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95 votes
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Why A=2 and B=1 in the call signs for Spirit and Opportunity?

On MER we numbered the builds, but used letters for the launches. So MER-1 was built before MER-2. MER-A would both launch and arrive first, and MER-B would launch and arrive second. When we started, ...
Mark Adler's user avatar
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46 votes
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What was the last message to Opportunity today (13 Feb '19)?

From ArsTechnica: Late Tuesday night, scientists at NASA's Jet Propulsion Laboratory sent their final data uplink to the Opportunity rover on Mars. Over this connection, via the Deep Space Network, ...
Ingolifs's user avatar
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24 votes
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Why did Spirit (MER-A) lose a wheel?

No explanation has been established for the wheel failure, although a motor brush failure is one possibility. Source: Mars Exploration Rover Spirit End of Mission Report
Organic Marble's user avatar
23 votes
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Why do the more recent landers across Mars and Moon not use the cushion approach?

Propulsive landing is now a proven technology and a factor of 1,000 more accurate. According to NASA Facts; Mars Exploration Rover: With the heat-shield portion of the aeroshell pointed forward, the ...
uhoh's user avatar
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20 votes
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How did the Mars Exploration Rovers (Spirit & Opportunity) land upright?

It turns out that there was. In this video produced for JPL (which I must have watched a thousand times as an excited kid), it is shown whichever of the three possible "not-bottom" sides/petals of ...
Anton Hengst's user avatar
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16 votes

Why do the more recent landers across Mars and Moon not use the cushion approach?

The 2007 paper The challenges of landing on Mars gives a decent introduction to the subject, and the evolution of Mars landing methods. First generation: Viking. Propulsive landing, lander on legs. ...
Hobbes's user avatar
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12 votes
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What modifications would be necessary to make to a Mars rover to let it land on Phobos or Deimos?

The very low gravity would require a total redesign. Phobos is the larger body and has a surface gravity of around 0.6 milli-g, or around 1500 times less than here on Earth. The newest rover, ...
John McCarthy's user avatar
12 votes
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Opportunity's last tau was 10.8; what does that mean and how is tau defined and measured?

Vacuum would have a $\tau$ of zero. An opacity of $\tau$ means that the atmosphere is reducing the direct intensity of light from the Sun, if it were directly overhead, by a factor of $e^{-\tau}$. It ...
Mark Adler's user avatar
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12 votes
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What was the driving record of each rover on Mars in one sol, and when?

I have an answer for only the MERs and MSL. I have no idea how to find this information for Sojourner. For Curiosity: 144.04m on Sol 385 (source). I processed that data in excel, but I don't know ...
Michael Stachowsky's user avatar
8 votes

What modifications would be necessary to make to a Mars rover to let it land on Phobos or Deimos?

A partial list of subsystems that would need to be redesigned: Since the gravity is low, there's a high chance that you will flip over at some point. You will need to ensure that you can flip back, ...
Florent's user avatar
  • 81
8 votes

What was the driving record of each rover on Mars in one sol, and when?

New Martian records for the Perseverance rover ! On sol 340 (Feb. 2, 2022) the rover drove 237.78 m, but the following day the driving distance was even 240.73 m. (according to the Perseverance ...
Cornelis's user avatar
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8 votes

Why a rover bounces after landing on Mars?

You're talking about the Mars Exploration Rovers. They landed using airbags. To do what you suggest, they'd have to vent the airbags with great precision at the moment it hits the ground. If the ...
Hobbes's user avatar
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6 votes
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Have the rovers on Mars encountered anything unrecognizable to geologists?

Have the rovers on Mars encountered anything unrecognizable to geologists? Yes, sort-of: These are similar to structures on Earth that are produced by life, so they have people scratching their heads!...
uhoh's user avatar
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6 votes

Why was a nuclear battery system not used for the Mars Spirit and Opportunity rovers?

Mars Spirit and Opportunity rovers exceeded expectations by working for many years than the planned 90 day mission. Ninety days was not the planned mission. It was instead the bare minimum amount of ...
David Hammen's user avatar
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5 votes
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Why was a nuclear battery system not used for the Mars Spirit and Opportunity rovers?

Spacecraft design is based on conservative, pessimistic estimates, "stuff that's proven to work". When those estimates are (usually) exceeded, the next generation "faster horse" ...
SE - stop firing the good guys's user avatar
5 votes
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Why hasn’t SpaceX sent anything to Mars yet?

Missions to Mars are infrequent, take a lot of time between concept development and launch (several years to well over a decade), and cost a lot. A whole lot. The launch cost is a small fraction of ...
David Hammen's user avatar
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4 votes

Rover wheel placement

Why the wheels are placed where they are is probably due to combination of factors, such as weight distribution, foldability, loading forces, etc. But for the turning it doesn't matter, as the outer ...
Ludo's user avatar
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4 votes

"Why don't they use the little helicopter to fly just above the rover's solar panels and blow the dust off?"

The Mars 2020 rover, Perseverance, does not use solar panels for power. It uses a radiothermal generator to generate its power. As a result, there are no solar panels on the rover to clean. The only ...
notovny's user avatar
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3 votes
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Which Mars probe went to the highest elevation and which one to the lowest on Mars so far?

I combed through Wikipedia's list of Mars missions and found all of the successful landers/rovers and included the Chinese Tianwen-1 though it has not landed successfully as of this answer. I got the ...
BrendanLuke15's user avatar
3 votes
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How many spacecraft bounced like a ball on Mars? How many tried to?

The Mars Pathfinder mission, which landed on Mars in 1997, used inflatable bags. The bags were inflated when Pathfinder was 355 m above the ground. Once the lander was 355 m above the ground, airbags ...
Fred's user avatar
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2 votes
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Do we use masers, lasers or infrared lasers to send data from deep space back to Earth? If not, why not?

"Why don't current missions already use small masers..." So we have already been using conventional traveling wave tube amplifiers for microwave communications in space. Ka band is around 30 ...
uhoh's user avatar
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2 votes
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Acoustics in Space

Not yet, but Mars 2020 will. Scott Manley did a video on the subject, starting somewhere around here. Basically Mars 2020 will fire lasers at something, listening to ...
PearsonArtPhoto's user avatar
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2 votes

Why a rover bounces after landing on Mars?

Firstly, the bumping appears more dramatic because of the lower gravity. An object bumping on Mars will go 2.6 times higher on Mars than something with the same velocity on Earth. Secondly, the ...
SE - stop firing the good guys's user avatar
1 vote

Rover wheel placement

Each of Curiosity's wheels have a drive motor, but only the four outer wheels are steerable. The suspension system is based on rocker-bogie system on the Pathfinder rover. The term "rocker" ...
Fred's user avatar
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