Gemini: We can rebuild it, we have the technology

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mrmorris

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I've recently become interested in the notion of a contender for Bigelow's prize designing a modern version of the Gemini capsule -- upscaled to 5-6 people. I posted the thought in the M&L section, but didn't get much discussion before the thread was buried. This is the better forum for it, so I'm re-posting here in the hopes that it will fare better.<br /><br />I've been trying to determine where technology advances could be utilized in a new & improved Gemini capsule that would make it lighter, and improve its capabilities. Just for starters, the fuel cell tech on the Gemini was *very* bleeding edge. The P3 cells GE finally came up with the the Gemini 5 mission and beyond had the following specs:<br /><br />2 cells<br />Rated output of one kilowatt. <br />25 inches in length and 12.5 inches in diameter.<br /><br />I *can't* find a weight figure anywhere. The electrical systems on the equipment module as a whole weighed 648 pounds, but I don't know how much of that was the fuel cells. The 1.5 Kw fuel cells for Apollo weighed 250 pounds apiece, but they were a different FC tech. The GE cells then <b>probably</b> weighed in at 120-150 pounds each. <br /><br /><br />I found that the patent for the Gemini-class cells was picked up by a Canadian researcher by the name of Ballard. He made significant advances in the power density of them and reduced their manufacturing costs. Ballard Power Systems is now is a leading edge firm in supplying fuel cell technology. Their commercially available Nexa Power Module fuel cell system has the following specs:<br /><br />1.2 Kw<br />46 Amps<br />22"x10"x13"<br />29 lbs<br /><br />This implies a 180-220 pound reduction in the weight of a modern gemini capsule from updated fuel-cell technology alone (with .4 kW additional power available).<br /><br />I'd be interested in other posters ideas on similar targets for weight reduction and performance improvements -- in particular using COTS equipment.<br />
 
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scottb50

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I would agree most of the systems and structure used in Gemini could be updated, composites, micro-circuitry, ect., at a considerable savings in weight and increase in reliability. <br /><br />I wonder if enough could be saved to bring back the original wing parachute idea. The lander would be similar to todays ultralights and land on conventional runways. I would think it could be integrated into the capsule design with extendable landing gear with no need to compromise the heat shield. Making it re-usable would be another plus.<br /><br />Whether you could do it with five or six people and still use a Delta or Ariana launch vehicle would be a deciding factor. <div class="Discussion_UserSignature"> </div>
 
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jcdenton

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Anyone know what the cost of a Gemini capsule was in today's dollars? Also with these modifications, is there any estimate as to how much it will cost now?<br /> <div class="Discussion_UserSignature"> </div>
 
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najab

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><i>Anyone know what the cost of a Gemini capsule was in today's dollars? </i><p>Like most space vehicles, the limited production run makes cost estimates unreliable - do you want the development cost included or just the unit cost? Each Gemini capsule was different and included upgrades and changes from lessons-learned making it harder still.<p>I would <i>guess</i> that if you were to 'freeze' the configuration and start assembly line production the baseline cost would be something like $5-10 million per unit.</p></p>
 
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mrmorris

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<font color="yellow">"I wonder if enough could be saved to bring back the original wing parachute idea.</font><br /><br />The paraglider wasn't dropped primarily due to weight, but rather because they had problems getting the system fully functional. On the other hand, it *did* weigh more than the parachutes, and that made the mission planners somewhat more amenable to dropping the idea -- as it gave them a larger weight reserve.<br /><br /><font color="yellow">"...extendable landing gear with no need to compromise the heat shield"</font><br /><br />Also -- the skids for the paraglider landing didn't project through the heat shield. They were attached to the side of the capsule, not the bottom.<br /><br /><font color="yellow">"...and still use a Delta or Ariana launch vehicle would be a deciding factor"</font><br /><br />I've actually been looking at the Falcon V. Even before the recent upgrading of it's projected launch capacity -- there was a good possibility that it could handle an upsized Gemini. <b>With</b> the recent increase -- there should be plenty of reserve. Pulling from my original post and calculations:<br /><br /><i>Gemini <br />Crew Size: 2. <br />Typical orbit: 246 km circular orbit, 30.2 deg inclination. <br />Length: 5.67 m. Maximum Diameter: 3.05 m. <br />Mass: 3,851 kg. <br />Associated Launch Vehicle: Titan 2 <br /><br /><br />Titan 2 ICBM modified for Gemini: <br />LEO Payload: 3,600 kg. Apogee: 300 km. <br />Core Diameter: 3.05 m. (10 ft) <br />Total Length: 32.80 m. <br />Mass: 150,530 kg. <br />Liftoff Thrust: 2,090.00 kN. <br /><br />Falcon V: <br />Payload: 200 km, 28 deg 4,200 kg <br />Core Diameter: 3.4 m (11 ft) <br />Total Length: 29 m. <br />Mass: 286,000 lb (129,700 kg) <br />Liftoff Thrust: 357,500 lb (1,590 kN) <br /><br /><br />The Falcon V is actually a pretty good match for the Titan 2 used to launch Gemini. It's a very similar size, and can theoretically lift ~600kg more mass to a 200 km orbit. When you consider three more c</i>
 
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mrmorris

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The engine tech has also advanced significantly since Gemini. The specs on the Gemini main engine per Astronautix are:<br /><br />Main Engine: 120 kg. <br />Main Engine Propellants: N2O4/MMH. <br />Main Engine Propellants: 322 kg. <br />Main Engine Isp: 273 sec. <br /><br />By contrast -- the shuttle orbiter maneruvering engines also use N2O4/MMH -- but have an isp of 316 sec (no specs on weight). An upsized Gemini capsule then shouldn't have to increase propellant mass in proportion to the increase in weight.<br /><br />If SpaceX were to design such a capsule -- they would probably use their Kestrel engines. They too would provide a significant isp increase over the original Gemini engine:<br /><br />Kestrel Weight: ~53 kg (calculated: 7,500 lb thrust / TTW of 65)<br />Kestrel Isp: 325s <br />
 
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mrmorris

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Of course the Gemini capsule actually had three parts, the equipment module, adapter module, and re-entry module. Only the re-entry module was recovered. A modern version would likely be designed with only two sections (I can't see doing it with only one without compromising the heat shield).<br /><br />EM: Contained communications and instrumentation electronics, drinking water, cryogenic oxygen, and fuel cells, Orbit Attitude Control Thrusters (OACT).<br /><br />AM: Contained solid rocket boosters (used for de-orbit) and maneuvering thrusters.<br /><br />RM: Contained astronauts, parachute, radar, inertial guidance, the remaining electrical equipment, and re-entry attitude thrusters.<br /><br />I haven't actually seen anything which sequenced the series of events and logic around the separation of the three modules, but based on the arrangement of the equipment/etc. in each, I assume it went like this:<br /><br />- The three modules remained connected until time for the capsule to return.<br />- The EM module is jettisoned.<br />- The solid-rockets on the AM fire a retrograde burn to slow the capsule for re-entry.<br />- The AM is jettisoned and burns up in the atmosphere.<br />- The RM enters atmosphere and parachutes to an ocean recovery.<br /><br />Presumably then, the logic for this separation was to minimize the amount of propellant needed for the retrograde burn. By placing much of the electronics/etc. in the equipment module -- the SRBs could be smaller. From the wireframe diagram below -- it <b>appears</b> that there was actually significant open space in the AM at least, and possibly a significant amount in the EM as well. These modules look to be mass-limited rather than space-limited. The fact that the Gemini-B was able to move things around enough to fit a 'Crew-Transfer' tunnel through the AM and EM modules to a space station would seem to support this.<br /><br />I can see a modern capsule built around a Gemini-like architecture with only a re-entry module an
 
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mrmorris

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The original Gemini Re-entry Module used a one-shot ablative heat shield which weighed 144 kg (317.46 lbs). Since we're hoping that the modern capsule will be reusable (and to save weight and minimize maintenance), I looked up the specs on modern Thermal Protection Systems. The best studied seems to be the Adaptable Robust Metallic Operable Reusable (ARMOR) TPS. This was planned for the X-33 and NASA has supposedly done considerable testing with samples of it. It's sturdier than the shuttle tiles, requires less in the way of waterproofing, and is easier to maintain (according to marketing, anyway... <img src="/images/icons/smile.gif" /> ). Depending on the thickness of the ARMOR TPS, weights were in the range of 1.6 lb/ft2 -> 2.0 lb/ft2 in the NASA whitepaper I found. Assuming the heat shield were for a much larger return capsule (figure 10' in diameter at the base), a heat shield for our modernized Gemini capsule would then be:<br /><br />pi*r2 = 3.14 * 25 = 78.5 ft2 (figure 80 sq ft)<br /><br />80 ft2 * (1.6 - 2.0) lb/ft2 = 128-160 lbs<br /><br />The heat shield for the upsized capsule then would be about 160- />190 pounds less than that of the original Gemini.
 
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scottb50

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If the main purpose of the ship is to reach an orbiting Station there is no need for the various sections or supplies for the crew or extended mission times, originally part of Gemini. There is also no reason why the de-orbit motor couldn't be in the front, or top, where the Gemini parachutes were, with a turn around manuever like Shuttle does. This would leave the TPS to it's own function with no extranious attachments. Re-usability would be a key factor and I really see no reason why that wouldn't be possible.<br /><br />I would still think expanding Gemini to 5-7 people would require a much bigger launcher than the Falcon though, even with available weight savings. It might also be possible to build different sizes, say a three seat vehicle or a ten to twelve seat vehicle by expanding the initial design, I would think a Delta 4, or an equivelent vehicle could do it.<br /><br /> As I remember the Gemini was considered an ideal configuration for re-entry stability, whether scaling up would alter the dynamics is another thing. Cost would depend on demand though, I'm sure a Delta could be much cheaper if they built three or four times as many. <br /><br />I think a capsule design, with runway landing capabilities could be even more economical with a reusable, flyback booster and space re-usable upper stage. Maybe not as asthetic as Shuttle, but better than Soyus, it would get the job done until something better comes along.<br /><br />No use making the Gemini upgrade more complicated than it needs to be, it would have to provide fairly direct ascent to an orbital station and return only. Changes to other orbits would need to be handled from there, which is a much simpler problem anyway. <div class="Discussion_UserSignature"> </div>
 
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mrmorris

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<font color="yellow">"There is also no reason why the de-orbit motor couldn't be in the front, or top, where the Gemini parachutes were"</font><br /><br />There's at least one reason -- the DO SRBs serve double-duty as part of the escape system in case of a booster failure. There's no way that a five-person Gemini could use ejection seats for emergency escape, so the capsule itself will need an escape mechanism.<br /><br /><font color="yellow">"I would still think expanding Gemini to 5-7 people would require a much bigger launcher than the Falcon though, even with available weight savings."</font><br /><br />I'd honestly like to see what figures you're basing this on. The original Gemini massed 3851 kg. From my earlier post on WAGs for weight reductions (amended with my harder data posts on fuel cells and heat shield in <b>bold</b>). I also changed a couple of WAGs and included my reasonings.<br /><br /><i>WAGs made on possible mass changes for a 5-person Gemini capsule: <br /><br /><b>Heat Shield Mass: 144 --> 72 (-72 kg) <font color="orange">** use of ARMOR TPS **SHOCK** my original 72kg WAG was on the nose!</font><br />Fuel Cells: (120 kg) -- /> 27 kg (-93 kg) <font color="orange">** use of modern fuel cells</font>/b><br /><br />Structure Mass Total: 1048 -- /> 746 (-302 kg) <font color="orange">** - 25% due to use of composites/etc.</font><br />Electrical/Electronic (minus FC): 380 -- /> 125 (-255 kg) <font color="orange">** use of modern electronics</font><br />Crew Seats and Provisions: 426 kg -- /> 350 (- 126kg) <font color="orange">** There are more seats. However -- they will not be ejection seats, will use lighter materials, and the module contains less provisions since there is no extended flight.</font><br /><br />Re-Entry module stretch: (+100 kg) <font color="orange">** Originally I posted 200kg for this. However -- I think with the elimination of the equipment module</font></b></i>
 
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mrmorris

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With the Gemini redesigned to a 2-piece system, and the primary RCS no longer being jettisoned in orbit -- the Reaction Control System in the nose of the re-entry capsule can be eliminated (- 133 kg), and a reasonably large space opens up. With the size reductions of modern electronics -- all of the electronics of the original Gemini that were split between the RM and EM sections should be able to fit into the forward portions of the capsule. By placing the vast majority of the electronics (including the fuel cells) in close proximity -- further weight reductions will be possible due to fewer wiring and connections requirements.<br /><br />This could be the first spacecraft built with truly modern electronics. The Gemini used a 59-pound IBM dinosaur as its flight computer. <br />Picture a system that's built around a high-end laptop as the main computer. It's seated in a port replicator that is connected to the systems of the capsule via a combination of USB, serial, and parallel ports as well as an ethernet network. Video is ported to a pair of 23" LCD monitors for the pilot and copilot. The instrument panel is connected to the laptop as a USB device (a keyboard isn't really suitable for spacesuit gloves). All of the sensor equipment: gyros, radar, inertial guidance, etc. are connected to the laptop as ethernet devices.<br /><br />This would give the capsule computing power and instrument integration an order of magnitude (at least) greater than the shuttle. Radiation hardening is not really an issue for the lengths of time involved in the missions as planned. If the capsule will be staying in orbit for an extended period of time (i.e. docked to the station) -- the laptop can be pulled from the replicator and placed in a shielded location. Also -- given the costs involved -- the main computer can be replaced every single flight. For that matter -- laptop manufact
 
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najab

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><i>Radiation hardening is not really an issue for the lengths of time involved in the missions as planned.</i><p>Radiation hardening is an issue for <b>any</b> operations in Earth orbit. It only takes one random upset to kill the crew, and they aren't called random for nothing.<p>I wouldn't use a laptop for a couple of reasons - firstly it is heavier that what is needed and secondly it is almost impossible to use a standard PC for realtime control operations. There are COTS realtime card-based computers that are much smaller and lighter, plus they have the advantage of being certified for use in hazardous environments. Drop one of these into a polythene box and you have all the computing power you need.</p></p>
 
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mrmorris

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Cool! Was starting to get a little worried about talking to myself. That's one of the first signs of... um... I forget what it's one of the first signs of, but it's not good.<br /><br /><font color="yellow">"Radiation hardening is an issue for any operations in Earth orbit. It only takes one random upset to kill the crew, and they aren't called random for nothing."</font><br /><br />OK -- if you truly think that the possibility of a radiation induced failure is that high (I don't -- but can't supply empirical evidence) -- make the 'port replicator' an enclosed box. Slide the laptop into it and close the door. The box is made of a material which provides radiation shielding. You'll need to force air through the box so the laptop doesn't overheat, but this is no biggie.<br /><br />The laptop -- well inside the capsule already, and inside a second enclosure designed to protect against radiation should be safe to all reasonable expectations given its mission. Flight times will be on the order of hours, not weeks or months.<br /><br /><br /><font color="yellow">"I wouldn't use a laptop for a couple of reasons - firstly it is heavier that what is needed..."</font><br /><br />Sony VAIO® T160P/L Notebook<br />VGN-T160P/L<br /><br />• Processor Name Intel® Pentium® M Processor Ultra Low Voltage 733 (1.10GHz1, 2MB L2 Cache)1 <br />• Hard Drive 40GB<br />• Memory 1GB PC-2700 333MHz DDR (512MB x 2) <br />• Modem Integrated V.90 modem (RJ-11) <br />• Ethernet 10BASE-T/100BASE-TX Ethernet with RJ-45 interface <br />• Estimated Battery Life 4.0-8.5 hours <br /><font color="orange">• Weight 3.04 lbs. with standard battery </font><br /><br />It's hard to beat three pounds. Even if you can -- in a manned LEO ship like we're referring to -- that's chickenfeed if it provides additional capability.<br /><br /><font color="yellow">"... and secondly it is almost impossible to use a standard PC for realtime control operations. "</font><br /><br />I have <b></b>
 
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najab

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Yes, Pentium/Athlon processors have a lot of power, but the systems built with them (more specifically the operating systems) are not suitable for realtime operations. The fact is that the PC architecture was designed for running spreadsheets, not flying aircraft. One example is the fact that even the most recent PC operating systems - Linux/Windows XP - both make use of interrupts to handle I/O operations. A realtime OS has to be able to do asynchronous I/O without resorting to interrupts: imagine an aircraft where the rudder interrupt service routine kept getting interrupted by the engine managment routine since it had a higher priority!<p>There <i>are</i> Realtime operating systems that run on PC hardware, but I suspect that it would be more trouble than it is worth to try and get them to support a laptop and it's quirky hardware. Much easier (and lighter) to use a slot PC, after all they are specifically designed with process-control in mind - you can even use the card cage to provide much of your radiation shielding.</p>
 
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najab

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Oh, the other thing. You do realise that the image I attached to my earlier post is the <b>entire</b> PC. All you need to do is attach a keyboard, monitor and power to that card. They weigh about three quarters of a pound.
 
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mrmorris

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<font color="yellow">"...make use of interrupts to handle I/O operations."</font><br /><br />In the system I postulated -- the vast majority of the I/O is handled via devices on an ethernet network. Interrupts don't come into play. It's conceivable (very very barely) that the sensors/telemetry/etc. of a spacecraft might produce enough data on the ethernet to cause large amounts of collisions. However -- I submit to you that if this is the case -- the Shuttle Orbiters are a hoax. Their processors couldn't handle data at the rates it would take to swamp a 100-Base-T switched duplex network and therefore we're all the victims of a mass hallucination.<br /><br />Likewise even if we *were* using an interrupt-driven I/O system and OS, modern PCs poll so fast that it will be able to service interrupts faster than the required equipment will be able to produce them.<br /><br />You *cannot* convince me that the shuttle running at .44 MHz can asynchronously service routines faster than a 1.1GHz Laptop can synchronously service them. It's simply ludicrous. Since the craft we're talking has flight operations <b>much</b> simpler than those of the shuttle, the thought that the laptop will not have the power to service them becomes... unthinkabke.<br /><br /><font color="yellow">"Much easier (and lighter) to use a slot PC, after all they are specifically designed with process-control in mind - you can even use the card cage to provide much of your radiation shielding. "</font><br /><br />It's a difference in philosophy. There are definitely positive aspects to a card-slot PC. <br /><br />- A real-time OS<br />- Modest weight reduction ~4 pounds to ~2 pounds is *not* 'much lighter'. Every gram counts in unmanned, interplanetary operations, but not for an LEO taxi.<br />- Imbedded radiation shielding.<br /><br />I just believe there are advantages to a laptop-based system and a standard OS.<br /><br />- Easier upgrade path. Once the programs to run the sensors are deve
 
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najab

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<p>> I/O is handled via devices on an ethernet network. Interrupts don't come into play...The NIC will generate interrupts.>Their processors couldn't handle data at the rates it would take to swamp a 100-Base-T switched duplex network...Woah there - switched fast Ethernet - what happened to keeping things simple? >Since the craft we're talking has flight operations much simpler than those of the shuttle, the thought that the laptop will not have the power to service them becomes... unthinkabke.I never said that you couldn't run a space vehicle with a laptop and non-realtime OS, it's just not, IMHO, a good idea. Four letters: BSOD (or, if you are a Linux fan, two words: kernel panic). Traditional OS's aren't famous for being able to continue running when the &%$#@! starts flying.All the potential advantages of laptops apply to slot-based PCs. For example, that jpeg was off a vendor website. That's a standard Pentium-III processor, it takes regular DDR memory and has Ethernet and USB 2.0 built in, pretty much the same as a laptop, minus the battery, screen and keyboard. You can run any OS on it, and can run the same OS and software on PCs for testing purposes. I just figure why use a whole laptop when a card will do?As an aside, I don't know that I'd want to have a hard drive on my spaceship - I can't imagine what would happen if the OS decided to swap out some memory to disk during the vibration of launch - mission aborted due to a hard drive crash?!>Can I hope then that you like the rest of my upsized Gemini?Nah, actually I was planning to beat you into submission about the computing power, then once you accepted my superior techincal prowess I'll redesign the rest of your puny little capsule design!<br /><br /><br /><br /><br />Seriously though, it's sounding good to me so far!</p>
 
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mrmorris

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<font color="yellow">"Woah there - switched fast Ethernet - what happened to keeping things simple?"</font><br /><br />Um. I have this running at my house. I have a 16-port 100-Base T full-duplex switch in my laundry room that services outlets throughout my house (2 in MBR, 4 in computer room, 1 in kitchen, 3 in breakfast nook, 4 in great room, 1 each in kids BRs). I do lots of gaming. <br /><br />Did I mention that I was a computer geek? <img src="/images/icons/smile.gif" /><br /><br /><font color="yellow">"As an aside, I don't know that I'd want to have a hard drive on my spaceship - I can't imagine what would happen if the OS decided to swap out some memory to disk during the vibration of launch..."</font><br /><br />I assume you jest -- setting swapfile parameters is simple. <br /><br />Having a hard drive on a spaceship would be invaluable. The improved recording capability of hard drives over tape-based systems like those on the shuttle orbiters would be hugely useful.<br /><br /><font color="yellow">"Seriously though, it's sounding good to me so far!"</font><br /><br />S'cool. I'm running out of material though. Getting hard to find detailed specs on the rest of the Gemini so I can locate and compare contemporary equivalents. I'm trying to locate things like masses/sizes/ratings of modern ECS, RCS thrusters, communications equipment, etc.<br /><br />Unfortunately -- there's just not much to choose from. The only 'modern' spacecraft with the requisite systems is the shuttle, and I haven't even found hard specs on that type of thing for it.
 
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mrmorris

Guest
Does anyone know how to get access to NASA-produced manuals/books? Specifically:<br /><br /><b><i>"Fundamental Techniques of Weight Estimating and Forcasting for Advanced Manned Spacecraft and Space Stations" by Willie Heineman, Jr.; NASA TN D-6349</i></b><br /><br />Amazon doesn't find it and a Google search only turns up the website I found where the guy referenced it as his source for Gemini mass breakouts, so the sucker must be pretty obscure.<br /><br />However -- the site that referenced it gave some interesting breakouts on the weights of Gemini subsystems. The totals unfortunately don't match up to Astronautix perfectly, and I don't know which is correct (although <b>both</b> might be, as the masses would have changed from mission to mission).<br /><br />If this is correct, then over 600 pounds was for crew provisions! The longest Gemini mission was seven days -- so this wouldn't be completely shocking, but it means the Gemini-II (aka space station taxi) has another big target for reduced mass. Also -- I'd estimated the original fuel cells at 240-280 pounds (and ignored the weight of the batteries in the RM). This site indicates that the power sources of the RM/EM total to 535 pounds. Using the modern fuel cells then would mean a weight reduction of ~500 pounds (my original estimate was 180-220).<br /><br />Considering that the new Falcon V stats already appeared to have some reserve lifting capacity over what would be needed -- it may end up that the Gemini-II might be able to carry a larger crew than planned (I was aiming for six, but seven or eight seems potentially doable), or a combination of people and cargo. <br /><br />I would expect that the design would allow for unused seats to be easily removed and the resulting space/mass to be usable for lifting cargo to the station.
 
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mrmorris

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<font color="yellow">"I wonder if enough could be saved to bring back the original wing parachute idea. The lander would be similar to todays ultralights and land on conventional runways. "</font><br /><br />I hadn't realized that the X-38 paraglider tests had gone as far as they did. The tech looks mature enough to use on the Gemini-II.<br /><br />The V131R weighed in at ~15,000 pounds and had a 735-sq.m parafoil. The Gemini-II is currently sitting around 9,200 lbs at a lower end (with several hundred pounds of misc. weight imbedded) to 11,500 pounds at an upper end ( />6 people plus cargo). At these weights, the Falcon V can still carry the G2 to the ISS. The parasail, however, can be decreased in size for the lower weight. The parasail size bounds would be in the realm of: <br /><br />9200 lbs: 61% * 735 - 448 ft2<br />11500 lbs: 77% * 735 - 566 ft2<br /><br />
 
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mrmorris

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<font color="yellow">"A realtime OS..."</font><br /><br />OK, you win. We can use Wind River's VxWorks RTOS. VxWorks was the OS for the X-38 avionics -- the closest NASA has gotten to a cutting-edge crew-return vehicle recently. With avionics software already in existence for fighters and such -- the G2 can have a leg-up on its avionics suite. Re-inventing the wheel is so Pleistocene...
 
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yurkin

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Hmmm<br />I think the CEV should be designed to carry a minimum five people. That means that an autonomous version can carry enough cargo to sustain the crew of a space station. So it should be designed to be launched on an EELV heavy. By reducing the number of flights and using a launch vehicle designed for reliability the risk is substantially reduced. Even as a tourist vehicle it can only carry one paying tourist plus a pilot. So the one tourist is going to pay for the total cost of the flight. Gemini would be a good starting point to build a scaled up CEV but I don’t think a two person capsule is of much use. <br />
 
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mrmorris

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<font color="yellow">"Gemini would be a good starting point to build a scaled up CEV but I don’t think a two person capsule is of much use. </font><br /><br />Apparently you haven't read much of the thread. The whole premise is in reference to an upsized capsule derived from Gemini -- 5 people or more.
 
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scottb50

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I would think a parafoil would add to the overall weight but would make it much more functional. After all I doubt the Navy would deploy for a recovery of a commecial vehicle and the costs would be prohibitive for a commercial venture to cover the probable recovery area as well as extend from there in case of a problem, not mention travel expenses. Ease of recovery is as important as launch if there is to be a commercial market.<br /><br />The only alternative would be closer to the X-38 with wings, but then weight climbs considerably and I doubt a low cost booster would even work. The Europeans found that out years ago, the weight of a winged vehicle expands exponentially with everything that gets added to it.<br /><br />One interesting fact I found is that the weight of Gemini was more than twice that of the Mercury capsule, from which it descended, to carry one extra person. Being able to sustain a crew for extended periods obviously added considerably to the overall weight.<br /><br />The biggest problem I can see would be the physical size required to add three or more seats and the requirement to get everything into a single package to allow simple re-usability, unlike Gemini and Apollo which used non-returnable equipment sections. Limiting the mission to a short duration with in orbit docking would greatly reduce the requirements though. <div class="Discussion_UserSignature"> </div>
 
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mrmorris

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<font color="yellow">"...Gemini was more than twice that of the Mercury capsule..."</font><br /><br />Yes -- extended missions added lots of weight. <br />Plus the Mercury had only attitude and re-entry thrusters. <br />Plus the Gemini had EVA capability.<br /><br /><font color="yellow">"The biggest problem I can see would be the physical size required to add three or more seats and the requirement to get everything into a single package to allow simple re-usability"</font><br /><br />I still see two sections as a reasonable option. The legacy Adapter Module of Gemini contained little but some structural members and the de-orbit SRBs. The Equipment Module contained a much of the electronics, the fuel cells, drinking water, and the main RCS propellants. <br /><br />A modernized Gemini could fit everything from the Equipment Module except the main engine into the Recovery Module. The main engine could be incorporated into a modestly expanded Adapter Module (the legacy one had significant open space).<br /><br />As with the original Gemini -- the AM would be jettisoned after the re-entry burn. However -- all that is lost is some structural elements, expended SRBs and the thruster nozzle from the main engine. SRBs are almost always considered to be one-shot expendables, and the main engine nozzle would be equivalent to second/third stage booster nozzles. They're designed to be expendable. Making something reusable doesn't mean that it's cheaper to operate. <br /><br />With the electronics *vastly* shrinking in size and weight (I'm working on specifics currently), redundant features from the EM/RM eliminated, and the Adapter Module better utilized -- a significant amount of space will open up from the rearrangement -- even without stretching the overall capsule.<br /><br />Just a few examples -- the onboard computer couldn't fit all of its programs in memory and so had an 'Auxiliary Tape Memory'. This weighed 26 pounds and filled about .4 ft2 of space i
 
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