Free-return Mars flyby questions

[DerpenWolf]

So after seeing a few proposals to do fly by of mars a few questions came to mind.

1. How much Delta-V would it take to go from LEO to mars (not getting into a stable orbit, just passing by) and back? (So far from what research I have done I am seeing that it would only require about 6.5Km/s of Delta-V, however I am very uncertain of this data)

2. How long would the trip take? (What is a fast yet non uber Delta-v consuming route? What is a slower more fuel efficient route? etc..)

3. What is the expected radiation dose for the length of the trip? I have seen plenty of statistics on how much exposure one would receive if they had done a landing mission with the crew staying on the surface for some 500 days but not much involving a relatively fast free return mission.

4. Assuming you have a crew of three or four and are using modern day recycling systems, how much food and water might you need for the trip?

[metaphor]

1. It would only take about 5 km/s from LEO, since your only propulsion besides small corrections is the burn out of LEO. (for example)

2. About 500 days (1.4 years). However, there are launch windows every 2 years that take less delta-v (about 4.5 km/s) but a longer trip time (about 750 days / 2 years) and have a higher Mars periapsis.

3. The unshielded radiation dose is probably around the same as the one measured by Curiosity on the way to Mars (1.8 mSv/day). So for a 500-day mission that would be 0.9 Sv, for a 750-day mission that would be 1.35 Sv. The radiation dose for a 2.7-year Mars surface stay mission would be around 1 Sv (unshielded).

4. One person would probably need around 1 kg of supplies per day, which is 2 tons for a crew of 4 over 500 days (assuming water recycling).

[Kosmic Debris]

Thanks for the question and response - interesting reading It seems more than well within reach even with current capabilities, even on a single launch with a heavy ELV.

[Soda Popinski]

So after seeing a few proposals to do fly by of mars a few questions came to mind.

1. How much Delta-V would it take to go from LEO to mars (not getting into a stable orbit, just passing by) and back? (So far from what research I have done I am seeing that it would only require about 6.5Km/s of Delta-V, however I am very uncertain of this data)

2. How long would the trip take? (What is a fast yet non uber Delta-v consuming route? What is a slower more fuel efficient route? etc..)

3. What is the expected radiation dose for the length of the trip? I have seen plenty of statistics on how much exposure one would receive if they had done a landing mission with the crew staying on the surface for some 500 days but not much involving a relatively fast free return mission.

4. Assuming you have a crew of three or four and are using modern day recycling systems, how much food and water might you need for the trip?

All answers based on NASA's Mars Design Reference Architecture 5.0

1- Between 3.5 to 4 km/s depending if propulsion or aerobraking is used for the orbital insertion. (Fig 4-2)

2- About 200 days for the crewed vessel (section 4.1)

3- Don't know for a fly - by, but a longer 900 day mission (500 days on Mars) was about 1 Sievert (raises cancer risk by about 6%)

4- The mission that NASA proposes includes about 10 tons of food, but with water being produced at Mars from the atmosphere + Earth sourced hydrogen. So... a lot. Now on the ISS, about 95% of the water (either 93 or 97%) gets recycled, but I'm not sure over what time period (5% loss a day is different than 5% loss a year).

For really in depth, read the 2009 addendum: http://www.nasa.gov/pdf/373667main_NASA-SP-2009-566-ADD.pdf

That's where I got the radiation dose from.

[Headhunter09]

He's talking about a flyby, AKA not entering orbit or stopping to replenish perishables.

[Soda Popinski]

True, but I don't see why it would take longer to get there in a fly-by than a landing. I just gave the other numbers as a base line, but would obviously be less due to less time out there.

One thing to consider, is a fly-by and return viable? Would there be an Earth return launch window when you get to Mars? Or will they have to loiter in orbit until it opens up?

[Kryten]

One thing to consider, is a fly-by and return viable? Would there be an Earth return launch window when you get to Mars? Or will they have to loiter in orbit until it opens up?

There are windows for free-return trajectories from Mars, but they're not common. The next is 2018, but the first one after that is 2031.

[metaphor]

There are windows for free-return trajectories from Mars, but they're not common. The next is 2018, but the first one after that is 2031.

There are free return trajectories to Mars available all the time, the ones in 2018 and 2031 are just the short ones (500 days instead of 700+). Like the one Inspiration Mars is using.

True, but I don't see why it would take longer to get there in a fly-by than a landing. I just gave the other numbers as a base line, but would obviously be less due to less time out there.

One thing to consider, is a fly-by and return viable? Would there be an Earth return launch window when you get to Mars? Or will they have to loiter in orbit until it opens up?

A 500-day flyby would take longer and require more delta-v because you have to be on a trajectory such that the gravity assist from Mars can take you back towards Earth, like this:

Edited February 7, 2014 by metaphor

[Nibb31]

Additionally, these flyby trajectories put your approach on the dark side of Mars, meaning that you won't see anything, which makes the whole idea of a manned 500-day trip pointless.

[Soda Popinski]

A 500-day flyby would take longer and require more delta-v because you have to be on a trajectory such that the gravity assist from Mars can take you back towards Earth, like this:

Ah, that makes sense. I forgot about the free-return in the OP.

[Albert VDS]

Sure you are at the dark side when closest to the planet, but you start off seeing it in direct sunlight.

[maccollo]

Additionally, these flyby trajectories put your approach on the dark side of Mars, meaning that you won't see anything, which makes the whole idea of a manned 500-day trip pointless.

They will see it as they approach and leave, and then they will be able to see the sun set and rise over Mars.

I wouldn't' call that pointless.

[Drunkrobot]

Why throw away the fly-by vehicle when you're ready for the landing? An Aldrin cycler (yes, THAT Aldrin) takes the concept of a space station (a long-term habitat for humans in space), takes it out of LEO, and puts it into a special trajectory, that gives it consistent fly-bys of two bodies in solar orbit (most designs involve an Earth-Mar-Earth-Mars trajectory).

A Mars mission usually involves launching three main components to the Red Planet- a small orbital vehicle for the crew to reside in during the launch and the final few days before Earth reentry (imagine a Soyuz, or an Orion), a lander to get down to the surface and back into Mars orbit, and a large, long-term space to live in during the coast between worlds. The third component is usually the largest and heaviest of the three. The Aldrin cycler replaces it, so the mission rocket only needs the necessary ∆V to rendezvous the short-term spacecraft/lander duo with the cycler, slashing the payload requirements. There's no limit to what size the cycler can be, it could be an ISS-clone with a larger pantry and a radiation shelter, and nobody doubt's such a station could make the journey.

If we ever do a manned fly-by mission before a landing attempt, we'll probably put the ship into a cycler-orbit, and repurpose it for the big mission.

Edited February 8, 2014 by Drunkrobot

[NikkyD]

Whenever i think about mars missions and the long trips, my biggest concern is the psychological stability of the crew. Earth orbit is still somewhat "safe" whereas on-route to mars is just OUT THERE. 500 days in a tin can, if something goes wrong ppl are gonna go nuts. You cant really train ppl for that.

[Drunkrobot]

Whenever i think about mars missions and the long trips, my biggest concern is the psychological stability of the crew. Earth orbit is still somewhat "safe" whereas on-route to mars is just OUT THERE. 500 days in a tin can, if something goes wrong ppl are gonna go nuts. You cant really train ppl for that.

People have survived for months stranded on wreaked ships and frozen wastelands, in an age where the food was horrible, discipline was handed out with a whip, and the best painkiller available for when you needed an amputation was alcohol. If the human mind can survive that torment for that long, then a crew with constant contact with their loved ones, a mission that they believed in, and an entire planet cheering them on should be able to keep it together.

[Kryten]

People have survived for months stranded on wreaked ships and frozen wastelands...

And people haven't. For all of the Mawsons or Admundsens there are Andrées and Crawfords, and there are likely to have been plenty more we've no way of knowing about.

[DerekL1963]

Whenever i think about mars missions and the long trips, my biggest concern is the psychological stability of the crew. Earth orbit is still somewhat "safe" whereas on-route to mars is just OUT THERE. 500 days in a tin can, if something goes wrong ppl are gonna go nuts. You cant really train ppl for that.

Submariners manage under conditions that would drive others insane. (Though some say that's because they've a protective inoculation of a different form of insanity.)

[Motokid600]

People have survived for months stranded on wreaked ships and frozen wastelands, in an age where the food was horrible, discipline was handed out with a whip, and the best painkiller available for when you needed an amputation was alcohol. If the human mind can survive that torment for that long, then a crew with constant contact with their loved ones, a mission that they believed in, and an entire planet cheering them on should be able to keep it together.

Well said. WERE GOING TO MARS MAN, CAN YOU BELIEVE IT?!

Saying that every time I wake up would be all the morale I need. Then once the red planet appears in the window.. "Jim how long has it been?" " Who cares.."

I do hope that we can give the future crew good meals atleast. Give me that, room to stretch and I'd be good.

[Aghanim]

There is one thing that are certain for the crew sanity: artificial gravity. So they wouldn't lose their bone mass, so they could do activities normally like we do on Earth. Like eating. Or peeing (yes, that is serious. Removing the need of space toilet is something)

[DerekL1963]

There is one thing that are certain for the crew sanity: artificial gravity.

[[Citation Needed]]

[hugix]

There is one thing that are certain for the crew sanity: artificial gravity. So they wouldn't lose their bone mass, so they could do activities normally like we do on Earth. Like eating. Or peeing (yes, that is serious. Removing the need of space toilet is something)

You're in space! You've just gotta be weightless. It's part of the experience.

I don't think AG is needed. First of all. When weightless you're able to utilize more space inside the craft. Look at the ISS how it doesn't have a ceiling. Every inch of space is used.

and bone mass and that sort can be combatted by a lot of training. Hell you're 500+ days in space doing not much. You might as well just train your muscles.

[LordOfTheOrbits]

With training you can only stop muscle decay, but no bone decay.

[Nibb31]

There are pharmaceutical solutions to bone decay. They are being experimented and refined in long term stays on the ISS.

Artificial Gravity is a technology that we know nothing about. It will take decades and lots of experimentation to get it to a TRL compatible with a manned interplanetary mission.

[Nibb31]

They will see it as they approach and leave, and then they will be able to see the sun set and rise over Mars.

I wouldn't' call that pointless.

It is absolutely pointless from any scientific perspective. You couldn't make any useful observations and you wouldn't have to time to teleoperate any useful experiments on the ground.

If all you want is the experience of watching a Mars sunrise and sunset through a 20cm porthole, then you could reproduce that with an IMAX projector for a fraction of the cost.

[Nibb31]

If we ever do a manned fly-by mission before a landing attempt, we'll probably put the ship into a cycler-orbit, and repurpose it for the big mission.

The cycler concept is only useful for hab space really, which is only a small fraction of the total mission. Any consumables or experiments need to go up and down with the shuttle craft, so you really won't be reusing much for each mission.

You still need to rendez-vous with the cycler, which is on an interplanetary trajectory, which means that the shuttle craft needs to have enough delta-v to get itself into that interplanetary trajectory itself. It also needs to carry the crew, the supplies for 2 years, the equipment, and the propellant for the cycler ship and the lander. Basically, the shuttle-vehicle needs to have the same mass as a conventional Mars Transfer Vehicle (ie. Copernicus), minus the hab module.

If you're reusing the Mars lander, then it will also have to inject itself into the cycler's orbit in order to rendez-vous, so you are going to need a really massive SSTO lander.

When you look at the details, you don't save much mass at all by using an Aldrin cycler.

Edited February 10, 2014 by Nibb31