Commander Lewis’ comment that the Hermes crew would never be on another space mission has precedent in the Apollo 7 ‘mutiny’. I was a bit disappointed that the movie showed Martinez in the Ares 5 crew. I was happy for Martinez, but yes after pulling a stunt like he did there is no way NASA would give him a valuable slot on another mission.
My guess, as a civilian, is that if the Hermes crew had failed to rescue Watney and somehow survived, they would have been forced out of the astronaut corps and (as applicable) the military - all very quietly. They probably would have been allowed to retire, under unofficial threat of a very public and messy trial.
Stranger, the way it works - this is shown in the movie as well - is there’s a big ring of equipment that fits like a collar on the bottom. The same engines used for the first ascent stage are used for the landing, this seems like an obvious weight savings. (it’s a 2-stage rocket, in both the book and the movie)
When it lands, the rocket is nearly dry of fuel. What it does land with is just enough finished fuel + oxidizer for the landing, and a significant quantity of liquid hydrogen. I don’t know it if uses aerobraking, I would expect the reentry profile probably brakes down to terminal velocity for an egg shaped object that is mostly empty of fuel, and then a suicide burn for landing.
After landing, the ring of equipment at the bottom synthesizes more fuel and oxidizer, using nuclear heat/electricity from an RTG, CO2, and H2. It makes methane and LOX from this. Now, a key plot point in the book is it also makes hydrazine as well. I don’t know where the nitrogen comes from, or what the synthesis is. And, there were tanks full of hydrazine - excess from the fueling operation - for Watney to burn to water - available right there at the bottom of the rocket. Also, there was an iridium catalyst available handy somewhere as well.
Now, some of the Mars proposals involve somehow extracting water from the martian soil, the issue is, the equipment to move all that earth into some kind of processing machine to get all that water out is a lot of heavy machinery, probably equal in size and mass to a bulldozer + wood chipper on earth. Hydrogen, OTOH, is the lightest element in the universe - the heavy part is the cryostat and the cryocoolers to keep it contained.
Laws only go as far as you can find a jury, anywhere, willing to convict. I don’t know if prosecutors could put together a pool of people willing to convict astronauts for trying to rescue their comrade no matter how many people they pulled for jury duty.
The ion engine has a maximum of 2 mm/s/s acceleration. The ability to aerobrake allows them to maintain higher velocity for longer in order to reduce the trip time.
Yes, but it raises the mass of the whole vehicle. With VASIMR, you can adjust your ISP to your trip time and power supply. I suspect you would be better off carrying more propellant mass instead of an aeroshell, and running the VASIMR in a lower ISP mode (basically throwing more propellant out the engine a lot slower) instead.
Fairly easy to work this out. If the aeroshell is 10% of the mass of the vehicle, and you gear down to 1000 ISP, and you can only safely shed 6000 m/s with the aeroshell…huh. More propellant only gets you 1000 m/s.
10%, though, is probably totally wrong. As you hurtle through the thick martian atmosphere, you experience large G-loads on the structure of the ship. That means you have to reinforce your whole ship to tolerate them. And, of course, there’s the danger factor - loading up more propellant, even spending a little more time on your journey sounds a lot safer than risking burning up on a hot aerocapture.
To my above post : I meant to say as you fly through the thickest portion of the thin martian atmosphere. Which is another issue - as I understand it, the reentry heating is a lot worse when you are traveling at high speeds through thin air. So an aerocapture on Mars would be an extremely hot maneuver and you’d be flying extremely low.
From what I recall in the book, the hydrazine and the catalyst was from an RCS system on the lander stage (the catalyst being part of each thruster). I’m not entirely sure why this would be left behind. However, it seems plausible enough that the MAV would need a beefy RCS system for landing, no RCS system for the first ascent stage where the ascent engines provide plenty of control authority, and a much smaller RCS system for the upper ascent/orbital stage.
At lower atmospheric density, speed is higher at the same dynamic pressure. That poses a problem with aerobraking and landing on Mars because there is both much more heating due to more time spent at speed until aerodynamic breaking slows down the vehicle, and less density of gas to carry away heat by convection once the spacecraft slows down. But aerobraking is essentially “free”, e.g. it doesn’t add a burden to the propellant load, so it is just a trade between the additional inert weight of an aeroshield versus the saving mass of propellant and the inert mass of propellant storage and insulation; however, that comes with the risk and uncertainty of an aerocapture maneuver, especially for a large vehicle. Most Mars crewed mission architecture concepts since 2000 use propulsive deceleration for the carrier vehicle, and essentially all used it in the entry and descent phases of a lander vehicle, typically an inflatable toroidal or conical supersonic decelerator plus a supersonic retropropulsion system for targeted descent and terminal landing.
Did Mark Watney live completely in his suit the entire time he drove the vehicle to the other base? Once he was in the new ship and could take the suit off, he was shown trying to tend to the pressure sores all over his body.
In the book he created himself a bedroom with tent fabric. I thought the sores were from not showering and nutritional deficiency. I guess the spacesuit explanation makes more sense, those Mars surface suits are supposed to be really tight, like this.
It was a lot more telegenic to show him underneath his rover after a hard night of driving, look at the stars. Literally sleeping under the stars. I guess he must have plugged his suit into the rover’s power and air supply. I wouldn’t want to sleep on battery like that, dependent solely on the life support system in a spacesuit. Not that the rover would be that much more comfort.
Surplus hydrazine left over from the landing…
Several staged sets of chutes deployed automatically to slow our descent, then Martinez manually piloted us to the ground, using the thrusters to slow descent and control our lateral motion. He’d trained for this for years, and he did his job extraordinarily well. He exceeded all plausible expectations of landings, putting us just nine meters from the target. The guy just plain owned that landing.
Thanks, Martinez! You may have saved my life!
Not because of the perfect landing, but because he left so much fuel behind. Hundreds of liters of unused hydrazine. Each molecule of hydrazine has four hydrogen atoms in it. So each liter of hydrazine has enough hydrogen for two liters of water.
I did a little EVA today to check. The MDV has 292 liters of juice left in the tanks. Enough to make almost 600 liters of water! Way more than I need!
There’s just one catch: Liberating hydrogen from hydrazine is…well…it’s how rockets work. It’s really, really hot. And dangerous. If I do it in an oxygen atmosphere, the hot and newly liberated hydrogen will explode. There’ll be a lot of H2O at the end, but I’ll be too dead to appreciate it.
Did anyone else think the book and movie glossed over how dangerous hydrazine is? I don’t see how Watney could be alive after releasing it in the Hab to make water that way. Or is it not as dangerous as I’ve been led to believe?
Methylhydrazine is used as a high-energy fuel in military applications. Acute (short-term) inhalation exposure to high levels of methylhydrazine may cause lacrimation, eye redness, nasal and respiratory irritation, headache, malaise, vomiting, diarrhea, ataxia, anoxia, cyanosis, tremors, and convulsions in humans. Acute exposure to methylhydrazine in humans has also been observed to affect the blood, kidneys, and liver. Methylhydrazine is highly corrosive and irritating to the skin, eyes, and mucous membranes of the respiratory system in humans and animals. Chronic (long-term) inhalation exposure to methylhydrazine has been observed to impair function of the kidneys and liver, affect the blood and spleen, and cause convulsions in animals. EPA has not classified methylhydrazine for carcinogenicity.
In monopropellant rocket applications it is typically loaded remotely and sealed in passivated stainless steel lined tanks. We are briefed to be aware of a “fishy” smell, but what the briefings invariably never seem to consider is that most launch sites are on the ocean so everything smells like fish, and by the time you smell hydrazine you’ve already experienced significant exposure due to the low threshold. Keeping it cold would limit the volatility (flash point at 265 K, freezing point around 220 K). If I were going to try to do this I would probably try to convert it to hydrazine monohydrate, which is still toxic and carcenogenic but at least less volatile. I’d still wear a respirator, gloves, and a hood, or maybe a spare pressure suit. Was Watney not wearing any protection?
