Mars Orbit Rendezvous - low-cost and reusable spacecraft

RobertDyck · 2002-12-06 04:06:19

This is a development of the idea I posted on "Mars Direct Rethought".

To start with, keep the crew down to 4 astronauts. Apollo included 3 astronauts, only 2 of whom landed on the Moon. There are psychologists who argue for a whole town, but this is the initial manned mission to Mars so we need explorers who have the "right stuff". The "right stuff" for Mars means independence and fortitude for a 2 year mission.

The spacecraft would be assembled in Earth orbit using existing launchers. It would be better to have Energia or Shuttle-C, but it doesn't look like they will be available. Proton, Angara 5, Ariene 5, Delta IV Large, Atlas V, and the Space Shuttle will be available.

The spacecraft would travel from Low Earth Orbit into a highly elliptical, high Earth orbit. There is no need to raise the perigee, once the apogee is high enough the spacecraft will leave Earth. Since so many launch vehicles are designed to deliver payloads to Geosynchronous Transfer Orbit, we should use that. Once the spacecraft is in GTO, astronauts would be delivered via a crew taxi.

The taxi would be a capsule capable of returning all 4 astronauts and Mars samples to Earth via direct entry from interplanetary velocity. This would be larger than either the Soyuz descent module or Apollo command module, and the heat shield would have to be more robust, so the capsule would be a new design. Whether it is a cone like Apollo or "headlight and windshield" like Soyuz is a matter for the engineers to argue. In either case, the crew taxi would have a small service module with manoeuvring thrusters to dock with the Mars spacecraft, and capable of controlling its flight path back to Earth.

Once crew were onboard, the spacecraft would depart for Mars using electric propulsion. Whether the electric drive is ion, hall effect or magneto-plasma dynamic is a competition for engine designers. The Russian thruster anode layer hall effect thrusters currently have the same Isp as ion thrusters, so Russia's Energomash can compete directly with NASA's Glenn Research Center. There is current development for a nuclear reactor to power the thruster, but for now let's design for solar-electric propulsion.

The life support system would be electrolysis of water, augmented by a Sabatier reactor to conserve water. The water recycling system from the Johnson Space Center's Advanced Life Support Project had a 97% water recycling efficiency, including water from all sources. This combination has greater than 95% oxygen and water recycling.

The interplanetary habitat would be based on TransHAB and designed for zero-G, including exercise machines. Food and consumables would be sufficient for the round-trip, either a free return or both of the outbound and inbound legs of a normal mission.

Upon reaching Mars the spacecraft would use aerocapture to enter Mars orbit. During aerocapture, the solar panels must be folded and stowed. The surface habitat would be just a capsule and an inflatable habitat. There is no need for more room than one seat for each astronaut until on the surface of Mars. The surface habitat would not have the micrometeor shield because Mars has an atmosphere, so the surface hab would be lighter than TransHAB. The roof would be sturdy enough to support sand bags (regolith bags) for radiation protection. The surface hab would include a recycling life support system, food for the surface stay, and a 2-person open rover.

This would be preceded by a Mars Ascent Vehicle. Similar to the MAV of NASA's Design Reference Mission, it would use ISPP to create propellant and just carry the astronauts and samples to Mars orbit. Unlike DRM, the MAV would be the Trans-Earth Injection stage to return the orbiting spacecraft back to Earth. The MAV would not be pressurized and would not have life support. Astronauts would ride in their space suits (with sample containers).

Waiting beside the MAV would be a cargo craft that landed by radio beacon. The cargo craft would contain an inflatable laboratory, lab equipment and supplies, as well as a backup supply of food for the surface stay. It would also have a pressurized rover. Life support for the lab would normally be provided by the habitat, but as a backup the life support system of the pressurized rover could supply the lab. This provides a complete backup for the surface habitat with minimal redundant equipment.

Upon return to Earth, the interplanetary spacecraft would aerocapture into Earth orbit. If something went wrong with the spacecraft, the crew taxi could separate and return on its own. For a normal mission, the crew taxi would separate after the interplanetary spacecraft was parked in GTO. It would be left in GTO where it could be refuelled and resupplied by a cargo spacecraft to prepare it for a second mission.

So this would use solar-electric propulsion for the Earth-Mars trip, but chemical propulsion and ISPP to return. Aerocapture and direct entry from high orbit avoids propellant use. The interplanetary spacecraft is reusable, with a new lander for each mission. Cargo and the MAV are delivered separately so a slow, fuel efficient trajectory can be used.

Eventually the MAV could be replaced with a reusable one, but it would have to carry fuel to replenish the interplanetary craft's electric thrust system. Propellant for ion or hall effect thrusters is xenon or krypton, for magneto-plasma dynamic it's hydrogen. Mars atmosphere contains 0.00003% krypton and 0.000008% xenon.

Mark S · 2002-12-06 07:41:48

To start with, keep the crew down to 4 astronauts. Apollo included 3 astronauts, only 2 of whom landed on the Moon. There are psychologists who argue for a whole town, but this is the initial manned mission to Mars so we need explorers who have the "right stuff". The "right stuff" for Mars means independence and fortitude for a 2 year mission.

This is where I disagree with Zubrin and a lot of the MS folks. A crew of three was good enough for Apollo, but those were two-week missions and part of a sometimes-hasty program to beat the Soviets. The Mars astronauts will be away from home for 2.5 years. Imagine spending 2.5 years with only three people--you'd better be rally good friends with them, because they're all you have!

It might be a good idea to send two crews of four on two separate spacecraft. Doubling up on flghts to Mars adds more redundancy, which is always good in a high-risk mission.

TJohn · 2002-12-06 13:07:01

As always, RobertDyck, Good post! You may have answered somewhere before, but do you work in the Aerospace field? You have some extremely thought out ideas.

RobertDyck · 2002-12-06 15:06:41

Am I in the Aerospace field? Well, I am trying. I always wanted to be an aerospace engineer since I watched the Apollo program as a child, from Apollo 1 through Apollo 17, Skylab and Apollo-Soyuz. I am now trying to start my own aerospace company, and have started submitting bids to NASA and the Canadian Space Agency. I submitted a notice of intent for the Next Generation Ion Engine. I tried to convince Robert Zubrin to let myself and other members of the Mars Society submit a bid for a Mars Scout mission under the name of the Mars Society. Although I have several highly qualified individuals on the team, some with the Mars Society and others not, I thought a bid would carry more weight if we had the name of the Mars Society on it. At least the Mars Society could fulfill the public outreach requirement of the contract, something I feel the Mars Society is ideally qualified to do. However, Dr. Zubrin felt my proposal was too much. So I am now bidding on contracts simply under the name of my company. I did present a poster on an advanced life support system at the 4th Canadian Space Exploration Workshop. I have submitted a request to present that same work as a paper at the Humans In Space symposium this May. I feel my idea for a life support system is much better than the system described above, but it is new and the previously mentioned system is already proven. I'll push my idea for a life support system after I have built hardware to prove it works.

By the way, my avatar is the logo for my company: Ardeco Aerospace, a division of Ardeco Consulting Ltd. Ok; that sounds impressive for a small start-up company, but the company must have a name. Ardeco Consulting Ltd. had originally been established to develop computer software, including real time software for embedded systems including flight systems. I'm trying to branch out to pursue my dream of owning an aerospace company. The products I'm interested in pursuing are a spacecraft bus for a micromission spacecraft, an ion thruster for that spacecraft bus, an advanced life support system, and Mars regolith simulant.

Eventually I would like my company to be the one that produces the first colonist ship to Mars; not the spacecraft for the first manned mission, but a commercial interplanetary spacecraft to carry colonists for permanent emigration to Mars. That may be a long way off, but within my life time. So call me a dreamer.

Mark S · 2002-12-07 07:58:21

Once crew were onboard, the spacecraft would depart for Mars using electric propulsion. Whether the electric drive is ion, hall effect or magneto-plasma dynamic is a competition for engine designers.

That's a pretty big decision to make. This summer's Russian proposal used ion engines, but it enabled a two-year mission with only 30 days to stay on Mars. On the other hand, VASIMR plasma engines may allow 90-day transits each way with stay times of similar duration to the transit. VASIMR is the more promising "high risk, high payoff" technology that will make Mars achievable.

RobertDyck · 2002-12-07 11:37:15

That is very true. One individual at the last Mars Society conference told me he doesn't think the Earth's production of xenon is sufficient to supply a manned mission. If ion or hall thrusters for the cargo craft may require too much xenon. Xenon is a trace gas in Earth's atmosphere and a byproduct of liquid air production. This does raise the question of where Russia would get it for their hall effect thruster proposal.

The engines themselves have gone through some interesting developments. The NSTAR ion engine had a nominal specific impulse of 3100 seconds and a thrust of 92 milli-Newtons. The exact Isp depended on throttle setting. The XIPS ion thruster used on Boeing's model 702 satellite has Isp 3800s and thurst 165mN. Russia's D100 hall effect thruster has an Isp of 3970s and thrust of 300mN. Russia had theoretical work on paper that said a Thruster Anode Layer (TAL) hall effect thruster could produce an Isp of 8000s. A paper presented at this year's AIAA conference showed work by the Glenn Reserach Center on "High specific impulse, High power ion engine operation". The 50cm ion engine demonstrated an Isp of 5210s and they believe they can increase that to 8300s.

The VASIMR engine has the promise of Isp at 9000s. However, the VAriable Specific Impulse Magntoplasma Rocket is designed to permit lower Isp at higher thrust. Trading off efficiency for thrust was intended to permit rapid acceleration away from Earth followed by high efficiency during cruise to Mars. Princeton is working on magnetoplasmadynamic (MPD) without the specific impulse variability. The crew taxi may make the low Isp, high thrust mode of VASIMR unnecessary. One presentation from the Glenn Research Center said MPD can achieve an Isp up to 7000s at 1 megawatt, and Isp increases with power. GRC is now working on a 30 megawatt version. The advantage to VASIMR or MPD is that hydrogen is easier to obtain, both on Earth and Mars. The down side of hydrogen is that it requires a larger fuel tank.

I think it is fair to plan for electric propulsion with Isp in the 8000-9000 second range.

soph · 2002-12-07 11:44:54

but the plasma might be more useful for outer solar system or asteroid belt missions, then.

it seems to me that so many of these mission plans would be made easier by the development of a scramjet ssto...i wonder if somebody will come out with one in the next 10 years...

RobS · 2002-12-07 23:12:34

Thank you, Robert, for a very interesting posting. I have a question about the use of ion engines, though. How long will it take a manned mission to get to Mars with such an engine? To fly to Mars from a GTO, if you do it quickly and close to the Earth, takes 1.3 km/sec; but if you use an ion engine you need 3.8 km/sec instead. My source is Arthur C. Clarke's book *The Promise of Space,* which shows that a flight to Mars requires (from the surface of the Earth) 26,000 mph if you apply the energy close to Earth, but 25,000 mph (to escape from Earth) and 7,000 mph (in interplanetary space) to adjust the spacecraft into an orbit that reaches Mars.

The mass ratio for 1.3 km/sec using hydrogen-oxygen engines is 1.34 (0.34:1 fuel to payload). The mass ratio for 3.8 km/sec using a 5,000 second ion engine is 1.08 (0.08:1 fuel to payload). So you save a lot of fuel, sure. But it'll take two or three months longer to get up to that speed, won't it? And if you accelerate to a higher speed, that burns more fuel and decreases the advantage.

-- RobS

Palomar · 2002-12-13 13:35:30

Am I in the Aerospace field? Well, I am trying. Maybe I shouldn't say more than that. Some people might challenge my posts

*Wow. Mr. Robert, you are such a mega-brain that I'm surprised you'd be concerned about someone being able to challenge you [!]. Of course, most of your posts are above my head, including those of a few other folks here [regarding the physics and high-tech stuff]...so it might be possible someone else here could challenge you [what do I know?]

Maybe you're just too danged modest, Mr. Robert!

I just wish I could understand more of the high-tech posts. ??? Physics -- bah.

--Cindy

dicktice · 2002-12-13 14:33:38

Robs: How about boosting your ion rocket to Earth escape velocity by means of a tether attached to (a) space station (b) conglomeration of LEO space junk. Or, in the case of Mars, either or both of the moonlets? Over to you.

RobertDyck · 2002-12-13 16:54:46

RobS, I'm sorry for the delay replying to your question. I had relied on Christopher Hirata to calculate the trajectory for me while he was a 4th year student at CalTech, but he is taking his Ph.D. at Princeton now and too busy. I have been trying to figure out how to calculate the trajectory myself. It's a bit tricky because continuous thrust the whole trip produces a hyperbolic spiral, not an elliptical transfer orbit. I did calculate the Delta-V to escape from GTO with zero interplanetary velocity: 779 metres per second applied at perigee assuming perigee is 407km altitude (same as the International Space Station).

My calculations are based on data I have available: altitude of geosynchronous orbit to 5 significant figures (35,786km above surface), Earth radius at the equator to 6 significant figures (6,378.14km), but the mean distance from Earth or Mars to the Sun and mass of the planets and Sun to only 4 significant figures. I would appreciate it if someone could give me more precise figures.

A faster trip will always take more fuel. With chemical rockets a Hohmann transfer takes eight and a half months, but Robert Zubrin demonstrated it only takes 10% more fuel to reduce that to 6 months.

The basic idea, however, is that continuous thrust the whole trip for a straight line course would cover the distance in the same time but leave you with twice the speed at the end, because the average speed would be the same. If fuel efficiency is twice as high that calculates to the same fuel load for the same transit time. The space shuttle's main engine is the highest efficiency of any chemical rocket: Isp is 455 seconds in vacuum. For Cindy , that means one pound of fuel can produce one pound of thrust for 455 seconds. At 5210 seconds the fuel required is roughly 1/11th as much to accelerate the same mass to the same speed. The mass you have to accelerate includes the fuel itself, which decreases the mass you must accelerate so it decreases fuel required further. Since continuous acceleration requires an ending speed twice as high, that still means roughly 1/6 as much fuel. It is more dramatic if you use engines with 8300 second Isp. The trajectory is not a straight line, and the Sun's gravity gets weaker as you move away, and acceleration increases as you expend fuel if you keep thrust constant, so it's more complicated.

RobertDyck · 2002-12-13 17:25:42

Cindy: I changed my reply back to what I had originally entered. I was scared that someone would accuse me of being presumptuous when I say I am seriously attempting to start a new aerospace company.

I am also concerned that my statement about Dr. Zubrin may appear to be a criticism. It was Dr. Zubrin's books that led me to seriously attempt to get into aerospace, and the Mars Society has provided me with industry contacts to get as far as I have. Prior to the last Mars Society conference the person I support for the steering committee had asked his supporters what issues should be brought before the committee. I had stated my desire for more technical projects and felt bidding for NASA contracts was a way to get 10's of millions of dollars. I asked him to find a diplomatic way to raise the issue with the committee, but he forwarded my message as-is to the entire steering committee with copies to the Chapters Council and a couple other email lists. I'm afraid that made me look like an opponent of our illustrious founder. Aaaa! I just wanted to argue to do more, be bold, and to empower average MS members to get involved with real technical projects.

Palomar · 2002-12-14 09:27:00

I asked him to find a diplomatic way to raise the issue with the committee, but he forwarded my message as-is to the entire steering committee with copies to the Chapters Council and a couple other email lists. I'm afraid that made me look like an opponent of our illustrious founder. Aaaa! I just wanted to argue to do more, be bold, and to empower average MS members to get involved with real technical projects.

*I totally understand. I've experienced something similar, involving a chief medical officer [no less!] of a large clinic. It's as though someone else commits a serious social gaffe on "your behalf." It's as pleasant as acid reflux, or biting into a lemon.

--Cindy

RobS · 2002-12-15 00:14:41

Regarding tethers, they have the potential to make a big impact on the total mass needed for a flight between planets. But who knows when one will be built. We don't even know yet whether the technology will actually work when placed in orbit.

-- RobS

dickbill · 2002-12-16 16:44:54

Hi all,

Since hydrogen is so light and requires big tanks, very inconvenient, is it possible to send water or water ice in orbit, hydrolyze it with solar energy and fill an inflatable tank which could then wait in orbit, like in the ISS and serve for a trip to Mars ?
I realize that sending 20 tons of ice in the ISS is very expensive, maybe more than just sending the hydrogen tank already filled with liquid H2/O2.

RobS · 2002-12-17 15:25:19

So far, no one has developed the technology to keep liquid hydrogen liquid. The energy to electrolyze water into hydrogen and oxygen can be obtained, but developing the equipment is the trick.

Part of the problem is that we still know very little about the environment of space. I was reading about the International Space Station the other day. Someone calculated that static electric charges could build up on the station as a result of the huge solar panels that could be so strong that astronauts could get shocked and the space shuttle could get shocked when docking. So they spent $27 million to build equipment to neutralize any possible electrical fields. It turns out, the ISS did not have electric field problems and the money was a waste; but they had no way of knowing ahead of time and couldn't take the chance. These are the kinds of problems that make creation of new equipment so slow and expensive.

-- RobS

dickbill · 2002-12-17 16:01:30

So far, no one has developed the technology to keep liquid hydrogen liquid. The energy to electrolyze water into hydrogen and oxygen can be obtained, but developing the equipment is the trick.

-- RobS

You mean the only way is to keep it cold?. Then the idea of an inflatable tank filled in orbit with liquid H2 and O2 and the size of the Hidenburg dirigible balloon, is difficult because it needs to be kept cold.
We need to satellite an icy comet around earth to make a reserve of propellant. I hope that when the next one comes to visit us, we could catch it.

RobertDyck · 2002-12-18 00:38:20

You can keep liquid hydrogen liquid by letting a little boil off. That boil-off reduces temperature to keep the remainder cold. A porous plug can ensure the boil-off does not cause cavitations within the liquid. This works fine if you are using the hydrogen as propellant, since the lost hydrogen is simply fed into the engine. Apollo could keep cryogenic propellants liquid for days without significant loss. One trick was that the outer skin provided shade for the propellant tanks. If you want to keep it longer than that you would need a cryogenic plant to capture the boil-off and re-liquefy it. That re-liquefied propellant could be pumped back in. The cryogenic plant and pump would require electricity, which could be fed by solar panels. This sounds simple, but no one has built a zero-G cryogenic plant before. New technology often has surprises. For example, Apollo had to stir the tanks to prevent the cryogenic liquid from stratifying in zero-G. If it stratifies it could react if you disturb it by draining a bit for fuel. That isn't an issue for smaller tanks, and not an issue for storable propellants, but it was for Apollo. I expect a large cryogenic hydrogen depot would have the same concern.

dickbill · 2002-12-18 11:23:20

... Apollo had to stir the tanks to prevent the cryogenic liquid from stratifying in zero-G. If it stratifies it could react if you disturb it by draining a bit for fuel. That isn't an issue for smaller tanks, and not an issue for storable propellants, but it was for Apollo. I expect a large cryogenic hydrogen depot would have the same concern.

How large could that tank be ?
I mean, if you carry 20 tons of ice to the ISS, after hydrolysis you get at best 2/16 (approximate atomic mass ratio of H2O)= 1/8 for H2, that is about 2.5 tons of H2. That is pitiful compared to the space shuttle tank with its 700 tons of propellant.
I am not expert but you won't go very far with that and it looks ridiculously expensive.
Now, with a shuttle C, the possibility to carry 100 tons of ice in orbit looks maybe more attractive.
Would it be better to extract ice from the moon polar region and send it to low earth orbit in a precise spot where it could be captured by some giant net ?

Because here is the point: the perspective to refuel any spaceship in low earth orbit brings completely new horizons to the space conquest, everybody agrees with that.

dicktice · 2002-12-19 09:03:18

Regarding tethers, they have the potential to make a big impact on the total mass needed for a flight between planets. But who knows when one will be built. We don't even know yet whether the technology will actually work when placed in orbit.
-- RobS

Oh, it'll work alright. Robert Forward started a business based upon it, and I believe since his death (which I still can't feel the loss of, on account of not having read all his stuff yet) the firm goes on. Should be available under: Space tethers.

dicktice · 2002-12-19 09:14:29

Hi all,
Since hydrogen is so light and requires big tanks, very inconvenient, is it possible to send water or water ice in orbit, hydrolyze it with solar energy and fill an inflatable tank which could then wait in orbit, like in the ISS and serve for a trip to Mars ?
I realize that sending 20 tons of ice in the ISS is very expensive, maybe more than just sending the hydrogen tank already filled with liquid H2/O2.

Gee, I like the idea of an ice-ship of sorts, which could (1) shield you from solar flares (2) supply hydrogen and oxygen by electrolysis from low-voltage thermoelectric generation (3) onboard water. No, seriously, the mind boggles at your idea. And, where to obtain the water: Why, from dead comets in Earth-crossing orbits, of course--and a good thing too, since we'd better locate and go get them...before they get us!

dickbill · 2002-12-19 11:19:53

dicktice wrote:

,Dec. 19 2002,15:14
Gee, I like the idea of an ice-ship of sorts, which could (1) shield you from solar flares (2) supply hydrogen and oxygen by electrolysis from low-voltage thermoelectric generation (3) onboard water. No, seriously, the mind boggles at your idea. And, where to obtain the water: Why, from dead comets in Earth-crossing orbits, of course--and a good thing too, since we'd better locate and go get them...before they get us!

well, comets are not so close even when they cross our orbit. The closest source of water after earth is on the moon, frozen in the craters in the poles.
Do anybody know if there is other potential propellant in the moon, it doesn't have to be necesseraly water.

dicktice · 2002-12-19 17:08:23

Eventually I would like my company to be the one that produces the first colonist ship to Mars; not the spacecraft for the first manned mission, but a commercial interplanetary spacecraft to carry colonists for permanent emigration to Mars. That may be a long way off, but within my life time. So call me a dreamer.

Would that I were young as that...my dream is: live to see the first person(s) reach mars and (dare I dream further?) find water-ice no more than a metre down!

dicktice · 2002-12-19 17:17:41

dickbill: On the contrary: Dead comets--easier to reach, energywise, than the Moon--populate space between the orbits of Venus and Earth, above and below the ecliptic plane, which are not easily observable from Earth due to the Sun's glare. "Earth-crossing" was not what I meant, but the name of the above-mention comet (and asteroid) population escapes me (Amour?). Anyway, how about discussing this further?

dickbill · 2002-12-20 11:04:47

dickbill: On the contrary: Dead comets--easier to reach, energywise, than the Moon--populate space between the orbits of Venus and Earth, above and below the ecliptic plane, which are not easily observable from Earth due to the Sun's glare. "Earth-crossing" was not what I meant, but the name of the above-mention comet (and asteroid) population escapes me (Amour?). Anyway, how about discussing this further?

dicktice,
1) how could we catch a comet and put it in orbit, low earth orbit close to the ISS being the best for convenience.

2) Would a 10km icy comet core stay stable in that position without desintegrating ?

3) would it be not better to keep the comet in its position, wherever it is, and extract/hydrolyze the water IN SITU, then send the inflatable tanks filled with H2/O2 back to Earth ?

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