Jump to content


  • Posts

  • Joined

  • Last visited


990 Excellent

Profile Information

  • About me
    Senior Rocket Scientist

Recent Profile Visitors

3,931 profile views
  1. The big AGRs I worked on were low-hum quiet if you stood on top of the pile cap (but the gas circulators at the bottom were quite noisy, and the turbine-generator sets were deafening). I never worked on a liquid-cooled reactor for comparison though.
  2. Aye, but what a nozzle will do is focus the plasma, so more of the energy is directed along the thrust vector instead of escaping radially into space.
  3. As far as I'm aware the N1's odd shape was because the tanks were spherical, as opposed to cylindrical, as the USSR didn't have the required materials knowledge to produce sufficiently strong cylinders. The big taper in each stage was a consequence of having two spheres of different sizes to hold fuel and oxidiser.
  4. Okay, that all makes sense. But it still seems like an engineering problem (smaller than, say, producing grams of positrons), so I still think it's strange they're so settled on high-Z materials for the concept designs. @kerbiloid, the thrust vector is still going to be normal to the pusher plate, whether it's curved or not. Any off-axis thrust will be cancelled out if the plate remains symmetric.
  5. But what would be the advantage of using tungsten as the ablative material rather than carbon? A back-of-the-envelope calculation tells me that the halving thickness of carbon would be 10 times that of tungsten, but carbon has about 1/10th the density of tungsten. The overall mass of ablative material needed to absorb a given fraction of the X-ray flux is the same, but the tungsten has an atomic mass number 15 times that of carbon, so ablating carbon should give, all other things being equal, 15 times the exhaust velocity. Am I missing something here?
  6. So we all know antimatter is the most energy-dense fuel known to humankind. However, it is expensive to produce and difficult to store. One of the proposed drive concepts is a "Positron Ablation Engine", which tries to mitigate this by using positrons as the fuel. They're cheaper to produce than anything containing antiprotons, and they're easier to store, as they're charged and you can use a magnetic trap. The problem with positrons is when they annihilate, they release gamma rays, which are hard to redirect to produce thrust. A positron ablation engine (http://www.projectrho.com/public_html/rocket/enginelist2.php#positronablat , http://www.niac.usra.edu/files/studies/final_report/1147Smith.pdf) annihilates the antimatter inside lead capsules, which absorb the gamma rays, turn into plasma and radiate X rays. These X rays are absorbed by the pusher plate or parabolic nozzle, causing the outer layer of that to ablate, producing more plasma, which expands and produces thrust with an ISp of up to 5000s-1 I've got a few questions about the design people in the forum might be able to give an answer to: -The ablative material used is normally a high melting-point solid, which makes sense. However, all the designs I've seen use Tungsten or Silicon Carbide. Why not Carbon? Similar melting point, but far lower molecular mass, which should result in much higher exhaust velocity, no? -Why the lead? I know X rays are more easily absorbed than the pusher plate material, but if you have a thick enough layer and get 100% absorbtion, why does that matter? Surely the RMS velocity of the ablating material will be the same. -Why a pusher plate or parabolic nozzle design? The positrons emit gamma rays omnidirectionally, so this results in 50% of the energy being emitted into space (and positrons are expensive!). Why not react them in a chamber that's mostly enclosed, with a small opening into an engine bell? If your chamber walls are ablating away anyway you're not really subject to a temperature limitation.
  7. I've seen it on my drysuit before, I didn't know it had a name, thanks!
  8. Yeah, I guess the way I'd do it would be: -High strength tarp. -Epoxy to hab canvas to form a seal. -Sew through the overlapped area to take the load. -Epoxy a set of skinny patches over the sewed areas to seal off the needle holes. With the right materials, adhesive and contact area, the epoxy could maybe do the job all on its own (it's pretty powerful stuff, coming from someone who has accidentally epoxied his shoe to the floor :S )
  9. It's a 1 bar pressure difference across a 2mm hole, I'd say a few layers of duck tape would be plenty to seal it for now before they can get a patch epoxied on.
  10. It's a British English thing. Turtles live in the sea, tortoises live on the land. In American English they're all just called turtles.
  11. The Royal Palace of Nitori was lavish to the point of being vulgar, the perfect location for another drinks-reception-come-press-conference. Set on an ancient volcanic plug at the heart of the city of the same name, it towered above the narrow streets and townhouses of the old walled city, and the apartment blocks of the lower classes surrounding that. Jadra pulled up in the courtyard in a brand new, cherry red sportscar, gifted to her after her successful mission to space. At first she had tried to turn it down, embarrassed. It was then explained to her that the car wasn't for her benefit, it was a symbol to show what could happen to ambitious peasant farmers if they did what they were told, and that she would be seen driving it to public events if she knew what was good for her. She'd discovered that once she looked past the ostentatiousness of the car, she could appreciate it as a piece of engineering, and when she opened it up on the winding roads back to the Estate where she grew up, it was very fun to drive. She revved the engine one last time, enjoying the sound of the eight cylinders echoing off the walls of the building, before handing the keys to a uniformed Kerbal to park in one of the bays below the palace. Flashbulbs popped as the as she walked along the red carpet into the reception room. Giant mirrors on the walls reflected the crowds of reporters waiting to hear her story. She walked o the front of the room, and after a short introduction from her public relations attachée, an ever present almost since her feet had first touched the ground, she began to speak. She described the acceleration of the rocket, the juddering of every rivet, the feeling as each ring staged. She'd been told she'd been received extremely well, the lower classes identifying with the way she spoke and acted, and the upper classes viewing her as a curiosity. She was always nervous standing up at these functions, but as she got into her stride, the nerves slowly eased. As she painted the picture of her capsule arcing slowly over the Tespen Sea, the light shining off the water and the clouds like delicate paint strokes far below her, she thought how strange it was that she, who could barely summon up the courage to speak at a family dinner, had a room of the most high-profile reporters and dignitaries in the country hanging on her every word. As she finished talking them through the reentry, the gradually increasing g-force, the jerk of the parachute opening, after an endless second of terror after deployment, and the surprisingly soft landing on marshy ground, the room stood and applauded her, as she stood awkwardly, soaking it all up. Next came the questions. The usual pre-vetted stuff about how proud she must be, what a great achievement it was for the nation, and so on. Jadra's attachée picking out reporters from the crowd with a flick of her pen. As she was answering a routine question about how it felt to be weightless, a lanky Kerbal at the back of the room, wearing glasses and a brown sweater cut across her. "How does it feel to only have been the second Kerbal in space?" Jadra stopped, unsure of how to respond. As she opened her mouth to speak, the Kerbal was grabbed by a security guard, and began to be dragged towards the door. He wrestled free for a second, and shouted: "Was it worth it? All those Kerbals who died in the Javelin accident? Were their lives worth it Jadra?!" He grunted in pain as the security guard clubbed him with his baton, before dragging him out through the door. "Sorry Jadra", whispered her attachée, "One of the 'reporters' from some underground rag. I have no idea how he got in here, but I intend to find out. Don't worry, it won't happen again." She then turned to address the room. "My apologies, but Jadra has several extremely important functions to attend to this evening, as I am sure you will understand, now, if you would like to follow me through to the West Ballrom, you will be served with refreshments and have the chance to meet some of the military team responsible for the space program" The reporters and dignitaries filed out through a giant set of gilded double doors, and Jadra was left on her own in the reception room, looking at a hundred reflections of herself in the wall mirrors.
  12. I'm more concerned about the fact that they seem to be using solar panels as structural elements
  13. It seems pretty unlikely, there are plenty of Pluto-like objects out there, and their composition seems pretty different to that of Uranus.
  14. This happened quite a lot on older aircraft carriers (back when planes had lower stall speeds). An aircraft carrier steaming at 25 knots into a 40 knot headwind could have a plane land pretty much vertically, level with the deck (although I've read some pretty hairy accounts of the effects of waves on this equation!)
  15. Wasn't there some anime about a Japanese space programme consisting of teenagers, because they were lighter? Get your dry mass down with female cosmonauts
  • Create New...