[phire]

You can absolutely use engineering to limit the g forces. It's just a matter throttling back the engines near the end of a stage and/or staging sooner. For example, Gemini peeked at 6.4g, Apollo peeked at 4g and the Space Shuttle peeked at 3g.

3g is low enough that most humans shouldn't black out, even without training.

I'll also point out that professional astronauts are expected to remain functional for the entire assent (including emergencies, where g forces might peek much higher), which is not required for passengers.

[rqtwteye]

“Gemini peeked at 6.4g”

I remember reading that the Titan 2 pushed so hard that even the astronauts, who were pretty tough test pilots back then, were happy when the engine finally shut off.

[bodhiandphysics]

Astronauts also need to be able to survive 1) high g reentrues (apollo reached 7 gs on reentry) and abort modes, which can be very high acceleration indeed

[phire]

Yes, though you can engineer reentry too.

For example, the space shuttle uses it's wings (and body) to generate quite a bit of lift and spread the reentry over a much longer period. the g-forces during re-entry. It's 10min at 1.7g.

Though that's from LEO. Apollo came in directly from the moon at a much higher velocity, resulting in ~7g; For the Apollo missions that never left earth orbit, reentry was more like 3.5g.

A space ship aiming to carry untrained passengers will pick designs and mission profiles that are within their passengers abilities to withstand for both launch and reentry. Apollo picked a design and mission profiles with 7g reentry acceleration because they knew their trained astronauts could withstand it.

As for abort.. it's only limited spikes of high-g you only need it to be survivable for the passengers, while the pilots need to be able to control it.

[prox]

Starship does kinda do a shuttle wing entry right?

[phire]

Yeah, it has some lift. Not as much as the space shuttle, but more than apollo.

I couldn't find published numbers for reentry.

I know it hits 2.5g for a second during the final flip maneuver, I suspect they have engineered it to hit about the same during reentry.

[prox]

Cool stuff!

[andyjohnson0]

IIRC the peak for Mercury-Redstone was alightly higher than Gemini at about 7g.