I'm not sure if I should be mentioning this or not, but some recent discussions we were involved in with representatives from ESA have created a very interesting notion: ESA wants to extend the lifespan of ISS beyond the current 2016 "sell by date". They want to build their own Upgrade Module which would allow them to do so. Only snag is that they really need an HLLV to lift such a heavy module.
One area that, AFAIK, is mission critical but gets surprisingly little public recognition is the matter of radiation shielding. Once the vehicle is outside the Earth's magnetosphere, it will be flying through the solar wind (basically high-energy alpha- beta- and gamma-radiation) as well as some of the more exotic creatures in the form of cosmic rays, which might be travelling at near-c.
We want a system whereby the International partners can realistically contribute, and where domestically the Atlas, Delta, Falcon, Taurus and whoever else develops the capabilities are all be able to provide significant quantities of supplies and/or crew to the station. And that means staging in LEO.
Quote from: kraisee on 02/02/2009 04:19 pmWe want a system whereby the International partners can realistically contribute, and where domestically the Atlas, Delta, Falcon, Taurus and whoever else develops the capabilities are all be able to provide significant quantities of supplies and/or crew to the station. And that means staging in LEO.Yes, in the short/medium term. But before you're ready to do a LLO precursor mission, many years from now, it might be a consideration.
One area that, AFAIK, is mission critical but gets surprisingly little public recognition is the matter of radiation shielding. Once the vehicle is outside the Earth's magnetosphere, it will be flying through the solar wind (basically high-energy alpha- beta- and gamma-radiation) as well as some of the more exotic creatures in the form of cosmic rays, which might be travelling at near-c. There has to be a reasonable attempt to mitigate the total dosage that the crew experiences during the mission (I've seen estimates as high as 900 days as a Mars flight duration - remember that Mars has no magnetic field, so astronauts on the surface would still need protection from solar flares). I've seen that some work has been done on active electromagnetic sheaths for protecting manned spacecraft, but I bet that they are power-hungry. What is the current state-of-the art for passive (structural) shielding?Attention would also need to be given to designing a 'storm shelter' in the crew vehicle to increase survival probability against a solar flare. I've read that an armoured 'box' of lead, gold foil and a water-filled cavity might do the job. It also occurs to me that the spacecraft might be within the radiation stream for several days, so the shelter would need basic life-support such as liquid water, atmospheric recycling and basic waste management.Additionally, the shelter would need duplicate flight controls. We cannot presume that the flare would happen during interplanetary coast or a parking orbit, so it must be possible to execute burns and other manoeuvres from within the shelter.
I think there's a potential for an HEO/GEO station for something like routine transfer between Mars and Earth, but it seems to add an extra layer of complexity for the Lunar phase and I just don't see how that actually pays off.
Without doubt though, I am already convinced that there is a strong case to be made for a staging area at EML-2 at some point in the future. There are lots of clear and unique advantages to be had from there.
From what I have read, a layer of polythene makes a better barrier than lead, because it converts the radiation into less harmful products. In fact, anything with lots of hydrogen in it is apparently good- hence water shielding. I have also read that NASA reccomend a barrier density equal to about a ten centimetre layer of water (sorry, I cannot find the source for this).
Ben, We have been investigating the options which a Methane propulsion system would create. Obviously, its a great technology to have for returning from a Mars mission where the Methane can be extracted from the Martian atmosphere via fairly straight-forward ISRU technologies. But we've been looking at what effect it would have if we applied it to the Lunar architecture first, as a testbed. The numbers indicate that an LSAM Descent Stage the same physical size as the current one, but powered by LOX/CH4 instead of LOX/LH2, would offer significantly greater payload mass to the Lunar surface. It's a potentially massive upgrade to the system if we were to implement it. We could potentially start delivering useful payload modules to the Lunar surface massing over 35mT -- even more if we could fill the LSAM's LOX tanks at an LEO Depot too.{snip}
Why just use the jupiter rocket as a way of getting out of Earth orbit? The size and weight of the payloads it can carry mean there are new possibilities inside the Van Allan belts as well as outside of them.
The numbers indicate that an LSAM Descent Stage the same physical size as the current one, but powered by LOX/CH4 instead of LOX/LH2, would offer significantly greater payload mass to the Lunar surface.
Quote from: kraisee on 02/02/2009 03:10 am The numbers indicate that an LSAM Descent Stage the same physical size as the current one, but powered by LOX/CH4 instead of LOX/LH2, would offer significantly greater payload mass to the Lunar surface.Can you say more about this? Is it because you have less boil-off / need less insulation with methane?
He said physical size, not mass. CH4 is considerably denser than LH2, more than enough to offset its lower isp. The lander would end up heavier, and higher performance, but be the same size.
Quote from: Kaputnik on 02/25/2009 12:59 pmHe said physical size, not mass. CH4 is considerably denser than LH2, more than enough to offset its lower isp. The lander would end up heavier, and higher performance, but be the same size.Ah, I see. In what way would that be an improvement though? I thought launch mass capacity was currently the limiting factor, not volume.
If 6 month missions are performed on the Moon and Mars the mass of the zero boil off hardware or the extra hydrogen or both has to be allowed for. LOX/LH2 engines are not as good as they look.