If a fist-sized artefact was to attach itself to a space telescope (of near-term build, such as the Nancy Grace Roman) situated in L2 of a Lagrange point, would Ground Control be able to detect it?
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$\begingroup$ Very obviously, a fist-sized ball of lead attached off-axis will come immediately to the attention of ground control, as soon as they try to reorient the telescope. A fist-sized ball of aerogel, not so much. $\endgroup$– AlexPCommented Oct 9, 2021 at 8:30
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$\begingroup$ The orb would be metallic, intentionally weighted so as to draw attention to itself. (Thank you for that idea). Plot requires that ground control obtains a clear impression of the artefact's exterior, also the interior, if plausible (lidar scan?). $\endgroup$– calamusCommented Oct 9, 2021 at 8:43
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$\begingroup$ I’m voting to close this question because I don't see any world-building connection. To me this looks like a question best answered by Space Exploration $\endgroup$– StephenG - Help UkraineCommented Oct 9, 2021 at 12:58
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3$\begingroup$ Please refrain from adding further specifications to the question once you start getting answers. Edits shall not invalidate existing answers. $\endgroup$– L.Dutch ♦Commented Oct 9, 2021 at 13:33
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$\begingroup$ @StephenG I asked a related question in Space Exploration but doubted they would welcome a question like this one, since it implies the fictive... $\endgroup$– calamusCommented Oct 11, 2021 at 9:02
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4 Answers
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The effect an extraneous object would have on a body in space can be several. The first that comes to mind is that it will alter both its inertial mass and its momentum of inertia, meaning that any maneuver aiming in changing the body orientation and/or velocity would result in a slightly different result than expected.
- Example: the rockets are fired for a time $t^*$ to deliver a force $F^*$, resulting in an expected $\Delta v^* = F^*/M \cdot t^*$. The real result will be $\Delta v = F^*/(M+m) \cdot t^*$
Same goes with rotating the object: the slightly different momentum of inertia will result in a slightly different rotation.
The more noticeable the effect will be the more massive is the extraneous object and the more distant from the axis of inertia it is located.
However this would only tell that something is attached to the satellite, it won't allow to image it.
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$\begingroup$ You can get a pretty good idea of the object's weight and volume by rotating the satellite. You should be able to tell that you have an object of X kilograms, with a center of mass at Y centimeters away. $\endgroup$– Ryan_LCommented Oct 9, 2021 at 20:21
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Dutch already answered the part about the impact the foreign object will have on the satellite's intertia so I won't go further into that.
As for this:
the attached artefact started transmitting data to the telescope, which part of its instrumentation would receive the data?
Space based telescopes have two ways of getting data from their exterior:
Via the optical sensors. But notice that telescopes focus on very faraway things. If you attach something to the lens, it's like attaching something to an eyeball of a person. They won't be able to see fine details of the object. They will also possibly freak out and have a very bad time.
Artificial satellites in general receive commands via radio signals. The Hubble, for example, talks to Earth via the Tracking and Data Relay Satellite System. Your device could emulate the commands Hubble receives from NASA's Goddard Space Flight Center, for example, causing the satellite to rotate in some way.
Please notice that all communication follows very specific computer protocols and space based telescopes are not messaging machines. If you feed their radio channels with garbage data they will just ignore it assuming it is noise from some nearby source - if the noise persists and is from a very close source, such as your device, ground control will use Occam's Razor to decide that the telescope is broken and should be decommissioned. If however you do send proper commands to the satellite, ground control will think the device has been hacked. Fingers will be pointed, an international situation will arise and worst case scenario, that starts a war among some countries.
answered Oct 9, 2021 at 10:42
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It will be detected.. position deviations and rotational inertia changes
For a "hard science" answer, knowledge of weights involved is relevant. When the weight of this spying device changes the telescope's inertial properties, these deviations could be noticed on the ground very soon. Space telescopes are very precise instruments.
Also very small deviations,
The attached object will cause a change of mass and consequently a small change of orbit. This could mess up communications. Position registration using accurate GPS will show the change, e.g. within a few days..
For positioning a telescope accurately, gyro's or small jet outlets provide a certain action force, to rotate the telescope in a particular direction. These devices are calibrated and because the rotational inertia changed, positioning will not be accurate anymore.
Recalibration of positioning devices and gyro's will tell the scientist some object has attached itself to the telescope. The mass and the location of this object can be calculated very precisely.
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The part of this question the other answers don't yet deal with is:
If it was immediately detected by its weight affecting the telescope's orientation, would ground control be able to image the object, or get some idea of its shape & size?
To which the answer is ... yes, by pointing another camera/telescope at it.
An amatuer astononer by the name of Ralf Vandebergh takes photos of the ISS with his 10 inch telescope from here on Earth. There are some nice details here: https://astronomy.stackexchange.com/questions/666/how-powerful-a-telescope-would-allow-me-to-view-the-astronauts-aboard-iss-do-a-s The resolution of his pictutes is 1m per pixel, and while I'm sure a modern observatory could achieve better, those images already have significant atmospheric distortion. At some point atmospheric distortion becomes the major noise source, and switching to a a nearby space-based telescope could provide whatever quality image you like. A sattelite capable of imaging the ground at 1m/pixel can almost definitely provide high resolution images of your parisite, but ......
The challenge is convincing someone to point their telescope at you sattelite. To the best of my knowledge this is not commonly done.
So I don't have any hard science math here. Part of that is because I am lazy, part of that is because there are no constraints on this part of the question: As phrased, a valid solution is spacewalk with a handheld camera. Similarly, in the days of the space shuttle sattelite retrieval was an option, so for all I know, ground control could return the sattelite to Earth as soon as they detect something wrong with it: aka they could examine the object with a scanning electron microscope!
So I'm not really sure what math to put here!
