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So we've had a question asking why Perseverance had a camera to record the landing and one asking if Curiosity did, but I can't find any information about why Curiosity did not have a camera on board to record the landing. You'd think that the scientists and engineers would want to record it so that they'd have more information about how the landing went.

According to the NASA page on Perseverance's cameras,

When the Curiosity rover landed on Mars, it recorded the descent and landing with its Mars Descent Imager or "MARDI" camera. The view was extremely valuable to engineers; it helped them understand what happens during one of the riskiest parts of the mission.

They recognize the usefulness of MARDI, so why not have one looking at the sky crane as well?

These new eyes and ears of Perseverance are assembled from easily available commercial hardware. The cameras and microphone are being flown as a "discretionary payload," which means it's an optional add-on that will be an asset, but is not required for the mission.

I guess it adds to the weight and was not considered mission critical, but since Perseverance was able to find the room and be larger than Curiosity, I think they should have been able to fit them on.

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I think it's important to understand the timeline here. The footage we've all been amazed by was acquired by a collection of slightly-hardened small, light, high-quality commercial off-the-shelf (COTS) cameras, helped by a fast, very-low-power processor (I think a Qualcomm SnapDragon: this processor is much faster than Perseverance's main processors!) and cheap, copious, flash memory. The two guiding principles for the system were (from memory: they mention this in the press conference) 'do no harm' and 'it can't matter if it does not work'.

I don't know when the final decision to add this to Perseverance was made, but I will assume 2017 (three years before launch in 2020). Well, I have an iPhone 8, which came out in 2017. It has a camera module which would be pretty suitable for this, and its processor similarly would be more than competent. It probably doesn't have enough memory (32GB) but that's because I didn't need more: clearly it could have.

But probably they were doing component selection well before that: say 2015: so the right device to look at might be the iPhone 6s. This would also be pretty adequate I think.

Testing of components for Curiosity began in late 2004, and design was largely complete by November 2008 (Wikipedia), which I will take as the drop-dead date for anything like this: also three years before launch. If we assume that component selection was made two years before that again, we're now in 2006.

In 2004 the first GoPro was released: it used 35mm film. In 2006 the first digital GoPro was released, which could record for 10 seconds.

The first iPhone came out in 2007 It had a 2MP camera (could it do video? probably it could). There were 'smart' phones before that but probably the smartphone era really dates from this: a year after they probably had to make the component choice for Curiosity. In 2006 I think I had a Motorola Razr, which was a nice-looking phone. I think it has a ~1MP camera, and it could probably do rudimentary video. I have some pictures from it, which are terrible.

And in fact Curiosity did record the landing: MARDI could shoot 4 frames a second, and recorded the entire landing. I don't know if this captured video was compressed before upload: I would suspect not however, as it would have been very demanding for the computational resources of Curiosity (MARDI has 8GB of flash). MARDI is very definitely not a COTS system, and represents what was possible in the mid 2000s when things were being finalised for Curiosity.

For Curiosity to have recorded multiple video streams as Perseverance did would have required multiple, probably large, non-COTS cameras and computational resources which would probably have completely swamped the available power on the rover. This would have seriously impacted on the mission: it would have hugely violated the 'do no harm' rule.

So this is why. The amazing video we have seen from Perseverance exists because smartphones exist: that technology simply did not exist in 2006. Although it is hard to remember (especially if you are not old enough to remember), the technology that is now cheap and which we all take for granted was once extremely expensive, and before that did not exist at all.

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  • $\begingroup$ This is a plausible explanation, but do you have a source that it was the (or a major) deciding factor? $\endgroup$
    – Phiteros
    Mar 3, 2021 at 9:35
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    $\begingroup$ @Phiteros: I think a line of reasoning from 'the technology to do this did not exist' to 'it was not done' is safe. $\endgroup$
    – user21103
    Mar 3, 2021 at 10:47
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    $\begingroup$ This answers hits the gist of it: people seriously underestimate just how much digital photography and especially video making has leaped forwards in the last 15-20 years. When I compare the first digital camera I got a a teenager, before smartphones existed, with current smartphones, its mind-blowing. I mean, memory card sizes were measured in single digit and low double digit megabytes. $\endgroup$
    – Polygnome
    Mar 3, 2021 at 11:30
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    $\begingroup$ @DarrelHoffman: yes, that's what I meant by 'didn't exist': obviously good digital video cameras existed, but they didn't exist within the power/mass/size budget. $\endgroup$
    – user21103
    Mar 3, 2021 at 14:37
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    $\begingroup$ You've added a lot of detail here that I think is really good. This is a good answer to the question, but I'm going to leave it open for a little bit to see if anyone else has a more primary source. I recognize it's unlikely, but I want to allow for the opportunity. $\endgroup$
    – Phiteros
    Mar 3, 2021 at 22:15
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I guess it adds to the weight and was not considered mission critical,

Short: You answered the question on your own.

Long: You answered the question on your own. Remember KISS! Keep It Simple and Stupid!

PS:

I think they should have been able to fit them on.

"Be able to do something" is not equal with "It is reasonable to do something"

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    $\begingroup$ I understand those principles, but I am more interested in finding out if there is a reason that, given the engineering benefits, it was decided not to add this small complication. This answer is pretty much opinionated, and I'm looking for something with a source. $\endgroup$
    – Phiteros
    Mar 3, 2021 at 7:02
  • $\begingroup$ The problem will be: there will be plenty of sources, why something has been done. But you won't find anything, why something has not been done... $\endgroup$
    – CallMeTom
    Mar 3, 2021 at 7:20
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    $\begingroup$ That's not necessarily true. There are probably records of how they discussed it, but then decided against it. Or someone with an insider's knowledge on the situation can expound more on the exact details as to why it was left off. Sure, such information may be hard to come by. I certainly didn't find any in my search. But that's not to say it does not exist. There are many questions which end up unanswered on here. $\endgroup$
    – Phiteros
    Mar 3, 2021 at 7:28
  • $\begingroup$ For example, consider this question. It's impossible to answer with a no, because you wouldn't be able to prove it. But there is the possibility that someone could answer with a yes and provide an example. $\endgroup$
    – Phiteros
    Mar 3, 2021 at 7:29
  • $\begingroup$ @Phiteros It's possible to answer "no" so far as nothing being recorded about such an incident (I've not checked, I'm simply stating a scenario where a no answer could be given). $\endgroup$
    – ProgrammingLlama
    Mar 4, 2021 at 6:39

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