XPath to retrieve an attribute of the n-th child element of its parent
===

I have the following XML:

    <ModuleInfo xsi:type="NMEAGPSInfo" name="NMEAGPS" id="f77f721c-8287-4609-80d4-4458011219ff">
        . . .
        <Satellites Number="3" Quality="2">
            <Satellite IsInUse="true">
                <Code>28</Code>
                <SignalToNoiseRatio>22</SignalToNoiseRatio>
                <Elevation>18</Elevation>
                <Azimuth>285</Azimuth>
            </Satellite>
            <Satellite IsInUse="true">
                <Code>08</Code>
                <SignalToNoiseRatio>20</SignalToNoiseRatio>
                <Elevation>46</Elevation>
                <Azimuth>312</Azimuth>
            </Satellite>
            . . .
        </Satellites>
        . . .
    </ModuleInfo>

I need an XPath to retrieve the value of the IsInUse attribute of the n-th Satellite tag.

I've been using this XPath: a:Satellites/a:Satellite[1]@IsInUse

But it doesn't work.

Tony