Trip to Mars on hypergolics

[fredinno]

4 minutes ago, Rune said:

 

If you meant at the start of the mission, then you are misunderstanding other things. Leaving EML1/2 is free, mathematically speaking. You will leave it in a random trajectory if you do nothing, actually, and some of those random trajectories become actually hyperbolic, and thus escape trajectories already. Now if you want to leave it quickly, along a defined trajectory, yes, you do need some dV to control things. If you were to use EML 1/2 as a staging point, you wold do just that, letting the ship fall in a slow, chaotic trajectory over a few weeks into a low perigee, high apogee orbit with a semi-major axis very similar to the Moon's (the requirement to be synchronous with it, to have the option to keep changing your orbit "for free" every 28 days). Then, at your closest approach, you would kick yourself into your chosen hyperbolic escape trajectory, and be on your way with a very small Pe quick. But I am not equipped to calculate the dV requirements of such a maneuver, and I can almost guarantee you aren't either. You would need one of the very custom programs JPL uses to handle complex integrations of the n-body problem around boundary condition, and run them in a very beefy computer for a few weeks to optimize the results.

Source?

It seems fishy... going out from EML-1/2 should leave you in a roughly-circular Earth Orbit...

6 minutes ago, Rune said:

Let me be clear, the point of going to an Earth-Moon lagrange point before heading into interplanetary space is not to lower the total amount of dV (even tough it can do just that). It seems you keep on believing that's what I'm trying to do here. Instead, the point is to break the ejection into smaller burns, that allow a better stage efficiency and a smaller ejection burn. The benefit is felt on any mission that employs limited Isp or fuel transfer, dramatically decreasing the requirements of the escape maneuver and thus decreasing the size of the ejection stage(s). It also goes very well with reusability, bringing many roundtrips into the realm of chemical propulsion, thanks to the diminished ejection requirements, and is the reason EML 1/2 always crop up in discussions about fuel depots. They are short of another halfway point, between LEO ad the rest of the solar system.

Yes, but without a fuel depot (presumably fuel from the Moon, otherwise LEO is probably better, offering greater orbital flexibility) it's kind of stupid to stage in EM-1/2.

Yes, the ejection burn is lower, but guess what? You can carry all the cargo on separate missions, lowering the individual vehicle mass, and increasing TWR. Not only that, you can do a 2nd burn for cargo, since passing through the Van Allen is less of a problem (only carrying the HAB on the manned mission). You probably will be able to get away with a 2nd earth departure burn for crew too, since any HAB will require a "Storm Shelter" for solar storms, so any humans can go inside that during the pass through the radiation belts.

10 minutes ago, Rune said:

That is easily solvable by launching big stages empty, as is indeed the scenario I was talking about (I did write about <40mT stages carrying >400mT of propellant, I'm sure of that!). As I also showed above, even very inefficient fuel delivery vehicles can compete on price with superboosters, mostly because they launch on rockets with much better price per kg.

No, that's not how things work. Super-boosters like Saturn V have larger payload fairings (10+ meters diameter) than EELV-class boosters, which max out at 5 meters diameter. Length is also limited by how long of a payload you can offset with the control mechanisms on the rocket. Thus, more modules are the only choice. And if you have a super-booster, you'd probably want to use it at least once a year to make it viable cost-wise. Thus, you need to use it to launch the fuel, to give the rocket a reasonable launch rate. It's either one or the other.

 

[Rune]

47 minutes ago, fredinno said:

Source?

It seems fishy... going out from EML-1/2 should leave you in a roughly-circular Earth Orbit...

Try this one. Hitten captured form a highly eccentric orbit without fuel, for example, as is explained there, and you can also look into the story with the ICE spacecraft, whose capture form a Halley-crossing orbit (after it had been on Earth-Sun's L1 doing its primary mission!) failed. Of course, it's a collection of such obscure mathematical tricks exploiting the more exotics aspects of the n-body problem, that not many people know it even exists, much less how it works, much less are capable of doing it themselves. Before you ask, no, I don't know how to do it! And BTW, before you raise the very next objection I know you are going to raise (Hitten's trip took three months), know that there is a continuum of solutions, so some are fast and cheap, others are slow and expensive, and everything in between.

47 minutes ago, fredinno said:

Yes, but without a fuel depot (presumably fuel from the Moon, otherwise LEO is probably better, offering greater orbital flexibility) it's kind of stupid to stage in EM-1/2.

Yes, the ejection burn is lower, but guess what? You can carry all the cargo on separate missions, lowering the individual vehicle mass, and increasing TWR. Not only that, you can do a 2nd burn for cargo, since passing through the Van Allen is less of a problem (only carrying the HAB on the manned mission). You probably will be able to get away with a 2nd earth departure burn for crew too, since any HAB will require a "Storm Shelter" for solar storms, so any humans can go inside that during the pass through the radiation belts.

I am doing this for the minimum payload, the transfer Hab. Doubtful you can go any smaller than that... After working out the numbers, I also have pretty tiny transfer stages, around 100mT fueled and somewhere under 10mT dry. So I totally don't get what you are saying here.

Which of course is the reason EML 1/2 brings a benefit, otherwise the Earth departure stages would be about twice the size (MR~3.8 on the ejection alone), instead of identical to the return stage (not quite a lucky coincidence ). Also, assembling in LEO you would have to assemble at a specific plane, for a specific insertion at a specific date, while a Lagrange point allows for a lot of flexibility around that for a relatively small stationkeeping bill. I'm told by NASA (you can glean it from recent presentations) that DRO is another of those really handy points at the top of Earth's Hill sphere where it makes sense to stop, on account of really low parking fees.

47 minutes ago, fredinno said:

No, that's not how things work. Super-boosters like Saturn V have larger payload fairings (10+ meters diameter) than EELV-class boosters, which max out at 5 meters diameter. Length is also limited by how long of a payload you can offset with the control mechanisms on the rocket. Thus, more modules are the only choice. And if you have a super-booster, you'd probably want to use it at least once a year to make it viable cost-wise. Thus, you need to use it to launch the fuel, to give the rocket a reasonable launch rate. It's either one or the other.

Sigh... a 25m tall, 5m diameter cylinder would hold about one thousand metric tons of water, 2Πr²xh and all that. MMH/NTO propellants are denser than water at stoichiometric rates. So a 2.5m tall, 5m diameter tank is about the biggest thing we need, to hold ~100mT of propellant. Wait, the transit hab will be longer even if it is packed as an inflatable that fits a EELV fairing, won't it? Damn, I no longer need the superexpensive SHLV at all if I can raise the pieces to EML1/2 and then refuel them again! I guess I could still use it to inject the payloads to EML1/2 and only need to refuel there, if it was a political imperative... 

 

Rune. Did I address all your concerns now?

Edited March 24, 2016 by Rune

[lobe]

On 3/23/2016 at 7:32 PM, Rune said:

All big components (Lander, surface Hab, transit vehicle) are sized to around 40mT.

Just re-reading through this to make yet another amendment to my mission plan (trying for Earth-Moon Lagrange-1 this time, and maybe some refinements on the mass of tankage+engines), how on Earth is anything going to be sub 40 tonnes (just found out I have been spelling tonnes tons)? Even with a lower mass of 11.9 ( I calculated 24.5 tonnes before @DBowman mention the BVA doc) for supplies, I still think for a transit hab the mass is going to be close to 100 tonnes. I would assume for any Mars mission the lowest payload mass will be 100 tonnes, at the very least 80 tonnes. For even the lander and the Mars hab the transit masses were still around the 150-200 tonne range. 

Edited March 25, 2016 by lobe
Made a mention

[DBowman]

 

2 hours ago, lobe said:

how on Earth is anything going to be sub 40 tonnes

I've lost track of your crew size? is it 4 or 6? BAV says 9 m³ / crew is 'performance' and 18m³ (from memory could be wrong) for 'optimal'. Cygnus 'regular' is 1500kg for 18.9 m³ and 'enhanced' is 1800 for 27m³. Enhanced is regular with an extra 'segment', probably you can add a few more segments without major structural change, so a 'triple plus enhanced' ( +3 more segments ) could be 2700kg for 51m³  - about 3 crew at optimal, 6 at performance. If one made the trans hab from docking a couple of those a single hab failure would leave you at 'performance' level. Dock them to an airlock, docking, & 'other stuff' module it would mass like 10 ton? double to 20 ton for extra structure and fittings, add supplies and then you have 8 ton left for an Earth reentry vehicle and margin. Am I under budgeting?

In one scenario the transit vehicle does a flyby that it can optionally capture from, providing a safe abort. The 'Mars Descent Ascent Vehicle' would have been sent earlier and be waiting in Low Mars Orbit to be remote control docked, similarly the return insertion and Earth recapture stages. You could leave the transit hab in high elliptical orbit and transfer to a previously sent Mars Orbital Hab - this could have the surface stay supplies (so the transit vehicle only needs flyby supplies).

There are a million ways to slice it, but using Cygnus as a rough cut analog it seems like you could do something for 40 ton.

[lobe]

I like using Skylab because it looks comfy, for even six people. How is this not comfy?

[Rune]

3 hours ago, lobe said:

Just re-reading through this to make yet another amendment to my mission plan (trying for Earth-Moon Lagrange-1 this time, and maybe some refinements on the mass of tankage+engines), how on Earth is anything going to be sub 40 tonnes (just found out I have been spelling tonnes tons)? Even with a lower mass of 11.9 ( I calculated 24.5 tonnes before @DBowman mention the BVA doc) for supplies, I still think for a transit hab the mass is going to be close to 100 tonnes. I would assume for any Mars mission the lowest payload mass will be 100 tonnes, at the very least 80 tonnes. For even the lander and the Mars hab the transit masses were still around the 150-200 tonne range. 

I remembered that Transhab, an inflatable habitat designed for Mars missions by NASA, was around 37mT, so I rounded to the nearest round number. For comparison, the Salyut habitats were around 20mT. I haven't even thought about the lander yet, I figure if you work out a reasonable thing to get the crew there and back, you can always find a way of making the cargo one-way flights. As long as the lander is under 120mT (and I remember lander designs under that), it could use the same departure stage, and the surface Hab should be lighter on account of not needing to take off.

 

Rune. BTW, I think EML2 is supposed to be a bit better for this kind of thing than L1.

[DBowman]

10 minutes ago, lobe said:

I like using Skylab because it looks comfy, for even six people. How is this not comfy?

Sure, what's not to love (apart from the mass...) - I especially liked the 'hamster wheel' videos.

[lobe]

5 minutes ago, Rune said:

Rune. BTW, I think EML2 is supposed to be a bit better for this kind of thing than L1.

I will go with EML-2 then. I really do not think trans hab was applicable to the Apollo Application Project or even any project other than Constellation.

[fredinno]

23 hours ago, Rune said:

Try this one. Hitten captured form a highly eccentric orbit without fuel, for example, as is explained there, and you can also look into the story with the ICE spacecraft, whose capture form a Halley-crossing orbit (after it had been on Earth-Sun's L1 doing its primary mission!) failed. Of course, it's a collection of such obscure mathematical tricks exploiting the more exotics aspects of the n-body problem, that not many people know it even exists, much less how it works, much less are capable of doing it themselves. Before you ask, no, I don't know how to do it! And BTW, before you raise the very next objection I know you are going to raise (Hitten's trip took three months), know that there is a continuum of solutions, so some are fast and cheap, others are slow and expensive, and everything in between.

...Yeah...

I'm going to take the safe route, and not build a Mars mission based off gravitational anomalies that may or may not take months to get from point A to point B. No thanks.

23 hours ago, Rune said:

I am doing this for the minimum payload, the transfer Hab. Doubtful you can go any smaller than that... After working out the numbers, I also have pretty tiny transfer stages, around 100mT fueled and somewhere under 10mT dry. So I totally don't get what you are saying here.

Which of course is the reason EML 1/2 brings a benefit, otherwise the Earth departure stages would be about twice the size (MR~3.8 on the ejection alone), instead of identical to the return stage (not quite a lucky coincidence ). Also, assembling in LEO you would have to assemble at a specific plane, for a specific insertion at a specific date, while a Lagrange point allows for a lot of flexibility around that for a relatively small stationkeeping bill. I'm told by NASA (you can glean it from recent presentations) that DRO is another of those really handy points at the top of Earth's Hill sphere where it makes sense to stop, on account of really low parking fees.

Yeah, and you need more launches overall due to not being able to use the Oberth effect. And no, I'm not going to use the Interplanetary Transport Network, to play it safe. And you need to do orbital inclination changes to get to Lagrange points, you know. An international mission could still be stationed at a low inclination, like Cape Canaveral, or French Guiana, by making the part built internationally, and the launches by only nations that can access the Mars mission location. The ISS was done so that Russia could launch their own modules too, so that was why it needed such a high inclination.

Going to L-points requires inclination changes to 0 degrees inclination. It's far less of a deal going to Mars. At most, you're losing 300 m/s per launch, and that's if you are launching polar (very unlikely).

And come on. We have plenty of experience with orbital rendezvous transfer windows. It's not a huge deal.

On 3/24/2016 at 1:47 PM, Rune said:

Sigh... a 25m tall, 5m diameter cylinder would hold about one thousand metric tons of water, 2Πr²xh and all that. MMH/NTO propellants are denser than water at stoichiometric rates. So a 2.5m tall, 5m diameter tank is about the biggest thing we need, to hold ~100mT of propellant. Wait, the transit hab will be longer even if it is packed as an inflatable that fits a EELV fairing, won't it? Damn, I no longer need the superexpensive SHLV at all if I can raise the pieces to EML1/2 and then refuel them again! I guess I could still use it to inject the payloads to EML1/2 and only need to refuel there, if it was a political imperative... 

...And why would you use Hypergol for Earth Ejection? You want H2/O2, so that you get higher ISP, an lower overall mission mass (and higher TWR). Boil off is not as huge of a deal if you can launch fast enough, and with Saturn V with 4 SRBs, you can launch an enormous amount to LEO in one year. And cryogenic fuels will need a larger tank.... especially H2/O2, which would probably need a tank at least 6-7 meters wide. Not to mention NASA considered the 8 meter diameter faring too small for its SLS/Orion Mars mission proposals, and wanted 10, and even 12 m diameter fairings (even though they used inflatable heat shields, to reduce mission mass, and use as much of the thin Martian atmosphere to slow down as possible.

Inflatable HABs are impossible for a 70s mission, like this one- the tech was not yet there yet.

12 hours ago, lobe said:

I like using Skylab because it looks comfy, for even six people. How is this not comfy?

It's comfy, but very heavy, at ~70 tons. https://en.wikipedia.org/wiki/Skylab

11 hours ago, DBowman said:

Sure, what's not to love (apart from the mass...) - I especially liked the 'hamster wheel' videos.

What 'hamster wheel' videos?

11 hours ago, lobe said:

I will go with EML-2 then. I really do not think trans hab was applicable to the Apollo Application Project or even any project other than Constellation.

No, the tech did not even exist by then. HOWEVER, you can use a "wet workshop" to save launch mass. Here: https://en.wikipedia.org/wiki/Wet_workshop

Of course, you need a lot more missions to test THIS, and aerobraking, but you can live in it a year with resupply before docking it with the Mars vehicle to make sure it works perfectly.

[DBowman]

24 minutes ago, fredinno said:

What 'hamster wheel' videos?

hamster wheel a little way in I wonder if they planned it that way? You might be able to get a good workout using 'body inertia' (cf body weight exercises).

[Rune]

2 hours ago, fredinno said:

Yeah, and you need more launches overall due to not being able to use the Oberth effect.

I've already explained you why that is wrong. You can look it up above.

2 hours ago, fredinno said:

a Mars mission based off gravitational anomalies that may or may not take months to get from point A to point B.

And why that is wrong, too, in the very same post you quote.

2 hours ago, fredinno said:

And you need to do orbital inclination changes to get to Lagrange points, you know.

Aaand you guessed it, that is wrong too. Starting to see a trend here... mayhap you don't have the theoretical knowledge to judge mission trajectories by their merits in a rational fashion? Could be, this is, after all, rocket science. Please note this isn't intended as any kind of insult, of course, just an observation to the effect that I have already explained all this stuff in this thread. I am forced to conclude that you didn't understand me, else you must be trolling me.

2 hours ago, fredinno said:

...And why would you use Hypergol for Earth Ejection? You want H2/O2, so that you get higher ISP, an lower overall mission mass (and higher TWR). Boil off is not as huge of a deal if you can launch fast enough, and with Saturn V with 4 SRBs, you can launch an enormous amount to LEO in one year. And cryogenic fuels will need a larger tank.... especially H2/O2, which would probably need a tank at least 6-7 meters wide. Not to mention NASA considered the 8 meter diameter faring too small for its SLS/Orion Mars mission proposals, and wanted 10, and even 12 m diameter fairings (even though they used inflatable heat shields, to reduce mission mass, and use as much of the thin Martian atmosphere to slow down as possible.

You said my stages would be too small, so I show you they can be as big as you want. Then you say they wouldn't fit a small launcher, and I tell you they can, with room to spare. And then you go on and say here... what exactly, that the ones you would use wouldn't, so they are the only way to do it? Just how desperate for me to be wrong are you? In my book, what you said here is basically that I am right, and storable stages offer many advantages over other fuels, in spite of their lower Isp. The architecture I've been referring to here has NO need for large diameters. Yes, it has a high IMLEO. That doesn't mean it's more expensive (quite the opposite, actually, if you consider all the implications), but it does mean it is way more robust. Little technological development is needed, and economies of scale come into play in a big way to lower cost and increase reliability, not to mention the vehicle sizes end up being very reasonable and close to what today is current practice.

Regarding the high diameter comments in general, NASA wants those things you mention to perform aerocaptures and direct entries... which is something I have discarded from the start, when I started talking about capture burns and slow aerobraking with unshielded structures. Not that I have mentioned landers at all, but if I do, rest assured I won't invoke large diameters or exotic technology... like inflatable structures, which the soviets totally didn't use to, say, perform the first spacewalk in history... oh wait, they actually did.

Still, I will just stick to Salyut-like aluminum cans, those would work about the same, so since I have only ever used Transhab as a mass estimate for a transit hab, I think I'll be fine.

 

Rune. As to why use hypergols for Earth ejection, simple, the same reason you would use it for anything else: it would be vastly cheaper, safer, and easier to do so.

 

Edited March 25, 2016 by Rune

[fredinno]

15 minutes ago, DBowman said:

hamster wheel a little way in I wonder if they planned it that way? You might be able to get a good workout using 'body inertia' (cf body weight exercises).

Probably not, Skylab was originally designed so you could build a large space station off the tanks of a IV-B without using a Saturn V via wet workshop. Never happened that way, but I guess "jogging on the walls" is a nice bonus.

[DBowman]

3 hours ago, fredinno said:

Probably not, Skylab was originally designed so you could build a large space station off the tanks of a IV-B without using a Saturn V via wet workshop. Never happened that way, but I guess "jogging on the walls" is a nice bonus.

I rather meant the 'micro' design issue of putting that ring of lockers (or cabinets or whatever) right around the circumference in the middle of the big open space.

[fredinno]

6 hours ago, Rune said:

Rune. As to why use hypergols for Earth ejection, simple, the same reason you would use it for anything else: it would be vastly cheaper, safer, and easier to do so.

http://www.astronautix.com/props/n2o4udmh.htm

Quote

1959 production amounted to 60,000 tonnes per year. In carload lots of one-ton cylinders, the price was $ 0.15 per kg. By 1990 NASA was paying $ 6.00 per kg due to environmental regulations.

Quote

The price in 1959 for tank-car quantities was under $ 1.00 per kg. Engineering studies indicated a price of $ 1.00 per kg with large scale sustained production. But due to its toxic nature, production and transport costs soared in response to environmental regulations. By the 1980's NASA was paying $ 24.00 per kg.

I don't call that cheap. And yes, I know fuel is a low part of a mission's cost, but UDMH NO24 is not safe (high toxicity) either. Easier, sure, but not really safer and cheaper. However, we might be able to get away with this in the 70s...

 

Quote

The ITN makes particular use of Lagrange points as locations where trajectories through space are redirected using little or no energy. These points have the peculiar property of allowing objects to orbit around them, despite lacking an object to orbit. While they use little energy, the transport can take a very long time.

https://en.wikipedia.org/wiki/Interplanetary_Transport_Network

That bolded part is a bad idea for a manned Mars mission.

Edited March 26, 2016 by fredinno