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Exoscientist

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    Mathematician
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    Mathematics, physics, science, futurism, spaceflight, science fiction

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  1. Why not? NASA wants an extended upper stage, except the one proposed by Boeing would be too expensive, adding another $1 billion per launch to the cost. This stage in contrast is already developed so would be much cheaper. Note this also eliminates the need to develop a new carbon-fiber advanced SRB for the Block 2 and that attendant cost. Furthermore it would save on the ~$1 billion launch cost for the SpaceX proposal while at the same time making it a single launch per mission architecture. The intention is to make spaceflight to the Moon routine. This is much more likely to happen under a single launch architecture. Also, SLS launches can be less expensive under a reusable approach. As for your proposals for lunar missions I like the idea of several approaches to accomplish it. Note that for example SuperHeavy/Starship could also do it in a single launch architecture with the addition of a third stage. Robert Clark
  2. Here’s the Silverbird Astronautics estimates for the payload capacity using the Ariane 5 as the upper stage. The specifications shown below, with the 5-segment SRB data estimated by 25% scale up of the Space Shuttle SRB’s data. And the results for the LEO payload: The estimated payload for TLI is found by putting -1.0 in for the hyperbolic C3 value for “Escape trajectory” field. This is a number that indicates it’s just below escape velocity for a free return trajectory around the Moon in case the mission has to be aborted. So both the LEO payload of 150 tons and the TLI payload of 60 tons are above even the Block 2 payload capacity that would use advanced carbon fiber casing for the SRB’s. Input data taken from:
  3. You seem to be agreeing with me in this prior comment on the SpaceX discussion thread that the tanker Starship is at 50 tons dry mass not the 100 tons of the passenger Starship: . But that’s the essence of the argument that the tanker Starship can carry significant payload as an SSTO expendable. Then a reasonable estimate of the mass of reusabilty systems still allows significant payload as a reusable SSTO for the Starship.
  4. There are 3 MAJOR problems with using the overlarge Starship as the lunar and Mars landers. 1.)As we discussed, this approach would be highly inefficient in accordance to the key measure of launch size for large space projects. For the lunar missions 20 to 40 times larger than what was needed for the Apollo missions. And for the Mars missions, 5 times larger than the single launch Zubrin approach. Robert Zubrin discusses 2 other serious issues in his interview on The Space Show from Feb. 2020: https://www.thespaceshow.com/show/11-feb-2020/broadcast-3459-dr.-robert-zubrin 2.)At about 30 minutes in, he discusses the thrust ejecta issue for a large lander on the Moon. An analysis showed the ejecta scaled at lander size to the 2.5th power. This paper estimate a 40 ton lander would throw up 470 tons of ejecta: https://www.lpi.usra.edu/exploration/publications/MetzgerEtAl_SSERVI ESF2019_LanderPlumeEjecta.pdf The Starship weighs 100 tons dry. Give it a cargo of 100 tons. It also needs to return to the Gateway, so give it 100 tons propellant. The landed mass is now 300 tons. This is 7.5 times more than the 40 ton lander estimate used in the paper. The paper says the ejecta scales by the 2.5th power. So the ejecta is greater by a factor of 7.5^2.5 = 154, which brings the ejecta mass to 154*470 = 72,000 tons. Worse, from the methane/lox high exhaust speed the ejecta would have enough speed to escape the Moon’s gravity. A large proportion of the 72,000 tons of ejecta would be headed toward Earth. SpaceX claims to address this problem by using thrusters high up. But the physics seem to argue against this working. If high up and directed outward at an angle, that would prevent the crater being directly below the rocket. But while spreading the thrust outwards would reduce the impact thrust on any small area, the total area would be larger resulting in just as much ejecta. Actually, it conceivably could be worse. The proportion of thrust directed downward still has to be the same to cancel out the vehicles gravity. But if a large proportion of thrust is thrown away, being directed outward, the total thrust has to be larger than before. This means you need a larger propellant load than before, and so a larger lander, and so a worse ejecta problem. Note also, ejecta means mass is sent back in the direction towards the thrust. SpaceX is attempting to prevent a crater directly below by angling the thrust outwards. But this will cause some ejecta to head back towards the lander also. How much? It could be tons. It could tens of tons. It could be thousands of tons. We don’t know. 3.) Zubrin notes in the interview that to run the plants to produce the return propellant on Mars would take 10 football fields worth of solar cells or a nuclear power plant. This would take an inordinate amount of cargo mass to be sent to Mars to produce the return propellant. Marcus House in his video series also discusses the problem, and considers it so daunting for the Starship that we would be better off just transporting the return propellant from Earth, obviating the advantage of the Mars Direct approach of getting the return propellant from Mars. Robert Clark
  5. Since NASA is paying SpaceX $3 billion for 2 to 3 landings, in effect NASA is paying $1 billion to $1.5 per landing. The use of the already built Ariane 5/6 would be a small fraction of that. Robert Clark
  6. Funnily enough Zubrin’s proposal of staging off the Starship accomplishes a Mars mission at only ~200 tons IMLEO at a single launch and it is better than the SpaceX plan:
  7. Good point. Apollo did it at 3 million kilo launch mass. SpaceX 50 years later, with advances in materials and propulsion, proposes to do it at 50 million kilo launch mass and perhaps as much as 100 million kilo launch mass if Zubrin is right. Another way of saying this is the measure of large space projects known as “initial mass to LEO”, IMLEO, both stage mass and payload mass delivered to LEO. This was a common way of comparing Mars architectures. It can also be used for comparing any large space project. For Apollo it was 130,000 kilos. For the SpaceX plan it would be 2,500,000 kilos and perhaps as much as 5,000,000 kilos according to Zubrin. This for a single lunar mission. Robert Clark
  8. We are agreed on that. But the thing to remember is the only reason why the Gateway was proposed was that without an extended upper stage, the SLS didn’t have enough power to send the Orion to low lunar orbit. But NASA couldn’t afford the extended upper stage proposed by Boeing. But with an upper stage already built and flying reliably by the ESA for decades such a stage could be made available relatively cheaply, i.e., compared to building such a stage entirely from scratch. Robert Clark
  9. The intent is to make manned spaceflight to the Moon routine, or at least as routine as flights to the ISS are now. That’s not going to happen when it takes 8 to 16 launches of a Saturn V class launcher for a single mission to the Moon. By the way, Robert Zubrin estimated it would actually take ~20 launches of the Starship under the current proposal that has the Starship meetup with the astronauts in the Orion capsule at the Gateway to take them to the Moon and then back again to the Gateway, and then from there using the Orion for the trip back to Earth. This is because of the large amount of fuel needed for going back and forth to the Gateway: Op-ed | Toward a coherent Artemis plan. by Robert Zubrin — May 18, 2020 https://spacenews.com/op-ed-toward-a-coherent-artemis-plan/https://spacenews.com/op-ed-toward-a-coherent-artemis-plan/ It is extremely important to keep in mind the only reason why NASA proposes using the Gateway in the first place is because the SLS without an extended upper stage does not have enough power to take the Orion to low lunar orbit about the Moon and back again. With an extended upper stage, that eliminates the need for the, much derided, Gateway with its great added cost and time delay, and eliminates the need for the ~20 flights for the Starship. The SLS could mount the mission to the lunar surface by itself with no need for the Starship. Note the ESA is actually more in favor of a lunar base than is NASA. By the supplying an Ariane 5/6 to serve as the extended upper stage for the SLS that would go a long way to insure that it happens. Bob Clark
  10. Alien hunters should look for city lights from 'urbanized planets,' study suggests. By Leonard David published about 21 hours ago Lights from alien cities are an intriguing potential technosignature. https://www.leonarddavid.com/search-for-extraterrestrial-technology-city-lights-from-urbanized-planets/ Bob Clark
  11. Even Apollo-era TPS was at ~15% of landed mass. Landing gear at about 3%, so < 20% of landed mass for both. Even subtracting off from the payload a mass of 20% of landed mass could still give you a reusable SSTO vehicle at over 100 ton payload. Robert Clark
  12. Elon also says in that video the tank mass is at 80 tons. Then if SpaceX can reduce the tank wall thickness from 4 mm to 3 mm as they expect that’s cutting 25% off the tank mass, or 20 tons. Then the expendable SSTO Superheavy payload could be 175 tons to 135 tons, depending on if the SuperHeavy dry mass, prior to the tank mass saving, were 160 tons to 200 tons. The grid fins also can be reduced in weight. Elon was unhappy with their mass in the video at 3 tons each for a total mass of 12 tons. Their mass can be reduced to a fraction of this weight using ceramics, subtracting an additional 10 tons from the dry mass, increasing the expendable payload to somewhere in the range of 185 tons to 155 tons. Robert Clark
  13. Elon seems to be acknowledging the larger number of engines on this vehicle increased the likelihood of this occurring: 12:29 AM · Jul 12, 2022·Twitter for iPhone 296 Retweets 52 Quote Tweets 4,583 Likes
  14. Operational simplicity for rapid deployment if needed. Also the same vehicle can be used to come back or rescue if not needing first stage left back at the launch site. Robert Clark
  15. I’m not actually sanguine about the 33 engines on the Superheavy being in common use for passenger flights, either for a TSTO or a SSTO. Better would be to develop the 9-engined Starship either as a first stage booster, with a mini-Starship as upper stage or as an SSTO. Robert Clark
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