totm nov 2023 SpaceX Discussion Thread

[magnemoe]

1 hour ago, sevenperforce said:

Not without LF engines.

True, however this can be added, for simplicity, could you get enough trust with an 3 bar pressure feed engine? With 3-4 engines you could use trust compensation for maneuvering. 
ISP is pretty irrelevant, might even be worth it doing an powered landing with this, other option is to jettison the passenger module and parachute land it.  
Yes this require to putting avionic and other systems up there but it would not add much weight relative to starship itself, with powered landing it would even work on moon or mars if you have an base there.

[sevenperforce]

1 hour ago, tater said:

Such a tug has ~10,500 m/s dv empty.

With 100 tons cargo it's 7400 m/s. Going someplace like EML-2 is ~3500m/s, so that tug with 100t can drop that 100t at EML-1, then have a lot or dv left (as it's now much lighter). It can absolutely come back to Earth, and propulsively brake in LEO, then get retanked, and do it again.

There's some math to be done here, I think.

We don't know what the TPS will weigh, yet, but let's say it comes in close to the shuttle high-temp reusable surface insulation (the black stuff) which was 9.2 kg per square meter. Covering half of a 45-meter-high, 9-meter-wide cylinder with this would come to 6.44 tonnes. A little more if the Starship TPS is heavier; a little less if it isn't. We'll assume that a returning aerobraking pass would be high-altitude enough to control with hot-gas thrusters alone; 2-3 passes are fine if needed.

Let's go with 80 tonnes and give it regular tanks. Some reference numbers (I'm using <> to indicate propulsive 1-way and >) to indicate aerobraking one-way):

• GTO-1 <> LEO = 2.27 km/s; GTO-1 >) LEO = 0.02 km/s
• EML-1 <> LEO = 3.77 km/s; EML-1 >) LEO = 0.77 km/s
• EML-2 <> LEO = 3.43 km/s; EML-2 >) LEO = 0.33 km/s
• LLO <> LEO = 4.04 km/s; LLO >) LEO = 1.31 km/s
• Earth escape <> LEO = 3.22 km/s; Earth escape >) LEO = 0.02 km/s
• GEO <> LEO = 4.33 km/s; GEO >) LEO = 2.06 km/s
• Jovian Transfer <> LEO = 8.8 km/s; Jovian Transfer >) LEO = 3.06 k/ms

Thus round-trip payload capacity is as follows for going propulsive only:

• GTO: 1232 tonnes
• EML-1: 479 tonnes
• EML-2: 592 tonnes
• LLO: 402 tonnes
• EE: 674 tonnes
• GEO: 330 tonnes
• Jovian transfer: -4 tonnes

And for using TPS (assuming 10 tonnes to be safe):

• GTO: 1268 tonnes
• EML-1: 532 tonnes
• EML-2: 645 tonnes
• LLO: 452 tonnes
• EE: 727 tonnes
• GEO: 373 tonnes
• Jovian transfer: 89 tonnes

So adding 10 tonnes of TPS offers a distinct advantage to any destination, with a bigger advantage for higher-energy orbits. Obviously these payloads are vastly bigger than what would ordinarily be delivered, even with LEO orbital assembly, so the tug would almost never need to be fully fueled. But TPS wins in every situation...moreso if it is not quite 10 tonnes.

The fact that the tug is SO overpowered for every single use inside the Earth-moon system is why I am not really so sure it is the best choice to begin with. It would be useful for BLEO payloads but those will be rarer (and anything going to Mars will need full TPS anyway) so why bother?

34 minutes ago, magnemoe said:

True, however this can be added, for simplicity, could you get enough trust with an 3 bar pressure feed engine? With 3-4 engines you could use trust compensation for maneuvering. 

Definitely not enough thrust with a 3-atm pressure-fed engine.

If you add another Raptor up there, you're golden. Or you could put all the RCS bottles up there and use repurposed 10-tonne RCS thrusters for escape engines.

Quote

ISP is pretty irrelevant, might even be worth it doing an powered landing with this, other option is to jettison the passenger module and parachute land it. 

Powered landing would have too many variables and require too much dV. Better to do a splashdown.

Edited October 1, 2019 by sevenperforce

[magnemoe]

5 minutes ago, ThatGuyWithALongUsername said:

Ooh, you gave me an idea, how about this:

Take a CREW variant and make the same modifications. Launch it into orbit. Hey, you can even go a bit past LEO with some tankers. Then send up crew, drain the tanks, and make the whole thing a giant "wet lab" space station. Plenty of room for long-term experiments.

Starship is large enough already I think, its as large internally as IIS. Wet workshop also require you to insulate the thing. 

The crew version has an decent sized cargo hold and you could easy set that up as an lab to do orbital experiments who would require adding an module to ISS. 
You would want to do some long term experiments in orbit anyway to test out life support system for real. 
An mixed mode version think space shuttle layout would also make sense doing stuff like satellite repair or even return for reuse. No it did not work for the shuttle because of cost, 20 million and the option to reach GEO changes this a lot. 

For standard satellite launches spaceship is overkill, true, so use the crew version, put satellite in the cargo bay launch to orbit, deploy satellite, then spend a couple of extra days in orbit. 
Lots of international ferries in Europe operate as mini cruse ships for an two day trip, this is often most of their income. An Swedish ferry to Latvia had the port in Latvia close down for rebuilding, it was still worth it just to do an one day cruise.  
This is a restaurant on one of the larger ones, eaten there many times. 

The round windows are passenger cabins. 

[tater]

 

[sh1pman]

Quote

Koren: Why did you post that tweet?

Bridenstine: We are working really hard as an agency to get to a day where when we announce a cost and schedule, we can have credibility. Our contractors have to be as committed to that as we are. I was getting a lot of calls from the media about this event, and so we just sent a tweet and said, look, we look forward to this, this is exciting, but at the same time we expect our contractors to be as committed to the programs that the American taxpayer has invested in.

Koren: Both SpaceX and Boeing are behind schedule on Commercial Crew. You told CNN last night that Starliner’s flight is still months away. Why single out SpaceX?

Bridenstine: I don’t. I’ve been critical of all contractors that overpromise and underdeliver. We are not singling out anybody.

https://www.theatlantic.com/science/archive/2019/10/elon-musk-jim-bridenstine-starship-commercial-crew/599218/

[CatastrophicFailure]

15 minutes ago, sh1pman said:

Bridenstine: I don’t. I’ve been critical of all contractors that overpromise and underdeliver. We are not singling out anybody.

Ahh. Ahhh. AHHHHH...

BULLCHOOO!

Dust... dusty in here... <sniff>

Edited October 1, 2019 by CatastrophicFailure

[Scotius]

Yeahhh... He didn't single out anybody. Except he did.

And as for the Starship... am i the only one hoping one of the first "true" missions of Crew Starship will be to Hubble telescope? With JWST moving forward at glacial pace, we might need to extend Hubble's life yet again...

[tater]

I like Bridenstine, but that tweet was crap.

[Barzon]

24 minutes ago, CatastrophicFailure said:

Ahh. Ahhh. AHHHHH...

BULLCHOOO!

Dust... dusty in here... <sniff>

How about when Jim said that if Boeing couldn't complete SLS, that they would find other contractors? That to me seems like being critical of "all contractors that overpromise and underdeliver."

[tater]

11 minutes ago, Barzon said:

How about when Jim said that if Boeing couldn't complete SLS, that they would find other contractors? That to me seems like being critical of "all contractors that overpromise and underdeliver."

We're not talking about the totality of what he's said, we're talking about that one tweet, about Commercial Crew. Boeing will get about twice as much money as SpaceX, and they are actually behind SpaceX right now. Bridenstine also knows that there is nothing that SpaceX can really do to push it to go faster.

Commercial Crew suffered from the budget being raided for... SLS. SLS, which is also over budget (not possible with Commercial Crew), as well as late.

A great example is the SLS Core Stage Pathfinder. Started in 2016, it was supposed to be done in '17---entirely sensible since it's a metal tube that only needs to not fall apart with no forces on it except gravity. Instead it's done in 2019. For a metal tube that does nothing... how long does it take to make SLS core sized tubes, even tubes that can do something? A few months. Heck, a flying tube---with engines---probably cost less than the pathfinder thing (and it was probably over budget, since it was late).

Edited October 1, 2019 by tater

[CatastrophicFailure]

1 minute ago, tater said:

A great example is the SLS Core Stage Pathfinder. Started in 2016, it was supposed to be done in '17---entirely sensible since it's a metal tube that only needs to not fall apart with no forces on it except gravity. Instead it's done in 2019. For a metal tube that does nothing... how long does it take to make SLS core sized tubes, even tubes that can do something? A few months. Heck, a flying tube---with engines---probably cost less than the pathfinder thing (and it was probably over budget, since it was late).

Well, I mean, it does need to weigh just so... ooh, and there’s those wireframe not-engines, too, real artist’s work there, youbetcha... 

[tater]

5 minutes ago, CatastrophicFailure said:

Well, I mean, it does need to weigh just so... ooh, and there’s those wireframe not-engines, too, real artist’s work there, youbetcha... 

This is worse, frankly. It's a very precise analog of the actual core stage in terms of balance, etc... why not just build another real tank, then FLY IT? I wasn't joking that the pathfinder likely cost more than the Starship in Boca Chica right now (a cost entirely dominated by the cost of the engines, BTW---not made of wire).

[Raven Industries]

I'd say as a general rule, if you're the head of any government agency, you've voided the right to complain about delays, inefficiency, and cost overruns from anyone else. 

[tater]

31 minutes ago, Raven Industries said:

I'd say as a general rule, if you're the head of any government agency, you've voided the right to complain about delays, inefficiency, and cost overruns from anyone else. 

And it's not even Bridenstine's fault, honestly. The delays got set long before he was around.

 

Also, putting the payload section back on the ground for various installations at a more reasonable altitude (they never got the fairings on around the forward flaps, for example).

 

[Barzon]

22 minutes ago, tater said:

And it's not even Bridenstine's fault, honestly. The delays got set long before he was around.

 

[LIKE]

[jadebenn]

Despite the somewhat incendiary headline, this is a high-quality article about the whole CCrew situation. It also goes into some detail about Jim Bridenstine's motivations behind the Twitter spat.

Reading between the lines, he doesn't think their schedule estimates are credible, was frustrated with CCrew delays, and was sick and tired of being bombarded with questions about Starship, so he lashed-out.

Quote

Bridenstine: We are working really hard as an agency to get to a day where when we announce a cost and schedule, we can have credibility. Our contractors have to be as committed to that as we are. I was getting a lot of calls from the media about this event, and so we just sent a tweet and said, look, we look forward to this, this is exciting, but at the same time we expect our contractors to be as committed to the programs that the American taxpayer has invested in.

Also, looks like we'll be buying more Soyuz seats after all.

Quote

Jim Bridenstine, NASA's administrator, said in an interview on Monday that he is not confident in [SpaceX's three-to-four month estimate]. The space agency will likely have to purchase more seats aboard Russian-made spacecraft in 2020, he said, to ensure US astronauts have continued access to the space station because of ongoing delays with its Commercial Crew program, he said. That program includes Crew Dragon and a Boeing-built capsule, Starliner, which is also years behind schedule.

[...]

Bridenstine referred to Crew Dragon's explosion as a "catastrophic failure," and said one of the reasons he's skeptical of the idea that Crew Dragon will be ready in the near future is because the updated emergency abort system "has not been qualified" and has not been tested.

 

Edited October 1, 2019 by jadebenn

[tater]

8 minutes ago, jadebenn said:

Reading between the lines, he doesn't think their schedule estimates are credible, was frustrated with CCrew delays, and was sick and tired of being bombarded with questions about Starship, so he lashed-out.

This is true, but the tweet was still not great. It could have been more generalized, or it could have been less specific about Commercial Crew WRT SpaceX, since Boeing is farther behind, and getting paid 2X into the bargain (they have not flown to ISS). SLS is in much worse shape cost/schedule wise as well, and SLS didn't have money snatched away to fund CCrew (harming both providers).

He's bombarded about Starship questions because Starship is actually interesting to people, and development is not happening at a glacial pace. Whatever happens during SS testing, it is 100% guaranteed to be interesting. Green run? Not even slightly interesting (I've see a large number of shuttle engines fired in the last decades, this is the same). SS 20km hop? It flies, and either we have some RUD, or we see it skydive, and flip and land, or some combo (including a RUD, lol). If they succeed, they move on, if not---they will have 4 vehicles to test before they get SH done (each of which might be cool science fiction looking rocket flights, or gigantic explosions). Not boring.

Even when SLS does fly... it's a not all-up, uncrewed mission to nowhere. SLS flights don't start looking interesting until Artemis-2. By then we get to watch BO try and not explode giant rockets. Fun time to like rockets and be alive.

[jadebenn]

I'm not making excuses for him. It was pretty unprofessional for someone in his position. Just wanted to post that quote as it's the closest to a confirmation we'll ever get.

[CatastrophicFailure]

23 minutes ago, jadebenn said:

Bridenstine referred to Crew Dragon's explosion as a "catastrophic failure,"

I swear, I was no where near the place, I was never even in the same time zone! 

It was the one-armed man with the candlestick on the grassy knoll...

I want my phone call. 

[tater]

9 minutes ago, jadebenn said:

I'm not making excuses for him. It was pretty unprofessional for someone in his position. Just wanted to post that quote as it's the closest to a confirmation we'll ever get.

Well, we all saw the video, lol. RUD is definitionally catastrophic.

[jadebenn]

Just now, tater said:

Well, we all saw the video, lol. RUD is definitionally catastrophic.

I was referring to the twitter exchange. 

 

[tater]

I meant his description of the static test failure.

[Raven Industries]

Setting aside the frustrations and/or conduct of a certain government administrator, I'm wondering if making Starship modular would be a good idea, and if Elon has considered it at all. If you make the cargo versions bay door open wide enough, you could maybe just slot crew modules and whatever else you want into the space. You could maybe have the plumbing for the extra engines crew version would require as part of the cargo version, and just slot in however many Raptors you need. I don't know if that would be efficient or safe or worthwhile at this scale, or any scale, but I was thinking it might help if there is ever a time when being able to change the balance of cargo vs crew versions quickly might be useful.  I don't know, what do you all think?

Edited October 2, 2019 by Raven Industries

[ThatGuyWithALongUsername]

1 hour ago, Raven Industries said:

Setting aside the frustrations and/or conduct of a certain government administrator, I'm wondering if making Starship modular would be a good idea, and if Elon has considered it at all. If you make the cargo versions bay door open wide enough, you could maybe just slot crew modules and whatever else you want into the space. You could maybe have the plumbing for the extra engines crew version would require as part of the cargo version, and just slot in however many Raptors you need. I don't know if that would be efficient or safe or worthwhile at this scale, or any scale, but I was thinking it might help if there is ever a time when being able to change the balance of cargo vs crew versions quickly might be useful.  I don't know, what do you all think?

What about windows? Sounds picky, but probably important for crew mental health.

[Raven Industries]

7 minutes ago, ThatGuyWithALongUsername said:

What about windows? Sounds picky, but probably important for crew mental health.

I suppose we could go the classic sci-fi route and just have screens that look like windows, but that's a good point.