{snip}IMHO going any further than that would become completely impracticable. You'd have to start splitting the vehicle up into chunks, and require the crew to link these together 'in the field'. Nobody builds rockets that way on Earth, why presume it would work on Mars?
Also, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.
Quote from: savuporo on 08/25/2009 08:42 pmAlso, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.Take a look at the MER data for why solar cells on Mars are less than ideal. Although the rover arrays could produce over 900W peak under ideal conditions the rovers got stranded for up to 5 months at a time waiting on enough power to move. Dust accumulation on the panels is only part of the problem, the planet wide dust storms which can last several months can reduce the opacity of the atmosphere down to 1%. Even under ideal conditions you only get about 25% of the power per day due to the day/night cycle, atmospheric absorbption, and sun angle.I would be much more comfortable with an RTG augmented with some batteriers.
I was making a simple point, if you need your landed 1 mt chunks to make rendezvous with prelanded hab/base/gear in the landing ellipse, you can do it with precharged battery-powered mobile equipment.
Quote from: savuporo on 08/26/2009 06:58 amI was making a simple point, if you need your landed 1 mt chunks to make rendezvous with prelanded hab/base/gear in the landing ellipse, you can do it with precharged battery-powered mobile equipment.It's a very risky approach to land people in a rover (let's say a 3mt rover with one crew and charged batteries), if your batteries run out in a couple of hours and you need to get to your base to recharge the rover. What, if your rover after landing is stuck and you need to do an EVA to free it? What if you encounter a problem while on route to the base? Of course in that case the astronaut could try to reach the base on foot. But is that really acceptable from a safety point of view?
We should be realistic here. There is no way a Mars mission would send each crewmember to Mars separately on a separate pressurized rover only to fulfill some ridiculous "small chunk to surface" requirement.
Yes we should be realistic, and live within our means. If we have capability to launch 20mt chunks to orbit, then lets use it to build the exploration program. If we have capability to land only 1mt at a time on mars with technology at hand, then design with that.
Its entirely plausible that the first people to land on mars will not be paid by public, but by private money, and the risks that such crew would be willing to take would be entirely different from your line of thinking.
Quote from: Kaputnik on 08/25/2009 10:04 pm{snip}IMHO going any further than that would become completely impracticable. You'd have to start splitting the vehicle up into chunks, and require the crew to link these together 'in the field'. Nobody builds rockets that way on Earth, why presume it would work on Mars?Simple, we do not know any other way of getting the mass of the ascent stage down to 2500 kg.
Another alternative: in the australian ASTRONOMY Magazine there was a story that said that Braun & co say that with an inflatable supersonic decelerator replacing the parachute that landing masses of 15 tonnes would be practical. (20 tonnes at entry interface)
Also, current UltraFlex solar arrays on Mars are at 105w/Kg, likely more in short future ( i dont know about MSL spec ), a dedicated solar array/charging point rover would likely be able to pack at least half of its weight of unfoldable arrays.Again, i dont see why 1 ton landed is not enough for anything ?
One way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested. Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.
Quote from: DLR on 09/01/2009 06:17 amOne way to get around shroud volume issues would be to use an expandable aerodynamic decelerator, like the inflatable heatshield NASA just recently tested. Imagine a circular heatshield launched on a rocket with a 10m fairing expanding to 25m ... such a thing could conceivably bring down cargo in the range from 50t to 60t, just what you need for Semi-Direct missions.NASA will likely re-qualify their Viking parachutes for a wider flight envelope (larger diameter and deployment at higher Mach numbers) before researching and developing an almost entirely new technology (even though inflatable heat shields are hugely promising for both planetary and Earth applications). Since it is likely that by using these improved parachutes they'll be able to land >30t on Mars, inflatable heat shields will probably have to wait.
Whatever works is good enough. We don't need to go "exotic" just for the sake of doing it. If conventional, proven technology works, then we should use it. However, absent technology development of a folding technique (or inflatable heat shield add-ons) for Viking-shaped heatshields and parachute technique, we ain't going to see >30mt to the Martian surface.
I believe that a 10m PLF will be needed in order to contain the lander plus a simply enormous inflatable heatshield -- something in the order of 30-50m diameter.