A bit of thought exercise got these questions brewing in my head.
Say man finally gets ready for his first trip to another planet (let’s pick Mars, since it’s the Planet of the Hour). I think I’ve read that a trip to Mars would take about 9 months.
How does the flight path look? Do you aim for the spot where Mars should be in 9 months and make course corrections along the way if there are delays? Choose a flight path that keeps Mars in sight?
I know almost nothing about the practicalities of space travel, which will probably be evident in my next question. I’m assuming that space navigation involves some sort of orienteering based on known positions of things in relation to others at a given point in time. If that’s accurate, what would happen if the crew of a spacecraft lost consciousness for an undetermined amount of time, and was unable to contact anyone back on Earth to find out what day/time it is, and further was unable to even see Earth itself. Would that affect their ability to navigate?
And finally - do we currently have the technology to send someone to another planet?
A Hohman orbit is how it would probably be done. You aren’t ‘aiming’ directly at the rendezvous, you do everything on curves.
Navigation is mostly done with stars, not planets. They’re going to be there, so no, a ship out of sight and contact with Earth won’t find itself lost. There should be several accurate timepieces on board, but I think they could even reset their time without Earth’s help.
I think we do have the tech, but it needs some refinement. That will take testing, which means we couldn’t leave tomorrow from the current state of things.
Well, the Phoenix probe was entirely automated, as far as I can tell. In fact NASA even knew 9 months ago exactly what day it would land on Mars: May 25. It takes 15 seconds communication each way, so remotely steering it to the surface wasn’t an option.
I’m not sure how the guidance systems work, but I assume a human probe would be automated also, with the option of human intervention if required.
There’s a whole lot of logistics issues surrounding food and water that would have to be overcome before we could send humans. With 18 months travel time and a few months on mars we’re talking a lot of food. We would almost certainly have to rely on melting Mars’ ice for water while there, and growing food of some sort.
Given the orbit of Mars, you’re not aiming at the planet itself, but rather where it will be in 9 months. So you’re not keeping it in sight, you’re not even catching up to it, since it’s orbital speed is faster than the spacecraft. You’re moving out to where it will be and letting it catch up to you.
If you lost contact or consciousness, unless you also lose every computer system (in which case you’re completely fucked), you’re not going to lose track of your course or what day and time it is. Even if everything reset, a proper astronaut should be able to figure out where Earth was and point the antenae that direction to regain signal - ANY signal.
The only case I could imagine where you’d never regain contact with Earth was one where the Earth simply did not exist anymore. Say a previously unseen asteroid came through and turned Earth into an orbiting smoke ring. Then it doesn’t matter what Earth Date/Time it is anymore, and you may as well concentrate on your new (short) life on Mars.
I don’t think there’s any need for steering as such. Mars is a clearly visible destination and its movement is precisely mapped. And you don’t run into many obstacles in outer space. If it takes you nine months to travel to Mars at the speed your vessel moves, you just aim for where Mars wll be in nine months and launch. Nine months later you and Mars will arrive at the target location at the same time.
No obstacles, but as post 2 notes you don’t move in a straight line, since the Sun’s gravity and the relative velocities of the Earth and Mars must both be taken into account.
I don’t know how precise things are today, but during Apollo there were several scheduled burns during the flight to make necessary, minor, course corrections. Even the smallest deviation from the desired course can get you very far away. Anyhow, the tricky part isn’t getting there, it is getting there expending minimum energy.
We could very easily send a human being to any planet in our solar system, and probably to many extrasolar planets, as long as it doesn’t matter particularly whether he’s alive when he gets there.
I guess for the purposes of this conversation, we can assume that getting him there and back alive and in one piece are the key priorities. I’m also thinking more from a technical standpoint than a logistical one; what if we got a Breatharian who didn’t need sustenance aside from breathable air?
I’m guessing that a shuttle like Discovery wouldn’t be capable of making the trip?
Thanks for all the answers so far; very satisfying to my inner 5 year old that wants to be an astronaut when she grows up.
The two biggest problems with sending people to Mars are both human-biology related. The first is loss of fitness due to zero gravity. Going by cosmonauts who spent long periods aboard the Mir complex, you wouldn’t be fit to do anything strenuous after nine months of zero g. This means some sort of centrifugal conditioning every day will be necessary; if rotational gravity has to be provided for the whole crew quarters throughout the trip, it will add a layer of cost and complexity to the ship design. The second problem is radiation exposure. Long term exposure to cosmic rays is bad enough, and getting caught by a solar flare would be worse. There doesn’t seem to any practical way of providing fully adequate shielding; the current focus is on finding medicine-based ways to cope with increased radiation exposure.
Ah, yes, that was a fun thread. But the “once you pass a certain point” there is inconceivably further away than anything in our Solar System. In-system, you can very easily navigate as precisely as you’d like: The apparent size or brightness of the Sun will tell you how far away you are from it, and where it appears in the sky will tell you what direction you are from the Sun. If you know the date and time, the current positions of the planets are easily calculable, and you’ll be able to find at least some of them by eye (which could in turn tell you the date and time, if you somehow managed to lose track of that).
There are planned TCM (trajectory correction maneuver) events scheduled into the cruise phase of spacecraft. Sometimes they are used to tweak the landing ellipse (say if the project scientists and engineers want to aim for a slightly different spot). Sometimes the initial trajectory of the spacecraft is calculated to miss the target slightly- this is so that the final stage of the launch vehicle itself isn’t also carried straight to the target. So after separation, the spacecraft would get the TCM while the last stage of the launch vehicle would continue on in the original trajectory, missing the planet.
I don’t keep up on this myself, I guess. It sounds like there aren’t any excercise machines that will work as well as gravity - right? I suppose I could understand that - there are just too many connector thingies inside of us that need to be stressed a little to keep them fit - right?
It isn’t just a matter of exercise–in fact, there are specialized exercise machines to help prevent muscle atrophy in freefall–but the fact that in the absence of acceleration the heart muscles atrophy, the skeletal system begins to decalcify, and other health issues arise. Our bodies are evolved to function in a 1G environment, and don’t cope so well under null acceleration. A transportation system that could simulate gravity via centrifugal rotation would be adequte for this task, but even this seemingly modest technology has yet to be demonstrated on a human scale in space, and the gyroscopic effects can add suprising complexity to the propulsion dynamics of the spacecraft.
To address the questions of the o.p., it takes about 8.5 months each way in a low energy Hohmann orbit to reach Mars; however, once you are there, you have to wait over a year (actually about 15 months) in order for Mars to be in the right position to return to Earth on the same Hohmann-style transfer orbit. So it’s not just 17 months of support and supplies; it is 32 months, or over two and a half years. So far, no one has demonstrated anything close to 32 months of self-sufficiency in a space-based platform, so based on current propulsion technology, no, it isn’t feasible to perform manned interplanetary missions. (Using something like nuclear pulse or radioisotope-salt propulsion could raise the efficacy of high thrust propulsion by over an order of magnitude, but nobody seems excited about sending nuclear propellants into orbit.) The issue of protection against solar radiation outside the Earth’s protective magnetosphere (which Mars would not provide, having essentially no magnetic field itself) is also a substantial, although not irresolvable, issue.
The actual navigation (or more properly, astrogation) is comparatively trivial, especially when contrasting to navigation through Cambridge (either the English or Massechusettes version). Heck, we’ve managed to navigate probes out beyond Neptune to within a few kilometers using a cupful of propellant to adjust course, and this is essentially based on orbital mechanics, angle rate measurements of the probe’s signal, and a little bit of perturbation theory. As long as you don’t ufck up and mix the units, getting to Mars is no big trick, though by no means foolproof.
What sort of delays are you anticipating? Stopping to pick up hitchhikers? Stopping to ask for directions (only if the astronauts are female)? Or is Mars hesitating along its orbit?
15 minutes, actually. (Although that varies considerably, since at different points in their orbits the two planets are as little as 35 million or as much as 250 million miles apart.)
For starters, you can’t get directly to Mars from here. You have to take the 113 to the Sea of Tranquility, connect up to the 188 Outbound to Phobos, and then wait for the connecting train: either the 18 or the 18A will get you there.
Of course, you could go directly to Mars on the 214, but that’s a Sundays-only route, and it connects through Phobos and Deimos.