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How to design a lighter Orion
I don't know if latest weeks' rumors about a "too heavy" Orion are true (or not) however, I think that "save weight" always IS good (for every kind of spacecraft) then, starting from this page, I will publish some articles and updates with useful suggestions to "save weight" on the Orion design, so, if the Orion actually is "overweighted" it may go back to the right weight, while, if Orion has no extra weight, these suggestions may be applied to increase the Orion's "net payload" like (e.g.) add a longer life support.
My first suggestion to save (about) 1-2 mT of weight, litererally, is "cut the Orion's edges" to have the same internal space with smaller external dimension. That is possible since the real internal space of the Orion doesn't exactly match the external shape of the capsule, infact the edges and the top of a full cone-shaped capsule (fig.1) are too narrow to add any useful internal space or additional habitable volume for the astronauts, then, that parts of a capsule are only a "dead weight" we can/must "cut" to save up to 2 mT of weight from the current (estimated) 9.5 mT Orion mass to only (around) 8 mT.
I've already suggested five months ago to build the Orion with a different shape in my "EggCEV" article and (this month) to join a smaller Orion and an inflatable module in my "BigelowOrion" article but the simplest way to have (both) the same (or more) internal space and less total weight, is to shift from a (space-unefficient) "cone" shape to a (space-efficient) "Truncated Biconic Shape" (TBS) as shown in fig.2 (that resembles, in part, some of the early "alternative CEV concepts").
As you can see in the capsules shapes comparison (fig.3) the 4.5 m.TBS Orion has the same (or more) internal space with a slightly smaller external dimension and (most important) less weight that's (mainly) due to a -20% smaller thermal shield (the heaviest part of a capsule) that (thanks to less surface and less volume) may have -25% less weight vs. the 5 m. Orion's thermal shield!
But the advantages of a TBS Orion go over a capsules' mass reduction, since a 15-20% lighter Orion needs a 15-20% lighter LAS (from current 6 mT to 5 mT) a 15-20% lighter SM (from 3.8 mT to 3 mT) 15-20% less propellent (from 8 mT to 6.5 mT) and (very very important) a 15-20% smaller rocket (thanks to a reduced Orion's GLOW, from 21.5 mT to less than 17.5 mT without the LAS or less than 22.5 mT with the LAS instead of over 27.5 mT!) so, every Ares-I's design (also with a standard 4-seg.SRB and a less powered J-2x) will be able to lift the Orion without problems!
One of the questions about the Truncated Biconic Shape Orion is the allocation of theoxygen, water and fuel tanks in the new shape, without the cone edges. In the standard cone-shaped Orion these tanks are allocated around the bottom edges of the capsule (fig.4) to leave for the astronauts a rounded internal habitable volume shape, while, in the Truncated Biconic Shape Orion the same tanks can, still, be allocated in the bottom of the capsule, but, grouped in four sides (fig.5) having the additional advantage of a (much more rational, comfortable and ergonomic) 4x4 m. squared internal habitable space on the bottom part of the capsule (at the astronauts' seats level) while the mid-top parts remain conical. Another option (fig.6) to have much more internal habitable space, is to put them vertical thanks to the less sloped shape (fig.7) of the TBS-Orion.
Every capsule has its sides exposed to the hot plasma at reentry but the Truncated Biconic Shape Orion (despite its less sloped shape) may have no particular problems at reentry since it's just a little bit different from a cone-shaped Orion and very much different from a "bell-shaped" 2.17 m Soyuz Reentry Module (not a "biconic" capsule, but very close to a cylinder!) that has accomplished 100+ successful reentries in the atmosphere despite its (6 cm.) thermal shield (fig.8) is not particularly thick nor particolarly larger/higher than a cone-shaped capsule (look at the point of attack between the shield and the capsule near the blue arrow) then a Truncated Biconic Shape Orion doesn't need a thermal shield thicker than those that will be designed for the 5 m. (Earth-direct reentry) lunar-Orion.
However, if a truncated biconic shape may give some aerodynamic problems at reentry or (simply) if we want a better thermal shield, the (too much rounded) shield of the 5 m. cone-shaped Orion (fig.9) can be modified to have a keen shape and angle (fig.10) or a small "negative slope" (fig.11) or a capsule with less diameter than shield at its base to form a little "step" (hidden with a small aerodynamic fairing at lift-off) between the thermal shield's attack and the capsule's body (fig.12) able to keep the hot plasma flux away from capsule. Of course, all these capsules and shields' shapes need hundreds wind-tunnel sessions to know how they work together and which capsule/shield shape is the best!
January 28 - 2007
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Copyright © 2007 Gaetano Marano - All rights reserved - base images used for the drawings are © NASA and RSA