totm nov 2023 SpaceX Discussion Thread

[RCgothic]

9 minutes ago, SpaceFace545 said:

please explain this

Reference to the computer game Portal.

Edited May 6, 2021 by RCgothic

[tater]

1 minute ago, SpaceFace545 said:

please explain this

You can disagree with colonizing Mars (I certainly do), but the capability to send large masses to space (or Mars) comes with existential risk mitigation for the ride. The same would be true of Blue Origin's goals (Bezos is one of "Gerry's kids" an L5, orbital habitat guy). A transportation system that gets large masses to space that does not cost many billions per flight, and indeed drops costs towards FedEx overnight package delivery rates per kg means we can get large spacecraft built.

This mitigates risk because if we were to detect an Earth-crossing threat, we'd have the ability to try and divert it. That's simply impossible right now.

Musk will talk the risk mitigation bit by virtue of having a self-sustaining colony on Mars (large enough to not need Earth, with enough people to have genetic diversity), but if that is even possible, the colony is not actually needed for that purpose, because if we can send 1000 ships to Mars every 2 years, we can move an asteroid.

[SpaceFace545]

1 hour ago, tater said:

Actually, the existing drone ships could work. Look above. F9 is 3.7m in diameter, SS is substantially smaller than the gear footprint of F9.

It could but I don't know if you'd want it to land on a tiny little platform in the middle of the ocean. Especially if their are people inside of it. I think the best landing site would be a massive expanse of concrete somewhere in the middle of the desert. Precision landing doesn't need to be a factor if you don't want it to be.

[Spaceman.Spiff]

Just now, SpaceFace545 said:

It could but I don't know if you'd want it to land on a tiny little platform in the middle of the ocean. Especially if their are people inside of it. I think the best landing site would be a massive expanse of concrete somewhere in the middle of the desert. Precision landing doesn't need to be a factor if you don't want it to be.

I think they mean for test flights. Humans won't fly (IMO) on Starship for at least 5 years after its first orbital flight.

[tater]

1 minute ago, SpaceFace545 said:

It could but I don't know if you'd want it to land on a tiny little platform in the middle of the ocean. Especially if their are people inside of it. I think the best landing site would be a massive expanse of concrete somewhere in the middle of the desert. Precision landing doesn't need to be a factor if you don't want it to be.

That platform is not little. 52x91m.

Starship is about the same height as that F9, and 2.43X as wide as the F9 booster without the legs. It fits there just fine.

People is not a thing for a while, we're talking about flying the uncrewed version (which will be done a long time before any SS carries people from Earth). They will certainly do testing to a barge I would think. Initial orbital testing they might soft-land in the ocean as they did for F9. This would be the safest approach.

3 minutes ago, Spaceman.Spiff said:

I think they mean for test flights. Humans won't fly (IMO) on Starship for at least 5 years after its first orbital flight.

Yeah, humans on Starship from and back to Earth would scare the p!#$ out of me.

Lunar SS is fine because the crew gets to it and gets home without those risks (though the various capsules have their own chance of LOC events).

[Spaceman.Spiff]

3 minutes ago, tater said:

Yeah, humans on Starship from and back to Earth would scare the p!#$ out of me.

Lunar

Theres so much about the reentry and more importantly the bellyflop which is.... sus. I wonder how bad the total G's are. 

smh DearMoon is planned for 2023. 

[RCgothic]

 

Just now, Spaceman.Spiff said:

I think they mean for test flights. Humans won't fly (IMO) on Starship for at least 5 years after its first orbital flight.

Yup, nobody is proposing launching SN20 as a crewed demo and landing it on an ocean platform.

The difficulties for Starship's crew rating are:

1) No abort system on launch (from earth).

2) Re-entry.

3) Bellyflop manoeuvre.

4) Propulsive landing.

None of those apply to crewed operations in space. Crew rating a version of starship that only operates only in space is therefore no big deal. There's a good chance lunar starship would be safer than any of the other options as due to size it has increased endurance and system redundancy.  NASA particularly liked the Lunar Starship dual independent crew refuges.

[KSK]

16 minutes ago, RCgothic said:

Reference to the computer game Portal.

Yep - and if you’ve played Portal you’ll know that it’s an... ironic statement in its original context.

Edited May 6, 2021 by KSK

[tater]

1 minute ago, RCgothic said:

None of those apply to crewed operations in space. Crew rating a version of starship that only operates only in space is therefore no big deal. There's a good chance lunar starship would be safer than any of the other options as due to size it has increased endurance and system redundancy.  NASA particularly liked the Lunar Starship dual independent crew refuges.

yeah, it also has mission redundancy.

The other 2 vehicles are 2 crew (NT needed to build a completely new, larger lander for a "sustainable" later mission version, presumably for more billions—and Alpaca was not really 2 crew as it has negative landed cargo mass), and the entire cabin IS the airlock. So if someone has a suit problem, the mission is over, and they go back to Orion—since both have to be able to have functioning suits for either to egress the vehicle. LSS has 2 airlocks. Even 1 actual airlock means that any crew member could have a suit problem, and the rest can EVA. For a LOM on EVA, they'd have to lose all the suits (they have room for spares, BTW), OR lose not 1, but 2 airlocks.

[SpaceFace545]

10 minutes ago, tater said:

That platform is not little. 52x91m.

Starship is about the same height as that F9, and 2.43X as wide as the F9 booster without the legs. It fits there just fine.

People is not a thing for a while, we're talking about flying the uncrewed version (which will be done a long time before any SS carries people from Earth). They will certainly do testing to a barge I would think. Initial orbital testing they might soft-land in the ocean as they did for F9. This would be the safest approach.

Yeah, humans on Starship from and back to Earth would scare the p!#$ out of me.

Lunar SS is fine because the crew gets to it and gets home without those risks (though the various capsules have their own chance of LOC events).

Starship  is relatively more complicated than landing a facon9. a falcon9 is practically a dart and can be "glided i guess" to where it needs to go. Where as starship isn't a dart. Its an awkard piece of machinery with a very complicated landing system.

[Spaceman.Spiff]

Just now, SpaceFace545 said:

Its an awkard piece of machinery with a very complicated landing system.

They may look different, but the main idea of a propulsive landing is similar for all cases.

[RCgothic]

Guidance isn't one of Starship's problems. It has aerodynamic control that has worked well since SN8. It hasn't missed the pad yet.

 

 

[SpaceFace545]

1 minute ago, RCgothic said:

Guidance isn't one of Starship's problems. It has aerodynamic control that has worked well since SN8. It hasn't missed the pad yet.

that is true but from my knowledge starship has only flown in optimal conditions. On the sea the conditions are never optimal.

[Beccab]

1 minute ago, SpaceFace545 said:

On the sea the conditions are never optimal.

Not really. Falcon 9 only launches when recovery conditions over the ocean are optimal

[Spaceman.Spiff]

Just now, SpaceFace545 said:

only flown in optimal conditions.

Did you not see the SN11 flight? it was foggy and wet. Plus, its not going to land on a barge. its more than likely going to try and RTLS landing.

[SpaceFace545]

Just now, Spaceman.Spiff said:

Did you not see the SN11 flight? it was foggy and wet. Plus, its not going to land on a barge. its more than likely going to try and RTLS landing.

wind

 

[RealKerbal3x]

7 minutes ago, SpaceFace545 said:

Starship  is relatively more complicated than landing a facon9. a falcon9 is practically a dart and can be "glided i guess" to where it needs to go. Where as starship isn't a dart. Its an awkard piece of machinery with a very complicated landing system.

The entire point of those flaps is to guide the vehicle to a precise landing point, as we've seen happen with these test flights. If they couldn't accurately steer Starship during entry/landing, it wouldn't be great for reusability.

 

[RCgothic]

Wind is likely to be less of a constraint for Starship than F9. Starship has a lower fineness ratio which makes it less susceptible to wind shear.

[SpaceFace545]

4 minutes ago, RCgothic said:

Wind is likely to be less of a constraint for Starship than F9. Starship has a lower fineness ratio which makes it less susceptible to wind shear.

I disagree, when you think of it, starship is a slow moving object that's basically falling through the air column and it can only steer itself to a certain degree where falcon9 is a supersonic dart, its very skinny whereas starship is fat. You can give starship the best software and engineering in the world but it physically has a larger margin of error and that will only grow when it is going faster and higher.

[Spaceman.Spiff]

7 minutes ago, SpaceFace545 said:

I disagree, when you think of it, starship is a slow moving object that's basically falling through the air column and it can only steer itself to a certain degree where falcon9 is a supersonic dart, its very skinny whereas starship is fat.

Also F9 uses an additional burn to slow down. Which doesn’t help this or the “complexity” argument. 
 

What?
 

[sevenperforce]

3 minutes ago, SpaceFace545 said:

11 minutes ago, RCgothic said:

Wind is likely to be less of a constraint for Starship than F9. Starship has a lower fineness ratio which makes it less susceptible to wind shear.

I disagree, when you think of it, starship is a slow moving object that's basically falling through the air column and it can only steer itself to a certain degree where falcon9 is a supersonic dart, its very skinny whereas starship is fat. You can give starship the best software and engineering in the world but it physically has a larger margin of error and that will only grow when it is going faster and higher.

I agree with @RCgothicthat Starship has less of a wind problem on descent problem than F9 but I don't think fineness ratio is the operative issue.

Fineness ratio is an important variable on ascent because a skinnier rocket has a larger bending moment relative to high-altitude winds and so structural stability (not guidance) is an issue.

On descent, structural stability is no longer the issue; it's a question of guidance. Starship falls more slowly than F9, yes, but it is also much heavier with a more even distribution of mass. A supersonic dart with all the mass on the prograde end is extremely susceptible to wind buffeting its "lightweight" end and causing torque around its center of mass. In contrast, even very high winds aren't going to change Starship's inertia very much. 

Just now, Spaceman.Spiff said:

Also F9 uses an additional burn to slow down. Which doesn’t help this or the “complexity” argument. 

What?

Eh, the entry burn is just a constraint imposed by the relatively low strength and temperature resistance of aluminum-lithium alloy.

I'm still amazed that those little legs caught it successfully. Although the two-engine landing burn probably helped with that:

 

[tater]

25 minutes ago, SpaceFace545 said:

that is true but from my knowledge starship has only flown in optimal conditions. On the sea the conditions are never optimal.

We're talking about a test campaign.

If they don't care about wasting Starships (and they build them pretty fast, and for what I think is shockingly low cost), then they will do the first orbital reentry tests in open ocean to a soft landing.

If they can hit the coordinates after reentry, then soft land, they can certainly do so on the barge.

 

[Spaceman.Spiff]

So what do y’all think will happen with 15? Will they try again? If so, how long will inspection and possible refurb/replacement of the engines take?

Or will it hit the scrap heap?

[Serpens Solidus]

SN15 would have missed the barge

[RCgothic]

Whilst starship looks slow, its terminal velocity for most of its fall is upwards of 200mph. Skydivers can manage a 1:1 glide ratio and Starship is based on similar principles.

Even if Starship can only glide half as well, that counters 100mph winds. That doesn't seem overly restrictive, and SpaceX don't seem particularly worried about it either.