SLS and what asteriod will we go to

SpaceNut · 2014-02-04 20:55:15

Astronauts launched aboard the Orion crew capsule and Space Launch System rocket would rendezvous with the captured asteroid material in lunar orbit, and collect samples for return to Earth.

NASA Posts Final Asteroid Workshop Report

An unprecedented response followed the release of the RFI: the agency received 402 responses, 40 percent of which were from individuals and members of the general public.
All the ideas were evaluated and rated. 96 of the ideas were chosen to explore in greater depth at the Asteroid Initiative Workshop, held in two parts at the Lunar and Planetary Institute in Houston, Texas.
The NEOWISE spacecraft was reactivated in September 2013 to search for near-Earth asteroids that could be potential targets for the ARM.

At least the rocket is getting used and man will finally go beyond LEO....

Tom Kalbfus · 2014-02-04 21:58:26

I wonder why they want to put it in Lunar Orbit and not Earth-Moon L5 or L4 as Gerard O'Neill suggested? I understand those Largrange points are fairly stable, and they are future sites to potential O'Neill colonies, If we want to practice capturing asteroids, why not direct them there?

GW Johnson · 2014-02-05 11:55:55

SLS/Orion does not provide a feasible way for men to travel beyond cis-lunar space. It will never go to an asteroid in-situ out there somewhere, except unmanned, which is a total waste.

Yes, with this capability we can "explore an asteroid" brought by robots to cis-lunar space. (So could Falcon-Heavy/Dragon, and cheaper.)

No, with just this capability (whether SLS/Orion or F-H/Dragon), we cannot explore with men beyond cis-lunar space.

Two to four weeks, maybe a couple of months, in a cramped capsule is just about the psychological limit. And, as the mission goes several weeks, possibility of getting hit with a lethal solar flare rises sharply, especially near solar max.

Even if you add a Bigelow hab to it you can't get much beyond a year without serious-to-fatal microgravity disease effects. Mars is 2+ years away round trip, and we have absolutely no evidence to suppose that its reduced gravity is enough to be therapeutic, because no fractional-gee health studies have ever been done. None at all. Not with real fractional gee. Bed rest is a poor surrogate at best, and inapplicable totally at worst. And that's the truth of it.

What we are building so far is only the capability for doing things on or around the moon, not to go "out there" anywhere. Concentrating on this alone is effectively a way of saying we're not going to Mars.

Any outfit serious about going beyond cis-lunar space will be looking at spacious hab modules, artificial gravity, water/wastewater radiation shielding, and practical landers. And, most importantly, they will be looking at a supple space suit to enable construction in space of the vehicles to do all those other things.

I see no mainstream efforts to do any of those things, which is why I am so pessimistic-sounding.

GW

Tom Kalbfus · 2014-02-07 08:03:58

What's wrong with bringing asteroids into orbit around Earth? Isn't that the whole point of bringing back asteroids, so we can mine them in Earth orbit and make space colonies out of them? I mean if you want habs going to Mars, what better source for building them than the materials that make up the asteroids? I mean compare the tonnages of what you can launch into orbit with the tonnages of asteroids that you can bring into Earth Orbit. Asteroids provide excellent shielding from solar flares., and asteroids can be used as reaction mass in mass drivers, I saw proposals for that way back in the 1970s.

GW Johnson · 2014-02-07 13:47:20

Tom:

What's wrong is us screwing up: hitting Earth instead of LEO. Hitting Earth is a lot harder to do if you aim out near the moon. Much later, with experience, asteroids to LEO for mining becomes reliable enough to be safe.

This kind of thing will be limited to very small asteroids for several decades to come. The bigger ones are the more interesting ones with the most volatiles. Those are out in the main belt.

Any ship good enough to take men to Mars could visit the main belt, especially with some hotter propulsion fitted to it.

The very best targets are way out there, and mostly too large to divert. That's why I think diverting very small asteroids to Earth vicinity is a side path off to the side of the road we really should be traveling.

GW

Last edited by GW Johnson (2014-02-07 13:48:18)

SpaceNut · 2014-02-07 20:03:08

The links indicate unmanned capture and use of an orion but thats what seems to be cloudy.
http://www.nasaspaceflight.com/2013/07/ … n-mission/
http://www.nasaspaceflight.com/2013/04/ … challenge/
http://www.nbcnews.com/id/50398762/ns/t … near-moon/
a $2.6 billion asteroid-retrieval mission that could deliver a space rock to high lunar orbit by 2025

SpaceNut · 2014-03-23 20:02:17

http://nasawatch.com/archives/2014/03/n … ses-a.html

NASA to Host Media Teleconference on an Asteroid Initiative Broad Agency Announcement
"NASA will host a media teleconference at 3 p.m. EDT Friday, March 21, to discuss the same-day release of its Asteroid Initiative Announcement of Opportunities."
NASA Asteroid Redirect Mission Broad Agency Announcement
"NASA intends to issue has issued an Asteroid Redirect Mission Broad Agency Announcement (BAA) on March 21, 2014. NASA is developing concepts for the Asteroid Redirect Mission, which would use a robotic spacecraft to capture a small near-Earth asteroid, or remove a boulder from the surface of a larger asteroid, and redirect the asteroid mass into a stable orbit around the moon. Astronauts aboard the Orion spacecraft launched on the Space Launch System would rendezvous with the asteroid mass in lunar orbit, and collect samples for return to Earth."

An Asteroid Initiative Opportunities Forum will be held at NASA Headquarters on March 26, 2014, and proposers will have a chance to ask questions about this Announcement. The meeting agenda and registration information is posted on the BAA website at http://www.nasa.gov/asteroidinitiative

NASA's asteroid initiative includes two separate, but related activities: the asteroid redirect mission and the grand challenge. NASA is currently developing concepts for the redirect mission that will employ a robotic spacecraft, driven by an advanced solar electric propulsion system, to capture a small near-Earth asteroid or remove a boulder from the surface of a larger asteroid. The spacecraft then will attempt to redirect the object into a stable orbit around the moon.

Astronauts will travel aboard NASA's Orion spacecraft, launched on the Space Launch System rocket, to rendezvous in lunar orbit with the captured asteroid. Once there, they will collect samples to return to Earth for study.

Excelsior · 2014-03-23 21:45:14

What are we going to do when we get there?

There is no room in the budget for anything other than the SLS/Orion combo.

Quaoar · 2014-03-24 01:54:20

SpaceNut wrote:

NASA's asteroid initiative includes two separate, but related activities: the asteroid redirect mission and the grand challenge. NASA is currently developing concepts for the redirect mission that will employ a robotic spacecraft, driven by an advanced solar electric propulsion system, to capture a small near-Earth asteroid or remove a boulder from the surface of a larger asteroid. The spacecraft then will attempt to redirect the object into a stable orbit around the moon.
Astronauts will travel aboard NASA's Orion spacecraft, launched on the Space Launch System rocket, to rendezvous in lunar orbit with the captured asteroid. Once there, they will collect samples to return to Earth for study.

I's a completely new technology to develop: if they really want to do that seriously (I belive not) they will employ more time and money than landing men on Moon and even on Mars.

Asteroid redirect capability may be usefull to avoid a deep impact, but i dont think it can be done completely unmanned. Astronauts has to go first to make geological prospection, study the best despin and moove strategy on the basis of asteroid structure (solid rock or granular aggregate), then fix the hardware. But to do such things, we have to built first a real reusable space ship with artificial gravity and flare protection, able to years long space cruise.

Last edited by Quaoar (2014-03-24 02:02:55)

GW Johnson · 2014-03-25 09:59:16

Quaoar put his finger on the needs for going to Mars or anywhere else further than the moon. That's the habitat and protection technologies for long-duration flight. Up to a 3 years or so, we can use packed supplies as expendables for life support; beyond that, we'll need a functioning closed-cycle ecology (something we don't yet have). We'll need artificial gravity (not only for health protection, but also to make many life support functions easier, and for basic comfortable living). We have it with spin. We'll need radiation protection from solar flares, we have it with 20 cm of water/wastewater. Beyond about 3 years, we'll also need to counteract cosmic rays (something we don't really yet know how to do) in solar min years when the flux is maximum.

Problem is, I don't see any of those things being worked on in any significant way by any of the space agencies. NASA is focused on trying to find a mission for its politically-mandated reprise-on-steroids of Apollo-Saturn: Orion-SLS. "Is it Mars, or the moon, or is it something to do with asteroids?" Some years ago they cancelled the medical centrifuge module for ISS: so much for finding out "how much gee is adequate?" And instead of spending what little money there is developing the ways for men to travel long distances, NASA would rather develop an itty-bitty asteroid-capturing robot without the science to support credible design requirements, so that it need only use its moon rocket technology with the men.

Moon rocket technology. All that cash to reprise a technology we had, and then frittered away, 40+ years ago. What a waste!

And even then, the Saturn family was originally a suite of Army ICBM designs, not one of them a real moon rocket design. The big Saturn just happened to be barely big enough to use as a moon rocket, but only after some real cleverness got adopted from outside NASA (the lunar orbit rendezvous concept). Von Braun did the Saturns for the US Army, before NASA grabbed him. Apollo-Saturn mission architecture was made to fit an existing family of ICBM designs. People too often do forget how we got there.

GW

Last edited by GW Johnson (2014-03-25 10:03:38)

SpaceNut · 2014-03-25 18:39:08

The space craft is closed due to spaces natural void of anything to make life possible except the suns solar energy.
Going beyond 3 years means more supplies, larger ship and way more power to make everything work.

NASA Seeks Proposals on Asteroid Redirect Mission Concepts Development

Following evaluations of the proposals, NASA plans to select no more than 25 proposals and make total awards of as much as $6 million.

GW Johnson · 2014-03-28 09:53:55

A logical question: how is using only circumlunar-capable manned technology a "steppingstone along the way to Mars"?

Another logical question: how is $6M to be construed as significant support for efforts really aimed at doing anything? This sounds more like buying PR with small business set-aside monies.

GW

Last edited by GW Johnson (2014-03-28 09:55:41)

RedStreak · 2014-03-31 03:18:28

GW Johnson wrote:

A logical question: how is using only circumlunar-capable manned technology a "steppingstone along the way to Mars"?

Short answer: making sure the space toilet meant for 3 years use doesn't epically fail on day 3. What makes this more frightening is the fact astronauts often traditionally have beans before launch for good luck much as JPL people have peanuts. Put these factors together and if you have the option of running back home for a replacement...lord do you ever want that liberty.

Long answer: Basically same reason as the space station was originally justified, which is testing out life support and how to wiggle around in space. The ISS is stuck within the magnetosphere; cislunar craft would at least be beyond that layer of protection and farther from supplies. If LEO is getting-feet-wet and Mars is up-to-your-neck, then Lunar space would amount to calf-deep-wading. Going out to an actual asteroid with astronauts about waist-deep, but the ARRM concept seems set on putting things in lunar orbit for now.

When it comes to reaching Mars the whole idea is on the weak side, but then again NASA claims to be set on taking things methodically.

GW Johnson · 2014-04-01 09:30:38

I think we have learned most of what we need to know in LEO (how to move, how to dock little modules into big structures, some refueling with storables, and that microgravity induces: bone loss, vision loss, [(edit 4-1-14) heart and circulatory system damage], and immune system damage, and 450 days or so exposure is about the max). Things still unanswered but answerable at ISS are how much artificial gee would be therapeutic, would a supple MCP spacesuit work, and how to do refueling with cryogenics.

Those items listed plus radiation protection are the critical items for sending a crew to Mars and back (or the main asteroid belt, or to an NEO, or to Venus orbit, or to the surface of Mercury), and getting them home safe and healthy. Of those items, we could do without the "how much gee is enough" answer, although knowing it could save a bunch of money. [(edit 4-1-14) Just do one full gee's worth of artificial gravity. That's what we evolved in, we KNOW it will work.]

Radiation protection: we know the answer to solar flare -- 20 cm of water or wastewater is an effective shield. For solar min when the GCR is max, the spacecraft structure will attenuate it from 60 rad annually to near the astronaut's exposure limit of 50 rad annual. But, if the mission is 2.5 years round trip to Mars, you probably do not want to fly that crew outside the Van Allen belts again, because of the astronaut career limits.

So, a supple space suit, practical artificial gravity, and the water/wastewater radiation shield are the true remaining limitations keeping us from sending men into deep space.

All three are now supported by existing science and engineering technology, and all 3 need merely specific hardware designs with concomittant verification processes to be flight-ready. Supple spacesuit: MCP done as vacuum-protective underwear with conventional outer garments as appropriate to the task at hand. Practical artificial gravity: 4 rpm max at 56 m radius for 1 full gee, until and unless we find lower gee to be therapeutic. Radiation: already described above.

Doing the asteroid redirect mission (ARM) accomplishes none of the things we really need. And further, we don't need SLS-Orion to do the ARM. Falcon-Heavy with manned Dragon plus a modified Centaur could do exactly the same thing, for one whale of a lot less money.

And THAT is why I think the ARM is NOT a steppingstone along the way to Mars. It doesn't even make logical sense to do it, if the real goal is men-to-Mars, etc.

ARM only makes sense if the goal is keeping powerful congressmen's districts happy with gravy-train projects. It has already been admitted in public that the rationale for SLS-Orion is politics: congress mandated it.

GW

Last edited by GW Johnson (2014-04-01 15:48:12)

Tom Kalbfus · 2014-04-02 07:12:00

GW Johnson wrote:

Tom:
What's wrong is us screwing up: hitting Earth instead of LEO. Hitting Earth is a lot harder to do if you aim out near the moon. Much later, with experience, asteroids to LEO for mining becomes reliable enough to be safe.
This kind of thing will be limited to very small asteroids for several decades to come. The bigger ones are the more interesting ones with the most volatiles. Those are out in the main belt.
Any ship good enough to take men to Mars could visit the main belt, especially with some hotter propulsion fitted to it.
The very best targets are way out there, and mostly too large to divert. That's why I think diverting very small asteroids to Earth vicinity is a side path off to the side of the road we really should be traveling.
GW

How much mass is required to build a Stanford Torus? I'll bet there are near Earth asteroids with the same mass and greater. We don't need to go out to the main belt to find such asteroids. What we need to do is find a large enough near earth asteroid and attach a mass driver that will throw rocks out with sufficient speed to change the orbit of such an asteroid. The Moon can come in handy here, but instead of parking the asteroid into Lunar orbit, we use the Moon's gravity to slow the asteroid down into an elliptical Earth orbit, as the mass driver can only accelerate slowly. the Moons gravity can slow an asteroid down from just above the local escape velocity from Earth to just below the escape velocity, then we use the mass driver to slowly slow down the asteroid until the Moon's gravity no longer threatens to fling it back out into interplanetary space. The mass of the torus would be 10 million tons, so all we have to do is find a 10-15 million ton asteroid, the extra mass would be for reaction mass for the mass driver. First thing to do would be to stop the rotation of the asteroid so the mass driver can be pointed in the right direction consistently. A 500 ton asteroid is about the mass of the ISS I believe yep the mass is 450,000 kg which is almost 500 tons, So if we can capture that 500 ton space station, perhaps we could make a space station out of it. Maybe the asteroid could be sent on a transfer orbit to Mars. A Mars transfer vehicle doesn't have to be as massive as 500 tons, the rest would make excellent Solar flare shielding.

GW Johnson · 2014-04-02 20:49:16

Tom:

I cannot answer your question about the mass to construct a "Stanford Torus". I have never even heard that name before. Please define.

There's a lot more to construction besides mass.

Exactly how does anyone propose to create structural materials out of loose sands, dusts, and rocks of all sizes? If you melt and recast material like that, one whale of a lot of energy is required. Where will it come from? And, no rock fiber I ever heard of is going to be able to replace concrete and steel, as far as structural properties are concerned. That stuff resembles rock wool, the crappy attic insulation.

There are very few asteroids that you could call "space rocks", meaning monolithic structures in-situ. Some are metallic, a minority stony minerals. Most (a vast majority) of the smaller asteroids (under 100 miles dimension) seem to be completely-loose rubble piles. Some fraction of those seem to be cemented-together to one extent or another by ices buried inside. Another majority fraction seem to be quite dry, fluffy, and loose. Some of these have already been seen to fly apart when the centrifugal force of their rotation rate exceeds their mutual gravitational force. The smaller they are, the more likely it seems they are dry, loose, and rather fluffy.

How do you attach anything to a loose rubble pile like that? There is negligible friction on a stake driven in, because there is negligible normal force exerted by the gravity of the material upon the sides of the stake. That makes friction forces pretty near zero. Pull laterally on a stake like that, and the particles making up the asteroid merely part and flow around the stake. Again, little force at all. There's almost no resistance to driving the stake in, or extracting it, for the same reason.

De-spin one of these things so you can stuff it in a can or a bag? One of these loose, fluffy, dry rubble piles that seems to be the vast majority of the smallest objects? Just how will you do that? It'll fly apart the moment you touch it, in any direction, with any force exceeding the vanishingly-small force of self-gravity.

It's questions like this that make me think NASA's asteroid-redirect mission is nothing but a fool's errand.

GW

Tom Kalbfus · 2014-04-03 17:17:20

The energy source is simply the Sun, that is the most convenient form of energy in near Earth Space. as for what a Stanford Torus is, I copied this from Wikipedia:

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

{{for|fictional structures for living in space|Space stations and habitats in popular culture}}

[[Image:Stanford torus external view by Don Davis AC76-0525.jpg|thumb|right|Exterior view of a Stanford torus. Bottom center is the non-rotating primary solar mirror, which reflects sunlight onto the angled ring of secondary mirrors around the hub. Painting by Donald E. Davis]]
[[Image:Internal view of the Stanford torus.jpg|thumb|right|Interior of a Stanford torus, painted by Donald E. Davis]]

The '''Stanford torus''' is a proposed design<ref>{{cite news| url=http://settlement.arc.nasa.gov/75SummerStudy/Table_of_Contents1.html| title=Space Settlements: A Design Study|year=1977| author=Johnson, Holbrow|publisher=National Aeronautics and Space Administration}}</ref> for a [[space habitat]] capable of housing 10,000 to 140,000 permanent residents.<ref>Johnson. NASA Study, pg 1, "The Overall System", pg 60, Summary</ref>

The Stanford torus was proposed during the 1975 NASA Summer Study, conducted at [[Stanford University]], with the purpose of speculating on designs for future space colonies<ref>Johnson. NASA Study, pg VII, "Preface"</ref> ([[Gerard O'Neill]] later proposed his [[Bernal sphere#Island One|Island One]] or [[Bernal sphere]] as an alternative to the torus<ref>Gerard K. O'Neil, "The High Frontier", William Morrow & Co., 1977, p149</ref>). "Stanford torus" refers only to this particular version of the design, as the concept of a ring-shaped rotating space station was previously proposed by [[Wernher von Braun]]<ref>Von Braun, W.:Crossing the Final Frontier, Colliers, March 22, 1952</ref> and [[Herman Potočnik]].<ref>Hermann Potočnik: The Problem of Space Travel (1929)</ref>

It consists of a [[torus]], or [[doughnut]]-shaped ring, that is 1.8 km in diameter (for the proposed 10,000 person habitat described in the 1975 Summer Study) and rotates once per minute to provide between 0.9g and 1.0g of [[artificial gravity]] on the inside of the outer ring via [[centrifugal force]].<ref>Johnson, NASA study, p46</ref>

Sunlight is provided to the interior of the torus by a system of [[mirror]]s. The ring is connected to a hub via a number of "spokes", which serve as conduits for people and materials travelling to and from the hub. Since the hub is at the rotational axis of the station, it experiences the least artificial gravity and is the easiest location for [[spacecraft]] to dock. Zero-gravity industry is performed in a non-rotating module attached to the hub's axis.<ref>Johnson. NASA Study, Chap. 5</ref>

The interior space of the torus itself is used as living space, and is large enough that a "natural" environment can be simulated; the torus appears similar to a long, narrow, straight glacial [[valley]] whose ends curve upward and eventually meet overhead to form a complete circle. The population density is similar to a dense suburb, with part of the ring dedicated to agriculture and part to housing.<ref>Johnson. NASA Study, Chap. 5</ref>

==Construction==
The torus would require nearly 10 million tons of mass. Construction would use materials extracted from the [[Moon]] and sent to space using a [[mass driver]]. A mass catcher at [[Lagrangian point#L2|L2]] would collect the materials, transporting them to [[Lagrangian point#L4 and L5|L5]] where they could be processed in an industrial facility to construct the torus. Only materials that could not be obtained from the Moon would have to be imported from Earth. [[Asteroid mining]] was an alternative source of materials.<ref>{{cite web | url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770014162_1977014162.pdf | title=Space Settlements: A Design Study | publisher=NASA Technical Reports Server | year=1977 | accessdate=October 20, 2012 | author=Johnson, Richard D.; Holbrow, Charles | pages=201}}</ref>

==General characteristics==
* Location: Earth–Moon [[Lagrangian point#L4 and L5|L5 Lagrangian point]]
* Total mass: 10 million tons (including radiation shield (95%), habitat, and atmosphere)
* Diameter: {{convert|1790|m|mi|abbr=on}}
* Habitation tube diameter: {{convert|130|m|ft|abbr=on}}
* Spokes: 6 spokes of {{convert|15|m|ft|abbr=on}} diameter
* Rotation: 1 [[revolution per minute]]
* Radiation shield: {{convert|1.7|m|ft|abbr=off|sp=us}} thick raw [[lunar soil]]

Last edited by Tom Kalbfus (2014-04-03 17:20:40)

SpaceNut · 2014-04-04 19:31:33

While a Station would make it easier to explore for a longer period of time it does not really help make it cheaper to do or possible due to scale of operations to make it happen....

GW Johnson · 2014-04-05 09:48:54

OK, I followed Tom's link in the post above and found out what a "Stanford Torus" really is: a scaled-up version of the wheel space station idea dating from the late 1930's. It's an idea that makes a great deal of sense, by itself as if cost were no object. But, we never built one due to the costs of shipping its structures and parts up from Earth, as Spacenut suggested in his post just above.

That's where the proposals to use off-Earth mass for its construction are coming from: not having to fly up out of a big gravity well, which is horribly expensive, as we all know. There's nothing wrong with the off-Earth mass idea, except in its conversion to useful building materials. Those materials must have tensile strength (internal air pressure = hoop stress, and centrifugal force = longitudinal stress in the ring). Those materials must be capable of being joined in space, too.

My question is this: how do you convert rocks and rock dust into something that can be had in sheet, plate, and forged shapes, with tensile strength comparable to steel or aluminum, and which won't tear out around rivets, and which will respond favorably to welding? Even if you use a nickel-iron asteroid (rare as they are), where is your steel going to be made? Naturally-occurring nickel-iron is not a suitable construction material.

I have seen asteroid mass-based proposals before. I have never seen a credible answer to my questions about conversion to useful construction materials.

GW

Terraformer · 2014-04-05 13:08:48

Perhaps Basalt fibre, if a suitable asteroid could be located? Maybe even make the main load bearing part as a single piece of basalt...

Tom Kalbfus · 2014-04-05 13:15:11

GW Johnson wrote:

OK, I followed Tom's link in the post above and found out what a "Stanford Torus" really is: a scaled-up version of the wheel space station idea dating from the late 1930's. It's an idea that makes a great deal of sense, by itself as if cost were no object. But, we never built one due to the costs of shipping its structures and parts up from Earth, as Spacenut suggested in his post just above.
That's where the proposals to use off-Earth mass for its construction are coming from: not having to fly up out of a big gravity well, which is horribly expensive, as we all know. There's nothing wrong with the off-Earth mass idea, except in its conversion to useful building materials. Those materials must have tensile strength (internal air pressure = hoop stress, and centrifugal force = longitudinal stress in the ring). Those materials must be capable of being joined in space, too.
My question is this: how do you convert rocks and rock dust into something that can be had in sheet, plate, and forged shapes, with tensile strength comparable to steel or aluminum, and which won't tear out around rivets, and which will respond favorably to welding? Even if you use a nickel-iron asteroid (rare as they are), where is your steel going to be made? Naturally-occurring nickel-iron is not a suitable construction material.
I have seen asteroid mass-based proposals before. I have never seen a credible answer to my questions about conversion to useful construction materials.
GW

I have a suggestion, what if you spun up a nickle-iron asteroid? what would happen? Some asteroids may be piles of rubble, but others could be large rocks. Try this experiment, pick a rock up off the ground and spin it on a potters wheel with sufficient velocity such that it experiences 1g of centrifugal force on its outer edges. Would a solid granite break up under the centrifugal force it experiences. Some asteroids aren't round, seems likely that an asteroid that is a rubble pile would be likelier to be rounder than one that was not. Suppose we found a non-round nickle-iron asteroid that was about 1.8 km on its long axis and using ion thrusters began spinning it up? Do you think we could make it spin at a rate of once per minute without it breaking up into smaller pieces? A spin rate of once per minute will produce 1 gravity of centrifugal force on the asteroids outer extremities, probably all the loose material will fly off into space, but if the asteroid is one solid rock, it may hold itself together, and then perhaps would can build a Stanford torus out of its material as it spins. We'd just have to be careful not to weaken its structure as we mine it. We don't actually need a full Earth gravity either, perhaps lunar gravity would suffice, we could build smelter plants to process iron ore into steel, I mean we can do this on Earth, but as proof of concept, we could try creating a vacuum chamber under a dome and see if we can manufacture steel in a vacuum. What do you think? this would be cheaper than sending something into space and trying it.

One idea that's been talked about was building a giant mirror in space, could be a Solar Sail, that focuses sunlight on one spot in the asteroid, which we spin. The suns rays makes the center spot molten and the spin of the asteroid pushes the molten material outward, as it pushes against the outer cooler rock it cools and hardens. The asteroid spins slowly as we focus sunlight on it, eventually it hollows out. Other proposals involved heating water inside that expands outward as the asteroid become molten forming a bubble, which becomes the basis of a Bernal Sphere. Once it cools you can spin it up for gravity and live on its inside.

We need to try this out! There are plenty of asteroids to experiment on, we just need to try these things and see what happens The first step would be to spin up an asteroid so that centrigal forces exceed the asteroids gravity, I think for some spinning asteroids this may already be true.

I'd say start with what nature has already provided us and work from there. Perhaps with a space probe visit to a rapidly rotating asteroid.
_________________________________________________________
Abstract
A survey of 62 small near-Earth asteroids was conducted to determine the rotation state of these objects and to search for rapid rotation. Since results for 9 of the asteroids were previously published (Pravec, P., Hergenrother, C.W., Whiteley, R.J., Šarounová, L., Kušnirák, P., Wolf, M. [2000]. Icarus 147, 477–486; Pravec, P. et al. [2005] Icarus 173, 108–131; Whiteley, R.J., Tholen, D.J., Hergenrother, C.W. [2002a]. Icarus 157, 139–154; Hergenrother, C.W., Whiteley, R.J., Christensen, E.J. [2009]. Minor Planet Bull. 36, 16–18.), this paper will present results for the remaining 53 objects. Rotation periods significantly less than 2 h are indicative of intrinsic strength in the asteroids, while periods longer than 2 h are typically associated with gravitationally bound aggregates. Asteroids with absolute magnitude (H) values ranging from 20.4 to 27.4 were characterized. The slowest rotator with a definite period is 2004 BW18 with a period of 8.3 h, while 2000 DO8 and 2000 WH10 are the fastest with periods of 1.3 min. A minimum of two-thirds of asteroids with H > 20 are fast rotating and have periods significantly faster than 2.0 h. The percentage of rapid rotators increases with decreasing size and a minimum of 79% of H ⩾ 24 objects are rapid rotators. Slowly-rotating objects, some with periods as long as 10–20 h, make up a small though significant fraction of the small asteroid population. There are three fast rotators with relatively large possible diameters (D): 2001 OE84 with 470 ⩽ D ⩽ 820 m (Pravec, P., Kušnirák, P., Šarounová, L., Harris, A.W., Binzel, R.P., Rivkin, A.S. [2002b]. Large coherent Asteroid 2001 OE84. In: Warmbein, B. (Eds.), Proceedings of Asteroids, Comets, Meteors – ACM 2002. Springer, Berlin, pp. 743–745), 2001 FE90 with 265 ⩽ D ⩽ 594 m (Hicks, M., Lawrence, K., Rhoades, H., Somers, J., McAuley, A., Barajas, T. [2009]. The Astronomer’s Telegrams, # 2116), and 2001 VF2 with a possible D of 145 ⩽ D ⩽ 665 m. Using the diameters derived from nominal absolute magnitudes and albedos, the remainder of the fast rotating population is completely consistent with D ⩽ 200 m. Even when taking into account the largest possible uncertainties in the determination of diameters, the remainder must all have D ⩽ 400 m. With the exceptions of 2001 OE84, this result agrees with previous upper diameter limits for fast rotators in Pravec and Harris (Pravec, P., Harris, A.W. [2000]. Icarus 148, 589–593) and Whiteley et al. (Whiteley, R.J, Tholen, D.J., Hergenrother, C.W. [2002a]. Icarus 157, 139–154.

Last edited by Tom Kalbfus (2014-04-05 13:30:51)

GW Johnson · 2014-04-05 17:02:32

Five points:

1. What I have been trying to tell everyone is that almost none of the asteroids are monolithic pieces of rock. Virtually all of these things under 100 mile size are very loosely-aggregated piles of rubble. If that were not true, then most meteors would strike the surface of the Earth instead of being mid-air burnups or explosions (bolides).

A solid rock over 0.25 inch (6mm) diameter survives Earth entry at meteor speeds (around 37 miles/sec). We've already seen it in the melt crust depth. Most meteors are burnups or bolides. Therefore most small asteroids are very loose rubble piles. QED.

Ground truth has always been very far from remote observations, for some centuries now, so I would NOT put much faith in remote observations trying to tell you how many of these things are solid objects vs loose rubble piles. One cited remote observation paper is NOT proof, not at all.

2. What good is basalt fiber if you have no matrix with which to make a composite? I mean, for making structural materials, not ropes or loose-weave fabrics.

As for melting this stuff in-situ and hoping to form fibers or bubbles by spin effect and/or gas inflation is not a reasonable proposition. That sort of thing barely works for glass blowers, and then only with very specific composition requirements. Screw that up, and none of the glass blowing approaches work at all. These things are very most definitely not silica glass composition.

3. Itokawa is a ground-truth example of a loose rubble pile asteroid (the Japanese probe touched down on it), which is very most definitely not anything approaching spherical in shape. So the notion that rubble piles should be nearly spherical is quite incorrect.

A rubble pile about to fly apart from centrifugal forces is more like a prolate ellipsoid, although not exactly. There is a belt of debris piled up around the equator of the spin. It actually forms a sharp ridge around that equator. At the poles of the spin are the lowest surface elevations. We've already seen objects like this, and I saw a news report the other day that one of these was observed breaking up.

4. There is a steel-making process that works under either an inert atmosphere or even better a vacuum: it is the electric furnace. But it works only with scrap steel, not with any sort of ores. Composition refinement is controlled only by what you put in the furnace.

5. A very small minority of these objects will be monolithic chunks of nickel-iron alloy, monolithic unless cracked by prior collisions, I might add. It would be more difficult to melt one of these than one of stony minerals. The meltpoint temperatures are simply much higher.

"Mining" one of these nickel-iron objects would be very difficult as well, because the material is so hard. It's not formable, it's not forgeable, it's not weldable. It's just not a useful construction material, as it naturally occurs. But it is hard. So drills won't work very well.

I think the larger rubble-pile mineral bodies would be better mining targets, at least near-term. That's because the volatiles inside them as ices would be more valuable in the near-term, and easier to obtain.

The notion of using concentrated solar energy to drill out a spinning mineral asteroid into a hollow shape via melting, I like. That one actually almost sounds feasible to me. I am not sure if the process can be controlled well enough, but who knows? (Nobody, until we try it in-situ.)

GW

Tom Kalbfus · 2014-04-06 05:37:06

Well one way to mine a nickel-iron asteroid is to spin it up, and if it breaks up you've mined it, and if it doesn't you've got some solid piece of nickel-iron asteroid. I'll bet some of the smaller chunks that fly apart after this process are solid. Have you ever considered that spinning up an asteroid till it breaks apart is one method of mining it?
My guess is such an asteroid won't explode like a bomb, the asteroid were talking about is on a scale similar to a Stanford torus, in that is about 1.8 km on its long axis. The asteroid would take a while to spin up, rock and dirt will pile toward the equator and objects will fly off the crust and go into orbit as the asteroid gradually increased its rate of spin. The trick is how to spin it up. Maybe long cables wrapped around the asteroid might be the best way. A rocket actually attached to the asteroid's crust might get buried under dirt and rubble as the stuff rolls toward the equator. One idea I had would be to wrap the asteroid in a cable mesh that has a higher melting point than the asteroid material. A Tungsten cable net might do the trick, then we concentrate solar energy on it to melt the rubble together.

Last edited by Tom Kalbfus (2014-04-06 05:45:23)

GW Johnson · 2014-04-07 09:37:25

Mining by spin-up to break-up? 1.8 km long dimension, 1 hour spin period, using the data above.

Lesse, 900 m radius at 1 rev/hour (or .0166666 rpm, or .000277777 rev/sec, or .00175 rad/sec). The centripetal acceleration would be r*w^2 = .00276 m/s (or .00028 gee). That sounds roughly comparable to the gravitational binding acceleration, without actually running a numerical check on it, so the numbers here are at least sort-of realistic. Under rotation, the "tip speed" is r*w = 1.58 m/s.

About 4 times that tip speed is the speed each chunk leaves the breakup, assuming it breaks up at 1 rev/hour. That's 6.3 m/s for the minimum delta-vee to go chase down each individual chunk and return it to the vicinity of the asteroid for processing. If it breaks up at faster rotation rates, this speed is proportionally higher. Time may be important, forcing you to fly a lot faster than that, in order to chase down each chunk, but we'll ignore that. If the asteroid breaks up into thousands, or perhaps tens of thousands, of chunks, you'll spend an awful lot of propellant chasing them down. Thousands to tens of thousands of m/s worth of delta-vee.

The alternative is to catch the chunks by some sort of net or enclosure that you must erect about an already-spinning asteroid. There are two problems with this, even assuming we have the technical capability to do such a thing (which we do not, right now): (1) the battering it gets with the chunks is unevenly-distributed, which eventually causes a collision with the spinning asteroid not yet fully broken-up (that would likely destroy the net). (2) how do we successfully erect a flexible net-like enclosure when the pressure of the sunlight on the illuminated side wants to push it outward into the side facing darkness (i.e., light pressure squashes your net until it contacts the spinning asteroid inside, again destroying the net). Plus, if it really is a net, it will "leak" all the small bits through the mesh. The smallest ones are the easier-to-process ones.

All of that speculation has still ducked the original question: if the asteroid is pieces loosely bound by gravity, how do you push on it to spin it up faster, without tearing it up the moment you try to apply your force? If it's solid, that's no problem. But, even a nickel-iron object will have suffered lots of collisions and be severely cracked internally. I'd bet no two of them have the same structural integrity.

That last suggests that the enclosure option would "work" if the asteroid broke up the moment you pushed on it to try and spin it up. But, it will break up into big chunks as well as little ones. Your enclosure must be strong enough to counter the impact of some really massive objects (tens of thousands of tons, moving several m/s, distributed very unevenly in space and time. If the asteroid were structurally stronger, you've got ten thousand ton chunks moving at dozens to hundreds of m/s, which is even worse. The enclosure would most likely have to be made of some "unobtainium" material. I seriously doubt steel could do this.

GW

Terraformer · 2014-04-07 15:53:26

What about just enclosing it, and then mining it? The enclosure is there to stop it from flying apart when you grab chunks, not to allow you to change its spin.

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