Exoscientist

I was surprised when reading this: DARPA moving forward with development of nuclear powered spacecraft. by Sandra Erwin — May 4, 2022 https://spacenews.com/darpa-moving-forward-with-development-of-nuclear-powered-spacecraft/ The article discusses that DARPA is funding nuclear powered propulsion to cislunar space. This is space in the vicinity of the Moon. The only reason why you would want it nuclear powered is you want to get there rapidly, in a matter of hours instead of days. What military purpose could there be for getting to the Moon in hours? Robert Clark

An upper stage for the SLS could be made by combining two Centaur V’s. This might allow a single launch Artemis lunar landing architecture, no SpaceX Starship launches required: Possibilities for a single launch architecture of the Artemis missions. http://exoscientist.blogspot.com/2022/10/possibilities-for-single-launch.html However, I used the Silverbirdastronautics.com payload estimator that has rather large error bars. I’d like to see a Kerbal Real Solar System mod to get a better estimate. Robert Clark

The X-33 tiles were well tested, as well were as the Starship tiles: 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/20040095922/downloads/20040095922.pdf The metallic tiles had better resistance to impact and rain than the ceramics at about the same weight, and would not require water proofing. They also would have closer thermal expansion properties to the steel Starship. Fig.3 Layered metallic sheeting separated by insulation. Fig.21 Metallic TPS at same weight of ceramic tiles, ~10kg/m^2

Problems with the heat tiles discussed here: Perhaps they should try the metallic heat tiles developed for the X-33? About same weight and thermal protection as ceramics , but were screwed on with bolts, and have superior impact and rain resistance. Robert Clark

Actually, it was. And SpaceX went so far as detailing how long they expected it would take to make these total 16 launches per mission: SpaceX CEO Elon Musk details orbital refueling plans for Starship Moon lander. By Eric Ralph Posted on August 12, 2021 First, SpaceX will launch a custom variant of Starship that was redacted in the GAO decision document but confirmed by NASA to be a propellant storage (or depot) ship last year. Second, after the depot Starship is in a stable orbit, SpaceX’s NASA HLS proposal reportedly states that the company would begin a series of 14 tanker launches spread over almost six months – each of which would dock with the depot and gradually fill its tanks. … In response to GAO revealing that SpaceX proposed as many as 16 launches – including 14 refuelings – spaced ~12 days apart for every Starship Moon lander mission, Musk says that a need for “16 flights is extremely unlikely.” Instead, assuming each Starship tanker is able to deliver a full 150 tons of payload (propellant) into orbit after a few years of design maturation, Musk believes that it’s unlikely to take more than eight tanker launches to refuel the depot ship – or a total of ten launches including the depot and lander. https://www.teslarati.com/spacex-elon-musk-starship-orbital-refueling-details/ Blue Origin didn’t raise this objection arbitrarily about the number of launches. It’s because it was in the actual proposal SpaceX made to NASA, and on which SpaceX based their charge to NASA for their mission plan. If they now claim the number of refueling launches will only be 4, then they should amend the amount they are charging NASA for their plan. Robert Clark

Actually, the mass of the Starship as an expendable is the entire point of the matter. From that you see you can get quite high payload as an expendable rocket. In fact, it’s in the same percentage of gross mass range of other currently in use expendable rockets. About the SpaceX lunar plan, it is an extremely important thing to know if NASA, and the U.S. tax payers, are getting jobbed if the original ~$3 billion price was based on ~16 flights per mission when it will only take ~4 launches per mission. Robert Clark

The point I’m making is that in reading the proposal to NASA the ~16 launches per mission were built into the contract. Suppose instead that in the original contract they said it would only take ~4 launches per mission using the stripped down 40 ton mass of the lander. Then that contract price should have been less. Robert Clark

Starship will use 30 tons of propellant as ballast in the nose on landing to help maintain stability: Note this will only be used on landing so would not be included for accounting of the mass as an expendable stage. The nose cone and nose cone barrel weighs ~17 tons. SpaceX will also save about ~7 tons off the tank mass on shaving down the tank thickness from 4mm to 3 mm. That's 54 tons off the 120 tons often cited for the Starship "dry mass", bringing it down to 66 tons. The attempt here is to estimate the dry mass as an expendable stage. But there's still the mass of the TPS, landing legs, and flaps. For the landing legs we can estimate that as following the Falcon 9 booster model of ~10% of the stage dry mass, so ~12 tons for the legs on Starship, when SpaceX is going by 120 tons as the dry mass. So we're now down to ~54 tons as an expendable dry mass. And the TPS? On the NasaSpaceflight.com forum that has been estimated as from 5 to 10 tons. So the expendable dry mass might be down to 44 tons. Then there is still the mass of the flaps that needs to be subtracted off for the expendable dry mass. Quite conceivable then that the expendable dry mass might be less than 40 tons. This is important to know because this is the form of the stage that would be used as the lunar lander, as SpaceX is intending it to be expendable in their lunar plan. Note also the payload section would also be removed in this configuration, with the lunar crew module being directed attached to the tank section via an adapter. Elon acknowledge this configuration would be much lighter and would therefore take fewer refuelings: If the Starship expendable without payload section or reusability systems would only mass ~40 tons then that needs to be acknowledged by SpaceX if that means the launches that needs to be paid for the U.S. taxpayers could be cut from ~16 to ~4. See discussion here: https://exoscientist.blogspot.com/2022/09/the-nature-of-true-dry-mass-of-starship.html Robert Clark

Good point. Robert Clark

With the hurricane threatening to force another rollback, leaving you with only one rollback left before the $2 billion vehicle has to be scrapped for parts, this becomes of increasing importance to find a solution. That NASA is dithering on the decision makes it clear the limit on rollback is a serious consideration. Even this fan solution if it works as a stop gap measure might be acceptable. One possible problem though is it might work too well. It might obscure the fact that a serious leak is occurring. Robert Clark

Thanks for that. Surprising scientifically that the same material can be magnetic or non-magnetic depending on how you work it. Robert Clark

This NASAspaceflight video also speculates SpaceX might be considering an expendable Starship version, with no heat shield or flaps: Robert Clark

Or could some very strong neodymium magnets be included in the tiles so they are kept on magnetically against the steel airframe? Robert Clark

Saw this discussed on the NASASpaceflight forum: ____________________________________________________________ Don't know if you know about it but this site has some useful articles https://www.nasaspaceflight.com/2022/09/starship-next-phase-of-testing/ https://www.nasaspaceflight.com/2022/08/booster-7-additional-tests/ ____________________________________________________________ https://forum.nasaspaceflight.com/index.php?topic=50748.msg2409134#msg2409134 With every test firing of the Starship some tiles pop off. There is some speculation Starship may be launched on the first test flight without the tiles, obviously in an expendable mode. Here’s a picture of the pins that hold on the tiles: It seems you could get stronger type pins than that. For example you could use spring-loaded wing nuts: Apparently SpaceX does not want to glue the tiles on like what happened with the shuttle because it takes too much maintenance time for replacement and refurbishment. But with the wing nuts you can adjust the strength to be removable but strong enough to hold on during flight. By the way, according to the discussion in that thread on NasaSpaceflight.com SpaceX is looking to improve on the tiles they are using. I advise considering mathematician and engineers GW Johnson’s ultra lightweight, reusable TPS material: Robert Clark

The current plan is to not reuse the lander because it would take too much propellant weight to return it. The Starship without payload section could get twice the payload as an expendable SSTO as the Falcon 9 as an expendable. Here's a more representative image of the Starship as a lunar lander without a crew capsule(Orion): Robert Clark

Note that SpaceX does not need the passenger section, or thermal protection, or upper and lower flaps for the lunar lander version of the Starship. In fact it probably can even do without a fairing, with the Orion capsule attached above the tank with an adapter for its smaller diameter. SpaceX wants to argue it might only take 4 refuelings for the lunar mission. Then they should acknowledge that this form of the Starship with no passenger section, i.e., with the upper rings above the tank removed, might only mass 50 to 60 tons. But that would mean this format of the Starship could do 40 to 50 tons payload to LEO as an expendable SSTO. Then any reasonable estimate for reusability systems would still allow significant payload as a reusable SSTO. Robert Clark

That would be embarrassing if the answer were that simple! Robert Clark

The image is only to illustrate the case with much reduced payload section and therefore much reduced dry mass. In actuality to estimate the dry mass for the Starship as SSTO, just as in the SuperHeavy case you first start with stage in this form (sans grid fins), i.e., with no fairing: Then add on fairing mass. For a smaller rocket need smaller fairing. The Falcon 9 fairing for example is only ~2 tons. So the dry mass would not be 85 tons. That’s the estimated dry mass with the full payload section of the full rocket four times larger. Estimate the dry mass without this payload section. As you said you can do that just counting rings. Without that section, the dry mass is 20 to 30 tons lighter, depending on if you also include lightening the tanks by reducing wall thickness from 4 mm to 3 mm. Then add on a much smaller fairing, likely only 2 to 4 tons. As I said, I suspect Elon when saying the Starship can’t carry much payload as an SSTO he’s using the original full size payload section incurring a 20 to 30 ton weight penalty. Robert Clark

The scaling in the version with the reduced fairing section is wrong. It makes it look like the tank is being stretched. No, same tank just reduced fairing size. Note for the SSTO version of size 1/4th that of the full two-stage you would expect the payload to be smaller so the fairing should be as well. Since the dry mass is smaller, the thermal protection, landing legs, and flaps mass should be as well. So you should first calculate what the expendable payload is then add on the, smaller, TPS, legs, and flaps mass. I redid the image, eyeballing it to make tanks appear same size in both versions. Robert Clark

Key question: how much mass is that empty payload section above the Starship main tank? I have a suspicion Elon leaves this on when claiming the Starship can't carry much payload as SSTO. In other words, for the SSTO version, instead of looking like the 1st image below it should look like the 2nd: Robert Clark

No those SSTO's that Tater cited were reusable. Remember the 2-3% payload for the SuperHeavy/StarShip is because of the 50% payload loss on full reusability. That's a large loss in payload. That's a key part of the argument for why reusable SSTO's become competitive with reusable TSTO's. Without the 50% payload loss, the SH/SS payload would be 4-6%. Robert Clark

Yes. But the phrasing there leads me to believe the Mach 20 mentioned is the actual speed that needs to be reached for the 6,000 mile range. So the comparison should be to the actual speed of orbital velocity. Robert Clark

Single Stage Point to Point Up To 6000 Miles With Mach 20 Starship May 31, 2019 by Brian Wang https://www.nextbigfuture.com/2019/05/single-stage-point-to-point-up-to-6000-miles-with-mach-20-starship.html To go 6,000 miles would take Mach 20, about 6,800 m/s. But 6,000 miles is only half the longest distance of 12,500 miles, half the Earth's circumference. But orbital velocity is 7,800 m/s. When you launch eastward you get 400 m/s for free from Earth's rotation so an orbital rocket only needs 7,400 m/s. This is just 10% more than the 6,800 m/s suborbital velocity proposed. So just a 10% higher speed gets you full coverage to anywhere on Earth as well as orbit. Robert Clark

I was quite startled to read from space reporter Eric Berger that the SLS rocket can only do 2 more rollbacks before it is decertified(!) Huh? A $2 billion spacecraft just gets thrown away, unused!?! Eric Berger @SciGuySpace Also, per a source, NASA has certified the SLS rocket for just two more rollouts from the VAB. So if they were to roll back to VAB this month and then back to the pad, they would have just one roundtrip left. So that's kind of a serious constraint on this hardware. 5:14 PM · Sep 7, 2022 120 Retweets 28 Quote Tweets 1,526 Likes https://twitter.com/sciguyspace/status/1567622377185415173?s=21&t=5LtvwPXyKM1uFyyqGcs9WA As this article shows hydrogen leaks during fueling have been a recurrent problem going back 40 years with the Shuttle: Years after shuttle, NASA rediscovers the perils of liquid hydrogen "Every time we saw a leak, it pretty quickly exceeded our flammability limits." ERIC BERGER - 9/3/2022, 6:38 PM https://arstechnica.com/science/2022/09/years-after-shuttle-nasa-rediscovers-the-perils-of-liquid-hydrogen/ These quick disconnect fittings that are the source of the problem are quite low tech: Valve Disconnect A closeup of the 7-inch quick disconnect that will be replaced on the hydrogen vent line to the Ground Umbilical Carrier Plate of space shuttle Discovery's external fuel tank. The replacement will be made on Launch Pad 39A at NASA's Kennedy Space Center in Florida. A leak of hydrogen at the site during fueling caused the STS-119 mission to be scrubbed at 2:36 p.m. March 11. Photo Credit: United Space Alliance March 11, 2009 Surely someone can up with a more advanced tech solution that will stop the hydrogen leaks in a quick disconnect system??? Robert Clark

You’re not considering that 2 -3% for the SH/SS is coming from making it fully reusable. So those ~2% payload reusable SSTO’s are comparable to the reusable TSTO’s. Robert Clark