![]() A large civilian craft compared to a human. Essentially, you make things big because you have to, not because you want to.īut suppose you don’t care about making the most effective spacecraft, you just want to go big. There is actually very little stopping you from making enormous lasers or railguns, but simply making them bigger doesn’t actually improve their effectiveness or power, it only makes them deal with thermal and mechanical stress better. The less massive you make everything, the greater the delta-v and thrust you’ll have. The smaller (volumetrically) you can make everything, the less armor you’ll need. Generally, lower limits are all the rage because you want to make everything small, compact, and low mass. The majority of the drone is reaction mass to offset the mass of the weapon and radiators.īut these are all lower limits. A small drone compared to the size of a human. If your missile has no warhead, their lower size limit is based on the rocket motor generally.įor drones, it is similarly the mass and volume of the weapons on that drone which limit the size of them. Thus, for missiles, their warhead tends to determine just how small you can make the missile. This lower limit is due to Critical Mass needed for fission. The smallest nuclear device ever made was the W54 at about 20 kg and the size of a large suitcase. For instance, nuclear warheads have a minimum size. There are certain minimum size limits that show up with drones and missiles, too. In the era of widespread, highly advanced Additive Manufacturing, these benefits are less pronounced, however. In that case, the redundancy is with the spacecrafts themselves, rather than with the subsystems.Īnother consideration is that smaller subsystems can be manufactured more cheaply on assembly lines compared to single large subsystems. ![]() However, bunching all of your crew together in a single module is a major liability in combat.Īlternatively, rather than making a single large spacecraft with highly redundant systems, some playtesters went the route of smaller spacecraft with no redundant systems. As a crew module expands in size, this overhead reduces proportionally to the number of people within. Similarly, crew modules come with significant overhead, such as the plumbing for the sewage and air recirculators. This actually happened on the Apollo 13 mission, and they were able to continue their mission (until later failures). If one rocket failed unexpectedly, they still had 80% of their thrust remaining. The Saturn V used five rockets for its first stage. Clearly, there is a balance to be struck, between redundancy and efficiency. Compare a stray shot taking out all of your thrust versus taking out only one-tenth of your thrust. On the other hand, those ten lower efficiency thrusters would probably be preferred in combat to the single high efficiency thruster because of redundancy. Larger singular systems distribute mass better and require fewer complex parts than many smaller systems. A single 200 kN rocket thruster, for example, will perform more efficiently and be less massive than ten 20 kN thrusters. Much of that difference is in the NTR’s enormous nozzle.Ī trend with sizing of subsystems is that systems tend to work more efficiently when larger. The NTR is roughly 60 times as long, and masses 6000 times as much. A Nuclear Thermal Rocket (NTR) next to a Magnetoplasmadynamic (MPD) Thruster at the bottom of the image. This means you often want to keep your weapons and subsystems as small as possible, but it’s physical limits that force them to grow larger. However, scaling it up in size reduces the power per volume and power per area so it won’t melt when activated. As outlined in The Photon Lance, scaling a laser up or down in size produces very little difference in power output. But these laws are almost never linear, and often hit ultimate limits. Power usage is more or less the primary way to increase effectiveness of systems, and size is generally the way to reduce thermal and mechanical stresses caused by this power use. Let’s take a look at size limits of subsystems. ![]() With missiles and drones, there is no obvious lower size bound either. However, there is no clear upper size bound. At the very least, your spacecraft needs to be able to fit people. Crewed spacecrafts very obviously have a lower size bound, since you can’t really miniaturize people like you can lasers or rocket engines. When designing a spacecraft, certain questions inevitably arise concerning how it should be sized. A large (190 m) capital ship compared against the Space Shuttle Orbiter (37 m). Just how big can you feasibly make a spacecraft? The size of an aircraft carrier? The size of an asteroid? How about the size of a small moon? Today we will look at scalability of spacecrafts and the systems within. ![]()
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