The paper itself provides much more insight into the actual physics behind this [1]. The article doesn't really do the paper justice in my mind, based on my knowledge of the subject matter (although I appreciate the intent of providing an accessible means to introduce the topic).
I wrote my MSc thesis on weak capture trajectories and the concept of the Weak Stability Boundary [2] that was introduced by Ed Belbruno. It's a fantastic aspect of the gravitational 3-body problem and has been probed from a number of different perspectives over the last two decades, including tying in the phenomenon of weak/ballistic capture into our understanding of the structure of invariant manifolds and the periodic orbits about the Lagrange libration points.
Disclaimer: Francesco is my boss but I haven't spoken to him yet about the paper.
TL;DR: Ballistic Capture aka "Low-energy transfer" is being rekindled by NASA, Boeing, Belbruno, Topputo and colleagues. Fly the spacecraft ahead of Mars in formation of the planets orbit relative to the sun allowing gravity to gradually slow the spacecraft down. This saves on fuel/weight for entering orbit at high velocity.
Unfortunately, Belbruno's work may stay unused because he has a penchant for patenting it. The idea of low energy transfers aren't new and Belbruno didn't invent them, but you can apparently patent individual trajectory strategies. That also means any commercial venture would shy away from talking to him for fear they may be litigated against (which has happened).
Another thing to notice is these trajectories are no good for manned travel as they can take years or decades extra, they are even slower than the more traditional multi-planet slingshot maneuvers.
Buzz Aldrin is very passionate about colonizing Mars [1]. He says there are two big things that have to be accomplished before we can colonize Mars. The first is to train astronauts to live in a confined isolated space for 260 days (the length of a journey to Mars) [2]. This alternative journey trajectory increases the 260 days.
The second is harder: We need to go to Mars at least three times and bring back the men and women successfully. Once is not enough. Three proves we've mastered the engineering, financial, physical, and physiological aspects.
Unless you're envisioning spacecraft with literally hundreds of astronauts, the first will be anything but easy to solve. Doesn't help having an awesome spaceship if everyone on board goes batshit crazy after six months.
Bubbleheads are tested in Submarine School for compatibility with the idea of living in the intellectual equivalent of a sewer pipe for months on end with each other. I'd assume NASA would do the same. End of the day make sure you know who holds the keys to the weapons locker.
If in 1500 you dropped some European settlers in the Americas, there a high chance they'll survive. If in 2014 you drop some settlers in Mars, they would surely die.
Plenty of robots must be sent beforehand to build greenhouses, setup solar panel arrays, dig deep tunnels to provide shielding against cosmic radiation, etc.
A one way trip is more feasible. Resources spent on supplying a base will yield more knowledge, if slightly less PR.
Furthermore, if there are indigenous biologic agents there, I don't think we want them coming back. Like the Greek expedition to Asia Minor, Mars is a burn the ships mission.
Elon Musk has said from the beginning of SpaceX that trips to Mars would have to return as well. It's not because of the humans but because the cost of producing the space ships will be so large that it's not feasible to shoot them to Mars once and leave them there; they have to be reusable.
> The principle behind all of its vehicles is total re-usability; every single system must be able to be serviced and pressed back into operation. This is to cut down on the already astronomical cost of space flight (pun intended), making it more affordable for private companies to conduct missions into the heavens. The company’s main goal is to eliminate the equipment cost for space travel, leaving fuel as the only financial burden.
> It's not because of the humans but because the cost of producing the space ships will be so large that it's not feasible to shoot them to Mars once and leave them there; they have to be reusable.
The problem with the return trip is Earth reentry. Coming in at interplanetary speeds (falling to the sun from a "height" of Mars' orbit to Earth's), it is impossible for humans to reenter the Earth's atmosphere safely. It's barely possible from the moon.
This means that there has to be about as much deceleration before reentry than there was there was acceleration on the way out. So now you have to carry double the fuel, and the fuel to carry that, etc. This vastly complicates the problem with a manned mission to mars.
Lunar speed reentry is quite feasible, and has been practiced. Apollo did it fine, and Orion did it a few weeks ago. State of the art ablative shields, like the PICA-X used on Stardust and Dragon, are quite capable of handling entry at Mars transfer speed. (Lunar entry profile is about 11km/s, Mars 13-14km/s--though it can go as high as 20km/s deformation on design.)
The real problem with the return trip is getting off Mars. Specifically, putting enough propellant on the surface to get you back up. Sure, it's easier than Earth, but it's still a planet. If NASA were serious about Mars, they would be sending prototype ISRU plants every cycle, because having rocket fuel waiting for you on the surface is the real enabling technology for Mars exploration. Or Lunar or Venus for that matter.
It's not just getting fuel to Mars. It's building and operating launch infrastructure there. Unmanned LEO missions from KSC get delayed and fail. On Mars there won't be spare parts or separate ground crews, and the spacecraft will have to be readied having been through launch and touchdown cycles rather than a slow gentle roll from a VAB to launch pad.
The speed of light means no real time support from Houston. If ten people go out, then ten people have to get an interplanetary space program established on Mars. It ain't gonna be a matter of pushing the easy button.
This is one reason why it's often thought that a long-term station in Earth orbit (possibly at one of the Lagrange points) is a pre-requisite for a Mars mission. So, you could decelerate to the station instead of to re-entry. But, it is possible if one sent enough supplies ahead.
One way of handling things if there's a long-term station is to build the ship to Mars in space (or at least refuel at the station). If you send the return fuel ahead (or find a way to make it while at Mars) you aren't required to carry a large amount of fuel.
You still have to carry twice the fuel. What about a refuel station orbiting mars? Replenish the mars fuel station with fuel before the manned mission departs, they can just use that fuel stored at Mars when they return from the manned mission.
That doesn't mean you have to return from the ground. Have the large reusable craft swing by Mars without slowing down, dropping off a small daughter ship/lander, and continuing back to Earth.
Not really. Either we are going to inhabit Mars as residents or just spend money on space tourism. If we're intending to inhabit it, then the deal has to be one way. Otherwise, sending machines is vastly more cost effective.
> two big things that have to be accomplished before we can colonize Mars
Colonizers could probably live on packaged food from here 'til Judgment Day (or as long as Earth is willing to send always more supplies), but I would still add the maintenance of man-made ecosystems for food production to the list of big problems that we have not yet solved.
>> The first is to train astronauts to live in a confined isolated space for 260 days
Bubbleheads can do that, current and ex.
>> We need to go to Mars at least three times and bring back the men and women successfully.
I don't know that the delicacy of the orbital entry described is going to be sufficient for long term operations. It sounds like an artistic dance combined with luck. I think the old wing it into space at high velocity then put on the brakes method is more deterministic. Whole transportation systems on Earth function this way.
Yes. Beyond food and supplies, people would have to either want to spend their lives while on Mars in containerization or there would have to be a large pressurized common area for work and socialization. With a thin atmosphere stuff falling from space is a problem as it would be on the Moon so building underground would be required. That's why I think going to Venus first makes sense, get people used to the long travel periods living in confined spaces dependent on machines.
A spacecraft could double as living space on the planet, alongside whatever other prefab buildings they bring along. A cargo hold packed full of prefab walls could itself double as building space, once emptied. Also there would be more opportunities to leave those spaces to go outside.
It would certainly still be cramped by conventional standards, but conceivably much less so than the flight there.
How much of a given total cost of a launch to Mars is the fuel? According to the article, it shaves 25% off the fuel costs - but what percentage of the total is that, let's say, for the past few missions?
It seems that the bigger advantage of this is adding a few months but doing away with waiting for a launch window. Definitely great for equipment, though it would put two months' worth of extra stress on actual human travelers.
According to the article, it shaves 25% off the fuel costs
Yes, by the facts and speculation reported in the article kindly submitted here, the headline phrase "on the cheap" is plainly wrong, and "anytime" is an exaggeration, as the overall trip time will tend to be longer for most such missions. The article also notes, "The burn-free, capture altitude is also quite high—some 20,000 kilometers above Mars, far beyond where science satellites set up shop to scrutinize the planet up close. But taking along just a little extra fuel can then gently lower a ballistically captured spacecraft into scientifically valuable, standard orbits of around 100 to 200 kilometers like those achieved with Hohmann transfers—or even onward to the Martian surface for a landing." So one part of the article says that the mission will take less fuel (to leave the vicinity of earth), while another part of the article says that the mission will have to carry along extra fuel (in the Mars exploration modules) to arrive at a location where useful science can be done. The bottom line here is that these missions will still be about as expensive as current missions, and manned flight to Mars and back will be staggeringly expensive.
It might not be great for humans, but it's good for cargo mass. Send the big stuff the slow way earlier and the people the fast way with a later departure.
Launch costs for small Mars missions are on the order of a third of the project budget. Fuel is cheap... on the ground. But paying to send it to Mars is not.
Less fuel means more payload, which means more science or less cost (because you don't have to build so exotically to save weight.) Either way is good. Only in a radically different launch cost regime will we cease to care about efficiency of transfer.
My KSP-fu is failing me here... how is it possible to match Mars' circular solar orbit at a slower velocity? Wouldn't a different velocity imply a different orbital distance from the sun?
> My KSP-fu is failing me here... how is it possible to match Mars' circular solar orbit at a slower velocity?
You aren't actually trying to match it; as I understand this kind of orbit is a slightly slower (so slightly closer, on average) orbit that the vessel achieves somewhat ahead of Mars, so that when Mars passes it, Mars' gravity is enough to capture the vessel. In essence, some of the energy to match the orbit comes from Mars itself (slowing down Mars, but for any realistic spacecraft this is completely negligible because of the enormous mass ratio between the planet and the craft.)
Sounds like it's that thing in KSP where you time your insertion to The Mun's sphere of influence just right so you don't have to burn retro to achieve Munar orbit. Basically hit it so that you do gravity-assisted deceleration, and end up in orbit around it—typically badly elliptical orbit, but that's cheap to correct.
Mars' orbit is not circular, and spacecraft's would not be, either. They would be in slightly different (and intersecting, or nearly so) elliptical orbits, which would allow Mars to gravitationally capture the spacecraft when it approached closely enough.
Is performing a second burn to circularize a craft's orbit to near-sync with Martian orbit really cheaper than a deceleration burn? In fact, that would just be a complete Hohmann transfer.
I'd guess the target orbit for a craft performing this maneuver would still have a periapsis in the neighborhood of Earth's orbit, meaning it'd still be very unlike Mars' orbit until the craft was captured by Martian gravity.
(googles a bit)
It looks like these exploit Lagrange points somehow[1]. Precision maneuvers and weird, long routes to the target body. I'm not quite following how this works with only two bodies (Sun and Mars), versus the Sun-Earth-Moon trio. Wikipedia claims the Mars Orbiter Mission used a low-energy transfer at some point, but I can't figure out whether that was for the insertion into Martian orbit or some earlier maneuver it performed.
With nuclear pulse propulsion, we could send a craft to Mars in 2-3 weeks, safely, any time, and on the cheap.
The mass that can be transported is quite enormous, so we could piecemeal launch the components of a huge habitat and vast amounts of supplies into an outer orbit of Earth, robotically load them onto the pulse ship, and then shoot that baby to Mars.
Probably the slowest part of the plan would be launching the stuff into orbit. They scrubbed the idea of launching using nuclear pulse propulsion because of the dangers of radioactive fallout. Too bad, because that would have made things even simpler.
Web design tip (that I just made up). If you're going to have an annoying, large header bar appear above the text when the user scrolls, don't put a drop-shadow under it. It looks like an object is hiding the text, which it is, but is very distracting compared to a flat border.
I've gotten into the habit of doing: right click, inspect element, and then "delete node" on these headers. I really should create a chrome extension to reduce the friction in doing this.
For a fun (fictional) take about life on Mars, I'd recommend reading The Martian by Andy Weir ( amazon link: http://www.amazon.com/The-Martian-Novel-Andy-Weir-ebook/dp/B... ). The book was a wild read, and does a tremendous job showing the myriad difficulties humanity must overcome in order to colonize Mars.
What this really means is that cargo deliveries to Mars can be made any time in the orbital cycle; it's not necessary to wait for a close approach. The trip takes a few months longer, but can be started at any time. Useful if there are ever any significant operations on Mars.
I was surprised that they described a Hohmann Transfer as a "brute force approach to attaining orbit." I would have described it as the non brute-force approach to changing orbits.
Yeah, exactly. It also seems like this low energy technique is more or less a Hohmann transfer to a different point in Mars's orbit. The energy is saved by not arriving at Mars with a big velocity relative to the planet, which feels kind of extraneous to the question of whether a Hohmann transfer is used or not. Maybe it's the final Hohmann transfer into orbit around Mars they are referring to? That would make sense. Or is that obvious?
Honestly I think they just got the terminology wrong. The only difference between this and a normal Hohmann is the means used to get the final change in velocity at the end. By which time the whole "transfer" part of the show is over. Otherwise it's just a normal transfer orbit.
I wrote my MSc thesis on weak capture trajectories and the concept of the Weak Stability Boundary [2] that was introduced by Ed Belbruno. It's a fantastic aspect of the gravitational 3-body problem and has been probed from a number of different perspectives over the last two decades, including tying in the phenomenon of weak/ballistic capture into our understanding of the structure of invariant manifolds and the periodic orbits about the Lagrange libration points.
Disclaimer: Francesco is my boss but I haven't spoken to him yet about the paper.
[1] http://arxiv.org/pdf/1410.8856v1.pdf
[2] http://en.wikipedia.org/wiki/Low-energy_transfer