Drop Tube Elements

[Enthalpy]

Despite their low relative speed, the experiment needs vacuum in the bubble to achieve a good microgravity. Not air drag makes parasitic forces here, but buoyancy. I give here illustrative figures with the usual 1Pa residual pressure and a 4m*D1m experiment shell in a 5m*D2m vacuum bubble.

The drag compensation engine can apply 300N briefly on the 100kg vacuum bubble. The resulting air pressure gradient, 37µPa/m, exerts 0.1mN on the 200kg experiment, or 0.06*10^-6g.

The bungees bring 54m/s within 10m, that's over 15g at the peak - nobody expects microgravity then - and buoyancy pushes with 6mN. The pressure gradient then oscillates with 30ms period. One acoustic damping time (0.1s?) reduces the effect to 1*10^-6g.

Each opposing pair of guiding rolls needs a viscoelastic damper: polyurethane, Viton... If the suspension oscillates at 5Hz and the track is straight within 5mm peak, the resulting 5m/s² produces 0.07mN or 0.1*10^-6g.

The same side movements result in 0.2m/s air speed, in which Cx=0.4 creates only 0.3µN.

The vacuum bubble operates hence at a residual pressure similar to a vacuum tube, but is much smaller, so the vacuum is achieved faster, more easily, and can improve further for better microgravity.

A thought for my father.
Marc Schaefer, aka Enthalpy

[Enthalpy]

 

I was just thinking about reusing already made hole for mine's elevator.

http://en.wikipedia.org/wiki/Zero_Gravity_Research_Facility

I don't see any water.

Hole should be properly sealed from either side.

 

While neither Wiki nor Nasa claim the hole at Glenn facility was previously a mine shaft, it's clear that water leaks are the same difficulty, whatever the bore was initially intended for.

 

At Nasa's Glenn center, the hole is fully cemented - and within the concrete walls, a steel tube is airtight. I'm not convinced that mine shafts are cemented: since the mines themselves are not, miners have to pump the water out anyway, so I suppose they leave the shaft naked as well where the materials are sound enough.

 

Reusing a mine shaft would imply to dry it first, and then either continue to pump water out permanently, or cement the walls and the bottom. Nothing tragic, but it's a cost. For me, the true benefit would be the bigger depth if available, as 600m depth double the fall time over 150m height.

 

Both a tower and a bore can host the vacuum bubble option, which can retrofit an existing drop tube.

[Enthalpy]

Stopping the shuttle with bungees permits to start a new flight immediately, but is difficult to design and bring to run, much so because the behaviour of reused parts during a 180km/h contact is hard to imagine, as I know from crash-test hardware at 120km/h. Since immediate restart is a compelling advantage for a drop tube but is a design risk, I believe the designs should be tried and improved in a tight iterative process before the costly vertical tower is built and freezes to the propulsion and vacuum options.

I propose to test horizontally the shuttle's propulsion and stopping, on a purposely built short track with one catapult-brake at each end. Beyond the sketched parts, the trial track needs bunkers at least around each end, fast video, data acquisition and more.

Much can be tested, repetitively, not necessarily everything nor at the same time:

• Propulsion and stopping. Bungees' behaviour, adjustment, (not sketched) setting drive.
• (Not sketched) the rake and the rewind drive.
• The railway, wheels, suspension.
• The vacuum bubble and its seals.
• The drag compensation engine and its control, with a track long enough.

Marc Schaefer, aka Enthalpy