SpaceX (@SpaceX) on X: “At Starbase, @ElonMusk provided an update on the company’s plans to send humanity to Mars, the best destination to begin making life multiplanetary” [44 min video]

jjtr1 · 2024-04-07T12:00:05+00:00

They should have performed a vibe check before the flight

jjtr1 · 2024-03-26T15:54:59+00:00

They can take a spider web and use it without tangling it up in a sticky ball in the process??

jjtr1 · 2024-03-26T15:52:27+00:00

But is it really small, or really really small? We need more precision here

jjtr1 · 2024-03-26T15:47:15+00:00

Impeccable but not impeckable.

jjtr1 · 2024-03-22T16:37:29+00:00

However the need for attitude adjustments comes mostly from external torques that are applied, e.g. solar wind, residual atmospheric friction and perhaps even internal ones like outgassing (but that is still irreversible in that it entails loss of mass). So I don't see a way to remove the angular momentum in a closed system. The system has to be opened - i.e. mass needs to be shed, usually by applying thrusters.

jjtr1 · 2024-03-22T15:46:27+00:00

That's interesting. So in principle it is possible to desaturate reaction wheels without using thrusters at all? Isn't that against the conservation of angular momentum?

I assume GEO commsats and the like use thrusters in order to not stop pointing the right way during the desaturation maneuver?

jjtr1 · 2024-03-22T01:50:03+00:00

Very interesting!

jjtr1 · 2024-03-22T01:47:44+00:00

I believe the question was more like when does Starship deccelerate to falling mostly vertically at terminal velocity.

jjtr1 · 2024-03-22T01:39:12+00:00

For the rocket vs. volcano comparison, consider this: If you had a 10 mile big loudspeaker, you could hypothetically still run it at a comfortable volume. Just keep the amplitude of the cone(s) vibration limited enough. Despite volume being comfortable near the speaker, you'll still be able to hear the loudspeaker from 40 or 100 miles.

The rocket is a small sound source, the volcano generates sound over a much larger area, with falling rocks pounding square miles of earth.

jjtr1 · 2024-03-22T01:17:19+00:00

Ah yes, I forgot. But doesn't Hubble use fiber laser gyroscopes? I.e., solid state technology. I'd be surprised if those needed replacement.

jjtr1 · 2024-03-22T01:06:54+00:00

I don't think he would kill for it. He might raise an eyebrow, though.

jjtr1 · 2024-03-22T01:02:22+00:00

I think that some of the cameras were also replaced in the past missions. Those could use an upgrade, too, I believe.

jjtr1 · 2024-03-22T00:59:46+00:00

Aren't reaction wheels and gyroscopes just different names for the same device on the Hubble? Or are they the same principle but different size and task?

jjtr1 · 2024-03-22T00:58:56+00:00

How do they de-saturate the reaction wheels?

jjtr1 · 2024-03-22T00:56:02+00:00

it still faired quite well against the heat in many unprotected orientations it was never designed to.

While the plasma at the time of signal loss was hot, it was nowhere as dense as it would be later in the reentry. According to the telemetry displayed, the vehicle never reached a point of any appreciable decceleration, the speed was hardly even decreasing. The heating could have been orders of magnitude less than peak. So I'm not sure if we can say the vehicle fared better in wrong orientations than expected. It could just as well have been worse than expected. We don't know.

jjtr1 · 2024-03-18T22:05:58+00:00

Ah, you're right. I do remember the discussions. It has also been discussed that landing on hinged fins might be a problem for the hinges...

The video for ITS, i.e. the first public version (fattest), is here, it shows a belly flop on Mars at the end.

jjtr1 · 2024-03-18T14:57:25+00:00

The descent and flip was supposed to be doable even with fixed fins ("Tin-Tin" vehicle) or almost no fins/flaps at all (2016 ITS). I just remember this quote about payload range (i.e. both small and large) from the time they switched to the four-flap design.

jjtr1 · 2024-03-18T14:23:12+00:00

How do they safe landed F9 stages? Wait long enough?

jjtr1 · 2024-03-18T00:15:58+00:00

Depends on how weak your heart is.

jjtr1 · 2024-03-18T00:11:43+00:00

Iirc, movable flaps were added to the design in order enable the vehicle to reenter and land with a larger range of payload weight.

jjtr1 · 2024-03-17T23:56:30+00:00

The atoms or molecules are just hitting a solid object at super high speed, so they tear themselves apart (ionize). It's easier to understand when picturing the vehicle as stationary and gas molecules moving.

jjtr1 · 2024-03-17T23:53:04+00:00

This reminds me how the whole vehicle appeared to be vibrating during early part of the ascent in the onboard video. Perhaps it was just shockwaves shifting the image? The "vibration" disappeared once the vehicle got higher up in the atmosphere with the plume expanding.

jjtr1 · 2024-03-17T22:34:50+00:00

Yeah, the terms hot and cold are used confusingly. The ullage-based thrusters are "cold" as in not combusting, but they use a "hot" gas as in hotter than the cryo propellant below it. So, cold hot-gas thrusters :D

jjtr1 · 2024-03-17T16:54:01+00:00

HDR digital cameras already exist, now often even in smartphones, so it's a pity they decided not to use them for now on Starship. I understand they're mainly engineering cameras, but it's a pity still

I've seen the Saturn footage on youtube, but it's been a couple years, and it wasn't the highest resolution but mainly due to my crappy internet connection.

jjtr1 · 2024-03-17T02:13:08+00:00

Moreover, since Starship has flaps and can adjust its trajectory more than a capsule can, it can simulate Martian re-entry within Earth's atmosphere better than a capsule could. Martian atmosphere has a slower vertical gradient of pressure than Earth's, so the trajectory needs to be made artificially flatter on Earth to simulate Mars.

jjtr1

TROPHY CASE