5 ms·

My understanding is that "ballistic" means without any form of propulsion (except the initial one sending it on its way). In other words, like a projectile (or

by FabHK 8y ago

My understanding is that "ballistic" means without any form of propulsion (except the initial one sending it on its way). In other words, like a projectile (or a ball), just subject to the forces of gravity and air resistance. In other words: falling, yup. (But note that one could "fall" upwards or sideways initially - not like Arthur Dent [1], but like a bullet (or indeed rocket) fired upwards). [1] The Hitchhiker's Guide to the Galaxy states: "There is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. ... Clearly, it is this second part, the missing, that presents the difficulties."

stult 8y ago
I believe the Soyuz SAS has engine thrusters for the landing sequence. So ballistic may mean the thrusters were not operable and they may have landed a bit harder than normal (normal for an abort sequence at least). Meaning they were still under canopy, just falling at a higher impact velocity than intended. So maybe rather than a gentle landing at 5m/s it was more like a car crash at 20 m/s. Beats blowing up with the rocket or hitting the ground at terminal velocity, though, and presumably the reports of "good condition" mean there are at most some concussions and broken bones.
- dsfyu404ed 8y ago
  >there are at most some concussions and broken bones. If you're strapped into a bucket seat with your back to the impact it's gonna take a fuckton of Gs to break bones. The astronauts would not be in "good condition" if they experienced that kind of a landing. They would be calling it a crash at that point.
- FabHK 8y ago
  Wikipedia has some pertinent (and interesting) details: > The Descent Module (Russian: Спуска́емый Аппара́т, tr. Spuskáyemy Apparát), also known as a reentry capsule, is used for launch and the journey back to Earth. Half of the Descent Module is covered by a heat-resistant covering to protect it during reentry; this half faces the Earth during re-entry. It is slowed initially by the atmosphere, then by a braking parachute, followed by the main parachute which slows the craft for landing. At one meter above the ground, solid-fuel braking engines mounted behind the heat shield are fired to give a soft landing. One of the design requirements for the Descent Module was for it to have the highest possible volumetric efficiency (internal volume divided by hull area). The best shape for this is a sphere — as the pioneering Vostok spacecraft's Descent Module used — but such a shape can provide no lift, which results in a purely ballistic reentry. Ballistic reentries are hard on the occupants due to high deceleration and cannot be steered beyond their initial deorbit burn. That is why it was decided to go with the "headlight" shape that the Soyuz uses—a hemispherical forward area joined by a barely angled (seven degrees) conical section to a classic spherical section heat shield. This shape allows a small amount of lift to be generated due to the unequal weight distribution. So, maybe ballistic refers to the fact that no lift was generated? (A glider is not considered ballistic, even though it has no propulsion.) An, and indeed, that's what Wiktionary says: > ballistic entry: when an entry vehicle has only drag with no apparent lift. An axisymmetric entry vehicle would have no apparent lift if its angle-of-attack time averaged out to zero, e.g. sinusoid angle-of-attack centered or trimmed about zero lift. https://en.wikipedia.org/wiki/Soyuz_(spacecraft)#Descent_module https://en.wikipedia.org/wiki/Soyuz_(spacecraft)#Descent_mod... https://en.wiktionary.org/wiki/Appendix:Glossary_of_atmospheric_reentry https://en.wiktionary.org/wiki/Appendix:Glossary_of_atmosphe...
  - mcguire 8y ago
    Here's a diagram of the descent module, if you are having trouble with the description: https://i.stack.imgur.com/BUYME.png https://i.stack.imgur.com/BUYME.png Edit: BUYME?
  - rzzzt 8y ago
    The standard landing experience is described in an ESA video: https://youtu.be/-l7MM9yoxII?t=1086 https://youtu.be/-l7MM9yoxII?t=1086
- sp332 8y ago
  An interview on BBC Newshour said that a normal Soyuz landing could go as high as 6 G's, and max acceleration this time was 6.7 G's. So certainly on the rough side (6 G's is bad enough!) but not that far out of normal. Even a shock of 9 G's is expected to be survivable, although that would take a lot more recovery.
orbital-decay 8y ago
Ballistic in the Soyuz context means not using any aerodynamic lift, as oppposed to gliding reentry which is using lift, is controllable, and imposes much less Gs on the crew. Neither one uses any propulsion (expect for a specialized RCS which is used to control the roll while gliding).
- FabHK 8y ago
  It's not entirely clear to me why there's less acceleration on the gliding entry. It can't really be that the speed is bled off over a longer distance, right (in other words, I assume that the high-g phases are rather punctual than extended), and intuitively it would seem that, coming in at high speed, "gliding" (ie with lift) would lead to quicker deceleration than just "bleeding off" speed in the ballistic fall, ie higher g. Could you elaborate on the difference between the usual and ballistic mode, and when the high g-load occurs?

by FabHK 8y ago

stult 8y ago

I believe the Soyuz SAS has engine thrusters for the landing sequence. So ballistic may mean the thrusters were not operable and they may have landed a bit harder than normal (normal for an abort sequence at least). Meaning they were still under canopy, just falling at a higher impact velocity than intended. So maybe rather than a gentle landing at 5m/s it was more like a car crash at 20 m/s. Beats blowing up with the rocket or hitting the ground at terminal velocity, though, and presumably the reports of "good condition" mean there are at most some concussions and broken bones.

dsfyu404ed 8y ago
>there are at most some concussions and broken bones. If you're strapped into a bucket seat with your back to the impact it's gonna take a fuckton of Gs to break bones. The astronauts would not be in "good condition" if they experienced that kind of a landing. They would be calling it a crash at that point.
FabHK 8y ago
Wikipedia has some pertinent (and interesting) details: > The Descent Module (Russian: Спуска́емый Аппара́т, tr. Spuskáyemy Apparát), also known as a reentry capsule, is used for launch and the journey back to Earth. Half of the Descent Module is covered by a heat-resistant covering to protect it during reentry; this half faces the Earth during re-entry. It is slowed initially by the atmosphere, then by a braking parachute, followed by the main parachute which slows the craft for landing. At one meter above the ground, solid-fuel braking engines mounted behind the heat shield are fired to give a soft landing. One of the design requirements for the Descent Module was for it to have the highest possible volumetric efficiency (internal volume divided by hull area). The best shape for this is a sphere — as the pioneering Vostok spacecraft's Descent Module used — but such a shape can provide no lift, which results in a purely ballistic reentry. Ballistic reentries are hard on the occupants due to high deceleration and cannot be steered beyond their initial deorbit burn. That is why it was decided to go with the "headlight" shape that the Soyuz uses—a hemispherical forward area joined by a barely angled (seven degrees) conical section to a classic spherical section heat shield. This shape allows a small amount of lift to be generated due to the unequal weight distribution. So, maybe ballistic refers to the fact that no lift was generated? (A glider is not considered ballistic, even though it has no propulsion.) An, and indeed, that's what Wiktionary says: > ballistic entry: when an entry vehicle has only drag with no apparent lift. An axisymmetric entry vehicle would have no apparent lift if its angle-of-attack time averaged out to zero, e.g. sinusoid angle-of-attack centered or trimmed about zero lift. https://en.wikipedia.org/wiki/Soyuz_(spacecraft)#Descent_module https://en.wikipedia.org/wiki/Soyuz_(spacecraft)#Descent_mod... https://en.wiktionary.org/wiki/Appendix:Glossary_of_atmospheric_reentry https://en.wiktionary.org/wiki/Appendix:Glossary_of_atmosphe...
- mcguire 8y ago
  Here's a diagram of the descent module, if you are having trouble with the description: https://i.stack.imgur.com/BUYME.png https://i.stack.imgur.com/BUYME.png Edit: BUYME?
- rzzzt 8y ago
  The standard landing experience is described in an ESA video: https://youtu.be/-l7MM9yoxII?t=1086 https://youtu.be/-l7MM9yoxII?t=1086
sp332 8y ago
An interview on BBC Newshour said that a normal Soyuz landing could go as high as 6 G's, and max acceleration this time was 6.7 G's. So certainly on the rough side (6 G's is bad enough!) but not that far out of normal. Even a shock of 9 G's is expected to be survivable, although that would take a lot more recovery.

orbital-decay 8y ago

Ballistic in the Soyuz context means not using any aerodynamic lift, as oppposed to gliding reentry which is using lift, is controllable, and imposes much less Gs on the crew. Neither one uses any propulsion (expect for a specialized RCS which is used to control the roll while gliding).

FabHK 8y ago
It's not entirely clear to me why there's less acceleration on the gliding entry. It can't really be that the speed is bled off over a longer distance, right (in other words, I assume that the high-g phases are rather punctual than extended), and intuitively it would seem that, coming in at high speed, "gliding" (ie with lift) would lead to quicker deceleration than just "bleeding off" speed in the ballistic fall, ie higher g. Could you elaborate on the difference between the usual and ballistic mode, and when the high g-load occurs?