Crowlspace: Journey to Planet 9
For years “planet 9” referred to Pluto.
Unfortunately, Pluto has been downgraded to dwarf-planet status, (in-spite of the spectacular fly-by of New Horizons).
Now there is much speculation that Planet 9 is a cold gas giant, perhaps even a small brown dwarf.
In this article by Adam Crowl, he dishes on potential rocket systems that could get probes like New Horizons there in decades, not centuries:
Power, Distance and Time are inextricably linked in rocketry. When leaving the Earth’s surface this is not so obvious, since all the sound and fury happens for a few minutes, and silence descends once the rocket enters orbit, free-falling indefinitely, at least until drag brings it back down. For slow journeys to the Moon, Near Earth Asteroids, Mars, Venus etc. the coasting Hohmann Transfer orbits and similar low-energy orbits, are all typically “sudden impulse” trajectories, where the engines fire for a few minutes to put a spacecraft on a months long trajectory.
For trips further afield – or faster journeys to the nearer planets – the acceleration time expands to a significant fraction of the total journey time. Ion-drives and solar-sails accelerate slowly for months on end, allowing missions like “Dawn” which has successfully orbited two Main Belt objects, Ceres and Vesta, all on one tank of propellant. Given more power an electrical propulsion system can propel vehicles to Mars in 2-3 months, Jupiter in a year and Saturn in under 2. Exactly how good the performance has to be is the subject of this post.
Firstly, an important concept is the Power-to-Mass ratio or specific power – units being kilowatts per kilogram (kW/kg). Any power source produces raw energy, which is then transformed into the work performed by the rocket jet. Between the two are several efficiency factors – the efficiency of converting raw heat into electricity, then electricity into jet-power, which includes the ionization efficiency, the nozzle efficiency, the magnetic field efficiency and so on. A solar array converts raw sunlight into electricity with an efficiency of between 20-25%, but advanced cells exist which might push this towards 40-50%.
Let’s assume a perfect power source and a perfect rocket engine. What’s the minimum performance required for a given mission? The basic minimum is:
Power/Mass is proportional to (S^2/T^3)
That is the Power-to-Mass ratio required is proportional to the displacement (distance) squared, and inversely proportional to the mission time cubed. For example, a 1 year mission to Jupiter requires 1,000 times the specific power of a 10 year mission.
The minimum acceleration case is when acceleration/deceleration is sustained over the whole mission time. When acceleration is constant, it means a maximum cruise speed (i.e. actual speed of vehicle) of 2 times the average speed (defined as total displacement divided by total mission time).
Another result, from a mathematical analysis I won’t go into here, is that the minimum specific power mission requires a cruise speed that is 1.5 times the average speed and an acceleration+deceleration time, t, that is 2/3 the total mission time T.
Remember that kinetic energy is 1/2.M.V^2, thus specific kinetic energy per unit mass is 1/2.V^2.
The power required – which is work done per unit time – is a trade off between acceleration time and mission time. Say the mission time is 10 years. If all the acceleration is done in 1 year, then the cruise speed required is 1/0.95 times the average speed, but power is proportional to the speed squared divided by the acceleration time: P = (1/2).V^2/t = (1/2).(1/0.95)^2/1 ~ 0.55, whereas in the case of constant acceleration, the average specific power is (1/2).(2)^2/10 = 0.2. For the case of minimum power it’s (1/2)*(3/2)^2/(2/3*10) = 0.16875 – just 84.375% the constant acceleration case and ~31% the 1 year thrust time.
So what does it take to get to Planet 9? If we use the distance of 700 AU to Planet 9, and a total trip time of 10 years, that means an average speed of 70 AU per year. To convert AU/yr to km/s, just multiply by 4.74 km/s, thus 331.8 km/s is needed. Cruise speed is then 497.7 km/s and the specific jet-power is 1.177 kW/kg, if we’re slowing down to go into orbit. Presently there are only conceptual designs for power sources that can achieve that sort of specific power. If we take 20 years to get there, the specific power is 0.147 kW/kg, which is a bit closer to possible.
Space reactor designs typically boast a specific electrical power output of 50 W/kg to 100 W/kg. Gas-core nuclear reactors could go higher, putting out 2,000 – 500 W/kg, but our applied knowledge of gas-core reactors is limited. Designs exist, but no working prototypes have ever flown. In theory it would use uranium tetrafluoride (UF4) gas as the reacting core, which would run at ~4000 K or so and convert heat to electricity via a magnetohydrodynamic (MHD) generator. Huge radiators would be required and the overall efficiency of the power source would be ~22%. In fact there’s a theorem that any thermal power source in space has its highest specific power when the Carnot efficiency is just 25%, thanks to the need to minimise radiator area by maximising radiator temperature.
More exotic options would be the Fusion-Driven Rocket or a space-going stellarator or some such fusion reactor design with a high specific power. In that case it’d be operated more as a pure rocket than powering an electrical rocket. Of course there’s the old Orion option – the External Nuclear Pulse Rocket – but no one wants to put *potential* nuclear warheads into orbit, just yet.
– See more at: http://crowlspace.com/#sthash.hYmlMqQ6.dpuf
From another great post on Centauri Dreams:
The star HIP 85605 until recently seemed more interesting than it may now turn out to be. In a recent paper, Coryn Bailer-Jones (Max Planck Institute for Astronomy, Heidelberg) noted that the star in the constellation Hercules had a high probability of coming close enough to our Solar System in the far future (240,000 to 470,000 years from now) that it would pass through the Oort Cloud, potentially disrupting comets there. The possibility of a pass as close as .13 light years (8200 AU) was there, but Bailer-Jones cautioned that distance measurements of this star could be incorrect. His paper on nearby stellar passes thus leaves the HIP 85605 issue unresolved.
Enter Eric Mamajek (University of Rochester) and company. Working with data from the Southern African Large Telescope (SALT) and the Magellan telescope at Las Campanas Observatory in Chile, Mamajek showed that the distance to HIP 85605 has been underestimated by a factor of ten. As Bailer-Jones seems to have suspected, the new measurement takes the star on a trajectory that does not bring it within the Oort Cloud. But in the same paper, the team names an interesting system called Scholz’s Star as a candidate for a close pass in the past.
Studying the star’s tangential velocity (motion across the sky) as well as radial velocity data, the team found that despite being relatively close at 20 light years, Scholz’s Star shows little tangential velocity. That would imply an interesting encounter ahead, or one that had already happened. Mamajek explains:
“Most stars this nearby show much larger tangential motion. The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had ‘recently’ come close to the solar system and was moving away. Sure enough, the radial velocity measurements were consistent with it running away from the Sun’s vicinity – and we realized it must have had a close flyby in the past.”
Image: Artist’s conception of Scholz’s star and its brown dwarf companion (foreground) during its flyby of the solar system 70,000 years ago. The Sun (left, background) would have appeared as a brilliant star. The pair is now about 20 light years away. Credit: Michael Osadciw/University of Rochester.
The paper on this work, recently published in the Astrophysical Journal, determines the star’s trajectory, one that shows that about 70,000 years ago, it would have passed some 52,000 AU from the Sun. This works out to about 0.82 light years, or 7.8 trillion kilometers, quite a bit closer than Proxima Centauri, and probably close enough to pass through the outer Oort Cloud. The star was within 100,000 AU of the Sun for a period of roughly 10,000 years.
Scholz’s star (W0720) is a low-mass object in the constellation Monoceros also tagged WISE J072003.20-084651.2 and only recently discovered (by Ralf-Dieter Scholz in 2014) thanks to its dimness in optical wavelengths, its proximity to the galactic plane and its low proper motion. Adaptive optics imaging and high resolution spectroscopy has demonstrated that the star is actually a binary, an M-dwarf with a companion at 0.8 AU that is probably a brown dwarf.
The question that immediately comes to mind is what kind of object the Scholz’s star system would have presented in the night sky some 70,000 years ago. The answer is not dramatic, for at its closest approach the binary would have had an apparent magnitude in the range of 11.4 (note: there is a typo in the paper, as noted here, which had specified an apparent magnitude of 10.3). This is five magnitudes, or a factor of 100 times, fainter than the faintest naked eye stars. But the paper notes that M-dwarfs like this one are often given to flare activity that might have made Scholz’s star a brighter object. From the paper:
If W0720 experienced occasional flares similar to those of the active M8 star SDSS J022116.84+194020.4 (Schmidt et al. 2014), then the star may have been rarely visible with the naked eye from Earth (V < 6; ∆V < −4) for minutes or hours during the flare events. Hence, while the binary system was too dim to see with the naked eye in its quiescent state during its flyby of the solar system ∼70 kya, flares by the M9.5 primary may have provided visible short-lived transients visible to our ancestors.
And take a look at this graph, which Eric Mamajek published on Twitter yesterday.
As you can see, Scholz’s Star was moving out. If it had been visible, what would ancient skywatchers have made of it? We also have to wonder what other close encounters our Solar System may have had with other stars. Note this point from the paper about M-dwarfs:
Past systematic searches for stars with close flybys to the solar system have been understandably focused on the Hipparcos astrometric catalog (García Sánchez et al. 1999; Bailer-Jones 2014), however it contains relatively few M dwarfs relative to their cosmic abundance. Searches in the Gaia astrometric catalog for nearby M dwarfs with small proper motions and large parallaxes (i.e. with small tangential velocities) will likely yield addition candidates.
So much still to learn about M-dwarfs!
Project Dragonfly Lives!
Here is another great post from Centauri Dreams, written by Andreas Hein. Good stuff.
2089, 5th April: A blurry image rushes over screens around the world. The image of a coastline, waves crashing into it, inviting for a nice evening walk at dawn. Nobody would have paid special attention, if it were not for one curious feature: Two suns were mounted in the sky, two bright, hellish eyes. The first man-made object had reached another star system.
Is it plausible to assume that we could send a probe to another star within our century? One major challenge is the amount of resources needed for such a mission. [1, 2]. Ships proposed in the past were mostly mammoths, weighing ten-thousands of tons: the fusion-propelled Daedalus probe with 54,000 tonnes and recently the Project Icarus Ghost Ship with over 100,000 tonnes. All these concepts are based on the rocket principle, which means that they have to take their propellant with them to accelerate. This results in a very large ship.
Another problem with fusion propulsion in particular is the problem of scalability. Most fusion propulsion systems get more efficient when they are scaled up. There is also a critical lower threshold for how small you can go. These factors lead to large amounts of needed propellant and large engines, for which you need a large space infrastructure. A Solar System-wide economy is probably needed, as the Project Daedalus report argues .
Image: The Project Icarus Ghost Ship: A colossal fusion-propelled interstellar probe
However, there is a different avenue for interstellar travel: going small. If you go small, you need less energy for accelerating the probe and thus less resources. Pioneers of small interstellar missions are Freeman Dyson with his Astrochicken; a living, one kilogram probe, bio-engineered for the space environment . Robert Forward proposed the Starwisp probe in 1985 . A large, ultra-thin sail which rides on a beam of microwaves. Furthermore, Frank Tipler and Ray Kurzweil describe how nano-scale probes could be used for transporting human consciousness to the stars [6, 7].
At the Initiative for Interstellar Studies (I4IS), we wanted to have a fresh look at small interstellar probes, laser sail probes in particular. The last concepts in this area have been developed years ago. How did the situation change in recent years? Are there new, possibly disruptive concepts on the horizon? We think there are. The basic idea is to develop an interstellar mission by combining the following technologies:
- Laser sail propulsion: The spacecraft rides on a laser beam, which is captured by an extremely thin sail .
- Small spacecraft technology: Highly miniaturized spacecraft components which are used in CubeSat missions
- Distributed spacecraft: To spread out the payload of a larger spacecraft over several spacecraft, thus, reducing the laser power requirements [9, 10]. The individual spacecraft would then rendezvous at the target star system and collaborate to fulfill their mission objectives. For example, one probe is mainly responsible for communication with the Solar System, another responsible for planetary exploration via distributed sensor networks (smart dust) .
- Magnetic sails: A thin superconducting ring’s magnetic field deflects the hydrogen in the interstellar medium and decelerates the spacecraft .
- Solar power satellites: The laser system shall use space infrastructure which is likely to exist in the next 50 years. Solar power satellites would be temporarily leased to provide the laser system with power to propel the spacecraft.
- Communication systems with external power supply: A critical factor for small interstellar missions is power supply for the communication system. As small spacecraft cannot provide enough power for communicating over these vast distances. Thus, power has to be supplied externally, either by using laser or microwave power from the Solar System during the trip and solar radiation within the target star system .
Image: Size comparison between an interplanetary solar sail and the Project Icarus Ghost Ship. Interstellar sail-based spacecraft would be much larger. (Courtesy: Adrian Mann and Kelvin Long)
Bringing all these technologies together, it is possible to imagine a mission which could be realized with technologies which are feasible in the next 10 years and could be in place in the next 50 years: A set of solar power satellites are leased for a couple of years for the mission. A laser system with a huge aperture has been put into a suitable orbit to propel the interstellar, as well as future planetary missions. Thus, the infrastructure can be reused for multiple purposes. The interstellar probes are launched one-by-one.
After decades, the probes start to decelerate by magnetic sails. Each spacecraft charges its sails differently. The first spacecraft decelerates slower than the follow-up probes. Ideally, the spacecraft then arrive at the target star system at the same point in time. Then, the probes start exploring the star system autonomously. They reason about exploration strategies, exchange and share data. Once a suitable exploration target has been chosen, dedicated probes descend to the planetary surface, spreading dust-sized sensor networks onto the pristine land. The data from the network is collected by other spacecraft and transferred back to the spacecraft acting as a communication hub. The hub, powered by the light from extrasolar light sends back the data to us. The result could be the scenario described at the beginning of this article.
Image: Artist’s impression of a laser sail probe with a chip-sized payload. (Courtesy: Adrian Mann)
Of course, one of the caveats of such a mission is its complexity. The spacecraft would have to rendezvous precisely over interstellar distances. Furthermore, there are several challenges with laser sail systems, which have been frequently addressed in the literature, for example beam collimation and control. Nevertheless, such a mission architecture has many advantages compared to existing ones: It could be realized by a space infrastructure we could imagine to exist in the next 50 years. The failure of one or more spacecraft would not be catastrophic, as redundancy could easily be built in by launching two or more identical spacecraft.
The elegance of this mission architecture is that all the infrastructure elements can also be used for other purposes. For example, a laser infrastructure could not only be used for an interstellar mission but interplanetary as well. Further applications include an asteroid defense system . The solar power satellites can be used for providing in-space infrastructure with power .
Image: Artist’s impression of a spacecraft swarm arriving at an exosolar system (Courtesy: Adrian Mann)
How about the feasibility of the individual technologies? Recent progress in various areas looks promising:
- The increased availability of highly sophisticated miniaturized commercial components: smart phones include many components which are needed for a space system, e.g. gyros for attitude determination, a communication system, and a microchip for data-handling. NASA has already flown a couple of “phone-sats”; Satellites which are based on a smart phone .
- Advances in distributed satellite networks: Although a single small satellite only has a limited capability, several satellites which cooperate can replace larger space systems. The concept of Federated Satellite Systems (FSS) is currently explored at the Massachusetts Institute of Technology as well as at the Skolkovo Institute of Technology in Russia . Satellites communicate opportunistically and share data and computing capacity. It is basically a cloud computing environment in space.
- Increased viability of solar sail missions. A number of recent missions are based on solar sail technology, e.g. the Japanese IKAROS probe, LightSail-1 of the Planetary Society, and NASA’s Sunjammer probe.
- Greg Matloff recently proposed use of Graphene as a material for solar sails . With an areal density of a fraction of a gram and high thermal resistance, this material would be truly disruptive. Currently existing materials have a much higher areal density; a number crucial for measuring the performance of solar sails.
- Material sciences has also advanced to a degree where Graphene layers only a few atoms thick can be manufactured . Thus, manufacturing a solar sail based on extremely thin layers of Graphene is not as far away as it seems.
- Small satellites with a mass of only a few kilograms are increasingly proposed for interplanetary missions. NASA has recently announced the Interplanetary CubeSat Challenge, where teams are invited to develop CubeSat missions to the Moon and even deeper into space (NASA) . Coming advances will thus stretch the capability of CubeSats beyond Low-Earth Orbit.
- Recent proposals for solar power satellites focus on providing space infrastructure with power instead of Earth infrastructure [18, 19]. The reason is quite simple: Solar power satellites are not competitive to most Earth-based alternatives but they are in space. A recent NASA concept by John Mankins proposed the use of a highly modular tulip-shaped space power satellite, supplying geostationary communication satellites with power.
- Large space laser systems have been proposed for asteroid defense 
In order to explore various mission architectures and encourage participation by a larger group of people, I4IS has recently announced the Project Dragonfly Competition in the context of the Alpha Centauri Prize . We hope that with the help of this competition, we can find unprecedented mission architectures of truly disruptive capability. Once this goal is accomplished, we can concentrate our efforts on developing individual technologies and test them in near-term missions.
If this all works out, this might be the first time in history that there is a realistic possibility to explore a near-by star system within the 21st or early 22nd century with “modest” resources.
I remember when the original Project Icarus study came out in the 1970s and I was absolutely enthralled with it.
At last, interstellar exploration could be possible, not fantasy.
Then the Icarus came out a couple of years ago. The ship was more advanced, but the size doubled. How is that possible in this age of miniaturization?
I think it’s because people love the idea of Battlestar Galactica or U.S.S. Enterprise sized interstellar craft.
You gotta have powerful engines and weapons to cope with angry aliens, right?
Andrea Hein is being smart and paying respect to Robert Foward and Freeman Dyson by writing this study with up to date ideas which encompasses Cube Sat tech and other commercial space company technologies.
Project Dragonfly: The case for small, laser-propelled, distributed probes
Centauri Dreams: Creative Constraints and Starflight
I discovered Karl Schroeder’s work when I was researching brown dwarfs some years ago. Who knew that somebody was writing novels about civilizations around these dim objects? Permanence (Tor, 2003) was a real eye-opener, as were the deep-space cultures it described. Schroeder hooked me again with his latest book — he’s dealing with a preoccupation of mine, a human presence in the deep space regions between ourselves and the nearest stars, where resources are abundant and dark worlds move far from any sun. How to maintain such a society and allow it to grow into something like an empire? Karl explains the mechanism below. Science fiction fans, of which there are many on Centauri Dreams, will know Karl as the author of many other novels, including Ventus (2000), Lady of Mazes (2005) and Sun of Suns (2006).
by Karl Schroeder
My newest science fiction novel, Lockstep, has just finished its serialization in Analogmagazine, and Tor Books will have it on the bookshelves March 24. Reactions have been pretty favourable—except that I’ve managed to offend a small but vocal group of my readers. It seems that some people are outraged that I’ve written an SF story in which faster than light travel is impossible.
I did write Lockstep because I understood that it’s not actual starflight that interests most people—it’s the romance of a Star Trek or Star Wars-type interstellar civilization they want. Not the reality, but the fantasy. Even so, I misjudged the, well, the fervor with which some people cling to the belief that the lightspeed limit will just somehow, magically and handwavingly, get engineered around.
This is ironic, because the whole point of Lockstep was to find a way to have that Star Wars-like interstellar civilization in reality and not just fantasy. As an artist, I’m familiar with the power of creative constraint to generate ideas, and for Lockstep I put two constraints on myself: 1) No FTL or unknown science would be allowed in the novel. 2) The novel would contain a full-blown interstellar civilization exactly like those you find in books with FTL.
Creativity under constraint is the best kind of creativity; it’s the kind that really may take us to the stars someday. In this case, by placing such mutually contradictory — even impossible — restrictions on myself, I was forced into a solution that, in hindsight, is obvious. It is simply this: everyone I know of who has thought about interstellar civilization has thought that the big problem to be solved is the problem of speed. The issue, though (as opposed to the problem), is how to travel to an interstellar destination, spend some time there, and return to the same home you left. Near-c travel solves this problem for you, but not for those you left at home. FTL solves the problem for both you and home, but with the caveat that it’s impossible. (Okay, okay, for the outraged among you: as far as we know. To put it more exactly, we can’t prove that FTL is impossible any more than we can prove that Santa Claus doesn’t exist. I’ll concede that.)
Read the rest here…
78,000 People Want To Go To Mars ( With Mars One )
The Mars One organization released this announcement on Tuesday:78,000 sign up for one-way mission to MarsAmersfoort, 7th May 2013 – Just two weeks into the nineteen week application period, more than seventy-eight thousand people have applied to the Mars One astronaut selection program in the hope of becoming a Mars settler in 2023.
Mars One has received applications from over 120 countries. Most applications come from USA (17324), followed by China (10241), United Kingdom (3581), Russia, Mexico, Brazil, Canada, Colombia, Argentina and India.
Bas Lansdorp, Mars One Co-Founder and CEO said: “With seventy-eight thousand applications in two weeks, this is turning out to be the most desired job in history. These numbers put us right on track for our goal of half a million applicants.”
“Mars One is a mission representing all humanity and its true spirit will be justified only if people from the entire world are represented. I’m proud that this is exactly what we see happening,” he said.
As part of the application every applicant is required to explain his/her motivation behind their decision go to Mars in an one minute video. Many applicants are choosing to publish this video on the Mars One website. These are openly accessible on applicants.mars-one.com.
“Applicants we have received come from a very wide range of personalities, professions and ages. This is significant because what we are looking for is not restricted to a particular background. From Round 1 we will take forward the most committed, creative, resilient and motivated applicants,” said Dr. Norbert Kraft, Mars One Chief Medical Officer.
Mars One will continue to receive online applications until August 31st 2013. From all the applicants in Round 1, regional reviewers will select around 50-100 candidates for Round 2 in each of the 300 geographic regions in the world that Mars One has identified.
Four rounds make the selection process, which will come to an end in 2015; Mars One will then employ 28-40 candidates, who will train for around 7 years. Finally an audience vote will elect one of groups in training to be the envoys of humanity to Mars.
I’m not surprised most of the applicants are from the U.S., but the number of applicants from China does a little bit.
Maybe it shouldn’t though, the Chinese maybe looking for lebensraum ( elbow room ), what with over a billion people and all.
Mars might be an appealing bit of real estate to them.
Mars One receives 78,000 applications in 2 weeks for Mars settlement
Falcon Heavy or Space Launch System For Lunar Exploration ?
From America Space:
There have been occasional suggestions that NASA should scrap its Space Launch System (SLS) in favor of SpaceX’s Falcon Heavy for fulfilling its beyond low-Earth orbit needs . The claim forwarded by some is that the as-yet-untested-and-unflown 53 mt low-Earth orbit (LEO) (200 km @ 28°) Falcon Heavy is now “cheaper” than the as-yet-untested-and-unflown SLS. Furthermore, canceling the SLS would supposedly save NASA $10 billion—money that could otherwise be used to fund such programs as the Commercial Crew integrated Capability (CCiCap), to conduct a flight test of Orion on a Falcon Heavy, and to focus on building a small-scale space station in the area near the Moon. One issue not addressed by proponents of canceling SLS is whether it is a good idea to couple a nation’s human exploration spaceflight capabilities to a private company. An issue which appears to be altogether ignored, is the Falcon Heavy’s small lunar payload capability and the impact this would have on an already complex and risky endeavor such as lunar exploration.
According to SpaceX, the Falcon 9 Heavy, also called the Falcon Heavy, will have a 53 mt (metric ton) payload capacity to LEO of 200 km with an inclination of 28° . Such a LEO payload capability will be impressive, allowing SpaceX to launch nearly twice the payload of a Delta IV Heavy or an Atlas V, and to do so more cheaply than either. But when it comes to launching payload to a geostationary transfer orbit (GTO) or beyond, the Falcon 9 Heavy falls far short of either the Delta or Atlas launchers. With a GTO payload of barely over 12 mt, the Falcon 9 Heavy is at least 1 metric ton, or 1,000 kg, under what either the Delta IV Heavy or Atlas V can deliver to the same point in space.
The Falcon 9 Heavy is, much like United Launch Alliance’s Delta IV Heavy, a triple-bodied version of the company’s Falcon 9 launch vehicle. Photo Credit: SpaceX
The Falcon 9 Heavy’s GTO payload deficiency relative to the existing EELV launch vehicles has other down-stream effects as to its appropriateness for beyond-Earth orbit (BEO) crewed exploration. It is safe to assume that the Falcon Heavy’s low-lunar orbit (LLO) payload capacity will not top much above 10 mt . How will the Falcon 9 Heavy’s meager LLO payload capacity enable a meaningful return to the Moon? And why even talk about the Falcon Heavy as a possible launcher of crewed lunar exploration when each of the Delta IV Heavy and Atlas V launchers can send over 1,000 kg more than the Falcon Heavy to the Moon? Moreover, while the Delta IV and Atlas V have extensive flight histories, the Falcon Heavy has no such experience.
Advocates of using the Falcon Heavy don’t just want to rewrite who takes us beyond-Earth orbit, but more fundamentally how such missions are built. Reliance upon the Falcon Heavy for launching a beyond-Earth exploration program means some hard choices as to mission architecture. Traditionally, crewed exploration beyond low-Earth orbit has focused on minimizing complexity, and therefore risk and cost, by using a heavy-lift rocket (HLV). The logic behind using an HLV for lunar exploration in the past was that fewer launches correlated to less risk. The Falcon Heavy’s 10 mt capability means that any lunar exploration program will have to be one of assembling pieces/parts in low-Earth orbit, where the Falcon Heavy’s (LEO) 53 mt payload capacity can really shine. Some have claimed that centering a beyond-Earth exploration program on the Falcon Heavy does not mean ending the Orion spacecraft program. They point this out because Orion is the only spacecraft designed from the ground up for beyond-Earth exploration. Certainly, a Falcon Heavy can place an Orion crewed and service module in low-Earth orbit. But several additional launches will be needed to send Orion and her crew to the Moon. A lunar crewed mission using the Falcon Heavy would mean assembling, at necessary LEO locations, a crewed vehicle, a lander, a trans-lunar injection stage, a stage to get the crewed spacecraft and lander into LLO, and possibly a separate stage to enable the crewed spacecraft to return to Earth .
While supporters of an all-commercial approach frequently tout the company’s laudable accomplishments, they just as frequently ignore the limitations of both the Falcon Heavy launch vehicle and the Dragon spacecraft. Photo Credit: SpaceX
One problem with a non-HLV approach to lunar exploration is that if a replacement Falcon Heavy and payload are not handy, any launch failure could very well mean a scrubbed mission. So a non-HLV approach necessarily means an inventory of not just a spare Falcon Heavy, but of duplicate spaceflight hardware—or designing hardware and refueling stations such that a delay of weeks or months would have only a marginal impact on the mission. Solving all of these unknown-unknowns (or unk-unks in engineering speak) associated with multiple launches, assembling a mission in LEO, in-space refueling at an orbiting location, among others flowing from a non-HLV approach to beyond-Earth exploration, could see the cost advantage of using the relatively unproven Falcon Heavy largely, if not completely, evaporate.
A beyond-Earth exploration program using the Falcon Heavy in an HLV architecture has its own downsides and associated costs. In order to enable the Falcon 9 Heavy to be a capable beyond low-Earth orbit launcher, funds will certainly be needed to create a new cryogenic second-stage. This will be needed because, in its current configuration, a Falcon 9 Heavy could not even launch one 11.6 mt Unity node module, much less a 20 mt Bigelow BA 330 Nautilus module. Even with a brand new second-stage, reliance upon the Falcon 9 Heavy to build, visit, and maintain a lunar orbiting outpost will dictate doing so in very small chunks; the number of launches will then begin to add-up, as will the complexity, risk, and cost. A Falcon Heavy cannot place an Orion spacecraft even in high-Earth, much less lunar, orbit. So reliance upon the Falcon 9 Heavy for beyond low-Earth missions in an HLV-based lunar mission architecture would only set NASA up to cancel Orion and go with Dragon for our nation’s crewed space exploration needs.
While it may be true that the Dragon spacecraft has a heatshield capable of allowing the spacecraft safe reentry into the Earth’s atmosphere, little else of Dragon is crew, much less lunar mission, capable. SpaceX’s Dragon is currently a participant in NASA’s commercial crew and cargo programs. One goal of NASA’s commercial crew program is to enable spacecraft built and operated by commercial space companies to get crews to and from the International Space Station by late 2017. But the requirements for a crewed spacecraft tailored for low-Earth orbit are different than those for beyond-Earth orbit. For one, a LEO capable spacecraft need only be capable of hours of operation, where a lunar spacecraft needs a capability of days. This means that the use of the Falcon Heavy as a means to returning humans to the Moon very likely means funding further enhancements, and verifying those enhancements to the Dragon spacecraft. As with over 90 percent of the funding for Falcon 9 and Dragon, this additional financial burden would fall upon NASA’s, and therefore the U.S. taxpayer’s, shoulders. Even with an enhanced Falcon Heavy launcher and Dragon spacecraft, more than one Falcon Heavy launch would still be needed to support a crewed lunar landing mission. Several Falcon Heavy launches would be needed to build a lunar orbiting outpost.
NASA’s SLS has the full support, to include funding, of Congress. As such, efforts to cancel the system in lieu of one that favors the company that SpaceX supporters approve of is not likely to occur. Image Credit: NASA
Or NASA could send a crewed lunar mission or build a lunar outpost with far fewer SLS launches. That’s because the very first iteration of the SLS, the Block I, will carry twice the payload of a Falcon Heavy to the Moon. The SLS Block II will have a lunar payload capacity nearly 3–4 times that of the Falcon Heavy, depending upon what engines are selected for the SLS’s advanced booster.
Beyond the SLS’s substantial payload advantage for lunar missions, the question of cost remains. Are 3 or 4 Falcon Heavy launches really cheaper than just one SLS Block II launch? That is a hard question to answer given that both launchers are still effectively “paper” rockets. In factoring launch costs, there is the cost of the launch vehicle, the launch pad, launch support, and post-launch management, just to name a few.
The bigger problem for those wishing to end the Space Launch System program is that it is currently ahead of schedule. According to John Elbon, Boeing VP & General Manager, Space Exploration, “We’re on budget, ahead of schedule. There’s incredible progress going on with that rocket” . Canceling a rocket that is ahead of schedule would be difficult at best. Given that Congress has, over three votes, not only supported SLS but increased its funding over amounts sought by the Obama Administration, the odds of opponents getting SLS canceled are slim-to-none.
Space Launch System opponents suggest that the SLS program should cancel until a mission requiring such a rocket is identified. John Shannon, also with Boeing, recently stated, “This ‘SLS doesn’t have a mission’ is a smokescreen that’s been put out there by people who would like to see that [program’s] budget go to their own pet projects. SLS is every mission beyond low Earth orbit. The fact that NASA has not picked one single mission is kind of irrelevant” . It bears mentioning that a good part of the reason there is no meaningful mission for the Orion-SLS is because the Obama Administration has not agreed with Congress that, as Congress noted in its 2010 NASA Authorization Act, cislunar space is the next step in our efforts beyond Earth and that the SLS is an integral part of that step.
Moreover, both short- and long-term missions for SLS have emerged in recent months. Within the 2014 FY Budget Proposal Request, NASA was directed to retrieve an asteroid, place it in lunar orbit, and then send astronauts to study it. The vehicle of choice is SLS. During a recent interview, NASA Deputy Associate Administrator for Exploration Systems in the Human Exploration and Operations Mission Directorate Dan Dumbacher stated on AmericaSpace that the long-term mission for SLS was to send astronauts to Mars.
Mr. Jillhouse sings the acolades of the Space Launch System as others sing them about SpaceX’s Falcon9 rockets. What he fails to mention is the SLS’s massive program slippages and muti-billion dollar cost overruns, versus commercial’s million dollar overruns and schedule slippages. It’s not even in the same ballgame, let alone ballpark.
Also the point should be that NASA should’ve bid the SLS job out in order to save the taxpayers money, but the function of SLS isn’t primarily for beyond Earth orbit exploration.
It’s to provide jobs in states that have NASA centers. And that’s why these projects are perpetually underfunded, just enough money is sent in order to keep people employed as long as the politicians can make it possible.
Maybe in the end the SLS will get finished and work as advertised. If I live long enough.
NASA’s first manned outpost in deep space may be a repurposed rocket part, just like the agency’s first-ever astronaut abode in Earth orbit.
With a little tinkering, the upper-stage hydrogen propellant tank of NASA’s huge Space Launch System rocket would make a nice and relatively cheap deep-space habitat, some researchers say. They call the proposed craft “Skylab II,” an homage to the 1970s Skylab space station that was a modified third stage of a Saturn V moon rocket.
“This idea is not challenging technology,” said Brand Griffin, an engineer with Gray Research, Inc., who works with the Advanced Concepts Office at NASA’s Marshall Space Flight Center in Huntsville, Ala.
“It’s just trying to say, ‘Is this the time to be able to look at existing assets, planned assets and incorporate those into what we have as a destination of getting humans beyond LEO [low-Earth orbit]?'” Griffin said Wednesday (March 27) during a presentation with NASA’s Future In-Space Operations working group.
A roomy home in deep space
NASA is developing the Space Launch System (SLS) to launch astronauts toward distant destinations such as near-Earth asteroids and Mars. The rocket’s first test flight is slated for 2017, and NASA wants it to start lofting crews by 2021.
The SLS will stand 384 feet tall (117 meters) in its biggest (“evolved”) incarnation, which will be capable of blasting 130 metric tons of payload to orbit. Its upper-stage hydrogen tank is big, too, measuring 36.1 feet tall by 27.6 feet wide (11.15 m by 8.5 m).
The tank’s dimensions yield an internal volume of 17,481 cubic feet (495 cubic m) — roughly equivalent to a two-story house. That’s much roomier than a potential deep-space habitat derived from modules of the International Space Station (ISS), which are just 14.8 feet (4.5 m) wide, Griffin said.
The tank-based Skylab II could accommodate a crew of four comfortably and carry enough gear and food to last for several years at a time without requiring a resupply, he added. Further, it would launch aboard the SLS in a single piece, whereas ISS-derived habitats would need to link up multiple components in space.
Because of this, Skylab II would require relatively few launches to establish and maintain, Griffin said. That and the use of existing SLS-manufacturing infrastructure would translate into big cost savings — a key selling point in today’s tough fiscal climate.
“We will have the facilities in place, the tooling, the personnel, all the supply chain and everything else,” Griffin said.
He compared the overall concept with the original Skylab space station, which was built in a time of declining NASA budgets after the boom years of the Apollo program.
Skylab “was a project embedded under the Apollo program,” Griffin said. “In many ways, this could follow that same pattern. It could be a project embedded under SLS and be able to, ideally, not incur some of the costs of program startup.”
There has been much caterwauling in the space advocacy community about the Space Launch System ( ne, “The Senate Launch System” ) concerning its cost and lack of purpose and/or destinations.
Of course, the thing was designed by Congress in order to fund a jobs program in the NASA Centers for the good voters of those districts. But it’s a seriously underfunded program, with just enough money to keep the civil servants of NASA employed, with just enough contractor support to keep them happy.
In the meantime, ideas like Skylab II, the Spacehab at EML-2 and the asteroid capture scheme rear their ugly heads and claim they’re economical in these austeric times.
My money is still on Elon Musk, Bob Bigelow, Dennis Tito and company.
Advanced Oort Cloud Civilisations?
From Centauri Dreams:
Jules Verne once had the notion of a comet grazing the Earth and carrying off a number of astounded people, whose adventures comprise the plot of the 1877 novel Off on a Comet. It’s a great yarn that was chosen by Hugo Gernsback to be reprinted as a serial in the first issues of his new magazine Amazing Stories back in 1926, but with a diameter of 2300 kilometers, Verne’s comet was much larger than anything we’ve actually observed. Comets tend to be small but they make up for it in volume, with an estimated 100 billion to several trillion thought to exist in the Oort Cloud. All that adds up to a total mass of several times the Earth’s.
Of course, coming up with mass estimates is, as with so much else about the Oort Cloud, a tricky business. Paul R. Weissman noted a probable error of about one order of magnitude when he produced the above estimate in 1983. What we are safe in saying is something that has caught Freeman Dyson’s attention: While most of the mass and volume in the galaxy is comprised of stars and planets, most of the area actually belongs to asteroids and comets. There’s a lot of real estate out there, and we’ll want to take advantage of it as we move into the outer Solar System and beyond.
Comets and Resources
Embedded with rock, dust and organic molecules, comets are composed of water ice as well as frozen gases like methane, carbon dioxide, carbon monoxide, ammonia and an assortment of compounds containing nitrogen, oxygen and sulfur. Porous and undifferentiated, these bodies are malleable enough to make them interesting from the standpoint of resource extraction. Richard P. Terra wrote about the possibilities in a 1991 article published in Analog:
This light fragile structure means that the resources present in the comet nuclei will be readily accessible to any human settlers. The porous mixture of dust and ice would offer little mechanical resistance, and the two components could easily be separated by the application of heat. Volatiles could be further refined through fractional distillation while the dust, which has a high content of iron and other ferrous metals, could easily be manipulated with magnetic fields.
Put a human infrastructure out in the realm of the comets, in other words, and resource extraction should be a workable proposition. Terra talks about colonies operating in the Oort Cloud but we can also consider it, as he does, a proving ground for even deeper space technologies aimed at crossing the gulf between the stars. Either way, as permanent settlements or as way stations offering resources on millennial journeys, comets should be plentiful given that the Oort Cloud may extend half the distance to Alpha Centauri. Terra goes on:
Little additional crushing or other mechanical processing of the dust would be necessary, and its fine, loose-grained structure would make it ideal for subsequent chemical processing and refining. Comet nuclei thus represent a vast reservoir of easily accessible materials: water, carbon dioxide, ammonia, methane, and a variety of metals and complex organics.
Energy by Starlight
Given that comets probably formed on the outer edges of the solar nebula, their early orbits would have been more or less in the same plane as the rest of the young system, but gravitational interactions with passing stars would have randomized their orbital inclinations, eventually producing a sphere of the kind Jan Oort first postulated back in 1950. Much of this is speculative, because we have little observational evidence to go on, but the major part of the cometary shell probably extends from 40,000 to 60,000 AU, while a projected inner Oort population extending from just beyond the Kuiper Belt out to 10,000 AU may have cometary orbits more or less in the plane of the ecliptic. Out past 10,000 AU the separation between comets is wide, perhaps about 20 AU, meaning that any communities that form out here will be incredibly isolated.
Image: An artist’s rendering of the Kuiper Belt and Oort Cloud. Credit: NASA/Donald K. Yeomans.
Whether humans can exploit cometary resources this far from home will depend on whether or not they can find sources of energy. In a paper called “Fastships and Nomads,” presented at the Conference on Interstellar Migration held at Los Alamos in 1983, Eric Jones and Ben Finney give a nod to non-renewable energy sources like deuterium, given that heavy elements like uranium will be hard to come by. Indeed, a typical comet, in Richard Terra’s figures, holds between 50,000 and 100,000 metric tons of deuterium, enough to power early settlement and mining.
But over the long haul, Jones and Finney are interested in keeping colonies alive through renewable resources, and that means starlight. The researchers talk about building vast mirrors using aluminum from comets, with each 1 MW mirror about the size of the continental United States. Now here’s a science fiction setting with punch, as the two describe it:
Although the mirrors would be tended by autonomous maintenance robots, the nomads would have to live nearby in case something went wrong… Although we could imagine that the several hundred people who could be supported by the resources of a single comet might live in a single habitat, the mirrors supporting that community would be spread across about 150,000 km. Trouble with a mirror or robot on the periphery of the mirror array would mean a long trip, several hours at least. It would make more sense if the community were dispersed in smaller groups so that trouble could be reached in a shorter time. There are also social reasons for expecting the nomad communities to be divided into smaller co-living groups.
Jones and Finney go on to point out that humans tend to work best in groups of about a dozen adults, whether in the form of hunter/gatherer bands, army platoons, bridge clubs or political cells. This observation of behavior leads them to speculate that bands of about 25 men, women and children would live together in a large habitat — think again of an O’Neill cylinder — built out of cometary materials, from which they would tend a mirror farm with the help of robots and computers. Each small group would tend a mirror farm perhaps 30,000 kilometers across.
The picture widens beyond this to include the need for larger communities that would occasionally come together, helping to avoid the genetic dangers of inbreeding and providing a larger social environment. Thus we might have about 500 individuals in clusters of 20 cometary bands which would stay in contact and periodically meet. Jones and Finney consider the band-tribe structure to be the smallest grouping that seems practical for any human community. Who would such a community attract — outcasts, dissidents, adventurers? And how would Oort Cloud settlers react to the possibility of going further still, to another star?
While by no means is this is a new theory, ( note the Jules Verne story ), it presents the scenario of the very slow spreading of intelligent biological life through-out the Galaxy ( see Slow Galactic Colonization, Zoo Hypothesis and the Fermi Paradox ).
Now here’s a thought; could a potential alien Oort Cloud civilization be the basis of the Ancient Astronaut Theory and the legends of the Sumerian Gods, the Anunnaki?
There’s no hard evidence of that of course, but there are Pluto-sized and larger objects in the Kuiper Belt glowing in the infrared, a sign that was said to represent a Dyson Sphere type civilisation.
Either these are natural objects such as Brown Dwarf stars, or potential alien civilisations whom don’t care whether they are detected in the infrared or not.
And that’s disturbing.
Did Voyager 1 Leave The Solar System?
For about three hours on Wednesday, Voyager 1 had left the solar system — before a rewritten news release headline pulled it back in. Voyager 1, one of two spacecraft NASA launched in 1977 on a grand tour of the outer planets, is now nearly 11.5 billion miles from the Sun, speeding away at 38,000 miles per hour. In a paper accepted by the journal Geophysical Review Letters, William R. Webber of New Mexico State University and Frank B. McDonald of the University of Maryland reported that on Aug. 25 last year, the spacecraft observed a sudden change in the mix of cosmic rays hitting it.
Cosmic rays are high-speed charged particles, mostly protons. Voyager 1’s instruments recorded nearly a doubling of cosmic rays from outside the solar system, while the intensity of cosmic rays that had been trapped in the outer solar system dropped by 90 percent.
The American Geophysical Union, publisher of the journal, sent out the news Wednesday morning: “Voyager 1 has left the solar system.” NASA officials, surprised, countered with a contrary statement from Edward C. Stone, the Voyager project scientist. “It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space,” Dr. Stone said. He said that the critical indicator would be a change in the direction of the magnetic field, not cosmic rays, for marking the outermost boundary of the solar system. In their paper, Dr. Webber and Dr. McDonald (who died only six days after Voyager observed the shift in cosmic rays) did not claim that Voyager 1 was in interstellar space, but had entered a part of the solar system they called the “heliocliff.” The geophysical union then sent out another e-mail with the same article but a milder headline: “Voyager 1 has entered a new region of space.”
Eventually Voyager 1 will leave the Solar System and there will be no dispute about it.
In the meantime, mainstream science will learn and post about the outer edges of the Solar System as Voyager 1 creeps along at .00002 lightspeed ( 37,500 mph ) .
Of course there are those in mainstream media and science who believe that mankind will never leave the Solar System because they proclaim that spacecraft will never be built that go faster than that.
Already the Pluto probe New Horizon traveling at 54,500 mph is breaking Voyager’s speed record and will probably leave the Solar System before Voyager does!
I’m certain in 100 years star probes will be launched toward Alpha Centauri and Tau Ceti that reach appreciable percentages of lightspeed bypassing all of our old interplanetary probes and perhaps in several centuries, mankind’s interstellar colonies will be picking up these old probes to study them, like old time capsules!
Where’s Voyager 1? That Depends.
Hat tip to the Daily Grail.
To Ply The Martian Way
From Centauri Dreams:
Existential risks, as discussed here yesterday, seem to be all around us, from the dangers of large impactors to technologies running out of control and super-volcanoes that can cripple our civilization. We humans tend to defer thinking on large-scale risks while tightly focusing on personal risk. Even the recent events near Chelyabinsk, while highlighting the potential danger of falling objects, also produced a lot of fatalistic commentary, on the lines of ‘if it’s going to happen, there’s nothing we can do about it.’ Some media outlets did better than others with this.
Risk to individuals is understandably more vivid. When Apollo 8 left Earth orbit for the Moon in 1968, the sense of danger was palpable. After all, these astronauts were leaving an orbital regime that we were beginning to understand and were, by the hour, widening the distance between themselves and our planet. But even Apollo 8 operated within a sequenced framework of events. Through Mercury to Gemini and Apollo, we were building technologies one step at a time that all led to a common goal. No one denied the dangers faced by every crew that eventually went to the Moon, but technologies were being tested and refined as the missions continued.
Inspiration Mars is proposing something that on balance feels different. As described in yesterday’s news conference (see Millionaire plans to send couple to Mars in 2018. Is that realistic? for more), the mission would be a flyby, using a free return trajectory rather than braking into Martian orbit. The trip would last 501 days and would be undertaken by a man and a woman, probably a middle-aged married couple. Jonathan Clark, formerly of NASA and now chief medical officer for Inspiration Mars, addresses the question of risk head-on: “The real issue here is understanding the risk in an informed capacity – the crew would understand that, the team supporting them would understand that.” Multi-millionaire Dennis Tito, a one-time space tourist who heads up Inspiration Mars, says the mission will launch in 2018.
Image: A manned Mars flyby may just be doable. But is the 2018 date pushing us too hard? Image credit: NASA/JPL.
We’ll hear still more about all this when the results of a mission-feasibility study are presented next weekend at the 2013 IEEE Aerospace Conference in Montana. Given the questions raised by pushing a schedule this tightly, there will be much to consider. Do we have time to create a reliable spacecraft that can offer not only 600 cubic feet of living space but another 600 for cargo, presumably a SpaceX Dragon capsule mated to a Bigelow inflatable module? Are we ready to expose a crew to interplanetary radiation hazards without further experience with the needed shielding strategies? And what of the heat shield and its ability to protect the crew during high-speed re-entry at velocities in the range of 50,000 kilometers per hour?
For that matter, what about Falcon Heavy, the launch vehicle discussed in the feasibility analysis Inspiration Mars has produced for the conference? This is a rocket that has yet to fly.
No, this doesn’t feel much like Apollo 8. It really feels closer to the early days of aviation, when attention converged on crossing the Atlantic non-stop and pilots like Rene Fonck, Richard Byrd, Charles Nungesser and Charles Lindbergh queued up for the attempt. As with Inspiration Mars, these were privately funded attempts, in this case designed to win the Orteig Prize ($25,000), though for the pilots involved it was the accomplishment more than the paycheck that mattered. Given the problems of engine reliability at the time, it took a breakthrough technology — the Wright J-5C Whirlwind engine — to get Lindbergh and subsequent flights across.
Inspiration Mars is looking to sell media rights and sponsorships as part of the fund-raising package for the upcoming mission, which is already being heavily backed by Tito. I’m wondering if there is a breakthrough technology equivalent to the J-5C to help this mission along, because everything I read about it makes it appear suicidal. The 2018 date is forced by a favorable alignment between Mars and the Earth that will not recur until 2031, so the haste is understandable. The idea is just the kind of daring, improbable stunt that fires the imagination and forces sudden changes in perspective, and of course I wish it well. But count me a serious skeptic on the question of whether this mission will be ready to fly on the appointed date.
And if it’s not? I like the realism in the concluding remarks of the feasibility study:
A manned Mars free-return mission is a useful precursor mission to other planned Mars missions. It will develop and demonstrate many critical technologies and capabilities needed for manned Mars orbit and landing missions. The technology and other capabilities needed for this mission are needed for any future manned Mars missions. Investments in pursuing this development now would not be wasted even if this mission were to miss its launch date.
Exactly so, and there would be much development in the interim. The study goes on:
Although the next opportunity after this mission wouldn’t be for about another 13 years, any subsequent manned Mars mission would benefit from the ECLSS [Environmental Control and Life Support System], TPS [Thermal Protection System], and other preparation done for this mission. In fact, often by developing technology early lessons are learned that can reduce overall program costs. Working on this mission will also be a means to train the skilled workforce needed for the future manned Mars missions.
These are all good reasons for proceeding, leaving the 2018 date as a high-risk, long-shot option. While Inspiration Mars talks to potential partners in the aerospace industry and moves ahead with an eye on adapting near-Earth technologies for the mission, a whiff of the old space race is in the air. “If we don’t fly in 2018, the next low-hanging fruit is in ’31. We’d better have our crew trained to recognize other flags,” Tito is saying. “They’re going to be out there.”
In 1968, faced with a deadline within the decade, NASA had to make a decision on risk that was monumental — Dennis Tito reminded us at the news conference that Apollo 8 came only a year after the first test launch of the Saturn 5. Can 2018 become as tangible a deadline as 1970 was for a nation obsessed with a Moon landing before that year? If so, the technologies just might be ready, and someone is going to have to make a white-knuckle decision about the lives of two astronauts. If Inspiration Mars can get us to that point, that decision won’t come easy, but whoever makes it may want to keep the words of Seneca in mind: “It is not because things are difficult that we dare not venture. It is because we dare not venture that they are difficult.”
There are a lot of nay-sayers out yonder decrying Tito’s idea as suicidal and a waste of money. But as recently as a couple of months ago questionnaires were sent out asking for volunteers to sign up for a one way trip to Mars (Mars One), even if there’s a better than even chance of dying at any moment of it.
The results were astounding.
Tito’s idea of sending an older married couple is nothing short of public opinion genius and if successful, could be the format of any future Mars colonization efforts.
Not to mention the technologies needed for the crossing.