Star Tek–Exploiting the Final Frontier: Counterspace Operations in 2025 (1996) [pdf]
&gt;&quot;Gravity Gradiometer<p>System Description.<p>Gravity gradiometers are instruments and systems that detect mass density
contrasts. Recent gravity gradiometer research has focused on sea-based submarine detection applications. 
This concept goes several leaps forward and proposes its use in space as a passive detection system.<p>Concept of Operations.<p>With multiple gravity gradiometers located on multiple satellites in orbit,
approaching “foreign bodies” can be passively detected. Data and measurements gathered could be
combined with data from other detection devices in Kalman filtering or data fusion algorithms to enhance
detection and even identification probabilities.&quot;<p>This is interesting, the concept of a Gravity Gradiometer.<p>I did not know that these existed, before reading this article.<p>The following seems to be a good (albeit, somewhat commercial) page about this technology:<p><a href="https:&#x2F;&#x2F;www.lockheedmartin.com&#x2F;en-us&#x2F;products&#x2F;gravity-gradiometry.html" rel="nofollow">https:&#x2F;&#x2F;www.lockheedmartin.com&#x2F;en-us&#x2F;products&#x2F;gravity-gradio...</a><p>These are apparently supposed to be used in space, from a satellite, and are supposed to measure data about the earth.<p>But, I&#x27;m wondering (from a purely theoretical basis) if a &quot;Poor Man&#x27;s Gravity Detector&quot; could be created...<p>Postulated theory of operation: Use two waves (they could be beams), two frequencies from the electromagnetic spectrum, and measure the time they take to cross (bounce back) from a specific distance.<p>The idea would be that a lower frequency beam -- would be more affected by gravity than a higher one (although, perhaps this would be reversed, I don&#x27;t know, experimentation is needed), and that any microscopic difference in the amount of time for the beams to be reflected might indicate the presence of higher or lower gravity.<p>Of course, the prerequisite to creating something like this would be to have a way to test it.  That is, first create a device that creates a miniscule amount of gravity (which I wouldn&#x27;t know how to do -- although one guess would be that large amounts of a heavy metal would generate a microscopicly increased gravity field around it (like a milimeter away from its surface); for example, a large ball or other object made out of iron...)<p>Anyway, an interesting article!