Nisi cognitio finitas, infinitum sit necesse est ignoratio
Interplanetary flight, Planets, Moons, ‘Roids and Comets – plus dust
The next Chinese space-craft, Shenzou VIII and Shenzou IX, will be unmanned – to start with – but the next manned mission, Shenzou X, will dock with one (or more) and form an orbital laboratory complex. In otherwords a Space Station. Attach a couple of propulsion modules and the Lab could be launched Moonwards, forming a Moon-Lab, just like the proposed “Wet-Lab” Skylab II that was discussed in the late 1960s as a cheaper Moon-Lab option.
Chinese News Coverage on the Plan
SpaceX’s Falcon 1 finally makes it to ORBIT!
Falcon-1 flight 4 at SpaceX
Low-Cost Rocket Makes it to ORBIT
NASA Spaceflight report
…but will it mean orbital access for 1/10 the cost??? Only time will tell…
The Carnival of Space Week 72 is up and running. Informative stuff.
Also informative is this little gem… Space Elevator: Physical Principles …which covers the derivations and consequences of the main physical aspects of a basic space elevator. Written by Ranko Artukovi? of Zadar, Croatia, and definitely worthwhile for all hard-core applied maths freaks and space-nuts.
From impeccable mathematical applied-physics to dubious applied physics we have Brian Wang’s latest on the EM-Drive… Superconducting Radio-Frequency Cavities for High Q …the table he gives makes me rather dubious about the EM-Drive’s utility.
Effect of increased Q for the Emdrive
“Q” appears to be the number of reflections within the microwave cavity before the wave is absorbed. So while the static thrust of a high Q cavity is very high it very rapidly loses thrust as speed increases, so much so that to levitate with such a drive seems rather unstable. It would be an incredible thing, if true, but the EM-Drive is yet to be demonstrated in free-fall. That will prove whether it really does convert EM energy directly into kinetic energy. By my rough figuring the first quoted figure above indicates that the EM-Drive is turning EM energy into KE at 60% efficiency at 3 km/s. Not bad.
Near Earth Objects (NEOs) might be dormant comets – well 5-10% of them, anyway…
Comets Disguised As Asteroids
…which makes them a very handy resource for propellant, shielding and whatever else you want to do with comet stuff. Check out Anthony Zuppero’s Neofuel for the details.
Hal Levison, dynamicist and cosmogonist, estimates here that 6% or more of NEOs are old Jupiter-family comets… which implies some very handy water and kerogen in interplanetary space.
You might ask “Ocean? Surely it’s still there where it’s always been?”
For the last 500 million years that has been more or less true, though sea levels have varied substantially, but in general things have been as always. But before that? A news bite from PhysOrg suggests evidence that a lot of seawater has ended up in the mantle. Part of the ocean has drained away. This would have had dramatic effects on the available land-levels and the potential for Life to benefit from shallow water – much of the deep ocean is desert, feed only by what is produced in the continental shallows. It may be no coincidence that the first macroscopic life, seaweed/macroalgae, appeared some billion years ago.
Looking back in Net-Time there’s also this curious research by some Japanese geoscientists…
Leaking Earth could run Dry
…a BBC news-bite from Sept 8, 1999. But still pretty much on the money. Shigenori Maruyama and colleagues estimated that sea-levels had dropped by 600 metres in the last 0.75 Gyr and the oceans would be gone in another billion. More or less in line with the new research that suggests half Earth’s water has drained into the mantle since the ocean formed. While that might sound like a lot it’s a depth of 5.3 kilometres of water, when averaged over the Earth’s surface. Just 0.25% of Earth’s total volume and the mantle’s total volume is 83%. Thus a drop of water in a bucket of lava…
Addendum
Eldridge Moores, a Professor Emeritus of Geoscience, has suggested for some years that sea-levels have declined over geological time, though due to a different process. By his reckoning the oceanic crust was thicker and thus isostasy meant the average ocean depth was shallower – meaning all that water covered the continents too. Only mountain peaks poked above the waves. Then, roughly as Rhodinia began forming, the thicker crust gave way to thinner oceanic crust and that super-continent of the day rose from the waves over the next few hundred million years.
When Earth Dried Out
How many times have I heard people fretting over the Solar Wind blowing a planet’s atmosphere away when talking about the terraforming of Mars or the Moon. People… not going to happen in a hurry. The Solar Wind is on average 5 million particles (mostly protons, just like the Sun) per cubic metre travelling at 400 km/s at Earth’s distance from the Sun – thus the flux (number passing through per square metre) is 400,000 m/s*5,000,000 /m^3 = 2E+12 protons per square metre per second. Their collective energy flux is their kinetic energy times their number flux – i.e. 1/2*(400,000)^2*(2E+12)*m(p)… where m(p) is the proton mass (1.673E-27 kg)… so we’re talking 2.68E-4 J/s. Less than 0.3 milliWatts per square metre. The sunlight is 1365 W/sq.m some 5.1 million times stronger, but qualitatively the two are quite different in how that energy is distributed. A proton slamming into an oxygen atom at 400 km/s is quite a bump. If all the momentum went from proton to atom, the atom would fly away at 25 km/s. But ions and atoms tend to collide elastically and bounce off each other. To conserve momentum and energy, the proton reverses direction and slows a bit, while the atom is flung away at high speed. But when trillions of atoms and ions are involved it’s not just one interaction – many could occur and eventually the ion might share its momentum with quite a few oxygens before escaping to space. So there’s three outcomes – one interaction between ion and atom, an even share (on average) of ion momentum, and finally an even share of ion energy. Surprisingly the first is the least efficient – an upper Venusian atmosphere some 6,200 km in radius loses just 6.4 kg/s. The second case loses 2.5 atoms (assuming 10 km/s escape speed at altitude) per ion – thus 16 kg/s. The third case sends 100 atoms into the void per ion – 640 kg/s. Sounds respectable but Venus has 4.6E+20 kg of gas to space… meaning 2.3 trillion years, 0.911 trillion years and 0.023 trillion years respectively to lose Venus’s air via the solar wind. A long time.
So why is Mars described as losing all its air in the early days? Back when the Sun was young its Wind was up to 1,000 times stronger. Mars, being smaller than Venus, would lose its air very rapidly in those days (Venus would still take billions of years in scenario 1 &2), but not now the Sun is better behaved. There are complications to this picture too – magnetic fields and ionization of the impacted atoms – but the basic picture is pretty straightforward. Solar Wind erosion is SLOW…
The ESA pulled off its first asteroid flyby on the Rosetta comet-probe mission…
Steins: A diamond in the sky
…after an Earth gravity-assist maneuver, 13 November 2009, another asteroid, 21 Lutetia, is due for a flyby July 10, 2010, and the target comet, 69P/ Churyumov-Gerasimenko, will be reached in c. May 2014. The HST has taken “close ups” of the target comet, revealing a nucleus somewhat larger than the original target, Comet Wirtanen, but the comet lander should be up to the task just fine. There are also computed images images of 21 Lutetia from its lightcurve… Thirty Main Belt asteroids from their lightcurves …though such guesstimates should be taken with a grain of salt.
The Carnival of Space is on at Discovery Space Blog and it’s in alphabetical order, just for something different. No contribution from moi this week as I’m mulling over different bits of space news and trying to write an essay about a new theory of Lunar origins, but was sidetracked by the recent discovery of variable radioactive decay. The Jenkins-Fishbach Effect is a variation in radioactive decay that seems to be correlated with the Sun’s activity – no one has a good theory for what might cause it (if it’s a real correlation) so there’s several competing models, one being variable neutrino flux from the Sun. It’s interesting and potentially explains the very difficult C-14 dating anomalies (for example the fact that C-14 dates between 800 and 400 BC all give the same answer.)
If the variation is neutrino driven then objects on eccentric orbits will show different decay histories and potentially more (or less) heating. Mercury, for example, has an eccentricity of over 0.2 and thus its orbital variation in insolation is very high. Has its radioactives decayed differently to Earth’s and the Moon’s?
Mercury is half a Mars. It’s 2/3s iron-alloy core and has an uncompressed density of 5.3 (Earth is just 4.08), which makes it the densest planet. But it is so close to the Sun that it is also the fleetest, thus not showing any signs of being overly leaden. At a mass of 0.0553 Earths (Mars being 0.10745) it very nearly is half a Mars, but packed into a volume of 37.3% of Mars. Thus it is Mars missing its upper mantle. Like Mars it has polar caps, revealed by RADAR in the early 1990s. Its sidereal rotation period (‘day’) is 59 days, while its year is 88 days – a ratio of 2-to-3. Thus its solar day, or sol, is exactly 2 years or 3 ‘days’ long. Its eccentricity is 0.205630, so its orbit (a = 0.387098 AU) varies from 0.466697 AU to 0.307499 AU, and its insolation from 4.59 Earths to 10.58 Earths, thus making its surface temperature range from 558 K to 688 K at its subsolar point. However its rotational axis is almost perpendicular to its orbital plane – thus it has no seasons, and its polar regions stay much cooler on average. Near the Poles it only gets as hot as Earth’s Moon, and the vast shadows of its polar craters remain cold enough for ice to accumulate, apparently lofted there as water vapour by its very thin atmosphere.
Mercury also has a dipole magnetic field akin to Earth’s but weaker. Thus its surface is protected from the raw solar wind, though its arctic regions must encounter a lot of ions, perhaps combining the protons with surface oxides to make water. The recent visit of “Messenger” (first flyby of three before orbital insertion) also spotted several volcanoes, indicating occasional eruptions of volatiles from within – most likely sulfur compounds and water – which will migrate to the poles, perhaps before being snatched away by the solar wind. Thus the ice-caps might be an acidic mixture, with benefits for any colonization efforts. Life can not live on plain water alone.
Because Mercury’s core is relatively accessible will that make it a desirable object for mining efforts? That seems reasonable because Mercury has large amounts of solar energy too, to power mineral extraction, refining and export. Yes, export. A next-to-nonexistent atmosphere and lots of sun means Mercury is perfect for gigantic mag-lev launchers. Also its proximity to the Sun means that Hohmann transfer windows are relatively frequent to ALL the other planets. Here’s some transfer times for Hohmann, Elliptical and Parabolic orbits…
| Planet | Distance | Hohmann | Elliptical | Parabolic |
| Venus | 108.2 | 75.54 | 39.54 | 23.79 |
| Earth | 149.6 | 105.47 | 55.68 | 38.06 |
| Mars | 227.9 | 170.49 | 90.16 | 67.11 |
| Ceres | 413.9 | 361.67 | 190.15 | 149.70 |
| Jupiter | 778.6 | 853.73 | 445.30 | 359.60 |
| Saturn | 1433.5 | 2032.43 | 1053.88 | 860.59 |
| Uranus | 2872.5 | 5597.78 | 2890.44 | 2374.36 |
| Neptune | 4495.1 | 10841.1 | 5588.60 | 4600.00 |
…times in Earth days, distance is to the Sun in millions of km. Orbital transfers are computed from Mercury’s average distance to the Sun, to the target planet’s average, thus it varies a bit depending on actual position. A Hohmann orbit is the minimum energy transfer – exactly half an orbital ellipse from one planet to the other. The elliptical is a segment of a transfer ellipse, in this case a quarter of the ellipse (i.e the target planet’s radius is equal to the transfer orbit’s semi-major axis.) And the parabolic is a Solar escape orbit. As you can see the transit times are pretty rapid for the inner planets, as orbits go. Venus is mere weeks away and even a trip to Jupiter is under a year for a parabolic orbit. As we’re talking bulk cargo this probably isn’t odious with sufficient planning. Faster trips, for personnel, will need much higher energies.
So, in theory, Mercury could supply metals to all the inner planets and the near asteroids. You might wonder: why couldn’t the metal asteroids supply the rocky asteroids more quickly? Surely they’re closer?
Problem is that asteroids aren’t continually in convenient positions for a minimum energy transfer. Take Ceres (rock/ice) and Vesta (rock/metal), some 2.767 AU and 2.362 AU from the Sun respectively. Ceres takes 4.6 years and Vesta takes 3.63 years to orbit the Sun. Between transfer windows is, on average, over 17 years because their orbital periods are so close together. Yet Mercury’s windows to Ceres open up every 0.254 years. Thus it’s easy to see the advantage. Of course things are a bit complicated by the orbital eccentricity of both – Ceres’ is about ~0.08 – but the principle remains the same. That and sunlight that’s 37 times stronger on average.