Phobos First

SpaceNut · 2019-07-15 21:05:23

Post 11 reposted

kbd512 wrote:

More thinking out loud, but trying to find a way to do this without nuclear reactors...
As long as we're considering the infrastructure required, what if we just kept all the power to make return-to-Earth propellant in orbit?
We could avoid the hard requirement for fission reactors if we're smarter about how we use solar power. The surface environment is brutal for photovoltaics and Lithium-ion batteries. The dust and insolation levels during dust storms kill everything we send there, so let's skip that to the extent we can. Even if we had robots running around every day with CO2 guns to blow the dust off the panels, it would only craze the plastic over time and there are multiple football fields of panels to keep relatively clean. RTG's can supply always-available local power for life support functions, given the low power consumption of the new generation of life support systems. We're talking about a few kilowatts at most and we'll have power galore during the day to make propellant or recharge batteries. The satellites could also supply process heat for chemical reactions or for fusing / baking regolith bricks.
Perhaps we could use Na/NiCl2 batteries since those don't explode, can operate over wider temperature ranges, and last for many years. Sodium Nickel-Chloride is not quite as energy-dense as Lithium-ion, but still 200Wh/kg+. Lithium-ion needs to be operated outside to avoid fireworks from runaway reactions and the associated release of toxic chemicals. Since Na/NiCl2 could be kept inside or warm at night from its own internal heat- it's a molten salt battery, the packaging mass requirements are lower.
CO + CO2 has an Isp which is entirely sufficient to reach orbit. Zubrin stated that CO + O2 would come at an energy cost of about ~10MWh/t. Well, if the Mars Ascent Vehicle was around the size of NIMF, the propellant could be made purely from Martian atmosphere in less than a year. We just need MOXIE to make CO and O2, which is what it's designed to do, and will actually be tested on Mars prior to arrival.
If we also had a non-nuclear / solar-powered PROFAC in orbit that was powered by the Solar Power Satellites / SPS, it could make Argon for electric propulsion cruise power and CO/O2 for orbital transfer. These devices skim the upper atmosphere to collect propellants over weeks to months of operation. The propellants can then be transferred to departure stages in higher orbits. The SPS supplies power for propulsion instead of a nuclear reactor, drastically reducing the mass of the device. Since we don't carry return propellant from Earth, nor even from the surface of Mars, the energy requirements plummet. Any orbit-to-orbit transfer propulsion system combining SEP with CO/O2 is much more controlled than screaming interplanetary reentries. The SPS could also provide supplemental braking power for new comers. CO/O2 will provide TEI thrust, whereupon an Argon-fueled SEP cruise stages take over.
Anyway, this drops our power requirements by at least half, if not to a quarter of what LOX/LCH4 requires, to say nothing of all the propellant transfer missions saved and the tons of propellant to take things to and from the surface of Mars.

tahanson43206 wrote:

For kbd512 ....
Re #11 ...
? Phobos ?
(th)

SpaceNut · 2019-07-15 21:09:41

The ISS battery packs would be just that ticket and with the use of film cells there would be nearly continuous energy since its not being blocked by a slow rotation and its above the atmosphere to gain even more energy.

I would say that it would be just a source for return from a moons mission or down mass of fuels to mars surface but can we break into mars orbit for a phobos mission as we know that fuel is the issue for parking in mars orbit....

kbd512 · 2019-07-15 23:03:30

SpaceNut,

We're leaving out the best part. Ascent Solar's bare modules, the kind going to Jupiter on JAXA's solar sail mission, are 1,100W/kg to 1,400W/kg. These CIGS thin film modules have already been long-duration tested in LEO by JAXA. They can be punctured without failing completely, because the surface of the thin film is covered with a grid of electrical interconnects. You only lose power from the portion of the solar cell that was destroyed by whatever hit it. It's more durable than silicon wafers with soldered electrical interconnects and much lighter for the amount of power produced. They've teased at 2,000W/kg+ bare module, but have not publicly released any further details.

The 1m^2 inlet diameter PROFAC can collect up to 400kg of O2 per day in LEO at a 100km orbital altitude. I presume an appropriate modification can collect a similar quantity of CO2 from Mars or Venus at appropriate orbital altitudes. The 1m^2 PROFAC requires ~400kW of power to produce enough thrust to stay in orbit. The solar powered variant will be a featherweight version of PROFAC without a multi-ton 10MW reactor onboard, ~1t vs ~10t for the fission reactor powered variant. In this case, multiple SPS hang out in geosynchronous orbits, feeding power to the surface or to PROFAC to maintain altitude and liquefy propellants using a small pump and heat exchanger. The heat exchangers / radiators will be tiny at the temperatures that highly focused MW-class beams can produce. Radiation damage from the reactor will be eliminated.

Falcon Heavy can easily ship this stuff to Mars. Starship or SLS would be better still, but not required.

Edit:

We only have to deliver this stuff to Mars orbits using a combination of Argon-fueled X3 and existing chemical rockets. We already have this sort of stuff. It's an engineering project, rather than a science project. All the propellant required to soft land a multi-MW solar power array made from much tougher, but heavier panels is saved for food / water / habitation / tools. AI-enabled robots with human-like dexterity don't need to be developed to autonomously construct a solar generating station many football fields in size without any human input. That would still be great to have for other purposes, but that sort of robotics is still many years of basic research and exhaustive testing down the road.

tahanson43206 · 2019-07-16 08:18:56

for kbd512 re #53 ...

Earlier in other topics about Phobos, there has been extensive discussion about using tethers. It might turn out that a light tether would be able to dip a collector such as you've described down into the atmosphere and return it to Phobos for processing.

The earlier discussion (as I recall) was about using tethers to deliver vehicles gently to the atmosphere, where they could fly to their destinations.

(th)

kbd512 · 2019-07-17 20:55:27

tahanson43206,

Phobos is something like 9,000km from Mars, so it'd be a really long tether. I think free-flying satellites that can change orbits would be better for operational considerations, such as not overflying the colony, since they're dipping into upper reaches of the Martian atmosphere to fill propellant tanks.

SpaceNut · 2019-09-02 15:15:41

I can hardly believe how quickly the topics are burried into the past.
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#51 2019-07-15 21:05:23

Re: Phobos First

#52 2019-07-15 21:09:41

Re: Phobos First

#53 2019-07-15 23:03:30

Re: Phobos First

#54 2019-07-16 08:18:56

Re: Phobos First

#55 2019-07-17 20:55:27

Re: Phobos First

#56 2019-09-02 15:15:41

Re: Phobos First

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