Racescort666

@sevenperforce I ran the numbers for Centaur. I didn't do exactly what you asked, I was still comparing the mass difference of equal dV for a given payload. This is also assuming that a Metholox engine scales and will maintain a 198.5 TWR when scaled down to produce 99.2 kN of thrust. Interesting finding: for the New Horizons launch on an Atlas V 551, it would have had a faster escape trajectory with the Metholox design. The payload was around 2615 kg (New Horizons + a Star 48B) which puts the upper stage at 23 228 kg vs Centaur's 25 692 kg so the stage separation speeds would be higher. Not that New Horizons needed more velocity since it had to slow down after the Star burn.

@sevenperforce Centaur is something I can look into since I have the relevant numbers at hand. There are not currently any Methelox engines in the R10 thrust range but it's probably safe to assume that the technology scales easily with the same TWR. I'll have to look into it. It's worth noting that Centaur's kg/m2 is 14.5 while the ET is 19.9. Oops, my bad, I forgot to include the part that was specific to NTRs: if you're using hydrogen, they require active cooling for extended use, if you use something like water or ammonia, they don't but still retain very high ISP.

This is what I was trying to get at. I was referring to active cooling of the propellant to prevent/manage boil off. Maybe NTRs work better for larger payloads, I only looked at them for smaller ones. The other problem with NTRs is that they don't scale like chemical rockets do, which is maybe where I was forming my opinion of them.

That's the point though, between the engines and the tankage, it's not that light. Yes, you reach a median value where all is equal but you definitely take a mass hit where the tanks are concerned; the ET is over 3 times the mass of the Metholox in the 1 engine example. I will be the first to admit that I haven't looked at this from all angles but the increase in specific impulse isn't all it's cracked up to be. As for NTRs, optimally, they require a spherical tank. Practically, they need active fuel cooling to be useful beyond an Earth departure burn. In which case, chemical generally works out better (or Ion but that's another topic).

Long winded introduction in spoiler: I put together a hypothetical situation to compare the Space Shuttle ET mounted with 1 SSME to a Metholox powered stage with 1 engine. For this exercise, I was interested in what the mass of a Metholox powered stage would come in at. In other words, attach 1 SSME to ET, fire, how much dV? (14.3 km/s) Use the rocket equation to figure out a Metholox stage with the same dV and compare mass. Raptor: Thrust: 1900 kN TWR: 198.5 Mass: 977 kg ISP: 380 s Fuel Mix: 3.8 SSME: Thrust: 2279 kN TWR: 65.9 Mass: 3527 kg ISP: 452 s Fuel Mix: 5.9 ET: Gross mass: 760 000 kg Dry mass: 26 500 kg Notes: Metholox stage: 119 331 kg including tank, fuel, and engine. o_O this can't be right... Nobody shoots an empty fuel tank into space for fun so I decided to account for a payload. You can see in the plot below how the stage mass changes as payload increases. There are a couple of things going on behind this plot, first the dry mass of the SSME + ET doesn't change (about 30t), second the Metholox stage dry mass does change (4.4t to 13.6t). At the cross point of the blue and purple lines (20t payload) the Metholox stage is 11 385 kg close to 1/3 of the dry weight. Interesting that there is a payload range where Metholox has the advantage. I suspect that it has to do with the dry mass to payload ratio. Also, TWR for this whole deal is about 0.25 with a 20t payload. Interesting... what if we add... MOAR BOOSTERS: Changing up the plot a bit, here we have a 3 engine hypothetical situation. For the ET+SSME contraption, it's probably not too far off of Shuttle-C with no SRBs. With more engines the cross point moves up to 30t and the TWR is 0.73 at the cross point which is in the range of common upper stages. Anyway, there was no real science here and I suppose that if we want to go someplace in a hurry, Metholox might be a decent strategy. Maybe if you wanted to send the Hubble Space Telescope on an escape trajectory... Closing thoughts: this situation is kind of unrealistic, could I come up with a more realistic situation to better reflect a hypothetical Metholox upper stage? Yes, probably. I think the point remains that there is possibly a situation where a higher density fuel makes more sense from a mass standpoint than a hydrogen powered one though.

There is something missing from the discussion of economic feasibility: how much does it cost to bring platinum back to earth? We have a good idea of how much it costs to send stuff to space, we can make some reasonable assumptions on how much platinum we can get a hold of, but say we've found an asteroid that has the platinum we're looking for (also, prospecting isn't cheap either), what then? How much does it cost to tractor an asteroid back to LEO or Lunar orbit or wherever your processing facility is? Do you process it in it's original orbit? It seems like it would be easier to process it in a more accessible orbit but is there a cost break between onsite processing or moving the asteroid to an orbit that already has infrastructure? There will be byproducts that could be monetized but that's not really part of this discussion. I think the questions are: What is the mass of the asteroid/mass of platinum? How much dV do you need to get to your target asteroid? How much dV is needed to bring the asteroid to the processing facility? How big (heavy) is an asteroid processing facility? How do you get the platinum down to the surface? In a ship? Ballistic? If you want the raw metal, I assume a chunk of metal would be pretty easy to get down, you just crash it into the ground or the ocean at a speed where it doesn't break up too much. However, if that is not an option, what kind of spacecraft would you have to build to bring one down safely?

Sorry about the off topic post (especially a month and a half late) but I wanted to add that new year’s eve the lady and I saw Star Wars and visited the Cape Canaveral Air Force missile museum. I wish I had been following this thread in a timely manner. I hope you have gotten a chance to see The Last Jedi by now.

Does it make me a terrible person for rooting for the humans in the movie Avatar? Also, there were some neat things about Passengers but the super-creep factor wrecked the whole movie for me. Bad science wise, you can still swim in zero-g since you push on the water; if the ship is constantly accelerating, why aren't they always falling toward the drive section?; when they arrive at the destination planet, the ship is firing it's engines the wrong way.

I was going to say/ask something very similar. The flat-earthers should not be given a single shred of attention so can we please stop talking about them. They have dug their heels in on their position and are simply looking for attention in order to validate themselves. This forum is about science and the best course of action, I feel, is to simply ignore them.

My gf said that she can get to YouTube but it says restricted when she tries to play it. She was going to have her kids watch but it looks like no dice.

Wha? Switch camera?

MUSIC!!!

I was like "oh, if real life were like KSP, you could just throw a Centaur and you'd have a solution." Then I ran the numbers, < 800 m/s, never mind... Good thing I'm a big enough nerd to run the numbers before making that suggestion. Also, Centaur is too long to fit in a Falcon payload fairing.

@CatastrophicFailure, I have been hyped. There was no controlling it. A good weather forecast sometimes does that.

+1 point to Stargate SG-1 for realism I guess... Also, I'm glad I'm not the only one who thought The Core was mega cringeworthy. While we're at it, one more thing that always bothered me about The Martian: communication. Our current rovers are capable of communicating and relaying information through the orbiters so why in a hypothetical future with near constant observation of the martian surface does this same capability not exist? How do the Ares' crews communicate with Earth at night? I gave the killer storm a pass as a plot device (something had to strand Watney and it gave the story more of a "shipwreck" feel) and The Martian started out as Weir's fictional blog posts as a stranded astronaut. I was going to say something about Gravity and orbital mechanics but I don't remember. I would say that the grievances of the orbital mechanics by the people on this forum are justified. The people on this forum understand orbital mechanics better than most of the general public and know what it means to try and get from one orbiting vehicle to another. As for Interstellar, I put it in the same bin as Star Wars and Star Trek. Lots of ooh-ahh, some technobabble, with the slight difference of a really cool looking black hole. Han shot first, George let go.

[snip] Anyway, on topic: things that annoy me in movies is when a nuke randomly goes off (or a major plot point is that it might go off). Wrong, they have to be set off, they're basically a miracle of precisely timed explosions and neutron injection.

I can't believe we went 6 pages in this thread and no one mentioned the movie Signs. I think I have to agree with many of the other commentators that there is an uncanny valley of science in a movie. If you try really hard to make your movie realistic and miss some glaring mundane detail, it's about as cringeworthy as running from the slasher into a knife factory rather than to the police station. That being said, I'm enjoying Dark Matter on SyFy because it's got about as much phlebotinum as Star Trek and doesn't really try to explain science any further.

The Space Shuttle SRBs landed under parachute. They send divers to plug the nozzle and they pump the water out so they float then they just tow them back to the cape.

I don't know if I'd call this a random science fact or not but according to Aerojet Rocketdyne, they can throttle the RL10 from 104% to 5.9% Source: http://www.rocket.com/files/aerojet/documents/Capabilities/PDFs/RL10 data sheet Feb 2016.pdf (page 2, 2010 milestone)

My gf says the same thing. I tell her that's crazy talk.

Is this a Sea Dragon type of rocket? Because the other thing you’d have to worry about is seawater freezing to your rocket.

I’m sure there are others on this forum which will disagree but for rapid deployment of satellites, air launch to orbit is the fastest. The military and DARPA have been looking into this for a long time. Pegasus is currently the only operational vehicle and its viability as a rapid response launch system is somewhat questionable. I suppose if the Air Force has spacecraft already mounted to Pegasus rockets and some L-1011s sitting around, they could get a bird in the air pretty quickly. The thing is though, this would only be a temporary solution and likely only as a response to an attack on a satellite. It would be a stop-gap to cover whatever lost capability. And whether such a system exists is purely speculative. Anyway, it’s doubtful that this is what Zuma is/was and rapid response is really best for air launch which is arguably the best use of air launch.

YAY!!! I’ll be back in the states by then (barely) and I’ll be able to watch!! Screw work, I’m watching history happen. Also, @Ultimate Steve, I agree, you should absolutely be allowed to watch. This is something that should be promoted in an educational setting. I’m going to tell my gf that she should have her class watch.

I've maintained 1 Earth gravity my entire lifetime but I've only gone in a bloody circle.

I have a friend who worked for NASA and he frequently talks about NASA's first A. Also, he put together a pretty good slideshow over on oppositelock a few years back: https://oppositelock.kinja.com/i-heart-experimentation-1440920258 Yes, they still do a lot with aircraft and aeronautics, it's just not as widely publicized as the wiz-bang rockets. IMO, NASA is a research organization and has no business building rockets that aren't pushing new concepts when their commercial counterparts are much more cost effective at doing the mundane. They should have the knowledge and the capacity to do research.