• Content count

  • Joined

  • Last visited

Community Reputation

853 Excellent

About peadar1987

  • Rank
    Senior Rocket Scientist

Recent Profile Visitors

1483 profile views
  1. Of course. But I'm not arguing that the Shuttle is terrible, or that it is better or worse than any other spacecraft, I'm just disagreeing with Yobobhi's claim that "the Commies were bad at engineering".
  2. Cost is a pretty big handicap. If I want to put a 1000kg payload in orbit, cost and reliability are the two things I'm going to use to decide which launcher is "best". Which is why the Soyuz is the "best" launcher for a lot of the applications we've had for the past 30 years, and is still flying whereas the Shuttle has been retired, in spite of its superior technical capabilities in certain areas. All engineers are given a budget. If you meet the design brief within the budget then you're a good engineer. Bigger budgets don't make better engineers.
  3. You're completely missing the point. The 747 is better than the Shuttle at what it was designed to do. The Shuttle is better than the 747 at what it was designed to do. Heck, my lawnmower is better than the shuttle at what it was designed to do. Just using total up-mass per launch as the be-all and end-all of launcher comparison is far too simplistic. The Apollo LEM descent stage could put a payload of 4,700kg on the Moon. The Shuttle could put zero payload on the moon. Does this mean that the LEM was categorically a better spacecraft, or simply that it was designed for a different purpose?
  4. May be useful to start an arms race and bankrupt your rivals?! Other than that, orbital weapons platforms don't give any particular advantage* *Unless we start developing unprecedentedly powerful and efficient laser weaponry, in which case the huge, unobstructed field of view from an orbital platform would be of some benefit.
  5. So just after a quick google: 4.5kWth, 42kg: 4.4kWth, 29kg: 2kWth, 22kg: 4.1kWth, 35kg: These are portable heat pumps so will be designed to be relatively lightweight, but mass won't have been the #1 optimisation criterion. Specific powers are about 100-150W/kg, so I'm guessing if mass was a major issue you could probably design one with a specific power of 200-250W/kg. Again, for your temperature question, it's not something that would really come up. The temperature is a design parameter, and there's no real reason to compare systems that produce a different temperature output, you will always just go with the one that produces the minimum temperature that satisfies the design brief.
  6. Ah right, no idea. Any thermodynamic systems I've worked on are firmly attached to the ground, so mass is right down the list of parameters I'd be optimising.
  7. Well giving Mars an atmosphere of ~6% the pressure of earth's would mean your blood wouldn't boil at atmospheric pressure, and you could breathe with an oxygen mask, and go outside wearing (extremely) warm clothes. Mars has a surface gravity of 0.38g, and a surface area 0.28 that of earth's, so an atmosphere 82% of the mass of earth's would give the same surface atmospheric pressure. An atmosphere 6% as thick as earth's would therefore have a mass of 2.5*1017kg. A decent sized comet (let's say Halley's comet) has a mass of about 1014 kg, so even if that's all ice and volatiles you'd need to smash 1,000 of them into the planet to give you that atmosphere. Your best bet would probably be to redirect an icy Jupiter or Saturn Trojan. However, that's currently far, far out of our technological reach. You'd need some sort of nuclear fusion torch drive. The other option is "building" an atmosphere from gases produced in-situ on the Martian surface. I don't know enough chemistry to say what the best candidate for that would be.
  8. Are you talking about mass flow rate of the working fluid, or mass flow rate of thermal fluid (water for a water source, air for an air source, not really relevant for a ground source)? Normally you just talk about J/kg, which gives the amount of power per kg/s of flow rate (whichever one you prefer, although the thermal fluid is the more usual one). The output temperature is normally fixed for a given operation, so you don't need to take it into account as a variable when comparing systems for the same application. If you were concerned about comparing cycles with different outlet temperatures, you could compare them based on Second Law Efficiency. This has a few different definitions, but the most simple is just the Coefficient of Performance of the cycle divided by the Carnot Coefficient of Performance, which is given by COPCarnot=Tcold/Thot-Tcold. This will just be a percentage, and standard values are roughly 50%, as far as I have seen.
  9. Nope, the Russians didn't see a need for a spacecraft with the capabilities of the Shuttle, and therefore weren't working on it until the Shuttle program was revealed and the military demanded something with the same capabilities. Buran started development 3 years after the Shuttle, and first flew 7 years after the Shuttle. That's not the hallmark of a bad engineer. Also worth noting is that the Soviet Space Program received considerably less funding than the US equivalent. This source (from the CIA) estimates that the US program was receiving roughly 40% more funding. The Soviets weren't great at economics, but they absolutely, categorically were not bad engineers. As for the Dragon, it is not better or worse than the Shuttle. It was designed for a completely different job, namely delivering cargo and crew to space cheaply, and it does it far better than the Shuttle ever could. You might as well say that a 747 is "better" than the Shuttle because it carries more payload. It's true, but irrelevant.
  10. Rotational kinetic energy of the earth = 2.138×1029 J Orbital kinetic energy of the earth = 9*1031 J Chicxulub impactor = 4.2*1023 J (all from wiki) World nuclear arsenal = 6400Megatons = 2.7*1019 J (from here. Not sure of the accuracy of the source, but it gives an idea of magnitude)
  11. Obligatory post in every Mars terraforming thread. -The magnetic field has very little effect on radiation dose rates at the surface of earth (or a terraformed Mars). The vast majority of the shielding comes from the mass of the atmosphere itself. -While the magnetic field does protect the atmosphere from being stripped by the solar wind, atmospheric loss happens over the timescale of millions of years, so if we have the capability to give Mars an atmosphere, we have the capability to top it up or retain it. If magnetic field was a deal breaker, then Venus would be out as well, because not only does it also not have a magnetic field, it experiences far higher solar radiation than Mars.
  12. You rest your case that the N-1 program failed because Commies are inherently worse at engineering?
  13. So outboard motors tend to vent their exhaust below the water, close to the prop (apparently to reduce noise). This seems to be the cause of most of the bubbles I've seen in the wake when driving powerboats. From seeing large prop-driven ships moving at low speed, I don't seem to remember the wake being too frothy, mainly just turbulent water. Most of the froth, if there is any, seems to be cause by air being entrained by the bow slamming down after going over a wave.
  14. I've driven a RIB pretty close behind a fast ferry (This ugly brute) Not close enough to get hit by the jets from the impellers, but close enough that the water was still fizzing. There was no real noticeable drop in the buoyancy of the RIB, or the power from the prop when we entered the frothy water.
  15. Much of the ISS was designed for the STS to put in orbit, mainly because STS was there, not because STS was inherently a better way of putting them up. Most sections could have been redesigned for Proton without any loss in functionality. The only thing I can think of that only the STS could have done was the Hubble repair. And this is coming from a massive, posters-on-the-wall fan of the STS.