My reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?
Quote from: Coastal Ron on 10/06/2014 12:54 amMy reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?I envision for Commercial Capsule's some type of mission module that the capsule will dock to after launch similar to how the Apollo CSM docked to the LM after TLI. The mission module will be fairly light structurally since it isn't intended for re-entry. Could be even a Bigelow inflatable. The module will be discarded shortly before re-entry into Earth’s atmosphere.
Need to get over the 'discard after use' concept... is there any reason that an inflatable could not autonomously aero-break into a HEO and await reuse? The capsule could be separated and reenter while the aero-breaking of the mission module begins. We're not going anywhere if we cannot get past leaving debris trails along each mission's flight path.
I would think a careful look at cost would be in order. What would be the additional mass required to have a "mission module or inflatable" be able to aero-break in a HEO while coming back from a BEO manned mission considering the velocities involved. Not saying it is impossible but this needs to be looked at.
Sure, but that doesn't mean choosing direct return to Earth is an example of the Apollo paradigm.
I see the most promising path as commercial transport to a commercially operated LEO way station, followed by commercial transport to a waiting NASA MTV based at L1/L2 (using as many commercially available components as possible, such as Bigelow habs) which is supplied by commercially operated tankers at L1/L2, Sun Mars L1/L2 and Phobos / Deimos / LMO. Eventually, there could also be commercially operated way stations at L1/L2, Sun Mars L1/L2 and Phobos / Deimos / LMO.Aerobraking back to LEO is very difficult...
...propulsive return to LEO is expensive...
...while propulsive return to L1/L2 and direct return from L1/L2 to Earth are both cheap and straightforward. I don't see much benefit from changing to a separate LEO capsule for return, especially since the return capsule from L1/L2 can be a properly modified Dragon or CST-100.
Now doubt there is a lot that we still need to work out to implement a reusable transportation system. NASA has been wanting to invest in some of technologies we'll need, and some is being done in private industry, but it certainly needs more work.So in the near-term the cheaper solution will likely involve throwing away perfectly good hardware, and that is going to barrier to doing more in space because we are not able to lower the costs fast enough.To change this is going to require a change in mindset, and the willingness of Congress to allow NASA to help perfect a number of needed technologies. But based on the spending priorities Congress currently has I'm not sure when NASA will be able to help with this challenge, so that leaves it up to the private sector.
Today that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.
Ok, this is a bit off topic, but...Anybody know if anything has been done about using a generated magnetic field on a ship, interacting with Earth's magnetic field, to act as a sort of magnetic aerobraking system?If possible, it sure would save on the TPS materials on Crew Return Vehicles.
Quote from: Coastal Ron on 10/07/2014 08:08 pmToday that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.I think the only part that wouldn't be reusable would be the SM of the capsule. I suspect that could be made reusable later, and that aerobraking just a SM is easier than a whole capsule. But I wouldn't like it to be the first step, since I think it's too ambitious. As for a very ambitious long-term plan, I think NASA's OASIS architecture was very nice, except for the fact that it saw all in-space elements as traditional NASA projects, rather than commercial-crew-like competitive procurement of resupply services.
Quote from: pathfinder_01 on 10/07/2014 02:32 amIn terms of going to and from the region of the moon direct reentry to earth would probably be the best bet. It costs less in delta V and you get your vehicle back on the ground where it can be inspected and reused(in theory).To me that's like saying all Boeing aircraft would have to land in Everett WA to be inspected and refueled after every flight. It's hard to scale a transportation system like that.
In terms of going to and from the region of the moon direct reentry to earth would probably be the best bet. It costs less in delta V and you get your vehicle back on the ground where it can be inspected and reused(in theory).
Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).
Quote from: Coastal Ron on 10/07/2014 08:08 pmDragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).What is type of engine is providing the Delta-V change for entering/exiting EML1/2?
Quote from: RobotbeatNotCoastalRonMakeSureToEditProperlyPleaseDragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).What is type of engine is providing the Delta-V change for entering/exiting EML1/2?
Quote from: JasonAW3 on 10/07/2014 08:57 pmOk, this is a bit off topic, but...Anybody know if anything has been done about using a generated magnetic field on a ship, interacting with Earth's magnetic field, to act as a sort of magnetic aerobraking system?If possible, it sure would save on the TPS materials on Crew Return Vehicles.Jon Goff has talked about possible solutions that involve magnetic fields. I should PM him about this.He also wrote an article about the subject back in 2010 on his website:MHD Aerobraking and Thermal Protection Part III: Aerobraking and Aerocapturehttp://selenianboondocks.com/2010/02/mhd-aerobraking-and-thermal-protection-part-iii-aerobraking-and-aerocapture/
First, not Ron, Jason.Second, I didn't entirely make myself clear, so let my clarify.As I understand it, it is possible to create a Magnetic Sail that would allow a craft to lift itself out of Earth orbit, via the planet's magnetic field. (I read one article that suggested it may be possible to launch from teh Earth's surface with a Magnetic sail, but I think thats a bit far fetched). What I was suggestion was, as a craft is returing to Earth, use a magnetic sail as a sort of "deep space parachute" to bleed off eneough velocity of the entire craft, (Mars mission craft, habitats, engines, etc.) so that the entire craft can make orbit around the Earth and teh ERV Capsule would only have to resist the reentry from LEO rather fronm a high velocity BEO return. Obviously, using susch a system to achieve Mars orbit would be impossible, due to teh practically complete absense of a Martian magnetic field, therefor aero braking becomes a necessity. It also occures to me that a craft using a nuclear rocket is likely to also be suing some sort of Magnetic shielding to protect teh crew from solar and nuclear radiation. If so, it may be possible to use this shield as a Magnetic sail to give the craft an additional boost via Earth's Magnetic field.
Electrodynamic tethers (EDTs) are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy.[1] Electric potential is generated across a conductive tether by its motion through a planet's magnetic field.