Tuesday, July 13, 2004
Skylab to Mars
In his 1996 novel “Voyage” Baxter uses a vehicle based on a Saturn Orbital Workshop as the habitat core – i.e. a Skylab. Tacked on to that basic core is the Mars Excursion Module and an Apollo CSM. Missing is the Solar Telescope that the first Skylab deployed so successfully. Skylab was actually several components – the ATM [Solar Scope], an airlock, docking adapter and the Workshop itself. That massed 74,230 kg.
Less the ATM and it’s just 63,050 kg, plus 30,329 kg for a fuelled up Apollo CSM, and 24,947 kg MEM, which gives a grand total of 118,326 kg for the basic stack. I think the “Endeavour” in the novel had a J-2 rocket engine still attached, like early Skylab designs, and hence could boost itself out of Mars orbit.
Fuel wise I am unsure what delta-vee Baxter imagines the “Endeavour” uses. He has the ship fly-by Venus to get a boost out to Mars, but I am unsure if this really saves all that much fuel. What it does do is cut the total time away – the waiting time on Mars is just ~ 30 days, rather than the hundreds needed for a direct Hohmann transfer. Total trip time for 1986 – the alternate history date from the novel – is about 630 days.
Posted at 12:39 pm by Adam
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Here’s an interesting little table I found at an educational site about the Sun…
Computer Model of the Sun at 4.5 Billion Years
% radius Radius (10^9 m) Temperature (10^6 K) % Luminosity Fusion Rate (J/kg-s) Fusion Power Density (J/s-m^3)
0.00 0.00 15.7 0.00 0.0175 276.5
0.09 0.06 13.8 33.0 0.010 103.0
0.12 0.08 12.8 55.0 .0068 56.4
0.14 0.10 11.3 79.0 .0033 19.5
0.19 0.13 10.1 91.0 .0016 6.9
0.22 0.15 9.0 97.0 0.0007 2.2
0.24 0.17 8.1 99.0 0.0003 0.67
0.46 0.32 3.9 100 0.000 0.000
0.69 0.48 1.73 100 0.000 0.000
0.89 0.62 0.66 100 0.000 0.000
reference: B. Stromgrew (1965) reprinted in D. Clayton Principles of Stellar Evolution and Nucleosynthesis, New York: McGraw-Hill, 1968.
Solar Modelling is so good these days that helioseismological [solar seismology] studies have confirmed the figures down to ~ 0.01%. We understand the guts of the Sun better than the guts of the Earth. What a paradox! Even more so because now we know that neutrinos oscillate and all the neutrino detectors that showed a short-fall from the Sun were just blind to the majority of neutrinos. Hence we can “see” nuclear fusion happening in the Sun’s guts, but we’re still unclear as to what powers the geodynamo, for example.
From this source… Sun Layers
Posted at 11:38 am by Adam
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Monday, July 12, 2004
Old NASA stock just lying around…
Apparently NASA still has four Saturn Vs just lying around, plus a Skylab they donated to the Smithsonian, two test Shuttles [Pathfinder and Enterprise ], a number of mothballed Apollo Command Modules, and various odds and ends. So what could be done with that much hardware? Where could we go?
Stephen Baxter suggests using Space Shuttle Discovery as a deep space vehicle [DSV] and using the remaining Saturns and Shuttles to haul propellant to LEO to send the whole thing to Saturn and Titan. Sounds insane at first, but Cassini has dramatically proven the concept of multiple orbital slingshots to get to the Outer Planets for minimal fuel expenditure. However a manned mission that takes ~ 2450 days to get into Saturn orbit, plus some months to line-up for Titan, is an immense feat of closed biosphere engineering.
Baxter uses the Space Station hab module, a Space Station docking node and a Spacelab sub module for his mini-biosphere in his novel Titan, all powered by trustworthy Topaz nuclear reactors built by the Russians. What I would like to do here is post some figuring based on his design and give you all a look at the results. Personally I think he has over-estimated the LEO mass, but I’m not yet sure.
So watch this space for some links and figures from Mark Wade’s Encyclopedia Astronautica and my verdict on facticity.
Posted at 2:21 pm by Adam
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Monday, July 05, 2004
Cassini SOI approach details…
Cassini’s arrival orbit was of interest to me at one point because of Stephen Baxter’s fictional “Discovery”, which was a Shuttle modified for long duration flight to Saturn and Titan. Using a Space-Station module for habitat, some old Russian nuke-reactors [Spektras I think] and extra fuel haulled up to LEO, the Saturn-Titan mission was a one-way flight to be resupplied by Earth – unless Earth turns to crap in the meantime, as in his novel “Titan”.
“Discovery” performs a successful SOI – except for an explosive decompression from a ring-fragment – but burns for 100 minutes at 0.1 gee. That implies a dV ~ 6 km/s, but Cassini’s actual SOI was a mere 0.626 km/s, which means Baxter used the wrong figures. Kind of odd since he had copied the “Discovery’s” flight-plan directly from Cassini – every event day in the long voyage is direct from Cassini’s chief events. Since the launch was set in 2008 this is unlikely – the planets would rarely line up for exactly the same flight-plan.
Here’s Cassini’s approach by orbital radii that I could get figures for…
Radial Distance (km) Speed (km/s) Notes
158,500 22.5 Ring plane
24.00 SOI burn begin
80,230 31.50 Periapsis
30.40 SOI burn end
Cassini began its journey with 3,132 kg of propellant – good old space-storable N2O4/UDMH. That mix gets 3,028 m/s exhaust velocity, and Cassini’s main engine puts out 445 N thrust. Total dV ~ 2,500 m/s. A previous major burn was at the last aphelion before the Venus/Earth swing-by that sent Cassini to Jupiter/Saturn – it lasted 88 minutes.
The SOI burn lasted 96.4 minutes and used 850 kg of Cassini’s propellant . Here’s a table summarising the different burns so far – that I have records of…
Duration (minutes) Mass Used (kg) Notes
88 776 Deep Space Maneuver
6 53 TCM 20
1.2 10.6 TCM 21
96.4 850 SOI
61.8 545 Periapsis raise
253.4 2235 Summation
102 897 difference
The trick now – as far as recreating Baxter’s figures for “Discovery” goes – is working out the dV needed to send the vehicle on its way from LEO. Baxter has four revived Saturn V’s reconditioned to orbit fuelled up Saturn IVB stages at LEO to boost the Shuttle on its way. That’s a lot of hardware, but that’s chemical rockets for you. Once in orbit the Shuttle can dump its SSMEs – which are superfluous for N2O4/UDMH burns – and save lots of extra weight by dumping the tail plane. All up a real “Discovery” would probably mass +90 tons. And then there are the space-propellant tanks, and the Saturn IVB stage dry-masses to add up…
A fuelled “Discovery” is 230 tons – my BOTE calculations – and Saturn IVB loaded is 119.9 tons, 13.3 ton dry. A Saturn IVB’s engine is a LH2/LOX rocket with an Isp ~ 421 sec in space. If “Discovery” needed 3.5 km/s to send it on its way then the mass ratio is 2.334. At least three Saturn IVB rockets would be needed, so the “Discovery” plus booster mass would be ~ 270 tons “dry”, and 630 tons gross. In the novel Baxter has four other shuttles scrapped to be made into Shuttle-C heavy lift vehicles, giving basically two big fuel tanks tacked on to a Saturn IVB core.
Posted at 12:55 pm by Adam
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Friday, July 02, 2004
Ok… Cassini for real…
Cassini parked itself into Saturn orbit at c. 1336 local time… while I was minding the kids, hence distracted. An orbital insertion into a looping ellipse that will take about seven weeks to reach apoapsis, and the next big burn of about 392 m/s. The ring pictures are incredible and very odd.
A detailed timeline of the whole manoeuvre can be found here…
Saturn Orbital Insertion
…Cassini managed to shave off 626 m/s today, so another 392 m/s of dV should go smoothly. She’s a good ship, designed to work even when major systems go off-line.
Another timeline of interest is her mission overview…
Slightly dated since the Huygens mission is now due early in 2005 due to a communications glitch. Otherwise a valuable overview.
Now these links I just ran into and the pix are way cool…
MOBITAT… mobile habitat
Makes sense but the devil is in the details. Moon-dust is nasty on joints so I wonder how long the Mobitat will be mobile…
Posted at 9:11 am by Adam
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Thursday, July 01, 2004
Cassini has arrived safe and well… belated
Watch this space… if all goes well.
Posted at 1:39 am by Adam
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Sunday, June 13, 2004
Cassini at Saturn
After over six long years of interplanetary tennis rallying Cassini has almost arrived at Saturn and has snapped some very cool pics of Phoebe. Phoebe looks pretty battered as moons go which implies a lot of space-debris in circum Saturnian space…
Here’s an earlier pic of Saturn which is absolutely awesome…
…and it makes you realise how small our world is, since that planet is just under 10 times the width of the Earth. That’s three circumnavigations of the globe just to span that planet. The rings are about 25 times as wide as our planet – 8 circumnavigations. Imagine that in the days of sail – literally years of travelling.
But its distance from us dwarfs that size comparison – Saturn is over one hundred thousand times the span of the Earth away. An orbital satellite can circle the world in 90 minutes in a low Earth orbit – and Saturn is over thirty thousand “orbits” away. That’s the equivalent of over 5 years of orbitting the Earth. Cassini took over six, but it started out a lot quicker than low orbit speed of just 7.8 km/s – something like 28 km/s in its initial solar orbit. So why did it take so long?
Cassini masses in at over several tons and the launcher that sent it on its way couldn’t give it enough kick to get to Saturn. As a result Cassini had to circle the Sun a few times and get a speed boost from Venus and Earth’s gravity and orbital motion. In 2000 it got another boost from Jupiter before finally curving gracefully out to Saturn. Those long graceful curves are the main cause of such a long voyage even at ~ 30 km/s, as well as a steady slowing by the Sun down to much lower interplanetary speeds.
Here’s a fairly clear timeline and explanation of Cassini’s voyage, though pitched at school students by the sounds of it…
…so on day 2460, just over six-and-a-half years, Cassini will brake sufficiently to be captured into a long orbit around Saturn. After that the main mission begins, with Huygens dropped off to visit Titan on day 2588 (6th November 2004) and arriving on day 2609. Pretty cool. So in November we will see pictures of Titan’s oily lakes… can’t wait!
In his 1996 novel “Titan” Stephen Baxter actually copied the Cassini timeline directly for his manned Saturn mission of 2008, but I’m not sure the planets will be anything like correctly aligned for the same orbital travel times. I’d really like to know if he checked the figures at all, or just borrowed holus bolus.
Posted at 10:20 am by Adam
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Thursday, June 10, 2004
Stereo-printing is a technology that is becoming indispensible. Prototyping machine components, computer boards or just about anything is becoming cheaper and more refined, more perfect. A tank or vat of precursor material can be sintered, cured, hardened and layer by layer a solid component created from software and raw materials. This is the idea made solid, just like Plato imagined for all physical processes.
Inspired by such techniques, tissue culture scientists are wondering if 3-D prototyping technology can’t be applied to making working organs. Simple organs can already be crafted from a framework that cultured tissue then grows onto and ultimately replaces, thus forming the new organ. That’s fine for some body structures, but others have complex systems of nerves and blood and lymph vessels that need replication. Not easy to emulate.
But with 3-D printing and micro-control of individual cells we might yet see the 3-D printing of whole, working organs. If you’ve seen the re-animation sequence from “The Fifth Element”, that’s the kind of thing we are talking about as the logical conclusion of such advances.
Magnetic-resonance imaging and related medical imaging technology are getting good enough to image individual cell positions – thus imagine a whole body scan converting your body into a software representation that can be re-printed in flesh. But just because we can bring flesh back, can we “breath life back into it?”
I say yes. Why am I so hopeful? Because we are also advancing to the point of being able to suspend people indefinitely. A medical hypothermia treatment is being developed that will allow open-heart surgery and the like without heart-lung machines because the body will be slowed and cooled below the point where blood flows rapidly. Organs will be frozen for storage and ultimately cryopreservatives will allow living people to be suspended indefinitely.
A frozen person awaiting “reanimation” is akin to a newly printed body awaiting the first stirrings of life. But how will the “mind”, “soul” or “program” that was a person be restored to a “body-print”. This is the most difficult aspect of the concept. We do know that memory is stored in our brains as some kind of neural change, but just what? One theory I read years ago is that neuronal spines are irreversible switches akin to individual memory bits within a computer. Spines have two positions, extended and retracted, and this is perfect for a permanent memory bit – a physical flip-flop circuit – to preserve memory in the thermally noisy environment of a living brain.
If so then ultra-resolution MRI will allow recording of neurones, their dendrites and their spines. We know how to make neurones grow dendrites and we’re on the verge of knowing how spines are controlled, hence I am optimistic that brains can be replicated with high fidelity. If the neuronal spine memory theory is correct – and I have seen data to that effect – then perhaps the mind/soul/program can be re-stored, or at least copied as software.
Thus if we can find an indelible medium to store our body/mind pattern onto we can restore it to life, and indefinitely extend organic life. But will a high-fidelity re-print be you, me or anyone he/she was recorded/reprinted from? Are we just software run in wetware, software that can be “rebooted” as need arises? Or is there something more?
Posted at 5:12 pm by Adam
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Thursday, June 03, 2004
sorry for the break… and rotovators
Life can be hectic, hence not a lot of blog. But thinking goes on. Here’s one resultum… rotovators.
Initially I tried rotovators with arms that were integer fractions or multiples of Earth’s radius. Could get pretty close to zero relative velocity with enough fiddling but it’s hard synchronising with the ground. Matching relative angular velocities between arm and ground to get multiple touch-downs in a day means several 100 m/s difference between tip and ground. A multi-armed rotovator with ~ 8-12 arms mitigates this somewhat.
Alternatively I’ve gone for orbits that are integer fractions of geosynchronous orbital period. Two to consider: 1/9 and 1/13 ratios. The relative velocity between the radius vector of the centre-of-mass and the turning Earth are then 1/8 and 1/12 of geosynchronous orbit [times between pick-ups just shy of 3 hours and 2 hours respectively for each arm.] The 1/12 ratio rotovator has a radius of 1248 km and a spin-gravity of 3.5 g. Pick up speed is 211 m/s. The rotovator itself spins 6 times relative to one lap past the pick-up point, hence 72 times/day.
Theoretically a two armed rotovator in such a mode can pick up from 12 equidistant points along the equator once every hour. Hard to manage I’d suspect, but possible theoretically. I can imagine mag-lev accelerated cargo-pods at 12 ports ringing the planet hurled off into space at apogee at ~ 13.3 km/s, a hyperbolic excess of 9.35 km/s. Saturn anyone? The system’s kinetic energy would need to be huge so each pod released meant only minor loss or else it would be too hard to reboost.
At a fractional period of 1/8 relative, to the pick-up point, the rotovator is rotating just 3 times per lap at 1.05 g. And the pick up speed is a mere 38 m/s. Advantage is obvious, even if the frequency is lower. Only six pick-up points result, with a wait time of 90 minutes. Hyperbolic excess at the other end is a respectable 8.9 km/s [tip speed 11.8 km/s relative to fixed stars.]
What I want to know is how would the Rotovator be reboosted between pick-up and release? The change in moment-of-inertia means the rotovator’s c-o-m is no longer at orbital altitude unless the system is reboosted. Light payloads and heavy rotovator mean this is minor and reboost can be provided electrically – plasma jets and/or electric-motor effect in the Earth’s magnetosphere. The details would make an interesting study.
If ever the Earth needed evacuating then a team of 12 rotovators could pick up from 12 ports around the equator once every 5 minutes. With 300 person passenger pods that would mean some ~ 43,200 people per hour, 1,036,800 per day and 378,691,200 per year, some 6% of Earth’s population. With a growth rate of ~ 2% that would mean 25 years for evacuation, but just 15 years with ZPG.
Hmmm… of course the other evacuation option is to launch city-mass [~ 8,000,000 ton] Orion-style nuclear vehicles using 10 megaton pulse units. If we’re desperate enough…
[culled from my post to a yahooGroup... http://groups.yahoo.com/group/space-elevator/ ]
Now if we did want to haul Earth’s populace en-masse the pods would be insufficient for long-duration travel. Instead they would be flung out at escape velocity and picked up by space-tugs to be marshalled together into rotating rings of 12 – 20 for artificial gravity. A central core vehicle would provide power, provisions and propulsion – perhaps plasma sails to provide radiation protection as well. These would steadily cruise into the outer solar system to whatever planet of refuge was suitable – like Saturn in Michael McCollum’s novel…
Cool! Nice cover-art by Don Dixon for this one, though in reality Saturn’s rings would have vaporised under a hotter Sun.
Posted at 11:29 am by Adam
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Monday, May 10, 2004
More Power from the Sun…
Recently very high efficiency solar-cell materials have been developed.
Here’s one news bite on a zinc-manganese-tellurium compound that may produce
solar cells with 50% efficiency – experimental silicon cells get get 28%,
while expensive commercial cells get 15 – 20%, cheaper ones 10%.
…a shorter summary at Space.com…
…here’s news on lead-selenide cells from ScienceDaily…
…and older news on indium-gallium-nitride which might be the closet thing
to a full-spectrum material yet…
Zinc-manganese-tellurium materials seem ideal, but the
Gallium-indium-nitride material will do just as well. Here are the links…
…for a cell this is multi-junction but it
covers the whole spectrum. Zn-Mn-Te is in a single material and as a result will be easier to make.
From my point-of-view I reckon solar concentrator cells are the best option.
From what I have read cells improve in efficiency with light intensity – up to 31% for doped silicon
- and also less semi-conductor is needed since the rest is mirror. Ultra-thin mirrors,
perhaps aluminium vapour deposited on carbon-nanotube sheeting, would be ideal to cut back
on the mass requirement which I reckon is the real killer for SPS applications.
Ultra-light carbon sheets like these…
…which should be easier to make in quantity, especially
with the new nanotube making techniques. Cool stuff. If any of this pans out it makes the Moon
less inviting for solar-cell making. The Moon has lots of metals, they’re just
very diffusely mixed or tightly
bound chemically. Commercial metal ores on Earth have been concentrated by
geological and biological processes usually involving water, bacteria and
plate tectonics. The Moon has no water [except for insignificant frosting in
the regolith], no bacteria and no plate tectonics, hence no mineral
concentration. What it does have is a lot of silicon, titanium and aluminium
tightly bound to oxygen. With sufficient power such rocks can be pyrolysed
to separate these elements for making solar-cells. This is not easily
Dr. David Criswell is a physicist who has been the main investigator into
the Moon solar-power concept, but he has been quiet about a few problems…
1. Because the Moon is 10 times further than GEO the beam will spread 100
times more and require bigger collectors on Earth.
2. The Earth turns a lot faster than the Moon orbits it, hence the
transmitter or receiver has to turn to compensate complicating construction
and inflating expense.
3. The Moon itself turns its face relative to the Sun and so the power-plant
is in darkness 14.765 days at a time. This also requires turning solar
collectors or else the power will vary with the incident angle of the
Sunlight. Criswell wants to wrap a band of solar-cells around the Moon to
compensate which is an immense task in itself and means power will be
intermittent until this is complete.
4. He believes that processing on-site lunar soil is the best feature of his
system since it means no power-cells need haulling to the Moon or into
orbit. But raw materials costs is a minor component of solar cell costs. I
wonder just how much infrastructure will be needed to wrap the Moon in a
band of solar-arrays and to build all those steerable microwave
transmitters. The price will be astronomical.
5. All the current advances in PV cells is away from silicon towards
thin-film PVs, usually organic based, for which no resources exist on the
Near Earth Asteroids [NEAs] do contain water and organic kerogens, as well
as minerals, thus providing perfect industrial feed-stocks for making PVs.
For some NEAs the orbital transfer costs less than a trip to the Moon, hence
delivering industrial equipment isn’t a problem. Or mass-drivers can fling
ores Earth-wards for capture in GEO. Or nuclear-steam rockets can deliver it
All expensive, but feasible once a mature space presence is established -
Posted at 1:16 pm by Adam
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