architeuthis

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About architeuthis

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    Spacecraft Engineer
  1. Gotta love that 1950's style optimism: the neighborhood kids build a moon rocket in their back yard Rocketship Galileo style. In the spirit of the OT, the only serious explicitly 'garage team to orbit' type project is Paul Breed's Unreasonable Rocket. He has been working most of the required building block for his 50-gram picosat payload and OTRAG-style launch vehicle for most of the last 10 years. I've seen some of his stuff in person, like his 3D printed HTP/RP-1 bipropellant rocket engines, and his composite propellant tanks -- it's extremely impressive work. A somewhat more realistic, yet still enormously ambitious project for amateurs is simply reaching the von Karman line itself. AFAIK only one team has managed this so far: the CSXT team with their 'Go Fast' extremely large single stage solid fueled rocket back in 2004. There are a number of teams vying to reach the von Karman line now, including Coppenhagen Suborbitals, Boston University's Rocket Propulsion Group, TU DELFT's DARE team, and the Portland State Aerospace Society. Some people (university students) are calling it the 'mini-space race'. I'm guessing one of these teams will manage the feat within the next 5 year or so. The question remains as to who will it be.
  2. I think it might be a while before we see a cubesat deployed at LEO perform an transfer to lunar orbit under its own power. That said there are several lunar cubesat projects underway: NASA is offering (3?) ride share opportunities on the SLS shakedown flight EM-1 in 2018. A number of teams are competing for these slots, among teams from UCSD, Cornell, MIT. There's alot more information here, here and here. Most are definitely bigger than 2U, the UCSD Triteia is a 6U for instance. AFAIK these will be the first ever cubesats to leave Earth's sphere of influence. I agree that subsystems design for ops beyond LEO is an interesting challenge. I'm guessing that these cubesat will have relatively tiny link budgets (S-band on omni-directional antennas, probably very small transmit power budgets), they will need very large tracking antennas here on Earth. Rad-harding and fault-tolerant computing requirements will no doubt increase in cis-lunar space and beyond as well.
  3. Just buy it. It's an amazing, mind expanding read. It was nominated for a hugo.
  4. I thought I would 'resurrect' this lovely thread with a nice video from a sub-orbital sounding launch. Luckiest shot ever starts at 00:55.
  5. SLS was not my first choice. IMO the Augustine commission tried to kill Constellation for good reasons. Clearly, a big part of its raison d'etre, at least as far as the U.S. Congress is concerned, is naked political patronage of the old shuttle suppliers. I have always favored the alternate model for manned space exploration based on commercial medium lift/orbital propellant depots/on-orbit servicing and assembly which I see as much more robust and sustainable under the present and likely near-future circumstances than huge heavy lift rockets. ...That said, I find the profound pessimism about SLS widespread amongst my fellow space nerds (as sometimes evidenced in these forums), to be counterproductive. And a bit depressing besides. SLS will fly, probably as early as 2018. As far as putting boot in the martian regolith is concerned it is the best thing since the Saturn V to actually leave the realm of fantasy and PowerPoint presentations. In fact NASA has a solid plan for actually getting us there by the mid-2030's. A plan that doesn't make ridiculous assumptions about flight rates, game-changing technologies, 'Kennedy moments', or massive budget increases. This is exactly the kind of incremental planning NASA should have continued to pursue since the Apollo landings (instead of having to restart from scratch every new Presidential administration). Apollo seems more and more like science-fiction with each passing year. This is the closest we've been in decades to actually being able to manifest manned missions beyond LEO. I'm extremely inspired by SpaceX's achievements and their huge ambitions. They need to help Americans remember how to 'think big' about space. But Elon Musk is not the messiah. John Galt, (or at least his shareholders) will only go to Mars if there is a compelling business case for doing so. SpaceX is not profitable enough to fund MCT from retained earnings. They may never be (even with perfect reusability of Falcon 9). The launch services market is simply not that big. NASA needs coherent political support to advance its mission. We should all stand behind them. They're goddamn amazing. Things are somehow incredibly finally looking up. Why can't we just appreciate it?
  6. It's a hybrid hypergolic/SEP system as I said. Most of the delta-v is provided by SEP. I saw several presentations on this from folks at NASA GRC, Langley, and JPL at AIAA's 2015 Space conference. This is basically the current thinking on what's achievable in terms of manned Mars exploration with the realistic constraints of no budget increases, and only 2 SLS flights per year on average. If you're interested here is some more information: https://www.nasa.gov/sites/default/files/files/20150408-NAC-Crusan-EMC-v7a.pdf http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150009466.pdf
  7. Hydrogen can diffuse through solid walls. This can be mitigated with cryocoolers as you mentioned, hence the "zero boil-off", but even there there are some limitations. For one thing there are non-condensible effects problems due to thermal stratification, Marangoni convection and insulation from the Knudsen layer that are unique to microgravity. Alas zero boil-off technologies are still at low TRL and are a big part of the reason NASA probably isn't going to be flying any missions with NTR in the near future. The old studies for NERVA in the 1970's handwaved the problem of long-term storage of cryogenics in space away. These days we understand a bit more clearly that the problem is not a super easy one. The IR telescopes you mention use 30-80K cryocoolers, or helium vapor cooling (not cold enough to condense hydrogen at realistic tank pressures for NTR). The current state-of-the-art 18K space rated crycooler can only remove something like 2W, which is not nearly enough. The first real technology demonstrator mission for zero boil-off, CRYOTE, was not funded by congress in 2014. This is why NASA is moving in the direction of hypergolics/SEP (and away from anything requiring long-term storage of cryogenics) for future manned exploration missions beyond LEO.
  8. Could you please expand a bit on your reasoning? Why is 2018 ridiculous?
  9. That is the purpose of of a shock cone. The spatular nose on a hypersonic vehicle is largely to increase the L/D ratio.First, a bit of context. Waverider concepts first surfaced in the early era of hypersonics research (the 1950's). The basic idea is to design airfoils specifically to position attached shocks that trap spanwise flow, generating additional lift (called compression lift). The initial waverider concepts were delta winged with blended conical bodies and downturned wingtips, and blunt drooping leading edges. You can see a bit of this heritage in the XB-70 Valkyrie project. Then in 1966, British RAE (Royal Aircraft Establishment) researchers Pike & Kuchemann came up with a novel waverider design called the Kuchemann Tau. The Kuchemann Tau's spatular nose further increases the L/D ratio for the aircraft.
  10. I recently attended the AIAA Space 2015 conference in Pasadena. I watched a number of interesting presentations. While I was there I got the distinct sense that NASA's manned mars vision is starting to become more concrete. The Evolvable Mars Campaign architecture, as it's called, is planned to send 4 people to Phobos in 2035 or so, using SEP/space storable hypergolic hybrid propulsion on a reusable vehicle. Manned missions to Mars surface would follow shortly afterwards. People seem to be rallying around this idea for several reasons: reuse->long term sustainability, better than flags & footprints Apollo on steroids DRA5 nearly all of the required technology is high TRL, low development risk no more than 2 SLS cores per year could fit in NASA's current budget if indexed for inflation don't need to fully commit to the strategy till early 2020's; before then much of the dev work is synergistic with current missions/flexible path My impression is that there is alot support for this coming from the NASA GRC and KSC centers. At the Satellite Servicing Capabilities Office at GSFC, where I currently work, we're developing related technologies (on-orbit autonomous servicing, hypergolic and xenon refueling).
  11. Because it's cryogenic hydrogen with a saturation temperature of 20K! That is really cold! If you don't refrigerate that stuff or at least insulate it realllyy well it'll all boiling away and your tanks will be empty long before you reach Mars orbit, leaving you stranded (or worse, you can't even brake into orbit without aerocapture).
  12. If the MTV uses cryogens and the mission architecture assumes no martian ISRU, then it seems likely that propellant depots will developmentally precede the MTV. Zero boiloff, cryogenic fluid transfer, acquisition and mass gauging technologies are still at low technology readiness levels. A depot could double as a technology demonstrator mission, and enable the accumulation of a stockpile of propellant in orbit in parallel to launches of the MTV (rather than waiting till it is fully assembled, and checked out, on orbit). This parallelization should help reduce mission schedule risk (likely to be substantial for such a complex mission anyway). On the other hand using depots adds an additional logistical cycle to the process; this means more chance for something to break or for leaks to occur. In the near term propellant depots have commercial applications, and are frankly much more likely to exist in the near term than a Mars mission.
  13. I also read Halliday and Resnick's Fundamentals of Physics as a mechanical engineering undergrad, and I can attest that it is a good introductory text in physics. A more modern, integrated and readable alternative text would be Chabay and Sherwood's Matter and Interactions. Both books assume an elementary proficiency in differential and integral calculus, with a small bit of vector calculus in the electromagnetism sections.
  14. You can use the magnetic field to repel charged particles from the sun (or if you have a really powerful static particle accelerator you can point that at the magnetic field to accelerate the spacecraft). I believe this concept is called a magsail, and is the basis of a delightful hard-SF novel, 'Permanence', by Karl Schroeder. Here is a brief synopsis.
  15. Even with perfectly efficient solar panels Saturn is problematic because of the inverse square law of radiation. I'm not sure who the author of this image is but it captures the essence of the problem nicely. Cassini with solar panels instead of RTGs (note that Cassini only drew 700W or so of power, far below the practical requirements of any useful electric propulsion of scale):