Posts by RGClark

RGClark · Human missions

tahanson43206 wrote:

For RGClark...
Here is an image GW asked me to post for you:
https://i.imgur.com/W4DXxet.png
(th)

Thanks for that, GW. I wanted to ask in regards to the “hot metal” TPS, the heat would rapidly propagate to the upper side of the vehicle. This means the radiative surface area would double, thus doubling the heat emission.

Shouldn’t this improve the survivability?

Bob Clark

RGClark · Human missions

I discussed in the blog post the inflatable conical shield being investigated to allow the Cygnus cargo capsule to be reusable had the same ballistic coefficient as the Starship of ca. 60 kg/sq.m IF you take the dry mass of the Starship at the expendable 40 tons.

The problem is this conical shield was sized for a returning craft of mass of ca. 5 tons and it’s not certain how the conical shield would scale to higher mass, such as the Starship.

But there might be an example that would give us a reusable thermal shield for a vehicle the size of Starship. I’m thinking of the X-33/Venturestar.

The length in meters was 38.7m and width 39m. For the dry mass, the total gross weight was 2,186,000 lbs, propellant weight 1,929,000 lbs, and payload weight 45,000 lbs; giving a dry weight of 212,000 lbs, or 96,400 kg.

Using a hypersonic drag coefficient of 2, and considering the triangular planform requires multiplying by 1/2 the length*width to get the area, the ballistic coefficient calculates out to be 96,400/(2*1/2*38.7*39) = 64 kg/sq.m.

Remarkably close to the ballistic coefficient of the Starship at the 60,000 kg mass of the expendable’s dry mass + fairing mass.

But the added weight of the metallic shingle TPS of the X-33/Venturestar can’t be too high to allow the ballistic coefficient to remain close to this value.

The areal density of the metallic shingle TPS was about 10 kg/sq.m:

REUSABLE METALLIC THERMAL PROTECTION SYSTEMS DEVELOPMENT
Max L. Blosser*, Carl J. Martin*, Kamran Daryabeigi*, Carl C. Poteet **
*NASA Langley Research Center, Hampton, VA, USA
** JIAFS, The George Washington University, Hampton, VA, USA
https://ntrs.nasa.gov/api/citations/200 … 095922.pdf

The metallic tiles had better resistance to impact and rain than the ceramics at about the same weight.

Fig.3 Layered metallic sheeting separated by insulation.

Fig.21 Metallic TPS at same weight of ceramic tiles, ~10kg/sq.m.

At a 10 kg/sq.m. areal density, the added weight covering just the lower half of the Starship would be (1/2)*Pi*9*50*(10 kg/sq.m.) = 7,060 kg, proportionally small enough that the ballistic coefficient would still be ca. 60 kg/sq.m.

This would be advantageous in that you don’t need added wings and you don’t need an additional conical shield.

BUT for this to work SpaceX would have to go back to the smaller, expendable mass of the Starship. SpaceX had tested the X-33 metallic shingles and concluded they were inadequate. But that was with temperatures developed with the higher 150+ ton Starship. With a lighter dry mass, much reduced temperatures result.

Bob Clark

RGClark · Human missions

kbd512 wrote:

I'd like to point out how ridiculously low 18.75kg/m^2 (3.84lbs/ft^2) truly is. That is the wing loading equivalent of the average ultra-light aircraft, none of which are made from materials that will withstand 800C. For a 150,000kg dry mass vehicle, the heat shield surface area is 8,000m^2. A regulation American football field is 57,600ft^2, or 5,351m^2, which means the heat shield would need to be 1.5X the size of a football field. For all practical purposes, we don't build any flying vehicles of that size.
…

I discussed before I think SpaceX is not taking the best approach to developing the Superheavy/Starship. They were spectacularly successful with the Falcon 9 by first getting the expendable version, then proceeding to reusability. If they had taken that approach with the SH/SS they would already be flying the expendable version and perhaps even also the partially reusable one, i.e., reusing the booster only, a la the Falcon 9.

Note then for the expendable version the dry mass of the Starship might have been as low as 40 tons:

Elon Musk @ElonMusk
Probably no fairing either & just 3 Raptor Vacuum engines. Mass ratio of ~30 (1200 tons full, 40 tons empty) with Isp of 380. Then drop a few dozen modified Starlink satellites from empty engine bays with ~1600 Isp, MR 2. Spread out, see what’s there. Not impossible.
https://x.com/elonmusk/status/1111798912141017089?s=61

Then with the ca. 20 ton fairing, the needed ‘wing’ area need to be added might be ca. 1,800 sq.m. But this wouldn’t be as heavy as regular wings with their thickness to generate aerodynamic lift. It would only have the character of a thin plate since it is meant only to be a drag decelerator.

Bob Clark

RGClark · Human missions

Thanks for that, GW. Your updated version of Fig 6. is closer to the Dr. Akin result of approx. stagnation temperature 800°C for a ballistic coefficient of ca. 20 kg/sq.m:

Your updated Fig 6:

beta%20study%206%20rev.png

This is in the range of the max. service temperature for some steel alloys:

beta%208.png

Bob Clark

RGClark · Human missions

kbd512 wrote:

Dr Clark,
Antonov AN-225's wing area was 905m^2 and wing tank fuel capacity was 375m^3.
Concorde's wing area was 358m^2 and internal fuel capacity was 119.5m^3.
For Starship to have 1,800m^2 of wing area, the wing's fuel capacity would be at least 600m^3, which is a third of Starship's present propellant capacity. Since 304L stainless is such a weak structural metal relative to its mass, the wing would need to carry propellant and be shaped to resist both internal pressurization loads and aero loads lower in the atmosphere. This proposal would increase the weight of Starship to impractical levels, which is why it won't be done. A lifting body Starship, which may or may not remain within tolerable mass limits, would require a complete redesign to provide 1,800m^2 of lifting surface area.

Keep in mind how huge Starship is. Jet fuel, kerosene, is a bit less than water’s density of a ton per cubic meter. Then the Antonov’s wing fuel load would be about 300 tons and the Concorde’s about 100 tons. The Starship carries 1,200 tons of propellant.

But it’s a bit like comparing apples to oranges. In this scenario the “wing” would not be carrying fuel. It would only be acting as a drag decelerator, a la the ‘parashield’.

Still, I’d like to see what could done with true wings using high lift/drag aerodynamics at hypersonic speed. This would undoubtedly make the wings smaller.

Optimum Mach 25 waverider [from Bowcutt, Anderson and Capriotti, 1987

Bob Clark

RGClark · Human missions

GW Johnson wrote:

Bear in mind that lifting bodies have a substantially-lower lift curve slope that delta wings, in turn less than swept wings, and that in turn less than straight wings. There is more to available lift than just wing area! By around a factor of 2 to 3! Planform shape is a big influence, as is wing section shape (lifting body vs airfoil). Especially considering the differences between subsonic and supersonic/hypersonic designs!
That being said, I have been looking closely at Bob's suggestion that low ballistic coefficient might eliminate the need for heat shielding. I am running a generic study across a very wide range of ballistic coefficients, to see what the peak stagnation heating rates and peak deceleration gees look like, as well as end-of-hypersonics altitudes, for fixed entry speed and entry angle below horizontal, in Earth's atmosphere. These are at fixed mass and hypersonic drag coefficient, with a fixed "nose radius"/diameter ratio. I vary diameter. Just generic, but well within the ballpark.
I will not take this through any realistic vehicle designs, but it will provide design constraints in terms of surface stagnation zone temperatures, and average pressures across the heat shield at peak deceleration. Both are crucial heat shield parameters.
GW

Thanks. I would be interested in seeing your conclusions.

Bob Clark

RGClark · Human missions

SpaceX is having difficulty finding an effective thermal protection system for Starship. I had earlier speculated that if it were giving sufficiently large wings, it could go completely without TPS. The possibility was occasioned by this article:

Wings in space.
by James C. McLane III
Monday, July 11, 2011
Wing loading (the vehicle’s weight divided by its wing surface area) is a prime parameter affecting flight. The antique aluminum Douglas DC-3 airliner had a big wing with a low loading of about 25 psf (pounds per square foot of wing surface). At the other end of the spectrum, the Space Shuttle orbiter has a high wing loading of about 120 psf. This loading, combined with an inefficient delta-shaped wing, makes the orbiter glide like a brick. A little Cessna 152 private plane features a wing loading of about 11 psf and modern gliders operate down around 7 psf. A space plane with huge lifting surfaces and a very low wing loading might not require any external thermal insulation at all. Building a space plane with a wing loading of, say, 10 psf should not be an impossible proposition. Perhaps some day it will be done.
http://www.thespacereview.com/article/1880/1

I found a further article that allows this possibility to be further constrained:

SpaceOps 2010 Conference
25-30 April 2010, Huntsville, Alabama AIAA 2010-1928
Applications of Ultra-Low Ballistic Coefficient Entry Vehicles to Existing and Future Space Missions
David L. Akin∗
Space Systems Laboratory, University of Maryland, College Park, MD 20742
https://spacecraft.ssl.umd.edu/publicat … hieldx.pdf

As discussed there the relevant parameter is actually ‘ballistic coefficient’, (mass)/(drag coefficient*drag area), β = m/CD*A, given in metric units kg/m^2, where the drag area is by cross-section.

The author uses a slightly variant definition given in units of pascals where up in the numerator is given the weight in Newtons. But it’s easy to convert to the more commonly used version by dividing by g, 9.81 m/s^2, i.e., about 10. He estimates when ballistic coeffcient is below 200 Pa, or about 20 kg/m^2 in the more common units, the max temperature during reentry would be ca. 800°C. This should be a temperature stainless-steel is able to withstand.

I estimated an additional wing area of 36m*50m = 1,800m^2 would allow the max temperature to stay below the 800°C point:

Reentry of orbital stages without thermal protection, Page 2.
https://exoscientist.blogspot.com/2025/ … thout.html

Bob Clark

RGClark · Human missions

Video interview of Zubrin discussing his recent article in Unherd:

Robert Zubrin: How humans will live on Mars.
https://youtu.be/BCX9YPAZa5A?si=2Q8Hnxj1U_aTyqkY

He thinks SpaceX could succeed at a manned Mars mission, but Elon’s recent statement of a manned mission by 2028 is overly optimistic.

Interestingly, he says if Elons fails it would be for the reason I suggested: hubris.

Bob Clark

RGClark · Human missions

Robert Zubrin again presents the argument a Starship Mars mission would be better implemented by using smaller lander stage to do the actual landing rather than the Starship itself:

The flaws in Musk’s Mars mission
Our future lies on the Red Planet.
Robert Zubrin
April 1, 2025 6 mins
Furthermore, it needs to be done correctly. SpaceX’s Starship, which claims to be the world’s most powerful reusable launch vehicle, promises to be a terrific asset. But Musk insists that it should be the only vehicle used for the mission. While a Starship upper stage could be refuelled on orbit by tanker Starships, enabling it in theory to fly from Earth orbit to Mars, its 100-tonne mass makes it suboptimal for use as an ascent vehicle. It would make far more sense to develop and use a similar but much smaller vehicle — a “Starboat” if you will — to travel between the surface of Mars and its orbit. Starship plus Starboat could enable highly efficient missions to Mars. But this will require a programme leadership capable of speaking truth to power.
https://unherd.com/2025/04/the-flaws-in … s-mission/

Bob Clark

RGClark · Other space advocacy organizations

What's on the agenda for the April meeting?

Bob Clark

RGClark · Interplanetary transportation

Several thin-film solar cell research efforts have come up with better than 1kW/kg power density solar cells, the power density needed for VASIMR. The highest one I’ve seen is this:

Solar-cell-packin' drone uses sunlight for on-the-spot recharging
By Ben Coxworth
April 19, 2024
Created by scientists at Austria's Johannes Kepler University Linz, the lightweight, flexible cells are made of a semiconductor material known as perovskite, and they're less than 2.5 micrometers thick – that's just 1/20th the width of a human hair. And importantly, they're 20.1% efficient at converting sunlight into electricity, plus they boast a power output of up to 44 watts per gram.
In a proof-of-concept test of the technology, the scientists mounted a ring-shaped array of 24 of the cells on a commercially available CX10 miniature quadcopter, which was dubbed the Solar Hopper. The array made up just 1/25th of the augmented aircraft's total weight, with the cells themselves making up only 1/400th.
https://newatlas.com/drones/solar-cells … -sunlight/

It is notable though that last sentence in this passage suggests the structural elements make up the greatest component of the weight. Still, being out of the Earth’s gravity and at very low acceleration for our application, the structural elements would be much reduced.

Bob Clark

RGClark · Human missions

New high temperature ceramic heat shield material promoted to SpaceX to solve their heat shield problems:

AN OPEN LETTER TO ELON MUSK.
Dr. Ed Pope
https://www.linkedin.com/feed/update/ur … 4910300160

Published 3/14/2025
MATECH, Cal Nano aim to commercialize UHT composites.
The partnership’s combined technological advances and manufacturing prowess will target the scale-up and industrialization of FAST SPS for high-temp and UHT composites serving aviation, defense.
https://www.compositesworld.com/news/ma … composites

GW, perhaps you should pitch your high temperature ceramic directly to SpaceX.

Bob Clark

RGClark · Interplanetary transportation

The Air Force is planning on funding point-to-point rocket cargo transport:

Air Force picks remote Pacific atoll as site for cargo rocket trials
By SETH ROBSON STARS AND STRIPES • March 4, 2025
https://www.stripes.com/theaters/asia_p … 26030.html

Bob Clark

RGClark · Interplanetary transportation

Implications of the coming era of commercial heavy launch: point-to-point transport for both cargo and passengers.
https://exoscientist.blogspot.com/2025/ … ra-of.html

Surprisingly, just standard FedEX cargo aircraft delivery for the longest distance transpacific routes costs over $100/kg. Then when SpaceX does manage to get the cost orbit to $100/kg the cost for Starship transport at less than 1 hour travel time will be less than aircraft cargo delivery rates for the longest routes that might take a full day.

In my blog post I argue that SpaceX already has this capability for such low cost launch with the Starship. It only has to take the approach, proven so successful with the Falcon 9, of first doing expendable launch, then partial reusability. Full reusability is unnecessary, and the recent failures with Starship suggest is more difficult than SpaceX expected.

With such a strong financial motive for such fast point-to-point cargo delivery there is no doubt it would be implemented. Then at high flight rates this would serve to improve launch reliability, thereby bringing about such fast point-to-point transport for passengers as well.

People have criticized SpaceX developing Starship on the grounds there would be no consistent market for such large mass to orbit. But this would be a key market, point-to-point cargo and soon thereafter passenger transport.

Bob Clark

RGClark · Human missions

Another expert engineer criticizes the multi-refueling approach SpaceX is taking to get to the Moon and Mars as a bad approach, former high ranking NASA official Daniel Dumbacher:

SpaceX Needs A New Mini-Starship To Land Humans On The Moon And Mars.
By Kevin Holden Platt, Contributor. Kevin Holden Platt writes on space defense…
Mar 17, 2025 at 11:33pm EDT
…
“Our approach today has a very low probability to match the ‘before 2030’ milestone for landing humans on the Moon,” Daniel Dumbacher, who formerly served as Deputy Associate Administrator of NASA’s Human Exploration and Operations Mission Directorate, in charge of the Artemis lunar landings, testified at the hearing.

While he didn’t mention the fiery breakup of SpaceX’s Starship during its January flight demo, Dumbacher, now a professor in aeronautical engineering at Purdue University, said that the ship’s need to be refueled with super-cooled liquid oxygen and methane in low Earth orbit via multiple dockings with still-to-be-developed tankers - a complicated operation that has never been tested - before each flight to the Moon involves an assemblage of complex technologies that might not be perfected within the next five years.

“We might have to build a lander - we might have to scale down the current lander,” Dumbacher told the House, “so that we get to that 2030 landing.”

To avert potentially spiraling problems with testing the colossal Starships during the countdown to this new Moon quest, he said, “I’d get myself a simplified lander - so that I can get to the Moon - that does not require multiple launches.”
…
https://www.forbes.com/sites/kevinholde … -and-mars/

Bob Clark

RGClark · Human missions

Actually, I have given examples where Elon ignored basic principles of spaceflight engineering. The flame trench fiasco is one of many:

Read over those comments by Robert Zubrin I linked in post #2019. That he makes this point so vociferously suggests it’s because it’s basic spaceflight engineering being ignored: to get to high delta-v destinations use staging.

Bob Clark

RGClark · Human missions

kbd512 wrote:

Dr Clark,
All the personal attacks against Elon Musk, for whatever your personal motivations happen to be, won't solve a thing.

It’s not personal. It’s purely engineering. It’s literally basic spaceflight engineering that Elon is ignoring. No true Chief Engineer would ignore such principles. Basic principles in engineering are being repeatedly ignored by Elon. SpaceX has many very good engineers. But Elon repeatedly ignores their recommendations.

That is literally the only reason why Starship is not already delivering high payload mass to orbit.
If you read any of the biographies of Elon a common feature that emerges is Elon is brutal in firing those who he feels their engineering is not up to the job. He can’t see that he is that person now.

Bob Clark

RGClark · Human missions

GW Johnson wrote:

…
This thrust oscillation in the Raptor-3's is large enough that I consider it "combustion instability". At the old rocket plant, we never allowed a design out the door with oscillations that large.
GW

There’s no telling if this will ever be solved with Musk serving as Chief Engineer. Look up ‘hubris’.

Bob Clark

RGClark · Human missions

Another article discusses this critical review of Will Locket and also the opinion of Robert Zubrin that SpaceX is taking the wrong approach in wanting to land the entire Starship on the Moon or Mars:

Mini-Starship or bust? Experts clash over SpaceX’s future.
https://floridamedianow.com/2025/03/spacexs-future/

As Zubrin notes, standard spaceflight engineeering says you add an additional, smaller upper stage to do high delta-v destinations. Zubrin has made this point numerous, numerous times:

https://x.com/robert_zubrin/status/1374 … 00896?s=61

https://x.com/robert_zubrin/status/1725 … 79000?s=61

https://x.com/robert_zubrin/status/1278 … 20833?s=61

https://x.com/robert_zubrin/status/1256 … 45728?s=61

https://x.com/robert_zubrin/status/1256 … 18819?s=61

https://x.com/robert_zubrin/status/1256 … 25249?s=61

https://x.com/robert_zubrin/status/1192 … 85987?s=61

https://x.com/robert_zubrin/status/1192 … 15552?s=61

https://x.com/robert_zubrin/status/1192 … 24192?s=61

https://x.com/robert_zubrin/status/1178 … 41184?s=61

https://x.com/robert_zubrin/status/1127 … 78464?s=61

https://x.com/robert_zubrin/status/1127 … 68961?s=61

And finally,

Robert Zubrin @robert_zubrin
Starship can revolutionize Earth to orbit. But for landing on the Moon or Mars we need to stage off it. Using Starship as a lunar lander is like using an aircraft carrier for white water rafting.
https://x.com/robert_zubrin/status/1178724273025933312?

Zubrin has also argued this directly to Musk and Musk has always stubbornly refused it. Stunning when you think about it, but the development problems with the Starship could be solved with one simple, and I say obvious, move: hire a true Chief Engineer to lead the development. But Musk is too close to it to see that he is the problem.

Bob Clark

RGClark · Human missions

“Angry Astronaut” discusses a critical review article of the Starship that claims it can’t be made to work:

Engineer claims that SpaceX Starship can't be fixed! Is he right?
https://www.youtube.com/live/CxEcTXTgiM … sl-0yQVCmi
(There is an audio glitch at the beginning of the video. Fast forward to the 7 minute point.)

In the video, Angry disagrees with the authors conclusions, the article being here:

Starship Was Doomed From The Beginning.
The fatal flaw SpaceX can’t overcome.
Will Lockett
Published in
Predict
8 min read
https://medium.com/predict/starship-was … 3bf809539c

The authors primary argument is the desire to make the upper stage reusable is making it too heavy. Angry Astronaut critiques this argument by saying the Space Shuttle was 100% reusable. This is not correct for the entire Space Shuttle system since the external tank was expendable. But it is true that the upper stage, the orbiter itself, was reusable.

Still, it has long been discussed in the field a criticism of the space shuttle system was how heavy that upper stage was compared to the payload. The dry mass of the shuttle orbiter was about 80 tons. But the payload was about 24 tons. The reusable upper stage was nearly 4 times heavier than the payload.

This is backwards in accordance to how normal rockets work. Normally you want to make that dry mass for the upper stage as low as possible since every extra kilo added to an upper stage dry mass subtracts directly from the payload possible.

Normally, the payload would be multiple times more than the dry mass of the upper stage. For instance for the F9 the payload is ca. 20 tons, but the upper stage dry mass is only ca. 4 tons. And for the Saturn V the payload to LEO was 100+ tons, while the dry mass of the upper stage, the 3rd stage, was only ca. 15 tons.

Quite interestingly, in regards to the Starship the payload for V1 according to Elon is only in the range of 40 to 50 tons, despite the original plan of 150 ton capacity. And indeed the dry mass of the Starship V1 is in the range of 160+ tons, quite analogous to the ratio for the reusable Space Shuttle orbiter of the dry mass of the upper stage being ca. 4 times more than the payload.

SpaceX recognized this is too low a payload for a rocket of the Superheavy/Starship size and wants to make the rocket larger to get to its desired payload capacity. Both attempts of flying the larger V2 upper stage resulted in the stage exploding in flight. The author of this critical review article argues its because of the need to lighten the dry mass of the vehicle to get the desired payload.

I don’t know if that is the case, but it should give SpaceX pause that in the V1 version, the one we know so far that can get to orbit, the payload had the same small proportion of the dry mass of the upper stage as did the Space Shuttle of only one fourth.

Bob Clark

RGClark · Human missions

NSF - NASASpaceflight.com
@NASASpaceflight
Interesting: SpaceX is looking to hire a Propulsion Systems Engineer, responsible for designing, analyzing, and building feedline system to feed Raptor engines on Starship.
https://boards.greenhouse.io/spacex/job … 607806002…
GlzFCVNXcAEgohI?format=jpg&name=medium
https://x.com/NASASpaceflight/status/18 … 5587286458

Repeated engineering failures stem from the top. First, hire a true Chief Engineer. Then follow standard industry practice of doing full-up(all engines), full mission duration, full thrust static tests.

Bob Clark

RGClark · Human missions

Finally, people are starting to ask the tough questions about the SpaceX development of Starship:

Twin Test Flight Explosions Show SpaceX Is No Longer Defying Gravity.
Consecutive losses of the Starship rocket suggest that the company’s engineers are not as infallible as its fans may think.
…
But these two Starship explosions were a step backward in SpaceX’s development process, as the flights could not even repeat the successes of earlier test flights, and they perhaps show that the company’s engineers are not as infallible as fans of the company sometimes like to think.
“There’s this persona that has built up around SpaceX, but you’re starting to see that they’re human, too,” said Daniel Dumbacher, a former NASA official who is now a professor of engineering practice at Purdue University and chief innovation and strategy officer for Special Aerospace Services, an engineering and manufacturing company whose customers include NASA, the United States Space Force and some of SpaceX’s competitors.
https://www.nytimes.com/2025/03/08/scie … -musk.html

Repeated engineering failures stem from the top. SpaceX needs a true Chief Engineer making the engineering decisions.

Bob Clark

RGClark · Science, Technology, and Astronomy

Calliban wrote:

One thing that is clear for all of the proposed approaches to fusion power is that scale matters. The reason is simple. One of the inputs into the lawson criterion is average confinement time.
https://en.m.wikipedia.org/wiki/Lawson_criterion
Confinement time increases as the size of the system increases. Ions escape through surfaces. As scale increases, the ratio of surface area to volume decreases. And it takes more time for an ion to cross a larger confinement radius. This tells us that for any fusion system, technical viability improves as systems scale up. For inertial confinement systems, to meet the lawson criterion the following condition must be met:
Plasma density x compressed radius > 1 gram / cm2.
But there are obvious problems with achieving this in real life. Doubling the diameter of a pellet or magnetic confinement chamber, increases plasma volume by a factor of eight. That increase in size implies increased capital cost and there is a limit to what can practically be afforded. There are also limits to the size of a powerplant that can be accomodated within a national grid. A 10GWe fusion reactor would be a very difficult addition to most grid systems.
Maybe a solution to this problem is improved transmission. HVDC would allow a single unit to serve a larger geographic area.

An amusing approach to the Lawson criterion: Lorentz contraction. Many think of Lorentz contraction as relative, that is, things only appear to shrink as they go faster. This is the case in relativity theory as long as both are traveling inertially, i.e., without acceleration. However, if one is accelerated then the Lorentz contraction is absolute, i.e., both the at rest body and the accelerated body both agree that the accelerated one has shrunk.

Length Contraction is NOT an Illusion!
https://m.youtube.com/watch?v=TxW6_E3uLuo

The situation is analogous to the twin paradox: if motion and time are relative why is it the moving twin ages more slowly? The difference is the moving twin in returning to the starting point was accelerated thus underwent actual time dilation: both he and the at rest twin agree the moving twin had his time slowed.

So whatever the factor needed for the Larsen criterion to reach sustained fusion, accelerate the target plasma at the required relativistic speed, like in atomic accelerators, so the Lorentz gamma factor equals that.

Amusingly, this might be testable in small university or even amateur labs since small accelerators such as Van de Graaff accelerators exist.

Bob Clark

RGClark · Interplanetary transportation

There is much handwringing at NASA as it appears the Artemis missions will be cancelled. However, in point of fact we are now at a point in the development of spaceflight that manned lunar missions can be mounted for what we are now spending just for flights to the ISS, as long as they are commercially financed.

Then we now have the capability to be at the long-desired position of having a sustained, habitable presence on the Moon:

Could Blue Origin offer its own rocket to the Moon, Page 2: low cost crewed lunar landers.
https://exoscientist.blogspot.com/2025/ … ocket.html

As part of the calculations I came to a surprising conclusion, the production cost, as opposed to the price charged to a customer, for a manned space capsule might be only a few ten's of millions of dollars.

Bob Clark

RGClark · Human missions

Anomaly at end of Starship long duration static test?

SpaceX @SpaceX
The extended firing tested new hardware and cycled the six Raptor engines through multiple thrust levels to recreate different conditions seen within the propulsion system during flight. Data from the test will inform upgrades to the ship’s hardware and flight profile ahead of the next launch.
https://x.com/spacex/status/1889799440652763145?s=61

BUT:

Zach Golden @CSI_Starbase
Synchronizing the audio from this video answers a few questions.
It does not sound like there was a single engine relight after shutdown as some have suggested. Instead there is an audible pop that is accompanied by a quick flash.
https://x.com/csi_starbase/status/18895 … 22976?s=61

TheSpaceEngineer @mcrs987
mystery popping components are my favorite
https://x.com/mcrs987/status/1889517378704154850?s=61

The flames were seen coming out of the flap hinge of Starship in IFT-7 at about 7 minutes into flight:

https://x.com/csi_starbase/status/18800 … 56706?s=61

Given stage separation is about 3 minutes into flight, the flames were seen about 4 minutes after the ship’s engine ignition. A test should go at least that far, though ideally all the way to the 6+ minute burn time of the ship. If it requires additional nitrogen and water supplies being added to the test stand, then so be it.

Also, a greenish tinge seen in this clip from the exhaust just for a moment at the start of the clip is a hallmark of copper burning:

https://x.com/mcrs987/status/1889517378704154850?s=61

Bob Clark

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#9 Re: Human missions » Starship is Go... » 2025-04-03 08:44:00

#10 Re: Other space advocacy organizations » NSS Houston Chapter Events » 2025-04-03 07:31:59

#11 Re: Interplanetary transportation » VASIMR - Solar Powered? » 2025-03-28 16:18:13

#12 Re: Human missions » Starship is Go... » 2025-03-27 14:38:40

#13 Re: Interplanetary transportation » With commercial heavy launch: point-to-point rocket transport. » 2025-03-24 14:21:22

#14 Interplanetary transportation » With commercial heavy launch: point-to-point rocket transport. » 2025-03-22 16:06:47

#15 Re: Human missions » Starship is Go... » 2025-03-21 17:58:20

#16 Re: Human missions » Starship is Go... » 2025-03-21 01:57:45

#17 Re: Human missions » Starship is Go... » 2025-03-20 14:27:41

#18 Re: Human missions » Starship is Go... » 2025-03-20 08:38:31

#19 Re: Human missions » Starship is Go... » 2025-03-20 08:33:13

#20 Re: Human missions » Starship is Go... » 2025-03-18 08:00:42

#21 Re: Human missions » Starship is Go... » 2025-03-13 06:54:57

#22 Re: Human missions » Starship is Go... » 2025-03-10 09:34:12

#23 Re: Science, Technology, and Astronomy » Fusion power in the offing? » 2025-03-04 08:41:56

#24 Re: Interplanetary transportation » Could Blue Origin offer its own rocket to the Moon? » 2025-02-21 10:55:49

#25 Re: Human missions » Starship is Go... » 2025-02-14 15:10:36

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