totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

Just now, Lisias said:

But such L/D on subsonic speeds will not hold, and the thing would fall as a rock.

Well, yes. "Fall as a rock" is a feature, not a bug.

Just now, Lisias said:

The SS needs to do a flip and land standing on her feet - what means that the total weight at landing must not exceed the available thrust (and maneuverability) from two engines - otherwise you would need yet more fuel on landing, what implied on less payload on descent (and on ascent too!).

It can land on three engines if it needs to. Not a problem. If you need to reserve more propellant on ascent to give yourself more propellant reserves on landing, you do so. No big deal.

[SpaceFace545]

Here me out: but what if you swapped out starship's fins for wings. Lets not kid ourselves, this thing is never going past earth's SOI. It's a tin can when empty and wings would allow it to glide down, a much safer and reliable approach.

[CatastrophicFailure]

45 minutes ago, sevenperforce said:

The only pure ballistic re-entry vehicles (i.e., no lift) that humans have ridden are the Soyuz capsules

Er... Vostok/Voshkod? Pure spheres...

27 minutes ago, Lisias said:

But such L/D on subsonic speeds will not hold, and the thing would fall as a rock.

Not quite a rock, they've already demonstrated pure aerodynamic control during terminal descent: close enough to the pad for the engines to get it the rest of the way. F9 also has a 1:1 LD ratio as just a cylinder with fins. 

[.50calBMG]

You can't call something safer and more reliable if the thing you are comparing it to has never been tried before. And before it gets said that starship has crashed more times than it landed successfully, so did falcon 9 until it didn't, so did airplanes before they didn't. 

As for leaving the Earth's SOI, that's literally what it is being built to do. Just because it hasn't done it yet doesn't mean it never will. Any plane that gets built sits a bit before it flies for the first time, but it always ends up doing exactly that. 

[sh1pman]

42 minutes ago, SpaceFace545 said:

Lets not kid ourselves, this thing is never going past earth's SOI

NASA pays them to make a Starship whose purpose is to stay in Moon’s SOI and sometimes land on it. So you mean that NASA are idiots or kid themselves? 

[sevenperforce]

1 hour ago, CatastrophicFailure said:

Er... Vostok/Voshkod? Pure spheres...

Whoops, yes. I meant the Soyuz family. Modern Soyuz is still derived from Vostok and Voshkod.

1 hour ago, CatastrophicFailure said:

Not quite a rock, they've already demonstrated pure aerodynamic control during terminal descent: close enough to the pad for the engines to get it the rest of the way. F9 also has a 1:1 LD ratio as just a cylinder with fins. 

I will note that the F9 booster achieves its 1:1 L/D ratio only in the lower atmosphere. Can’t do that during hypersonic reentry.

1 hour ago, SpaceFace545 said:

Here me out: but what if you swapped out starship's fins for wings. Lets not kid ourselves, this thing is never going past earth's SOI. It's a tin can when empty and wings would allow it to glide down, a much safer and reliable approach.

Try standing on an overturned soda can.

Also, a better glide ratio brings back the problems of the Shuttle orbiter’s AoA.

[Lewie]

1 hour ago, SpaceFace545 said:

Here me out: but what if you swapped out starship's fins for wings. Lets not kid ourselves, this thing is never going past earth's SOI. It's a tin can when empty and wings would allow it to glide down, a much safer and reliable approach.

Look, you’ve made your point clear. We get that you don’t believe that Starship will ever succeed. No need to keep dragging this on.

Many accomplished people said Falcon 9 could never work...now look. Over 90 successful landings. Who’s to say that Starship will never leave our SOI? It’s not even worth arguing, man. 

[Guest The Doodling Astronaut]

47 minutes ago, Lewie said:

Look, you’ve made your point clear. We get that you don’t believe that Starship will ever succeed. No need to keep dragging this on.

Many accomplished people said Falcon 9 could never work...now look. Over 90 successful landings. Who’s to say that Starship will never leave our SOI? It’s not even worth arguing, man. 

Starship does have a lot to prove of itself. I don't think there is nothing wrong of being skeptical. But I do think Starship will leave the SOI of Earth. My question is how practical will Starship be in some cases. SpaceX has done many things that they later ditch for practical reasons. So I think with the rapid progress and design change nature of SpaceX, Starship is a promising vehicle for finally landing humans on Mars.

 

[HvP]

Half of me anticipates Starship entry tests because I want to see history being made.

The other half of me anticipates Starship entry tests because I want to see this comment thread finally move on...

[Beccab]

Cryo proofing is in progress, ice has formed and starship is venting. It looks further along than the last cryo and no tiles have fallen off yet.

Currently about 4 hours into the test

Edited September 30, 2021 by Beccab

[JoeSchmuckatelli]

Anyone who's ever been in the military knows this thread has become the verbal (textual?) equivalent of 'the time when we toss rocks'.

.

.

.

We are just filling time.  Lots of anticipation for the show to start up again.

Just imagine it's a cocktail party - someone says something you disagree with but don't feel like debating, feel free to move on and get a drink.

 

 

 

(At least you will have a tasty beverage to show for it.)

Edit - I go to all that trouble typing my clever poast - and look what @Beccab does: hit's submit a half second before I do.

SMH

[Lisias]

6 hours ago, sevenperforce said:

Well, yes. "Fall as a rock" is a feature, not a bug.

And as a consequence of such feature, the descent cargo capability of the vehicle is hindered, and this was the whole point of my argument that started on the following post:

 

6 hours ago, sevenperforce said:

It can land on three engines if it needs to. Not a problem. If you need to reserve more propellant on ascent to give yourself more propellant reserves on landing, you do so. No big deal.

Yes, it's a big deal because it impacts negatively on the cargo capacity of the vehicle.

If I'm going to need 20 extra tons of fuel on landing, this means that I will have 20 tons less cargo capacity available on the ship - both for ascent and descent, being this the whole point of my argument: you can't bring down the same weight your vehicle can send up.

And in the case of Starship, this difference appears to be pretty significant.

Edited September 30, 2021 by Lisias
tyops as usulla...

[tater]

 

 

5 minutes ago, Lisias said:

you can't bring down the same weight your vehicle can send up.

Why does this matter even a little? The extra mass to LEO is, like every other rocket, mostly propellant. Nothing needs to be brought down that is any great mass.

[Lisias]

2 minutes ago, tater said:

Why does this matter even a little? The extra mass to LEO is, like every other rocket, mostly propellant. Nothing needs to be brought down that is any great mass.

Because people are speculating on using SS to bring things down. And I'm argumenting that the descent cargo capability is way less than the ascent.  

 

5 hours ago, CatastrophicFailure said:

Not quite a rock, they've already demonstrated pure aerodynamic control during terminal descent: close enough to the pad for the engines to get it the rest of the way. F9 also has a 1:1 LD ratio as just a cylinder with fins. 

Yep. But the heavier the vehicle are, harder is for the fins to do their job timely (if at all, too much weight, too higher terminal velocity, way harder for the fins' actuators to work!!).

You see, I'm  not disputing the technical viability of the vehicle to land. I'm disputing how much cargo it can bring down from space.

[CatastrophicFailure]

38 minutes ago, Beccab said:

Cryo proofing is in progress

[tater]

35 minutes ago, Lisias said:

Because people are speculating on using SS to bring things down. And I'm argumenting that the descent cargo capability is way less than the ascent.  

Ah, I think I'm with you. Any vehilce designed for say P2P with large cargo will probably be purpose built for that (CM alone would be a nightmare).

[RCgothic]

11 hours ago, Lisias said:

But such L/D on subsonic speeds will not hold, and the thing would fall as a rock.

So what? Once starship hits subsonic the peak heating is long past.

In the subsonic regime it only cares about drag for terminal velocity, not L/D, for glide slope. 

Also, 3 SL raptors can hold up 6 times Starship's weight. Shuttle's wings peaked at 1.7Gs. Starship definitely has a lot more margin on landing.

Edited September 30, 2021 by RCgothic

[Beccab]

Best picture of the tiles that were blown off during monday's cryo test (no new ones blown off during tonight's test), spacex is currently evaluating between between making custom shaped tiles right around the vent (ala shutttle RCS) and straight up glueing the tiles in that spot reducing the blanketed area

[Lukaszenko]

5 hours ago, Lisias said:

If I'm going to need 20 extra tons of fuel on landing, this means that I will have 20 tons less cargo capacity available on the ship - both for ascent and descent, being this the whole point of my argument: you can't bring down the same weight your vehicle can send up.

I'm not sure this is entire true. You only need a fraction of the delta-v to bring stuff down as you need to bring stuff up (hundreds of m/s, as opposed to thousands). So if, for instance, we bring up an empty starship, we could conceivably bring down more mass than is possible to ever bring up (assuming the rest of the ship is designed to do so). 

[sevenperforce]

6 hours ago, Lisias said:

Because people are speculating on using SS to bring things down. And I'm argumenting that the descent cargo capability is way less than the ascent.  

[T]he heavier the vehicle are, harder is for the fins to do their job timely (if at all, too much weight, too higher terminal velocity, way harder for the fins' actuators to work!!).

You see, I'm  not disputing the technical viability of the vehicle to land. I'm disputing how much cargo it can bring down from space.

Let’s do the maths, then. Aspirational dry mass of Starship is 85 tonnes. We know the header tanks hold 30 tonnes of propellant. Thus, a notional 100-tonne return payload would increase its total entry mass by a factor of 87%. This means terminal velocity goes up by 87% and the stagnation forces on the flaps go up by 250% during free-fall.

However, because speed has gone up, the control authority of the flaps also goes up. So the flaps will be able to handle the control as long as they are structurally able to handle the stagnation forces. And since the vehicle nominally experiences much more than the one gee of free fall during intermediate entry, that’s no problem.

As far as the kick-flip is concerned, having additional mass towards the nose actually makes it easier, because the Raptors have a larger moment arm around the center of mass. Starship will need more prop reserves to land, but that’s fine.

Starship probably can’t take 100 tonnes to LEO and bring it all back in one go, but no one is expecting that.

 

[Spaceman.Spiff]

1 hour ago, Beccab said:

Best picture of the tiles that were blown off during monday's cryo test (no new ones blown off during tonight's test), spacex is currently evaluating between between making custom shaped tiles right around the vent (ala shutttle RCS) and straight up glueing the tiles in that spot reducing the blanketed area

They'll probably end up drilling a hole in the tile and calling it a day. 

[AtomicTech]

13 hours ago, SpaceFace545 said:

Here me out: but what if you swapped out starship's fins for wings. Lets not kid ourselves, this thing is never going past earth's SOI. It's a tin can when empty and wings would allow it to glide down, a much safer and reliable approach.

Nope! If I've learned anything from SpaceX is that they will get the job done one way or another. Starship promises the next generation on space exploration and it will deliver.

[JoeSchmuckatelli]

8 hours ago, tater said:

Nothing needs to be brought down that is any great mass.

Refer to my question above... 

Yeah, it does not matter now - as we are desperate to develop capacity to get off the planet - but someday we will want to bring stuff back, and I want to know how effective SS would be as a descent vehicle. 

[Deddly]

Just a thought, SpaceX's mantra literally starts with:

1) Make your requirements less dumb. 

This is because "everyone is wrong some of the time." 

It's cool that SpaceX has helped to ignite a passion for spaceflight, but we would do well to remember point 1 of that mantra - it's not like SpaceX and its gifted engineers can do no wrong. They may very well have made big mistakes - time will tell.

In the meantime, this thread is not a SpaceX fan club. Exciting news as well as arguments both for and against their choices all belong here. Please don't make SpaceX detractors feel unwelcome here because, remember - everyone is wrong some of the time; maybe that's SpaceX, or maybe it's you or me.

Discuss openly and constructively, but a wise person does not dismiss a person for their diverging opinion. 

[Beccab]

5 minutes ago, Deddly said:

a wise person does not dismiss a person for their diverging opinion. 

 

14 hours ago, SpaceFace545 said:

Lets not kid ourselves, this thing is never going past earth's SOI.