The Ashtanga is not the only force in the Anti-Spirals fleet...the Nanda-class is a mechanical monster which dwells within the Galactic Spiral Abyss, and is found in the manga, novels and script. It's size is even bigger than that of the moon-sized Super Galaxy Dai-Gurren. Thankfully,
I've already done the scaling for the size of Super Galaxy Dai-Gurren, which will make things much easier...
260 pixels = 3474.2km
1 pixel = 3474.2km/260 = 13.3623077km
13.3623077km X 153 = 2044.43308km
13.3623077km X 484 = 6467.35693km
13.3623077km X 51 = 681.477693km
43 pixels = 681.477693km
1 pixel = 681.477693km/43 = 15.8483184km
129 + 92 + 143 + 211 + 95 + 56 + 29 + 59 + 63 + 71 + 95 + 165 = 1208 pixels
15.8483184km X 1208 = 19144.7686km
And the Nanda vanishes off-panel, meaning it's ultimately even
longer.
Final Results
Nanda-class's length = >19144.769km