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Assuming it's not intentionally obscured. If I were building an interstellar vehicle to send to/past possibly hostile alien worlds, it wouldn't have headlights

Assuming it's not intentionally obscured. If I were building an interstellar vehicle to send to/past possibly hostile alien worlds, it wouldn't have headlights.

AnIdiotOnTheNet 8y ago
If it is decelerating toward us it will have to be dumping significant amounts of hot propellant at least roughly in our direction. You can't obscure that with known physics as far as I'm aware. If you're going to involve unknown physics, the theory becomes a lot more unlikely.
api 8y ago
You can't do stealth in space. Thermodynamics won't let you. If you're using a whole lot of energy you will light up in the infrared. Parent's point is valid except for the fact that they might not be lighting off the deceleration stages one after the other. There could be a time gap, and maybe a significant one. Gaps between firings would be likely because that's one way you could steer. You could time firings to aim for e.g. an orbital insertion around Jupiter, which would be easier since Jupiter is so massive. You could also use Jupiter or another gas giant to aerobrake with some kind of ablative shield like in the film 2010. It's fairly likely that whatever physicists' nightmare propulsion system an expendable interstellar rocket stage would use would be something that is hard to turn off once you light the candle, so each stage might be an all or nothing thing. It would be interesting to use the JWST, an infrared telescope, to look at areas of the sky where an inbound craft coming along this sort of interstellar trajectory might be. A probe or spacecraft would have to have its own power source. This would be way dimmer than a lit deceleration stage, but JWST might be able to see it. If it's using energy at all it must have radiators due to the second law. Of course if this hypothesis were valid and they lit another deceleration stage, it would absolutely be visible if we looked in the right place. It would be very very bright in the infrared and probably in visible light too. Hell if it's something insane like an antimatter driven fusion rocket you might be able to see it with the naked eye.

Assuming it's not intentionally obscured. If I were building an interstellar vehicle to send to/past possibly hostile alien worlds, it wouldn't have headlights.

AnIdiotOnTheNet 8y ago

If it is decelerating toward us it will have to be dumping significant amounts of hot propellant at least roughly in our direction. You can't obscure that with known physics as far as I'm aware. If you're going to involve unknown physics, the theory becomes a lot more unlikely.

api 8y ago

You can't do stealth in space. Thermodynamics won't let you. If you're using a whole lot of energy you will light up in the infrared. Parent's point is valid except for the fact that they might not be lighting off the deceleration stages one after the other. There could be a time gap, and maybe a significant one. Gaps between firings would be likely because that's one way you could steer. You could time firings to aim for e.g. an orbital insertion around Jupiter, which would be easier since Jupiter is so massive. You could also use Jupiter or another gas giant to aerobrake with some kind of ablative shield like in the film 2010. It's fairly likely that whatever physicists' nightmare propulsion system an expendable interstellar rocket stage would use would be something that is hard to turn off once you light the candle, so each stage might be an all or nothing thing. It would be interesting to use the JWST, an infrared telescope, to look at areas of the sky where an inbound craft coming along this sort of interstellar trajectory might be. A probe or spacecraft would have to have its own power source. This would be way dimmer than a lit deceleration stage, but JWST might be able to see it. If it's using energy at all it must have radiators due to the second law. Of course if this hypothesis were valid and they lit another deceleration stage, it would absolutely be visible if we looked in the right place. It would be very very bright in the infrared and probably in visible light too. Hell if it's something insane like an antimatter driven fusion rocket you might be able to see it with the naked eye.