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If the Mars rover Curiosity had been equipped with lights, would it be able to drive or do other work in the evening? This could be some combination of LED headlights, wheel-lights, and/or a spotlight on the movable robotic arm,

Since the chances of a deer crossing in front of the rover are pretty remote, and in general the rocks stay put (although there are notable exceptions! see below) they'd only have to flash maybe once per second or even less most of the time. Most efficient LED lights are pulse width modulated anyway, and LED flash units for cameras exist, so this would not necessarily represent a large power drain.

There are two sources of heat already available on board Curiosity to potentially keep things within operational temperatures - the circulating fluids warmed indirectly by thermal infrared radiation from the MMRTG, and electrical heaters powered by the MMRTG electrical output directly. And of course the presence of the MMRTG means that Curiosity (unlike previous Mars rover designs) does not rely on daylight for electrical power. Although I don't know if these are sufficient to enable evening operations. I'm thinking there is residual warmth in the spacecraft and Martian surface in the evening (as opposed to the morning)

I'm not suggesting that this is a good idea for the Curiosity mission, this would add complexity, weight, and risk with marginal benefits. However it seems to me this could be done, though there may be factors I haven't considered. There will be future rover missions on Mars and other bodies, so I am asking about a Curiosity-with-lights as a reference point.

below: Things do occasionally move on Mars. From Tall boulder rolls down martian hill, lands upright, "The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter recorded this view on July 3, 2014." Click for larger view.

enter image description here

uhoh
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    They'd need to reprogram the vision system so it can translate between daytime and nighttime views: the same terrain would look quite different. – Hobbes Sep 14 '16 at 07:58
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    @Hobbes that's a really good point. I may have been only thinking a few, maybe at most 10 meters ahead, where enough day-lit imagery was still available to mostly understand the upcoming terrain, and the night illumination was mostly for avoidance of things already known to be out there. Long distance night navigation suddenly sounds really difficult with Curiosity's existing imaging systems. – uhoh Sep 14 '16 at 08:39
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    So, is this question about whether Curiosity could do this, or about whether the concept would be viable in a future Mars rover design? – user Sep 14 '16 at 21:07
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    @MichaelKjörling I've adjusted the wording to focus specifically on the Curiosity rover with only the addition of strategically placed LED lights. A question about the best technology for a rover designed to operate without sunlight would be a logical next question, and if nobody else asks it first and it hasn't been asked already, I might ask it. – uhoh Sep 15 '16 at 00:56
  • @Hobbes A "headlight" on the movable robotic arm would at least allow comparison of upcoming terrain illuminated from slightly different angles. That is at least a little bit like sunlit images taken at different times of the day for shadow analysis but certainly not the same. – uhoh Sep 15 '16 at 01:32
  • Easier to have multiple lights, cycle through them, and perform analysis on the shadows. – Innovine Sep 15 '16 at 05:00
  • @Innovine Arm allows you to both place and point a light in a far wider range of configurations (both vertically and horizontally) than a set of static chassis-mounted lights. You'd only use it when necessary, perhaps to resolve an ambiguous terrain feature, or to illuminate a work area. "...some combination of LED headlights, wheel-lights, and/or a spotlight on the movable robotic arm" – uhoh Sep 15 '16 at 05:08
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    It's a lot more energy effective to install additional bulbs though, and if you're waving the arm around all the time it's additional wear on the motors. Led lights don't weigh or cost much, so placingethem in different locations is reasonable, cheap and unlikely to impact rover operations in any way. Credit to you for the idea of shadow analysis though – Innovine Sep 15 '16 at 05:13
  • @Innovine again, "You'd only use it when necessary perhaps to resolve an ambiguous terrain feature, or to illuminate a work area." You need to add in the mass of the copper wire necessary to power each light, and the additional logic and solid state relays necessary to turn each one on and off. – uhoh Sep 15 '16 at 05:22
  • If you are going to drive at night it'll be very necessary. Whatever. – Innovine Sep 15 '16 at 05:40
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    One point to consider - comms. Because Mars orbits futher out, then (generally speaking) Earth is in the sky during the day, but not at night, or at least not for very long. Depending on quite how comms are handled, this could limit the usefulness of non-daylight operations. – Andrew is gone Sep 15 '16 at 08:06
  • @Andrew I was under the impression that these days Curiosity executes a significant amount of autonomous motion not necessarily requiring comms. Am I wrong? Ok maybe answer here instead! – uhoh Sep 15 '16 at 08:25
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    @Hobbes Curiosity has taken images at sunset and sunrise, and I think night time too, of Phobos and Earth. Imaging the same terrain day and night could be helpful for future autonomous 25 hours a day rovers with much more than Curiosity's poor 1/6 of a horsepower electric effect. – LocalFluff Sep 15 '16 at 11:01
  • That would have entailed larger batteries among other things if your lights are going to last very long, there's payload considerations involved in this for the original launch costs, the decision not to include night lights may have been as simple as that. – Pelinore Apr 07 '18 at 13:53
  • @Pelinore as I already mentioned in the 2nd paragraph of the question, LED lights can be "on" for milliseconds at a time, and only "flash" when the cameras are required to record a image. It would not be the way people use flashlights or headlights. – uhoh Apr 07 '18 at 15:11
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    I don't have time for an answer right now, but this paper addresses some of the navigational issues: http://digital.library.ryerson.ca/islandora/object/RULA%3A4596/datastream/OBJ/download/Star_tracker_and_lidar_based_night-time_planetary_navigation.pdf – called2voyage Apr 10 '18 at 19:18
  • Don't humans pilot it? Would another limitation be staffing? – Magic Octopus Urn Jun 15 '18 at 10:55
  • @MagicOctopusUrn not even close. For a start see How much can the Mars rover Curiosity do autonomously, after four years of operation? but you'll have to do more reading to understand how it's operated. – uhoh Jun 15 '18 at 12:36
  • One major problem I see is that the rover isnt able to send or receive signals from earth during the night period – Lonely Fox Aug 08 '20 at 23:45
  • @LonelyFox I'm not sure that's true for two reasons: 1) I asked "...could it drive or work in the evening?" rather than in the middle of the night for thermal reasons, it may be too cold to for some things to operate at 2 AM local time, but for a short time after sunset all parts may still be warm enough. It's core is warmed by circulating fluid from its RTG so the computer will be okay. 2) The rover generally drives and samples on its own without constant control. It stores data and images and sends them to Earth periodically, so there's no need to send or receive signals during these times – uhoh Aug 09 '20 at 01:04
  • @LonelyFox see for example How much can the Mars rover Curiosity do autonomously, after four years of operation? and possibly Are NASA (and ESA?) deep space spacecraft now generally able to store and forward messages between themselves? – uhoh Aug 09 '20 at 01:09
  • @LonelyFox Curiosity generally either waits for a favorable satellite pass to sent its stored data and images to Earth, or occasionally when there are scheduled opportunities, sends directly to Earth: Has the Curiosity rover ever communicated directly with Earth via its high-gain antenna? Signal strength & data rate? – uhoh Aug 09 '20 at 01:09
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    @uhoh 1) my brain did not register the “evening” part thank you for the clarification 2) I did not know the rover mostly used satellites for its data transfer. I thought it always used its high gain gain for that. Thank you for correcting that. – Lonely Fox Aug 09 '20 at 01:11
  • @LonelyFox Welcome to Space! I'm in awe of this mission and Stack Exchange is a great place to share information about it. :-) – uhoh Aug 09 '20 at 01:39

3 Answers3

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TLDR: The rover is power limited not daylight limited

Lights are not sufficient to enable nighttime driving.

  1. The rover is limited by available power. The RTG produced ~114 W at the start of the mission, dropping to 54 W by 2025. It requires 45-70 W during sleep, at least 150 W when awake and 500 W during driving.
    This means the rover can only drive for a few hours a day. Then it has to stop, sleep and recharge its batteries. On most days, the rover is active for 6 hours, with up to 3 hours spent driving.

  2. The rover drive and steering motors have to be heated up to above -55 ºC before driving. At night, when the ambient temperature is lowest, this can take 2 hours or more, plus a lot of electrical power, which reduces the power budget for the rest of the day. The RTG cannot heat the motors directly: the Freon loop that conducts heat from the RTG does not extend to the drive motors. If possible, driving is scheduled for the warmest part of the day (early afternoon) to minimize the amount of electrical heating, but for planning purposes it's advantageous to start driving earlier (often around 11.00) to have more time for post-driving activities.

While driving at night might be technically possible if you have lights, you'd be spending more energy to cover the same distance, compromising science operations by reducing their power budget.

Source for 1 and 2: Emily Lakdawalla's excellent 'The design and engineering of Curiosity'.

johnDanger
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Hobbes
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    This is an excellent answer, thank you for working this through so thoroughly! – uhoh Jun 15 '18 at 12:51
  • The optimization level they achieved, considering the low power provided by the RTG, is absolutely incredible. I mean, with 100 watt they move a vehicle, runs a computer and several scientific tools.The rover uses a 200 MHz BAE RAD75 processor, with 256 MB RAM, a 2 GB Flash, and it runs VxWorks operating system. – noun Oct 24 '19 at 15:55
  • "dropping to 54 W by 2025." The half-life of Plutonium 238 is 87.7 years, so after so many years the power should be 57 W. If every 10 years the power would drop by 10 %, the half-life would be less than 87.7 years, so it would be safe to say that within 20 years the power would drop to no more than 80% of the starting 114 W ! – Cornelis May 01 '20 at 15:01
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    @Cornelisinspace in addition to Pu decay, the thermocouples degrade, so power is always less than Pu decay alone suggests. – Hobbes May 01 '20 at 15:35
  • Does offer provide any electrical power budget information that might help address At what incline would curiosity require twice the electrical power to drive compared to a flat grade?? – uhoh Jul 25 '20 at 04:27
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The Curiosity's radioisotope thermoelectric generator output is limited for the heating elements. "The MMRTG produces less power over time as its plutonium fuel decays: at its minimum lifetime of 14 years when electrical power output is down to 100 watts." https://en.wikipedia.org/wiki/Curiosity_(rover)

The RTG continuously charges 2 batteries. When the batteries are depleted the Curiosity has to sit while the batteries get charged by the RTG. A balancing act of functions can be performed not to fully deplete the batteries called float mode. The batteries serve as a medium between the RTG and the electronics.

The Curiosity's 2 batteries( used for higher electrical demands) will be stressed more by adding any lights and the extra ("electrical heaters strategically placed on key components" to operate [wiki]) will require more electricity.

(The temperatures at the landing site can vary from −127 to 40 °C (−197 to 104 °F); therefore, the thermal system will warm the rover for most of the Martian year.Wiki) I could not find where optimal temperature for operation, but it would be safe to presume from current electric machinery after freezing temperatures the efficiency drops dramatically.

After so many degrees below freezing oils and lubricants tend to gel up making for mechanical resistance in the parts. Extreme cold is bad for any vehicle.

The RTG is directly connected to the heating elements to run at night would requires more heating elements to warm more parts equaling more drain on the Curiosity current batteries shortening the operational life in the short and long run. Lights are not the problem its just far more efficient to run in the day using less electricity for heating.

Most lithium-Ion batteries have a limited number of times it can charged from a depleted state of about 3000 times or 3000 days, but if kept in float mode above freezing they could last much longer. Also charging at night while it is cold is better for batteries.

It could have been build to bigger, heavier, and more high tech to see at night but what is at night that you can't see in the day?

Muze
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  • "100 watts per hour" is a rate of power generation change. Demand on an RTG would be measured in watts, but the rate at which RTGs produce power is entirely controlled by their construction afaik. Do you have a source for the limitation claim? – Erin Anne Apr 09 '18 at 01:27
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    @ErinAnne He probably meant 100 watt-hours per hour ;) – 0xDBFB7 Apr 09 '18 at 03:01
  • Some cursory Googling indicates the 100W rating is EOL power generation for the RTG...that whole paragraph just smells off to me. – Erin Anne Apr 09 '18 at 05:11
  • At the start of the mission, the RTG produced ~114W (with small daily variations due to ambient temperature. – Hobbes Jun 15 '18 at 10:25
  • @Hobbes I got that but could be adjusted down and was said 100 watts was ideal even it could do 114. thanks for the vote – Muze Jun 15 '18 at 13:16
  • @ErinAnne you are right I didn't see more than the wiki link and had to fill in some blanks. – Muze Jun 15 '18 at 13:19
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Problems with nighttime roving:

  1. Power- Not really an issue with Curiosity, as it is nuclear powered. A portion of this power, however, will be used to manage thermal issues at night.
  2. Ability to see land- This might be the biggest issue. Moving at night will make things much harder to see the terrain of the land, which makes it more likely to make mistakes. Lighting works best if it is off axis. While you can do this to some extent, it would be very difficult to do right, and difficult to test.
  3. Thermal issues- Mars is much colder at night. This increased coldness makes it more likely for things to be more brittle. Moving at night could cause things to break.
  4. Communication- This isn't really an issue, as Curiosity uses relay rovers to communicate. In fact, this is one of the main activities that Curiosity does at night, transmit it's data, so it doesn't have to stop and talk during the valuable day.

Bottom line, it could be done, but it adds a lot of risk. It can be done, but it adds a lot of risk. I'm sure it will happen some day, when a rover to Mars can be had for much less then $2.5 billion, but for now, it is simply too risky to do.

PearsonArtPhoto
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  • Power is of course the primary issue, and as you said not really a problem for Curiosity. Thermal issues are actually secondary, but I find your bullet on it completely uninformative. There is some good free literature out there that could be used to elaborate on that point. Ability to see is definitely a big (tertiary) issue, but it is a solvable problem and there is literature available on it. I find this answer to be lacking. Your conclusion addresses this as if it is a question of "will it be done". It is not. It is a question of "could it be done", and I feel your answer is short of that. – called2voyage Apr 10 '18 at 19:15
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    Curiosity uses a mechanically-pumped circulating fluid (CFC-11) system to bring some of the 2000 W of heat from the RTG into other areas, and so for the most part this does not compete for electrical power. – uhoh Apr 10 '18 at 19:16
  • It looks like you might not have been ready to post this answer yet. I see repeated sentences, and even though you say "...it adds a lot of risk" the only risk you've stated is brittleness. – uhoh Apr 11 '18 at 09:03
  • I see you say: "[...] Curiosity [...] at night, transmit it's data, so it doesn't have to stop and talk during the valuable day.". Why does it have to stop to talk? Not enough power to operate both antenna and other equipment? I think the main benefit of driving at night would be to efficiently use its time. However, if the night is already occupied by "talking" (or other stuff) that it can't do during the day, then this benefit vanishes. – BlueCoder Apr 12 '18 at 10:12
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    The pointing has to be very precise to talk, and as you stated, it takes a considerable amount of power to talk, which stresses the power budget. – PearsonArtPhoto Apr 12 '18 at 10:25
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    I seem to recall that it uses the night to recharge the batteries that complement energy usage during the day. – Diego Sánchez Apr 13 '18 at 15:17
  • I thought this is worth a +1 but already up voted it – Muze Oct 03 '18 at 01:49