Artemis 2 launch - humans return to the Moon after 54 years

[.Scott]

Artemis, twin of Apollo.
Fitting name for the second series of manned moon missions.

And she personified the Moon. But Artemis was the older of the twins.

 

[PeterDonis]

Did the rocket speed up when moon's gravity became stronger than earth's?

I'm not sure I would expect it to, because the trajectory it's following is so far from the Moon, as compared with the Apollo missions. I haven't run the numbers, but I suspect the Moon's force is just curving the trajectory, not speeding it up.

 

[Charles Link]

I did find from one article in a google that the expected speed at closest approach would be 3,139 m.p.h. I am lead to believe the website that showed no increase all day and a decrease to below 1,000 m.p.h. was inaccurate.

Edit: I found a video on Facebook that may offer at least a partial explanation: The rocket passes the moon to the left of the moon and then loops to the right when it is behind it, with the moon moving right to left. The 3,139 number might be the speed relative to the moon. I estimate the moon's right to left speed at about 2,000 m.p.h. Edit: With a google I see the moon moves about 2,288 m.p.h. in its orbit around the earth.

Meanwhile an acceleration of the rocket to the right will create a velocity component to the right that adds as a vector to the forward velocity component (relative to earth) and may not affect the speed w.r.t. the earth all that much.

 

[Jonathan Scott]

The area brightness of an object does not depend on distance.

True of course, and presumably relevant in this case, but to avoid confusion this needs to be accompanied by the important point that if the angular size of an individual object (such as a star) is smaller than the sensor or eye resolution then the apparent brightness is decreased accordingly (which is presumably the main factor limiting the number of stars which we can see with the naked eye).

 

[pinball1970]

Metro UK today, Wiseman said humans have "not evolved" to see images like the ones they are seeing.

 

[DennisN]

Some gorgeous photos here:

Artemis II Lunar Flyby (NASA)
Quote: "The first flyby images of the Moon captured by NASA’s Artemis II astronauts during their historic test flight reveal regions no human has ever seen before—including a rare in-space solar eclipse. Released Tuesday, April 7, 2026, the photos were taken on April 6 during the crew’s seven‑hour pass over the lunar far side, marking humanity’s return to the Moon’s vicinity."
https://www.nasa.gov/gallery/lunar-flyby/

Examples:

A Setting Earth

Shadows at the Edge of Lunar Day

Shadows Across Vavilov Crater

They got better Moon photos than me!

Of course it is impossible for us terrestrial astrophotographers to get the Earth in a shot without faking it, but how can we at PF counter this novel threat from these four upstarts sitting in a tin can?

Can I spend a fortune and buy dedicated gear for Moon photography? (maybe, but I won't )
Can @timmdeeg get himself a new super expensive lens?
Does @russ_watters have any unknown tricks up his sleeve?
Can @Andy Resnick conjure up some optical magic with his gear?
Can @collinsmark direct his monstrosity of a scope towards the Moon and pull off some stunts?

What to do, what to do?

 

[DennisN]

Look, here is one of the upstarts taking photos:

Photographer at Work

art002e009295 (April 6, 2026) – Astronaut Jeremy Hansen captures an image through the camera shroud covering window 2 of the Orion spacecraft. The camera shroud, essentially a curtain with a hole for the lens to pass through, is used to prevent light from the cabin from reflecting on the windowpanes.
Image Credit: NASA

Source: https://www.nasa.gov/image-detail/amf-art002e009295/

I think this is close to cheating; he was one lucky dude and got really, really close to his subject (the Moon), and furthermore he is enjoying the benefits of zero gravity.
Bah! And I bet he is using image stabilization too on his camera. I'm telling you, he had it easy.

(I'm only joking, of course )

 

[sophiecentaur]

I'm not sure I would expect it to, because the trajectory it's following is so far from the Moon, as compared with the Apollo missions. I haven't run the numbers, but I suspect the Moon's force is just curving the trajectory, not speeding it up.

The closest approach to the moon is much greater than for the Apollo missions. That would, of course, be a much lower energy requirement. Thinking in terms of orbital energy for the lunar encounter, the GPE change is much less for the pass by of Artemis pass than going down to a low lunar orbit and then landing and takeoff.
It does surprise me that they didn't choose to carry that much extra fuel to allow a lower lunar orbit. Future landings would obvs need the full amount of fuel. I couldn't imagine that the navigation would have been a problem.

 

[Filip Larsen]

https://arstechnica.com/space/2026/...design-to-fix-orion-spacecrafts-leaky-valves/

Orion helium leak no threat to Artemis II reentry, but will require redesign.
After leaks on Artemis I and II, Orion’s next flight to the Moon will need new valves.
[...]
The valves are inside the European-built service module, which the Orion spacecraft will jettison just before reentering the atmosphere Friday evening.

 

[pinball1970]

There was an issue with heat shield in 2022 with Artemis 1.

https://www.nasa.gov/missions/artem...use-of-artemis-i-orion-heat-shield-char-loss/

They will be coming in a steeper angle so less time at high temperature but will that not also create more friction?

 

[mfb]

NASA stream for reentry (landing in ~1.5 hours)

A steeper angle will lead to a higher peak heat load but the heat shield is designed for that. It's the slow, long-term heating in deeper layers that caused the ablation.

True of course, and presumably relevant in this case, but to avoid confusion this needs to be accompanied by the important point that if the angular size of an individual object (such as a star) is smaller than the sensor or eye resolution then the apparent brightness is decreased accordingly (which is presumably the main factor limiting the number of stars which we can see with the naked eye).

The discussion was about a nebula, not a point source.

 

[neilparker62]

Some snapshots taken from the live stream. Times as recorded on my cellphone. GMT+2

23:49

01:54

02:07

02:09

 

[Charles Link]

In regards to posts 60 and posts 63 above, I did a calculation assuming the total energy of the rocket stays constant using the gravitational potentials of the earth and moon, and that calculation showed the rocket should speed up considerably, up to about 2600 m.p.h. I determined that calculation to be in error though.

The moon, the source of the second gravitational potential was moving at about 2200 m.p.h. Thereby, the rocket didn't move across the gravitational potential enough (in the reference frame of the earth) to get the complete $dW=\vec{F} \cdot d \vec{s}=\Delta(mv^2/2)$. Instead, much of the closure in distance was because of the motion of the moon. The way I initially treated it as a static/fixed gravitational potential was incorrect. To apply the method of gravitational potential to get the change in $v^2$, it seems it is necessary to go to the reference frame of the moon. Thereby I have concluded that the nasa data showing no increase in speed measured w.r.t. the earth, (the speed stayed nearly steady at about one thousand m.p.h.), even in its closest approach to the moon, was apparently completely valid.

I thought I was somewhat clever in applying the use of two gravitational potentials to compute the $v$, but it seems that if one or both of the two sources are moving, the method can not be used to compute the kinetic energy of the 3rd body in the simple straightforward manner that I tried to employ.

Note: This was the first time I ever tried to work a problem involving two gravitational potentials at the same time. It would have worked if the moon were stationary, but it isn't.

 

[Charles Link]

The calculation with the moon's gravitational potential does indeed work in the rest frame of the moon. To compute it, we can to a good approximation simply ignore the effect of the earth when the rocket is near the moon. For initial conditions, we can put the rocket 6000 miles from the path of the moon, moving forward with $v_o=1000$ m.p.h. and the moon to the right a distance of 20,000 miles and moving right to left at a speed of $v_m=2200$ m.p.h. That makes it so the moon is a distance (measured from its center) of $r_{mo}=21,000$ miles. In the reference frame of the moon, the rocket is approaching the moon at a speed of $v_{mo}=2400$ m.p.h.

We have with conservation of energy $\frac{mv_{m1}^2}{2}- \frac{GM_m m}{r_{m1}}=\frac{mv_{mo}^2}{2}-\frac{GM_m m}{r_{mo}}$. Nasa gives that at closest approach $v_{m1}= 3139$ m.p.h. at 4067 miles from the surface, so that with a radius of the moon of about 1100 miles, $r_{m1}=5,170$ miles (at closest approach). Putting in the known constants, I get $v_{m1} \approx 3200$ m.p.h. ,(at closest approach), in good agreement with Nasa.

(It may be worth repeating what was mentioned in post 73 above that this conservation of energy expression is not valid if the speeds used are those measured in the reference frame of the earth. The results of doing the calculation in that manner are completely incorrect).

Since at closest approach the rocket is now moving approximately left to right, (at 3200 m.p.h. w.r.t. the moon, with the moon moving right to left at 2200 m.p.h. w.r.t. the earth), the speed of the rocket in the rest frame of the earth will still be $v=1000$ m.p.h. approximately. Thereby the speed of the rocket measured in the reference frame of the earth didn't change appreciably during the last part of the approach to the moon. The above calculation is in complete agreement with this. (Note: The direction changed, but the speed didn't).

It may be worth noting that to do the arithmetic above, I used $v_{esc}=25,000$ m.p.h. and $v_{esc}^2=2GM_e/R_e$ with $R_e=4000$ miles, and $M_m=M_e/81$ approximately.

 

[Charles Link]

I'd also like to comment on the first photo of post 66. I think what looks like the moon's shadow is simply the earth illuminated by the sun from the side. If it were a solar eclipse, it would occur at the time of a new moon. The new moon according to a google occurred on april 17, 2026. The astronauts did get a solar eclipse when they flew around the moon, but the earth did not have a solar eclipse that day.

 

[mfb]

Over 10000 pictures taken during the mission

 

[sophiecentaur]

Over 10000 pictures taken during the mission

I should hope so too! Thats probably only a tad more than a modern wedding.

 

[Charles Link]

To comment more on my post 74 above, I dug out my Kleppner and Kolenkow mechanics textbook from college, and the path neglecting the earth in the rest frame of the moon is an unbound hyperbolic trajectory. Given the speed at the minimum point was 3140 m.ph. at a distance of 5170 miles from the center of the moon, the entire trajectory can be worked out in the reference frame of the moon. Knowing the moon's approximate speed in orbit around the earth, I used 2250 m.p.h., one can transfer back to the earth's reference frame, and what is found, also using energy considerations in the frame of reference of the moon (in its rest frame), that the initial velocity when the rocket crossed the path of the moon was almost straight ahead at somewhere between 950 and 1000 m.p.h., which in the rest frame of the moon becomes at an angle with a speed of about 2650 m.p.h. In the rest frame of the moon, this speed increased to 3140 m.p.h. from left to right, but going back to the earth's frame of reference, it is just under 900 m.p.h. It appears the earth slowed the moon by about 20 m.p.h. per hour and the calculations support this.

I have some Nasa data of the flyby from about 4:00 PM to 5:00 PM CST that Wednesday, but I'd be interested in getting a data point at the time when the rocket crossed the moon's path, which I estimate to be around noon. The distance could be interesting. My calculations show, (using the hyperbola), it should be just under 17,000 miles from the center of the moon, or just under 16,000 from the moon's surface. I also think the rocket may have had a slight velocity component from left to right at that point of perhaps 100 m.ph., but this may be beyond what the uncertainty in my calculations can accurately determine. I also might not have a perfectly precise number for the speed of the moon=something that the Nasa engineers no doubt knew very accurately. The earth also played a slight role in the trajectory, so it would no longer be a perfect hyperbola in the rest frame of the moon.

and note, contrary to what we might have guessed, the rocket did not pick up speed when measured in the rest frame of the earth in its encounter with the moon. Part of the reason is that the moon was off to the right from the rocket when the moon's gravity became stronger than earth's, instead of being directly in front of the rocket.

It may be worth mentioning, the hyperbola around the moon, which is the precise path without the effects of the earth, has a symmetry to it, so that the path after the point of closest approach is a mirror image of the path before it. In addition, the hyperbola has an asymptotic behavior to it, and for this case, when transformed back to the earth's rest frame, the path looks like a ribbon that crosses itself below the moon. The asymptotic speed in the rest frame of the moon is about 2000 m.p.h., with a y component of velocity of about 850, and an x component of about 1850, so that in the rest frame of the earth, it actually has an x component right to left of about 400 m.p.h. far from the moon, with this calculation being the result from the perfect hyperbola, using the maximum speed number at distance number at closest approach.

Once again, I could use the Nasa data from noon that day, if anyone has it.