Question about the F-22 and it's radar.

"D. Strang" wrote in message
news:HNpbc.4808$zc1.3884@okepread03...
"Kevin Brooks" wrote
"D. Strang" wrote
The F/A-22 also has an inherent air-to-surface
capability." It can already lug a couple of JDAM's. So how does that
even
*require* an optimized ground mapping radar to allow it to strike
ground
targets with significant precision?

I'm not a bombardier, but I think the SAR radar is necessary for the
INS
inputs. The INS being only updated by the GPS, and only if the GPS
isn't being jammed (which will be unlikely down the road). I think I
read
where GPS only doubles the accuracy of the INS (50 feet versus 100
feet).

Without SAR, and GPS being jammed, you'll need a good pair of TACAN's,
which some enemies don't seem to provide :-)

I have yet to hear that a SAR update is required. Doing so would require
the
preloaded data for the terrain (so that the SAR would have something to
relate its picture to). From what i understand, the weapon gets its
update
from the aircraft (through its own INS), then after release it uses GPS
to
improve the accuracy of its own INS. If SAR was required, then I guess
the
A-10 would never be certified to carry JDAM...?

An A-10 at altitude? What a waste. They were designed to be down with
the
tanks...

The way I picture it, and I admit I may be completely bogus on this, but I
picture the navigator finding a reference point (coordinates), and then
using
the SAR to find the point in weather, and then updating the INS from this
point. You wouldn't need SAR if the point was available by other means,
or the target could tolerate greater than 100 foot error. For example, if
a 2k/lb jobber hit 500 foot from my house, I'd still be dead, and the
house
would be destroyed :-)

I am guessing that the primary means of updating the aircraft INS is via
GPS; maybe BUFFDRVR or one of the folks who has a clue can answer that
question. Otherwise you'd have a wee bit of a problem if your target was a
coastal one and your ingress was from over the water, or if you were
dropping it over a nice, relatively flat desert plain where you could not
get much in the line of significant terrain features from which to perform
your update, etc.

Brooks

"Kevin Brooks" wrote

"D. Strang" wrote

The way I picture it, and I admit I may be completely bogus on this, but
I
picture the navigator finding a reference point (coordinates), and then
using
the SAR to find the point in weather, and then updating the INS from
this
point. You wouldn't need SAR if the point was available by other means,
or the target could tolerate greater than 100 foot error. For example,
if
a 2k/lb jobber hit 500 foot from my house, I'd still be dead, and the
house
would be destroyed :-)

I am guessing that the primary means of updating the aircraft INS is via
GPS; maybe BUFFDRVR or one of the folks who has a clue can answer that
question. Otherwise you'd have a wee bit of a problem if your target was a
coastal one and your ingress was from over the water, or if you were
dropping it over a nice, relatively flat desert plain where you could not
get much in the line of significant terrain features from which to perform
your update, etc.

On-board SAR's main purpose in fighters is autonomous targeting. As far as I
know, no fighter is planned to have GMTI functions but SAR imaging has been
a standard function for a long time. Other targeting options of course
include off-board sensors and Guys On the Ground. GPS is unlikely to be
jammed for aircraft since any ground based jammer is going to be 'way out of
the main lobe of an AJ GPS antenna. JDAM and SDB are going to get AJ
antennas as well.

There is an issue with geolocation. From what I've read in AvWeek,
geolocation errors are the dominant error term in the JSTARS to JDAM loop.
B2s (again according to AW) are the most accurate platform for RADAR imaging
and targeting, which is surprising.