One Month to Mars -- Methods for Very Fast Settler Transit

[Vultur]

...you don't need artificial gravity to survive ordinary Mars trip times.

Region 3, ISS 1-8, 150 days.

Region 4, Soyuz 31, 140 days.

With large crews, you'd probably worry about outliers.

Are we discussing crews, or settlers?

Mars settlers do not need 100% bone density.

Settlers, obviously.  It's strange that you care less about their health.

I don't "care" less about their health per se. But early settlers of any pioneering environment necessarily accept higher risks. Compared to the other risks of doing this, the gravity stuff is just not that significant.

Also, I simply don't see why someone who will spend the rest of their life in 38% gravity lacking the bone density, muscle strength, etc. needed for 100% is necessarily a problem. The re-acclimation times you are talking about are for original performance *in Earth gravity*.

I don't have the adaptations (genetic/inborn or physiological/acquired) to function well in the high Andes or Tibet. But I don't see that lack as a health problem since I don't live there and have no reason to expect to ever do so.

the solution set is empty.

But you haven't evaluated or even listed potential solutions yet.  For 2039.

I pretty much did, and the set *is* empty.

Chemical: Isp far too low

Electric propulsion: too low thrust for 1 month journeys, without power production that isn't possible to develop and deploy by then.

Sail propulsion: *way* too low thrust, without ridiculous lasers that couldn't possibly be built by then

Nuclear thermal: options that could exist by 2039 (like DRACO or a hypothetical revived NERVA) have far too low Isp. Options that might have sufficient Isp (open-cycle gas core) can't be developed by 2039.
 
Exotic propulsion (nuclear-salt-water rocket): can't be developed by then

The incredibly short time span makes it impossible. Even with free braking, you don't have the delta v.

The only thing that could possibly be developed in 15 years with sufficient thrust and Isp is nuclear pulse, which is impossible in that timeline for non-technical reasons (cost and politics).

[LMT]

I don't have the adaptations... to function well in the high Andes...  I don't see that lack as a health problem since I don't live there...

Like the Andes, Mars presents challenges.  A relevant difference:  tour operators don't need the FAA's written permission to hike the Andes.

[Vultur]

I don't have the adaptations... to function well in the high Andes...  I don't see that lack as a health problem since I don't live there...

Like the Andes, Mars presents challenges.  A relevant difference:  tour operators don't need the FAA's written permission to hike the Andes.

I don't see how you can say that is relevant, but the politics of using nuclear material in space is off topic?

The political barrier, if any, to getting humans to Mars (assuming it is not government funded, e.g. Elon Musk's "accrue assets for Marshlands plan) would be planetary protection requirements (much as I personally think the entire concept of PP is a relic of the same 60s era ignorance of biology that gave us quarantines for returning Apollo astronauts), not risks taken.

[LMT]

I don't have the adaptations... to function well in the high Andes...  I don't see that lack as a health problem since I don't live there...

Like the Andes, Mars presents challenges.  A relevant difference:  tour operators don't need the FAA's written permission to hike the Andes.

I don't see how you can say that is relevant, but the politics of using nuclear material in space is off topic?

Who knows the difference between a lawyer and the law?

[deltaV]

Rehabilitation After International Space Station Flights
The [newer ISS] rehabilitation program lasts for 45 days...  Some crew members subjectively indicated the need for a longer rehabilitation period..."

~45 days to get used to gravity again is not a big problem if you're doing a long-stay mission with ~500 days on the Martian surface. If people decide it isn't OK artificial gravity is a better solution than nuclear thermal since artificial gravity is probably cheaper, lower risk, and would cut exposure to zero gee by more, to a few hours or days near Earth and near Mars.

Astronauts’ brains take a hit during long spaceflights
"We found that the more time people spent in space, the larger their ventricles became,"

That seems tolerable since the change doesn't seem to cause any obvious symptoms. If it isn't ok, artificial gravity and/or radiation shielding are probably better solutions than nuclear thermal.

Moraguez, M., Miller, D. and Vanatta, M., 2018, July. Mass-Optimal Transit Time for Acceptable Effective Radiation Dose on Manned Deep Space Exploration Missions. 48th International Conference on Environmental Systems.

That paper seems mostly reasonable. One minor quibble is they assume that Mars orbit insertion is done propulsively and assume no ISRU so the hab has to do three burns in sequence: Earth departure, Mars arrival, and Mars departure. Direct atmospheric reentry and ISRU will reduce IMLEO (but are less trivial to model). They also optimize IMLEO, which with modern reusable launch vehicles may not be well correlated with cost. With the most difficult radiation model (Cucinotta, Figure 7) they find an optimized IMLEO of ~1000 tonnes at transit duration 146 days each way. That IMLEO consists of 50 tonne hab for 4 people, ~6 tonnes food, ~47 tonnes radiation shielding, and enough propellant (380s specific impulse) for around 8.7 km/s of delta vee (Figure 5). That ~1000 tonne IMLEO is only ~6 Starships of cargo. Most of that IMLEO is radiation shield (they assumed water), propellant, or tanks, all of which are cheap. Those ~6 Starships per mission will probably be at least an order of magnitude cheaper than a nuclear thermal propulsion program at plausible NASA mission rates of about 1 mission per synodic period. So radiation concerns do not justify 1 month transits. (They seem to have modeled transit hab mass only so more IMLEO is probably needed for the lander, surface equipment, and ascent vehicle. If the hab is based on Starship the IMLEO will be somewhat greater since Starship masses more than 50 tonnes.)

Artificial gravity may not require significant additional mass. Do something like connect two Starships with a 1800 m tether (which puts each Starship's nose 1800 m / 2 from the center of mass) and rotate them at 1 RPM, which provides (2 pi / minute)^2 * (1800 m / 2) of artificial gravity, which is about 1 gee. If each Starship with payload and landing propellant masses M that tether if made of zylon fiber (specific strength 3766 kN m / kg) would mass only about (1.8 km * M * 9.8 m/s/s) / (3766 kN m / kg) = 0.0047 M times a safety factor. So the tether is only about 0.3% of the mass of the two Starships and would be even smaller if lower gravity or higher RPM were found to be acceptable. Artificial gravity would make engineering harder in some ways, e.g. antennas would have a harder time tracking Earth, and easier in other ways, e.g. testing on Earth would be more similar to flight conditions and existing Earth designs would be more likely to work well. Having to send 2 Starships isn't ideal but is likely to be much cheaper than a nuclear thermal program and if you design the Starships for twice the usual number of crewmembers they would provide fault tolerance through redundancy.

[TheRadicalModerate]

Artificial gravity may not require significant additional mass. Do something like connect two Starships with a 1800 m tether (which puts each Starship's nose 1800 m / 2 from the center of mass) and rotate them at 1 RPM, which provides (2 pi / minute)^2 * (1800 m / 2) of artificial gravity, which is about 1 gee. If each Starship with payload and landing propellant masses M that tether if made of zylon fiber (specific strength 3766 kN m / kg) would mass only about (1.8 km * M * 9.8 m/s/s) / (3766 kN m / kg) = 0.0047 M times a safety factor. So the tether is only about 0.3% of the mass of the two Starships and would be even smaller if lower gravity or higher RPM were found to be acceptable.

This always seemed to me to be an obvious way of dealing with microgravity restrictions.  IIRC, it's not completely simple, though:  weird stuff (like people walking around) can cause the whole system to precess, and it's tricky to un-precess it, especially with a non-rigid connector.  It also makes solar storm shelters a lot more complicated.

Still, it seems a lot simpler than engineering a squintillion-watt space nuclear reactor.

There's absolutely no reason to have the acceleration greater than 3.72m/s², even for temporary visitors.  That's what they'll be walking around in when they land.  (Maybe they need to swap in a longer cable for Earth return trips.)  And I'd put the design acceleration somewhere lower than the nose, maybe 15m below it.  That takes your tether length down to about 650m.

This does put your tankage in tension.  That's not something the Starship structure was engineered to endure.

IIRC, there's a whole thread devoted to cheap spin gravity solutions.

Artificial gravity would make engineering harder in some ways, e.g. antennas would have a harder time tracking Earth...

I suspect you need dynamic counterweights crawling around on the tether, so you might as well have the comm arrays crawling around at the center of mass.

The trickier one is that you'd really like to put the nose to the sun to help keep the prop cool in transit.  But again:  deployable sunshade for tankage vs. squintillion-watt reactor?

Having to send 2 Starships isn't ideal...

If you're doing this for a mass settlement program, I'd argue that pairing ships up is better.  Always nice to have some redundancy if something bad happens.

[deltaV]

There's absolutely no reason to have the acceleration greater than 3.72m/s², even for temporary visitors.  That's what they'll be walking around in when they land.

We don't yet know if Mars gravity is more like Earth gravity or more like zero gravity in its health effects. If it's the latter then spending ~500 days in Mars gravity on Mars itself would be healthier than spending a total of ~800 days in Mars gravity on Mars and in transit. It may not be much harder to provide artificial Earth gravity than Mars gravity (the mass of the tether doesn't matter much either way), so why not lower the risks? Maybe reduce the rotation rate a few weeks before landing on Mars so the astronauts can learn to walk in Mars gravity during a time when they're less busy and less in the public eye. After the first mission we'll have data on how bodies respond to ~500 days of Mars gravity and can use that to decide if reducing the artificial gravity to Mars level in later missions makes sense.

[TheRadicalModerate]

There's absolutely no reason to have the acceleration greater than 3.72m/s², even for temporary visitors.  That's what they'll be walking around in when they land.

We don't yet know if Mars gravity is more like Earth gravity or more like zero gravity in its health effects. If it's the latter then spending ~500 days in Mars gravity on Mars itself would be healthier than spending a total of ~800 days in Mars gravity on Mars and in transit. It may not be much harder to provide artificial Earth gravity than Mars gravity (the mass of the tether doesn't matter much either way), so why not lower the risks? Maybe reduce the rotation rate a few weeks before landing on Mars so the astronauts can learn to walk in Mars gravity during a time when they're less busy and less in the public eye. After the first mission we'll have data on how bodies respond to ~500 days of Mars gravity and can use that to decide if reducing the artificial gravity to Mars level in later missions makes sense.

If Mars gravity isn't healthy enough for colonization, then this whole endeavor is a fool's errand.

I don't think there's a prayer of incurring the complexity required to do a tethered spin gravity system on an early expedition.  We know that ISS astronauts spend >6 months in microgravity and are only briefly debilitated when they get weight back.  I suspect that's good enough for an early mission.

The real question is what you have to do at scale for settlement.  That's not mission #2, or even mission #20.  It's more like mission #50.  Plenty of time for the pathfinders to experiment in there, and plenty of time to work out tethered dynamics with cargo, so you don't kill a couple of crews.  Plus, by then, we'll have crews that have been on Mars for 3-4 synods, and we'll have a much better answer on the gravity issue.

[LMT]

If Mars gravity isn't healthy enough for colonization, then this whole endeavor is a fool's errand.

Early results are encouraging, but of course surface ring gyms could supplement, if necessary.

If flight AG can be dropped, that's a useful simplification.

[deltaV]

If Mars gravity isn't healthy enough for colonization, then this whole endeavor is a fool's errand.

True, but Mars gravity being somewhat unhealthy is consistent with non-settler exploration. Anyone thinking about settling should also think about exploring in hopes of getting funding from government or private explorers.

We know that ISS astronauts spend >6 months in microgravity and are only briefly debilitated when they get weight back.  I suspect that's good enough for an early mission.

I agree. The best plan for the first crewed Mars mission is probably 4-6 month zero gee transits with the astronauts dealing with zero-gee like ISS astronauts do. My claim is only that artificial gravity is a much better idea than one month transits.

[LMT]

Fusion Microexplosion Propulsion

This method gives a theoretical Isp of up to ~ 1 million s (Schmidt et al. 2000).

Winterberg's 2004 "Mini Fission-Fusion-Fission Explosion" design specifies 10 kg of high explosives to start the nuclear sequence.  Methalox might serve here; LCH4 is miscible in LOX, forming a uniform methane / oxygen mixture (MOX).  (image)

MOX has been shown to be a high explosive with a TNT equivalence greater than that of C-4.

Here MOX surrounds Winterberg's container, which is < 20 cm in diameter, holding shells of aluminum, beryllium, U238 / Th232, and D-T gas around < 1 gram of fissile core.  In use, fusion delivers to the MOX:

...a gain of ∼ 10^3, releasing an energy equivalent to a few tons of TNT...

Corresponding Isp is around 13,000 s (trading high native fusion Isp for high thrust).

The design could utilize methalox ISRU, with LOX harvested from Earth's thermosphere and LCH4 possibly from Deimos.  Also, fusion tankers could transfer Deimos LCH4 to Earth orbit.  In this way, the crew tugs' most massive consumable (MOX) is stocked efficiently where needed.  In effect, notional on-orbit ISRU methalox infrastructure is now integrated and repurposed within a newer fusion transport system.

Proven fusion tech is of course another point in favor.

Comparisons?

Refs.

Blackwood, J.M., Skinner, T., Harrison, S.J., Whitworth, B., Hays, M.J. and Wilde, P., 2023, May. An Interim Set of TNT Curves for LOX/LNG Explosions. In 12th International Association for the Advancement of Space Safety (IAASS) Conference.

Schmidt, G., Bonometti, J. and Morton, P., 2000. Nuclear Pulse Propulsion - Orion and Beyond. In 36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit (p. 3856).

Winterberg, F., 2004. Mini fission-fusion-fission explosions (mini-nukes). A third way towards the controlled release of nuclear energy by fission and fusion. Zeitschrift für Naturforschung A, 59(6), pp.325-336.

[LMT]

[Friedwardt Winterberg has] "perhaps not received the attention he deserves".

ResearchGate:  F. Winterberg's research

[LMT]

Helicity Comparison

Helicity Space is inventing new fusion tech for their Helicity Drive.

In the plot below, Helicity compares the first 4 planned Drive iterations to other engines, in terms of specific thrust power vs. Isp.

They omitted Winterberg's fission-fusion-fission engine, which does work.

Which quick-thinking poster will be the first to correct that omission and stick the pin?

[Vultur]

These things could work, but not realistically by 2039.

If you remove the 2039 constraint, there are tons of possibilities.

[LMT]

These things could work, but not realistically by 2039.

If you remove the 2039 constraint, there are tons of possibilities.

It seems you couldn't stick the pin, "Vultur".

Who understands the rocket equation, etc., well enough to stick the pin, first?

[LMT]

A Smaller, Lighter, Cheaper "3F" System

Remarkably, it seems MOX can shrink the fission-fusion-fission system ("3F" perhaps) far below the baseline of Winterberg 2004. 

Blackwood et al. 2023 emphasizes that MOX has "160% TNT equivalence".  High explosives with similar relative effectiveness have detonation speeds around 8.6 km/s, considerably faster than Winterberg's baseline 5 km/s.  Plugging into Winterberg's sizing estimates, the system shrinks to:

- container diameter ~ 11 cm

- fissile core ~ 0.3 grams

Here 3F efficiency remains very high in an even smaller detonation.  The smaller detonation reduces the structural challenges associated with fusion blast effects.

[Emmettvonbrown]

So, is this thread your own little sandbox ? will you end talking only to yourself ?

Sorry but it baffles me.

[LMT]

So, is this thread your own little sandbox ? will you end talking only to yourself ?

Sorry but it baffles me.

You couldn't stick the pin, either?  If posters aren't comfortable with the rocket equation, etc., we can't really explore rocketry options.  Just checking.

[Emmettvonbrown]

Well I have an idea where you could stick that pin but a) it would break the forum rules and b) it might be painful to you.

[Eric Hedman]

This thread is devolving predictably into something that is likely to be locked.