To the moon, Icarus, to the cool moon!

    Icarus was an impetuous teenager, not heeding his father’s advice to keep clear of the hot sun. Would he have succeeded, had he humoured his father and aimed for the cool moon instead?

    In other words, is human-powered space flight possible?

Pedalling in the air

    The Icarus-Daedalus story doesn’t concern space flight, of course. Rather it reminds us, among other things, that flight is problematic, human-powered flight in particular. But in 1979 the cyclist Bryan Allen overcame the problems of muscular flight. On June 12 that year Allen succeeded in pedalling his muscle-powered aeroplane Gossamer Albatross across the English Channel, a flight that took him less than 3 hours.

    In 1969 the Apollo XI crew proved that human space flight was possible, but that it burnt inhumanly huge amounts of energy. Lately Burt Rutan’s SpaceShipOne has shown that human space flight can be accomplished with considerably less energy.

A bicycle made for space

    Do these two developments in combination indicate that we may one day see an astronaut pedalling herself/himself into space, powered by nothing else than his own muscles?

    It would be interesting to try to calculate whether or not this is possible, in principle at least.

    What it boils down to is to have a human pedal her/himself up to the speed of 11.2 km/s, the minimum velocity needed to escape the Earth and enter space. Mr. Bryan Allen pedalled his Gossamer Albatross at an average speed of 29 km/h, i.e. at about 0.008 km/s. This is clearly a far cry from the necessary escape velocity.

    What we obviously need to do is to accumulate the modest energy flow of the human pedaller (about 300 - 600 W) over a period of time, until it reaches the necessary kinetic escape energy, and then shoot it out all at once. However, collecting momentum in this way cannot be done in the atmosphere, because of the aerodynamic drag caused by the surrounding air. But it can be done in vacuum.

Particle science in a vacuum

    We will dress our human-powered astronaut in space garb and place him/her in a small airtight capsule. Next we let her/him pedal in a circular vacuum tunnel, going around and around, picking up speed at each turn. Particle scientists have built huge vacuum tunnels, e.g. the old LEP (Large Electron-Positron collider) tunnel at CERN outside Geneva, with a diameter of 9 km, so in principle this seems doable. The capsule should be magnetically suspended inside the tunnel, to reduce friction. The propulsive force from the astronaut’s pedals may also be transferred magnetically.

    So our astronaut can go on pedalling and accelerating until he/she is tired. Resting poses no problem -- the astronaut’s capsule will continue at practically unreduced constant speed even when the astronaut ceases pedalling. Because there is no air resistance and very little friction in our tunnel, remember? Whenever the astronaut goes back to pedalling, the speed of the capsule is again on the increase. It’s a one-way street -- the speed of the capsule only goes up, never much down.

Feeding and pooping

    The ground crew outside the vacuum tunnel will see to it that the astronaut is fed, oxygenated, watered and pooped. At regular intervals a service module is accelerated to the exact speed of the capsule, travelling next to the capsule, but on the outside of the tunnel wall. At feeding/pooping time packages are quickly shot into and from the capsule via air locks in both of the vehicles and the tunnel wall. I don’t know how to make this work in practice. But it might work in principle.

The time frame

    How long will the astronaut have to stay in his capsule to reach escape velocity and then soar into space? Let us assume that the capsule + astronaut weighs a total of 200 kg and that the astronaut’s pedalling power is 500 W (Bryan Allen generated 400 W of pedalling power during his 3 hours of muscle-powered Channel flight).

    The kinetic energy at the escape velocity of 11.2 km/s is (E = ½m*v^2 = ½*200*(11.2*10^3)^2), about 1,25*10^8 J. This figure divided by the astronaut’s power output (500 W) gives us the required time in seconds. Dividing by 60*60*24 results in the number of 24-hour days, which comes to 292 days, or approximately 300 days of active pedalling.

Sleeping and resting

    The astronaut has to sleep and rest as well, so we can draft the following time budget:

          Daytime work: 300 days Daytime rest: 300 days Sleep: 300 days Total: 900 days = approx. 2.5 years

    So after about two-and-a-half years, the ground crew can open a door in the vacuum tunnel and let the astronaut soar into space. Hence in principle a person can go to space in 2.5 years, if powered by human muscle-power alone.

Possible centrifugal squashing

    Mind you -- IN PRINCIPLE. There are umpteen questions left hanging, e.g. the obvious one concerning the capsule hitting tough air when released from the tunnel. They are mostly left as an exercise for the reader.

    There is a minor problem of dimensions here, too. When the astronaut goes around and around in her/his circular tunnel, and the speed starts building up, then the centrifugal g-forces will become noticeable. The problem depends on how wide we would like to make the circle. If the tunnel were made large enough to encircle the entire globe at the equator, then there is no problem -- the astronaut will be weightless.

    But using the LEP tunnel in Geneva, with its diameter of 9 km, would squash the astronaut beyond recognition when the speed reaches escape velocity. In all probability the tunnel would have to be made very wide, maybe a quarter of the diameter of the Earth, for the astronaut to be able to endure the centrifugal g-forces.

2.5 years and untold billions, but principally possible

    Nevertheless, we have shown that -- in principle -- human individuals could pedal themselves into space under muscle power alone, provided that they are prepared to devote 2.5 years of the their life to the task (and incur astronomical tunnel-building costs).

    How the astronaut gets back to Earth, by his own power? Well, that was never included in this exercise.

    Calast suggests that re-entry could be done by accelerating fecal matter in the same way as described for the capsule on ground, and then ejecting it in the opposite direction from the way you want to go.
    -- Thanks, the pedalling astronaut feels much relieved, with a new understanding of the Jet-Poop concept!

    maxClimb and Cletus the Foetus say, and rightly so, that Daedalus actually completes his escape from Minos by flying, so the Icarus-Daedalus story doesn't insinuate that human powered flight is impossible.

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