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Scott Manley

@DJSnM

Feb 29

The NTSB has the initial report on the jet that crashed on a highway in Florida. Oil pressure warnings on both engines.
The throttles were set to the idle position, but that's the kind of thing you'd do when you're committed to a forced landing.
data.ntsb.gov/carol-repgen/a…

One fuel sample showed a small amount of water.

The right wing hit a road sign and that's likely what spilled a lot of fuel leading to the fire.

Read 6 tweets

Scott Manley

@DJSnM

Feb 25

There are lots of comments about the Nova-C lander being too tall, contributing to the tip over on landing.
Let's consider why it's this shape:
Firstly the landing legs are as wide as they can get for the Falcon 9 fairing without requiring a deployment mechanism.

Secondly, the core of the vehicle is the propulsion, and two propellent tanks. These are mounted inline because it makes for the lightest design, the propellent tanks are different sizes and masses so putting them side by side makes balancing more complex.

A common way to avoid the asymmetric mass problems is to use pairs of tanks, here's the Morpheus lander as an example.
But, this in turn means adds a lot of mass between more material needed for the tanks, extra plumbing, valves and structure.
Inline tanks save mass.

Read 6 tweets

Scott Manley

@DJSnM

Aug 12, 2023

When the UK Atomic Energy Authority was formed in 1954 it was given a coat of arms appropriate for a British institution, and like any coat of arms it’s full of symbolism.
Firstly, the motto ‘E Minimis Maxima’ - ‘from the smallest, the greatest’, i.e. atomic energy.

The black shield with silver spots references a graphite moderated reactor with silver uranium rods, and the inverted triangle with Red and yellow bolts shows the energy released.

This is controlled by a pair of red Pantheons, themselves restrained by gold chains. The Pantheons, each have 13 6 pointed stars and 2 7 pointed stars - totalling 92 points - the atomic number of uranium.
The collars have 5 spikes, the atomic number of Boron.

Read 4 tweets

Scott Manley

@DJSnM

Aug 10, 2023

So here's my full explanation for why the Vikram Lander in Chandrayaan-2 crashed back in 2019. We still don't have much data to go on, but a few news pieces of information give us a working timeline.
It crashed because of software problems and a valve not operating properly.

Thisis an overview of the descent plan, and a screen grab of a presentation showing the actual timeline. For the first 624 seconds the spacecraft is performing rough braking with full thrust from all the engines. This phase operated correctly with no problems.

The next phase was to begin fine navigation for landing, cutting the thrust and performing a 38 second 'camera coast' where the spacecraft held a specific attitude while the navigation sensors checked the terrain to figure out where the landing site was.

Read 11 tweets

Scott Manley

@DJSnM

Apr 20, 2023

So now I’ve got a minute to talk. In some ways the Superheavy flip after engine failures resembles those seen by Astra and Firefly.
The vehicle flipped because fins and flaps mean the center of drag is in front of center of mass, so it’s aerodynamically unstable.

Eventually the aerodynamic forces exceed the capabilities of the engines to keep it straight and it naturally flips. The engines continued to burn through the backflips.
Stage separation may have failed because of lateral forces beyond those designed.

With low thrust the vehicle would be below its planned trajectory and would need increased Angle of attack to get back on course. But increasing AoA eventually puts the vehicle beyond the point that engines can overcome the aerodynamic instability.

Read 5 tweets

Scott Manley

@DJSnM

Dec 4, 2022

People were asking for an explanation of these weird ass transfer orbits used by spacecraft these days, they use the gravity of the Earth, moon and sun to enter into lunar orbit without making any major engine burns.

There's 2 main things here, ballistic capture where something goes into orbit without an engine burn, and weak stability boundary orbits where you try to exploit areas of gravitational potential where opposing forces cancel out.