Should we send humans or robots to Mars?

Oldfart1939 · 2017-04-22 22:15:18

Just a note: Lithium in the shielding of fission reactors is the normal source of Tritium. This is tremendously interesting, but skeptic that I am, not gonna' hold my breath....

Oldfart1939 · 2017-04-22 22:18:20

After reading the referenced paper in the above link, the assumption and statements made by the professors about the infeasibility of chemical propulsion put me off a little... I'm not willing to wait another 20 (or 40) years for this speculative technology to get us to Mars. Maybe it can be used to get us to Titan?

kbd512 · 2017-04-23 02:41:56

Oldfart1939,

I think chemical rockets are infeasible for colonization purposes. For exploration purposes, chemical rockets are within the realm of affordability and mission duration feasibility. It's the Ricky Bobby affliction. I'm goin fast, mama!

As a former sailor, I can tell you that six months with no land in sight is doable, but pushing it. People stop paying attention to what they're doing because they've been doing it for so long that it's routine, no matter how dangerous. You'll see people, no matter how otherwise intelligent, casually stroll across the LA during recovery operations without looking at the wires or the jets coming in at 165 knots. I call this the "I did it before and I didn't get killed, so what?" syndrome. A 3 month cruise is pretty standard. A 1 month cruise is like, "We just got out here. What are we stopping for?" That's a totally unscientific observation of the behavior of sailors at sea, but I think a 3 month cruise is about right. Nobody will get complacent and they won't get there so fast that they never properly adjust to life at sea.

elderflower · 2017-04-23 03:40:34

GW said "Hydrogen peroxide-kerosene is hypergolic ignition, but has not ever actually flown, except experimentally. Lots of ground tests have been done. "
This isn't quite correct. I expect it will apply to US rocketry, but not everyone else's.
The brief and now abandoned UK space program carried out several launches and put up one satellite before cancellation. All were propelled by HTP and Kerosene. 86% HTP was used without any adverse incidents due to the HTP. I think they restricted the concentration to allow use of a silver catalyst to breakdown the HTP. From the photos I also think they used it HTP rich as there is a completely clear exhaust. Isp achieved was about 250 secs. This combination is hypergolic and can be stopped and restarted virtually at will. Wikipedia articles on Black Knight and Black Arrow rockets are a good starter on these.

Last edited by elderflower (2017-04-23 03:47:22)

elderflower · 2017-04-23 03:52:47

Good luck scrunching lithium foil in an atmosphere of almost anything that isn't Argon.

Oldfart1939 · 2017-04-23 08:18:42

My preference would be to resurrect the NERVA program; with some decent technology upgrades, we could see Isp of 900 seconds. There have been some other approaches to using fission/nuclear that we need to explore as well. That's a technology that is well within our grasp, and which would allow a shorter transit time to Mars. This is a simple approach based not on corporate and University "forward looking statements," but historical achievements.

I'm with GW on a feature of having that Moon base; as an experimental nuclear rocket test facility. Meanwhile, we keep chugging ahead with chemical propulsion.

SpaceNut · 2017-04-23 08:44:26

"Chugging ahead with chemical propulsion" means getting stages empty to orbit for refueling, selection of fuels that do have reduced boil off types and a means to produce at the destinations end such that the stage can be refueled again.

I favor man getting off LEO onto the moon and to mars I am tired of robotic missions that barely leverage any science for manned missions forward in a Human presence on either and while we are at it lets toss in Venus as well at least in cloud city form until some future state to when man can be on its surface.

GW Johnson · 2017-04-23 10:06:06

We've been sending robots to Mars for 52 years now. It's time for men to go.

Same story for the moon; we've been sending nothing but robots to the moon ever since men last landed on it. The last man on the moon was 45 years ago. It's time to go back and actually do something.

Exploration missions tend to be small in scope and to endure great difficulties. Colonization efforts require bigger vehicles and less deprivation. This situation hasn't changed in more than 500 years now.

I think the sense of the last few posts is correct: use what you have right now (which is chemical propulsion) to go now. Try out all the things needed for colonization, but do NOT bet the lives of your explorers on them.

When we go later to set up the permanent base that eventually becomes the colony, we'll need bigger ships, much bigger and much faster. The best waiting-in-the-wings technology for that is nuclear pulse propulsion (think 2-4 gee vehicle acceleration at 20,000 sec Isp, in a ship that has 11,000 ton "wet" weight and a 9000 ton "dry" weight). If kbd512's fusion rocket can be made ready by that time, it might be even better.

GW

elderflower · 2017-04-23 13:35:26

Tritium is generated in the heavy water tanks of Candu reactors and their successors. This and the up front cost of all that heavy water have rendered this type of reactor unpopular in most applications. India is still developing them, I believe, as they will consume very low enriched, or even non-enriched material. Also they will burn Thorium, with which India is well endowed.
Mars has a much higher proportion of deuterium than has Earth, and this would be further concentrated as colonists electrolyse it to get hydrogen and oxygen, so this type of reactor might be useful on Mars. It's product tritium could then be used in the proposed fusion rockets.
The same might apply to Ceres and Callisto except that there would probably be more difficulty in finding nuclear fuel on an ice coated world.

Oldfart1939 · 2017-04-23 16:08:52

GW Johnson wrote:

We've been sending robots to Mars for 52 years now. It's time for men to go.
Same story for the moon; we've been sending nothing but robots to the moon ever since men last landed on it. The last man on the moon was 45 years ago. It's time to go back and actually do something.
GW

GW-

IMHO, it's been PAST time for men to go to Mars and return to the Moon, for 35-40 years.

Last edited by Oldfart1939 (2017-04-23 16:10:38)

louis · 2017-04-23 17:24:59

Very true...! But now the time has come. I really can't see anything to stop this. Even if Musk were to be vaporised tomorrow, the technology will still be there. Humanity is ready to go.

Oldfart1939 wrote:

GW Johnson wrote:
We've been sending robots to Mars for 52 years now. It's time for men to go.
Same story for the moon; we've been sending nothing but robots to the moon ever since men last landed on it. The last man on the moon was 45 years ago. It's time to go back and actually do something.
GW
GW-
IMHO, it's been PAST time for men to go to Mars and return to the Moon, for 35-40 years.

SpaceNut · 2017-04-23 19:44:54

If Space x vanished tomorrow we are left with the old pork suppliers which means we have not the funds anymore to go anywhere....

I do agree that nuclear use in space, on the moon or mars is a must but its getting the baby steps started such that we can continue to go in order to make that dream a possibility....

GW Johnson · 2017-04-25 11:04:36

Sorry about not being knowledgeable of hydrogen peroxide-kerosene use outside the US.

The data I've been quoting come from a Pratt and Whitney vest-pocket Aeronautical Handbook from 1969. A briefer form of the same data is in my copy of the AIAA Aerospace Design Engineers Guide, dated 1993. Fewer combinations are included, but molecular weight and specific heat ratio data are included, unlike the old Pratt handbook. Some of you might actually have one of these.

The AIAA handbook includes a decent section on solid propellant rockets as well, including basic properties, typical burn rates, and hazard classifications, as well as performance potential. I see that modern composite-modified double base now uses AP, not just AN. Its performance with AP equals that of composite propellants now. That was not true in the 1960's. The choice is now among which hazards and which smoke problems you wish to accept, and which processing hazards you can tolerate.

GW

Oldfart1939 · 2017-04-25 12:02:11

From a chemist's viewpoint, Hydrogen Peroxide make the least sense of any oxidizer; it simply sits there and decomposes by itself. The Germans were pretty bold to try it in the Me163 rocket fighters! That was only partially successful, and a lot of pilots died from explosions.

LOX seems to be about the safest, although NTO probably comes in a distant second place.

With regard to chemical propulsion, we've already reached the ultimate potential; limited by that old Enthalpy content. Even though liquid Fluorine appears attractive, as does liquid Hydrogen, both have built-in limitations we're not willing to experience. The Id of lH2 works against it's use in longer missions. The combination of Hydrogen and Fluorine -> HF is totally unacceptable. Too toxic, too corrosive.

Last edited by Oldfart1939 (2017-04-25 12:02:42)

elderflower · 2017-04-25 15:33:53

Except, maybe, for decomposing metallic hydrogen, which was touched on in another thread a while back. Otherwise it will be back to NTR, NERVA or possibly fusion rockets for large, powerful engines. As these are all speculative at the moment we have to plan on what we know about now.

Peroxide has drawbacks, but it also has advantages. You don't have to wait around for it to explode, you do have to monitor it- it will give notice of accelerating breakdown. Keeping it cold and using stabilisers will allow it to be stored for quite a while (at lower concentrations than GW envisages). It's not cryogenic, 85% starts freezing about -20C. After breakdown over a silver or platinum catalyst it will be hypergolic with most fuels. You can use the same stuff as a monopropellant for thrusters. If it spills you apply lots of water. Toxicity is limited. People use it for rocket belts and small tip jet helicopters. It can be used with or without additional fuel to drive turbines for pumps and generators. Without fuel it can be a source of oxygen for people. It is dense and easily transported and would probably make a good booster oxidiser. I don't think it should be dismissed, whilst hydrazine or RFNA and NTO for instance, are not.

Oldfart1939 · 2017-04-25 17:15:58

Elderflower-

The only technology available in a realistic time frame is resurrection of the NERVA rocket. That has an Isp of ~ 900 seconds, which is enough to consider once we get the Mars colony established. I am willing to predict that we could have a fully functional prototype in <5 years and one flyable in 7-8 years.

elderflower · 2017-04-26 03:33:26

That would be a really good timescale, Oldfart. I wouldn't bet on it though for early missions unless you are looking for an excuse to delay them. For early manned missions we have to go with what we've got, or nearly got such as Falcon Heavy, and not plan for what we might have in 5 years. Even Musk encounters unforeseen things and has to step back now and then.

RobertDyck · 2017-04-26 04:51:26

NERVA is a bit more than speculative. Of course NERVA is a solid core NTR. Development of NERVA was complete in the early 1970s, NERVA 2 was complete in 1974 with Isp=825 seconds. All that was left was to test fly it in space. In 1991 they did a study, with computer analysis and computer simulations, updating the design. That engine should produce Isp=925 seconds.

I have argued they should design a new NTR, taking design features from Timberwind. That engine was actually developed, completed in 1990. The launch vehicle to use it was under development, but halted in 1992 when nuclear activists lobbied Congress. It had Isp=1000 seconds, but that was simply achieved by increasing temperature. The problem was it increased temperature so much that fuel elements agglomerated together, making it non-restartable. It was a pebble bed reactor, it produced hot spots between fuel elements, the face of fuel elements in that hot spot melted, causing the fuel elements to melt together. The big advantage was reactor mass was dramatically reduced. Timberwind 45 was an engine that produced thrust 45,000 kgf in vacuum, but engine mass 1,500 kg. The 1991 version of NERVA produced thrust 34,000 kgf in vacuum, engine mass 8,500 kg.

Oldfart1939 · 2017-04-26 06:57:47

elderflower-
I only pointed out the NERVA system from the pack of other speculative projects. This should definitely be a futurist move and not affect current and ongoing chemical propelled vehicles. I'm enthusiastic about Musk's Falcon Heavy, and I believe that a few more "tweaks" to it will reach the 70 metric tonne to LEO performance--if not even higher.

SpaceNut · 2017-04-26 20:46:46

I think nuclear as put would be a great boost for the future but its a decade even when funded down the road before it would be used.
I think the first steps needed is to solve payload mass to mars to at least closer to 10 mT before we can send men as going with the dragon payload of just 2 mT allowing for 2 men in a capsule to land with several preload events still leave a need to solve how do we get back to orbit as the Super Draco engines will not due to return man back to orbit for the return trip home.

Oldfart1939 · 2017-04-26 21:06:14

SpaceNut-

I believe that the answer to your question will be somewhat eclectic; it will be neither the Mars Direct architecture, nor the old Von Braun "take it all along" system. We seem to have rigorously addressed the Oxygen system on other threads, so I'm just speculating that we could manufacture the orbital return LOX as an in situ resource, and bring along enough UDMH to get back to Mars orbit because Oxygen is the preponderance of mass needed. My earlier stated mission architecture was reliant on LOX for the deep space oxidizer. The spacecraft parked in LMO for Earth return will out of necessity be fueled with UDMH and NTO, since simply waiting there for 18 months is too long to retain LOX.

louis · 2017-04-27 03:17:44

As long as you make orbital assembly a key feature of your mission architecture, you can simply deliver an additional tank for the return journey at a later point. Doesn't matter if it's a slower journey, if we are talking about supply. In fact I think Mission One needs to be failsafe so probably not a bad idea to have both a return tank delivered and propellant being made on the Mars surface. A reusable ascent vehicle would be one way of getting the propellant to the Mars surface.

I am thinking there is merit in a dual purpose ascent vehicle that would have both a separate (detachable) life support module for carrying humans and a separate, detachable fuel tank.

Oldfart1939 wrote:

SpaceNut-
I believe that the answer to your question will be somewhat eclectic; it will be neither the Mars Direct architecture, nor the old Von Braun "take it all along" system. We seem to have rigorously addressed the Oxygen system on other threads, so I'm just speculating that we could manufacture the orbital return LOX as an in situ resource, and bring along enough UDMH to get back to Mars orbit because Oxygen is the preponderance of mass needed. My earlier stated mission architecture was reliant on LOX for the deep space oxidizer. The spacecraft parked in LMO for Earth return will out of necessity be fueled with UDMH and NTO, since simply waiting there for 18 months is too long to retain LOX.

elderflower · 2017-04-27 04:07:28

Whatever is the designed fuel for the lander would also be the second stage fuel for mars orbit rendezvous on the return trip. We aren't likely to see a capsule with two sets of engines! First stage fuel for this phase will preferably be LCO/LOX as this is easiest to manufacture, and two sets should be complete, fuelled and ready to launch before any attempt to land men from orbit. First stages should have enough grunt so they can get back to their launch location and land ready for the next trip. Also first stage design needs to allow for landing or otherwise attaching a capsule on top.
A launch abort will consume all the fuel in the capsule so in this event, somewhere down range there will be some possibly-injured crew. They will have to be collected or refuelled using a rover, or hopper if they are in range, maybe even a relay of trips to establish supply depots. Possibly a spare capsule or means to refuel the aborted one might be dropped from orbit.
Now half of my surface crew will stay for two oppositions and half for only one. The first mission then delivers six people in two landings and the second replaces the first three who only stay for one opposition. Apart from this first group, everybody stays for two oppositions, giving a long term presence. The experiences of the first group will be useful to assist designs for future expansion, new bases, new equipment, new science and engineering etc. and the people will be intensively studied during preparation for the next missions.
At all times there are sufficient launch facilities to get all the people back to orbit, and to rendezvous with a return ship. If all six have to be evacuated back to earth or ISS this might get a bit crowded, so it will be luxurious for three on a scheduled return to earth orbit. Once we have established that we can support the permanent presence with ISRU facilities, green house etc, we may decide to increase numbers, open a new base or take along other specialists.
I think all this will be doable over a half dozen opposition cycles, using only Falcon Heavy, or something like it and refuelling in earth orbit and Mars orbit (for Mars landing and ascent capsules) from tankers launched from Earth containing easily stored propellants. I wouldn't intend to launch ISRU produced fuels to Mars orbit until serious colony building starts and production has been well proven. Reurn fuel must be ready at all return launch opportunities.

louis · 2017-04-27 18:05:22

Elderflower -

Isn't there a conceptual difference between a EDL craft and an ascent craft.

The EDL craft needs to have sufficient life support on board if something goes seriously wrong with the EDL. Landing is a far more dangerous manouevre than ascending into orbit. That means a lot of mass for EDL.

The ascent craft could in my view be a lot lighter on mass and in fact could be a multiple use vehicle. So it might take humans up and (fuel) supplies down.

elderflower wrote:

Whatever is the designed fuel for the lander would also be the second stage fuel for mars orbit rendezvous on the return trip. We aren't likely to see a capsule with two sets of engines! First stage fuel for this phase will preferably be LCO/LOX as this is easiest to manufacture, and two sets should be complete, fuelled and ready to launch before any attempt to land men from orbit. First stages should have enough grunt so they can get back to their launch location and land ready for the next trip. Also first stage design needs to allow for landing or otherwise attaching a capsule on top.
A launch abort will consume all the fuel in the capsule so in this event, somewhere down range there will be some possibly-injured crew. They will have to be collected or refuelled using a rover, or hopper if they are in range, maybe even a relay of trips to establish supply depots. Possibly a spare capsule or means to refuel the aborted one might be dropped from orbit.
Now half of my surface crew will stay for two oppositions and half for only one. The first mission then delivers six people in two landings and the second replaces the first three who only stay for one opposition. Apart from this first group, everybody stays for two oppositions, giving a long term presence. The experiences of the first group will be useful to assist designs for future expansion, new bases, new equipment, new science and engineering etc. and the people will be intensively studied during preparation for the next missions.
At all times there are sufficient launch facilities to get all the people back to orbit, and to rendezvous with a return ship. If all six have to be evacuated back to earth or ISS this might get a bit crowded, so it will be luxurious for three on a scheduled return to earth orbit. Once we have established that we can support the permanent presence with ISRU facilities, green house etc, we may decide to increase numbers, open a new base or take along other specialists.
I think all this will be doable over a half dozen opposition cycles, using only Falcon Heavy, or something like it and refuelling in earth orbit and Mars orbit (for Mars landing and ascent capsules) from tankers launched from Earth containing easily stored propellants. I wouldn't intend to launch ISRU produced fuels to Mars orbit until serious colony building starts and production has been well proven. Reurn fuel must be ready at all return launch opportunities.

SpaceNut · 2017-04-27 19:37:39

EDL is Entry, Descent, and Landing Configuration..

Ascent only uses the EDL to get to the surface for use for a return to orbit and beyond dependant on design.
Current rover https://mars.nasa.gov/mer/mission/space … shell.html
https://mars.jpl.nasa.gov/msl/mission/spacecraft/

elderflower, the fuel LCO/LOX sure is easy to manufacture but its a poor fuel for a rocket to which there are no known engines to use it. The Mars hopper vehicle (with a specific impulse of approximately 250 s), was proposed principally because carbon monoxide and oxygen can be straightforwardly produced by Zirconia electrolysis from the Martian atmosphere without requiring use of any of the Martian water resources to obtain Hydrogen.

Here is another forum topic Carbon Monoxide for fuel on Mars
Which has the Experimental evaluation of the ignition process of carbon monoxide and oxygen in a rocket engine.

https://ntrs.nasa.gov/archive/nasa/casi … 179358.pdf

A chemical Approach to Carbon Dioxide Utilization on Mars

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