It is certainly POSSIBLE to do this - however, there may well be NO substantial demand for it - and so, it is simply not worth a manufacturer, to take the time, and trouble, to do the engineering required, and to manufacture it - because there is NO money in it for them, to do so!!
SAS, is Serial Attached SCSI - and there ARE SCSI USB adaptors available - or were - although the last time I looked. they were hard to find, and were fairly expensive. Essentially, these are a USB to SCSI protocol converter, plus a PARRALLEL SCSI physical, electrical interface - either a narrow, or wide SCSI. Converting THIS parrallel data, to a serialized version - that is, one bit after the other, sequentially - is what SAS is - so it IS technically possible (even if NO physical commercially available hardware may currently exist), to convert this, into a SAS interface - albeit, probably a limited one - as SCSI has many commands, and a typical USB - to - SCSI adaptor, may only give you a small, but useful, minimal subset, of the entire SCSI command set protocol - and will be limited, by the nature, and limits, of the USB interface itself. Especially pre-emptive, and Master states, and parallel processing commands - that are probably used, in a proper SAS HBA situation, in an industrial SAS server.
Still, this would be useful enough, in many situations - even if NOT, for running a live server from! (BackUp for instyance, in a small business scenario, or recovery perhaps - if recent backups are NOT available - Shame on YOU...)
Personally, I haven't found such a device, available commercially - and although, technically, I could probably cobble up something, and manufacture it - there simply isn't any money in it, that I can see, and sorry, but I have better things to do, with my private time...
Oh, and just to let you know - SATA, is simply a serialized version, of the ATA (i.e.Serial ATA), parrallel HDD interface - which competes, or competed, against the SCSI parrallel interface - so the actual, basic, physical, silicon technological devices to serialize the SCSI signals, are already available (although, mostly, they would be in a specialized SATA chip, at the moment - discrete devices are, or at least were, available, last time I looked)- and are currently being used, in USB-SATA external drives, and active converter cables. It's just that no-one, it seems, has bothered to do the same, for SAS devices,because there is not enough demand for them! Essentially, the task is virtually the same - just a different protocol, and electrical specification. They are BOTH, Hard Disk Interfaces, and you need to connect them, to a Computer - they are just two different schemes, to do the same thing - but they have different capabilities, and compromises - and mainly, SAS is professional, and cost is less important than performance, and reliability - and SATA is domestic, where Cost, is more important, than performance, and reliability, is less catastrophic, financially - even if, it is no less devastating!! SO BACK IT UP!!
[See ECL and PECL devices - these are high speed, Balanced, Differential, Emitter Coupled Logic devices - suitable for 6Gbps, and higher data transfer speeds. See "http://pdfserv.maximintegrated.com/en/an/AN291.pdf" for an introduction to them.] Devices like these, and similar, are used internally, to SATA, and SAS, as the silicon semiconductors, that handle the conversion, and transfer to, and from, the high speed serial data interfaces. I have designed with these, myself, in the past.
And YES, USB, and SAS are incompatible - but then, so is USB, and SATA - but someone designed an interface device for USB to SATA, and manufactured it, and are currently selling them. And it seems, that no-one has done that, for USB to SAS - YET!! The needs of the professional IT industry, it seems, doesn't have the demand. OR, maybe, their BackUp regimes, simply makes this type of device unnecessary.
RWK.20160503_6-46pm.