Re: QDR Released

On Mon, 06 Feb 2006 15:46:28 GMT, "Arved Sandstrom"
<asandstrom@xxxxxxxxxxxxx> wrote:

"Jack Love" <jackxxloveyy@xxxxxxxxxxxxx> wrote in message
On Sun, 05 Feb 2006 21:45:39 GMT, "Arved Sandstrom"
<asandstrom@xxxxxxxxxxxxx> wrote:

[ SNIP ]
As far as ionization goes, it may not be an insurmountable problem. The
shuttle (granted, it has a shape advantage) doesn't experience comm
blackout, for example. Can an RV be shaped so as to do what the shuttle
in conjunction with the satellite(s)? I dunno. But more to the point, why
worry? Use GPS where you can (midcourse) and stick to INS for the
Not true: the shuttle experiences a 10-15 minute blackout : "At
approximately 265,000 feet, the spacecraft enters a communications
blackout, which lasts until the orbiter reaches an altitude of
approximately 162,000 feet. Between these altitudes, heat is generated
as the spacecraft enters the atmosphere, ionizing atoms of air that
form a layer of ionized gas particles around the spacecraft. Radio
signals between the spacecraft and the ground cannot penetrate this
sheath of ionized particles, and radio communications are blocked for
approximately 16 minutes."

It all depends on what cite you read, and when the material in the cite was
effectively written. You'll note that even in the above, it says "radio
signals between the spacecraft and the ground". Point being, with the TRDSS
satellites, and careful positioning of the S-band antennas on the shuttle,
it is generally possible to communicate between the shuttle and a TRDSS
satellite through a hole (or near-hole) in the plasma envelope. It's not
100%, but it's no longer the case that _all_ comm with the shuttle is lost
for such a long period of time.

Point taken. Though the data bandwidth of TDRSS (at least when I was
familiar with it) wasn't that marvelous :).

The incoming trajectory of a warhead will
be far different than the shuttle, so I'm not sure what it's blackout
window is likely to be. I would think it's likely to be very much
toward the end of the trajectory and probably not get over until a
lower altitude. When I looked it up a while ago the velocity at
impact for an ICBM warhead to be Mach 10. Not giving much time at
[ SNIP ]

I'm thinking that the designers may not much care about the terminal comm
blackout. The INS is very likely capable of determining required
corrections, and it will have much more time than just a second to make its

Subject to debate, of course: INS isn't sufficient by itself for max
accuracy and needs updates from alternate sources which just aren't
going to be available IMO. Supposedly they are getting 90m accuracy
and that ain't bad at all.