Tag: space exploration

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The Sagan Paradox, Chapter 5: Cosmos Eating Space Probes and Sagan’s Response

SELF-REPLICATING PROBES

In the context of the Extraterrestrial Intelligence Search, in 1980 the mathematical physicist and cosmologist Frank J. Tipler published a paper, “Extraterrestrial intelligent beings do not exist.”

Reference: Extraterrestrial intelligent beings do not exist, Tipler, F. J.

Tipler sought a universal principle to explain the Fermi Paradox: the apparent absence of extraterrestrial beings on Earth. He contended that if extraterrestrial intelligent beings existed, then their manifestations would be obvious. Conversely, since there is no evidence of their presence, they do not exist.

Von Neumann Probes

Frank Tipler argued that if any extraterrestrial civilization ever built self-replicating von Neumann starprobes, those probes would grow exponentially. They would fill the galaxy in a few million years. Since we don’t see them here, Tipler concluded there are no other intelligent civilizations.

  • Tipler assumed each probe would land on a new world and make just one or a few copies before moving on. However, he had no reason to limit its reproduction so drastically.

  • Even if each probe were only 10 grams and doubled once per decade, in about 150 generations we’d have the mass of an entire galaxy. This conversion to machines would be on the order of 1 followed by 54 zeros grams (1 quindecillion tons). Moreover, this transformation would occur in less than 15 million years.

  • Because we see no evidence of such galaxy-eating machines anywhere, Tipler said no one else ever invented them. Therefore, no one else is out there.

SAGAN’S RESPONSE

Carl Sagan pondered the arithmetic of Tipler’s solipsist argument. His response is a classic in the realm of science and philosophy. He draws attention to the limitations of our current knowledge and the vastness of the universe. By stating, “Absence of evidence is not evidence of absence,” Sagan cautioned against jumping to conclusions based on what we don’t know.

Sagan and William I. Newman challenged Tipler’s assumptions and conclusions, proposing a more realistic colonization model based on population growth and organization. This alternative model estimates a galaxy-crossing time of approximately one billion years, significantly longer than Tipler’s few million years.

Sagan further suggests that self-replicating probes are subject to evolutionary divergence, imposing unacceptable risks to altruistic extraterrestrial intelligent life (ETI). The ETI only communicate with other ETI through signals. This argument assumes that self-replicating machines are essentially uncontrollable because they must evolve.

Sagan and Newman also propose that the emergence of powerful weapons of mass destruction may impose a universal brake on unchecked expansion. This could potentially limit the spread of advanced civilizations. Ultimately, they emphasize the importance of experimentation in resolving the Fermi Paradox. Systematic searches using radio telescopes and other tools are necessary to settle the question of whether we are alone in the universe.

Reference: The Solipsist Approach to Extraterrestrial Intelligence, by Sagan / Newman 1983QJRAS..24..113S Page 113

Terrestrial Shortsightedness

Imagine New York in 1894, its streets choked with the clatter of hooves. Its futurists were drowned in calculations of manure. They predicted that by 1944 New York would drown in horse manure.

The futurists only saw linearity: more carriages, more waste, an apocalypse of filth. However, they could not fathom the silent revolution already stirring—the internal combustion engine, the horseless carriage—a paradigm shift that would render their equations relics.

So too might we falter when envisioning the starfarers of tomorrow. To assume interstellar travel or contact must devour suns is to chain possibility to the physics of this moment. What of the technologies unimagined? The spacetime shortcuts, the dark energy harnessed, the self-replicating probes born of nanoengineering? The cosmos whispers of mysteries we have yet to decode.

Carl Sagan may have cautioned Tipler that his reasoning could mirror that of the horse-cart prophets. One may fail to see beyond the boundaries of the known. The universe is not merely a puzzle to solve with present tools. It is also a frontier that reshapes the solver. As we once tamed fire and split the atom, so too might we one day dance with the fabric of spacetime itself. The answer to the Fermi paradox may not lie in the scarcity of civilizations. It may lie in the humility of our assumptions.

After all, the stars are not merely endpoints. They are teachers. Their greatest lesson might be this: To traverse the light-years, we must first learn to think in ways as boundless as the dark between galaxies.

Reference: The Great Horse Manure Crisis of 1894
By the late 1800s, large cities all around the world were drowning in horse manure. The London Times predicted in 1894 that in 50 years’ time, every street in London would be buried under nine feet of manure.
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Can We Have Artificial Gravity In Spacecraft?

Why has nobody built rotating spacecraft to simulate gravity?

Pictured: a fairground ride from the 1950’s, I call it a GRAVITY DRUM.

A whole spacecraft is expensive to rotate, but small spaces on space stations or ships could easily be rotated.

Can those small spaces be big enough to provide meaningful and healthy artificial gravity?

From my physics knowledge I recall that gravity and acceleration are the same.

If I remember correctly, 1 g is equal to an acceleration of 9.81m/sec per second. In other words, a wheel with a circumference of 10 meters would have to be spun about once per second to simulate 1 g in Zero gravity? Not quite.

Alas, it’s a bit more complicated than that, and thankfully we don’t have to spin the wheel quite so fast. That’s a bonus!

Here are a few handy calculators to work out wheel sizes and rotation rates to simulate Earth gravity:

SpinCalc, solves for gravity, radius and rotation rate,

Circle Calculator, solves for diameter, radius and circumference.

A wheel with a circumference of 10 meters would have a diameter of 3.18 meters. This would be a handy size for artificial gravity experiments, even on Earth.

Would it be comfortable to spend any time in this? The wheel should rotate at about 24 RPM to simulate 1 g. It could be compartmentalized in to 1 x 2 meter beds, holding ten crew.

So at least during their rest period spacefarers would have the benefit of normal gravity. The astronauts are lying on the inside of the wheel, a bit like in the fairground ride illustration but with more privacy.

Is it feasible to built such small Drum Gravity units?
How would the human body react? (Artificial Gravity by Centrifuge).

We know that the negative effects of zero gravity are really serious and numerous. Even 2.5 hours of daily treadmill exercise are insufficient to prevent these effects:

  1. fluid redistribution: Bodily fluids shift from the lower extremities toward the head. This precipitates many of the problems described below .
  2. fluid loss: The brain interprets the increase of fluid in the cephalic area as an increase in total fluid volume. In response, it activates excretory mechanisms.
  3. electrolyte imbalances: Changes in fluid distribution lead to imbalances in potassium and sodium and disturb the autonomic regulatory system .
  4. cardiovascular changes: An increase of fluid in the thoracic area leads initially to increases in left ventricular volume and cardiac output. As the body seeks a new equilibrium, fluid is excreted, the left ventricle shrinks and cardiac output decreases.
  5. red blood cell loss: Blood samples taken before and after American and Soviet flights have indicated a loss of as much as 0.5 liters of red blood cells.
  6. muscle damage: Muscles atrophy from lack of use. Contractile proteins are lost and tissue shrinks. Muscle loss may be accompanied by a change in muscle type.
  7. bone damage: Because the mechanical demands on bones are greatly reduced in micro gravity, bones essentially dissolve.
  8. hypercalcemia: Fluid loss and bone demineralization conspire to increase the concentration of calcium in the blood.
  9. immune system changes: Loss of T-cell function may hamper the body’s resistance to cancer — a danger exacerbated by the high-radiation environment of space .
  10. interference with medical procedures: Bacterial cell membranes become thicker and less permeable, reducing the effectiveness of antibiotics.
  11. vertigo and spatial disorientation: Without a stable gravitational reference, crew members experience arbitrary and unexpected changes in their sense of verticality.
  12. space adaptation syndrome: About half of all astronauts and cosmonauts are afflicted. Symptoms include nausea, vomiting, anorexia, headache, malaise, drowsiness, lethargy, pallor and sweating.
  13. loss of exercise capacity: This may be due to decreased motivation as well as physiological changes.
  14. degraded sense of smell and taste: The increase of fluids in the head causes stuffiness similar to a head cold.
  15. weight loss: Fluid loss, lack of exercise and diminished appetite result in weight loss. Space travelers tend not to eat enough.
  16. flatulence: Digestive gas cannot “rise” toward the mouth and is more likely to pass through the other end of the digestive tract “very effectively with great volume and frequency” .
  17. facial distortion: The face becomes puffy and expressions become difficult to read, especially when viewed sideways or upside down.
  18. changes in posture and stature: The neutral body posture approaches the fetal position. The spine tends to lengthen.
  19. changes in coordination: Earth-normal coordination unconsciously compensates for self-weight. In weightlessness there is a tendency to reach too “high” .

Compared to these adverse effects of zero gravity, here are some studies by a psychologist named Graybiel from 1977 on the effects of rotating a human on his own axis here on Earth, like on a spit (from https://psycnet.apa.org/record/1980-22567-001).

GRAYBIEL ROTATION COMFORT ZONES

Graybiel concluded that 
1.0 RPM: even highly susceptible subjects were symptom-free, or nearly so
3.0 RPM: subjects experienced symptoms 
5.4 RPM, only subjects with low susceptibility performed well
10 RPM, adaptation presented a challenging but interesting problem. Even pilots without a history of air sickness did not fully adapt in a period of twelve days.

The “adaption” that Graybiel is talking about is the getting used to the absence of the rotation, after the body had been spun.

What that feels like we all remember from childhood.:

Pirouette

I must say that spit rotating a human on his own axis in the horizontal under the influence of Earth gravity is most likely to be very far removed from what a human may experience in an artificial gravity drum in weightless space.

I’d go as far as to say that Graybiel’s rotation comfort zones have absolutely nothing to do whatsoever with artificial gravity by centripetal force. All he proved in his paper “Somatosensory motion after-effect following earth-horizontal rotation about the Z-axis” is that the after effect of spinning someone rapidly is disorientation of the vestibular system of the ear, leading to dizziness, aka vertigo.

But let’s see if these Graybiel’s comfort zone figures can be applied.
The SpaceX Mars rocket is going to have a diameter of 9 meters. Would it be possible to create a comfortable habitat for sleeping or resting spacefarers within the confines of this rocket?

A 9 meter drum would need to rotate at 14 RPM to simulate 1 g, or at 8 RPM to achieve 1/3 of Earth gravity. Graybiel’s findings would indicate that the space available on the SpaceX Mars rocket would be too small.

However, I believe that the gravity (centripetal force) acting on the body as it lies down, not spinning about itself and on one level , will be more comfortable than twirling rapidly around one’s own axis.

In Drum Gravity Bed Units there would be no head-to-foot acceleration gradient.

DRUM GRAVITY BED UNITS
The drum gravity bed units are conceived of as an add-on module to a spacecraft or space station, be it in transit, orbit or on the Moon, Mars or asteroids to provide more natural gravity.

Have prototypes of this concept been built?

In a certain way: Yes! The first picture in this post is a fairground attraction from the 1950’s.

Did humanity really forget from the ’50s how easy and fun it is to enjoy artificial gravity? Apparently the fairground visitors subjected themselves to the experience voluntarily and enjoyed it.

“Rotor Ride”

Simple gravity devices like this could help spacefarers to maintain their health, after the device is tweaked.

A BIGGER MODEL

Rotating wheel space station — Wikipedia

Here are the calculations on the von Braun wheel from 1952 used in the movie 2001: A Space Odyssey:

They envisioned a rotating wheel with a diameter of 76 meters (250 feet). The 3-deck wheel would revolve at 3 RPM to provide artificial one-third gravity. It was envisaged as having a crew of 80.

Fast forward 70 years (not much has happened since the 1950’s):

SAHC HUMAN CENTRIFUGE
The SAHC human centrifuge began testing and operations in about 2020. It’s to investigate the tolerability and use of artificial gravity on astronauts and their health, to counter the effects of weightlessness. What’s taken so long?

The machine measures 5.6 meters in diameter. 
It would be small enough to put in the SpaceX Mars rocket. But it needs a few more seats.

https://www.dlr.de/me/en/desktopdefault.aspx/tabid-1961/2779_read-14523/

Centrifuge with lying test person

–

With the Short-Arm Human Centrifuge (SAHC) in Cologne — provided by the ESA — artificial gravity will be created to afford fundamental research in medicine and human physiology. The main focus is on the possibility to extend e.g. bed-rest studies to test methods of artificial gravity based counter-measures for medical risks due to weightlessness.

Technical data:

Max. radius at outer perimeter: 2,8 m
Max. overall payload: 550 kg

Max. centrifugal acceleration
(foot level, test subject height 185 cm): 4.5 g
Max. revolution of centrifuge rotor
(software limit): 39 rpm

Scientific applications

  • Development of effective countermeasures for neuromuscular and skeletal degeneration of astronauts using Artificial Gravity, etc…

This is an article by Erich Habich-Traut for the Contact Project,
https://contactproject.org

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