Author Topic: Manned Mars Lander  (Read 13700 times)

Offline Hyperion5

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Manned Mars Lander
« on: 11/08/2013 03:41 PM »
Over the years NASA, the private sector and even other governments have commissioned studies of what a manned Mars lander might look like.  The most recent NASA effort thought they would be horizontal landers and operate as they're shown in this video:



As you can see, these landers would feature six descent engines, a disposable heat shield, a disposable aeroshell on their back, four landing legs and would also use a trio of parachutes to slow down.  The crew habitat lander would differ only in having a Mars Ascent Vehicle placed at its center, ready to go upon mission's end.  Recently there's been talk of reusable Mars landers or at the very least of using existing Spacex Dragons to land crew on the Red Planet (see Mars One).  So I thought, why not have a thread where we can debate which of the many Mars lander concepts had it down best?  I put this thread here in Advanced Concepts on meekGee's advice. 

It appears to me that there are really only two basic types of Mars landers:

Horizontal landers: long horizontal cylindrical landers that land on their belly.  These are the type currently favored by NASA. 
Vertical landers: often cone-shaped that vaguely resemble the Apollo LM in landing.  Vertical landers were what NASA originally envisioned for landing on Mars back in the 1960s. 

After this point things we can now divide the landers even further:

Mars direct ascent landers: The lander functions as its own Earth Departure Stage and makes a direct descent to the Martian surface.  Depending on the design, the whole lander may or may not make the ascent back to orbit and then make the burn for Earth.  This design may depend on ISRU to be feasible. 
Mars Orbit Rendezvous landers: The approach the Constellation program envisioned, the lander is docked to a Mars Transfer Vehicle or an EDS.  Once inserted into LMO, the lander detaches, enters Mars atmosphere and lands.  Depending on the design, only part of the lander may return to the MTV or EDS as the Mars Ascent Vehicle". 

Of course, let's not forget one last crucial category:

Reusable Mars landers: A Mars lander that not only can land and ascend on and off Mars, but do it repeatedly and reliably.  There is some talk that Spacex envisions something like this for the future, though it would require some serious heat-shield cooling and probably some ISRU capability. 

Non-reusable Mars landers: The envisioned NASA approach that much like Apollo leaves bits and pieces of defunct lander segments on Mars once the mission's over.  This approach has the advantage of mass savings and performance optimization at the expense of needing new landers for every mission. 


Let people know what approaches you feel are best for such a craft and why.  I am a big proponent of shielded engine ports mounted into the sides of the landers much like Super Dracos will be mounted onto the Dragon, but that's just me.  Tell us why you believe how your envisioned Mars lander would work or at least what things you think any Mars lander ought to have and what it should not. 

« Last Edit: 11/08/2013 04:04 PM by Hyperion5 »

Online simonbp

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Re: Manned Mars Lander
« Reply #1 on: 11/08/2013 06:35 PM »
One of the traditional bugaboos about designing a Mars lander has been the problem of supersonic retro-propulsion. This is a problem since any reasonable aeroshell has a terminal velocity of several Mach. So you need either supersonic retro-propulsion or heavy parachutes to brake to subsonic first (and then subsonic retro-propulsion). The original Mars Voyager proposals in the 1960s used supersonic retro-propulsion, but JPL couldn't get it to work. So, when a half-size Mars Voyager was resurrected as Viking, a supersonic parachute was added. All subsequent JPL landers/rovers have used this design. I recall Rob Manning giving a presentation to us JPL interns in 2006 saying that supersonic retro-propulsion would be the best thing for Mars EDL, but that noone knew how to get it working.

That was until last month. On the first Falcon 9 v1.1 flight, SpaceX demonstrated supersonic retro-propulsion on the first stage (that was the part of the recovery that actually worked). If SpaceX really have cracked the code on this, then they will be able to land much easier on Mars than any proposals since the Mars Voyager days.

Offline 93143

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Re: Manned Mars Lander
« Reply #2 on: 11/08/2013 07:50 PM »
SpaceX demonstrated supersonic retro-propulsion

What were the atmospheric conditions during the retro burn, vs. the conditions encountered by a Mars lander following the heat shield portion of the deceleration?

Technically, every manned LEO spacecraft since Vostok 1, in addition to the odd unmanned vehicle, has performed supersonic retropropulsion; it's called a deorbit burn.  The conditions matter.
« Last Edit: 11/08/2013 10:01 PM by 93143 »

Offline Dalhousie

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Re: Manned Mars Lander
« Reply #3 on: 11/08/2013 08:07 PM »
Horizontal lander.  It's a much better configuration for use after landing and has many advantages during EDL as well.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline M129K

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Re: Manned Mars Lander
« Reply #4 on: 11/08/2013 08:08 PM »
Adding the ESA Mars Excursion Vehicle from the 2004 Overall Architecture Assessment study (IIRC, it's basically a European DRM and will be updated in the future) to the thread. It is very tall and looks unstable, to be honest. It can support the crew of three for 30 days, and carries an inflatable heatshield/aeroshell in space, and uses parachutes and retro propulsion for landing. I like the design for shorter duration missions, but the mission designed around it is just atrocious.

Advantages of a lander like this is that no additional cargo lander is required, no ISRU is required, and both the Hab and MAV are placed there in just one vehicle. With an on-orbit mass of 42 tons, it's reasonable by Mars lander standards, and can do everything needed for shorter stays. However, for longer missions it is obviously flawed. A separate cargo lander could fix most of its flaws though.
« Last Edit: 11/08/2013 08:29 PM by M129K »

Offline Lobo

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Re: Manned Mars Lander
« Reply #5 on: 11/09/2013 12:53 AM »
One of the traditional bugaboos about designing a Mars lander has been the problem of supersonic retro-propulsion. This is a problem since any reasonable aeroshell has a terminal velocity of several Mach. So you need either supersonic retro-propulsion or heavy parachutes to brake to subsonic first (and then subsonic retro-propulsion). The original Mars Voyager proposals in the 1960s used supersonic retro-propulsion, but JPL couldn't get it to work. So, when a half-size Mars Voyager was resurrected as Viking, a supersonic parachute was added. All subsequent JPL landers/rovers have used this design. I recall Rob Manning giving a presentation to us JPL interns in 2006 saying that supersonic retro-propulsion would be the best thing for Mars EDL, but that noone knew how to get it working.

That was until last month. On the first Falcon 9 v1.1 flight, SpaceX demonstrated supersonic retro-propulsion on the first stage (that was the part of the recovery that actually worked). If SpaceX really have cracked the code on this, then they will be able to land much easier on Mars than any proposals since the Mars Voyager days.

That's going to be one of the challenges to landing large landers on Mars I think.  I'd heard that payloads about the size of the MSL are about as big as can be done with the existing types of EDL systems, as the parachute becomes too big to deploy reliably or something.  (I remember something like that).  So to go larger, new EDL Systems are needed.  Mostly likely, replacing the parachutes with more retropropulsion for deceleration.

I think there's a couple ways possibly around the issue if firing an engine into the thin Martian supersonic slipstream if that's a problem.

One is to have a big jettisonable aeroshield, with retro engines protected behind it.  When the engines are lit, the shield kicks off and impacts the surface.  That way the engines don't light into a supersonic slipstream.  I would think once they are lit and pressurized, the thin Martian air wouldn't be able to to enger the nozzle and be a problem.  The exhaust plume expelled out the bottom should overpower and basically split the slipstream.

See pics below.

Another is something like RedDragon where the nozzles are tucked back just out of the slipstream and the heatshield creates a bit of a splash efffect in the atmosphere (see picture below as well).  As long as those nozzles are tucked in enough, they shouldn't have supersonic Martian air coming into them I don't think.  I would guess this is the concept behind why RedDragon's superdraco's are expected to work for landing on Mars.
If so, you can scale that up with larger engines.  Perahps bigger methalox enignes in a scaled up geometry of Dragon.  It's not as efficient to have engines positioned like that because of their outward angle.  But it should hopefully be feasibel for landing purposes.  A Mars ascent vehicle of some sort can have engines directly under it for better efficiency for ascent.


Offline Lobo

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Re: Manned Mars Lander
« Reply #6 on: 11/09/2013 01:35 AM »
So, maybe we can start the discussion with the minimalist approach. 

We'll start with something SpaceX-y and hypothetical, as they are least seem to be putting forth some effort to getting to Mars.
Assume for the same of this post, that SpaceX makes a new LV they call FalconX.  They make it a scaled up Falcon9.  They put nine 611klbf metholox engines on the booster, and one on the upper stage.  Maybe that puts around 90mt to LEO.
Maybe a tri-core heavy with crossfeed can put 300mt to LEO.  (for the sake of this example).
So we have a lot of capacity.  I think for a very efficient system, TMI capacity is about 1/3 of LEO.  The new Boeing numbers for SLS Block 1B reflect that.  But this LV will be methalox not hydrolox, so instead of throwing 100mt through TMI, we'll say maybe 85mt, for this example.

So how simple and/or reusable could we make this?

How about a scaled up Dragon capsule  Call it SuperRedDragon (SRD).  It's thrown to TMI, it directly desceds through EDL, and lands on poweful methalox Raptor engines of some type.  It lands empty but has a tank of LH2 to make enough methalox to ascend and burn directly for TEI.  Back at Earth, the SRD heads directly to earth EDL, and lands with is residual propellants as Dragon will.  It'll be much lighter on the way home as several tonnes of equipment and consumables will be left behind.   It'll be an empty shell with a hab unit on top.

This would be similar to Zubrin's Mars Direct, but where Zubrin pictured using a 130mt Ares SDHLV, and does it in two launches, this would have a boosters more than twice that powerful, and could -maybe- do it in just one launch. 

Now, this could be economically efficient, but it won't be mass efficient.  So it won't a lot of landed mass of equipment.  I think we'd be happy if it could just get itself down, and back to earth, with a few tonnes worth of small rovers, experiments, and such. 
And while engines angled out like Dragon's would be ok for descent and landing on both Mars and Earth, they take a big performance hit for ascent and TEI.  So I think such a SRD would need some sort of engine nozzles which are stowed like Superdracos for descent, but could extend and rotate down for ascent and TEI.  Then retract back to the stowed position for EDL at Earth, so they'd be protected during Earth reentry.   That'd be a technological hurdle, but I don't know if it'd be a deal breaker.  It wouldn't need to extend or retract during descent or ascent, only on the surface, and then retract some time between TEI and Earth EDL.  I think if that could be engineerd, it could improve the odds of this all-purpose vehicle working.

Again, it sounds a bit optimistic, but Zubrin thought something like that but one a smaller scale would work for the ERV. 
An unmanned one could be sent first.  Then the next crewed ones are within a rover distace of it, so it could be used as a backup.  I picture a big Dragon, with a hab area on top, and tall cylinderical fuel tanks in the middle.  Then a donut shaped equipment deck around it under the hab area with a door that opens downward and makes a ramp.  Like the picture below, but the door opens down rather than sideways, and there'd not be a truck there unloading.  The cargo would be rolled down the ramp to the surface.
O2 could be mined from the CO2 in the atmosphere, and most water would be recycled like on the ISS.  A Sabatier reactor combines the LH2 with atmospheric CO2 to make Methalox for fuel.
A few similar concept pics below.  The question is, could a single vehicle like this do everything and get all the way back to Earth?  If so, maybe now you have Elon's hinted at reusable MCT?  The tri-core FXH would at least have reusable boosters, even if the core and upper stage are expended.
On Earth, it can be refurbished and launched again.   (although after a mission like that, I'd be pretty surprised if they actually reused the thing).

If FX has a core of say 7m wide, you -should- be able to get maybe a 12m SRD/PLF on it.  Maybe 14m.  Would be a lot of wind tunnel testing on going that much wider than the core, obivously.  So if there was a 14m wide SRD, that should be a pretty good sized lander.  I think Zubrin's landers were in his Ares booster PLF which was 10 I think.  And they seemed pretty big, and this would be even bigger than those.   
For a colony, you have an expendable variant that doesn't have the LH2 tank, no hab area on top, and just lands unmanned with as much equipment as it can carry to support the crews already on site. 

It's a starting point anyway.  As Hyperion pointed out, there's lots and lots of ways to go with it. 
« Last Edit: 11/09/2013 01:48 AM by Lobo »

Offline Hyperion5

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Re: Manned Mars Lander
« Reply #7 on: 11/09/2013 01:58 AM »
I'd heard that payloads about the size of the MSL are about as big as can be done with the existing types of EDL systems, as the parachute becomes too big to deploy reliably or something.  (I remember something like that).  So to go larger, new EDL Systems are needed.  Mostly likely, replacing the parachutes with more retropropulsion for deceleration.

See the 2:40 mark of the video in the first post.  The lander, which clearly masses considerably more than the Apollo Lunar Module, is deploying not one but 3 parachutes.  These deploy after the back aeroshell is left behind, allowing the parachutes to unfurl.  As the parachutes unfurl the descent engines kick in.  I believe Steven Pietrobon mentioned that this approach chops the descent delta-v required from the engines to a mere 500 m/s.  That's an impressively low figure for landing something 50 mt or more on Mars.  I don't know what the figure would be doing an all-propulsive approach, but it'll be significantly more than that. 

I think there's a couple ways possibly around the issue if firing an engine into the thin Martian supersonic slipstream if that's a problem.

One is to have a big jettisonable aeroshield, with retro engines protected behind it.  When the engines are lit, the shield kicks off and impacts the surface.  That way the engines don't light into a supersonic slipstream.  I would think once they are lit and pressurized, the thin Martian air wouldn't be able to to enger the nozzle and be a problem.  The exhaust plume expelled out the bottom should overpower and basically split the slipstream.

Again, I reference the video.  It appears that NASA envisioned its Constellation landers having a big jettisonable aeroshield with retro descent engines protected behind it.  It's when the parachutes fully deploy that the bottom aeroshield/heat shield drops off and the engines fire up.  If ignition in these conditions were a large problem, I would not expect NASA to have dedicated the time and resources to create a video detailing how they'd land on Mars using Ares-launched payloads. 

Another is something like RedDragon where the nozzles are tucked back just out of the slipstream and the heatshield creates a bit of a splash efffect in the atmosphere (see picture below as well).  As long as those nozzles are tucked in enough, they shouldn't have supersonic Martian air coming into them I don't think.  I would guess this is the concept behind why RedDragon's superdraco's are expected to work for landing on Mars.

If so, you can scale that up with larger engines.  Perahps bigger methalox enignes in a scaled up geometry of Dragon.  It's not as efficient to have engines positioned like that because of their outward angle.  But it should hopefully be feasibel for landing purposes.  A Mars ascent vehicle of some sort can have engines directly under it for better efficiency for ascent.

I'm curious, but are all the Mars landers you envision Mars Orbit Rendezvous types or would you ever consider a direct ascent lander?  I ask because the rough estimates are that a 9-Raptor per core Falcon X Heavy would fling more than 110 mt through TMI.  It's so much mass you could feasibly pull it off.  Of course the problem I see is getting back off of Mars. 

http://www.angelfire.com/md/dmdventures/orbitalmech/DeltaV.htm

From   To   Delta-V (km/s)
LEO   Mars Surface   4.8
LEO   Lunar surface   6.2
Mars   LMO   4.4
LMO   Mars    0.05
LMO   Earth return   3.4
Lunar surface LEO 3.2


Total delta-v required

To Mars surface and back to Earth: 22 km/s (12.6 km/s required for everything beyond LEO)
To lunar surface and back to Earth 18.8 km/s (9.4 km/s required for everything beyond LEO)


It seems pretty clear from the math that Spacex or anyone else for that matter would be hard-pressed to pull off a Mars direct ascent approach.  It'd work superbly if all they cared about was getting payloads to the surface of Mars though.  Matter of fact, it requires only 77.4% of the delta-v needed (beyond LEO) to land on the Moon for you to land on Mars.  Now if only there wasn't that dire fact about half of all missions to Mars ending in failure adding a huge asterisk to that.  My guess is if that if anyone wants to mount a round-trip mission, pretty much all the landers will have to be Mars orbit rendezvous types.  Otherwise you're adding a lot of unnecessary propellant and structural mass to the mission that could otherwise be put into useful cargo and habitat mass. 


Offline Hyperion5

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Re: Manned Mars Lander
« Reply #8 on: 11/09/2013 02:11 AM »
Horizontal lander.  It's a much better configuration for use after landing and has many advantages during EDL as well.

Steven Pietrobon was just as adamantly telling me a few months ago that any Mars lander should be vertical because it simplifies the design.  Could you please list the advantages you believe or know that a horizontal lander would have besides for use after landing? 

Offline go4mars

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Re: Manned Mars Lander
« Reply #9 on: 11/09/2013 02:14 AM »
I still like the idea of deep throttling landers, so that they can reusably stack and stage for ascent from Mars (trans-earth inj).  Whether parallel staged or otherwise, lower stages return to Mars, top one heads to Earth.  But I think that's just me who likes that idea.  All I've ever heard back on that idea is crickets.
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Offline Lars_J

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Re: Manned Mars Lander
« Reply #10 on: 11/09/2013 04:16 AM »
I think a horizontal lander would indeed be superior if you wanted to land the maximum amount of cargo one-way, and have it easily accessible to unload.

BUT - if you want a reusable lander that will do ascent as well, that pretty much requires a vertical deep throttling lander.  IMO.

Offline M129K

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Re: Manned Mars Lander
« Reply #11 on: 11/09/2013 07:58 AM »
Horizontal lander.  It's a much better configuration for use after landing and has many advantages during EDL as well.
ESA evaluated both options, they picked a vertical lander. It's probably not as obvious as you think.

Offline Oli

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Re: Manned Mars Lander
« Reply #12 on: 11/09/2013 12:32 PM »
A few documents.

The Challenge for Mars EDL (presentation):
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100017668_2010017622.pdf

Mars Exploration Entry, Descent and Landing Challenges (paper):
http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2006-0076.pdf

Fully-Propulsive Mars Atmospheric Transit Strategies for
High-Mass Payload Missions
(paper):
http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf


------------------------------------------------------------------------------------------


The problem with capsules is that you'd need huge diameters. The MSL had already a 4.5m diameter heat shield.

You could go full-propulsive but in that case the payload mass fraction is rather pathetic. In the paper above the baseline vehicle is 60t in low Mars orbit, of which 8.7t are payload delivered to the surface. Of course those 60t need to be transported from LEO to LMO, which brings total LEO departure mass to around 350t (ISP of 350s).

« Last Edit: 11/09/2013 02:18 PM by Oli »

Offline guckyfan

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Re: Manned Mars Lander
« Reply #13 on: 11/09/2013 02:44 PM »
The problem with capsules is that you'd need huge diameters. The MSL had already a 4.5m diameter heat shield.

You could go full-propulsive but in that case the payload mass fraction is rather pathetic. In the paper above the baseline vehicle is 60t in low Mars orbit, of which 8.7t are payload delivered to the surface. Of course those 60t need to be transported from LEO to LMO, which brings total LEO departure mass to around 350t (ISP of 350s).

Don't go int LMO, go in directly like MSL did. Brake with your heatshield as far as the diameter allows and then do a propulsive landing.

Offline Oli

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Re: Manned Mars Lander
« Reply #14 on: 11/09/2013 03:16 PM »
^

I just wanted to delete my previous comment. Full-propulsive in this case means no significant heatshield requirement, but IMO its kind of pointless.

For example the Austere Human Mission to Mars uses 13m diameter landers with ~53t payload:

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41431/1/09-3642.pdf

A combination of heatshield and retropropulsion.
« Last Edit: 11/09/2013 03:17 PM by Oli »

Offline Rocket Science

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Re: Manned Mars Lander
« Reply #15 on: 11/09/2013 04:05 PM »
Could we please have the links for these images?
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Offline Hyperion5

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Re: Manned Mars Lander
« Reply #16 on: 11/09/2013 04:18 PM »
A few documents.

The Challenge for Mars EDL (presentation):
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100017668_2010017622.pdf

Mars Exploration Entry, Descent and Landing Challenges (paper):
http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2006-0076.pdf

Fully-Propulsive Mars Atmospheric Transit Strategies for
High-Mass Payload Missions
(paper):
http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2009-1219.pdf


------------------------------------------------------------------------------------------


The problem with capsules is that you'd need huge diameters. The MSL had already a 4.5m diameter heat shield.

You could go full-propulsive but in that case the payload mass fraction is rather pathetic. In the paper above the baseline vehicle is 60t in low Mars orbit, of which 8.7t are payload delivered to the surface. Of course those 60t need to be transported from LEO to LMO, which brings total LEO departure mass to around 350t (ISP of 350s).

In one of the papers you posted the payload mass fraction with 1000 second Isp NTRs was an astoundingly bad 8.7%.  I believe that was for full retro-propulsion from mach 3 without aeroassist or parachutes.  The other papers were giving far lower propellant mass fractions as well of around .3-.2, compared to .6-.4.  The part that most impressed me was that larger landers required less delta-v to land and consequently had lower propellant mass fractions. 

Since it makes the math easy to follow, how would a 100 t Constellation-style lander fare in landing mass on Mars?  Let's say it has descent engines with 380 seconds of Isp.  According to this paper (http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2006-0076.pdf) the resulting propellant mass fraction then ought to be around .24.  This is roughly similar to the propellant mass fraction of airliners.  Could we then reasonably expect such a lander to land payloads similar in proportion to airliners?  If so, I would expect the max payload to mass around 30 tonnes.  If not, then how much payload should we expect to land on Mars with such a vehicle? 

Offline spectre9

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Re: Manned Mars Lander
« Reply #17 on: 11/10/2013 12:58 AM »
SRP is the next big challenge.



I like seeing what happens to the flow.

Offline Lobo

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Re: Manned Mars Lander
« Reply #18 on: 11/10/2013 04:58 AM »
^

I just wanted to delete my previous comment. Full-propulsive in this case means no significant heatshield requirement, but IMO its kind of pointless.

For example the Austere Human Mission to Mars uses 13m diameter landers with ~53t payload:

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41431/1/09-3642.pdf

A combination of heatshield and retropropulsion.


Ahhhh.....

Yes, this is a little more like what I had in mind.  Except the lander has deployable rockets that much be deployed during EDL.  With a shape like Dragon having less sidewall angle, SpaceX seems to feel confident that the engines can be fixed and still do the retro propulsion to land.  And that saves having to have a mechanism that needs to actuate during such a stressful time on the craft. If one engine were to not deploy right, the lander is a smoking crater.

However, if it lands like Dragon, then the engines could still deploy out and down around the edges of the heat shield so that they are pointed directly down for ascent and then TEI burn for greater efficiency. 
Then the engines would be deployed on the ground while the lander is at rest, rather than during EDL.  The astronauts could assist them in some manual way if there were any issues. 
And then after TEI, they would be retracted prior to EDL on Earth.  Again, not during the stresses of EDL.  And if there was an issue with retracting them, well they have a long ride home to get the issue resolved. 

But...a point here is that NASA seemed to think it feasible at some level for a lander to have engines that actuate out and deploy and then light into the slipstream.  So maybe it's not too big of a deal?




Offline Lobo

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Re: Manned Mars Lander
« Reply #19 on: 11/10/2013 05:17 AM »

See the 2:40 mark of the video in the first post.  The lander, which clearly masses considerably more than the Apollo Lunar Module, is deploying not one but 3 parachutes.  These deploy after the back aeroshell is left behind, allowing the parachutes to unfurl.  As the parachutes unfurl the descent engines kick in.  I believe Steven Pietrobon mentioned that this approach chops the descent delta-v required from the engines to a mere 500 m/s.  That's an impressively low figure for landing something 50 mt or more on Mars.  I don't know what the figure would be doing an all-propulsive approach, but it'll be significantly more than that. 


PAge 19 of this document talks about this.

Mars Exploration Entry, Descent and Landing Challenges (paper):
http://www.ssdl.gatech.edu/papers/conferencePapers/IEEE-2006-0076.pdf


"Supersonic propulsive descent
Following hypersonic entry, a vehicle intending to land on
the surface of Mars must slow itself from supersonic
velocities to a speed appropriate for a soft landing. This last
deceleration phase, which involves only a few percent of the
vehicle’s remaining kinetic energy, has been initiated in past
robotic missions below Mach 2.1 using some combination
of parachutes and rocket-propelled descent. From Figure 20,
it is clear that a Mach 2 initiation of this phase is not
sufficient for the high mass entry systems associated with
human exploration. The total descent time from Mach 3 or 4
to landing is on the order of two minutes. During this phase,
several vehicle configuration changes are required. In a
matter of seconds, the vehicle will need to re-orient itself, an
aeroshell and/or back shell may be jettisoned, parachutes
may deploy, engines may start, navigation and hazard
avoidance sensors must operate, and landing gear may
deploy. In this very dynamic phase of flight, robust event
sequencing and timeline margin are critically important.
To date all parachutes utilized in the robotic Mars
exploration program have been derived from the technology
effort that led to the Viking flight project. These systems
have been limited to diameters on the order of 10-20 m and
supersonic deployments below Mach 2.1. As discussed in
Section 5, in an effort to improve landed mass, the robotic
exploration program may pursue a large diameter supersonic
parachute, likely no larger than 30 meters and deployed at
velocities below Mach 2.7 (in response to thermal
constraints). As a result of the large masses involved,
parachutes sized for human exploration systems would
represent a significant departure (in both size and
deployment Mach number) from their robotic counterparts.
In addition, due to their size, such systems will require
significant opening times. For example, to decelerate a 100 t
vehicle from Mach 3 conditions to 50 m/s near the Mars
surface would require a supersonic parachute diameter on
the order of 130 m. Similarly, a 50 t vehicle requires a
supersonic parachute diameter on the order of 90 m. While
clustered supersonic chutes are an option, the size of such
systems would still result in large timeline penalties for
opening. As such, an all parachute approach for Mars
human exploration vehicles, similar to the concepts now
used for robotic landers, is likely impractical."


It was something like this that I was thinking of.  I guess it's not so much the parachutes can't be made big enough, but that they might take too long to deploy.

It continues with some more info:


"While parachutes alone are inadequate for slowing large
payloads at Mars, the all-propulsive solution results in high
propellant mass fractions and requires aeroshell separation
and propulsive descent initiation to take place at supersonic
speeds. As such, a trade study was conducted to quantify
how a large, supersonic parachute could mitigate these
issues. In this assessment, aggressive assumptions were
made in regard to parachute deployment conditions
(Mach 3) and altitude requirements for the subsequent
descent and landing events. Figure 24 shows the parachute
sizes required to decelerate a payload from Mach 3 to Mach
0.8 at an altitude of 2 km. A Mach number of 0.8 was
chosen to mitigate the aeroshell separation and re-contact
concerns of current robotic landers. Figure 24 shows that a
30 m, Mach 3 parachute allows for a subsonic propulsive
deceleration maneuver if entry masses are below
approximately 33 t. This same parachute can slow the
vehicle to Mach 1.0 at 2 km for entry masses less than 50 t.
For entry masses above 50 t, a larger chute is required (with
a significant opening time penalty), or the propulsive
deceleration maneuver must begin supersonically.
An additional benefit of this approach is that the parachute
can be used to separate the payload from the aeroshell.
Atmospheric uncertainty is a major driver for parachute assisted
descent. The results described above are for a
nominal atmosphere. If a conservative density is modeled,
the 30 m parachute is only practical for entry masses below
approximately 20 t. Parachute assisted propulsive descent
still requires significant propellant mass fraction to bring the
vehicle from Mach 0.8 to a soft landing. The propellant
mass fraction required for just the cross range maneuver (to
protect pre-landed assets on the surface) will actually
increase for a parachute-assisted system because the burn is
started much later in the descent. Overall, the total
propellant mass fraction required for descent and landing
will decrease from 20-30% of entry mass for an all propulsive
system (see Fig. 23), to a range of 12-18% for a
parachute assisted system.'


However, where this whole equation changes, is they are trying to maximize landed mass, understandably.  And this lander is probably not trying to get back of the ground.  However, any vehicle that needs to get back to Mars orbit, or do a directly return from the surface, will need a LOT of propellant.  with large tanks for that propellant.  So if you are designing to maximize usage of components and minimize elements rather than maximize landed mass, then it could be ok that there's a large dV penalty for propulsive supersonic retropropulsion.  The lander would have the fuel tank capacity as it needs much more than that to get back to Earth.  It lands burning up it's stored methalox, and then refuels on the surface with it's LH2 store.  Then lifts itself back off the surface.  And burns for Earth.  Or rendezvous with a MTV and is discarded. 

Such a lander would probably not be able to land very much cargo on the surface, but if it could actually work, it would maximize element use, and minimize individual elements.  A simple system with minimal elements, but not perhaps very efficient in the amount of equipment it can drop off on the surface. 
In a single new vehicle development, you have your Mars Transit Hab, your lander, your Mars Ascent Vehicle, and your Earth Return Vehicle.  And you get to land it all back on Earth.  The side advantage is this can probably take off form Mars and land on Earth with a decent amount of Mars samples compared to a more traditional architecture that only lands say, an Orion Capsule back on Earth.



« Last Edit: 11/10/2013 05:41 AM by Lobo »

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