Talk:StarTram

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Untitled[edit]

Altough the idea is online, I doubt its physical realisation.

  • Flying at 10km/s in the lower stratosphere, i.e. at altitude of 20 km, creates really much drag, c.f. Space Shuttle Columbia disaster.
  • Magnetic levitation of a weight of several ton over a distance of 20 km is probably not possible with 2009 materials and currents.

Stefan.K. (talk) 20:09, 27 November 2009 (UTC)

That equation is for a wire very close to another wire relative to the length of the latter. It is based on F=BIL, with B the field of an infinite wire. The ground wire must be a lot longer than 20km, this article should name the proposed length? 88.159.72.164 (talk) 12:07, 3 July 2010 (UTC)


With the large expansion of this article from being a short stub before, more concerns are now implicitly addressed within it, including linking to mention of Dr. Maise's background in fluid mechanics, heat transfer, rarefied gas dynamics, and reentry heating during his 25-year career at Brookhaven National Laboratory, with the ability to calculate the stresses involved in hypersonic flight conditions. As a less experienced mechanical engineer myself, I'd be hesitant to second-guess the StarTram team there. (A projectile taking damage like the 15-25 centimeter hole in Columbia's wing in the Space Shuttle Columbia disaster mentioned would be a separate matter of course).

For general perspective, it may be surprising what is doable with a sufficient available mass budget and design specifically for high speed atmospheric passage, like I've seen it determined that a quite elongated projectile with the right heat shield could survive launch at 17 km/s (approaching LEO being 8 km/s though the angle of launch is different) from the ground by a mass driver for nuclear waste disposal, that velocity being Solar System escape velocity. While not the best reference link because at the moment I'm only finding an abstract online, see here for instance. (The Wikipedia page on mass drivers needs some work, having some no-math assumptions not really supported by references within).

Even Gen-1 StarTram projectiles are fired from above more than half of the atmosphere's mass (as one can see looking at a standard atmosphere table for pressure at 6 km versus sea level).

The StarTram Gen-2 variation aiming to magnetically elevate a launch tube to 22 km (as opposed to the simpler mountaintop launch of Gen-1 or Gen-1.5) does have much extra challenge. It is intended to compensate for variable wind loading on the structure and the degree of bending from such (as one can see in the papers), but of course such would be rather complicated in practice. Cost estimates for that part could be particularly debatable. With that said, though, the article now better shows how it works, and see the now-linked papers for more details, like the design operating current (2E5 A/cm^2) is only 40% of the critical current in NbTi (under the calculated maximum azimuthal magnetic field of locally 2.67 Tesla), with a substantial safety factor and engineered redundancy in case a cable failed. The Gen-2 concept is counter-intuitive since people have never seen billions of dollars of superconducting cable concentrated in one place specifically to maximize the magnetic field for long-distance levitation of another astronomical-current superconducting cable array.

In the article, I can't get off-topic, but hopefully readers can indirectly guess the multiple development paths conceivable. One could be beginning on MagLifter scale, then working up to something close to the 4 km/s Gen-1.5 StarTram variant (mountaintop launch including passenger capsules, no extra elevation of the launch tube). If more concerned about reducing length than having the full spectrum of the general populace be eligible passengers (rather sending only medically screened individuals in top condition with tolerances similar to those of NASA test pilots in the old g-force testing), higher acceleration like 6-10g would allow passenger launch from just about a 50 to 85 mile acceleration tunnel. Get to 4 km/s, and most of the rest of the way to 8 km/s LEO might be from a Momentum exchange tether in orbit, just a very small rocket burn. A tether of 2 km/s to 4+ km/s is exponentially easier to be doable and practical than one of 8 km/s there, pretty good synergy. The current version of the Non-rocket spacelaunch article doesn't explicitly cover the important option of combined, hybrid systems, although, to follow Wikipedia rules, appropriate reference links would need to be given if I (or anyone else) was to add mention of such.

--Sokavik (talk) 12:14, 27 April 2011 (UTC)

Why try to achieve solar escape velocity from earth? Perhaps one of the first sets of payloads that should be sent up, if the per Kg cost can be indeed be made very low with the initial systems, should be the components of another linear accelerator to be assembled in orbit, using a similar energy storage system but recharged by solar arrays, and long enough to send an LEO payload into lunar transfer orbit. Then bootstrap that to throw up additional components for another accelerator...and so forth. A series of much shorter accelerators, then, suffering no power loss from atmospheric drag, *and* able to run in reverse to bring payloads back to earth, can then serve as a network for going pretty much anywhere we please. But perhaps Sokavik was just mentioning this possibility to show that the more modest design described in the article was feasible.

But I'm also not sure why all the trouble is being considered for an ultra-elevated tube for Gen2. The G force on the payload at the point of release is a function of the ratio of the force of atmospheric drag to mass, the former being a function not merely of air density but of projectile shape and surface area. We can decrease this ratio by either making the capsule more dense (if you really don't have any more useful dense payload, just add some lead to it; more power is then needed to accelerate it, but you don't need a whole new launch system for human payloads), or simply making it larger, so that the area/mass ratio goes down, until we bring the 10-12G force down by a ratio of 10 or so. This obviously means a larger and more expensive system, but then you can still keep it anchored to the ground without any weird and dubious engineering for electromagnetically elevated shafts which have to deal with wind, lightning, and all sorts of similar problems. And in exchange you get a larger capsule with more capacity. If we're serious about getting major payloads into space, this may be worth it.67.217.31.180 (talk) 02:28, 19 August 2011 (UTC)

Why a part of the mass driver wouldn't be buried?[edit]

I have a small question, it may interest someone? Hi, my english is not perfect, i didn't read and understand all the article, but why for instance they won't create a underground tunnel long by 40-50 km, with 30g acceleration, rather than a 40-50 km launch pad?

It would permit theoretically to launch craft up to 1500 km.

Thanks

--Nicobzz (talk) 11:27, 15 September 2011 (UTC)

Error in calculations.[edit]

The calculations for atmospheric deceleration in the Gen 1 section are incorrect. Using the cited numbers, one would achieve an initial deceleration of 20.2 gees, not 12 gees. At an altitude of 6000 m, the air density given by the ICAO Standard Atmosphere is 0.660 kg/m^3.

In Frink notation, assuming a circular cross section, and the equation for drag:

F = 1/2 density v^2 area Cd

the calculation is:

a = pi (1 m)^2
F = 1/2 0.660 kg/m^3 (8.78 km/s)^2 a 0.09
F / (40 tons) -> gee

which gives 20.2 gee.

I notice that the document here uses different numbers for launch altitudes and drag coefficients: http://www.startram.com/resources/StarTram2010.pdf?attredirects=0&d=1

Feel free to fix it according to whatever you think the right numbers should be, but make it self-consistent! --Eliasen (talk) 08:49, 20 April 2012 (UTC)

Incorrect Interpretation?[edit]

I noticed this line:

As of 2010 operating maglev systems levitate the train by approximately 15 millimeters (0.59 in).[31][32] For the Gen-2 version of the StarTram, it is necessary to levitate the track over up to 22 kilometres (14 mi), a distance greater by a factor of 1.5 million.

It struck me that the first part references the levitation of the train in maglev systems, while the second part says track. Also, it would not make much sense to require the train to levitate 22 kilometers. If the train is to remain inside the narrow tube, it cannot levitate 22 kilometers. Looking back, I noticed this:

The Gen-2 variant of the StarTram is supposed to be for reusable manned capsules, intended to be low g-force, 2 to 3 g acceleration in the launch tube and an elevated exit at such high altitude (22 kilometres (14 mi)) that peak aerodynamic deceleration becomes ≈ 1g.[1] Though NASA test pilots have handled multiple times those g-forces,[19] the low acceleration is intended to allow eligibility to the broadest spectrum of the general public.

Note that it says the track will need to be elevated 22 kilometers. I believe that someone confused elevated track with levitating train, researched the 15 millimeter train levitation, and did the calculation on their own. This line should probably be removed, as it is incorrect and misleading. Mazetron (talk) 06:38, 15 March 2013 (UTC)

Generation 2 Section[edit]

The following section was removed by a user claiming "WP:INUNIVERSE problems". I have read that page and cannot possibly see how the section violates that guideline. It is well referenced and makes it perfectly clear that it it a proposal and not actually implemented, for instance "supposed to be", "is estimated to be", "the design considers", etc. It seems to have the same writing style as the rest of the page. I think it is nicely written. If there are any problems with it, please discuss here or change the article instead of simply deleting it. Theorem41 (talk) 15:17, 21 March 2015 (UTC)

Here is the text of the section:

The Gen-2 variant of the StarTram is supposed to be for reusable manned capsules, intended to be low g-force, 2 to 3 g acceleration in the launch tube and an elevated exit at such high altitude (22 kilometres (14 mi)) that peak aerodynamic deceleration becomes 1g.[1] Though NASA test pilots have handled multiple times those g-forces,[2] the low acceleration is intended to allow eligibility to the broadest spectrum of the general public.

With such relatively slow acceleration, the Gen-2 system requires 1,000 to 1,500 kilometres (620 to 930 mi) length. The cost for the non-elevated majority of the tube's length is estimated to be several tens of millions of dollars per kilometer, proportionately a semi-similar expense per unit length to the tunneling portion of the former Superconducting Super Collider project (originally planned to have 72 kilometres (45 mi) of 5-meter (16 ft) diameter vacuum tunnel excavated for $2 billion) or to some existing maglev train lines where Powell's Maglev 2000 system is claiming major cost-reducing further innovations.[1] An area of Antarctica 3 kilometres (1.9 mi) above sea level is one siting option, especially as the ice sheet is viewed as relatively easy to tunnel through.[3]

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,[4] compressive or inflated aerospace-material megastructures).[5] 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.[6][7] In the example of niobium-titanium superconductor carrying 2 x 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.[8] Theorem41 (talk) 15:17, 21 March 2015 (UTC)

  1. ^ a b Cite error: The named reference StarTram2010 was invoked but never defined (see the help page).
  2. ^ NASA: Bioastronautics Data Book SP-3006, page 173, Figure 4-24: Human Experience of Sustained Acceleration
  3. ^ Cite error: The named reference FAQ was invoked but never defined (see the help page).
  4. ^ Gerard K. O'Neill (1981). 2081: A Hopeful View of the Human Future. 
  5. ^ Canonical List of Space Transportation and Engineering Methods
  6. ^ Cite error: The named reference Gen2 was invoked but never defined (see the help page).
  7. ^ "Magnetic Force Between Wires". Retrieved April 24, 2011. 
  8. ^ Cite error: The named reference Engineering was invoked but never defined (see the help page).

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The "Magnetic Force Between Wires" one is just the bare equations about wires. It has to do with it, but is not a reference that shows anything about the Star Tram.88.159.65.76 (talk) 21:44, 30 August 2016 (UTC)
Right, but that is not from the article, it is from the discussion section above. The placement of the references is a bit unintuitive, I changed it. --mfb (talk) 11:57, 1 September 2016 (UTC)

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