Title says it all. I am puzzled why Orion will be traveling faster than Apollo.
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4$\begingroup$ Could you provide a source with Orion reentry velocity value? $\endgroup$– HeoppsNov 18, 2022 at 11:56
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1$\begingroup$ From where did you get this information? $\endgroup$– UweNov 18, 2022 at 15:37
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$\begingroup$ @Uwe it was mentioned in the NASA live coverage at least once. I’m pretty sure it’s because Orion will go further out than Apollo, but there should be a reference to substantiate. $\endgroup$– LudoNov 18, 2022 at 17:50
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1$\begingroup$ @uhoh good catch, I should have specified inertial speed reference! $\endgroup$– BrendanLuke15Nov 27, 2022 at 18:45
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1$\begingroup$ @BrendanLuke15 more like a "good nitpick" :-) $\endgroup$– uhohNov 27, 2022 at 21:47
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1 Answer
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The premise of the question is questionable. According to Apollo By The Numbers, the maximum reentry velocity among all Apollo missions was achieved by Apollo 10, which peaked at 36397 ft/sec. For all missions, the reentry velocity was just above 36000 ft/sec or 24545 mph.
This NASA page says that Artemis I will re-enter at 24500 mph, but clicking through to the linked Artemis I Reference Guide, on page 3:
This flight test will demonstrate the performance of the SLS rocket on its maiden flight and gather engineering data throughout the journey before Orion returns on a high-speed Earth reentry at speeds of more than 25,000 mph. The high-speed lunar velocity reentry is the top mission priority and a necessary test of Orion’s heat shield performance as it enters Earth’s atmosphere...
(emphasis mine)
25000 mph is 36667 ft/sec, so that would be a faster re-entry than any of the Apollo missions.
"Artemis I Trajectory Design and Optimization" (link to PDF) confirms (page 4):
The return trajectory targets a high speed atmospheric entry on the order of 36,000 ft/s (11 km/s), suitable for demonstrating the performance and effectiveness of the Orion Thermal Protection System (TPS) heat shield, as well as relevant environments prior to the first crewed launch of the system.
But also here the reentry speed is in the same order of magnitude as those for the Apollo mission, not necessarily higher. So there seems to be some uncertainty.
Both resources mentioned that the higher reentry speed is necessary to for testing of the heat shield. The second paper mentions (on page 3) that the last burn of Orion is named "Return Powered Flyby", which to me sounds a bit like "floor it and see how fast we can go back".
We'll find out in a few weeks how fast Orion actually reentered.
Edit (13 May 2023):
The NASA page on Artemis-I Mission Facts section has been updated and now* states:
Re-entry speed: 24,581 mph (Mach 32)
This seems oddly specific to be an estimate, but I couldn't find a paper to substantiate this number. At 24581 mph or 36052 ft/sec (39559 km/h) Artemis-I's reentry speed would be slightly slower than Apollo.
*) The archive.org capture around the time I posted the original answer shows 24500 mph for re-entry speed.
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2$\begingroup$ I'll try to remember to update this post in December, after the landing. $\endgroup$– LudoNov 25, 2022 at 21:47
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2$\begingroup$ Apollo by the Numbers is crewed flights only - it looks like Apollo 4 was very slightly faster than 10, at 11140m/s (NSSDC) - ~36550 ft/s. $\endgroup$ Nov 28, 2022 at 12:26
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1$\begingroup$ To add - this 1972 report rates Apollo 4 slightly higher (36,628 ft/s) and also gives a figure for Apollo 6 (32,830 ft/s - it was aiming to replicate Apollo 4's trajectory but had problems). $\endgroup$ Nov 28, 2022 at 13:11
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1$\begingroup$ Meanwhile, the 1974 Apollo Experience Report gives a design target of 36,333 ft/s, with 36,545 ft/s as the reported inertial velocity for Apollo 6 - it explicitly states "at 400,000 ft" so possibly this point was slightly off peak velocity. $\endgroup$ Nov 28, 2022 at 13:18
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2$\begingroup$ Following the return burn, ESA are now quoting "speeds of 39 590 km/h", which is almost exactly 24600 mph (so that's probably the figure it was converted from). I guess we're still on an estimated value for the time being, but it is now being quoted as very slightly slower than Apollo - ~36080 ft/s. $\endgroup$ Dec 5, 2022 at 20:19