As far as “lithobraking” goes, one major chunk of the supplies needed for a Mars mission would be water. Water doesn’t break or become nonfunctional: What if you just froze a big lump of water, and did just crash it into the surface? Surface temperatures on Mars will usually be cold enough to keep it frozen, so it’d only disappear as fast as it could sublime away, and if it broke into pieces, no big deal.
Stranger : I know that orbital rendezvous are really hard, supposedly. But the existing dragon spacecraft has already done them. Yes, it only got within a few meters of the ISS because NASA didn’t want to risk a collision, but it is fully capable of docking.
So, here’s the pieces : SpaceX develops a dragon spacecraft with the right shape to aerobrake on mars. It manufactures a prototype, and sends it to Mars to test it. The spacecraft is shaped differently, but uses identical internal systems. That article I linked described burning 16 tons of fuel to get a landing, for a 42 ton landing mass. The author does a raft of graphs modeling the reentry. Aerobraking works until around 700 m/s, and it’s rockets after that.
We already know SpaceX can manufacture one half of a docking system that works, so they make the other halves, and weld them onto some kind of hub-structure.
You’re right, structural stresses during the trans-mars injection would be too high if you simply had a mess of modules connecting by docking ports out in space. By “lashing”, I meant connecting steel cables between specific points on the modules via EVAs and tightening them.
As for the difficulty of several years without resupply, it isn’t 3 years. It’s 6 months. SpaceX would have spare rockets and landers on standby ready to go, that they could stuff full of emergency spare parts and supplies and launch.
So, they launch all the pieces, dock them together, and I guess launch tanks of RP-1 + L-02 as the last step, as well as the rest of the crew. Everyone’s aboard, you burn off the RP-1/L-02 doing the trans-mars injection burn, and then it’s 6 months of waiting.
You would have something like 10 separate landers, each a slight variant on the spacecraft they already have. The idea is, you put the crew aboard the ones that look the healthiest when you get near Mars, and the cargo split between the others.
There is a big nasty problem with landing ellipses - you obviously want every lander that makes it down to land within a short distance of one another.
As for life support, well, the basic strategy would be a lot of parallel and redundant systems. The crew would have 3d-printers, lots of tools, and lots of spares for suspect components. You’d have to do a shakedown test - manufacture 10 or so sets of the life support systems that you plan on using, and test them in sealed rooms with real or simulated crew.
I mean, how complex does a life support system have to be? You have water tanks, pumps. A waste-water tank, and a low-pressure distillation machine. You have a tank of algae with LEDs above it, various pumps and fans to bubble air through the tank.
If you have a mountain of spare parts, and you trying to build everything using components that are as similar to each other as possible, it doesn’t seem at all unfeasible to “MacGuyver” your way to a working system when things break.
Then you would need various backup systems using differing parts and differing designs.
The thing is, for maybe 5 billion of the 10 billion pricetag mentioned above, you could in fact manufacture all of the rockets and do all of the launches. You could purchase existing life support equipment that might or might not work, and a mountain of spare parts. You could build and launch crude cylinders that might work for habitation during the trans-mars journey, and build and launch the docking ports connect everything together.
You’re basically saying that an efficient and determined group of people could not come up with workable solutions to the other problems that will probably work for a mere 5 billion dollars.
Remember, the Soviets/Russians put about 5 billion, total, into the entire Mir program. Sure, it wasn’t the greatest space station - but it did work, and nobody died. At the same cost efficiency, we could have launched 20 Mirs for the price of the current ISS. They might all be mediocre stations…but 20 stations populated by 3-6 people beats 1, I think.
None of this is going to happen until we have high thrust, nuclear powered rockets that can take us to Mars in two weeks. those 8 month transfer orbits would expose people to too much radiation.
Let’s look at some simple energy calculations just to get a rough scale of the problem without consideration for the particulars of the propulsion system. Let’s assume that a hypothetical powered landing Dragon capsule follows roughly the same reentry profile as the Apollo capsule (this is highly conservative in favor of the Dragon as the Apollo CM had a L/D of about 0.35 versus 0.18 for Dragon). That means that the vehicle would be moving at somewhere at a Mach number between 0.3 and 0.7 at an average altitude of 9 km, and a resulting average ground speed of 150 m/s. The dry mass of the Dragon is about 4200 kg. That gives it a total energy (potential plus kinetic) of E = mgh + 1/2mv^2 = 370*10[SUP]3[/SUP] MJ. The usable energy of a NiTet/MMH propellant at a mix ratio of roughly 1.7 is something slightly greater than 9 MJ/kg of propellant; let’s call it 10 MJ/kg for simplicity. Assuming we can fly a perfect trajectory with no waste to gravity drag, we’ll require 37 tons of propellant, which will occupy roughly 30m[SUP]3[/SUP], or three times the pressurized volume of the capsule, notwithstanding the mass of tankage and propulsion systems. If you assume a 45 degree angle for the thrusters, multiply mass and volume by a factor of 1.41. Given that the advertised payload mass to LEO is ~53000 kg, you can see that expending 60% to 80% of this on propellant to perform a powered landing of the capsule is indeed risible.
Are you asking if it is feasible to ship elements up and attach them together, or whether we can manufacture a ship out of in-situ resources? The answer to the former is yes, as has been demonstrated with the International Space Station. However, it took over a decade and an estimated US$150B to assemble the ISS, which does not have a propulsion system suitable to achieve an interplanetary trajectory, does not have a power source that would provide sufficient power for onboard systems at Mars orbit, and requires regular resupply in order to maintain operation. The answer to the latter is no, we cannot construct a spacecraft from orbital materials given the current state of the art, but that is the obvious and desirable solution which both avoids the need for costly and risky shipment of components from the Earth’s surface to orbit, and the design constraints imposed by having to built a vessel based upon what you can fly in individual payloads.
You seem to be assuming that the entire business of “docking” and “lashing” components together is all worked out, and it just remains for SpaceX to produce manufacturing drawings and fab it all up. The reality is that we have demonstrated the ability to dock and assemble small, lightweight payloads; not to handle large, bulky, and heavy payloads, secure them together in a fashion which they can withstand relatively high thrust. I know it must seem like this is just longshoreman type work and you can send up Bruce Willis and his rigging crew to do this in a few hours, but actually handling and assembling even small structures in free fall conditions is extremely difficult. On the ISS, the modules (which are lightweight, mostly empty structures) are manipulated with the on-board Mobile Servicing System (colloquially named the Canadarm2), and only minor final assembly tasks are performed via EVA. This is not a trivial activity to be dismissed out of hand; it will require substantial development of mechanisms and processes which have not been previously demonstrated.
A pseudo-Hohman trajectory to Mars is typically between 8 to 9 months, and that opportunity is less than once a year. (2020 does have an opportunity for a 193 day transfer with C3 of 13.2 km[SUP]2[/SUP]/s[SUP]2[/SUP] and a delta-V at Mars of 3.6 km/s, which is about the shortest transfer interval available using chemical propulsion.) If you don’t understand how available trajectories to Mars work, you cannot credibly evaluate how readily such a mission could be performed.
So, your plan, such as it can be described, is to send a veritable junkyard of parts plus some random hydroponics, and assume that that the crew can work it all out? Do you understand that a single failure of a critical system even for a few hours can result in loss of crew and mission? I have to ask, do you think that the Apollo program was successful because a few engineers drew up some random plans for a rocket and lander and a bunch of technicians used this as a general guideline to bolt together something roughly based on those plans and it was all held together by astronauts with bubblegum and bailing wire?
In the aerospace and rocket launch industry we have a well-worn saying: “Failing to plan is planning to fail.” In the original post asked about an engineering opinion of the feasibility of a low cost Mars mission. You’ve been provided with detailed explanations of why just hacking things together on a shoestring isn’t feasible for this scope of mission, especially when success of the mission is dependent upon maintaining the health and functionality of a human crew. Assuming that things will all work out is a recipe for disaster and loss of all the investment of time and budget, not to mention lives of the crew.
Stranger
No. First, the standard transfer orbit is 6 months to Mars. Second, the expected dose is only around 0.66 Sv. The headline is expectedly hyperbolic, but as the text says, a 1 Sv dose only increases the risk of cancer by 5%. A one-way trip would therefore be in the realm of 2%.
These figures are barely worth mentioning as it is, but in the context of someone retiring on Mars it’s even less relevant.
This is crazy talk. I don’t know which numbers you plugged in, but regardless you’re off by 3 orders of magnitude (I’ll use Earth gravity):
4200*(9.819000 + 0.5150*150) = 418 MJ
Not 370,000 MJ. With Mars gravity the number is reduced to 187 MJ.
Also, I have no idea why you’re including potential energy. Fuel efficient powered landings use suicide burns. You coast to terminal velocity and burn at the last moment when potential energy is negligible. The SuperDraco engines are designed for a launch abort system and have crazy thrust–they could decelerate at around 6 gees if necessary. You wouldn’t do that for a manned landing but the reserve capacity gives a nice safety margin.
The Dragon capsule is subject to the same rocket equation as anything else. With a reduced ISP of 212 (300/sqrt(2)), 150 m/s of delta V only requires 314 kg of propellant. 500 m/s needs 1142 kg.
No, this is not correct. The average time of a Hohmann transfer is around 260 days. There are rare opportunities for shorter periods at the expense of a high C3 energy and the high end of delta-V at Mars, but that results in a substantial reduction in payload per energy expended or propellant carried. The “Mars cycler” trajectories offer some shorter transit periods but also at high energy levels to rendezvous and often long periods between useable synodic periods.
You seem to be neglecting the additional radiation that would be experienced on the surface of Mars. With its lack of a magnetosphere and thin atmosphere, the exposure on the surface is nearly the same as being in transit. Of course, you could burrow 10 meters below the Martian surface…which is perfect if your idea of retirement is living the remainder of your life in a bomb shelter. Or you can spend your days on the surface with a progressively increasing likelihood of developing cancer or other chronic radiation-related illnesses out of the reach of palliative medicine. Sounds like a great plan for retirement.
Stranger
Upon doing a bit more research, I withdraw this claim. 6 months is a lowball number for rare transfer windows; the average seems to be more like 7 months. Doesn’t change the overall point, though–the radiation dose isn’t enough to worry about unless you’re NASA and obsessed with PR.
Damn, you beat me to my own correction :). I was actually surprised at the variation and incorrectly assumed that the average window wouldn’t be much more than the minimum window. My bad.
Yes, but I was responding to ralph124c’s proposition that we’d need a nuclear rocket to reduce the transfer time. Obviously this is unrelated to the dose received on the Martian surface.
The surface dose is 0.64 mSv/day. Let’s assume that you spend 8 hr/day on the surface and the remaining time underground. That comes to 0.078 Sv/yr, or 13 years for a 1 Sv dose. That doesn’t sound like terrible odds to me.
Dr. Strangelove, Stranger certainly doesn’t need my help, and it’s possible he has made a mistake in math somewhere, we’re all human, but…
You do understand you’re talking to an (very probably) actual steely-eyed missile man, right? Look back over his posting history, when he talks about some of the things NASA has done, there’s a definite “and then we” vibe in there. This is a guy who knows his shit about the space program, inside and out, upside and down.
Look, Elon Musk is a cool, smart guy, no doubt. But what Mr. Musk has been doing lately is throwing out half-baked, badly underthought ideas* and saying, “why not try this?” He then gets millions of dollars worth of free analysis and design work done for him for free by the great interwebs. It’s somewhat brilliant except that so far all his ideas have related to things that those same bright people have already been stewing on for years. If there’s an easy answer to getting to Mars, we probably would have heard of it before now, right?**
- Like his steel tube transport idea that took about 3 seconds to demolish simply based on thermal expansion of the tube. Yeah, you might could engineer around that, but then it’s no longer really the same idea and no longer doable under the stated budget (not that it really ever was, but certainly not after you add all those joints to it). This strikes me as much the same way.
** This whole thread reminds of that scene (probably apocryphal or just flat made up) in From The Earth To The Moon where the two guys are pitching their idea of just sending men to the moon as quickly as possible and then keeping them supplied while they figure out how to get them home. I liked the NASA guy’s response “Gentlemen, I’m sorry, but there is no way on God’s green Earth that we would EVER do anything like that.”
I’m aware of that and absolutely respect his experience, and have both enjoyed and learned a great deal from his posts. But I’m also one to question the numbers no matter who is posting them. Maybe I made a mistake too; I’ll own up to it (and did so on the transfer orbit time above)–that said, I don’t see how his numbers add up. I look forward to his response.
In other news, although I am a software engineer by trade, my own satellite, a cubesat, is due to be launched to the ISS on the 19th. However, there is a chance of further delay due to the minor emergency they had on the ISS.
Not that this makes me an expert by any means, but I’ve interacted with enough folks in the industry to see that there’s a degree of… I dunno, protectionism, or conservatism. Not sure what exactly, but it brings to mind Clarke’s first law:
When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
So in all cases I say show me the math. Sometimes it adds up and sometimes not. Musk is overenthusiastic, but IMHO that’s just the Silicon Valley spirit at work. Think out loud and get the response. Don’t be too tied to a single strategy. Don’t treat long experience as gospel truth because of the assumptions built into it. And so on.
We’ll see if it works out in the long run, but in the meantime SpaceX is showing great success, and so I don’t think the naysayers get a free pass any more, especially when they have a vested interest (ULA, cough) in the status quo.
If Mars was paved with gold? Shipping it back to earth would be prohibitive-so suppose we mined it and cast it into bars…and kept it on Mars? We then issue depository certificates-establishing ownership.
Sorta like having your gold stored in a vault (that you cannot get into)on earth. Would such gold have value?
See the Bitcoin threads for a discussion on how something with no intrinsic value can nevertheless be useful as a currency. Short answer is that your proposal could conceivably work, but the price would have nothing to do with the actual price of gold, and instead be mostly related to the scarcity and utility of the certificates. You might as well print certificates for invisible unicorns–it would work just as well.
First off, congratulations! But understand, that with cubesats there is always the chance of further delay. When I was at Montana State, I watched as their cubesat program got delayed by something like 3 or 4 years, just by virtue of being perpetually at the bottom of the launch pecking order, and even when they did get a launch, the mission was only 90% successful (defined beforehand by the project leaders as “working payload is delivered successfully to the launch site, and then blows up on launch”). Which of course added further years (though they did eventually get a 100% successful similar satellite).
Thanks!
Our total delays are so far up to around 7 months, which really isn’t so bad in the grand scheme of things. It helps that we’re actually a paying customer due to our Kickstarter campaign. And frankly, the delays helped us build a better product, and I am pretty confident about things. We have a small but very solid team. Our backup unit is currently in Australia with one of our ground stations, and despite having a known-flaky radio, we’ve been quite successful in operating it remotely from here in California (obviously, most of that distance was through the internet, not the radio link, but the radio segment was realistic aside from distance).
We were cautioned about the Explorer-1 and M-Cubed incident: don’t use too strong a magnet! Like most cubesats, we do have attitude control magnets, but they are fairly weak. Also, we have spring-loaded solar panels that deploy after a while, and I suspect there is a good chance they could swat away another cubesat on the off chance they got stuck together.
Attitude control magnets, eh?
Regarding my “lashing” idea : you know those winches they put at the front of offroad vehicles?
Where there’s a drum, and a steel cable wrapped around it. You can unspool the winch, hook up to something, and then apply tension.
You could build a space-rated version that has a mechanism (strain gauges, motor current, or some similar sensor) to precisely apply a certain amount of tension. A brake engages once the tension level is right to lock the cable at that point.
You’d mount these winches at key points along the spacecraft you are planning to “lash” together. You’d develop a structural loading model : basically, you’d have a 6 way docking hub, and the modules attached to the lateral ports - as in, outwards in a radial direction away from the module that has your rocket engine - are the ones you have to strap down.
The only thing the astronauts have to do is leave their capsule, grab a winch cable (astronaut inside the capsule throws the winch motor into reverse), clamber or jet over to an attachment point installed on the center shaft, and connect it up.
Undoubtedly, this would be harder than it sounds, but nowhere near as complex as the repair EVAs that have already been done. And I do acknowledge that there are nasty problems with this - such as materials that work fine on earth, like those cables, acting completely differently out in space.
Also, you would do the trans-mars injection burn at a relatively low rate of acceleration. Looking at a delta-v table, you have about 2k delta V you need. You could do the burn over several hours and not increase the needed delta-v by very much.
Anyways, yes, you would need to plan. And, similarly, my idea of a mountain of spare parts for your life support system would need some level of testing and modeling.
One final comment. 100 billion to put 6 people on Mars is just stupid. I think I have established that in fact you could purchase and launch hardware that might work for a tiny fraction of that cost. You could probably try 10-20 times using a cheaper method. You could do a 5-10 billion expedition, then, when the crew die on the way, you just pack more of the stuff that broke the last time and do another launch.
Callous? Politically untenable for NASA? Sure. But, probability is that the cost to get to a successful mission would be a lot less than spending 100-200 billion to do it perfectly the first try.
So you think we might be able to get 6 people to Mars for about the cost of replacing a 3-mile-long bridge?
Are you including the cost of keeping these people alive for a while, or do they just plant a flag and die?
Kill 6 people on a slapped together Mars mission and you wont get the chance to try again for a generation.
Spending 100 billion over 10 years to develop the infrastructure for a primitive science camp might be doable - launch vehicle(s), in-situ resource extraction and basic power generation all need development. Retiring on Mars in luxury anytime soon? I don’t think so.
Aaaaaand we got cancelled. But not before flying to Chicago (on our way to Virginia)! Miraculously, we managed to get flights back to SFO within a couple of hours. I think this qualifies as my first $500 burger.
Next launch opportunity is no sooner than Jan 13. We’ll see…
Yep. It’s a passive system. A magnet aligns the cubesat to Earth’s field, and a magnetic dissipation material keeps it from oscillating. Eventually it winds up in a reasonably stable orientation.
You have a serious momentum problem here. As soon as you start winching in the modules, the only thing that will stop their motion is bumping into you.
Also, anything that requires an EVA is already pretty dicey. EVAs are stressful and inefficient, and astronauts spend hours doing relatively trivial tasks. It would be really nice to avoid them. Fortunately, space is an ideal environment for automated systems.
Here’s a slightly different tack. Each module comes with several docking points, each of which has a 6 DoF platform (similar to this). You use thrusters or a robot arm to get the module within range of the points; each platform has a camera or other sensing device so that it can spot its mating pair and gently attach. It then pulls the platform inward and engages a mechanical lock. Each point has electrical connections at the least; probably water and coolant hookups would be useful as well.
