h a l f b a k e r y
It's the thought that counts.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
Build a big vacuum tube* to space inflated with helium.
The huge column would be neutrally buoyant so that it
could rise to over 100km altitude. The central tube a
couple of metres wide would be evacuated. The pipe is
gently curved eastwards so that the exit angle is similar
to that used by current rockets.
To allow the tube to extend above the
altitude at which
helium balloons cease to be effective, the tube would
contain a number of smaller tubes that contain
'obstructions'. Air is blown through these pipes from the
bottom and the resulting friction creates more lift. The
is then directed downwards at the lip of the main tube
an extra little push.
I lack the knowledge necessary to calculate the power
available from the moving air or how feasible it is over
such a long distance, but to improve the effective range,
the air would start off hot and moving fast, then would
cooled as it gets higher in the tube. This system would
on a large volume of air moving rather than high
To avoid deceleration of the air due to gravity, the mass
of the air cannot exceed that of the outside air.
This is similar to the Space Fountain concept, but much
easier to engineer IMHO.
Inevitably, some air will get into the top of the tube.
is pumped out from the bottom continuously, but at the
time of launch, a series of pre-launch disks are launched
up the tube at relatively low velocity to force the air out
the top of the tube. They then parachute back to earth
be used again. The last cleaning disk leaves the end of
tube seconds before the main launch vehicle.
This brings us to the launch mechanism. This is a simple
magnetic rail, with the power coming from the rail
than the launch vehicle. In fact the sled on the launch
vehicle is a stage which detaches soon after leaving the
top of the tube. It should not be a problem to transmit
power 100km or so, but this could be aided by wind
turbines tethered near the tube at stages, solar power or
the 'obstructions' mentioned earlier could be turbines.
The main problem is that the tube will need to be
to prevent it thrashing about in the wind. I think
it to the earth would be impractical due to the cable
weight, but it could be tethered to itself to add
A few ground tether cables could be used by containing
them within their own buoyancy tube and perhaps double
up as the power cables. Anyway, these are mere details,
way below my pay grade.
Back of envelope calculation:
Assuming the structure weighs 100kg per metre, it would
need to be about 35m in diameter at sea level. I have no
idea how this would need to change at altitude.
<aside>Space elevators are not really like a conventional
elevator in that it is not contained within a shaft. They
should be called Space Cable Cars.</aside>
As a bonus, we can add arms to it and sell used cars to
*Can someone tell me the name of a tube with hollow
walls, similar to a dewars flask but without a base?
Inflatable Space Elevator
Vaguely similar idea [marklar, Aug 20 2015]
||Did you Google "space hose"?
||//Did you Google "space hose"?// No, as that
requires knowing that it is called a Space Hose. I
have now though and got a relevant result, but I
was far more interested by "How to Organize
Closet Space with Vacuum Hose" which was
||Anyway, the idea on Physics Forums is remarkably
similar and it mentions the N-prize. There's even a
mention of the flailing man, which makes me think
I must have seen the idea before and regurgitated
it from my subconscious.
||Edit: Ah, just found the idea on the bakery.
||Is this idea sufficiently different, given the
different tubes (vacuum, lift hose, helium) and
||[+] A long skinny blimp/dirigible with an evacuated tube + linear accelerator in the middle is neither the fish of "Space Hose", nor the fowl of "strawberry launcher" though it uses (independently created) elements of both to produce something that's more viable than either.
||I don't see any way something can be "tethered to itself" to limit contraction in any dimension unless you're planning on spinning up one of the components (in which case you're limiting expansion).
||"double walled evacuated sleeve" ? "Dewar's sleeve" ?
||Personally I wouldn't bother with the pre-launch disks: if the end of the tube is high enough, just evacuate it supersonically from the bottom... maybe have an airtight trapdoor at the top that's opened just prior to launch. (The downwards pressure on the closed hatch would be measured in pounds, not tons as at sea-level)
||But... you're limited to about 50km altitude: even if your contraption only weighs 20kg per linear metre (since at this point you've ditched the blimp and the heavy vacuum container), every km adds 20 tonnes to the force necessary to keep the contraption from falling over. [edit: hmm... rocket motors aren't that heavy]
||There are material limits as to how tall
something can get.
||[FlyingToaster] Yes, pumping 1000 tonnes of air per
second is a tall order, not so much at sea level but
once it is at 10 millibars that's a huge volume.
||But still, the idea is to get past most of the
atmospheric drag and be moving reasonable
quickly without burning rocket fuel, so if this can
be done by 50km altitude, it only needs to be this
||// tethered to itself // It is curved, so it would
actually have to be attached to its elf along the
inner side of the curve to prevent it straightening.
I doubt this would help much with stability
though, probably best to have the neutrally
||[RayfordSteele] Why, when it is neither piled or
||How is it then supported? I must've missed
||[RayfordSteele] The lower section is weightless due
to it being filled with Helium. The upper part is lifted
by drag from air pumped upwards and the thrust as
the same air is directed downwards at the top.
||Somehow I doubt that's enough structure to
do the job.
||Helium has weight, hence filling something with helium makes it weightless ? I think some laws of physics are being bent, or at least semantic abuse is occurring.