Daily Shaarli
May 24, 2023
Wikipedia's information is a little ambiguous:
The booster's tanks were reported as holding 3,600 t (7,900,000 lb) of propellant, consisting of 2,800 t (6,200,000 lb) of liquid oxygen and 800 t (1,800,000 lb) of liquid methane. However, current booster prototypes can only hold 3,400 t (7,500,000 lb) of propellant.
Depending on how current "current" was when that was written, the booster carries no more than around 800 tons of methane fully loaded; 14% would be 112 tons. Add another 30% or so for Starship and we're up to 145 tons.
The total amount of methane in the atmosphere is about 5,000,000,000 tons, so this is an increase of about 0.0000029%.
Note that the FTS is designed to get combustion started, so most of the remaining methane was actually burned. Even if none of the methane burned, the destruction of another 344,000 Super Heavy boosters late in ascent would increase atmospheric methane by 1%. //
for comparison May 22, 2023 Pipeline Technology Journal: Two Fields In Turkmenistan Leak More Greenhouse Gases Than The UK: Leaks Could Be Easily Fixed estimates 2.6+1.8=4.4 million tons per year (2022) for just these two newly-discovered leaks. So the max here is 0.0002 "newly-discovered annual Turkmenistan leak units". It is true that burning it and converting it to CO2+H2O might be greener, but... –
uhoh
11 hours ago
A:
After depressurization of the cabin though there is, obviously, no environment to condition, and during repressurization fresh oxygen needs to be supplied at high flowrate from oxygen tank at cryogenic-temperature to fill the entire cabin. What heating mechanism was applied to heat up the supply of fresh cryogenic oxygen for CM cabin repressurisation?
P.S. In original question I asked about repressurization of both CM and LM, but it seems LM stored oxygen in compressed gas form rather than cryogenic liquid or supercritical fluid, therefore I have removed LM from the question.
A:
Unsurprisingly, it worked exactly like it did in shuttle.
To assure uniform flow, the capillary restrictors are coiled around a warm water-glycol line to increase the oxygen temperature.
Page 2.7-3
The aforementioned oxygen supply capillary restrictors are wound around the line routed to the space radiators and relief valves. The other line is routed to the mixing valve. To insure proper operation of the oxygen supply restrictors, in the line between the cryogenic O2 storage in the S/M to the surge tanks in the C/M during cabin repressurization, full water - glycol flow through the line to the space radiators is required. Sufficient heat must be available to prevent cryogenic oxygen entering the C/M oxygen system and preclude the possibility of freezing the water-glycol. To achieve this, the mixing valve must be manually placed to the full closed position 15 to 30 minutes before repressurization and remain closed until the surge tank returns to maximum pressure after repressurization of the C/M.
Statistical Ars Legatus Legionis
12y
50,437
Also the longer the slant the larger area the weather is impacting you. If the beam is coming in close to the horizon it isn't just the weather where you are that matters it is the weather along the entire slant potentially a thousand or more kilometers away. It could be bright sunny day where you are at and the signal has to punch through a dozen storm systems to get to you.
It is why Starlink was such a big deal for the Antarctica bases. Prior to that they were limited to very expensive MEO constellation services or a 2 or 3 GSO sats (one of the TRDS sats) that are actually at an 8.7 degree inclination instead of the normal 0. The sats are in GSO not GEO. It means the sats trace a figure eight around the equator instead of being exactly on it. It also means that they move in the sky as seen from Earth which is very much non-ideal for most applications BUT it means that for roughly 12 hours out of each day they are just barely over the horizon from the Antarctic bases to allow service. Bad news that 12 hour availability window shifts by 3 minutes each day. Being a network engineer in Antarctica prior to SL must have been a challenge prior to SL.
The Antarctic specific satellite mission is the only polar GSO service I know of. SL pretty much overnight changed that. Not only are their official SL dishes but there are now dozens of user owned terminals. Throughput to Antarctica was in the 1 to 5 Mbps range for decades and now is in the hundreds of Mbps and gigabits is possible with enough user terminals.
To date Astranis has raised $550 million and is well capitalized for growth with a team of 300 people. The company has already built four more satellites—one of which will serve a customer in Peru, two for airline Wi-Fi, and one for an unspecified customer—that will launch on a dedicated Falcon 9 mission later this summer or early fall.
Now that the company has confidence that its custom-built technology works, it plans to scale up production to two satellites a month, Gedmark said. The 1-meter-by-1-meter satellites, which have a mass of around 400 kg, will be built to serve whatever demand there is, wherever in the world it's needed.
"We’re just going to keep launching them as long as there is demand," he said. "And we think there will be a lot of demand for that. We absolutely plan to launch dozens and then hundreds."
The Brother whatever-it-is will print return labels for online shopping, never run out of toner, and generally be a printer instead of the physical instantiation of a business model.
Here’s the best printer in 2023: the Brother laser printer that everyone has. Stop thinking about it and just buy one. It will be fine!
Seriously, ask around or just look in the background of Zoom calls: there’s a black Brother laser printer sitting there. Some people have the bare-bones Brother HL-L2305W, which costs like $120. We have the $270 Brother MFC-L2750DW, which adds a sheet-fed scanner,
Max Gergel, who graduated with a degree in chemical engineering from the University of South Carolina in 1942, founded and ran the successful Columbia Organic Chemical Company. A Nobel Prize-winning biochemist once said in a speech that he was encouraged by Gergel, describing him as “an unusually nice man.”
The chemist also had a boat and enjoyed sailing, especially to a house he had in Jamaica.
He also wrote two books, including the 1977 memoir Excuse Me Sir, Would You Like to Buy a Kilo of Isopropyl Bromide? In them, he wrote about how he had helped in the development of the first atomic bomb, as well as in developing weapons for Israel.
But in that varied and interesting life, one thing was missing: a bar mitzvah.
And so, at 96, with the assistance of Rabbi Hesh Epstein, co-director of Chabad of South Carolina in Columbia, Gergel participated in the coming-of-age Jewish ceremony.
A day later, he passed away.
“He did everything he needed to do, and his journey was over, I guess,” said Epstein. “I guess that was his last mitzvah that he needed to do.”
South Africa is heading into the southern hemisphere winter with the prospect of the country's worst-ever power cuts - up to 16 hours a day. The roots of the problem lie in poor management, corruption and sabotage.
Short presentational grey line
Late one Thursday afternoon, last November, a maintenance contractor reached his hand under a huge rotating shaft at an ageing power station in South Africa.
It took the man just a few seconds to unscrew a steel plug, smaller than a coffee mug.
As he moved away from the scene, precious lubrication oil quickly began seeping from the innards of the shaft. The steel bearings inside overheated and before long the coal mill, and with it one of the station's eight turbines, ground to a sudden, and expensive, halt.
What is certain is that the sabotage at Unit 4 was not an isolated event.
Instead, it was one relatively small act in a vast, ongoing, and highly successful criminal enterprise that involves murders, poisoning, fires, cable theft, ruthless cartels and powerful politicians.
It is an enterprise that risks derailing international attempts to nudge South Africa away from its dependence on coal and towards renewable energy sources. //
At major road junctions across the nation, unemployed and homeless men now earn a few rand from drivers in exchange for directing cars when the traffic lights are off.
The image of people in luxury vehicles tossing coins to beggars for helping them navigate the country's failing infrastructure seems like a fitting metaphor for the current struggles facing this deeply unequal society.
Editor’s note: based on industry research (from Chrome and others), and the ubiquity of HTTPS, we will be replacing the lock icon in Chrome’s address bar with a new “tune” icon – both to emphasize that security should be the default state, and to make site settings more accessible. Read on to learn about this multi-year journey.
Q:
Does anyone know what the approximate Apollo cabin temperature and humidity was kept at? I am curious if the unusual 100% O2 atmosphere affected other aspects of the cabin air.
A:
From this NASA report:
https://history.nasa.gov/SP-368/s2ch5.htm
The design range for temperature and humidity control in the Apollo Command Module was 294° to 300°K (70° to 80°F) [i.e., 21 to 27 °C] with a relative humidity of 40 to 70 percent. Similarly, the design range for the Lunar Module was 291° to 300°K (65° to 80°F) [i.e., 18 to 27 °C] with a relative humidity of 40 to 70 percent.
We are in a new era. And the erasure of gay men and lesbians is intensifying.
ANDREW SULLIVAN //
These activists, marinated in critical gender and queer theory, have picked several unnecessary fights and, especially since the convulsions of 2020, have pushed and pushed a woke revolution until a dangerous backlash was inevitable. //
we have to be insistent that the gay experience is distinct and different and not intrinsically connected to either queer ideology or the trans experience. We have to demand that children’s bodies — gay, straight, trans, gender-conforming and gender-nonconforming — be left alone. And we must do all we can to make sure that the trans-queer revolution does not result in what it seems to be moving toward: the eradication of homosexuality from public life.
MMarsh Ars Praefectus
7y
3,252
Subscriptor
From a "can it be done?" tech standpoint, I think this is very cool.
From a "can you offer a profitable and economical service this way?" standpoint, I'm not optimistic, for a few reasons.
The first problem is the latency, of course. That's going to be just as bad as with any other GEO satellite. We put up with it for decades when there was no better option, but now that LEO constellations exist, a 700 ms ping time is a hard sell unless there are other compelling advantages.
Which brings us to the competition. Inmarsat and Iridium, being part of GMDSS, have the advantage in the commercial maritime market. Starlink is rapidly replacing Viasat and Hughes in the terrestrial residential, business, and vehicle-portable markets; OneWeb and Kuiper ought to be nipping at its heels sometime soon. Who is the target market for a product that can't compete with Inmarsat or Iridium on coverage, and can't compete with Starlink on throughput or latency?
And then you get to the tech aspects of it. Yes, it's possible to put a small satellite in GEO and relay comms from it, and it's an impressive technical achievement. But the physics of antennas and of RF propagation don't change. How much performance was given up to make it work with less power and smaller antennas? Could more efficient use of that same RF spectrum have been achieved with a larger satellite with more power, more spot beams, and larger antenna apertures to allow the use of tighter geometry in those spot beams?
If the target market is Alaska, then in the panhandle (eg. Ketchikan) you're aiming your ground station antennas about 35° above the horizon. That's tolerable as long as you have clear land or ocean to the south. Up in Anchorage, though, that angle drops to 29° and in Nome it's 25°. Hold your hand at arm's length, put your thumb on the southern horizon, and stretch your pinky vertically above it to full span; that's 25°. If there are trees or mountains or weather below that mark, you have no chance of using any GEO satellites from that location.
if you're going to use osb, keep the noise frequency and material mu in mind. For wood that's about 700Hz for 1". Use an app like Spectroid to determine the frequency of your rain noise. If it's 1400Hz, then a half inch will work, 2800Hz=1/4", whereas if it's 350Hz, then you'll need 2" to absorb the wavelength. You'll get hardly any Db attenuation from 1/2 wavelength thickness, and a linear-like reduction from 1/2Mu to 1Mu, where it will be mostly blocked.
Max Gergel was a Columbia, South Carolina native, 1942 graduate of the University of South Carolina, and a chemist. In 1977 he authored the memoir, Excuse Me, Sir, Would You Like to Buy a Kilo of Isopropyl Bromide? He later wrote a sequel, The Ageless Gergel. In 1998, he was featured in the Fall issue of the USC Chemist, a newsletter published by the Department of Chemistry and Biochemistry.
Anecdotal, autobiographical sketch of Max Gergel and his adventures as a young (then older) mad scientist building the business Columbia Organic Chemicals.
Despite a higher risk of a fire, pure oxygen also has some advantages.
First, the internal pressure of the vessel is only a fifth of a normal breathing mix, allowing less structural load on the hull of the spacecraft. The resupply system is also simplified, because a system including nitrogen must have an extra tank for the nitrogen. (If you had them mixed, you end up with a higher and higher nitrogen pressure over time). A small mass saving is therefore achieved. For a minimal spacecraft where you simply open the hatch and vent the cabin air when performing an EVA, pure oxygen simply means less air wasted. Nitrogen narcosis seems to not be an issue, as I find it difficult to imagine an accident of increase in the pressure.
As for the decision making process in the early US space programme, the slightly higher complexity of a nitrogen system must have felt a little redundant. The early US Mercury and Gemini also used pure oxygen, but the early Soviet spacecraft, like Vostok, used a normal atmospheric breathing mix. Note that modern EVA suits do still use pure oxygen. ///
At 5 PSI there is not enough atmosphere to support fire, even with 100% oxygen atmosphere.
Q:
I am curious what aspects of the Apollo program were impressive/advanced from an engineering perspective, in the 1960s and 1970s. That is, what would have made an educated engineer say, “Wow, they solved that problem?”
I ask the question because I know that as an engineering layperson I know I have very poor intuitions about what is technically difficult in spaceflight. For instance, I only learned from this website that maintaining 1 atm of pressure in a spacecraft isn't very difficult. Also, some technologies like pressure suits and rocket engines had already been developed. So it is not obvious (to me) what the actual innovations and engineering achievements of the program were.
A:
There was no one breakthrough that made it possible. The "big deal", in the mind of the world, was just that an obviously very hard thing was accomplished. And, if you doubted how hard it was, people can point out that no one has done it again in more than fifty years.
However, there are some good examples of challenging problems that had to be solved.
Problem 1: Rocket Size. Before Apollo, everyone thought we would send the top of a multi-stage rocket to the moon, it would land on its tail and launch again to return to earth. When you run the numbers on that, you end up with a pretty big lander requiring a lot of fuel, and a huge launcher to send it on its way; much larger than Saturn. The trick ended up being to only send down a little bug, and even leave part of that behind on the moon. If we had stuck with the giant lander we would never have been ready in time.
Problem 2: Rendezvous. The new method required being good at approaching and docking with another spacecraft. That's a hard enough problem that, even though the physics was well understood, they didn't really see the issues until they actually tried it. (I always get annoyed when characters in science fiction stories fail to foresee problems that the science should have told them beforehand, but sometimes that's how it works.) Wisely they tried it in Gemini in low earth orbit and had the hang of it by Apollo.
Problem 3: Rocket Size (Again). Even with the trick (called Lunar Orbit Rendezvous) used to solve Problem 1, they needed a much bigger rocket than anyone had built before. And so they built it. To get it to the launch pad, they built the crawler transporters, some of the largest land vehicles built up to that time, and to have a protected place to stack the stages, they built the Vehicle Assembly Building, one of the largest buildings by open volume in the world. I think seeing a tower the size of a 36-story skyscraper rise into the sky made a lot of people say, "Wow, they solved that problem?" I was too young at the time, but it was the initial uncrewed Apollo 4 launch of the Saturn V that made my dad think, "Huh, they might actually pull this off!"
There are many many more, but it was really the cumulative effect of solving thousands of hard problems that was the big deal. //
Number 2 is a small example of the large original research involved. A guy, later known as "Doctor Rendezvous", did his Ph.D. thesis at MIT on it in 1963. His next job was to fly it! Here's Buzz Aldrin's thesis: dspace.mit.edu/handle/1721.1/12652 –
Adam
May 19 at 1:38
The "slow down to catch up, speed up to slow down" stuff of orbital rendezvous was reportedly very confusing to the non-engineer test pilots and required someone like Buzz Aldrin to truly figure out. It's one thing to draw the equations out on paper but a whole other thing to actually do it in the cockpit. –
Jörg W Mittag
May 17 at 19:48
@JörgWMittag I think its still confusing to a lot of people today, mainly because of the terms "slow down" and "speed up" in that phrase are ... wrong, but appropriate? –
Moo
May 17 at 21:32
@Moo - If you go faster, you also go higher. Now that you're higher, you've got farther to go, so you're actually going slower –
Richard
May 18 at 18:36 //
A:
what has ALWAYS impressed the heck out of me is the sheer magnitude of scale involved... not physical size (although its size was truly impressive) but rather the huge number of complex problems that needed to be all solved in a complex optimization matrix to arrive at a suitable overall solution. This was the largest systems integration project ever to date and on a tight timeline. Project management on an unheard of scale and scope. That to me was the "Wow... they solved THAT problem" thing.
Yes. Apollo was a triumph of project management as much as, or maybe even more than, it was a technological feat. –
Wayne Conrad
May 18 at 2:40
I would argue that project management was born within the Apollo program. I don't think it even had a name beforehand. –
Vladimir Cravero
May 18 at 8:18 //
A:
It was fractally hard.
Everything they did was Voltroning hard problems together to solve other hard problems. And this was all done in a coordinated way on an incredibly tight timescale.
The long answer would fill a series of books. E.g. for a high level overview of the effort involved in the LEM alone, you can look at Tom Kelly's Moon Lander (and you should; it's great).
But to put a quick gloss on top of it, Apollo was not an aerospace engineering triumph, Apollo was a systems engineering triumph. Everyone solved hard problems in every field, but the real accomplishment was orchestrating those solutions in a way that led a seven-year program from zero to the moon.
Apollo systems engineering built upon Polaris (see en.wikipedia.org/wiki/UGM-27_Polaris). –
Jon Custer
May 18 at 20:42
@JonCuster Sort of, but it's more complicated than that. I'm not putting a history of SE in this answer though. Recommend Morris' "Management of Projects" from 1990 or so if you want an overview of the most relevant thread for Apollo/ –
fectin
May 19 at 0:55
The first digital logic gate built from vacuum tubes appears to have been invented by Bruno Rossi in 1930. Rossi, an Italian physicist studying cosmic rays and radioactivity, was not working on computing equipment but rather sought to detect near-simultaneous events from multiple Geiger-Müller tubes, His Rossi coincidence circuit was an n-input AND gate which identified coincident pulses from multiple detectors with a time resolution of one millisecond.
With an inverting output, this circuit would be a NAND gate 1, from which any Boolean function can be computed and flip-flops constructed as a data storage element.