Mars Crew Landers - Two Stage or Single Stage?

[redliox]

An interesting question occurred to me recently.  On Earth, to reach LEO alone you require a delta-v of over 9 km/s, a heavy burden to achieve with Single-Stage-To-Orbit craft.  However, at Mars, the same feat only requires 4 km/s roughly.  Going further, areosynchronous only needs 5 km/s and a complete escape from Mars 6.5 km/s.  This means the same technology taken from Earth can do A LOT at Mars!

So the question I pose is: should the first Mars lander be a single stage or two stage vehicle?

One reason I pose this question is the agenda of reusability.  When we tried SSTO development on Earth, it stalled out more than once.  It will be easier to achieve orbit (indeed ANY orbit) at Mars, but SSTO tends to be a hefty development project.  Most schemes go for two stages exactly like the Apollo LEM, but sadly both stages end up disposed.  In the long run, wouldn't there be some gain in recovering the lander, even just the ascent stage?

[spacenut]

A Mars lander could be designed with two stages.  The bottom may not need engines, but it would be legs, cargo, and such.  Emptied out of say solar panels, electric vehicles, and other cargo, the empty bays could become living space.  The vehicles could park underneath for charging.  The return portion could have engines mounted on the sides, like the Dragon, but larger.  It could perform the single stage to orbit without all the weight, and return to earth.  These engines would also perform the landing.  Maybe two sets of tanks, with the empty ones on the bottom portion to be purged and also used for habitat, or for manufacturing and storing fuel, water or lox.  This might be called a stage and a half. 

[nadreck]

I don't know if the first one should be, however a lander that can refuel in orbit, land at an unprepared site, then take off again to the refuelling depot in orbit will be a very valuable asset to real exploration of Mars.

[Oli]

I guess you mean the Ascent vehicle, which, in an expendable design, is just the cargo of the lander.

An example. 5t payload to LMO, 4.1km/s, 320s, structural mass fraction (of both stages without payload) of 10%.

GLOW 1 stage: 26.33t
GLOW 2 stages: 22.91t

To areosynchronous orbit, 5km/s.

GLOW 1 stage: 43.54t
GLOW 2 stages: 32.88t

Same with isp of 360 (CH4, assuming same struct. mf).

GLOW 1 stage: 32.88t
GLOW 2 stages: 26.26t

So I'd say to AMO with storables it could be worth the trouble. Otherwise not*, especially not with ISRU.

*with a struct. mass fraction of 10%. The ascent stage in the Raftery concept for example has a struct. mass fraction of 14.3%, in that case you save around 13t (30t vs. 43t) to AMO even with CH4.

Edit: Ah you're thinking about reusability. I'd say by then you have ISRU so it's not worth it to have 2 stages.

[mike robel]

Maybe it would make sense if the HAB module descended separately and stayed on the surface and then crew lands separately in a single stage to orbit vehicle for trips to and from orbit.

The hab tanks could be used for propellant manufacture in between missions as well as provide storage for lwaste products (liquid and solid) to be recycled into something usable.  Other tanks could be used for living quarters or perhaps adapted for some other use by dismounting them and taking tem apart.  (they would be designed to be taken apart for use in something like a radiation shelter or parts of a green house.)

[redliox]

Maybe it would make sense if the HAB module descended separately and stayed on the surface and then crew lands separately in a single stage to orbit vehicle for trips to and from orbit.

A hab would be a one-way lander, useful but the crew will need a round-trip vehicle eventually.  So I'm talking about something entirely different from a hab setup; more like something akin to an Orion-lite made for Mars travel.

[mike robel]

I think perhaps you disregarded the 2nd part.  The crew ascent/descent vehicle, in my scheme, is reusable and goes from Martian orbit to the surface and back.  Perhaps it has the tankage and payload to bring fuel to the Earth Return Vehicle.

[gbaikie]

An interesting question occurred to me recently.  On Earth, to reach LEO alone you require a delta-v of over 9 km/s, a heavy burden to achieve with Single-Stage-To-Orbit craft.  However, at Mars, the same feat only requires 4 km/s roughly.  Going further, areosynchronous only needs 5 km/s and a complete escape from Mars 6.5 km/s.  This means the same technology taken from Earth can do A LOT at Mars!

Yes. That is main reason Mars is better than Venus.
I wondered about Venus in terms of Single-Stage-To-Orbit craft. It involves floating platforms which launch rockets- Mars at least has the merit of being less complicated. But sooner we have Mars settlements the sooner we get settlements on Venus and Mercury. Of course same reason the Moon is appealing and if we get Mars settlement we get to point of using the moon to provide SPS for Earth. Which is not currently viable and soonest might be around 50+ year from the present. And Mars settlement could be 30 to 40 years in the future. So 10 or 20 year after Mars settlement harvesting  solar energy from Space and beaming it to Earth surface seems like something one could invest money in [it's trillion dollar market- and studies indicate it's possible if Earth launch was less than $100 per lb. Or with Moon at $100 per lb to GEO
it in some way better than Earth launch of $100 per lb to GEO. Moon can launch football field size solar arrays and etc, and with the trillion business driving down launch cost, it could get to $1 per lb and solar panels costing about same to make on the Moon as they do on Earth.
So Moon and Mars is all about starting markets in space, which will lower costs and allow unlimited and cheap electrical power from Space to Earth surface- of course that also means electrical power in space is same price or cheaper than on Earth surface. Which means all kinds of fantastic stuff could be done in space- getting to Mars in 2 weeks with ion rockets with beamed powered, and having as cheap rocket fuel in space also make Earth SSTO easier- using rocket power at orbit, makes getting to Earth surface with same velocities of suborbital re-entry- so SpaceshipOne level of re-entry, not shuttle like re-entry.***
But even more fantastical are L-5 colonies and space elevators on all the planets. Limiting the advantages of low gravity world- or their main function is to serve so as to enable Earth to be spacefaring planet.
It's a journey which leads back to Earth.
Though next question would be star travel. There is a lot reasons not to travel to the stars- or it's quite possible we spacefaring for 1000 years before sending a human to the stars. Or Fermi paradox could explained by huge difference of spacefaring as compared to traveling to the stars. Or going to stars might be more of matter of drifting towards the stars and fractions of lightspeed travel might begin as more of means of  reaching the outer limits of this drifting- traveling to other human civilizations  which have drifted beyond the Oort cloud.
Or if you can have 1000 meter diameter telescopes why not do star travel using them? And also by this time we might have some deep [insane] religious attachments to planet Earth.

So the question I pose is: should the first Mars lander be a single stage or two stage vehicle?

One reason I pose this question is the agenda of reusability.  When we tried SSTO development on Earth, it stalled out more than once.  It will be easier to achieve orbit (indeed ANY orbit) at Mars, but SSTO tends to be a hefty development project.  Most schemes go for two stages exactly like the Apollo LEM, but sadly both stages end up disposed.  In the long run, wouldn't there be some gain in recovering the lander, even just the ascent stage?

When first read that, I didn't understand it. But do you mean, a sort of backward Earth SSTO? Or like starting from Earth orbit, and returning back to Earth orbit? Except one doing it with Mars?

It seems one would want a fatter first stage and it seems it would nice to be able to convert the first stage into living quarters. And since living quarters don't need rockets, be able to remove the rockets to be used for some reusable rocket.
A problem with rocket stage used as living areas is one should have shielded living quarters.
You land the rocket, then move the rocket to a hole, or move dirt so it's around the rocket.
And/or design the rocket so that fuel tanks on outside can filled shielding ballast- dirt or water [perhaps even CO2 liquid].
One think about it is you bringing a launch pad for the second stage which goes to orbit- so it's like the Apollo Lunar LEM in that way also.

One could also think about it or describe as landing a BA 330 with the addition of stage which can reaches Mars orbit. So BA-330 is fat: Diameter    6.7 m:
Length    13.7 m
http://en.wikipedia.org/wiki/BA_330
But bringing second perhaps want it fatter than this. And generally I think one lands horizon where with stage you probably want vertical landing. Oh, BA 2100 is fatter:
Length    17.8 m (58.4 ft)
Diameter    12.6 m (41.3 ft)
http://en.wikipedia.org/wiki/BA_2100
Maybe one land on Mars with second stage empty, but land it so first stage would have extra fuel, and therefore if it landed according to plan, one fills the second stage. If needed more rocket fuel to land, then would not have enough rocket and need get more.
Or second stage could be say 1/4 full and so crew [which would be on second stage] would have abort option, if something goes wrong the first stage landing.

*** Edit: A variant of this is refueling suborbital trips from orbit. So using something like mechanical tether
allows rocket fuel in orbit to refuel and sub-orbital trip and so the suborbital vehicle can use rocket fuel to to decelerate. So delta-v to do a suborbital trip halfway around world is close to delta-v of getting to orbit, and re-entry would similar re-entry from orbit. So getting fuel from orbit allows one use rocket power rather heat shields to slow down. So you go halfway around the world and use less fuel than airplane would [and be much faster].

[redliox]

Experimenting with the math behind Martian SSTO.

For starters, if we presume a SSTO ship masses 20 metric tons, at launch it will weigh 79 mt altogether, with obviously 59 being propellant to inject 5.1 km/s of velocity.  Quite a hefty amount for the labor, although it would suffice.

Took another angle, and looked at the SpaceX Dragon 2: http://en.wikipedia.org/wiki/Dragon_V2
The D2 is supposed to be about 4.2 mt dry, likely more presuming that only refers to the capsule weight.  However, even presuming just the capsule alone it is a capsule capable of keeping the crew alive for a week.  Assuming we're talking about a Mars lander that is only used for travel (and not so much as a hab), a week would be a generous amount of time to match anything between low to synchronous orbits - the average satellite sent from French Guiana only needs a matter of hours, a day tops, to go from a GTO to its place in GEO.  An orbiter in areosynchronous would be just as reachable, especially if its intentionally station-keeping over the base site.

Using D2 as a model, yet doubling its mass to give it 'robustness' and Martian adaptations, I start with a calculated dry mass of 8.5 for a whole SSTO ship.  40 tons of methane/oxygen with an ISP of 380 would give almost 6.5 km/s of delta-v, enough to marginally escape.  For the 5.0 km/s for 'synch orbit, 24.5 mt of fuel would be the minimum required, and likewise for low orbit this is 16.5 mt.

So a 10 mt SSTO Martian vehicle might be possible from commercial vehicles; real trick being combining the launcher and its engines into the vehicle as well.

[Archibald]

Congrats, you realized SSTO is easier on Mars than on Earth. Mind you, it is even easier on the Moon. That's one of these bizarenesses of Life...

[redliox]

Congrats, you realized SSTO is easier on Mars than on Earth. Mind you, it is even easier on the Moon. That's one of these bizarenesses of Life...

Except in matters of fuel production.  I'm doubting it will be that easy since, even for the Moon, the LEM was a two-stage vehicle that was entirely disposed during the Apollo flights.

[Russel]

My vote is for a single stage propulsive lander which then acts as a single stage ascent vehicle. Quite apart from being efficient mass wise, simplicity is the essence of reliability.

[redliox]

My vote is for a single stage propulsive lander which then acts as a single stage ascent vehicle. Quite apart from being efficient mass wise, simplicity is the essence of reliability.

Agreed.  My only concern is how feasible it could technically be.  I want to say it would be a decent stretch taking something like Dragon 2 and putting it into this role, but at least that's an example of a good starting point.

People, both within NASA and us space enthusiasts, seem to want habs sent seperately rather than a makeshift one-way crew vehicle.  If that's the case, then maximizing the crew lander seems a way to make a good investment.

[Hauerg]

Congrats, you realized SSTO is easier on Mars than on Earth. Mind you, it is even easier on the Moon. That's one of these bizarenesses of Life...

Except in matters of fuel production.  I'm doubting it will be that easy since, even for the Moon, the LEM was a two-stage vehicle that was entirely disposed during the Apollo flights.

First things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?

[redliox]

First things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?

Nice point.  Inversely, what would be there to gain from either a two-stage  lander or a SSTO lander for Mars?

For two-stage, landing permanent equipment, and for single less vehicles you need to replace for later.

[Russel]

My vote is for a single stage propulsive lander which then acts as a single stage ascent vehicle. Quite apart from being efficient mass wise, simplicity is the essence of reliability.

Agreed.  My only concern is how feasible it could technically be.  I want to say it would be a decent stretch taking something like Dragon 2 and putting it into this role, but at least that's an example of a good starting point.

People, both within NASA and us space enthusiasts, seem to want habs sent seperately rather than a makeshift one-way crew vehicle.  If that's the case, then maximizing the crew lander seems a way to make a good investment.

Well, I pretty much have a good design figured out in my head and it weighs a few tonnes empty.

The basic principle is its a vehicle that's designed with one purpose in life. Landing on Mars. Ascending from Mars. That's it. Its not a long term habitat. Its not designed to land on Earth. But the thing I keep trying to impress upon people is that if you want to cut the return fuel problem down to size what you need is an ascent vehicle that does the job of getting people off the surface and safely to an orbiter, and that's it.

I'm not sure I can parse the "habs sent separately" and "maximizing the crew lander" bits.

[RanulfC]

An interesting question occurred to me recently.  On Earth, to reach LEO alone you require a delta-v of over 9 km/s, a heavy burden to achieve with Single-Stage-To-Orbit craft.  However, at Mars, the same feat only requires 4 km/s roughly.  Going further, areosynchronous only needs 5 km/s and a complete escape from Mars 6.5 km/s.  This means the same technology taken from Earth can do A LOT at Mars!

Yes. That is main reason Mars is better than Venus.

Mars-vs-Venus is another thread, possibly but I wouldn't suggest it as its complicated AND divisive and not at all as clear as one could hope.

I wondered about Venus in terms of Single-Stage-To-Orbit craft. It involves floating platforms which launch rockets- Mars at least has the merit of being less complicated.

"Less complicated" due to many of the factors that simply make it "not-Earth" and MORE complicated for various reasons of the same. (Hint: you can use "air" breathing engines on Venus which you can't on Mars due to the lack of same "air" in the first place but again we do NOT want to go there HERE specifically )

Moon is "easier/cheaper" than both Mars and Venus and yadda-yadda... Will point out this is the Mars section and leave it at that

Congrats, you realized SSTO is easier on Mars than on Earth. Mind you, it is even easier on the Moon. That's one of these bizarenesses of Life...

Except in matters of fuel production. I'm doubting it will be that easy since, even for the Moon, the LEM was a two-stage vehicle that was entirely disposed during the Apollo flights.

As note the expendability of the LEM is a design feature and not a 'bug' and the case for propellant production has been shown to be "valid" depending on what assumptions you base your argument on. As long as you do NOT assume that what is the "best" propellants for Mars happen to be universal, (they are proving very much to NOT be so) your economics is very much "locally" based.

But I'm going to point out that ORIGINALLY the Apollo SM/CM were supposed to be the "take-off-and-Earth-return" stage and were so designed and built and it could in fact "do" landing and SSTO to lunar orbit. (No margin mind you but it was technically possible)

Using the simple metric of delta-v, (and its quite simple really ) the Moon is easier than Mars, which is easier than Venus, which is easier than Earth...

But on-subject, for 'high-traffic' (multiple use) you want something that doesn't stage if you can avoid it because re-stacking/refurbishing takes infrastructure and labor. If you have to "stack" something you want it as plug and play as possible. Lower traffic and first journey's you want reliability over reuse.

My vote is for a single stage propulsive lander which then acts as a single stage ascent vehicle. Quite apart from being efficient mass wise, simplicity is the essence of reliability.

Agreed.  My only concern is how feasible it could technically be.  I want to say it would be a decent stretch taking something like Dragon 2 and putting it into this role, but at least that's an example of a good starting point.

People, both within NASA and us space enthusiasts, seem to want habs sent seperately rather than a makeshift one-way crew vehicle.  If that's the case, then maximizing the crew lander seems a way to make a good investment.

Well, I pretty much have a good design figured out in my head and it weighs a few tonnes empty.

The basic principle is its a vehicle that's designed with one purpose in life. Landing on Mars. Ascending from Mars. That's it. Its not a long term habitat. Its not designed to land on Earth. But the thing I keep trying to impress upon people is that if you want to cut the return fuel problem down to size what you need is an ascent vehicle that does the job of getting people off the surface and safely to an orbiter, and that's it.

I'm not sure I can parse the "habs sent separately" and "maximizing the crew lander" bits.

The basis of the idea is that the "crew-lander" serves multiple purposes because its an "early" vehicle in most cases and not a dedicated one. MCT for example HAS to perform multiple functions, while the MRM missions its a lander with some capability to be used as a Hab in an emergency only, parsing a "single-purpose" orbit-to-surface-back-to-orbit vehicle is kind of hard for modern folks It goes against actual "experience" (lunar) and current assumptions where as it was quite obvious "back-in-the-day" as long as you didn't assume SST-everywhere atomic rocket ships.

Randy

[JasonAW3]

A Mars lander could be designed with two stages.  The bottom may not need engines, but it would be legs, cargo, and such.  Emptied out of say solar panels, electric vehicles, and other cargo, the empty bays could become living space.  The vehicles could park underneath for charging.  The return portion could have engines mounted on the sides, like the Dragon, but larger.  It could perform the single stage to orbit without all the weight, and return to earth.  These engines would also perform the landing.  Maybe two sets of tanks, with the empty ones on the bottom portion to be purged and also used for habitat, or for manufacturing and storing fuel, water or lox.  This might be called a stage and a half.

Actually, I suspect that that is how the MCT will land Cargos and Habitat modules.  It's logical, would allow a to orbit abort and act as an additional buffer between the reentry heat and the actual fuel and crew, thus lowering the risk to colonists arriving. 

[TrevorMonty]

http://www.thespacereview.com/article/3085/1

This article on Hercules mars lander is interesting. I suspect just a power point rocket but it's entry shape landing design are very similar to SpaceX ITS and Masten XS1 proposal.

http://masten.aero/xs-1/

Masten XS1 could be basis of reuseable Mars lander. Unlike ITS it is more realistic size for initial exploration missions.

[laszlo]

Congrats, you realized SSTO is easier on Mars than on Earth. Mind you, it is even easier on the Moon. That's one of these bizarenesses of Life...

Except in matters of fuel production.  I'm doubting it will be that easy since, even for the Moon, the LEM was a two-stage vehicle that was entirely disposed during the Apollo flights.

First things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?

Technically, the LM was a single stage lander. Only one engine was used to decelerate and land. Nothing was jettisoned, not even empty fuel tanks.

Its payload was an SSTO spacecraft. Again, single engine, nothing jettisoned while ascending to lunar orbit.

So while it consisted of 2 parts (SSTL carrying SSTO), each part was a single stage flier.