Reentry and landing.
- Thread starter Blue Ghost
- Start date
Unfortunately, the deckplans of most ships show them constructed as airliners, not buildings. The most notable exception is the mercenary cruiser, and it isn't streamlined.
Xerxeskingofking
SOC-13
well, given access to internal grav, the direction of "down" on a starship interior is effectively arbitrary, except at transition point to the outside. a person on the ship cant tell if what the external grav field is doing. the ship could be sat upside down relative to the planet, and no one onboard would notice unless they look out a window, or the power fails. it would be very disconcerting for someone looking out a ship coming into to land if it banks and they see the horizon tilt but don't feel it. pilots might find it advantageous to program the bridge grav plates to allow some sensation of tilt or people might get motion sickness.
It is less about the orientation of the ship and more about how it maneuvers. In that the majority of the horizontal velocity is scrubbed off so the majority of the maneuver is about gravity and thrust.
Honestly I take the Star Wars route, in that very few ships are ever truly in orbit.
The orientation of the ship matters if it is streamlined. You also need thrust at the rear of the vessel.
In the context of this thread, I am talking about landing on a world, especially one with an atmosphere. "Down", especially in relation to thrust exhaust, is quite important.
My original notion (back in the '80s, and based on just the 3 LBBs, SF reading, and input from the ref at the time) was that streamlined hulls were tailsitter prolate spherioids*, and used retractable drag-reducing aerospikes in the "up" direction of travel to deflect hypersonic airflow. (The fusion rocket exhaust would serve the same purpose on descent.)
Currently, I figure it's managed with gravitic fields -- which is your concept using a slightly different alloy of handwavium.
*minimized maximum dimensions and surface area, which made sense if the Jump Drive was a radiated field effect or conducted across the hull. Decidedly non-cinematic, but then my SF experience at that point was almost entirely text-based...
Yes and no, consider the directional thrusters coupled with contragrav. The visuals will very similar...
Each edition of Traveller has been a bit different on how M-drives worked. For example, GT explicitly used vectored thrust.
MT does, too... well, vectored gravitic thrust... 100% to about 10°, 50% at 90°, 25% at 170°
I've always been under the impression that Grav Lifters act more like a "cold thrust" that looks like the Type S in this cover.
Never been a fan of them looking like nothing a-la Star Wars repulsorlift. Vehicles would have a lower-powered 'Plate' making them have less raw thrust but be safer from failures, while starships have a handful of thrusters built in as part of the streamlining process.
Never been a fan of them looking like nothing a-la Star Wars repulsorlift. Vehicles would have a lower-powered 'Plate' making them have less raw thrust but be safer from failures, while starships have a handful of thrusters built in as part of the streamlining process.
Not sure where I got the drawing, but it does have a small lander in the back. Or I mistook the Jump drive for one.
The Free Trader I have seen in the past, unable to find the drawing, looked like a lift body of the type vaguely similar to the one NASA tried out about 1960. But larger.
Timerover51
SOC-14 5K
With respects to air rafts making it to orbit, I simply do not allow it. According to Maxwell Hunter in Tjrust Into Space, it takes about 4 kilowatts to put a pound of mass into orbit. So, to put an air raft at 4 tons into orbit would take 4 kilowatts times 8820 pounds/4000 kilograms means that it will take 35.28 Megawatts used with 100% efficiency to put the air raft into orbit. To do that in 8 hours means your power plant is putting out a minimum of 4.41 Megawatts per hour. A kilowatt is equivalent to 1.34 horsepower. A Megawatt is equivalent to 1,340 horsepower. Multiply that by 4.41 Megawatts gets you a minimum power output of the air raft power plant of 5,909.4 horsepower per hour. The air raft has a top speed of 100 kilometers per hour in a standard atmosphere. A World War 2 B-17 had a top speed of around 300 miles per hour/482 kilometers per hour on an output of 4,800 horsepower per hour. Compare the B-17 size and drag to the air raft.
Now, tell me again how an air raft with a top speed of 100 kilometers per hour in the atmosphere can get into orbit.
Now, tell me again how an air raft with a top speed of 100 kilometers per hour in the atmosphere can get into orbit.
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mike wightman
SOC-14 10K
Through the magic of grav technology and vehicle scale fusion reactors.
Firstly, four displacement tons is not a unit of mass but rather volume. This is a common mistake. Your weight is probably wrong considering an Air/Raft will both be built with High-TL composites and lack wheels, tires, and other accoutriments common to a wheeled vehicle. Most of those weigh 4000lbs ot less and I doubt it weighs anymore than a Sedan, probably much less.
Second, you’re applying the rocket equation, a mathematical constant of how hard it is to get X amount of payload into Y orbit and the energy needed to fight gravity on the way up. That’s all well and good - just not with a vehicle whose entire premise is flying by modifying gravity.
How much energy does manipulating gravity take? I dunno but presumably little, yet either way the 3I have made it practical. Unlike your B-17 example, Air/Rafts ignore the atmosphere and don’t lose thrust at extreme altitude due to atmospheric starvation. By their nature, Air/Rafts ignore the immediate conditions provided there’s gravity to play with.
Timerover51
SOC-14 5K
An air raft is supposed to be able to be made at Tech Level 8, and is supposed to be able to carry 4 tons of cargo. To carry 4 tons of cargo, which I assume is actually mass, not volume, you need a reasonably substantial vehicle. I will stick with the 4 tons of mass rate, and simply assume that it might be carrying something.
The energy requirement has absolutely nothing to do with the rocket equation, but simply indicates how much energy is required to put one pound of mass in orbit around Earth. That energy can come from a black powder rocket, Space Shuttle launch, Cavorite, Dean Drive, or the air raft lift and drive propulsion mechanism, but it has to be supplied. That does assume 100 per cent efficiency, so the actual energy required is going to be considerably more.
How much energy does manipulating gravity take? I do not know, but I do know that it will take 550 foot-pounds of energy to lift one pound to 550 feet in one second in Earth's gravity. That is what one horsepower can do. As for ignoring the immediate conditions, the following comes from LBB Book 3, page 23, 1981 edition, my emphasis.
An air raft has a cruise speed of 100 kilometers per hour in a standard atmosphere, with a top speed of maybe 120 kilometers per hour. That gives it range of between 62 and 75 miles per hour, or about the speed on an Interstate Highway. That is it. No faster. That gives it a power plant capable of forward motion comparable to the average car, so around 60 horsepower, or about 45 kilowatts. Then it has to add the energy cost of countering gravity based on the weight of the raft, passengers, and cargo. Now, you are telling me that this air raft, which cannot keep up with the average traffic speed on a U.S. Interstate, can generate enough forward motion to go into a stable orbit around Earth, requiring a velocity, however delivered, of around 26,000 feet per second. I fear that my "willing suspension of disbelief" becomes very unwilling at this point.
Straybow
SOC-14 1K
I think there is a forum limit to picture size, above which courtesy demands a thumbnail. Many computers can't do a full 1920.
Unless that guy is a about 3m stature, that ship looks much too small, about 50 dT. A 747-400 is well under 80 dT. The air raft is about the size of a 9 passenger van, which is less than half of 4 dT (roughly 23 m³ fully enclosed). An air raft that requires 4dT to ship should be the size of a U-haul truck, at minimum.
[/nitpicking]
Hey, why is the stupid post editor adding two extra blank lines to my white space between paragraphs?
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