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Comment by Toenex | Hacker News Reader

I was always a little dubious of the 90 day mission length. It sounded like NASA were just giving themselves a "yeah we meant that to happen" get out if things went bad.

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You need to keep in mind that the rovers also needed to survive the six months in transit in once piece, and the airbag-assisted landing in one piece, both of which add necessary reliability and durability factors to make sure that the thing lasts even the 90 days. Also, you need to keep in mind that those cleaning events came out of left field. Yeah, they were expecting to maybe get a few extra weeks out of the rovers, but because the wind behaved in a manner that was completely unexpected, the panels weren't as dust-caked as was expected, which had always been the real limiting factor.

  > the panels weren't as dust-caked as was expected

Common, this is such a lousy excuse. If dust was a big problem I'm pretty sure they would have designed a dust-cleaning device.

Such as what, exactly? I'm sure it was considered, but it's not that simple. Would it involve air blasts? Liquid? A squeegee? The sand/dust content wasn't exactly known so a scraping motion would potentially scratch the glass surface and make things worse. Compressed air would take a tremendous amount of energy to compress and a liquid is heavy.

It was considered. Weight is a huge factor, and when the features were triaged it was dropped.

Or maybe they overspent and built something too good. They could have had a much smaller budget if they really wanted a 90 day mission.

Keep in mind that the lifetime of this mission is actually pushing other missions out of scope. The budget needed to continue support of Opportunity could be dollars spent elsewhere. So, overspending doesn't make sense. They're roughy, $128 million (combined for both rovers) over their operating budget [0].

[0] http://en.wikipedia.org/wiki/Mars_Exploration_Rover

It was $820M to send the rovers to Mars, and $128M to extend that by 10+ years; the main cost was in getting them there intact. Yes this money displaces spending on other missions, and there are diminishing returns for applying the same tools to the same small part of Mars, but mostly these years have just been bonus.

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