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For Quaoar re #4
Thank you (again) for posting the link to the Kalpana study. The paper includes history that adds perspective on the subject.
The name Kalpana remembers an Indian who died in the Columbia Shuttle disaster. (th)
In fact the space habitat was named after her.
I hope that every one in the Large Ship community takes the time needed to study this paper.
One benefit (for me for sure) was additional insight into the question of longitudinal stability.
This paper gives 1.3r as the maximum length before a cylinder becomes unstable.
I'd like to see more about this phenomena, because I find it counter intuitive. I would expect a longer cylinder to be more stable than a shorter one, but this is the second paper that makes this assertion that has come to my attention.
the first was a video that (I think) Void brought to our attention.
In any case, the amount of radiation protection mass proposed for a living habitat is out of the question for Large Ship. The answer has to be dynamic shielding, which SpaceNut has bravely decided to investigate.
The problem to be solved is the arrival of iron nuclei traveling at 70% of the speed of light, and from any direction.
The only tools that I know of to provide protection are the two electric fields: electrostatic force, and magnetic force.
The solution may well require clever deployment of both forces.
This topic is about instability due to movement of mass inside a rotating cylinder, and the paper addresses that factor. The deployment of weights on cables is innovative and it may be practical for a living habitat, but it is clearly not suitable for Large Ship.
(th)
To deflect the 2 GeV protons - the vast majority of GCR - you need a 20 Tesla field: if your habitat is a torus, you have to put the main coil along the outer circumference, plus a secondary coil along the inner one to cancel the field in the living quarters. With the new high temperature superconductors the mass penalty of the coils is not excessive on a 5000 ton spaceship and you can also enhance the effect inflating the field with small amount of plasma puffs.
You can build a toroidal habitat connected to the axis by four radii. Each radius has a cargo container mounted on a truck and an electric motor that move the container outside and inside to keep the center of mass on the axis, using your cargo as a ballast without extra mass penalty.
For Quaoar re #2 .... Thank you for giving this new topic a robust push out of the cradle!
The mass of Large Ship is (arbitrarily) defined as 5000 metric tons, for the purposes of the various calculations that must be done as the concept develops.
The mass of a single human being is given (by Google) as 62 kg globally, and 80.7 kg in region called North America.
I expect that a member fluent in physics will be able to show the perturbation that ** will ** occur as 62 kg moves about in the interior of the periphery of Large Ship. The issue is not the disturbance caused by a single mass moving about, but instead, the very significant possibility of reinforcing perturbations on the interior of the vessel.
RobertDyck has previously published a suggestion that water might be moved about inside the vessel in response to disturbances of equilibrium, as you have done. Your post includes the concept of "fast acting pumps", which was not included in the earlier post by RobertDyck (as I remember it).
Until a person with advanced physics skills shows up, I am going to assume the potential problems are non-trivial at minimum, and severe if unattended.
A strict discipline of planning coordinated movements of personnel and mass on opposite sides of the axis or rotation seems (to me at this point) to be a requirement for your science fiction novels which make use of rotation to achieve artificial gravity.
Since MOST science fiction writers are NOT physicists, or even familiar with science concepts beyond a single required class in high school, it is not surprising (to me for sure) that NOT one of them (that I have seen so far) has added momentum management into the story line.
You have an opportunity to break that mold, and to achieve some distinction if you explore this aspect of space flight in fiction.
(th)
The problem of momentum management was also addressed by the project team of space habitat Kalpana One, who used long steel cables with weights at their extremity, extended outside the habitat, and fast acting electric motors for real time spin balancing.
Large Ship Prime is: Large scale colonization ship by RobertDyck
This topic is offered to collect knowledge, insights and best practices for maintaining longitudinal stability of the vessel as it flies
"Large Ship" is (arbitrarily) defined as 5,000 metric tons, for the purposes of calculations to be posted in this topic.
Humans have learned how to build and deploy rotating devices for hundreds of years:
Per Google:
Barrel rifling was invented in Augsburg, Germany in 1498. In 1520 August Kotter, an armourer from Nuremberg, improved upon this work. Though true rifling dates from the mid-16th century, it did not become commonplace until the nineteenth century.
Rifling - Wikipedia
en.wikipedia.org › wiki › Rifling
About Featured SnippetsA characteristic of ** all ** rotating devices, from the first bullets to the latest NASA spacecraft (eg, deep space probes) is that mass is distributed inside the device so that momentum about the axis of rotation is even.
The Large Ships, regardless of design, will ** all ** be required by the Laws of Physics to maintain precise control of mass inside (and attached to) the vessel.
It is likely that humans will be able to move about in their cabins without disturbing the stability of the rotating vessel. However, movements between cabins will (I suspect) need to be coordinated with a corresponding movement on the opposite side of the axis of rotation.
Since humans have no experience with this situation, it is understandable that everyone involved in thinking about it may be oblivious of this operational requirement. This is just not something that readily comes to mind.
I asked Google if anyone has been thinking about this anywhere on Earth, and a preliminary result looks encouraging:
Spinning Brains - NASA
www.nasa.gov › vision › space › livinginspace › 23jul_spin
Jul 23, 2004 · Inside a spinning spaceship, on the other hand, there would be an ... In each case, your brain makes on-the-fly Coriolis adjustments.I cannot see this reference from the machine in use at the moment, but I suspect it does ** not ** extend to planning for mass management in a large vessel.
Large aircraft, such as those used by the military to send tanks around the world, employ specialists called "Load Masters". These are generally non-commissioned officers who are responsible for seeing to it that the load to be carried is placed so that the center of mass of the aircraft coincides with the center of mass of the load, so that the pilot can control the machine. An example of an incorrectly positioned load is available in the not-too-distant historical record, when an aircraft took off from an Asian air field (probably Afghanistan) and the pilot was unable to achieve level flight.
The crew of Large Ship will most certainly include the celestial equivalent of the Load Master. Depending upon the sensitivity of the vessel to individual mass movements, the Load Master may have control of movements of passengers and crew outside the cabin.
(th)
If the masses of the passengers and crew is little respect the mass of the whole ship, their movements will have an imperceptible effect on the center of mass, otherwise the ship needs a liquid ballast system with sensors and fast acting pumps, for a real time compensation of the movement of people: in this case, the water ballast may also be used to screen the storm cellar from solar proton events.
Post made for 3-body software in orbital mechanics
I've found this study where is explained how to insert in a Mars prograde orbit coming from Earth, flying over the sunward hemisphere
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fhanspeterschaub.info%2FPapers%2FUnderGradStudents%2FConicReport.pdf&clen=1695636&chunk=true
SpaceX Starship, designed for entering in Earth and Mars atmosphere many times, will have a steel hull, covered with PICA-3 tiles: very sturdy and thermal resistant, but also quite heavy.
I don't know if it is possible to conceive a much lighter pure reinforced carbon-carbon monolithic starship, covered with ablative PICA-3 tiles (or it will be too expensive).
I would like to explore the feasibility of an ablative structural hull, for a one-way spaceship like a cargo or a habitat designed to land on Mars surface and remain there forever: instead to built a steel hull and cover it with ablative tiles, why not to study some kind of fiber reinforced ablative hull economically molded like a GRP saiboat?
Is it feasible?
And if so, which material could be the best candidate for that purpose?
Somebody with access to real 3-body software needs to answer this planetary orbit approach question for both Quaoar and me.
GW
I've no 3-body software but I would try to solve the problem anyway using the patched conic approximation with impulsive maneuvers, given that the laws of mechanic are time and space symmetrical.
Case 1
Let's think to the inverse case: an ideal ship with a prograde and perfectly circular low Earth orbit at 400 km of altitude (orbital radius 6771 km). She fires her ideal rocket over the sunward quarter of the LEADING hemisphere, gaining instantaneously 3.46 km/s of deltaV, and escape in an hyperbolic orbit, flying over the sunward side of the Earth in opposite direction of the planetary motion vector.
When our ship crosses the edge of the Earth's sphere of influence (1,496,505 km of radius) she finds herself at the aphelion of a prograde elliptic Homann orbit direct to Venus.
It's quite easy to calculate the aphelion of this orbit: it is tangent to the asymptote of the escape hyperbola, so its radius is equal to the Sun-Earth distance at the insertion point minus the impact parameter (the distance of the asymptote from the Earth center) of the hyperbola. But I'm not able to do the same with the time, so let's simply call it T and say that our ship reaches the aphelion of the Earth-Venus transfer orbit T hours AFTER the Sun-Earth vector has passed this point.
Surely, the real trajectory of our ship will be different from my approximation, but we have sent many probes to Venus, so we know for sure that this kind of maneuver is possible.
Case 2
So let's imagine to use the other half of the same transfer orbit, traveling this time from Venus to Earth: this time our ship will reach the aphelion T hours BEFORE the Sun-Earth vector will pass this point: our ship will enter in the Earth SOI and find herself on a hyperbolic trajectory whose asymptote is tangent to the aphelion of the transfer orbit.
The arrival hyperbola is exactly specular to the departure one, so our ship will fly over the sunward quarter of the Earth's TRAILING hemisphere, fire her rocket, losing instantaneously 3.46 km/s of deltaV, and insert herself in a prograde LEO.
Even in this case, the real trajectory will be different from my approximation, but if Case 1 is possible (and it is), Case 2 must be possible the same.
With very high-Isp propulsion, is there some reason why you can't approach ahead of or behind a planet, and then slow down or catch up to be "captured" into orbit?
Is that not exactly how we've sent a growing number of these probes to investigate the outer planets and asteroids or comets?
If those Mach-effect thrusters actually work, then it's only a matter of supplying power, rather than propellant. At that point, the solution is to put more power behind the propulsion system or to simply accept longer transfer times and to appropriately shield the ship's occupants from radiation effects.
My novel is set in future where humanity is in decline and has lost interest in space exploration, so even if they live in the year 2222, they still use 1970 nuclear rocket technology with NERVA derived solid core NTR.
After thinking about it, I might well be wrong thinking that one has to enter low orbit in a retrograde direction when outbound from the sun.
Prograde orbital direction at Mars (from Earth) or at Earth (from Venus) is parallel to planetary motion on the shadow side, but opposite it on the sunward side. It is the opposite orbit speed that gets subtracted from the vehicle's "near V" to determine the lower dV, while the parallel orbit speed gets added for the far higher dV.
The analog to the Apollo figure 8 orbital entry (retrograde on the side facing away from Earth) has the apohelion just past the center of Mars (or Earth) for the gravity-driven swing-around into the retrograde orbit direction, on the shadow side.
But, what if your transfer apohelion is a tad short of the center of Mars (or Earth) and you time things to arrive a bit before Mars (or Earth) can get there? The notion is to have the planet gravity pull you from Vfar to Vnear, except toward the planet on the sunward side, ending more-or-less tangent to the adjacent surface, probably around the backside (as referenced to planetary motion direction).
It would take a real orbital trajectory code capable of analyzing 3-body problems, to work this out. But my hunch is that there has to be a way to do this, so that journeys outbound from the sun can still enter low prograde orbits about planets, without incurring huge dV's to do so.
I have no such software. I only have the equations for the 2-body problem solution that is in all the old textbooks. That is what I implement in the spreadsheet stuff, with jigger factors for gravity and drag losses, and the Vnear vs Vfar energy correction for local 3rd-body gravity pull. What I do isn't navigation, it is just estimating reasonable design requirements for vehicle mass ratios.
Somebody with access to real 3-body software needs to answer this planetary orbit approach question for both Quaoar and me.
GW
Thank's GW
Do you know if Mars Reconnaissance Orbiter and other probes insert themselves in prograde or retrograde orbits?
Going from Earth to Mars, when you get to Mars via Hohmann transfer, you are moving parallel to Mars's motion, but slower by around 2 km/s. Mars is trying to run over you swiftly from behind. As the vehicle and Mars get closer, Mars gravity adds to the velocity difference by accelerating the vehicle toward the planet, so you have a lot more speed to deal with than just the 2 km/s. If you land direct, you can use hypersonic friction drag to dissipate the difference in velocities. But you have to strike near tangentially at the edge of the disk, to keep your angle below local horizontal very shallow (around 2 degrees). Otherwise, you have no chance for air friction to slow you, you just snack the planet at interplanetary speeds.
For a prograde orbit about Mars, it is "Mars's speed" plus the orbit speed that you have to deal with. If you look at a retrograde orbit about Mars, then it is "Mars's speed" less the orbit speed that you have to deal with. But the "Mars speed" I am talking about is the oncoming planet's 2 km/s plus the attraction of its gravity as it nears you. Off Hohmann, this is near 5.5 km/s. Low orbit speed is near 3.5 km/s.
So entering prograde orbit your delta-vee is nearer 5.5+3.5 = 9 km/s. Entering retrograde your delta-vee is nearer 5.5 - 3.5 = 2 km/s.That same effect (on a smaller scale) is EXACTLY why Apollo orbited the moon retrograde.
You can estimate the gravitational speed-up effect as the difference "far" from Mars (the 2 km/s difference between Mars's speed and your speed about the sun) using Mars escape velocity: Vnear^2 = Vfar^2 + Vesc^2. Use escape at orbital altitude, not surface escape. They are not the same.
Returning to the Earth is different. Your transfer perihelion velocity is greater than Earth's orbital velocity about the sun, so you are effectively running into the Earth from behind. Correcting for the attraction of gravity, your Vnear at direct entry interface is around 12+ km/s. You need to strike tangential to the disk to have a low trajectory angle below horizontal, in order not to just smack the planet still at 12 km/s.
A prograde orbit is trying to move away from you, so the delta vee to enter it is your Vnear of 12 km/s, less the low orbit velocity of 8 km/s, for about 4 km/s. On the other hand a retrograde orbit is moving toward you as you approach, so that your Vnear of 12 km/s plus orbit speed of 8 km/s produces a 20 km/s delta vee, or thereabouts.
The lesson here is that moving out from the sun, you want to enter a retrograde orbit about your target planet. When moving in toward the sun, you want to ender a prograde orbit. It makes a big difference to the orbital transport ship's delta-vee, and there is no real way around that, that I understand. But I'm no expert.
GW
Thanks GW is ever a pleasure to hear your lessons
So an orbit-to-orbit ship traveling from Venus to Earth in a Hohmann orbit, arrives in the Earth SOI with a hyperbolic speed of 2.5 km/s and reaches the perigee at 400 km of altitude (escape velocity 10.85 km/s) with a speed of SQR(2.5^2+10.85^2) = 11.13 km/s.
The orbital speed at 400 km of altitude is almost 7.67 km/s, so our ship will have a LEO insertion burn of 11.13-7.67 = 3.46 km/s of deltaV if her orbit is retrograde or 11.13+7.67 = 18.8 km/s (!!!) if her orbit is prograde.
18.8 km/s are prohibitive even for a solid core NTR, so our ship is forced to insert in a retrograde orbit as I thought (It's correct?).
It's very difficult to refurbish an orbit-to-orbit ship parked of a retrograde LEO, so a solution may be to insert our ship in a very high elongated retrograde orbit with the apogee at the L1 Earth-Sun Lagrange point (perigee velocity 10.82 km/s) and dock her on a deep space L1 habitat connected by shuttles to LEO: the perigee insertion burn will have 11.13-10.2 = 0.31 km/s of delta V plus almost 0.54 km/s of apogee L1 insertion burn. The whole maneuver has a deltaV of only 0.85 km/s, but the transfer orbit to Earth-Sun L1 adds 37.5 days to our Venus-Earth travel (plus other 37.5 days of shuttle travel from L1 to LEO).
However, the crew can leave the spaceship with a small entry vehicle and perform a direct EDL from the transfer orbit, while the mother ship continues her travel to L1 unmanned.
Could you please explain the detailed physics why orbital insertion would require entering a retrograde orbit? As far as I can see, you could directly enter a prograde orbit.
When I travel from a inner planet to an outer planet, I reach it at the aphelion of my hohmann transfer orbit, and the orbital speed of my ship is smaller than the orbital speed of the planet. So when I enter in the planet SOI, to minimize the deltaV of my insertion burn, I suppose to approach the planet with a retrograde hyperbola facing the dark side and firing my rocket with the nose of my ship in the direction of the insertion orbit...
But, wait a minute: can I also maneuver my ship to enter in the planet SOI with a prograde hyperbola facing the sunlight hemisphere of the planet? It's the same?
In this case the problem is solved.
As a SF writer, I often try to figure a future where interplanetary travels are routine: many scientific station orbit around Mercury, Venus, Earth, Mars, the main belt asteroids and the jovian satellites, connected by big orbit-to-orbit spaceship, like GW Johnson's modular space-train
https://exrocketman.blogspot.com/2013/1 … -2013.html
This kind of spaceships are not supposed to perform atmospheric entry and landing, but only to travel from the low orbit of the planet to the low orbit on another, doing all maneuvers propulsively and being refurbished in orbit by shuttle-tankers.
For a Earth-Mars or Mars-Earth transfer it's perfect, but what happens when this kind of spaceship returns from Venus, using a Hohmann orbit?
As far as I can understand, she is forced to insert herself in a retrograde orbit around Earth, where it's very difficult to be refurbished (a retrograde LEO mission has almost 10.2 km/s of deltaV vs. 9.2 km/s of a classic prograde orbit insertion) and there is also a high risk of satellite debris impact.
So, how to solve this problem, without consuming tons of propellant to invert the orbit?
I figured to insert the spaceship in a very high retrograde circular orbit (200-300,000 km), then make a change of plain, to match the inclination of Moon orbit, perform a fly-by around the Moon and use her gravity to invert the orbit with a half 8 maneuver. At this point we can lower the perigeo at 400 km and circularize the orbit.
A better idea is highly appreciated.
A big problem of NTRs, exposed by GWJ in a precedent topic, is the long duration of start-up and cool-down, which makes them unfit for low delta-V short burns like course correction maneuvers. For that reason the designed-but-never-built NTR spaceship Copernicus was forced to store tons of NTO-MMH for RCS and course corrections.
A potential solution of this problem is the NTR-based OMS system exposed in this study:
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fntrs.nasa.gov%2Fapi%2Fcitations%2F20180006734%2Fdownloads%2F20180006734.pdf&clen=1873598
The NTR is a low enriched uranium NTR derived from the old NERVA. The orbital maneuvering system is tied to the nuclear rocket and uses the same hydrogen propellant, which enters into the core via an auxiliary circuit and is expelled through a secondary nozzle (in a bimodal NTR the core is maintained hot for all the mission to produce electric power, so the OMS system is always ready for use).
This kind of OMS thermal rocket has an exhaust velocity of 5000 m/s, less than the main rocket, which is about 9000 m/s, but far above a NTO-MMH OMS like that of the Space Shuttle, and also has the advantage to use the same propellant of the main engines.
Hi Quaoar, long time no see!
Bigelow laid off all (88) employees in March 2020, blaming it on the pandemic. The expressed intent was to restart and rehire after the pandemic. So far that has not happened. To me, it looks like the pandemic will never end, it will morph into something endemic, like the various flus, mumps, measles, etc.
The longer they stay closed, the more likely it seems to me that they will never reopen. Those layoffs started a decade earlier. It was just the last 88 that went in March 2020. That suggests other troubles besides the pandemic.
GW
Now I'm very busy with mass vaccination program, so I've few time to follow the forum.
I'm very sad for bigelow. They have creativity and their big habitat redesigned with centrifugal decks could be very good for an orbit-to-orbit ship, like your rigid baton.
Happy new year for all from Italy
Just food for thought. I rather liked the Bigelow designs, and am sorry to see them go.
GW
Hi, GW
I heard Bigelow had some trouble during pandemic. Do you think they will not survive?
The ISSI still within Taliban territory, gee whom would have thought...
What are the Taliban doing about it?
ISIS and Taliban probably collaborate, like the good cop and the bad cop. It seems to me to see the same script of the British retreat from Kabul, when Akbar Khan promised to not attack the Brits, but had them massacred by mountain tribes: Oh, I'm sorry guys, they are not my boys!
SpaceNut,
If the previous Captain says the ship needs to set sail in 8 months time, but his successor proceeds to twiddle his thumbs for 8 months rather than preparing the ship and crew to set sail, then leaves half of his sailors stranded onshore while he finally decides to sail the ship home, and blames the previous Captain on top of that, then he's so incompetent that he needs to be relieved of command. If the new Captain disagrees with the previous Captain's sailing schedule, then he's obligated to adapt his plans accordingly. Since we left Afghanistan, the new Captain clearly didn't disagree with the previous Captain's plan, but he totally and incomprehensibly botched an otherwise simple plan to set sail.
Your pithy metaphor doesn't work here. I hope you know that. More than 10,000 of our people, your fellow Americans, are now trapped behind enemy lines, subject to the tender mercies of a bunch of ruthless bloodthirsty savages. Every single time the Democrats are presented with an opportunity to show some real leadership, all we get is total apathy and nihilism. Their apologists can never seem to explain why they do what they do, because it doesn't even make sense to them.
I'm not a supporter of the Donald, but it has to be said that he never trusted the Talibans: he only trusted his bombers, he kept ready to take-off and destroy all the poppy fields if they broke the agreement. But his successor demobilized the air force, abandoned all the air bases and all know what happened next.
For Quaoar re #95
Your comment is interesting.
As a medical doctor, you might be able to imagine yourself in the position of a commander of a unit.
If the medical director of your facility commands you to remove yourself and your staff in an emergency, you would follow the orders.
If the medical director commands you to bring patients with you while saving staff, you would follow those orders.
In this case, the US (Donald Trump) had negotiated removal of US troops if the Talliban would stop shooting at them.
Donald Trump DID NOT negotiate for removal of civilians, let along Afghan nationals.
The Talliban kept their part of the bargain, and so did the US military, following the orders of Donald Trump.
There are some who might argue the negotiations with the Talliban were poorly done, short sighted and a disaster waiting to happen.
In the present circumstance, the negotiated plan was executed, disaster ensued, and troops returned to the disaster scene to save as many as possible.
Recriminations will echo for decades, but the goal of the negotiations was to stop the killing of American soldiers, and that seems to have been achieved.
(th)
Trump may have his faults, but now the commander in chief is Biden, and he had the moral duty to protect at least US citizens (if not US allies), but he failed to do it. Leaving 15000 Americans in the hands of these barbarians who will likely use them as hostage is not a good result.
I've never been in the military, but common sense suggests to firstly bring home all the civilians then take out the soldiers, not vice versa.
For SpaceNut re #91
There are some interesting aspects of the present situation .... The gent who is (apparently) heading up the Talliban these days was a co-founder with the original leader. They both attended an islamic school, and they developed the Talliban concept when the Soviets were on their adventure. He spent several years in a Pakistani prison, apparently at the request of the United States. Then, (apparently) the Trump administration requested his release from prison, and negotiated with him to enable the US to wind down operations in Afghanistan. The deal was that the Talliban would not continue killing Americans, and the Americans would get out.
That is more or less what happened.
The publicity campaign orchestrated from the media facilities of the former Afghan government was (according to reports) professionally done.
However, NO one interviewed in the coverage I saw thought that the pretty words of the Talliban leader has anything to do with what is to come.
The best guesses I heard were that the Talliban will restrain themselves while the US pulls any and all opposition out of the country, and then lower the boom.
The one assurance that most pundits thought the Talliban ** would ** keep is to NOT allow attacks on other nations from Afghanistan. That would be astonishingly stupid, and stupid these folks are not.
(th)
The Talibans promised to be peaceful and non violent, then in Jalalabad they massacred a crowd of protesters (maybe their concept of non-violence is just a bit different from ours). I also have seen a video where Afghan soldiers were executed by the Talibans after surrendering. And that's only the beginning.
US has blocked the Afghan government founds in Americans banks, but almost 15000 US citizens are still in Afghanistan: I strongly hope to be wrong, but it's not so unreal to foresee a very sad scenario where hostages are held for years in exchange for unlocking the money.
Very accurate kbd512 assessment of the situation in Afghanistan, its the next few months to years that will tell of the choices we and others have made....
Seems the Taliban are willing to not interfere with Kabul evacuations resume while Biden defends U.S. withdrawal
Do not pay attention to what your enemy says but to what he does
Sun Tsu
NASA unfortunately, seems to believe that ANY degree of risk is unacceptable. After frying Grissom, et. al. and losing 2 shuttles with crew, they've become too risk adverse.
"If you are looking for perfect safety, you will do well to sit on a fence and watch the birds"
Wilbur Wright
I just read this article yesterday and afterwards it hit me that this could contain a partial answer to the Fermi Paradox regarding alien civilizations. The various planet finding studies have shown that a preponderance of rocky planets seem to be "Super Earths" and are considerably larger that Terra. That means a huge gravitational well from which chemical propulsion rockets would be unable to escape. If they cannot get to space, then they can't be traipsing around the galaxy to visit other planets. Here's the article as published in Space.com: https://www.space.com/37414-earth-50-pe … stuck.html
SpaceNut; not sure this post should be in this category so feel free to move to a more appropriate venue, should one exist.
Living on a superearth is not such a disadvantage as we usually think: orbital deltaV and gravitational acceleration are greater, but intelligent aliens can develop some kind of very efficient laser ablative propulsion, just separating the power source from the spaceship, and reach the space more efficiently and eco-friendly than us. If the superearth is in synchronous rotation near a red dwarf star, it has a highly insolated substellar zone and permanent winds from the light and the dark hemisphere, so our hypothetical aliens will likely develop a civilization based of sustainable wind and solar power rather than fossil fuels, with far less risk of self-destruction due to climate change and climate disaster-induced wars (one of the possible solution of the Fermi Paradox is that technological civilization annihilate themselves when fossil fuels run out).
Mastering laser and photovoltaic technologies will probably bring them to develop efficient laser-sail, opening the doors for interstellar travels
For Calliban re #3
SearchTerm:Turbine wind - design considerations in general and for Mars in Particular see #3 above
SearchTerm:Wind turbine design equation with explanation(th)
An evolution is the bladeless vertical Tacoma Vortex, which oscillate in the wind moved by Von Karman vortex.
The mole thing was a ridiculous design from the word get-go. Nothing like that has ever been seriously proposed for use here on Earth. Why would it ever work on Mars?
Answer: it could not possibly work in most real-world scenarios.
And what could it possibly do if it encountered a big underground rock on Earth, or on Mars?
Answer: nothing.
I saw a report on AIAA's "Daily Launch" that confirms some other reports I had seen: the weather station and seismology instruments work just fine, but the mole and its related heat flow sensor instrumentation have proven to be a total failure, after 2 desperate years of trying. The lander is still operational, in terms of those weather and seismology instruments.
To drill through any kinds of soils and rocks requires a twisting drill. That drill requires both a torque to turn, and an end load to penetrate. Those forces and torques are the same to penetrate the same kinds of rocks, anywhere in the solar system, regardless of the local gravity. It is a question of material strength. We already know how to apply both adequate torques and adequate end loads, using hydraulics or electrics, for many kinds of rocks and soils.
The problem is the resisting reaction forces, especially in low gravity environments. That is elementary statics. Those reaction forces depend almost exclusively upon weight and the related friction. Which in lower gravity requires more dead-load mass than on Earth. On Mars, the dead-load mass is 1/0.37 = ~2.7 times higher mass, to achieve the same weight force, and same friction force, by which to supply the same reactions for torque and end load on the drill.
As a corollary, for an asteroid with 0.01 gee surface gravity, you need factor 100 times larger mass. At 0.001 gee surface gravity, you need 1000 times the mass. On the moon at 0.165 gee, you will need 6 times the mass. At essentially zero gravity, you would need an infinite mass.
That is just what it takes to make a real drill bit rig work. Period. There simply is no way around that sort of physics.And before you say "just stake it down", take a moment to think through what it really takes to "stake something down". You still have to supply the same end load to penetrate a soil or a rock with a stake. That's just what it takes to bust your way through this stuff, whatever it is.
Now, once you have done that, what holds the stake in the material that you just penetrated?
Friction! Friction that depends upon the weight (not the mass !!!) of the material adjacent to the stake.
Stake forces in very low gee are simply going to be negligible. And there is no way around THAT little piece of inconvenient physics, either.
These same arguments apply to bulldozer blade (or bucket) operation on Mars, too.
GW
Is it possible to drill in an asteroid using upward firing rockets to simulate the gravity load?
Quaoar, that is an interesting question. The pressure inside the bulb will change dramatically as the mixture heats up during startup. It would need to be much less than 1bar under shutdown conditions. The limit in total pressure that you have stated, would limit the chamber pressure to no more than 2bar. Surging of gas outside the core is unlikely to be acceptable, as it would lead to reactivity swings. So I think it is safe to say that whilst the light bulb could have excellent ISP, it is a relatively low thrust propulsion system.
Another problem with the light bulb is that rapid thermal transients would result in thermal gradients in the glass that would fracture it. Heat up and cool down need to be slow. It also raises questions of how the engine can tolerate large temperature differences between the propellant gas on the outside and fission core gas on the inside. If the bulb is hot enough, it will become more ductile and less brittle, but loses a lot of tensile strength. The general conclusion seems to be that propellant gas must be relatively diffuse to avoid high rates of heat transfer (and erosion) of the glass. That implies a low chamber pressure, probably no more than a few mbar and low power levels overall. All unanswered questions in my mind. But this sounds like a low thrust propulsion system, with thrust levels similar to electric propulsion.
The trick is that the hot uranium plasma fuel never touches the quartz wall because there's a cold neon vortex between them. But the problem is about the pressure difference between the chamber and the bulbs: I don't know how much pressure a quartz bulb can withstand but if the chamber pressure at full thrust is 500 atm, the pressure inside the bulb must be almost the same, and when chamber pressure decreases during the cool-down the pressure inside the bulb must decrease with the same rate, otherwise the bulb might explode or implode.
The reference design has a mass of 15800 kg, a thrust of 596.7 kN and a Isp of 1826 s with an expansion ratio of 545, a chamber temperature of 6667 K and a chamber pressure of 500 atmosphere.