So, a Hohmann orbit is simply an elongated earth orbit which puts the satellite in Mars path, correct?
I was watching Understanding Space Travel, from the Discovery Channel, and it has Wayne Lee, the mission planner for Mars operations at NASA’s Jet Propulsion Laboratory, describing a different trajectory in which the spacecraft is put into an orbit around the sun which intercepts Mars. (Gif animation)
Is there a name for such a trajectory and which is better for getting to Mars?
The most probable state of the art solution is to send seven or eight missions, the first few unmanned, and use them to establish remote replenishment stations in orbit around mars, and finally around earth.
You get to test run the system each time to be sure that you are going to be able to thread the needle at each step of the final trip. First, you establish the Mars Mission return cash of non perishables, fuel, electronic replacements, reaction mass. You practice docking with it without ground control assistance several times, in lunar orbit.
Then you send out the Mars Lander, unmanned, and orbit it around Mars. It has docking ability and several modules available for its landing, and Mars take off missions. You probably also send a second unmanned Lander to establish that your landing site is useful, and load that up with resupply stuff, for the layover period of the mission.
Now you launch your Mars outbound resupply module, with enough rockets, and fuel to make the Hohmann Transfer orbital change burn for your final vehicle. With everything in place, you send the perishable supplies for outbound, land, return segments to their appropriate location, and verify that everything is in place. Then, your actual trip begins, first to the outbound resupply module, then to the Mars Lander module, then to the surface, then assemble your shelter. Then you have layover. During this time, you will have some ability to do real science. Then it’s time to start packing up, and transmitting your data. (Mars Rocks are going to be grains of sand, and smaller, with the cost of energy.)
Now comes Mars liftoff, dock with the return resupply module, and head back to Earth, while launching the Earth Landing module, back home. Dock with the landing module; jettison the cargo with ablative survival type low fuel Landers. Transfer to the Shuttle, or current equivalent. Come home to a tickertape parade.
The overwhelming barrier to this sort of solution is that it requires a continuous dedication to eight very expensive space missions, covering three or more election cycles, and almost no increase in benefit to what one would expect of eight non manned missions to three or four other targets.
I ain’t seein’ it happen.
Tris
You mean, like the Apollo program?
Yep. And if we can convince the Russians to try it, with a weapons capable platform, it’s a done deal.
Like I said, state of the art.
Tris
Well, I was thinking more along the lines of some sort of mechanical hiccup or crew issue that slows things down for a bit.
After a certain point–leaving Earth orbit–the ship will be in a ballistic trajectory–they’ll fire their engines at the start, and then coast the rest of the way, until it’s time to fire up the engine again to decelerate and enter Mars orbit. There can’t be a delay any more than a falling rock can be delayed.
Now, there may be points along the way when minor engine burns are needed to correct and fine-tune the course. If all the crew die of the Space Plague–well, mission control could transmit the orders to the ship by remote control, for all the good it will do. If the crew are all killed by the ship’s computer, which has gone homicidally psychotic, and which then erases itself in a fit of remorse, shutting down all the ship’s flight control systems, then I suppose at the end the ship will just sail right on past Mars and go on orbiting the Sun, or else it will plow into the planet at a high rate of speed.
Fire up the engine again to accelerate and enter Mars orbit actually. The Hohmann transfer orbit is an ellipse around the Sun (see Saltire’s link in post #2 ) that touchs the orbits of Earth and Mars. If they do nothing when they reach the orbit of Mars the craft will continue on its orbit, falling back down towards the orbit of the Earth. To stay out in Mars orbit you have to accelerate to make your ellipse into a circle. (Actually it’s not quite that simple - you can make use of Mars’ gravity to help you get into an orbit arounfd the planet.)
If you want to know more try some of Heinlein’s juveniles from the '50s, particularly Space Family Stone (The Rolling Stones in the US).
With current technology, can we build a Mars lander that could actually launch back into space for the return trip? I don’t think we can.
We can make vehicles capable of launching from Earth - with much denser atmosphere and twice the gravity. Not easy engineering task, but not impossible. Remember - you only have to get back couple of guys and handful of samples into orbit, not the whole interplanetary ship.
I just feel strangely compelled to point out that growing food, even for a three year mission, is not necessary from a nutrition standpoint. Even without using canned food technology, packing a vessel with multiple years worth of food was routine for various 18th century navies (it took them a bit to figure out the vitamin C thing, but they got it down eventually).
Now, it might make sense to use plants to capture solar energy to recover oxygen from CO2, but then again it might be more reliable to use solar panels and some electrically driven non-biological reaction.
Yeah, but three years worth of beans is really heavy. And a spaceship big enough to carry them is also heavy. This would mean a bigger ship to be launched from Earth, and more fuel. I think this is a main part of the motivation for suggesting raising food enroute.
A truckload of Tang and Space-Food sticks should do it.
Can we? What sort of vehicles are those? If we have such vehicles, why do we need massive booster rockets for the Space Shuttle?
I’m pretty sure that’s the coolest thing I have ever read.
Because Space Shuttle is BIG. To reach orbit from the ground just modified SM-3 missile is enough (vide recent satelitte interception story). Of course couple of astronauts are a little heavier, but probably something akin to train car-sized ballistic missile would be more than enough.
Some of the links weren’t clear that the Hohmann transfer orbit was around the sun, but I see now that it is, at least for the purpose of going to Mars. So disregard my earlier post. Or, alternately, see my earlier post for an animation of a Hohmann transfer orbit.
Well, the OP did make it very clear that they knew very little about space travel. I think asking about delays is not a ridiculous question under the circumstances.
The launch of a rocket booster–even a small, suborbital one, much less a “train car-sized ballistic missile”–is actively supported by dozens of people who integrate, inspect, and test the vehicle at every stage before it is emplaced and ready to launch. To do the same from a remote site would require assembling a orbit-to-ground-to-orbit vehicle on the ground at Earth, transporting it into orbit in toto (or at least in pieces easily capable of being integrated by a handful of astronauts in freefall), rendezvousing with the spacecraft, surviving 8.5 months in transit, landing it, and being confident in its reliability after another 15 months on the ground, and then living the ground crew and whatever samples or equipment need to be recovered.
This is not an infeasible task–we did it on the Apollo program with primitive avionic technology–but it is far from a trivial exercise, especially with the length of the layover and much higher surface gravity of Mars, well beyond present demonstrated capability. Think of something like the DC-X, scaled up but with the added requirement of being functional after two years of non-service. Peter Morris is right; currently we do not have the basis to build a returnable landing module for Mars; just getting a few pounds of samples returned to Earth is a capability-stretching exercise; sending living people, putting them down on the planet, bringing them back up and then home with any reasonable expectation of success is outside of our experience at this point.
As for the Hohmann transfer, it is essentially an arc of a unpowered ballistic elliptical orbit around the Sun which starts at the position and tangent vector of the originating body at its orbital speed (plus a little nudge to achieve escape from its sphere of influence and get the right eccentricity for the desired trajectory) and terminates at the position and tangent vector of the target planet so that it is captured in the sphere in influence of that body. Because the only thrust required is that necessary to achieve escape velocity (and usually a little nudge at the other end to assure capture and circularize the orbit) it is a “minimum energy” orbit that requires the least amount of propellant. You can get there faster, of course, by expending more propellant and using the thrust to advance the orbit (in orbital mechanics terms, an impulse maneuver or “delta-v”), but it takes a surprising amount of energy to do accomplish even a modest reduction in transit time, and until constant thrust propulsion of sufficient magnitude to influence a really large craft is available, it just isn’t feasible to do this.
I recommend Prussing’s Orbital Mechanics, chapters 6 & 7, for a clear mathematical treatment of the issue of ballistic transfers between two celestial bodies.
Stranger
A neat idea if we were serious about establishing a long-term presence on Mars (manned missions every two years for an indefinite period), but unfortunately it suffers from the “mega-giant economy size” drawback common to many space proposals: it doesn’t make one trip to Mars cheaper, it makes twenty trips only 3-4 times as expensive as one trip. Except right now we can’t even afford the one trip. I sometimes dispair that we won’t go to Mars until someone comes up with a way to build a spaceship out of discarded packing crates and used fry grease :rolleyes:
No, on second thought if you could build such a spaceship, NASA would reject it because it wouldn’t be expensive enough. :rolleyes: :rolleyes:
Tell me more, please. I know nothing about this SM-3 of which you speak. I looked it up on Wikipedia, and if I understand right, it requires VLS to launch it. It isn’t self contained, is is? Or maybe I’m misunderstanding.
A Mars lander would need to be entirely self contained, capable of getting back into space without either a specialised launch pad, or a crane to lift it into position. Does the SM-3 fit that description?
