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mars rovers life expectancy
I read an article that said the life expectancy of the mars rovers was 90
days. Isn't it too short for $800 million machine? What limits it to 90 days? |
#2
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mars rovers life expectancy
pesso wrote:
I read an article that said the life expectancy of the mars rovers was 90 days. Isn't it too short for $800 million machine? What limits it to 90 days? Considering what they've found already, I'd say we got a very good deal indeed by any standards. The cost of the whole program was only about one third more than a Shuttle flight, and individual Shuttle flights tend to do far less of interest than what the rovers are doing. The three limiting factors on the mission duration a 1.) The need to get adequate solar power to operate; the Martian winter is coming on, and the sun angle is getting lower in the sky, so that the rover's top-mounted solar arrays aren't generating as much electricity as they were when they first landed. There is probably some small loss of solar panel efficiency due to their exposure to solar wind related radiation on the surface, which slowly but surely degrades solar cells. 2.) Dust build-up on the top of the solar arrays causing less sunlight to reach them and generate electric power. 3.) The thermal stress on the rover's electronics caused by the day/night temperature swings, which will eventually cause the wiring connections to begin to fail. All that having been said though, NASA is hoping that the rovers operating life goes beyond the 90 days- maybe by quite a bit- the planned missions for the Voyager spacecraft were for them to get to Jupiter and Saturn; the missions would be considered successful if those two planets were reached. But both kept right on working, so Voyager 2 was able to reach Uranus and Neptune as a bonus mission, as NASA had hoped. Pat |
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mars rovers life expectancy
In article ,
says... snip What's making a really significant difference is that, as Mars heads into southern summer and northern winter, it's also moving away from periapsis and towards apoapsis. Ooops! I meant northern summer and southern winter. At the current time, the southern hemisphere is what gets the shorter, warmer summers due to their coincidence with periapsis. Doug |
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mars rovers life expectancy
Doug... wrote:
Just one minor nit, Pat. The seasonal change is, indeed, responsible for a lowering in the amount of sunlight getting to the solar cells, but it doesn't have a lot to do with how high the sun gets in the sky. The height of the sun at zenith isn't changing a whole lot yet -- remember, both rovers are located near the equator. What's making a really significant difference is that, as Mars heads into southern summer and northern winter, it's also moving away from periapsis and towards apoapsis. Since Mars' orbital eccentricity is currently *much* greater than Earth's, that means that the change in the solar energy reaching the ground on Mars between periapsis and apoapsis is *far* greater. Works fine as to total hours of sunlight per season, but not as fine as regards the Sun in position in the sky for any rover that has solar arrays facing straight up toward the zenith of the heavens; only at the periods balanced between the two seasons of the two Martian hemispheres does the light fall upon the solar arrays at a near perpendicular angle. Equinoxes good. Movement toward the solstices bad. Pat |
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mars rovers life expectancy
Doug... wrote:
Ooops! I meant northern summer and southern winter. At the current time, the southern hemisphere is what gets the shorter, warmer summers due to their coincidence with periapsis. Both rovers are effectively at the Martian equator- "Summer" and "Winter" to them are but a matter of details and a few hundred miles of latitude. pat |
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mars rovers life expectancy
Doug... wrote:
What's making a really significant difference is that... it's also moving away from periapsis and towards apoapsis. Since Mars' orbital eccentricity is currently *much* greater than Earth's, that means that the change in the solar energy reaching the ground on Mars between periapsis and apoapsis is *far* greater. Doug, With 1.52 semimajor axis and .093 eccentricity, I'm getting 1.37 AU perihelion and 1.66 AU apohelion. 1.37/1.66 = .83 ..83^2 = .69 I believe you are correct that Mars' greater eccentricity makes a substantial difference between periapsis and apoapsis insolation. -- Hop David http://clowder.net/hop/index.html |
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mars rovers life expectancy
In article ,
says... Doug... wrote: What's making a really significant difference is that... it's also moving away from periapsis and towards apoapsis. Since Mars' orbital eccentricity is currently *much* greater than Earth's, that means that the change in the solar energy reaching the ground on Mars between periapsis and apoapsis is *far* greater. Doug, With 1.52 semimajor axis and .093 eccentricity, I'm getting 1.37 AU perihelion and 1.66 AU apohelion. 1.37/1.66 = .83 .83^2 = .69 I believe you are correct that Mars' greater eccentricity makes a substantial difference between periapsis and apoapsis insolation. According to a very well-done book I've been poring over, "Mars, The Mystery Unfolds" by Peter Cattermole, the difference between perihelion and apohelion insolation is on the order of 40%. That's QUITE a difference. Doug |
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mars rovers life expectancy
Doug... wrote:
In article , says... Doug... wrote: What's making a really significant difference is that... it's also moving away from periapsis and towards apoapsis. Since Mars' orbital eccentricity is currently *much* greater than Earth's, that means that the change in the solar energy reaching the ground on Mars between periapsis and apoapsis is *far* greater. Doug, With 1.52 semimajor axis and .093 eccentricity, I'm getting 1.37 AU perihelion and 1.66 AU apohelion. 1.37/1.66 = .83 .83^2 = .69 I believe you are correct that Mars' greater eccentricity makes a substantial difference between periapsis and apoapsis insolation. According to a very well-done book I've been poring over, "Mars, The Mystery Unfolds" by Peter Cattermole, the difference between perihelion and apohelion insolation is on the order of 40%. That's QUITE a difference. Doug 1/.69 is about 1.45 so my figures can land in the same ball park. The percentage varies depending on whether you're considering (apohelion insolation/perihelion insolation) or (perihelion insolation/apohelion insolation) Hop David http://clowder.net/hop/index.html |
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