""" fetch_artemis2.py Fetches Artemis II trajectory and orbital elements from JPL Horizons and writes artemis2_data.json to the current directory. Run once manually to test, then schedule with cron every 10 minutes: crontab -e */10 * * * * cd /path/to/your/webroot && python3 fetch_artemis2.py Requires: requests pip3 install requests """ import requests import json import math import os from datetime import datetime, timedelta, timezone EARTH_RADIUS_KM = 6371.0 HORIZONS_URL = 'https://ssd.jpl.nasa.gov/api/horizons.api' OUTPUT_FILE = 'artemis2_data.json' # Horizons rejects the request if START_TIME is before the trajectory exists. # Clamp start to the first available epoch - never request pre-launch data. LAUNCH_TIME = datetime(2026, 4, 2, 2, 1, 0, tzinfo=timezone.utc) # 2 mins past first epoch HOURS_AHEAD = 240 # 10 days forward from now # Step sizes VECTOR_STEP = '1 h' # 1-hour position steps (~250 points over mission) ELEMENTS_STEP = '6 h' # 6-hour orbital element steps def horizons_request(params): """Make a request to JPL Horizons and return parsed JSON. Builds the URL as a plain string to avoid requests double-encoding the single-quote delimiters that Horizons requires around values. """ # Build query string manually - Horizons needs literal single quotes # around most values, which requests.get(params=...) would double-encode qs = '&'.join(f"{k}={v}" for k, v in params.items()) url = f"{HORIZONS_URL}?{qs}" print(f"\n DEBUG URL: {url[:120]}...") try: resp = requests.get(url, timeout=30) resp.raise_for_status() data = resp.json() if 'error' in data: print(f" Horizons error: {data['error']}") return None return data except requests.exceptions.Timeout: print(" Request timed out.") return None except requests.exceptions.RequestException as e: print(f" Request failed: {e}") return None def parse_vectors(result_text): """Parse CSV vector output from Horizons $$SOE...$$EOE block.""" records = [] in_data = False for line in result_text.split('\n'): if '$$SOE' in line: in_data = True continue if '$$EOE' in line: break if not in_data or not line.strip(): continue parts = line.split(',') if len(parts) < 8: continue try: x = float(parts[2]) y = float(parts[3]) z = float(parts[4]) vx = float(parts[5]) vy = float(parts[6]) vz = float(parts[7]) records.append({ 'time': parts[1].strip(), 'x_km': round(x, 3), 'y_km': round(y, 3), 'z_km': round(z, 3), 'vx_kms': round(vx, 6), 'vy_kms': round(vy, 6), 'vz_kms': round(vz, 6), 'range_km': round(math.sqrt(x*x + y*y + z*z), 3), 'speed_kms': round(math.sqrt(vx*vx + vy*vy + vz*vz), 6), }) except (ValueError, IndexError): continue return records def parse_elements(result_text): """Parse CSV orbital elements from Horizons $$SOE...$$EOE block. CSV columns (0-indexed): 0 JDTDB 1 Cal_Date 2 EC (eccentricity) 3 QR (periapsis distance, km from Earth centre) 4 IN (inclination, deg) 5 OM (longitude of ascending node, deg) 6 W (argument of periapsis, deg) 7 Tp (time of periapsis passage) 8 N (mean motion, deg/s) 9 MA (mean anomaly, deg) 10 TA (true anomaly, deg) 11 A (semi-major axis, km) 12 AD (apoapsis distance, km from Earth centre) 13 PR (sidereal orbit period, s) """ records = [] in_data = False for line in result_text.split('\n'): if '$$SOE' in line: in_data = True continue if '$$EOE' in line: break if not in_data or not line.strip(): continue parts = line.split(',') if len(parts) < 13: continue try: ec = float(parts[2]) qr = float(parts[3]) a = float(parts[11]) ad = float(parts[12]) records.append({ 'time': parts[1].strip(), 'eccentricity': round(ec, 8), 'semi_major_axis_km': round(a, 3), 'perigee_dist_km': round(qr, 3), 'apogee_dist_km': round(ad, 3), 'perigee_alt_km': round(qr - EARTH_RADIUS_KM, 3), # apogee is meaningless when ec >= 1 (hyperbolic trajectory) 'apogee_alt_km': round(ad - EARTH_RADIUS_KM, 3) if ec < 1.0 else None, 'inclination_deg': round(float(parts[4]), 6), 'hyperbolic': ec >= 1.0, }) except (ValueError, IndexError): continue return records def fmt_dt(dt): # Horizons strongly prefers month abbreviation format e.g. 2026-Apr-02 18:00 # Numeric month format (2026-04-02) can cause rejection on some queries return dt.strftime('%Y-%b-%d %H:%M') def run(): now = datetime.now(timezone.utc) # Start from launch time (trajectory start) or 48h ago, whichever is later start = max(LAUNCH_TIME, now - timedelta(hours=48)) stop = now + timedelta(hours=HOURS_AHEAD) print(f"Fetching Artemis II data from JPL Horizons...") print(f" Window: {fmt_dt(start)} -> {fmt_dt(stop)} UTC") # ── Vectors ── print(" Requesting state vectors...", end=' ', flush=True) v_data = horizons_request({ 'format': 'json', 'COMMAND': "'-1024'", 'EPHEM_TYPE': "'VECTORS'", 'CENTER': "'500@399'", 'START_TIME': f"'{fmt_dt(start)}'", 'STOP_TIME': f"'{fmt_dt(stop)}'", 'STEP_SIZE': f"'{VECTOR_STEP}'", 'VEC_TABLE': "'2'", 'OUT_UNITS': "'KM-S'", 'CSV_FORMAT': "'YES'", 'OBJ_DATA': "'NO'", }) if not v_data: print("FAILED") return False vectors = parse_vectors(v_data['result']) if not vectors: print("FAILED - no data in response (trajectory not yet available)") return False print(f"OK ({len(vectors)} points)") # ── Orbital elements ── print(" Requesting orbital elements...", end=' ', flush=True) e_data = horizons_request({ 'format': 'json', 'COMMAND': "'-1024'", 'EPHEM_TYPE': "'ELEMENTS'", 'CENTER': "'500@399'", 'START_TIME': f"'{fmt_dt(start)}'", 'STOP_TIME': f"'{fmt_dt(stop)}'", 'STEP_SIZE': f"'{ELEMENTS_STEP}'", 'OUT_UNITS': "'KM-S'", 'CSV_FORMAT': "'YES'", 'OBJ_DATA': "'NO'", }) elements = [] if e_data: elements = parse_elements(e_data['result']) print(f"OK ({len(elements)} points)") else: print("FAILED (continuing without elements)") # ── Find current position index ── now_ms = now.timestamp() * 1000 current_idx = 0 best_diff = float('inf') for i, v in enumerate(vectors): # Horizons time format: "A.D. 2026-Apr-01 18:00:00.0000 TDB" # Strip prefix and suffix for parsing t_str = v['time'] try: # Remove "A.D. " prefix and " TDB" / " UT" suffix clean = t_str.replace('A.D. ', '').split(' TDB')[0].split(' UT')[0].strip() t = datetime.strptime(clean, '%Y-%b-%d %H:%M:%S.%f').replace(tzinfo=timezone.utc) diff = abs(t.timestamp() - now.timestamp()) if diff < best_diff: best_diff = diff current_idx = i except Exception: continue current = vectors[current_idx] if vectors else None # ── Write JSON ── output = { 'fetched_at': now.isoformat(), 'current_idx': current_idx, 'current': current, 'vectors': vectors, 'elements': elements, 'mission_info': { 'name': 'Artemis II', 'spacecraft': 'Orion / Integrity', 'horizons_id': '-1024', 'launched': '2026-04-01T22:24:00Z', } } tmp = OUTPUT_FILE + '.tmp' with open(tmp, 'w') as f: json.dump(output, f, separators=(',', ':')) os.replace(tmp, OUTPUT_FILE) # atomic replace - safe for live webservers alt = current['range_km'] - EARTH_RADIUS_KM if current else 0 print(f" Written {OUTPUT_FILE}") print(f" Current position: range={current['range_km']:,.0f} km, altitude={alt:,.0f} km, speed={current['speed_kms']:.3f} km/s") return True if __name__ == '__main__': success = run() if not success: print("\nFetch failed. If this is shortly after launch, the trajectory") print("data (-1024) may not yet be published in JPL Horizons.") print("Try again in a few hours.")