The SLS: too expensive for exploration?

RobertDyck · 2016-05-15 09:15:55

Tom Kalbfus wrote:

Lunar orbit isn't stable.

Are you bored? This is silly. First, Lunar orbit is stable. Low Earth Orbit is not because there's a little atmosphere. Atmospheric drag causes anything in LEO to slow, causing it to fall, which speeds it up. But drag causes it to slow, so it falls. You have to be about 800km up to be stable, at which point you're in the Van Allen belts. That's not a coincidence; the same atmosphere that causes drag in LEO keeps out the plasma of Van Allen belts. But the Moon doesn't have atmosphere. And the Moon doesn't have a magnetic field, so no Van Allen belts either. Lunar orbit is stable.

Tom Kalbfus wrote:

You know its a pity those Nova rockets didn't get built, they would have been great for going to Mars!

Nova? Watch this: The Launch of Apollo 4

You can hear Walter Cronkite freak out as the building he's in shakes. And you want a rocket even larger? Tell you what, there is SLS. Saturn C5 was supposed to lift 130 metric tonnes to LEO, or 45t to trans-Lunar trajectory. Saturn V as built could lift 118t to LEO, or 47t to trans-Lunar. Shouldn't be a surprise that Saturn V was optimized for the Moon. SLS block 2 was supposed to lift 130t to LEO, but SLS block 2B will lift less to LEO and the same or more to the Moon or Mars. So similar. In 2012, Pratt & Whitney Rocketdyne (now Aerojet Rockeydyne) said SLS block 2 using their liquid boosters with a pair of F-1B engines each could lift 150t to LEO. That would require a core stage with 5 SSME, and an upper stage with J-2X. Doesn't look like that's not going to happen, but it's the closest to Nova you're likely to get.

Last edited by RobertDyck (2016-05-15 09:18:29)

Terraformer · 2016-05-15 09:34:33

Well, the stability of Lunar orbit depends on altitude. Low orbit is unstable, because the mass isn't consistent - the orbit will gradually be distorted until you impact the surface.

If we have an actual base, I would expect it to be well stocked with food. 200kg is enough for a years emergency supply for an adult human (more like 100kg if you go heavy on the fats), so there is no reason to try to cut mass there. As long as their recycling systems can last then, they should be able to hold out for a rescue. Having a deep larder in an isolated base is just good sense. It also means there's plenty of time for a rescue mission to be organised, enough time perhaps to find out what went wrong and avoid the mistakes.

Or they could try to grow potatoes and live on those. Eh. The Selenite probably wouldn't be as successful though.

Tom Kalbfus · 2016-05-15 10:24:31

RobertDyck wrote:

Tom Kalbfus wrote:
Lunar orbit isn't stable.
Are you bored? This is silly. First, Lunar orbit is stable. Low Earth Orbit is not because there's a little atmosphere. Atmospheric drag causes anything in LEO to slow, causing it to fall, which speeds it up. But drag causes it to slow, so it falls. You have to be about 800km up to be stable, at which point you're in the Van Allen belts. That's not a coincidence; the same atmosphere that causes drag in LEO keeps out the plasma of Van Allen belts. But the Moon doesn't have atmosphere. And the Moon doesn't have a magnetic field, so no Van Allen belts either. Lunar orbit is stable.

Tom Kalbfus wrote:
You know its a pity those Nova rockets didn't get built, they would have been great for going to Mars!
Nova? Watch this: The Launch of Apollo 4
https://i.ytimg.com/vi/SM2KWCMrOYw/hqdefault.jpg?custom=true&w=320&h=180&stc=true&jpg444=true&jpgq=90&sp=68&sigh=8YF-TOp-FZq_bKWUBkC_DBhse_Y
You can hear Walter Cronkite freak out as the building he's in shakes. And you want a rocket even larger? Tell you what, there is SLS. Saturn C5 was supposed to lift 130 metric tonnes to LEO, or 45t to trans-Lunar trajectory. Saturn V as built could lift 118t to LEO, or 47t to trans-Lunar. Shouldn't be a surprise that Saturn V was optimized for the Moon. SLS block 2 was supposed to lift 130t to LEO, but SLS block 2B will lift less to LEO and the same or more to the Moon or Mars. So similar. In 2012, Pratt & Whitney Rocketdyne (now Aerojet Rockeydyne) said SLS block 2 using their liquid boosters with a pair of F-1B engines each could lift 150t to LEO. That would require a core stage with 5 SSME, and an upper stage with J-2X. Doesn't look like that's not going to happen, but it's the closest to Nova you're likely to get.

What's wrong with big? So long as it gets the job done, that's all that matters! It would be easier to put together a manned mars mission with a Nova rocket, you don't need to coordinate multiple launches. A Nova could do Mars Direct, you could land a hab on the planet, and an Earth Return Vehicle, but with Nova, those things could be bigger! And with reusable rocket stages, a Nova would be cheaper to launch! What if we could bring down the cost of a Nova launch to merely that of a Saturn V with throwaway stages, would it be worth it? Suppose you could do that by recovering the bottom Nova Stage and reuse it several time, and you just manufacture more of the upper stages for each mission. Sound like a good deal?

Last edited by Tom Kalbfus (2016-05-15 10:24:44)

GW Johnson · 2016-05-15 12:20:10

There never was any Nova hardware ever built. And Saturn C-8 was not the only paper design referred to as Nova. If there had been any hardware, it would have been just as one-shot/non-reusable, and just as expensive pound-for-pound as Saturn 5.

To use Tom's argument against him, he thinks reducing number of launches by flying bigger rockets makes things cheaper. It does not. If it did, then ISS would not have cost $100B to build. I think we could build a new one with today's rockets only (not even Falcon-Heavy) for about 10% that price. They're all much smaller launch weight and price than was shuttle.

It's not about size, it's about smarts. There's smart ways to do things, and there's stupid ways. NASA, being a government bureaucracy, seems compelled to try stupid first. At the cost of 3 crews so far.

As for solid strap-ons or solids as ICBM's, the discussion a few posts above correctly refers to the "wooden round" nature of a solid: years of storage followed by instant use. That's a huge advantage over any conceivable liquid system. The Russian R-7 is liquid propellant, so were our original Atlas, Titan, and Thor missiles. But we quickly saw the advantage of the solids and went to Minuteman and Polaris/Poseidon. So did the Russians with SS-18, etc.

I will say this about ICBM's: usually the "bus" that carries and deploys the warheads and decoys has precision propulsion, using storables like hydrazine blend / NTO. You don't get the precision for min CEP out of straight solids. But for satellite launch, straight solids are good enough. The old Scout launcher was a 4-stage solid. It had one flight test failure out of four, then a perfect record over 3 decades and thousands of launches. That right there is proof of a safe, man-ratable solid, although Scout was never man-rated (too little to carry a man).

By the way, those were all single O-ring joints on the case ends on all those motors!

The posts above fail to focus on the other huge advantage of a solid: higher frontal thrust density for a given stage cross section than any other kind of motor at all. That's why they are still so popular as launch SRB's (strap-ons). Nothing else gives that kind of push, and at low speed first stage conditions, Isp is less relevant by far than gross frontal thrust.

Maybe hybrids will mature enough to be used in preference to solids, and maybe not. Hybrids potentially offer almost as much frontal thrust density at a bit better Isp, plus the ability to shut down. Except that, nearly all the companies who have made them insist on adding solid oxidizer to the fuel grain in order to achieve burn rate. As a result, none really shut down when you stop the LOX. So what's the point?

The closest thing to a proper hybrid that I know of, is the rubber-acid motor used in Spaceship Two. It really does shut down.

GW

RobertDyck · 2016-05-15 13:11:23

One design criteria of ISS was to keep Russian engineers busy. Bill Clinton and his administration didn't want unemployed Russian engineers designing ICBMs for rogue nations. But replace it now? Why? We have ISS, so just use it. Don't replace it, don't decommission it, just use it. But if we were to design a new one, I've said before the 1970s design with 2 Skylab modules makes more sense. That would have required 4 launches of Saturn 1B including airlock, multiple docking adapter, and 2 manned missions. Each Saturn 1B cost less than a single Shuttle launch. If you wanted to do it today, a self-launching station as a custom upper stage for Falcon 9. Skylab was 6.6m diameter, the fairing for Falcon 9 is 5m, but current ISS modules are also 5m diameter. Falcon 9 can lift as much mass to LEO as Saturn 1B; actually a tiny bit more. So a self-launching upper stage should be as big as a Skylab workshop. Now that would be something! If you replaced the current upper stage with LOX/LH2, wouldn't that increase lift capacity? So even more mass than Skylab? EUS as a launch-wet workshop, 8.4m diameter, on a single Falcon 9 core stage? Anyway, moot point, we have what we have.

GW Johnson · 2016-05-15 16:48:01

RobertDyck:

I did NOT say we need to replace ISS. I said we could build exactly the same thing again, for about 10% of the cost, launching the same modules with rockets we already have.

If you are interested, I would NOT build exactly the same thing again, if and when replacement in the 2020's becomes necessary. Sooner or later, it will need replacement, because what is up there will wear out.

I would build a much larger volume out of things like Bigelow B-330's, but modified for a different internal configuration. I would dock these together in a baton shape, with solar panels, docking facilities, and flywheels in the center. I would spin it end-over-end for artificial gravity.

To this, I would add a fly-in-formation non-spinning zero-gee facility, which would be a module resembling a shuttle bay with arm, enclosed within a space frame covered in aluminized Mylar blankets. I would hang lights inside, and lots of solar panels outside. This is the zero-gee unpressurized work space for assembly and repair on-orbit. The lighting eliminates visibility problems, and being within the reflective blankets, brings workpiece temperatures up to near room temperature, by means of the radiated power in the lighting.

That kind of facility does not require the kind of idiotic spacesuits we have been using. All that is needed is vacuum-protective underwear, plus a pressure-breathing helmet and tidal-volume bag. You can even work barehanded up to about 30 minutes, if need be.

GW

RobertDyck · 2016-05-15 19:13:45

Sorry. There is some talk about "decommissioning" it. Boeing wants to build another. This talk became so serious that Russia has plans to separate their parts, and keep them in space. Congress passed a bill demanding that ISS stay. So Congress doesn't want to waste money, but someone wants to.

I like your spinning inflatable thing. However, instead of separate I would connect zero-G and artificial gravity sections. The TV show "Extant" shows a good example: season 1 episode 1, the season premier. The hub module has a rotation bearing with the zero-G section. So walk down a ladder from the hub to the artificial gravity section, without have to go outside. The show has a silly Hollywood plot, but shows an interesting station design.

Last edited by RobertDyck (2016-05-16 09:46:58)

GW Johnson · 2016-05-16 08:22:59

Hi RobertDyck:

I went with separate for two reasons: (1) you could add propulsion to the repair/assembly bay portion, and send it off to do jobs, and (2) we currently have no developed, off-the-shelf technology for lubricated bearings that function for extended lifetimes in vacuum.

I think that if we do come up with the spin bearing technology and hardware, we could take the two separate components and dock them together, just like you describe. I just didn't want that piece of technology to delay the station we need, when we need it, sometime after 2024.

My guess is that the Russian modules will also be showing their age when the current ISS is decommissioned and disassembled. Anything they build with those will prove unsafe. We've already seen overage modules before, in the Salyut series and in Mir. Aging hardware does not respect political boundaries, it simply "is".

GW

SpaceNut · 2016-05-19 20:46:12

I remember a recent article on NASA and Roscosmos discuss ISS suicide plunge requirements

Meeting (TIM) to refine procedures relating to the disposal of the Station at the end of its service life, or in the event of an emergency. The deorbit burn capability – which won’t exist until at least 2017 – requires multiple docked vehicles firing in unison to push the Station to its fiery demise.

The Station is expected to continue operations until at least 2024, a date that could be extended as far as 2028. However, the financial and logistical support from its international partners may eventually be overtaken by the condition of critical hardware required to keep the orbital outpost operational.
Technical evaluations have shown the Station is likely to be able to press through to 2028, around the time NASA is expected to start dedicating major elements of its funding towards missions to Mars.
While the hardware-limiting factor requires no immediate demand for a deorbit plan, an emergency scenario – where the Station becomes crippled and has to be evacuated – would potentially call for its disposal within a relatively short timescale.

But as mentioned by Rob on the windows that the space junk is the only thing that could hurt the station....

ISS End-of-Life Disposal Plan

GW Johnson · 2016-05-20 15:09:33

I do not understand why they think this deorbit-ISS thing is so hard to do, and that the capability will not exist until 2017. Further, it seems to be based only around Orion and Soyuz. Soyuz thrust capability is limited, and Orion won't fly again until 2018 at the earliest, now. The one that flew was essentially a boilerplate mass model with a heat shield, not the real McCoy.

Yet they are paying for Dragon in two versions, the Cygnus, and even the Dreamchaser, plus the Boeing CST-100.

Here's a really stupidly-simple idea that doesn't even need a capsule, and likely could be done by late this year, if need be:

Launch a very slightly-modified Falcon-9 with additional propellant tanks and some maneuvering thrusters and their propellant, inside the payload shroud, along with a docking ring compatible with the station. This might work best before the final crew departs, as they can do the docking with the arm. The modification ties the propellant tanks in the payload shroud to those in the second stage. You do not separate payload from second stage.

The Falcon-9 payload is listed as 13 tons to LEO at 23.5 deg out of Canaveral. I'm guessing that's maybe 10 tons to the ISS orbit. Lets say we get to carry only 5 tons of additional propellant inside the payload shroud. That's about 10,000 lbm of propellant, to be fired through a demonstrably-restartable second-stage engine at around 320 sec Isp. There's something like 3.2 million pound-sec of total impulse available from such a rig. So, how much impulse do they need to deorbit the damned thing, anyway?

Assuming the station is near 100 tons, and we add 20 tons to it with the second stage plus propellants, mass ratio is 120/115=1.043 or thereabouts, trying to be very conservative. For Isp near 320 sec, exhaust velocity is near 10,000 ft/sec. I compute a delta-vee capability near 420 ft/sec. That's 1.6% of the basic orbital velocity. For heaven's sake, isn't that enough?

The biggest problem I can forsee with this is that the ISS probably cannot support the full thrust of a Falcon-9 second stage, without breaking up. If that's the case, then launch some MMH-NTO and a couple of Super Draco's in that payload shroud instead. Let them burn through the same 5 tons of propellant.

The fact that this contingency wasn't in the design from day 1 bespeaks the same error they made with Skylab decades ago. They should have learned from Skylab. The Russians certainly did. The Salyuts and Mir all had self-deorbit capability built in.

There's really no excuse for this to be an issue at all.

GW

Last edited by GW Johnson (2016-05-20 15:11:40)

Terraformer · 2016-05-20 16:27:32

Isn't the station a lot more than 100 tonnes? Last I heard, it was over 400...

GW Johnson · 2016-05-20 18:39:17

You're quite right. I looked it up. 419.5 tons (metric).

So we use a Falcon-Heavy and 20 tons of propellants, instead of Falcon-9 and 5 tons. It's supposed to fly this year.

I'd say use Dragon v2 except that its internal propellant store is only 1.2 tons. We'd need to connect that with some large propellant tanks. Easier to just send the tanks, an engine of suitable thrust, plus a docking ring.

GW

Last edited by GW Johnson (2016-05-20 18:40:03)

RobertDyck · 2016-05-21 00:47:29

I had quoted a statement by NASA years ago. They stated they needed a docking adapter that could mate a 100 ton Shuttle to a 100 ton station. The Russian docking adapter would do the job, but all NASA had was the Apollo docking adapter. It could dock CSM to LM, but certainly not the much heavier Shuttle. But that statement referred to an earlier phase of station construction. Sorry if this created confusion.

GW Johnson · 2016-05-21 10:14:15

Aw, that's OK. I didn't know the numbers myself. It only matters to the propellant tonnage you need to deorbit the thing. Kluging up a payload of tanks, a suitable engine, a docking ring, plus some guidance ought to be a relatively easy and fast thing to do. There could be many ways to do it, including some multiple of the current Cygnus and Dragon cargo vehicles. The "trick" is getting the extra tons of propellant up there.

I'm just very frustrated to find out that NASA has nothing in place to take care of this problem, even after two decades. They literally have not yet thought this through. That is SIMPLY INEXCUSABLE after the 1979 crash of Skylab onto Australia, plus the example of the Russians building in deorbit capability ever since Skylab, and their Cosmos 954 crash in Canada the previous year.

I've not run the orbital mechanics to see what delta vee is required to turn that orbit into a surface-grazing transfer ellipse. But I'd be very surprised if the delta vee exceeded 1% of orbital velocity. It should be in the ballpark of 250 fps = 80 m/s. That ain't very much.

For hydrazine-NTO with Isp near 300 sec, exhaust velocity ought to be in the neighborhood of 9600 fps = 2.9 km/s for just about any small engine or thruster rig using those propellants. For 1% orbital as the delta-vee, I get a required mass ratio of 1.026 or thereabouts.

Assuming 420 tons for the ISS plus only half the delivered deorbit payload to be deorbit propellants, I'd estimate we need to send no more than about 12 tons of propellant up there in a 24 ton payload vehicle to do that job. Too much for Atlas-5, but a piece of cake for Falcon-Heavy.

If instead the payload vehicle is 3/4 propellants, things lighten up to about 12 tons of propellant in a 16 ton vehicle. Atlas-5 could launch such a thing to the ISS.

If the payload vehicle is 85% propellants, it lightens further to a 13 ton vehicle carrying 11 tons of propellant. Perhaps even Falcon-9 could send that.

Again, we're talking about a small engine, a docking ring, some propellant tanks, and some plumbing plus minimal guidance and attitude thrusters, arranged to fit within the existing shrouds. It ain't hard, and it need not take more than a year to build and demonstrate functionality.

So why is this still a looming issue?

GW

SpaceNut · 2016-05-21 17:44:23

GW Johnson wrote:

So why is this still a looming issue?

1 Loss of life in building it
2 emence costs to build
3 lack of anyone other than a few tourists that have been able to go an live there even if only for a few weeks
4 the obsurdness of dumping it into the ocean

Are there other reason?

GW Johnson · 2016-05-21 21:59:04

Worrying about deorbit is necessary because eventually the thing is going to wear out, and start becoming dangerous to its occupants.

We've already seen this problem with the Salyuts and Mir. (Skylab wasn't occupied most of the years it was up there, so we didn't see it with that one.)

The projected date range for this with ISS is somewhere between 2024 and 2028, I believe from what I have read. It'll be about 3 decades old by then. If it follows the same pattern as Mir, about half the systems will not function hardly at all, and a module or two will be unpressurized and unrepairable.

If there's a fire, we might have to bring it down sooner. A fire already happened on one of the Russian stations, it was a stroke of luck it was not destroyed with loss of crew.

You can't assemble these things from the lightest-weight modules built by the low bidders, and expect them to last forever. Stuff built to last requires a different design approach that we just have not seen yet in the space business.

GW

Last edited by GW Johnson (2016-05-21 22:00:59)

SpaceNut · 2016-05-22 08:44:48

First module up was 20th November 1998 with the First ISS Segment Launches by Russia. The first segment of the ISS launches: a Russian proton rocket named Zarya (“sunrise”). 4th December 1998 was the First U.S.-bult component launches Unity, the first U.S.-built component of the International Space Station launches—the first Space Shuttle mission dedicated to assembly of the station. 7th February 2001 U.S. Lab Module Added
Destiny, the U.S. Laboratory module, becomes part of the station. Destiny continues to be the primary research laboratory for U.S. payloads.

Since it appears that lifetime of modules is just 20 years we should already be in full design and build mode to replace these modules if we want to continue to have an orbiting space presence....

Tom Kalbfus · 2016-05-22 09:00:05

Seems no me Skylab deorbited just fine, no one got hurt. One idea is to put something in orbit high enough so it doesn't deorbit, what if we raised the altitude of an orbit to 1,000 kilometers? Seems to me then that it wouldn't deorbit within anyone's lifetime. An orbit of 1,000 km has a period of 105.62 minutes, and orbit of 200 km has a period of 88.96 minutes according to this orbit calculator:
http://orbitsimulator.com/gravity/artic … ator2.html

I think 1,000 km would make a nice "graveyard orbit" we wouldn't have to worry about it coming down for a long time. The reason why we use a low orbit is because it is relatively free of radiation.

GW Johnson · 2016-05-22 10:30:26

"Seems no me Skylab deorbited just fine, no one got hurt." --- was a matter of plain dumb luck. The odds favor an ocean impact by 3 to 1, simply the ratio of ocean area to land area. It's unlikely to hit a boat or ship at sea, because of the same area ratio as odds.

Skylab came down over land in western Australia. It did property damage. No one was hurt by the same plain dumb luck. One of the pieces of debris recovered was a film vault weighing over a ton. Items much smaller than that are quite lethal if they hit somebody, even at just 100 mph.

It is ethically unconscionable not to attempt to avoid this risk, once you understand it exists. That crash was in 1979. A lot of stuff got launched since then without any attempt being made to avoid this problem in the design. THAT is what I object to, and it includes ISS.

And don't think the Skylab incident was unique. The Russian nuclear spy satellite Cosmos 954 crashed in Canada only a year or two before. Its plutonium reactor core gravely-polluted a lake where it fell. Great Slave Lake, if memory serves.

Most of the uncontrolled reentries have hit the sea, as the odds say. But the consequences for land strikes have already been severe with Cosmos 954. I've witnessed more than one fall of something big into the Gulf of Mexico. The odds say that sooner or later one of those will hit land, again. A lot of those spy machines are about the size of a small bus.

Orbit lifetimes are longer at 1000 km than 300 km, yes, but not long enough. Most of the other reactor-powered Russian satellites got parked in orbits with perigees out in the van Allen belts (900 miles 1300 km). Cosmos 954 was supposed to be one of those, but its parking rocket blew up.

Just food for thought.

GW

Tom Kalbfus · 2016-05-23 10:40:52

Seems to me the dangerous part was the reactor, not the fact that it hit Earth, if there was no reactor, it would be just another meteor. Lots of meteors hit the Earth all the time, some of them even do damage! And don't forget Space Shuttle Columbia! As they say, accidents happen, that Cosmos 954 was an accident, it wasn't supposed to happen, and there is no way we can guarantee that accidents won't happen in the future either. I think boosting a satellite to a higher orbit might be a better option than deorbiting it, because then the deorbiting might go wrong and it might land in the wrong place. For geosynchronous satellites, you might want to consider accelerating those to escape velocity, or perhaps impacting them on the Moon, they might be fine if we just left them right where they are. Geosynchronous orbit is long lasting, we can probably collect them and recycle them in time.

Last edited by Tom Kalbfus (2016-05-23 10:42:28)

GW Johnson · 2016-05-23 12:05:12

More junk strikes the surface from re-entering objects than anybody wants to admit. Actually, most of it does. Skylab was still mostly one chunk after the hypersonics were completely over. It was peak wind pressure decelerating through Mach 1 about 20,000 feet that finally crushed it to fragments. Same thing happened to Columbia's crew cabin.

When fragments moving 100 to 300 mph strike the surface, damage occurs. Even if it's the sea, you kill fish. On land, the risk of hurting people is much higher, because that's where most of us are. If it's going to enter at all, it is incumbent on us to control where it comes down, to minimize these risks. That's just ethics.

If you put it up there not on an escape trajectory, then eventually it will come down. Above 500 miles or so, it takes a very long time, centuries maybe. But we are obligated to consider what happens when it does, and we have long ignored that. For convenience.

And don't let lightweight construction fool you into thinking it will burn up 100%, because it does not. Those who claim it does are lying to you, for convenience. The original Atlas booster was a stainless steel balloon so thin it would crush under its own weight if not pressurized a few psi. You'd think that would burn up completely; but a chunk of the internal plumbing from John Glenn's booster washed up on an African beach. It was identified from the serial number on the part, which was not damaged by entry heating.

This issue has been known but ignored since the early 1960's. For convenience. How unethical!

The space junk problem is a similar neglected-ethics problem, actually.

GW

Tom Kalbfus · 2016-05-24 20:44:19

GW Johnson wrote:

More junk strikes the surface from re-entering objects than anybody wants to admit. Actually, most of it does. Skylab was still mostly one chunk after the hypersonics were completely over. It was peak wind pressure decelerating through Mach 1 about 20,000 feet that finally crushed it to fragments. Same thing happened to Columbia's crew cabin.
When fragments moving 100 to 300 mph strike the surface, damage occurs. Even if it's the sea, you kill fish.

I think the fish have greater worries than being hit by space junk! Space Junk is not the greatest cause of fish death, the largest one is overfishing, then their is pollution, and of course natural predators try to eat them! The fish killed by falling space junk are quickly replaced and hardly noticed at all by the natural ecosystem. Fish die from a lot of causes, falling space junk is far down the list.

On land, the risk of hurting people is much higher, because that's where most of us are. If it's going to enter at all, it is incumbent on us to control where it comes down, to minimize these risks. That's just ethics.

A lot more people get hit by falling airplanes than by falling space junk.

If you put it up there not on an escape trajectory, then eventually it will come down. Above 500 miles or so, it takes a very long time, centuries maybe. But we are obligated to consider what happens when it does, and we have long ignored that. For convenience.

one has to ask whether it is worth the effort, rather than spending the effort to save a lot of lives in many other ways. It would probably be more important to prevent asteroids from hitting the Earth, than to worry about space junk. Most space junk is light weight, most of it burns up in the atmosphere, and falls where no one lives. What about lightning strikes, how do we prevent those? More people get killed by lightning strikes and tornadoes than get killed by falling space junk, if we can prevent people from getting killed by lightning strikes, we can save more lives that way at much less expense.

And don't let lightweight construction fool you into thinking it will burn up 100%, because it does not.

What is does do is slow down more quickly and what is left is falling no faster than a plummeting airplane. A piece of space junk would kill you just as would a falling airplane, and falling airplanes are much more common, because those are more likely to crash in populated areas, because that is where they land and take off from. Space junk has an equal chance of hitting any nit of land that falls under its orbit.

Those who claim it does are lying to you, for convenience. The original Atlas booster was a stainless steel balloon so thin it would crush under its own weight if not pressurized a few psi. You'd think that would burn up completely; but a chunk of the internal plumbing from John Glenn's booster washed up on an African beach. It was identified from the serial number on the part, which was not damaged by entry heating.

It was not damaged because it slowed down before it could entirely burn up, but slowing down makes it less dangerous! A solid iron/nickel meteor slows down much less that a light weigh aerospace frame than comes plummeting down from orbit!

This issue has been known but ignored since the early 1960's. For convenience. How unethical!
The space junk problem is a similar neglected-ethics problem, actually.
GW

The chances of you being struck by lightning are much greater efforts that can be made to reduce the chances of lightning strikes will be more productive that the same amount of effort to reduce the chances of falling man made objects from in space hitting you.

GW Johnson · 2016-05-25 10:29:31

Tom, your arguments strain credulity sometimes. A 100 mph piece of aluminum weighing 1 ounce is just as deadly whether it comes from an airplane or a piece of space hardware.

BECAUSE IT IS DEADLY is why most people consider it both prudent and ethical to do everything they can to prevent aircraft from crashing or shedding pieces in flight, in spite of the low probability of this ever hitting anybody on the ground.

It ain't about the probability, it is about the unacceptableness of the outcome. (Which is something probabilistic risk estimate techniques ignore, and that is a fundamental risk management error.)

We do not always succeed. So what? It is still incumbent on us to try, if we can.

So also it is with space junk. This is an area where we have been ignoring this problem for mere convenience, in spite of the fact that the means to mitigate it are now within our grasp, unlike the 1950's and 1960's.

GW

Last edited by GW Johnson (2016-05-25 10:33:02)

SpaceNut · 2016-05-25 19:40:53

Even a frozen piece of styrofoam can damage....

Back to the topic of SLS as an exploratory vehicle its fails but as a heavy lifter of large chunks it does do lots better.

Tom Kalbfus · 2016-05-26 07:23:34

GW Johnson wrote:

Tom, your arguments strain credulity sometimes. A 100 mph piece of aluminum weighing 1 ounce is just as deadly whether it comes from an airplane or a piece of space hardware.
BECAUSE IT IS DEADLY is why most people consider it both prudent and ethical to do everything they can to prevent aircraft from crashing or shedding pieces in flight, in spite of the low probability of this ever hitting anybody on the ground.
It ain't about the probability, it is about the unacceptableness of the outcome. (Which is something probabilistic risk estimate techniques ignore, and that is a fundamental risk management error.)
We do not always succeed. So what? It is still incumbent on us to try, if we can.
So also it is with space junk. This is an area where we have been ignoring this problem for mere convenience, in spite of the fact that the means to mitigate it are now within our grasp, unlike the 1950's and 1960's.
GW

What about our efforts to divert large asteroids, the outcome of one hitting the Earth is unacceptable, yet we have made no effort to move near earth asteroids into safer orbits that do not threaten Earth! We depend on the low probability of such an event happening to justify not spending the money to divert them. And Near Earth asteroids are relatively small compared to the others, it is within our technological means to divert them, though it would be expensive to do so. Part of the expense can be compensated for by mining those same asteroids, or maybe all of the expense can. Now a safer orbit doesn't have to be further out from the Sun. If we can divert an asteroid that is orbiting the Sun so that it orbits Earth instead, so it can be better exploited, that would be a safer orbit. The problem here is we're shifting the problem from that of orbital mechanics to that of human behavior. IF some people can divert asteroids to safer orbits, other people may choose to divert asteroids to more dangerous orbits, so they can be used as weapons, so it also becomes a defense issue. Maybe we need a Space Navy to be in charge of mining and diverting asteroids. The United States is the foremost space power, we sure don't want the Iranians to be playing with asteroids. Space junk is only the tip of the ice berg, even our largest satellite can't wipe out an entire city if it hits the Earth (Assuming that nuclear warheads aren't involved), there are some asteroids that can!

Last edited by Tom Kalbfus (2016-05-26 07:24:19)

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