#195 - Jack van Loon - Artificial Gravity
This week we are joined by Jack Van Loon talking about the ethics of gravity deprivation. We cover some of the basics of gravity and how it might be simulated in a spaceship.
A person moving in zero gravity feels a pitiful helplessness. One wrong move and you find yourself spinning wildly. Everyone becomes a baby again in outer space, laboriously learning how to walk.
Prof. Dr. Ulrich Hans Walter
German physicist/engineer and a former DFVLR astronaut.
Jack J.W.A. van Loon obtained his PhD in bone cell biology and mechanosensing at the Academic Center for Dentistry (ACTA) at the VU-University in Amsterdam and has experience in space and gravity-related research for more than a quarter of a century. In this time he was Co-I and PI of several space experiments onboard the Shuttle, Bion, Soyuz the ISS and parabolic flight. He was experiment coordinator for all life sciences and educational experiments for the Dutch Soyuz mission DELTA (astronaut André Kuipers) In 2017 he received the ELGRA Medal for his exceptional contributions to the field of Gravitational and Space Life Sciences Research. In the same year he received from the International Academy Of Astronautics (IAA) an award for the book “Generation and Applications of Extra-Terrestrial Environments on Earth" and is a cooperating scientist at the TEC-MMG Lab of the European Space Agency (ESA) technology centre, ESTEC, in Noordwijk, the Netherlands.
Congratulaitons to China and UAE
Both have launched successfully.
Hope on the Japanese H-IIA on the 19th July
Tianwen-1 on the Long March 5 on the 23rd July.
Hopefully, the Americans will launch Perseverance/Ingenuity on 30th July on an Atlas V (the plutonium has been loaded)
Jack J. W. A. van Loon et al.
Is it ethical to withhold gravity? No, it is not! Career space workers, as well as future space tourists, should be provided with adequate levels of gravity in order to mitigate or completely abolish the microgravity-related pathologies we currently see. It is technologically feasible and financially achievable but most of all unethical not to do so.
We can lick gravity, but sometimes the paperwork is overwhelming.
Wernher von Braun
Our interview today is about the ethical necessity for gravity and how it is not acceptable to expect astronauts to put up with the ill effects from the lack of gravity.
If we were talking about how radiation makes the muscles decrease in mass by 30% after only a 100 days in space, that radiation is causing astronauts to have impaired vision, the hearts are changing shape and getting weaker, the blood is reducing in volume, that radiation was causing astronauts heads to expand, That radiation is causing your bones to leach away and release calcium into your soft organs tissue, that the immune system gets massively compromised. ..you would be terrified and scared of going to space, but Gravity deprivation IS absolutely causing all those things. I don’t know why we find it so much more terrifying when radiation causes illness than when other things do. The funny thing is Radiation will also be REALLY bad news for astronauts on a trip to mars ...but today is about gravity.
So what do we need to know.
Well here on Earth Gravity is the force that we perceive as the force that holds us to the floor, it’s actually a fictitious force ...but we’ll come to that later.
Newton was the first person to get a grip on gravity and got a pretty good equation for apples fall on your head. But Einstein is the true master of gravity. He noticed that it’s actually in possible to tell the difference between gravity and acceleration at 1G if you can’t see out the window. The equivalence principle, this led him to realise that maybe the force of gravity is a bit like the force you feel in the car when turning around a tight bend, and the tight bend is actually the curving of spacetime, caused by the mass of the palate literally bending the spacetime and creating a gravity well. This is best demonstrated by the heavy ball on a rubber sheet and objects getting in obit around it.
So what did I mean by fictitious force, well it is all about frames of reference and when you are driving in a car around a bend it actually feels like you are being pushed away front the bend, but there isn’t really a force, it’s just you want to go in a straight line, the same can be said of the Coriolus effect which was space word of the week episode 121. Quick recap, if you were to launch an Ariane 6 from CSG but instead of launching east and using the spin of the earth to get you a free bit of speed, you went due north, the Vega rocket would have the speed of the spin of the earth at the equator about 1000mph, but as it flies north it will still have this 1000mph east speed, however, the earth below the further north you go the slower it is going. About 766 mph at New York, so the rocket will be bending to the right, just like winds do in fact which is why all hurricanes north of the equator rotate anticlockwise and all hurricanes south rotate clockwise. Coriolis will become important later.
Anyway back to Einstein equivalence principle if we can’t tell the difference between acceleration and gravity lets just accelerate at 1g and have artificial gravity, er not practical ….although if you could find the energy to do this it would be great for interstellar travel and even across the whole milky way, but let’s not get sidetracked.
Astronauts, when they go to the international space station, feel lots of fictitious forces, they certainly feel real. But the acceleration of the rocket in the first place gives them 3Gs, plus the normal acceleration due to actual gravity. But the gravity on the international space station is almost the same as it is on earth, but it is free-falling, and so are the astronauts inside, but it just so happens that it is moving very fast 17100mph so that it keeps missing the earth as it falls.
So they experience microgravity, which is great for experiments and stuff, but terrible for the health. So what can be done!
Well, we’ve talked about linear acceleration, like in the rocket, being identical to gravity, well what about a rotating structure like in sci-fi and use the old centrifugal force.(the transmission of centripetal acceleration via normal force in the non-rotating frame of reference)
Artificial gravity can be created using a centripetal force, ie directed towards the centre of the turn, required for any object to move in a circular path. In the context of a rotating space station, it is the normal force provided by the spacecraft's hull that acts as centripetal force. Thus, the "gravity" force felt by an object the centrifugal force perceived in the rotating frame of reference as pointing "downwards" towards the hull. In accordance with Newton's Third Law, the value of little g (the perceived "downward" acceleration) is equal in magnitude and opposite in direction to the centripetal acceleration.
Put another way the force (centrifugal) you feel pushing you down onto the floor of the spacecraft, is really the fictitious counterpart of the force (centripetal) of the hull stoping your body going in a straight line. Like the seat of your car.
So let’s build rotating space craft.
How big is the structure?
The G you can achieve is related to two components, how fast you are spinning and how far from the centre you are.
Unlike gravity the force pushes out from the centre and the centrifugal force is directly proportional to the distance from the center of the habitat. With a small radius of rotation, the amount of gravity felt at one's head would be significantly different from the amount felt at one's feet. Like the tidal forces of a blackhole essentially.
Similarly the linear velocity of the habitat should be significantly higher than the relative velocities with which an astronaut will change position within it. Moving in the direction of the rotation will increase the felt gravity (while moving in the opposite direction will decrease it)
Then there is the coreolis effect, unlike a linear acceleration there is no equivalence principle, If you move your head you vestibular system will really feel this change in velocity and you will probably be sick.
So there is a sweet spot that takes spin rate, radius, coreolis and a few other things into account. And it’s pretty much bad news when it comes to cost.
In other words radius big enough that you can stand and your head won’t be in no gravity and your feet in 1 g, say about 2m! Needs probably to be about 20m at least for that alone.
But there are two types of movement sickness, moving with the movement of spin would make you either feel lighter or heavier, we can cope with this well, and actually maybe not notice, unless you are throwing a ball. But moving across the direction of travel causes lots of issues, and that may constrain things enormously, as you feel like your being tipped over. Also experiments have shown that in rotating rooms, people just can’t get used to anything rotating faster than 1RPM, it makes you sick. But experiments have been only done on earth so maybe this sickness has been exaggerated as the room is always spinning at a right angle to gravity so it could be that you can get used to 6rpm. Meaning that you could have a 20m radius spinning space ship at 6rpm say.,
Let’s have a look at 2 recent proposals.
Nautilus-X (Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration)
rotating 12m diameter wheel space station concept
Mark Holderman and Edward Henderson of the Technology Applications Assessment Team of NASA.
Cost 3.7 billion dollars (cheaper than the Orion capsule) for the spacecraft version
Using off the shelf parts, like bigelow inflatables
5 years build time
6.5m x 14m corridor that is the inside of a hoop
The centrifuge includes both "inflatable and deployed structures" and could "utilize Hoberman-Sphere expandable structures".
The rotational hardware would be derived from Hughes 376 spin-stabilized ComSats..
The centrifuge would first be tested on the ISS. The estimate of the cost and time: "<39 months $84-143M" for a 9.1m diameter version.
"impart Zero disturbance to ISS micro-gravity environment ".
The goal is to deliver the system with a single Delta-IV/Atlas-V launch.
2011 worked stopped on this project :(
Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion
Craig H. Williams, Leonard A. Dudzinski, Stanley K. Borowski, and Albert J. Juhasz
Glenn Research Center, Cleveland, Ohio
A conceptual vehicle design enabling fast, piloted outer solar system travel was created predicated on a small aspect ratio spherical torus nuclear fusion reactor.
The initial requirements
could deliver a 172 mt crew payload from Earth to Jupiter rendezvous in 118 days,
with an initial mass in low Earth orbit of 1,690 mt.
Engineering conceptual design, analysis, and assessment was performed on all major systems including artificial gravity payload, central truss, nuclear fusion reactor, power conversion, magnetic nozzle, fast wave plasma heating, tankage, fuel pellet injector, startup/re-start fission reactor and battery bank, refrigeration, reaction control, communications, mission design, and space operations.
Detailed fusion reactor design included analysis of plasma characteristics, power balance/utilization, first wall, toroidal field coils, heat transfer, and neutron/x-ray radiation.
Technical comparisons are made between the vehicle concept and
the interplanetary spacecraft depicted in the motion picture 2001: A Space Odyssey
The crew payload was comprised of three rotating Laboratory/Habitation (Lab/Hab) Modules
attached to the fixed Central Hub via three connecting Tunnels (Figure 7).
A three-module configuration was recommended to reduce dynamic instability in the rotating structure.
The Lab/Hab Modules were the primary laboratory and habitation facilities for the crew, and where most of the astronauts’ time would be spent in a constant 0.2 g artificial gravity environment.
They were 7½ m in diameter, of sufficient height to permit a two-story layout, and each contained crew accommodations for at least four crewmembers, as well as scientific, health care, and recreation equipment
Discovery II keeps a Martin Marietta design parameter of a 17 m rotation arm, though a lower rotation rate of 3.25 rpm was used to produce an artificial gravity level at the Lab/Hab floor of only 0.2g.
Artificial gravity (g’s) 0.2
Rotation rate (rpm) 3.25
Rotation arm (m) 17
Maximum walking-to-rim speed ratio 0.17
Radial gravity gradient (milli-g’s/m) 12
The amount of artificial gravity required for crew health has been the subject of considerable study, however, insufficient experimental data exists to answer with certainty even the most basic design questions affecting human physiological wellbeing.
It is this lack of basic human health effects data that drives spacecraft designers to consider other effects, such as locomotion, in order to at least bound the design problem.
In general, it is thought that a minimum of 0.2g (~lunar gravity) might be sufficient to at least facilitate locomotion based on the Apollo experience.
Radial Coriolis forces can become a problem when the maximum walking speed is greater than ~1/4 of the maximum rim speed (if the motions are collinear).
Tangential Coriolis forces can become a problem when an astronaut moves (or moves another object) in the radial direction (i.e., from the artificial gravity region towards the zero-g hub) when the gravity gradient changes significantly with respect to the height of the astronaut.
Thus acceptable rotation speed and radius parameters are interrelated and require more assessment of human physiology and locomotion requirements.
Human subjects have shown to be readily adaptable to rotation rates up to 6 rpm (up to 10 rpm if given specialized training).
To minimize Coriolis effects, the corresponding minimum rotation arm was also thought to be at least 15 m.
Smallstars a Youtuber, does an amazing video using Starships as artificial gravity
3 starships to be precise. The goal of the Gravity Link Starship concept is to provide a spin gravity that re-uses the main engines, taps leftover fuel, and avoids impractical space construction and spacewalks.
The GLS is basically a hub ship, like the hub of a wheel. Instead of humans and cargo, the payload bay of the GLS is filled with truss that can robotically fold out and lock into place serving as the wheel's spokes.
Once on the way to a distant destination like Mars, 2 Passenger Starships will make their approach to the attachment points at the ends of the deployed truss. Once attached, one Starship remains fixed while the other one slowly rotates its orientation on its swivel joint.
At this point the main engines will facing opposite each other and will be used to spin the system, thus creating a centripetal force equal to Earths' gravity.
When the desired spin speed and by extension amount of artificial gravity force is achieved, both Starships will swivel themselves into a resting position which is an orientation in line with the truss so that gravity is pulling in the correct direction, down towards the bottom of the ships.