Differences between revisions 76 and 77
 ⇤ ← Revision 76 as of 2022-08-03 08:58:48 → Size: 19137 Editor: KeithLofstrom Comment: ← Revision 77 as of 2022-10-20 02:15:02 → ⇥ Size: 19139 Editor: KeithLofstrom Comment: Deletions are marked like this. Additions are marked like this. Line 89: Line 89: '''19) Partial space elevator:''' A surface-to-beyond-geostationary space elevator requires unobtanium for planets as large as Mars. However, using available engineering materials and 20x taper ratios, an orbiting space elevator hanging Marsward from Phobos can reach down close to the top of the Martian atmosphere, with enough pendulum action to subtract most of the angular velocity. Phobos average orbital velocity is 2138 m/s at 9376 km average radius. Projected to 200 km above the Martian equator (3396 + 200 → 3596 km radius) at Phobos periapsis (9236 km) yields a tether length of 5640 km, an average bottom radius of 3736 km, for an average tip speed of (3736/9376)*2138 m/s → 852 m/s, relative to a Mars equatorial rotation velocity of ( 2π * 3396000m / ( 24.6229 * 3600s ) ) → 241 m/s, for an average relative speed of 611 m/s. That is considerably slower than 5030 m/s escape velocity - a supersonic glider can use that velocity to provide considerable cross-range. '''19) Partial space elevator:''' A surface-to-beyond-"geo"stationary space elevator requires unobtanium for planets as large as Mars. However, using available engineering materials and 20x taper ratios, an orbiting space elevator hanging Marsward from Phobos can reach down close to the top of the Martian atmosphere, with enough pendulum action to subtract most of the angular velocity. Phobos average orbital velocity is 2138 m/s at 9376 km average radius. Projected to 200 km above the Martian equator (3396 + 200 → 3596 km radius) at Phobos periapsis (9236 km) yields a tether length of 5640 km, an average bottom radius of 3736 km, for an average tip speed of (3736/9376)*2138 m/s → 852 m/s, relative to a Mars equatorial rotation velocity of ( 2π * 3396000m / ( 24.6229 * 3600s ) ) → 241 m/s, for an average relative speed of 611 m/s. That is considerably slower than 5030 m/s escape velocity - a supersonic glider can use that velocity to provide considerable cross-range.

# Phiphteen Reasons phor Phobos phirst

On my todo list is writing a paper: "Phiphteen reasons phor Phobos phirst". The list has actually grown to 28, and seems to be growing to "Phorty reasons..." A too-long "summary" follows.

While some believe purely robotic exploration can work for Mars as it will on Earth's moon, the very long distances make observation/decision loops very slow, and nearly impossible at conjunction, when the Sun blocks optical data transmission. Replacing or upgrading scientific instruments on Mars takes a large fraction of a career. We do NOT need to send boots to Mars, but it is vital to create and deliver new instruments rapidly, in response to the discoveries we make.

Even if hypothetical Mars life shared early ancestry with Earth, it would have diverged radically as conditions worsened, evolving towards biochemical "Life 2.0" compared to different-conditions Earth. Towards the end, the food chain would break down, and isolated dead bioforms (probably plankton-like) would die but not rot, perhaps in very cold shaded places near the poles. Surviving molecular traces will likely be extremely rare and require a planetwide robotic search in "peculiar" places. However, if we find the remains of Martian microbes, a few "very odd" molecules could add a long-baseline parallax view of molecular biology, greatly expanding the range of artificial bioengineering.

Perhaps we can find these long-baseline views by reasoning and simulation alone. I'm skeptical; "the universe is not only queerer than we suppose, but queerer than we can suppose" (Haldane). If Mars was the only other home of life in the solar system, it may offer our only chance to observe (and extrapolate from) "queer" bio-molecules.

The hunt for those rare Martian molecules might take decades, processing tonnes of candidate rock samples, but the long term economic benefit of artificial life that is mutually indigestible with Earth Life 1.0 might be worth quadrillions of dollars.

Direct human exploration (and unpredictable errors) could preclude this forever.

A manned lander crashing into Mars after a nine month journey from Earth will carry many "human-poop-years" of gut microbes; "kilo-Avogadros" of bio-molecules, dispersed by impact and the Martian winds. Finding a few trace Martian xeno-molecules with that overpowering noise signal would be practically impossible.

Mars is a terrible place to live. A healthy habitat requires thick radiation shielding and near-one-gee centrifugal gravity. Ask Dr. Joan Vernikos, retired NASA life sciences director, about "gee".

Water on Mars? Recent research suggests that most "Martian polar ice" may actually be smectite clay with the same radar signature. See the July 2021 Geophysical Research Letters "A Solid Interpretation of Bright Radar Reflectors Under the Mars South Polar Ice" https://doi.org/10.1029/2021GL093618

Even very cold ice has a finite vapor pressure - it will slowly evaporate. Above the surface, water molecules will be exposed to solar UV. The hydrogens will split from the oxygen, and rise to the top of the thin Martian atmosphere, then boil off into space. I'd love to find usable quantities of water on Mars; I expect we will at best find hydrated minerals, requiring vast amounts of resource-consuming processing to release tiny quantities of hydrogen/water. There is vastly more water in Sahara Desert sand.

### Phiphteen reasons phor Phobos phirst

A manned station on a Phobos pole, controlling robots on the surface via arrays of small LMO "low Mars orbit" relay satellites, is a much better place for survival:

1) 4 km/s less delta V between Earth and Phobos, compared to the Mars surface, and 4 km/s less return delta V. Vastly more mass can be delivered for the same Earth launch.

2) Direct Phobos landing by a gossamer interplanetary vehicle. Phobos surface gravity is 600 microgees, and escape velocity is 11 meters per second.

3) Robotic pre-manned-mission construction - launch crew AFTER there is a safe and tested place for them to live.

4) A 10 meter fractional-wheel vertical-axis centrifuge, 10 rpm (1 gee) habitat. It can be dimensionally and functionally identical to the interplanetary mission spacecraft itself, so that in an emergency, the habitat itself can be detached from Phobos and used to return to Earth.

5) A nuclear power source at the other end of the arm, shielded by the 10 meter plug of rock in the center. Consumables and waste shifted across the arm for balance.

6) A 20 Pascal-loaded ( 1/5000 Earth atmosphere pressure) cantilever tent supports 3 meters of rock shielding. The habitat itself is cantilevered off the rotating arm to circle in a trench under the tent.

7) Crew ingress/egress up the arm to the pivot, then over ziplines from the pivot to locations on the surface outside.

8) A crew of humanity's most clever and versatile instrument builders living for years on Phobos, assembling new analytical instruments from component stockpiles. Delivering assembled probes to the Martian surface to follow up new discoveries as they are made. Discovery-driven science packages can be constructed and delivered anywhere on the Martian surface in days, not decades.

9) The same tools can be used repair the crew habitat or return vehicle. Imagine Apollo 13, but using warehouse stock to build and replenish a new LOX tank.

10) 85% sunlight to rotating sun-tracking photovoltaics above the "poles". Phobos axial tilt is 26 degrees to the ecliptic, "night" is a one hour Mars eclipse every 7 hour 40 minute orbit. Or,

• 10a) a "space solar power satellite", tethered 20 km "above" farside Phobos, beyond the Phobos L2 point. The radial acceleration, minus Phobos gravity, is approximately 1 mm/s². Enough to keep aluminum high voltage power wire tethers taut; one to north-side Phobos, one to south-side Phobos. These will only be in Phobos shadow for a few minutes once per orbit, near Mars equinox, eclipsed by both Mars and Phobos simultaneously. Perhaps we can "rotisserie" the wires, so that a shiny side always points towards the Sun, and a black-anodized heat-emissive side points towards deep space. Supercold aluminum is stronger and much lower resistance than warm.

11) Base-local polar PV is good for half the Martian year. After arrival, during Phobos-polar summer, build a high voltage power line to the opposite pole of Phobos, 10 km away, migrating most of the solar panels twice Mars-annually.

12) 90% of Mars surface is in direct view every 8 hours, the rest via observation and relay satellites in polar orbit.

13) TINY (sub-kilogram) and NUMEROUS Mars surface robots, just big enough to carry a science package, and track and laser-link to orbiting relay satellites overhead. Terabytes per day collected on Phobos, then "big optics laser-linked" direct to Earth, or relays at Earth-Sun L4-L5 during conjunction.

• 13a) The laser uplink can be a Vertical Cavity Surface Emitting Laser (VCSEL) mounted on an electrostatically steered micromirror, a few milligrams, observed with a tracking telescope on the relay satellite orbiting (WAG) 100 kilometers overhead and +- 200 km crossrange.

14) All the talent of Earth will be minutes to hours away, interpreting data and choosing the next opportunities, while engineering teams design and test the next instruments to be assembled and landed from the mission's component stockpile.

15) WE DON'T KNOW WHAT WE WILL DISCOVER, and what we will choose to focus on after we discover it. A versatile base that can connect in milliseconds to small robots everywhere on Mars will allow us to deploy situationally unique robots to follow up new discoveries, decisions to deployment in days, not decades.

No more spam in a can. Send Homo Faber, return Earth-saving discoveries soonest, while keeping Mars clean and sterile.

• We've spent 4 billion years evolving in and trillions of dollars (mostly for weapons development) to climb out of Earth's habitable gravity well (escaping those weapons).
• Why spend more trillions to ruin another unique but life-hostile gravity well, when there are millions of asteroids and comets to convert from threats to economic bonanzas?
• Why accept exo-planetary surface contamination and tiny Carnot efficiencies, when gossamer mirrors in interplanetary nano-gravity and vacuum offer a 5700 Kelvin heat source and a 3 Kelvin heat sink?

Paraphrasing Tsiolkovsky, why climb out of our cradle full of baby poop, only to drop into another inferior cradle and make more baby poop, obliterating the priceless scientific messages written on it?

ps: is "Φiφteen reasons φor Φobos φirst" indexable?

16) If "footsteps on Mars" are required for geopolitical and funding and morale reasons, the landing should be a brief two-crew excursion from the permanent base on Phobos. Two lander+return vehicles will be available, plus spare parts. Homo Faber technicians at the base will thoroughly test both vehicles after arrival but before deployment. They will land an uncrewed backup vehicle first, while monitoring telemetry from the lander, and from video from robots stationed nearby. If all goes well, a three day visit to make speeches, launch golf balls, etc. If the crewed lander is disabled, the astronauts can return in the spare ascent vehicle. If accident disables both astronauts, Mars surface robots can carry them into the ascent vehicle and launch them back to Phobos base. Worst case, the robots also remediate any bio-contamination an accident might cause, so that does not spread beyond the landing site.

17) Phobos L2 space elevator. Mars-Phobos L2 is 11 km spacewards of the Phobos surface; a counterweight above that radius can support a tether suitable for launch from Phobos to high Mars orbit. A solar array another 7 km above L2 is at the "tandem eclipse point"; when it is eclipsed from the Sun by Mars, Phobos will also be eclipsed, blocking no additional sunlight to the solar array.

18) Beyond L2 and the solar array, perhaps a pendulum tether launching to a Deimos L1 tether, a climb to Deimos, and then another climb to a long Deimos L2 tether, launching mass to Mars escape, perhaps even to a trans-Earth trajectory (TBD ... I haven't done the Deimos calculations yet)

19) Partial space elevator: A surface-to-beyond-"geo"stationary space elevator requires unobtanium for planets as large as Mars. However, using available engineering materials and 20x taper ratios, an orbiting space elevator hanging Marsward from Phobos can reach down close to the top of the Martian atmosphere, with enough pendulum action to subtract most of the angular velocity. Phobos average orbital velocity is 2138 m/s at 9376 km average radius. Projected to 200 km above the Martian equator (3396 + 200 → 3596 km radius) at Phobos periapsis (9236 km) yields a tether length of 5640 km, an average bottom radius of 3736 km, for an average tip speed of (3736/9376)*2138 m/s → 852 m/s, relative to a Mars equatorial rotation velocity of ( 2π * 3396000m / ( 24.6229 * 3600s ) ) → 241 m/s, for an average relative speed of 611 m/s. That is considerably slower than 5030 m/s escape velocity - a supersonic glider can use that velocity to provide considerable cross-range.

20) Pendulum space elevator: A stronger and cleverly tapered space elevator can be designed to oscillate like a pendulum, rotating at the bottom with additional velocity, actually landing on the Martian surface with zero relative velocity at Phobos periapsis. Martian landers can descend the tether synchronized to the swing, converting forward momentum into more swing, and reach a roll-on/roll-off platform at the bottom. This would obviate the need for rockets, though the descent mechanism must dissipate a lot of heat. A subsequent ascent would be slow and require too much energy.

• Space elevator note: Megastructure tethers are amusing to contemplate, and may be physically realizable, but they are slow, and cannot access all of Mars beyond a narrow band around the Martian equator. Tether systems may be useful for mature Martian civilization, but they are a time-wasting distraction for Martian mission design. Do the math, and be ready to educate and refocus time-wasting "visionaries", so they do not divide attention and delay deployment of the core mission - finding ancient molecules.

21) Strong sunlight: Ground-pounders on Earth are stuck with a diffuse solar light source interrupted by the Earth's rotation, and nighttime. Mirrors in space can receive continuous sunlight, and concentrate light to the same power density and temperature as the surface of the Sun. This is true at any distance from the Sun, though the mirror radius must grow linearly with distance (and area as the square) as the distance increases. Mars at aphelion gets less than 40% of Earth sunlight, so a mirror near Phobos would need to be almost 3 times larger than a mirror near Earth for the same power collected; on the other hand, the tidal distortions of Mars gravity are 10 times smaller than Earth's at the same orbital radius, so a large Mars (or Phobos) concentrating mirror might need less structural correction than a mirror near Earth.

22) Asteroid zero: Asteroids, supplemented by intercepted comets for water and volatiles, will eventually be converted to habitats. There's enough material out there to build more than a thousand Earth surfaces, as cylindrical rotating habitats inside thick cylindrical radiation shields, mirrors and light ports at the poles. We can first perform that conversion on "small" Deimos; assuming 10 tonnes per square meter of shielding, Deimos-version-2 could have 200,000 square kilometers of surface area, divided into thousands of rotating one gee cylinders; more area than Greece. Phobos could be converted into the surface area of France.

23) Agriculture: While unmodified humans are vulnerable to radiation, ordinary plants can grow and reproduce in 400 rad/year environments (mentioned here better citation needed). Microbes have evolved to grow in reactor cooling water; it is possible that we can genetically engineer food crops that grow in zero gee aquariums with moisture and low pressure CO₂.

Cycling CO₂ and H₂O in, and O₂ out, we can create vastly larger zero gee farms to support millions of people in smaller, radiation shielded, one gee cylinders. Phobos and Deimos are the first steps to an asteroid belt converted to living habitat, vastly more populous than our tiny and fragile Earth. What we learn from studying Martian molecular fossils may be essential for this transformation.

24) Calibrating the universal gravitational constant: Phobos is small enough that a weight moving up and down a pendulum tether will shift its center-of-mass measurably. The ratio of the movements will establish the ratio of the masses. Combined with the measured gravity of Phobos, and a lot of perturbation calculations involving Mars and the Sun and Jupiter, we can estimate G more accurately than we can with elaborations of a Cavendish balance.

25) Calibrator for Radio Astronomy: In the very long term, large radio receiver dishes at the Earth-Sun L4 and L5 Lagrange positions will be used for ultra-accurate distance measurement to distant pulsars and other radio objects. They will have ultraprecise clocks; extrapolations of the nuclear transition clocks that Dr. David Wineberg is developing at the University of Oregon. But as the old saying goes, if you have one watch, you know what time it is; with two watches you don't. A third clock on Phobos (and a fourth on Deimos, and others on asteroids) can create a mesh ensemble of clocks that calibrate each other, and also calibrate the gravitational field of the Solar System.

• 25a) Earth's Moon will be a poor calibrator; Earth weather and ocean tides perturb it too much.

26) Accessable core: The average radius r of Phobos is 11.1 km, the average density ρ is 872 kg/m³, the average surface gravity g is 5.7e-3 m/s². Assuming uniform density, and the average gravity halfway to the center is half of the surface gravity. Hence, the hydrostatic pressure at the center of Phobos is ½ ρ r g or 27 kPa, about 27% of Earth sea level air pressure, and less than EVA space suit pressure on the International Space Station (cabin pressure is 101 kPa, similar to Earth). Digging an 11 km tunnel to the center will be approximately as difficult as digging an 11 km canal on Earth.

27) There are probably hollow spaces inside Phobos, with surfaces formed as much as a billion years ago, which have been shielded from radiation and impact since then. The history revealed by the core of Phobos will be a time capsule spanning the era of animal life on Earth. There may even be ejecta from Earth impacts in the upper layers of Phobos, perhaps even some vacuum-preserved Earth fossils, though Earth's Moon is probably a better place to look.

28) Mars is poisonous. Perchlorates are toxic and carcinogenic, as are hexavalent chromium compounds, perhaps other UV-generated oxidizing molecules are toxic as well. No microbes to swot up that free energy, no water chemistry and geology and subduction to neturalize, concentrate, and bury toxins. Is Mars the Draino Planet?

Acknowledgment: The brilliant Dr. Geoffrey Landis at NASA Glenn developed the most important principles first, decades ago:

Footsteps to Mars: An incremental approach to Mars exploration: Journal of the British Interplanetary Society, Vol. 48, pp. 367-342 (1995) Geoffrey A. Landis, NASA John Glenn Research Center 302-1, 21000 Brookpark Rd., Cleveland, OH 44135

Teleoperation from Mars orbit: A proposal for human exploration☆: Acta Astronautica Volume 62, Issue 1, January 2008, Pages 59-65

Other References:

NASA's Mars Fact Sheet: . . also data for Phobos and Deimos. BTW, Phobos seems to be stretched Marsward (subplanetary axis) by Martian tidal forces, and along its orbit, perhaps by solar tidal forces. That may be a coincidence - Phobos is lumpy, irregular, and inhomogeneous, not a smooth ellipsoid. Also not very dense - there may be voids and water ice (!!) inside.

PhobosPhirst (last edited 2022-10-20 02:15:02 by KeithLofstrom)