The Martian

[Ghostrider]

A novel by Andy Weir. Feels like Cast Away on Mars with MacGyver in Tom Hanks' character place. Sounds fun. Or maybe not. Well, anyway now you know and knowing is half the battle.

 

[Nicholander]

I've read this book, and someone NEEDS to make a mod for it, NOW.

 

[francisdrake]

'The Martian' is an excellent read! Thrilling and realistic.
I made a concept of the Hermes spacecraft mentioned in the book and posted some pictures at DeviantArt.

I imagined Hermes as a 80 m long spacecraft, powered by ion engines and slowly spinning to provide artificial gravity.

 

[Nicholander]

Hmm? Why are the Ion engines in the front? And where are the solar panels? Oh, it's RTG powered. But why? You're just going to Mars, not Jupiter! I would've imagined something a bit like the canceled Copernicus.

 

[Shifty]

A novel by Andy Weir. Feels like Cast Away on Mars with MacGyver in Tom Hanks' character place. Sounds fun. Or maybe not. Well, anyway now you know and knowing is half the battle.

Having a MacGyver as the main character changes the whole character of the story. It's actually more like Apollo 13, where thing after thing goes wrong and each time one problem is surmounted with a unique and brilliant solution, another rears its head. The novel is excellent, fast paced and exciting; a thriller rather than a space procedural. The main character is kind of like a John Scalzi character, with a fun, likable, sarcastic wit. Matt Damon is supposed to star in the movie version, but the role struck me as more similar to Sam Rockwell's character in Moon.

 

[francisdrake]

Hmm? Why are the Ion engines in the front? And where are the solar panels? ...

Well, it is a concept, and there are probably more than one solutions to this. I looked for the bits of information strewn around the book and figured out a few more. For example, the 124 days travel time lead to a certain flight path and velocity.

The ion engines in this concept are located near the vessels' center. They can be swiveled sideways to allow continous thrusting while the vessel is rotating for artificial gravity.

A reactor is mentioned in the book. Calculating power requirements from thrust gave me a thermal output of 10 MW, which is a lot for a space-based system. This would be hard to achieve by solar power, especially further out in Mars orbit.

 

[Nicholander]

Hmm... I see, but, though it's a bit picky, I think there only being one docking port is a bit problematic. See, that's we the MDV goes, but if it's launched before the crew, where does the crew's spacecraft dock? Also, the habitation module seems a bit small for a more then a year long journey, or maybe you just made the EVAing astronauts in that one picture on your DeviantArt to large.

 

[francisdrake]

The idea is to have the Mars descent vehicle pre-deployed in Mars orbit. Hermes will dock to it. I'd rather prefer to take the lander with the manned mission, but this would significantly increase the mass and size of the Hermes crew vehicle.

Regarding the size of the hab: The astronauts are to scale, the hab is not big. I made it 7.6 m dia x 12 m long. It provides living space on three floors. The size is comparable to Bigelows BA 330 hab, which is considered to be big enough to accomodate 6 astronauts for a prolonged mission. Hope the crew does not get cabin-fever in there.

 

[Nicholander]

Nice image! But, if I remember correctly, Hermes spun so that it would create 1G on the bit of the habitation module closest to the walls, but since it doesn't have a wheel or anything sticking out, it looks like it would have to spin really fast. Is it possible to keep communication systems, Ion engines attitude, and other system functioning correctly at that spinning speed?

 

[Shifty]

Nice image! But, if I remember correctly, Hermes spun so that it would create 1G on the bit of the habitation module closest to the walls, but since it doesn't have a wheel or anything sticking out, it looks like it would have to spin really fast.

I calculate about 4 seconds per revolution to produce 1g at the outer diameter, which doesn't seem to fast. There would be a real problem with Coriolis effects though: it would be easy to become weightless by walking against the spin. And with a 2.5m radius, the apparent weight gradient would be pretty severe; a 2m person's head would be near weightless.

 

[PeterRoss]

Wiki about Coriolis effect in rotating spacecraft:

These forces act on the inner ear and can cause dizziness, nausea and disorientation. Lengthening the period of rotation (slower spin rate) reduces the Coriolis force and its effects. It is generally believed that at 2 rpm or less, no adverse effects from the Coriolis forces will occur; at higher rates some people can become accustomed to it and some do not; but at rates above 7 rpm few if any can become accustomed.

 

[MaverickSawyer]

Nice image! But, if I remember correctly, Hermes spun so that it would create 1G on the bit of the habitation module closest to the walls, but since it doesn't have a wheel or anything sticking out, it looks like it would have to spin really fast. Is it possible to keep communication systems, Ion engines attitude, and other system functioning correctly at that spinning speed?

You're not spinning about the long axis... Hermes tumbles end over end, with the spin axis in the direction of travel and the ion engines rotated to point in that direction.

 

[Nicholander]

But, as described in the book, it has areas with 0G in the habitation area, so if it was tumbling end over end, there would be no 0G areas, so you're incorrect.

 

[ISProgram]

At the center of the spin axis, there would be weightlessness. Isn't that where the hab is?

 

[Nicholander]

Where the Ion engines is is where the center of the spin axis is.

 

[francisdrake]

It is as MaverickSawyer says: The vessel rotates end-over-end. The gravity is only 0.4 g in the hab, about the same as on Mars. For this 3 rpm are sufficient (r=40 m).

The book describes an astronaut climbing upwards from the 'reactor room', then downwards into the living quarters. I ignored this on purpose :hmm:
There is no need for a 'reactor room', there are no serviceable parts to the reactor. I put it as far away from the hab as possible, to reduce radiation exposure. Together with the Brayton power converter and the radiator wings it acts as a counterweight for the spin.

 

[MaverickSawyer]

It is as MaverickSawyer says: The vessel rotates end-over-end. The gravity is only 0.4 g in the hab, about the same as on Mars. For this 3 rpm are sufficient (r=40 m).

The book describes an astronaut climbing upwards from the 'reactor room', then downwards into the living quarters. I ignored this on purpose :hmm:
There is no need for a 'reactor room', there are no serviceable parts to the reactor. I put it as far away from the hab as possible, to reduce radiation exposure. Together with the Brayton power converter and the radiator wings it acts as a counterweight for the spin.

Exactly. The inverse-square law, combined with a shadow shield, are your friend with the reactor on the boom like that.

 

[Shifty]

It is as MaverickSawyer says: The vessel rotates end-over-end. The gravity is only 0.4 g in the hab, about the same as on Mars. For this 3 rpm are sufficient (r=40 m).

The book describes an astronaut climbing upwards from the 'reactor room', then downwards into the living quarters. I ignored this on purpose :hmm:
There is no need for a 'reactor room', there are no serviceable parts to the reactor. I put it as far away from the hab as possible, to reduce radiation exposure. Together with the Brayton power converter and the radiator wings it acts as a counterweight for the spin.

Makes sense. At that rotational velocity, you'd gain/lose about 25% of your (Martian) weight by walking spinward/anti-spinward due to Coriolis effects. Seems reasonable to try to prevent straight line walking paths along the spin-ward axis.

Also, jumping 2 feet straight up into the air (easy in Martian-like gravity) would displace you by about a foot spinward from your starting location. Probably smart also to build in low ceilings.

 

[ex-orbinaut]

OK, I am looking for this book...

 

[francisdrake]

Just for Info, this is Andy Weir's website: http://www.andyweirauthor.com/

A link where an orbit-calculation app is displayed, with scenarios from the book: http://www.wired.com/2014/02/the-martian-software/