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Everything posted by RCgothic

  1. Except that when you hold your breath and that 14% residual volume expands 4x the pressure drops correspondingly to 1/4, which would then actively extract oxygen from your blood. Being a small volume, the partial pressures will equalise some, so it's not quite as bad as 3/4 of a total vacuum. But 60-75% as bad is still pretty bad.
  2. I misremembered. I found the Google report, it's actually 17 seconds to respond to alerts and take back control. To actually react intelligently is another matter entirely. The situation you describe sounds like a pilot with hands on anticipating the situation that they need to rectify. In an emergency whilst operating on automatic the manual operator may have been reading, snoozing, facing the wrong direction. They aren't going to have the situational awareness of an alert pilot anticipating that they're going to have Also 'often completed in less than five seconds' is not 'everyone completes in less than five seconds'.
  3. Studies have shown it takes at least 12 seconds for a passenger to become adequately aware and in control in an emergency situation. Vehicle accidents happen so quickly that a manual override is totally useless. Yes, a system failure will lead to deaths. So you design a system that cannot fail catastrophically or with redundant back ups as much as possible. Automated vehicles will be orders of magnitude safer than manually operated ones. They don't get tired. They don't get distracted. They can look in every direction at once and see through light obstructions. They can talk to each other in order to better manage traffic and reduce possibility of collision. They will never get reckless or exceed the safe operating envelope. They cannot be medically incapacitated at the controls. They can have back ups for failed components. Humans were not designed for piloting vehicles. To suggest we're somehow superior to a purpose designed system is human chauvinism.
  4. Four engines. In the event of failure, two have sufficient power to stay aloft at max throttle, with the third providing trim for offset load. Obstacles and noise issues can be mostly avoided by a minimum height for non-vertical flight. Power lines in the UK aren't higher than 55m And anything taller than that would be both mapped (regulatory requirement) and detectable by the onboard collision avoidance system. Drones won't move as fast as aircraft, so the 200m mandatory minimum distance can probably be reduced. They'll also talk to each other to keep out of each other's way ideally.
  5. Yet on screen evidence suggests it's safe enough to walk around in only a mask. That's either a goof or an indication that H2S is on the order of ppm. LCL0 is on the order of 600ppm (inhaled?) for 30 mins, or 800ppm for 5min. Max US regulatory exposure is 20ppm (inhaled?). Lung surface area is approx 25 times greater than skin surface area (conservatively). It's also thinner and more readily diffused across. It therefore stands to reason that a lethal inhaled concentration of ~800ppm atmospheric equates to less than the regulatory equivalent skin dose. Put another way, the concentration required to kill you if you're wearing a mask by diffusing through skin would be of the order 20,000ppm or 0.02%. If Pandora's atmosphere is around 800ppm it should be safe to wear a mask and lethal in approximately the observed time frame without one. H2S is detectable at around 10ppb, so the smell of Pandora's atmosphere would be very, very strong.
  6. Sorta. If you're in a plane or spaceship that depressurises it's a bad idea to hold your breath because the pressure in your lungs will dangerously over-inflate them without external pressure on your chest. And then once you've breathed out the zero/near zero partial pressure of oxygen in your lungs causes the oxygen in your blood to diffuse out down the pressure gradient and you've got 30s. It's actually a similar situation if you find yourself in an atmosphere at sea level composed of pure nitrogen, carbon dioxide, or other composition with zero oxygen concentration. Breathing normally, that's still a zero partial pressure of oxygen which will suck the oxygen out of your blood by diffusion. 30s. Unless you hold your breath. If you don't breath in the oxygen free atmosphere, then the air in your lungs maintains partial gas pressures not that different to that in your blood. It'll slowly deplete oxygen and accumulate CO2, but the driver is the gas concentrations in the blood. There's no sudden loss of partial pressure to suck the gasses out and you can last a lot longer. So then you have Pandora. That's not a lack of oxygen or a lack of atmosphere. That's toxic gasses. If you breath normally, there's suddenly a partial pressure of toxins in your lungs that force their way into your bloodstream. But if you hold your breath, it's pretty much equivalent to holding your breath normally. The colonel wasn't in immediate danger unless he took a breath. No toxins in the lungs means none in the bloodstream.
  7. Nasa is doing well in the probe department. NASA is not doing well in the manned spaceflight department. Even if SLS/Orion avoids cancellation they have far too few missions planned. This area currently feels anaemic and weak. SpaceX has done a fine job recovering 4 boosters and have designed a damn fine kerolox engine in the Merlin 1D.
  8. The Falcon 9.1 FT is the coolest rocket because it uses super-cryogenic propellants.
  9. Binary planets are fine. They'll gradually spiral out until they're both tidally locked, but can be otherwise stable. The Earth and Moon probably isn't too far off being a binary. The moon isn't that much smaller than Mercury after all, and is actually influenced more strongly by the sun than by earth (Uniquely amongst moons and their parent planet). Another definition is that the centre of mass of a binary should lie outside both bodies, which it will in the earth-moon system in another few hundred million years. One issue with that definition is that unless the two bodies are exceptionally close in mass it generally leads to very distantly orbiting binaries. You're unlikely to find a third significant mass orbiting such a pair, though you could get an insignificant mass orbiting just one of the parent bodies, or very far out around both. Another interesting factoid is that the barycenter of Jupiter/Sun is actually outside the sun. Does that make the solar system a binary star/planet? Jupiter doesn't meet any of the criteria to even be considered a brown dwarf. Food for thought.
  10. I know this was a bad mission, but can we stop killing Orion missions please? The launch rate is awful enough as is! We need to fund things properly! Permanent moon base by 2025! Boots on Mars by 2035! Let's get some proper infrastructure up there! I cannot believe how hard people are making this. In 1960 we hadn't even put a man in space. Nine years later, moon! And 50 years later we can barely fund four manned missions over a decade? Come on people! This is so frustrating.
  11. I that case the payload is essentially negligible. Plucking numbers essentially out of the air: Spacecraft: Let's say guidance and telemetry can be handled by a smartphone. ~100g. There's a minimum volume of monopropellants that would be effective for control. Call it a half-litre plus tankage, maybe 400g. So minimum 0.5kg for the spacecraft. 2nd stage: Payload is 0.5kg, plus engine, plus tank. Assume it does most of the work, 6.8km/s orbital insertion. Atmosphere negligible. Smallest H2/LOX engine I could find is India's CE-20, but it weighs 590kg and has 45kN thrust. ISPvac of 443. A bit overpowered... Stage would weigh about 4.6mt with 3.6mt of fuel and 370kg of tanks at a 10:1 tankage ratio (cryogenic). An Airbus Aestus based second stage (N2O4/MMH, 111kg, 30kN, 325 ISPvac) would weigh about 1.6mt, with 1.4mt of fuel and 70kg tanks (20:1 non-cryogenic). TWR a bit ridiculous at 2 to 17, but I assume our postage stamp doesn't care much about that. So let's go with the Aestus. Burn time is 144s, which sounds not ridiculous. The first stage needs to boost this to 100km and 1km/s. Diameter (engine) is 1.31m. Nitrogen Tetroxide is mixed at a 1:9 ratio with hydrazine. The average density is 0.93g/cm3 and required volume 1.46m3. That would fit in a slightly elongated spherical tank (~15 cm cylindrical section) with internal bulkhead, which would be hilariously stubby, but then we already know this is massively over-engined. Engine is 2.2m long, stage approx 1.3m dia and 4m long including spacecraft as a cone. 1st Stage: Payload is second stage (1.55mt) to 100km altitude and 1000m/s at that point. Needs to fight atmosphere. Gravity approximated as 9.8 all the way to orbit. If atmosphere is negligible above 10km, then you'd need to be travelling 1660m/s as you passed 10km assuming a coast from there to orbit. Climb to 10km is a bit of a guess. You need at least 442m/s, plus extra to fight gravity, plus extra to fight air resistance. Assuming 2G acceleration, let's call gravity losses 220m/s and probably the same again for air losses. Earth's rotation at the equator gets us 465m/s. That's 2.1km/s. Let's call it 2.5km/s for margin. The smallest 1st stage engine I can find is our friend Space X's Merlin 1D FT. RP/LOX, 756kN, 470kg, ISPsl 282, can deep throttle. It needs approx 3.2t of fuel to get the job done. 160kg tankage. TWR a truly ridiculous 4.5 to 14 even at 40% throttle. Burn time 30s. The Merlin 1D is actually smaller diameter than the Aestus, so we keep our diameter at 1.3m. Density of RP/LOX is approx 1g/cm3. 3.2m3 required. That's a hemi-ended cylinder approx 2.8m long for tanks. Engine is 2.9m. First stage approx 5.7m tall. 1st stage mass: 5.4t. Total craft mass: 6.9t. Total craft size: 1.3m diameter by 10m tall. These are just my crude back of the envelope scopings dependent on what's available engine-wise according to Wikipedia. I'm sure someone else could come up with something better.
  12. You could never recover all the energy from an exhaust to create new fuel. It's not a reversible process, as has been discussed. You could scavenge temperature from other sources (solar, aerobraking) to accelerate a propellant or fabricate a fuel from component raw materials. But heat gives very poor return as an energy source compared to chemical sources, and you'd still need to carry a propellant or fuel materials with you. It would be easier to just bring fuel. This isn't really practical for a craft that doesn't spend a long time scavenging energy and propellant mass.
  13. I doubt that 1kg rocket would get to space. Aerodynamic drag gets more significant as you get smaller thanks to increased surface area to volume ratio.
  14. The satellite usually does its own insertion, yes.
  15. So this launch is going to be too supersynchronous orbit? That's even worse than last time, right?
  16. I wasn't actually complaining about a low exhaust temperature! 5000'C is actually quite high as you and my edit have noted. I was just musing that it couldn't be made infinitely high... But Solar Thermal Electric could probably better the 5'000'C of pure Solar Thermal (for an additional mass and thermal efficiency penalty).
  17. Isn't there a maximum temperature that can be reached by solar light concentration? Thought a recent xkcd what-if covered it. 5000'C. With a max temp that means max exhaust velocity, which limits ISP. Of course that's probably better than chemical rockets, so maybe no problem. Solar thermal electric would probably have better ISP for a fuel limited design, even with the corresponding efficiency penalty.
  18. This is mostly because the orbital velocity out there is so slow. In this part of the solar system extra dv pays real dividends. New horizons made it in 1/10th that time. Of course you also have to have the dv budget for capture and return, but some fuel could be mined once you got there and the rest is just a sufficiently large rocket. For mind-bending quantities of large. These are just things that require budget, not impossibilities.
  19. Of course we could, money no object. All it takes is dv and time. It would be much harder than reaching Eeloo, but the main obstacles are budget and reason to go. Nothing PB666 mentioned makes doing it impossible.
  20. I think this is quite confusing, and a bit garbled, particularly bringing in Newton's laws which aren't really relevant to max q. At any instance there are three basic forces acting on a rocket: Thrust, Drag and Gravity. The Newton's first law merely states that an object in motion remains in motion unless acted on by an outside force. This is, these days, a statement of the obvious and not specifically relevant to max q. Newton's second law can be written to state that the rocket's acceleration is the residual force on the rocket divided by the rocket's mass. This is only slightly relevant to max q, allowing us to divine something about the magnitude of each force from the rocket's acceleration over its flight. The force due to thrust is a designed and understood value. The force due to gravity is easily derived. The force due to drag is tricky to calculate. But because you can watch the rocket to determine its acceleration, you can use the second law to work back and determine what the drag is. That's where the second law is useful. Newton's third law states that each force has an equal and opposite reaction. This merely means, e.g., that for all the force drag is exerting on the rocket, the rocket exerts an opposite force on the air. It does NOT mean that the forces acting on a body have to be balanced - per the second law there could be no acceleration if this were the case. In considering a rocket we only care about the force acting on the rocket and don't really care what forces act on the air, or the exhaust, or the Earth so the third law is not specifically relevant.
  21. The solid booster fire command isn't given until the SSMEs are verified on, and the hold-down bolts are detonated at the same instant. Once the shuttle's SRBs were ignited, the vehicle was committed to liftoff. But even so I hesitate to contemplating a full firing of the boosters on the pad whilst strapped to a full tank of hydrogen until the sound suppression system exhausts its 300,000 gallons in just 20s...
  22. The Space Shuttle was particularly problematic because the solid rocket boosters couldn't be shut off and would cook anything attempting to get away from the failing boosters. Between booster ignition and booster separation: Structural failure of any part, (booster, tank or shuttle) was not survivable. Significant booster thrust differential was not survivable. Failure of a booster to properly ignite was not survivable. One or two main engines out was survivable on condition everything held together until after booster separation. Three main engines out was not survivable. Basically IMO the only business solid rockets have anywhere near manned launches is in the launch-escape system and ullage motors. The sooner they replace the SLS solids with advanced kerolox boosters the better.
  23. I think it's worth mentioning that there were reasons for the different launch profiles under consideration. Direct Ascent was the least complex, although it required the largest rocket and the most fuel. Remember that in the initial stages of mission planning, nobody had ever attempted a docking in space. They didn't even know how to rendezvous! As most KSP'ers know, it's pretty counter-intuitive and even by Gemini 4 they hadn't worked out the orbital mechanics. Buzz Aldrin had to write a doctoral thesis on the subject. Direct Ascent is the profile for people who don't know how to rendezvous and dock rockets. Earth Orbit Rendezvous was the cheapest option on the table, because it used the smallest rockets. But as previously mentioned in this thread, the logistics are complicated. You either need to have all the rockets ready to launch near-simultaneously, requiring duplication of assembly facilities, launch pads, mission control rooms etc, or you need to plan for a long in-orbit dwell time which is also non-trivial due to loss of ISP for hypergolics or fuel boil-off for cryogenic stages. And do all those missions have to be sent up manned? At the time automation wasn't great, so probably. Manned systems are a load of payload you wouldn't otherwise have to send up. Also, nobody had ever assembled anything in orbit, which was another complication. And complications add risk, development time, and dilute the budget savings. Lunar Orbit Rendezvous is a nice compromise if you can master the docking. It requires a medium-sized rocket (in moon rocket terms, obviously the Saturn V turned out to be the largest ever built), and only one docking rendezvous and docking in lunar orbit. That's ultimately why it was chosen. Dual Orbit Rendezvous is a hybrid of Earth Orbit Rendezvous and Lunar Orbit Rendezvous with both use of in-orbit assembly and a separate lunar lander, and is the theoretically best approach should all the challenges be mastered.
  24. Today I fought a Kraken. I'm on a hard no saves no reverts no respawn career, and after an EVA over the ice caps I was afflicted by a bug. Spaceship 1, which has made many successful tourist flights, suddenly was not slowed by atmospheric entry. And the heat shield wasn't working properly. Fortunately, if I alt-f4 out it didn't kill my kerbals and gives me another go at it. But I had to do this about eight times and re-install install all my mods before the kraken relented. Grrr, Bug, basically.