Adeldor t1_jeac70g wrote

Beyond the possibility of Hawking radiation, all current understanding has it that nothing can cross back out from a black hole's event horizon.

And /u/__Raptor__ is correct. Black holes certainly don't "spit stars out." In fact, large star life cycles end with black holes. If CNN said otherwise, they're quite wrong, perhaps misunderstanding orbital ejection of objects outside the event horizon - a phenomenon common to all multi-body orbiting systems, not just black holes.


Adeldor t1_jcvv9kj wrote

Unlike heavier-than-air flight, this isn't in the category of a technical problem yet to be solved. It's more along the lines of not being able to reach temperatures below absolute zero.

By all understanding, FTL travel between two points in space appears to be impossible even when attempting to bypass direct FTL travel through that space via wormholes or Alcubierre drives. Alcubierre himself has doubts regarding his drive, indicating it has the potential to violate causality, a point supported by Prof. Allen Everett. Such violation is anathema to most cosmologists and physicists.

In other words, the speed of light is set not by light itself, but by causality. It is deeply fundamental to the nature of the universe. Even were FTL travel possible, it'd only be through phenomena such as multiple forking universal timelines, that is, one way trips out of "our" universe.

Meanwhile, beyond this somewhat dated paper (PDF) refuting White and Juday's claims, I couldn't find any refereed papers or sources for their interferometer. Have you one to provide?


Adeldor t1_jay1f1t wrote

No, he did not cut off service. Starlink provided service and hardware free of charge after the Ukrainian vice prime minister's plea for help. No one realized the war would drag on for as long as it has, and after a while Musk wanted the US to pay for future service, just like Raytheon et al are being paid.

Meanwhile, the service continues uninterrupted, with the quoted Ukrainian minister saying Musk is "one of the biggest private donors of our future victory."


Adeldor t1_jaxzcb9 wrote

Hubble's orbit has decayed over time. If proposals to reboost it come to pass (by SpaceX, no less), the problem will be ameliorated. If not, the telescope's near end of life anyway.

Meanwhile, future spaceborne telescopes are destined increasingly for far orbits (eg L2) to avoid the biggest photobomber of all - the Earth itself. In LEO it obscures nearly half the sky, limiting greatly what can be observed when - especially for long duration exposures. Far orbits bypass both that and satellite constellations.


Adeldor t1_jaifbtv wrote

Don't conflate my comments with political denial. The point of my responses:

  • the sky is not falling (if you'll pardon the pun). Astronomers - professional and amateur (I count myself among the latter) - continue to operate successfully, what with the tools that are available now to ameliorate the effects of yet higher flying satellites (illuminated for longer periods) and aircraft (illuminated at all hours of the night).

  • Truly global high speed, low latency internet has huge benefits on society, from providing access to remote communities, to assisting those defending their lands. Even without considering the impossibility of global mobile operation otherwise, there's no other kind of system capable of such ubiquitous coverage.

  • a longer term/fuzzier point - beyond terrestrial mitigations, space based observatories are and will be supplementing ground-based telescopes. The technologies that make constellations cost effective will no doubt feed into making more space-borne instruments feasible.

I've seen it written that Elon Musk, Jeff Bezos, etc don't own the sky, and this is certainly true. However, neither do astronomers. Constellations are beyond the point of proving their dramatic worth, so they're here regardless of opinion. Observatories and constellation operators will work together and cooperate because there's no alternative.


Adeldor t1_jai9c1w wrote

Yes, the Rubin telescope is more sensitive. Nevertheless, in general, the numbers I extracted apply. Meanwhile, regarding that telescope, they go on to say:

> ... depending on the time of year, the time of night, and the simplifying assumptions of the study. Mitigation techniques that could be applied on ESO telescopes would not work for this observatory although other strategies are being actively explored." [Emphasis added]

Regarding other constellations, yes, their higher orbits will be more of an issue. One of the good side effects of Starlink's low orbits is the short period of twilight illumination.

But again, astronomy is in no way experiencing an "existential threat." It's a ridiculous exaggeration. There will be effects. There are and will be workarounds and mitigations. And the sky will be shared.


Adeldor t1_jahsf9s wrote

You speak of misinformation, then misrepresent what I wrote with this:

> You are attempting to create an impression that there is no problem, and that everything has been or will be mitigated. [emphasis added]

In fact I wrote:

> There will be effects, but they are in general minor, or there are mitigating actions being taken now ... [emphasis added]

I neither wrote nor implied "no problem" and "everything has been or will be mitigated." Those are your words. Further, I provide the links for everyone to read the full releases in context, in an explicit attempt to avoid the very sin you seem to imply I'm committing.

Regardless, constellations are here now. Their worth has been proven, Starlink at least and professional observatories are working together to share the sky, and astronomy is not facing an existential threat, per that click-bait headline.


Adeldor t1_jagvvp1 wrote

That was then. The current Scientific American doesn't hold a candle to its former self. IMO the decline started when they ceased publishing substantial scientific projects and experiments such as these in their Amateur Scientist column. So no, it isn't now "as good as it gets."

Regardless, the direct statements from professional observatories carry more weight, and that SciAm title is unquestionably click-bait.


Adeldor t1_jafswvk wrote

Instead of blatant click-bait magazine articles, here are the opinions on the subject directly from major professional observatories (a variation of a comment I made a while ago):

Below are four links to professional observatory opinions, with salient quotes. There will be effects, but they are in general minor, or there are mitigating actions being taken now, from satellite design modification to filtering software and timing.

  • "The study finds that large telescopes like ESO's Very Large Telescope (VLT) and ESO's upcoming Extremely Large Telescope (ELT) will be "moderately affected" by the constellations under development. The effect is more pronounced for long exposures (of about 1000 s), up to 3% of which could be ruined during twilight, the time between dawn and sunrise and between sunset and dusk. Shorter exposures would be less impacted, with fewer than 0.5% of observations of this type affected. Observations conducted at other times during the night would also be less affected, as the satellites would be in the shadow of the Earth and therefore not illuminated." [1]

  • "Yet despite the increase in image streaks, the new report notes that ZTF science operations have not been strongly affected. Study co-author Tom Prince, the Ira S. Bowen Professor of Physics, Emeritus, at Caltech, says the paper shows a single streak affects less than one-tenth of a percent of the pixels in a ZTF image ... Prince says that software can be developed to help mitigate potential problems; for example, software could predict the locations of the Starlink satellites and thus help astronomers avoid scheduling an observation when one might be in the field of view. Software can also assess whether a passing satellite may have affected an astronomical observation, which would allow astronomers to mask or otherwise reduce the negative effects of the streaks." [2]

  • "Most recently, the NRAO and GBO have been working directly with SpaceX to jointly analyze and minimize any potential impacts from their proposed Starlink system. These discussions have been fruitful and are providing valuable guidelines that could be considered by other such systems as well ... Among the many proposals under consideration are defining exclusions zones and other mitigations around the National Science Foundation’s current radio astronomy facilities and the planned future antenna locations for the Next Generation Very Large Array." [3]

  • More recently, the National Science Foundation has published an astronomy coordination agreement, detailing procedures and designs aimed at minimizing interference and interaction between observatories and Starlink (both ways, as observatories use sky-pointed lasers to create artificial stars for focussing and the like). [4]

Meanwhile, professional and amateur astronomers both have tools now to deal with the existing satellites and (far worse) night flying aircraft.


Adeldor t1_jaewmj7 wrote

A few months ago I had a go at calculating the annual costs of the currently operating satellites. It doesn't factor in launch pad and other non-recurring and standing costs, but it does give an idea. I repeat it below:

  • Currently ~3000 satellites at ~$250k each, and each lasting 5 years
  • One Falcon 9 launches ~50 satellites, at a marginal launch cost of $15,000,000 (used booster + fairings)

So, total launch cost is:

  • $250,000 * 50 + $15,000,000 = $27,500,000, or $550,000 per satellite
  • The satellites last 5 years, so the per year cost is $110,000 per satellite

Thus, for all 3000 satellites, the current annual cost to build and launch is ~$330,000,000.

Of course, they're adding satellites, version 2 is coming out, Starship will reduce marginal launch costs by maybe an order of magnitude, ground operations and development costs are not included here, blah blah blah. Nevertheless, this might give a glimpse of the expense side.


Adeldor t1_jaeuc70 wrote

The Δv required to send anything from Earth orbit into the sun is far higher than that required to eject it from the solar system. Less Δv still is required to have it reenter the Earth's atmosphere. The practicalities of imparting the required velocities is, however, non-trivial.

To get an idea of the Δv required to get anywhere departing Earth - from the Sun to leaving the solar system - this map helps.


Adeldor t1_jacwkb5 wrote

Their orbits are low enough, were Starlink to quit launching and every satellite malfunctioned (IOW couldn't be deliberately deorbited as they are normally), within a few years there'd be none left in orbit.

And I don't consider equipment providing low latency, high speed internet service everywhere on the planet trash.