3 ms·

I feel like if you were close enough for a gravity assist, wouldn't the tidal forces just tear the probe apart?

Tostino 2y ago
Not necessarily. If you replaced the sun with an equivalent mass black hole, none of the orbits of the planets would change.
- tsimionescu 2y ago
  Sure, because none of the planets are anywhere near close enough to the sun to experience tidal forces. But if you were to approach the sun VS a sun-mass black hole, at some distance the difference would become noticeable through tidal forces (ignoring the massive difference in emitted radiation, of course).
- jebarker 2y ago
  I'd like to see a simulation of what that would look like. I mean, if by magic the sun was replaced with an equivalent mass black hole in an instant would anything be visible from earth before the inevitable freeze?
  - utensil4778 2y ago
    From Earth's perspective, you wouldn't see anything interesting except for the sun vanishing. Gravitationally, all that matters is the absolute mass, so all the dynamics of the solar system stay the same. A black hole of 1 solar mass has a radius of something like 3km. Totally invisible from Earth. You probably wouldn't even see any gravitational lensing. All we would see is the sun there one moment, and then nothing the next. Life on Earth would continue for a while, but the planet would eventually freeze over. So, nothing interesting. The sun vanishes and then some time later you freeze and/or starve to death.
    - jebarker 2y ago
      Ah, thanks for the explanation. They key thing I didn't realize is that it'd only be 3km!
sandworm101 2y ago
The tidal forces would be no different than using jupiter for an assist. You would still have the probe pass by at several thousand, several tens of thousands of kilometers. A close-in gravity assist may look better on paper, but the practicalities and speeds of such a thing are risky. One small error and the mission would be over quick, launched out at a radically incorrect trajectory.
- tsimionescu 2y ago
  Isn't the whole advantage that you could get much closer to the center of mass of the black hole compared to a planet, thus gaining much more kinetic energy per unit thrust, but also risking higher tidal forces?
  - sandworm101 2y ago
    On paper yes, but doing so also reduces the time for the burn. Probes have very low-thrust engines. Even during a jupiter slingshot they barely have time to accellerate much on thier own. Often they do not bother, relying totally upon the grav assist to accellerate. The danger too of a closer approach is that something gets miscalculated. Get too close and an inevitable tiny misalignment will throw you onto a wild unwanted trajectory. There is no gps out there. Knowing exactly where and how a probe is moving isnt easy.

Not necessarily. If you replaced the sun with an equivalent mass black hole, none of the orbits of the planets would change.

tsimionescu 2y ago
Sure, because none of the planets are anywhere near close enough to the sun to experience tidal forces. But if you were to approach the sun VS a sun-mass black hole, at some distance the difference would become noticeable through tidal forces (ignoring the massive difference in emitted radiation, of course).
jebarker 2y ago
I'd like to see a simulation of what that would look like. I mean, if by magic the sun was replaced with an equivalent mass black hole in an instant would anything be visible from earth before the inevitable freeze?
- utensil4778 2y ago
  From Earth's perspective, you wouldn't see anything interesting except for the sun vanishing. Gravitationally, all that matters is the absolute mass, so all the dynamics of the solar system stay the same. A black hole of 1 solar mass has a radius of something like 3km. Totally invisible from Earth. You probably wouldn't even see any gravitational lensing. All we would see is the sun there one moment, and then nothing the next. Life on Earth would continue for a while, but the planet would eventually freeze over. So, nothing interesting. The sun vanishes and then some time later you freeze and/or starve to death.
  - jebarker 2y ago
    Ah, thanks for the explanation. They key thing I didn't realize is that it'd only be 3km!

sandworm101 2y ago

The tidal forces would be no different than using jupiter for an assist. You would still have the probe pass by at several thousand, several tens of thousands of kilometers. A close-in gravity assist may look better on paper, but the practicalities and speeds of such a thing are risky. One small error and the mission would be over quick, launched out at a radically incorrect trajectory.

tsimionescu 2y ago
Isn't the whole advantage that you could get much closer to the center of mass of the black hole compared to a planet, thus gaining much more kinetic energy per unit thrust, but also risking higher tidal forces?
- sandworm101 2y ago
  On paper yes, but doing so also reduces the time for the burn. Probes have very low-thrust engines. Even during a jupiter slingshot they barely have time to accellerate much on thier own. Often they do not bother, relying totally upon the grav assist to accellerate. The danger too of a closer approach is that something gets miscalculated. Get too close and an inevitable tiny misalignment will throw you onto a wild unwanted trajectory. There is no gps out there. Knowing exactly where and how a probe is moving isnt easy.