Landing on the moon to "test" the Mars landing makes almost no sense. The a moon is just to different, landing on mars can be trained much better on Earth or on Mars itself.
The simuliertes are not enough to make it sensible if you don't have another reason to land on the moon too.
There's gravity and a rock. Ignoring all the differences these still two extremely hard things to solve first before you start thinking of anything else.
The Earth has a full atmosphere with winds, an expansive array of magnetic and electric fields, and a much much higher gravitational pull then Mars or the moon. About a factor of 10 removed from mars and about a further factor of 10 removed from the moon.
You'd obviously need more fuel, and fuel that can burn in a completely different atmosphere then it's intended to run in. It's an invalid test for the kind of useful metrics that would be obtainable in a "pure" vacume out in space.
Rockets carry oxidizer along with fuel, so the composition of the local atmosphere doesn't really figure. Also, your factors are way off; Martian gravity is a bit shy of 0.4g, and lunar gravity a bit proud of 0.1.
Finally, we don't need to land on the moon, or Earth, or anywhere else, to validate a method of landing on Mars, because we already know how to land on all of those things. We've done it plenty of times before, in all cases; the difference between doing it manned and doing it unmanned is purely one of mass.
We've only landed light things on mars, curiosity is the heaviest at 889kg, and the methods used don't scale easily.
Anything that can sustain humans for an extended period of time is going to weigh a lot more. EDL (Entry descent and landing) is a solvable problem, but it's not a solved one. You can find lots of recent work on it by googling that term.
Not to disagree that we can test on Earth better than the moon. Mars has a light atmosphere, but it doesn't have no atmosphere.
I wonder if there's an altitude you could do a "landing" at that would be thin enough atmosphere and weak enough gravity to get close to Martian conditions.
NASA does indeed use high-altitudes on earth to test Mars aerobraking, atmospheric entry, and supersonic parachute deployment[0]. For the actual terminal descent and landing speeds are low enough the atmosphere is not significant, you can just test that at sea level.
Gravity will still be too high, gravity at the ISS is 0.89 times gravity on the ground and you obviously need to be lower than that. But it's definitely the closest we can get to a large scale martian atmosphere.
You're wrong about the gravity. The escape velocity of Mars is 5 km/s, half of Earth's and twice the Moon's. The surface gravity is also .4G which is about half the Earth's and two and a half times the Moons. So they're all a lot closer together than you said.
The Moon has no atmosphere to use to shed speed. Very different animal than a Mars landing, to the point where it'd need a totally different landing vehicle than Mars.
Think heavy, shielded Apollo command modules versus the spidery lunar landers.
There's about .7kPa of atmos on mars. I'd have a hard time seeing how that would meaningfully influence escape or entrance velocity. In fact it should make entry easier because you'll have a higher resistance coming in meaning you'll have to do a lower deceleration burn.
Could you provide a source, of someone with experiance in this sort of work, telling me why this is the case? Why does this completely change the game? Why is a moon landing not the eaisiest "we know basically what we're doing"?
Money quote: “There’s too much atmosphere on Mars to land heavy vehicles like we do on the moon, using propulsive technology completely,” said Manning, “and there’s too little atmosphere to land like we do on Earth. So, it’s in this ugly, grey zone.”
I believe that comment is more or less based on the shuttle landing and/or the soyuz capsules (eg parachutes) - but as far as I can tell, SpaceX is the only one currently capable (and using) propulsive landing on earth - so essentially they've already leapfrogged the grey zone to a large extent.
Makes me wonder whether testing a propulsive landing on an airborne drone barge is feasible? A blimp with a well-insulated large pad on the top - though I'm not sure how you'd effectively anchor it in the air - probably a active propulsion system as well.
You can bounce on the atmo and by passing threw it multible times you can bleed away speed. Then you can fly your capsule like a wing for a bit losing even more speed.
That's why a Dragon 2 can land on Mars, but not on the Moon.
Sure, if you ignore all the other problems. Why not fly to the Venus and test there? Why not on Saturn? The reason is simple, the cost of doing so outweighs the benefits of doing so.
Look, its simply almost as expensive to make such a test on the moon, as it is on mars. If mars is your goal, then testing on the moon makes absolutely no sense.
People seem to believe that because the moon is closer, it means its much easier there. The reality is that the deltaV is not that different, plus mars gives nice tools to actually land, like an atmosphere.
> plus mars gives nice tools to actually land, like an atmosphere.
Actually Mars is a pretty difficult place to land. The atmosphere is just thick enough to require heavy heat shields, but too thin for parachutes to be sufficient.
Still, you can get rid of most of the velocity for a Mars landing using aerobraking alone. To land on the Moon you'll be bringing all of that delta-V with you as fuel. Landing a Dragon on Mars already takes a lot of propellant: https://youtu.be/ZoSKHzziLKw
Even if Mars's atmosphere only kills 90% of your orbital velocity instead of the 99% you'd get on Earth[1] you're still saving a humongous amount of fuel, far more than the mass of the heat shield you have to carry along. If you're designing a new heat shield for each mission then the added complexity might make that not worth while but SpaceX is reusing the same heat shield design they've been testing on Earth so that isn't a concern.
OTOH, if you are "rapidly" (insofar as that is possible in space technology) iterating on some aspect of the system that is relatively insensitive to the differences between the Moon and Mars, the Moon being closer shortens your cycle time considerably. Delta-V isn't the only cost you might be concerned with.
True, but nobody has the money to develop something that needs multible moon test mission before it ever gets used productively.
Also, SpaceX has actually thought about the problem quite a bit and until somebody payed them they clearly said they are not going to do anything moon related.
They clearly did the same calculations. Moon is only worth it, if you actually want to go to the moon.
You can repeat that as often as you want, that does not make it true.
SpaceX clearly did not think that for their mars architecture needed a moon testing step. Mars concepts such as Mars Direct did not include such a step.
Unless you have extreme time pressure its much, much, much preferable to test on Earth and Mars, rather then the Moon. Earth because it's by far the cheapest, and it shares a reasonable amount with Mars, and Mars because that's where you want to go anyway.
The only advantage that the moon has is that it is closer than mars in pure distance. That advantage is eradicated when you consider the much more important DeltaV.
No. The Moon is in orbit around the Earth and both the Earth and Mars are in orbit around the sun. The Moon varies between 360,000 and 400,000 km away and the closest Mars gets to us is 54,600,000 kilometers. Those numbers are a bit of an exaggeration because how much fuel you need is just as important as absolute distance/time to travel and for that you need 4 km/s of delta-v to get from Earth orbit to Moon orbit and 5.7 km/s to get to Mars orbit.
I meant that the Earth is closer to Mars than the Moon is, not that Mars is closer to Earth than the Moon is (of course it isn't, that would make for a big, big blood moon)
Exactly and that's not mentioning the benifit of being able to easily recover a failed prototype or even just analysis of a failed prototype.
Imagine trying to diagnose a problem that comes up 10 months into the program after the probe is no longer in a direct visual path or while communications via microwaves start taking 10-20 seconds from point to point.
There are too many questions to be answered before we can just say "you know while we're at it lets just risk the lives of 10-20 people, who cares right?"
On the other hand, 10-20 people in a bus out of control on a mountainside can get in the news, even if it ends in tragedy. But we don't color our whole view of auto travel because of it. We don't make policy or even many business decisions because of it.
Space travel can be dangerous. We will likely lose some crews. Rescue will always be too far away to matter. But I think folks will do it anyway.
The simuliertes are not enough to make it sensible if you don't have another reason to land on the moon too.