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.

People need to get out of the Space Race mindset. It doesn't fit what's going on right now and it's also not a good model to follow in terms of robust space exploration and human spaceflight.

The "omg, a Space Race! how lovely!" reactions remind me of this tweet:

https://twitter.com/afraidofwasps/status/1177301482464526337?lang=en

> Guy who has only seen The Boss Baby, watching his second movie: Getting a lot of 'Boss Baby' vibes from this...

All of the "orbits" or pseudo-orbits at the Lagrange points are within a very large volume. At the Sun-Earth L1 and L2 points the typical orbit is a halo orbit or a Lissajous orbit which loops around the Lagrange point at a distance of typically a few hundred thousand kilometers (on a similar scale to the Earth-Moon distance). In a practical sense the volume available for spacecraft to use the points is so enormous that we are unlikely to run into any crowding constraints any time soon.

The primary advantage of early-generation NTRs is that they can operate with pure hydrogen, that's it. Doing that allows them to have an exhaust velocity of around 9 km/s. And because the rocket equation is exponential with respect to the ratio of delta-V and exhaust velocity NTRs start to look really good for single digit or low double digit delta-V. With a stage mass ratio of 5:1 you can achieve a delta-V of 14.5 km/s, which is a lot to work with. In contrast, with the same stage mass ratio you'd achieve maybe 40% of that delta-V with a LOX/methane stage.

However, things stop looking so rosy very rapidly. Because NTRs use a heavy reactor and rely on low-density hydrogen it is very challenging to achieve high stage mass ratios, which limits performance. Also, because liquid hydrogen is super cryogenic and has a high boil-off rate it is very challenging to build a high efficiency NTR which has significant longevity for deep space propulsion. Even if you can bring boiloff rates under control with thermal control systems and active cooling all of that stuff adds mass which again cuts into the stage mass ratio.

All of which conspires to make the most compelling use of a first generation NTR something like a trans-lunar (or interplanetary) kick stage for crewed missions. Which might be fine, but is still pretty limiting, and likely results in only a small number of NTRs ever being built.

I guess it's very fortunate we live in a time where small scale orbital rocketry can be taken for granted. It's still nice to see more players enter the field, especially with different approaches.

Starship (or at least that systems architecture) definitely solves more problems than NTRs.

NTRs are interesting, but I don't think they're as magical as many people claim. One of their biggest problems is that first generation NTRs have a super narrow niche of applicability. In the long run they might be more useful in more scenarios, but you have to get from here to there for that to happen.

That's not the only shenanigans, that's just one example.

They cracked the code. For Artemis they helped put together the "National Team" along with Lockheed Martin, Boeing, and many others. They figured out how to shmooze and lobby with the best of the best in the aerospace biz. Now they're a major sub-contractor for ULA and they've got their hooks into all the juicy government contracts.

Erosion, water and the atmosphere. The atmosphere protects the surface from some impacts, causing a larger number of small sized impactors to blow up in the air before reaching the surface and forming a crater. A similar effect happens with smaller impactors that hit the ocean and aren't large enough to make a crater in the ocean floor. The big factor though is erosion and plate tectonics. If you look at the surface of Mars most of that crust is ancient, billions of years old. On Earth the crust gets recycled constantly due to tectonics and volcanism. The big island of Hawai'i is a fraction of a million years old, for example, and the ocean floor keeps getting recycled in a process that keeps most of it under 150 million years old.

Then you have erosional processes due to the air, the water cycle, life, etc. Mountains get worn down, surface features get changed by rivers and shorelines, rocks get changed and moved around, life covers up or erodes surface features, etc. There's a huge crater in the Yucatan peninsula from the impactor that ended the reign of the dinosaurs 66 million years ago, but it's not easily visible to the naked eye because of all the erosional processes that have occurred since then. Remnants of older craters have been found but they are also not easily visible because of erosion. Smaller craters have a tendency to get completely erased by geological activity and erosion.

It's complicated. It could push some species to extinction, which would generally be considered bad.

The woman's name is Roman, I used it.

> They now think the dark energy is vacuum energy in older black holes .

That may be the case, but this is not how science works. Science isn't some Matlock-esque stage play where the hero rushes up, presents incontrovertible evidence, everyone says "yeah, that explains it" and then that's the end. Science is almost always a slow process of building a case piece by piece, layer by layer, which incrementally increases the likelihood of one specific explanation (competing theory) being true while eliminating alternative explanations.

The new idea of black holes being a source of dark energy is right now just a competing hypothesis, not an accepted fact. It may be true, it may not be, we don't know because we don't have enough observational evidence to say for sure. Science is the process of figuring out how to attempt to falsify a theory, collecting observational data, and seeing the results. It's possible that this theory will ultimately win out, but right now it's still just one of many potential ideas about dark energy.

Let's just call it the Roman Space Telescope or RST for short.

This telescope is mostly a survey instrument, able to image roughly 1/4 of the sky every 5 years to a resolution of 0.11 arcseconds. For comparison, Hubble's resolution maxes out at 0.04 arcseconds, so it won't be quite at that level but it'll still be an enormous amount of very high quality data. Because of its large field of view and 0.3 gigapixel camera it'll return well over a terabyte of data per day (compared to JWST's ~30 gigabytes per day). Combined with JWST and the Vera Rubin Observatory these next generation telescopes will very much usher in a new era of high throughput data-rich astronomy.

There wasn't exactly a fixed schedule for Apollo missions, they could happen during any time of the year (within the launch windows during each lunar period, of course), there's nothing that would have prevented a launch from happening during that 4 month period other than just luck. The operational cadence of the program resulted in no missions happening at that time, but they could have.

Spoilers: it's going to be UT/GMT for a long time until someone figures out something better.

I think it's pretty likely that the majority of planetary bodies throughout the universe which have hosted life have done so for a comparably short period of time. Worlds like our Earth where life persists for several billions of years and develops into advanced multi-cellular life are probably fairly rare. Though on the other hand, there are so many stars and planets even in a single galaxy that there may be many such worlds in the Milky Way even if they make up a tiny percentage.

That's a completely different part of NASA. This is planetary science. Which is made up of uncrewed interplanetary spacecraft missions. Examples being: Cassini, Juno, New Horizons, Curiosity, Perseverance, DART, Lucy, Neowise, Osiris-Rex, etc. In general these missions have been considered to be extremely cost effective and well run.

In addition to the five spacecraft there are 4 rocket upper stages which are on escape trajectories from the solar system (Pioneer 11's upper stage is probably stuck orbiting the Sun because it would have had to have made gravity assists at both Jupiter and Saturn to escape, which is unlikely). There are also the small yo-yo de-spin weights for the New Horizons kick stage.

They are far too dim. Remember that light falls off with 1/r^2 distance from the Sun, while at the same time the intensity of light received at Earth falls off with 1/r^2 distance from the Earth. For objects in the outer solar system many tens of AU away from both the Earth and the Sun the result is that the distance from the Sun and the distance to the observer (which is usually near the Earth) are similar, since at such scales the Earth and the Sun are very close together. This means that brightness falls off roughly with a relationship of 1/r^4 distance from the Sun/Earth. Meaning that an object 100 AU away is not just 10,000x dimmer than 1 AU away but 100 million times dimmer.

We can just barely see giant balls of rock and ice that are hundreds of km across in the outer solar system, a tiny bit of metal just a few meters across at most is basically invisible to our optical and infrared telescopes.

Not particularly. Anti-matter may seem exotic but it's just a part of regular life. Every few seconds a potassium-40 atom in your body will decay in a way that produces a positron (anti-electron) which annihilates with an electron and releases gamma rays. That's one among many common anti-matter reactions that occur regularly around us and within us. High energy reactions are just part of our world, and we live with them. The amount of anti-matter coming from distant galaxies is tiny and not something to worry about on a personal level.

Pounds used to be a unit of force. https://en.wikipedia.org/wiki/Pound_(mass)

"Coal gas" (which can be produced from coal, charcoal, or even wood) used to be widely plumbed through major cities into people's homes where it was used for things like heating and cooking. Coal gas is basically the product of incomplete combustion and it contains a various mixture of different combustible and non-combustible gases including hydrogen and most importantly large amounts of carbon monoxide.

And this is precisely why there is the "trope" of committing suicide by putting your head in the oven, because with an oven fueled by coal gas if you blow out (or don't light) the pilot light and turn on the gas you will rapidly build up an area of high concentrations of carbon monoxide inside the oven. And if you put your head in there you will very quickly lose consciousness and then die as the carbon monoxide begins to convert all of the hemoglobin in your blood incapable of transporting oxygen.

Eventually people, mostly, grew wise to the risks of piping such potent poisons into people's homes and switched to the comparatively much safer natural gas (especially as it began to become more available with the boom in the petroleum industry).

However, I'll point out that natural gas usage is actually very old, dating back to the early iron age in some places, like parts of China which used bamboo pipes for drilling wells for shallow natural gas deposits and transporting the gas to the point of use, most especially to evaporate the water from brine in order to produce salt.

What is the point of this comment? Vera Rubin's work has been substantial and important, the fact that it built on the work of others and isn't somehow 100% novel is not some big "gotcha", that's how science works. The Special Theory of Relativity built on as much of Lorentz's work as Einstein's, if not more so. Edwin Hubble proposed "Hubble's Law" 2 years after Lemaitre proposed the same exact thing, and Hubble's work shadowed the work of others like Slipher that had established a relationship between distance and redshift. That's how science works, it's collaborative.

There are almost certainly interstellar meteorites, but they are probably exceedingly rare, and none have been identified yet, per se.

There's a much larger flux of space dust which lands on Earth, which can leave behind micro-meteorites, some of that dust is of interstellar origin.

China is the only country with a human spaceflight program that hasn't killed anyone in a spacecraft yet.

There's plenty to criticize about China and about China's space activities, but I don't see much evidence that the safety of their spacecraft is on that list at present.