totm nov 2023 SpaceX Discussion Thread

[tater]

 

 

[CatastrophicFailure]

21 hours ago, Ultimate Steve said:

I spent four semesters and a summer working on this little guy:

Mazel Tov. 

18 hours ago, Ultimate Steve said:

The satellite is equipped with a software defined radiometer.

Does it have a Goo? Any proper science requires  Goo. 

[RCgothic]

1 hour ago, RCgothic said:

I've double-checked the table maths and the referenced Sopegno Et Al article.

Table 4 does indeed use only a 250km orbit, but Sopegno uses 500km. The correct DV of target altitude should be 3315m/s not 3430m/s in Lines 3 and 4. So the DV losses for lines 3 and 4 should be 1069m/s and 1060m/s respectively, not 954m/s and 945m/s.

The commenter is accurate. Maybe do a minimum of legwork yourself before casting aspersions next time.

Also, intuitively, all other things being equal on a nearly airless body, the higher the TWR the less the gravity losses. Line 2 having higher losses than Line 1 despite higher TWR warrants further explanation IMO.

 

Also, 3430m/s for a 250km orbit is only accurate to 3sf. (3427.34m/s).

[Ultimate Steve]

Goodness, going from 33 R2s to 35 R3s will save nearly 35 tons on the booster.

I really wish they would come out and say if their numbers are sea level isp and thrust or vacuum isp and thrust. Should be possible to double check with some effort, in another community the consensus is that those numbers are vacuum isp and sea level thrust.

95 tons of engine hardware alone on current super heavy boosters. That is a lot of mass.

2 hours ago, CatastrophicFailure said:

Does it have a Goo? Any proper science requires  Goo. 

Tucked away in a corner of the SDR's SD card, there is a picture of a KSP craft which I believe has a goo canister. 

[RealKerbal3x]

It's been a hot minute since I last posted in this thread, apparently

11 minutes ago, Ultimate Steve said:

Goodness, going from 33 R2s to 35 R3s will save nearly 35 tons on the booster.

I got curious earlier and graphed out the data we got from SpaceX's Twitter, and the mass reduction is definitely the most mental thing. The fraction of the total mass that consists of vehicle-side hardware drops off massively with Raptor 3, presumably due to the deletion of shielding and the CO2 purge system. For each engine, it's less than 200kg and constitutes just over 10% of the engine hardware's mass.

I considered calculating exhaust velocity and mass flow rate as well, but given that the thrust value is apparently for sea level while the Isp value is in vacuum (as you said), I figured it probably wouldn't give me an accurate result.

[AckSed]

So just to be clear, we have:

a thrust-to-mass ratio that approaches the Merlin 1D, already one of the lightest engines for its thrust

on a full-flow staged-combustion methalox rocket engine

that's meant to be mass-produced in the hundreds to thousands

providing 280 tons of thrust per engine

and they think they can make it better?

I'm torn between full starry-eyes and cautious disbelief.

[Meecrob]

On 8/2/2024 at 7:39 AM, Exoscientist said:

 Article in Nature does not find Mars Starship missions feasible:

About feasibility of SpaceX's human exploration Mars mission scenario with Starship.
Scientific Reports
volume 14, Article number: 11804 (2024) 
https://www.nature.com/articles/s41598-024-54012-0

  Bob Clark

If I didn't know any better, it would seem to me that lamewad humans usually have infinite ways to poke holes in solutions they do not fully grasp.

On 8/2/2024 at 4:42 PM, Ultimate Steve said:

I spent four semesters and a summer working on this little guy:

And he's going up on the NG-21 mission tomorrow morning!

Yo buddy, you are gonna need a LOOOOONG cable if you are using that for telemetry! (just messin') Let us know how it goes!

Edited August 3 by Meecrob

[tater]

3 hours ago, Ultimate Steve said:

I really wish they would come out and say if their numbers are sea level isp and thrust or vacuum isp and thrust. Should be possible to double check with some effort, in another community the consensus is that those numbers are vacuum isp and sea level thrust.

Yes. That's what it is.

[darthgently]

10 hours ago, Exoscientist said:

 

 However, the comment is from an anonymous user posting from a social media account. So we can’t know if the commenter has any knowledge in the field.

  Bob Clark

[Appeal to Authority flag on play]

Knowledge of poster's knowledge in the field is irrelevant.   All that matters whether the presented analysis is correct or not. Are the citations referred to valid or not?

[Ultimate Steve]

Stop it, you're this close to having me doing a deep dive on that paper and posting a half novel long post here about it and get no sleep tonight haha.

Back to the raptor 3. 35 tons less engine on super heavy is monumental. And that's in addition to everything else. That's a very large percentage improvement in dry mass from the engines alone. Even if Super Heavy somehow massed 350 tons that is a 10 percent mass decrease, again, from engines alone.

[darthgently]

9 hours ago, AckSed said:

So just to be clear, we have:

a thrust-to-mass ratio that approaches the Merlin 1D, already one of the lightest engines for its thrust

on a full-flow staged-combustion methalox rocket engine

that's meant to be mass-produced in the hundreds to thousands

providing 280 tons of thrust per engine

and they think they can make it better?

I'm torn between full starry-eyes and cautious disbelief.

When I consider the mind boggling power and efficiency gains with ICE auto engines from the first early  prototypes to what is possible now and it becomes easier to imagine something better than Raptor 3

[mikegarrison]

So what happened to all the wires and ECUs and pressure taps, etc.? Did they move internal, or did SpaceX just figure out a way to control the engine without them?

[darthgently]

3 hours ago, mikegarrison said:

So what happened to all the wires and ECUs and pressure taps, etc.? Did they move internal, or did SpaceX just figure out a way to control the engine without them?

Both, from what I gather.  Also I wonder how much of that rat's nest was debug-oriented data gathering and experimental designs that didn't make the final cut

[Ultimate Steve]

And, mission is orbital!

[tater]

 

 

[Ultimate Steve]

 

Couldn't find the cygnus thread so I guess it's going here. Hopefully it is something that can be fixed with a settings change or quick software update. 

[darthgently]

2 hours ago, Ultimate Steve said:

And, mission is orbital!

Congrats! 

[CatastrophicFailure]

1 hour ago, Ultimate Steve said:

 

Couldn't find the cygnus thread so I guess it's going here. Hopefully it is something that can be fixed with a settings change or quick software update. 

That does indeed seem to be the case:
 

How does this potentially affect your progeny? Is it onboard Cygnus for deployment from the ISS?

 

 

[calabus2]

11 hours ago, mikegarrison said:

So what happened to all the wires and ECUs and pressure taps, etc.? Did they move internal, or did SpaceX just figure out a way to control the engine without them?

The vast majority of those pipes and equipment were for sensors. After years of gathering data they understand the design and performance characteristics and the vast majority of that sensing equipment isn't necessary and due to the weight loss your rocket can now carry more payload. 

[Ultimate Steve]

1 hour ago, CatastrophicFailure said:

 

How does this potentially affect your progeny? Is it onboard Cygnus for deployment from the ISS?

It will be deployed from the ISS, I believe from the Nanoracks airlock. If Cygnus doesn't reach the ISS, it is game over. Granted it looks like they probably have the issue sorted. It is looking like maybe a 1 day delay or so at this point? But that depends on what trajectory they replace the current one with.

The ground station is not yet set up though (the guy in charge dragged his feet ordering a new antenna rotator for well over a year) and the last semester the team was downsized down to the two seniors who knew what they were doing the most, and now that we've both graduated, this means that the team of newbies, who won't even be meeting for the first time until a month from now at the earliest have to figure out antenna pointing and moving the ground station software to the server on the roof, as well as a few other things. Given how effective I was as a newbie, this is a big ask. I would have much preferred to retain at least one non senior so that there could be some team continuity, but that decision was above me.

The CubeSats typically get deployed 1-3 months after launch, I have no idea where we are on that spectrum and I have no idea if we have any say in when that is, I was pretty well insulated from the administrative side of things.

Basically, that's a lot of words to say "We will take any delay we can get". The biggest tragedy would be for it to work flawlessly but we would never know because the ground station didn't get put together.

[tater]

https://arstechnica.com/space/2024/08/nasa-likely-to-significantly-delay-the-launch-of-crew-9-due-to-starliner-issues/

Crew-9 might move from August 18 to Sept 24. This is of course related to Starliner.

[tater]

 

[darthgently]

11 minutes ago, tater said:

 

This is a beautiful shot.  I'm going to put it in the same league as the best out there in the last few decades of rocket footage.

[darthgently]

Not sure this is official, but if they are really going for the catch, it is perfect

 

[Exoscientist]

On 8/3/2024 at 12:53 PM, RCgothic said:

I've double-checked the table maths and the referenced Sopegno Et Al article.

Table 4 does indeed use only a 250km orbit, but Sopegno uses 500km. The correct DV of target altitude should be 3315m/s not 3430m/s in Lines 3 and 4. So the DV losses for lines 3 and 4 should be 1069m/s and 1060m/s respectively, not 954m/s and 945m/s.

The commenter is accurate. Maybe do a minimum of legwork yourself before casting aspersions next time.

Also, intuitively, all other things being equal on a nearly airless body, the higher the TWR the less the gravity losses. Line 2 having higher losses than Line 1 despite higher TWR warrants further explanation IMO.

 

 

 I didn't say he was wrong, only that we couldn't know if he was knowledgeable in the area. But we can see that he was being disingenuous in implying the difference was sizable. The difference is relatively small so the conclusions still hold.

  Bob Clark

Edited August 6 by Exoscientist