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A 230 foot long tape deployed from the satellite Prox-1 greatly reduced how long it took to deorbit. The tape was described as electrically conductive.

Was that property intended to help the satellite deorbit faster, or was the tape's atmospheric drag sufficient?

(Illustrations suggest that the tape is about 70 m x 0.1 m, or 7 m^2. It weighs "less than 2 pounds" or roughly 700 g, for an areal density of 100 g/m^2. Mylar is 1.4 g/cm^3, so if this is Mylar, its thickness is 0.07 mm = "2 mil," industrially common when foil-covered like a party balloon. But why foil-covered instead of just pure polyester?)

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    $\begingroup$ A chapter in Randall Munroe's "How To" says that an A4 sheet of paper would survive re-entry without burning up. Should we expect strips of Mylar to start decorating our planet, then? $\endgroup$
    – Camille Goudeseune
    Commented Jan 24, 2020 at 6:06
  • $\begingroup$ possibly related, a long conductive thing space.stackexchange.com/a/34123/12102 and 1, 2, 3 $\endgroup$
    – uhoh
    Commented Jan 24, 2020 at 6:44

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Because it's using Earth's magnetic field to create drag. It's one of several passive deorbiting systems.

An electromagnetic tether uses a conductive tether to generate an electromagnetic force as the tether system moves relative to Earth’s magnetic field.

NASA: State of the Art of Small Spacecraft Technology, 12. Passive Deorbit Systems

In-Space Propulsion andDe-orbit of Satellites in LEOUsing Electromagnetic Force, Deepak Prem R has a nice illustration of how this works.

enter image description here

As the satellite orbits in the low earth orbit, where there is appreciable density of electrons, a current is passed in the conducting wire. This current interacts with the earth’s magnetic field and a force is developed. By changing the orientation of the current element, the direction of force can be varied in accordance to the Fleming’s left hand rule. ...it can always be used to raise or lower the altitude.

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  • $\begingroup$ I'm having a hard time understanding how that works. The image of the Roll-Out DeOrbiting device (RODEO) shown in your link also shows a length of metalized film but relies on aerodynamic drag. So I've just asked What fraction of Terminator Tape™'s drag comes from interaction with Earth's magnetic field as a function of altitude? Is it ever important? $\endgroup$
    – uhoh
    Commented Jan 24, 2020 at 7:36
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    $\begingroup$ @uhoh I've added an illustration and paper that explains how it works in more detail. As for what portion is electromagnetic drag and what is aerodynamic drag, I don't know. Tethers Unlimited's data sheet only says it uses both "neutral particle drag and passive electromagnetics drag". $\endgroup$
    – Schwern
    Commented Jan 24, 2020 at 7:57
  • $\begingroup$ excellent, thank you! $\endgroup$
    – uhoh
    Commented Jan 24, 2020 at 7:58
  • $\begingroup$ So by the left-hand rule, moving the vertical tape through Earth's magnetic field induces an upward current in it; the current loop is closed through stratospheric plasma (i.e., ionized gas, i.e., conductive); and "back EMF" slows it down just like in an electric motor. $\endgroup$
    – Camille Goudeseune
    Commented Jan 24, 2020 at 18:04

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