totm nov 2023 SpaceX Discussion Thread

[Minmus Taster]

4 hours ago, darthgently said:

If only it were merely raising an eyebrow and not torching things

Edit: see my next post for an explanation, there was a misunderstanding.

Edited Monday at 03:58 PM by Minmus Taster

[darthgently]

2 hours ago, Minmus Taster said:

Define "torching things

Maybe get out more and seek broader news sources.  Literally torching things

[Minmus Taster]

1 hour ago, darthgently said:

Maybe get out more and seek broader news sources.  Literally torching things

Edit: in light of an important clarification I'd like to apologize. I didn't make the connection with the Tesla incidents and assumed it was a metaphor. That's my bad.

Edited Monday at 03:56 PM by Minmus Taster

[tater]

The actual arson attacks in question are unrelated to SpaceX. Stop with deranged nonsense so the thread doesn't have to be cleaned.

 

ObSpaceX:

NROL-69 launches in about 2 hours

[Minmus Taster]

8 minutes ago, tater said:

The actual arson attacks in question are unrelated to SpaceX. Stop with deranged nonsense so the thread doesn't have to be cleaned.

 

ObSpaceX:

NROL-69 launches in about 2 hours

I apologize, I assumed that it was a metaphor. I don't follow news related to Tesla.

On that note I love the patch, I'm assuming the launch is classified?

[tater]

Just now, Minmus Taster said:

On that note I love the patch, I'm assuming the launch is classified?

Yeah, and we have to assume the sat has some cool origami to deploy.

[tater]

 

[tater]

Heheheeheheheh

[Minmus Taster]

Just now, tater said:

Heheheeheheheh

Noice 

[Codraroll]

4 hours ago, tater said:

Heheheeheheheh

I won't post that scene from Austin Powers because it's probably against the spirit of the forum rules, but I will remind you of its existence.

[grawl]

4 hours ago, tater said:

Heheheeheheheh

Bruh....

[tater]

I so want Bezos to post "welcome to the club."

[magnemoe]

23 hours ago, tater said:

Heheheeheheheh

its an camera angle thing. 

[Exoscientist]

On 3/20/2025 at 6:34 PM, Ultimate Steve said:

Here is my Starship terminal velocity spreadsheet, I recommend you mess around with it yourself:

https://docs.google.com/spreadsheets/d/1u6JzCNra7bFj1BVYvQm_XSVkjNFsqdjO9h5TVaydp9Q/edit?usp=sharing

I would not put any stock in the results as there are too many unknowns. However I'm confident in it enough to put an extreme upper bound on block 1 landing (not dry) mass at 350 tons with a more reasonable value at 250 tons.

The methodology is using the telemetry from flights 4, 5, and 6 during the terminal phase of descent, just before engine startup, and estimates of the in-stream area and drag coefficents of Starship's various components to calculate the mass at that point in flight.

I do not think that even with Starship's substantial mass growth, that the actual dry mass is above 200 tons as that was what Mk 1 was waaaay back in 2019. As you can see, this analysis does very little but state the obvious. Unless for some reason I'm correct and Starship really is that heavy at landing.

There are many sources of error:

Area errors:

• Starship's exposed areas were calculated through pixel counting. They are likely somewhat wrong due to perspective and human error. Thus the flap areas are wrong.
• My estimation of the exposed area of the Starship nose cone is likely off by somewhat.
• I did not account for the flap covers at all. I assumed the flaps were flat plates, 100% of the area of which moved if I remember correctly (I did this math a while ago).
• We do not really know what the average flap angle is during descent.

If the area increases, starship's mass increases and vice versa.

Drag coefficient errors (BIG DEAL, a lot of errors here):

• The drag coefficient of something you build out of shapes is not simply the area-weighted average of those shapes. They interfere and you can't just look up the drag coefficient of a Starship. I did the weighted average approach which is quite error prone.
• For all of my calculations I pulled the first number for "Shape drag coefficeint" off of google.
• The open bottom of the cylinder is expected to increase drag.
• The lack of an exposed face on the other side of the cylinder is expected to decrease drag.
• The drag coefficient for an angled plate is less than a flat one but there's no easily googleable way to figure that out. I used to know the math for that sort of stuff but that notebook is currently several states away and I don't want to re-learn flat plate compressible aerodynamics right now.
• I am likely overestimating the drag coefficient of the nose cone.

If the actual CD is higher, it will translate to an increase in Starship's dry mass.

Velocity errors (who knows):

• SpaceX telemetry reports one velocity scalar. Vertical velocity is not listed separately, and I expect that Starship will have some horizontal velocity - e.g. It may "glide" in with an extremely steep glide slope. If it does this, there's also lift to take into account, meaning the drag calculations are way off. Starship going crossrange (actual downwards velocity is lower than listed velocity) will significantly lower Starship dry mass. At the upper end, 2m/s of difference is like 7 tons lighter (IFT 4 102m/s -> 100m/s)
• SpaceX telemetry may not be perfectly accurate (the least of our worries)

Atmospheric conditions:

• I assumed 1.175kg/m3 atmospheric density at the landing site. This varies, and while Starship is below 1km or so (if I remember right), the atmospheric pressure may not be that high. A lower atmospheric pressure will linearly correspond to a decrease in Starship landing mass.

Flight by flight error sources and data:

• Flight 4 missed the target by 6 kilometers (I think this was from a CEO tweet or interview or something) and may have been booking it crossrange to attempt to get to its landing site. It also had a massive gaping hole in one of (at least that we know of) its flaps. Therefore I would not put too much stock into how its terminal velocity of 102.22m/s corresponded to a landing mass of 339 tons.
• Flight 5 had a terminal velocity of 92.2m/s and an estimated landing mass of 276 tons. Landing was onsite so crossrange velocity errors should be lower than flight 4.
• Flight 6 had a terminal velocity of 84.17m/s and an estimated landing mass of 230 tons. Landing was onsite so crossrange velocity errors should be lower than flight 4.

General errors:

• The calculation used was subsonic flow.

Distinguishing estimated landing mass from dry mass:

• Starship has an unknown propellant load at this point in the flight. The header tanks and feedlines contain the landing propellant but it is unknown exactly how much is used during the landing burn or how full they are (though I presume they are pretty full). Unsure if remaining propellant is vented or not.
• Depending on temperature, the mass of the remaining ullage gas in the tank could range from like 5 tons to like 40 tons depending on temperature and tank pressure.
• Starship displaces somewhere around 3.5ish tons of air at sea level and will "appear" that much lighter than it actually is from this analysis
• Is the nose cone pressurized? If so, with what and how much pressure?

 

Conclusions:

• This is an extremely bad way to estimate Starship's dry mass.

There are very many numbers which you can slightly tweak and they would still fall within the reasonable range that jump Starship's landing mass up or down by more than ten tons. I doubt we will get anywhere with this model but if you have any ideas let me know. Two things that would really help are if someone with CFD experience could try to figure out a vague estimate of Starship's actual drag characteristics, and when we get a ship  catch in some number of months, we might get a long range tracking shot showing the ship's approximate glide angle.

 Thanks for that. I discussed before I think it was a mistake for SpaceX not to go with expendable version of the Superheavy/Starship first then proceed to reusability, once the expendable version was proven. This approach was spectacularly successful with the Falcon 9. Taking this approach with the SH/SS they would now already be launching 250 tons to orbit, 10 times greater than the payload of the F9. And with the success at catching the SH booster, we may assume the per kilo cost would be reduced further still by partial reusability. Quite likely we would have single launch manned missions both to the Moon and Mars with partial reusability of less than $100 million cost now at less than what we are currently spending just for manned missions to the ISS.

 The approach that SpaceX is taken to reuse of the upper stage is also poor. Elon once estimated the dry mass of the Starship upper stage could be as low as just 40 tons as an expendable. Now the various modifications to the Starship for reusability, the dry mass is estimated as 160+ tons, an increase by a factor of 4 or likely more.

 For an orbital rocket you should try to minimize the weight growth of an upper stage as much as possible since that subtracts directly from payload. In that regard SpaceX should examine the possibility of using wings for landing instead of powered, vertical landing.

 Wings using lift can reduce the speed of descent thus decreasing the heat load on return, thereby reducing the thermal protection needed. The thermal protection used so far by SpaceX has not been successful. Reducing the heat load could reduce the amount of thermal protection needed. In fact, it might be it could even be reduced to zero.

 A surprising article:

Wings in space.
by James C. McLane III
The Space Review
Monday, July 11, 2011
Wing loading (the vehicle’s weight divided by its wing surface area) is a prime parameter affecting flight. The antique aluminum Douglas DC-3 airliner had a big wing with a low loading of about 25 psf (pounds per square foot of wing surface). At the other end of the spectrum, the Space Shuttle orbiter has a high wing loading of about 120 psf. This loading, combined with an inefficient delta-shaped wing, makes the orbiter glide like a brick. A little Cessna 152 private plane features a wing loading of about 11 psf and modern gliders operate down around 7 psf. A space plane with huge lifting surfaces and a very low wing loading might not require any external thermal insulation at all. Building a space plane with a wing loading of, say, 10 psf should not be an impossible proposition. Perhaps some day it will be done.
http://www.thespacereview.com/article/1880/1

 At the current overweight Starship mass, wings might be too large and heavy to get to this low wing loading but it might work if SpaceX went back to the expendable dry mass of only 40,000 kg. At such a mass, with the cross-section of the stage being 9 meters by 50 meters, and using the cross-section area of the cylindrical stage as “wing area”, the psf would be 40,000*2.2(pounds)/9*50*3.28² (sq.ft.) = 18 psf. 

 Still not at the 10 psf point. But it’s close so that added wing area needed would be small:

 

 Typically, wings amount to about 5% to 10% of the dry mass. For such small wings it would be closer to the smaller number so only 2,000 kg added weight, and the psf would still be about the same 10 psf number.

 That Space Review article though gives no references where this contention of a 10 psf needing no thermal protection was derived. 

 Can your spreadsheet calculate speed at intermediate points during descent? You would need to be able to do this for a calculation for the heating induced by the speed at each altitude and air density during the descent.

  Bob Clark

[tater]

1 hour ago, magnemoe said:

its an camera angle thing. 

Absolutely artful camera placement.

[RCgothic]

No we wouldn't have single launch crewed missions to Moon/Mars now because the crew spacecraft doesn't exist, and still wouldn't exist even if there'd been prior intent.

[darthgently]

For those who don’t think SpaceX is thinking very far ahead on this Mars thing, 2 years ago from the man who brought us Merlins and Raptors…

 

[zolotiyeruki]

20 hours ago, Exoscientist said:

 For an orbital rocket you should try to minimize the weight growth of an upper stage as much as possible since that subtracts directly from payload. In that regard SpaceX should examine the possibility of using wings for landing instead of powered, vertical landing.

 Wings using lift can reduce the speed of descent thus decreasing the heat load on return, thereby reducing the thermal protection needed. The thermal protection used so far by SpaceX has not been successful. Reducing the heat load could reduce the amount of thermal protection needed. In fact, it might be it could even be reduced to zero.

 

 

 

20 hours ago, Exoscientist said:

For an orbital rocket you should try to minimize the weight growth of an upper stage as much as possible since that subtracts directly from payload. In that regard SpaceX should examine the possibility of using wings for landing instead of powered, vertical landing.

 Wings using lift can reduce the speed of descent thus decreasing the heat load on return, thereby reducing the thermal protection needed. The thermal protection used so far by SpaceX has not been successful. Reducing the heat load could reduce the amount of thermal protection needed. In fact, it might be it could even be reduced to zero.

It sounds like you're describing an upsized Space Shuttle.  Even with wings, it required a heat shield.  I would hope we're all aware of what happened when the heat shield tiles were damaged.

In KSP, it's possible to design a spaceplane to survive reentry without a heat shield, but 1) it's not trivial, 2) KSP's model is far more forgiving than real life, 3) KSP's parts are far more heat-tolerant than real life materials, and 4) you're only going 2,400 m/s in LKO, vs 7km/s in LEO.

[Exoscientist]

3 hours ago, zolotiyeruki said:

It sounds like you're describing an upsized Space Shuttle.  Even with wings, it required a heat shield.  I would hope we're all aware of what happened when the heat shield tiles were damaged.

In KSP, it's possible to design a spaceplane to survive reentry without a heat shield, but 1) it's not trivial, 2) KSP's model is far more forgiving than real life, 3) KSP's parts are far more heat-tolerant than real life materials, and 4) you're only going 2,400 m/s in LKO, vs 7km/s in LEO.

 

 One of the criticisms of the Space Shuttle was it was so heavy, as an upper stage, for the payload it could get to orbit: ca. 80  ton dry mass, for only a ca. 20 ton payload. That’s the reverse of what it should be. For instance, for the Falcon 9 the upper stage has a ca. 4 ton dry mass for a ca. 20 ton payload. Note that if Elon’s estimate of the expendable Starship’s dry mass as 40 tons was accurate, then at a payload of 200 to 250 tons, the payload to upper stage ratio would be in the expected  range of about 4 or 5 to 1.

 The Space Shuttle heavy weight resulted in poor, i.e., high, wing loading. From Grok:

Query: What was the Space Shuttle orbiter wing loading in pounds per square foot?

Response:  
…
Final Answer:
The Space Shuttle orbiter's wing loading was approximately 91 psf at launch and 76 psf at landing, with slight variations depending on the specific mission and payload. These values reflect its design as a reusable spacecraft optimized for both atmospheric reentry and gliding to a runway landing.

 The Space Review article wanted a wing loading of 10 pounds per square foot(psf) to require no thermal protection:

Wings in space.
by James C. McLane III
Monday, July 11, 2011
The Space Review
Wing loading (the vehicle’s weight divided by its wing surface area) is a prime parameter affecting flight. The antique aluminum Douglas DC-3 airliner had a big wing with a low loading of about 25 psf (pounds per square foot of wing surface). At the other end of the spectrum, the Space Shuttle orbiter has a high wing loading of about 120 psf. This loading, combined with an inefficient delta-shaped wing, makes the orbiter glide like a brick. A little Cessna 152 private plane features a wing loading of about 11 psf and modern gliders operate down around 7 psf. A space plane with huge lifting surfaces and a very low wing loading might not require any external thermal insulation at all. Building a space plane with a wing loading of, say, 10 psf should not be an impossible proposition. Perhaps some day it will be done.
http://www.thespacereview.com/article/1880/1

 If the expendable Starship did have a dry mass of 40 tons, 88,000 pounds, and say added wings gave wing loading of 10 psf what does KSP say the heating would be during reentry?

  Bob Clark

Edit: I suppose this would have to be carried out in the Real Solar System mod rather than KSP itself.

Edited Wednesday at 06:00 PM by Exoscientist
Clarity.

[tater]

Wings don't work on Mars.

[zolotiyeruki]

My understanding is that, regardless of the wing loading, re-entry heating is still really, really hot.  A large wing may be able to reduce the peak flux by slowing you down higher in the atmosphere, but then you're just trading heavy heat shield tiles for heavy wings, and you *still* have to worry about the heat.

From what I've heard, NASA didn't want the big wings that the space shuttle had.  It was the military that wanted the cross-range capability (which it never used). 

[magnemoe]

On 3/24/2025 at 4:53 PM, tater said:

Yeah, and we have to assume the sat has some cool origami to deploy.

Good chance for that. Its obviously classified but if radar stuff you want an large antenna. 

[magnemoe]

3 hours ago, darthgently said:

For those who don’t think SpaceX is thinking very far ahead on this Mars thing, 2 years ago from the man who brought us Merlins and Raptors…

 

Spinning around the bottom and gravity is now up. 
Now its probably simpler to rearrange stuff like showers, toilets, sinks and other furniture in zero-g than using an long bar or wire to generate spin gravity. 

[Exoscientist]

9 hours ago, zolotiyeruki said:

My understanding is that, regardless of the wing loading, re-entry heating is still really, really hot.  A large wing may be able to reduce the peak flux by slowing you down higher in the atmosphere, but then you're just trading heavy heat shield tiles for heavy wings, and you *still* have to worry about the heat.

From what I've heard, NASA didn't want the big wings that the space shuttle had.  It was the military that wanted the cross-range capability (which it never used). 

 Still, I’d like to see the calculation. In the Space Review article, the idea was first proposed by the legendary spaceflight engineer Maxime Faget. So I’d like to see some calculations supporting or disproving it.

  Bob Clark

Edited Thursday at 03:42 AM by Exoscientist
Typo

[Ultimate Steve]

Hypersonic aerothermodynamics is hard and counter intuitive. Granted I only have an undergraduate's perspective on it (basically nothing) but I know enough to know that you are not going to get a good accurate answer by just using wing loading and whatever a large language model gives you.