Moonguy

Consider an unmanned lunar cargo lander that delivers 5,000 kg to the lunar surface. The delta-v for landing from a low lunar orbit is 2,100 m/sec. and the Moon's gravity is .16 Earth's. Now, consider that same lander used to land a payload on Mercury from a low Mercury orbit where the delta-v involved is 3,200 m/sec. Mercury's gravity is .38 Earth's. All of the physical characteristics of the lander must remain the same, only the payload mass can be altered. How much payload must be off-loaded to accomplish the landing? Thank you. . .

The Shuttle experiment ended when the tether snapped. It was one of those embarrassing failures no one at NASA likes to remember.

This is huge news, but I am curious why it was not posted under 'Medical Science'?

Exactly how do we define a 'killer' asteroid? Asteroids currently zipping past Earth range around one to two kilometers in size. Is this large enough to prompt the mass extinction events that have occurred periodically? Or is a larger body required?

Actually, this sounds like the '60's sci-fi movie 'Marooned'. Only it was the American (Apollo) that was stranded and a Russian spacecraft (Voskhod?) came up to rescue. A good yarn if patently unrealistic. . .

Actually, they would need a pressure suit. You can deliver oxygen to the lungs at sufficient pressure without a suit. The problem is that, on Titan, the air pressure is 45% greater than at Earth's surface. Our skin surface, like everything else about us, evolved in Earth's atmospheric pressure and is suited to that. If you increase the pressure 45%, you would get gas diffusion effects into the subcutaneous tissues and eventually the blood stream. Not a good thing when cyanide is one of the chemicals in the 'air'. Other chemicals like ethane permeate into the tissue - in this case at higher pressure - and exert changes to blood cell DNA. It is one of the causes of certain forms of leukemia.

1) The Tanker departs on a solar sail, so we only need the easiest departure point. Most cargo missions will depart from L3, but the Tanker takes on water from the Moon, so Tankers depart from orbits closer to the Moon but with easy departure velocities. That would be either L1 or L2. On reflection, L2 might actually be better as it does not interfere with operations (depots) in the L1 orbit. 2) The Tanker is an expendable unit. There is no need to worry about coordinating or synchronizing the Tanker's orbit for either picking up the crew (for the return to Earth) or for follow-on missions. 3) Also, the Tanker's orbit only needs to intersect Mercury's orbit at one of its nodal crossing points just once. A one-year circular orbit which intersects Earth's orbit and subsequently intersects Mercury's orbit at a node, while Mercury is passing through that node, should be fairly easy to establish. It just may take a couple of years for the sail to spiral into the appropriate orbit. That is why producing propellants from water is preferred over storing cryogens for 'years' before the crew can use them. 4) Water can be stored passively. Cryogens would need liquefaction equipment even with a small boil-off rate to avoid gas build-up. With no crew onboard for most of the time, the chances for problems increases. 5) The MOTS we discussed earlier is deployed before any crews launch to Mercury. The 185-ton mass includes the MOTS' dry mass, the dry mass of two manned Mercury Landers and 100 tons of water. The crew should be able to produce propellant sufficient for return to Earth from that for at least one mission. It depends on the mass of the Crew Module payload and that is still being worked out for this concept . 6) Another advantage to expending the Tanker is that the crew does not have to constrain their stay time on Mercury to the Tanker's orbital period. They can extend their mission stay time indefinitely if needed. Alternately, once the crew arrives at Mercury, they would have at least a year before the Tanker is anywhere near Mercury. Whether it would be near enough for use in a return flight. . .I just do not know for certain at this point. At present I am working on a piece for the Facebook group site concerning Sheltering the crew on Mercury. I hope to have it posted before the weekend. You might want to check into that to get more details. . .

1) All water/cryogens comes from the Moon. There is no Depot involved. All water/propellant transfers are direct to vehicle. 2) 'Departure Stage' is a misnomer. The stage carrying a solar sail only delivers a payload of 15 tons to the L1 point. The 15 ton payload includes propellant production equipment, a habitat module and the solar sail. At L1, the tanks of the delivery stage are filled with water, the solar sail deploys and the entire assembly departs into a heliocentric orbit with a one-year period. This orbit intersects the orbit of Mercury at one of the nodal crossings. 3) The sail and its payload - now called a Tanker - may have to make one or more orbits before the crewed vehicle is ready for launch. Preserving cryogens for that long is difficult. 4) The Crewed Vehicle launches 'some time later' as Mercury is positioned for encounter. The Crewed Vehicle launches into the same exact orbit as the Tanker when the Tanker encounters Earth. Assuming a successful rendezvous and docking, the crew occupies the Tanker Habitat for the cruise phase of the flight - approximately 78 days. 5) Prior to Mercury encounter, the crew processes water into cryogens and fills the tanks of the Crewed Vehicle's propulsion system. At encounter, the Crewed Vehicle performs the MOI and rendezvous with the MOTS. 6) To return, the Crewed Vehicle performs the same maneuvers as at launch from Earth. The Tanker used for return would not necessarily be the one they arrived on. The Tankers are single-launch items and regarded as expendable. their total mass when filed with water is 185 tons. This demands very minimum mass for the Crewed Vehicle injection mass as all of the maneuvers are budgeted up to 10 km/sec.

The 'Cycler' concept has dropped off the radar. For now, the idea is to focus on the first few ('Alpha') missions based on non-recovered systems. A departure stage is sent to L1. This unit carries a payload of 15 tons. This includes a solar sail (3880) kg, a self-deploying habitat (NOT a 'tin can'), and a docking module. The stage is equipped with water electrolysis units (as in the case of the Cycler), liquefaction and propellant transfer equipment. At L1, the propulsion stage's tanks are filled with up to 100 tons of water. The solar sail and habitat module are deployed and the cluster departs from Earth on a transfer intercept course to Mercury's orbit. This course is elliptical and actually crosses Earth's orbit twice. Much later (1 year+?), a second launch delivers a crewed capsule to the same L1 location where it is refueled with cryogens. As the cluster vehicle approaches, the crewed capsule launches into the same trajectory, where it eventually conducts rendezvous and docks with the cluster. The crew remains on board the cluster for the balance of the transfer, which takes about 78 days. Prior to Mercury encounter, water from the cluster's supply is processed into cryogens sufficient for either an orbit injection at Mercury (with subsequent rendezvous with the afore-mentioned MOTS) or it can be outfitted for a direct descent to Mercury's surface. Such a mission could be supported by existing Atlas, Delta or Falcon systems. the upper stage elements would be derived from the Advanced Centaur systems.

Virtually everything you are saying is why I am confident about the 'transportation problem' (to Mercury) being solved. I particularly agree with you about the need for new ideas to 'percolate'. I grew up in a space advocacy that torpedoed itself with incessant arguing over 'where to go first' or who's idea for how to go was better. . . It made the entire movement a joke. Sadly, I have to admit I engaged in many of these arguments. I like to think I have evolved to where I see the value in 'synergy'. In the present case, this means using Mercury to boost astronomy and planetary exploration efforts and human settlement of Mars and other venues. A Mars settlement effort would provide a needy customer for things Mercury can provide economically. Less clear to me is what a Mars settlement would do to pay for the goods it got from Mercury. Its an interesting question, but I have not had time to work on it.

All of the life-support and agricultural technology issues are already being worked on in the interest of lunar and Mars exploration. The assumption here is that Mercury simply draws on technologies developed with experience from those two venues. The same goes for mining and mineral processing technologies. This is one of the reasons why the Mercury project is so cost effective. There is very little 'Mercury specific' technology needed, at least not in the early stages. Transportation is probably the biggest exception. Solar thermal is my choice for sending crews to Mercury, but has not been considered by NASA for lunar or Mars operations. They still think in terms of the J2-X, lunar water mining and (gulp!) L2 depot/station for departure. Goes a long way top explain why NASA can't sell their program to the public. . .

The entire purpose of the project is to establish a permanent base on Mercury to make Mercury useful. The economics strongly favor a base over a brief visit. So the first crew has the challenge of setting up a base that can house an engineering crew and a science/exploration crew. This includes a lab where hundreds of kilograms of rock samples can be examined instead of the minimal amount that could be sent back on a return flight. The construction work can be done at night under lights with the goal of having the base covered (as needed) as soon before sunrise as possible. As a thought experiment, a 10 meter thick shield covering a base that had a 25 m x 25 m footprint (625 m2) would keep a bulldozer with a 2 m3 bucket busy for about 260 hours, assuming an average of 5 minutes to transport/dump each bucket load. That is just over ten days. Obviously using two bulldozers would cut that down to less than a week. . . On Mercury, the average density of regolith poured to make a shield mass 10 meters thick would have an average density of 1.9 metric tons /m3. A 10-meter shield would therefore weigh 19 x .38 or 7.22 metric tons per square meter of surface on the base. This corresponds to roughly 30 kg/in2 or 13.5 lb/in2. More could be added to just exactly equal one full atmospheric pressure inside the base, if it were inflatable. Essentially zero pressure differential increases safety margins. During the daytime, the crew would remain in the base and maintain the base's agricultural system. The 88-day daytime is long enough to see some crop plants all the way through their growth cycle to harvest. Chances are the crew would have the garden up and running long before sunrise, so the second sunset would see the crew with a full harvest in place, all of the critical systems set up and perhaps hundreds of rock & soil samples examined before the next crew arrives.

Radiation dangers are about how much exposure you allow the crew to have. The mass of the crew module for the inter-planet transfer phases is critical in this respect. Right now, the concept of choice is for a laminate radiation shield and use of both potable and waste water (in separate units!) to absorb radiation. It is easy to design shielding mass for any given material or even a series of layered material. The hard part is putting it all together in a mass that can be launched for well below the national debt in cost. The most dangerous exposure time is the period when the crew begins its descent to the surface to rendezvous with the pre-positioned surface elements waiting for them. If the crew descends over the night side, they are blocked from the Sun's heat and most deadly radiations but the spot on the surface where they are to rendezvous would be just a few days (less than a week) away from sunrise. Not enough time to deploy the first base (~ 1 day) AND cover it with enough regolith to secure against radiation AND deploy energy units, So the crew descends over the day side where they are assaulted by the heat from Mercury's surface as well as the Sun. Putting the base near one of the poles and having the crew enter Mercury orbit over the poles eases the problems somewhat. What I do not know at this point for a certainty is what thickness of regolith is needed to reach the NASA baselines for exposure limits. For that reason, I just assume a depth of ten meters regolith all around. That is a lot of regolith to move around. . .

Good clarifications, thanks! Regarding the reflector/concentrator, why are they made of anything rigid at all? Solar sail films already exist with 10 GRAM/m2 density. They ;also have 90% reflectivity. The materials available - at least the samples I have held in my hands - are strong enough to be integrated into an inflatable structure or even a mechanical arrangement like that in an umbrella. Adding scrim or other items to strengthen the reflector material is easily accommodated well with in the 1 kg/m2 mass limit. The system you describe has a lot of flexibility. I have to think a solar thermal stage would be easier to develop than a nuclear thermal stage. The higher Isp (1267 vs ~950) sure looks like ample incentive. Sort of gets you to wondering why. . .

This occurred to me while I was reading the earlier posts: Would it not be possible to channel the concentrated light into the thrust chamber through fiber-optic cables? This would make the orientation of the reflectors independent of the thrust vector. The light from the fiber-optics concentrates inside the chamber as in other concepts, but does not require the chamber to be designed with exotic materials in order to allow light through. I have not had time to check it out, but it would seem this could scale sufficiently for use by a manned vehicle. . . especially one going to Mercury (or Venus).