by Paul Gilster | Nov 6, 2017 | Advanced Rocketry |
Although I want to start the week by looking at hybrid propulsion technologies, let’s start by considering developments in ion propulsion before going on to see how they can be adapted for future deep space missions. Hall thrusters are a type of ion engine that uses electric and magnetic fields to manipulate inert gas propellants like xenon. The electric field turns the propellant into a charged plasma which is then accelerated by means of a magnetic field [see reader ‘Supernaut’s correction to this in the comments below].
We’ve seen the benefits of ion engines in missions like Dawn, which has recently received a second mission extension to continue its work around the asteroid Ceres. Now we learn that a Hall thruster called X3, developed at the University of Michigan by Alec Gallimore, has received continuing design modification by researchers at NASA Glenn and the US Air Force, scaling up the low thrust levels produced by conventional ion engines. A series of tests have demonstrated results that have implications for future manned space missions.
In fact, the X3 breaks all previous Hall thruster records, producing 5.4 newtons of force compared with the earlier 3.3 newtons. As noted in this University of Michigan news release, the X3 design also doubles the operating current record, reaching 250 amperes vs. 112 amperes, while running at slightly higher power levels than previous designs. A Hall thruster with higher power and improved thrust levels could shorten travel times, a significant factor as we work to mitigate radiation problems for human crews on long interplanetary missions.
At Glenn Research Center, doctoral student Scott Hall (University of Michigan) worked with NASA’s Hani Kamhawi on experiments to test the improved thruster, using the only vacuum chamber in the United States large enough to cope with the X3’s exhaust, even though the sheer amount of xenon can still cause some of it to drift back into the plasma plume, affecting the results. An upgraded vacuum chamber at the University of Michigan should be ready in early 2018.
Image: A side shot of the X3 firing at 50 kilowatts. Credit: NASA.
The work at Glenn involved four weeks to set up the thrust stand, mount and connect the thruster with propellant and power supplies, deploying a custom thrust stand to bear the X3’s weight. 25 days of testing then produced the results above in a project funded by NASA’s Next Space Technologies for Exploration Partnership. The next step here will be to integrate the X3 with power supplies now being developed by Aerojet Rocketdyne. By the spring of next year, new tests at NASA Glenn using the Aerojet Rocketdyne power processing system are expected.
Image: The X3 nested-channel Hall thruster with all three channels firing at 30 kW total discharge power. Credit: University of Michigan.
These developments in current Hall thruster technology are exciting in themselves and have implications for the near-term in missions to destinations like Mars. But I’m also interested in pursuing how we might move ion technologies in new directions by creating hybrid designs, with Kuiper Belt objects and the gravitational focus at 550 AU as potential destinations. With laser methods now in the spotlight as Breakthrough Starshot continues its analysis of a mission to Proxima Centauri, hybrid ion engine designs boosted by laser power are coming into consideration. I’ll take a look at the possibilities in tomorrow’s post.
by Paul Gilster | Sep 16, 2016 | Advanced Rocketry |
Larry Klaes has been a part of Centauri Dreams almost since the first post. That takes us back to 2004, and while I didn’t have comments enabled on the site for the first year or so, I remember talking to Larry about my Centauri Dreams book by email. Ever since, this author and freelance journalist with a passion for spaceflight has contributed articles, comments and ideas, as he does again today. Project Orion caught Larry’s attention as a way of using known technologies to enable daring deep space missions. The essay below gives us an overview of Orion and its possibilities, looking at a concept that never flew but still captures the imagination. In addition to his active freelancing, Larry has been editor of SETIQuest magazine and president of the Boston chapter of the National Space Society. He now writes regularly for SpaceFlight Insider, where this article originally appeared.
by Larry Klaes
Image: Project Orion concept. Image Credit: Adrian Mann.
At their most fundamental level, all rockets past and present were and are, basically, controlled bombs. Their fuel consists of materials and chemicals which, when activated/combined in the proper sequence and amount, create a series of explosive reactions. The resulting energy release is then directed in a manner so that the resulting exhaust comes out of the end of the rocket away from the payload sitting atop it and the direction that its builders want to send that payload. That is essentially Sir Isaac Newton’s third law of motion put into practice.
When this technological setup works, we have a successful mission. However, when something goes awry, we end up with a vehicle that can go from a powerful and fast means of space transportation to an inadvertently dangerous weapon. As just one large example, if the famous Saturn V rocket – which sent humans to the Moon for Project Apollo between 1968 and 1972 – had ever exploded, the 6.5-million-pound (2,950 metric tons) fully fueled booster would have created a destructive event equivalent to the detonation of a small nuclear bomb, minus the radiation. Thus the reason that no one (excluding the three mission astronauts, of course) was ever allowed within three miles (4.8 kilometers) of the launch pad at Cape Kennedy when a Saturn V was lifting off into space.
Image: Artist’s rendition of NASA’s Project Orion. Credit: NASA.
The former Soviet Union had several real world examples of just such a catastrophe with their equivalent N1 rocket, which they were using to compete with the United States in the race to place a man on the Moon by 1970. Every one of their N1 tests (all unmanned) ended in dramatic failure, with one rocket explosion on the ground practically vaporizing its launch pad and heavily cratering another pad with debris half a mile (almost one kilometer) away.
So now imagine a rocket design where the fuel used were actual bombs detonated on purpose – and nuclear bombs at that. It was known as Project Orion.
Not surprisingly, Orion was born during the Cold War, when the United States and the Soviet Union were squaring off against each other by stockpiling nuclear weapons to let each other know that an attack by one nation using such devices would be fatal for the other, along with most other places on Earth. This concept was called Mutually Assured Destruction, or MAD for short.
In the United States, the power of the atom was also being sold as a way to make life better for everyone. Nuclear power plants were being touted as a cleaner and much more efficient way to generate electricity for our civilization. The binding force of the atom was even seriously considered as a replacement for the fossil fuels powering our land, sea, and air vehicles.
The Ford Motor Company went so far as to come up with a car they called the Ford Nucleon, where a single nuclear fuel rod would keep this automobile of the future operating for over five thousand miles before a new fuel rod was required. The Ford Nucleon never got past the model stages, but the point is that a major American car company took the idea seriously, at least for a while.
Image (click to enlarge). Credit: Rhys Taylor.
If nuclear power could be plausibly applied to mere ground transportation, then using it to send heavy space vessels into the “final frontier” only made even more sense at the dawn of the Space Age. Both superpowers were cranking out those very methods of propulsion at an ever-increasing rate.
In an example of turning swords into plowshares, Project Orion was envisioned as a vessel carrying a supply of hydrogen bombs to be ejected out the stern of the spaceship one at a time. The bomb would then be detonated mere seconds later, where the resulting plasma would encounter a large, thick, shock-absorbing “pusher plate” attached to the end of the spaceship that would simultaneously allow Orion to be moved forward while protecting the ship from the blast and radiation. Each new bomb detonation that followed would push the vessel faster and faster, allowing Orion to reach just about anywhere in the Solar System within one year or the nearest star system, Alpha Centauri, in just over one century under one mission scenario.
Project Orion was worked on under a contract by the United States Air Force (USAF) at the General Atomics company from 1958 to 1965. Project models for Orion soon matched and exceeded the grand space dreams of the era due to its novel method of propulsion.
One team member, the famous Freeman J. Dyson of the Institute for Advanced Study in Princeton, New Jersey, envisioned a ship with a total mass of 400,000 metric tons (881,849,049 pounds) of which three-quarters of that weight would consist of 300,000 one-megaton H-bombs weighing 1,000 kilograms (2,205 pounds) each. The rest of the weight would be split between the payload and ship structure and the ablation shield. Detonating the bombs every three seconds (until the supply ran out in ten days under this scenario) would keep the acceleration at a comfortable 1 g, or gravity.
Image (click to enlarge): General Atomics Orion spaceship concept. Credit: William Black.
The plans for Orion were anything but timid. Manned Mars missions using this vessel would have been sent in 1965, followed by a mission to the ringed planet Saturn in 1970! The spaceship in the film 2001: A Space Odyssey, the USS Discovery, was originally designed as an Orion type craft aimed at Saturn in the novel version. The author of the film’s screenplay and novel, Arthur C. Clarke, was also a member of Project Orion. Not only could Orion have conducted a round-trip voyage to Pluto in just one year, but Dyson also calculated a version that could flyby Alpha Centauri in about 130 years at 3% light speed. By comparison, the Voyager space probes will take 77,000 years to reach the distance of our celestial neighbor 4.3 light-years away. The team even considered a massive Orion that could serve as an interstellar ark, which became the vehicle of choice in the 2014 television mini-series Ascension.
As a further reflection of the era, Project Orion was more than just a paper dream. The team built a working 7-foot (2.1-meter) scale model (non-nuclear of course) they called Hot Rod. Launched in 1959 at Point Loma, California, Hot Rod survived five successive explosions that struck its pusher plate and sent the vehicle faster and higher with each detonation. The test vehicle then parachuted safely to the ground, proving that Orion was as least technically feasible. Gulf General Atomic later donated Hot Rod to the Smithsonian in 1972, where it was long on display at the institution’s Air and Space Museum but is currently in storage. However, a scale model of the completed Orion vessel is publicly viewable at the Steven F. Udvar-Hazy Center in Chantilly, Virginia, in their Rockets and Missiles exhibition. This model was donated to the Smithsonian in 1979 by the General Dynamics Corporation.
Image: Project Orion ‘Hot Rod’ Propulsion Test Vehicle. Credit: Smithsonian National Air and Space Museum.
In the end, Orion was terminated neither by physics nor technology but by politics and a growing public fear of nuclear power. The Partial Nuclear Test Ban Treaty signed in 1963 forbids testing nuclear devices of any kind everywhere but underground. Two years later, the USAF canceled the project’s budget. Orion became a legendary symbol of an era known for both its far-reaching dreams and excesses of power. To this day, Orion is still the only feasible mean of interstellar travel, both robotic and manned, that could actually be built with current technology and knowledge.
So could (and would) Orion be revived some day? While the United States and Europe (via the European Space Agency) could make the vessel a reality, Orion’s very means of propulsion remain among the major hindrances to such a plan for the foreseeable future. At present, the greatest chance for Orion lies with China. They not only have the means and the resources to undertake such a grand project (as well as vast, remote regions where they could safely test and launch the vessel), but Orion would be a logical extension of their current strivings for major science and technology goals. This author notes that he has no actual knowledge if China has ever conducted or will ever conduct such a project, only that of all the spacefaring nations on Earth, they make for the most realistic choice at present for reviving Orion.
Image: Orion in flight. Credit: William Black.
Russia is another possibility for building Orion on a similar scale as China, but their current geopolitical issues make such prospects questionable on multiple levels. India might also be a contender for their own Orion down the road, but such a future remains to be seen. There are several other nations which have both their own space and nuclear programs, but the thought of them building an Orion in the near future is both questionable and concerning.
As Project Orion has always been about big dreams with even bigger goals, then perhaps we can one day hope that Orion will not only become a method for turning nuclear weapons away from Earth and our species and aim them toward the stars for peaceful purposes, but also that Orion might become a way that we can explore and colonize space together as one humanity.
Image: Project Orion to Mars. Credit: NASA.
For more information on Project Orion, see the following:
Project Orion: The True Story of the Atomic Spaceship, by George Dyson, An Owl Book, Henry Holt and Company, New York, 2003.
These documentary videos on Project Orion here and here, and George Dyson TED Talk here.
For those want even more information about Project Orion and its variants, you must see Atomic Rocket’s pages on it here.
More links to updated information on Project Orion:
http://www.nextbigfuture.com/2016/01/orion-thunderwell-and-nuclear-space.html
http://www.nextbigfuture.com/2014/01/winterberg-reinvents-project-orion.html
http://www.nextbigfuture.com/2009/02/updated-project-orion-nuclear-pulse.html
by Paul Gilster | Aug 2, 2016 | Advanced Rocketry |
Thinking about Eugen Sänger’s photon rocket concept inevitably calls to mind his Silbervogel design. The ‘Silverbird’ had nothing to do with antimatter but was a demonstration of the immense imaginative power of this man, who envisioned a bomber that would be launched by a rocket-powered sled into a sub-orbital trajectory. There it would skip off the upper atmosphere enroute to its target. The Silbervogel project was cancelled by the German government in 1942, but if you want to see a vividly realized alternate world where it flew, have a look at Allen Steele’s 2014 novel V-S Day, a page-turner if there ever was one.
I almost said that it was a shame we don’t have a fictionalized version of the photon rocket, but as we saw yesterday, there were powerful reasons why the design wouldn’t work, even if we could somehow ramp up antimatter production to fantastic levels (by today’s standards) and store and manipulate it efficiently. Energetic gamma rays could not be directed into an exhaust stream by the kind of ‘electron gas mirror’ that Sänger envisioned, although antimatter itself maintained its hold on generations of science fiction writers and scientists alike.
Enter the Antiproton
Sänger’s presentation at the International Astronautical Congress in 1953 came just two years ahead of the confirmation of the antiproton, first observed at the Berkeley Bevatron in 1955. Now we have something we can work with, at least theoretically. For unlike the annihilation of electrons and positrons, antiprotons and protons produce pi-mesons, or pions, when they meet. Pions don’t live long, with charged pions decaying into muons and muon neutrinos, while neutral pions decay into gamma rays. Those charged pions, however, turn out to be helpful indeed.
By the early 1980s, Robert Forward had realized that superconducting coils could be used to channel such charged pions, producing the kind of directed exhaust stream that so frustrated Sänger. Forward described the ‘magnetic nozzle’ in his book Mirror Matter (Wiley, 1988), but his first paper on the subject appeared in 1982, along with other papers on antimatter propulsion from Brice Cassenti and David Morgan, all of these in the fecund pages of the Journal of the British Interplanetary Society. Morgan (Lawrence Livermore National Laboratory) envisioned a three-meter nozzle using magnetic coils to channel charged pions, with an exhaust velocity fully 94 percent of the speed of light.
The gamma ray problem is still there, but in these designs, they appear in the exhaust well behind the rocket, even as the energy of the charged pions is used to heat a propellant like hydrogen or water which becomes the exhaust. Using methods like these, we could extract up to 50 percent of the energy unlocked by the annihilation of protons and antiprotons.
In broader terms, what Forward was proposing was to replace tons of chemical propellant with milligrams of matter. In a study he performed for the Air Force Rocket Propulsion Laboratory, he advocated the creation of facilities specifically dedicated to producing antimatter, as opposed to relying on the production of antimatter in particle accelerators as a by-product of other work. In this way, he believed, the cost could be brought down to about $10 million per milligram. Remember that a milligram of antimatter produces about the same energy as 20 tons of chemical fuel, making antimatter at this price level a better deal than chemical propulsion.
We’re not at Sänger-esque levels of specific impulse (3 X 107 seconds), but Giovanni Vulpetti was able to show later in the 1980s that a rocket working with the pions of proton/antiproton annihilation was capable of a specific impulse of 0.58c. Even so, antimatter’s numerous problems continue to bedevil us. Some of Robert Frisbee’s work in the same decade overcomes the antimatter storage issue by creating spacecraft thousands of kilometers long. These fantastic designs are rapier-thin and massive, hardly the sleek starships most science fiction has led us to expect, unless we look into SF’s most extravagant imaginings.
Image: Here’s one way of getting around those huge Frisbee rockets. This is Richard Obousy’s concept for VARIES, the Vacuum to Antimatter Rocket Interstellar Explorer System. Here the starship uses an immensely powerful laser to generate its own antimatter fuel, relying on Julian Schwinger’s work showing that electron-positron pairs can be generated out of the vacuum of space itself. Credit: Adrian Mann.
Excuse the digression, but Frisbee’s work calls up the memory of one of Paul Linebarger’s stranger stories. Writing as Cordwainer Smith, Linebarger created a short fable called “Golden the Ship Was – Oh! Oh! Oh!,” which ran in Amazing Stories in April of 1959. And just as Frisbee’s vast designs stretch physics to the limit by way of showing how unlikely an antimatter starship is at our current level of understanding, Linebarger’s golden ship is in most ways a chimera, although the powers threatening the Earth do not understand what they are seeing:
“That one ship is ninety million miles long, Your Highness. It shimmers like fire, but moves so fast that we cannot approach it. But it came into the center of our fleet almost touching our ships, stayed there twenty or thirty thousandths of a second. There it was, we thought. We saw the evidence of life on board: light beams waved: they examined us and then, of course, it lapsed back into nonspace. Ninety million miles, Your Highness. Old Earth has some stings yet and we do not know what the ship is doing.”
The pleasures of Cordwainer Smith are likewise vast and I won’t give anything more away about this short tale (you can find it reprinted in The Rediscovery of Man (NESFA Press, 1993). But back to proton/antiproton annihilation, which gets an interesting new wrinkle in the work of Friedwardt Winterberg. As examined in these pages by Adam Crowl (see Re-Thinking the Antimatter Rocket), Winterberg looks at how a plasma made of matter and antimatter in equal parts (an ‘ambiplasma’) can undergo extreme compression. Let me quote Crowl:
Essentially what Winterberg describes is generating a very high electron-positron current in the ambiplasma, while leaving the protons-antiprotons with a low energy. This high current generates a magnetic field that constricts rapidly, a so-called pinch discharge, but because it is a matter-antimatter mix it can collapse to a much denser state. Near nuclear densities can be achieved, assuming near-term technical advancements to currents of 170 kA and electron-positron energies of 1 GeV.
What we get is a gamma ray flux that is highly directional, forming a gamma-ray laser, a beam of gamma rays that, in conjunction with the annihilation chamber’s magnetic fields, produces thrust. The work draws on Winterberg’s thinking on deuterium fusion rockets (he was a key contributor to the original Project Daedalus starship design) and the magnetic compression of ions. Here we get a concept that would surely have delighted Eugen Sänger, as it provides for a highly directional gamma ray thrust that was the cornerstone of the photon rocket.
All these concepts assume substantial production of antimatter and major breakthroughs in storage, but in the nearer term, we will continue to explore antimatter’s possibilities in catalyzing nuclear fusion reactions, or intriguing spacecraft designs like Steven Howe’s ‘antimatter sail.’ In Howe’s work for NASA’s original Institute for Advanced Concepts, small amounts of antimatter are used to create fission as they encounter a sail impregnated with uranium. For more, see An Antimatter Driven Sail to the Kuiper Belt.
As we learn more about storage, and in particular methods involving stable antihydrogen (a positron and an antiproton), we can hope that methods of antimatter production, and even antimatter collection in the outer Solar System, will become better understood. It will take experimentation with tiny amounts of antimatter to help us understand its possible contribution to deep space exploration.
The Forward paper cited above is “Antimatter Propulsion,” JBIS 35 (1982), pp. 391-395. Brice Cassenti’s paper on antimatter is “Design Considerations for Relativistic Antimatter Rockets,” JBIS 35 (1982), pp. 396-404. David Morgan’s paper is “Concepts for the Design of an Antimatter Annihilation Rocket,” JBIS 35 (1982), pp. 405-413. Richard Obousy’s paper on VARIES is “Vacuum to Antimatter Rocket Interstellar Explorer System,” JBIS 64 (2012), pp. 378-386. Check the JBIS website for availability. The Winterberg paper is “Matter-Antimatter GeV Gamma Ray Laser Rocket Propulsion” (2011 — preprint).
by Paul Gilster | Jan 8, 2016 | Advanced Rocketry |
Building a space infrastructure is doubtless a prerequisite for interstellar flight. But the questions we need to answer in the near-term are vital. Even to get to Mars, we subject our astronauts to radiation and prolonged weightlessness. For that matter, can humans live in Mars’ light gravity long enough to build sustainable colonies without suffering long-term physical problems? Gregory Matloff has some thoughts on how to get answers, involving the kind of space facility we can build with our current technologies. The author of The Starflight Handbook (Wiley, 1989) and numerous other books including Solar Sails (Copernicus 2008) and Deep Space Probes (Springer, 2005), Greg has played a major role in the development of interstellar propulsion concepts. His latest title is Starlight, Starbright (Curtis, 2015).
by Gregory Matloff
The recent demonstrations of successful rocket recovery by Blue Origin and SpaceX herald a new era of space exploration and development. We can expect, as rocket stages routinely return for reuse from the fringes of space, that the cost of space travel will fall dramatically.
Some in the astronautics community would like to settle the Moon; others have their eyes set on Mars. Many would rather commit to the construction of solar power satellites, efforts to mine and/or divert Near Earth Asteroids (NEAs), or construct enormous cities in space such as the O’Neill Lagrange Point colonies.
But before we can begin any or all of these endeavors, we need to answer some fundamental questions regarding human life beyond the confines of our home planet. Will humans thrive under lunar or martian gravity? Can children be conceived in extraterrestrial environments? What is the safe threshold for human exposure to high-Z galactic cosmic rays (GCRs)?
To address these issues we might require a dedicated facility in Earth orbit. Such a facility should be in a higher orbit than the International Space Station (ISS) so that frequent reboosting to compensate for atmospheric drag is not required. It should be within the ionosphere so that electrodynamic tethers (ETs) can be used for occasional reboosting without the use of propellant. An orbit should be chosen to optimize partial GCR-shielding by Earth’s physical bulk. Ideally, the orbit selected should provide near-continuous sunlight so that the station’s solar panels are nearly always illuminated and experiments with closed-environment agriculture can be conducted without the inconvenience of the 90 minute day/night cycle of equatorial Low Earth Orbit (LEO). Initial crews of this venture should be trained astronauts. But before humans begin the colonization of the solar system, provision should be made for ordinary mortals to live aboard the station, at least for visits of a few months’ duration.
Another advantage of such a “proto-colony” is proximity to the Earth. Resupply is comparatively easy and not overly expensive in the developing era of booster reuse. In case of medical emergency, return to Earth is possible in a few hours. That’s a lot less than a 3-day return from the Moon or L5 or a ~1-year return from Mars.
A Possible Orbital Location
An interesting orbit for this application has been analyzed in a 2004 Carleton University study conducted in conjunction with planning for the Canadian Aegis satellite project [1]. This is a Sun-synchronous orbit mission with an inclination of 98.19 degrees and a (circular) optimum orbital height of 699 km. At this altitude, atmospheric drag would have a minimal effect during the planned 3-year satellite life. In fact, the orbital lifetime was calculated as 110 years. The mission could still be performed for an orbital height as low as 600 km. The satellite would follow the Earth’s terminator in a “dawn-to-dusk” orbit. In such an orbit, the solar panels of a spacecraft would almost always be illuminated.
For a long-term human-occupied research facility in or near such an orbit, a number of factors must be considered. These include cosmic radiation and space debris. It is also useful to consider upper-atmosphere density variation during the solar cycle.
The Cosmic Ray Environment
From a comprehensive study by Susan McKenna-Lawlor and colleagues of the deep space radiation environment [2], the one-year radiation dose limits for 30, 40, 50, and 60 year old female astronauts are respectively 0.6, 0.7, 0.82, and 0.98 Sv. Dose limits for men are about 0.18 Sv higher than for women. At a 95% confidence level, such exposures are predicted not to increase the risk of exposure-related fatal cancers by more than 3%.
Al Globus and Joe Strout have considered the radiation environment experienced within Earth-orbiting space settlements below the Van Allen radiation belt [3]. This source recommends annual radiation dose limits for the general population and pregnant women respectively at 20 mSv and 6.6 mGy (where “m” stands for milli, “Sv” stands for Sieverts and “Gy” stands for Gray). Conversion of Grays to Sieverts depends upon the type of radiation and the organs exposed. As demonstrated in Table 1 of Ref. 3, serious or fatal health effects begin to affect a developing fetus at about 100 mGy. If pregnant Earth-bound women are exposed to more than the US average 3.1 mSv of background radiation, the rates of spontaneous abortion, major fetal malformations, retardation and genetic disease are estimated respectively at 15%, 2-4%, 4%, and 8-10%. Unfortunately, these figures are not based upon exposure to energetic GCRs [3].
In their Table 5, Globus and Strout present projected habitat-crew radiation levels as functions of orbital inclination and shielding mass density [3]. Crews aboard habitats in high inclination orbits will experience higher dosages than those aboard similar habitats in near equatorial orbits. In a 90-degree inclination orbit, a crew member aboard a habitat shielded by 250 kg/m2 of water will be exposed to about 334 mSv/year. To bring radiation levels in this case below the 20 mSV/year threshold for adults in the general population requires a ~12-fold increase in shielding mass density [3].
But Table 4 of the Globus and Strout preprint demonstrates that, for a 600-km circular equatorial orbit, elimination of all shielding increases radiation dose projections to about 2X that of the habitat equipped with a 250 kg/m2 water shield. If shielding is not included and this scaling can be applied to the high-inclination orbit, expected crew dose rates will be less than 0.8 Sv/year [3]. This is within the annual dose limits for all male astronauts and female astronauts older than about 45 [2].
Early in the operational phase of this high-inclination habitat, astronauts can safely spend about a year aboard. Adults in the general public can safely endure week-long visits. Pregnant women who visit will require garments that provide additional shielding for the fetus. Some of the short-term residents aboard the habitat may be paying “hotel” guests. As discussed below, additional shielding may become available if development of this habitat is a joint private/NASA project.
Is Space Debris an Issue?
According to a 2011 NASA presentation to the United Nations Subcommittee on the Peaceful Uses of Outer Space, space debris is an issue of concern in all orbits below ~2,000 km. About 36% of catalogued debris objects are due to two incidents: the intentional destruction of Fengyun-1C in 2007 and the 2009 accidental collision between Cosmos 2251 and Iridium 33 [4].
The peak orbital height range for space debris density is 700-1,000 km. At the 600-km orbital height of this proposed habitat, the spatial density of known debris objects is about 4X greater than at the ~400 km orbital height of the International Space Station (ISS) [4]. As is the case with the ISS, active collision avoidance will sometimes be necessary.
Atmospheric Drag at 600 km
An on-line version of the Standard Atmosphere has been consulted to evaluate exospheric molecular density at orbital heights [5]. A summary of this tabulation follows:
Atmospheric Density, km/m2 at various solar activity levels
| height | Low | Mean | Extremely High |
| 400 km | 5.68E-13 | 3.89E-12 | 5.04E-11 |
| 500 | 6.03E-14 | 7.30E-13 | 1.70E-11 |
| 600 | 1.03E-14 | 1.56E-13 | 6.20E-12 |
Note that atmospheric density levels at 600 km are in all cases far below the corresponding levels at the ISS ~400 km orbital height. But orbit adjustment will almost certainly be required during periods of peak solar activity.
Since the proposed 600-km orbital height is within the Earth’s ionosphere, there are a number of orbit-adjustment systems that require little or no expenditure of propellant. One such technology is the Electrodynamic Tether [6].
Habitat Properties and Additional Shielding Possibilities
A number of inflatable space habitats have been studied extensively or are under consideration for future space missions. Two that could be applied to construction of a ~600-km proto-colony are NASA’s Transhab and Bigelow Aerospace’s BA330 (also called B330).
Transhab, which was considered by NASA for application with the ISS and might find use as a habitat module for Mars-bound astronauts, would have a launch mass of about 13,000 kg. Its in-space (post-inflation) diameter would be 8.2 m and its length would be 11 m [7]. Treating this module as a perfect cylinder, its surface area would be about 280 m2. Transhab could comfortably accommodate 6 astronauts.
Image: Cutaway of Transhab Module with Crew members. Credit: NASA.
According to Wikipedia, the BA330 would have a mass of about 20,000 kg. Its length and diameter would be 13.7 m and 6.7 m, respectively. The Bigelow Aerospace website reports that the approximate length of this module would be 9.45 m. It could accommodate 6 astronauts comfortably during its projected 20-year operational life.
Both of these modules are designed for microgravity application. Since the study of the adjustment of humans and other terrestrial life forms to intermediate gravity levels might be one scientific goal of the proposed 600-km habitat, the habitat should consist of two modules arranged in dumbbell configuration connected by a variable-length spar with a hollow, pressurized interior. The rotation rate of the modules around the center could be adjusted to provide various levels of artificial gravity. Visiting spacecraft could dock at the center of the structure. It is possible that the entire disassembled and uninflated structure could be launched by a single Falcon Heavy.
Image: The pressurized volume of a 20 ton B330 is 330m3, compared to the 106m3 of the 15 ton ISS Destiny module; offering 210% more habitable space with an increase of only 33% in mass. Credit: Bigelow Aerospace.
One module could support the crew, which would be rotated every 3-6 months. The other module could accommodate visitors and scientific experiments. It is anticipated that visitors would pay for their week-duration experience to help support the project. Experiments would include studies of the effects of GCR and variable gravity on humans, experimental animals and experiments with in-space agriculture. The fact that the selected orbit provides near-constant exposure to sunlight should add a realistic touch to the agriculture studies. These experiments will hopefully lead to the eventual construction of in-space habitats, hotels, deep-space habitats and other facilities.
The possibility exists for cooperation between the developers of this proposed 600-km habitat and the NASA asteroid retrieval mission. Under consideration for the mid-2020’s, this mission would use the Space Launch System to robotically retrieve a ~7-meter diameter boulder and return it to high lunar orbit for further study [8]. The mass of this object in lunar orbit could exceed half a million kilograms. It is conceivable that much of this material could be used to provide GCR-shielding for Earth-orbiting habitats such as one considered here. As well as reducing on-board radiation levels, such an application would provide valuable experience to designers of deep-space habitats such as the O’Neill space colonies.
——-
References
1. S. Beaudette, “Carleton University Spacecraft Design Project; 2004 Final Design Report, “Satellite Mission Analysis”, FDR-SAT-2004-3.2.A (April 8, 2004).
2. S. McKenna-Lawlor, A. Bhardwaj, F. Ferrari, N. Kuznetsov, A. K. Lal, Y. Li, A. Nagamatsu, R. Nymmik, M. Panasyuk, V. Petrov, G. Reitz, L. Pinsky, M. Shukor, A. K. Singhvi, U. Strube, L. Tomi, and L. Townsend, “Recommendations to Mitigate Against Human Health Risks Due to Energetic Particle Irradiation Beyond Low Earth Orbit/BLEO”, Acta Astronautica, 109, 182-193 (2015).
3. A. Globus and J. Strout, “Orbital Space Settlement Radiation Shielding”, preprint, issued July 2015 available on-line at space.alglobus.net).
4. NASA, “USA Space Debris Environment, Operations, and Policy Updates”, Presentation to the 48th Session of the Scientific and Technical Subcommittee, Committee on the Peaceful Uses of Outer Space (7-9 February 2011).
5. Physical Properties of U.S. Standard Atmosphere, MSISE-90 Model of Earth’s Upper Atmosphere, www.braeunig.us/space/atmos.htm
6. L. Johnson and M. Herrmann, “International Space Station: Electrodynamic Tether Reboost Study, NASA/TM-1998-208538 (July, 1998).
7. “Transhab Concept” spaceflight.nasa.gov/history/station/transhab
8. M. Wall, “The Evolution of NASA’s Ambitious Asteroid Capture Mission”, www.space.com/28963-nasa-asteroid-capture-mission-history
by Paul Gilster | Oct 5, 2015 | Advanced Rocketry |
Our choice of orbits can create scientifically useful space missions that can be operated at lower cost than their more conventional counterparts. How this has been done and the kind of missions it could enable in the future is the subject of James Jason Wentworth’s essay. An amateur astronomer and interstellar travel enthusiast, Wentworth worked at the Miami Space Transit Planetarium and volunteered at the Weintraub Observatory atop the adjacent Miami Museum of Science. Now making his home in Fairbanks (AK), he was the historian for the Poker Flat Research Range sounding rocket launch facility. His space history and advocacy articles have appeared in Quest: The History of Spaceflight magazine and Space News.
by J. Jason Wentworth
In the 1990s, then NASA Administrator Daniel S. Goldin introduced the “Better, Faster, Cheaper” paradigm for space missions. While NASA’s subsequent experiences led many engineers to modify that to “Better, Faster, Cheaper–choose two,” the goal of low cost has remained a primary goal for space mission planners. One way to reduce the cost of a mission is to select a trajectory that requires the least possible change of velocity (called Delta-V by engineers and orbital dynamicists) to achieve the mission’s objectives. This requires less propellant aboard the spacecraft, which results in a smaller and lighter spacecraft, which in turn can usually be lofted by a smaller and less expensive launch vehicle. (Very high-energy missions such as New Horizons are exceptions. In such cases, launching the smallest possible spacecraft merely makes such missions possible within a practical flight duration–even when using the most powerful launch vehicles available–because the velocities required for even the lowest-energy trajectories are so high.)
Another factor that affects the spacecraft’s required amount of onboard propellant is the stability of the mission orbit. If frequent orbital adjustments are necessary for any reason, a larger propellant reserve will be required, which will bump up the probe’s size and mass. The type of spacecraft stabilization system that is used also has an influence on the propellant reserve. A three-axis stabilized probe in orbit around the Moon, the Sun, another planet, or any other body will require more thruster firings (to point its sensors and imaging system at its target body, and to aim its high-gain antenna at Earth) than will a spin-stabilized spacecraft, so the latter can operate for many years using very little propellant for attitude control.
The spin-stabilized Pioneer spacecraft all exhibited this characteristic of very long life. Perhaps the most impressive of the series (besides the Sun-orbiting Pioneer 6 – 9 interplanetary probes, which lasted for multiple decades; two of them may still be functioning) was the Pioneer Venus Orbiter, which returned images of and data on the planet (and Comet Halley) for nearly 14 years, in the hostile thermal and solar radiation environment around Venus. [1] In March of 1986 Pioneer 7 also flew within 12.3 million kilometers (7.6 million miles) of Halley’s Comet and monitored the interaction between the cometary hydrogen tail and the solar wind. It discovered He+ plasma produced by charge exchange of solar wind He++ with neutral cometary material. [2]
Image: Orbit attitude of Pioneer Venus 1 between 1978 – 1980 and 1992. Credit: NASA/Ames.
Since the space age began, other trajectories besides the classical Hohmann transfer ellipse have been devised to get satellites and space probes to their destination orbits or worlds. These are used to minimize the necessary Delta-V, or to optimize planet arrival times, or both. Some geosynchronous satellites are now first injected into “super-synchronous” transfer orbits from their initial low-altitude parking orbits, from which they are later maneuvered downward into their 24-hour operational orbits. The Pioneer Venus Orbiter traveled along a similar path to Venus; it was boosted from its parking orbit around the Earth into a solar orbit that initially passed outside the Earth’s orbit about the Sun before curving inward to intercept Venus in its orbit.
Other unusual types of orbits exist, some of which were discovered when asteroids were found to be moving in them, and they are also useful for low-Delta-V (and thus lower cost) space missions. The best-known ones are halo orbits and the tadpole-shaped Lissajous orbits, in which several spacecraft have traveled around the Sun-Earth L1 and L2 Lagrangian points and the Earth-Moon L1 and L2 points.
Enter the Horseshoe Orbit
A more recently-discovered path (which a 2011 Centauri Dreams article, Stable Orbit for a Newly Discovered Companion, discusses) is the horseshoe orbit, which got its name from its shape. [3] A small object in such an orbit goes around the Sun in a normal, low-eccentricity (close to circular) elliptical orbit in the direct (prograde) direction, but since its orbit has nearly the same period and shape as the orbit of a nearby planet (Earth, in the case of the horseshoe-orbiting asteroids discovered to date), gravitational interactions with Earth create the horseshoe path (which occurs only in the Earth-centered reference frame, as the asteroid orbits around the Sun normally). This celestial “dance” works as follows:
As the asteroid is about to pass the Earth in its slightly lower, more rapid orbit, the Earth’s gravity pulls it toward itself; this speeds up the asteroid, which causes it to move farther from the Sun (and thus into a higher orbit), and this then causes the asteroid to slow down, because objects in higher orbits move more slowly. In its higher, slower orbit, the asteroid then begins to drop behind the Earth, slowly “drifting” backwards all the way around the Sun (from the Earth’s perspective–the asteroid is orbiting the Sun in the same direct [prograde] direction as Earth, just more slowly). Many years later, as the asteroid again approaches Earth (from ahead of our planet this time), the Earth’s gravity slows down the asteroid, which causes it to fall into a lower, faster orbit around the Sun. Now moving faster than the Earth (inside Earth’s orbit), the asteroid slowly “drifts” all the way around the Sun again (moving forward this time, from Earth’s perspective), after which it repeats the whole horseshoe orbit cycle again. [4]
Image: A horseshoe orbit, showing possible orbits along gravitational contours. In this image, the Earth (and the whole image with it) is rotating counterclockwise around the Sun. Credit: Wikimedia Commons.
While other asteroids in horseshoe orbits with respect to Earth have been found before, their orbits aren’t long-term stable. Within a certain range of distances, orbital eccentricities, and velocities, however, stable horseshoe orbits are possible, and the asteroid 2010 SO16 (the subject of the Centauri Dreams article in Reference 3) is in one, having possibly followed its current orbit for up to two million years. In addition, it is possible–as 2010 SO16 might have done, as is mentioned in the article–for asteroids (or other objects, such as spacecraft) to librate (migrate) from Lissajous orbits around the Sun-Earth L4 or L5 Lagrangian points into stable horseshoe orbits. Migration from a horseshoe orbit back into a Lissajous orbit might also be possible, and what an unpowered asteroid could do, a self-powered space probe could likely also do–using little propellant.
Another unusual kind of orbit is the quasi-satellite orbit, in which NEAs (Near-Earth Asteroids) have also been discovered. [5] A quasi-satellite is in an orbit around the Sun that has a 1:1 resonance with the orbit of a particular planet. This causes the quasi-satellite to stay close to that planet over many orbital periods. A quasi-satellite’s orbit has the same period as the planet’s orbit, but the quasi-satellite’s orbit has a different–usually greater–eccentricity than the planet’s orbit. As observed from the planet, the quasi-satellite appears to move in an oblong retrograde loop around the planet, although both bodies are orbiting the Sun in direct (prograde) orbits.
Orbital Dynamics and ‘Fuzzy Boundaries’
Pioneer E (which would have been named Pioneer 10 if it had not been lost in its failed launch on August 27, 1969) was the fifth and last of the series of solar-powered, drum-shaped Sun-monitoring interplanetary probes that began with Pioneer 6 in December of 1965, and Pioneer E was intended to orbit the Sun as a quasi-satellite of Earth. Had it reached its planned solar orbit, Pioneer E (which was launched–and lost–with the TETR C test and training satellite, the intended third “practice” satellite for the Apollo tracking and communications network) would have passed inside and outside the Earth’s orbit, alternately speeding up and slowing down relative to Earth. This would have kept Pioneer E within 16 million kilometers (10 million miles) of Earth during the spacecraft’s design lifetime of from six months to two and one-half years. [6] (It would likely have operated for much longer than two and one-half years, as its sister probes Pioneer 6 – 9 demonstrated.)
Image: Artist’s conception of the Pioneer 6-9 spacecraft. Credit: NASA.
Orbit changes could be done using even less propellant (virtually none, in some cases) by employing Dr. Edward Belbruno’s principle of gravitational “Fuzzy Boundaries,” which involve the physics of chaos. [7, 8, and 9] This was first demonstrated in 1991 after Japan’s first lunar probe, the combined Hiten/Hagoromo spacecraft, ran into difficulties. Launched on January 24, 1990, the craft was injected into a highly-eccentric elliptical Earth orbit that passed beyond the Moon. The tiny Hagoromo lunar orbiter separated from Hiten during its first lunar swing-by and fired its solid propellant retro-rocket as the vehicles passed the Moon; while Hagoromo entered lunar orbit as intended, its radio transmitter failed when its retro-rocket fired (optical telescopic observation from Earth confirmed its entry into lunar orbit), which rendered it scientifically useless. [10] On March 19, 1991, Hiten performed the first-ever aerobraking maneuver, skimming the Earth’s atmosphere to change its orbit.
Having learned of Hagoromo’s transmitter failure, Edward Belbruno approached ISAS (the Institute of Space and Aeronautical Science) and offered to help them get their still-functioning Hiten lunar flyby spacecraft into lunar orbit. The probe, which was in a highly-eccentric Earth orbit, was moving much too fast during its lunar flybys to brake into lunar orbit using its onboard propellant. But by utilizing his “Fuzzy Boundaries” method, which involved using the combined gravity of the Moon and the Earth, on October 2, 1991 Hiten’s flight controllers were able to maneuver the probe into a preliminary, temporary lunar orbit using almost no propellant. After that, Hiten was targeted to fly through the Earth-Moon L4 and L5 points to collect data on any meteoric dust that was thought to possibly have accumulated there (none was detected). On February 15, 1993, Hiten was directed into a permanent lunar orbit, where it remained until it was deliberately crashed on the lunar surface on April 10. [11]
Image: An artist’s conception of the Hiten spacecraft. Credit: JAXA.
A Panoply of Applications
Stable horseshoe solar orbits and quasi-satellite solar orbits–entered and/or exited with the aid of Dr. Belbruno’s “Fuzzy Boundaries” method, making use of planetary as well as solar gravity–would be useful for Pioneer 6 – E type solar monitoring probes, which could observe portions of the Sun that cannot be seen (at any given time) from Earth. They could also, in concert with solar observations from Earth (or from Earth satellites), make stereo observations of solar features at many places along their horseshoe or quasi-satellite orbits. These same solar probes could also, as the Sun-orbiting Pioneer 7 interplanetary probe did, encounter and examine comets that pass through or near their orbits (flybys of asteroids that pass them would also be possible). If necessary, such probes could modify their horseshoe or quasi-satellite orbits (speeding up or slowing down, as needed) in order to make closer flybys of comets and asteroids (and later return to their original orbits) using very little propellant. Or, the probes could utilize solar sail propulsion (a simplified heliogyro sail should work nicely) to make such orbit changes, using no propellant at all.
Another application for horseshoe and quasi-satellite solar orbits would be to place NEO (Near-Earth Object) space telescopes in such orbits, much closer to the Sun than Earth’s distance. These locations would enable the spacecraft to see Earth-crossing NEOs whose orbits keep them mostly inside Earth’s orbit, and objects that could become dangerous to Earth in the future (via gravitational encounters with Venus and/or Mercury) would also be visible to these spacecraft. (To telescopes on or near the Earth, the sunlit sides of these small, often dark-colored objects face away from our planet, making them virtually impossible to see in the Sun’s glare, and Earth-based telescopes could never search for them in a truly dark sky because they would never be far from the Sun.) The B612 Foundation and its aerospace industry partner Ball Aerospace plan to send their NEO-seeking Sentinel space telescope to a Venus-like solar orbit for this reason. [12 and 13]. A horseshoe orbit or a quasi-satellite orbit “threaded around” Venus’ orbit about the Sun could reduce the necessary Delta-V (and thus the spacecraft’s launch vehicle and onboard propellant requirements) by utilizing Venus’ gravity to help establish–and later maintain by itself–either type of orbit for the Sentinel spacecraft.
Image: The Sentinel Space Telescope, being built by the B612 Foundation. Credit: B612Julie (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons.
Closer to home, Earth-centered horseshoe orbits–in which evenly-spaced communication, weather, or Earth resources satellites could “cycle” around the Earth as if on a circular conveyor belt (with two sets of spacecraft, on the inner and outer edges of the “belt”)–could provide global coverage not only of Earth, but they could also serve as communication relays for the lunar farside and for the Earth-Moon L2 point behind the Moon. (For circum-terrestrial horseshoe orbits, the Moon’s gravity would serve the same function that the Earth’s gravity does for Sun-centered horseshoe orbits that are “threaded around” Earth’s orbit about the Sun.) They could also provide close-up lunar observation to monitor time-variant lunar phenomena (the lunar “dustosphere’s” monthly cycling under the influence of Earth’s magnetotail, lunar meteorite impacts during meteor showers, TLP [the luminous Transient Lunar Phenomena], etc.).
Surprisingly, even low-cost suborbital interplanetary missions are possible. In addition to gathering data on the time-variant phenomena of the interplanetary environment, they could also collect dust, ice, and gas samples from comets that pass relatively close to Earth. NASA’s simple, inexpensive solid propellant Scout satellite launch vehicle, manufactured by LTV (Ling-Temco-Vought) using existing “off-the-shelf” rocket motors, was also used for several high-altitude suborbital probe missions that reached tens of thousands of kilometers into space. [14] (A rocket that ascends to an altitude of one Earth radius or higher is considered a space probe rather than a sounding rocket, because reaching one Earth radius requires a rocket velocity that is equal to Low Earth Orbit [LEO] orbital velocity.) The U.S. Air Force’s Blue Scout vehicles (which were similar to the NASA Scout vehicles for the most part, but were somewhat different because they were produced by a different contractor, the Ford Motor Company’s Aeronutronic Division) also flew numerous probe missions. [15 and 16] One in particular, a Blue Scout Junior launched from Cape Canaveral on August 17, 1961, reached an altitude of 225,000 kilometers (140,000 miles)–more than halfway to the Moon–on a suborbital flight lasting days. Unfortunately, the payload’s transmitter failed during the final (fourth) stage’s burn, rendering the flight scientifically useless. [17 and 18]
Image: The Blue Scout Junior. Credit: Peter Alway/Encyclopedia Astronautica: http://www.astronautix.com/index.html.
In his 1957 book The Making of a Moon: The Story of the Earth Satellite Program (and in its 1958 post-Sputnik revised second edition), Arthur C. Clarke pointed out that by launching suborbital vehicles at velocities approaching Earth’s escape velocity, their payloads could reach altitudes of millions of miles before falling back to Earth. [19] Interestingly, the altitudes achieved begin to increase dramatically at only 35,000 kilometers per hour (22,000 miles per hour), significantly below Earth’s escape velocity. As he wrote: “A rocket launched vertically at 22,000 miles an hour–or four thousand miles an hour faster than a satellite–would reach an altitude of about fifteen thousand miles before gravity checked its speed and it fell back to Earth. Slight further increases in velocity would give altitudes of millions of miles, until at the critical speed of 25,000 miles an hour the rocket never came back at all.”
Such vehicles could be very small–the 7.3-meter (24-foot) long, balloon-launched Project Farside probe rockets of the late 1950s, which reached nearly orbital velocity and rose to altitudes of between 3,200 and 5,000 kilometers (2,000 and 3,100 miles) with 1.4 to 3.3 kilogram (3 to 5 pound) payloads, could have reached the vicinity of the Moon with the addition of a fifth stage, which was proposed. [20] But this proposal was not proceeded with, possibly because the electronics technology of those days likely wouldn’t have enabled such small payloads to return meaningful data from the Moon’s distance (the frequent failures of the Farside vehicles’ payload transmitters also didn’t encourage much confidence in more ambitious ventures). But today a full suite of instruments, an S-band or X-band telemetry transmitter, and their solar cell or battery power supply could be accommodated in payloads of that mass range.
Image: Working on Project Farside. Credit: Parsch, Directory of U.S. Military Rockets and Missiles: http://www.designation-systems.net/dusrm/app4/farside.html.
Existing high-performance multi-stage sounding rockets could, if topped with multiple high-velocity stages, boost heavier payloads to such velocities (similar vehicles have boosted artificial meteors to velocities far in excess of escape velocity, beginning in 1957). [21 and 22] Such “souped-up” sounding rockets, or small–particularly air-launched satellite launch vehicles with additional upper stages, such as Orbital Sciences Corporation’s Pegasus XL and the upcoming Boeing ALASA (Airborne Launch Assist Space Access) system–could loft small suborbital interplanetary probes. [23 and 24] This capability would make possible low-cost, rapid comet sample return missions to “targets of opportunity,” comets such as IRAS-Araki-Alcock and Hyakutake that pass within a few million kilometers of Earth.
Image: The Pegasus XL launch vehicle operated by Orbital Sciences Corporation. Credit: NASA.
The recoverable portion of the spacecraft could use a deployable aerogel particle collector that would be housed in a small, blunt re-entry heat shield similar to that of the Pioneer Venus Small Probes or the Japanese Hayabusa and Hayabusa 2 asteroid sample return probes. The expendable section of the spacecraft, which would burn up upon re-entry into the Earth’s atmosphere, would carry fields and particles instruments and an imaging system. At other times, such suborbital probes could collect intact meteoroids from meteor shower streams for return to Earth, and/or they could gather data on the far regions of Earth’s magnetosphere and magnetotail, including their interactions with the solar wind and the solar magnetic field. Since the parent bodies of many meteor shower streams are now known (most originate from comets–a few are from asteroids), suborbital probes would offer inexpensive, frequent, and regular opportunities for collecting samples of these objects.
By substituting subtlety and cleverness for brute force, and by letting some mission targets come to their probes more than vice-versa, many new, scientifically useful, and inexpensive space missions would become practical and affordable. In addition to garnering new knowledge, such missions would also provide more frequent opportunities for young scientists, engineers, and orbital dynamicists to gain hands-on experience in designing and executing deep space missions–experience that would be of great help to them when the time comes to tackle the more ambitious outer solar system and observatory missions that NASA hopes to fly in the coming decades.
——-
References
1. Pioneer Venus Project Information, National Space Science Data Center website: http://nssdc.gsfc.nasa.gov/planetary/pioneer_venus.html
2. Pioneer 6, 7, 8, and 9, Wikipedia article: https://en.wikipedia.org/wiki/Pioneer_6,_7,_8,_and_9
3. Stable Orbit for a Newly Discovered Companion, Centauri Dreams article: https://centauri-dreams.org/?p=17484
4. Horseshoe orbit, Wikipedia article: https://en.wikipedia.org/wiki/Horseshoe_orbit
5. Quasi-satellite, Wikipedia article: https://en.wikipedia.org/wiki/Quasi-satellite
6. TRW Space Log, Winter 1969-70, Vol. 9, No. 4, Pioneer E, TETR C entry on pages 40 – 43.
The National Space Science Data Center http://nssdc.gsfc.nasa.gov/ has a Pioneer E mission page at http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=PIONE.
7. Edward Belbruno, Wikipedia article: https://en.wikipedia.org/wiki/Edward_Belbruno
8. Edward Belbruno : Mathematics, Astrophysics, Aerospace Engineering (Edward Belbruno’s Official Website): www.edbelbruno.com
9. SpaceRoutes.com website: http://www.spaceroutes.com/intro.html
10. Hiten (Muses-A) JAXA webpage: http://www.isas.jaxa.jp/e/enterp/missions/hiten.shtml
11. Hiten, Wikipedia article: https://en.wikipedia.org/wiki/Hiten
12. Sentinel Space Telescope, Wikipedia article: https://en.wikipedia.org/wiki/Sentinel_Space_Telescope
13. Sentinel Mission website (mission overview page): http://sentinelmission.org/sentinel-mission/overview/
14. LTV (Vought) SLV-1 Scout, Designation Systems article: http://www.designation-systems.net/dusrm/app3/lv-1.html
15. Ford RM-89 Blue Scout I, Designation Systems article: http://www.designation-systems.net/dusrm/app1/rm-89.html
16. Ford RM-90 Blue Scout II, Designation Systems article: http://www.designation-systems.net/dusrm/app1/rm-90.html
17. Ford RM-91 Blue Scout Junior, Designation Systems article: http://www.designation-systems.net/dusrm/app1/rm-91.html
18. Blue Scout Jr, Encyclopedia Astronautica article (with launch chronology): http://www.astronautix.com/lvs/bluoutjr.htm
19. The Making of a Moon: The Story of the Earth Satellite Program by Arthur C. Clarke, pages 149 – 150 (First Edition, Published 1957 by Harper & Brothers Publishers, New York, NY, Library of Congress catalog card number: 57-8187 [a post-Sputnik revised edition, the same book with that update, was published in 1958])
20. Aeronutronics Farside, Designation Systems article: http://www.designation-systems.net/dusrm/app4/farside.html
21. Possible Challenge to Sputnik on Unmanned Spaceflight website: http://www.unmannedspaceflight.com/lofiversion/index.php/t1955.html
22. The First Shots Into Interplanetary Space by Professor Fritz Zwicky, California Institute of Technology Library website: http://calteches.library.caltech.edu/181/1/zwicky.pdf
23. Boeing to Design DARPA Airborne Satellite Launch Vehicle, Boeing.com website: http://www.boeing.com/features/2014/03/bds-darpa-contract-03-27-14.page
24. DARPA’s ALASA space launch system from airplane, wordlessTech.com website: http://wordlesstech.com/darpas-alasa-space-launch-system-from-airplane/
by Paul Gilster | Jul 21, 2015 | Advanced Rocketry |
If you’re a Centauri Dreams regular, you’re familiar with Adam Crowl, an Australian polymath who is deeply involved in the ongoing Project Icarus starship design study. Adam maintains a blog called Crowlspace where interesting and innovative ideas emerge, some of them related to earlier work that has been largely forgotten in our era. A recent post that caught my eye was on Ernst Stuhlinger’s ‘umbrella ship,’ a kind of spacecraft that, when introduced to the world on Walt Disney’s 1957 TV show Mars and Beyond, surely surprised most viewers.
The umbrella ship, as Adam notes, looks nothing like what readers of the famous space series in Collier’s (1952-1954) had come to associate with manned travel to other worlds. Wernher von Braun was then championing massive rockets to be engaged in the exploration of Mars, an exploratory operation that would send a fleet of vessels to the Red Planet. Unlike tiny capsules of the kind we used to reach Earth orbit and explore the Moon, these would be large vessels to be sent in great numbers. The expedition would be described by its designer in a book von Braun wrote in 1948 called Das Marsprojekt (translated into English in 1953).
What von Braun depicted and what both Collier’s and Disney immortalized was a fleet of ten spacecraft that would send 70 crew members to Mars, the spacecraft to be built in Earth orbit using reusable space shuttles. While von Braun radically revised the plan in 1956 and scaled it back substantially, Ernst Stuhlinger was working with an entirely different concept.
Image: Ernst Stuhlinger’s Umbrella Ship, built around ion propulsion. Notice the size of the radiator, which disperses heat from the reactor at the end of the boom. As Adam notes in his blog piece, the source for this concept was a Stuhlinger paper called “Electrical Propulsion System for Space Ships with Nuclear Power Source,” which ran in the Journal of the Astronautical Sciences 2, no. Pt. 1 in 1955, pp. 149-152 (online version here). Credit: Winchell Chung.
No chemical rockets for Stuhlinger. While von Braun envisioned his fleet using a nitric acid/hydrazine propellant, Stuhlinger was interested in electrical propulsion, producing thrust by expelling ions and electrons instead of combustion gases. He noted in the paper that using chemical reactions to produce thrust created a high initial mass as compared to the payload. To reduce this mass problem, he saw, it would be necessary to increase the exhaust velocity of the propellant. Accelerating propellant particles by electrical fields made the numbers more attractive, as the paper notes in its summary:
A propulsion system for space ships is described which produces thrust by expelling ions and electrons instead of combustion gases. Equations are derived from the optimum mass ratio, power, and driving voltage of a ship with given payload, travel time, and initial acceleration. A nuclear reactor provides the primary power for a turbo-electric generator; the electric power then accelerates the ions. Cesium is the best propellant available because of its high atomic mass and its low ionization energy. A space ship with 150 tons payload and an initial acceleration of 0.67 x 10-4 G, traveling to Mars and back in a total travel time of about 2 years, would have a takeoff mass of 730 tons.
Image: Wernher von Braun and Ernst Stuhlinger discuss the Umbrella Ship concept at Walt Disney Studios. Credit: NASA MSFC.
Adam works out the details, drawing from the Stuhlinger paper itself and deriving some quantities through his own work. We get a payload, including landing vehicle and crew habitat, that is about 20.5 percent of launch mass, an impressive figure indeed. We’re also saddled with low acceleration, as you would expect. The Umbrella Ship would take about a year to reach Mars, while a chemically propelled ship as analyzed by Stuhlinger would make the journey in about 260 days. The longer the travel time, the greater the hazard, which was in many ways unknown to Stuhlinger, as Adam comments:
These days we wouldn’t want a crewed vehicle spending weeks crawling through the Van Allen Belts, but back when Stuhlinger computed his trajectory and even when the design aired, the Belts were utterly unknown. Now we’d have to throw in a solar radiation “storm shelter” and I’d feel rather uncomfortable making astronauts spend two years soaking up cosmic-rays in interplanetary space. Even so, the elegance of the design, as compared with the gargantuan Von Braun “Der Mars Projekt” for example, is a testament to Stuhlinger’s advocacy of electric propulsion.
But what an interesting design to emerge in the 1950s, and it’s ironic given the above remark that when Explorer 1 was launched in 1958, Stuhlinger was at the controls of the timer that, in those relatively primitive days of space technology, handled rocket staging. Explorer 1 was the satellite that discovered the Van Allen belts in the first place. A German infantryman (he was wounded outside Moscow and later served at Stalingrad), Stuhlinger joined the German V-2 effort and worked closely with von Braun, later coming to the United States as part of Operation Paperclip. In the 1950s, he actively collaborated with von Braun on the Disney films Man in Space, Man and the Moon and Mars and Beyond.
Stuhlinger would spend a great deal of time on ion thrusters using either cesium or rubidium vapor, accelerating positively charged ions through a grid of electrodes. Today, he is considered a pioneer of ion propulsion, well known for his book Ion Propulsion for Space Flight (McGraw-Hill, 1964). He would serve as director of Marshall Space Flight Center’s Space Science Laboratory until 1968 and later as MSFC’s associate director for science, going on to become a professor at the University of Alabama in Huntsville and a senior research assistant with Teledyne Brown Engineering. Ernst Stuhlinger died in Huntsville in May of 2008.
