On Sat, Mar 15, 2025 at 08:32:54PM -0700, Traveller Mailing List wrote:
>
> ============================================================
>
> [ ...snip... ]
>
> The crux is that in Traveller, you don't need a Deathstar. Even small ships could
> perform this attack. Indeed, it could probably be performed sans crew. Just jump
> to some location well outside the starsystem and before you disembark to your
> getaway craft, tell the computer to accelerate toward Alderan and not to let up on
> the gas. It will take a long time for the ship to reach relativistic velocities,
> but there's nothing stopping it from doing so.

You never needed a Deathstar. Lobing high velocity rocks at a planet would be just as
damaging in the Star Wars universe as it is in real life. In fact, doing so at the planet of
Mandalore would have been just as effective as the nukes that the Empire used, assuming that
I have the story right. Both Heinlein's _"The Moon is a Harsh Mistress"_ and Babylon 5
featured at least the threat of bombarding a planet's surface from space. I say at least the
threat because I haven't read the Heinlein book but according to the plot summary on
Wikipedia, it happens in Book 3.

>
> However, there's one potential problem, and it has to do with stealth or rather
> the lack thereof, as this attack (in my uninformed opinion) requires the element
> of surprise. I'm no physicist, but I'm guessing that any object accelerating to a
> relativistic velocity will unavoidably collide with the interstellar medium, a
> very thin fog of hydrogen atoms. The current best guess is that there's about one
> atom per cubic centimeter, or about a million per cubic meter. Any object
> colliding with them will likely tear away electrons and perhaps generate some
> radiation in the process, perhaps enough to give the target planet some advance
> warning, assuming they're got any astronomers worth their salt. I'm imagining
> there would be some sort of detectable emission, and so if the planet has
> detectors in orbit watching for this sort of thing.... Obviously, it all boils
> down to the sensitivity of the detectors and how much radiation would likely be
> emitted.
>
> I've looked for information on the sensitivity of sensors in Traveller, and I
> haven't found very much. My guess is that the best version (the set with the
> highest correspondence to reality) are the rules outlined in the T4 version of
> Fire, Fusion, and Steel, pgs. 72-73, where it says that for Passive EMS, detection
> probability can be derived from the signal strength (Table 195 on page 109), which
> is itself computed using this formula: signal signature + sensor sensitivity
> (Table 198 on page 110) – range (Table 194 on page 109). But what would those
> values be for this specific scenario?
>
> Assuming the planet gets advanced warning, its SDBs can move to intercept. If they
> can hit the near-c object before it reaches the target, the explosion will, I'm
> guessing, vaporize the incoming threat. Actually, any impact, even a small one,
> would (again I'm guessing) turn the incoming payload into a white hot plasma. It
> would be very tricky, because due to the relative speeds, they'd only get one
> shot, but if they could connect with it, I'm thinking it would be like a nuclear
> explosion in space, one that spreads from the point of impact like a cone, so only
> a small fraction of the initial payload would ever hit its target, although even
> this might still be enough to disrupt the target planet's magnetic field, assuming
> it has one.
>

If you make some assumptions, it's not to hard to figure things things out here. My
assumptions:

- You can detect the rock by the radiation it's generating at about the mean orbit of Pluto;
- It's a straight line shot from the detection point to Earth.

From that I get the following table of lead times.

     Speed (%c) | Lead time (hrs)
     ----------------------------------------
         10.00% |  48.007
         25.00% |  16.002
         50.00% |   5.334
         75.00% |   1.778
         90.00% |   0.593

Notes:
`pluto_distance: 39.482au (Pluto's mean orbital radius from wikipedia)`

------------------------------------------------------------

At higher speed, it could work because the authorities wouldn't have enough time to mount a
response. But it seems that the withering effect of the _interplanetary "void"_ would be a
factor. My aim in creating the table was to see if there's a sweet spot where the withering
effect would be minimized but the time would still be short enough. That might be true near
0.25c.

All of this is rendered moot by the fact that plantoid hulls exist so if someone built a
planetoid hull with Jump-3 and Manuever-3 and then surplussed it, someone else could buy it,
take it out to the oort cloud, refuel it and accelerate it to 0.1C and then use Jump-3 to
have it appear well within the orbit of Pluto. If I recall correctly, 100 diameters for
Sol is just past one AU. If said rock was a planetoid ship that jumped into the system
inside the orbit of Jupiter, you'd have some 6 hours to a muster a defense.

This is just one way that it could work. The best guess for the orbital speed of the rock
that killed the dinosaurs is 20km/s. That's 0.00667%c. The question is: **does a speed exist
between 0.0000667c and 0.1c or even 0.25c, response time 1.85 hours, at which a Traveller
defense agency would not have time to respond to a rock lobbed at a planet?**

--
Chris

      __o          "All I was trying to do was get home from work."
    _`\<,_           -Rosa Parks
___(*)/_(*)____.___o____..___..o...________ooO..._____________________
Christopher Sean Hilton                    [chris/at/vindaloo/dot/com]