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

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The Flight Readiness Review for Artemis 1 has concluded, with the launch scheduled for August 29, 2022, at 12:33 UTC, and backup windows available from September 2 to September 6. This mission will mark the first uncrewed flight of the Space Launch System (SLS) and the Orion capsule, which will orbit the Moon before returning to Earth. Extensive NASA coverage is planned, and over 100,000 visitors are expected to witness the launch. However, the launch faced delays due to technical issues, including engine conditioning problems, raising concerns about the timeline of the $21 billion program. If successful, Artemis 1 will establish the SLS as the most powerful operational rocket, paving the way for future crewed missions to the Moon and beyond.
  • #181
Vanadium 50 said:
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.
.Scott said:
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.
 
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  • #182
mfb said:
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.
 
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  • #183
 
  • #184
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.
 

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