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Enthalpy

Manned Mars Mission

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Hello you all!

Astronauts going to Mars shall be protected from radiations. Since exotic shields look inconvenient now, and unless this one brings the necessary improvement
http://www.scienceforums.net/topic/80982-shield-astronauts/
Nasa seeks to accelerate the manned transfers between both planets, something really hard with chemical propulsion. My Solar thermal engine enables that.
http://www.scienceforums.net/topic/76627-solar-thermal-rocket/

For my Solar thermal engine, I use here Isp=1267s computed by tinkering Propep. The heavy mission uses D=10m concentrators to let each engine push 5.3N near Mars and if possible 12.4N near Earth - the launcher's fairing must accommodate this size.

Computed as decribed there
http://www.scienceforums.net/topic/83284-non-hohmann-to-mars/#entry806564
the short trips are so demanding that besides using the better engine, some hardware must be preset on Martian orbit, and aerobraking seems necessary; a short stay on Mars, around opposition, is ruled out by the short trips, so the crew will need to stay nearly two years there.

Marc Schaefer, aka Enthalpy


----- Return leg, with aerobraking -----

Expectedly the most difficult, because the return vessel must be put at Mars first.

The Earth reentry vessels dives at 17643m/s - heat shields already worked at 30km/s. Due to Earth's curvature, a capsule would be too brutal. The vessel is a glider, winged to achieve as much lift as drag or more, which uses downlift to stay for long at a good altitude. Remembering that 7910m/s balance 1G, 17643m/s need 4G downforce, and hypersonic L/D=1 (the HL-20 achieves more) would combine to 5.6G.
http://www.usu.edu/mae/aerospace/publications/AIAA_2006_1033%20copy.pdf

 

The glider can abandon the return leg habitat before reentry, though landing the habitat would be interesting. For three astronauts, some souvenirs, the glider, the habitat for 80 days with its life support, without propulsion nor propellants, I count 20t.

Near Mars, the Solar thermal engine accelerates the vessel from 1323 to 7337m/s. It ejects 13t hydrogen, starting at 34t. This phase lasts for 10 days thanks to 44 concentrators and engines, and adds less than 5 days travel.

One LR-10B oxygen+hydrogen engine starts from a 200km Martian orbit at 3454m/s, adding there 1607m/s to reach the 1323/s above Mars' gravity. It burns 15t propellants, so the vessel weighs 50t in Martian orbit, where it was put in advance.

----- Return leg, without aerobraking? -----

Braking to low Earth orbit by a Solar and then a chemical engines is unaffordable, like 250t starting near Mars.

The Solar engine braking to a location far above Earth, after a chemical and then a Solar engines accelerate the vessel from low Martian orbit need almost 90t there, an awful lot.

The least unreasonable: start from far above Mars, say a Langrange point, accelerate and brake by the Solar engine to a location far above Earth. This accepts almost 70t in Martian orbit, but the crew must first reach this point from Martian surface, needing more propellants and time, and at Earth, they waste time again to board the preset reentry capsule and dive to Earth. One good point: some hydrogen can shield the astronauts during the trip.

----------

I prefer the aerobraking option and evaluate the rest with the corresponding mass.
I described elsewhere hydrogen and oxygen storage in tanks of metal+foam+MLI hold by polymer straps.

Marc Schaefer, aka Enthalpy

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Already an "oops"... :embarass:Back from Mars in 80 days needs 9622m/s asymptotic speed there.

As well, the optimum share expects 1927m/s asymptotic speed from the chemical engine, and because it means only 1.7% more start mass, I request even 2927m/s from it.

Then, the Solar stage provides 6695m/s, starts at 36.1t and expels 15.0t, still using 44 ten-meter concentrators. The chemical departure stage provides 2241m/s at the 200km, 3454m/s Mars orbit, by burning 23.9t; one or two RL-10B shall push the initial 61.7t.

Reentering Earth's atmosphere at 17643m/s versus ground still holds, but this implies 4.0G downforce, or combined 5.6G if the drag equals the lift. The wing area is reasonable, since the chosen altitude tunes it.

---------

I've found no good way to leave Mars with the Solar engine only. Lagrange points take weeks to reach at Mars or Earth. An elliptic Martian orbit is easier to reach and leave from Earth, but its orientation is too costly to change and differs between arrival and departure; it's also hard to reach from Martian surface, unlikely in one stage. A high circular Martian orbit is even farther from the surface; that's a backup design.

A short trip without aerobraking at Earth would be difficult even with the Solar engine.

---------

A trip slightly longer would save much mass. Maybe my shield setup or an other permits it:
http://www.scienceforums.net/topic/80982-shield-astronauts/

If a leg lasting 180 to 200 days becomes acceptable, then the same 9622m/s asymptotic speed at Mars departure enable to pass at 0.85 to 0.65 AU from the Sun between Mars and Earth, and this permits to stay 31 to 212 days on Mars instead of two years, as computed with NonHoMarsInwardsOpposition2.xls there
http://www.scienceforums.net/topic/83284-non-hohmann-to-mars/#entry807661

One can save mass for the short stay option as well: with 7000m/s asymptotic speed to leave Mars, the leg takes 220 days to stay 17 to 52 days on Mars. It all depends on shielding.

Marc Schaefer, aka Enthalpy

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----- Preset 62t equipment on a 400km Mars orbit -----

The solar thermal engine does it over a 259 days economic Hohmann transfer.

----- Mars

The vessel brakes much in advance and passes at 600km altitude with 125m/s below the escape speed, see xls:
MarsCargoArrival.zip

Arriving with asymptotic 2649m/s, capture to 3390+400km/58,000km costs 2727m/s. A 400km circular orbit takes 1245m/s more, with many 1000s kicks around periapsis only; I sum to 4200m/s.

isp=1267s and 100kg/t inert mass let eject 26t hydrogen and start the deceleration with 91t. Fourty-four 10m concentrators push 216N near Mars, or 2.4-3.3mm/s2; it takes boring 160 days to the circular orbit, but the equipment is in place and tested before launching the crew.

----- Earth

Climbing to a 6370+400km/194,000km from circular 400km takes 2994m/s, escape and acceleration to 2945m/s additional 2955m/s. The climbing kicks extend 1000s around perigee, and I sum to 6100m/s.
EarthCargoDeparture.zip

This consumes 62t hydrogen, starting from Leo with 159t. The same concentrators achieve 501N near Earth, or 3.2-5.2mm/s2, so climbing takes some 130 days before the Hohmann launch opportunity.

----- Variants?

The RL-10B would start with 236t at Leo, with Oberth effect at both planets.

The vessel could aerobrake at Mars, but not with the concentrators deployed, and retracting them all is challenging.

Accelerate chemically, aerobrake at Mars, deploy the equipment's concentrators later? The start mass at Leo is similar. I prefer to have well-tested solar engines ready at Mars and avoid the risks of aerobraking.

The solar engines could spiral faster to a high circular orbit than kick to an elliptic one, but this costs much mass.

The last (first) kick near Earth (Mars) can be stronger to exploit the Oberth effect. Used for 1000s at isp=500s instead of 1267s, the Solar engine pushes 2.5x stronger but consumes hydrogen 2.52x faster. This gains 3% mass at Earth.

The vessel could have a chemical engine just for that last kick, after the solar engine achieves the elliptic orbit. More complicated, but it does gain mass.

A gravity assist at our Moon is more useful with the Solar engine's faint acceleration: possibly 16% mass gained, hard to compute by hand. Though, it takes a slow, very elliptic orbit before, imposes departure windows asynchronous with Mars, and constraints the Earth orbit's inclination.

Marc Schaefer, aka Enthalpy

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Illustration of the transfer of heavy equipment to Mars orbit:

 

post-53915-0-56255100-1402330316.png

 

Very classical, except that the solar thermal engine uses several hundred kicks between the low and the elliptic orbits, and also pushes and brakes far from the planets.

"Strong" indicates the times, one at each planet, where the Oberth effect multiplies a kick, so that specific impulse can be traded for thrust, say by operating the solar thermal engine in a high-flow mode.

Marc Schaefer, aka Enthalpy

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Do you find it frustrating when no one replies, agrees, or challenges?

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Thanks for caring!

If someone jumps in, just fine! If not, it doesn't worry me. My messages are rather descriptions, but on a forum, members don't need an additional invitation to discuss, do they?

This young thread has been viewed 165 times as of today, so I imagine some readers have even come back.

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----- Descent to Mars and ascent -----

This is a script from and to a 3390+400km Mars orbit (orbital=3362m/s) and the ground (3.711m/s[super]2[/super], escape=5027m/s, rotation ~180m/s), starting with 60t in orbit.

 

post-53915-0-41104900-1402846308.png

----- Propulsion

The ascent engine pushes 180kN for 15m/s[super]2[/super] through four 0.8m nozzles; gases expand to 4.3kPa and 3445m/s=351s. The descent engine pushes 1050kN for 20m/s[super]2[/super] through four 0.8m nozzles; gases expand to 39kPa and 3010m/s=307s. Adding the ascent engine during the descent would land only 0.4t more but would test it early. The descent engine must be separated before ascent, the descent tanks preferably.

A first propellants option pressure-feeds oxygen and 3,7,11-tri(methylaza)-tridecane. The fuel shall be storable on Earth and Mars, and produced easily
http://www.chemicalforums.com/index.php?topic=56069.msg272080#msg272080
but it could be pentamethyl-dipropylene-triamine (Jeffcat ZR-40, Polycat 77, mp -78°C) or farnesane, phytane. Ascent oxygen would fit in a graphite fibre compact tank, multilayer insulated and hold by straps in a vacuum shell as in
http://www.scienceforums.net/topic/73798-quick-electric-machines/#entry738806
1kg/day evaporation needs a few watts of active cooling. The descent oxygen needs no vacuum, only foam and multilayer insulation. Chamber pressure is 36bar dropping to 18bar, with helium stored at 90K and 240bar in graphite tanks. The ascent tanks and helium weigh an estimated 106kg/t of propellants if the ascent fuel is a radiation shield.

Alternative propellants are Mon-33 (toxic) and farnesane, both storable on Mars, pumped by this cycle
http://www.scienceforums.net/topic/83156-exotic-pumping-cycles-for-rocket-engines/?p=805383
the exhaust speed happens to be the same, the lighter tanks must compensate the pumps - the real advantage is the flexibility to arrange all tanks, preferably as radiation shields.

----- Descent

A 216m/s kick de-orbits in a quarter turn, leaving 55.9t.

The D=10m vessel aerobrakes from ~3700m/s with its 0.8t heat shield separated thereafter, then with a first parachute opened at 800-1000m/s, made of high-temperature polymer. Truly big parachutes, like three (plus redundancy?) D=27m, bring the fall to 100m/s. They weigh 3t and separate ~600m above ground, leaving 52.1t.

The descent engine brakes to zero; this costs 123m/s. It then allows the pilot to hover three times 20s (233m/s together) and hop twice to a better location 200m away (130m/s together). Operations near the ground need 486m/s from the engine, which leaves 44.3t landed.

This includes dry propulsion, the ascent module, three dressed astronauts, some shielding, equipment to improve the shields, mission and repair tools, mobility - and habitat and regenerative life support for two years, so this mass is easily used.

----- Ascent

12t lift off. A Hohmann transfer would cost 3840m/s without Mars' rotation nor atmospheric drag; with some orbital manoeuvres, I take 4100m/s, which leaves 3.6t in orbit - including dry propulsion, three dressed astronauts with some shielding, and souvenirs.

Marc Schaefer, aka Enthalpy

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Yes, I have been following, please keep posting.

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Why anyone would volunteer to go to Mars I can't imagine. I understand the Moon was once described as magnificent desolation. And Mars seems similar if not worse. And to spend several months journeying there in a confined tin can, only to be confronted by a desolate landscape; sounds like a recipe for experiencing torment and madness.

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Why anyone would volunteer to go to Mars I can't imagine. I understand the Moon was once described as magnificent desolation. And Mars seems similar if not worse. And to spend several months journeying there in a confined tin can, only to be confronted by a desolate landscape; sounds like a recipe for experiencing torment and madness.

Something like ocean crossings of a few centuries past? :rolleyes:

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Why anyone would volunteer to go to Mars I can't imagine. I understand the Moon was once described as magnificent desolation. And Mars seems similar if not worse. And to spend several months journeying there in a confined tin can, only to be confronted by a desolate landscape; sounds like a recipe for experiencing torment and madness.

That is fine. There will be more space for the rest of us.

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There is something attractive about it. Hiking across Olympus Mons. Watching the Sun peak over the edges of Valles Marineris.

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There is something attractive about it. Hiking across Olympus Mons. Watching the Sun peak over the edges of Valles Marineris.

 

 

the bottom of Valles marineris is low enough for liquid water to exist, very interesting place...

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Something like ocean crossings of a few centuries past? :rolleyes:

I think there's a vast difference between crossing an ocean and being stuck on a desolate alien landscape with air one can't breathe or even exist in without a spacesuit. Not to mention the nearest human habitation being an unreachable distance away.

 

I understand human frustrations occur on the International Space Station, so what would happen on Mars perhaps one can only contemplate - all the ingredients for madness if you ask me.

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I think there's a vast difference between crossing an ocean and being stuck on a desolate alien landscape with air one can't breathe or even exist in without a spacesuit. Not to mention the nearest human habitation being an unreachable distance away.

 

I understand human frustrations occur on the International Space Station, so what would happen on Mars perhaps one can only contemplate - all the ingredients for madness if you ask me.

As I said, no one is asking you to go. Feel free to be part of the next demonstration of the effect of natural selection on homo sapiens. We need control samples.

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Something like ocean crossings of a few centuries past? :rolleyes:

I think there's a vast difference between crossing an ocean and being stuck on a desolate alien landscape with air one can't breathe or even exist in without a spacesuit. Not to mention the nearest human habitation being an unreachable distance away.

 

I understand human frustrations occur on the International Space Station, so what would happen on Mars perhaps one can only contemplate - all the ingredients for madness if you ask me.

 

Yes, I got your take on madness from your post that I was replying to. Repeating it adds nothing. As Ophiolite points out, you don't have to go if you don't want to. Moreover, madness knows no restriction on circumstance as evidenced by folks who go mad where breathing is free and human habitation is a whisper away.

 

Exploration and adventure are as exploration and adventure do. Lead, follow, or get out of the way. :)

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----- Crew's leg to Mars, with aerobraking -----

 

For an 80-days trip not including the acceleration overcost, the vessel moves away from Earth with asymptotic 80° and 11575m/s, and arrives at Mars with asymptotic 10308m/s, or 11468m/s versus a non-rotating ground.

The vessel with crew and life support is to weigh 20t at Mars; 500m/s of tri(methylaza)tridecane and oxygen for orbit corrections and rendezvous with the preset descent-ascent module bring it to 24t. The vessel brakes by Mars' atmosphere only; it's a glider to provide 35m/s2 downlift. A 6m2 wing would suffice at 20km height, so higher is possible - the Martian atmosphere is very variable, but the preset return and descent-ascent modules observe it, and the wing copes with some variations.

The solar engine accelerates near Earth from asymptotic 5283m/s to 11575m/s by expelling 17t hydrogen, beginning at 42t. Twenty 10m concentrators achieve it in 10 days. This propulsion is thrown away before aerobraking.

A chemical engine brings the composite to the 5283m/s above Earth gravity, more than optimum 4283m/s to save concentrators. Four RL10B (optionally with common turbopumps and actuators) burn 76t propellants in 800s. This expended stage starts at 400km Low-Earth-Orbit with 124t, so the vessel could be bigger.

I wish to unfold and test the Solar engine before sending the crew away from Earth. The unfolded engines must then withstand 1G, which also permits to test on Earth. Integration isn't obvious.

A sketch of the transfer should follow.

----- Variants -----

Aerobraking at Mars to reach orbit is a risk. Braking there with a (bigger) solar engine instead, followed by a chemical one, would need 280t on Leo. The departure chemical stage can weigh 160t for 2600m/s if the vessel and departure solar stage total 120t, and be launched separately to Leo. Unfolding the concentrators gets easier.

Presetting the descent-ascent module took fourty-four concentrators, the return vessel as well. Joining them on Martian orbit would improve the acceleration of the return vessel.

The twenty solar engines of the crew's leg to Mars could be separated earlier before Mars and have a bit of hydrogen more to brake autonomously. One more rendezvous with the return vessel, limited benefit.

Keep the glider vessel for the return leg! This saves 20t from 62t preset in Martian orbit, and since the leg to Mars needs less launch capacity, the vessel can grow.

Marc Schaefer, aka Enthalpy


Yes, I have been following, please keep posting.

 

Nice of you!

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I'm sorry, but I find the consequences of confining a human to the restrictions of a journey to, and a period spent, on Mars to be beyond human endurance.

 

But on the other hand, perhaps if only volunteers infected with Toxoplasma Gondi were considered as candidates maybe it'll work. Might not be too difficult as I understand it's estimated that 30% of the human population is infected. Infection, I further understand, endears us with penchant to take risks - perhaps those base jumpers I've just seen on TV news (UK) are infected!

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It really wouldn't be that different than being on a submarine. In terms of contacting friends/family, it would actually be better.

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It really wouldn't be that different than being on a submarine. In terms of contacting friends/family, it would actually be better.

I'd suggest it's far removed from being on a submarine.

 

Apart from long delayed voice communication, on Mars you'd be incomplete isolation from humanity with nothing to look at other than a barren landscape. And looking and testing rocks for signs of life, or previous life, will quickly become the most boring activity one could imagine. Which is in complete contrast to being on a submarine, whereby all one has to do is blow the ballast tanks and you'd be breathing the good fresh air. Not so on when stuck on Mars. It'll probably be worse than the psychological effects of being locked in a dungeon.

 

But whoever wants to go, then good luck to them.

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I keep thinking they should learn to walk before they run and build something permanent on the moon first.

 

Sending a community there would be a lifetime commitment to sending them supplies.

 

What if the funding dries up for this in 50 years after a generation of new young martians. All those beautiful pictures we see on video every week will be forced to starve or worse because nobody here wants to keep paying.

 

A moon based community would offer greater chances at rescue or replacing personnel, and could even score high in the tourist industry. Chances are less billionaires would opt for mars based on it's distance.

 

It may cut our chances of finding a real Russell's Teapot (I'd put one there), but it makes much more sense.

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I keep thinking they should learn to walk before they run and build something permanent on the moon first.

 

Sending a community there would be a lifetime commitment to sending them supplies.

Probably end up like the ISS, whereby nobody knows what it's there for!

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Same as in my previous message, but with colour: crew's transfer from Earth to Mars, with aerobraking.

The sketches follow no scale at all, nor are all solar engines represented. Speeds are asymptotic and relative to each planet.

post-53915-0-98940300-1403651532.png post-53915-0-49378800-1403651547.png

Good downlift by the wing keeps the glider in Mars' atmosphere long enough for a bearable deceleration.

The same orbit inclination for the descent-ascent module and the return module is useful, to cumulate the solar engines, or if rats have eaten the biscuits at one vessel; then the inclination is ecliptic or nearly, which restricts the landing sites to -25 to +25° latitude with some plains available.

This script needs no accurate landing site. It also permits redundancy, with two descent-ascent modules that can help the crew in orbit or on the surface, and two return modules. 180° phasing in orbit doubles the docking opportunities, saving time. This redundancy needs five launches for the first mission only, dropping to three for the following ones.

Marc Schaefer, aka Enthalpy

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Probably end up like the ISS, whereby nobody knows what it's there for!

What I don't understand is why you feel compelled to keep posting here. What's your skin in the game? If it's just that others quote your posts then pretend I never did it and leave the folks here alone to discuss how they think it should/could be done.

 

On that front: NASA's New Mega-Rocket, Orion Capsule on Track for Future Test Flights

A new era of space exploration supported by a history-making new mega-rocket and a spacecraft designed to deliver humans into deep space could be on the horizon for NASA.

 

The space agency is gearing up to build the largest and most powerful rocket in history. The huge launcher, called the Space Launch System (SLS), will move a new spacecraft dubbed Orion, designed to send up to four astronauts farther into the solar system than ever before. A short list of destinations includes the moon, nearby asteroids and, eventually, Mars.

...

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What I don't understand is why you feel compelled to keep posting here. What's your skin in the game? If it's just that others quote your posts then pretend I never did it and leave the folks here alone to discuss how they think it should/could be done.

 

On that front: NASA's New Mega-Rocket, Orion Capsule on Track for Future Test Flights

That's coincidental, because I don't know what your objection is based on.

 

Human psychology, I would've thought, to be a major factor in a trip to such a place. Being locked up in a confined tin can, and then perhaps only a slightly bigger tin can whilst domiciled on a distant alien landscape with unbreathable air at an unsurvivable pressure (without the aid of a claustrophobic spacesuit), and the possibility, probably a high possibility, of being marooned is very serious test of human sanity.

 

If your location is anywhere near London UK, I'd suggest you go and view the Apollo 10 command capsule in the Science Museum. How they remained compos mentis confined in that thing I don't know.

 

I recall a TV program whereby someone was being introduced to wearing a spacesuit (prior to a U2 flight). The guy freaked out. And even after said U2 flight he reported it being very difficult to endure. And enduring such confinement, I'd suggest, is nothing compared to a Mars trip.

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