Gemini: We can rebuild it, we have the technology

[mrmorris]

<font color="yellow">"But that is beside the point as you've still not addressed such things as preping for a water landing etc."</font><br /><br />You mentioned water landings only in reference to being a problem with the top exit. You never asked a question about it. <br /> <br /><font color="yellow">"I'm only pointing out that it may require more equipment than you seem to be calculating. (But on that note, if your landing system includes air-bags to help with the landing shock, could those be used for floatation if needed? Duel use is good)"</font><br /><br />Most of the RM is going to be a big hollow shell and the pressure vessel will do just as well for keeping water out as it does for keeping air in. Gemini-X3 won't sink, so extra flotation is superfluous. We especially wouldn't want more flotation at the base where airbags would be positioned (this would point the exit <b>down</b>). In fact -- you'd want it to ride low in the water to reduce rolling. Two things will assist in water landings. For one, the CG will be towards the bottom of the craft, which will mean that's the section that the capsule will tend to 'roll' to after a water landing. Second -- the section below the feet of the PV (where the propellants tanks are) is outside the PV, and as with the original Gemini, will allow water to enter between the outer skin and PV -- dropping the capsule lower in the water. In addition, the 'crumple zone' at the base will also allow water to enter. The end result should be a capsule that becomes stable in a feet down position with additional weight towards the blunt end of the craft tending to keep the nose pointed diagonally upwards.<br /><br />One of the reference documents I read (I don't have it at the moment and I'm not going to look for it right now) was a study done in the early 70's on the landing accuracy of a capsule design with an offset CG. It did some statistical analysis on the various landing errors of the Mercury and G

 

[mrmorris]

RLV News posted my rebuttal to Dave Ketchledge's remarks about capsules vs. lifting-bodies. <img src="/images/icons/smile.gif" />

 

[dschmelzer]

I read the rebuttal over at RLV News and have a related question. Does anybody know the Gs going up on a Falcon V and the original Geminis?

 

[mrmorris]

<font color="yellow">"Does anybody know the Gs going up on a Falcon V and the original Geminis? "</font><br /><br />The original Gemini pulled ~6 G's max during boost:<br /><br /><i>"At T+145 seconds, when the acceleration has climbed to nearly 6g's, the first stage engine shutdown arm relays are energized."</i><br /><br />Calculating the G's for Falcon V is a bit tricky -- since it doesn't exist yet. It's made more complicated by the fact that they are supposedly working to increase the thrust of the Merlin engine. However -- based on the stats of Titan II and the current documented stats for Falcon V:<br /><br /><i>Titan 2 ICBM modified for Gemini: <br />Mass: 150,530 kg. <br />Liftoff Thrust: 2,090.00 kN. <br /><br />Falcon V: <br />Mass: 181,400 kg<br />Liftoff Thrust: 2,237 kN</i><br /><br />The Falcon V has a slightly larger mass (181,400 kg vs. 150,530 kg), and a slightly larger thrust (2,237 kN vs. 2,090kN). You can assume then that the acceleration will be comparable to the Titan II. The ratio of FV's mass to that of T2's is 1.205, whereas the ratio of thrust is 1.070, so I'd expect the V will probably have a *little* bit lower acceleration. However, max G's occurs at the end of the boost phase when most of the first-stage fuel has been used up and I have no idea what the relative masses of the two will be at that point.<br />

 

[dschmelzer]

Thanks for that info. This squares roughly with the Gs pulled by the Falcon I. See Figure 6.1 in the payload user guide...<br /><br />http://www.spacex.com/payloaduserguide.pdf

 

[grooble]

Hey Morris, the price of Falcon 1 may reduce, which means Falcon 5 may reduce in price too. Makes the bigelow thing more profitable.

 

[mrmorris]

<font color="yellow">"... Falcon 5 may reduce in price too..."</font><br /><br />There's also the fact that if SpaceX does the ASP themselves, then they get to double-dip. They already (presumably) will make a profit at the 15.9 million. <br /><br />Also -- the added volume of launches should reduce their cost per launch (triple-dip).

 

[mrmorris]

G-X3's destination now has a name -- <font color="orange">CSS-Skywalker</font> Very interesting article on Bigelow's Space Stations here.

 

[mrmorris]

Almost more interesting than the above article is the related one about Bigelow's advanced concepts. Check out the slideshow. His 'Nautilus Moon Cruiser' is particularly interesting. (BTW -- I'm not claiming <b>likely</b> -- just interesting). He shows it with a Soyuz docked, but the concept would work even better with a G-X3. <img src="/images/icons/smile.gif" />

 

[grooble]

Hey morris i don't know what your heat sheild requirements are but check this out:<br /><br />http://uplink.space.com/showflat.php?Cat=&Board=freespace&Number=153737&page=0&view=collapsed&sb=5&o=0&fpart=<br /><br />The guy withstood 3600 degrees with a helmet on his head that wasn't even finished being made ready.<br /><br />i wonder if you could strip out the heat sheild and replace it with this stuff, cheaper AND lighter i think.

 

[mrmorris]

<font color="yellow">"The guy withstood 3600 degrees..."</font><br /><br />Fire Paste may well be real -- it may well not be real. The demos are fairly convincing. However -- even if it sheds heat as well as he claims -- there are other factors. Will it crack and flake off in vacuum? Can it withstand the force of air pressure at hypersonic velocities? Dunno. <br /><br />At any rate -- there's no way for me to get specifications on mass, etc. of it, so I'd prefer to stick with the Dow Corning Ablative that is a known quantity.

 

[mrmorris]

(From a thread in M&L)<br /><br /><font color="yellow">"Any idea what the payload fairing of Falcon V weighs? Not really much need for that with G-3X so there's another weight saving. "</font><br /><br />At this point, I'm confident mass isn't an issue. Or at any rate -- I'm confident that there are hurdles remaining that are much higher than saving a few kilograms here and there. First and foremost, I really want to see Falcon I have a successful flight. If that happens, I have a great deal more confidence that the single biggest hurdle can be met (namely building the Falcon V itself).<br /><br />I'm positive that given sufficient time and capital, it's possible to create a five-person spacecraft that can be launched on a booster of Falcon V's stated specs. The challenges that I find myself thinking about and researching at this point revolve around finding the components and technologies for the subsystems of G-X3 that can be developed in the shortest possible time for the smallest amount of investment capital. The three failure points that loom largest are:<br /><br />1. Falcon V never gets built.<br />2. V is built, but ASP expires before development is complete.<br />3. V is built, but development funds run out before G-X3 is complete.<br /><br />I can't do anything about #1, but #2 and #3 are something that can be made less likely given sufficient inspiration.

 

[severian]

Personally, considering their achievements so far, and the backing the Elon Musk has put into it, I would be astonished if the Falcon V doesn't successfully go into surface before the end of 2007. <br /><br />As for GX-3 being built, well...<br />SpaceX plan to win the ASP themselves, and hence, need something to do it in. Considering the weight restrictions on the Falcon V, if they do decide to use that launch vehicle (as opposed to a later, bigger one), the design has _got_ to be very similar to the GX-3.<br /><br />As for will they use the "GX-3 design" - keep in mind that what you have written is more of a specification than a technical design. But if, as you have stated before, you send a full report to SpaceX about it, I'm sure they might find it very useful.

 

[psion]

<b>mrmorris on 12/01/04:</b><br /><blockquote><font class="small">In reply to:</font><hr /><p>OK -- does anyone know how to get access to Johnson Space Center docs? Specifically I want to find:<br /><br />JSC-26938: Procurement Specification for the Androgynous Peripheral Docking System for the ISS Missions<p><hr /></p></p></blockquote><br /><br />Mrmorris, I wanted this document for my own purposes as well. If you still need it, you can download it from my server here.<br /><br />I hope you find this helpful.

 

[nacnud]

Thanks for that, I was hopeing someone would find it <img src="/images/icons/laugh.gif" />

 

[mrmorris]

<font color="yellow">"...what you have written is more of a specification than a technical design."</font><br /><br />Absolutely. There is absolutely no way for me to <b>design</b> Gemini-X3. What I have done is to mix and match the specs from numerous different pieces of equipment. Start with the specs of the original Gemini -- drop off the specs of the equipment that are obsolete or irrelevant to the mission of G-X3, then add in the specs for modern equipment.<br /><br />I'm not so much trying to design a spacecraft as I am trying to demonstrate the <b>feasibility</b> of designing a spacecraft. In general -- people 'in the know' about space assume that a 5-6 person craft would require a much larger booster than the Falcon-V. You can see this at the beginning of this thread, and more recently in a thread in M&L where no less than shuttle_guy takes it as a <b>given</b> that such a craft should weigh in the realm of 20,000 kg. I was in the same category myself. I originally started this research when someone else indicated the possibility of using the F-V to lift a Gemini-style capsule on the xprize board. I looked up the specs expecting to see that it was impossible -- only to find that it perhaps... just... might... *be* possible. All of my research since then has simply made it more and more evident that this can be done.<br /><br />As for sending my doc to SpaceX. I don't hope that they'll take my doc and build Gemini-X3 as speccd out. I hope that they might take my doc and find one or two items of interest in it that they might incorporate into <b>their</b> G-X3 equivalent. The more I read about them -- the more I feel they have a Gemini-like capsule sitting in a CAD file somewhere. Most of what I'm doing here is just for fun. I like complex mental exercises, as I've said repeatedly. But the thought that something I thought of might, just possibly, with lots of luck, make it into an actual spacecraft... is incredibly unlikely. But it wou

 

[aaron38]

Mrmorris,<br /><br />First I'd like to say great job on this thread!<br /><br />I saw earlier posts that the Gemini-X3 would likely be powered by lithium-ion batteries. Last week the research firm Altair announced a major breakthrough in lithium-ion technology that will allow them to have three times the power of existing Li-ion batteries.<br /><br />I couldn't find any mention of how that power increase tranlates to W/kg or W/litre improvements, but I would expect them to be sizeable.<br /><br />If this research pans out, it should give your concept design more margin.<br /><br />http://www.evworld.com/view.cfm?section=communique&newsid=7681

 

[couvillion]

This is a great thread, I would like to give some feedback on the idea.<br /><br />Gemini is a great starting point for a capsule design. Since your analysis is primarily parametric. I would like to give some of my thoughts as to why the Gemini design was better than Mercury or Apollo. Gemini had a very small pressurized crew cabin, just big enough for two Gus Grisson sized men, most equipment was in unpressurized space and accessible from the outside by work crews. This made the craft easier to build and check out. Gemini was designed this way because of the problems with Mercury led to long pad times trying to replace failed parts, and arguably this problem (having to preform work inside a cramped space) lead to the Apollo one fire. Another good reason to have stuff outside the crew cabin is that anything that goes into the people space will need a much higher level of testing for any possible side effects that might hurt people than stuff that is outside that space. Finally pressurized space is heavy the smaller the pressurized vessel the better.<br /><br />My suggestions for a new Gemini are a APAS adapter in the nose, a pressure cabin sized for your astronauts coming back to a CBM (Common Berthing Mechanism) sized bulkhead to the rear (assuming that this sizes up well). I believe that a capsule capable of matching these interfaces can have a very long lifetime as a building block. Behind that I would put any additional equipment needed that is deemed important to be reusable. There is no rule that says that the back of the crew cabin has to back up to the heat shield. The heat shield I should be a unit replaceable heat shield, that chould be designed to be either ablative or not. I consider a reusable heat shield to be iffy and would not want to have a back up plan for it. Behind that a equipment module for any stuff not to be reused, and deorbit engines if they are solid.<br />

 

[mrmorris]

<font color="yellow">"...most equipment was in unpressurized space and accessible from the outside by work crews...."</font><br /><br />There are some upsides to putting the equipment in unpressurized spaces. However, there are a lot of downsides as well.<br /><br />- ECS becomes more complicated and adds mass because cold plates must be utilized to keep the equipment at a viable operating temperature. With equipment in the pressurized space -- air cooling is possible and regulating the heat generated by electronics becomes part of the cabin temperature control system.<br /><br />- Equipment must be designed for vacuum operation and much more extreme environmental tolerances. This will greatly increase cost and complexity as it will eliminate many COTS options that would have worked inside the regulated cabin environment.<br /><br />- It will be subjected to higher temperatures and stresses on launch/re-entry, increasing the risk of failures and decreasing lifetime. On a reusable craft -- we want the equipment subjected to the minimum stress possible.<br /><br />- Equipment will be completely inaccessible to crew during the mission, so there is no possibility of diagnosing or repairing any in-flight failures.<br /><br />- Radiation levels will be higher outside the crew cabin, requiring higher rad tolerances for electronics.<br /><br />- If you look at the diagrams of the original Gemini -- there was a great deal of 'wasted' space in the unpressurized equipment areas between the PV and the hull. I'm not sure why you think that pressurized space is heavy. In and of itself, it is not. As a general rule, as the pressurized space of a spacecraft goes up -- so does the mass, but this is due to a slew of other factors. It's true that Gemini was heavier than Mercury and Apollo was heavier than Gemini -- but you can't claim that this is due to pressurized space. This is especially true when comparing the 1970's Soyuz and Apollo. I forget the exact specs, but I recall

 

[couvillion]

- "...but you can't claim that this is due to pressurized space."<br /> The mass of a pressure vessel is proportional to its volume see http://yarchive.net/space/launchers/fuel_tank_scaling_laws<br />- "What does the bulkhead size have to do with anything?"<br /> Because a pressure vessel mass varys with volume, the crew cabin should be as big as needed and no bigger for mass efficent launches. If having a CBM sized bulk head results in too big of a cabin design, it's not a workable idea. Alas.<br /><br />- "This is especially true when comparing the 1970's Soyuz and Apollo. I forget the exact specs, but I recall reading an article that the Soviets were very pleased that the Soyuz had three(?) times the habitable volume for approximately the same mass as the Apollo CM."<br /> I think you have this backwards, probably the same volume for a third of the mass. I haven't double checked the data, however. The reason for this was not that cabin size doesn't matter but that return capsule, (+heat shield, parachutes ..) was minium size needed. Half the crew cabin didn't come home at all. http://www.astronautix.com/articles/wastolen.htm<br /><br />The trade off of were to put equipment indeed are many, and depends on what you think the capsule will be doing and the nature of the equipment. I don't think we have the information to debate the subject with any meaningful results.<br /><br />- "Other than the CBM bit, I don't see anything different from what I've proposed on this thread."<br /> Indeed I haven't much to add to the dicussion. However I want to give you some thoughts on what factors made Gemini a successful design.

 

[mrmorris]

<font color="yellow">"The mass of a pressure vessel is proportional to its volume"</font><br /><br />True. You can also state that the mass of a rock is proportional to its volume. In fact -- all else kept equal -- the mass of any material object is proportional to its volume. <br /><br />However -- I understand what you're referring to. If the PV size were doubled -- the mass would more than double. This has the potential to be a valid point except for the fact that the differences in the PV size that are germane to the discussion are nowhere near that level. Since we're not talking about increasing the exterior dimensions of the craft, and those dimensions are *barely* adequate for a 5-6 person crew in and of themselves, placing equipment outside the PV might allow the size to be reduced anywhere from 10-20%. Reducing the PV size by 15% will not make a significant difference in the mass of the overall vessel. This is especially true because if the equipment space is made in the same fashion as that of the original Gemini -- the PV would consist of flat-sided panels -- leaving a curved volume between the PV and the outer hull free for equipment. If instead the PV bulkhead curves to fit the outer hull -- there is not a significant increase in material, and in fact -- the bulkhead can actually be thinner because a curved panel resists pressure better than a flat one. This has the potential to result in a net mass <b>reduction</b> for the larger volume.<br /><br />It will likely make a significant difference to the crew, however, as that will be a significant fraction of the pressurized volume that isn't already filled with a solid object. I haven't done a volumetric analysis of the G-X3, but it is probably in the realm of 9-10m3. A 15% reduction then would turn a 10m3 space into an 8.5 m3 space.<br /><br /><font color="yellow">"I think you have this backwards..."</font><br /><br />I wish I could find the article. Unfortunately it's one of the

 

[quikely]

I think you have it wrong that putting the CG in the nose makes the craft stable during reentry. This is in fact the opposite of what you want. You want the CG low, close to the heatshield. The diagram makes this clear if you consider the pitching moment induced by the lift and drag forces.

 

[teije]

<font color="yellow"> Does anybody know the Gs going up on a Falcon V and the original Geminis? </font><br /><br />On the spaceX website in their update section they have this (and other things) to say about the structural testing of the Falcon V:<br /><br />quote:<br />Maximum g load at first stage burnout<br />At first stage burnout, the vehicle is accelerating at about 6.5 g’s and the upper stage is exerting about a 65,000 lb load on the inter-stage. Failure would show itself as buckling somewhere between the top of the first stage tank and the bottom of the second stage tank. The vehicle is essentially in vacuum at this point and moving at about 8,000 to 9,000 ft/s, so there is no significant aerodynamic load. <br /><br />Teije<br /><br />Btw,<br />great thread!

 

[mrmorris]

<font color="yellow">"I think you have it wrong that putting the CG in the nose..."</font><br /><br />Anything is possible. However -- this is not on my authority. My statement is based on the calculations done for the ACRV in patent number 5,064,151. This was done by a group of NASA engineers, presumably using fairly sophisticated formulas and modelling techniques. The relevant text from that patent:<br /><br /><i>"The other aerodynamic consideration was the moment slope (Cm-alpha) which determines the aerodynamic stability of the vehicle. A negative Cm-alpha defines a statically stable vehicle in which restoring forces are generated if the angle-of-attack is disturbed away from zero (note that dynamic stability is not guaranteed). The more negative the Cm-alpha, the more statically stable the vehicle behaves. FIG. 5 shows the Cm-alphas of the three original candidates and the final return vehicle design. They are plotted as functions of the c.g. position from the nose of the vehicles (Xcg). <b>In all cases, the closer the c.g. is to the nose, the more negative Cm-alpha becomes and the more stable the vehicle is. </b><br /><br />The calculated locations of the Xcg's for the respective vehicles are shown on their corresponding curves. Although the final return vehicle design did not achieve the stability of the MOSES or spherical designs, it is approximately 50 percent more stable than the Apollo design. The return vehicle c.g. was computed to be about 45 in. behind the nose at entry. The aerodynamic center was calculated to be approximately 170 in. behind the nose in the hypersonic regime. "</i><br /><br />While your diagrams look rally nice -- the aerodynamics of hypersonic flight are complex enough that NASA builds a new supercomputer every few years to improve their ability to model how things happen in that regime. Are you an aeronautical engineer? What's your area of expertise?

 

[quikely]

Your own statement proves my point. " In all cases, the closer the c.g. is to the nose, the more negative Cm-alpha becomes and the more stable the vehicle is. " They are referring to the nose as the apex of the heatshield - the stagnation point. Because the CP moves further away from the "nose" at hypersonic speeds, the vehicle is actually more stable at high speeds. It will tend to oscillate at subsonic speeds. This is typical of reentry capsules. See http://naca.larc.nasa.gov/reports/1958/naca-rm-l58e07a/naca-rm-l58e07a.pdf<br /><br /><br />I've been working on my own ideas in this area for some time now. Good luck.<br />And yes, I am an aerospace engineer.