʻi, Point Arguello, Guaymas, Quito). These are not the antenna sites, so expect errors of tens of kilometres. The ships moved, so they are left out. |
| Coastlines | Natural Earth 1:110m via the world-atlas package |
| The orbit, the elevations, the checks | My code on this page. It agrees with my Python version to within about 5 metres. |