UK's Manned Mars mission Concept

[metaphor]

Ok, I see what you meant. I did not even consider anything but a Hohmann transfer because it's absolute madness to do what you are describing as Conjuction-class as the first mission. It has a huge list of disadvantages. Timing requirements are stricter. The delta-V on both departure and arrival are much higher. This means significantly more fuel needed for the mission and much smaller margin for error, which increases risk to the mission, especially on Mars arrival, where you'll have to kill the delta-V just right or either smash into the Red planet or end up completely screwed in interplanetary space. The launch windows are also much smaller. You can miss the Hohmann transfer window by as much as a month on the return trip without that much extra delta-V requirement. And then there is duration. The 30-60 day mission can be done with a very light lander. A 600 day mission will not even be able to land as a single lander. You'll have to drop the supplies separately and that's an entire list of additional risks.

And the only real advantage for the first mission is shorter transit time. If the duration of Hohmann transfer was prohibitively long, then yes, I understand the rush. But it's not. We can keep astronauts healthy for 300+ days in microgravity. Russians have done over 400 days on Mir. Even with the stay on Mars being as short as it is, this isn't as much of a limiting factor as all of the issues above. Even if problems develop, they will not be mission-critical, and certainly no the sort of stuff to endanger the entire crew.

No, absolutely not. Opposition launch is the only way to go for early missions. Once we have something up there to provide a safety net, we can start doing these faster, riskier missions.

The "fast-transit" trajectories are just slightly modified Hohmanns. They really don't take much more delta-v than a perfect Hohmann transfer. What does take a lot more delta-v is the Mars return burn for an opposition-class mission.

The lowest-energy possible transfer from LEO to LMO and back takes about 7.8 km/s of delta-v, with about 300 days outbound, 380 days at Mars, and 300 days inbound. Shortening the transfer to 190 days each way with 560 days at Mars gives 8.4 km/s of delta-v. Shortening it even more to 150 days each way with 600 days at Mars gives 9.4 km/s of delta-v.

A low delta-v opposition class mission takes about 11.3 km/s of delta-v, with 200 days outbound, 30 days at Mars, and 260 days inbound. If you stay much past 30 days at Mars, the return-to-Earth delta-v starts getting much higher.

For some example trajectories see NASA's trajectory browser.

Sure the opposition-class mission has the advantage of not needing to use a big surface habitat, and fewer supplies (600 days' worth instead of 900 days' worth). But the disadvantages outweigh that. They only have 30 days on the surface of Mars, and a lot of that time would be spent getting used to Mars and checking out all the systems, not leaving much time for exploring other than flags and footprints. More time in deep space means higher radiation doses. The return leg has to pass within 0.7 AUs of the Sun resulting in increased radiation and higher thermal loads on the spacecraft. The Earth reentry would be at a much higher speed (14 km/s+ as opposed to ~11.5 km/s) requiring a much more capable heat shield (since heating goes up as the third power of the speed). And the mission would require a much higher delta-v.

Assuming a chemical engine with 450 Isp (that's about as high as chemical engines go) and a 10-ton payload, the lowest-energy 7.8 km/s mission would take 49 tons of fuel. The 190-day-transfer 8.4 km/s mission would take 57 tons of fuel. The 150-day-transfer 9.4 km/s mission would take 74 tons of fuel. And the short opposition-class 11.3 km/s mission would take 120 tons of fuel.

For a lot more info than you wanted to know about a Mars mission, see NASA's Design Reference Mission 5.0. The part about a conjunction-class versus opposition-class mission is on page 47.

[POTKC]

Does anyone find the way they keep saying 'Hopefully', 'We hope' and 'Fingers crossed' about some of the most critical mission stages just slightly worrying?

[DerekL1963]

Micrograv is one thing. Radiation is quite another. Mir and the ISS both orbit inside Earth's magnetosphere, whereas your prospective Mars mission would be in interplanetary space, fully exposed to solar radiation (Curiosity's radiation instrument was running the whole way to Mars, and measured that the total radiation exposure on the way there was something like 2/3 NASA's maximum lifetime dose for astronauts, ONE WAY - meaning that one mission would put you over the limit by as much as 30%).

I don't know about NASA standards, but radiation standards in general are pretty conservative in my experience. They're based on statistics, as there isn't a hard number LD50 dosage for radiation exposure, and they're set to minimize potential risk.

[metaphor]

I don't know about NASA standards, but radiation standards in general are pretty conservative in my experience. They're based on statistics, as there isn't a hard number LD50 dosage for radiation exposure, and they're set to minimize potential risk.

The data from Curiosity's rad instrument shows the radiation dose in interplanetary space is about 660 mSv per year, while the radiation dose on the surface of Mars is about 150 mSv per year. I think the NASA maximum lifetime dose for astronauts is 1 Sv (=1000 mSv). That means that a mission that requires 6 month transits to and from Mars and a 2 year stay on Mars would barely meet NASA radiation standards if the astronauts had not spend any previous time in space. Of course they can always use more shielding than on Curiosity to bring the dose down.

[NGTOne]

The data from Curiosity's rad instrument shows the radiation dose in interplanetary space is about 660 mSv per year, while the radiation dose on the surface of Mars is about 150 mSv per year. I think the NASA maximum lifetime dose for astronauts is 1 Sv (=1000 mSv). That means that a mission that requires 6 month transits to and from Mars and a 2 year stay on Mars would barely meet NASA radiation standards if the astronauts had not spend any previous time in space. Of course they can always use more shielding than on Curiosity to bring the dose down.

And that's assuming they don't raise the threshold for long-term missions, AND more research isn't done into the human body's ability to adapt to higher-than-normal levels of radiation (it's been suggested that it's possible for a population to live in a much-higher-than-background area for an extended time and not show any increased levels of radiation poisoning symptoms than you or I - there's a little town somewhere in the Middle East where the rad level is something like 80 times background, and apparently the population is as healthy as would be expected elsewhere).