I saw a made-for-TV movie of Cold Equations many years ago where they totally reworked it to be a “blame the big corporations” episode instead. (The epidemic they were going to take care of was fake news, apparently). The story is much better.
I doubt a stowaway would unbalnace the rocket - the main engines gimbal for just such a reason.
Apparently one of the other issues is ISS capacity. During the launch it was mentioned that the US module had been reconfigured for 4 berths, but with the existing US astronaut already on board, that meant the fifth wheel - the pilot - would probably string up a hammock in the docked capsule. ISS life support had been beefed up for a crew of seven.
I guess my view is that the parachutes have be overbuilt, because there is so much natural variation in their dynamics. SpaceX actually found that NASA’s models for parachute line strength requirements were wrong, and had to redesign their chute system based on the results. NASA had been going for decades with a model that had much less margin than they thought.
Fortunately, as you note, parachutes are cheap in dollars and mass, and so every system has had lots of redundancy, and a complete failure would have been unlikely. Still, you never want to be in a situation where you’re actually spending the margin you built in.
In contrast, rockets have very predictable performance. Just a few parameters tell you everything you need to know. There’s still some random variation, as you pointed out–it’s just way, way less than with parachutes. A bright high-schooler can take a rocket design and tell you within a few percent how much mass it can send to LEO. You aren’t going to get anywhere near that good with the mass limit of a parachute design, even with a room full of PhDs.
You are of course right that scale matters. The Apollo space suit backpacks were left on the Moon, just so that they could bring a few extra pounds of samples back. A full extra human would have been impossible.
Another aspect is that the results of falling short of rocket performance are a lot more binary than with parachutes. If you run out of fuel 100 meters above ground (i.e., you made it >99.9% of the way down), you will not be happy. Or, if you land with 50 m/s of excess delta V (out of 8000 m/s in orbit), you will also have a bad day. But a parachute system that lands at 5 m/s instead of 4 is probably going to be ok.
All good points. Thank you. Margin is margin enough until it isn’t.
And yes, the inherent random imponderables end up being added into the base load so you’ll still have margin when all the noise lines up against you. Which means systems solving noisier problems, e.g. parachutes, end up with more margin in the vast majority of cases than systems solving less-noisy problems, e.g. thrust variation.
Yowza about NASA’s parachute calcs! I have to suspect there are some more dirty calcs & invalid rules of thumb hiding in NASA’s specs left over from 1950s astronautics practice driven by the limitations of 1950s data gathering and 1950s calculation ability.
With modern tools we may well just make bigger better GIGO faster, but time-honored doesn’t really mean time-tested given the small sample size of all US astronautics operations by comparison to the sample size in any other high tech industry.
By way of cite, incidentally (since I wanted to refresh my own memory as well):
It turns out NASA, SpaceX and Boeing have all been using faulty load assumptions from Apollo parachute data to design their modern parachutes.
“I look at what Apollo published and what they did and I now recognize they probably weren’t carrying as much safety factors as they thought they were," Machin said.
So parachute engineers today are dealing with a triple whammy of issues: Trying to make lighter parachutes based on Apollo load assumptions that probably weren’t operating within safe margins.
“NASA had, since the Apollo program, a way of determining the loads in the risers on the parachutes,” SpaceX COO Gywnne Shotwell said in a December meeting with journalists as reported by SpaceFlight Now. “They made a (conservative) assumption … from the Apollo program. We did it. Boeing did it. We were just following their standard."
This causes a problem called asymmetrical load distribution in which the parachute doesn’t inflate evenly and therefore isn’t effective.
“As you drive that parachute lighter and lighter, your safety margins become less and less and during the testing with SpaceX we found out that the asymmetry factor is in fact an issue,” Hempe said.
The parachute industry had a collective aha moment and got to work making major changes.