You are not logged in.
Quaoar wrote:GW Johnson wrote:There's at least two wildly-different versions of gas core, too.
GW
Which are?
I can think of three off the top of my head. Nuclear Saltwater, Nuclear Lightbulb, and Coaxial.
The type of GCNR I had in mind was a coaxial flow open cycle vessel using Americium fissile material and tungsten seeded hydrogen propellant. The reactor would probably have a toroidal core shape to inhibit fuel loss and maximize the propellant's exposure to the thermal flux produced by the core. This complicates flow somewhat but also solves lots of other problems. Ideally, initial models would not require external radiators and thus would be limited to an Isp between 2500s and 3000s. I want to determine how small a reactor could be created to replicate the thrust level of the RL-10 and retain desirable operating characteristics (relatively small quantity of fissile material required for operation, low fissile material loss, modest operating pressure, lightweight moderator, no external radiator required for heat rejection, minimal seeding material required for nozzle cooling).
The tungsten-seeded hydrogen propellant can protect the walls of the containment vessel and nozzle for thermal flux required to achieve an Isp of up to 7000s. With a system that achieves an Isp of up to 3000s, no radiator is necessary. For Isp ranges between 3000s and 6500s, a radiator is required. One of the odd but serendipitous things determined through actual experimentation was that the seed material was only required until the hydrogen was heated to 15,000K, at which point it rapidly became opaque (absorbed radiated photons from the UF6 plasma) at the operating pressures involved. Increasing the operating pressure increased the opacity of the propellant.
Actual experimentation with Americium demonstrated a dramatic reduction in fissile material required to sustain fission. Using UF4 and UF6 for fissile material requires much larger core radii or a more reflective (heavier) moderator. It was determined that there was an optimum moderator thickness of about .46 meters (if using UF6, not Americium). The moderator accounts for a significant portion of the system's mass (unless a higher Isp is desired, at which point radiator mass is a significant portion of the system's mass).
Everything I've read says that this is entirely doable with current materials tech and simply requires funding. If I'm wrong, then I am, but all the scientists who actually did experiments directed towards development of this technology had results that were favorable for continuing development. Then the politicians killed funding.
I advocate for development of NTR tech because it strikes a balance between power and efficiency. If we complete the argument Impaler made in his last post, either more power generation mass or more reaction mass are required to "go faster". The Boeing SEP tug is already at the limit of what a fully evolved SLS booster could lift. If more funding was directed to SEP technology development by canceling costly and redundant capsule systems (Orion and CST-100 immediately come to mind), then perhaps by the time SLS is ready to fly we could have a SEP tug ready to test as well. Impaler shot that idea down.
We can spend money on Cadillac class capsule systems that don't carry the supplies necessary to make a trip to Mars or we can spend money on the propulsion and environmental control tech required to simply get us there and then concern ourselves with how fancy our ISS servicing spacecraft are.
I don't want to wait 20 years for tech to "improve", I want to know what we can do between today and the time SLS is man rated. Why waste time and money playing with space rocks or developing 3 different vehicles to service ISS when we can send a SEP tug and dummy payload to Mars?
Offline
Like button can go here
The "bad guys" I was referring to were not our arguing friends. But that's a valid point you make.
That image of a Boeing lander model looks surprisingly (maybe not so surprisingly) similar to what I got for a single-stage lander concept. Except that I made mine conical for streamlining during ascent, and easy heat protection during descent.
Mine was one-stage, though. I had both pressurized and unpressurized spaces in it. The idea was to "camp out" in the lander during the surface stay. I did use a small self-landing capsule as a control cabin/bail-out lifeboat. Something like a Dragon.
Bail-out capability only makes sense if you have a back-up lander with which to attempt a rescue. But if you do have multiple landers, it becomes a moral imperative.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
Offline
Like button can go here
Quaoar: to answer your earlier question to me, I only had in mind two broad categories of gas core thermal engines. Those are open cycle and closed cycle. I'm not familiar at all with something called "saltwater" somewhere just above. I've been outside the industry for 2 decades now (one of those industry "consolidations" got me, where they fire half the workers, keep all the upper level managers, and live off the backlog for about 3 years until they can bail-out with their "golden parachutes"), making it very hard to stay abreast of things.
Nuclear saltwater is something Zubrin came up with. The gist is this: You dissolve a fissile salt in water, and put it in thin tubes of a neutron moderator. For thrust, you pump this saltwater into the reaction chamber, where it becomes critical. The saltwater becomes plasma and exits the reaction chamber. The jury is still out on whether one could build an engine capable of withstanding the reaction.
Offline
Like button can go here
The "bad guys" I was referring to were not our arguing friends. But that's a valid point you make.
That image of a Boeing lander model looks surprisingly (maybe not so surprisingly) similar to what I got for a single-stage lander concept. Except that I made mine conical for streamlining during ascent, and easy heat protection during descent.
Mine was one-stage, though. I had both pressurized and unpressurized spaces in it. The idea was to "camp out" in the lander during the surface stay. I did use a small self-landing capsule as a control cabin/bail-out lifeboat. Something like a Dragon.
Bail-out capability only makes sense if you have a back-up lander with which to attempt a rescue. But if you do have multiple landers, it becomes a moral imperative.
GW
Ya the aftermath of politicians making work programs without the funds, defunding programs that are on the verge of sucess and changing directions for existing programs all have there impact on space when it comes to NASA but with a company like Space X its a bit different game that if there is enough commercial requests to pay for a launch service.
The bailout life boat can only as you note work if there is a seperate unit waiting all fueled up, or if there is already an inbound mission soon to land but the cycle makes that difficult and otherwise its up to the crew to survive with what they have remaining until help arrives.
As to the lander mass and style of it the one in the image sure looks small for living area and gives the impression that its a one size did it all for the mission duration which makes the landing mass way out on the doable capability for powered landing.
Offline
Like button can go here
Page 1 is ION drive but plan does not address artificial gravity or radiation.
Page 2 discusses nuclear versus solar for power
Page 3 more of the same
page 4 continued arguments but questions cost of sls and number of launches and starts to open up other methods
page 5 rounding up SEP and nuclear
current page 6 is options for type of nuclear materials that could be used.
Offline
Like button can go here
Rogozin Dials Up The Complaints And Makes Threats
http://nasawatch.com/archives/2021/06/r … l#comments
"The United States agreed to transfer Russian space rocket complex "Sea Launch" under the condition that it will not compete with the US company SpaceX Elon Musk , said General Director of " Roscosmos " Dmitry Rogozin. "Specific strict restrictions were introduced when signing this contract for the transfer of two Sea Launch vessels to a Russian company (S7 - ed.) - an obligation that we do not have the right to use this Sea Launch in competition with Elon Musk," he said during parliamentary hearings in the State Duma. "Okay? That is, the US government, government lawyers act as a client of, in fact, a private company (SpaceX - ed.). Or maybe it is not a private company in this case, if with the help of state sanctions we are limited to compete with SpaceX?" "- added Rogozin."
Russia's space chief threatens to leave International Space Station program unless U.S. lifts sanctions
NASA Invites Media to Launch of Boeing’s Orbital Flight Test-2
https://www.nasa.gov/press-release/nasa … ht-test-2/
Autonomous Moon Buggy By GM And Lockheed For NASA
https://www.compositesworld.com/news/lo … ver-design
Offline
Like button can go here
Boeing’s Starliner launches to International Space Station after delays
Offline
Like button can go here
First Ever Manned Boeing Starliner Test Flight on New Atlas Booster Successful
https://theaviationist.com/2024/06/05/f … starliner/
Boeing already launched old payloads to Mars with the older Delta an expendable launch system,
Starliner, formerly known as CST-100 (Crew Space Transportation 100), is a space capsule privately developed by Boeing to carry up to seven people to and from low earth orbit to carry crews to the ISS and the planned Bigelow Aerospace Orbital Space Complex.
https://space.skyrocket.de/doc_sdat/starliner.htm
With rising price, more delay and cost increase Boeing had faced scrutiny from NASA's inspector general
Offline
Like button can go here