Tuesday, September 21, 2004
ESA Pluto Orbiter Probe
While the USA is ahead of the world in Space, the rest of the world is working to change all that. The ESA’s Advanced Concept Team has come up with a Pluto Orbiter Mission, which is powered by several advanced RTGs and uses a Xenon ion-drive to speed up the flight…
Pluto Orbiter Probe
It’s quite an ambitious concept and would have a decent science return – if they gave it enough propellant it could visit a Kuiper-Belt Object too, albeit slowly. Actually a better combined mission would be Neptune/Triton and several KBOs, as Neptune and Triton’s gravity fields would allow gravitational swing-bys to boost the probe out to its more distant targets. Triton, I think, is more interesting than Pluto because it has clearly suffered relatively recent catastrophic melting and probably still has fluid beneath its icy crust.
This link discusses the evidence for an ocean under Triton’s ice…
…hence some ~ 27 km down, or shallower, there might be an ocean, perhaps an exotic brew of water/ammonia. Cold, cold, cold… but still fluid and perhaps sufficiently enriched by organics to allow interesting chemistry. An on-going strong energy-supply is needed to kick-off life, which might not be available on Triton, but it does make living there easier if you’re immigrants.
Posted at 11:06 am by Adam
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Saturday, September 18, 2004
Voyage… the details
Stephen Baxter’s book “Voyage” is a fictional recreation of a 1986 mission to Mars as it might have happened, based on real events in our own time-stream. Hence it is “historical fiction” more than it is “science fiction”, but interesting to me for its proposed system for getting to Mars.
At first “Voyage” follows the post-Apollo recommendations for a Mars mission as an ultimate goal. In the original Space Transportation Group’s plans Saturn-Apollo was to be extended in its capabilities by a nuclear-powered third-stage, set to come into service by 1978 or 1980. In the “Voyage” alternate history NASA suffers a disastrous set-back when its new Apollo-N suffers an explosive reactor rupture, killing the astronauts slowly with a high radiation dose. Nuclear space-tugs are decisively put on indefinite hold after that.
The original Mars plan was for all nuclear propulsion, and chemical propulsion ruled out. But this wasn’t an absolute necessity. By halving the crew to just three and using a Venus swing-by to boost the vehicle the Ares mission goes ahead anyway. How do they manage it?
Some important up-grades are needed to the basic Apollo-Saturn core:
# Saturn-VB… by using four Solid-Rocket Boosters the basic Saturn-V is then able to orbit 400 kilopounds to Low Earth Orbit. This was a real design that never flew because the Space Shuttle killed off Saturn. Here’s some background at Mark Wade’s Encyclopedia Astronautica entry on Saturn V variants. If you browse the various designs you might notice how versatile a vehicle Saturn potentially was.
# MS-IIC… modified second stage becomes the Mars Insertion Booster. Also modified, without engines, to become large capacity propellant tanks. The MIB is the core of Ares, providing the power to get out of Earth Orbit and to brake into Mars Orbit. Once exhausted it is staged off at Mars and a modified S-IVb stage is used to get the Ares home.
# Apollo Block V… the Apollo Command and Service Modules (CSMs) that flew astronauts were all Block II. In “Voyage’s” time-line Block III and IV service the Skylabs and Moonlabs that follow. Block V is the deep-space version, able to take +18 months of hot/cold extremes, radiation and micro-meteorites. Not as much propellant as Block II in the SM.
# Mars Excursion Module… the only new spacecraft of the whole Ares stack. It’s essentially a giant Apollo CM wrapped around an Ascent Vehicle that separates and docks with the orbitting Ares after the surface mission is complete. MEMs were extensively studied in the 1960s and typically massed ~ 25 tons.
Launching a Saturn MS-IIC, the modified second stage isn’t ask big a task as I initially thought – that’s basically what Skylab did in 1973. Skylab itself was a modified S-IVB third-stage, which carried no engines or propellant – it was a ‘dry’ Saturn Orbital Workshop. Hence the S-IIC did most of the work of putting itself and Skylab into orbit, virtually the core of Ares orbitted in one go.
Which makes me wonder: how easy would it have been to orbit a S-IVB stage around the Moon as a ‘wet’ workshop? Pretty simple really. Of course Apollos launched by Saturn-Vs would be the only ones able to reach it, but a real ‘Moonlab’ would have been an enduring reminder that humans had been to the Moon.
Posted at 11:34 pm by Adam
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Saturday, September 11, 2004
Bombing Triton II
After Nereid smashes into Triton “hot” debris will rain down all over that little moon, probably sublimating into gas all the ices bar water ice. A massive shockwave will break-up an immense area of crust. According to at least one researcher Triton shows all the signs of having a thin ice crust over an ocean-thickness of water/ammonia – the surface is poorly cratered compared to similar moons and has huge disrupted areas already. Perhaps Nereid wouldn’t be the first super-impactor in Triton’s history?
Makes sense since a whole cloud of cometoids as big as Nereid orbit just beyond Neptune and some even cross its orbit. If any planet and moon will show signs of giant comet strikes it will be Neptune/Triton. But what melted a whole half a moon? That’s how much area looks like refrozen strawberry ice-cream! Hence after impact a huge ocean will be revealed, shrouded in a thick greenhouse blanket, perhaps enough to keep things warm for a few millennia.
Triton orbits around Neptune in an orbit opposite to Neptune’s own rotation – a retrograde orbit – indicating a catastrophic past. Something disrupted Neptune and its moons… and you can probably guess the usual suspects. Pluto and Charon, planet and moon, just beyond Neptune’s orbit have been indicted for planetary disruption. Here’s a good summary of just how…
Pluto’s Dark Past
…but they’re not the only candidates for planetary collision. Marvin Herndon suggests a rather curious origin for the Earth – and Venus, since it is virtually identical – in this recent paper…
…you might wonder what is distinctive about ‘protoplanet’ in the title. An old term describing a gaseous cloud condensing directly into a Jovian planet under its own gravity. Hence a model contrary to the prevailing core-accretion model which builds up planets from small chunks of ice/rock until they’re big enough to pull in H/He gas in space around them. That’s right – Earth and Venus are the cores of a Jupiter scale planet.
So how did they lose all that gas??? Planetary collision is the only mechanism I know of that can supply the energy needed, but how did they collide? Michael Woolfson’s Capture Theory is the only current model that explicitly produces Earth and Venus via collision. Stephen Droxley did a PhD on modelling the process, available here…
Modelling the Capture Theory
…but he doesn’t describe the collision itself. Here’s an article from the Royal Astronomical Society’s magazine…
Solar System Origins
Posted at 11:44 pm by Adam
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Wednesday, September 08, 2004
Stephen Baxter in his “Manifold: Space” novel has a character cause the collision of two of Neptune’s moons, Nereid and Triton, to give Triton an energy boost, making it more habitable for Aboriginal refugees from Earth. So I ask: what would such planetary engineering require?
Name Semimajor axis (10^3 km) (Neptunian Radii) Orbital Period (Days) Inclination (degrees) Eccentricity Orbital Velocity
Triton (NI) 354.76 14.328 5.876854R 157.345 0.000016 4.39 km/s
Nereid (NII) 5,513.4 222.67 360.13619 7.23 0.7512 1.11 km/s
As you can see Triton is about as close to Neptune as Earth’s Moon is to Earth, but about 4 times quicker. Nereid is a long, long way out. Such an orbit would be unstable around the Earth and it would become a Near Earth Asteroid.
An important feature of Nereid’s orbit is its high eccentricity – it actually orbits between 1.3717 million km and 9.655 million km, reaching 2.953 km/s at the low point and a mere 0.4195 km/s at the high point. Quite a roller-coaster ride. Also the eccentricity means that Nereid spends ~ 74% of its orbital period higher than the average distance, and a mere 26% of the time closer to Neptune.
To crash Nereid into Triton requires lowering the low-point (the periapsis) by losing velocity at the high point (the apoapsis.) To lower Nereid into Triton’s orbital path – conveniently opposite to Nereid’s – it needs to shed ~ 196 m/s. How much would that require in time and rocket thrust?
Firstly, Nereid is 340 km across and masses ~ 30 quadrillion tons. Deccelerating it by 196 m/s takes ~ 6×10^21 Newtons of force in total. That’s a lot of force! Baxter deploys huge ion engines to do the job, but they’re probably the worst for the job. Rockets are characterised by exhaust velocity and their jet-power. Ion drives generally have a high exhaust velocity but a low jet power – maybe 100 megawatt for advanced ones. Nuclear Thermal Rockets however have a medium exhaust velocity and a very high jet power – up to terawatts of power for very large NTRs.
A high-end NTR can get 10,000 m/s jet velocity, hence a velocity change of 200 m/s will need ~ 1/50th of the total mass to be moved, expelled as propellant. In Nereid’s case that’s ~ 600 teratons of mass – probably a mix of methane, ammonia and water ices extracted from Nereid directly. Spread over several years of thrusting (~ 60 million seconds), that’s 10 million tons/second, and a 500,000 terawatt jet-power. An incredible figure. Baxter, we might say, glossed over the difficulties involved.
Alternatively we might deploy a fusion engine of some sort – probably a pulse drive – with a very high exhaust velocity and jet power. For the same thrust-time a fusion drive with ~ 10,000,000 m/s exhaust velocity has a power of 500 exawatts – 1000 times the previous power-levels. Insane amounts of energy. Like exploding 120,000 megaton bombs every second…
Assuming we do bomb Triton with Nereid, what will it be like? The impact speed is ~ 10.4 km/s, and the total energy released is ~ 1.6×10^27 Joules… or about 400 billion megatons TNT equivalent (FYI… TNT packs about 4.2 megajoules/kilogram, hence a megaton is ~ billion times that, some 4.2 petajoules.) Assuming Triton’s ice-crust is at ~ 38 K about ~ 700 km of crust would melt all over the moon. However that simplifies far too much. If Triton were just ice and rock then it’s about 56% rock, collected in the core, and the ice is just ~ 240 km thick. Nereid’s remains would probably penetrate the ice and heat-up the core via direct collision.
However there are good chemical arguments that suggest Triton has a lot of carbon dioxide and methane ice, plus an outer layer of nitrogen/ammonia ices. The resulting ferment would leave Triton with a much thicker atmosphere for a long, long time.
Posted at 1:34 am by Adam
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Monday, September 06, 2004
Three new Neptune-mass planets announced in the last week and many more to come I am sure. Quite a large time of observation precedes declaring a planet in a journal article – the official point at which a discovery is accepted – and I would guess dozens of candidates are being watched.
California & Carnegie Planet Search
More mini-planets, Kuiper Belt cometoids, are being discovered all the time too. Here’s the latest listing from the IAU [the International Astronomical Union]…
…as you can see there are heaps of them – 813 when I accessed the page to write this, doubltess more next time you or I look back. A related group are the Centaurs and Scattered Disk Objects here…
…Sedna [its unofficial name] is 2004 VB12 or Minor Planet 90377, since it just graduated to having a number. The IAU is deliberating on ‘Sedna’ as its name, so calling it that is still ‘informal’. A recent news-flash is the curious prospect that Sedna is an exoplanet captured off a passing brown- or red-dwarf star…
Sedna Origin Solved?
…Sky&Telescope news-links get archived pretty quick so follow it now. Wouldn’t it be cool if it was an exoplanet on our cosmic doorstep??? But there is an even more curious possibility. Another group of small objects is listed here and currently without a category… what if there’s a few old alien probes in amongst the jumble? With sufficient engineering a probe could be self-repairing and indefinitely powered by solar and/or fusion power. It might even be able to self-replicate, albeit slowly else there’d be a few missing planets by now. Perhaps it or they watch us, waiting for our venturings forth into their territory.
Posted at 10:51 am by Adam
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Friday, September 03, 2004
Is ET calling us?
Well I’ve moved house and I am slowly returning to normal life… whew! What a labour! No wonder moving house is one of the Great Stress Events in life. Since I went off-line it seems that SETI@Home might’ve had a hit! A signal from out in space ~ 1,000 light-years away. Here’s a news link…
So it seems to be hype over a repeat found by data-miners in Germany. Little wonder really, since the 1420 MHz frequency used by SETI is decades old for space-transmission. Lasers are far, far better – but what if ET sent us a message instead? Via space-probe, that is…
BBC Alien probes
MSNBC ET should write
The point made by the article referenced is that sending large amounts of data on small, slow probes will probably need less energy than beaming all over the place with radio. This is quite true, even more so because solar-sail propelled probes would have a ZERO energy cost to the sender, except for planetary launch costs. Sent on a solar fry-by to ~ 0.01 AU a solar-sail with a thrust-mass ratio of just 2 would have a peak velocity of ~ 400 km/s. Even faster for gossamer probes with higher ratios – up to 36,000 km/s I have read, tho easier to aim for just 3,600 km/s.
Just imagine countless message-probes sent out like dandelion seeds…
Posted at 12:56 pm by Adam
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Tuesday, August 10, 2004
I am about 3 weeks behind for Uni and I’m moving house, hence this is a farewell before a hiatus. Sorry to all my fans… all three of you… (just kidding, I hope)
Some cool links…
KSC’s Apollo Program page
That one links to lots of information on Apollo, including PDFs of old press releases.
Cool mission to Mercury, but SLOW! Don’t you wish NASA had nuke stages for pushing probes around quickly???
Mercury Meeting 2001
Seemingly an old link, but our knowledge hasn’t changed much since Mercury is still years away via probe. Thirty Years since Mariner X. Thirty. More than that since Apollo…
Man Conquers Space
The Way we should’ve conquered Space, according to Wernher von Braun and Chesley Bonestell c. 1952-54. Now a movie, made by an Aussie… cool.
So long for now. Back ~ two weeks or so. Assignments due 27/29th August and Moving c. 25-29 th. Yikes!
Posted at 3:08 pm by Adam
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Sunday, August 08, 2004
Programming in C
Occasionally the mundane is interesting, like my subject CSC1401… beginning with C, as the textbook puts it. Cool stuff – now I have all these groovy software tools for writing code… 😉
Crimson Editor is one such tool – old hat to all you hackers, but new to me. Let’s you write code like you were writing Word documents, but numbers lines and checks syntax for you too. I guess once all the pleasures of C have been explored I will have to graduate to C++, which apparently has a free compiler available. But there are other free compilers out there too for all sorts of languages.
Posted at 3:54 pm by Adam
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Thursday, August 05, 2004
Apollo XI plus 35…
20 July, 1969… Neil Armstrong and Buzz Aldrin touched down in the Sea of Tranquility on the Moon. And they had a reasonable expectation that their visit would not be their last. However 35 years later, Neil and Buzz and the rest of us aren’t any closer to re-visiting their first Base Camp on that dusty plain.
What was once only a dream, became a reality, and yet is now a mere memory – why?
A hint can be found in how they did it – Apollo/Saturn. Cost a lot to develop and then NASA abandoned it, yet it never had a failure. In fact, aside from Apollo XIII in 1970, the system had fewer malfunctions than the Space Shuttle. But NASA had to give it away to sell a “cheaper” manned program to Nixon – or else there was going to be NO manned program, and maybe not much of an unmanned one either.
Nixon wanted to end the whole mad Moon-rush and redeploy the resources for all sorts of things. Hence no Apollo 18 or 19, though the equipment had all been built and was ready to go. Skylab survived by being too close to completion.
Another point is that the Shuttle got sold partly because of it fit in with the USAF’s needs – something the purely civilian Apollo-Saturn could never do because it wasn’t an aerospace plane. The USAF loved aerospace planes – the X-15 had been flying for years, the Dyna-Soar program had come close to fruition and they were actively researching lifting-bodies – and a huge manned vehicle just didn’t suit. The Gemini program suited them better – it used their Titan rockets and was the basis of their Manned Orbital Laboratory. Apollo-Saturn stank too much of NASA.
So Neil and Buzz and all the rest never got to go back. A shame IMHO. A few more Apollo Moon-shots into the 1970s would have made for a greater impetus in the 1980s. But maybe Voyage is right – all the spectacular unmanned achievements of the 1970s/80s been passed-up to pay for it.
Posted at 11:56 am by Adam
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Skylab to Mars IV
I found since last entry that my estimates for dv around Mars are really ultra-sensitive to Mars’ orbital position. Hence the propellant mass quoted is potentially off the mark. When Mars is at aphelion the dv is about ~ 1 km/s lower than if Mars was at perihelion. Early September 1986 would find Mars at aphelion, but where would Venus be for the sling-by from the novel? Working on it currently. Transfer time is ~ 384 days, meaning a launch in August 1985.
BTW The mission flight-plan from Voyage is an Opposition Class Hohmann transfer. Usually the dip past Venus is on the way back from Mars to reduce the re-entry velocity at Earth. But it works the other way too, it seems.
And I am wondering about the propellant choice – UDMH/N2O4 is very space friendly, but there are other options for fuels and oxidisers out there. Liquid oxygen is the very definition of cryogenic, but keeping it liquified doesn’t take a lot of equipment or power, especially if the tank was wrapped in reflective insulation, for example. A mix of RP-1 and LOX has a decent amount of kick, an Isp ~ 353s, but LOX and UDMH can get ~ 363s, which is cool. Definitely better than the N2O4/UDMH mix of Apollo. The mix is a lot denser (0.97 vs 0.28 gm/cc) than the LH2/LOX used in the Saturn IV-B, so if we assume the tanks are lighter, but the cooling system makes up the difference, then the Interplanetary Maneuver Stage (IMS – another TLA) can mass ~ 13.5 tons like the Saturn IV-B + IU combination.
Propellants that have been tried in real rockets can all be found here…
Interesting mix is LH2/LF2 – hydrogen and fluorine – which would have a highly toxic exhaust, hydrofluoric acid! Yikes! Glad the rocket makers settled on LH2/LOX for high performance – only exhaust is steam.
Posted at 11:41 am by Adam
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