Starship is now Stacked - Page 1
Forum section: electronics / general

author: Brumby
author_rank: Unknown
timestamp: August 06, 2021, 01:20:33 pm
content: First time it's all together....

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2021, 07:53:05 pm
content: And 29 Raptor engines on the bottom.

author: TimFox
author_rank: Super Contributor
timestamp: August 06, 2021, 09:04:03 pm
content: That photograph looks more like 1952 science-fiction movies than did similar pictures of NASA equipment.

author: Red Squirrel
author_rank: Super Contributor
timestamp: August 06, 2021, 09:40:55 pm
content: Woah I never realized it was that long. Going to be awesome seeing that fly.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2021, 11:27:45 pm
content: Quote from: TimFox on August 06, 2021, 09:04:03 pmIt does. I half expect to see a Tektronix 545 oscilloscope on a cart in the background.Quote from: Red Squirrel on August 06, 2021, 09:40:55 pmThat's what she said!Rockets benefit from economy of scale because fuel is a minor cost which is why something likeSeadragoncould have worked.See attached, but consider that the Shuttle derived SLS shown below are larger than they otherwise would be because of the low propellant density of hydrogen.

author: StillTrying
author_rank: Super Contributor
timestamp: August 06, 2021, 11:40:02 pm
content: I always think rocket engines look too flimsy when you consider that at lift-off twice the weight of the whole rocket is resting just on them.

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2021, 12:01:38 am
content: Quote from: StillTrying on August 06, 2021, 11:40:02 pmThe pressure on the inside of the expansion nozzle prevents buckling of the higher part where the compression force is greater.The numbers listed in that comparison are for cargo delivered to orbit. The total liftoff weight is like 30 times greater so 5000 tons for Starship.

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2021, 10:02:46 pm
content: The Russians tried the same amount (~30) of the first stage engines with their Moon N1 rockets in 60ties, afaik.All N1 rockets they fired exploded, however..PS: While watching Elon's SNxx experiments, always been remembering the book written by Jules Verne - From the Earth to the Moon.Verne's 1865 Moon rocket looked almost identical to the Elon's one, also made of steel..

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2021, 02:21:52 am
content: Quote from: imo on August 07, 2021, 10:02:46 pmI had the same thought when I learned how many Raptor engines would be used, and even the Saturn 5 had problems and that was only 5 engines.I guess it makes sense to do a full scale test with a usable Starship on top instead of a test mass because the real thing will be landing without the mass of any payload, so they get an opportunity to test both under real conditions.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2021, 06:54:48 pm
content: Quote from: David Hess on August 07, 2021, 12:01:38 amPresumably the engine bells are still susceptible to, err, bell mode resonances, also seen in speaker cones. Are these addressed by damping and reinforcing rings? Although I can't see any, and they look pretty thin. I'm just visualising the closely spaced outer ones clanging together!

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2021, 07:29:55 pm
content: Quote from: Gyro on August 08, 2021, 06:54:48 pmI have read various accounts of rocket design and they do all kinds of things to prevent that sort of problem including avoiding power ranges where known resonances are excited.I recently ran across a similar problem with my new workstation. It has 3 x 140mm front fans for filtered positive pressure cooling and from previous experiences, I expected that having all three fans running at the same RPM would cause annoying audible resonances and beat frequencies. So I planned ahead of time to force the fans to spin at slightly different speeds and testing showed that solved the expected problem which did develop. In retrospect I am surprised nobody makes PC fan controllers with this as a feature and it got me dreaming about the best circuit to phase lock multiple fans to slightly different frequencies.

author: rdl
author_rank: Super Contributor
timestamp: August 08, 2021, 07:38:08 pm
content: Rockets do not sit on the engine bells. There is a structure at the base for this purpose and there are hold down clamps attached to keep everything steady. The engines hang from this structure. At launch when the engines ignite, the hold down clamps keep the vehicle in place until the system is confirmed to be working correctly. Only then is it released.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2021, 08:01:52 pm
content: Quote from: rdl on August 08, 2021, 07:38:08 pmIt would be kind of difficult to get them to light if they did!You could certainly say that the rocket is sitting on the engines when in flight though.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2021, 08:17:08 pm
content: Quote from: David Hess on August 08, 2021, 07:29:55 pmThat must be a hell of a juggling exercise, there will be various overtone modes, as well as the fundamental. Presumably the combustion is a fairly broadband noise source too. I'm glad it's not my problem!Have they done a test firing with all 29 engines running yet? I think I would have remembered that one. Maybe it's the sort of test that you can only do in the air!

author: mrflibble
author_rank: Super Contributor
timestamp: August 08, 2021, 09:41:06 pm
content: Quote from: Gyro on August 08, 2021, 08:17:08 pmNope, not yet. Of the 29 engines currently fitted, 5 have not been subjected to a test firing at all. Booster 4 is expected to be moved back to production site for additional work, somewhere during the coming week.Until those 29 engines perform their simultaneously controlled explosions, here's some Saturn V static firing instead:https://youtu.be/-rP6k18DVdg?t=183

author: pqass
author_rank: Super Contributor
timestamp: August 08, 2021, 09:46:49 pm
content: Quote from: Gyro on August 08, 2021, 08:01:52 pmThe gimbal mount looks to be the size of a hardhat sitting directly on top of the combustion chamber.See attached F1 and Raptor engines close-up.When the business-end is lit, 690 (F1), 230 (Raptor) tonnes of force pushes up on this one point!(images from Wikipedia)

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2021, 09:55:18 pm
content: Quote from: mrflibble on August 08, 2021, 09:41:06 pmThat's a great video. If anything, that giant blowlamp is more impressive than watching it disappear into the sky (apart from maybe clearing the tower). The noise level must have been beyond imagining!

author: rdl
author_rank: Super Contributor
timestamp: August 08, 2021, 10:12:19 pm
content: This one has a close view of the F-1 engines on the Saturn V at launchhttps://youtu.be/DKtVpvzUF1Y

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2021, 11:55:52 pm
content: Quote from: pqass on August 08, 2021, 09:46:49 pmThat makes the pressure in compression about 2500 pounds per square inch which is hardly anything. The structure attaching the mounts (engine bus?) is in bending and has much greater requirements.

author: GlennSprigg
author_rank: Super Contributor
timestamp: August 10, 2021, 01:49:07 pm
content: Relatively short Interplanetary flights aside... I've always wondered about the almost 'fruitfulness' of initial/futureattempts at Stellar travel, as 10 or 20 years later, newer & fancier machines willovertake them mid-flight!!

author: Gribo
author_rank: Frequent Contributor
timestamp: August 10, 2021, 04:59:20 pm
content: By your logic, Columbus should have waited for the 747.

author: TimFox
author_rank: Super Contributor
timestamp: August 10, 2021, 06:42:44 pm
content: During the "Age of Discovery" (say, prior to WW I), there were long expeditions (often a few years) to explore hitherto-uncharted parts of the globe, but the only one I can think of where one party overtook another was the "race" of Scott and Amundsen to the South Pole. Of course, both parties knew that the other was doing the same thing, starting at close to the same time.I can only imagine the state of mind of Scott when he finally reached the geographic South Pole and saw a Norwegian flag already there, with a polite letter from Amundsen.There were three important personalities involved in Antarctic expeditions at that time:Scott (Royal Navy) was incompetent: he thought he could learn skiing when he got to Antarctica. He saw no reason to adopt barbaric practices from uncivilized indigenous peoples who lived in cold regions of the globe. There was an important lecture at the Royal Geographic Society about how to navigate at extreme latitudes, attended by both Scott and Amundsen, but only Amundsen learned anything.Amundsen (Norwegian private citizen) was so competent as to be boring. He had previous experience with arctic conditions in Norway and Greenland, had been on one Antarctic expedition already, and found useful materials and practices from the locals. He did not lose any of his company.Shackleton (Merchant Marine, not involved directly in the South Pole part of the expedition) is the interesting character: he learned from his mistakes and also did not lose a man, even in his later failed expedition.

author: Gyro
author_rank: Super Contributor
timestamp: August 10, 2021, 08:02:30 pm
content: Quote from: GlennSprigg on August 10, 2021, 01:49:07 pmThat was the subject of the SF short story 'Far Centaurus' by A. E. van Vogt. They arrive to find a completely different advanced civilization that finds them too unpleasantly smelly to be allowed out!https://en.wikipedia.org/wiki/Far_Centaurus

author: ejeffrey
author_rank: Super Contributor
timestamp: August 10, 2021, 08:10:31 pm
content: Quote from: David Hess on August 08, 2021, 02:21:52 amThey have already flow the falcon heavy with 27 merlin engines split across 3 cores. 29 larger engines on a single core is obviously a different situation but I think comparing to a 60 year old soviet rocket with a host of other issues and limitations is probably not very relevant either.

author: rdl
author_rank: Super Contributor
timestamp: August 10, 2021, 08:34:52 pm
content: Speaking with over 50 years of hindsight and no offense intended, the N1 was an incredibly bad design and it would have taken a miracle for it to actually put something in orbit.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2021, 04:08:48 am
content: Quote from: ejeffrey on August 10, 2021, 08:10:31 pmBut other rockets displayed problems not evident when testing fewer engines, likepogo oscillation.

author: iMo
author_rank: Super Contributor
timestamp: August 11, 2021, 07:16:20 am
content: Sure, we cannot compare the rocket technology of that time, but at least they had similar launch towers (1969)More on its 30 engines issues onhttps://www.popsci.com/this-rocket-failed-to-put-soviets-on-moon/http://www.russianspaceweb.com/n1_5l.html

author: mrflibble
author_rank: Super Contributor
timestamp: September 01, 2021, 07:37:44 am
content: Quote from: David Hess on August 11, 2021, 04:08:48 amSome time ago there was mention of maybe doing a static fire of 9 engines first. Not sure what the current status of that plan is...This one:"Depending on progress with Booster 4, we might try a 9 engine firing on Booster 3"https://twitter.com/elonmusk/status/1417277335863140363