It's a 143 SiLence. Yup, not a Science but a Sil
Same mould as a Double Up Sirena- good spotting!
It doesn't feature in any of the WW archives or old O'Brien catalogues, I think the Science only came as a 142...? Maybe it was produced under license or something- I bought it used, it was probably an eBay job.
Either way, the clean, uncluttered base is real nice on rails & sliders, and I love the slipperyness on landings. As you can see I've bashed the hell out of it, and it still edges OK. Well, just about OK