SpawnDev.BlazorJS.NexStar

SpawnDev.BlazorJS.NexStar provides a robust NexStarService for communicating with and controlling Celestron NexStar telescopes directly from a browser using the Web Serial API in Blazor WebAssembly.

Built on top of SpawnDev.BlazorJS, this library enables full hardware access without requiring a backend server.

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🔭 SpawnDev NexStar App

Launch NexStar Control

The repository includes SpawnDev.BlazorJS.NexStar.App, a full-featured Progressive Web App (PWA) demonstrating the library's capabilities.

App Features:

• Telescope Control:
  • Complete directional slewing with variable rates.
  • GoTo coordinates (RA/Dec).
  • Tracking mode selection (EQ North, EQ South, Alt-Az, Off).
• Object Browser:
  • Catalog of 110 Messier objects and bright alignment stars.
  • "Quick Access" panel showing objects currently visible from your location.
  • Filter by constellation, magnitude, and type.
• Satellite Tracker 🛰️:
  • Real-time tracking of orbital objects (ISS, Starlink, weather satellites, etc.).
  • Fetches TLE data from CelesTrak with offline caching.
  • Automatic telescope slewing to track selected satellite.
• Plane Tracker ✈️:
  • Real-time tracking of nearby aircraft using ADS-B data.
  • Displays callsign, altitude, speed, and distance.
  • Calculate look angles and track aircraft with telescope.
• Alignment Helper:
  • Real-time suggestions for best alignment stars based on time and location.
  • Visual tracking of alignment status.
• Location Services:
  • Sync telescope time and location with browser data.
• Fallback USB Support:
  • For Android devices, uses Web USB API to connect via Prolific PL2303 driver.
• Dark Mode:
  • Optimized dark red/black UI for viewing in low light environments.

Data Sources & Credits

Feature	Source	License
Satellite TLE Data	CelesTrak	Free for non-commercial use
Aircraft Data	OpenSky Network	Free API (non-commercial)

Dependencies

Package	Purpose
SGP.NET	SGP4 orbital propagation for satellite tracking

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💻 Library Features (SpawnDev.BlazorJS.NexStar)

Core Capabilities

• Web Serial Connectivity: Direct serial port selection and connection via browser.
• Web USB Connectivity: Fallback connection method for Android devices using Web USB API.
• Command Protocol: Implementation of the Celestron NexStar communication protocol.
• Position Tracking:
  • Real-time RA/Dec and Az/Alt monitoring.
  • Automatic polling and state management.
• Astronomy Math:
  • Built-in utilities for coordinate conversion (Equatorial <-> Horizontal).
  • LST (Local Sidereal Time) calculation.
  • Visibility calculations based on observer location.
• Catalogs:
  • Integrated database of alignment stars and Messier objects.

Installation

dotnet add package SpawnDev.BlazorJS.NexStar

Usage Example (Program.cs)

using SpawnDev.BlazorJS;
using SpawnDev.BlazorJS.NexStar;

var builder = WebAssemblyHostBuilder.CreateDefault(args);
builder.RootComponents.Add<App>("#app");
builder.RootComponents.Add<HeadOutlet>("head::after");

// Add BlazorJSRuntime (Required for Web Serial/USB)
builder.Services.AddBlazorJSRuntime();

// Add NexStarService
builder.Services.AddSingleton<NexStarService>();

await builder.Build().BlazorJSRunAsync();

Common Usage Examples

@inject NexStarService NexStar

<button @onclick="Connect" disabled="@NexStar.SerialPortSelected">Connect</button>
<button @onclick="Disconnect" disabled="@(!NexStar.SerialPortSelected)">Disconnect</button>

@if (NexStar.SerialPortSelected)
{
    <p>Model: @NexStar.Model | Aligned: @NexStar.IsAligned</p>
    <p>RA: @NexStar.CurrentRa?.ToString("F4")h | Dec: @NexStar.CurrentDec?.ToString("F2")°</p>
    <p>Az: @NexStar.CurrentAz?.ToString("F2")° | Alt: @NexStar.CurrentAlt?.ToString("F2")°</p>
    
    <button @onclick="GoToM31">GoTo M31 (Andromeda)</button>
    <button @onclick="StopSlew">Stop</button>
}

@code {
    // Connect to telescope (opens device picker)
    private async Task Connect()
    {
        if (await NexStar.SelectPortAsync())
        {
            Console.WriteLine($"Connected to {NexStar.Model}");
        }
    }

    // Disconnect from telescope
    private async Task Disconnect() => await NexStar.DeselectPortAsync();

    // GoTo a specific RA/Dec coordinate (M31 Andromeda Galaxy)
    private async Task GoToM31()
    {
        double ra = 0.712;   // RA in hours (0h 42m 44s)
        double dec = 41.27;  // Dec in degrees (+41° 16')
        await NexStar.GotoRaDecAsync(ra, dec);
    }

    // GoTo using Az/Alt (useful for terrestrial or satellite tracking)
    private async Task GoToAzAlt(double az, double alt)
    {
        await NexStar.GotoAzAltAsync(az, alt);
    }

    // Slew manually (for directional buttons)
    private async Task SlewNorth() => await NexStar.SlewFixedAsync(SlewAxis.Dec, SlewDirection.Positive, 5);
    private async Task SlewSouth() => await NexStar.SlewFixedAsync(SlewAxis.Dec, SlewDirection.Negative, 5);
    private async Task SlewEast()  => await NexStar.SlewFixedAsync(SlewAxis.Ra, SlewDirection.Positive, 5);
    private async Task SlewWest()  => await NexStar.SlewFixedAsync(SlewAxis.Ra, SlewDirection.Negative, 5);

    // Stop all slewing
    private async Task StopSlew() => await NexStar.StopAllSlewAsync();

    // Set tracking mode
    private async Task SetTracking(TrackingMode mode) => await NexStar.SetTrackingModeAsync(mode);

    // Sync current position (after centering on a known star)
    private async Task SyncPosition(double ra, double dec) => await NexStar.SyncRaDecAsync(ra, dec);

    // Set telescope time/location from browser
    private async Task SyncTimeLocation()
    {
        await NexStar.SetTimeAsync(DateTime.UtcNow);
        // Location can be set via NexStar.SetLocationAsync(lat, lon)
    }
}

Key Properties

Property	Type	Description
SerialPortSelected	bool	True if connected to telescope
IsAligned	bool	True if telescope is aligned
Model	string?	Telescope model name
CurrentRa / CurrentDec	double?	Current RA/Dec position
CurrentAz / CurrentAlt	double?	Current Az/Alt position
TrackingMode	TrackingMode	Current tracking mode

Key Methods

Method	Description
SelectPortAsync()	Opens device picker, connects to telescope
DeselectPortAsync()	Disconnects from telescope
GotoRaDecAsync(ra, dec)	Slew to RA/Dec coordinates
GotoAzAltAsync(az, alt)	Slew to Az/Alt coordinates
SlewFixedAsync(axis, dir, rate)	Manual slew at fixed rate (1-9)
StopAllSlewAsync()	Stop all motion
SyncRaDecAsync(ra, dec)	Sync position after centering
SetTrackingModeAsync(mode)	Set tracking (Off, AltAz, EqNorth, EqSouth)

Requirements

• A browser with Web Serial API support (Chrome, Edge, Opera).
• A browser with Web USB API support (Chrome on Android).
• A Celestron NexStar telescope (or compatible mount).
• A USB cable connected to the telescope's hand controller port.

Tested Platforms

• Windows (Chrome): Verified working with Web Serial API.
• Android (Chrome): Verified working with Web USB API (using minimal PL2303 driver).
• Web Serial: Generic Support
• Web USB: Generic Prolific PL2303 Support