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Test of solar sail for de-orbiting smallsat ends successfully

Capitalism in space: The Canadian company Space Flight Labs announced yesterday that its first test of a solar sail for de-orbiting a small satellite ended successfully last month.

The CanX-7 (Canadian Advanced Nanospace eXperiment-7) was a three-kilogram, 10x10x34cm satellite that was launched on September 26, 2016. The satellite was funded by the Defence Research and Development Canada, the Natural Sciences and Engineering Research Council, COM DEV Ltd. (now Honeywell), and the Canadian Space Agency.

According to SFL [Space Flight Labs] “the satellite successfully completed a seven-month aircraft tracking campaign before deploying its drag sails in May 2017 to demonstrate drag-sail based deorbiting.” SFL said it took five years for the drag sail to deorbit the satellite and without it the satellite wouldn’t have burned up in the atmosphere for roughly another 178 year.

When the four drag sails, each about one square meter in size, were deployed, engineers immediately measured an increase in the orbital decay rate. Though it still took five years to force a de-orbit, the system removed the satellite from orbit much sooner than otherwise.

The system is aimed at the smallsat market, satellites too small for other proposed removal methods that also might remain stranded in orbit for a very long time because of their small size.

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  • Phill O

    We they able to control the reentry? Was it so small that no fragments could reach earth?

    Just a couple of questions relating to safety on earth, due, in part, to the flagrant disregard of safety by the Chinese.

  • Phill O: This is a smallsat. It is tiny. It burns up in the atmosphere. There is no threat to the ground.

    The purpose of the test was simply to hurry that de-orbit along so that the defunct satellite was less of a threat in orbit to other orbiting satellites.

  • Is it really correct to call these “solar” sails? Solar sails per se catch momentum from sunlight (or the solar wind) to change their orbit(s). It sounds like these sails merely balloon the satellite’s atmospheric drag, resulting in earlier reentry than otherwise.

  • pawn

    I don’t know if the sails are orientable but if they point away from the sun, half of their orbit the solar drag will increase their orbital velocity and the other half will decrease it.

    The half that would be increasing it would be in the shadow of the earth for a variable percentage of the time depending on it’s inclination.

    So in this half it would only have a percentage of the thrush it would normally balance out the two halves. The net change in orbital velocity just from the solar “drag” or thrust would be negative.

    I don’t know if this is how it works but I can see a way in which it could be using the solar “wind” so to speak.

  • pzatchok

    From the picture it looks like the sails are over half the mass or the 3 kg small sat, The wires must role up like a measuring tape.
    For larger sats an inflatable system might work better.

    Granted this would work well but how do we attach them to the ones we already have deployed?

    It would be a good backup system to add to all satellites.

    Plus if a few solar small solar panels were added the extra power could be used to help operate it during its 5 year de-orbit, and re-entry.

  • Jeff Wright has an article that might apply to larger sails called “Geometrically engineered rigid island array for stretchable electronics.” Centauri Dreams talks about new sails.

  • Edward

    Michael McNeil asked: “Is it really correct to call these “solar” sails?

    Probably not. The article calls it a drag sail, clearly meaning atmospheric drag.

    According to SFL “the satellite successfully completed a seven-month aircraft tracking campaign before deploying its drag sails in May 2017 to demonstrate drag-sail based deorbiting.” SFL said it took five years for the drag sail to deorbit the satellite and without it the satellite wouldn’t have burned up in the atmosphere for roughly another 178 year.

    Phill O asked: “[Were] they able to control the reentry?


    First, according to the article:

    The drag sails performed better than designed, …

    Suggesting that their model for the drag sail’s performance is not yet correct.

    Second, a five year deorbit mission means that the action took somewhere in the neighborhood of 30,000 revolutions around the Earth, making the reentry location almost as predictable as a roulette game. As Robert noted, small satellites that are not designed to survive reentry don’t, so it is not important where or when the reentry occurs.

    Third, the amount of drag at any given moment depends upon the density of the atmosphere at each location through which the satellite and sail are sailing. this density depends upon solar effects that affect the atmosphere as well as upon the local atmospheric surface barometric pressure and temperature. Higher pressures mean that there are more air molecules over that location, suggesting that the atmosphere extends higher (is more dense at higher altitude) than lower pressure locations, and higher temperatures also tend to extend the atmosphere higher than cooler locations.

    Fourth, and perhaps most important, the intention of this device is for the deorbit to be passive rather than active. This allows for the disposal of the satellite without active control. It is less expensive than having ground controllers working to bring it down, and it allows for the ability of sail deployment in a passive manner should the satellite fail on orbit (e.g. an active signal is necessary for the sail to remain stowed, but if the power fails or the control computer fails, the signal to keep it stowed stops, and deployment occurs).

    This mission has proved the concept, and it suggests that a one square-meter drag sail could be able to perform a reentry within the suggested 25-years (depending upon initial orbital altitude).

    The photograph in the article makes it look like the cross-section of the sail is a similar size to a standard geostationary communication satellite, and the article tells us that the cross-section is four square meters. Although this does not seem too bad, the real risk of collision increases with increasing cross-sectional area. Considering that the cross-sectional area of the sail is about four hundred times greater than the cubesat itself and that the sail brings the cubesat out of orbit in only 1/35th of the time, the conclusion is that the sail increases the real risk of an actual collision by ten times, an order of magnitude greater chance of collision than without the sail.

    However, since the actual location of a satellite is not well predictable into the future, collision warning systems place a “danger zone” of a couple of kilometers or so in radius, whether the satellite is 10cm on a side or 10 meters. Thus, deorbiting cubesats, or any satellite, sooner than later is very desirable, as it reduces the incidents of close encounters and the number of times living satellites have to maneuver out of the way of dead-debris satellites.

    This is why the Inter-Agency Space Debris Coordination Committee recommends that every satellite launched to low Earth orbit be able to de-orbit itself within 25 years of the end of its mission. The less time a satellite remains in orbit, the fewer times it will contribute to close encounter incidents. The conclusion: the drag sail is overall a better solution than the increase in danger that it presents.

    From the article:

    “Orbital debris is a big concern for the space industry, and the passive de-orbit technology demonstrated on CanX-7 is an advantageous solution for nano- and microsatellites,” said SFL’s CanX-7 Mission Manager, Brad Cotten. “The mission verified that SFL’s lightweight drag sail technology is a more cost-effective and less complex method for deorbiting smaller satellites than traditional propulsion techniques.”

    It may be more cost-effective and less complex, but traditional propulsion techniques could deorbit a smaller satellite in a matter of days or even in half an orbit (3/4 hour), and that is an even better solution. This clears an obsolete satellite immediately (and, less important, gives a much more predictable reentry point). This sail could be used as either a primary deorbital system or as a backup should the satellite fail before a reentry command can be given.

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