totm nov 2023 SpaceX Discussion Thread

[tater]

2 minutes ago, magnemoe said:

An real suborbital jump could give valuable data on heating, And they need to test superheavy under load. so just lob SS up have if fly for some time, the do an burn to reverse its trajectory and land. 

Yeah, they could. I suppose it's a mild EDL test, but if SH is involved, I'd tend to call it a launch, not a "hop" in the way we have seen so far anyway.

13 minutes ago, zolotiyeruki said:

Is there a corrosion issue with storing LOx in a mild steel tank?

I think such tanks are made of stainless.

[magnemoe]

1 minute ago, tater said:

I think such tanks are made of stainless.

SS uses stainless tanks anyway.  for mild steel I think of stuff like rebar and bargain bin tools. All run into destroying the screw trying to unscrew it. If the screwdriver get destroyed instead you was fooled. 
Yes you have the tricks of putting an 2 meter long pipe over an wrench and jumping on it. 

[cubinator]

The other thing you get from a 100 km hop is supersonic flight, which Starship hasn't yet done.

[JoeSchmuckatelli]

2 hours ago, mikegarrison said:

OK, no, I guess they showed SpaceX sending out crews in the next Mars transfer window, so a few years from now

You need aggressive goals to achieve phenomenal things.  Even if you don't meet your time line... everyone is amazed by what you did accomplish. 

 

The key, I think, is that SpaceX is not beholden to Congress - and some parts that just HAD to be built in Senator Grumpus' state (even if that state isn't known for its high tech manufacturers). 

[tater]

 

[tater]

 

[sevenperforce]

2 hours ago, tater said:

 

All that makes good sense.

Catching Starship? I'll have to see it to believe it.

[tater]

3 minutes ago, sevenperforce said:

Catching Starship? I'll have to see it to believe it.

Yeah.

Seems nuts.

 

Of course landing on the launch clamps seemed nuttier.

[SOXBLOX]

5 hours ago, StrandedonEarth said:

kilogallon

Is this an Imperimetric unit?  

Just joking, I know it's a thing.

7 minutes ago, sevenperforce said:

Catching Starship? I'll have to see it to believe it.

Why would they want to? I mean, it has to land sans catching rig on the Moon and Mars anyway. Why use it only on Earth?

Edited April 9, 2021 by SOXBLOX

[sevenperforce]

8 minutes ago, tater said:

Yeah.

Seems nuts.

Of course landing on the launch clamps seemed nuttier.

Both involve a very convenient violation of the rocket equation, which is admittedly very nice.

But Starship? Aish. The mechanics are fairly straightforward. A big net with a robust pully system. Maybe use some water displacement. But at 67 m/s bellyflop descent speed and a putative deceleration limit of 2 gees, you need 114 meters of braking distance. If you are generous and allow 3 gees, that's still 76 meters of braking distance. That's...frankly...insane.

11 minutes ago, SOXBLOX said:

Why would they want to? I mean, it has to land sans catching rig on the Moon and Mars anyway. Why use it only on Earth?

I know, right?

I have always been a proponent of "use the legs on Mars that you must use on Earth because anything else is STUPID."

But I suppose if you have 100 Earth landings for every 1 Mars landing then perhaps making single-use sacrificial Mars landing legs becomes attractive.

[StrandedonEarth]

41 minutes ago, SOXBLOX said:

5 hours ago, StrandedonEarth said:

 

Is this an Imperimetric unit?  

Standard Imperial 

What they really need is some sort of extra air brake near the nose to pull the nose up. Skipping the wild sloshing of the flip burn maneuver. 

Edited April 9, 2021 by StrandedonEarth

[Flying dutchman]

5 hours ago, tater said:

 

Almost looks like a little russian tks capsule.

Edited April 9, 2021 by Flying dutchman

[SOXBLOX]

1 hour ago, StrandedonEarth said:

What they really need is some sort of extra air brake near the nose to pull the nose up. Skipping the wild sloshing of the flip burn maneuver. 

I think we have those. They're like big bedsheets, with lots of ropes that tie them to a hardpoint. 

 

1 hour ago, StrandedonEarth said:

Standard Imperial 

LOL!

[RCgothic]

I also think catching starship in a net is nuts. Even with a ridiculously long breaking distance a net that size is not inertialess. An impact at 70+m/s isn't fun for reusability.

Lots of TPS on SN15:

 

 

 

Edited April 9, 2021 by RCgothic

[KSK]

That's like one of those 'figure out the next number in the sequence' puzzles.

 

[Ultimate Steve]

So we are looking at 15-20k tiles for the whole starship? That's a lot of tiles.

[RealKerbal3x]

13 minutes ago, Ultimate Steve said:

So we are looking at 15-20k tiles for the whole starship? That's a lot of tiles.

At least the large majority are a common design, rather than there being literally thousands of unique tile shapes like Shuttle had.

[Brotoro]

I'm not clear why people think you have to catch a Starship at bellyflop speed.  You could still do the flip and braking maneuver, then drop it onto a net.  It would have to be a sufficiently flame resistant net, maybe made of metal cables.  And the support towers holding up the net could pivot inwards, turning the flat net into a 'bag' to catch the Starship mostly vertically.

Cylindrical balloons around the rim of the net could inflate to cushion the sides of the Starship.

[Hannu2]

13 hours ago, Meecrob said:

Storage tanks are not storage tanks though. There are commercially available storage tanks for applications that exist right now. Starship is a different scale though. The evidence is they built a storage tank bigger than any tank they bought commercially.

What is the difference in this case? Methane and liquid oxygen are common chemicals in industry and they are used in enormous quantities in many processes. Spacex's tank farms are small and trivial compared to for example those of LNG ship terminals or oil refineries. As far as I know they must obey the same industrial standards set by laws. I do not see any good reason why very standard off the shelf liquefied gas tanks would not work for SpaceX.

It is strange decision to build own tank, but maybe they developed something in welding process and decided to make a tank instead of dummy test rings. If their welding quality is enough for rocket it certainly fulfills all standards needed for storage tank. It is not straightforward to just weld a tank and store thousands of cubic meters dangerous liquid in it. Probably even bureaucracy needed to get permission to use tank for storing dangerous chemicals is quite time consuming and expensive. I am not sure if aerospace certificates is accepted for industrial storage use (I hope USA has easier bureaucracy but in EU country I would not even ask). If you buy a tank from experienced company they have all needed certificates already.

 

 

[tater]

8 hours ago, Flying dutchman said:

Almost looks like a little russian tks capsule.

Maybe the neuralink monkey as pilot?

[Terwin]

12 hours ago, sevenperforce said:

Both involve a very convenient violation of the rocket equation, which is admittedly very nice.

 

 

12 hours ago, sevenperforce said:

I have always been a proponent of "use the legs on Mars that you must use on Earth because anything else is STUPID."

But I suppose if you have 100 Earth landings for every 1 Mars landing then perhaps making single-use sacrificial Mars landing legs becomes attractive.

There is no need for Tanker SS to ever land anywhere but the launchpad, and you will have multiple tanker landings for each Moon or Mars landing, so at worst the median SS launch as no need for legs.

Not to mention that every pound of legs you leave behind you can deliver at least one additional pound of fuel to orbit on Tanker. (and leaving your sacrificial legs behind on mars save a lot of fuel for the return, not to mention the pre-refined steel that is easy to re-purpose by colonists)

(and as an extra bonus, the cheaper tankers(mission parts cost = just a bigger tank) will almost always be life leaders for verifying all of the common parts(engines, tiles, flaps, metal fatigue, etc))

 

[zolotiyeruki]

If you're going to catch SS in a net, you could also add parachutes to slow the descent.  Since stopping distance is proportional to the square of the starting speed, assuming constant deceleration, dropping the terminal velocity, say, in half would reduce the stopping distance by 75%.

The approach seems a bit odd to me, given SpaceX's decision to scrap a similar approach with the fairings.  Of course, the fairings have a much lower vertical velocity, and are presumably much more susceptible to wind, and SpaceX have figured out how to fish them out of the ocean without damage.

I *would* be concerned about potential damage to heat shield tiles with a Giant Net approach.

How much lighter would SS be without the propellant needed for the flip, hover, and landing?  How much would that affect its terminal velocity?

[sevenperforce]

7 minutes ago, zolotiyeruki said:

If you're going to catch SS in a net, you could also add parachutes to slow the descent.  Since stopping distance is proportional to the square of the starting speed, assuming constant deceleration, dropping the terminal velocity, say, in half would reduce the stopping distance by 75%.

Parachutes would make Starship far more susceptible to wind conditions and thus make it harder to hit the landing net.

7 minutes ago, zolotiyeruki said:

The approach seems a bit odd to me, given SpaceX's decision to scrap a similar approach with the fairings.  Of course, the fairings have a much lower vertical velocity, and are presumably much more susceptible to wind, and SpaceX have figured out how to fish them out of the ocean without damage.

The fairings did not have control surfaces, and so there was no way to guide them down to the net without a steerable chute. The steerable chute allowed them to guide the fairings into the net...but also allowed the fairings to touch down gently in the water, so they realized they didn't need the net at all.

Starship has the flaperons for control so they can probably hit the net every time without much trouble. 

7 minutes ago, zolotiyeruki said:

I *would* be concerned about potential damage to heat shield tiles with a Giant Net approach.

Hugely concerned. I can't imagine that contact with anything at 67 m/s -- no matter how much give it has -- will be good for heat shield tiles.

7 minutes ago, zolotiyeruki said:

How much lighter would SS be without the propellant needed for the flip, hover, and landing?  How much would that affect its terminal velocity?

IIRC the ballpark for landing propellant is on the order of 10-20 tonnes. Even if it was twice that much, it wouldn't have any meaningful impact on terminal velocity.

[StrandedonEarth]

2 hours ago, tater said:

Maybe the neuralink monkey as pilot?

 

[KSK]

2 hours ago, tater said:

Maybe the neuralink monkey as pilot?

I suppose so, if you want to ham it up.