OpsLog/cmd/satdiag/main.go

// Command satdiag answers "is this pass real, and is that Doppler right?" from
// a station's own cached elements, without launching OpsLog.
//
//	go run ./cmd/satdiag <data dir> <locator> <satellite>
//
// It prints which element set the satellite resolved to and how old it is, the
// look angle now, the range rate BOTH as the propagator reports it and as the
// range actually changes, the Doppler each transponder would be given, and the
// next passes. It exists because a wrong Doppler and a wrong satellite look the
// same from the front — an operator saying "the frequency moves enormously" —
// and the two are told apart by these numbers in a second.
//
// It found the range rate the SGP4 library reports being wrong by a factor of
// 250 and of the wrong sign. Not part of the build.
package main

import (
	"fmt"
	"os"
	"strings"
	"time"

	"hamlog/internal/sat"
)

func main() {
	dir := os.Args[1]
	grid := os.Args[2]
	name := os.Args[3]

	f := sat.NewFetcher(dir)
	els, at, err := f.LoadCache()
	if err != nil {
		fmt.Println("cache:", err)
		os.Exit(1)
	}
	store := sat.NewStore()
	store.Replace(els, at)
	fmt.Printf("elements: %d, fetched %s (%s ago)\n\n", len(els), at.Format(time.RFC3339), time.Since(at).Round(time.Minute))

	birds, err := sat.LoadBirds(dir)
	if err != nil {
		fmt.Println("birds:", err)
	}
	b, ok := birds.Find(name)
	if !ok {
		fmt.Println("no frequency plan for", name)
		os.Exit(1)
	}
	// The same resolution the app does.
	var el sat.Element
	found := false
	if e, ok := store.GetNORAD(b.NORAD); ok {
		el, found = e, true
		fmt.Printf("elements found BY NORAD %d → %q\n", b.NORAD, e.Name)
	} else if e, ok := store.Get(b.Name); ok {
		el, found = e, true
		fmt.Printf("elements found by name → %q (NORAD %d)\n", e.Name, e.NORAD)
	} else {
		for _, a := range b.Aliases {
			if e, ok := store.Get(a); ok {
				el, found = e, true
				fmt.Printf("elements found by alias %q → %q (NORAD %d)\n", a, e.Name, e.NORAD)
				break
			}
		}
	}
	if !found {
		// Last resort, exactly as satElement does: scan every element name and
		// compare on letters and digits alone. This is how "JAS-2 (FO-29)" and
		// "FO-29" meet, and leaving it out of the diagnostic made a satellite
		// that resolves perfectly well in the app look unresolvable here.
		for _, n := range store.Names() {
			if b.Matches(n) {
				if e, ok := store.Get(n); ok {
					el, found = e, true
					fmt.Printf("elements found by SCAN → %q (NORAD %d)\n", e.Name, e.NORAD)
					break
				}
			}
		}
	}
	if !found {
		fmt.Println("NO ELEMENTS")
		os.Exit(1)
	}
	fmt.Printf("epoch: %s (%s old)\n", el.Epoch.Format(time.RFC3339), time.Since(el.Epoch).Round(time.Hour))
	fmt.Println("line1:", el.Line1)

	lat, lon, okGrid := gridToLatLon(grid)
	if !okGrid {
		fmt.Println("bad locator:", grid)
		os.Exit(1)
	}
	obs := sat.Observer{Lat: lat, Lon: lon}
	fmt.Printf("observer: %s → %.4f, %.4f\n\n", grid, obs.Lat, obs.Lon)

	now := time.Now().UTC()
	p, err := el.Track(obs, now)
	if err != nil {
		fmt.Println("track:", err)
		os.Exit(1)
	}
	fmt.Printf("NOW  %s : az %.1f el %.1f range %.0f km\n", now.Format("15:04:05"), p.Az, p.El, p.RangeKm)
	fmt.Printf("  range rate REPORTED by the library : %+10.3f km/s\n", p.RangeRate)
	fmt.Printf("  range rate MEASURED (d range / dt) : %+10.3f km/s\n", numericRate(el, obs, now))

	for _, tp := range b.Transponders {
		sh := sat.Doppler(p, tp.DownLo, tp.UpLo)
		fmt.Printf("  %-28s down %d → %d (%+d Hz)   up %d → %d (%+d Hz)\n",
			tp.Label, tp.DownLo, sh.DownHz, sh.DownHz-tp.DownLo, tp.UpLo, sh.UpHz, sh.UpHz-tp.UpLo)
	}

	fmt.Println("\nnext passes (min el 0):")
	passes, err := store.Passes(el.Name, obs, now, now.Add(12*time.Hour), 0)
	if err != nil {
		fmt.Println("passes:", err)
	}
	for i, ps := range passes {
		if i >= 8 {
			break
		}
		fmt.Printf("  %s → %s  max %.1f°  az %.0f→%.0f\n",
			ps.AOS.Format("15:04:05"), ps.LOS.Format("15:04:05"), ps.MaxEl, ps.AOSAz, ps.LOSAz)
	}

	// The extremes of the Doppler across the next pass, which is the honest
	// answer to "does it move that much".
	if len(passes) > 0 {
		ps := passes[0]
		var lo, hi int64
		for tt := ps.AOS; tt.Before(ps.LOS); tt = tt.Add(10 * time.Second) {
			q, err := el.Track(obs, tt)
			if err != nil {
				continue
			}
			d := sat.Doppler(q, b.Transponders[0].DownLo, 0).DownHz - b.Transponders[0].DownLo
			if d < lo {
				lo = d
			}
			if d > hi {
				hi = d
			}
		}
		fmt.Printf("\ndownlink Doppler across that pass: %+d Hz … %+d Hz (span %d Hz)\n", lo, hi, hi-lo)
	}
}

// gridToLatLon is the six-character Maidenhead centre.
func gridToLatLon(g string) (float64, float64, bool) {
	g = strings.ToUpper(strings.TrimSpace(g))
	if len(g) < 4 {
		return 0, 0, false
	}
	lon := float64(g[0]-'A')*20 - 180
	lat := float64(g[1]-'A')*10 - 90
	lon += float64(g[2]-'0') * 2
	lat += float64(g[3]-'0') * 1
	if len(g) >= 6 {
		lon += float64(g[4]-'A') * (2.0 / 24)
		lat += float64(g[5]-'A') * (1.0 / 24)
		lon += (2.0 / 24) / 2
		lat += (1.0 / 24) / 2
	} else {
		lon += 1
		lat += 0.5
	}
	return lat, lon, true
}

// numericRate is the range rate measured rather than reported: the distance a
// second later minus the distance a second earlier, over two seconds. It cannot
// disagree with physics, so it is the reference the library's own figure is
// checked against.
func numericRate(el sat.Element, obs sat.Observer, at time.Time) float64 {
	a, e1 := el.Track(obs, at.Add(-time.Second))
	b, e2 := el.Track(obs, at.Add(time.Second))
	if e1 != nil || e2 != nil {
		return 0
	}
	return (b.RangeKm - a.RangeKm) / 2
}