If Curiosity had lights, could it drive or work in the evening?

Space Exploration Asked on January 2, 2022

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.

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3 Answers

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'.

Answered by Hobbes on January 2, 2022

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.

Answered by PearsonArtPhoto on January 2, 2022

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."

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?

Answered by Muze on January 2, 2022

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