2001: A Space Odyssey – Discovery, 1. The Centrifuge

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Kubrick’s 2001: A Space Odyssey was a watershed moment in cinema history.  It was one of the most meticulously conceived movies depicting humans in space.  The movie was released in 1968, before NASA had even landed men on the moon.   The interplanetary spaceship, Discovery is perhaps one of the most iconic spaceship designs in cinema history.   While it deviates from Clarke’s description in the book, it is quite similar to a Leslie Carr drawing in form.   Here was one of the first interplanetary ships to deviate from the V2 or “flying saucer” forms.

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Nuclear space ship – Leslie Carr – from “Interplanetary Flight” by Arthur C. Clarke

Part 1 The Centrifuge

Prior to 2001, astronauts either floated around in their ship, or walked about as if full Earth gravity was keeping them oriented to the desired floor.  The Discovery was different.  It had a centrifuge withing the crew area that generated a force, simulating gravity.   This is dramatically shown with the opening scene on the ship showing Frank Poole jogging around the centrifuge.

It isn’t clear from the movie how much artificial g was experienced by the astronauts, but the book 2001: The Lost Science indicates that the it was 0.2 to 0.3g.  It must have been guesswork as to whether this was sufficient for optimal health, and may have reflected Clarke’s hopes that low gravity would improve health.

Given this value, and the radius of the centrifuge as 16 feet,  it must have been rotating at 6 revolutions per minute to generate approximately 0.2g at the centrifuge floor in the Discovery.  Which is interesting, because Frank’s jogging would have had very different effects depending on the direction he took.

The rotation rate of 6 rpm gives a speed of about 7 mph, a fast jog or run.  If Poole ran at that speed in the same direction as the spin, he would increase the effect or artificial g to about 0.8g.  He would feel distinctly heavier.   Another effect would be that his body would tend to rotate forward towards the floor, forcing him to try to lean back to correct this.

If however he ran in the counter-spin direction,  he would experience some very strange effects.   If he ran at 7mph, he would negate the effect of the spin and his feet would experience zero g. he would lose traction and start to drift away from the floor.   Furthermore, as he accelerated to 7mph, any rotation that his body experienced would generate very different g in different parts of his body.  Frank probably needed to exercise before meals, just in case.   The video below shows such a simulation of a very similar situation by NASA.  Note how the subject tries to keep himself oriented and his drift off the centrifuge wall when running in the counter-spin direction.

While the centrifuge in the Discovery is probably too small to be very comfortable, none of the space agencies has done any serious work to date to determine what level of g we need to generate, nor what centrifuge radius would be comfortable enough to be worth the extra mass and complexity of a spaceship.

References

1.   2001: A Space Odyssey

The BIS Lunar Spaceship Ship – pt2: Centennial Flight?

It is 2039, the 100th anniversary of the British Interplanetary Society’s (BIS) publication of their design for a lunar spaceship.  The public interest in human space exploration has blossomed with the successes of commercial spaceflight.  Funded by a billionaire space entrepreneur turned  philanthropist and media sponsorship, the BIS built an updated version of this vintage design.
The spaceship redesign retained the classic elements – 5 equally sized launch stages and a monolithic moon lander.  Dimensions and weights were kept as close to the original design as possible.  Changes were made to the flight profile and of course used more modern components.
Could a 21st century version work, where the early 20th century version would not?

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Spaceships Refueling in Free Orbit   – Drawing by R. A. Smith
One change was to have the moon ship fueled in orbit.  This was more in line with later thinking by the BIS, as shown in the drawing above.  This saved launching the fueled ship and allowed just 4 stages to put the ship in orbit.  (Refueling, whether using stables for horses, foreign port coal and oil bunkers for steam ships and airports for airplanes has long made sense.  Nasa also is now considering orbiting fuel depots for spacecraft).   A second change was to use the 5th stage to put the moon ship into lunar orbit, rendezvous with it again after departing the moon and returning it to Earth orbit.  This allowed the moonship to require less fuel for the landing and moon departure,  avoid the risky aerobraking maneuver for return to Earth, and for the entire 5th stage and moonship to be reused for future flights and as an orbital tourist attraction.  The velocity cost of returning to earth orbit is approximately an extra 3 km/s, now totaling 19 km/s.
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Illustration of mission plan for new BIS Lunar spaceship in 2039
The original 1 tonne capsule was kept to the same weight, but was now built from spun carbon fiber, allowing more generous consumables.  Windows were kept to a minimum and replaced with hi-resolution cameras and thin film display screens.  Navigation is much simpler and supported by satellites, replacing  the mechanical coelostat for star fixes.
The launch stages were reduced to 4 of the 5 stages, with an intention of lifting lunar ship to orbit.  Replacing the solid rockets, are batteries of hybrid engines, with a higher specific impulse, based on paraffin with liquid oxygen (LOX) oxidizer.  Not only were these engines higher performance, but also safer and could be shut down in case of a problem.  A major benefit of the multiple engines in each stage was that the thrust for each can be individually controlled.  Computers controlling the individual rockets ensure the launch stack stays precisely on track.
On return to Earth orbit, a Skylon space plane with crew compartment was selected as an appropriate way to return the astronauts to Earth.

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The 20 km/s velocity change is more than enough to meet the 19 km/s velocity budget.
4 stages with hybrid rocket motors now have sufficient energy to reach orbit, with a cumulative velocity of 8 km/s.  The orbital fueled 5th stage carries the lander to the moon and back to Earth.  The liquid fuels chosen are easy to handle and store.  If necessary they could be upgraded to higher performance fuels, such as LH2/LOX which have 50% greater exhaust velocities. (Note that the 5th stage calculations are split for the 2 stages it is used in the flight).

While the redesigned lunar spaceship is a far cry from the spaceflight technology mow in use in the 2030′s, it showed how innovative the original design was, and that it could fly with relatively few changes.

 References

  1. Interplanetary – A History of the British Interplanetary Society, Parkinson, B,(2008) British Interplanetary Society 
  2. High Road to the Moon, Parkinson, B, (1979) British Interplanetary Society

The Moon – Clavius Base and TMA-1

Clavius Base, situated in Clavius Crater is the location of the moon base in the Arthur C Clarke novel, “2001: A Space Odyssey”.

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Clavius is situated near the lunar south pole.  The base was founded in 1994 and is located beneath the surface of the crater floor to protect the agricultural areas and human station crew from the harsh surface conditions that vary from extreme heat to extreme cold.

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Clavius Crater.  Clavius Moonbase is located under the surface

The alien monolith, designated TMA-1 for teh intense magnetic field that it emitted is located in Tycho Crater.  This crater is located north of Clavius Crater.

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Tycho Crater.  The site of TMA-1 – The Monolith

The origin of the movie and novel for 2001: A Space Odyssey, is the short story, The Sentinel.  In the short story, the location of the the alien artifact, a crystal pyramid was located on a peak in the lunar Appenines, in the south wall of the Mare Crisium.    The pyramid is located on the surface and protected by a force field of some type.   In 2001: A Space Odyssey, the shape has changed to a 16:9;1 rectangular monolith, and which is buried under the surface of Carter Crater, so that its unearthing and exposure to the sun signals the presence of intelligent life arriving.

The BIS Lunar Spaceship – pt1: Could it have worked?

In 1939, a small technical committee of the British Interplanetary Society audaciously designed the first spaceship to land astronauts on the moon and return them to Earth. The design was a radical departure from fictional spaceships, looking like a large cylinder with a hemispherical capsule at the top.  This design prophetically presaged the real space launchers to come.

 

The designers had known that a single monolithic ship would be impractical as the structure to fuel mass would be be impossibly small.  As H.E Ross said:

“(…) it will require about 1000 tonnes of fuel to take a 1 tonne vessel to the moon and back, so our problem has been to design a 1 tonne spaceship with containers for 1000 tonnes of fuel attached outside and detachable.”

It looks like they did a back of envelope calculation assuming that they needed about 16 km/s of total velocity change for launch, Earth escape, lunar landing and escape, with an aerobraked reentry to Earth.  Repeating this, gives a reasonable best performing rocket exhaust of about 2315 m/s.  Of course no rocket then, or now, can carry 1000 tonnes of fuel with an empty weight of just 1 tonne.

So they designed the rocket with stages, each being discarded, just like its descendant, the Apollo Saturn 5 did.

But in those pre-war days, the committee did not believe it was possible to build powerful liquid fuel engines to lift their spaceship.  So they resorted to solid fuel rockets, with only a small liquid fuel engine for the lunar landing.   Those solid rockets were small, nothing like the size of the space shuttle solid rocket boosters.

There were 5 stages of equal size to reach Earth escape velocity, each stage comprised of 168 individual solid rockets that would generate thrust and then be immediately discarded to save weight.  The ship contained a total of 2000 such rockets, loosely bound together in a hexagonal arrangement.

The overall design of the ship is shown below.

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The 1939 BIS Moon ship.  Note the equal size stages, filled with identical solid rockets.

The moon lander itself was large compared to the Apollo Lunar Module, 6 meters in diameter, and revolving about 17x per minute to create an artificial gravity.  Yet despite its size, the bare capsule housing the 3 astronauts was supposed to weigh about a ton, about  the weight of a Toyota Corolla without its engine.  Compare that to the Apollo Lunar Module ascent stage that weighed nearly 2 1/2 tonnes, or the Apollo Command Module that actually made Earth reentry at 5 1/2 tons.    Clearly this was to be a minimal, seat of the pants mission!

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Drawing of the moon ship stowed at the top of the rocket.

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Later version of moon ship.  Drawing by R A Smith

Like the Apollo Lunar Module, the BIS ship had 4 shock absorbing legs, to land on the lunar surface.

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The BIS moon ship landing on the moon.  Note the vernier engines to keep the descent stable.  Drawing by R. A. Smith.

The technical committee needed to make the design work with a more realistic fuel to mass ratio, which they thought might be 90%.

The table below shows my very simplified calculations using the BIS’s guess for rocket exhaust velocity.   Unfortunately, the total velocity change falls far short of that required.   If the ship had been launched, it wouldn’t have even made orbit, let alone sent the lunar space craft on an escape trajectory to the moon.  Note that the overall mass at launch 1118 tonnes is very close to the 1112 tonnes the BIS calculated for their design.

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Simple performance estimates for the BIS Moon ship stages and space craft, using the estimated exhaust velocity for the engines.

Of course the committe understood that they needed fuels with much higher energy and exhaust velocities, perhaps as high as 1/4 of the required total final velocity change.  If we arbitrarily increase the exhaust velocity to 3400 m/s, the numbers suggest that the design might work.  The 5 solid rocket stages will gain the necessary 11 km/s Earth escape velocity, and the lunar lander can meet the 4.8 km/s velocity changes to land and then take off for a return to Earth.

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Simple performance estimates for the BIS Moon ship stages and space craft, using a higher, 3400 m/s exhaust velocity for the engines.

While the 3400 m/s exhaust velocity is well within the performance of modern liquid fuel rockets, it is unfortunately outside of the performance envelope for solid rockets, the best of which are still below 3000 m/s.

The conclusion we must draw, is that this early design done at a time when aircraft still used propellers for flight and had just transitioned to aluminum airframes from primarily wood and canvas a decade earlier, was very flawed.   Like experiments in early powered flight using steam engines, the solid rockets in the design were just too weak to make the design work.   The assumption that the returning capsule could do a number of aerobraking maneuvers, skipping in and out of the atmosphere  to allow eventual reentry without a substantial heat shield is highly optimistic to say the least.    Within 20 years, the US and Russia had developed powerful rockets and were on teh threshold of launching humans into space, wit

 

In part2, I will revamp the Moon Ship for a flight

 References

  1. Interplanetary – A History of the British Interplanetary Society, Parkinson, B,(2008) British Interplanetary Society 
  2. High Road to the Moon, Parkinson, B, (1979) British Interplanetary Society

 

Aries 1B Moon Ship – Chemical or Nuclear Propulsion?

The Aries 1B moon ship in 2001: A Space Odyssey is a clear descendant of the lunar landers described by Arthur C. Clarke in The Exploration of Space and their realization as the Apollo Lunar Module that landed on the moon in 1969.

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The Aries 1B landing at Clavius base – still from the film.

In the movie, the ship takes Dr. Heywood Floyd from the space station in Earth’s orbit to Clavius base on the moon.

The question to be answered, is: “Does the design work with chemical rockets, or does it need something more potent?

In “2001: The Lost Science”, and echoed in “The Spaceship Handbook”, it is stated that the ship uses chemical rockets, probably LH2/LOX.   This might be considered surprising as both the Orion spaceplane and the interplanetary ship, Discovery, both use nuclear engines.   In the novel, Clarke writes about a plasma exhaust that implies a power plant that is not chemical.  he wrote:

There was none of the power and fury of a takeoff from Earth – only an almost inaudible, far-off whistling as the low-thrust plasma jets blasted their electrified streams into space. The gentle push lasted for more than fifteen minutes, and the mild acceleration would not have prevented anyone from moving around the cabin. But when it was over, the ship was no longer bound to Earth, (…)

To answer the question, we need to determine the likely mass of the Aries 1B, its fuel payload and likely engine performance.

The most difficult is to estimate its mass.   Given its luxurious interior, it perhaps most resembles a spaceship version of an executive jet.  Executive jets typically assume passenger and luggage weights around 110 kg, and when compared to their structure weights, the passengers are in the ballpark of 15% of the empty airplane.  The movie version has the Aries 1B carrying 24 passengers, with a crew of 4.  Using this data, the Aries masses about 20,500 kg, and 23,600 kg with a full complement of passengers and crew.

The fuel she can carry is determined by the Aries’ fuel tank volume, which is dependent on her dimensions and the location of the tanks.  “<em>2001: The Lost Science”</em> indicates that the Aries has a diameter at the “equator” of 45 feet, about 13.6 m.  The passenger section takes up this midsection.  Above the passenger deck is the galley, and then the flight deck.  Assuming that all the fuel is located between the passenger deck  and the engines,  I estimate that there is about 320 cubic meters of space for the fuel or propellant tanks.   Given this volume constraint, the mass of fuel will therefore depend on its density.

Required Performance

Starting from Earth orbit, the ship needs to add nearly 3.2 km/s velocity to completely escape Earth’s gravity,  and another 2.4 km/s to land on the moon, a total of about 5.6 km/s.  If the ship only refuels on the moon, then it needs to be able to meet a total velocity change of 11.2 km/s.  If the ship can refuel in earth orbit as well, then only 5.6 km/s is needed for each leg of the journey.  Intriguingly,  “<em>2001: The Lost Science”</em> suggests that there are heat shields to protect the Aries when reentering Earth’s atmosphere.  The Aries isn’t obviously designed to return to earth like an Apollo or Soyuz ship, so I take it to imply that she may use aerobraking to shed her return velocity to return to LEO (low Earth orbit).   If so, she would only need 8 km/s of extra velocity for a 2 way journey between refueling stops.

If we use Clarke’s description of the departure from Earth orbit, 15 minutes of engine burn would need about 1/3rd of a g to reach the extra 3.2 km/s for escape velocity.  This would also be adequate performance to land on the Moon too.

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Passenger section. Business jet roominess. – still from the film.

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Passenger section.  Flight attendants discussing their mysterious VIP passenger – still from the film.

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Galley section is zero-g.  Elevator in the back accesses the passenger section, while the flight deck is accessed from one of the floors.

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Zero-g Flight deck in the “nose” of the ship and orientated perpendicular to the passenger section.
Chemical Rockets

The best chemical propellants have an exhaust velocity of 4500 m/s.  This means that the ship needs to have a mass ratio of about 3.5 for a one way trip, and about 12 for a two way trip if it only refuels on the moon.

LOX (liquid oxygen) has a density of 1140 kg/m3, while LH2 (liquid hydrogen) has a low density of 70 kg/m3.  This averages to 427 kg/m3.   Therefore the this high performance fuel cannot mass more than 137,600 kg in the available space.  Using the rocket equation, we get a maximum velocity change of 8.6 km/s.

This allows the Aries to make a 1 way trip to the moon or back, with refueling at each end of the journey, like a modern airliner.  If we allow aerobraking, then it could make a 2 way journey, refueling at either the Moon or Earth orbit.  However, Aries cannot make a 2-way journey purely using rocket propulsion.

Unless aerobraking is accepted, it is probably best to assume that the Aries is refueled at each destination.  Today, with the discovery of possible water at the lunar south pole, it would make sense for the water to be shipped to Clavius base for processing.  The resulting LH2 and LOX would be used to fuel Aries on the moon, and perhaps shipped to Earth orbit as well for refueling spaceships.

Nuclear Rockets

We can probably discount Clarke’s suggestion that the Aries has a plasma jet rocket engine.  Today, such engines are low thrust and require a lot of electrical power.  The mass of a nuclear power plant to power the engines for short periods would not make sense.  The movie version of Aries has no obviously large radiators to dump its waste heat.

A more conventional nuclear rocket, like Nerva, typically gets its high performance by heating low mass hydrogen.  This gives such rockets a high specific impulse.   However it comes at a cost of large tanks, as LH2 has a low density as we have seen.  In the context of the Aries’ limited volume for fuel storage, this low density results in a fuel mass of just 22,400 kg.

Assuming about 900 specific impulse, the velocity change is about 6 km/s,which is enough for a one way journey, refueling at each end of the journey.  Like the chemical rocket, it cannot achieve a 2 way journey with one refueling.  It is also not sufficient to make a 2 way journey with aerobraking.    This performance looks disappointing as it appears less useful than chemical rockets.   However, there is an advantage in that the cost to deliver just 22,400 kg of fuel to LEO is a lot less than the 137,000 kg of LH2 and LOX for the chemical rocket.  In addition, any lunar water can now supply oxygen to Clavius base, rather than burning it as oxidant.

As the low density of the liquid hydrogen prevents Aries from achieving the convenient 11.2 km/s velocity change that allows it to manage a 2 way journey, can it be solved using other, denser propellants?   The problem with denser propellants is that the exhaust velocity is dependent on the mass of the molecules in the exhaust.   Using water, or even liquid argon, requires a specific impulse that exceeds that of tested nuclear rockets.  Only hypothetical liquid or gas core reactors would have the necessary performance to make this work.

Conclusion

The most likely propulsion system for Aries is chemical rockets using LH2/LOX.  This requires refueling at the end of each journey, at the space station and at Clavius.   If aerobraking at Earth is possible,  then a 2 way journey is within reach.    Replacing the engines with nuclear thermal rockets and liquid hydrogen as the propellant, provides slightly reduced performance, allowing 1 way journeys only.  They do have the advantage of being cheaper to supply with propellant, although replacing the nuclear fuel core would also have to be considered.   Changing the propellant does not provide any major performance improvements withing the design specification of the Aries as given.

References

  1. 2001: A Space Odyssey, Stanley Kubrick & Arthur C. Clarke (movie)
  2. 2001: A Space Odyssey, Arthur C. Clarke
  3. 2001: The Lost Science,  Adam Johnson
  4. The Spaceship Handbook, Jack Hagerty

Colonizing Mars

Mars ain’t the kind of place to raise your kids
In fact it’s cold as hell” – Rocket Man by Elton John

The first thing to know about Mars is that it is cold.  Temperatures range from around −153 °C at the poles in winter to a high of around 20 °C during summer at the equator, a warm summer day on Earth.  At the poles CO2, which melts at −78.5 °C, freezes out of the atmosphere and covers the water ice caps.  Despite its harshness, it is better than the Moon, which has temperatures between  shaded and sunlit areas of  around -203°C to 117 °C.   As Mars is no longer geologically active, this means that water is mostly in the form of ice.  Except at the poles, this ice is below the surface. Since temperatures can rise above freezing, this means that water might become liquid near the equator, possibly even at the surface.  There have been tantalizing hints of water as dark areas in gullies have been interpreted as water.  Mist has also been observed in the Valles Marineris canyon.

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Mists in the Valles Marineris.   Nasa

Accessible water would completely change the prospects for colonization.  Unfortunately at this point we don’t know how pure any of the water is.  The Phoenix lander indicated that toxic perchlorates are present in the soil which might mean that the water would have to be processed to be of use.

So far the living conditions are similar to that of Antarctica (−90 °C  to 15 °C), only without a breathable atmosphere.

The next problem is that Mars has no effective magnetic field and an atmosphere less that 1% of Earth’s.  This means the surface is protected neither from the solar wind, nor cosmic rays.   Stay outside unprotected by a substantial protection from the radiation and your cancer risk rapidly increases.  Living on mars would be the same as staying in space from a radiation hazard perspective.  As a colonist, you would want to live below ground, or at least with a heavy soil or rock layer above you for protection.

The very thin atmosphere is not a good protection from meteoroids either, another reason to stay beneath the surface for protection.

A third problem is dust.  Mars is famous for its dust clouds.  They particles are abrasive and will coat everything.  Worse, the fine particles will get in between moving parts of exposed parts degrading them.  Space suit seals, motors, hinges and any parts with surfaces that move against each other will be problematic unless protected in some way.

Are there any useful attributes of Mars for colonization?    As mentioned earlier, water is available at the poles as ice, and may be abundant as subsurface frozen aquifers or even glaciers nearer the equator.   Water is the most important resource in the solar system – usable as fuel,  life support and even structural components, like igloos.  The availability of water is key to any colonization effort.

Local resources will also be needed for construction of more extensive habitats.   Stone is certainly available, although cutting it may be problematic.  Magnesium carbonate rocks have been found, as well as gypsum.  This suggests that the colony could build concrete-like structures.  The Romans built concrete with volcanic ash as an ingredient, and there are a lot of extinct volcanoes on Mars that may have ash in usable form.   Mars has readily available iron in the form of hematite that can be easily collected by the colonists and smelted.

Building structures on Mars isn’t as simple as on Earth.  The almost complete lack of atmosphere means that a pressurized habitat will have to contain that air with about 10 tonnes per square meter structure.  That requires about 2 to 3 meters of dirt in the lower Martian gravity.   As we have already determined that we need radiation protection on Mars, it makes sense that we use this approach to keep the habitats under pressure as well as managing the radiation risk.

Human ingenuity in adapting to terrestrial environments is well known.  While most depictions of Mars colonies assume a high tech approach, it seems more likely that low tech approaches will be needed to allow extensive villages, towns and eventually cities to develop.   These places will likely be made of local bulk resources and situated beneath the surface for protection.

It seems likely that some of the experience gained from building Antarctic research buildings could be adapted to Mars.  The buildings will need to be insulated, possibly draw power from a nuclear reactor.  Solar would work too, although the panels will need to be cleaned of dust routinely.

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Star Wars Tatooine set.  Is this a more realistic idea for a Martian colony structure?

Recently it was proposed that a one way colonization effort, Mars One, be attempted.  As there will be no guaranteed rescue, the colonists will need to be able to adapt local resources for their needs.  If this project should happen, the most valuable outcome may well be the techniques to adapt Martian resources.

References

  1. Project Boreas: A Station for the Martian Geographic North Pole,   Charles Cockell (ed.)
  2. The Case for Mars: The Plan to Settle the Red Planet and Why We Must

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Mars – Our Next Home?

Mars has long been the dream of many as a second home for humans.  As late as the 1960′s Mars was thought to be an old, dying world, drying out, but with a thin atmosphere possible sufficient to not require a pressure suit.

Until the probe flybys, the only maps of Mars were crude telescopic maps, often embellished with detail that may have been more in the mind of the observer than the planet.  In particular, the channels (canali) that Schiaparelli observed may have been optical illusions.

Perhaps surprisingly even Werner Von Braun designed a grand Mars mission with only these c

 

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Map of Mars – Giovanni Schiaparelli.  Note that the south pole is at the top.

The illusion of dark green areas, possibly vegetation, and channels, now interpreted as canals by Percival Lowell, gave rise to speculations of Mars as world populated with intelligent beings trying to maintain their world by husbanding its scarce water resources.   Mars was now an exotic place, perhaps not populated by princesses, but not a dead world like the moon.  The painting below, by the renowned Chesley Bonestell illustrates how we thought Mars might look.  Red deserts with low eroded hills.  Dark blue skies dues to the thin atmosphere.  Channels surrounded by vegetation.  Bonestell has carefully hedged his bets, showing the channels as straight, yet with irregular edges, which could be interpreted as either natural or engineered.

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This view of Mars was changed irrevocably with the Mariner 9 mission in 1971.
This showed a cratered world, with no sign of the channels or vegetation.  Below is an image of Olympus Mons, the highest volcano in the solar system, sent back by Mariner 9.

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Olympus Mons – Mariner 9

The same view from the Mars Global Surveyor.  The resolution has improved dramatically, showing clear evidence of gullies, possibly due to water erosion.  Olympus Mons is found at 18.65°N 226.2°E, which would place it in Elysium in the old Schiaparelli map.

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Olympus Mons – Mars Global Surveyor

Each subsequent mission to Mars, whether orbiters or landers has given us a view of an very interesting world, possibly with large water reserves frozen as subsurface glaciers or aquifers.  The Phoenix lander probably detected frozen water just below the surface.

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Map of landers and rovers on Mars. 

Curiosity is now exploring Mars looking for evidence that conditions were suitable for life in the past.  The surface is a much more interesting than we thought just a decade or so ago, with many signs that water may have flowed on the surface in an earlier epoch.

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Curiosity rover near Yellowknife Bay (Dec 7th, 2012)

Arthur C Clarke wrote his novel The Sands of Mars when the only maps available were those like Schiaparelli’s.   He set his Mars colony in Aurora Sinus, which can be seen 10 degrees south of the equator below the bright Argyre area.  His envisioning of the colony was similar to the painting by Leslie Carr below, which was used to illustrate how a colony might look in Clarke’s non-fiction The Exploration of Space.  It may look quaint to our eyes, but it is remarkably similar to many more modern visions.

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Martian Base – painting by Leslie Carr,  in “The Exploration of Space” by Arthur C Clarke

While more modern ideas of Mars bases are still primarily surface structures,  the need for radiation protection may require living below the surface.  Cities carved into the mountains as described by Alexander Jablokov in River of Dust may be the best solution for long term colonization unless the surface can be terraformed.

References

  1. The Sands of Mars,   Arthur C. Clarke (1951)
  2. River of Dust,    Alexander Jablokov (1996)
  3. The Exploration of Space,  Arthur C. Clarke (1951)
  4. The Conquest of Space, Willy Ley,& Chelsey Bonestell (1949)

 

Apollo Lunar Module

The Apollo Lunar Module was arguably the first spaceship built for exclusive operation in space.  She was sturdy enough to be carried to orbit above the Saturn V third stage.  She was then boosted to lunar orbit by the Apollo Service Module.  Once in orbit, the lower descent stage effected the lunar landing.  The descent stage was left on the moon, as the ascent stage returned to lunar orbit with the 2 astronauts and the lunar rock samples.

Nasa had not just departed from sending massive ships from the earth to moon landing and return, as depicted in the movie Destination Moon, but also from the idea of launching a moon ship from Earth orbit to a moon landing and return to earth, as suggested by the British Interplanetary Society decades earlier.

Minimizing weight was imperative. The lunar module was barely thicker than aluminum foil in parts.  There were no seats, the astronauts piloted the vehicle standing up.

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Because the Lunar module just had to descend and ascend to lunar orbit, the fuel demand was low.   The moon has an escape velocity of 2.38 kn/s, and to achieve lunar orbit at an altitude of 80 km requires a velocity of about 1.7 km/s.

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Apollo 11 Lunar Module “Eagle”.

To land, the descent stage must have enough fuel to kill the orbital velocity and land carrying the ascent stage.

The full weight of the fueled ascent and descent stages is about 14.9 tonnes, and the descent stage carried 8200 kg of Aerozine-50 fuel and nitrogen tetroxide (N2O4) oxidizer.   The Isp of this propellant is 311 seconds with a propellant velocity of 3 km/s.  The rocket equation:

                          V = Ve * ln(M0/M1)

gives us a potential velocity of 3 * 14.9/(14.9-8.2) = 2.4 km/s.  This is more than enough to land our vehicle..

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View of Lunar Module control panel.

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Apollo 9 Lunar Module “Spider”.  Earth orbit test vehicle

Applying the rocket equation to the ascent stage,  where the fueled mass is 4700 kg, and the fuel is 2350kg, we get a potential velocity of 2.1 km/s.  Again more than enough to achieve lunar orbit rendezvous with the Apollo Command Module.

Apollo 17 Lunar Module “Challenger”.  The last astronauts to leave the moon.

One the astronauts rendezvoused with the Command Module, the ascent vehicle was discarded, and usually sent back to crash on the moon.

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Apollo 11.  Lunar Module “Eagle” ascending to lunar obit and rendezvous with the Command Module “Columbia”

This approach to the moon landings allowed for a smaller spacecraft to land on the moon.  Instead of a large vehicle that needed to land and ascend with the fuel needed to return to Earth, only the fuel needed to land the combined Lunar Module vehicles to land and to orbit the ascent vehicle  was needed.

We will see how this compares with a trip from earth orbit to other approaches in another article.

References

  1. Apollo Lunar Module 
  2. From the Earth to the Moon 

X-15

 

The X-15 was the first winged spaceship that kissed space.    It set speed records (Mach 6.7 – 4520 mph) and height records (354,200 ft – 67 miles)x-15-2

Painting of X-15 in powered assent – Nasa

The X-15 was conceived in the 1950′s to test hypersonic and extreme altitude flight, using rockets rather than jets.   The XLR99 rocket engines used dry ammonia (NH3) and liquid oxygen (LOX) for the fuel and oxidizer.

Although the thrust to weight ratio was 2, the X-15 could not take off from a runway, but was carried aloft under the wing of a B-52 bomber.  The spaceplane was then released around 50,000 feet for its flight.

The X-15 was a testbed for high speed flight, requiring a special heat resistant metal, Inconel-X to withstand the extreme frictional heating of the air at high Mach numbers.   At extreme altitude, the wings were useless to control the aircraft, so the pilot used small reaction engines to control the plane.

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X-15 during descent for landing on a dry lake bed

Now let us examine the flight profile of the record 354,000 ft high altitude flight, by Joe Walker on August 22, 1963.

There are several distinct stages:

  1. Airlift by B-52 to 45,000 ft.
  2. Boost phase for approximately 85 seconds
  3. Ballistic flight to the fringes of space
  4. Reentry and landing.

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Example X-15 extreme altitude flight path

The air lift takes the airplane to around 45,000 ft (13,700 m) with a velocity of about 500 mph (224 meters/s).  Then the rocket is ignited, which burns through about 15,000 lbs of fuel during the burn.  The XLR-99 engine generates a thrust of about 70000 lbf (313 kN), enough to accelerate the fully fueled 34,000 lb airplane to over 2g (20.m/s/s).  After 85 seconds, the engine cuts off, fuel exhausted, and the airplane is sent on a ballistic path, that at its peak exceeds the Kaman line designation for the beginning of space at 100 km.  The final speed of the X-15 was 3794 mph, (1697 m/s).

The acceleration can be computed from the initial airspeed and the final speed

  V(final) = V(initial) + acceleration x time

1697 = 224 + a x 85.8    =>  a = 17.2 m/s/s  (1.76g)

If we use the rocket equation to get the final velocity, using the fully fueled wt of 34000 lbs, 15000 lbs of fuel and an Isp of 279 for the XLR-00 at altitude, we get a final velocity of 1815 m/s, not so far from the actual final speed.  We can also use Newton’s Force = mass X acceleration equation to get an average acceleration and speed, which gives an acceleration of 2.05g and a velocity of 1956 m/s, again within the ballpark of the flight data.

To reach altitude, the airplane must be pointing upwards, and it is the vertical component of the velocity that is providing the vertical thrust to achieve altitude.   How much vertical velocity the plane has is determined by the angle of attack.

Plugging in values angles of attack, 35 degrees will generate values for the altitude that work for Joe Walker’s flight.   This results in an altitude of 200,000 ft (61,000 m) after engine burnout, and 357,000 ft (109,000 m) at peak ballistic altitude.  The ballistic phase is 99 seconds from burnout to peak altitude and the same coming back down.  200 seconds is withing the right ballpark of the 3 minutes (180s) depicted in the flight profile picture above.

By the time the X-15 has reached its altitude records, the space program was using ballistic rockets throwing capsules into space, starting with Mercury and still the main approach today.   Yet the X-15 was the epitome of what a reusable spaceplane should be, and its development path was leading to the cancelled X-20 DynaSoar spaceplane and the operational space shuttle fleet.

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X-15-A3.  Canceled development.

Interestingly, the concept of an air launched sub-orbital space plane has been revived and is the same approach used by Virgin Galactic for its commercial service.

 References

1. At the Edge of Space: The X-15 Flight Program
2. The X-15 Rocket Plane: Flying the First Wings into Space (Outward Odyssey: A People’s History of S)

Dan Dare – Spacefleet Interceptor

 

If you grew up in Britain in the 1950′s and 1960′s, loved space, and wanted adventure, Eagle comic’s Dan Dare was just the ticket.  Our chisel jawed hero saved the earth from alien villains like the Mekon countless times.   Dare needed space ships, fast ones, that could traverse the solar system in a few weeks at most.  While not his most famous ship “Anastasia” (Annie), I have always loved the sleek styling of the Space Fleet interceptor.

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Space Fleet interceptor.  Eagle, “The Moonsleepers” – illustration by Keith Watson, 1965

The ships are classic V2 derived shapes, but with transparent canopies reminiscent of WWII bombers.  Unlike V2′s, they have quite a lot of room inside their hulls, with engines at the rear (see last picture).  They can take off from Earth, and navigate deep space.    How could they do this?

The original creator of Dan Dare, Frank Hampson, probably well understood that rockets needed fuel, and lots of it.  He would have known about the V2′s that hit London during WWII and possibly about the experiments carried out by the US after the war with captured V2′s.  So he came up with the idea of “impulse waves” to drive the space ships. These waves were broadcast to the ship and stored if necessary.  Where did that idea come from?  My guess is that he knew about Tesla’s wireless power transmission work back at the end of the previous century.  There is a brief explanation of the use of impulse waves to drive the ships in the first Dan Dare story.

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Impulse wave broadcast.  Frank Hampson, Eagle 1951

This is perhaps the first time the idea of beamed energy for space ships was depicted, an idea that is only now being taken much more seriously.

No further details were ever given, although we know that these mysterious waves can be shielded, and that the energy stored in the onboard impulse wave cylinders could be released catastrophically, destroying the craft.

Given an energy source, how might it be used?   The energy could be released directly in the form of a beam, or be used to accelerate a propellant to very high velocity.

Let us consider the latter and see what sort of performance is required. In the very first story, an impulse wave ship, the Kingfisher, takes about a week to reach Venus.   A straight line distance at closest approach gives us a distance of about 40 million kilometers.  Assuming rapid acceleration and deceleration at each end of the journey and a constant velocity for most of the journey,  the average speed is 66 km/s.   If we assume that just 10% of the ship is fuel, we need an exhaust velocity of  1262 km/s, or 1,262,000 m/s.   This is about 14x better than existing ion engine performance, so perhaps within plausible bounds, although the energy required is enormous.  Given the constant beaming, the ship could accelerate to the halfway point and then decelerate.  Maximum velocity at the turnaround point would be 133 km/s and the acceleration a very modest 4.5% of g.

Put into perspective, if the rocket masses about 10 tonnes,  the energy to accelerate it to Venus is about the same as that contained in 2 kg of Uranium 235.   If the energy was being transmitted to the ship, the ship must receive about 2 GW of beamed power.   This is about the power output of a typical large power station.  Allowing for minimal losses, this means that just one of the ships needs a dedicated power station to power it.  The difficulties of powering a full fleet are obvious.  The space Fleet ships are also very maneuverable, so the problems of  tracking them would be very severe.

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Cutaway of Mk4 Space Interceptor – Space Fleet Operations Manual

Lovely as the idea is, we must conclude that Dan Dare lives in an alternative reality where the power requirements of Space fleet’s ships are lower.  But as we’ve seen, just 2 kg of fissile U-235 might generate the energy needed.  If Space Fleet could liberate the energy of Uranium directly, without requiring propellant, they might be in business.

References

  1. Dan Dare: Pilot of the Future (Dan Dare Collector’s Editions)
  2. Dan Dare: Pilot of the Future- The Final Volume, 12th Deluxe Collector’s Edition (Volume v)
  3. Dan Dare: Spacefleet Operations (Owners’ Workshop Manual)