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Everything posted by wumpus

  1. Note that Draco is optimized for vacuum, Superdraco needs to operate in the atmosphere (and at low pressures as well), this may be a big reason in the difference in Isp. No idea about superdraco not being restartable: being hypergolic, most of the issues are moot. I'm guessing that it has turbopumps (couldn't find data), as it appears considerably more complicated than you would expect from a pressure fed engine. Certainly it is designed to be reusable, the only reason they'd only bring enough fuel to start the turbopumps once is that it only fires for aborts: no need to fire it again.
  2. And for an 8 year update (before it is wisely locked again), this format apparently *does* exist, but is only used for situations where the "billion year lifespan" might be useful. Not sure what the tech takes, but I'd guess that it involves using scanning electron microscopes for both reading and writing. It doesn't look like anybody has ever read written data except for verification and experiments. But the "arch-foundation" appears to like making these things as some sort of non-flamible library of Alexandria, or perhaps future Dead Sea scrolls. Don't expect to buy a writer from Amazon to back up your drive.
  3. Early on, there was an issue with the whole craft shaking as it transitioned from day to night (presumably every 45 minutes). Not sure if they ever sorted that out or just learned to live with it. I remember a "letter to the Washington Post" claiming that NASA should have dropped everything and made some adjustments based on offhand comments from their next-door northern neighbors (you can see the NSA from the Goddard assembly building) without any explanation (they were still "Never Say Anything").
  4. Interesting assumption. I'd assume that the K-Pg extinction asteroid might have been similar to Halley's comet, except that it would be rocky instead of an iceball. Although for all we know, Halley's might have an irridium core (we know from the tail that it is an iceball). So while we can predict when Halley's comet will return, can we predict its trajectory before we see it? It is trivial to send out a DART-like probe to bop its Pe beyond the inner planets, but by the time it starts passing Neptune it is too late. I'd assume that had the dinosaurs had at least 21st century tech for several thousand years they could have easily performed the "DART the K-Pg asteroid" out of the way if they knew it was coming, but does the Kuiper Belt redirect things? Sure it is *sparse*, but it barely takes any force at all at that distance to significantly alter the orbit near the Sun.
  5. And I get December 11, 2021. Not sure if it is fixed, or simply my browser is more willing to interpret dates (see Excel for extreme cases).
  6. I think the bigger question is how they expect to get this thing in better condition than it is now. The SRBs were stacked relatively early and the "shelf life" is ticking. They already have issues with leaks and are going to roll this thing back and forth again. If they want to launch it, somebody is going to have to decide to light the candle, probably with less than perfect confidence of success.
  7. Today I learned that Gargamel bicycles a lot... Or possibly motorcycles. Or even challenges records at the Salt Flats. But I think its bicyclists are most likely to take aeronautic drag personally.
  8. As far as I know, the system is called "Phalanx". Supposedly the term means the whole system from the RADAR to weapons control, but the media typically just refers to the gun itself as "Phalanx". This sounds like what I was working on in the 1990s, where they were trying to tie all the communications of the ship together, some long alphanumeric string lost to time like AN/Q80, which tied together a bunch of systems including "Phalanx". All our company did was build trainer RADAR consoles, computer-monitor map tables (no idea if anyone set up the projection system to show any big football games), and submarine monitor relays (a monitor that let you choose from various video inputs). The whole notion of "Commander's" probably doesn't make any sense to the Navy. Presumably everything is fed to the captain anyway. Having the weapons system controlled by anyone not onboard ship doesn't sound like something they'd be happy about, although I suspect they beam E2C/D/F RADAR information from the "eyes in the sky" to various surface ships.
  9. Old models are being shown to be obsolete by Webb data. Fortunately Webb is providing much more accurate data to construct new models. Why do I get the idea that the old models are only as accurate as they are thanks to Hubble data?
  10. Both the SLS and Saturn V use hydrogen as a major component of fuel (everything but the boosters for SLS, everything past stage 1 for Saturn V), so I'd expect that a more modern methane-based rocket might not scale the same as a Saturn V. Also if you are building an extra large rocket, making it wider starts making a lot more sense making the thing taller. Rockets are made tall both for aerodynamic reasons, and logistical. The falcon 9 is sized to be put on a truck and moved via US roads. I remember an aside from Scott Manley stating that the Falcon 9 (block 5) was roughly at the limit of length for a rocket that fits the Falcon 9 width requirements. And don't forget that they didn't build straight to the limit. They incrementally increased the size of the thing and only after 4 more upgrades got to the limit. If you are dealing with the square-cube issue for thrust, don't forget SRBs. They deal out nearly arbitrary amounts of thrust even if they are much more expensive than what Jeb taught you in KSP (but the ISP isn't nearly as bad). Check out the AJ260 for a really big SRB.
  11. Anyone know how this effects the proverbial "hydrogen car"? I'm guessing that the "gas pump tank" would be more or less at ground temperature, and the hydrogen would rapidly drop in pressure/temperature down the pipe as it encountered a relatively empty tank. Temperature fluxuations would also be a thing, but certainly not hundreds of kelvin.
  12. I googled expecting to see an IBM hard drive model 3030, but instead it was the 3340. The "30-30" came from 30MB (fixed stack) and a stack of 30 MB removable storage. No idea how much each disc held, but wouldn't be surprised if it was ~1MB. Thus named after the famous .30-30 Winchester rifle.
  13. I'd have to assume a parabolic pusher plate would work better (assuming any momentum bearing particles/photons would be reflected due retrograde). If you have an explosion in the "combustion [now detonation] chamber" the whole idea is to reduce the speed of the expanding gasses inside the chamber at the throat to barely subsonic speed, followed by allowing them to expand in the parabolic bell at maximum velocity. A nuclear explosion doesn't work that way at all. There have also been attempts at non-nuclear pulsed detonation engines. These were a somewhat hot research topic in the 1990s, but appeared to have gone nowhere. One recent paper on them remarks that since the explosions are pulsed, the fuel going into the detonation chamber doesn't need high pressure, thus no turbopumps (although using atmoshperic air isn't mentioned). I doubt that building a low-mass detonation chamber is reasonably easier/cheaper/more reliable than turbopumps, but that is a benefit. Also the things are about as loud as possible, with all those supersonic shockwaves moving at audio frequencies...
  14. Yep. Maximum thrust. Now plug that thrust into the rocket equation and see how much delta-v you get.
  15. Slightly more in the absolute scale. Hugely more on the relative scale. Which strongly implies that all spacecraft/satellite/whatever damage comes from man-made items whizzing around space.
  16. Prevention: use mylar/Al foil as a screen. Dust particles hit the screen and explode, hopefully into pieces too small to bother the craft. As far as I know, this is already in use. And I'm not sure any craft has ever needed evasive action while going through the asteroid belt (early ones couldn't perform any). If you need assistance finding the leak (presumably by sound), duct tape will work fine. And you probably have the aero-grade tape on board, which should be even more effective. Air pressure will hold it in place, but I'm sure somebody will want a "permanent fix". Said fix will likely lose more air (assuming you remove the patch) than the patch would ever leak out. Also removing the patch may be difficult. It is unfortunate that the only steel hulls I've heard of in space are all stainless steel. Otherwise I'd recommend using a magnet as a short term patch.
  17. I think the real question is how do you decelerate an orbital craft (more likely yet another staged specific vehicle) down to the venusian wind speed, capture the payload from the balloon, and then accelerate back to orbital velocity and dock with the main craft? This at least breaks down the number of stages significantly (and reduces the amount that has to be shielded from the full wrath of Venus's heat) but really doesn't reduce the total delta-v needed. The sample return is a huge addition to the problem. It adds huge amounts of delta-v and requires all kinds of thrust as well. Also fun if you have to deal with the heat of a Mercury approach with virtually the entire ship. As an aside, if you want the entire vessel to see at least 8 planets, you want to launch well before 1972 to get to Venus/Mercury/Mars first. I think the size of Apollo-era guidance computer was a good sized cubesat on its own, and the mechanism to grab a return sample won't be that small (note that "obtaining samples" has been notoriously hard in practice).
  18. Thoughts on 1972 tech: Wasn't that roughly the time the nuclear thermal rocket was grandfathered into the current readiness state? That makes it a lot easier. You really don't want to do this without a NTR. Communications to and from 1972 tech would be iffy. Pretty sure the only reason they can still communicate with one of the Voyager probes is thanks to some extreme (old school) hacking that updated the radio coding. Trying to get put control and communications for the return sample will require a fairly hefty return vehicle. "Return sample". Picking a particle out of a ring of a gas giant is one thing, but if you require a ground sample from Venus you are asking for something well beyond 1972 tech, and likely 2022 tech. Look what has gone into just getting a sample back from Mars, and remember that you have to sample and return almost immediately to your entire rocket melting. You also have scaling working against you (see the fun in landing on Eve in KSP), so will need a significantly bigger rocket than the smaller (pre-1972) rockets used to escape Earth's atmosphere. I'd also assume that such a rocket would have to be hypergolic (how are you going to keep cryogenic fuel liquid during the descent and ascent on Venus)? Which means a huge amount of hypergolics launched from Earth (try to sneak in before the clean water act...). Calculating the trajectories: pretty sure you are limited to patched conics, just like KSP. The fancier orbital tricks (interplanetary highway) wouldn't be discovered until later, and your most powerful computer available is the CDC7600 (Cray 1 was 1975). 34MHz, less than 4M (Meg, not Gig) of RAM, 10MFlops.
  19. In the space race, there were hard deadlines. You couldn't get the customer to make changes and then bloat the time and materials budget changing them left and right (exception that proves the rule: there were massive changes after Apollo 1, but the deadline didn't move). Also there was still competition among defense contractors. The contractor who let us lose to the USSR would not be popular in getting massive Congressional handouts. I'm less sure about blaming NASA management. Most of the big disasters (budgetary and literal) are in the high profile cases that brings excessive congressional oversight. The low visibility missions seem to work much better. If management works better with less micromanaging, I'd have a hard time thinking they are the problem (unless the problematic managers all get themselves promoted into high visibility roles, a common problem for any organization as it scales up).
  20. Sustainer stage reuse was routine from 1981-2011, albeit with extreme refurbishing costs. And the 50-66% almost certainly isn't just the rocket, the upper stage has a single engine (10% of the engine costs) and far less mass (not to mention fairing reuse). 30-40% of those costs have to be in the launch, with the army of highly trained professionals launching the thing, not to mention all the costs bringing the booster back and various tests needed. Much of the key to the success of Falcon 9 reuse is that the booster doesn't get anywhere near orbital velocity. So it doesn't need a heat shield (although it does need a back-burn) and all the issues the shuttle had with tiles (as far as I know, Starship is using tiles as well. Different tiles, but they couldn't find a better solution even with the warning of Shuttle experience.
  21. The SSMEs provided 1,180,000lbs of thrust for ship weighing 4,480,000 lbs (the SRBs provided most of the thrust). I'd recommend the RD-170s instead (or a new methane engine). Sure, the SSMEs are refurbishable, but that really isn't going to happen with SSTOs. SSTO with reuse is significantly less in reach (so much I keep telling Spacescifi that he needs "magic" Isp to do it). Getting the SSTO to orbit requires significant rocket science. Getting it down so it can fly again requires much, much more. Neither the means of surviving re-entry nor the means of landing can be done without adding mass. And the current state of the art requires a lot of mass, especially for the landing. You're arguing that just getting to orbit (with some payload) is possible but hardly showing any way to land the SSTO. Without reuse, SSTO makes no sense. If you are throwing away the rocket, what good is it to throw it all away at once as opposed to in pieces? You'll always have more payload and less rocket required with TSTO. And with reuse it is currently impossible.
  22. SSTOs can reach orbit. But you have to subtract the weight of all the launch engines (that provide a TWR>1, so a lot of mass) as well as all fuel tanks that could be discarded in a TSTO. At least one TSTO rocket can recover 90% of the engines and 90% of the mass of the (empty) rocket. At least one TSTO rocket in production should reach 100% for both. SSTO can carry minimal payload (if that). They certainly don't allow for the mass of a heat shield to cover the entire (massive, if any significant payload is considered) rocket, nor any means of landing. The "means of landing" is critical: Falcon 9 stages need to be around 10% full for recovery. Try to find a SSTO that has a payload anywhere near 10% of its total mass, and try replacing it with fuel (and don't forget the mass of the heat shield). So SSTO is only considered for expendable rockets where payload is not a consideration, nor the extra cost of the overpowerful engines needed to lift the silly thing into orbit. And they will inevitably be much more expensive for the same payload as a TSTO. Sounds like a NOGO for the foreseeable future.
  23. To be honest, the original question can be answered with some physics and roughly a single guessable parameter. Step 1: figure out just how powerful "navigational shields" are. These shields have to withstand constant bombardment of various particles (electrons, protons, alpha particles) hitting the ship at nearly the speed of light (granted, we really don't know how fast federation ships go before they switch to warp drive. Perhaps the aren't impressive). Step 2: guess how much stronger "shields" are than "navigational shields". It should be fairly significant. Step 3: calculate how many particles would hit the shield and what their energies are. Since a 25th century craft should survive a 20th century attack (surely the klingons/romulans/borg/villain-of-the-series have access to nukes), you really can use this to establish a lower bound for how much stronger "shields" are than "navigational shields".
  24. A lot would depend on whether you could get ink to copy from bronze/clay/whatever to papyrus. It would be a lot easier in Mesopotamia as they wrote on hardened clay (unfortunately I think Summerians/Babalyonians cuniform would require too many stamps, Egyptian might have worked). In fact, there was at least one Greek artifact (a vase? some sort of pottery) that appears to have text on it that was printed via individual stamps. But just one such piece of pottery, and didn't seem to take off. Don't underestimate the complexity of moveable type, it took a lot of modifications to get from the wine press to moveable type (check the length of time between the Chinese "whole sheet" printing press and the Korean "moveable type" press). Some of this may be exaggerated: I remember reading that the printing press required special ink, but it sounds almost identical to scribe's ink. Maybe the proportions changed? Was there ever a case where that wasn't suicide? There was one such attempt in the US civil war. The Captain kept the hatch open to see what he was attacking, and the resulting wave sunk the boat.
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