I feel like all this talk about payloads is distracting from what a huge challenge the EDL is going to be, which is the primary objective in the first place.
Quote from: Khadgars on 09/23/2016 10:11 pm I feel like all this talk about payloads is distracting from what a huge challenge the EDL is going to be, which is the primary objective in the first place.True. The core is the supersonic retro propulsion attempt. It seems everyone of NASA's large scale Mars plans needs it, as does SX's. I wonder how many people realize just how low Mars atmospheric pressure is. It's about 1/160 of Earths at the surface but at 80000 ft it's down to 0.08% of Earth SL, which is about 1/3 at the same height in Earth's atmosphere. the next question of course is how much of that velocity can they cancel with thrust alone? Thinking about it I'm guessing they are leaving engine start to late in the entry and relying on a fairly conventional initial stage, with PICX taking most of the brunt.
Certainly. But that isn't a reason to rule out SpaceX trying to put on some payload on this initial mission. Water ISRU is a lynchpin of this whole architecture, is low TRL, and so trying it as soon as possible is likely a priority for SpaceX (after demonstrating EDL, of course).
Quote from: Robotbeat on 09/23/2016 04:59 pmCertainly. But that isn't a reason to rule out SpaceX trying to put on some payload on this initial mission. Water ISRU is a lynchpin of this whole architecture, is low TRL, and so trying it as soon as possible is likely a priority for SpaceX (after demonstrating EDL, of course).Except the usable-supply-of-water-on-Mars part, that is. This is still a non-trivial problem to solve. Of course, SpaceX might "cheat" and send a few liters of water to Mars along with a sub-scale Sabatier reactor to process some Martian CO2 (and not coincidentally suck all the battery life from the Red Dragon, and then some).
...I wonder how many people realize just how low Mars atmospheric pressure is. It's about 1/160 of Earths at the surface but at 80000 ft it's down to 0.08% of Earth SL, which is about 1/3 at the same height in Earth's atmosphere....
Quote from: Robotbeat on 09/23/2016 04:59 pmCertainly. But that isn't a reason to rule out SpaceX trying to put on some payload on this initial mission. Water ISRU is a lynchpin of this whole architecture, is low TRL, and so trying it as soon as possible is likely a priority for SpaceX (after demonstrating EDL, of course).Except the usable-supply-of-water-on-Mars part, that is. This is still a non-trivial problem to solve. ...
By the way, on Earth, it's very rare for any land to be below sea level, but about half of Mars is below "datum," and some parts of Mars (Hellas Basin) actually have about twice the pressure as datum... so I don't really think it's fair to pick "datum" as analogous to "sea level"... I think early landing sites and early habitation will be more like -5km, which has almost 60% higher pressure/density than datum.
Quote from: Herb Schaltegger on 09/24/2016 12:44 amQuote from: Robotbeat on 09/23/2016 04:59 pmCertainly. But that isn't a reason to rule out SpaceX trying to put on some payload on this initial mission. Water ISRU is a lynchpin of this whole architecture, is low TRL, and so trying it as soon as possible is likely a priority for SpaceX (after demonstrating EDL, of course).Except the usable-supply-of-water-on-Mars part, that is. This is still a non-trivial problem to solve. ...Water is, in fact, ubiquitous on Mars. It exists over the whole planet in the atmosphere and in the regolith. In levels high enough that, with enough work, you can get usable amounts of it. And this is exactly the sort of thing you'd want to demo as soon as possible.
Anything that does not derive water the same way a later full scale architecture would, is not worth any complexity. If they really want to do anything that involves water they can bring a liter or two from earth.
Quote from: guckyfan on 09/25/2016 09:38 amAnything that does not derive water the same way a later full scale architecture would, is not worth any complexity. If they really want to do anything that involves water they can bring a liter or two from earth.Yes. I said as much just a dozen posts back.http://forum.nasaspaceflight.com/index.php?topic=41231.msg1587869#msg1587869
Producing water from the air is similar to later methods (getting it from regolith or dirty ice) & is simple enough to put on an early mission.Heck, a small scoop that gets some regolith and extracts some water from it also would be even more similar. Not too different than some of the instruments on Viking or MSL, but simpler.
Not a stunt, a demonstration, a proof of concept. Make it work, measure results, feed back into planning for the next time. What would you prefer in its place? It's not useful to just say no to something, say what you would prefer to be done.
Not a stunt, a demonstration, a proof of concept. Make it work, measure results, feed back into planning for the next time.
What would you prefer in its place?
It's not useful to just say no to something ...