4 ms·

What I'm getting from this, is that you can use weights to balance the mass of the spaceship during cruise conditions.

xarope 6y ago
Ships do this all the time (ballast), and anybody who's ever flown on a light aircraft or helicopter also knows the importance a pilot places on weight distribution. I guess what's surprising is that they needed that much weight (140+kg seems like a lot?) and couldn't redistribute existing componentry; guess the knapsack algorithm wasn't good enough, or that they just couldn't break up enough pieces? And yes, Cruise Mass Balance Devices sounds like the type of name a tired engineer would come up with to convince upper management...lol
- FredFS456 6y ago
  They can't redistribute existing componentry because of competing requirements: during cruise, the spacecraft needs to be balanced around the rotational axis (perseverance rotates at 2RPM in cruise). During re-entry, an asymmetric weight distribution is needed to generate lift.
xarope 6y ago
Surely you mean: "What I'm getting from this, is that you can use devices to balance the mass of the spaceship during cruise conditions"...j/k
numpad0 6y ago
Actually more like that you can eject weights to intentionally un-balance the mass of a spaceship so it'll glide rather than falling straight down. Atmospheric drag force center of drag and center of gravity to line up on a same axis, which force the craft to fly slightly sideways if spacecraft isn't perfectly balanced. Done carefully, it leads to direction of flight being slightly sideways, which is awkward but basically same as having lift towards that direction. Add roll control thrusters into the mix, and you get a really crude glider, with fixed pitch force, zero yaw control and barely controllable roll. With JPL-class engineering, such a spacecraft will be capable of actively correcting landing location.
- jcims 6y ago
  It’s like hypersonic curling
Aeolun 6y ago
Maybe they have both, and needed a name to distinguish the ejectable weights from the non-ejectable weights?

Ships do this all the time (ballast), and anybody who's ever flown on a light aircraft or helicopter also knows the importance a pilot places on weight distribution. I guess what's surprising is that they needed that much weight (140+kg seems like a lot?) and couldn't redistribute existing componentry; guess the knapsack algorithm wasn't good enough, or that they just couldn't break up enough pieces? And yes, Cruise Mass Balance Devices sounds like the type of name a tired engineer would come up with to convince upper management...lol

FredFS456 6y ago
They can't redistribute existing componentry because of competing requirements: during cruise, the spacecraft needs to be balanced around the rotational axis (perseverance rotates at 2RPM in cruise). During re-entry, an asymmetric weight distribution is needed to generate lift.

xarope 6y ago

Surely you mean: "What I'm getting from this, is that you can use devices to balance the mass of the spaceship during cruise conditions"...j/k

numpad0 6y ago

Actually more like that you can eject weights to intentionally un-balance the mass of a spaceship so it'll glide rather than falling straight down. Atmospheric drag force center of drag and center of gravity to line up on a same axis, which force the craft to fly slightly sideways if spacecraft isn't perfectly balanced. Done carefully, it leads to direction of flight being slightly sideways, which is awkward but basically same as having lift towards that direction. Add roll control thrusters into the mix, and you get a really crude glider, with fixed pitch force, zero yaw control and barely controllable roll. With JPL-class engineering, such a spacecraft will be capable of actively correcting landing location.

jcims 6y ago
It’s like hypersonic curling

Aeolun 6y ago

Maybe they have both, and needed a name to distinguish the ejectable weights from the non-ejectable weights?