Recent comments in /f/space

kittyrocket t1_jdaxxwb wrote

Reply to Virgin Orbit raising $200 million from investor Matthew Brown, closing deal as soon as Thursday by cnbc_official

I'd be really curious to hear the case Virgin Orbit made to Matthew Brown. I have a hard time envisioning a viable niche for their services. It seems like the small sat launchers are all counting on developing bigger rockets, but Virgin's technology just can't scale up in size because there's only so much a 747 can carry.

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lilrabbitfoofoo t1_jdawhvs wrote

Reply to Research team finds indirect evidence for existence of dark matter surrounding black holes by karmagheden

The same results can be achieved by just putting in an appropriate amount of cold normal matter (dust, rocks, planetoids, etc.) into the same functions. We still wouldn't be able to see any of this additional matter and so it would be "invisible" to the EM spectrum (meaning invisible to us).

This provides some evidence of matter being there, not its exotic form or imaginary nature as proposed by "dark matter" theories.

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I_Heart_Astronomy t1_jdav8b4 wrote

Reply to comment by Andromeda321 in The Northern Lights could dazzle the skies from Washington to New York on Friday, blown by winds from a giant 'hole' on the sun by thisisinsider

All the friends, family, and coworkers who know I'm into astronomy always say "are you looking forward to X?" when they hear something in the news, and I always say that there's a 95% chance it will be cloudy, so not really.

You know comet NEOWISE? Never had a single clear, moonless night when it was around. Not a single one. Most significant comet since Hale-Bopp and not a single clear night to see it at its peak. I got to see C/2022 E3 (ZTF) (the most recent notable comet) but it was nowhere near the brightness level that NEOWISE or Hale-Bopp reached. It was only just barely naked-eye. Because it was mediocre, it was clear. Had it been spectacular, it would have been cloudy.

I have been into amateur astronomy since I was a kid, and have NEVER witnessed a meteor shower at its peak time because of either the moon or clouds. That's 25 years of religiously observing the night sky and not ONCE have I had skies that were clear and moonless during the peak of a meteor shower.

So I just go out and observe when the conditions are good and I don't pay much attention to astronomical events.

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Mighty-Lobster t1_jdat4zw wrote

Reply to comment by boundegar in Research team finds indirect evidence for existence of dark matter surrounding black holes by karmagheden

>But... dark matter also doesn't interact with normal matter, so how would it create friction?

Dark matter interacts via gravity. Dynamical friction is a byproduct of gravity. When you have a large massive body inside a sea of much smaller particles, the large body's gravity changes the orbits of the particles near it in a way that creates an overdensity of small particles behind the large object. That overdensity creates a gravitational pull from those particles, in the direction opposite to the body's motion. Therefore, it behaves similar to a friction force.

Dynamical friction happens in any N-body system with a sea of "small" particles and some large particles. For example, it is the reason why supermassive black holes have to always be at the center of their galaxy. Dynamical friction with the stars would bring them in.

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MacTechG4 t1_jdaoc4u wrote

Reply to The Northern Lights could dazzle the skies from Washington to New York on Friday, blown by winds from a giant 'hole' on the sun by thisisinsider

And of course it’s going to be cloudy in my area….

CURSE YOU MOTHER NATURE! (And Perry the Platypus)

I was living in Vermont when there was a big display of Northern Lights (it was somewhere between 2003-2005, I don’t remember the exact date, but it was absolutely gorgeous (much like the linked picture)

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sithelephant t1_jdanidq wrote

Reply to comment by GothicGolem29 in The epic quest to build a permanent Moon base by Ok_Copy5217

That the Artemis program has a depressing paucity of ambition and that inbuilt into its DNA is several assumptions that are nearly barking mad.

If it all goes perfectly right, and every part of it performs as well as might be hoped, you get about 20 tons to and from the lunar surface, for a total of around some hundred billion dollars.

This works out to around five million dollars a kilo - you're never ever doing serious 'moonbase' type stuff on that sort of launch cost.

  • Among some of the baked-in assumptions are that propellant transfer in orbit is impossible, assembly in orbit is impossible, crew transfer in orbit is undesired. (These drive the use of SLS).

Then the selection of the gateway orbit was driven largely by Orion requirements, which is a whole nother pile of fish.

The use of SLS then sets the price expectation for Orion and all hardware that goes near the moon, again ballooning costs.

My hope for the program is that perhaps the translunar flyby flight by SLS goes ahead, at which time Starship is flying, and the new generation of launchers is coming online making a wholesale reconsidering of the program and scrapping most of the legacy elements worthwhile.

Leading to hundred ton payloads landing on the moon for less outlay than the two ton ones.

As context - if SpaceX gets propellant transfer working, with a couple of depots in orbit, and charges for launch the same price /kg as Falcon heavy, you end up with cargo on the moon costing $10K/kg, not $5000K/kg.

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