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Mars Science

MSL Landing Timeline: What To Expect Tonight 140

An anonymous reader writes "When the Curiosity rover lands on Mars later tonight, it'll be executing a complex series of maneuvers. JPL will be relying on the Mars Odyssey orbiter to relay telemetry back to Earth in time-delayed real-time, and if all goes well, we'll be getting confirmation on the success (or failure) of each entry, descent, and landing phase, outlined in detail here."
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MSL Landing Timeline: What To Expect Tonight

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  • by Anonymous Coward on Sunday August 05, 2012 @07:25PM (#40889775)

    Telemetry will be continuously relayed back to earth, true, but with not much less than about a 15 minute latency, owing to the fact that Mars roughly a quarter of a light-hour from earth right now.

    That IS indeed real time. Relativity tells us nothing can have an effect here in less time. I don't know if you're trolling or just ignorant, but by your definition you can never look at the stars, galaxies or nebulae in the sky in real time either because they're all at varying distances and we're seeing light that originated anything from about 4 to several million years ago. With telescopes you can go back billions.

  • by Anonymous Coward on Sunday August 05, 2012 @07:53PM (#40889951)

    The single most important criteria for something to qualify as "real time" in data communications is low latency. 14 and a half minutes is not low.

    Then by your definition NOTHING in space is real time. You look up into the sky and everything you're seeing is sending it's light to you from the past.

  • by Anonymous Coward on Sunday August 05, 2012 @07:54PM (#40889957)

    No, that's just your personal set of criteria that doesn't have anything to do with reality.

    Real-Time is without artificial delay. Yes, there's 14 minutes actual delay, but it's not artificial, it is literally the fastest possible time.

    If 14 minutes prevents it from being real time, then 14 seconds should too, as should 14 milliseconds, or 14 nanoseconds. All of them are arbitrary amounts of time, all of them are large amounts of latency relative to something.

  • by mark-t ( 151149 ) <markt.nerdflat@com> on Sunday August 05, 2012 @09:50PM (#40890613) Journal
    You draw the line at any signal latency that is too slow to meaningfully respond to in the context that the signal was originally sent from. There's a reason why interrupt handlers in real-time OS's need to finish their job in as few computing cycles as possible.
  • by Waffle Iron ( 339739 ) on Sunday August 05, 2012 @10:26PM (#40890761)

    Owing to the fact that we will know the lander has already reached the surface (in unknown condition) by the time we get the first signal it has entered the atmosphere

    Relativity says that there is a 14 minute delay in *some* frames of reference. In other frames of reference, the delay is longer. For others (those occupied by the radio signal photons, for example), the landing events and our reception of the signals happen simultaneously.

    Getting hung up over what you imagine is the "time delay" between two points in spacetime that are outside of each others' light cones is kind of pointless.

Perfection is acheived only on the point of collapse. - C. N. Parkinson