This interesting answer to Why did NASA intentionally crash-land the Curiosity and Perseverance sky cranes on Mars? leads me to wonder if the Curiosity and Perseverance rover computers were in charge the whole time, that during the long voyage from Earth to Mars it was their computers that JPL was talking to; they received commands from Earth via some high-gain antenna (and amplifier or radio) on the outside, fired the thrusters to spin up/down, processed star-camera data for attitude control, release the tungsten weights before reentry, pop the cover and shield, etc.

Question: Is this all true? Did the Curiosity and Perseverance rover brains do the driving from Earth to Mars? Or was there a separate flight computer for this work?

From this answer to Where does MSL end and Curiosity begin?:

Curiosity rover and MSL

  • $\begingroup$ Seems possible but frankly it's surprising to me. Sure, maybe it means fewer computers, but why would they burden the rover with programs it no longer needs once on land? Do they just delete those programs once the rover touches down? Seems possible, but out of left field, so I'd want to see references to be sure. $\endgroup$
    – user39728
    Commented Mar 18, 2021 at 3:35
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    $\begingroup$ @user39728 They didn't burden the rovers with software it no longer needs. The JPL has long had the ability to remotely update the fight software on their remote vehicles. After landing, the software that was needed for entry, descent, and landing was replaced with software needed to operate the rover as a rover (which wasn't needed on the rover until the rover became a rover). This switchover was one of the many reasons it took so long between landing and the first rover maneuver. $\endgroup$ Commented Mar 18, 2021 at 4:10
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    $\begingroup$ @DavidHammen First rule of fight software: don't talk about fight software $\endgroup$
    – Strawberry
    Commented Mar 18, 2021 at 13:43
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    $\begingroup$ Thanks @DavidHammen! I'm a little more educated now. As a reward my next comments will be slightly less dense :D $\endgroup$
    – user39728
    Commented Mar 18, 2021 at 15:29
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    $\begingroup$ The rovers have brains? Sounds like an insult to a real brain which is about 10^(10^(10^10))) times more intelligent? Or infinity if you allow division by zero? Otherwise, good question! And interesting answers. $\endgroup$ Commented Mar 19, 2021 at 8:54

2 Answers 2


Yes and no.

The no part first: Mars 2020 had sensors and effectors attached to the non-important parts of your diagram, many of which had various degrees of smarts.

  • Star trackers are very sophisticated cameras. The have their own computers that control mode (e.g., lost in space versus locked) and that perform pattern matching on an self-contained star map. The output of a star tracker is orientation (or attitude). That makes using a star tracker easy as pie for the main flight computer. The star tracker was not attached to the rover. It was ejected at some point during entry, descent, and landing.
  • Mars 2020 had another camera that was on the critical path for landing and was not attached to the rover. Cameras are also sophisticated instruments (but not nearly as sophisticated as a star tracker), and typically have microcontrollers. This lander camera (LCAM) took commands from the Vision Compute Element (VCE) and sent images to the VCE.
  • Modern thrusters take the amount of time they are commanded to be on over a smallish period of time. This means that the thrusters have to have their own microcontrollers and clocks with a time step that is considerably smaller than the time step used by the main computer's guidance, navigation, and control (GN&C) software.
  • One set of equipment that was redundant on the Mars 2020 vehicle was the communications system. The rover has its own communication system, and so did the vehicle as a whole. The rover's communications equipment was enshrouded until the shells were ejected. Modern communications systems also have embedded microcontrollers and precision clocks.
  • Another set of equipment that was redundant on the Mars 2020 vehicle were its Inertial Measurement Units (IMUs). The descent element had a set of IMUs distinct from those on the rover. An IMU is a smart sensor and is critical for navigation. IMUs, like thrusters, operate at fast rates. The non-gravitational accelerations output by an IMU are measurements taken at very fast rates that are accumulated by the IMU to generate the slower rate data to the main flight computer.
  • The VCE mentioned above was a computer system distinct from the main Rover Compute Element (RCE). The VCE had its own flight hardware, firmware, and software. The heart of the VCE was a RAD750, the same kind of computer used by the RCE. However, since the VCE was on the rover, it is fair to say that the rover drove Mars 2020 from entry interface on.
  • Finally, JPL drove the vehicle to Mars. Mars 2020 did not know where it was until shortly before the onset of entry, descent, and landing. While it is impractical to remotely drive a Mars rover on a minute by minute basis, that imperative did not exist during the cruise phase. All that the vehicle had to do during the cruise phase was to respond to infrequent commands from JPL to perform trajectory correct maneuvers.

Finally, the yes part: During entry, descent, and landing (EDL), it was without a doubt the rover's computers that controlled operations. The terrain recognition computer, the VCE, was on the rover, as was the rover's main flight computer, which performed EDL guidance, navigation, and control.


Short answer: yes.

Long answer is here (Thermal Response of the Mars Science Laboratory Spacecraft during Entry, Descent and Landing - Keith S. Novak):

Flyaway Segment: at E+431 sec (see Figure 6)

After the Bridle was cut, control of the DS was transferred to the DMCA. The DS traveled straight up above the Rover, before turning 45 degrees and thrusting away from the landing site. The DS flew away and impacted the Mars surface, as planned, at a safe distance (650m) away from the Rover. After touchdown, the Rover’s computer switched from EDL mode into surface operations mode and began autonomous execution of Rover activities for Sol 0. At Rover touchdown, the local time in Gale Crater was 15:03 LMST.

DMCA = Descent Motor Controller Assembly

See also Why did NASA intentionally crash-land the Curiosity and Perseverance sky cranes on Mars?

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    $\begingroup$ +1 This is a little more like "Who drove around to look fo a parking spot after the drive from Earth to Mars?" but it is certainly just as critical a part of the trip as any other! $\endgroup$
    – uhoh
    Commented Mar 18, 2021 at 9:18

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