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Lunokhod 1 found! But why lost in the first place?

  1. May 4, 2010 #1
    At long last, Lunokhod 1 has finally been http://www.dailygalaxy.com/my_weblog/2010/04/space-detectives-lasers-pinpoint-soviet-reflector-lost-on-moon-40-years-ago-.html" [Broken]. But why was it lost in the first place?
     
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  3. May 4, 2010 #2

    mgb_phys

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    Why would you ever know it's exact position?
    You have a reasonable idea where it landed because you can accurately time when the orbiter crosses the edge of the moon and when it de-orbits. So it's landing spot was known to a few 10s of km.

    But once the vehicle is on the moon the only accurate way to know where it is, is for the vehicle itself to tell you. You could equip the rover with a star tracker so it could precisely locate itself but whats the point? - That's not the science you are interested in.

    The radio signals it sends back spread out so unless you want to build a very large array receiver network to locate it precisely it could be anywhere on the moon. To receive the data stream you just need to point the antenna at the moon.

    More recent rovers and those on mars normally communicate with an orbiting vehicle that relays the data to earth, the orbiter passes overhead frequently so it is able to get a much better fix on eg. the mars rover's position.
     
  4. May 4, 2010 #3
    I'm not talking about the precise location. This thing has been utterly lost and silent for 40 years. Also, the researchers who found it realized that they were looking in the wrong place, being off by miles. Further, plenty of other robots don't get lost. I'm trying to figure out what went wrong with the robot, not why we couldn't pin its location down to the nearest centimeter.
     
  5. May 4, 2010 #4

    D H

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    Nothing went wrong with it. It was operational for 322 days, more than three times longer than what was planned/expected.

    Why would you expect to be able to pin down any lander's location to the nearest centimeter? That is a false expectation.
     
  6. May 4, 2010 #5
    If it was completely lost and silent for 40 years, then something went wrong. Surely the Russians didn't intend for it to work for a while and then disappear.

    It seems that you aren't reading very carefully. I very clearly said that I'm NOT, that is, NOT talking about the exact location. I am talking about the fact that it was utterly lost and wondering why.
     
  7. May 4, 2010 #6

    mgb_phys

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    The 'lost rover found' is mostly media hype.

    The rover was intended to work for 3months and then die. The time was limited by the radiothermal heater, it actually managed to work for 3x as long (space engineers tend to be conservative)

    The reason anyone has become interested in a dead piece of space junk is laser ranging. We measure the distance to the moon with a laser hitting some reflectors left behind by the Apollo missions and there are a few important scientific theories that can be tested by more accurate measurements.

    But the problem with using the same targets for all the measurements is that you are never sure if your results are due to some feature of the reflector, perhaps the coatings are having some effect or the position isn't quite what you thought.

    It happens that the 'lost' rover also had a reflector fitted but up to now nobody really cared (or had forgotten) because they had the Apollo ones - it was only for the more accurate laser rage tests that having a second independant target was important and so any effort was put into locating the Lunokhod 1.
    It's position to a few kms was known - but to find it on an image took a while. The images are only about 100m across and the object itself is only 2m long - you also have have the timing right so that the sun reflects off the object toward your camera.
     
  8. May 4, 2010 #7

    D H

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    Surely they did. Specifically, they expected it to work for a while and then stop working. It did not disappear. It simply got too cold and died. All space vehicles have a limited lifespan. Some carry fuel. When the fuel runs out those vehicles are dead. Others, like Lunokhod 1, carry radioisotopes for power and or heat. When enough of those radioisotopes have decayed those vehicles are dead. Yet others run purely on solar power. Solar cells degrade over time. When enough degradation has occurred those vehicles are dead.

    These are nominal end of mission scenarios. Sometimes things go wrong and the mission ends early. That is not what happened with Lunokhod 1. It exceeded its nominal life span by over 200 days.

    No, I'm not. You have some false expectations about us (the world's various space agencies) knowing where things are. Lunokhod 1 was found, and it was found within a few miles of where it was expected to be. That's not all that bad. You are assuming that this is bad.
     
  9. May 4, 2010 #8
    I can accept "die" without hesitation. What I am trying to get at is not "die" but "disappear". What went wrong that had us looking for it miles away from where it really turned out to be?

    My understanding is that there was a piece of equipment, a special kind of directional mirror, attached to both Lunokhod rovers, with the express intent of performing measurements. Surely someone cared about the mirrors, or their mass wouldn't have been added to the already expensive payload of the spacecraft. It can hardly be considered a dead piece of space junk when its sole raison d'etre is the expansion of human knowledge.
     
  10. May 4, 2010 #9
    No, you are assuming. My expectations are based on the admittedly naive observation that we do know where the other mirrors are and where the other Lunokhod vessel is. I am simply curious as to why we know where those are but we did not know where #1 was for so long.

    You are assuming that I have placed some value judgment. I am simply a human being with normal human curiosity, and I do not appreciate being told that my curiosity is invalid. Thanks for recusing yourself from this conversation.
     
  11. May 4, 2010 #10

    mgb_phys

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    The Apollo landing sites were better surveyed - partly because you intended to put people there, so a large part of the moon's surface was photographed looking for a flat landing spot. Although the eagle ended up landing a few miles from the original planned position after being piloted down manually. The lunakhod drove for 10s of kms from it's landing spot.

    The Apollo lander is a much bigger target but it has only recently been imaged by the same lunar imager mission that found the rover.

    I don't know if the Apollo astronauts on the surface or in the orbiter took star readings to fix their position accurately but we at least know craters they landed near and because the ranging experiment was a major part of the mission knowing their location was important.
    And we have been shooting at the prisms for 40 years so we have gradually narrowed down the accuracy.

    The lunar orbiters from the Apollo missions were mostly left in lunar orbit and will have impacted on the moon soon after but we don't accurately know their positions - unless some bored grad student is searching the lunar imaging pictures for them.
     
    Last edited: May 4, 2010
  12. May 4, 2010 #11
    From http://www.nasa.gov/mission_pages/LRO/news/lro-20100426.html" [Broken] article on the NASA site:

    Using information provided by NASA’s Lunar Reconnaissance Orbiter (LRO) instrument teams, researchers at the University of California San Diego successfully pinpointed the location of a long lost light reflector on the lunar surface by bouncing laser signals from Earth to the Russian Lunokhod 1 retroreflector.

    The vehicle was obviously not intended to disappear. I'm just asking the simple question, a question that maybe a little kid could have gotten away with: why did it disappear when the others didn't? Apparently something went not according to plan. Jeez, whatever happened to curiosity?
     
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  13. May 4, 2010 #12

    D H

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    I am not assuming anything. That you have placed a value judgment is very, very clear. Your words:

    That "what went wrong" is a value judgment. One more: Nothing went wrong. You are mistakenly assuming that something did go wrong.

    What you are doing is implicitly assuming that we do know where these things are to a very high degree of precision. That simply is not the case, particularly back in 1970. Precision landing is a rather recent development. There was a huge uncertainty in the landing locations of those early space probes, particularly the unmanned probes.

    Instead of asking what went wrong with Lunokhod 1, you should have been asking what went right with Lunokhod 2. The answer is simple: We got lucky.
     
  14. May 4, 2010 #13

    mgb_phys

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    Because knowing where it was was never particularly important so nobody put a lot of effort into locating it while it was operating (as long as you were close enough for the radio dish to get the data back) or pinpointing it's exact position since.
    It's main job was to drive around and sample rocks - which it did very well - it's reflector was never really used, and has only become important recently.

    We lost lots of other stuff, there are about 4, 10ton lunar orbiters lying on the moon somewhere - but we only know their position to a few 100km from their projected orbits.

    Remember finding/tracking an object's position takes effort - it's not just a matter of not forgetting.
    If it wasn't important to know the precise location why invest time/effort/payload/power/space in a tracking system when those resources could be used for more scientifically vital parts of the mission.
     
  15. May 4, 2010 #14
    Thanks for ruining my day when all I did was ask a simple question. If I'd wanted a scolding I would have just called my mother.
     
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  16. May 4, 2010 #15

    mgb_phys

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    Think how you would work out the position of an object on the moon.

    The easiest way from Earth is while it's still in orbit, you can time a radio signal accurately and measure very accurately when it crosses the edge of the moon (and the radio cuts out) then you can time the interval from the the last pass to when you fire the landing rockets. But this doesn't work perfectly - the moon isn't a uniform sphere so gravity is a bit more complex - this is what put Apollo off course.

    Once you are down you can fix your position in the same way a navigator on Earth did before GPS.
    You can use maps, take bearings from distinctive craters around you - just like you would locate mountain peaks while hiking.
    Or if you need a more accurate fix you can use a small telescope or theodolite to measure the position of known stars and fix your position to a few 100m, just as sailors and aircraft used to do. Nuclear missiles do this to fix their position in flight because a submerged submarine doesn't know where it is very accurately.

    Finally you can locate it from the Earth with a telescope picking up a radio signal - but to get high accuracy you need a very large telescope and a strong radio signal.
     
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  17. May 4, 2010 #16

    D H

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    You need to calm down, GreatBigBore. You have made value judgments by repeatedly asking what went wrong. I took umbrage at this. This is what I do for a living, and have done for a living for almost 32 years (30 days shy of 32 years).

    Why don't you start again and simply ask "Why did it take us 40 years to find the Lunokhod 1 retroreflector?"
     
  18. May 6, 2010 #17

    D H

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    We are not asking those of you who don't "know more or less EVERYTHING" to not ask questions about space. The problem with this thread was the continued insistence that something "went wrong."

    If you ask the question without making a value judgment you are likely to get a reasoned answer. To reiterate what was said in post #16, why don't you start again and simply ask "Why did it take us 40 years to find the Lunokhod 1 retroreflector?"
     
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