SpaceX News

[Betruger]

Why do you need catch pins? SS lands itself. It wouldn't have catch tower elsewhere than Earth and maybe Mars.

[Carl White]

Why do you need catch pins? SS lands itself. It wouldn't have catch tower elsewhere than Earth and maybe Mars.

Most likely there will be a version of SS without landing legs for Earth-to-LEO-and-back or even suborbital transport flights. The idea would be the same as for the booster, namely to have it on the pad and ready for the next flight quickly.

[mvanwink5]

Weight. Earth gravity > Mars >> Moon. Quick reflight for Starship Tanker for fueling the Moon trip, legs might need inspection, engines can kick up rocks & get damaged. Just some thoughts.

[paperburn1]

Why do you need catch pins? SS lands itself. It wouldn't have catch tower elsewhere than Earth and maybe Mars.

Why? As a general rule, a rocket with the highest delta-V capacity is going to need three kilograms of propellant for every kilogram of rocket+payload. The lower the total kilograms of rocket+payload, the lower the propellant mass required. The name of the game right now is get as much mass into orbit to build your space station. so every pound you keep on the ground (landing gear) is a pound you can put into orbit. Remember when grid fins folded? Some smart person figured out the drag penalty was less than the weight penalty of folding wings. You are right the first trips to the moon and mars will require landing gear but in a perfect world, That is the first thing to go. May I suggest a website that has a lot for these answers figured out for Sci-Fi writers. https://www.projectrho.com/public_html/rocket/

[Betruger]

Ive had prho bookmarked forever. Just thought I'd ask a simple pointed question. Thanks for clarifying. I don't have enough time for another hooby/deep reading subject.

[KitemanSA]

Why do you need catch pins? SS lands itself. It wouldn't have catch tower elsewhere than Earth and maybe Mars.

One other reason.
The closer to the ground you get your rocket exhaust, the less efficient and less controllable your engine gets. Falcon needs fairly long/heavy legs, and they do kind of a pre-calculated crash landing using ONE engine. It then need a long time to re-furbish. The interaction on Starship with three, trying to hover-land, must be a bear! Yes, they did it … ONCE … but with significant damage, hardly conducive to rapid re-use!

[jrvz]

For a detailed discussion of the catch hardware, I recommend "How SpaceX Caught Super Heavy - Explained" by RyanHansenSpace (currently https://www.youtube.com/watch?v=ub6HdADut50).

[Betruger]

Thanks Kiteman

[KitemanSA]

Thanks Kiteman

My pleasure.
But that did get me thinking. Yes, I know, a dangerous thing!!.
What would happen if they slightly dropped and strengthened the base skirt and then landed on a water cooled, elevated grill? Take a larger barge, cut a hole through the center, top to bottom with side ports, and place a set of risers round the hole with a high temp (tungsten?) grill on top. The rocket exhaust would pass thru the cooled grill and the ship could land on the base ring of its engine skirt without feedback from the ground/ocean surface. No legs per-se, just a bit of engineering on the skirt.


Hmmmmm!!!

[Giorgio]

No legs per-se, just a bit of engineering on the skirt.

It's hard, very hard.
You need to have shock absorbers to prevent the pressure wave generated by the landing force to propagate through the rocket shell, else the reverberating wave will make a carnage of the internal connection in the best scenario or will pop the top of the rocket like a cork from a bottle of wine in the worse scenario.
Alternatively this wave can be controlled by increasing the shell thickness or strengthening the whole body of the rocket.

All the above solutions will anyhow increase the mass to several tens of tons and greatly reduce his lifting ability.

This is why they abandoned the leg landing solution and switches to the catch tower solution during the first tests they made.
They was thinking to use the same disposable shock absorber packs that Falcon9 is using but the size and empty weight of the landing rocket/booster is just too high to make that solution practical.

[KitemanSA]

No legs per-se, just a bit of engineering on the skirt.

It's hard, very hard.
You need to have shock absorbers to prevent the pressure wave generated by the landing force to propagate through the rocket shell, else the reverberating wave will make a carnage of the internal connection in the best scenario or will pop the top of the rocket like a cork from a bottle of wine in the worse scenario.
Alternatively this wave can be controlled by increasing the shell thickness or strengthening the whole body of the rocket.

All the above solutions will anyhow increase the mass to several tens of tons and greatly reduce his lifting ability.

This is why they abandoned the leg landing solution and switches to the catch tower solution during the first tests they made.
They was thinking to use the same disposable shock absorber packs that Falcon9 is using but the size and empty weight of the landing rocket/booster is just too high to make that solution practical.

First, the base of the skirt is already quit strong, having to take the thrust at Max-Q.
Second, the original landing legs had to take the impact of the hard ground with wicked ground effects on the controllability of the rockets.
Third, the landing grill will allow for both far better control of the landing velocity, allowing a true hover touch down rather than Falcon-9’s hover slam. Further, it should also the allow the ability to build forgiveness into the landing surface, unlike a concrete pad.
I suspect they would find that the current strength of the skirt and base will be found sufficient by proper design of a compliant landing grill.

[Giorgio]

First, the base of the skirt is already quit strong, having to take the thrust at Max-Q.
Second, the original landing legs had to take the impact of the hard ground with wicked ground effects on the controllability of the rockets.
Third, the landing grill will allow for both far better control of the landing velocity, allowing a true hover touch down rather than Falcon-9’s hover slam. Further, it should also the allow the ability to build forgiveness into the landing surface, unlike a concrete pad.
I suspect they would find that the current strength of the skirt and base will be found sufficient by proper design of a compliant landing grill.

Thrust force at launch is structurally distributed at an higher point than the skirt itself, but even if we want to consider the design of a skirt strong enough to handle a landing you will still need a section with shock absorbers to structurally isolate the landing skirt from the rest of the rocket, not much take the impact of the landing but to prevent the pressure wave issue I mentioned before.

[KitemanSA]

Thrust force at launch is structurally distributed at an higher point than the skirt itself, but even if we want to consider the design of a skirt strong enough to handle a landing you will still need a section with shock absorbers to structurally isolate the landing skirt from the rest of the rocket, not much take the impact of the landing but to prevent the pressure wave issue I mentioned before.

Ummmm, are you talking about the BOOSTER? The booster has a proven catch process. I am talking about the SHIP.
100% of the force that accelerates the SHIP at launch goes thru the ship, and the force increases up thru Max-Q. If the SHIP skirt can take that, SURELY it can take a soft, “hover” touchdown.

[Giorgio]

Ummmm, are you talking about the BOOSTER? The booster has a proven catch process. I am talking about the SHIP.
100% of the force that accelerates the SHIP at launch goes thru the ship, and the force increases up thru Max-Q. If the SHIP skirt can take that, SURELY it can take a soft, “hover” touchdown.

Yes I was talking about the booster, but in general the issue is the same also for the ship even if more limited.
Your point on the forces during acceleration is a good one, and for sure the design of the ship skirt is more strong than the booster.
But one very important point is that the forces on the skirt of the ship during launch are progressive from Zero to MaxQ over a very long time, while during landing the forces goes from value "X" to value zero in a very short time. This force impulse is what creates the pressure wave propagation into the skirt that i was mentioning in my first post, and this is why you need shock absorbers.

[mvanwink5]

Tile survival whether on chopsticks or a pad (landing impact shockwave) is yet to be proven. Greater shock absorbing is possible with the chopsticks, still that said, Mars will have no chopsticks in the beginning. Perhaps the issue with landing shockwave & tiles is why EM has kept reentry active cooling on the table?
There will be ship legs for Moon & Mars.