T0 F1GHT tErrR0r!1

[tugrik]

Much of the media need to be kneed in the teeth. Repeatedly.

Reading the morning newspaper (on the web, of course), I come across this article. To sum up the article since the link will expire in a few days, they launched another GPS satellite. To quote, "We believe that GPS spacecraft is going to play a huge role in the war or terrorism", etc etc.

Oh, please. Give me a break already! We launch GPS satellites all the time. It's just how the GPS system works! The system is rather ablative. Old satellites eventually get de-orbited and new ones are flung up to replace them. Since I work for a GPS company that does long term orbit modelling as part of its core business I have to put a new entry in the LTO tables for each new PRN (satellite number) as it goes up, and remove the ones that get decomissioned. Still, the media latches on to it. Sensing this gets them some free publicity, the folks at Boeing grandstandingly painted "Let's Roll!" and "Spirit of 9-11" on the rocket.

This is the equivalent of saying "We delivered another newspaper to your doorstep today. TO FIGHT TERROR!". Oh, and just to prove it, we made our paperboys use rubber-bands that had "Spirit of 9-11" printed on them.

Comments

[revar.livejournal.com]

But... but... They're patriotic rubber bands! :)

[goldwing.livejournal.com]

Yeah, I didn't understand that on the news, either. So if a terrorist wants to use GPS for an attack, that means he'll be just a little more accurate because of the extra satellite up there. =-\

Tug, how do GPS units deal with the satellite changes? If satellites are failing and new ones are launched into orbit, do GPS units know to lock onto that new signal in the sky?

[buran.livejournal.com]

The new satellite is replacing an old one that is going bad. I imagine it will just seamlessly be dropped into place. The old one is moving elsewhere on the orbital plane it's on and going to standby.

[tugrik.livejournal.com]

For the most part the handhelds just listen on certain frequencies and the satellite ID's itself by PRN#'s. While the SVN (satellite vehicle number) is never re-used, the PRN (don't remember the acronym) for old ones is retired and used by new ones, so there's never any gaps. Your receiver simply hears and marks the satellite by its advertised number, and works with the almanac and ephemeris data to find out what to expect from that satellite's orbit. Then you start listening for the doppler-shift in the 'chips' (the regular clock-ticks the satellite broadcasts) and start doing happymath.

Give me a day to ask one of our orbital guys for the demo paperwork and I can type in a much more complete description if you want :)

[buran.livejournal.com]

Actually, this satellite was to have launched a fair while back, while the nose art was somewhat more topical. Some pad rat screwed up when operating a lifting crane while the satellite was being mated to the rocket, though, and damaged part of the rocket, so a lot of inspections and part replacements were necessary. This of course caused delays.

Though yes, the crap about the war on terror is misplaced -- the GPS system has been around since the late 1980s, when I believe it was known as NAVSTAR. (can you confirm that?)

http://spaceflightnow.com/delta/d295/

[tugrik.livejournal.com]

Still is, yupyup! Heck, part of my job entails decoding NANUs (Notice Advisory for NAVSTAR Users) and entering them into our long-term-orbit modelling system. The NANUs are emailed notifications describing orbital maneuvers, satellite maintenance, new birds, retirements, and all other kinds of things going on up there. A surprising amount is happening all the time in the GPS cloud.

GPS is just the 'sell it to the public' term. NAVSTAR sounds a bit too corny to market, though that's the actual name of the satellite system as a whole.

[tugrik.livejournal.com]

For your amusement, here's some sample NANU's from this past week.

The first one is your average 'out of service' marker -- when they expend fuel to lift the orbit slightly or otherwise do a maneuver or software change that will make the satellite unusable for GPS recievers for a short while. During this time the satellite has a flag for 'healthy' that's turned off, so receivers will ignore it when it's bad.

The 2nd one is the retirement of a satellite, which is most likely the one that's going to be replaced by the recent launch.

The 3rd one is a 'summary', doing a recap of the day's (or week's, sometimes) events.

The reason that we need to know these things for LTO is that we have to have our system remove the satellites from long-term modelling a full 24 hours before they go unhealthy, and not return them to service until 36 hours of healthy service has been restored. Long, NDA-ridden reasons for this, so I won't explain further. :)

--------------------- NANU1

NOTICE ADVISORY TO NAVSTAR USERS (NANU) 2003006
SUBJ: SVN17 (PRN17) UNUSABLE JDAY 025/0016 - JDAY 027/1922
1.     NANU TYPE: UNUSABLE
       NANU NUMBER: 2003006
       NANU DTG: 271923Z JAN 2003
       REFERENCE NANU: 2003004
       REF NANU DTG: 222334Z JAN 2003
       SVN: 17
       PRN: 17
       START JDAY: 025
       START TIME ZULU: 0016
       START CALENDAR DATE: 25 JAN 2003
       STOP JDAY: 027
       STOP TIME ZULU: 1922
       STOP CALENDAR DATE: 27 JAN 2003

2.  CONDITION: GPS SATELLITE SVN17 (PRN17) WAS UNUSABLE ON JDAY 025
    (25 JAN 2003) BEGINNING 0016 ZULU UNTIL JDAY 027 (27 JAN 2003)
    ENDING 1922 ZULU.

3.  POC: CIVILIAN - NAVCEN AT (703)313-5900, HTTP://WWW.NAVCEN.USCG.GOV
    MILITARY - GPS Support Center, DSN 560-2541,
    COMM 719-567-6616, GPS@SCHRIEVER.AF.MIL, HTTP://WWW.SCHRIEVER.AF.MIL/GPS

4.  TO UNSUBSCRIBE, PLEASE VISIT
HTTP://WWW.NAVCEN.USCG.GOV/GPS/SUBSCRIBE.HTM AND FOLLOW THE INSTRUCTIONS.

--------------------------------------------- NANU2

1.     NANU TYPE: GENERAL
*** GENERAL MESSAGE TO ALL GPS USERS ***
GPS Satellite SVN21 (PRN21) was decommissioned from active service on JDay
27 (27 Jan 03) as of 2200Z.  PRN21 is available for future satellite
vehicles.
*** GENERAL MESSAGE TO ALL GPS USERS ***
2.TO UNSUBSCRIBE, PLEASE VISIT HTTP://WWW.NAVCEN.USCG.GOV/GPS/SUBSCRIBE.HTM
AND FOLLOW THE INSTRUCTIONS.

--------------------------------------------- NANU3

NOTICE ADVISORY TO NAVSTAR USERS (NANU) 2003005
SUBJ: SVN35 (PRN05) FORECAST OUTAGE SUMMARY JDAY 023/2130 - JDAY 024/0453
1.     NANU TYPE: FCSTSUMM
       NANU NUMBER: 2003005
       NANU DTG: 240457Z JAN 2003
       REFERENCE NANU: 2003003
       REF NANU DTG: 161636Z JAN 2003
       SVN: 35
       PRN: 05
       START JDAY: 023
       START TIME ZULU: 2130
       START CALENDAR DATE: 23 JAN 2003
       STOP JDAY: 024
       STOP TIME ZULU: 0453
       STOP CALENDAR DATE: 24 JAN 2003

2.  CONDITION: GPS SATELLITE SVN35 (PRN05) WAS UNUSABLE ON JDAY 023
    (23 JAN 2003) BEGINNING 2130 ZULU UNTIL JDAY 024 (24 JAN 2003)
    ENDING 0453 ZULU.

3.  POC: CIVILIAN - NAVCEN AT (703)313-5900, HTTP://WWW.NAVCEN.USCG.GOV
    MILITARY - GPS Support Center, DSN 560-2541,
    COMM 719-567-6616, GPS@SCHRIEVER.AF.MIL, HTTP://WWW.SCHRIEVER.AF.MIL/GPS

4.    TO UNSUBSCRIBE, PLEASE VISIT
HTTP://WWW.NAVCEN.USCG.GOV/GPS/SUBSCRIBE.HTM AND FOLLOW THE INSTRUCTIONS.

[paka.livejournal.com]

I suppose that since Bush himself is the best example of someone using patriotism and other peoples' deaths for shameless advertising, you can't blame anyone who uses this war on terrorism as an excuse for advertising. But I hate that variety of bullshit.