Long over-due

It's about time I updated this thing. I've been so busy since this time last week I just haven't had the time do anything, really. Wednesday was the job interview at Snell & Wilcox. I found out a lot about the company during the day: basically, they make digital signal processing equipment for TV broadcasters. For instance, they make equipment for converting between various standards (e.g. PAL-NTSC, SDTV-HDTV), and they've got some pretty cool kit for that. They've also got a piece of equipment called Archangel for restoring archive film: they showed us a demonstration of some pretty appalling footage being restored very convincingly, removing loads of defects such as banding, shaking, interference, all sorts. Very very impressive. Unfortunately, they were running late, meaning that I left two hours late, and only got back to school at 2100 (after leaving school at 0630 in the morning); by which time I was so knackered that I just went to bed. Then on Thursday I had lessons and school mass in the morning, and then after a token showing at CCF to keep up appearances, I went home in order to go to a party in the evening: my friend G. was having her 17th birthday party at a bar in the town we've just moved to. And that was great fun, apart from... ...having to get up at 0545 in the morning to get to school in time for roll call. Then I slept through the usual boring drivel at end of term assembly (hours of pointless football statistics, mostly), before having a single lesson with Mr. P. where we just had a chat. And apart from that I just haven't really been bothered, even though I've had the time... just about... to write something here. I might find the time sometime later today, before I have to go to rehearse for Bye Bye Birdie.

Moon lecture

As I mentioned last Thursday, I gave a lecture today entitled "Going back to the Moon to Stay" for the school's Astronomy and Cosmology Society. Unfortunately only a few people turned up; I gave the lecture anyway, but the master who runs the society has asked me to do it again next term, so I'll do a transcript and put the slides online then. I've got a job interview tomorrow! This time it's at Snell & Wilcox. It doesn't look like exactly what I want to do, but it does look interesting. Their websites not hugely informative; hopefully whatever they say tomorrow should clarify what exactly the work would entail. Time for bed now - I need to get up at 0600 tomorrow!

Big ion propulsion systems

On Saturday I investigated SEP systems for spacecraft going from LEO to the Moon and having a relatively small LEO mass of 20 tonnes. In hindsight, some of my numbers were a bit dodgy; more realistic values are for 15 tonnes of non-propulsion equipment.

But what happens when there's a possible initial mass of 100 tonnes, as could be launched to LEO by a Saturn V?

At this scale, SEP doesn't make sense. Sticking to my maximum transfer time of 2 years, the math works out as follows: m_f / m₀ = 0.843, so 84.3 tonnes of payload and systems and 15.7 tonnes of fuel. Using just one ion thruster as before, a Δv of 6.33x10³ ms^-1 would take 100 years. That means that to transfer in 2 years, I'd need 50 thrusters, corresponding to 250 kW of power consumption.

That's an awful lot of power, and a solar panel array that big is just ridiculous, without even taking radiation degradation into account. So, nuclear power could be used instead. Up to 1993 as part of the Space Defence Initiative NASA developed a reactor designated the SP-100 [1]. This was capable of delivering power levels up to about a MW at between 10-50 kgkW^-1 (better specific mass at higher power). By the way: for the environmentalists, the SP100's nuclear fuel container is designed to reach the ground intact in the event of the reactor unexpectedly breaking up in the atmosphere. Additionally, I'm assuming a 1000 km starting orbit, and an orbital height of 700 km is considered by NASA to be "nuclear safe".

Pulling figures out of thin air, let's assume that a 250 kW reactor can be built at 30 kg/kW. That means that 7.5 tonnes would be power source. Additionally, I'd need 250 kW of ion thrusters, at about (yep, more made-up numbers) 13 kg/kW, another 3.3 tonnes.

Adding all that up, for 100 tonnes at LEO, I'd get 15.7 tonnes of fuel, 7.5 tonnes of nuclear reactor and 3.3 tonnes of thrusters, leaving 73.5 tonnes for payload. Very nice.

The real problem with what I'm doing here is the fact that no-one's done any research on really big spacecraft in the last decade or so, because there's been no requirement for such research. Everything's been kept small, cheap and efficient as far as possible (apart from the ISS, which is big, expensive and inefficient). I want to see things that are big, not too expensive and extremely efficient.

References:

[1] 'SP100 Power Source', NASA SpaceLink

Success

This year's academic prizewinners have been announced. I have won three:

• Further Maths
• Physics
• Music

This is the same number as I won last year. Winning the Music prize is particularly bizarre, as I don't study Music. However, I enjoy suprises, and it's nice that the amount of effort I put into my music has had some recognition.

A day off?

I'm having a day off today. I'm trying to get through the whole day without doing anything that resembles work in anyway. Yay! ...Shaft is on tonight on Channel 4 at 22:00. I'm going to watch it.

Power for ion propulsion

There's a few problems with ion propulsion from LEO to the Moon that I hadn't considered. The first problem is in providing the electrical power required.

Last week I suggested using solar panels. The problem with that idea is that the spacecraft will be travelling through the Van Allen belts, where there is a high level of ionising radiation. Ionising radiation destroys solar panels, so it's best to minimise the amount of time spent in the Van Allen belts.

Here's a rough approximation. The ion thruster I described last week (I_sp of 3800 s) had a thrust of 0.2 N [1]. Suppose the spacecraft has an initial mass of 20,000 kg (20 tonnes). That means the acceleration from this 5 kW thruster will be of the order of 1x10^-5 ms^-2. It'd take a long, long time (~ 20 years) to make a velocity change of 6.33x10³ ms^-1 at that rate of acceleration. 20 years, a large number of which would be spent in the Van Allen belts.

So what about increasing the number of thrusters? Let's say 2 years for a transfer is reasonable. Then 10 thrusters are needed, corresponding to 50 kW of power needed. If a solar array is degraded by 10-50% on a single transit through the Van Allen belt - and my spacecraft is spending quite a while there - I would need an initial capability of 100 kW. Unfortunately, the technology doesn't currently exist to make a deployable array that big. Additionally, the spacecraft would only be able to make one trip from Earth to the Moon.

Assuming that somehow there's been such a deployable array constructed and used, and since these (very heavy) arrays have been taken all the way to the Moon, it wouldn't be unreasonable to want to use them again. It would make sense to land them and use them to power a base. Only problem is, they'd need to be undeployed first. A good demonstration of the reason for that is as follows: take a strip of card (a bookmark, perhaps). Make a fist, and grip the middle of the strip between your thumb and the side of your index finger. With the strip horizontal, hold your fist a couple of inches above a table and allow it to drop. Watch what happens to the strip as your fist hits the table. Now imagine what would happen to the deployed solar array under an even larger shock. No-one's ever built a multiply-deployable array either: there's another challenge.

There is one possible solution to the Van Allen problem: run the solar panels at a high temperature (~ 400 K), when, in theory, they may be able to self-heal.

Next issue is mass. Once again, assuming 20 tonne initial mass and m_f / m₀ = 0.843, there is a requirement 3.14 tonnes of fuel. I'll round that to 3.5 tonnes to allow for the tankage factor. Typical specific masses for solar electric propulsion (SEP) systems are of the order of 20 kg/kW (I really think this is seriously underestimated), so a 100 kW system would have a hardware mass of 2 tonnes. That leaves 14.5 tonnes for payload and subsystems for lunar landing.

Now, what happens when the system scales up? A Saturn V was capable of sending 47 tonnes to the moon, and a hundred tonnes to LEO. What happens then?

References:

[1] JPL Advanced Propulsion Technology Group, 'Advanced Propulsion Concepts', Island One Society

Muir Mathieson Memorial Competition

Well, that was it: what I've been working towards all term. There were seven of us playing this evening: a flautist, a cellist, a bassoonist, a percussionist, a clarinettist, a violinist and myself. The standard was extraordinarily high: it was undoubtedly one of the highest quality concerts I've played in, if not the highest.

I played the Adagio und Allegro again, and unfortunately it didn't go very well. In fact, it was the worst I'd played it in weeks. I missed the top C in the Adagio; my tripletty bits were a mess; and at the end, my mouth went completely dry, and I couldn't get the right notes out at all.

Sigh.

Anyway, the runner-up was R., my friend the clarinettist (she played really stylishly) and the overall winner was S., who played the marimba amazingly. I was very impressed.

I'm glad I entered. It was definitely worth it, because not only has it really motivated my to practise a lot this term - I'm now playing as well as I've ever been, if not better - but it means that I've got a pretty convincing piece worked up ready for the school Open Day concert next term.

Anyway, it's in the past now. This week I'm going to be doing a lot of practise on my part for Bye Bye Birdie.

Business

Don't expect anything much from me before next Tuesday: I'm preparing a talk/presentation for the schools' Astronomy and Cosmology Society on lunar colonisation. I will of course place said presentation on the Internet once I've done it.

Planet or satellite

I had first lesson off this morning, so while doing some prep I listened to the Chris Moyles show on Radio One. Now, at 09:00 every day, Comedy Dave does a spiel called 'Tedious Link', where he has to connect the previous day's Tedious Link track to the current day's via a series of seemingly arbitrary (and extremely clever) coincidences. Now, today Dave made some reference to the Moon being a planet, which caused no end of uproar. Chris said that the Moon was a satellite, and Dave stuck by his statement that the Moon was a planet. And guess who they called up to resolve the issue? Sir Patrick Moore, the venerable astronomer, and presenter of "The Sky at Night". It was surreal, and very funny, because for 10 minutes it seemed as if Radio One had suddenly turned into Radio Four. Naturally, Sir Patrick clarified the issue: planets orbit stars, and satellites orbit planets. Chris was naturally very pleased with himself. I'm quite impressed by how willing Sir Patrick is to get stuck in and set the record straight, even at his age. He's a legend.

Lava tube feasibility

On Friday, the British Library finally sent me the paper on lava tubes [1] I'd been referred to by Tom Billings (getting hold of it was a non-trivial exercise). It was definitely worth the effort, however: it's very interesting indeed.

As I suggested on 2nd March, the problem with designing a lava tube-based outpost is that, at the moment, we've no way of knowing whether there actually is a lava tube where we think there is one. I was pleasantly suprised to find my speculation confirmed by Coombes & Hawke; they say, "There is one major problem to consider... the difficulty in confirming, absolutely, that a tube does in fact exist... and determining what its exact proportions are."

The best thing about this paper, however, is that it provides a table of very strong lava tube candidates, some more than a kilometre in width. Some of these lava tubes could be ideal sites, except for the unfortunate fact that none of the tubes assessed as 'prime candidates' are close to the equator. That's a shame, because an equatorial position would be the most fuel-efficient to get to.

Even so, it's possible that strategists might decide it better to go with a lava tube we know rather than spend a lot of money on techniques such as SPR in the hope of finding a more conveniently located site.

References:

[1] Coombs, C.R., and B.R. Hawke, 'A Search for Intact Lava Tubes on the Moon: Possible Lunar Base Habitats', in The Second Conference on Lunar Bases and Space Activities of the 21st Century (W.W.Mendell, Ed.), NASA CP-3166, Vol. I, p. 219, 1992

Homo sapiens

So on Saturday, someone decided to tell me that I need to get a life. 'Who cares,' they said, 'about all this rubbish you talk about?' Maybe I should explain why I'm so interested in space. I remember first becoming fascinated with space travel when I read a book by Arthur C. Clarke entitled Islands in the Sky. I almost forgot about it then for a few years, until when I was 14 or 15 I realized something that seems to me as if it should be obvious.

The human race is going to die. It's going to happen, one way or another. We will be extinct one day, and nothing that we can do about that: all we can do is delay that day as long as possible. But I look around me in the world today and I see that what's going to kill us will inevitably be the consequence of our sins.

Now, although that sentence was couched in religious terminology, I mean it in a totally non-religious way. Thinking about the way I behave, I realize that I am in a continual war between what I should do and what I want to do, and more often than not I do what I want. For example, last night after the Maths trip I should have done some horn practice, but instead I went to bed and read a book. This morning I should have got up at quarter past six so as to have enough time to do the things I need to get done before lessons, but I stayed in bed to twenty-five to seven. These are minor examples, of course, but they illustrate what I'm talking about.

Unfortunately, when taken at the scale of a nation, the pre-occupation with 'me' has terrifying consequences. Because a government continually feels the pressure of 'what the people want', it is forced to give the people what the people want rather than what they need. Take the USA for example. Its self-serving import/export policies and propaganda about the benefits of 'free trade' (we sell stuff to you happily, but won't buy your stuff except at huge rates of taxation) are born out of the desires of Americans to own big cars, comfortable houses and still to have plenty of time to drink beer in their local. Of course, that's not to say that people all over the world don't have the same basic desire to live in comfort. I do. But while we feather our nests, people all over the world haven't enough food to eat and barely enough water. That's neither right nor fair. I know good people who do many charitable things; a few who have given up a lot in the name of charity. But I know that they make up the minority of people; would that they were less exceptional. Perhaps what I'm talking about is the 'human condition'.

So what does that have to do with me? Because everyone is too preoccupied with what people want, rather than what they need, important things are being neglected and money that needs to be spent on scientific research is being directed elsewhere. We've known that Yellowstone National Park in USA is a giant semi-active caldera for a long time but because the chances of an eruption are so remote, less research is being done on it than should be. The fact seems to be ignored that an eruption of that particular volcano would result in the outright destruction of a large area of the USA, and would have extinction-level effects. Likewise, take an asteroid impact: we've known for thirty years that a large asteroid or comet hitting the Earth would be an extinction-level event. But such is the state of affairs that frequently-reported near misses aren't taken as a warning, but as another example of 'those crazy scientists crying wolf again'. As Terry Pratchett puts it, we are "...a race that watched million ton slabs of ice crashing into a planet which was in astronomical terms just next door, and then did nothing about it, because that sort of thing only happens in Outer Space".

But although I hope that through my future work I may be able to help with the danger to our race from outer space, I have really been plagued by the realisation that we have too many eggs in one basket. Although the Earth is a big, our survival is a fragile thing, and as we make the world smaller by our transport and communication infrastructures becoming continually more sophisticated, I see that we just increase the likelihood that something will kill us all. People first saw the effects of that in the SARS virus last year. Having seen the numbers, we were very lucky: the rate of infection was low enough that a serious epidemic was averted. If SARS had been a little more potent, a pandemic could have been on the cards. Another manifestation is terrorism. Terrorists can communicate so effectively nowadays, and that contributes to the potency of their attacks. Although I condemn terrorists and their activities, they do serve an important role in society: they remind us of how fragile our perceived security is. While we stay locked into one rapidly shrinking planet, these problems of war, disease, and the poor-rich divide will only get worse. What homo sapiens needs is some redundancy, so that if Earth suddenly ceases to be a going concern there will still be some of us somewhere to keep up the struggle.

This is my mission, to make our species capable of surviving an extinction-level event on Earth, or an infectious disease, or a nuclear war. But I won't be able to do that unless I can persuade people to do what they should rather than what they want, and governments to think not about the next five years but the next fifty. It won't be easy, but it is necessary. This will be my life's work.

Terrible weekend

I'm really fed up this morning. Because there's no CMS this morning (there's a concert this evening instead) I'm stuck at school for just one lesson, Physics with Mr H., right at the end of the morning. So once I finally get out of here after lunch, it's going to be about 2 hours on the bus to get home, and then I have to go straight out to get a bus to the concert. If it wasn't for Chopper's lesson (sure to be dull as ditchwater), I could have gone home last night, and spent most of the day with Lizzie. As it is, I've slaved over some nasty calculus, done a bit of horn practise, and updated my website.

Tomorrow should be better though: although I'll have to make my own way home from my horn lesson, in the afternoon I'm going to get my bike out, fix the flat tyre, and go off cycling: I'm going to find the best cycling route from our new house to Lizzie's place. Hopefully walking from Horspath to Cowley won't take too long... I'm glad I've managed to get out of singing in the Bach St. John Passion on Sunday, or it really would be a terrible weekend.

Speaking of website updates, I've added quite a bit: a new section about shooting, including my 2003 reports for the Buzz (the school newspaper). I've also added a concert diary, outlining some upcoming concerts I'm playing in.

Using ion propulsion

So supposing I've potentially got 20 tonnes into LEO, but I actually want to get something to the Moon, what's the fraction of that 20 tonnes that has to be propellant?

I'm going to assume that I can have my 20 tonnes in an orbit parallel with that of the Moon, at an altitude of 1000 km. I'm also going to assume that the only problem is getting out of the Earth's gravitational field, to a target orbit the same as the Moon's (i.e. an orbital radius of 384000 km). So from the equations for a circular orbit (see for instance an A-level Physics textbook) initial velocity v₀ = 7.35 kms^-1 and final velocity v_f = 1.02 kms^-1, giving Δv = 6.33x10³ ms^-1.

I'm going to make the blatant assumption that as much electrical power is available as I require, and use a high-powered ion thruster. Now, the example I looked up on the Internet [1] had a quoted specific impulse I_sp of 3800 s. I can use the fact that exhaust velocity is equal to specific impulse divided by the gravitational field strength on the Earth's surface (g = 9.81 ms^-2) to find exhaust velocity v_e = 37240 ms^-1. Then from the rocket equation in the form e^{-Δv / v_e} = m_f / m₀ the ratio of final mass to initial mass is 0.843.

This is interesting, because it implies that out of 20 tonnes in LEO 16 tonnes will make it to lunar orbit: a much better ratio than for a conventional booster! Assuming, however, the payload is destined for the Moon's surface, that sixteen tonnes must include: the ion engines themselves and fuel tankage; the solar panels required to power the ion engines; the landing retrorockets and enough fuel to land the payload; and the landing gear. So it's probable that less than half of the original 20 tonnes would consist of non-propulsion payload. But the setup would probably still be an improvement on a conventional chemical-rocket-only system.

References:

[1] IslandOne, Advanced Propulsion Concepts

Better with a 12-gauge

I'm finding indoor shooting incredibly frustrating at the moment. When shooting practise cards, I can do really well: I've got a really good 98 last week. But when it comes to match cards, I just shoot completely rubbishly. The last three cards have been 89, 90, 87 (today). It's infuriating: I don't know what's wrong with me. Sorry for lack of journal today: I'm still working on it.

Fly, flying away

I to RAF Benson during CCF today, to fly Tutors (the RAF's current initial training aircraft). This was my last time flying them as a cadet: we don't have any more flying sessions there booked this year. I had a half hour sortie. After takeoff, we flew towards Didcot, and then just about managed to find enough clear air to do some aerobatics. Doing a loop is very strange: you pull lots of Gs while you climb, and then you look upwards and backwards and see the ground come into view - a wierd feeling. There's a kind of momentary feeling of hanging, and then you're heading straight towards the ground, pulling heavy Gs again. It's even wierder when you're flying the plane yourself. We also did some upside-down flying, which was truly bizarre, hanging from your harness while looking up at the ground. I had a major headache for the rest of the day though, because my helmet was too tight. Oh well.

January results

Pure Mathematics 3: 79% (B) Mechanics 3: 88% (A) That really isn't good enough. I must work harder. Although I do have an A overall in A-level Maths now, which is a good thing really.

Heavy lift (sort of)

I've been trying to work out which single-shot launcher provides best performance to LEO, by looking at the Ariane [1] and Boeing Delta-IV [2] launchers (no particular reason; these are just the launchers I thought of as being capable). I got the latest versions of the documents I referred to available, but I suspect they may be a little out of date (four years old).

Another thing to note is that the Delta-IV is only available for US government launches now, because Boeing was finding the commercial market insufficiently lucrative.

I'm interested in the maximum lift capability to LEO, pretty obviously, and for my purposes I'll consider a 45° inclination orbit at an altitude of 1000 km.

The Ariane 5 ES costs about $150,000,000 a shot (probably more). It consists of two solid fuel boosters and a cryogenic (liquid hydrogen/oxygen) main stage, with a solid fuel upper stage. Its performance to a LEO as described is just over 18,000 kg.

The heavy variant of the Delta-IV (Delta-IVH) costs in excess of $120,000,000. This is the only figure I could find, and it's even more outdated than my documentation for the launcher; I suspect the true price is closer to $200,000,000. The launcher consists of three Delta-IV CBCs (cryogenic main stages) strapped together, with a cryogenic second stage. It's a pretty big launcher. Performance to the aforementioned orbit is about 22,500 kg, in a payload bay of comparable size to the Space Shuttle's.

So for sheer mass capability, the Delta-IVH beats the most capable current member of the Ariane family hands down, and has a comparable price tag.

References:

[1] Arianespace, 'Ariane 5 User's Manual', Issue 3 Revision 0, March 2000

[2] The Boeing Company, 'Delta IV Payload Planner's Guide', October 2000

Big and slow or small and fast

Yesterday I mentioned that I thought "development of the Moon should proceed... with most of the equipment and supplies being taken to the Moon in big, slow containers, while crew exchange happens in lightweight, fast spacecraft." What did I mean?

The ESA have a current project named SMART-1, a very small lunar orbiter mission. It was launched on the back of a big commercial satellite, into an orbit much closer in than that of the Moon. What's interesting is that it is currently using an ion drive to climb out of the Earth's gravity well to the moon, while hardly using any propellant at all (ion drives have a very high specific impulse). The downside is, of course, that it takes a very long time: SMART-1 will take eighteen months to move from the orbit it was inserted into at launch to its final lunar orbit.

I find this very interesting, because it suggests an interesting scheme for getting kit to the Moon. Big containers of non-perishable equipment and supplies could be thrown into a relatively low orbit, and then could engage ion drives to move themselves into lunar orbit (probably taking a couple of years or so), before using conventional methods for landing on the Moon. That would make most efficient use of the launcher's lifting capacity by minimizing the amount of propellant needed in the cargo. On the downside, it means two different types of engine and two different sets of propellant tanks are needed, as well some way of producing quite a lot of power.

Fortunately, power isn't too much of a problem: solar panels couild be designed to first be used to power an ion drive, and then detached as part of the unloading process and used at a lunar base.

Unfortunately, perishable goods (like astronauts) couldn't use that transit method, so an Apollo-style spacecraft would be needed to transfer personnel from Earth to Moon and back again. Ideally, the L/AV would be left at the Moon and refueled by visiting astronauts, to save on Earth launch mass. My slight worry is that we currently do not have a suitable launcher for this type of mission, unless the Russian Energia launcher is available or the Saturn V could be resurrected.

This scheme is an example of Lunar Surface Rendezvous (LSR) for freight, and Lunar Orbit Rendezvous (LOR) for personnel/perishable goods.

SITREP

I just thought that I've been so preoccupied with writing journal articles recently that I haven't thought about describing the things I've been up to recently.

Back in January I mentioned that I was working up Schumann's Adagio und Allegro for the school Instrumental Competition, and that my horn teacher thought I couldn't do it. The competition was on Friday, and contrary to his expectations, I did win! That makes it twice I've won now (I won it in 2001 playing Nocturne by Franz Strauss).

Of course, the big gig is on Friday 19th March, when I'm going to be competing against several of my friends from CMS. There are going to be seven of us competing, and the standard will probably be very high, so it could be quite exciting! Lizzie's coming along to listen, as are most of my family.

On Sunday Greg and I had a band call for a show we're playing in with OYMT, Bye Bye Birdie. The music's very hard, but it's good fun as well, and lots of people I know are involved. Evening performances are on the 31st March, and 1st, 2nd and 3rd of April at St. Helen and St. Catherine's School Abingdon. There are matinees on the 1st and 3rd of April. Come and see it, because it's going to be very good.

On Friday night Lizzie's family took me to the National Guild of Master Bakers' Oxford branch's annual dinner dance. Which was interesting: the food was very nice, but unfortunately the music and dancing was definitely somewhat dubious.

Next Saturday I'm playing in a CMS concert at Burford school...

I'm far too busy.

The Lunar Hostel scheme

Over the last few days I've been referring frequently to Kokh et al. [1] in their paper on the Lunar Hostel concept. But on Friday I stated that I disagreed with the main thrust of the paper. Why?

In essence, what they propose is to provide a "big dumb volume" on the Moon's surface (a "hostel") with absolutely minimal amenities, and have all the necessary life support systems etc. provided by visiting spacecraft.

I believe this to economically foolish, and I don't think any agency would fund this scheme. The problem is mass. Landing on the Moon takes a certain mass of propellant, and it's necessary to take the propellant needed to get back into orbit again with you. It's desirable to keep the amount of propellant you need to take onto the surface with you to a minimum, so that you can take more supplies, equipment etc. with you instead.

So if you're visiting a base, you want to leave as much as possible of the stuff you take with you behind. You don't want to land a huge piece of hardware for recycling the air inside the hostel, and lug it back into orbit again. The same goes for water systems. It'd be much more desirable to land a big tankful of water and then take an empty tank back to orbit than to land a toilet, a shower, a water recycling system, and so on, and then have to launch it all back.

In complete opposition to the LRS's idea, I think the way development of the Moon should proceed is with most of the equipment and supplies being taken to the Moon in big, slow containers, while crew exchange happens in lightweight, fast spacecraft with minimal functionality (a la Soyuz or Apollo).

References:

[1] P. Kokh, D. Armstrong, M.R. Kaehny, and J. Suszynski, 'THE LUNAR "HOSTEL": An Alternate Concept for First Beachhead and Secondary Outposts', The Lunar Reclamation Society, 1991

Applying the Moonbagel - 2

On Friday I began a discussion of how to apply the Moonbase hybrid-inflatable design.

I took the opportunity to draw a quick diagram to visualise what I was trying to describe. Access it from the Space section of my website. Please take a look.

As I mentioned on Friday, placing a floor inside a Moonbagel a third of the way up its diameter maximises usable floorspace, and this diagram illustrates the concept quite well. To me, the positioning looks like the optimal configuration for such a small module; in a larger module, I would put two floors in, at a third and at two thirds of the way up inside.

By now you've no doubt noticed the caption: "Moonbagel/Space Shuttle". That's because I chose the dimensions for this example quite carefully to fit into the Space Shuttle's main bay: the module as shown would fit into exactly a quarter of the bay, uninflated (the dashed outline).

I tackled another problem with this sketch. The bulkiest part of a module is the central core, which must contain hardware (wet & environmental systems) and the envelope, when uninflated. The original sketches show the core being held above a vacuum space by the pressure in the inflatable section. I don't like that configuration, because it would impose unnecessary stresses on the points where the ring meets the core. As shown, I've chosen a configuration where the base of the core is on a level with the base of the ring, and rests on the same surface.

Those are the main points I tried to fit into the diagram. Once I'd drawn it problems with it started appearing to me: I'm forever self-analysing. For instance, where should an airlock go? In this design, I can't find a suitable place to fit one. And where could the flooring be stored while in transit? Where could power cables connect to the module? The expansion coefficient isn't as big as it could be, either. However, I can't see a module much larger than this in its uninflated form being practical to move around on the Moon.

Applying the Moonbagel

Yesterday I said that the Moonbagel hybrid-inflatable [1] looked like a good design for basing a Moonbase design around. However, as I said, there are a few specifics that I feel should be addressed. Please refer to Kokh et al. so that you know what I'm talking about.

First, dimensions. Consider the floor to ceiling distance of the room you are (probably) seated in now. I expect that you will observe that the ceiling is 8' to 10' above the floor, i.e. 2.5 m to 3 m. This is because that is the amount of vertical space people feel comfortable in, so it would make sense to have that much headroom in a Moonbagel. But remember that the floor of an unmodified Moonbagel would be curved, like the inside of half-pipe. Unless the Moonbagel is decked, it would be difficult to make efficient and comfortable use of the space inside. If the Moonbagel was decked, it would be good place the decking about a third of the way up, so as to get the best trade-off between floorspace and headroom. The lower third of the space available could then be used, for example, for stowage.

But this brings me neatly on to the problem of radiation shielding. In order to get the most efficient possible usage of cargo mass as well as to improve the expansion ratio it would be sensible to have the walls as lightweight as possible. But there is no way that such lightweight walls - for the sake of argument 5 cm thick - would provide sufficient radiation shielding for the Moonbagel's inhabitants. Shielding would have to be provided by a lava tube or by regolith heaped over the inflatable. Assuming there is no accessible lava tube, and that the Moonbagel is 1.5 * 3 = 4.5 m tall, that means digging a hole 2.25 m deep, putting the Moonbagel in and inflating it, and then piling the regolith back over the top. There have been builders at my school recently. It took quite a long time for them to dig a hole 2 m deep, and required some heavy equipment[*].

Back to dimensions. For maximum strength and best unexpanded to expanded volume ratio, a 'slice' of a Moonbagel should be as close to circular as possible. However, the container fills the 'hole' of the torus.

I'm going to need a diagram to be able to elucidate my ideas further. A task for the weekend, maybe.

Footnotes:

[*] It's starting to seem inevitable that heavy earthmoving equipment will be needed for the construction of any size of permanent base, so I'm not going to dwell on it.

References:

[1] P. Kokh, D. Armstrong, M.R. Kaehny, and J. Suszynski, 'THE LUNAR "HOSTEL": An Alternate Concept for First Beachhead and Secondary Outposts', The Lunar Reclamation Society, 1991

Inflatable habitats

When thinking about the practical design of a Moonbase, the thing that always bothers me is the need for space. Unlike the ISS, a Moonbase would be under the influence of gravity, and so the usage of volume would be very different.

Reasons for needing the extra space apart (having provided it, it's certain that activities would expand to fill it) inflatable modules seem the best way to go about creating it. Why?

The shuttle has a limited volume in its main bay - hence the relatively small size of the ISS modules, but inflatables could provide a much more efficient use of the volume. Consider a balloon and a matchbox. Uninflated, you can fit the balloon inside the matchbox, but when inflated, the volume of the balloon is much, much larger than that of the matchbox. This isn't the best analogy - the anticipated inflation ratio is smaller, and the inflatable module would unfold rather than stretch to its inflated size, but it provides the necessary example.

The original proponents of inflatables for a Moonbase were Kokh et al. [1], who suggested several designs. One of their most important points is that pure inflatable designs are impractical because they require a lot of outfitting - they can have no built in furnishings, and because pure inflatables only come in spherical, cylindrical and toroidical configurations, there is always an inconvenient curved surface underfoot which needs to be decked over for comfort.

Kokh et al. suggest a 'hybrid inflatable', which consists of some hard elements which have inflatable volume expanding between them or out of them. Their favourite design was dubbed the 'Moonbagel': a hard cylinder containing equipment and inflatable walls that expanded out into a torus, the original cylinder filling the 'hole' of the torus.

As meritous as their work was, I personally disagree with the main purpose of their paper, and I will discuss that at a later date.

NASA later took an interest in the Moonbagel design with respect to providing living space for astronauts on the way to and from Mars. Their adaptation, called TransHab, incorporated foot-thick walls for radiation shielding and a central structure fabricated from a lightweight honeycomb material [2].

The Moonbagel concept seems very promising to me, with a few adaptations. I will discuss these tomorrow.

References:

[1] P. Kokh, D. Armstrong, M.R. Kaehny, and J. Suszynski, 'THE LUNAR "HOSTEL": An Alternate Concept for First Beachhead and Secondary Outposts', The Lunar Reclamation Society, 1991

[2] P. Kokh, 'TransHab and the Prehistory of its Architecture', The Lunar Reclamation Society, 1999

Lava tube initial steps

I've thought further about the problem of actually gaining access to a lava tube, and assuming it's the plan to build a long-term base in a lava tube, mission planners have two options:

1. Send a surface scouting mission - probably a rover - to a potential site, to ascertain whether the chosen lava tube is accessible. If not, a different site could be investigated, or a hardened shelter and excavation equipment could be sent with a crew to dig their way into the tube.

   Once an accessible site is found or access to a tube is cleared, send kit for setting up a base inside.

   Advantages: You don't go to the expense of sending a hardened shelter and heavy excavation equipment unless you have to.

   Disadvantages: For each site, an extra launch is necessary for a rover just to scout out the local area. Also, the project will take longer to get off the ground because of having to wait for the results of the rover's survey.

2. Assume lava tube access will be blocked, and send a hardened shelter, excavation equipment, and stuff for populating a tube immediately. If access is blocked, the crew will clear it, and set up a base.

   Advantages: doesn't require a surface scouting mission in advance, so quicker to implement.

   Disadvantages: the extra mass of a hardened shelter and heavy plant has to be sent every time.

Neither of these options are ideal, especially from a financial point of view. However, there are lava tubes on Earth which are directly accessible (the Oregon L5 Society uses such a lava tube as a moonbase simulation facility), so it's not unreasonable to assume that there are such lava tubes on the Moon. The problem is, how to locate them?

I expect that, at least initially, financial constraints will dictate that a beachhead will be a hardened shelter near to a lava tube, and that equipment for either gaining access to the lava tube or for establishing an inflatable-modules-covered-with-regolith base would come later, if the lava tube is inaccessible. Of course, if the lava tube is accessible immediately, then that's an added bonus.

Reloaded

My website is now back online at its new host! I've added a new section, 'Space', where I'm going to put space-related articles and resources I've written. The first thing I've made available is the talk I gave to the Windhover about the Columbia space shuttle accident.

Missing the obvious

Yesterday I outlined some design constraints for a beachhead Moonbase. Unfortunately, I've been missing a crucial fact over the last couple of weeks; this is a good example of why these journal entries are a learning experience.

While looking at some data on lava tube sites that have already been identified, something struck me: all the lava tubes that have been located so far have been rille discontinuities, i.e. the lava tube has collapsed at each end of the possible lava tube, probably leaving a lot of debris that would hinder access to the tube. I then also finally realised that entirely uncollapsed tubes would have no way in - they would be completely underground. The fact is that even if a lava tube was found from orbit that looked absolutely perfect for inhabitation, it is most probable that the tube would be inaccessible.

So, in order to gain access to a lava tube some heavy plant would very likely be required: bulldozers, excavators and possibly tunnelling equipment, none of which is going to be on the cards for a beachhead Moonbase (although I have some ideas about how some of this stuff could be made available).

So, having established that a beachhead Moonbase cannot be assumed to be located in a lava tube, I'm back to square one: how to protect astronauts from solar particle events and cosmic rays while they clear access to a lava tube. Well, one way would be with a metre or so of regolith. But heavy equipment is needed to move the regolith on top of the base. I really don't like the thought of astronauts being unprotected so far from home: if a big solar flare occurred, they would be to far away to return before it hit, and could easily suffer a fatal dose of radiation.

Which came first, chicken or egg? I will need to ponder this further.

Beachhead Moonbase design constraints

On Friday I suggested methods for supplying power to a Moonbase. But what would a Moonbase look like? To do this, I must first define what the requirements are, and what restricts my options.

Firstly, I am considering a "beachhead" Moonbase; that is, a first landing base with no current infrastructure. I am considering the minimum requirement.

Secondly, recall that we are going to site the base inside a lava tube. Because an orbital drop is never going to be able to land inside a lava tube, there's a requirement already: the base must be portable without too much inconvenience.

Thirdly, astronauts will need to get into and out of the base to carry out activities on the Moon's surface. So an airlock will be required.

Although power generation will be farmed out to a separate fuel cell generator (probably a sensible idea for safety's sake) there is still a lot of heavy equipment needed. Atmosphere regeneration, of course, and water management: what happens to water from showering or going to the toilet?

Additionally, a lot of other hardware is required: communications equipment, cooking equipment, furniture, medical kit; the list goes on and on.

According to my scheme, all of the features above must be available in my beachhead Moonbase. Tomorrow I will discuss the problems with some current proposed Moonbase designs.