SpaceX SN8 Launch

[darryl]

I watched the vid a few times. As stated, the engines cut out one by one, and came back on the same way. At each 'firing' there was an attitude correction made, and you can actually see the ship responding. It's of paramount importance that these systems work flawlessly, and as powerfully as need be for every possible circumstance. Perhaps it would be safer if there were six engines instead of three- an opposing pair fires and shuts off together, lessening the demand on the attitude control systems. Perhaps a minor malfunction can be tolerated, as opposed to when one thing goes wrong the ship crashes.

I've also wondered about distribution of the fuel, and how some sloshing around ( in complex ways) could place extra demands on the control system. If the tanks are built to prevent this, then they are heavier and more complex, so I'm assuming that only a minimum of extra attention has been paid to this. Lay a ship on its side and this could become a real problem.

I'm still wondering what conclusions they have come to regarding the low fuel header pressure. Haven't heard anything-

[RB211]

I watched the vid a few times. As stated, the engines cut out one by one, and came back on the same way. At each 'firing' there was an attitude correction made, and you can actually see the ship responding. It's of paramount importance that these systems work flawlessly, and as powerfully as need be for every possible circumstance. Perhaps it would be safer if there were six engines instead of three- an opposing pair fires and shuts off together, lessening the demand on the attitude control systems. Perhaps a minor malfunction can be tolerated, as opposed to when one thing goes wrong the ship crashes.

I've also wondered about distribution of the fuel, and how some sloshing around ( in complex ways) could place extra demands on the control system. If the tanks are built to prevent this, then they are heavier and more complex, so I'm assuming that only a minimum of extra attention has been paid to this. Lay a ship on its side and this could become a real problem.

I'm still wondering what conclusions they have come to regarding the low fuel header pressure. Haven't heard anything-

The short hop they did earlier had only one raptor engine, this time they went with three, I am pretty sure the final space going one is going to have at least 6 engines mounted.

[J Tiers]

Don't be fooled, the costs per launch DO matter. Budgets are not unlimited anymore, and expensive programs get terminated.

[A.K. Boomer]

Balance a stick on the tip of your finger and it is quite easy to do. .

I would not exactly call it "easy to do" the longer the stick the more predictability and then it can become somewhat second nature --- for a human that is, that can make instant 90 degree micro adjustments with their "base" as in if the things already landed on solid ground that your just manipulating, using angled thrusters at the very base to make corrections in mid air is a totally different feat... and in fact now that length works against you in totally sluggish response times, just some basic differences of the physics at play from the example you give to how they are actually having to function...

having control thrusters higher up WILL indeed create other issues but they could also save the entire rig from epic fail where as the other system cannot, once you touch down you better get it right or else your doomed, either way the basic concept is flawed, conditions need to be absolutely perfect or it's epic fail therefor the practicality issue comes into play, and so yeah they may have a little nitche where they will be held too without variations but even with that I know I will be seeing lots of crashes in the future due to the simple fact of instability...

https://youtu.be/jVSZdsAq4Bo

[Galaxie]

Regarding top mounted rocket engines, there would be problems related to positioning the engines so the exhaust clears the aft structure. There are only three ways I can think of to do it:

1) Attach the engines to extended structures so they are farther from the vehicle's centerline
2) Cant the engines at an angle
3) Place a heat shield on the aft portion

The problems with #1 are that thrust variations are magnified since they're not on (or close to) the centerline, and the engine gimbals would have to have a larger range of motion. (But maybe that's not really a problem?)
The problem with #2 is that the upward thrust is reduced due to the angle.
The problems with #3 are added weight and sideways thrust from the exhaust bouncing off the heat shield (see Robert Goddard's early design). Plus, it just looks dumb. 🤨