4 ms·

They seem very fragile? The one at 0:49 exploded just from tipping over. Perhaps because they're huge i guess.

marsRoverDev 9y ago
They're probably only built to withstand forces associated with a nominal launch to save on weight; being able to withstand tipping over is unnecessary if you can avoid tipping over in the first place.
JshWright 9y ago
They are literally thin walled fuel tanks with some rocket engines strapped to the bottom. A soda can dozens of meters tall would be an appropriate analogy.
bryananderson 9y ago
Every pound of weight you add to the rocket is a pound of payload that you can't put into space.
- JshWright 9y ago
  It's not technically 1:1 on the first stage. It varies a bit from launcher to launcher, but it's in the ballpark of 4:1 (you lose a pound of useful payload for every four pounds you add to the first stage). Your point is spot on though. Don't waste mass to account for failure modes that you can just avoid in the first place by landing upright.
ceejayoz 9y ago
> They seem very fragile? They're extremely fragile. In fact, they're stored pressurized because laying on their side would damage them without the pressure keeping the walls rigid.
- mikeash 9y ago
  My understanding is that they don't need pressurization while being stored, but do need it to withstand flight loads. This is in contrast to, for example, the older Atlas rockets, which had to be pressurized constantly and would collapse otherwise. Of course I can't find any authoritative source on this, although there are a lot of random internet folks like myself repeating the claim. And I guess I'm throwing one more on the pile here.
  - ceejayoz 9y ago
    I unfortunately can't find an authoritative source, either, but I recall a /r/SpaceX discussion where it was stated that hurricane prep includes maintaining power because they're (lightly) pressurized at all times.
    - mikeash 9y ago
      I wonder if they might maintain pressurization to increase strength in the event of some mishap, but it's not an instantaneous disaster if pressurization is lost. I recall reading that they have equipment to maintain pressurization while the boosters are trucked to the launch site as well, so it's not just flight loads, in any case.
      - JshWright 9y ago
        Yeah, they aren't balloon tanks (which absolutely require pressurization), but they do keep them pressurized as it improves their structural stability.
    - snrplfth 9y ago
      They're pressurized with nitrogen generally, just to keep them clean and dry inside. They're quite capable of standing or lying down while unpressurized though.
  - rory096 9y ago
    You're correct - the Atlas (ICBM as well as the current Centaur second stage) design that requires constant pressurization is known as a balloon tank.[0] SpaceX doesn't use balloon tanks, but it does pressurize tanks with nitrogen during transport to keep the tank walls rigid and prevent damage. [0] https://en.wikipedia.org/wiki/Balloon_tank https://en.wikipedia.org/wiki/Balloon_tank
mikeash 9y ago
Huge and thin. Proportionally, the walls are thinner than a soda can's.

They're probably only built to withstand forces associated with a nominal launch to save on weight; being able to withstand tipping over is unnecessary if you can avoid tipping over in the first place.

JshWright 9y ago

They are literally thin walled fuel tanks with some rocket engines strapped to the bottom. A soda can dozens of meters tall would be an appropriate analogy.

bryananderson 9y ago

Every pound of weight you add to the rocket is a pound of payload that you can't put into space.

JshWright 9y ago
It's not technically 1:1 on the first stage. It varies a bit from launcher to launcher, but it's in the ballpark of 4:1 (you lose a pound of useful payload for every four pounds you add to the first stage). Your point is spot on though. Don't waste mass to account for failure modes that you can just avoid in the first place by landing upright.

ceejayoz 9y ago

> They seem very fragile? They're extremely fragile. In fact, they're stored pressurized because laying on their side would damage them without the pressure keeping the walls rigid.

mikeash 9y ago
My understanding is that they don't need pressurization while being stored, but do need it to withstand flight loads. This is in contrast to, for example, the older Atlas rockets, which had to be pressurized constantly and would collapse otherwise. Of course I can't find any authoritative source on this, although there are a lot of random internet folks like myself repeating the claim. And I guess I'm throwing one more on the pile here.
- ceejayoz 9y ago
  I unfortunately can't find an authoritative source, either, but I recall a /r/SpaceX discussion where it was stated that hurricane prep includes maintaining power because they're (lightly) pressurized at all times.
  - mikeash 9y ago
    I wonder if they might maintain pressurization to increase strength in the event of some mishap, but it's not an instantaneous disaster if pressurization is lost. I recall reading that they have equipment to maintain pressurization while the boosters are trucked to the launch site as well, so it's not just flight loads, in any case.
    - JshWright 9y ago
      Yeah, they aren't balloon tanks (which absolutely require pressurization), but they do keep them pressurized as it improves their structural stability.
  - snrplfth 9y ago
    They're pressurized with nitrogen generally, just to keep them clean and dry inside. They're quite capable of standing or lying down while unpressurized though.
- rory096 9y ago
  You're correct - the Atlas (ICBM as well as the current Centaur second stage) design that requires constant pressurization is known as a balloon tank.[0] SpaceX doesn't use balloon tanks, but it does pressurize tanks with nitrogen during transport to keep the tank walls rigid and prevent damage. [0] https://en.wikipedia.org/wiki/Balloon_tank https://en.wikipedia.org/wiki/Balloon_tank

mikeash 9y ago

Huge and thin. Proportionally, the walls are thinner than a soda can's.