Sat-ND, 25.10.1997 -- Saturday Night Fever
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Atlas II-A launches DSCS
How high the sky
She Wore an Itsy Bitsy Teeny Weenie Yellow Polka Dot Cassini
The sixth Defense Satellite Communications System (DSCS) III satellite was launched from Cape Canaveral Air Station (CCAS) yesterday (Eastern Daylight Time.) And that was hopefully the last U.S. military satellite to appear in Sat-ND, at least for the next weeks.
At nine flights, the series of launches for the U.S. Air Force's Medium Launch Vehicle II program, including DSCS, is one of the largest single-user launch service programs for Lockheed Martin's Atlas. Lockheed Martin has commitments for 25 Atlas launches through the 1990s, including 17 commercial and 8 Air Force missions. One more mission remains in the 1997 manifest, and nine launches are forecast for 1998.
Once in final (geostationary) orbit, the satellite will join the Air Force's third-generation space constellation and support globally distributed users in all branches of the Defense Department with secure voice and high data rate communications. Built by Lockheed Martin Missiles & Space, DSCS III provides the backbone of the U.S. military's global satellite communications capabilities.
DSCS was used throughout the Gulf War and serves as a primary communications link for U.S. forces in Bosnia. Use of the system has tripled since the 1991 conflict and is currently in use by U.S. troops in Bosnia. DSCS spacecraft provide global coverage to all the U.S. military services, U.S. unified commands and the national command authority. They offer secure voice and high-data rate communications, antijam capabilities and features for enhanced survivability.
The DSCS III program began in 1976 and the first spacecraft was launched in 1982. Fourteen DSCS III satellites have been built. This launch increases the number of active DSCS III spacecraft in the constellation to 10. The satellites in the DSCS constellation are in a geosynchronous orbit providing tactical military communications to troops in the field as well as strategic communications for commanders and Pentagon officials.
Phase III satellites incorporate multiple-beam antennas and other enhancements for more flexible coverage than previous generations. The DSCS satellites provide great flexibility to adapt to changing military communication coverage and bandwidth needs. The satellites are also used aboard Air Force One to keep the U.S. president in constant communications.
See also: Floriday Today's Defense Satellite Communications System Fact Sheet
GPS navigation in space?
This mission also incorporated a small satellite experiment called Falcon Gold, which was built by cadets at the U.S. Air Force Academy in co-operation with the University of Colorado at Colorado Springs, to test the Global Positioning System signal at altitudes above the GPS constellation. Falcon Gold will remain attached to the Centaur stage and receive and relay GPS signals until the on-board batteries expire. This is the first step in determining if navigation using GPS is possible for spacecraft above the GPS constellation altitude (approx. 20,000 kilometres above the equator.)
What to do with a satellite that cannot tell its own altitude following an anomaly in its telemetry system? This is what happened to Intelsat 605. Engineers have now come up with an innovative solution.
First of all: there's not much wrong with the bird. The anomaly experienced on September 11 did not affect the commanding, payload or ranging/orbit determination capabilities of the spacecraft. The spacecraft is still receiving commands and executing them. The autonomous functioning of the spacecraft -- that is, its ability to operate routinely without ground intervention -- also has not been affected, Intelsat said in a statement.
"The major effect that we have experienced is in the area of spacecraft orbital attitude information," says Steve Stott, Intelsat Director of Satellite Engineering Support & Processes. "Therefore, since we can't get it from the spacecraft, we have devised a method to get it from the ground."
So, how high is it? To find out, a series of ground-based software monitoring programs were installed at selected ground stations at beam edge. They measure the RF signal strength and calculate the actual attitude of Intelsat 605 from it. According to Intelsat, this method is accurate enough to prevent any impact on services carried on the spacecraft.
"We believe that the solution we have devised will allow us to utilise this important resource within our system with total confidence in its performance integrity," stated Conny Kullman, Intelsat Vice President of Operations and Engineering.
The missing telemetry does not affect the spacecraft in any other way. It automatically stays in a spin-stabilised configuration with its solar arrays pointing towards the sun without any intervention.
See also: Intelsat's 605 Satellite Fact Sheet
Why on Earth should anyone want to visit Joe Montani's home page? Simple: It offers Planetary Astronomy Publications, Radio Astronomy Publications, Images, and even tells you how to contact Joe Montani. Most other home pages don't. Right? Right.
Okay, let's have a look at those images then. There is a scan of the front page of "Columbia", the magazine of Columbia University (Winter 1996;) then one of a stamp with a plane flying upside dow on it and the comment "Ever feel like this;" followed by a snap of Dr Love, the curator of the Insects Collection at the Smithsonian Institution; and finally one -- no, three images of the Cassini probe in space, taken two days ago "with the Spacewatch 36-inch telescope on Kitt Peak."
That's at least what Joe Montani says, and I have no reason to doubt. But being an ignorant anyway, those pictures remind me more of the following lines, which describe the effects of trendy chemical amusement aids on humans, than of any space probe:
"And all I see is little dots
some are smeared and some are spots."
(Talking Heads, "Drugs")
I almost forgot to include the URL: http://www.lpl.arizona.edu/users/jmontani/
BTW: You have to scroll down to the bottom of the page to see the Itsy Bitsy Teeny Weenie Yellow Polka Dot Cassini pictures.
Copyright 1997 by Peter C. Klanowski, pck@LyNet.De. All rights reserved.
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