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« The Uncommon Touch | Main | Why I'm Not In A Union »

OK, I've Reconsidered

OK, I've gone back and taken a look at Jeffrey Bell's Space Daily piece again.

In addition to the comments that Dwayne Day made on the previous post, he's wrong about architectures. I was a little confused on my first read, and I thought I agreed with the following:

People who say that a manned moon mission could be assembled in LEO out of small pieces launched on existing boosters like the new EELVs are dead wrong. This option was never seriously considered by either the Red Team or the Blue Team back during the Moon Race. It vastly magnifies the chances of failure.

Both Delta 4H and Atlas 5H can lift about 20 tons to LEO, so many launches would be needed for each moon flight. The need to design the moonship in many small pieces increases its total weight. Rumor suggests that the actual number coming out of current studies of this option are in the range of 6 to 9 launches (120-180 tonnes). If any one of these launches were to fail, the whole mission plan would be disrupted.

Also, there is no way we could produce the number of Delta 4H or Atlas 5H boosters it would take to support a serious moon program on top of all other launch requirements. Since each Heavy EELV uses three core stages in parallel, 18 to 27 stages would be dumped into the Atlantic for one Moon landing.

I actually do agree with much of this--I don't think that it's sensible to use EELVs for the new space initiative. Of course, I don't think that it's sensible to use expendables in general. My biggest disappointment in the new space policy is that it seems to have thrown in the towel on the possibility of getting low-cost launch.

If we were to launch the pieces on a reliable, low-cost launcher (a highly reusable space transport), then the concerns about a missed launch would be vastly mitigated, the pieces themselves would be much cheaper, and there would be spares in the event of a launch failure. Unfortunately, this is an option that no one seems to be considering now, because NASA screwed the pooch so badly on X-33 that the agency (totally irrationally) really seems to believe that it's not possible to build reusables, or lower launch costs significantly. And for the paltry goals that the agency has (even in the wake of the new space initiative), it's probably not.

It will only happen when the nation (not NASA) decides that we have to have routine affordable access to space, and puts in place policies to achieve that goal (which involve much more activity than NASA's space exploration goals). But once the goal is achieved, the trade space will become radically transformed, and articles like Jeffrey Bell's will be irrelevant.

Posted by Rand Simberg at March 18, 2004 05:30 PM
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I did not bother to read through the Bell piece all the way, because it became clear to me that he did not understand a lot of things. But I glanced at it again and I found yet another mistake: his reference to "Lunar Polar Orbiter." I happen to have several documents on NASA's late 1980s planning for a lunar probe. According to one JPL study ("Lunar Observer Mission Study," October 1988), NASA's interest in lunar probes was: 1974, Lunar Polar Orbiter; 1976, Lunar Polar Orbiter; 1983, Lunar Geochemical Orbiter; 1985, Lunar Geoscience Observer; 1988, Lunar Observer.

Bell obviously meant Lunar Observer, which was going to be a sister to Mars Observer, using many of the same instruments. (These instruments were later turned over to Mars Global Observer.) Lunar Observer was a big, expensive spacecraft and was canceled around 1992. NASA then proposed two "lunar scout" missions known as Lunar Resource Mapper and Lunar Geodetic Observer.

At the Goddard Symposium on Tuesday a Goddard Space Flight Center official discussed NASA's proposed 2008 Lunar Reconnaissance Orbiter mission. I suspect that we may hear some interesting things about non-NASA lunar probes in the next year or so.

Posted by Dwayne A. Day at March 18, 2004 07:00 PM


I agree with most of what you say as a broad perspective. It would be wonderful to have low cost reusables and NASA should not act as if the possibility does not exist. But Bell is wrong for many other reasons. He seems to be limiting our choice of launchers to Atlas and Deltas, even though the FAA considers Sealaunch Zenit 3SLs as US launchers for the purposes of its launch tech outlooks. Obviously not an authoritative source for nationality, but I find it likely the government would not have a problem using them in a pinch. For that matter, our recent experience hitching rides on Soyez's seems to indicate that the US isnt above using foreign launchers. The fact is that there is plenty of supply for EELVs on the market to deal with the exploration initiative. The futron corporation reports indicate a capacity of well over a hundred launches per year, more than enough for the exploration initiative.

The real stumbling block is the on orbit, or lunar, assembly. NASA has always chosen the big government booster approach to heavy missions, rather than going for a building block approach. I cant deny that this has probably been the most economical approach in the past, and may be now. The problem is that the superheavy lifter approach will not allow for private access to the market. If we want a real private market in space, we need to allow for lower cost access, whether that be by linked payloads from EELVs, for from low cost reusables. Either way, we need to shift some focus to the question of long term infrastructure that can be supported by unsubsidized private actors.

The question of one launch failure endangering the whole mission is also a strawman. While there is clearly work to be done on orbital assemlby, the ISS has shown that long term projects can withstand problems with a lot of individual launches (even if not with the greatest of efficiency). As the current plan dees not exactly call for a fevered pace, I think that the long term plan can allow for a missed launch or two.

Posted by Nathan Horsley at March 18, 2004 07:21 PM

Oops. My mistake. The extra Mars Observer instruments were turned over to Mars Global Surveyor.

Posted by Dwayne A. Day at March 18, 2004 07:30 PM

I thought Bell's article was quite well written, except for the launch vehicle part. For example, he is probably wrong when saying there aren't enough Delta IVs and Atlas Vs to support a manned lunar program. He forgets Boeing and Lockheed-Martin were proposing to launch up to 18 rockets per year, although those forecasts have been slashed by a factor of three due to the collapse of the commercial satellite launch industry. So there is considerable surplus capacity right now.

Rand wrote:

If we were to launch the pieces on a reliable, low-cost launcher (a highly reusable space transport), then the concerns about a missed launch would be vastly mitigated, the pieces themselves would be much cheaper, and there would be spares in the event of a launch failure.

I think I can agree about the other points, but would "the pieces themselves" really be much cheaper? I would argue the manned lunar spacecraft will have to be hightly reliable since it is operating hundreds of thousands of kilometers from home and consequently must be capable of safe, autonomous missions lasting 1-2 weeks.
The second issue is the required launch mass is much higher than for LEO missions, which to some extent negates the impact of $/kg launch cost reductions. E.g. a factor-of-ten space transportation cost reduction would have a huge impact on low-cost satellites and probably human space station operations, but it merely means a manned lunar mission would cost as much as today's Shuttle flights to low Earth orbit.


Posted by Marcus Lindroos at March 19, 2004 06:39 AM

Has anyone here been reading The Rocket Company, by Stiennon and Hoerr? It's here. It's billed as fiction, and it is, but they seem to have put a lot of thought into both the economic and technical side of reducing the cost of access to space.

The main reason I brought it up is that one of the major decisions they made was that the prototype and initial flight hardware would have a fairly small payload and anything large that needed to be launched would have to be assembled on orbit.

Posted by AndrewS at March 19, 2004 07:59 AM

One advantage I see for components launched on a (true)reusable launcher is that in event of most failure modes, a reusable spacecraft would most likely return the payload to Earth for another try later and with an expendable its going to become fish habitat somewhere in the Atlantic because there are no safe abort modes on an expendable to recover a payload.

Posted by Mike Puckett at March 19, 2004 08:10 AM is reporting the cancellation of certain technology programs, like the X-43 and a re-useable rocket engine.

Rand, is this decision consistent with your ideas about which direction NASA should head? If the plan is to focus ALL exploration money into CEV flying on EELV, is that a good thing, in your opinion.

Posted by Bill White at March 19, 2004 08:13 AM

No, it's not at all consistent (though I'm not sure that NASA should be developing engines--they don't have a very good track record on that, at least when it comes to reusables).

Overall, I'm quite concerned about the program direction, and am not optimistic about its success.

Posted by Rand Simberg at March 19, 2004 08:16 AM

I think I can agree about the other points, but would "the pieces themselves" really be much cheaper? I would argue the manned lunar spacecraft will have to be hightly reliable since it is operating hundreds of thousands of kilometers from home and consequently must be capable of safe, autonomous missions lasting 1-2 weeks.

It's not the reliability that drives up hardware costs, Marcus, it's the combination of reliability with low production rate and the need for very low weight margins. Cheap launch solves those two issues.

Posted by Rand Simberg at March 19, 2004 08:18 AM

Professor Bell has a new article up. A quote:

"A penetration would probably kill or seriously injure any astronauts in the punctured module, due to the shock wave and shower of high-speed fragments."

Having been in the Army and working in a armored cav unit and knowing something about the unauthorized penetration of armored vehicles, unless the crewmember was in the direct cone of debris and provided the overpressure did not nock the astronauts unconscious, it could be quite survivable. Yes, the hit he describes would not be fun but compared to an eight pound shaped charge warhead punching thru you hull with a jet of hot plasma and a copper slug going mach 25, it doesn't seem so bad. Armored crewmembers have survived much worse than professor Bell describes.

Posted by Mike Puckett at March 19, 2004 08:41 AM

Dr. Bell stikes again. Send this guy to slashdot - - - he'd be King Troll in no time.

On ISS punctures (and CEV punctures?) its the de-pressurization that is the killer. Using TransHab as the starting point allows for self sealing layers to be added in the fabric sandwich,a s well as water pockets for radiation protection.

Bell's bigger point is on JIMO - due to orbital debris, the new mission plan calls for immediate escape from LEO and a 50 ton launch package. Too big for Delta IV of Atlas V.

The Porject Prometheus guys now want shuttle C.

Hee! Hee!

Posted by Bill White at March 19, 2004 09:03 AM

I assume the ISS has spall liners on the inside as well. Spall liners can make a huge difference in survivability.

Does the ISS have kevlar spall liners?

Posted by Mike Puckett at March 19, 2004 09:06 AM

Does the ISS have kevlar spall liners?

I believe the question is whether they are big enough. Bell examines that in detail. Whether he is right? I don't know.

Posted by Bill White at March 19, 2004 09:15 AM

What Bell describes are not spall liners. Spall liners would be in the inside of the hull with no metal between them and the crew. The purpose is to catch the secondary missiles and you want to be beyond any potential missile generating layers.

Posted by Mike Puckett at March 19, 2004 09:20 AM

Thanks Mike, stuff like this is why I love the internet especially google. Okay, are spall liners part of current CEV and ISS design? If not, why not?

Self-sealing enhanced TransHab fabric still seems like a good technology to explore. If CEV is to seque into a Mars capable craft both radiation protection and ballistic protection seems essential and metal hulls generate secondary radiation which requires more shielding.

Posted by Bill White at March 19, 2004 09:28 AM

"Testing Spall Liners for Aluminium Armour

Spall is the name given to material ejected as a result of delamination or separation of the inner surface of an armoured structure as a result of warhead impacts outside the structure. Spall may also consist of parts of the warhead itself depending on the nature and success of the threat involved. The spall ejected from the armour will have a very high speed (as much as 1000 m/s), high temperature and high hardness. Spall may also be comprised of molten material depending on the type of warhead or armour involved. These factors increase the lethality of spall to both the vehicles internal systems and crew.

Spall is ejected in a three dimensional cone shaped pattern and hence the likelihood of producing crew and vehicle damage is increased with a corresponding increase in cone angle. This angle is used as the principal discriminator for determining the performance of a spall system. Other discriminators are the mass of spall fragments and their kinetic energy."

Posted by Mike Puckett at March 19, 2004 09:31 AM

Bell also writes this about LEO assembly:

In order to make any intelligent plans for implementing the new Space Initiative, we need to know how bad the space debris problem will be 20 to 50 years in the future. If it will not be possible to use LEO for prolonged assembly or parking of interplanetary vehicles, we will have to shift such operations at another site such as the Earth-Moon L-1 point. The Congress or the Aldridge Commission needs to force NASA to conduct a serious study of the future evolution of the orbital debris population and make specific predictions about what limitations this hazard will present to the manned missions proposed in the new Space Initiative.

The ideal group to do such a study would be the space debris research group at Johnson Space Center. Oddly enough, NASA tried unsuccessfully last year to de-fund this group and strip itself of any in-house experts on the debris threat! (Experienced NASA-watchers have learned to recognize this kind of behavior as a red flag. Like Saddam Hussein, NASA instinctively responds to bad news by quietly shooting the messenger who brought it. Has this organization already discovered disquieting information that offended the Space Lords?)

If this study is not done, we might find ourselves some years down the road with a lot of expensive nuclear space hardware that cannot be flown due to safety constraints. In the worst case, we might have some more dead astronauts who could have been saved with a little foresight and honesty.

The more things change the more they stay the same?

Posted by Bill White at March 19, 2004 10:02 AM

On the topic of failure probability for a mission based on EELV vs. a mission based upon a single launch.

Day says:

People who say that a manned moon mission could be assembled in LEO out of small pieces launched on existing boosters like the new EELVs are dead wrong. This option was never seriously considered by either the Red Team or the Blue Team back during the Moon Race. It vastly magnifies the chances of failure.

Actually, this depends on the definition of failure.

If the mission is designed to be assembled from major, independent and self-sustaining elements in LEO (say 8 of them for purposes of argument) and one of the launches fails, then you have 7 of the pieces successfully in a parking orbit. One additional launch, with a spare, and the mission could continue. Is this an example of a failure or a anomoly that can be handled and the mission still completed?

A single launch mission that has a launch failure incurs a very high cost in destroyed hardware, and more important to the mission, a long, long downtime while the monopoly booster is re-rated for launch.

While it is more likely that a multi-launch mission scenario will have a launch failure (given the same base launch failure rate) I believe that the ability to absorb a launch failure can be designed into the program. Given the inherent failure rate of launchers in general, I think this in the only prudent way to go. (Rand's makes this point, but he seems to only apply it to reusables).

What is needed, program-wise, to gracefully absorb a launch failure?

* Launch abort capability for the crew
* multiple spares for all components
* Launch Capacity available greater than average need.
* Multiple launch suppliers
* A design philosophy that any single component may not work.
* The political spin control ready to explain the a launch failure isn't a mission failure

An example? The GPS satellite constellation. Each satellite can be launched seperately. A launch could fail but the overall system can function (sometimes at a degraded level) despite a failure. Delta's are down? Launch on Atlas. You could launch two satellites (or three...etc) at once if that made sense from a launcher point of view.

Another example, this one a bit more controversial -- ISS. While not the perfect example, consider this; while the shuttle has been grounded, progress and soyuz has been able to keep the overall system functioning.

In conclusion it would be nothing short of engineering / management / design folly to design our return to the moon with anything but a multiple launcher, multi-supplier, failure tolerent system.

Posted by Fred K at March 19, 2004 10:51 AM

Having done hypervelocity penetration physics at a previous job...

Spall is much more of a consideration when you've got *thick* metal being penetrated. The relatively thin wall of a space station module would not have a large volume of material being spalled off by an impact. Also, in many cases, there's equipment attached to the wall that will take the edge off some of the spall. So, no, I don't believe the space station has spall liners.

Of course, we've got a completely different situation compared to anti-armor penetration. In anti-armor you've got kilos of material involved, but the speeds aren't terribly large when compared to orbital speeds. (Shaped charge jets are NOT in the plasma state and do NOT move at Mach 25 or such speeds [these are both extremely common misconceptions].)

OTOH, orbital debris penetration can occur over a very wide range of speeds and the penetrator may have enough energy to become partly vaporized (though generally it just becomes very finely divided). One problem I've not heard too much about, though, is that many of the man-made materials cluttering up LEO might just be pyrophoric under the conditions of bursting rudely into the interior of a space station module. Luckily, the resulting fire and any toxic combustion products will be taken care of by the resulting decompression... ;-)

- Eric.

Posted by Eric S. at March 19, 2004 10:56 AM

Eric (or anyone else with hard data on the subject),

You seem to hint at a less than rosy picture. What do you think about the bottom line survivability of an ISS (or other station) impact? In particular, would the decompression resulting from an impact by debris measuring approximately 1 cm (presuming non-pyrophoric) be likely to keep an astronaut from escaping the damaged component?

Posted by Nathan Horsley at March 19, 2004 11:41 AM

> It's not the reliability that drives up
> hardware costs, Marcus, it's the combination of
> reliability with low production rate and the
> need for very low weight margins. Cheap launch
> solves those two issues.

Oh, the lunar spacecraft hardware would likely be somewhat cheaper if launch costs were reduced, but how big would the difference really be? It seems you need extremely low launch costs and high flight rates for this to have much of an impact -- particularly since you will have to launch more mass if the spacecraft is heavier.
A typical NASA manned lunar spacecraft costs $0.5-1 billion per copy if you examine the late 1980s and early 1990s studies. Let's be extremely aggressive and assume spacecraft costs can be reduced to $20 million, or the approximate cost of a Soyuz. You have to add another $20 million for the R7 booster, which is capable of carrying 7t to LEO. A manned lunar landing mission would require 200 metric tons or so in LEO (according to most recent NASA studies), which means launch costs must fall to $50/lb before the total price of a manned lunar landing falls to the same level as a Soyuz trip to ISS!!
I am not saying that it cannot be done, but it seems the immediate impact of CATS on manned lunar missions won't be that great. This is because of the requirement for truly drastic launch cost reductions by a factor of 50-100, but also because the resulting total cost would remain at least on the same level as the current cost of a manned mission to low Earth orbit. And I think $40 million for a round-trip to the lunar surface and back to Earth sounds, well, incredible. NASA's late 1960s mission planners did optimistically assume very low launch costs (well, $300/lb at current rates) when proposing the post-Apollo Moon/Mars initiative, and the total cost per lunar mission would still have been ~$100-150 million or so if memory serves. In any case, this scenario requires lots of supporting infrastructure both in low Earth orbit and on the lunar surface -- in-situ propellant production and storage, reusable lunar spacecraft maintenance facilities etc.. I can envision a scenario where this evolves gradually (commercial LEO missions -> satellite servicing & deployment mission to GEO -> lunar orbit & landing), but it is quite understandable that the new lunar exploration initiative won't go the CATS route since it needs to minimize development time and R&D costs whenever possible.

I do think the Administration is making a mistake when not focusing on cheap access to space before planning a moonbase, though. We need to establish affordable "platforms" that can be justified on economic grounds and it is difficult to see how a $8B-a-year manned lunar effort will survive unless the benefits are truly spectacular.


Posted by Marcus Lindroos at March 19, 2004 12:19 PM

Eric, what is your opinion on basing CEV crew compartments on TransHab or other fabrics developed to advance beyond where we are now?

Use many layers of kevlar and other materials including dense foams to slow debris and then seal any hole?

Posted by Bill White at March 19, 2004 12:41 PM


Actually, I thought the current shielding is supposed to handle debris up to 1 cm in size. But the spectrum of possibilities range from (on the low end) developing a fracture or multiple small punctures or something similar --> slow leak, adequate time to exit to the module w/ Soyuz attached... TO, on the high end... (as a Marine colonel I used to work for would say) "hair, teeth, and eyeballs everywhere".


I'm not sure what penetration work they did on the TransHab w.r.t. debris in the 1-10 cm size range. I'd find it very hard to believe any case for 'self-sealing'. But then it may be more survivable just as a 'through & through' bullet wound can be more survivable than having the bullet hit bone, ricochet and shatter. IF you want to do your best to disrupt the impactor, one of the good ways to do that is to have interfaces between materials of greatly different densities and hardness (to create shocks inside the impactor, which tend to shatter/disrupt it), and to have spaced multiple layers (to allow distribution of the debris over a larger surface area). I'd be much happier inside a TransHab that's had some form of multilayer armor applique bolted on the outside.

Bottom line is that this is not anywhere near an insurmountable problem. Plus, some of the materials one might use in the applique armor can be materials that are also good radiation shielding. (I don't recall just what that material was that Marshall[?] came up with, but I remember thinking that it would make a good low density filler of an impact shield.)

- Eric.

Posted by Eric S. at March 19, 2004 01:49 PM

I believe simple polyethylene with "enchancements" is what Marshall was looking at. Hydrogen density is the key from what I read.

Posted by Bill White at March 19, 2004 02:00 PM

I LOVE google.

Ceramic body armor (like that worn by our troopers in Iraq) is made from boron carbide. Boron is a critical element in radiation protection.

Build the CEV out of Transhab fabric perhaps with an aluminum outer hard shell and finish with overlapping ceramic armor plates sewn into pockets in the final inner layer of kevlar.

As Constance Adams has noted, another advantage is that such a spacecraft would not radiate heat quickly. ISS is cold because its aluminum. Recall the Apollo 13 movie with Tom Hanks.

Anyway - IMHO this is the direction Constellation needs to go. Buy that SpaceHab stock today!

Posted by Bill White at March 19, 2004 02:28 PM

Not to further hijack this thread but you guys need to check out Nasawatch RFN!

Some Union Thug(tm) is threatning to sue Keith for taking some other union idiot to task for some remarks said visionless bureaucrat directed toward Burt Rutan and alt.spacers!

Posted by Mike Puckett at March 19, 2004 05:09 PM


Yes, B4C would be a good potential material. Actually, the shield you'd want would be Whipple-esque though. An Al outer plate at a standoff, perhaps w/ a Nextel backing; then a B4C layer (encased in Al or Ti cells to retain much of the B4C after any penetration) backed again by Nextel; a goodly layer of the 'doped' polyethylene; finally perhaps another layer of B4C cells.

Oh, and I thought there's also been some work on doing ceramic matrix composites...

- Eric.

Posted by Eric S. at March 19, 2004 05:40 PM

I've seen video of debris impact testing of aircraft grade 1/8 inch aluminum panels. 1 cm ball bearings were propelled at high speed, mind you not quite as fast as debris velocities in space. Of course the shot would go straight through no problem leaving an enormous hole. Then, a blanket comprised of several thin sheets of kevlar fabric was placed about .5 inch above the surface of the aluminum plate. The debris impacted the kevlar blanket, vaporized into a plasma jet that could be deflected by the aluminum plate with pitting to the surface and occasional pinhole size punctures. The key is the air space between the blanket and the plate. Modern vehicle armor is comprised of multiple layers of material of varying densities, including air pockets. The empty areas in the armor provide a buffer zone where the energy of the impact can dissipate before entering the crew compartment.

Really we should get the British involved with any kind of shielding research. Their military research into tank armor is by far the best in the world. So much so that Chrysler enlisted their knowledge when developing the Abrams main battle tank. Even most recently they can take the honors for developing a simple lightweight electrified armor that easily defeats copper based shaped charge warheads with just a few inches of armor instead of several feet.

Posted by Hefty at March 19, 2004 11:49 PM

You are Referring to the Chobam armor package of the M1 and Challenger series tanks.

The later M1's evem have an added layer of DU but that would be impractically heavy to use as shielding on Spacecraft.

And DU is pyrophoretic.

Posted by Mike Puckett at March 20, 2004 01:18 PM

I recently had reason to look into Boron-doped polyethylene radiation shields. NASA's own reports suggest that LiH is more promising. Unfortunately, I don't have the references on hand right now.

On the subject of on-orbit assembly, Kantrowitz gives an account of when the Gardiner Committee looked into on-orbit assembly here:

This was in 1961, and they concluded that on-orbit assembly would be 10 times cheaper than using heavy launchers (Kantrowitz doesn't say why though). Vice President Johnson classified their results top secret and they didn't see the light of day until 1996.

History suggests that embarrassment is a major driving force for NASA's technology investment decisions. Even recently, I was in the position of begging a code T representative for a small sum of research money to pursue a promising idea for low-cost on-orbit assembly of large structures. The representative made it clear that he was terrified of investing in something that was new, because it might fail, and his record would be tarnished.

It was like talking to the sum of all NASA management faults drawn into human form, wrong on so many levels... it took me weeks to calm down after that *takes deep breath*. In short, even if you had the exact answer in this blog to on-orbit assembly or low cost launch, NASA would not take you seriously and NASA would not care. They are linear thinkers, they will only recognize true advances in hindsight.

Quote for the day:

“Boy you guys in sales are all the same. You remind me of the farmer in 1850. If you asked him what he wanted, he would say he wanted a horse that was half as big and ate half as many oats and was twice as strong. And there would be no discussion of a tractor.”

From D.T. Kearns and D.A. Nadler, Prophets in the Dark: How Xerox Reinvented Itself and Beat Back the Japanese.

Posted by Kevin Parkin at March 21, 2004 06:20 PM

Keith, I just did a fast google on LiH. Lithium hydride, right? It appears to be a hazardous substance that reacts violently to water.

Among other things, LiH cannot be in direct contact with aluminium.

Isn't boron doped polyethylene is safe for use in children's milk jugs?

Posted by Bill White at March 22, 2004 09:45 AM

Bill, have just fished the reference out of the library again:

J.W. Wilson et. al. NASA Technical Paper 3662, "Radiation Analysis for the Human Lunar Return Mission" (Sep. 1997)

Page 5: "In both respects, hydrogen is a preferred material constituent; the higher the hydrogen content per unit mass of material, the better the shield properties (both the atomic and nuclear properties). Thus, polyethylene, other polymers, water, compressed methane (a possible rocket fuel), and LiH are all good materials."

Page 5 a little later: "Polyethylene is used as a high performance shield and shows significant advantage over regolith. Adding boron to the polyethlene to deplete the low energy (thermal) neutrons appears to be counterproductive because the added production of secondaries and the change in the atomic cross sections usually increase the dose. Lithium hydride is probably a better alternative."

Yes, I probably wouldn't mix the LiH shield with the drinking water :p

Posted by Kevin Parkin at March 23, 2004 09:36 PM

As for space station decompression, I don't think it's necessarily the catastrophic scenario that some might envisage.

As a quirk of gasdynamics it turns out that a hole in the space station, let's say 1 cm^2, will at worst vent air at Mach 1. If we know the pressure inside the space station (1 atm) then we can calculate the mass of air lost to be about 240 kg/s/m^2. Since the station has air reserves of about 200 kg, then the astronauts would have over two hours to don their spacesuits and find the hole, assuming that atmospheric pressure was maintained.

And if I were them, I'd put my space suits on and reduce the station pressure to conserve air (flow rate goes down linearly with pressure), then find the hole.

Even if the hole were 10 cm^2 there would be over 15 minutes to do something, assuming that the reserves could be pumped in fast enough.

So this got me thinking, what would the likely size of a hole be? Unfortunatley, I found some discouraging news:

"A major concern is whether the Americans will have the nerve to stay the course when inevitable mishaps occur. The station, like Mir, will require constant maintenance. It could not be shut down if America stopped shuttle flights for years as it did after the *Challenger* explosion. Russian engineers calculate that there is a 23% chance that the exposed Service Module will be punctured by orbital debris during the lifetime of the station. Although the alloy and type of construction there would contain any puncture within a 70x70-centimetre panel, they believe an impact on the American section would result in fractures propagating quickly across a 400x400-centimetre area, leading to explosive decompression, an uncontrollable spin and rapid break-up of the station. Fortunately the probability of such an impact is only 2%."


So, my question is whether there is a material we could have used that's less fracture-prone. What think the hypervelocity impact guys?

Posted by Kevin Parkin at March 23, 2004 10:41 PM

"For example, he is probably wrong when saying there aren't enough Delta IVs and Atlas Vs to support a manned lunar program. He forgets Boeing and Lockheed-Martin were proposing to launch up to 18 rockets per year"

They each have their factories set up for 40 CCB's per year. Using only the Atlas 552 that gives the capacity to boost 800T per year. Add Delta Medium+ (5,4), and you have a boost capacity of 1.25kT. Add Proton, Zenit, Angara, Falcon and Chang Zheng 5 (assuming China funds it) launches and you're talking several kilotons of capacity.

The argument that the private launch market can't fill space exploration needs is absolutely ludicrous.

Posted by Chris Mann at August 20, 2006 06:25 AM

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