The first Mars rover, Sojourner, traveled alone, but since that first landing in 1997, the vehicles sent to the red planet by NASA have all had twins. In 2004, the Spirit and Opportunity rovers went together, launched a month apart on June 10 and July 7, 2003. Spirit landed within the Gusev crater on January 4, 2004, and Opportunity arrived three weeks later. Spirit was operational for six years and Opportunity 14 years. They were the last Lewis-and-Clark type pairing, as the next two expeditions had remote twins that remained on Earth.

In 2012, the third mission, Curiosity, landed, and it’s still sending images to the NASA website, the most recent dated March 7, 2021. On that day, Curiosity had been on Mars 3,052 sols (longer than an Earth day, at 24 hours and 39 minutes), and its twin now shares a bay at NASA’s Jet Propulsion Lab (JPL) in California with Perseverance’s twin. Curiosity’s twin is called MAGGIE (Mars Automated Giant Gizmo for Integrated Engineering), and the Perseverance twin is called OPTIMISM, named after the motto of the team that built it: “No optimism allowed.”

For an idea of how complex and capable the missions have become, you need only look up the most basic specs. The first explorer, Sojourner, weighed 25 pounds, and Perseverance is 2,260 pounds.

Perseverance and its twin OPTIMISM are identical except for a couple differences. As OPTIMISM maneuvers around the simulated Mars landscape called Mars Park at JPL, it trails a sheath of cables that supply electrical power and an ethernet connection over which commands are sent to and received by its distant twin. Power on Perseverance is generated by a nuclear battery that drives a multi-mission radioisotope thermoelectric generator. Also, Perseverance has an on-board heating system while OPTIMISM uses a cooling system to keep it running in Southern California temperatures.

Perseverance’s Twin OPTIMISM at the Jet Propulsion Lab Mars Park. Image courtesy NASA


The industry group known as the Digital Twin Consortium defines an industrial digital twin as “an abstraction of something in the real world. It may be physical (a device, product, system or other asset) or conceptual (a service, process or notion). A digital twin captures the behavior and attributes of its physical sibling with data and life cycle changes.” The reason for this expensive duplication can be to provide simulation “as a kind of prototype to understand real-world behavior,” or, in the case of Perseverance, extraterrestrial behavior.

The engineers at NASA’s JPL understood the value of having two rovers for each mission as early as Spirit and Opportunity in 2004. They explained their specific reasons for Perseverance’s OPTIMISM. “Perseverance isn’t flying to Mars with a mechanic. To avoid as many unexpected issues as possible after the rover lands on Feb. 18, 2021, the team needs this Earth-bound VSTB (Vehicle System Test Bed) rover to gauge how hardware and software will perform before they transmit commands up to Perseverance on Mars. This rover model will be particularly useful for completing a full set of software tests so the team can send up patches while Perseverance is en route to Mars or after it has landed.”

One of the first images from Mars from Perseverance. Image courtesy of NASA


NASA lists four basic scientific objectives for Perseverance.

  1. Looking for habitability: Within a crater that might have been a previous reservoir of water the size of Lake Tahoe, the rover will attempt to identify past Martian environments that were capable of supporting microbial life.
  2. Seeking biosignatures: The rover will attempt to find signs of possible past microbial life, particularly in specific rock types known to preserve signs of life over time.
  3. Saving samples for later missions: Perseverance will collect rock core samples, seal them in containers, and then deposit these in areas that future missions can find and send back to Earth for analysis.
  4. Preparing for humans: There’s a machine on board Perseverance that can produce oxygen from the Martian atmosphere, something that will be essential if colonization is ever to be possible. The machine will be tested over time for its efficiency on the planet.


The one-ton Perseverance rover has quite an assortment of technology aboard, and the planners hope for years of useful service. Included in the array are the following:

Ground navigation systems with optical sensors feed data to a machine learning algorithm that allows self-navigation. This will enable the rover to cover far more ground than Curiosity, which constantly must seek assistance while moving around.

Other visual systems include a SuperCam laser micro-imager, Mastcam-Z panoramic cameras, and an X-ray imager called Pixel that scans the texture of the ground’s surface. The RIMFAX subsurface radar in the rear of the vehicle can penetrate to 10 meters and will be looking for geographic structures and water. And for the first time, two microphones will be aboard the rover to record the sounds of the planet. In all, there are 25 cameras on the rover and the lander assembly.

The Mars Environmental Dynamics Analyzer, orMEDA, weather station is mounted on the mast.

The power source is a thermoelectric generator that uses the heat from radioactive decay to generate electricity. The initial 110W at launch will gradually degrade with the generator losing half of its energy in 87 years.

The Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, oxygen-generating device will be testing a new system for creating oxygen for future travelers to the planet. It uses solid oxide electrolysis to convert the carbon dioxide in the Martian atmosphere into oxygen and carbon monoxide.

Acore-sampling drill will collect and save soil in something called the Sample Analysis at Mars instrument, or the SAM, which contains a mass spectrometer, a gas chromatograph, and tunable laser spectrometer. Another sample caching drill carves and extracts core cylinders of rock. Part of the system extracts the core from the bit and takes several images of the sample, calculating the volume of the sample, and then puts it in a tube. These tubes will be stored at various locations, and in 2026, a follow-up mission will collect them and send them back to Earth for more detailed analysis.

The Ingenuity helicopter, a drone with two reverse-rotating blades and a solar panel, is aboard to study the thin atmosphere of Mars.


The connections have been established, and now a second two-party conversation has begun between Perseverance and OPTIMISM. And like the calls continuing between Curiosity and MAGGIE, there’s a delay with responses taking between four and 24 minutes, but that isn’t bad latency really for 39 million miles.

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