Author Topic: What is the cheapest and fastest way to go to the moon or mars  (Read 24243 times)

Offline Ben the Space Brit

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Really, propulsion is everything.  With extant EDS-capable upper stages, there is currently no way of launching an EOR-assembly lunar mission where the crew ride out with the lander.  It is possible to send the cargo ahead using EOR and ion drive tugs and then send the crew out using two launches (one for Orion and one for the propulsion stage), although the time factor for crew launch would be very tight.

Realistically, crewed lunar missions must wait on the production of powerful enough upper stages that the time constraints on crew launch are relaxed.  That means waiting for SpaceX's Raptor and ULA's Common Centaur.  Both could launch an appropriately-equipped crew vehicle direct to LLO for a LOR mission.  Both could be available by ~2016

If you want to do EOR on your mission stack, you need to improve upper stage longevity.  That means ULA's ACES family or NASA's CPS.

Either that or go with propellent transfer instead.  Using prop transfer, you can launch the cargo 'dry', launch the Earth departure propellent with the crew, tank up the EDS after rendezvous and carry out TLI on Flight Day 2 or 3.  However, that's a hefty R&D program in its own right and would stretch out the timeline a lot.

If you want to land, you need to develop a lander.  There isn't any in serious development at the moment except the small Morpheus, which I believe was originally part of a plan to land Robonaut 2 on the Moon.  Scaling that up to serve as a two-way crew lander capable of supporting a significant service mission will be both expensive and take a while, even if the maximum number of lessons are learnt from Grumman's work on the LEM.

I'd say that, if you went by developing current medium ELVs, you could reach lunar orbit by 2018 for the Apollo 8 hemicenteniary and you just might get to the lunar surface by 2022 for the Apollo 17 hemicentiary.  Go with SLS and, whilst almost any realistic mass constraint is removed, the time-line shifts rightwards by as much as half a decade, mostly because of reduced mission development funds being available.
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Offline JohnFornaro

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I don't know how fast you all are going, but this sounded pretty fast to me:

From "Celestial Mechanics and Astrodynamics",1964, Victor Szebehely, editior, p. 56, there is a 36 hour trajectory to the Moon suggested.  It's seems like a lead and shoot trajectory.  Lead the Moon by a certain amount, fire off the rocket, and hit (not land, necessarily), 36 hours later.

It prompted me to ask about the delta-vee penalty for flying to the Moon, basically as fast as possible.
« Last Edit: 09/20/2011 02:44 PM by JohnFornaro »
Sometimes I just flat out don't get it.

Offline Robotbeat

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One of SLS's advantages, especially for Mars, is that it can launch very large pieces (both mass-wise and size-wise) in one shot, which helps with architecture design.

No, it doesn't, not if you allow for propellant transfer, as you should. As for crowds of anti-SLS posters: this whole site is pro-SLS by 2:1...
Propellant transfer doesn't solve the problem of Mars EDL. To land humans on the surface of mars the lander needs an entry mass of 100-150mt....
That's just plain false.

If you land an empty ascent vehicle beforehand that becomes filled with ISRU-derived propellants, nothing even near 100mT is needed as an entry mass (probably could make do with just 10mT or less landed dry mass at a time...). And besides, 100mT entry mass still requires ballutes or other more difficult EDL technology.

Heck, the Apollo lunar module, which could probably fit 3 in a pinch (after all, Apollo 17 had over 100kg of samples, plus the two astronauts), and had enough delta-v for a Mars ascent vehicle (if not thrust) weighed only about 4 or 5 tons dry and could have considerable weight shaved off if it used modern electronics and batteries and aluminum-lithium alloys

It also depends if you want a crew of 8 (like some of the Mars architectures had) or a smaller crew of 6, 4, or even 2 (say, for the short-stay missions... some crew could stay on orbit, ala Apollo).
I spent the evening looking over a few proposed Mars missions. Haha I didn't have anything better to do. Your claim that 10mt or less could would work doesn't seem doable. DRM 5 thinks 40mt is the smallest individual piece. Mars Direct uses ISRU and it requires the ability to land 28,500 kg on the Martian surface. The habitat, power, and life support is over 10mt for a crew of four. Its something that can't really be split up into smaller pieces.That doesn't include any consumables, lab equipment, space suits, rovers, backup spares, or astronauts. A crew of four is going to require 10.4mt of consumables alone. The ISRU parts don't fit under 10mt either.

For safety reasons the crew is going to need to land with plenty of consumables, a long range rover, and a habitat in case they land too far the other mission elements such as their ride home. A lot has to land with the astronauts in order to reduce the risk of an off target landing. Once again going by the Mars Direct figures that is going to be more then 10mt. The lowest mass landed element I can realistically and safely cobble together is at least 16mt from the elements in Mars Direct. I bet there was good reason to not even go that small by the study's authors.

I'm not saying that the full 130mt SLS is needed for a Mars mission. However, it looks like the Falcon Heavy is too small for the job even with advanced EDL technology, ISRU, and propellant depots. Its been proposed that the core version of SLS with a 70-100mt payload and propellant depots could be the best way to go. There would need to be more study of this concept but personally I am leaning in that direction.

Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?
Mars DRMs are not the minimum required for landing humans. I'm talking about the minimum size, not even necessarily the optimum size.

So, you made lots of assumptions:
1) minimum surface crew size 4 (again, no reason why 4 is the minimum required for a short-duration mission)
2) precision landing can't be relied on (the lunar-roving-vehicle had a mass of only 210kg, and had a range with 2 astronauts of almost 100km... modern batteries could do better, maybe twice as long)
3) the size of power, consumables (for less than 30 days), etc, can't be reduced
4) Mars Direct is the best possible option for lowest mass elements (it already assumes an HLV, so if the conclusion after looking at Mars DIRECT is that you should use an HLV, you are begging the question).

All the astronauts REALLY need to land with in case of an off-nominal landing is a small unpressurized rover, a couple of space suits with enough consumables to last a day or so while they drive to their landing spot. OR, you make an off-nominal landing so unlikely that those things aren't required, or that even an off-nominal landing would be within walking distance or a remote-controlled rover with enough range can be pre-landed, etc.

Halving the crew could have the effect of nearly halving the minimum entry mass.  We have a 6-person manned outpost right now that has crew that gets there and back with only a 3-person spacecraft. So, even if you lower the minimum crew to 2 or 3 doesn't mean your outpost can't support higher numbers. Far more important than having large numbers is getting there at all, in my opinion.
« Last Edit: 09/20/2011 03:29 PM by Robotbeat »
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Offline Lobo

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Well, those are two very different questions.

If the question is, "What is the cheapest/fastest way to get to the Moon", then the answer is probably a 2-launch SpaceX FH with a new hydrolox upper stage.  SpaceX could develop one of their own, or ULA could develop ACES, which would be preferable for other reasons.  Plus they already have hydrolox upper stages and have been designing ACES for some time.  THey could probably get there faster and more reliable than SpaceX, which would be starting from scratch with a brand new engine and tech.
So NASA can buy FH from SpaceX, and ACES from ULA.  Stack them at the VAB themselves on the modified Ares 1 ML.  Like NASA did with the stages of Saturn.
I would imagine if that was the PoR, you could get there in about 4 years.  (Please correct me if I'm wrong).
But you need a lander.  I think ULA's ACES-lunar proposal is a good one, and probably the fastest and best for non wide body LV's.  It's all based around 5m diameter stages and horizontal landers.  So you don't have to put anything too wide on the 3.6m FH cores.
If that became the PoR right now, I don't know how many years it would take to get the lander developed and built.  I think we have to assume 6-7 years.  Orion  CSM should be ready by then. 
So, maybe by 2018? 

If the question is going to Mars.  then either you need a whole new system that can be used for the Moon, but is big enought o go to Mars, like SLS, FX, FXX, or AVP3a.  FH and ACES would probably be too small in scale for MArs. Maybe, maybe not.  BUt if MArs is the ultimate goal, then you probably want something of larger scale, with wider payloads for the Mars heat shield, which will need to be probably wider than you could put on an FH.  Unless you used an aeroshell or hypercone or something.

Just my $0.02.  :-)

Online 93143

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Unless you used an aeroshell or hypercone or something.

DRM 5.0 already uses biconic aeroshells.  They're 10 m across and weigh 43 t.

Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?

Some of it seems to be circular reasoning, given a 130 tonne Ares V launcher what Mars mission can we design ( DRM 5.0 ) - its not surprising it came up with requiring a 130 tonne HLV.

Looks like you may have missed something...  [emphasis added]

Offline A_M_Swallow

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{snip}

All the astronauts REALLY need to land with in case of an off-nominal landing is a small unpressurized rover, a couple of space suits with enough consumables to last a day or so while they drive to their landing spot. OR, you make an off-nominal landing so unlikely that those things aren't required, or that even an off-nominal landing would be within walking distance or a remote-controlled rover with enough range can be pre-landed, etc.

Alternatively the astronauts land in the pressurised rover.  At 4 tons the rover is a bit heavy for a lander cabin but not impossible.  The lander control panel will need including.  The ECLSS will have to be designed to work on both the planet and in microgravity.

Online notsorandom

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I spent the evening looking over a few proposed Mars missions. Haha I didn't have anything better to do. Your claim that 10mt or less could would work doesn't seem doable. DRM 5 thinks 40mt is the smallest individual piece. Mars Direct uses ISRU and it requires the ability to land 28,500 kg on the Martian surface. The habitat, power, and life support is over 10mt for a crew of four. Its something that can't really be split up into smaller pieces.That doesn't include any consumables, lab equipment, space suits, rovers, backup spares, or astronauts. A crew of four is going to require 10.4mt of consumables alone. The ISRU parts don't fit under 10mt either.

For safety reasons the crew is going to need to land with plenty of consumables, a long range rover, and a habitat in case they land too far the other mission elements such as their ride home. A lot has to land with the astronauts in order to reduce the risk of an off target landing. Once again going by the Mars Direct figures that is going to be more then 10mt. The lowest mass landed element I can realistically and safely cobble together is at least 16mt from the elements in Mars Direct. I bet there was good reason to not even go that small by the study's authors.

I'm not saying that the full 130mt SLS is needed for a Mars mission. However, it looks like the Falcon Heavy is too small for the job even with advanced EDL technology, ISRU, and propellant depots. Its been proposed that the core version of SLS with a 70-100mt payload and propellant depots could be the best way to go. There would need to be more study of this concept but personally I am leaning in that direction.

Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?
Mars DRMs are not the minimum required for landing humans. I'm talking about the minimum size, not even necessarily the optimum size.

So, you made lots of assumptions:
1) minimum surface crew size 4 (again, no reason why 4 is the minimum required for a short-duration mission)
2) precision landing can't be relied on (the lunar-roving-vehicle had a mass of only 210kg, and had a range with 2 astronauts of almost 100km... modern batteries could do better, maybe twice as long)
3) the size of power, consumables (for less than 30 days), etc, can't be reduced
4) Mars Direct is the best possible option for lowest mass elements (it already assumes an HLV, so if the conclusion after looking at Mars DIRECT is that you should use an HLV, you are begging the question).

All the astronauts REALLY need to land with in case of an off-nominal landing is a small unpressurized rover, a couple of space suits with enough consumables to last a day or so while they drive to their landing spot. OR, you make an off-nominal landing so unlikely that those things aren't required, or that even an off-nominal landing would be within walking distance or a remote-controlled rover with enough range can be pre-landed, etc.

Halving the crew could have the effect of nearly halving the minimum entry mass.  We have a 6-person manned outpost right now that has crew that gets there and back with only a 3-person spacecraft. So, even if you lower the minimum crew to 2 or 3 doesn't mean your outpost can't support higher numbers. Far more important than having large numbers is getting there at all, in my opinion.
It was not me who made those assumptions, it was the designers of many different studies. There is a lot of agreement across many different studies in what is needed on the surface of Mars to make the mission work. There is just no way to reduce the minimum size of some of those mission critical elements below 10mt.

1: A crew of 4 is necessary due to safety. If a crew member becomes incapacitated the rest of the crew can compensate. The work load to make it back to Earth safely is just to much for one or two people to handle on their own. Besides reducing the crew doesn't make the biggest single mission elements any smaller.
2: How far away can we land and still make it to the other elements of the mission? The longer that distance the safer the mission. An Apollo type rover isn't going to work. Astronauts can't spend more then a day in their suits. Its not like they can get out of them to eat and do other body functions. Even if precision EDL is 100% reliable it doesn't change the fact that there are other mission elements aside from the landing party bigger then 10mt.
3: 30 days of consumables is 624 kg. Any less air, water, and food and the astronauts are not going to make it 30 days. A closed loop system is going to add more mass then it saves for a period that short. If they could have been made any smaller in the studies they would have. The authors did not pad these figures just so that they would need an HLV.
4: I focused on Mars Direct because you stated that ISRU would make the largest single landed item less then 10mt. Mars Direct is the most complete and detailed study utilizing ISRU propellant production. I was only looking at the landed portions of Mars Direct, with the question what had to be on the surface? I did not look at their conclusions for any other part of the mission from an inch off the Martian surface all the way back to the Cape.

I am not looking at this from a bias claiming that SLS is absolutely needed or not. My perspective is what do we need on the surface of Mars. Trying to make mission elements smaller rapidly increases complexity and risk and there is a point at which they can't be made any smaller. Some of that we are just going to have to live with since we are not going to be building a rocket big enough to launch an entire Mars Mission in one go. The question is what is the optimum size of a LV? My take on all of this is that an HLV of 70mt is likely necessary and retires a significant amount of risk, cost, and complexity. That is the broad consensus of the professional community. Right now the only contender is SLS. If it were Atlas Phase II, Falcon XX, AJAX, Jupiter, or any other HLV in that range I would support that too because that is what it will take to do a Mars mission.

Offline Robotbeat

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Apollo had 2 surface crew. How did they do it?

I buy the argument that maybe more crew are needed for the long trips in case someone gets sick, etc, but that's for the trips to and from. The surface mission can be short enough that you can get by with a few crew at a time.

Early Mars mission proposals had 70 crew. Yup, 70.

It's necessary for us to think creatively, beyond just what the various Mars DRMs proposed, in order to do a Mars mission within our lifetimes. If that means only 2 or 3 crew per descent or ascent vehicle because of EDL constraints, then that shouldn't be a show-stopper since that's what we do with Soyuz right now anyways. Just use twice as many descent and ascent vehicles.

EDIT: Shuttle tells us that NASA thought you need to (or at least should) do crew rotations all at once. Yet, three-seated spacecraft seems to work just fine with 6 crew (though it needs backup, obviously). So, that a NASA-origin Mars DRM shows 6 or 8 crew per ascent/descent vehicle is no reason why you can't do just fine with a smaller ascent/descent vehicle (and just use two or three of them if you want a larger surface crew...)

Mars EDL techniques scale up poorly, so having small vehicles works out better from a physics and engineering perspective.
« Last Edit: 09/21/2011 02:54 AM by Robotbeat »
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Offline MikeAtkinson

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Its interesting that in many proposed Mars mission I read over while compiling this post a lander mass around 130mt kept showing up. Anyone want to bet where the 130mt SLS payload requirement came from?

Some of it seems to be circular reasoning, given a 130 tonne Ares V launcher what Mars mission can we design ( DRM 5.0 ) - its not surprising it came up with requiring a 130 tonne HLV.

Looks like you may have missed something...  [emphasis added]

Most of the others assumed a HLV as well. The size of this HLV seems to have varied between 100 - 150 tonnes to LEO.

Proponents of HLV have almost always provided Mars missions (at least in outline) for their chosen launcher design.

Online Patchouli

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The cheapest fastest way to Mars I think would be to use a spilt/sprint class architecture like the 1987 Ride report but leverage things like SEP and LEO assembly and if possible an L1 depot.
The crew will take sprint class trajectories keeping the total mission time under 450 days.
The cargo would take a more conservative Holman transfer and make use of solar sails or solar electric propulsion.
I'd use Falcon Heavy and the 48 mT Delta IV heavy upgrade as the primary launch vehicles.

As for the MTV I'd base it one or two or more BA330s and it would be assembled in LEO.
Crew size would be six with future options to 12.
The MTV would then spiral out to L1 under solar power then top off.
Since ion is being used to lift the bulk of the mass from LEO to L1 it might be preferable to use methane in place of hydrogen propellants and just deal with the lower ISP as it would make boil off a lot less of a problem.

Next the crew will meet with the MTV at L1 using Orion or Dragon and it's ACES derived departure stage would fire.
NTR would be nice to have here.

The lander and hab would have been sent ahead of time.
The first mission will only be a 20 day surface stay as to allow catching back to Earth before it gets too far away.
The lander and MAV would be based off either lunar lander systems or VTOL sub orbital.

No ISRU MAV would use NOFBX propellant while the ISRU MAV/Lander methane lox.

Entry system heat sheild would be based off inflatable technology or a biconic DCY shape.
http://www.nasa.gov/topics/aeronautics/features/irve.html

Return same MTV is used and 12 hours before reentry crew enters Orion or Dragon and does direct return.
MTV captures in high ellipse and uses ion propulsion or electrodynamic tether to slowly return to LEO.
The MTV also could simply be disposed of by reentry or being left in solar orbit or crashed into the moon.


« Last Edit: 09/21/2011 07:54 AM by Patchouli »

Offline Warren Platts

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IMO, the cheapest and fastest way to Mars would be a simple (as in pretty much fully propulsive), reusable (cheaper since it can be used over and over again), all chemical (faster than SEP), architecture that was evolved from previous spacecraft a la the ULA Lunar plan.

Zegler et al. say their DTAL lander could easily be evolved for use on Mars. My own BOTE calculations suggest that a stretched tank DTAL lander (i.e, an ACES-71) equipped with a heat resistant titanium hull (so it could withstand the full 1 W/cm2) could land fully propulsively--no ballutes, parachutes, or heat shields required.

Then the ULA MTV has a crew capacity of 16 and a nominal delta v of 11 km/sec. If there was refueling capability in Mars orbit, the ULA MTV could cut the 1-way transit times by over half compared to the Hohman transfer; if refueling was deemed impractical (probably the case for the initial missions), it would have enough delta v to do a round trip taking Hohman transfers. Again, this would all be fully propulsive--no heat shields required.

The 7 hundred tonnes of propellant would only cost about $350 million, if refueled at L2 (with Lunar derived LH2/LO2).

See, so the whole thing would be faster and cheaper, since it would be a simple evolution from the ULA Lunar architecture, which is itself a simple evolution from the Centaur 3rd-stage architecture.

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Offline DLR

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I don't think we will use fully propulsive Mars landers. Ever tried firing a rocket into a hypersonic jet stream coming at you?

A Mars lander derived from ULA's DTAL would probably be equipped with a conical aeroshell and maybe a ballute, with propulsion being used for final deceleration and descent only. That way you save a lot of propellant as well.

Mars' atmosphere is a resource. Use it.
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Offline mmeijeri

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It is unlikely heavy payloads can be landed without using propulsion for substantially more than final descent and landing. Of course that doesn't mean you don't want to use aerodynamic deceleration to the maximum degree possible.
May Decatur do to SLS what Decatur did to the USS Philadelphia.

Offline Warren Platts

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I don't think we will use fully propulsive Mars landers. Ever tried firing a rocket into a hypersonic jet stream coming at you?

That's not the way it would work: the main burn happens in orbit above the atmosphere, and the lander essentially falls straight down, subsonically, until it achieves a terminal velocity, and then there's another burn right at landing.

Quote from: martijn
Topic Summary
Posted on: Today at 03:56 AMPosted by: mmeijeri 
Insert Quote
It is unlikely heavy payloads can be landed without using propulsion for substantially more than final descent and landing. Of course that doesn't mean you don't want to use aerodynamic deceleration to the maximum degree possible.

I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.
 
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Offline mmeijeri

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I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.

Hey, I'm all for that, in fact I've advocated just that. But eventually I think both propulsive braking and aerodynamic deceleration will play substantial roles. Large single-use heatshields that require huge fairings - not so much.
May Decatur do to SLS what Decatur did to the USS Philadelphia.

Offline Warren Platts

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I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.

Hey, I'm all for that, in fact I've advocated just that. But eventually I think both propulsive braking and aerodynamic deceleration will play substantial roles. Large single-use heatshields that require huge fairings - not so much.

Roger that my friend! :)
"Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”--Leonardo Da Vinci

Offline spacenut

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Jim has shown that a 10m heat shield can be folded in half to fit a 5m EELV.  There is also the possibility of an inflatable heat shield.  Mars' gravity and atmosphere is not as great as earth, like 35-40% I think. 

Offline Ben the Space Brit

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Mars' gravity and atmosphere is not as great as earth, like 35-40% I think. 

IIRC, Mars gravity is 0.28g and its atmosphere is 1mb, 1/1000 of Earth.

It is the latter that makes aerobraking a marginal (but not impossible) prospect and all-propulsive landing possible.
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Surface gravity 38% Earth, average surface pressure around 7mb.
Douglas Clark

Offline spacenut

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So air braking might be just as costly as propulsive braking or landing? 

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