Getting Started with my 3D Printer - One Step at a Time

Ten days ago, I posted about getting my 3D printer going.  Within a couple of days, I had assembled the printer, checked and double checked, then started working on the steps I need to get past to start using it.  I still haven't done anything useful with it. 

One of the essential steps to learn to do is to make the printer's bed, the surface prints are made on, both level so that the movement of the print head either in X or Y is always perpendicular to the Z axis (up down).  The movement in a 3D printer is different from that in a CNC mill.  The printer head is mounted to the X-axis, and the Z axis moves the X-axis up and down.  The Y axis moves the print bed forward and backward in the frame.   I can see why they do it this way, it's just... different from what I'm used to. 

The system controller is that little box on the right.  It has a nice little LCD, but it takes some getting used to.  I'm used to a 17" LCD monitor on a PC so much more information can be displayed and the keyboard allows more input options than the little knob at the bottom of the box.  On my PC, in whatever CNC program I'm using I can do immediate commands, like type "G01 Z2.00 F35"; which is telling it to move the Z axis to 2.00 inches (could be up or down depending on where it starts from) and go at 35 inches per minute.  On this little box, I scroll through menu selections, find "Move", find Z, spin the knob to 2.0 and click the little knob inward.  Say I send the mill to 2" but I wanted it at 3" instead.  I can hit a key that gets that entire command back, change the 2 to 3 and hit return.  On this box, I go back to Z and then crank from 0 to 3 instead of 2 to 3.  A minor thing, but their user interface could be easier to use. 

The print bed is that horizontal surface down around the bottom of the clear space in the printer's frame.  If you look at the front (closest to the camera), on the right, just below that print bed and above the blue knob, you'll see a large disk-like object.  That's the adjustment to level the front right side of the bed.  The one for the left front is visible below the left corner of the bed but it's a crowded image.  There are two identical such knobs in the back.  There is not an overall adjustment, say in the middle of the bed to lift the whole thing up and down.  On You Tube, you'll find at least a dozen videos on leveling a print bed; I ended up preferring this one.  Like learning to fall off a bike, you'll get lots of practice doing this. 

In that post 10 days ago, I mentioned learning to use a slicer program and described how it's the equivalent to CAM software for a printer.  After reviewing another handful of videos and websites, I decided to use the Cura slicer software by a printer manufacturer called Ultimaker.  They give away a home version of the software and charge for business use.  I found it relatively easy to use, but it still does some things that surprise me.  Here's a look at Cura's interface with a test design in it. 

Conceptually, leveling the bed is like tramming a mill, except I get the implication it has to be done regularly, while tramming is likely good for a long time.  The file in Cura is from that video channel I linked to before and the idea is you test your printer by printing a few passes around in that file.  You lightly rub the filament with a fingertip (the printer bed is 50C, or about 125F - hot but you're not really leaving your finger on it). This is a pass on my printer this afternoon.

On the lower right side you can see some gaps in the print.  It's my understanding that's from having the print head just a little too close to the bed and the fact it's in the front right says to lower that a little.  I did that and it did get better but I'm a bit cautious about chasing that around the system.  More tests are definitely coming.  I don't really understand how I could have two areas of thin printing, extending most of the way across in X, in two different places in Y, given how everything is adjusted.

While studying up on this printer, I find that one of the features some higher end printers are starting to come with is auto leveling.  This guy shows how to add it to my printer.  The system is called BLTouch, and it doesn't mess with those adjustment knobs, it does the correction in software.  The system measures the offset of the printer from level around the bed and then adjusts the extruder height during the print.  Given my years of designing control loops, this appeals to me, and adding this to the printer for about $50 sounds good. 

All this said, I haven't printed anything useful yet.  I had a little adapter for an experiment I want to try on my Webster engine that I designed and ported over to Cura to slice.  That's ready to print and Cura says it will take 12 minutes.  It might even print properly, since it's a small thing, 1-1/2 by 1/2" and 1/8" thick. 

It Happens Less than 5% Of The Time

But I find myself agreeing with a couple of Democrats.  Including a few that I have never agreed with: the Squad. 

It starts out almost that strange; I was looking at an article from FEE (the Foundation for Economic Education) about how Tulsi Gabbard was speaking out against John Brennan's dangerous push for new laws empowering surveillance against ‘religious extremists,’ ‘racists,’ ‘bigots,’ and even ‘libertarians.’  I've noticed a few times in the last couple of months that Ms. Gabbard has been sounding rational which led to a  "what's going on here?" reaction.   That probably prompted my noticing the article. 

I recall catching little of the Democrat primary debates, but in what I did see she sounded as loony as all the other candidates.  That leads me to say, "a politician who changes what they say with their audience - how novel," but kept noticing other quotes that were making sense.  Then she tweeted this:

@joebiden Your leadership is needed now to denounce those like John Brennan & Rep Schiff who are advocating for targeting half the country as potential domestic terrorists. Truly unite the American people around our Constitution & the rights that are endowed to us by our Creator.

In an interview on Fox News, she said this:

“We don’t have to guess about where this goes or where it ends,” Gabbard argues, “When you have people like former CIA Director John Brennan openly talking about how he’s spoken with appointees and nominees in the Biden administration who are already starting to look across our country for these types of movements… that in his words make up this ‘unholy alliance’ of ‘religious extremists,’ ‘racists,’ ‘bigots’ … even ‘libertarians.’”

“So, when you look at their process as they’re building this profile of a potential ‘extremist,’ what are we talking about?” she asked. “Are we talking about evangelical Christians? Somebody who is pro-life? Libertarians? People who attended a Trump rally?”

“[This would] lead to a very dangerous undermining of our civil liberties… and a targeting of almost half the country,” Gabbard concluded.

This is where the article takes a real hard turn into territory I never expected.  A letter signed by 10 progressive House Democrats, including Representatives Rashida Tlaib, Alexandria Ocasio-Cortez, Ayanna Pressley, and Ro Khanna, calls on leadership to “reject reactionary demands to further erode the rights and liberties of the American people."

My first reaction was that if I'm finding Rashida Tlaib saying something reasonable, I should look into some sort of counseling.  Then I read her tweet and the letter attached and felt better.  It turned I didn't need to look into counseling, just look into what she was actually saying.  Her logic is just as pretzel-twisted as always.  Her concern isn't Americans as a whole like Tulsi Gabbard appears to be saying.  Her concern is only if they're "of color" or especially Muslim-Americans.  If she accidentally gives some benefit to conservatives, that's just the price of doing good. 

Photo montage from FEE; Image credit to Wikimedia and Pixelbay.

The bottom line is that I can dismiss the squad's comments with the usual, "a broken clock is right twice a day."  Another example of the insignificant, almost-random chance of being right.  Congresswoman Gabbard, on the other hand, is making more sense.  She could be honestly changing over to more respect for the constitution.  She's ex-military after all, and could be drifting right as she gets older.  Of course she could also be benefiting from the news not quoting her when she says something insane.  At this point, though, she might be more constitutional and logical than John McCain was and seems to be more so than Mitt Romney is now.

There's Progress at Boca Chica, Just Not Flying

The last couple of days of watching the goings on at SpaceX Boca Chica have been strange.   The test flight was scrubbed due to weather on Wednesday, then scheduled for tomorrow.  Midday, the test count was halted again, this time because the FAA had notified SpaceX that their permission to conduct the test flight was rescinded.  Later in the day it became apparent the vehicle was being fueled again and viewers couldn't tell if it was to try a launch, or try to be ready to launch if approval came in, or simply another cryogenic test.

It's hard to determine what's actually happening because there's nothing published about it with enough detail to know.  Neither SpaceX or the FAA has said much of anything officially, although an FAA official made a pretty generic statement, “We will continue working with SpaceX to resolve outstanding safety issues before we approve the next test flight.”  That might seem more appropriate if this wasn't almost an exact duplicate of the vehicle from the last test and the mission profile that it flew. 

For his part, Elon Musk Tweeted:

Unlike its aircraft division, which is fine, the FAA space division has a fundamentally broken regulatory structure.

Their rules are meant for a handful of expendable launches per year from a few government facilities. Under those rules, humanity will never get to Mars.

Since everywhere else in the Fed.gov that we can see is undergoing regulatory expansion and regrowth, it's possible the FAA is looking at SpaceX again trying to figure what new, capricious regulations they could put on them and what kind of fees they can raise.  Trump ran a very laissez-faire administration and tons of redundant and outdated regulations were dumped.  Back in 2017, the administration had said that while they had asked regulatory agency heads to get rid of two old, useless regulations for every new one passed, and they had actually gotten rid of 22 regulations for every new one!

Late today, though, we got something we've never seen.  Two Starships on test stands within tens of yards of each other:

That's SN10 on the left, still being put on the test stand by Bluto the crane with Eileen to the right.  This is the launch pad camera on Lab Padre, not the usual Nerdle camera that I watch. 

Eric Berger at Ars Technica, one of the few level-headed reporters at Ars, put up a piece around the end of the day today with this take on what's going on.  He thinks there's an increased attention to safety in the area, possibly since there's still a small residential community on Boca Chica and something about the SN8 flight made the FAA more concerned about safety.  SpaceX evacuates the area when they're doing a test and puts the community up in a nearby hotel at their own expense.

They Keep Using That Word

 and I'm sure (1) they know what it means, and (2) hope that listeners don't.  

Reports are going around of Biden delivering addresses in which he is promising equity.  The Washington Times opens up with a statement that, “In the span of 13 minutes, President Biden used the word "equity" nine times. Be prepared to hear it a lot more.” 

At the televised briefing for reporters on Tuesday, White House press secretary Jen Psaki used the word five times. White House adviser Susan Rice was at the same briefing and used it 18 times.

Equity is one of those words that's deceptive so that it can get past a lot of people.  Many people confuse it with or assume it means equality, but it's actually the opposite of equality.  Equality is what made America the shining beacon on the hill.  Equality is embedded in the Declaration of Independence's statement that "All men are created equal."  Everyone has the same shot to make something of themself.  Everyone can't achieve the same results because we are never completely equal.  A population never has the same skills and desires across its entirety.  Some of us are good with math, some of us are dancers.  Some are born caring for strangers, while some are lawyers.

A dancer trying to be a consulting engineer would be about as successful as I would be in a dance off against Paula Abdul.

Equality, then, is about the starting line, not the finish line.  Equal opportunity to do what they want to do and how they want to do it and see how far they can get in life.  Equity though, is about the finish line; it's about equality of outcomes.  It says that if the dancer wants to design, for an egregious example, the flight control software on a Boeing 737 they should get the same outcome as the person who worked to become a software guru.  It's not equality of opportunity for equally qualified applicants, and what seems to be the official line is it's giving a hand up to the oppressed.  Inevitably, someone is going to get hurt.   

Meritocracy is gone.  The only way people who really aren't as good as others get the job is if the people who are better qualified are pushed out of the way.  There's not an infinite number of jobs, so if someone less qualified is put into the job, someone more qualified gets hurt.  Remember the Asian students who sued Harvard because they were pushed aside to make room for "affirmative action" students less academically qualified than they were?  Did you notice that the courts thought it was just peachy to discriminate against one group to let another group into the school, ruling in Harvard's favor over the Asian students?   Expect lots more of that. 

I find this concept drawing seems to summarize the situation pretty well. 

Equity sounds good in theory, but equity in practice rarely agrees with equity in theory.  The reality might well be nobody gets the results they want, or it might be only one of the three does.

Get used to hearing the word equity.  We're only one week into the Ho Jo administration so you'll be hearing it a lot.  Government is good at killing people and breaking things; they're good at putting people in prison.  Asking them to re-order society to improve outcomes is a mistake, provable by virtually every big program they've ever instituted.  Remember, poverty had been in a 20 year decline when LBJ declared war on it in 1964 and the poverty level reported by the Census Bureau is virtually unchanged since 1966.   

NASA's (and Our) Worst Week in Spaceflight

January 27th marks the start of the worst week of NASA history.  It's a peculiar fact that every accident that took the lives of the crew and destroyed the vehicle took place in the space of one calendar week, although those accidents are separated by decades.

 

January 27th, was the 54th anniversary of 1967's hellish demise of Apollo 1 and her crew, Gus Grissom, Roger Chaffee and Ed White, during a pad test, not a flight.  In that article, Ars Technica interviews key men associated with the mission and provides, for the first time I've seen, the audio of the test.  In the early days of the space program, one of the larger than life names we all came to recognize was Chris Kraft, who had become well known as the Flight Director who had directed all of the Mercury flights and many of the Gemini missions.  He was widely recognized for this masterful control.

Half a century later, the painful memories remain. “I was on console the day it burned,” he explained, sitting in his second-floor den, just a few miles from the control center that now bears his name at Johnson Space Center.

“I heard their screaming voices in the cockpit of the spacecraft,” Kraft recounted. “I heard them scream that they were on fire. I heard them scream get me out of here. And then there was dead silence on the pad. Within minutes we knew they were dead, and we were in deep, serious trouble. Nobody really said anything for 15 minutes, until they got the hatch open. We were sitting there, waiting for them to say what we knew they were going to say.”
....
There was plenty of blame to go around—for North American, for flight control in Houston, for technicians at Cape Canaveral, for Washington DC and its political pressure on the schedule and its increasingly bureaucratic approach to spaceflight. The reality is that the spacecraft was not flyable. It had too many faults. Had the Apollo 1 fire not occurred, it’s likely that additional problems would have delayed the launch.

“Unless the fire had happened, I think it’s very doubtful that we would have ever landed on the Moon,” Kraft said. “And I know damned well we wouldn’t have gotten there during the 1960s. There were just too many things wrong. Too many management problems, too many people problems, and too many hardware problems across the whole program.”

The ARS article is worth your time. 

The next day, January 28, is the anniversary of the Space Shuttle Challenger disaster.  Shuttle Challenger was destroyed on January 28, 1986, a mere 73 seconds into mission 51-L as a flaw in the starboard solid rocket booster allowed a secondary flame to burn through supports and cause the external tank to explode.  It was the kind of cold day that we haven't had here in some years.  It has been reported that it was between 20 and 26 around the area on the morning of the launch and ice had been reported on the launch tower as well as the external tank.  O-rings that were used to seal the segments of the stackable solid rocket boosters were too cold to seal.  Launch wasn't until nearly noon and it had warmed somewhat, but the shuttle had never been launched at temperatures below 40 before that mission.  Richard Feynman famously demonstrated that cold was likely the cause during the televised Rogers Commission meetings, dropping a section of O ring compressed by a C-clamp into his iced water to demonstrate that it had lost its resilience at that temperature.

There's plenty of evidence that the crew of Challenger survived the explosion.  The crew cabin was specifically designed to be used as an escape pod, but after most of the design work, NASA decided to drop the other requirements to save weight.  The recovered cabin had clear evidence of activity: oxygen bottles being turned on, switches that require a few steps to activate being flipped.  It's doubtful they survived the impact with the ocean and some believe they passed out due to hypoxia before that.   

Finally, at the end of this worst week, Shuttle Columbia, the oldest surviving shuttle flying as mission STS-107, broke up on re-entry 15 years ago tomorrow, February 1, 2003 scattering wreckage over the central southern tier of the country with most debris along the Texas/Louisiana line.  As details emerged about the flight, it turns out that Columbia and everyone on board had been sentenced to death at launch - they just didn't know it.  A chunk of foam had broken off the external tank during liftoff and hit the left wing's carbon composite leading edge, punching a hole in it.  There was no way a shuttle could reenter without exposing that wing to conditions that would destroy it.  They were either going to die on reentry or sit up there and run out of food, water and air.   During reentry, hot plasma worked its way into that hole, through the structure of the wing, burning through piece after piece, sensor after sensor, until the wing tore off the shuttle and tore the vehicle apart.  Local lore on this one is that the original foam recipe was changed due to environmental regulations, causing them to switch to a foam that didn't adhere to the tank or stand up to abuse as well. 

There's film from inside Columbia until the moment the vehicle is ripped apart by the aerodynamic forces.  I suspect the forces ripped apart their bodies just as fast.  

January 27 to February 1 is 6 days.  Not quite a full week.

On a personal note, I remember them all.  I was a kid living in Miami when Apollo 1 burned.  I was living here and watched Challenger live on satellite TV at work.  Instead of going outside to watch it as I always did, I stayed in the engineering lab and watched it on NASA Select.  Mrs. Graybeard was working on the unmanned side on the Cape, next door to the facility that refurbished the SRB's between flights, and was outside watching the launch.  It took quite a while for the shock to ease up.  I saw those spreading contrails everywhere for a long time.  Columbia happened when it was feeling routine again.  Mom had fallen and was in the hospital; we were preparing to go down to South Florida to visit and I was watching the TV waiting to hear the double sonic booms shake the house as they always did.   

 

I found out in 2019 from Reddit (via Pinterest) that there's a memorial on the moon to the astronauts and cosmonauts who died in the line of duty trying to make it to the moon.  No person has seen it since the Apollo 15 crew left it in 1971 when this picture was taken.  Has it survived?  Most likely.  There well may be micrometeoroid impacts, but probably nothing big.  The moon gets a meteor impact big enough to be seen from Earth on occasion; I'll bet that if they knew the Apollo 15 site had been hit, we'd have been told.  Whether the list is legible or not is a different question.  

The failure reports and investigations of all three of these disasters center on the same things: the problems with NASA's way of doing things.  They tended to rely on "well, it worked last time" when dealing with dangerous situations, or leaned too much toward, "schedule is king"; all as a way of gambling that someone else would be the one blamed for delaying a mission.  Spaceflight is inherently very risky, so some risk taking is inevitable, but NASA had taken stupid risks too often.  People playing Russian Roulette can say, "well, it worked last time", but having worked doesn't change the odds of losing.

 

In the story the other day about the FDA not approving another Covid vaccine, we talked about bureaucracies and how people get in trouble for doing the wrong thing, not for failing to do the right thing.  NASA has become an arthritic bureaucracy barely able to move.  I've worked on a satellite for the JPL and have been in tangent circles to NASA several times.  Insiders always thought the most amazing thing about NASA was that the engineers and technicians occasionally accomplished things despite the leadership.

 

Texas Tank Watchers - High Alert Tuesday and Wednesday

Starship Eileen (SN9) was declared flight ready for her hop to 12.5-kilometer (~40,000 ft) today.  The test flight was scrubbed due to weather, with winds consistently running around 20 mph and gusting to over 30.  Winds are looking to be better tomorrow, so if you want to watch and see if they've successfully fixed the issue that caused SN8 to crater the landing pad, start tomorrow.  Road closures are set for 8a-6p CST (1400-2400 UTC) and flight TFRs have been issued for Jan 26-27, same times.   

My personal take, just based on watching the operations there and the SN8 test flight, is that it's more likely to be later in the day; like after 3PM CST.  Today's operations narrowed that down to closures running noon to 6 PM and before the scrub there was public talk that it would be 4PM.

Over the weekend, it was possible to see them installing the Flight Termination System on Eileen's side.  Twitter user Jack Beyer posted this picture with the statement:

Starship SN9’s flight termination system has been installed! Pretty sure these two little white boxes are responsible for ending things in the unlikely event the vehicle gets out of control.

As you can see, Jack Beyer photo credit to NASASpaceFlight.com.   

Note that unlike last time, there is no indication that there will be a SpaceX live stream of this test flight.  I'll check again, possibly up to the last minute, but nothing to report at the moment.  Another consideration is that they're slower than they've usually been at changing the coming launch website for the next launch.

A Modification to my Webster Engine

After I got my engine running for the first time, a few people told me they thought it was shaking too much.  Some said it's a common problem with these little engines.  One or two told me they had modified their engine to make it more resistant to the forces causing it to wobble. 

The best place to start is to simply ask why does it wobble?  It seems to come down to the way the cylinder and head are supported.  Most everyone has seen that things supported just by one end aren't very secure compared to support at both ends or multiple points.  The cylinder is supported at one end; ideally it might be best to support it at both.  The head is mounted to the cylinder by four small diameter screws.  It's held to the base plate by one big screw and to the frame by two small screws on one side.  The cylinder gets the piston being pushed hard into it, and then being pushed hard back out by the combustion explosion.  The cylinder seems to rock forward when the piston pushes into the cylinder and then rock back down when the piston is pushed back out.

It just seemed if I could support the head and add resistance to movement forward and backward, that it should improve things.  This is what another modeler on forums said he had done. 

OK; so how do I do that?  The best place to add reinforcement is farthest from the plate, where the torque is the highest.  The problem is that the cylinder head isn't a big assembly and it's tough to find a place where a screw doesn't interfere with something.  The top of the head, the part holding the cylinder, is 1.500" inches across, and the combustion chamber is a 1.00" diameter by 0.5" deep bored out area, leaving a maximum of 0.250" between the walls and damaging something.  In the corners, where there's the most metal for me to put a screw into, the mounting 4-40 screws for the cylinder are located.

I started working on the drawings, looking for a place to put a couple of screws and quickly realized that the screws present in the assembly aren't shown as hidden lines, the convention in engineering drawings.  There was a note on the drawing that said, "Hidden lines omitted to help clarity."  Great.  I had to add them.  I found a place to add a couple of screws on the opposite side of the assembly from the two #6-32 screws.  I opted for #8-32 screws.  It would double the amount of resistance to the torque it's exposed to, but is it enough? 

With the two new holes, I laid out a small bracket to screw to the head on one end and into the base plate on the other (bottom rectangle).  You can see lots of hidden lines in this view; I added all of them. 

A little search around the shop led me to a piece of scrap the same thickness as the side plates (5/16" or 0.313").  It's left over from when I cut the two side plates in June of '19.  It had an odd shape, but I just needed to trim and square it up a little to have something usable.  A second search led me to find exactly two screws for each of the two places.  That meant I had what I needed to clean up the scrap and make a brace.

To be honest, taking my engine completely apart to add this is just about as appealing as rolling in a fire ant mound, so I spent some time trying to figure how to transfer these holes to the engine.  First, I'd clamp that bracket to the cylinder and use it as a guide to drill and tap the #8 holes.  Once it was held in place, I could measure the distance from the centerline of the two new, vertical holes to the two holes on the bottom right of the brace in my CAD program and then move the engine onto my mill (best drill press I have) to drill the holes to match the base. 

It actually all went together easily. I was mildly surprised but happy.  Pay no attention to the fact that the two 8-32 screws on the side holding the new bracket don't match.  One isn't stainless.    

Does it work?  I don't know.  I haven't had the time to test it, yet.

Rocket Lab Among the Select Few

This week, Rocket Lab had their 18th successful launch of their Electron booster from Mahia, New Zealand, like the majority of their launches, raising the number of satellites they've deployed to 97.  They use catchy nicknames for all of their missions, this one was "Another one leaves the crust."  The video here starts around t-1:00 minute and lasts through roughly 11 minutes after launch. The entire video is 53:48.

Rocket Lab has emerged as one of the select few in the small satellite launch business.  They seem to be a market leader.  With Virgin Orbit's successful mission to orbit, they've joined the club.  SpaceX, while focused on larger payloads, has developed a ride sharing mission approach that makes them a power player in that market segment, too.  They were scheduled to launch a Falcon 9 this morning that was to carry a record 133 satellites into orbit (the current record is 103 satellites carried on one mission) but it was scrubbed due to weather on the Cape.  It's set for tomorrow at 10:00AM EST on the Cape. They've already carried smaller ride share missions, two or three satellites, on their Starlink missions. 

Author Jamie Groh at Teslarati, thinks the number of launchers is going to grow this year.

Expect SpaceX, Rocket Lab, and Virgin Orbit to be joined by other small launchers looking to break into the market sooner rather than later. Another NASA Venture Class Launch Services provider, Astra – a California-based small satellite launcher that launches from Kodiak, Alaska – narrowly missed beating out Virgin Orbit for the third-place slot in the competition to deliver small satellites to orbit.

On December 15, 2020, Astra launched its small orbital-class vehicle, Rocket 3.2, for the second time from Pacific Spaceport Complex on Kodiak Island, Alaska. The vehicle soared past the Kármán line with the upper stage reaching its targeted altitude of 380 kilometers at 7.2 km/sec but falling just shy of achieving orbital velocity at 7.68 km/sec.

Astra believes the fix to achieve orbit is easy and they're planning to launch for paying customers on the next mission.  And that's just getting started.  Firefly, as reported at the start of the year, is preparing the first launch of their Alpha booster from Vandenberg Air Force Base, "soon."  

In December 2020, Astra and Firefly were awarded Venture Class Launch Services Demonstration 2 firm fixed-priced contracts by NASA’s Launch Services Program along with a third small class launcher, California based Relativity Space. Astra received $3.9 million in funding while Firefly was awarded $9.8 million and Relativity received $3 million to place CubeSats in Low Earth Orbit.

Firefly Alpha, first stage, prior to shipment to Vandenberg.  Firefly Aerospace photo.

The linked Teslarati article points out that there is a movement to smaller satellites such as CubeSats because it's more accessible to smaller companies, college research, and potentially individual researchers.  Lower cost access for these small payloads will help them and potentially create even more to launch.

I think it's safe to say we have broader access to space than ever before, and it's getting broader.
 

How Quickly The Images Return

Remember the recurrent imagery of Barack Obama as if he had a halo?  Talked about here in the first year of this blog, in 2010 which was the second year of the Obamanation.   Images like this were everywhere.  Obama with some back lighting like this or something that was more halo than background.

Back when I posted this, I captioned it, “White House photo - doing their part to feed the messianic image.  An excellent summary of some of the messianic imagery is here.”  Surprisingly, the link is still there and while it has its share of dead links, it has plenty of images to show what I'm talking about.

So what?  This week, The Blaze showed this image from the current issue of Jacobin, a magazine of the Democratic Socialists of America.  Nope.  No links from me. I don't want to give them even one hit of traffic.

Looks like we're instantly back in the regressive days of the Obamanoids.  The center figure, bigger than all the rest, is Biden.  Partly reminiscent of the Birth of Venus by Botticelli, but I'm sure intended to be Jesus.  In fact, if Biden is Jesus, above his head at the apex of the picture you find Obama.  Higher than Jesus?  Obama must be God!  Just below God, but higher than Biden, we find the Hildebeest; the Billary Clintons.  To his left from this view, we find Mario Cuomo and since he seems to be in supplication to someone in a white lab coat and holding a bottle of an injectable something, the white-coated guy must be Dr. Fauci.  To his right we find Comrades Pelosi and Schumer kneeling in reverence. 

The next level down, but still with halos and angel wings, must be news media.  Note the Twitter logos alongside Biden's knees and his ears.  On the right we see an interviewer and camera operator.  On the left, we see a group reading a book.  It's shame the title isn't legible.  Below Biden, well that's us commoners, just deplorable normies. Notice everyone above the very bottom has angel's wings.  Media hacks, doctors, corruptocrats, all get angel wings.  Workers who pay taxes to support all those parasites?  Not so much.

Note at the top, on either side of God, we find stylized military drones.  The better to smite you with! 

There have been many photos showing Biden with something that resembled a halo, like this one, but it takes an insane artist to produce something like the Jacobin cover.   

We're off to a gut-wrenching start with various voices on the left and in the administration vowing to deprogram anyone more conservative than Stalin, or worse than deprogram.  There was that lawyer from PBS (now unemployed) who said the Fed.gov should take all children of GOP voters and send them to re-education camps.  We've had the introduction of a bunch of irrational policy changes.  It's looking like the middle of the Obama administration all over again.  

If I think about it, I throw up a little.

Getting to Know the New Tools

At the end of my postings on rearranging the shop back on the 9th & 10th, I mentioned part of the reason was to make room for a 3D printer in the shop.  As I mentioned then, the starter printer I bought was the Creality Ender 3 V2.  After a problem with UPS, chalk it up to the shipping backlogs people are talking about, the printer arrived on the 16th, originally promised by the 11th.  After spending time getting my engine to run, today seemed like a good day to assemble the printer.  It's mostly done, except for the final stages of setup and a thorough check out. 

Creality photo, but you knew that.

Why did I go down this road?  Like lots of people, I've been intrigued by things I've read about 3D printing, known more broadly as AM - Additive Manufacturing, while the more familiar kind of machining is subtractive manufacturing.  Say I want to make something like the cylinder on my engine, very visible in the video Tuesday.  I start with a piece of metal, in that case a steel bar, and then using various tools and machines, subtract the right amount of metal in the right places until it matches the drawing.  With additive manufacturing, I'd start with nothing and then add material until it was done. 

Printing metal is far beyond what I can do, but as printers have become more common, more and more people are using the 3D printer to create tools to see how they can improve their work.  I was really surprised to see these guys using plastic tools to bend sheet steel 0.134" thick.  This was PLA plastic, the most common kind and not one we think of as being strong.  I've more regularly seen guys printing things that I'd think wouldn't be strong enough, like one guy who printed bevel gears for an engine he was working on and it worked.  I can't believe it's as strong as one cut from metal, but it was definitely strong enough.

A couple of years ago, I did a post on how to make metal things from plastic prints.  At the time, reader Ratus and I had a conversation in the comment section.  He said he was surprised I didn't have a printer already, to which I replied I was a bit surprised, too, but I was considering making one.  At that point, Ratus said something that stuck in a background process in my head, "Build? Ha! ... You can't buy all of the parts for one as cheap as an ender3 'kit'."  That's what put the idea of that particular printer in my mind.

A month ago, I put together an email to him and asked some questions, basically if that was still true and still a good way to go.  Ender has many model printers and I was seeing several newer models.  He was a great help in getting to this point.

The learning curve now is going to be centered on learning to use the Slicer software provided with the printer, at least at first.  The process is very similar to what I've been doing with my CNC machining.  Parts are designed in CAD and then go through the slicer, which is a different kind of CAM (Computer Assisted Manufacturing) program.  When presented with a solid model, all the software knows is the outside shape of the solid.  The CAM program outputs the path of a cutter that takes away (subtracts) everything except the shape.  You tell the slicer how thick the walls need to be and how much fill-in plastic is needed between those walls and it turns those into the slices or layers that the printer makes.  The printer puts down thin lines of heat-softened plastic. 

This shows the density of fill-in as a percentage of space inside a group of cubes. There are virtually catalogs of what the fill could look like instead of little hex-like bubbles: sharks, cats, honeycombs, you name it.  As density of the fill goes up, so does strength, weight and the amount of filament in the print.  It's another learning curve to climb.

Today's SpaceX Starlink Launch Set Several Records

SpaceX set four new records for the company but those tend to become mileposts other companies know about and see.  We were able to get a good view of the launch heading off toward the northeast, with liftoff at 8:02 EST this morning.  It was 49F with calm winds and the skies just had scattered, thin clouds. 

First record: this was the eighth launch for booster B1051.  A completely nominal launch with the 60 satellites deployed on schedule. 

Second record: B1051 landed successfully on the drone ship Just Read The Instructions - just as nobody has launched an orbital class booster eight times, nobody has landed a booster eight times. 

Third record: the turnaround time for B1051 since its last mission was an astounding 38 days. Just last summer, SpaceX broke the 35 year old turnaround time record set by the Space Shuttle Atlantis, which had been 54 days, with a second launch in 51 days.  Everyone had been making a big deal about cutting the old record by 3 days.  The leap from 51 to 38, 13 days is 25%, compared to the 3 day jump last summer is dramatically different. 

Fourth record: this requires a bit more explanation.  Today's launch was originally set for Monday (which would have been 36 days) but was held due to weather in the recovery zone.  The winds and seas were out of the limits for the recovery ships SpaceX has been using.  They decided that the winds were "close enough" to try; if the recovery went normally and the booster was in good shape, that extends their flight envelope.  If it didn't, and they lost the booster, then they had to stick to the lower wind limits.  B1051 nailed the landing. 

It has been frequently reported that the Falcon 9 was designed for 10 launches without "major refurbishment" - whatever that means.  They are inspected after every launch and anything questionable is either repaired or replaced.  B1051 is the most flown rocket in their fleet.  If they did even 50 day turnarounds, they could reach 10 flights with this booster in less than four months.  They have two more that have seven flights (if I'm remembering correctly) so that it seems like a safe bet they'll get to 10 flights of one booster this year.

A Major Milestone on my Tiny Engine

It ran for the first time today.  

The two weeks since I last wrote about trying to get the engine running haven't had any startling revelations.  Part of reason for the rearrangement of the shop two weekends ago (around the 9th and 10th) was to take a break from the engine.  I returned to it by around last Thursday and had gone through a lot of things to get the engine to turn over, including a diagnostic test of when the spark happens and a test of whether or not compression was adequate.  Nothing made a difference and let it run.  Last night, I took a used second string off a guitar because it was .013 diameter instead of the .015 I used on the one spring I've had doubts about.  Again, it wouldn't turn over and run.

Today, I remembered someone suggesting that I spin the flywheel faster while trying to get it to start.  I have a nearly 40 year old Black & Decker 3/8" VSR (Variable Speed Reversing), AC powered drill and compared it to the Ryobi drill-driver I've been using and it did seem to be faster.  So I tried the old B&D drill and the engine turned over and ran with very minimal playing. 

All in all it ran for maybe three minutes.  When it first started running I turned to grab my camera and turn it on, but it wasn't there.  I'd left it in the house.  I nearly ran into the house to grab it, came back and when I was trying to put the camera on the tripod, the engine (predictably) stopped running.  It took a while to get it to run for an extended run and not just 10 seconds now and then, but it finally ran and I hit the record button.  This one minute long video has a surprise ending.  Well, it surprised me.

I first tried to start the engine on December 8th.  I posted about the first part I made for this engine May 30th, 2019, about two weeks after deciding to make the Webster instead of the much more complicated engine I had been considering up till then.  Part of 2019 had no work done because of repairs I had to work on from our lightning hit on August 1st of '19, but I eventually got back to it.  Point is I've been working on this little engine one part at a time for over a year and a half. 

What next?  Well, as tempted as I am to say I'm done, I want to see if I can make it run a little better. It won't run for long periods because there's no radiator and cooling system - just room air.  But it would be nice to see if I can get it to run for a 2-3 minutes without fooling with things for more than 3 minutes to get it to start.  Then it will be time to mount it on a plaque and retire it.

Virgin Orbit Earned Their Name

Yesterday, Virgin Orbit became one of the rare group of companies that privately developed a rocket and successfully launched it into orbit.  The special twist is that with its LauncherOne rocket dropped from a 747 aircraft, the California-based company has become the first to reach orbit with an air-launched, liquid-fueled rocket.  Just last June, seven months ago, their last attempt ended in the loss of vehicle moments into the flight.  The fact they recovered and made it on their second try is noteworthy.

"This magnificent flight is the culmination of many years of hard work and will also unleash a whole new generation of innovators on the path to orbit," said Sir Richard Branson, the founder of the company. "Virgin Orbit has achieved something many thought impossible."

Something that struck me as unusual is that this flight had paying customers for small payloads into orbit; an ELaNa mission for NASA, Educational Launch of Nanosatellites.  It seems like quite a bet to gamble on a rocket that has never launched successfully.  The LauncherOne rocket paid off on the bet and delivered all nine satellites to orbit.

LauncherOne is a two stage rocket, and the upper stage reportedly was fired multiple times, leading to a very good test of the system. 

An air-launched rocket like this has some advantages over a ground launched vehicle; the "first stage," in this case a Boeing 747 called Cosmic Girl, is fully reusable and the aircraft has a wonderful history of reliability as well as a known ability to operate safely in inclement weather compared to launch from the ground.  Those upper stages that the rocket represents are still challenging.   

Compared to a reusable booster called the Falcon 9, LauncherOne gives up a lot of performance.  The F9 booster carries the second stage much higher, typically around 70 km or ~230,000 feet, and going much faster.  A 747 will fly around 35 to 40,000 feet.  The F9 at Main Engine Cutoff (MECO) will be going around 4500 miles per hr, while the 747 will be around 600 to 700 mph.

Air launched rockets have been done before, notably the Pegasus, which may now be an obsolete program, and which was a solid fuel rocket, not liquid fueled like LauncherOne.  Something not many people stop to think about is that when a rocket like that F9 shuts its main engine, the upper stage starts slowing down.  Because of that, they start the second stage quickly, within about 4 seconds, giving the booster just a sideways nudge to get it out of the second stage exhaust plume.  When the 747 drops LauncherOne, it also starts to slow and fall down.  Virgin Orbit had to design a liquid-fueled rocket that could be dropped horizontally from an aircraft, ignite its engines, and rapidly orient itself into a more vertical trajectory. 

A rocket dropped from an aircraft cannot ignite its engines immediately due to the proximity of the plane and its pilots. In the case of LauncherOne, the rocket's NewtonThree engine is ignited 3.25 seconds after being dropped. Main engine start comes at 5.2 seconds. During this time, the rocket is falling and losing the velocity it gained from the aircraft at about 30,000 feet.

Boeing 747 Cosmic Girl with LauncherOne on the release pod - Virgin Orbit photo.

It might not be "fair" to compare the LauncherOne to a Falcon 9.  The F9 carries bigger payloads; something like Rocket Lab's Electron might be closer to a 1:1 comparison, but it's reusability isn't really established yet; they've recovered one booster by picking it out of the ocean. 

Congratulations to the Virgin Orbit team!  Rocket design is hard; orbital rockets are harder.  It's good to see success.

Turns Out the FDA is Blocking Another Covid-19 Vaccine

Remember this post from the end of December, about how the first Covid-19 vaccine was available in January of 2020, but the FDA wouldn't approve it?  They wouldn't allow volunteers who would take the vaccine be exposed to the virus because it wasn't protocol. 

The FDA prohibited rapid "challenge trials"—where volunteers take the vaccine and then expose themselves to the virus in a lab, rather than waiting agonizing months to see how many catch the virus "in the wild." The challenge trials could have proved the effectiveness of the vaccine in weeks or a month or two. The FDA considered the risk to the volunteers to be too high.

The December article was based on one from the Foundation for Economic Education, and FEE does it again this weekend with "The FDA Is Holding Up a Cheap Vaccine as COVID Deaths Surge" by John Miltimore, Managing Editor.  This one concerns the Oxford-AstraZeneca vaccine, developed as its name implies, by Oxford researchers and produced by AstraZeneca.  In summary, it's based on a better known technology than both Pfizer and Moderna's vaccines (modification of an adenovirus - a cold virus), it's easier by far to handle than Pfizer's, still easier than Moderna's and it's the cheapest of the three vaccines by far. 

From American Council on Science and Health, November 2020.

The ability to handle the vaccine by keeping it between 36 and 46 F which most standard refrigerators will do, as opposed to -94F (Pfizer) which takes extraordinary measures and -4F (Moderna) which most standard freezers can do, will save money in getting the vaccines distributed.  Add that to $4/dose instead of $19.50 (Pfizer) and $37 (Moderna) and the economics are a slam dunk win for AstraZeneca.

The strongest argument for the AstraZeneca vaccine, though, may be the bottom line in that comparison.  AstraZeneca can produce and ship almost three times the amount of vaccines that Pfizer and Moderna can ship - combined.  Between the three, should we keep a commitment to using all three, that's likely enough to vaccinate everyone in the US that would accept vaccination.  (Note that all three require two doses)

Oh, the AstraZeneca vaccine has been approved by and is being administered in the UK.  It is being produced in Baltimore.  Really.  Baltimore.

It's worth pointing out the story behind the strange effectiveness rating of the AstraZeneca vaccine, of "62% to 90%" in the third row of that chart.  In the initial test, someone accidentally miscalculated the dosage and the experimental group got half the required dose on the first shot.  The mistake was found and the dosage doubled to normal for the second shot.  That group had 90% effectiveness.  When they did the second group with the "proper" dosage for both shots, the effectiveness was 62%. 

Peter Openshaw, professor of experimental medicine at Imperial College London, said the finding that a smaller initial dose is more effective than a larger one is good news because it may reduce costs and mean more people can be vaccinated.

“The report that an initial half-dose is better than a full dose seems counterintuitive for those of us thinking of vaccines as normal drugs: With drugs, we expect that higher doses have bigger effects, and more side effects,” he said. “But the immune system does not work like that.”

So what's up with the FDA?  Last time I remarked that it was a CYA move.  Someone said why should they care when nobody is ever held responsible for mistakes in Washington.  It's a bit more than that.  The FDA, like all agencies, is not there to protect the population, it's there to establish and follow procedures, as this two year old twitter exchange between Thomas Sowell and Christopher Manion talks about.  Both of them are very right.

In the Aerospace world where I worked all my career, the situation at my level was more results oriented than a bureaucrat, but it was common knowledge to talk about the guy who would sit in front of the Senate or House, on the evening news, saying he had no knowledge of the bad things going on.  

In a situation like this, think of the two errors that the FDA could possibly make.  Think of some dude at a desk where he wants to work without making waves for 40 years and retire with a fat pension.  Most especially, he really, really doesn't want to be the guy telling the senators running the inquiry that he did anything other than the black letter procedures he's supposed to follow.  He can make two mistakes.  He could approve a bad drug and cause lots of harm to people, or he could fail to approve a very good drug and still cause lots of harm to people.  In the first case, he's more likely to be sitting in that seat in front of the inquisition committee explaining why approving the bad drug was following procedures properly.  In the second case, when he fails to approve a good drug, people die but the bodies are buried in an invisible graveyard.

Bureaucrats get in trouble for doing the wrong thing, not failing to do the right thing.

SLS Green Run Engine Test Aborts After 67 Seconds

The SLS Green Run test of the core stage at Stennis Space Flight center aborted after about 67 seconds today.  The intended test was to be 8 minutes but somewhere just a few seconds short of the shutdown, the NASASpaceflight.com video narrators said they heard something like "MCF" - Major Component Failure - and soon thereafter the engines shutdown. 

Video capture about 30 seconds into the test. 

The commentators on the video say that before the test, someone (Boeing rep.?) had said they'd get just about everything they needed with a minute and a half test, so they came up short of that.  Not to put too much of a smiley face on the situation, but the test is also supposed to test things like the way the software would handle a contingency, and that apparently worked properly.  Everything seemed to shut down in a controlled way.  Nothing was apparently destroyed - the core stage is still in the test stand after the shutdown. 

Unfortunately, being a weekend, we're not likely to see anything official out of the SLS program discussing this for at least a couple of days while they analyze their data and try to understand why the system shutdown. 

The Origin of the Meme

Jason Buttril, the chief researcher for The Blaze network was researching the Refuse to be Silenced poster that many of us have talked about.  He found this obvious ancestor.

Screen capture from the BlazeTV live feed Thursday morning.  If you look closely at the full sized version, you can see the picture of Lady Liberty is degraded on the newer compared to older version.  Perhaps just copied from it and the degradation from successive copy generations?

Kinda puts the final nails in the coffin of the idea it's from right wing organizations, though, doesn't it? 

Thought I'd share. 

Eileen Not to Fly Real Soon

Strictly my take. 

When SpaceX completed their first-ever day with three tests of SN9, Eileen, on Wednesday the hop to 15 km seemed like the next thing we'll see.  That was Wednesday, today is Friday.  A few hours ago, Space.com reports that SpaceX has swapped out two of the three Raptor engines, which tells me they'll be doing another set of tests and static fire of those new engines before it flies. 

"Two of the engines need slight repairs, so will be switched out," SpaceX founder and CEO Elon Musk said via Twitter early this morning (Jan. 15). 

Musk did not give a target launch date for SN9. But he did say, in another tweet, that it's "probably wise" to perform another static fire with the vehicle after the engine swap is complete. So a weekend launch for SN9 seems pretty unlikely.

To say the Raptor is a complex engine is a bit of an understatement, but the advancements in engine design are what allowed it to set the world record in chamber pressure of 330 bar or ~4800 psi, corresponding to about half a million pounds of thrust in the relatively little engine.  It is frequently reported to be the first full flow, staged combustion cycle engine to be developed and fly. 

What does 330 bar mean?  For comparison, the Rocketdyne F1 engine that powered the Saturn V had a chamber pressure of 70 bar - a bit more than 1/5 the pressure of the Raptor.  The F1 engine was gigantic and used that 70 bar (1015 PSI) to achieve 1.52 Million pounds of thrust.  The Raptor is smaller and looking at half a million pounds of thrust.  That just means a vehicle needs three times as many Raptors as F1 engines to have the same thrust.  The Saturn V had five F1 engines; Starship Heavy will have 28 Raptors (last I saw).  That's 14 million pounds of thrust at liftoff, the most power rocket ever built, by far.

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On a different topic, but still from SpaceX Boca Chica, Teslarati reports that another test tank prototype is being built to pressure test - to destruction - assembly techniques and a different, lighter design.  The biggest difference is the use of 3mm in place of the current 4mm stainless sheet.  Thinner steel but the same alloy.  Remember SN7.1?  Same concept.  This test tank is already being called 7.2.

No dates are mentioned when this test might be done. 

The Intersection of Old Film Photography And Modern Makers

Something completely different that I find insanely cool, although I have no particular desire to own one or get involved.  

First, a little Grandpa Simpson story to get you acquainted.  When I was first getting interested in photography, the only big name cameras I knew were 35mm.  Nikon.  Canon.  Pentax.  Still the big names in photography. It took me a few years to get one and by then I had learned the reality that if you want to enlarge a picture, the bigger the negatives the more you could enlarge it.  I learned about view cameras that took glass plates as big as 8x10.  I had seen that for trips to the moon, not just once in a lifetime, but once in human history photography, NASA had used Hasselblad cameras as they had been using for most of the space program.  For use on the moon, they couldn't bring a large format view camera, taking pictures was a sidelight to the other things the crew had to do, so they brought a medium format camera, generally 6 by 6cm, smaller than the impractical cameras but considerably larger than the 35mm film at 24 by 36mm.  The film format you can buy is called 120 or 220, depending on the number of shots it will allow.

The advantages of the bigger film led to medium format being a high end camera for the very serious photographers or those that could justify the expense.  That was the case in the 1970s and for as long as I kept track.  

Imagine my surprise when Digital Photography Review (DPR), the weekly photography newsletter I get, featured an article, "These open-source medium format cameras are 3D-printed."  The article links to the store and story of Dora Goodman in Budapest, Hungary.  Ms. Goodman's company gives away the plans to print the camera parts yourself, or will sell you a finished Goodman Zone camera body for as little as $113.40 while the holiday sale is still in effect.  The body appears patterned after a very popular medium format camera, the Mamiya RB67  (from Mamiya Sekor, another major Japanese camera maker).  It currently uses the Mamiya film backs, although they will be selling their own backs soon. 

Now this is simply a camera body; a light-tight box with ways to interface to a lens, a shutter, and not much else.  Especially not a lens.  You may know that in the 35mm world, a "standard" lens is around 50mm (its photographs match most closely to how we see real life than focal lengths much shorter or longer); in the 6 x 7 cm world the equivalent is around 80mm.  A quality 80mm lens is going to set you back much more than the cost of the body.  For several lenses, you might need to sell a kidney.

PetaPixel, a serious photography devotee's place, did a story on these cameras and has more depth and lots more pictures, and there's a ton of links on both DPR and PetaPixel.  Like I said, I think it's insanely cool although I don't have much interest in following into medium format photography again.  It's cool because it's part of the paradigm of the convergence, the new industrial revolution.  It's personal fabrication; the intersection of home CNC, 3D printing, continually more powerful digital electronics, into what's called the Maker movement, in which interested people out-innovate the big guys.  It's a drum I've been beating on for years.

A Remarkable Day at SpaceX Boca Chica

I've been watching the activities at Boca Chica for quite a while now, and today was probably the most remarkable day of testing I've seen.  Like many people, I started watching the Lab Padre feed around mid-day in hopes of a static fire test.  Last night, they had extended the 8A to 5P road closure and were working toward a static fire by 8PM (CST).  That attempt was aborted in the last minute, prompting concerns and belief that they'd be troubleshooting and trying to repair whatever it was.  After that I was expecting to see a static fire at some point, no matter how late in the day

I never expected to see three static fires in one afternoon.  They've never done three static fires in one day before.  I'm not sure they've ever done two within 24 hours before. 

As you can see from the text at the bottom, this firing happened at 12:28:51 local time.  Right away, it didn't look like last night's attempt.  Within seconds, certainly within a minute of last night's abort, the vehicle was venting large clouds and conventional wisdom was Starship was detanking.  That didn't happen after this firing.  Soon, someone posted that Elon said they were going to do multiple firings today. 

To be clear, that time tag is EST, so 1:06 at Boca Chica, roughly 40 minutes after that screen capture.  I'm not sure what he was referring to as "two starts completed," unless one was some other time. 

By the end of the day that doesn't add up because they went on to have two more static firings today; the three were at 12:28, 2:23 and 3:37 PM.  Musk later tweeted, "all three static fires completed & no RUDs!" (Rapid Unplanned Disassembly). 

The next big milestone is clearly their launch for their re-try to do the same hop that SN8 almost completed. They believe they've got a temporary fix for the pressurization issue in the small header tank that they experienced on SN8, although they're said to be trying to come up with a fix that doesn't depend on helium as this one does. That's one less thing to take to Mars and one that requires special handling.  That flight will probably be Friday, but I have a hard time keeping up with these guys.  I can see them going for it tomorrow if the situations allow.

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While on the topic of space news, I went in search of when NASA intends to do a full up firing of their SLS core stage during its Green Run Testing.  According to the SLS website, NASA is now targeting this coming Saturday, Jan. 16 for the test. 

The Green Run test series is a comprehensive assessment of the rocket’s core stage prior to SLS launching Artemis missions to the Moon. The core stage includes the liquid hydrogen tank and liquid oxygen tank, four RS-25 engines, and the computers, electronics, and avionics that serve as the “brains” of the rocket. NASA has completed seven of the eight core stage Green Run tests, including loading and draining propellant for the first time during the most recent test, the wet dress rehearsal, on Dec. 20. During the upcoming hot fire test, all four engines will fire to simulate the stage’s operation during launch.

This will be a major milestone because the system has never been tested before and it will run for the full 8 minutes expected for a mission to orbit.  True, they're using space shuttle main engines (SSMEs) and those have an extensive and excellent life history, but the rest of the vehicle is nowhere near that mature.  The test will not be televised or video live streamed (at least this posting doesn't say so) but one may apply to listen to it by audio telecast on a conference call.  Details at that SLS Website link.