# Physical effects of microgravity

Astronauts experience increased blood to the upper body as well as optical problems while in a state of free fall being in a micro gravity environment.

My question is whether they would encounter the same biologic effects if orbiting at L1 or in interstellar space with the absence of the gravitational pull of a large mass? Has NASA ever considered this or are they going to keep trying to figure out why there blood moves to their heads while endlessly riding a roller coaster?

• What is the "roller coaster" to which you are referring? What is the "large mass" of which you say the gravitational pull would be absent at L1? – Anthony X May 4 '16 at 0:44
• Anthony the large mass in this case is the earth. L1... point at which the gravitational pull of earth is equal to that of the sun .theoretically a point of 0 g neither + or Minus – dennis schaffert May 4 '16 at 1:54
• Anthony I should add the analogy of a roller coaster is in relation to the down hill ride when hopefully one has not eaten to much before hand the G force encountered.some call it the thrill of the ride – dennis schaffert May 4 '16 at 1:59
• Are you asking whether the microgravity which could be experienced at L1 is different to the microgravity which could be experienced in low Earth orbit? – Anthony X May 4 '16 at 2:40
• @dennisschaffert Even at Earth-Sun L1, you would still experience the gravitational potential from every other particle in the universe, even if Sun and Earth's gravitational pulls cancelled each other, but this would still be minuscule. Though my understanding was that a majority of the blood circulation issues had to do with having to do less work with your muscles in a microgravity environment, not so much the constant free fall, so you could try finding a source on this claim? – V-J May 4 '16 at 10:11

There are lot of differences between a space station in LEO versus one in a pseudo-orbit about L1, cost and radiation hazard being two of the biggest. However, gravity is a non-factor as far as humans are concerned. People don't feel gravity. (No local experiment can, per Einstein's equivalence principle.) People and accelerometers instead feel everything but gravity.

In the case of people on the surface of the Earth, what they feel as "weight" is instead the normal force exerted by the ground on them. Our bodies depend in many ways on this sensible force being present. This normal force is not present in a non-rotating space station, whether that space station is in low Earth orbit, in a pseudo-orbit about the Earth-Moon L1 point, or on the way to Alpha Centauri.

"endlessly riding in a rollercoaster" implies that you think the astronauts' blood is forced to their head by negative G. That's not the case.

There's a simple test that can answer this. If blood flow to the head is caused by being in orbit of a planet, you'd find a measurable difference between astronauts positioned with their feet pointing towards Earth or away from it. You'd be able to solve the blood flow problem by declaring the zenith side of the ISS to be the floor, and have everybody work with their feet pointed away from Earth.

No such effect has been found.

Say an astronaut's blood is pushed somewhere by an outside force (gravity). That same force acts on the whole astronaut. Since the astronaut is not restrained (unlike when you're in a roller coaster), that force would eventually move the astronaut to one of the walls of the spacecraft. That doesn't happen.

Astronauts wind up with increased blood flow to the head because the body, including the heart, is designed to function in 1G. The heart pushes the blood "uphill" from the feet to the head against the force of gravity. Blood vessels have the right size so every body part gets enough blood in 1G even though blood flows more easily to the feet than the head.

In freefall, your blood is as weightless as the rest of the body, so the heart has much less resistance to work against. In the first few weeks after launch, the heart keeps working at the rate it's used to. Without gravity, this means increased blood flow, especially to the areas that are 'hard to reach' under normal gravity, i.e. the head.

• OTOH, on Earth, the blood pressure in feet is considerably higher than in the head while in upright position. This evens out when lying down, harmlessly, and is equivalent to the freefall situation - but prolonged upside-down position (hanging by one's legs, standing on the head etc) may cause serious health problems, so the question isn't entirely baseless - we're more than halfway towards a harmful situation when entering microgravity. – SF. May 4 '16 at 13:20
• A simple test seems the obvious answer, if the perspective is based on a static environment a zenith would be evident however both the ISS and the astronaut have momentum and velocity 18,000.00 miles an hour,counteracting the pull of gravity, adding two additional factors to the equation when adding these, the zenith side becomes nonexistent how ever the physical effects seem to remain.this seems to be apparent as seen on NASA's vomit comet training aircraft. – dennis schaffert May 5 '16 at 18:25
• The vomit comet alternates rapidly between 0G and +1.8G. Its effects on human physiology are rather different from the steady-state microgravity in the ISS. – Hobbes May 5 '16 at 19:05
• @dennisschaffert: There are effects, both short-term and long-term, too many to list them all, but none are nearly as dire as you seem to picture them. Most serious are frequent nausea and vomiting over the first few days until you get used to microgravity, muscle atrophy which is a serious concern after return but not actually impairing their space performance, and progressive distortion of eyeballs, causing eyesight to falter over time (and THIS is the actual limiting factor on mission duration; they'd simply go blind after some $1{1\over 2}$ year. ) – SF. May 5 '16 at 21:34
• @dennisschaffert Consider that an object at Earth/Sun L1 would have velocity on the order of 65,000 miles an hour (almost as much as Earth's orbital velocity around the Sun). Velocity is relative to your chosen frame of reference. The effects in question have nothing to do with motion, but everything to do with external forces (e.g. ground pushing up through your feet on Earth, the Moon, the seat aboard an aircraft) or their absence (whether in free fall or deep space). – Anthony X May 8 '16 at 18:03