"Thomas Schoene" wrote
Paul F Austin wrote:
"John Keeney" wrote

"Paul F Austin" wrote ...

TCDL provides 200Kbps downlink/10Mbps uplink service. That's
adequate for this kind of situatuational awareness. More downlink
would allow more raw

For how many nodes/UCAVs at once?

One for each TCDL link. What's your point?

How many TDCL links can you suport in a single geographic region? The
wider
the pipes are, they fewer a given segment of spectrum can support. There
are clever ways to stretch bandwidth, but there is ultimately a finite
limit.

That's true and it's a serious problem. First the obligatory disclaimer.
This is frankly outside my area, not being a RF comms guy, so if I step on
my crank, I'm sure someone will point it out.

Frequency diversity can carry you only so far. TCDL operates (on the return
link) over a 400MHz band with 5MHz channel spacing. I don't know if adjacent
channels can operate within LOS of each other but that's 80 channels at best
whose antennas can "see" each other. Directional links will carry you a ways
also since the operating band, Ku/K, is highly directional and the apertures
are small. TCDL is intended to work in other bands as well. Ka and Q bands
offers substantial available BW.

Certainly the problems of directional RF comms between maneuvering aircraft
are being solved as part of the IFDL development for F-22 and F-35. The F-22
IFDL antenna, providing hemispherical coverage and 78 switched beams weighs
5.4 pounds and occupies 250 cubic inches. This antenna
http://www.emsstg.com/defense/ant_data_link.asp operates in Q band
(30-50GHz) but gives you an idea of what's possible. An equivalent TCDL
aperture in Ku/K band would be larger because of the lower frequency.

Another answer may be LASER links, much work is going on in this area. When
I worked on a controller for LASER cross-links for (now defunct) Teledesic,
the spot size was about 6 inches in diameter into a receiver about 4X bigger
over GEO kinds of distances but that was for a non-maneuvering satellite
with known ephemeris. It did require a closed-loop tracker because even the
minimal vibrations in an orbiting spacecraft could cause the spot to walk
when working over those distances. The challenges of two maneuvering
aircraft communicating by LASER are substantial but given GPS and a stable
element at both ends, cooperative aiming should be possible.

All of these things are_possible_but they all cost money. If I start from
the position that UCAVs are candidates for future CAS/BAI missions, then the
projected UCAV is burdened with something like the ICNIA suite with things
like IFDL. A CAS UCAV won't be cheap. That's why I mentioned that some have
suggested a pilotless F-35 as a UCAV candidate. There will be_some_cost
advantages in such an aircraft but we're not talking about a $150K model
airplane with a pair of SDBs under the wings and a minigun slung under the
fuscelage.

This is the kind of thing that USENET lends itself least to since serious
trades require serious analysis. The information above came from 5 minutes
with Google and FAS's site. Handwavium is poor substitute for real
engineering. I apologize to John for getting a bit snippy in my answer to
him. I'm certainly not casting myself as an authority in these matters
who's_done_the trades touched on above.