GW Johnson Postings and @Exrocketman1 YouTube videos

GW Johnson · 2024-10-24 12:35:18

I have basically two space station articles posted on "exrocketman". One is an on-orbit propellant depot titled "A Concept for an On-Orbit Propellant Depot", dated 1 February 2022. The other is a concept for an on-orbit repair and assembly facility, titled "On-Orbit Repair and Assembly Facility", dated 11 February 2014.

There is no reason why both functions could not be fulfilled by one big facility built in orbit. I would suggest a low-inclination circular orbit in the 300-500 km altitude range, and I would include orbit modification propulsion into the design from the very outset. I would also try to combine thermal insulation with meteor shielding and with radiation protection in my designs.

To find these quickly on my "exrocketman" site, go to http://exrocketman.blogspot.com, and use the archive fast access tool on the left side of the page. Click on the year, then click on the month, then click on the title, if the article is not top-of-list for that month. I have a catalogue article of all the technical stuff I have posted there, covering a wide variety of topics. That one is titled "List of Some Articles By Topic Area", dated 21 October 2021.

I try to keep the catalogue article updated, but there are no guarantees.

To see figures enlarged, click on a figure. There is an X-out option top right of the page showing enlarged figures. It takes you right back to where you were, before you clicked on a figure to enlarge them.

GW

tahanson43206 · 2024-10-24 13:13:38

I'd like to (at least try to) encourage you to continue working on the combined depot concept.

This forum is available if you want a one-click presentation.

All that searching and finding is fine for a suitable audience.

(th)

tahanson43206 · 2024-10-24 17:25:27

This post is intended to hold links to two files prepared by GW Johnson as part of a set that covers Mars Colonization.

These two files are primarily about a lander, but the presentation included planning for an expedition, including staging of supplies using electric propulsion.

Notes on presentation:
https://www.dropbox.com/scl/fi/liabcp15 … bk83l&dl=0

Presentation:
https://www.dropbox.com/scl/fi/en1k18h6 … qghw5&dl=0

(th)

tahanson43206 · 2024-10-25 07:42:15

For GW Johnson...

In thinking about your reports of seeing different ads than I see, it occurred to me that Google is probably serving different ads to customers based upon all the information that they have collected about each of us. I see a lot of ads that tie back to inquiries I have made, or that are appropriate for my demographic.

In a spirit of scientific inquiry, I'd appreciate your creating a list of the ads you see when you click on the recovered ring video.

I'l do the same, and let's compare notes.

Please specifically record if you can skip or not. Some ads do not allow skip. These are generally political ads, I've noticed. You may get more than your fair share because of your stored data held by Google.

(th)

GW Johnson · 2024-10-25 08:22:29

In post 428, I checked both links. They both lead to the presentation notes file. I could not see the slide set.

GW

tahanson43206 · 2024-10-25 08:36:18

For GW Johnson re #430

Thanks for catching that. I corrected the link and the presentation should now load.

However, please think about where else to put the links. They will get lost pretty quickly if they are only in the one topic.

(th)

GW Johnson · 2024-10-25 09:39:20

I checked, it's OK.

These go with the other two slide sets I recently sent you: slides+notes for exploration vs experimental bases vs actual settlements, and slides+notes for unmanned direct cargo 1-way, delivering almost 40 tons. The single most important key to this approach is wanting to visit multiple sites in the 1 mission: that forces you to base out of LMO, not the surface! That is where I differ with most other mission plans. My approach is older. But it gets more done more quickly, and would actually be cheaper.

That leaves a whole lot yet to look at, such as an orbit-to-orbit transport for crews, and how to send landers and propellant ahead to LMO to support the landings and the return. But, implied by all of this (or most any other plan) is the need for a combined propellant depot and shipyard assembly facility in LEO.

As you can see, I learned the Korolev lesson of just build the bigger rocket. It worked for him.

GW

tahanson43206 · 2024-10-25 11:20:09

For GW Johnson....

Now that we have the links working, please give some thought to setting up a dedicated topic for the series you are working on.

You've already indicated (in private correspondence) that there might be a book in there somewhere, and this forum is a good place to build up a sequence of short pieces that eventually flow into a single entity.

This topic with your name on it is NOT the right place for a dedicated sequence.

We created the Course topic(s) with the flow in mind. Those could be fine tuned, because you were still creating content when we built those topics.

A Nation State is the size entity that would implement your overall vision, if the Nation State is on the large size, like China, India or perhaps the US.

It is possible that a consortium like the EU might be able to tackle something this size, but their policy of having to agree on everything suggests to me they'll never be able to agree on a project like this.

China is a likely candidate to pull this off on their own.

In any case, if you write a book, it should be written for the size entity that can pull it off, and not just for education of the public.

(th)

GW Johnson · 2024-10-25 14:57:22

I don't have enough for a book yet, for sure.

But I did do a Mars mission plan based out of LMO that visited multiple sites in the one mission. This was my Mars 2016 plan. The landers I recently sized supersede those landers. But the baton-spin crew orbit-to-orbit transport is about the same. I would use elliptic departure and capture for it at Earth. And sending landers and propellant ahead to LMO is the same issue it was in 2016.

The problem with any of this is the same as it was for Von Braun circa 1940: how do you assemble large things in Earth orbit? He did not know as much then as we do know today, about surviving long missions in space, and he knew nothing about the Van Allen radiation belts (discovered in 1958 by Explorer-1). But his basic orbit-to-orbit mission plan is still sound today. We just need to lower it from his 1000 mile altitudes, to about 200 mile altitudes, to stay out of the Van Allen belts. Especially the South Atlantic Anomaly. And, because of the Van Allen belts, we CANNOT send crew by electric propulsion (at least as we currently understand it).

Musk's Starship configured for Mars with "real" landing legs is much more appropriate to the settlement phase, when there are hard landing pads at Mars, and return propellant can be manufactured in quantity on Mars. Neither is true of the experimental base phase, and neither is true almost by definition in the exploration phase. Building hard pads and experimenting with propellant manufacture is PRECISELY what gets done in the experimental base phase, along with a lot of other life-support-related stuff.

Exploration answers the question "what all is there, and where exactly is it?". Experimental bases exist to figure out exactly how to live off the land, something NOT done during exploration. And until you answer all the issues from the experimental base phase, there is no ethical point to trying to start a settlement. PERIOD!

Why is this difficult to grasp? I've presented this before! At a Mars Society convention! To an audience who agreed with me!

GW

Last edited by GW Johnson (2024-10-25 15:08:05)

tahanson43206 · 2024-10-26 17:20:06

This post is a transfer from the Falcon 9 topic, where you had just pointed out that Falcon 9 burns kerosene and not methane.

For GW Johnson re methane leaks....

I just realized this is the Falcon 9 topic, and you've pointed out the Falcon 9 does not use methane.

I'll pick up in GW Johnson topic.

***
So here's my follow up question....

Might it be possible to set up little furnaces inside the Starship engine bay to burn any methane that might leak?

The output from the little furnaces would be co2, which would not contribute to combustion when it moves around the engine bay.

Would it make sense to set up little methane burners near any valves or joints that might leak methane?

Is this a strategy that might help to mitigate the risks due to use of methane as a propellant?

(th)

GW Johnson · 2024-10-26 17:48:07

To tell you the truth, I dunno.

I'd be very leery of deliberately setting fires where there could be a fuel gas leak, but that's just the fire protection engineering experience talking.

What we do with hydrogen welding gas is just do the plumbing "right" so that it does not leak. Standard gas bottles are typically loaded to 2200 psig. All the plumbing has to be good for more than that. And avoid risk of hydrogen embrittlement. At least methane does not have the embrittlement risk.

To the best of my knowledge, no one has ever handled methane at 4400+ psig before. I'm unsurprised that there are problems.

GW

tahanson43206 · 2024-10-28 08:38:23

for GW Johnson re Post in Starship topic ...

My take on it:
Following the link and reading the whole story, it says exactly what has already been posted on the forums. My point: this is now “official”, being published in an industry trade journal.
GW

I am reminded of the anxious moments when Neil Armstrong was tempting fate by moving the LEM landing site. My recollection is that the LEM may have been down to the last 3 seconds of fuel.

In the case of the Starship booster, the engineers had set a time limit for the booster to complete all the myriad tasks needed to position the catch pins over the chopsticks. If the timer had gone off, a completely separate set of software would have been invoked to try to move the booster away from the launch tower. ** That ** code has not yet been tested, and the only way it ** can ** be tested is with a catch failure.

(th)

GW Johnson · 2024-10-28 16:09:08

3 seconds of propellant left for Apollo 11 sounds about right. I know it was a small single handful of seconds.

The choice faced by Armstrong and Aldrin was absolutely-certain death from trying to land in a field of closely-spaced house-sized boulders (where the computer was taking them), or risking certain death if the propellant ran out before they could land (taking manual control). They were pretty much past the abort-back-to-orbit point. They chose the manual landing, and got away with it. Barely.

GW

GW Johnson · 2024-10-29 08:50:39

From AIAA’s “Daily Launch” for 29 October 2024:

NASA Finds Root Cause Of Orion Heat Shield Charring
Irene Klotz October 28, 2024

The heat shield for NASA's Artemis II Orion spacecraft was installed in June 2023 at Kennedy Space Center.
Credit: Cory Huston/NASA

NASA says it has determined why its Orion spacecraft returned from its 25-day Artemis I flight test around the Moon with unexpected charring in its heat shield.

Agency officials, however, declined to release its findings, pending ongoing internal discussions about next steps.

The finding was disclosed at two industry meetings on Oct. 28, with NASA’s Lori Glaze, acting deputy associate administrator for Explorations Systems Development Mission Directorate, speaking at NASA’s Lunar Exploration Analysis Group, and Lakiesha Hawkins, assistant deputy associate administrator for the Moon to Mars office, later addressing a question at the opening session of the American Astronautical Society’s 2024 von Braun Space Exploration Symposium.

“We have gotten to a root cause,” Hawkins said. “We are having conversations within the agency to make sure that we have a good understanding of not only what’s going on with the heat shield, but also next steps and how that actually applies to the course that we take for Artemis II.

“We’ll be in a position to be able to share where we are with that hopefully before the end of the year,” Hawkins said.

Among the issues uncovered by the Nov. 16-Dec. 11 Artemis I flight test was unanticipated charring of the Orion capsule’s ablative Avcoat heat shield material. The 16.5-ft.-dia. shield was designed to protect the spacecraft during atmospheric reentry speeds of up to about 25,000 mph and temperatures of nearly 5,000F.

Sensors in the Artemis I Orion capsule showed thermal conditions still met crew safety constraints during atmospheric reentry, but the heat shield’s performance did not match preflight thermal and mechanical computer models.

NASA in January delayed the follow-on crewed Artemis II mission to September 2025 from November 2024 in part to better understand the issue with the Orion heat shield.

Glaze said engineers have demonstrated and replicated the heat shield charring with tests at the Arc Jet Complex at NASA’s Ames Research Center. “We’re assessing what is the appropriate approach for Artemis II regarding the heat shield,” she said, noting that construction of the shield is complete.

Additional testing is underway, she added. “We expect that to be done by the end of November, and then we anticipate discussions with the administrator, who will make the final decision on how to proceed.”

Artemis II is planned to be a 10-day mission during which four astronauts—three from NASA and one from the Canadian Space Agency—fly around the Moon in an Orion capsule and return to Earth. That is to be followed about one year later by Artemis III, which features a landing on the south pole of the Moon.

My take on it:

The article indicates they went back into an arc jet tunnel and supposedly duplicated the effects they saw on Artemis-1. I suspect (opinion only) they angled the test articles to accentuate the effect of fluid shear forces across the little test article, and found the char layer shears off the virgin underneath too easily without the hex, for the flow conditions on an Orion heatshield shape.

Since they have declined to release those details, instead discussing what to do next, as the article indicates, I also suspect (again only my opinion) that this is risky enough for the Artemis-II crew to put them in a quandary. Do they change the heat shield to something better (costing a bundle of time and money), or do they go ahead and risk the crew? If they change it, what do they change it to?

I worked up what I consider to be the answers to those questions in a letter I sent to NASA Administrator Nelson some months ago. He never saw it, or they’d already know what to do. All I got as a reply was a rejection form letter for my “unsolicited proposal” to NASA. That was inappropriate on their part, because the letter explicitly said it was not a proposal to “do” anything for NASA, it was merely a sharing of knowledge and ideas.

Bureaucracy quite often shoots itself in the foot stumbling over its own Byzantine rules and procedures. The bigger they are, the worse this effect.

GW

Update 30 Oct '24: Today's AIAA "Daily Launch carries a similar Space.com story that says the same things, but includes photos of the erratic cratering damage to the Artemis-I heat shield. I tentatively conclude NASA management is desperate for their engineers to OK flying manned with the bad heat shield anyway. The engineers are trying correlate about how much cratering they get because there is no hex reinforcing the char in their Avcoat tiles. If it is not too bad in effect, and not too variable, they will OK flying manned as-is. That's what all the months of arc jet testing are all about. The problem is the variability. It will prove extreme, I predict. And NASA management will NOT like that outcome!

Last edited by GW Johnson (2024-10-30 10:31:13)

tahanson43206 · 2024-10-30 11:14:06

For GW Johnson re discussion with RGClark about methane fire in Starship booster...

This problem ** has ** to be solved.

How would you solve it?

This vehicle is supposed to perform launches several times a day, without extensive refurbishment between launches.

At this point, replacing the Hot Staging Ring appears to be needed.

(th)

GW Johnson · 2024-10-30 14:26:54

I don't know anything for sure, but it certainly appeared like a fuel-air fire in the engine bay of the descending Superheavy booster on Flight Test 5. As I indicated in the other thread.

There are a lot of possibilities as to where the leaking methane might be originating. This same effect has been seen at smaller scale in Raptor ground test videos, as flames enveloping some of the plumbing about the engine power head. Whatever is leaking, and there may be more than one thing, SpaceX really needs to identify it and fix it.

An oxygen leak is a much lower probability, but not zero. If such happens, sending pure oxygen into a fuel-air fire in the engine bay, then a huge, catastrophic, and fatal-to-the-vehicle explosion is inevitable. You shouldn't man-rate things with such problems unfixed.

GW

Last edited by GW Johnson (2024-10-30 14:27:24)

GW Johnson · 2024-11-01 09:45:53

From AIAA’s “Daily Launch” for 1 Nov 2024:

BREAKING DEFENSE
UK vows to ‘closely monitor all our supply chains’ after collapse of hypersonic supplier

The UK Ministry of Defence said it will continue to “closely monitor all our supply chains” as it reels from the collapse of Reaction Engines, the high speed propulsion manufacturer and industry lead on London’s quest to develop a reusable Mach 5 and beyond aircraft under the Hypersonic Air Vehicle Experimental (HVX) program.

My take on it: both the SABRE engine technology and the innovative cooling system used in it are now lost to industry. Very sad outcome. The detailed story said they never got completely out of start-up-style fundraising, which is not a way to indefinitely sustain a business.

From AIAA’s “Daily Launch” for 1 Nov 2024:

SPACE
Boeing can recover from its Starliner troubles, but it can’t afford any other misfires

The partial failure of Starliner’s mission doesn’t help Boeing’s effort to bounce back from its problems. The company’s reputation has not been irreparably...

My take on it: the full article discusses many things beyond just Starliner. Those include the 737MAX crashes, and the general notion of reputation damage. The article does not take on top corporate management’s causing this by prioritizing profit far above safety and reliability, with way too much cost-cutting in areas of activity that reduce safety and/or reliability.

From AIAA’s “Daily Launch” for 1 Nov 2024:

SPACENEWS
Chinese launch startup Cosmoleap secures funding for rocket featuring chopstick recovery system

Chinese launch firm Cosmoleap has secured more than 100 million yuan for the development of its Yueqian reusable rocket and a recovery system inspired by SpaceX. Cosmoleap announced more than $14 million in funding Nov. 1. Shenergy Chengyi, a Shanghai-based state-owned enterprise focusing on innovative investments, Tiangchuang Capital, an investment firm with a focus on emerging technologies, venture capital firm Baiyan Fund, Legend Capital, a venture capital firm supporting technological advancements, and investor Zhang Chao participated in the funding round.

My take on it: one has to wonder how serious this really is, or just copycat stuff aimed at looking good in the PR world.

GW

tahanson43206 · 2024-11-01 19:19:44

The pdf at the link below is short. It has one page of text and one page of illustration.

https://www.dropbox.com/scl/fi/9jfugo7e … vbebe&dl=0

This is a summary of GW Johnson's thinking about the benefits of launching a winged vehicle with a vertical phase to clear the atmosphere during ascent.

This forum contains a variety of ideas for launch. This short paper shows the advantage of the method pioneered by the Space Shuttle, demonstrated by the Soviet Buran, and used repeatedly by both US and Chinese military for their robot winged vehicle flights.

This is the technique planned for DreamChaser, if if ever gets off the ground.

(th)

kbd512 · 2024-11-02 19:41:11

We have solid empirical evidence indicating that wings are highly beneficial for passive vehicle stability during descent and landing, gliding cross-range to extend the landing point further from the point of reentry when required, and vehicle control during landing. Here on Earth, delta-winged lifting bodies help you land reliably, with less danger posed to the crew / vehicle structural integrity / innocent bystanders, specifically because no engine power is required to successfully land. All Space Shuttles which survived reentry achieved picture-perfect landings. The same cannot be said of vehicles that land using pure thrust from their rocket engines. We have enough data points now, from Space Shuttle flights and SpaceX Falcon Boosters, to make a fair comparison. Pure thrust is an active system requiring additional weight in the form of fuel and engine hardware and grid fin control surfaces. It's not "better than wings", it's merely a design trade-off. A totally fair comparison would use vehicle weight, successful landing attempts, and cost as the performance metrics. A failure rate above 1% would rule out either system as suitable for routine crewed flights. If you have a 1 in 100 chance of destroying the vehicle and killing everyone aboard during landing, most people would consider that far too high for a passenger service, even while accepting that space flight is intrinsically more dangerous than a commercial jet airliner.

chart%201.jpg

2023: No fatal accidents involving jet airliners and no hull losses (damaged beyond economical repair following a rough landing); this doesn't include biz jets, helicopters, or other small General Aviation aircraft
2022: 1 in 13.7 million passenger boardings
2008-2017: 1 in 7.9 million passenger boardings

Statistically speaking, continued advancements to jet airliners have resulted in them becoming the absolute safest type of long distance high speed travel, beating out fatal walking and running accidents not involving motor vehicles (slips and falls). If we perfect rocket engine and cryogenic propellant tech to the degree required, this is the fatal accident rate (zero or near-zero) that we're striving for. We know that we won't have quite the same level of success with much higher performance aerospace vehicles, but this is what the flying general public has come to expect.

We're presently much worse than the fatal accident rates for airliners in the 1930s, as it pertains to manned or man-rated spacecraft (if all reusable rocket launches had a crew aboard and were dependent upon a successful powered vertical landing). Flying was considered to be dangerous by the general public in the 1920s and 1930s, and for good reason. The fatal accident rate in 1932 was 14.96 per 100 million passenger miles. 1929 was the worst year on record, with a total of 51 fatal civil aviation accidents. Military aviation accidents were far higher than that, but so was the performance demanded of military aircraft. Reliability vs demanded performance is what we're fighting against when it comes to the reliability of rocket powered aerospace vehicles.

Here are some other recent aviation stats:
Helicopter fatal accident rate: 0.73 per 100,000 flight hours
General Aviation fatal accident rate: 1.049 per 100,000 flight hours
Experimental Aviation / Experimental Amateur Built (EAB) fatal accidents: 40 in 2023 (below the rate associated with lightning strike fatalities; 43 is the average number of fatal lightning strikes per year, for the past 30 years), 56 fatal accidents in 2022
EAB aircraft fleet has more than doubled since 1994 and flight hours have increased by 123%, but fatal accident rates have gone down
EAB hull loss on first flight is 0.6%, similar to loss rates on first flight for professionally built experimental aircraft of all types
~5.8% lost due to builder error of some kind at some point during the life of the airframe (FAA notes that this could be reduced substantially by performing a mandatory inspection of the engine and fueling system)
Private insurers charge the same or very similar rates for insuring EAB vs professionally built / maintained airframes, because there is little to no statistical difference across both fleets of General Aviation (GA) aircraft
Fatal accident rate for gliders is 1 in 4,000 flights, almost entirely attributable to pilot error

SpaceX Falcon Boosters have a successful landing rate, following completion of the test / tech development period, of 98.5% for the Block V booster models. That means there will likely be a fatal mishap rate of 5 vehicles per year if we fly once per day (365 flights per year), absent a dramatic improvement to the basic tech used. That is 11 TIMES worse than the glider accident rate, which would still be far too high for a routine passenger service (using low-time amateur glider pilots, rather than military pilots who have successfully completed test pilot school). It's much worse than that, though. A highly sophisticated computerized flight control system, which is supposed to react much faster than any human, has thus far only achieved a 98.5% successful landing rate for the non-experimental booster landing system. A Falcon booster is ostensibly simpler and easier to vertically land than a much larger / heavier / longer (higher CG) Starship.

The vast majority of all accidents across all types of aircraft are attributable to pilot error, not structural failure or build quality or maintenance issues. The top "killers" include running out of fuel- something which should never happen but frequently does anyway, controlled flight into terrain- a failure to aviate, spatial disorientation in IFR meteorological conditions, stall / spin during takeoff and landing- a failure to follow procedures by maintaining speed or attempting the "impossible turn" following engine failure. Many of the booster landing failures are attributable to running out of fuel, structural failure, engine failure, or guidance failure. That means we're "back to basics" when it comes to reducing the accident rate of vertical landing rockets.

As a general rule, helicopters (aircraft that land vertically using aerodynamic lift) and harriers (aircraft that land vertically using thrust from jet engines) have significantly higher accident rates, more intensive and expensive maintenance cycles, thus higher cost. Their very nature makes them much more complex and difficult to control in comparison to a winged glider or even a jet airliner. There's no plausible way to overcome that simple fact. By necessity, vertical landing vehicles are heavily optimized for a single yet critical flight regime (landing). At all other times, especially during forward flight (which is the overwhelming majority of the time for helicopters to harriers to rocket boosters), their designs are greatly compromised by that requirement to land vertically.

The engine performance and electronic control requirements to reliably land vertically are incredible. We've beaten the vertical landing problem into submission using engineering and an almost endless supply of money, but it remains a sub-optimal solution to the challenge of landing.

In the vacuum of space, on a low-gravity airless body such as Earth's moon or perhaps Mercury and Pluto, vertical landing is the only possible solution. Everywhere else, but especially Earth itself, there's enough atmosphere to take advantage of aerodynamic lift, so I think we should. I'm not stating that we cannot or should not continue to pursue vertical landing technology, but doing so represents a very high and expensive technological bar to clear, in comparison to gliding, to achieve the reliability required to attain acceptable fatal accident rates. Whenever something does go wrong with vertical landing, it's a near-guaranteed loss of vehicle and loss of crew. I've never seen a failed booster landing where the vehicle did not explode into a million pieces.

We have advanced rocketry to the point where very few of our rocket engines fail to ignite, explode during flight, or otherwise fail to respond correctly. That is good, because that's the first technological impediment. For reliable vertical landing, we improve our reliability of cryogenic oxidizer and fuel management, control software and system reliability, and not deviating from controllable flight due to faulty sensor input. That means we're either going to dump a lot more money into improving the reliability of those systems, which is fine if we get the result we're after, or we're going to deliberately choose to use aerodynamic lift and glide landings, because doing so eliminates most of the unsolved problems associated with powered vertical landings.

GW Johnson · 2024-11-02 22:17:50

No one can argue with you about landings, Kbd512. Capsules with chutes seem to work pretty good here on Earth, and so did the shuttle. I would say there might be a difference landing lower stages always unmanned, and upper stages that could be manned craft, like "Starship". There's no reason other than the costs of failures not to land lower stages as powered landings. SpaceX has already proved you can reach a good track record for that, as long as these are always unmanned.

It's the upper stages that are a different case entirely. If they are to be recoverable at all, they must be more than just a rocket stage, they have to be independent spacecraft that are entry capable. It is the entry capable that is the hard part, because only certain shapes are allowable, and the heat shielding will always be a heavy thing. Even the super ceramics are dense, and once fully hot, there's no practical way to hang onto them.

So, you are back to one of 3 things: capsules, spaceplanes, or powered landings. Only the first 2 of those 3 have any sort of track record yet. SpaceX is attempting the unproven one. But their results do show promise somewhere down the road.

What I was getting to with the short article was not about landing, it was about launch. Vertical launch into a non-lifting gravity turn leaving the sensible atmosphere at only modest supersonic speed gets you the lowest gravity losses, and the lowest drag losses by far!!!! You also have very modest ascent heating. Payload protection on these ascents is as much, or even more, about windblast protection.

Trying to fly entry-in-reverse with a lifting trajectory runs afoul of far-hypersonic speeds way down in the atmosphere, for the same heating rates as entry, but far longer exposure times, because you won't reach orbital-class speeds until you are almost above the entry interface altitude anyway. You heating problem is actually worse than entry, because of the longer exposure times. Your gravity loss is higher. And your drag losses to be covered are very likely larger than the orbital speed itself. Between that fatal issue, and the fact that in the extremely thin air above 60 km, there's just no sensible thrust available from any sort of airbreather (not even scramjet), that's really why the X-30 project went nowhere.

Those issues apply to any sort of upper stage spacecraft, be it a capsule, a spaceplane, or SpaceX's powered landing vehicle. You'll note that both shuttle and X-37B launch vertically onto a non-lifting gravity turn. Even the original early staged-airplane designs for shuttle launched vertically. Pretty much all the other lifting craft designs that had any real potential did, too. X-33 for one. The X-20 that was never built was another.

GW

tahanson43206 · Yesterday 11:43:16

For GW Johnson about Flight 6 landing in Indian Ocean...

Actually, I rather doubt that 2 is possible. It's bound to bust a tank, toppling over into the sea. If oxygen hits a fuel-air fire, the fire always explodes.

I don't know the answer to this, so am hoping it might be an interesting question.... What might we expect if the Starship is allowed to burn out all it's fuel and oxidizer before it settles into the ocean?

Even with liquids exhausted, there would still be gas in each tank, so the potential for that gas to ignite would still be present. If the ship can settle gently into the ocean so that water snuffs the engine compartment, then (theoretically) the tanks should allow the ship to float.

(th)

GW Johnson · Yesterday 13:58:50

The Starship upper stage is 50 m (165 ft) tall. When it touches down, the water will snuff the engines, but maybe not quite fill the engine compartment. That means any engine compartment fires may or may not be snuffed-out. The weight will shove that tail somewhere around 20-30-40 feet into the sea, leaving around 120-130-140 feet sticking out. That will fall over to one side and smack the sea at a pretty good clip. The odds of not breaking open a tank or busting a big plumbing line are close to nil.

The trouble here is that they have to do almost the same things as were done in flight 5 to stay within the launch license. To me, it seems more important to solve the hinge-line burn-through problem and demonstrate that solution, plus maybe try a Raptor re-start in space. Doing anything beyond crashing the Starship into the Indian ocean will require a new launch license from scratch. And that takes time to get approved.

They ought to be working on the next launch license already with the FAA. That assumes they already know what they want to try next, given better success with flight 6.

They dodged a bullet purely by chance on flight 5, being a reported 1 second away from commanding an abort instead of catching that booster. The words of SpaceX's own employees clue you in, as to why that happened: they didn't have all the software "saucered-and-blowed" the way they wanted.

Why wasn't it all done "right" before they flew? Musk pushing too hard. Pure and simple. He doesn't listen to his employees enough, and he has way too big a mouth; there's quite a track record of that, screwing up the FAA launch license processes, causing them to drag out.

GW

Last edited by GW Johnson (Yesterday 14:06:58)

tahanson43206 · Yesterday 15:58:02

For GW Johnson re #447

Thank you for additional insight into the upcoming flight. I did not see mention of my suggestion of burning all the fuel and oxidizer before settling into the water. It seems to me that doing that would reduce fuel for an explosion. It also seems (to me at least) that burning off the oxygen would take priority, although (come to think of it) oxygen in the air would combine with any fuel that might be left, so of the two, burning off the fuel might seem wisest.

You have pointed out that the ship would tip over but If water were allowed to enter the lower section of the vessel, then that would create a bottom weight that might allow the upper section to remain vertical in the water.

Wikipedia shows a cross section of Starship at: https://en.wikipedia.org/wiki/SpaceX_St … d%20oxygen.

The LOX tank is bottom most... If the fuel were exhausted while LoX remains, then that mass would be available to hold the vessel in a near vertical position.

The vehicle would still be top heavy, I'm sure.

(th)

GW Johnson · Today 09:40:59

At Starship upper stage landing, there's essentially nothing in the main propellant tanks but pressurized vapors. I don't know what pressure they are using, but it's enough to use those vapors for cold-gas attitude thrusters. That's a bomb waiting to go off, once the tanks crack open, letting the propellant gases mix. All you need is an ignition source to set it off. Methane-air lights easily. Methane-oxygen even easier.

The landing is done using propellants in the small header tanks in the nose. There's not a lot of propellant to begin with, as not a lot is needed to land an essentially-empty vehicle, but there would still be some liquid residuals in these header tanks after landing. Mass at landing is little different from dry-tanks mass, by maybe a single handful of tons at most, maybe at ton or so at minimum.

At 9 m outside diameter, the cross-sectional blockage area is some 63.6 sq.m. For a ship standing vertical in the water, you pick up 63.6 cu.m worth of displacement volume for each meter of length you have submerged. At about 1 ton/cu.m density of water (fresh, sea water is very slightly denser), that's 63.6 tons of buoyancy for every m worth of displacement volume you have submerged.

We will ignore the buoyancy of trapped air in the open-ended engine bay, some 3 m long, from what I read. If you believe the dry-tanks mass to be around 120 metric tons, you only need 2 m worth of length of submerged displacement volume to float the vehicle. 3 m for 180 tons inert, 1 m for 60 tons inert, etc. Adding in for the engine bay, at 120 tons inert, the tail end is 2+3 = 5 m below the surface to float statically, with buoyancy equal to weight. You might penetrate 2 to 3 times that temporarily, during dynamic landing transients.

(And those transients are far shorter than the time it would take to fill the main LOX tank even partly full of water!)

This vehicle is about 50 m long. The center of gravity is pretty near its middle, or it would not have flaps of roughly the same size at each end. That puts the cg some 25 m from the tail. Maybe 20, who knows for sure? Let's use 20 m for a nice round number.

Statically, that puts the cg some 20-5 = 15 m above the water surface. With the center of buoyancy under that surface by half the buoyant length, which is around 1 m. Cg above buoyancy center by about 16 m, compared to only 9 m diameter. That is wildly unstable! It must fall over! And rather quickly.

Now look at the dynamic transient during touchdown on the water. Let's assume worst case 3 times the static penetration of 5 m for 120 tons inert. That's 15 m penetration, subtracted from a 20 m cg position, for a cg still 5 m above the water, with a center of buoyancy located about 6 m below the surface, well below the cg. Cg above buoyancy center by 11 m, compared to a diameter of 9 m. It's still very unstable. It must fall over.

Note that for ships to be stable, they use heavy ballast down in the bottom. The idea is to pull the cg below the buoyancy center, although it will still be sort-of-stable as a rule-of-thumb, if the cg height above the buoyancy center is significantly less than the hull width. However, that's not a ship you can ride-out a storm in, without being capsized! Storm-proof is cg below buoyancy center. Period. ***

If it topples over and smacks the sea surface, things are going to break. Period. There are no flight-weight structures that will not break when that happens, as a sort of broadside impact. The forces are comparable to toppling over and smacking a concrete pad. Water starts behaving like concrete in terms of impact forces, at about 20 mph impact speeds and higher. That why you don't do a belly-flop off the high board at the pool!

If things break, the contained propellant gases will be released. All it takes is any source of ignition, like a flaming plume from a methane vent outlet, or a still-hot piece of anything from entry (there's multiple tons of still-hot heatshield tiles, plus recently-molten steel from the hinge line burn-through), to set off the explosion.

So, given all of this, why would anybody ever be surprised by the explosion fireball seen on flight 5 when the Starship ditched into the sea? That's pretty much a given, for just about any Starship ditch-at-sea scenario imaginable.

GW

*** Most cruise ships violate cg-below-buoyancy center. They have to steer clear of even minor storms, or else be capsized. Which is why I have no wish to ever travel aboard one of those top-heavy things! So far, they have not had a capsizing. But it is only a matter of time. And there is no getting aboard the lifeboats if you capsize! Thousands will die. Profit vs a low-probability with absolutely-intolerable consequences. Where have we seen that prioritization before?

Last edited by GW Johnson (Today 10:11:24)

tahanson43206 · Today 13:14:06

For GW Johnson re Starship landing in water...

Thank you for your detailed analysis in Post #449

Let me invite you (and all members) to consider this alternative scenario...

Suppose Elon and company open a portal at the top of the vehicle just before it enters the water.

My expectation is that water would enter as much of the vehicle as the buoyancy of the oxygen tank will allow.

Does this change the prediction for location of the Center of Gravity with respect to the Center of Buoyancy?

is there a poirt at the top of the vehicle that could be opened for this purpose?

Could a porthole be blown out just as the vehicle enters the water? That would be something the SpaceX team could add to the test without changing anything else in the approved launch plan. The benefit would be significant, if the Starship could be landed / floated for study.

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