RE: And I thought if Nanosail D was obseved flashing, means it's rotating

From: Ted Molczan (
Date: Fri May 27 2011 - 12:22:31 UTC

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    Marco Langbroek wrote:
    > To me, the rapid continuous flashing is indeed a sign it must be tumbling. While
    > occasional flaring might be due to changing solar angle and a fixed reflective
    > surface, rapid flashing is not likely explained that way.
    > With a light object such as this solar sail with presumably an unusually large
    > surface to mass ratio, I wonder what happens if a small meteoroid (or small
    > piece of space debris) hits a corner of it: could it transfer enough momentum
    > for the sail to start to tumble?
    This object is highly susceptible to the effects of SRP (solar radiation pressure), which can induce rotation, as well
    as perturb the orbit. I do not know whether SRP has contributed to the rotation that has been observed, but it's
    something to consider.
    There is some information on the expected attitude behaviour of the object in the Proceedings of the Second
    International Symposium on Solar Sailing July 20 - 22, 2010 New York, USA: 
    See the paper Status Of Solar Sail Technology Within NASA, which begins on numbered pg.27. In a quick search, I did not
    find any mention about SRP effects on NanoSail-D's attitude stability, but below are some interesting excerpts on
    "This demonstration flight has two primary technical objectives: (1) to successfully stow and deploy the sail and (2) to
    demonstrate deorbit functionality.[8] Passive attitude stabilization of the spacecraft will be achieved using permanent
    magnets to detumble and orient the body with the magnetic field lines and then rely on atmospheric drag to passively
    stabilize the sailcraft in an essentially maximum drag attitude."
    "Mission data was to be comprised by radar cross-sectional area data, optical images, and orbital elements. Radar
    cross-sectional area data and optical images were to be obtained by the U.S. Army's Reagan Test Site. This data would
    enable estimation of a lower bound on deployed sail area (lower bound only because the sail plane was likely not be
    normal to the line of sight during data acquisition and hence the projected area normal to the line of sight was to be
    measured). Estimation of the deployed area will be difficult during initial phases of the mission when the sail is to be
    "tumbling" about the Earth's magnetic field lines during part of the orbit and passively stabilized in the maximum drag
    orientation near perigee. Hence the estimation of deployed area from orbit data will depend on the latter phases of the
    mission when the orbit circularizes and the sail passively stabilizes due to aerodynamic torque in a relatively constant
    local vertical/local horizontal (LVLH) attitude. In the event that the sail does not stabilize prior to re-entry,
    orbital analysis would have allowed an estimation of an average ballistic coefficient that could have been correlated to
    an average area."
    Ted Molczan
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