One is power for the head, the other is ignition control of the TX (so you can't TX with your engine off and drain your battery). The two can be sourced from one 12 volt supply if ignition control isn't desired.
If there is +12V inside the control head from the radio you might be able to possibly make an internal connection inside the head to provide that power. You'd have to read up on the service manual to see if they send 12 volts to the head from the radio on one of the harness wires. If not, you're out of luck, unless there is a spare unused wire you can re-purpose for that function.
the W series head service manuals would be a good place to start.
You can jumper the heads for single supply and also to turn on when power is applied.
There should be a spare wire in the control head cable so you could jumper the interconnect and control head to power up from the radio 12V.
Never done this so not sure if there are any issues with the voltage drop to the head
I'm not sure if the Astro Spectra heads are well documented, but FWIW the older Spectra heads were very hard to find data on, the regular Spectra service manuals didn't include them, there was a huge "depot" service manual that actually had all the schematics, including all the heads and "modules" like the VCO's. They did this for the Quantar too, having a useless "service" manual, and a "real" "depot" service manual that was actually useful.
the older spectra head information was a bit scattered but there was some in the full DSM and in the options manuals.
At least on the Astro they did try to consolidate in one spot. Be nice if they updated it to include the later heads for the XTL and APX