Recent comments in /f/space

rocketsocks t1_jaf41q6 wrote

Reply to Why don’t we put air intakes on the lower stages of rockets? by Squiggin1321

It would seem to be so easy to take advantage of all the oxygen in the air but it turns out to generally be extremely not worth the trouble.

The first major problem is just getting the air and making use of it, which is insanely complicated and requires lots of complex machinery. We're talking turbojet, ramjet, or scramjet engines. And while it may seem that a rocket engine is insanely complex, they are actually a lot simpler than jet engines in many regards. The first liquid fueled rocket propelled vehicle flew about 20 years before the first jet powered aircraft, for example. Even more so it's incredibly difficult to design air breathing engines which operate over wide ranges of speeds and altitudes. Consider the SR-71 and the ridiculous level of engineering that went into that and how those speeds and altitudes are just baby steps compared to orbital launch. It takes about a minute and 45 seconds for a Falcon 9 to surpass the speed and altitude of the SR-71. It is very challenging to build an airbreathing engine that would be worth its weight.

Once you add airbreathing to a launch vehicle you would want to spend more time in denser atmosphere in order to maximize its usefulness. However, that's very problematic for several reasons. For one it creates much more drag to spend so much time in denser atmosphere, which saps efficiency. For another it adds more aerodynamic heating and strong aerodynamic forces forcing you to add more heat protection and increase the strength of the vehicle. All of which adds weight, complexity, and potential failure modes.

In contrast, if you just say no to airbreathing at all you end up with a simpler vehicle that only has rocket engines (saving weight and complexity) and you have a much simpler optimization problem for launch. You can climb out of the thick atmosphere early and do the majority of acceleration in vacuum or near vacuum.

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EricPostpischil t1_jaf3wnb wrote

Reply to comment by thetomahawk42 in Black holes may be quietly generating the force that is tearing the universe apart, experts say by dr_gus

I think the quotes were to point out the previous commenter’s use of Dr. Smethurst’s first name in that way could be considered diminutive. Unless Dr. Smethurst prefers to be known as Dr. Becky or the commenter has a personal relationship justifying the familiarity, it may be impolite to use “Dr. Becky.” If she does use that form, antiquemule may have been unaware of it or may consider it impolite nonetheless.

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HeebieMcJeeberson t1_jaf2eit wrote

Reply to Do Red Dwarfs Provide Enough Sunlight for Plants to Grow? by DevilsRefugee

There are a ton of variables but yes it's possible.

A red dwarf's luminosity is between a tenth and a ten-thousandth of our sun's, so even the brightest ones are dim. But sunlight hitting the planet Mercury is about 7x as bright as on Earth, and we've already observed exoplanets that are closer to their suns than Mercury is to ours. So a planet close to a red dwarf could theoretically get as much daylight as we do.

Also, lots of plant life exists in very low light conditions on Earth - and not just mushrooms etc. growing in caves. Plants under rainforest cover get as little as 2% of full sunlight. That's very much in the range of what plants out in the open could get on a world orbiting a red dwarf.

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_Hexagon__ t1_jaf19xf wrote

Reply to Starting again with space by Drotkowski

Youtuber Scott Manley and Everyday Astronaut for fun and interesting lessons on space, rockets and how it all works. The video game Kerbal space program for a fun and refreshing way to learn complicated things like orbital rendezvous or interplanetary missions in an easy and fun way. Books like "Carrying the fire" by Michael Collins or "Failure is not an option" by Gene Kranz to learn about the space race, the life of an astronaut and the Apollo program. TV shows like "From the earth to the moon" from HBO, "For all mankind" from appleTV and movies like Apollo 13 and First Man.

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