Exoscientist

A route to aircraft-like reusability for rocket engines. https://exoscientist.blogspot.com/2024/04/a-route-to-aircraft-like-reusability.html An interesting discussion on longevity of jet engines: The question I raise is whether this could also increase the reuse capability of rocket engines. Near the end I suggest, SpaceX is using this principle or running the engines at lowered power to increase engine life for the purpose of increasing the reliability of the Raptors. If they are, then they should explore the potential of this principle to also extend rocket engine reuse capability. Bob Clark

The trouble is if you run the numbers for the specifications SpaceX has cited for the SuperHeavy and Starship, i.e., their dry and propellant masses, and Raptor thrust and Isp, SH/SS should well be able to make 100+ tons to orbit as a reusable. I think NASA engineers were able to take the SpaceX proposal as a viable solution for an Artemis lander because their numbers checked out. But now we find the reusable payload for the current version is only 1/3rd the originally predicted 150 tons to orbit. What explains the drastically reduced payload capacity? This is a major issue because the current version can not perform the refueling functions of the Artemis lander missions at that low payload value. My opinion: I think NASA was blind-sided by that low announced payload value. SpaceX and NASA will have to be open about what that severe loss in payload, by 100 tons, stems from. Bob Clark

SpaceX should withdraw its application for the Starship as an Artemis lunar lander, Page 3: Starship has radically reduced capability than promised. https://exoscientist.blogspot.com/2024/04/spacex-should-withdraw-its-application.html Robert Clark

About 31 minutes in Elon suggests the current version V1 would be capable of 40 to 50 tons to orbit. This is bad because SpaceX sold NASA on the idea the Starship HLS could serve as an Artemis lander based on 150 tons to orbit reusable and “10ish” refueling flights. If the capability is max 50 tons, then it would take “30ish” refueling flights. If they intend to use version V2 then this is bad because it would require further qualification flights for the larger version and more importantly further qualification of the more powerful Raptor 3 engine needed. This last is doubly bad because I’d be willing to bet dollars to donuts that they never informed NASA that the current version couldn’t do it and further development would be required for the larger version. Bob Clark

I’d like to see them get some actual payload to orbit, even if it’s inert like water or liquid nitrogen. Bob Clark

SpaceX has completely dismantled the second OLM, located at the Kennedy launch site: Chris Bergin - NSF @NASASpaceflight The final Orbital Launch Mount (OLM) leg at KSC 39A has been demolished ahead of a likely pad redesign prior to East Coast Starship launches. https://twitter.com/NASASpaceflight/status/1775529100335108442 Evidently, NASA or SpaceX or more likely both were unhappy with the level of damage on an OLM after a Starship launch. They started dismantling it just one week after IFT-3. Rumor has it the new design will have a flame diverter. Bob Clark

SpaceX Starship has a serious problem that no one is talking about! https://www.youtube.com/watch?v=9SUbx3IkfRA His argument is the pad damage after each flight might take a month or more to repair. That would extend the time for all the refueling flights for the Artemis missions to a year or more. But when you have cryogenic propellant stored in orbit that long it results in severe boiloff problems. That means additional refueling flights to replace the propellant lost to boiloff. But at a month or more between flights, that means even longer time in orbit for the propellant and additional boiloff, so even more refueling flights. The result is the number of refueling flights becomes impracticality large. The answer might be you need a full flame diverter like used by Apollo to prevent pad damage. Gee, those Apollo guys really were smart. Bob Clark

Multiple sources give a 3,400 ton propellant load for the booster and 1,200 tons for the ship, for 4,600 ton max propellant load. The 4,500 ton total given in the SpaceX tweet is only 2% off this value. That could be just round off error or it could be you don’t want literally the tanks to be filled to the very top to allow for boiloff of the cryogenic propellant. Bob Clark

Oddly, not just suggesting it could reach orbit before the mission, Elon said it did reach orbital velocity after the flight: What max propellant load are you saying SH/SS could carry? Bob Clark

Thanks for that. Do you have a link where Beck said this? I’ve suggested that SpaceX intentionally ran the Raptors on IFT-2 and IFT-3 at reduced power, i.e., thrust, to improve reliability. This has broader implications than just the Raptor question: Can running a rocket engine at reduced thrust extend lifetimes? Can someone in rocket propulsion answer if this fact about jet engines also holds for rocket engines? If so, increasing a turbopump rocket engine power just 10% to 15% cuts engine life in half. And conversely, decreasing it by 10% to 15% doubles engine life. And would this still work if we repeated the concept multiple times? If we reduced the thrust by .9^5 = .60, i.e., to 60%, which most turbopump engines can manage, then we could increase the lifetime by a factor of 2^5 = 32 times? Then a Merlin engine with a lifetime of, say, 30 reuses by running it only 60% power could have its lifetime extended to 1,000 reuses? Is this a known fact about turbopump rocket engines their lifetimes increase radically by a relatively small decrease in their thrust levels? Bob Clark

He has an obvious error at item 4 -- "orbital" velocity. There is no indication whatsoever that Starship failed to reach its intended velocity or trajectory. That is a debatable point because Elon did say there was an 80% chance of the Starship reaching orbit on this flight: https://youtu.be/lCe8a7XcG8o But later SpaceX said they were planning a flight just under orbital velocity. So in that infographic from TonyBela.com it might be Bela was taking the reaching orbital velocity objective in item #4 from what Elon said. But there still remains the question of why didn’t IFT-3 reach orbital velocity? In the case of IFT-2 they vented LOX reducing the velocity it was capable of, and Elon even said if they had a payload and had not vented LOX they would have reached orbit. But they didn’t vent LOX on IFT-3 and SpaceX said they had a full propellant load and from the view of the propellant gauges the propellant was virtually expended in both stages. So why were they not able to reach orbit even though carrying 0 payload? Bob Clark

Thanks. I didn’t think of the uplinks. Even though it might not be possible to decrypt the signals, it might possible the spectrum is so unusual to be unlikely to be natural. Bob Clark

Interesting article here about researchers who had for a moment thought they might have detected evidence of intelligent extraterrestrial signals: https://astronomy.com/news/2021/12/technosignature-from-proxima-centauri--and-why-astronomers-rejected-it However, it is notable in their search that they excluded radio frequencies commonly used for communications on Earth so as not to accidentally detect those signals. But if those frequencies are commonly selected for use on Earth they also may be commonly selected on extraterrestrial systems. Then it is quite notable there are multiple plans worldwide for megaconstellations containing tens of thousands of satellites each. The question: how radio loud would the Earth be then when these tens of thousands of satellites are in place? How far away would the Earth be detectable then in radio frequencies from other systems? Would the Earth then have a peculiar radio spectrum that would be unlikely to be produced naturally? Because of the intereference from the Earth communications we couldn’t reliably detect such signals from other systems using the radio observatories on Earth. But how about the lunar far side? Astronomers want to maintain the radio silence on the lunar far side for scientific research in the radio spectrum: Astronomers call for radio silence on the far side of the moon. News By Leonard David( space.com-leonard-david ) published March 21, 2024 https://www.space.com/the-moon-far-side-radio-silence But it may also provide an ideal means to search for radio SETI. Bob Clark

Common Sense Skeptic, a well-known critic of SpaceX, presents an argument that considering all the mission objectives IFT-3 should not be regarded as a successful test: From the video : Bob Clark

How about showing it can get anywhere near the 150 tons payload to LEO claimed? What IFT-3 showed was a launcher with 0 tons to LEO payload capability, even when fully fueled and fully expending its propellant. Then how can it do Artemis Starship HLS refuelings when it gets 0 tons to LEO? Bob Clark