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3 hours ago, HvP said:

I'm curious as to how accurately the booster can control roll on the way to the catching mechanism.

It seems to me that even a very small rotation along the roll axis can move the catch points several degrees inward/outward around the barrel of the booster. If the catching arms are tangentially straight where they meet the side of the booster then they are likely to miss the catch points entirely unless roll control is perfect.

Remember that there are three engines at the very center of Superheavy. Those three engines can control roll by differential gimbal with pinpoint accuracy. No worries at all. Unlike Starship, which needs to drop to two or even one engine at landing, Superheavy needs all three engines to land and so it has AMPLE yaw, pitch, and roll control at the moment of catch.

3 hours ago, HvP said:

A curved catching claw would solve this problem, but it doesn't allow for those tank treads which they want to move the booster in and out.

A curved catching claw wouldn't solve the problem unless it was itself able to rotate around a plane.

3 hours ago, JoeSchmuckatelli said:

Also - grid fins should be stowed for launch n'est cie pas? 

Grid fins have a pretty substantial chord length by design (that's how they function, after all). Fold that chord over by 90 degrees, and you've got a very draggy object clinging to the side of your rocket.

The grid fins are constructed of relatively thin stainless steel. Their cross-sectional area when deployed is not very high; it's their rotation (increasing the AoA into the airstream) which offers control authority. Their cross-sectional area while folded is probably close to or higher than their deployed cross-section, and so the added weight of an actuation system would only be parasitic.

Imagine holding an empty toilet paper tube out your car window with the hole pointed into the airstream. The air will flow through the hole and the drag will be minimal. If you now turn that toilet paper tube sideways, the drag will be much greater. The same will be true of two dozen toilet paper tubes all glued together (which is basically what the grid fins are).

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53 minutes ago, sevenperforce said:

Imagine holding an empty toilet paper tube out your car window with the hole pointed into the airstream. The air will flow through the hole and the drag will be minimal. If you now turn that toilet paper tube sideways, the drag will be much greater.

Aaaaaaaand then you’re getting pulled over and ticketed for littering. :P

I mean, really, some people just have no appreciation for advanced aerodynamic research. :rolleyes:

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2 hours ago, sevenperforce said:

The grid fins are constructed of relatively thin stainless steel. Their cross-sectional area when deployed is not very high; it's their rotation (increasing the AoA into the airstream) which offers control authority. Their cross-sectional area while folded is probably close to or higher than their deployed cross-section, and so the added weight of an actuation system would only be parasitic.

Imagine holding an empty toilet paper tube out your car window with the hole pointed into the airstream. The air will flow through the hole and the drag will be minimal. If you now turn that toilet paper tube sideways, the drag will be much greater. The same will be true of two dozen toilet paper tubes all glued together (which is basically what the grid fins are).

This is not really true, though.

Folded to the side of the rocket they are mostly tucked into the boundary layer. When extended out, they are not.

And wires and mesh screens, etc., are draggy AF. Sometimes more draggy than a blunt body would be, because there is drag from the air going through the mesh that can be bigger than the drag of air being pushed around the side of a blunt object. This is why, when the rules allow, bike riders like to use disk wheels rather than spoked wheels.

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I am pretty sure SpaceX ran the trade study on the weight and complexity of folding grid fins and came to the conclusion that it was not worth it, but not because the grid fins as extended have negligible drag.

Edited by mikegarrison
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10 hours ago, HvP said:

I'm curious as to how accurately the booster can control roll on the way to the catching mechanism.

It seems to me that even a very small rotation along the roll axis can move the catch points several degrees inward/outward around the barrel of the booster. If the catching arms are tangentially straight where they meet the side of the booster then they are likely to miss the catch points entirely unless roll control is perfect.

A curved catching claw would solve this problem, but it doesn't allow for those tank treads which they want to move the booster in and out.

My guess is that the grind fins are backup catch points. I guess they don't want them as primary as you can easy damage them but bending the tips of them are better than loosing the ship. 
Roll is also pretty easy to control compared to the other stuff. 

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I wonder if Netflix is going to gloss over the personal sanitation concerns of 4 people spending 3 days in a vehicle with the interior space comparable to a Toyota Corolla... especially when said vehicle was designed to get its cargo to and from the ISS in a matter of hours, not days.

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1 minute ago, JoeSchmuckatelli said:

I wonder if Netflix is going to gloss over the personal sanitation concerns of 4 people spending 3 days in a vehicle with the interior space comparable to a Toyota Corolla... especially when said vehicle was designed to get its cargo to and from the ISS in a matter of hours, not days.

They always expected free flights and this contingency—the vehicle has a larger volume than the Apollo CM, and the toilet is at least a toilet, and not just bags with stick-um around the rim.

 

fecalbag.jpg

 

Apollo waste collection often took the astronaut almost an hour. Fully strip, etc. It's a question literally everyone has though, might be a good thing to cover. Every public talk I have seen by an astronaut has someone ask that question.

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2 minutes ago, tater said:

They always expected free flights and this contingency—the vehicle has a larger volume than the Apollo CM, and the toilet is at least a toilet, and not just bags with stick-um around the rim.

 

While true, the military (and astronauts were very military, in the apollo days) is very good at glossing over the "suck" inherent in military duties. Apollo sanitation would just be an extension of that.

The fact that Dragon is an improvement over apollo in that regard doesnt mean it isnt a step down from an Airstream camper.

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22 minutes ago, Rakaydos said:

While true, the military (and astronauts were very military, in the apollo days) is very good at glossing over the "suck" inherent in military duties. Apollo sanitation would just be an extension of that.

The fact that Dragon is an improvement over apollo in that regard doesnt mean it isnt a step down from an Airstream camper.

Yeah, it's certainly not awesome. Obviously not an insurmountable problem. Eat a low residual diet, etc. I know when I go backpacking, I tend to digest rather a lot an end up without a huge, um, residual. I've gone on some longer trips where I went several days without more than liquid waste.

 

BTW, weather is now 80% "go" for Inspiration 4.

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The large tube with the poop icon folds down. There is a separate collection system and tank for urine. Both are I assume negative pressure :D .

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12 hours ago, mikegarrison said:

Folded to the side of the rocket they are mostly tucked into the boundary layer. When extended out, they are not.

And wires and mesh screens, etc., are draggy AF. Sometimes more draggy than a blunt body would be, because there is drag from the air going through the mesh that can be bigger than the drag of air being pushed around the side of a blunt object.

Oh, I agree. I'm not saying that we know for sure that the drag while folded is greater than the drag while extended. I'm just saying that it's clearly close enough to the balance point that the added weight of a folding system wouldn't be worth it.

Also, drag on ascent is fairly low, all things considered. Grid fins are draggiest during the transonic regime due to shock interactions, and the transonic phase on ascent is at a very high altitude.

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31 minutes ago, sevenperforce said:

Oh, I agree. I'm not saying that we know for sure that the drag while folded is greater than the drag while extended. I'm just saying that it's clearly close enough to the balance point that the added weight of a folding system wouldn't be worth it.

Also, drag on ascent is fairly low, all things considered. Grid fins are draggiest during the transonic regime due to shock interactions, and the transonic phase on ascent is at a very high altitude.

Also, and this is an area they can optimize around, is that air flow through the fins during ascent and descent is obviously in different directions. There are plenty of shapes/structures/profiles that will be far less draggy in one direction than the other.

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1 hour ago, Beccab said:

profile_Starlink-2-1_Infographic_EN.png
Today's starlink mission profile from Vandenberg, 51 satellites with laser links for a 70 degrees inclination

Going to be trying to catch a view of this launch from a park that is aptly named Rocketship park! I'm still several hundreds of miles away from Vandenburg, but should see it in the dark just fine, if the weather is clear.

The weather in Southern California looks great so far today, nice clear blue skys!

See how things are closer to the launch :)

Edited by MKI
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26 minutes ago, MKI said:

Going to be trying to catch a view of this launch from a park that is aptly named Rocketship park

First time I saw a Vandenburg launch was from Rocketship Park just after Regan took office.  It absolutely freaked me out.  Actually, it was two launches - the exhaust plumes were notably distinct from regular contrails.  Just the week before, we had had our annual 'duck and cover' drills... so I was primed to freak.

Wasn't until later that my mom (who worked in aerospace) told me that it was probably a US Airforce launch from there. 

...

For anyone who's never been: its a fantastic place to see LA and the beach.  rocketship park torrance - Google Search

Side note: the original 'rocketship' structure got taken down at some point (back when people were taking down 'old' rickety structures and replacing with the uber-safe and boring stuff currently in playgrounds).  The rocketship was fantastic, wobbly and very scary for a little kid.  We loved it.  The local community complained so much that eventually the city dug up and re-installed the original rocket structure.  Years and years later I took my own kids to the place - and it freaked them out, too.  The original steel slide got put back too: and steel slides are waaay faster than the plastic junk in playgrounds today.  Many a kid has a skinned elbow or knee to remember that place

It's great!

 

MKI --- Really hope you see the launch: please take pics!

Edited by JoeSchmuckatelli
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42c2946a-72a8-4919-81c2-69dd5bc6117a_ins

  • The preparation of Inspiration4, is being awesome.
  • The launch will be in 2 days (15 September 2021), if weather collaborate this time.
  • There is a new TV Series about Inspiration4 with all crew and family, explaining the crew selection and also with Elon Musk interviews on netflix, for those that can watch I recommend!
  • The Idea is to inspire that every body, and not only an astronaut can go to space.

Origin of Inspiration4 name:

Inspiration=Because the big goal of the mission (first civilian orbital flight) is to inspire people all over the earth.
Nº4 because, There will be a crew of 4 in the Mission.
Nº4 because, It's the 4th crew mission after Space Shuttle

  • Jared Isaacman, have a tone of flight experience, will be the Leader of the mission.
  • Dr. Sian Proctor, is also pilot and her dad worked for NASA in the Apollo missions
  • Chris Sembroski, is the Mission Specialist.
  • Hayley Arceneaux, is a survival of cancer in her childhood, and at the present day work as physician’s assistant at St. Jude Children’s Research Hospital in Memphis, Tennessee, will be the first person with less than 30 years in space (29) and the first one that use a prosthesis in her leg.
  • All the crew represent all the good/best among the common civil population.

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  • A typical NASA Insertion Orbit is 200Km, ISS is at 408 km orbit,  but Inspiration4 will go to a AP of 575km:

bjRplPM.png

NOTE:

They will not get the Astronauts Wings, after the journey, once they didn't have done all the training of an Astronaut, but they have done a sub training of that process in the last months.

But they might earn the, official commercial astronaut wings with the FAA.

5 Days ago: All Crew have the tanning done is just a matter of doing the stack and the final preparations of the Crew Dragon Resilience (Dragon C207), will do the second flight:

7mOdb4D.png

- This is the new version of the crew dragon that that will do mission of three-day flight with exclusively private citizens on board

- The apogee will be 590 km and the inclination will be 51.6°

- The Crew Dragon Resilience will fly with Falcon 9 Block 5 booster B1062

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Next Step, Kennedy Space Center's historic Launch Complex 39A, 15 September 2021.

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I gotta agree with @tater. It makes more sense to me to have the grabber arm be mounted so it creates a compression force on the tower, not a tensile force. With compression, you have to have the tower fail, with tension, you only need to have the attach points to the tower fail.

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