Mars Orbiter and GPS - just curious : LUSENET : Millennium Salons : One Thread

I started a thread on the Y2kforum listserv about GPS and the Mars Orbiter disappearance. I thought I'd add to it here.

The original post is as follows:



I'm screwing in the plastic lock-down system for my greenhouse, feeling a little behind lately. A grey fall wind is starting to blow. National Public Radio is on, and I'm just pondering as I work.

A report about the Mars Climate Orbiter's recent disappearance due to a "rather significant navigational error" comes on, and this light goes off in my head.

Now, I may be a little jaded, and even a touch cynical just about now, in spite of my truly undying optimism, but I'm also a rocket scientist's daughter - one who grew up with a very smart man always solving problems like "why is this rocket falling over?" who tried to get his daughter to learn how to think.

And so I hear this "navigational error" bit and I can't help but wonder "GPS?" "navigational error?" "GPS?" It's a word association thing.

I just sent a post out this morning that my brother found for us and it mentioned the Thiokol episode. That's especially close to me because my stepfather had stood in front of Congress years ago and begged for a back-up to the Challenger, claiming that the commercial pressure on one shuttle would be much too great for effective safety procedures to bear.

O-rings and processors both seem like they could be similar potential failure points that would be hard to track, impossible to check, and about which there would be no option but to gamble they'd work if performance pressures were strong enough.

At a paltry 125 million dollars (cheap as far as probes go), there couldn't possibly have been a non-compliant GPS navigational system on that unit, could there?

No. No way.

Call me curious.


Cynthia Beal

-- Cynthia Beal (, September 24, 1999


Hey Cynthia ck out this thread over at Yourdan. Seems the craft hit the atmosphere a bit too deep.

-- Mitchell Barnes (, September 24, 1999.

Hi Jon!

Thanks for your response, included below. I'm putting it up on the Salons "Global" Forum at

and will answer you briefly here, but more indepth there, if time and

I'm somewhat aware of GPS - I remember my Dad working on aspects of it about 25 years ago, and my stepfather did some of the first LandSat work in Asia. My Dad specialized in guidance systems, and my stepfather in the management of aerial resource information use, primarily in Asia and South America.

We've been writing on this stuff for so long on the Forum that I forget most people don't have access to the groundwork research we lay-people pooled together a couple of years ago on things like GPS. In fact, I think the reason a lot of us are here is because we're naturally curious about such things, we like to think them through - the data available on the web can make a passing curiosity like "I wonder if GPS rollover could have had an impact on the Orbiter's navigational system?" something that can actually be pursued in the amount of time one might take to go to dinner and a movie.

Now, this probably doesn't sound like your idea of a hot date, but some of us are a little odd this way, I suppose.

I don't have the URL handy right now, but Mitchell Barnes (cc'd here, along with y2kforum and year2000 groups) did a bit of work with a couple of other people back in 1997? and discovered that there were several significant issues with GPS, and they weren't isolated to receivers. Harlan Smith also uncovered a couple of the GPS nuances. One of the ones that I think Mitchell pointed out had to do with the correct version of the star map.

I couldn't put my fingers on the note, but I spent a normal Mel-Gibson-Chase-Scene interval with Alta Vista and came up with the following links. I skimmed each of them, and they're interesting. I can't regurgitate all the technical data now, but in them you'll see that it may indeed be possible that something on the Orbiter was using something (time, position?) from a unit getting information from something vulnerable to the GPS Rollover. This could have even been a very small something that could have created an incremental but accumulating error.

If nothing else, the information in these URLs would suggest that Brian's proclamation of "Unlikely" is just a bit hasty.

BTW -There are 24 satellites. I think they're all fine per the Navy's testing done earlier this year (link is above), but the relationships seem complex and the NAVSTAR site is very clear about not being presumptuous in this matter.

As far as the public analysis of the fault goes, I suppose there will be a rather large disincentive on the part of the injured parties to think of it as Y2k related, unless they're self-insured. In which case, whoever has to absorb the loss costs might do some forensics to learn whether or not this sort of thing was the cause. It would be nice if they'd do it soon enough for others similarly potentially affected to learn of the problems, one way or another, and extrapolate into other potential problems that may lose more than just a multi-million dollar space probe.

Relevant Links:

NASA's Mars Climate Orbiter Believed To Be Lost go here

Mars Climate Orbiter Official Website go here

Mobile Robot Navigation by Jonathan Dixon Oliver Henlich, 10 June 1997. Imperial College, London. go here

A bit about the Launch vehicle's specs

Delta carries navigation satellite into orbit go here

Very good bit that explains GPS, especially the part about loading the ephemeris and the almanac that I believe was what Barnes was referring to as a potentially compromised function in some equipment at rollover (not millennium but GPS)

Really comprehensive GPS overview from UT at Austin Global Positioning System Overview go here

How GPS Works go here

Year 2000 event information on the NAVSTAR website Year 2000 Event Statement for Loran-C & DGPS go here

Y2K/Week Rollover go here

And here's a thread on Yourdon's Forum where the discussion may roll around a bit, too:

go here

Anyhow, that's it for this. If I post more on this, it will be at the Global Salon link mentioned above.

Regarding your particular point about the distance the satellites are from Mars and your thought that the distance would be too great to make a difference, I think that in the links above you'll see that for some navigation systems in use, those sorts of distances can become negligible or even completely irrelevant.

Thanks for jumping into the pot, Jon. I think this is a lot more interesting than football - or Mel Gibson (sorry, Mel.)

Now, back to work!



On Thu, 23 Sep 1999, Jon Belcher wrote:

> Cynthia, > The GPS system that we use on Earth depends on some 20 odd satellites > that broadcast to GPS receivers which use those signals to determine the > receivers postition. Since these satellites are between 35,000,000 and > 235,000,000 miles from Mars, I doubt they can help navigate a Mars > orbiter. > There is another NASA satellite that has been orbiting Mars since March, > 1998 called the Mars Global Surveyer. The GPS receivers on Earth require > signals from 3 satellites for 2-d location so a single satellite may not > be very useful if it has the ability to send such a signal. NASA's > website ( ) states that its > instruments include a laser altimeter for mapping the heights of Mar's > mountians but I don't know if it has any capability to assist another > satellite's navigation.

-- Cynthia Beal (, September 24, 1999.

snipped from comp.risks - mitch

Date: Wed, 6 Oct 1999 11:30:02 -0700 (PDT) From: Erann Gat Subject: ICD's save ISS: *not*!


Space Station Immune to Metric Mishap, NASA Says By Daniel Sorid, 05 Oct 1999

The International Space Station will not fall victim to the measurement units problems which ruined the Mars Climate Orbiter, according to a NASA spokesman. In the early 90s, engineers put together a so-called interface control document, which identifies the use of metric or English units for every piece in the station, according to NASA spokesman Dwayne Brown.

"This is not a new issue for us," Brown said. "It's so well documented that we don't have that problem." The document also shows where metric and non-metric units interact with each other, and calls for the development of adapters that standardize the units. "Engineers got together and said, 'Here's the piece of hardware. Let's see where they interconnect.' If we've got a metric piece and an English piece, that will show up very clearly in the document." [...]

There's one little problem with this theory: Mars Climate Orbiter had an interface control document too. (JPL is ISO9000 certified! We have documents for everything.) It was obviously not enough to save MCO; why should it be any different for ISS?

Most accounts in the press make the MCO disaster sound like a massive breakdown in communications, with one group of people doing everything in Metric and another doing everything in English units, and no one talking to anyone else for months on end. I was told this morning by a member of the MCO team that this is not true. Everyone knew that everything was supposed to be Metric across the board. The problem was a single number in the software that was accidentally entered incorrectly. The exact same thing has happened on at least one previous mission, but the problem was caught before it became a news story (that is, before we drove the spacecraft into a planet.)

Regular readers of RISKS will no doubt be shocked -- shocked! -- by these revelations.

Erann Gat [Usual disclaimers]

-- Mitchell Barnes (, October 13, 1999.

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