Exoscientist

Zubrin 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

If this new high temperature material is able to solve the Starship thermal protection issues, I think SpaceX would accept this relatively mild criticism anyway. Bob Clark

New high temperature ceramic heat shield materials promoted to SpaceX: AN OPEN LETTER TO ELON MUSK. Dr. Ed Pope https://www.linkedin.com/feed/update/urn:li:activity:7306136414910300160 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/matech-cal-nano-aim-to-commercialize-uht-composites Bob Clark

There are several variations of this inflatable heat shield idea. The most researched one is a conical inflatable heat shield. It’s being investigated for example as a heat shield to make the Cygnus cargo capsule reusable: Here’s a research article on it: HEART FLIGHT TEST OVERVIEW 9th INTERNATIONAL PLANETARY PROBE WORKSHOP 16-22 JUNE 2012, TOULOUSE https://websites.isae-supaero.fr/IMG/pdf/137-heart-ippw-9_v04-tpsas.pdf As discussed there the parameter used to measure the capability of a particular shape to slow down descent is not wing loading, weight divided by wing area, but the ballistic coefficient, (mass)/(drag coefficient*drag area), β = m/CDA, given in metric units. This takes into account the fact different shapes are more effective in slowing down the spacecraft by including the coefficient of drag CD as well as being more general than just looking at wings for the decelerator. In this report, the mass used for their analysis is 5,000 kg and the diameter of their conical decelerator is 8.3 meters. There is thermal protection applied but I gather less of it is needed since the conical aeroshell is just made of silicone rubber. If it is just ballistic coefficient determining this then for a spacecraft or stage about 9 times heavier, say, 40,000+ kg, then the area needs to be 9 times more, that is, a conical shell about 25 meters in diameter. This is useful for just drag decelerators, but is incomplete for winged reentry because it does not include the effects of lift. For instance if wings with high lift/drag ratio at hypersonic speeds were used the descent rate would be decreased even further. The hypersonic aerodynamics of the Space Shuttle have been described as falling “like a brick.” Then wings with high L/D ratio could greatly improve on this. Bob Clark

Still, I’d like to see the calculation. In the Space Review article, the idea was first proposed by the legendary spaceflight engineer Maxime Faget. So I’d like to see some calculations supporting or disproving it. Bob Clark

One of the criticisms of the Space Shuttle was it was so heavy, as an upper stage, for the payload it could get to orbit: ca. 80 ton dry mass, for only a ca. 20 ton payload. That’s the reverse of what it should be. For instance, for the Falcon 9 the upper stage has a ca. 4 ton dry mass for a ca. 20 ton payload. Note that if Elon’s estimate of the expendable Starship’s dry mass as 40 tons was accurate, then at a payload of 200 to 250 tons, the payload to upper stage ratio would be in the expected range of about 4 or 5 to 1. The Space Shuttle heavy weight resulted in poor, i.e., high, wing loading. From Grok: Query: What was the Space Shuttle orbiter wing loading in pounds per square foot? Response: … Final Answer: The Space Shuttle orbiter's wing loading was approximately 91 psf at launch and 76 psf at landing, with slight variations depending on the specific mission and payload. These values reflect its design as a reusable spacecraft optimized for both atmospheric reentry and gliding to a runway landing. The Space Review article wanted a wing loading of 10 pounds per square foot(psf) to require no thermal protection: Wings in space. by James C. McLane III Monday, July 11, 2011 The Space Review 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 If the expendable Starship did have a dry mass of 40 tons, 88,000 pounds, and say added wings gave wing loading of 10 psf what does KSP say the heating would be during reentry? Bob Clark Edit: I suppose this would have to be carried out in the Real Solar System mod rather than KSP itself.

Thanks for that. I discussed before I think it was a mistake for SpaceX not to go with expendable version of the Superheavy/Starship first then proceed to reusability, once the expendable version was proven. This approach was spectacularly successful with the Falcon 9. Taking this approach with the SH/SS they would now already be launching 250 tons to orbit, 10 times greater than the payload of the F9. And with the success at catching the SH booster, we may assume the per kilo cost would be reduced further still by partial reusability. Quite likely we would have single launch manned missions both to the Moon and Mars with partial reusability of less than $100 million cost now at less than what we are currently spending just for manned missions to the ISS. The approach that SpaceX is taken to reuse of the upper stage is also poor. Elon once estimated the dry mass of the Starship upper stage could be as low as just 40 tons as an expendable. Now the various modifications to the Starship for reusability, the dry mass is estimated as 160+ tons, an increase by a factor of 4 or likely more. For an orbital rocket you should try to minimize the weight growth of an upper stage as much as possible since that subtracts directly from payload. In that regard SpaceX should examine the possibility of using wings for landing instead of powered, vertical landing. Wings using lift can reduce the speed of descent thus decreasing the heat load on return, thereby reducing the thermal protection needed. The thermal protection used so far by SpaceX has not been successful. Reducing the heat load could reduce the amount of thermal protection needed. In fact, it might be it could even be reduced to zero. A surprising article: Wings in space. by James C. McLane III The Space Review 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 At the current overweight Starship mass, wings might be too large and heavy to get to this low wing loading but it might work if SpaceX went back to the expendable dry mass of only 40,000 kg. At such a mass, with the cross-section of the stage being 9 meters by 50 meters, and using the cross-section area of the cylindrical stage as “wing area”, the psf would be 40,000*2.2(pounds)/9*50*3.282 (sq.ft.) = 18 psf. Still not at the 10 psf point. But it’s close so that added wing area needed would be small: Typically, wings amount to about 5% to 10% of the dry mass. For such small wings it would be closer to the smaller number so only 2,000 kg added weight, and the psf would still be about the same 10 psf number. That Space Review article though gives no references where this contention of a 10 psf needing no thermal protection was derived. Can your spreadsheet calculate speed at intermediate points during descent? You would need to be able to do this for a calculation for the heating induced by the speed at each altitude and air density during the descent. Bob Clark

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_pacific/2025-03-04/cargo-rocket-pacific-johnston-atoll-air-force-17026030.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. I argue SpaceX already has this capability for such low launch cost 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: Implications of the coming era of commercial heavy launch: point-to-point transport for both cargo and passengers. https://exoscientist.blogspot.com/2025/03/implications-of-coming-era-of.html Bob Clark

If it is true its size and payload will be V2-like then ChatGPT was giving the right estimate of ca. 100 tons. Bob Clark

Quote, “These days Elon can do essentially whatever the hell he wants.” Bob Clark

Are they downgrading the performance of Starship V3? Starlink sats at 550 km orbit. By ChatGPT, 100 tons at 550 km orbit corresponds to ca. 105 to 110 tons at a 200 km reference orbit: Query: If a rocket can get 100 tons to 550 km high orbit, how much can it get to 200 km high orbit? Response: … Rough estimate: A simple approximation (ignoring atmospheric drag and other losses) could give you a 5-10% increase in payload capacity to the lower orbit. So if the rocket can place 100 tons into a 550 km orbit, it could likely place somewhere around 105 to 110 tons into a 200 km orbit, depending on specifics. But SpaceX said V3 should get 200 tons to LEO. Bob Clark

Thanks for that. Just basic spaceflight engineering principles suggest Starship is too heavy for the role of a lander. SpaceX hires very good engineers. They know this. Unfortunately the actual engineers get overruled by Elon: Bob Clark

Another article critical of the multi-refueling approach SpaceX is taking to get to the Moon and Mars, that discusses Zubrin’s view as well as that of 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/kevinholdenplatt/2025/03/17/spacex-needs-a-new-mini-starship-to-land-humans-on-the-moon-and-mars/ Bob Clark

I’ve mentioned before Zubrin and others have argued the point using Starship itself as the lander to the Moon or Mars is a bad approach. It is far too heavy for that role. Standard engineering practice is to add additional, smaller stages, to get to high delta-v destinations such as the Moon or Mars. Apollo for instance, even higher delta-v being round-trip, used 6 propulsive stages. An article discusses this argument of Zubrin of using a smaller mini-Starship as the lander as well as the critical Will Locket review article here: Mini-Starship or bust? Experts clash over SpaceX’s future. https://floridamedianow.com/2025/03/spacexs-future/ I discussed the estimate of a $90 million unit production cost of the Superheavy/Starship here: https://forum.kerbalspaceprogram.com/topic/159887-spacex-discussion-thread/?do=findComment&comment=4428912 Bob Clark

At least you were able to finally make it to make it to the front of the line. Next time we go, we’ll have to make it at the least crowded times of the day, even if it’s, say, 3am. Bob Clark