
StarTram - archgoon
https://en.wikipedia.org/wiki/StarTram
======
taneq
Cool sci-fi story hook, but the "Gen 2" magnetic levitation idea is _insane_.

> For the elevated end portion, the design considers magnetic levitation to be
> relatively less expensive than alternatives for elevating a launch tube of a
> mass driver (tethered balloons,[19] compressive or inflated aerospace-
> material megastructures).[20] A 280-megaamp current in ground cables creates
> a magnetic field of 30 Gauss strength at 22 kilometres (14 mi) above sea
> level (somewhat less above local terrain depending on site choice), while
> cables on the elevated final portion of the tube carry 14 megaamps in the
> opposite direction, generating a repulsive force of 4 tons per meter; it is
> claimed that this would keep the 2-ton/meter structure strongly pressing up
> on its angled tethers, a tensile structure on grand scale.[3] In the example
> of niobium-titanium superconductor carrying 2 × 105 amps per cm2, the
> levitated platform would have 7 cables, each 23 cm2 (3.6 sq in) of conductor
> cross-section when including copper stabilizer.[4]

> A SPESIF 2010 presentation stated that Gen-1 could be completed by the year
> 2020+ if funding began in 2010, Gen-2 by 2030+.[1]

Even assuming these numbers are right, I disbelieve that we'll have the
technology, let alone the resources, to magnetically levitate a megastructure
22 kilometers above the Earth, using 280 _million_ amps of current, in the
next 10 years. I don't think we even have a material strong enough to create
22km-long cables which can hold their own weight, let alone be useful as
tethers.

~~~
kristianp
Perhaps something like a launch loop would be easier than Gen 2:
[https://en.wikipedia.org/wiki/Launch_loop](https://en.wikipedia.org/wiki/Launch_loop)

~~~
taneq
I think most options are more feasible than Gen 2, from "just use Falcon
Heavy" all the way through to building a space elevator.

------
DarkContinent
Maglev trains are cool! There's actually one here on earth:
[https://en.m.wikipedia.org/wiki/Shanghai_maglev_train](https://en.m.wikipedia.org/wiki/Shanghai_maglev_train)

~~~
saagarjha
There’s more than just one. The Shanghai one is the fastest, though.

~~~
CamouflagedKiwi
There's a faster one in Japan, although it's not open to the public yet:
[https://www.bbc.co.uk/news/world-
asia-32391020](https://www.bbc.co.uk/news/world-asia-32391020)

~~~
leetbulb
Japanese trains are crazy. I rode the Shinkansen for a few hours. I actually
wondered at the time if it was maglev because the ride was so smooth, quiet,
and fast.

~~~
lunchables
It is really incredible, so smooth and quiet - and so fast! What surprised me
the most was how the track was banked in the curves like a race track.

------
dr_dshiv
Makes sense to have mass drivers like this on the moon or asteroids for
sending cargo (mined materials) back to Earth orbit. Reduces the need for
rocket fuel.

~~~
krasin
This is covered in-depth by Robert Heinlein in "The Moon is a Harsh Mistress"
([1], [2])

1\.
[https://archive.org/stream/TheMoonIsAHarshMistress_201701/Th...](https://archive.org/stream/TheMoonIsAHarshMistress_201701/TheMoonIsAHarshMistress_djvu.txt)

2\.
[https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress](https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress)

------
Tepix
Spaceline is another concept that makes access to space cheaper and easier to
achieve. It's a space elevator dangling from the Moon's surface into Earth's
gravity well.

Previous discussion:
[https://news.ycombinator.com/item?id=20895443](https://news.ycombinator.com/item?id=20895443)

