Plate solving (ASTAP)

ASTAP is the plate solver Starship integrates with. Free, fast, runs locally with downloaded star catalogs. Plate solving is a pure computation on the pixels of a FITS frame — it never moves equipment, so it's always safe to run.

What plate solving gives you

Point Starship at any FITS frame from your IMAGES folder and it hands the file to ASTAP, then reads back the solution:

• Centre coordinates — RA (hours) and Dec (degrees) of the middle of the frame
• Image scale — arcseconds per pixel
• Rotation — the sky position angle of the frame. Every successful solve updates the stored Camera position angle under Settings → Camera, so that field always reflects reality (manual edits there are overwritten by the next solve).
• Field of view — width × height in degrees
• Stars used and solve time

A solve also captures the full WCS terms (the CD matrix and reference pixel), which is what lets Starship translate a pixel you click on into a sky position.

Solving a frame yourself

Console → the plate-solve tile. Pick a file from the list and you get:

• Solve — solve using the mount's current pointing as a hint (when a mount is connected). If a hinted solve fails, Starship automatically retries once blind (whole-sky) before giving up, so a stale or parked mount readback never blocks a solve that would otherwise succeed.
• Blind solve — force a hint-free whole-sky search. Use it for frames that were not taken at the mount's current pointing (archived frames, files you dropped in). The field-of-view hint is still applied — that's a property of your optics, not your pointing.
• Solve & sync — solve, then sync the mount's pointing model to the solved position.
• Solve latest — solve the most recent frame in the IMAGES folder in one click.

After a solve you can act on the result without leaving the tile: → GoTo (plain slew to the solved coordinates), → Precise GoTo (the slew-and-center loop below), and ⟲ Sync from solved position.

Center here. On the Console's Last captured frame preview, click the Center here toolbar icon, then click a point on the image and confirm — Starship solves that frame and precise-slews the mount so the point you clicked lands in the centre. Requires a mount, camera and ASTAP.

Precise pointing (slew-and-center)

Precise GoTo runs a full slew → capture → solve → sync → re-slew loop, repeating until the solved position is within tolerance of the target (the Voyager GoTo++ / NINA slew-and-center equivalent). Configure it under Settings → Mount (Precise pointing): exposure, binning, tolerance (arcminutes), max iterations, and settle time. Sequencer slew steps run this automatically when the step has precise: true. Requires a camera and ASTAP.

Recenter after a meridian flip

This flow is now fully wired (it used to be a stub). Turn it on with Settings → Mount → "Plate-solve recenter after flip", and set the recenter exposure alongside it.

After the sequencer performs a meridian flip, if recenter is enabled it:

1. Takes a short exposure (the recenter exposure, default 5 s)
2. Plate-solves it
3. Syncs the mount to where it actually points
4. Re-slews to the intended target
5. Settles, then continues the sequence

This is what keeps an unattended German-equatorial mount on target across the meridian, correcting any pointing shift the flip introduced. It needs a connected camera and ASTAP; without them the recenter step reports an error and the flip fails safe.

Plate-solve actions in a sequence

Two mount actions in the sequence editor use plate solving:

• Plate-solve & sync — solves and syncs the pointing model. With a target in context it slews, solves, syncs and points precisely to that target; otherwise it corrects the pointing model at the mount's current reported position without meaningfully moving.
• Blind-solve & sync (recover) — captures at the current pointing, solves hint-free across the whole sky, and syncs the mount. Use this to recover a "lost" mount whose reported coordinates can't be trusted — it does not slew to a presumed target first, so it's correct even when the mount is confused.

Both are also available from the Console (Blind solve on the plate-solve tile, and the blind-sync recovery path).

Settings

Settings → Plate solver (ASTAP):

• Enable plate solver — master on/off.
• ASTAP executable path — leave blank to auto-detect astap_cli / astap.exe on PATH and in common install locations (C:\Program Files\astap, C:\astap, %LOCALAPPDATA%\Programs\astap), or point it at the executable directly.
• Initial search radius (deg) — how wide a hinted search looks (default 5°).
• Solve timeout (s) — how long to wait for ASTAP before giving up (default 60 s).
• Downsample — ASTAP's -z; 0 lets ASTAP decide. Force 2–4 to solve noisier, one-shot-colour, or short-sub frames more reliably.
• Test ASTAP — runs ASTAP with -h to confirm the executable actually works.

Settings → Camera has two solve-only overrides used by pointing / polar / rotate-to-PA frames:

• Plate solve gain override — gain for solve-only frames; blank = use the science gain.
• Plate solve binning override — binning for solve-only frames (higher bin = more SNR + faster solve); blank = use the per-task binning.

The field-of-view hint is derived automatically from [camera].focal_length_mm + pixel_size_um and the connected camera's reported sensor height. Set the focal length and pixel size under Settings → Camera and Starship passes the right FOV to ASTAP; leave either at 0 and ASTAP auto-detects the scale instead.

Installing ASTAP and its catalog

ASTAP needs a star database in its install directory to solve. Install the D50 database from the ASTAP site (it covers typical deep-sky FOVs); download a catalog matched to your image scale if D50 doesn't fit. Without a database ASTAP can't solve. We don't bundle catalogs.

When a solve fails

The most common causes Starship reports back:

• No stars in the frame — a daylight/indoor test, the cap left on, or clouds
• No star database installed (install D50 from the ASTAP site)
• The FOV hint is far off, or the search radius is too tight for how far the mount has actually moved

A hinted solve that fails always retries blind before reporting failure, so "no solution" usually means the frame genuinely has too few stars or the database is missing.