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Excuse me, I realize that this topic is a bit hypothetical, but as an ameterur SF writer I'm very courius about it. If some day we will have some sort of FTL drive and we will reach some superearth like Gliese 832c ( https://en.wikipedia.org/wiki/Gliese_832 ) what kind of lander can we use?
Gliese 832c has a mass of 5.7 Earth mass. Its radius is not known but I assume as worst case something like 1.5 Earth radii and a surface gravity of 2 gee. Surface to orbit delta-V is almost 14.6 km/s that easly become 18-20 with air and gravity drag.
I also hypothize its atmosphere is very dense, with a surface pressure of 3 bar, 16% oxygen, 83% nitrogen and 0.93% argon (these data are completely arbitrary but I choose them to allow my characters to survive).
FTL drive is some sort of magic box that move the starship from a star system to another, but it doesn't function in gravity well, where starships has to use convetional nuclear fission rocker, solid core, vapor core or gas core because they still don't have fusion (or they have but is too massive to be used on a starship).
There is alien life on the planet, so using gas-core rockets in and near ist atmosphere is illegal, so I hypotize that a lander has to use a simple rotor with tip-jets for descend and three expendable stage for coming back to orbit: 1st chemical LOX-LH2 rocket, 2nd vapor core NTR with LOX afterburner, 3th vapor core NTR. 2nd stage vapor core is transferred to first stage before jettison, to not contaminate planet atmpsphere. The lander should land almost empty and use local water for ISRU, using some RTG and/or solar panel.
I'm very interested in your opinions,
Thank to all
Last edited by Quaoar (2016-03-29 14:55:20)
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Why would you not use an NTR for launch? Obviously you'd need to solve the thrust issue, but the Isp is there to do it in a single stage.
Alternatively, you could use beamed power from an orbiting station, to create a virtual space elevator, going with Josh's suggestion to head to stationary orbit to keep it in line of sight.
Use what is abundant and build to last
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Why would you not use an NTR for launch? Obviously you'd need to solve the thrust issue, but the Isp is there to do it in a single stage.
Yes a solid core NTR with an exaust velocity of 10 km/s can reach almost 16 km/s of delta-V with a mass ratio of 5, but with a surface gravity of 2 gee there are a lot of gravity losses and I guess a NTR-SSTO also needs some kind of chemical side busters even with a LOX afterburner.
Alternatively, you could use beamed power from an orbiting station, to create a virtual space elevator, going with Josh's suggestion to head to stationary orbit to keep it in line of sight.
This is probably the best option for a civilized planet with a well extabilished human colony, but I guess it is difficoult to built all the facilities needed in the first exploration mission.
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However, the infrastructure would all be in the form of an orbiting starship that has a powerful laser on it. I don't think it would be that difficult for an exploration mission, certainly no harder than taking loads of disposable chemical stages...
Use what is abundant and build to last
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You could use a space fountain, the real problem is the escape velocity, not the gravity, although the gravity would be uncomfortable for humans. Just imagine you have a stream or particles in orbit around this planet, then you encapsulated them in a tube that stretches forming a perfect seal that keeps the atmosphere out. Now you shrink the diameter of that tube, while slowing it down so that it is stationary relative to the surface of the planet. The particles accelerate to faster than orbital velocity but are held to their orbital path by the circular tube, the centrifugal force supports the weight of the tub against gravity. The tube lowers until it is well within the troposphere of the planet, completely encircling it, and an air breathing vehicle takes off from it and lands on the planet's surface. When the mission is complete, it takes off and lands on the tube, the tube then stretches and rises into space, the tube accelerates by slowing down the particles inside until both are once again in orbit around the planet, then a high efficiency plasma drive takes a shuttle back to the mothership. The space fountain is rolled up after disassembly in orbit, and it is on to the next planet!
Last edited by Tom Kalbfus (2016-04-01 08:31:37)
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You could use a space fountain, the real problem is the escape velocity, not the gravity, although the gravity would be uncomfortable for humans. Just imagine you have a stream or particles in orbit around this planet, then you encapsulated them in a tube that stretches forming a perfect seal that keeps the atmosphere out. Now you shrink the diameter of that tube, while slowing it down so that it is stationary relative to the surface of the planet. The particles accelerate to faster than orbital velocity but are held to their orbital path by the circular tube, the centrifugal force supports the weight of the tub against gravity. The tube lowers until it is well within the troposphere of the planet, completely encircling it, and an air breathing vehicle takes off from it and lands on the planet's surface. When the mission is complete, it takes off and lands on the tube, the tube then stretches and rises into space, the tube accelerates by slowing down the particles inside until both are once again in orbit around the planet, then a high efficiency plasma drive takes a shuttle back to the mothership. The space fountain is rolled up after disassembly in orbit, and it is on to the next planet!
Another option may be an NTR SSTO with a mass ratio of 5 or 6 capable of an initial acceleration of 2.5 gee: a LOX afterburner may be used in at take-off. I've read a study about a foam-core NTR, using an uranium tricarbide foam with almost the same T/W ratio of the old Timberwind but without the hot spot problems, but I cannot find the reference.
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Tom Kalbfus wrote:You could use a space fountain, the real problem is the escape velocity, not the gravity, although the gravity would be uncomfortable for humans. Just imagine you have a stream or particles in orbit around this planet, then you encapsulated them in a tube that stretches forming a perfect seal that keeps the atmosphere out. Now you shrink the diameter of that tube, while slowing it down so that it is stationary relative to the surface of the planet. The particles accelerate to faster than orbital velocity but are held to their orbital path by the circular tube, the centrifugal force supports the weight of the tub against gravity. The tube lowers until it is well within the troposphere of the planet, completely encircling it, and an air breathing vehicle takes off from it and lands on the planet's surface. When the mission is complete, it takes off and lands on the tube, the tube then stretches and rises into space, the tube accelerates by slowing down the particles inside until both are once again in orbit around the planet, then a high efficiency plasma drive takes a shuttle back to the mothership. The space fountain is rolled up after disassembly in orbit, and it is on to the next planet!
Another option may be an NTR SSTO with a mass ratio of 5 or 6 capable of an initial acceleration of 2.5 gee: a LOX afterburner may be used in at take-off. I've read a study about a foam-core NTR, using an uranium tricarbide foam with almost the same T/W ratio of the old Timberwind but without the hot spot problems, but I cannot find the reference.
If you don't mind the radioactive pollution.
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If you don't mind the radioactive pollution.
NERVA contained nuclear material in fuel elements, so no radioactive exhaust. They were paranoid so designed it to launch cold, the reactor would only start once it was safely in Earth orbit. That meant if catastrophic failure occurred and rocket self-destruct, fuel elements would fall to the Earth with no fission fragments. However, it would never have radioactive exhaust. They tested NERVA at Jackass Flats to be sure. A new solid core NTR could have the same features, it's just a matter of design.
And to belabour the point: after the reactor started, fuel elements would still contain both nuclear fuel and fission fragments. Uranium was not just encased in ceramic, it was embedded in ceramic like raisins in raisin bread. So fission fragments would be contained in that ceramic as well. However, uranium is safe enough to handle with nothing but cheap plastic gloves you get with oven cleaner. Ceramic of the fuel elements would probably contain the uranium, so that would be safe to handle with bare hands, but if a rocket self-destructed or otherwise broke apart from catastrophic launch failure, then the ceramic could be cracked exposing some uranium. So it would be safer to use gloves. However, fission fragments are so radioactive that you want several feet of water between you and it. That makes cleanup far more problematic. So the "launch cold" thing was not to prevent radioactive exhaust, it was planning for catastrophic failure.
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So it would be safer to use gloves. However, fission fragments are so radioactive that you want several feet of water between you and it. That makes cleanup far more problematic. So the "launch cold" thing was not to prevent radioactive exhaust, it was planning for catastrophic failure.
I think catastrophic failure is an issue not impossible to deal with: Apollo 13 Lunar Module RTG generator is somewhere in the indian ocean, but it's still integer and no plutonium has leaked utlil now despite its unexpected atmospheric entry, because it was projected to not crash in case of launch failure. In the same way, it may be possible to project the NTR SSTO core to survive (or be ejected and parachuted) in case of launch failure.
Last edited by Quaoar (2016-04-13 17:00:15)
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I think it is about the same as reaching orbit from Saturn. I have some ideas on that score, and Saturn's rings are helpful.
http://newmars.com/forums/viewtopic.php … 64#p128964
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