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.
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.
[0] https://en.wikipedia.org/wiki/Low-Density_Supersonic_Deceler...
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.
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.
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.
Think heavy, shielded Apollo command modules versus the spidery lunar landers.
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"?
That's why a Dragon 2 can land on Mars, but not on the Moon.
Check out the Scott Manley video on Youtube for lots of details, https://www.youtube.com/watch?v=9zuFdVkVxpM.
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.”
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.
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.
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.
No one would be willing to fund anything that hasn't gone through at least one viability test on the closest short term analogous scale.
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.
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?"
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.
Say to me, "There's too much danger."
Say we could be lost,
And I reply, "I'm no stranger
To danger. That's the cost."
(Incidentally, this lovely song is a good answer to a lot of comments on this story.)
How many died conquering America? Exploring the poles? The Everest?
To this day people die in the Everest. It's their choice to risk their lives in such a way. Yet I don't hear people saying "don't go there".
Space is riskier, but also has more rewards.
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.
Here's a Wired article that talks about some of the issues - https://www.wired.com/2011/11/landing-on-mars/
[1] numbers vague guesses