I’ll note, since it is supremely interesting to me, that Starship is able to communicate with the ground during its whole reentry due to its sheer size and ability to connect with Starlink satellites. I assumed loss of signal due to reentry was a given for any spaceship!
Shuttle in its last days had antennas that protruded outside the plasma just enough for telemetry. Apollo and Artemis reentry are also direct entry from Lunar-Earth transfer orbit using ablative heat shields, so the plasma would be hotter and thicker than suborbital Starship shots with Shuttle style ceramic tiles.
I'm pretty sure it did not stick anything through the plasma sheet- that is impossible. You would eithe melt the thing or just shift the plasma sheet a bit. It forms as air is compressed on contact, simple as that.
What IIRC was actually done was that some antennas were placed on the back of the shuttle & its size was big enough that the plasma bubble would not fully envelope it - it would be open up to space. And that antenna on the back would communicate with TDRS satellites through this gap, enabling contact through the whole re-entry.
Starship does basically the same, just with Starlink satellites instead of TDRS.
Would this capsule had been been able to communicate if it was integrated with starlink or is the size more important? I'd imagine if they could have achieved communication via Starlink they would have done it, but just curious.
It's a function of the shape. On a capsule-sized spacecraft, the ionized plasma completely surrounds the craft, so no radio communications can get in or out. For an oblong-shaped spacecraft, like the Space Shuttle or Starship, the descent tends to be angled such that you have a "hole" in the plasma you can get a signal through.
No, the plasma forms a teardrop shape around small craft like Orion, completely cutting off radio comms. Larger craft like starship or the shuttle which have a roughly cylindrical shape (vs Orion’s circular cross section) aren’t fully enclosed by the plasma. The shuttle had a transmitter attached to its tail for later flights, which could send back telemetry during re-entry.
"Sprint accelerated at 100 g, reaching a speed of Mach 10 (12,000 km/h; 7,600 mph) in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,400 °C), requiring an ablative shield to dissipate the heat. The high temperature caused a plasma to form around the missile, requiring extremely powerful radio signals to reach it for guidance. The missile glowed bright white as it flew."
Awesome, thank you! I wonder if some kind of very long-tethered deployed antenna could enable this for the capsule or if the ratio of long-enough-to-work vs thick-enough-to-not-burn-off-completely just doesn't work. Time to read about the shuttle.
Also Orion and other capsules fall like a rock (steep reentry profile ) compared to shuttle/starship, which intentionally slow down the reentry and kinda glide (ballpark 10min with capsules compared to 30min with shuttle/starship).
tl;dr: capsules get fully enveloped in plasma due to their shape, size and reentry profile
The space shuttle, too, was able to communicate. I imagine the smaller the craft the smaller the angle you can "speak" out of and, below a certain size, it just doesn't work.
I was wondering about that, so I looked up the heat shield issues. It seems like their solution was very defensible and there was every reason to believe it would work out just fine. The plan that did not work as they wanted had a new idea, a double re-entry, and when the results were concerning they backed off to using a traditional single re-entry. That seems like a legitimate fix?
Scott Manley went into the details in a recent video.
The reason the heat shield failed was due to gas buildup inside the ablative material.
This was due to the skip reentry profile they used, where the craft does a single skip (as in skipping stones) during reentry. The high bounce caused the shield to be heated enough that the heat penetrated the material causing gas release but not enough that the material ablated. Thus gas would build up deep inside up until it caused large chunks to break off. They could reproduce this in tests.
The fix was two-fold. First they lowered the bounce height, so a much less pronounced skip, avoiding the lowered heating of the shield. And they tweaked the material formula a bit so it was more porous, allowing subsurface gas to escape rather than build up.
In my understanding of the Manley video, the materials change will only occur for Artemis 3, for which it will be irrelevant as that will not be leaving LEO.
Not sure why I'm being downvoted. Here's the segment where Manley explains this: https://youtu.be/shcj7MUK5BU?t=828 and this is also the section where Manley explains Artemis III is not going to the moon so it won't actually be testing this change.
> Engineers already are assembling and integrating the Orion spacecraft for Artemis III based on lessons learned from Artemis I and implementing enhancements to how heat shields for crewed returns from lunar landing missions are manufactured to achieve uniformity and consistent permeability.
Yes it was worrisome, but how could it not be even with the best tech we'll ever have - I feel relief still on every plane touchdown.
Bravo, Artemis team for an exceptional return to extra-orbital space travel.
The LOS was also more than 6 minutes as predicted (I measured a bit over 7 minutes). What a tension.
I wasn't clear, was the LOS just comms or a full loss of telemetry from the craft? Either way, terrifying.
Everything. No radio signals make it in or out of the capsule due to ionization from the heat and plasma of reentry.
I’ll note, since it is supremely interesting to me, that Starship is able to communicate with the ground during its whole reentry due to its sheer size and ability to connect with Starlink satellites. I assumed loss of signal due to reentry was a given for any spaceship!
Shuttle in its last days had antennas that protruded outside the plasma just enough for telemetry. Apollo and Artemis reentry are also direct entry from Lunar-Earth transfer orbit using ablative heat shields, so the plasma would be hotter and thicker than suborbital Starship shots with Shuttle style ceramic tiles.
I'm pretty sure it did not stick anything through the plasma sheet- that is impossible. You would eithe melt the thing or just shift the plasma sheet a bit. It forms as air is compressed on contact, simple as that.
What IIRC was actually done was that some antennas were placed on the back of the shuttle & its size was big enough that the plasma bubble would not fully envelope it - it would be open up to space. And that antenna on the back would communicate with TDRS satellites through this gap, enabling contact through the whole re-entry.
Starship does basically the same, just with Starlink satellites instead of TDRS.
Would this capsule had been been able to communicate if it was integrated with starlink or is the size more important? I'd imagine if they could have achieved communication via Starlink they would have done it, but just curious.
It's a function of the shape. On a capsule-sized spacecraft, the ionized plasma completely surrounds the craft, so no radio communications can get in or out. For an oblong-shaped spacecraft, like the Space Shuttle or Starship, the descent tends to be angled such that you have a "hole" in the plasma you can get a signal through.
No, the plasma forms a teardrop shape around small craft like Orion, completely cutting off radio comms. Larger craft like starship or the shuttle which have a roughly cylindrical shape (vs Orion’s circular cross section) aren’t fully enclosed by the plasma. The shuttle had a transmitter attached to its tail for later flights, which could send back telemetry during re-entry.
Well, provided you had a 30 MW microwave transmitter on board, you could punch through the plasma just fine, it has been done:
https://en.wikipedia.org/wiki/Sprint_(missile)
"Sprint accelerated at 100 g, reaching a speed of Mach 10 (12,000 km/h; 7,600 mph) in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,400 °C), requiring an ablative shield to dissipate the heat. The high temperature caused a plasma to form around the missile, requiring extremely powerful radio signals to reach it for guidance. The missile glowed bright white as it flew."
Awesome, thank you! I wonder if some kind of very long-tethered deployed antenna could enable this for the capsule or if the ratio of long-enough-to-work vs thick-enough-to-not-burn-off-completely just doesn't work. Time to read about the shuttle.
It's the shape and size.
Also Orion and other capsules fall like a rock (steep reentry profile ) compared to shuttle/starship, which intentionally slow down the reentry and kinda glide (ballpark 10min with capsules compared to 30min with shuttle/starship).
tl;dr: capsules get fully enveloped in plasma due to their shape, size and reentry profile
The space shuttle, too, was able to communicate. I imagine the smaller the craft the smaller the angle you can "speak" out of and, below a certain size, it just doesn't work.
Yes, I remember when they used the signal out the back through the plasma during reentry. It was astoundingly good!
It seems like they had limited telemetry for a short period before they did any audio
I was wondering about that, so I looked up the heat shield issues. It seems like their solution was very defensible and there was every reason to believe it would work out just fine. The plan that did not work as they wanted had a new idea, a double re-entry, and when the results were concerning they backed off to using a traditional single re-entry. That seems like a legitimate fix?
Scott Manley went into the details in a recent video.
The reason the heat shield failed was due to gas buildup inside the ablative material. This was due to the skip reentry profile they used, where the craft does a single skip (as in skipping stones) during reentry. The high bounce caused the shield to be heated enough that the heat penetrated the material causing gas release but not enough that the material ablated. Thus gas would build up deep inside up until it caused large chunks to break off. They could reproduce this in tests.
The fix was two-fold. First they lowered the bounce height, so a much less pronounced skip, avoiding the lowered heating of the shield. And they tweaked the material formula a bit so it was more porous, allowing subsurface gas to escape rather than build up.
No doubt there are people looking at the heat shield right now and saying "Hmmm."
I am very curious about what they're seeing, and how well the get-it-over-with solution worked.
It was a bold move and the results will be fascinating.
In my understanding of the Manley video, the materials change will only occur for Artemis 3, for which it will be irrelevant as that will not be leaving LEO.
Not sure why I'm being downvoted. Here's the segment where Manley explains this: https://youtu.be/shcj7MUK5BU?t=828 and this is also the section where Manley explains Artemis III is not going to the moon so it won't actually be testing this change.
And from an older NASA explanation: https://www.nasa.gov/news-release/nasa-shares-orion-heat-shi...
> Engineers already are assembling and integrating the Orion spacecraft for Artemis III based on lessons learned from Artemis I and implementing enhancements to how heat shields for crewed returns from lunar landing missions are manufactured to achieve uniformity and consistent permeability.
Yes, but it was the biggest opening for propagandists to latch on to for demoralizing and spreading fear/uncertainty/doubt about the mission.
Same! Glad everyone made it safe.