• New control technique uses solar panels

    From ScienceDaily@1:317/3 to All on Mon Jan 24 21:30:36 2022
    New control technique uses solar panels to reach desired Mars orbit


    Date:
    January 24, 2022
    Source:
    University of Illinois Grainger College of Engineering
    Summary:
    Aerospace engineers have developed a way to use articulated
    solar panels to steer the satellite during aerobraking, reducing
    the number of passes needed, resulting in potential savings in
    propellant, time, and money.



    FULL STORY ==========================================================================
    A satellite on a science mission to Mars aims for a low-altitude orbit,
    but the lower the orbit, the more propellant is required to enter
    orbit when arriving from Earth. To save propellant, a technique called aerobraking uses a small propulsive maneuver for orbit insertion to
    enter a large orbit; the satellite then makes many passes through the
    upper atmosphere, using drag on the solar panels to reduce the size of
    the orbit a little bit each pass until the orbit is the desired size for science operations. This aerobraking technique requires three to six
    months to complete and requires near-constant supervision by a ground
    team on Earth. Aerospace engineers at the University of Illinois Urbana- Champaign developed a way to use articulated solar panels to steer the satellite during aerobraking, reducing the number of passes needed,
    resulting in potential savings in propellant, time, and money.


    ==========================================================================
    "If we can rotate the solar panels, we can control how much drag is
    generated and we can actually steer during the atmospheric passes
    to control heating and energy depletion," said AE Professor Zach
    Putnam. "This means we can fly much closer to operational constraints,
    and aerobrake much faster." Putnam's Ph.D. student Giusy Falcone used
    the satellite's ability to rotate their solar panels and calculated how
    the panels could be used to optimize and control the drag.

    "Giusy developed a real-time algorithm that you might think of as an
    autopilot that uses information from the spacecraft's onboard navigation
    system to determine the angle of the solar panels in real time, based
    on current atmospheric conditions," Putnam said.

    The primary limiting factor during flight is the temperature of the
    solar panels. When a satellite hits the molecules in the Mars atmosphere,
    the friction heats up the panels, and over-heating the solar panels can
    kill the spacecraft.

    "Being able to steer the satellite during each atmospheric pass enables
    us to ensure we don't over temperature the solar panels while flying
    much closer to the thermal limit. This is a big improvement. Instead
    of aerobraking for three to six months, it might only take a couple
    of weeks." This study is about automating just one pass through the atmosphere. This process would be repeated many times during a complete aerobraking campaign, Putnam said.



    ==========================================================================
    He explained that as the satellite's orbit gets smaller and smaller, the
    time it takes to complete one orbit gets shorter until the orbits are so
    short that there isn't time to transmit information from the spacecraft to Earth, wait for a decision, then send commands back to make a correction.

    "Because it is automatic, Giusy's algorithm is particularly helpful
    at that last stage when the orbits are very rapid, but the algorithm
    can be used for the entire process." This is the first piece toward
    developing an autonomous capability for aerobraking that has implications
    for reducing cost and mission risk on a much larger scale.

    "The trip out to Mars takes somewhere between six to nine months. We
    can't really change that, but we think we can shorten the time it takes
    to aerobrake to a low-altitude orbit," Putnam said. "And the propellant
    onboard we save can be used to do other things like keep the spacecraft
    alive longer." Putnam said the current aerobraking method is also operationally intensive with a ground team working 24 hours a day for
    about six months.

    "You can imagine how expensive it is for a ground team working around the clock," he said. "There is also limited bandwidth for ground stations that
    can talk to Mars. We have only three and they're oversubscribed as it is.

    "This software would greatly reduce our reliance on ground
    stations. If we can automate it onboard and only have to check
    in with the spacecraft once a week, that would really bring costs
    down. And, it could be done by many satellites at the same time." ========================================================================== Story Source: Materials provided by University_of_Illinois_Grainger_College_of_Engineering.

    Original written by Debra Levey Larson. Note: Content may be edited for
    style and length.


    ========================================================================== Journal Reference:
    1. Giusy Falcone, Zachary R. Putnam. Energy Depletion Guidance for
    Aerobraking Atmospheric Passes. Journal of Guidance, Control,
    and Dynamics, 2021; 1 DOI: 10.2514/1.G006171 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/01/220124115032.htm

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