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#1 2014-09-07 07:58:39

Tom Kalbfus
Banned
Registered: 2006-08-16
Posts: 4,401

A Space Telescope is an unmanned probe

With the recent discoveries of extra solar planets, one wonders if this might change NASA's priorities somewhat with unmanned missions. It would be nice if we could get a direct image of some of these extra solar planets, especially the ones in the habitable zones of stars. We are also developing the SLS, but don't have a specific mission for it, though their is talk about exploring the asteroids and going to Mars. Now could the SLS launch a telescope which could image an extra solar planet, and how much would that be worth compared with exploring he other parts of the Solar System? I think we have barely scratched the surface of the possible Earthlike planets out their, and if we find one that is relatively close in interstellar terms, that would be a big boost for building an interstellar mission to get there. I think we could build a starship by the end of this century, and e could probably launch it by then to, but it would help if there was a destination that was worth investigating, an Earthlike planet would do fine, as their are not many of those in our own solar system, or else we can explore the asteroids, comets, gas giants, moons, and planets, they are all pretty much lifeless, and if they have life at all, it probably the most simple type. I also think we need a systematic approach to exploring the stars surrounding our solar system, Kepler was a great start, but it only looked in one direction.

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#2 2014-09-07 10:37:40

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,682
Website

Re: A Space Telescope is an unmanned probe

I dunno,  Tom.  Failing some incredible breakthroughs in physics and propulsion technology,  I don't see us building a practical starship any time soon.  Flight times measured in centuries to millennia simply are not practical when compared to our lifetimes of just under a century. 

That being said,  when those breakthroughs have happened,  and we are capable of interstellar travel with practical flight times,  I also wonder why we would care about habitable planets.  With technology like that available,  would we not be building our own habitats in space?  Why live at the bottom of a gravity well when you don't have to?

However,  from a public motivational viewpoint,  your interstellar planet-detecting space telescope idea has great merit.  I like it.  The Hubble did more than anything else in recent decades to stir support for some of the things NASA does.  Kepler was another,  just not as popular,  because no images were returned.  People understand pictures,  not data.  More are coming. 

We don't need a gigantic rocket like SLS to launch such a thing,  because it can be assembled in orbit from docked modules,  flung up there with rockets we already have,  like Falcon-9,  Atlas-5,  Delta-4,  and (soon) Falcon-Heavy.  Not to mention things like Ariane and Proton. 

The giant rocket potentially makes it cheaper to fling the stuff up there,  because there is a unit launch price break as "flingable" payload increases.  But it's a rather small effect once you exceed around 10 tons.  Using all of the above-named rockets to establish a unit price vs payload mass trend,  one would predict that SLS at (70-140 tons) should fly for around $500 / pound maximum,  and probably a lot less than that. 

Trouble is,  SLS won't ever be anywhere near that cheap (current projections look like $2000-2500 / pound),  because it's being developed by NASA,  not the commercially-competitive companies.  That's no better unit price than where we are right now with 10-20 ton payloads.  Even those numbers aren't reliable:  NASA is infamous for under-estimating costs. 

When there's a need for a giant rocket to launch 100+ ton payloads to orbit,  the commercial companies will come up with one that really is inexpensive:  under my $500 / pound figure.  Unfortunately for us,  the SLS will never be that rocket.  NASA knows nothing about how to simplify logistics,  which is where most of their super-high costs come from.  The support tail for the commercial rockets is the population of a small city.  For NASA,  it's multiple megalopolises. 

Meanwhile,  just as for the telescope assembly process,  any manned or unmanned mission we might like to accomplish can be assembled from docked modules in LEO with the rockets we already have.  That includes men to Mars,  asteroids,  the moon,  or anywhere else.  But,  that approach rules out Apollo-style one-rocket / one-mission designs. 

In point of fact,  NASA resisted doing a lunar lander until it was almost too late,  because that idea came from an outsider to the agency.  Until they decided to go with a lander instead of landing the entire Apollo cluster on the moon,  the best they could do was two Saturn-5's per moon mission,  with LEO rendezvous and some sort of on-orbit refueling.  At the time,  a lunar lander was actually less risky than on-orbit refueling with cryogenics.  It forced them to accept the outsider's idea,  which is how they got down to one Saturn-5 per flight to the moon. 

In retrospect,  had they done docking in LEO as well as at the moon (with the lander),  they could have gone to the moon with perhaps 3 Saturn-1 shots per trip.  And THAT is why I say the same processes,  done correctly,  would allow us to fly to Mars RIGHT NOW with the rockets we already have.  That architecture leads one to a generalized orbit-to-orbit transport design,  fitted with landers appropriate to the destination.  Such designs inherently accommodate artificial gravity by spin,  which has direct and indirect benefits to all aspects of crew life support.

Costs are reduced by making that rig reusable to the greatest possible extent,  and then using it for multiple trips on a variety of missions.  The very same ship could be used to visit Mars,  the asteroids,  Venus,  and Mercury.  Although,  the moon is really too close by to benefit fully from its use.  Build one or two,  and use them to do all of those things. 

What we did with Apollo only makes sense if you are racing hostile competition.  We don't do that anymore.  At least I hope not ever again.  It's too wasteful.

As for future developments in propulsion technology,  well,  just keep retrofitting the one or two ships you built.  Now there's more money to go around doing all the other things you really wanted to do.  Someday,  replace them,  using the same basic ideas,  just better components and technologies.  Before too long has passed,  you'll have bootstrapped your way into real starships. 

GW Johnson


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#3 2014-09-07 20:25:06

Tom Kalbfus
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Registered: 2006-08-16
Posts: 4,401

Re: A Space Telescope is an unmanned probe

Well lets say for argument sake, we discover an Earth like planet that is 500 light years away, and suppose we can build a starship that can reach that planet, say it goes half the speed of light, it will take 1,000 years for the starship to reach that planet, to send humans to that planet, will require 50 generations of humans living and dying onboard that starship, that is 5 generations per century with 10 centuries of travel time. I think we can get the population down to 100.
This is a good design for the habitat section:
II-Exterior-Rendering.jpg
I'd say about 13 people per rectangular habitat section would add up to about 104 passengers/crew per generation for the 1000-year mission. The propulsion needed to reach half the speed of light would consist of mini laser sails

http://www.foresight.org/Conferences/MN … index.html

Microscale lightsails for beam propulsion.

Combining the concepts of solar sailing and mesoparticles [Bishop, 1997c] leads to the notion of mesoscopic solar sails. A mesoparticle beam composed of thin film sails with nanoscale electronics and actuators may be able to accelerate, turn, and navigate itself to a target spacecraft. Its accelerator may be the Sun, or a laser located on a deep space 'relay station' [Bishop, 1997b]. The nominal length of the "accelerator" is the distance between the deployment of the sails and their impact against the spacecraftís pusher plate. This distance can range between several thousands of kilometers (using high performance sails with laser assist [Landis, 1989, 1995) and several light years (for interstellar travel) [Forward, 1984b].

In most of this study it is assumed the manufacturing tolerances are held to those of a capable nanotechnology [Drexler, 1992a], removing the need to analyze dispersion due to ballistic coefficient (mass-to-area) variations.

A thin film lightsail needs support against the photon pressure. For macroscopic sails, this support is provided by spars, weights on the ends of rotating members, and so forth [Drexler, 1979]. This is sometimes expressed as a fraction of the ëbareí sail mass-per-area, one value is 1.3 (total mass/area is 2.3 , load factor is 2.3/1.3) for a very high performance interstellar laser lightsail [Landis, 1995]. Drexler estimates a minimum structural mass-per-area of .03 gm/m^2 for sails larger than 10 km diameter. The areal density of 16 nm Al film is .043gm/m^2, a near-minimum for any lightsail.

As the width of the sail is scaled down from hundreds of meters to hundreds of nanometers, it becomes self-supporting, and the parasitic structural mass can be eliminated, doubling the acceleration performance.

The maximum areal dimensions of the unsupported film can be increased somewhat if need be by slight geometric departures from planar, such a radial crimping, rolled edges, and other compound surfaces (keeping the thickness in the incidence direction constant). A cone or other surface of revolution can provide passive stabilization.

Image44.gif

Figure 6. Acceleration performance of Solar sails at 1 AU (a1, in m/sec^2) vs. mass per square meter (ma, in grams/m^2).

Image45.gif

Figure 7. A minimalist, self-supporting steering mesoparticle lightsail The inherent stiffness of the film at small length scales substitutes for structural components. The mass for sensors and nanocomputers is distributed over the backside area (not shown). Control is effected by tensioning the four linear members at the corners.

The nominal thickness of a lightsail optimizes near the skin depth; some fraction of the incident light is allow to transmit through as a loss.

Image46.gif

Density of Aluminum

Image47.gif

Bounce coefficient

Image48.gif

Reflectance

Image49.gif

Solar flux ëconstantí

Image50.gif

Sail thickness

Image52.gif

Absorptivity Transmissivity

(16 nm Al @ 500nm incident wavelength)

An equation for acceleration of a flat plate sail perpendicular to the incidence vector is:
Image53.gifwhich yields .181 m/sec^2 for the 16nm film at one AU. A lightsail with these specs released from LEO adds 10 km/sec to its velocity vector while still in cis-Lunar space {Figure 14}.

Spherical Lightsail
In the course of researching this article, it was discovered that a proposal similar to this, for a macroscopic spherical solar sail, has already been made, as is often the case for inventors [web ref].

The sphere suffers a geometric disadvantage over the flat plate, to wit the frontal area is one-fourth the total surface area, and the useable surface is at an angle to the incident radiation. Its inherent simplicity and no need for attitude control, does make it attractive. A number of design parameters can be adjusted to minimize this deficiency, such as making the film semi-transparent to allow the use of the rear disk area in addition to the frontal area {Figure 8}. Using a material, or a surface microstructure, that has a reflectivity and absorptance that varies with the angle of incidence (high absorptivity at low angle of incidence) may also increase performance. An internal pressure insufficient to maintain sphericity against the light pressure may help increase the frontal area, as well as rotate much of the surface normal towards the incident light vector.

Minsky [Minsky, 1997] suggests a half silvered sphere incorporating nematic crystals (liquid crystals) in portions of the film for attitude and thrust vectoring. These would either switch from absorbing to transparent, absorbing to reflective, or transparent to reflective. In any case, the force on the affected area would change, effecting the vectoring.
Image54s.gif
[Full size Figure 8: 10K, 757 x 496 pixels]
Figure 8. A spherical lightsail with film thickness less than the skin depth (ëpartially silveredí) receives some additional thrust from its back surface.

Heliogyro, pivoting vanes
A more efficient design is a microscopic analog of the "Heliogyro", which has performance equal to the flat plate. The vanes that make up the sail can pivot about the long axis, allowing reaching. Vanes that are a few microns wide by a few microns long do not need to be tensioned by rotation, nor do they need the roller furling used in the original concept. The pivoting mechanism is thus greatly simplified; no swash plate (or equivalent) is required {Figure 9}.

Beamed propulsion is better than rocket propulsion, and it doesn't rely on exotic fuel such as antimatter to get those high speeds, we need to reach half the speed of light with this. As for the human passengers, we have 100, and we store genetic material to be implanted in the females to maintain genetic diversity for the 1000 year voyage, so this involves a total of 5000 humans living and dying over 50 generations to reach out target 500 light years away.

As for slowing down, the ship would rely on a magsail, the magsail could also be used for acceleration, first by the solar wind, and then by an onboard laser that ionizes the incoming mesoscopic laser sails, producing a stream of charged particles that can be deflected by the magsail, thus imparting the momentum of the incoming charge particle stream to the starship through magnetic interaction.

We must be careful not to involve exotic maybes such as warp drive (a real longshot) and antimatter (merely a longshot) Lasers we have, solar energy we have, light sails we have, magnetism we have, we can store frozen human egg cells we can rotate a habitat in space and we can get to space, all this is known technology, we just have to develop it to the point of economic viability and put these together in a starship concept and reach half the speed of light with it.

Last edited by Tom Kalbfus (2014-09-07 20:40:00)

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