NASA Artemis 1 going to the Moon (launched Nov 16)

[pinball1970]

Watched the launch last night from about 8:15 PST. ( With my fingers and toes crossed). Had to hit the hay shortly after. Glad to hear that everything went smoothly after that.

It launched as I was on the way to work. Glad it went well.

 

[mfb]

I don't think solid rocket boosters are a good choice, especially not with crew - but they make liftoff look really cool.

 

[.Scott]

I found this space.com article interesting.

With Artemis 1's launch window ticking away on Tuesday night (Nov. 15), Cairns, Garrett and Annis arrived at the mobile launch platform(opens in new tab) underneath the highly dangerous SLS vehicle at 10:12 p.m. EST (0312 GMT on Nov. 16) to stop the leak — and fast — or risk losing this launch opportunity. Once at the platform, the crew discovered that the packing nuts were "visibly loose," according to a statement by launch commentator Derrol Nail on NASA TV's media channel.

It is certainly "highly dangerous", but certainly comparable to the risk that the Astronauts will work with during the final minutes before the launch.
But it's the "visibly loose" that caught my attention. Before reading that, I was imagining something way more subtle.

 

[Borg]

Another interesting quote from the article:

In a testament to how rare the dangerous procedure was, NASA TV commentators interviewing the Red Crew added that Cairns said he has served on the crew for 37 years and had never before been called in for a repair on a fully-fueled rocket before last night's daring excursion.

 

[berkeman]

I found this space.com article interesting.

NASA's daring Artemis 1 'Red Crew' saved the day for the launch to the moon.

I wonder if the folks there at NASA have the same saying for their Red Crew that folks on our aircraft carriers do for their purple sailors: "If you ever see a sailor wearing purple who is running for any reason, run along with them". (The "Fuel Handlers" are in charge of refueling the aircraft and are identified by their purple colors)

 

[.Scott]

"If you ever see a sailor wearing purple who is running for any reason, run along with them".

The flame propagation speed for H2 can be about as high as 3m/s. The fastest speed reach by a human in a sprint is about 12.4m/s. It could be done - but not by me.

 

[russ_watters]

In Star Trek the guy in the red shirt only lasts about 5 minutes...

 

[nsaspook]

In Star Trek the guy in the red shirt only lasts about 5 minutes...

Unless you are this red shirt.

 

[Janus]

Unless you are this red shirt.
View attachment 317346View attachment 317347

Though technically, he did die in "The Changling" only to be brought back by Nomad.

 

[nsaspook]

Though technically, he did die in "The Changling" only to be brought back by Nomad.

It was just a reboot.

 

[mfb]

Orion is approaching the Moon (livestream)

About 2 hours until the closest approach.

 

[Dullard]

Pre-Apollo, safety rules were less...safe. I worked at the shuttle pad with an old-timer (I was young then, and am a 'old-timer' now) who told me that when they went on a tower with a hydrogen-fueled vehicle, they always took a straw broom. Hydrogen fires are invisible - waving the broom (which would burst into visible flame) in front of you was a 'good' way to avoid walking into one. Yikes!

 

[Filip Larsen]

https://arstechnica.com/science/202...the-moon-with-a-lonely-earth-in-the-distance/

NASA's Orion spacecraft flew to within 130 km of the Moon's surface on Monday morning after executing one of the most demanding maneuvers of its 25-day mission.

 

[phinds]

As a long time employee of NASA (many years ago) and a avid fan of science and science fiction, I am a firm believer in the long term need for space exploration, BUT ... in this particular case, I agree w/ the Economist's Nov 16, 2022 article about Artemis:

 

[phinds]

I don't want to get into copyright issues so I can't quote or link to the whole article (I pay for a print/digital subscription) but I think fair use makes it OK to quote part of the Economist article, so here's the thrust of their argument against it:

 

[Vanadium 50]

straw broom

Also used for high pressure steam leaks.

 

[nsaspook]

Artemis Launch Sound Experience​

 

[Filip Larsen]

https://arstechnica.com/science/202...d-the-moon-returns-an-instantly-iconic-photo/:

NASA's Orion spacecraft reached the farthest outbound point in its journey from Earth on Monday, a distance of more than 430,000 km from humanity's home world. This is a greater distance from Earth than the Apollo capsule traveled during NASA's lunar missions in the late 1960s and early 1970s.

(The quote original wrongly said "This is nearly double the distance between Earth and the Moon and is farther than the Apollo capsule traveled during NASA's lunar missions in the late 1960s and early 1970s.")

 

[Tom.G]

Ahem... whoever wrote that caption got their miles and kilometers intermixed.

The above-linked article has been corrected though.
https://arstechnica.com/science/202...d-the-moon-returns-an-instantly-iconic-photo/

from: https://moon.nasa.gov/inside-and-out/overview/

Average Distance from Earth:

238,855 miles | 384,400 kilometers

 

[Filip Larsen]

whoever wrote that caption got their miles and kilometers intermixed.

This is nearly double the distance between Earth and the Moon ..

Good catch, I assume you refer to this part of the article which I happily quoted without reading properly first. I think my brain was stuck in amazement seeing the Moon at nearly same angular size as Earth.

 

[.Scott]

Just to check:

Diameter of Moon: 2159 miles, about 48 pixels
Diameter of Earth: 7917 miles, about 30 pixels
Earth to Moon distance: 238900 miles

So, camera-to-moon distance / camera-to-earth distance = about (30*2159)/(48*7917) = 0.17.
Camera to Earth distance: 238900 *(1+0.17) = 280,000 miles or 450,000 Km
A fair estimate of the advertised 430,000 Km.

 

[mfb]

Orion is approaching the Moon again (NASA coverage). It is expected to make a 300 m/s burn in 35 minutes, putting it on a trajectory towards Earth.

Splashdown is planned for Sunday.

 

[mfb]

Splashdown in a bit under an hour.

NASA coverage
Coverage by Everyday Astronaut, future real astronaut (via dearMoon)

European Service Module has been separated, Orion keeps approaching the atmosphere.

Orion does a skip-reentry maneuver: Its first contact with the atmosphere has a very flat angle and comes with so much lift that it will leave the atmosphere again for a few minutes before it re-enters and stays there. This is a bit easier for the heat shield, and it gives NASA good control over the splashdown zone: No need to land in bad weather because you can control the distance between the first skip and the second entry.

 

[Vanadium 50]

European Service Module

European Service? Brought to you by the same people who brought you French waiters...

first contact with the atmosphere

I always wondered why the 60's and 70's missions didn't do this. "Easier on the heat shield" is one reason, but you really don't want to miss your splashdown target. That increases the recovery time, and these capsules are not as seaworthy as maybe one would like. (e.g. Liberty Bell 7)

 

[mfb]

Brought by the same people who brought you French waiters...

Huh?

A skip-reentry needs a much better control over the trajectory. If you are off by a bit you don't land 100 km away, you might land 1000km away or even on the other side of the planet - with a dead crew because the capsule alone has very limited life support. That's fine today where the capsules have GPS and nanosecond radar timing measurements and can calculate their trajectories in milliseconds, but Apollo didn't have that level of control.

Here is a 1966 discussion.

Edit: Successful splashdown.

 

[dlgoff]

@mfb
Looks like Orion splashed down successful:
https://www.newscientist.com/article/2350742-nasas-artemis-i-mission-has-ended-as-orion-splashed-down-on-earth/#:~:text=On 11 December, the Orion,first launch on 16 November.

 

[Vanadium 50]

Huh?

I guess you had to be there.

That document is very interesting, And amusing. However, it assumes the reader knows more than I do. Why the "no thrust" requirement for example? I can see a "not very much thrust" requirement for sure. Oh, I don't know how much GPS would help: R is the worst measured direction, and height above ground might be more useful. And nanoseconds? It is tough to time the rocket engines to better than microseconds.

However, I think I agree with the primary point: consequences for a missed maneuver, for whatever reason, are severe.

 

[mfb]

Where would the thrust come from? The capsule has attitude control, but the big engines and fuel tanks have been discarded.

GPS can measure your altitude with an uncertainty of a few meters without issues, probably less than a meter because there is no thicker atmosphere to consider. The flight time of radio signals exchanged with the capsule or reflected by the capsule can be measured with nanosecond precision as additional signal, similar to the concept of GPS.
Velocity measurements were somewhat good (~m/s) even during the Apollo era because Doppler shifts are easy to measure, but position uncertainty was often hundreds of meters and of course the live calculations were far less detailed. Here is an old document on tracking.

To make conditions extremely bad for the ground system, assume that contact was lost with the spacecraft when it departed the Moon. Only 8 hr before entry into the Earth's atmosphere, contact, and thus tracking, was restored. Assuming that one ground station and one ship can track the spacecraft at one sample per minute, the entry velocity error is approximately 1-1.5 m/s and the position error is approximately 1-2 km.

 

[Vanadium 50]

Where would the thrust come from? The capsule has attitude control

Exactly. That's why I am surprised the requirement was zero, not less than some amount.

 

[.Scott]

Huh?

A skip-reentry needs a much better control over the trajectory. If you are off by a bit you don't land 100 km away, you might land 1000km away or even on the other side of the planet - with a dead crew because the capsule alone has very limited life support. That's fine today where the capsules have GPS and nanosecond radar timing measurements and can calculate their trajectories in milliseconds, but Apollo didn't have that level of control.

Here is a 1966 discussion.

That 1966 discussion is interesting. It talks about "uncontrolled skips" and a very intentional "lob".

And there's another item I found interesting in that link related to reentry heating:

For heating, the general rule is that the higher the deceleration, the higher the peak heating rate and the lower the total heat.

But back to the "skip"...
The Apollo missions were carried on the ABC TV network with Jules Bergman reporting.

Every phase of these mission took hours, if not days - and they preempted a lot of normally scheduled programming. This led to folks like Jules Bergman filling air time with lots and lots of technical discussion - with most of the material provided by NASA.
Making it to the correct reentry corridor to avoid atmospheric skipping was discussed in detail - especially for Apollo 13.

But from the article linked to by @mfb , a form of skipping was apparently standard practice.

Phase 4: Ballistic Lob (KEPL)
Atmospheric exit and reentry are defined as those states at which the sensed acceleration falls below and then exceeds approximately 0.2g. In the time between these conditions no control is exercised save that of roll attitude hold with pitch maintained for proper aerodynamic trim.

 

[mfb]

Exactly. That's why I am surprised the requirement was zero, not less than some amount.

Attitude control thrusters give you something like centimeter per second corrections. Good enough to change the orientation of your spacecraft, but not enough to have a useful impact on your trajectory. Close enough to zero to just use zero.

But from the article linked to by @mfb , a form of skipping was apparently standard practice.

That was a proposal but not the trajectory the Apollo capsules used.

 

[.Scott]

That [Ballistic Lob] was a proposal but not the trajectory the Apollo capsules used.

Per the document you linked to, this was used for AS-202 - which was part of the Apollo program and included an CM-011 Apollo capsule (but without the crew couches).

Here is an excerpt from the NASA page describing the mission (my emphasis):

One hour and 11 minutes after liftoff, the CM separated from the SM and turned its heat shield in the direction of flight to prepare for reentry. At an altitude of 400,000 feet, or about 75 miles, the capsule encountered the first traces of the Earth’s atmosphere at a velocity of 19,440 miles per hour. The CM’s guidance system steered it through a double-skip reentry, first descending to an altitude of about 40 miles, then using the capsule’s lift capability to rise back to nearly 50 miles before continuing the final descent. This reduced physical loads on the capsule. The heat shield reached a temperature of about 1,500 degrees Celsius while the cabin interior never exceeded 21 degrees Celsius, or 70 degrees Fahrenheit.

However (also from the NASA link):

The splashdown point was 235 miles short of the targeted area, later determined to be caused by the CM’s lower-than-predicted lift-to-drag ratio. It took the prime recovery ship, the U.S.S. Hornet (CV-12), eight and a half hours to reach the capsule and execute the retrieval.

That was not enough to discourage NASA from using the skip.
SA-501 was an uncrewed mission that included a fully configured Apollo.

The quote below is from the NASA Apollo 4 web page :

At an altitude of 76 miles, while traveling at 24,974 miles per hour, the Apollo 4 Command Module encountered the first tendrils of Earth’s upper atmosphere, its heat shield absorbing the heat of reentry, reaching a temperature of 5,000 degrees Fahrenheit while the cabin temperature remained comfortable enough for a crew. After dipping down to an altitude of 35 miles, the spacecraft used its aerodynamic lift to briefly skip back out of the atmosphere, reaching a height of 45 miles before continuing the descent. This double-skip reentry reduced deceleration and heat loads on the spacecraft.

... and with better result:

Within 20 minutes of splashdown, U.S. Navy frogmen had attached a flotation collar around the spacecraft. After the Bennington pulled alongside the capsule, sailors hoisted it aboard, along with the spacecraft’s apex cover that protected the parachutes during flight and one of the three main parachutes. The entire recovery operation lasted about two hours.

The manned Apollo launches started with Apollo 7. So far, I have found no detailed descriptions of those reentries.

 

[nsaspook]

 

[mfb]

Hydrolox burns so cleanly that you can hardly notice the center core engines running at full thrust between the solid rocket boosters with their extremely bright exhaust.