The cold gas ISP is 50 meters/second.
{snip}I wonder, though, how hard it would be to make a propellant which is entirely inert and unpressurized, and can be spilled in a habitable area without causing harm, along with a system which, once you get it out of the habitable area and connected to a power supply, converts it into an effective propellant, in a process which needs to be actively powered and can't happen spontaneously no matter which substances are accidentally mixed. For something like this, it would need to happen fast, since they want to do same-day Earth return. Maybe they could sublimate or irreversably decompose something in an insulated pressure vessel, using a simple electric heating element or heated catalyst bed.{snip}
Modern version of the film bucket?
I wonder, though, how hard it would be to make a propellant which is entirely inert and unpressurized, and can be spilled in a habitable area without causing harm, along with a system which, once you get it out of the habitable area and connected to a power supply, converts it into an effective propellant, in a process which needs to be actively powered and can't happen spontaneously no matter which substances are accidentally mixed. For something like this, it would need to happen fast, since they want to do same-day Earth return. Maybe they could sublimate or irreversably decompose something in an insulated pressure vessel, using a simple electric heating element or heated catalyst bed.
"The TRV is designed to be stored in the habitable volume of the ISS and deployed on demand from the Japanese Experiment Module (JEM) airlock"So it will be stored in the pressurised volume until it's needed? For weeks or monthes?The real thing should be sent disassembled and stackable (IKEA style) and shipped in the dragons trunk. Otherwise it will be a huge waste of CRS volume.
Quote from: Nindalf on 10/19/2014 04:36 pmI wonder, though, how hard it would be to make a propellant which is entirely inert and unpressurized, and can be spilled in a habitable area without causing harm, along with a system which, once you get it out of the habitable area and connected to a power supply, converts it into an effective propellant, in a process which needs to be actively powered and can't happen spontaneously no matter which substances are accidentally mixed. For something like this, it would need to happen fast, since they want to do same-day Earth return. Maybe they could sublimate or irreversably decompose something in an insulated pressure vessel, using a simple electric heating element or heated catalyst bed.Doesn't this mostly describe tridyne?Cubesats have talked about splitting water, and using the subsequent Hs and Os, but that requires substantial energy to get enough propellant. Not sure if a battery could store enough, and solar panels are going to be bulky on something where every cubic cm or inch counts. And either the weight of the batteries/solar panels counts against the return mass, or they have to be replaced each time and add to the cost of the system.
This or something like it seems like a good idea.It kind of takes the wind out of the argument for a cargo version of Dream Chaser to compete for CRS2, though. Low-g and cross range like Dream Chaser, but the small scale is much better because it allows frequent small deliveries timed based on the needs of individual experiments.
Small Payload ??....looks very small from the pictures.....what kind of experiments on ISS would use and pay for this return capability vs. just waiting for a Cargo Dragon to do the job ??
Quote from: ChrisWilson68 on 10/19/2014 04:27 amThis or something like it seems like a good idea.It kind of takes the wind out of the argument for a cargo version of Dream Chaser to compete for CRS2, though. Low-g and cross range like Dream Chaser, but the small scale is much better because it allows frequent small deliveries timed based on the needs of individual experiments.Agreed, seems very useful. Not sure it really competes with DC though; DC's fundamental problem for CRS2 was where to get the several hundred million needed to bring it up to the operational level. I don't think CRS2 is about _developing_ new visiting vehicles, that was the pre-CRS1 set of contracts. Funding several hundred million through a billion or two contract means no profit would be possible for all of CRS2, and that big subcontract for Atlas V launches limits how much cost-savings they could generate in-house. Assuming DC were funded and available, I think the rapid sample return might lessen in a small way the urgency for returning vehicles, but the big vehicles will still handle all the bigger cargo, probably be required for all the frozen and powered returning cargo, and probably be preferred for nearly everything since it's nearly "free" after the delivery up to ISS is paid for. (This RV, on the other hand, costs upmass and upspace, and is a separate additional cost.)
This is relevant: http://blog.altius-space.com/2011/02/iss-micro-return-vehicle-concept/Almost like they ripped off your idea, Jon. (That, or JSC's idea.)...either way, fascinating how ISS is actually becoming something a lot more interesting than anyone would've guessed 10 years ago. I mean, Nanoracks has launched a heck of a lot of nanosats. A whole constellation for Planetlabs, even.
This seems bizarre to me - but what do I know. - What tiny/small payload is so time critical that this becomes economical? - It will take up significant pressurized payload space (& mass) going up - Handling this thing *inside* ISS seems dangerous.But again, I could be way off base.
