Perseverance ejected two 70 kg "cruise balance masses" just before it became an airplane, to move its center of mass off axis and increase its angle of attack from 0° to about 16° to make it steerable.

Shortly before it stopped being an airplane, it ejected six more tungsten "balance masses," in something called the Straighten Up and Fly Right (SUFR) maneuver. This reduced its AoA to less than 5° before deploying its parachute.

  1. How many kg were those six masses?
  2. Why were that many needed?
    If for sequential deployment to damp oscillations, why were so few needed? Why not spray a thousand, or even spray a heavy liquid?

Its 2012 predecessor Curiosity had 2x 75 kg and 6x 25 kg masses.

  • 2
    $\begingroup$ Thank you for putting Curiosity's masses for comparison. Nice question! $\endgroup$ – DrSheldon Mar 8 at 21:18
  • 1
    $\begingroup$ related and video (but doesn't answer this) Is Perseverance's heat shield's thickness radially symmetric? and screenshot: i.stack.imgur.com/V2Pcb.png which says 75 kg x 2 for Perseverance, though I don't think that's meant to be a precise authoritative number. And to think that here I was worried about a measly 6 kg of dead weight, now they're throwing 300 kg of "sand bags" overboard! $\endgroup$ – uhoh Mar 8 at 22:06
  • $\begingroup$ Damping oszillations by adding masses may be a bad idea. For a mass spring system oscillation frequency gets lower by adding masses but a damper is some thing different. To damp oscillations energy must be consumed but not stored as done by masses or springs. $\endgroup$ – Uwe Mar 9 at 1:43
  • $\begingroup$ @Uwe, the same total kg, only reduced more gradually. If damping even is the reason. $\endgroup$ – Camille Goudeseune Mar 9 at 3:37

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