Re-entry g's and Commercial Spacecraft selection

[darkenfast]

I didn't want to clutter up the new DC thread with this. I've noticed that one of the selling points by SNC is the fact that its re-entry g-load is a gentle 1.5, much like the Shuttle. I would guess that Dragon's will be close to 4. Now, on Shuttle, the top deck crew were sitting in a vertical position, and AIUI, the lower deck was configured for either vertical or horizontal seating for re-entry, so that long-duration returnees could be on their backs. In all the capsule designs of course, the g-loads are always in the same direction. I'm not sure how DC would handle a return if everyone was long-duration crew: will all the seats be movable or will the front two remain upright? Will the seat orientation be an issue in any abort scenario?Anyway, given that Dragon seems to be going for form-fitting couches, how important is the 1.5 vs 3-4 for long-duration flyers. Has our experience with Soyuz shown anything regarding this? In isolation from other factors, is it an important point in selecting a manned commercial provider? Thanks!

[Lee Jay]

Long duration station inhabitants have survived Soyuz ballistic entries (albeit, somewhat less than happily), so I don't think it's a huge issue for their long term health, though they might not feel that way during the peak of the g-loading in such a situation.

[Rocket Science]

When it comes to g related injuries some lessons we learned from the motorsports world is that it is not the maximum g’s that are dangerous but the duration of time at that sustained g. For example a 50g impact at 0.1s is more dangerous than let say a 150g at 0.01s duration…
 
For spacecraft  we have to consider the worst case ballistic entry and or partial parachute or airbag failure modes.

[jnc]

some lessons we learned from the motorsports world is that it is not the maximum g’s that are dangerous but the duration of time at that sustained g. For example a 50g impact at 0.1s is more dangerous than let say a 150g at 0.01s duration…

The picture must be a bit more complex than that, though, because ISTR that they decided that the problem with early (circa 1960ish) cars with the very strong metal tube frames was that in a crash, they decelerated too quickly, hence when they changed away from tube frames (although the change was for reasons other than driver safety, mainly) to structures which deformed/disintegrated on impact, and thereby absorbed energy and decreased the peak acceleration, that led to better outcomes for the drivers. (Ditto for the SAFER barrier stuff.)

Noel

[Rocket Science]

some lessons we learned from the motorsports world is that it is not the maximum g’s that are dangerous but the duration of time at that sustained g. For example a 50g impact at 0.1s is more dangerous than let say a 150g at 0.01s duration…

The picture must be a bit more complex than that, though, because ISTR that they decided that the problem with early (circa 1960ish) cars with the very strong metal tube frames was that in a crash, they decelerated too quickly, hence when they changed away from tube frames (although the change was for reasons other than driver safety, mainly) to structures which deformed/disintegrated on impact, and thereby absorbed energy and decreased the peak acceleration, that led to better outcomes for the drivers. (Ditto for the SAFER barrier stuff.)

Noel

Hey Noel,

Absolutely, deformable structures and shock absorption is part of the equation as is the “rate” of deceleration. Honeycomb structure at the base of the spacecraft, deformable-foam form fitting seats, and shock absorbers in the seat mounts all part of a complex equation. In general the occupant is the weakest link…

~Robert

[BrightLight]

In the images I have seen of the HL-20, all but one of the seats were vertical, with one seat for an incapacitated astronaut.  I don't have any recollection of the seat arrangement for the Dream Chaser other than vertical. Yet, the proponents of DC claim its lower landing G as a major plus for long duration space travelers. In contrast, SpaceX dragon-manned shows all seats in the quasi-horizontal position. Does the DC have the option for G optimized seats for return of long duration astronauts?

[Lee Jay]

Does the DC have the option for G optimized seats for return of long duration astronauts?

Reclined?  I think so.